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Review Articles

Where's the Leak in Vascular Barriers? A Review

Kottke, Melissa A.; Walters, Thomas J.

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doi: 10.1097/SHK.0000000000000666
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Abstract

INTRODUCTION

Direct tissue trauma, disease, or inappropriate resuscitation and/or ventilation strategies result in edema formation through physical disruption and chemical messenger-based structural modifications of the microvascular barrier. Typically presented as a secondary effect from injury, illness, disease, or medication, edema is thought of more as an amplifier to current preexisting conditions than an independent risk factor for patient deterioration. Improper management of edema is, however, costly not only to the patient, but also to the treatment and care facilities, as mismanagement of edema results in increased lengths of hospital stay, patient morbidity, and increased mortality (1,2).

Microvessels orchestrate local regulation of hydrostatic and oncotic pressures for nutrient and oxygenation of tissues and clearance of waste products. The ability of the microvasculature to be permissively permeable and adaptive to physiological stimuli enables tissue perfusion and homeostasis to be maintained through a myriad of stressors. Microvessel permeability also presents problems for acute and chronic disease states and traumatic injuries by permitting fluid accumulation within the interstitia. For example, in burn patients, structural damage and inflammation from burn result in increased vascular permeability. As a result of increased vascular permeability, intravascular volume drops and must be rapidly and aggressively resuscitated (3,4). Without restoration of the vascular barrier function, the increased permeability results in leakage of the administered fluids into the interstitial compartment leading to further complications such as abdominal and extremity compartment syndrome (5). Direct structural damage, changes in patient hemostasis, inflammation, and administered medications all present complications in burn and other critical care patients with regard to determining the best strategies to mitigate edema formation. Recent studies have sought to elucidate cellular signaling and structural alterations that result in vascular hyperpermeability in a variety of critical care conditions to include hemorrhage (6,7), burn trauma (8–11), and sepsis (12–16). These studies and many others have highlighted how multiple mechanisms alter paracellular and/or transcellular pathways promoting hyperpermeability. Roles for endothelial glycocalyx, extracellular matrix (ECM) and basement membrane (BM), vesiculo-vacuolar organelles, cellular junction and cytoskeletal proteins, and vascular pericytes have been described, demonstrating the complexity of microvascular barrier regulation. Understanding these basic mechanisms inside and out of microvessels aide in developing better treatment strategies to mitigate the harmful effects of excessive edema formation.

FLUID BALANCE AND EDEMA FORMATION

Starling's Law

Edema results from an imbalance in fluid filtration and uptake within a specific location or compartment. It can occur intracellularly or interstitially and results from an imbalance in interstitial fluid (ISF) and intravascular fluids (plasma). All cells within the body are bathed in ISF with all nutrients, wastes, and chemical messengers moving through ISF to cellular targets. ISF is low in protein concentration (approximately 50%–60% of that of plasma) and has high levels of sodium and chloride ions. Plasma suspends red and white blood cells and platelets and is contained within intravascular spaces. The balance between interstitial and intravascular fluids is dependent upon hydrostatic pressure and oncotic pressure differences across the intravascular (capillary) walls. It is also dependent upon capillary wall integrity, surface area, and the ability of lymphatic vessels to enable flow of excess ISF (17,18). In 1896, Ernest Henry Starling proposed that when the forces governing fluid movement across vascular and tissue compartments are in balance that fluid movement would cease (17,19). Hydrostatic forces, under Starling's view, would be governed by the difference between hydrostatic forces in the capillary and the interstitium. The oncotic pressure similarly would be determined by the pressure differences between the oncotic pressure in the capillary versus the interstitial compartment. Starling's equation in its modern form describes fluid flux across intravascular to interstitial spaces as the hydraulic conductivity (describing a barrier's leakiness to water) times net filtration pressure (the sum of the hydrostatic and osmotic forces acting across capillary walls). In normal tissues (intact selective barrier) under steady-state conditions, the net filtration pressure is positive resulting in net fluid movement into the tissues (Fig. 1A). Fluid movement is countered by removal of ISF by the lymphatics (17).

Fig. 1
Fig. 1:
Traditional Starling's Law and revised Starling's Law.Traditional Starling's Law (A). Figure modified from Levick and Michel (20). Filtration rate = Kf [(Pc−Pi) − σ(πc−πi), where σ is the reflection coefficient, πc the capillary oncotic pressure, π the interstitial oncotic pressure, (Pc−Pi) − σ(πc−πi) the net filtration pressure, Kf the filtration coefficient, Pc the capillary hydrostatic pressure, and Pi is the interstitial hydrostatic pressure. Revised Starling principle (B). The revised starling principle proposes that oncotic forces are determined by the local differences in protein concentration across the glycocalyx (πg) and by small compartments (beneath the glycocalyx, between cells, trapped by the basement membrane and pericytes) and not by differences in plasma and interstitial oncotic pressures. Modified from Levick and Michel (20). Cartoon highlights current understanding of the complexity of fluid movement through capillary endothelial glycocalyx, subglycocalyx, basement membrane (as depicted by structures between endothelial cells and pericytes), and pericytes to institial spaces. Filtration rate Kf [(Pc−Pi) − σ(πc−πg), where σ is the reflection coefficient, πc the capillary oncotic pressure, πg the subglycocalyx oncotic pressure, (Pc−Pi) – σ(πc−πg) the net filtration pressure, Kf the filtration coefficient, Pc the capillary hydrostatic pressure, and Pi is the interstitial hydrostatic pressure.

Capillary hydrostatic pressure varies along the length of a capillary and is highest at the arteriolar end and lowest at the venular end. At the arteriolar end of a capillary, the hydrostatic pressure may average between 35 and 45 mmHg, whereas the venular end may average between 12 and 15 mmHg (18). Higher hydrostatic pressure favors filtration of fluid from the capillary to the interstitial space, whereas lower hydrostatic pressures favor reabsorption. Capillary hydrostatic pressure is determined by arterial and venous pressures (PA and PV), and by the ratio of post-to-precapillary resistances (RV/RA). As venous pressure is on average 1/5th of arterial pressure, changes in venous pressure have a more profound effect on capillary pressure (21). Under normal conditions, oncotic pressure modestly decreases along the length of the capillary as some plasma proteins are filtered into the interstitial space. Albumin, and to a lesser degree globulins, are the main sources of oncotic pressure within the intravascular space. In normal physiological conditions, the interstitial compartment has protein levels 50% to 60% of that of plasma (22). This results in an inward-directed oncotic pressure across the capillary wall (18,22). The average hydrostatic pressure difference across the capillary wall promotes filtration of fluid out to interstitial spaces toward the arteriolar end of a capillary. Downstream at the venular end, the decreased hydrostatic pressure difference compared with oncotic pressure favors reabsorption of filtrate back into capillary. Together the hydrostatic and oncotic pressure gradients promote passage of essential nutrients to tissues and filtering of metabolic byproducts out of tissues.

When normal homeostatic mechanisms fail due to physical damage to the microvessel barrier, or extreme alterations in hydrostatic or oncotic pressures, edema formation occurs. For example, physical damage found in burn patients is coupled with decreased interstitial hydrostatic pressure within the first 2 h postinjury and decreased plasma oncotic pressure that is exacerbated following fluid resuscitation. Rapid, aggressive fluid resuscitation regimens in burn patients are necessary to reconstitute intravascular volume, which have been shifted to the surrounding interstitial space due to increased vascular permeability (3–5). As a result of increased vascular permeability, fluids administered to the patient continue to leak from intravascular spaces into the interstitial compartment, with nearly half of infused crystalloid volume lost to the interstitium (5). Restoring and maintaining oncotic and hydrostatic pressures (volume replacement) in critically ill and injured patients is one of the most important aspects of acute medical management.

Resuscitation of burn patients is critical to preserve and restore organ function, with fluid management as the top priority for the initial management of burn injury. Without effective and rapid intervention, hypovolumeia/shock can develop in these patients, as well as increased mortality (23). Recent advances in prehospital care and burn resuscitation training have significantly decreased under-resuscitation of these patients and have improved patient morbidity and mortality (24); however, the emergence of fluid creep due to over-resuscitation continues to be a significant problem for health-care providers (24–26). Over-resuscitation in burn patients is associated with multiple morbidities to include multiorgan failure, infectious complications, acute respiratory distress syndrome (ARDS), and compartment syndromes (27,28). From the selection of products used for resuscitation (29–31), the amounts administered (32,33) and the timing (34) of resuscitation all contribute to edema formation and potential multiorgan failure. Even with careful consideration of volume, composition, and timing, the use of Starling's Law to prevent edema formation has considerable problems still arise due to the oversimplified view of how edema formation occurs at the microvascular level.

Starling's Law revised

For the past three decades, the conventional filtration-absorption model (Fig. 1A) has been used as a basic guideline for more modern interpretations that were developed from clinical and laboratory outcomes (35–40). Capillary filtration and reabsorption were found to be significantly less than Starling predicted through modern measurement techniques of interstitial oncotic and hydraulic pressures. The difference in colloid osmotic pressure was found to be dependent upon a tightly regulated rapid equilibrium of oncotic pressure differences across the luminal endothelial surface layer and not dependent upon interstitial osmotic pressure. The endothelial glycocalyx, first observed by Luft in 1966, a meshlike matrix, poses a significant barrier to proteins and offers the highest resistance to diffusion of solutes through the endothelial barrier (41). Elegant studies performed by Adamson et al. (40) demonstrated that colloid osmotic forces opposing filtration were developed across the endothelial glycocalyx and that the oncotic pressure of the interstitia does not directly determine the fluid balance across the microvasculature. Observations by Adamson and others led to the creation of updated versions of the Starling hypothesis which now include the endothelial glycocalyx (42) (Fig. 1B). Current versions propose that the glycocalyx acts as the effective osmotic barrier, and oncotic pressure differences are determined by differences in protein concentration across the glycocalyx and not from global differences in tissue and luminal osmotic pressures. Thus, in the revised Starling's Law the subglycocalyx oncotic pressure (πg), and not the interstitial oncotic pressure (πi), is the primary determinant of transcapillary filtration (Jv) (Fig. 1B).

The glycocalyx is a dynamic structure composed of proteoglycans, glycoproteins, extracellular proteins and enzymes, hyaluronic acid, and thrombomodulin, and interacts with soluble plasma components. The composition of plasma and exogenous fluids directly impacts the thickness and structure of the glycocalyx. Thus, the composition of resuscitation fluids significantly impacts the functionality of the glycocalyx and its ability to serve as an interface between blood and inflammatory cells and as a potential sensor to changes in vascular pressure, flow, and shear stress for the underlying endothelia (41,43–45). Outside-in signaling through syndecans, PECAM-1, and glypicans with the cytoskeleton, junctional proteins, and caveolar domains within endothelial cells provide evidence that glycocalyx-mediated signaling also contributes to vascular permeability and derangement in the endothelial barrier function (46,47). A recent review by Chignalia et al. describes glycocalyx function in multiple animal trauma models, and highlights how various resuscitation fluids impact vascular permeability and edema formation. For example, solutions that contain albumin compared with hydroethyl starch decreased tissue edema development in animal models and were protective of the endothelial glyocacalyx. Albumin solutions prevented the loss of constituents of the glycocalyx or “shedding,” whereas hydroethyl starch solutions decreased glycocalyx thickness, which resulted in increased hydraulic conductivity, filtration, and edema formation (48). Woodcock and Woodcock in 2012 additionally discussed recent improvements in administered fluid therapies through the understanding and use of the revised Starling equation in trauma patients (34). Resuscitation strategies that limit damage to the glycocalyx, such as those discussed by Woodcock and Chignalia, protect the structure and function of the glycocalyx and limit transcapillary filtration through the maintenance of the oncotic gradient and cellular signaling cascades that maintain barrier function as discussed below.

MEDIATORS OF BARRIER FUNCTION

The role of transport pathways and cellular junctions in barrier function

The vascular barrier function controls solute and fluid movement inside and out of vascular tissues. The typical barrier is composed of a monolayer of vascular endothelial cells that has a subcellular BM and luminal ECM with dense glycocalyx. Also present are pericytes or a thin layer of smooth muscle are interspersed and regulate vascular pressure and flow (Fig. 2). Intact vascular barriers control solute and fluid movement through transcellular and paracellular mechanisms. Paracellular transport is mediated by adherens junctions, gap junctions, and tight junctions between adjacent endothelial cells (Fig. 3A). Adherens junctions are found more frequently than tight junctions in microvessels and comprise the predominant barrier to macromolecules in the vasculature (18). Gap junctions have not been demonstrated to directly contribute to barrier function; however, they are important mediators of cellular communication and can impact vascular function through transmission of calcium, charge, and other small signaling molecules such as IP3. Focal adhesion junctions are points of attachment between the endothelial abluminal membrane and ECM. Focal adhesions maintain contact between endothelial cells and the BM, and transmit forces and biochemical signals from the matrix (outside-in signaling) and the endothelium (inside-out) (50). Under stimulated conditions, focal adhesion junctions contribute to decreased barrier function in microvessels by acting as signal transducers and/or structural modulators (50) (Fig. 3B). Transcellular transport occurs through clathirin coated pits, caveloae, and vesicular vacuolar organelle (VVOs). VVOs can form transendothelial cell pores, allowing for the passage of large molecules and fluid through the endothelium. The localization and function of junctional proteins and vesicular bodies can be greatly influenced by inflammatory mediators, vasoactive substances, and mechanotransduction. Damaged cells and inflammatory cells produce signaling mediators that can directly increase vascular permeability. Examples include vascular endothelial growth factor (VEGF) (51,52), histamine (53,54), bradykinin (55,56), platelet-activating factor (PAF) (57–59), and leukotrienes (60,61). Thus, through disruption of cellular junctions or stimulation of VVO formation, paracellular and transcellular pathways, respectively, increase fluid and solute movement across the vascular barrier. Specific cellular signaling mediators that impair barrier function through increasing paracellular and transcellular pathways are further discussed below.

Fig. 2
Fig. 2:
Abluminal basement membrane, pericyte, and luminal glycocalyx impact on barrier function in microvessels.From inside-out, vascular endothelial cells respond to their environment and conditions through transmitted signals from the luminal glycocalyx, abluminal basement membrane, and pericytes.
Fig. 3
Fig. 3:
Endothelial barrier function (A): endothelial barrier function is largely dependent on the functioning and appropriate localization of junctional proteins and structures.In the microvasculature adherens junctions primarily provide cellular adhesion with tight junctions playing a more substantial role in the cerebral circulation. Focal adhesion junctions maintain endothelial connections to the basement membrane and gap junctions promote cellular communication between endothelial cells and pericytes. Barrier function disruption (B). Figure is a modified version from Mikelis et al. (49). Degradation of barrier function by inflammatory mediators and shear stress occur through mislocalization or loss of junctional proteins and endothelial contraction (as depicted in cartoon: red arrows) to promote gap formation. A complicated myriad of cellular signaling regulates the function and localization of many of these proteins and structures. Common vasoactive substances known to promote increased permeability activate signaling cascades (blue solid arrows designate upstream and downstream signaling partners, blue dotted arrows designate unknown connections) through their respective receptors and decrease barrier function. VEGF has been demonstrated to increase permeability through reduced expression of tight junction proteins ZO-1 and occludin, phosphorylation and redistribution of ZO-1 and occludin to intracellular compartments, FAK activation to stimulate focal adhesion turnover, PI3K-dependent actin reorganization, increased intracellular calcium and nitric oxide production, and Src/Rac/Pak-dependent phosphorylation and internalization of VE-cadherin. Increases in vascular permeability by histamine have been dependent upon increases intracellular calcium and nitric oxide production, and result in redistribution of VE-cadherin adhesion complexes through RhoA/ROCK, and VE-cadherin relocalizaton to focal adhesion junctions. PAF downstream effects include increases in intracellular calcium and NO, and filamentous actin redistribution that are Rac-1-dependent. Bradykinin signaling downstream of B1/B2 receptors increase nitric oxide formation and intracellular calcium, reorganization of filamentous actin, and actinomyosin contraction. Increased shear stress of the vascular endothelium results in integrin outside-in signaling and activates the PECAM-1, VE-cadherin, and Flk-1 mechanotransducer to signal inside-out through integrins and AKT-dependent activation of eNOS. Increased eNOS activity has additionally been demonstrated to result in NO-dependent gap formation through nitrosylation of β-catenin. FAK indicates focal adhesion kinase; PAF, platelet-activating factor; ROCK, Rho-associated protein kinase; VEGF, vascular endothelial growth factor; ZO-1, zona occludens 1.

Mediators of endothelial permeability

Cellular signaling cascades from VEGF and its receptors impact endothelial cytoskeletal and junctional proteins, as well as VVO formation. As described by Bates in his review in 2010, VEGF signaling results in marked ultrastructural changes that correspond with experimentally tracked increases in permeability (51). Multiple mechanisms including breakdown of VE-cadherin junctional contacts (51,62,63), activation of other Src-family protein-tyrosine kinases such as focal adhesion kinase (FAK) (63,64), and reductions in zona occludens 1 (65) and occludin (66) result in decreased tight and adherens junctions and increased permeability (51). VEGF and other vascular permeability factors, such as histamine and serotonin, cause interconnecting vesicles and vacuoles to open creating a system of VVOs, which are thought to provide an additional transcellular pathway for plasma and protein extravasation. The contribution of VVOs and transcellular transport to total measured vascular leak following stimulation by a permeability inducing factors, such as VEGF, remains to be investigated. Clinically, levels of circulating VEGF have been used as a damage marker for ischemia/reperfusion injury, burn damage, and severe trauma. In burn patients, high VEGF levels correspond to the presence of general tissue edema (67), whereas in severe trauma patients and sepsis patients VEGF can be used to predict sequential organ failure (68), edema, and mortality (69,70).

Histamine, like VEGF, increases vascular leakage through a myriad of mechanisms including vascular dilation, decreased tight and adherens junctions, and VVO formation. Recent studies have highlighted how histamine induces vascular permeability through nitric oxide (71), RhoA/Rho-associated protein kinase (ROCK) (49), and VE-cadherin-dependent pathways (71,72). Mikelis et al. (49) described a role for histamine activation of RhoA and ROCK and the redistribution of VE-cadherin adhesion complexes, where tension generated by actomyosin contraction promoted the relocalization of VE-cadherin adhesion complexes to focal adhesion junctions, and the formation of gaps disrupting the continuity of the endothelial barrier, resulting in vascular leak. Ashina et al. (71) additionally described a role for histamine-induced reorganization of VE-cadherin through NO- and RhoA/ROCK-dependent mechanism. Similar to histamine, bradykinin has also been recently described to signal through RhoA and ROCK and cause ultrastructural modifications that result in increased vascular permeability through tight junctions (73–75). Studies investigating how PAF increases endothelial permeability have demonstrated significant changes in actin filament polymerization that are independent of myosin light chain kinase (76,77) and dependent on Rac-1 (77). Other groups have focused on PAF-inducted intracellular calcium and NO-dependent gap formation (78,79). NO-dependent effects have additionally been described for VEGF (80) and bradykinin (81,82). The actions of NO on gap formation remain elusive; however, recent evidence suggests that nitrosylation of β-catenin by NO may mediate the dissociation of β-catenin from VE-cadherin leading to junctional destabilization (80). VE-cadherin expression may also be regulated by NO as treatment with NO-donors reduced VE-cadherin expression and increased indices of vascular leakage, whereas blockade of eNOS inhibited this effect (83). PAF is well known to contribute to increases in vascular permeability in sepsis and anaphylaxis (84,85). Recent studies have also linked vascular leakage in acute dengue infection to PAF, where PAF levels were significantly higher in patients with more severe forms of Dengue (85). Elucidating the exact contribution of PAF on clinical conditions is complicated as PAF crosstalks with bradykinin and leukotrienes. For example, in a model of PAF-dependent edema formation in the rat paw PAF was found to signal through the bradykinin B1 receptor, as edema and cellular damage from inflammation were attenuated following blockade of the B1 receptor (86).

Leukotrienes regulate vascular permeability by regulating other vasoactive mediators, such as VEGF, where blockade of the cysteinyl leukotriene receptor reduces NF-κB activity and VEGF expression (87). Cysteinyl leukotrienes also have direct effects on vascular permeability through activation of CysLT2 receptors and ROCK to induce endothelial contraction and gap formation (88). In animal models of ischemia/reperfusion, edema and tissue injury have been associated with rises in local and circulating levels of the cysteinyl leukotriene LTB4, where inhibition of LTB4 or PAF has been shown to decrease vessel permeability and reduce tissue injury (89,90). Thus, crosstalk and signaling similarities with inflammatory and other vasoactive mediators decrease endothelial barrier function by promoting ultrastructural changes, mislocalization of adherens junctional proteins and the creation of gaps, endothelial contraction, and modified vesicular transport systems to increase paracellular and transcellular transport.

In addition to vasoactive and inflammatory mediators, mechanical stretch has a tremendous impact on regulating barrier function within the vasculature. In ventilator-induced lung injury (VILI), experimental and clinical evidence suggest that mechanical forces (inflation pressure) from ventilation contribute to the destruction of capillary endothelium and alveolar epithelium, not just increased in microvascular pressure. The underlying mechanisms behind VILI-induced edema are poorly understood; however, recent studies have described roles for epidermal growth factor (EGFR) (91), gelsolin (92), and PECAM-1 (93), which have been previously demonstrated to regulate cellular signaling cascades that are activated upon mechanical stretch (EGFR (94,95); gelsolin (96,97); PECAM-1 (98,99)). Disturbed flow patterns following injury, occlusions, or various other pathological conditions enhance vascular permeability (100). Extensive fluid resuscitation following traumatic injuries dilutes natural blood products decreasing blood viscosity, and altering fluid flow patterns through increased turbulence. Increased vascular turbulent flow increases shear stress along the vessel wall, decreases the ability of vessels to perfuse surrounding tissues, damages endothelial cells, and increases the susceptibility of the vessel to develop lesions (100). Increased sheer stress results in irregular actin organization, changes in gene expression, molecular signaling, and junctional proteins (100–102). Small GTPases including Rho, cdc42, and Rac-1 are all activated through mechanosenstive pathways (as reviewed in (103)). In addition, ROCK (104), FAK (105,106), and various cation channels are activated directly or indirectly due to mechanical stretch. Where is the flow sensed? Currently, the glycocalyx and other luminal mechanosensitive proteins are thought to be responsible for sensing of changes in flow patterns and shear stress. Removal of glycocalyx by enzymatic digestion impaired flow mediated changes in actin reorganization (107) and shear-induced NO production (108). Removal of the glycocalyx, however, did not impact flow-dependent increases in cyclooxygenase production, suggesting other sensory mechanisms are responsible for flow-dependent in cyclooxygenase (109). Luminal mechanosensing and glycocalyx-dependent effects on the vascular endothelium have a tremendous impact on the ability of microvessels to regulate permeability. We next review the impact of abluminal structures and cells to include the BM and vascular pericytes on their respective contributions to mediating vascular permeability.

The role of the BM in vascular permeability

The BM is an important and often overlooked mediator of vascular permeability and edema formation. BMs are highly specialized extracellular matrices that are involved in regulation of tissue development, function, and growth, and can modulate local concentrations of growth factors and cytokines (as reviewed in (110)). BMs provide support to cells and act as a barrier maintaining cells and proteins on their respective side of the membrane. Remodeling in wound healing and neovascularization are additionally dependent upon the BM (111–113). BMs vary in thickness and composition, with site-specific differences in collagens (VIII/XV/XVIII for vascular endothelium), nidogen-1, nidogen-2, fibronectin, perlecan, and laminins (114,115). In the microvasculature, the BM presents a barrier to transmigration of leukocytes during immune surveillance or cancerous cells during metastasis (116). Transmigration occurs through proteolytic (matrix degradation)-dependent and -independent mechanisms. Independent mechanisms include leukocyte passage through areas where the BM protein deposition is low and aligns with gaps between pericytes on venular microvessels (117,118). These areas of low BM deposition enable cell passage without permanent restructuring and damage of the BM. As endothelial cells and pericytes both contribute to the development and maintenance of the BM, the variation in thickness and composition are presumably of physiological relevance for cellular communication or transmigration of cells. Thus, it is not surprising that imbalances of the carefully positioned and maintained BM result in vascular leakage of cells, proteins, and fluid into interstitial spaces. Natural changes in BM composition and structure occur with age and sex (119). Diseases including diabetes, immune disorders, and cancer also have a significant impact on BM composition and function. Age-dependent thickening of BM has been documented in different epithelial and endothelial tissues such as retinal tissues (120–122), vascular tissues in the eye, brain, the stria vascularis of the ear, and capillaries of the pectoralis muscle (121,123,124). Age-related changes in the BM include increased thickness, altered protein composition, and increased stiffness (120,125). The effect of aging is similar to that found in diabetes, traumatic brain injury, idiopathic edema, and nephrotic syndrome where thickening of the BM increases BM permeability to protein and promotes edema formation and vascular dysfunction (126,127). BM degradation in cancer and immune disorders enables irregular cellular breaches, BM stiffening, and inappropriate cellular death (128–130). Following burns, systemic microvessels in burned and unburned tissues rapidly develop gaps between endothelial cells which persist for days to weeks depending on the severity of the burn. Although multiple mediators contribute to the alteration of microvessel permeability in burn patients, the length of which cellular gaps persist suggests involvement of the BM (131). The precise contribution of a functional BM in regulation of vascular permeability remains ill-defined; however, it is evident that the BM through modulation of endothelial stability and through structure and charge contributes as a barrier for cells and proteins (Fig. 4).

Fig. 4
Fig. 4:
Vascular endothelial response following abluminal or luminal perterbation.The alteration of composition and thickness of the basement membrane in disease or injury results in abnormal control of blood flow and increased permeability. Increased basement membrane thickness (as depicted as increased yellow line width), as in diabetic retinopathy, results in a loss of endothelial cell: pericyte communication which overtime results in deattachment of pericytes from endothelial cells and cellular death. Macrophage infiltration into wounded tissue during wound healing results in degradation of the basement membrane, which promotes phenotypic drift of vascular endothelial cells and increased vascular permeability (as depicted by blue arrows for fluid movement). Alterations in the endothelial glycocalyx (green to red arrow for changes in glycocalyx thickness/composition) also results in abnormal control of blood flow and increased permeability. Trauma as in burn or ischemia/reperfusion injury shear the endothelial glycocalyx and impair glycocalyx outside-in signaling, resulting in the formation of gaps and increased permeability.

The role of pericytes in vascular permeability

Pericytes are contractile cells that sense and modulate microvessel blood flow, limit vascular permeability through direct coverage over interendothelial junctions and flow rate, and regulate BM remodeling (117,132). Pericytes reside on the abluminal surface of the BM with their long dendritic-like cytoplasmic processes surrounding the vessel. Constriction or dilation of pericytes and their processes decrease or increase the luminal space and regulate vascular blood flow. In a quiescent state, pericytes prevent microvascular leakage through arm-like projections that act as a physical barrier near interendothelial junctions (133). By controlling microvascular flow, pericytes additionally limit hydraulic pressure and microvascular leakage from capillaries. The production of vasoactive substances such as prostaglandins, VEGF, and transforming growth factor β (TGF-β) by pericytes also directly impacts endothelial barrier function and contributes to the formation of leaky vessels in disease and trauma (132), especially as TGF-β1 plays a critical role in the pathogenesis of acute lung inflammation through actin dissambly, mictrotuble collapse, endothelial contraction, and increased permeability (134). Pericytes additionally regulate vascular leak through promotion of vascular stabilization and endothelial survival. Established focal contacts with the vascular endothelium through the BM enable transmission of various signaling molecules that are important mediators of endothelial and pericyte survival (Fig. 4). Pericytes stabilize endothelial cells and limit proliferation and turnover (135,136) through contact-dependent and -independent pathways (137,138). Pericytes contact endothelial cells through protrusions (peg and socket) where the BM membrane is absent and are anchored together through focal adhesion junctions, cellular plaques, and gap junctions. Stablization of endothelial cells by pericytes was recently found to be RhoGTP and Rho-signaling-dependent, where activation of RhoGTP augmented pericyte contractility and impaired pericyte regulation of endothelial growth arrest through contract-dependent and -independent interactions (139). The myosin phosphatase-RhoA interacting protein through RhoA/ROCK activation was additionally found to regulate pericyte contact-dependent endothelial growth arrest and pericyte contractility (140). Pericyte function in the stabilization of vessels may not always be beneficial in terms of preventing or mitigating vascular permeability and edema formation as recent evidence indicates that pericytes may stabilize vessels into abnormal phenotypes that promoted leukocyte traffic and sustained leakage (141). Pericyte regulation of cerebral and renal microvascular blood flow (142,143) may be sensitive to hypoxemia and sympathetic activation. Ischemia resulted in increased cellular death of pericytes as compared with endothelial cells in the cerebral microcirculation as described by Hall et al. in 2014.

EXPERIMENTAL AND CLINICAL TREATMENTS

The regulation of microvascular permeability is complex with mechanosensing and vasoactive mediators having a tremendous impact on endothelial adherens and focal junctional protein localization and function. Furthermore, the composition and charge of glycocalyx and BM contribute to barrier selectivity of anionic proteins and total oncotic pressure. Pericyte and endothelial communication and stabilization in unstressed conditions are important in maintaining endothelial selective permeability; however, under duress pericyte stabilization may enable disastrous leaky vessels to persist. Heterogeneity in endothelial and pericyte populations as well as environment-driven differences in BM composition and thickness add an additional level of complexity to the basic concepts of permeability regulation discussed above. Although it is difficult to delineate the contribution of each component and calculate precisely how site-specific differences influence each variable, both luminal and abluminal perturbations influence vascular permeability. Experimentally and clinically an appreciation of the complexity of vessel barrier function has promoted research and led to improved patient care to include revised resuscitation practices, investigations into the use of protective or restorative pharmacological products, and improved ventilation strategies.

Moving beyond Starling's Law to improve patient resuscitation

Patient resuscitation strategies have continued to evolve over the past 50 years with the use of two crystalloid solutions, lactated Ringer's and normal saline, as the predominant solutions used to restore hemodynamic function in patients. Colloidal solutions, such as hydroxyethyl starch, were developed over 40 years ago to decrease the effective volume necessary for fluid resuscitation by increasing plasma oncotic pressure. They produce faster hemodynamic effects than crystalloid solutions (144); however, their efficacy has only been moderately better than crystalloids. Patient outcome has not been demonstrated to be significantly improved in their use, and in some cases colloidal use was harmful and associated with increased renal failure rate (144,145). Clinics use both colloidal and crystalloid fluids, with normal saline as the most common fluid worldwide. With increased awareness of the importance of endothelial glycocalyx and how the presence or lack of presence (following trauma or disease) impacts oncotic pressure (Fig. 1B), fluid strategies have been adapted to fit this new model of fluid flux and have recommended moderate and actively monitored volume loading to limit hemodilution and shedding of endothelial glycocalyx (146,147). The use of “plasma-extenders” such as those listed above has been crucial to improved patient outcome over the past century; however, they are not perfect replacements for plasma or whole blood. Preliminary studies using blood components (fresh frozen plasma, platelets, and red blood cells [RBCs]), conducted by the US Military and others, have demonstrated that component therapy and whole blood for massive transfusion improves mortality (148,149). Recent clinical and laboratory studies suggest that plasma-rich/crystalloid poor and limited volumetric expansion approaches increase survivability (150), decrease acute hypoxemia (151), and decrease vascular permeability (152,153). This method of “damage control resuscitation” has been widely adopted by the US Military and is currently being incorporated into civilian trauma centers (154–156). The increased survival rates and decreased edema are likely due to protective effects of limited plasma volume on the endothelial glycocalyx (157,158).

As many groups begin to embrace earlier use of blood and blood components, caution should be taken as several reports have also noted that transfusion of plasma is associated with increased risk of infectious complications and organ failure (as reviewed in (159)). The aforementioned studies conducted by the US Military and others are preliminary studies with limited patient numbers or are largely supported by preclinical animal models and require further testing and evaluation. Evaluation of the products and strategies for resuscitation are ongoing with differing perspectives between nations (a full review on current differences between European practices and American practices (160)).

Several recent reviews on fluid resuscitation strategies highlight advances and changes in protocols in fluid resuscitation and blood transfusion for severely injured patients (161,162). Spinella and Doctor in their review from 2014 discuss how storage duration of blood products significantly impacts RBC/hemoglobin oxygen-carrying capacity and that transfusion of stored RBC units to increase hemoglobin content and blood oxygen content is flawed and may, in fact, reduce oxygen delivery and regional flow. Thus, treatment of hemorrhagic shock should require attention to increasing regional flow and maintaining oxygen-carrying capacity. Spinella and Doctor also discuss the lack of multicenter randomized controlled trials on stored RBCs on adult trauma patients. Therefore, further prospective studies are necessary to develop standardized protocols for resuscitation using whole blood and blood components, and restrictive versus liberal fluid management strategies.

Pharmacological and albumin-based additives prevent glycocalyx degradation

Postulated therapeutic options to prevent degradation of endothelial glycocalyx include inhibition of “sheddases” which promote the loss of specific components of the glycocalyx (as reviewed in (163)) or offering protection through administration of antithrombin III or hydrocortisone (163,164). Interestingly, the administration of albumin with sequestered sphingosin-1-phosphate has also been found to be effective in reducing metalloproteinase-mediated losses in chondroitin sulfate and syndecan-1 (165) and could present a viable option for clinical use to protect the glycocalyx. Rapid restoration of the glycocalyx may also provide a clinical option to reduce edema formation and vasoregulatory dysfunction; however, not much is known about the mechanisms that offer accelerated resynthesis or the potential restoration/refill effect of endothelial caveolae of their rich deposits of glycocalyx (163). Thus, pharmacological or albumin-based additives that promote protection, regrowth, or redistribution placed in closely monitored resuscitation volumes of plasma-extenders offer novel treatment options to decrease vascular leakage.

Ventilation tidal volumes and future pharmacological treatments for VILI

Complications from severe trauma, burn, and shock that result in edema formation in the lungs pose unique challenges for providers as they must limit further damage and maintain patient oxygenation. Irregular stretch exerted on the vasculature by changes in lung volume and pressure by mechanical ventilation in trauma can worsen lung edema and inflammation in ARDS. ARDS is a medical condition that is characterized by widespread inflammation and edema in the lungs that may result from various conditions to include trauma, burn injury, pneumonia, and sepsis. Recent studies have suggested that ventilation strategies that limit tidal volume decrease lung injury, edema formation, and mortality for patients with ARDS (166–168). Currently, the use of limited tidal volumes in critically ill patients without ARDS is questionable (169). Decreasing tidal volumes may not be appropriate for all patients, as the beneficial effects of lower tidal volumes could be offset by an increased need for sedation and maybe even muscle paralysis (170). Increased use of sedatives and muscle relaxants could increase the incidence of ICU delirium and ICU-acquired weakness, both conditions have the potential to lengthen duration of ventilation and stay in ICU beneficial effects of lower tidal volumes could be offset by an increased need for sedation and maybe even muscle paralysis (170). Increased use of sedatives and muscle relaxants could increase the incidence of ICU delirium and ICU-acquired weakness, both conditions have the potential to lengthen duration of ventilation and stay in ICU. As there are no current bedside tools to provide an accurate assessment of aerated lung volume, healthcare providers must carefully tailor mechanical ventilation strategies to individual patients through indirect measurements.

As the debate on appropriate pressures and tidal volumes continues, other strategies to limit VILI including pharmacological treatments have been explored. Inhaled prophylactics and injectable pharmaceuticals concurrently or preemptively to target specific cellular signaling cascades responsible for vascular leakage have shown to be moderately effective in laboratory models. The stretch-sensitive ion channel transient receptor potential vanilloid 4 (TRPV4) was recently linked to mediate murine lung vascular permeability in a model of high mechanical ventilation (171). Blockade of TRPV4 by inhaled nanoparticles with the TRPV4 inhibitor ruthenium red decreased lung edema (172), demonstrating the potential of therapeutic nanoparticles for mitigating tissue injury and edema formation. Iloprost, a synthetic analogue of prostaglandin I2, has also been found to be protective against edema formation in mice models of mechanical ventilation injury (173). Indeed, hundreds of signaling mediators have been explored in laboratory models; however, none have been proven to be beneficial or effective for the treatment of VILI in patients (174).

Cell-based therapies

Cellular-based therapies provide novel treatments to regenerate and replace damaged cells within tissues to mitigate edema and improve functionality. Although not much work has been conducted with specific attention on edema formation and repair of the microvascular barrier, it is apparent that use of cell-based therapies is beneficial in models of tourniquet ischemia/reperfusion injury (175,176), burn (as reviewed in (177)), VILI (178), and lung contusion/hemorrhagic shock (179). In these models, the use of cellular therapies mitigated inflammatory responses and limited tissue damage. Presumably, with overall decreased inflammation and tissue death, edema and damage to the vascular barrier would be significantly decreased as well. Another approach to cell-based therapies does not include the addition of pluripotent cells (such as mesenchymal stem cells) and instead focuses on applying the broad repertoire of secreted trophic and immunomodulatory substances produced by the cells (secretome) (180). Further research is required to fully delineate the effectiveness of these therapies in clinical settings and to develop improved methodologies for collection and delivery of these products as the use of cell-based therapies is still largely unfeasible.

Experimental pharmacological treatments

Pharmacological targeting of key cellular signaling pathways that significantly contribute to endothelial gap formation, barrier breakdown, junctional destabilization, and cellular apoptosis through reactive oxygen species (ROS) formation presents novel treatments for the mitigation of edema (Table 1; 181–203). Rho and other small GTPases, as well as their associated pathways, have been targeted in many rodent models. The use of GTPase-dependent pathway inhibitors, such as Y-27632 (Rho-kinase inhibitor), are currently being validated in cancer treatments and pulmonary hypertension, but yet to have clinical trials in hemorrhage, sepsis, or burn. In rat models of hemorrhagic and septic shock, blockade of calcium-activated potassium channels (KCA) and/or ATP-sensitive potassium channels (KATP) significantly reduced edema and organ damage improving mortality. These ion channels are thought to be responsible for diminished vasoconstrictor properties in sepsis and hemorrhagic shock through hyperpolarization of the vascular smooth muscle. Excessive activation of these channels results in arterial hypotension and vascular hyporesponsiveness to catecholamines. Experimental success with KATP and KCA inhibitors has led to several clinical trials currently testing the ability of KCA or KATP inhibitors to improve vascular function and patient mortality in septic shock and stroke (Table 2; 204–211). Matrix metalloproteinases, such as matrix metalloproteinase-9 (MMP-9), can degrade collagen, laminins, and fibronectins with the ECM of microvessels and endothelial cells. Interestingly, inhibition of MMP-9 was effective in reducing edema and tissue damage in a rat model of I/R injury (Table 1), but has yet to be effective in a clinical setting for mitigating ischemic damage. The mitochondrial transition pore has also been a target of recent interest with significant decreases in ROS production and edema formation in rat hemorrhagic shock and thermal injury models (Table 1) and in reperfusion injuries following acute myocardial infarction in humans (Table 2). The studies and trials described above are a just a snapshot of current work that is being conducted to elucidate and treat injuries and diseases that disrupt microvascular barrier function. These pharmacological “tools” enable careful delineation of critical pathways in barrier disruption and provide a baseline for many clinical studies to test and evaluate effective treatments.

Table 1
Table 1:
Tested pharmacological agents to reduce edema and/or vascular dysfunction leading to edema formation in animal models
Table 2
Table 2:
Tested pharmacological agents to reduce edema and/or vascular dysfunction leading to edema formation in clinical trials

CONCLUSION

Through a basic understanding of how the BM, glycocalyx, and presence of pericytes all impact vascular permeability, better strategies and therapeutics will continue to be developed. Thus far, pharmacological treatments in laboratory models have been promising (Table 1); however, their ability to translate into human patients is not clear. Only small subsets of pharmacological strategies that have been proven successful in animal models have been tested or are currently under investigation in clinical studies (Table 2).

Beyond pharmacological treatments, additional research on the mechanisms of how blood components and whole blood improve patient mortality and decrease patient edema are necessary to continue to develop better therapeutic strategies, especially as storage requirements of such products are difficult. Understanding the mechanism of their protection is critical for producing plasma-extending products that offer the same protection without the logistical footprint or costs associated with blood products. Edema formation in tissue is not simply an imbalance of osmotic and hydrostatic forces, rather it is a complicated myriad of cellular responses to internal and external stimuli on microvessels through glycocalyx and BM sensing of tissue strain and pressure differences and coordinated signaling via the vascular endothelium to vascular pericytes.

REFERENCES

1. Stein A, de Souza LV, Belettini CR, Menegazzo WR, Viegas JR, Costa Pereira EM, Eick R, Araujo L, Consolim-Colombo F, Irigoyen MC. Fluid overload and changes in serum creatinine after cardiac surgery: predictors of mortality and longer intensive care stay. A prospective cohort study. Crit Care 2012; 16 3:R99.
2. Varadhan KK, Lobo DN. A meta-analysis of randomised controlled trials of intravenous fluid therapy in major elective open abdominal surgery: getting the balance right. Proc Nutr Soc 2010; 69 4:488–498.
3. Arturson G. Microvascular permeability to macromolecules in thermal injury. Acta Physiol Scand Suppl 1979; 463:111–122.
4. Salinas J, Chung KK, Mann EA, Cancio LC, Kramer GC, Serio-Melvin ML, Renz EM, Wade CE, Wolf SE. Computerized decision support system improves fluid resuscitation following severe burns: an original study. Crit Care Med 2011; 39 9:2031–2038.
5. Oliver RI: Burns, Resuscitation, and Early Management. In: de la Torre JI, ed. 2015. Updated November 24, 2015. Available at: http://emedicine.medscape.com/article/1277360-overview.
6. Zakaria el R, Li N, Matheson PJ, Garrison RN. Cellular edema regulates tissue capillary perfusion after hemorrhage resuscitation. Surgery 2007; 142 4:487–496.
7. Deng X, Cao Y, Huby MP, Duan C, Baer L, Peng Z, Kozar RA, Doursout MF, Holcomb JB, Wade CE, et al. Adiponectin in fresh frozen plasma contributes to restoration of vascular barrier function after hemorrhagic shock. Shock 2016; 45 1:50–54.
8. Wiggins-Dohlvik K, Han MS, Stagg HW, Alluri H, Shaji CA, Oakley RP, Davis ML, Tharakan B. Melatonin inhibits thermal injury-induced hyperpermeability in microvascular endothelial cells. J Trauma Acute Care Surg 2014; 77 6:899–905.
9. Stagg HW, Whaley JG, Tharakan B, Hunter FA, Jupiter D, Little DC, Davis ML, Smythe WR, Childs EW. Doxycycline attenuates burn-induced microvascular hyperpermeability. J Trauma Acute Care Surg 2013; 75 6:1040–1046.
10. Han JT, Zhang WF, Wang YC, Cai WX, Lv GF, Hu DH. Insulin protects against damage to pulmonary endothelial tight junctions after thermal injury: relationship with zonula occludens-1, F-actin, and AKT activity. Wound Repair Regen 2014; 22 1:77–84.
11. Murphy JT, Duffy S. ZO-1 redistribution and F-actin stress fiber formation in pulmonary endothelial cells after thermal injury. J Trauma 2003; 54 1:81–89.
12. Zhang J, Yang GM, Zhu Y, Peng XY, Li T, Liu LM. Role of connexin 43 in vascular hyperpermeability and the relationship to the Rock 1-MLC20 pathway in septic rats. Am J Physiol Lung Cell Mol Physiol 2015; 309 11:L1323–L1332.
13. Han J, Ding R, Zhao D, Zhang Z, Ma X. Unfractionated heparin attenuates lung vascular leak in a mouse model of sepsis: role of RhoA/Rho kinase pathway. Thromb Res 2013; 132 1:e42–e47.
14. Rizzo AN, Aman J, van Nieuw Amerongen GP, Dudek SM. Targeting Abl kinases to regulate vascular leak during sepsis and acute respiratory distress syndrome. Arterioscler Thromb Vasc Biol 2015; 35 5:1071–1079.
15. Feng H, Guo W, Han J, Li XA. Role of caveolin-1 and caveolae signaling in endotoxemia and sepsis. Life Sci 2013; 93 1:1–6.
16. Moreira RS, Irigoyen M, Sanches TR, Volpini RA, Camara NO, Malheiros DM, Shimizu MH, Seguro AC, Andrade L. Apolipoprotein A-I mimetic peptide 4F attenuates kidney injury, heart injury, and endothelial dysfunction in sepsis. Am J Physiol Regul Integr Comp Physiol 2014; 307 5:R514–R524.
17. Scallan J, Huxley VH, Korthuis RJ. Capillary Fluid Exchange. 2010; San Rafael, CA: Morgan & Claypool Lifesciences, 47–61.
18. Yuan SY, Rigor RR. Structure and Function of Exchange Microvessels. San Rafael, CA: Morgan & Claypool Life Sciences; 2010.
19. Starling EH. On the absorption of fluids from the connective tissue spaces. J Physiol 1896; 19 4:312–326.
20. Levick JR, Michel CC. Microvascular fluid exchange and the revised Starling principle. Cardiovasc Res 2010; 87 2:198–210.
21. Klabunde RE. Cardiovascular Physiology Concepts. 2nd ed2011; Baltimore, MD: Lippincott Williams & Wilkins, 186–193.
22. Reed RK, Rubin K. Transcapillary exchange: role and importance of the interstitial fluid pressure and the extracellular matrix. Cardiovasc Res 2010; 87 2:211–217.
23. Latenser BA. Critical care of the burn patient: the first 48 hours. Crit Care Med 2009; 37 10:2819–2826.
24. Luo Q, Li W, Zou X, Dang Y, Wang K, Wu J, Li Y. Modeling fluid resuscitation by formulating infusion rate and urine output in severe thermal burn adult patients: a retrospective cohort study. Biomed Res Int 2015; 2015: 508043.
25. Saffle JI. The phenomenon of “fluid creep” in acute burn resuscitation. J Burn Care Res 2007; 28 3:382–395.
26. Cartotto R, Zhou A. Fluid creep: the pendulum hasn’t swung back yet!. J Burn Care Res 2010; 31 4:551–558.
27. Klein MB, Hayden D, Elson C, Nathens AB, Gamelli RL, Gibran NS, Herndon DN, Arnoldo B, Silver G, Schoenfeld D, et al. The association between fluid administration and outcome following major burn: a multicenter study. Ann Surg 2007; 245 4:622–628.
28. Dulhunty JM, Boots RJ, Rudd MJ, Muller MJ, Lipman J. Increased fluid resuscitation can lead to adverse outcomes in major-burn injured patients, but low mortality is achievable. Burns 2008; 34 8:1090–1097.
29. Raghunathan K, Bonavia A, Nathanson BH, Beadles CA, Shaw AD, Brookhart MA, Miller TE, Lindenauer PK. Association between initial fluid choice and subsequent in-hospital mortality during the resuscitation of adults with septic shock. Anesthesiology 2015; 123 6:1385–1393.
30. McSwain NE, Champion HR, Fabian TC, Hoyt DB, Wade CE, Eastridge BJ, Proctor KG, Rasmussen TE, Roussel RR, Butler FK, et al. State of the art of fluid resuscitation 2010: prehospital and immediate transition to the hospital. J Trauma 2011; 70 (5 suppl):S2–S10.
31. Schreiber MA. The use of normal saline for resuscitation in trauma. J Trauma 2011; 70 (5 suppl):S13–S14.
32. Malbrain ML, Huygh J, Dabrowski W, De Waele JJ, Staelens A, Wauters J. The use of bio-electrical impedance analysis (BIA) to guide fluid management, resuscitation and deresuscitation in critically ill patients: a bench-to-bedside review. Anaesthesiol Intensive Ther 2014; 46 5:381–391.
33. Malbrain ML, Marik PE, Witters I, Cordemans C, Kirkpatrick AW, Roberts DJ, Van Regenmortel N. Fluid overload, de-resuscitation, and outcomes in critically ill or injured patients: a systematic review with suggestions for clinical practice. Anaesthesiol Intensive Ther 2014; 46 5:361–380.
34. Van Regenmortel N, Jorens PG, Malbrain ML. Fluid management before, during and after elective surgery. Curr Opin Crit Care 2014; 20 4:390–395.
35. Woodcock TE, Woodcock TM. Revised Starling equation and the glycocalyx model of transvascular fluid exchange: an improved paradigm for prescribing intravenous fluid therapy. Br J Anaesth 2012; 108 3:384–394.
36. Woodcock TM, Woodcock TE. Revised Starling equation predicts pulmonary edema formation during fluid loading in the critically ill with presumed hypovolemia. Crit Care Med 2012; 40 9:2741–2742.
37. Levick JR. Revision of the Starling principle: new views of tissue fluid balance. J Physiol 2004; 557 (pt 3):704.
38. Curry FE, Michel CC. A fiber matrix model of capillary permeability. Microvasc Res 1980; 20 1:96–99.
39. Michel CC. Filtration coefficients and osmotic reflexion coefficients of the walls of single frog mesenteric capillaries. J Physiol 1980; 309:341–355.
40. Adamson RH, Lenz JF, Zhang X, Adamson GN, Weinbaum S, Curry FE. Oncotic pressures opposing filtration across non-fenestrated rat microvessels. J Physiol 2004; 557 (pt 3):889–907.
41. Mehta D, Malik AB. Signaling mechanisms regulating endothelial permeability. Physiol Rev 2006; 86 1:279–367.
42. Michel CC. Starling: the formulation of his hypothesis of microvascular fluid exchange and its significance after 100 years. Exp Physiol 1997; 82 1:1–30.
43. Florian JA, Kosky JR, Ainslie K, Pang Z, Dull RO, Tarbell JM. Heparan sulfate proteoglycan is a mechanosensor on endothelial cells. Circ Res 2003; 93 10:e136–e142.
44. Weinbaum S, Zhang X, Han Y, Vink H, Cowin SC. Mechanotransduction and flow across the endothelial glycocalyx. Proc Natl Acad Sci U S A 2003; 100 13:7988–7995.
45. Mochizuki S, Vink H, Hiramatsu O, Kajita T, Shigeto F, Spaan JA, Kajiya F. Role of hyaluronic acid glycosaminoglycans in shear-induced endothelium-derived nitric oxide release. Am J Physiol Heart Circ Physiol 2003; 285 2:H722–H726.
46. Pahakis MY, Kosky JR, Dull RO, Tarbell JM. The role of endothelial glycocalyx components in mechanotransduction of fluid shear stress. Biochem Biophys Res Commun 2007; 355 1:228–233.
47. Weinbaum S, Tarbell JM, Damiano ER. The structure and function of the endothelial glycocalyx layer. Annu Rev Biomed Eng 2007; 9:121–167.
48. Chignalia AZ, Yetimakman F, Christiaans SC, Unal S, Bayrakci B, Wagener BM, Russell RT, Kerby JD, Pittet JF, Dull RO. The glycocalyx and trauma: a review. Shock 2016; 45 4:338–348.
49. Mikelis CM, Simaan M, Ando K, Fukuhara S, Sakurai A, Amornphimoltham P, Masedunskas A, Weigert R, Chavakis T, Adams RH, et al. RhoA and ROCK mediate histamine-induced vascular leakage and anaphylactic shock. Nat Commun 2015; 6:6725.
50. Wu MH. Endothelial focal adhesions and barrier function. J Physiol 2005; 569 (pt 2):359–366.
51. Bates DO. Vascular endothelial growth factors and vascular permeability. Cardiovasc Res 2010; 87 2:262–271.
52. Senger DR, Connolly DT, Van de Water L, Feder J, Dvorak HF. Purification and NH2-terminal amino acid sequence of guinea pig tumor-secreted vascular permeability factor. Cancer Res 1990; 50 6:1774–1778.
53. Majno G, Palade GE. Studies on inflammation. 1. The effect of histamine and serotonin on vascular permeability: an electron microscopic study. J Biophys Biochem Cytol 1961; 11:571–605.
54. Finsterbusch M, Voisin MB, Beyrau M, Williams TJ, Nourshargh S. Neutrophils recruited by chemoattractants in vivo induce microvascular plasma protein leakage through secretion of TNF. J Exp Med 2014; 211 7:1307–1314.
55. Hulstrom D, Svensjo E. Intravital and electron microscopic study of bradykinin-induced vascular permeability changes using FITC-dextran as a tracer. J Pathol 1979; 129 3:125–133.
56. Unterberg A, Wahl M, Baethmann A. Effects of bradykinin on permeability and diameter of pial vessels in vivo. J Cereb Blood Flow Metab 1984; 4 4:574–585.
57. Chung KF. Platelet-activating factor in inflammation and pulmonary disorders. Clin Sci (Lond) 1992; 83 2:127–138.
58. Evans TW, Chung KF, Rogers DF, Barnes PJ. Effect of platelet-activating factor on airway vascular permeability: possible mechanisms. J Appl Physiol (1985) 1987; 63 2:479–484.
59. O’Donnell SR, Barnett CJ. Microvascular leakage to platelet activating factor in guinea-pig trachea and bronchi. Eur J Pharmacol 1987; 138 3:385–396.
60. Dahlen SE, Bjork J, Hedqvist P, Arfors KE, Hammarstrom S, Lindgren JA, Samuelsson B. Leukotrienes promote plasma leakage and leukocyte adhesion in postcapillary venules: in vivo effects with relevance to the acute inflammatory response. Proc Natl Acad Sci U S A 1981; 78 6:3887–3891.
61. Joris I, Majno G, Corey EJ, Lewis RA. The mechanism of vascular leakage induced by leukotriene E4. Endothelial contraction. Am J Pathol 1987; 126 1:19–24.
62. Dejana E, Orsenigo F, Lampugnani MG. The role of adherens junctions and VE-cadherin in the control of vascular permeability. J Cell Sci 2008; 121 (pt 13):2115–2122.
63. Chen XL, Nam JO, Jean C, Lawson C, Walsh CT, Goka E, Lim ST, Tomar A, Tancioni I, Uryu S, et al. VEGF-induced vascular permeability is mediated by FAK. Dev Cell 2012; 22 1:146–157.
64. Abedi H, Zachary I. Vascular endothelial growth factor stimulates tyrosine phosphorylation and recruitment to new focal adhesions of focal adhesion kinase and paxillin in endothelial cells. J Biol Chem 1997; 272 24:15442–15451.
65. Antonetti DA, Barber AJ, Hollinger LA, Wolpert EB, Gardner TW. Vascular endothelial growth factor induces rapid phosphorylation of tight junction proteins occludin and zonula occluden 1. A potential mechanism for vascular permeability in diabetic retinopathy and tumors. J Biol Chem 1999; 274 33:23463–23467.
66. Kevil CG, Payne DK, Mire E, Alexander JS. Vascular permeability factor/vascular endothelial cell growth factor-mediated permeability occurs through disorganization of endothelial junctional proteins. J Biol Chem 1998; 273 24:15099–15103.
67. Infanger M, Schmidt O, Kossmehl P, Grad S, Ertel W, Grimm D. Vascular endothelial growth factor serum level is strongly enhanced after burn injury and correlated with local and general tissue edema. Burns 2004; 30 4:305–311.
68. Wada T, Jesmin S, Gando S, Sultana SN, Zaedi S, Yokota H. Using angiogenic factors and their soluble receptors to predict organ dysfunction in patients with disseminated intravascular coagulation associated with severe trauma. Crit Care 2012; 16 2:R63.
69. van der Flier M, van Leeuwen HJ, van Kessel KP, Kimpen JL, Hoepelman AI, Geelen SP. Plasma vascular endothelial growth factor in severe sepsis. Shock 2005; 23 1:35–38.
70. Pickkers P, Sprong T, Eijk L, Hoeven H, Smits P, Deuren M. Vascular endothelial growth factor is increased during the first 48 hours of human septic shock and correlates with vascular permeability. Shock 2005; 24 6:508–512.
71. Ashina K, Tsubosaka Y, Nakamura T, Omori K, Kobayashi K, Hori M, Ozaki H, Murata T. Histamine induces vascular hyperpermeability by increasing blood flow and endothelial barrier disruption in vivo. PLoS One 2015; 10 7:e0132367.
72. Wessel F, Winderlich M, Holm M, Frye M, Rivera-Galdos R, Vockel M, Linnepe R, Ipe U, Stadtmann A, Zarbock A, et al. Leukocyte extravasation and vascular permeability are each controlled in vivo by different tyrosine residues of VE-cadherin. Nat Immunol 2014; 15 3:223–230.
73. Ma T, Liu L, Wang P, Xue Y. Evidence for involvement of ROCK signaling in bradykinin-induced increase in murine blood-tumor barrier permeability. J Neurooncol 2012; 106 2:291–301.
74. Liu LB, Xue YX, Liu YH, Wang YB. Bradykinin increases blood-tumor barrier permeability by down-regulating the expression levels of ZO-1, occludin, and claudin-5 and rearranging actin cytoskeleton. J Neurosci Res 2008; 86 5:1153–1168.
75. Ma T, Xue Y. RhoA-mediated potential regulation of blood-tumor barrier permeability by bradykinin. J Mol Neurosci 2010; 42 1:67–73.
76. Adamson RH, Zeng M, Adamson GN, Lenz JF, Curry FE. PAF- and bradykinin-induced hyperpermeability of rat venules is independent of actin-myosin contraction. Am J Physiol Heart Circ Physiol 2003; 285 1:H406–H417.
77. Knezevic II, Predescu SA, Neamu RF, Gorovoy MS, Knezevic NM, Easington C, Malik AB, Predescu DN. Tiam1 and Rac1 are required for platelet-activating factor-induced endothelial junctional disassembly and increase in vascular permeability. J Biol Chem 2009; 284 8:5381–5394.
78. Zhou X, He P. Temporal and spatial correlation of platelet-activating factor-induced increases in endothelial [Ca(2)(+)]i, nitric oxide, and gap formation in intact venules. Am J Physiol Heart Circ Physiol 2011; 301 5:H1788–H1797.
79. Zhu L, He P. Platelet-activating factor increases endothelial [Ca2+]i and NO production in individually perfused intact microvessels. Am J Physiol Heart Circ Physiol 2005; 288 6:H2869–H2877.
80. Thibeault S, Rautureau Y, Oubaha M, Faubert D, Wilkes BC, Delisle C, Gratton JP. S-nitrosylation of beta-catenin by eNOS-derived NO promotes VEGF-induced endothelial cell permeability. Mol Cell 2010; 39 3:468–476.
81. Chavez A, Smith M, Mehta D. New insights into the regulation of vascular permeability. Int Rev Cell Mol Biol 2011; 290:205–248.
82. Feletou M, Bonnardel E, Canet E. Bradykinin and changes in microvascular permeability in the hamster cheek pouch: role of nitric oxide. Br J Pharmacol 1996; 118 6:1371–1376.
83. Yang B, Cai B, Deng P, Wu X, Guan Y, Zhang B, Cai W, Schaper J, Schaper W. Nitric oxide increases arterial endotheial permeability through mediating VE-cadherin expression during arteriogenesis. PLoS One 2015; 10 7:e0127931.
84. Vadas P, Perelman B, Liss G. Platelet-activating factor, histamine, and tryptase levels in human anaphylaxis. J Allergy Clin Immunol 2013; 131 1:144–149.
85. Jeewandara C, Gomes L, Wickramasinghe N, Gutowska-Owsiak D, Waithe D, Paranavitane SA, Shyamali NL, Ogg GS, Malavige GN. Platelet activating factor contributes to vascular leak in acute dengue infection. PLoS Negl Trop Dis 2015; 9 2:e0003459.
86. Fernandes ES, Passos GF, Campos MM, Araujo JG, Pesquero JL, Avelllar MC, Teixeira MM, Calixto JB. Mechanisms underlying the modulatory action of platelet activating factor (PAF) on the upregulation of kinin B1 receptors in the rat paw. Br J Pharmacol 2003; 139 5:973–981.
87. Lee KS, Kim SR, Park HS, Jin GY, Lee YC. Cysteinyl leukotriene receptor antagonist regulates vascular permeability by reducing vascular endothelial growth factor expression. J Allergy Clin Immunol 2004; 114 5:1093–1099.
88. Duah E, Adapala RK, Al-Azzam N, Kondeti V, Gombedza F, Thodeti CK, Paruchuri S. Cysteinyl leukotrienes regulate endothelial cell inflammatory and proliferative signals through CysLT(2) and CysLT(1) receptors. Sci Rep 2013; 3:3274.
89. Kubes P, Ibbotson G, Russell J, Wallace JL, Granger DN. Role of platelet-activating factor in ischemia/reperfusion-induced leukocyte adherence. Am J Physiol 1990; 259 (2 pt 1):G300–G305.
90. Bitencourt CS, Bessi VL, Huynh DN, Menard L, Lefebvre JS, Levesque T, Hamdan L, Sohouhenou F, Faccioli LH, Borgeat P, et al. Cooperative role of endogenous leucotrienes and platelet-activating factor in ischaemia-reperfusion-mediated tissue injury. J Cell Mol Med 2013; 17 12:1554–1565.
91. Bierman A, Yerrapureddy A, Reddy NM, Hassoun PM, Reddy SP. Epidermal growth factor receptor (EGFR) regulates mechanical ventilation-induced lung injury in mice. Transl Res 2008; 152 6:265–272.
92. Maniatis NA, Harokopos V, Thanassopoulou A, Oikonomou N, Mersinias V, Witke W, Orfanos SE, Armaganidis A, Roussos C, Kotanidou A, et al. A critical role for gelsolin in ventilator-induced lung injury. Am J Respir Cell Mol Biol 2009; 41 4:426–432.
93. Villar J, Muros M, Cabrera-Benitez NE, Valladares F, Lopez-Hernandez M, Flores C, Martin-Barrasa JL, Blanco J, Liu M, Kacmarek RM. Soluble platelet-endothelial cell adhesion molecule-1, a biomarker of ventilator-induced lung injury. Crit Care 2014; 18 2:R41.
94. Kippenberger S, Loitsch S, Guschel M, Muller J, Knies Y, Kaufmann R, Bernd A. Mechanical stretch stimulates protein kinase B/Akt phosphorylation in epidermal cells via angiotensin II type 1 receptor and epidermal growth factor receptor. J Biol Chem 2005; 280 4:3060–3067.
95. Iwasaki H, Eguchi S, Ueno H, Marumo F, Hirata Y. Mechanical stretch stimulates growth of vascular smooth muscle cells via epidermal growth factor receptor. Am J Physiol Heart Circ Physiol 2000; 278 2:H521–H529.
96. Chan MW, Arora PD, Bozavikov P, McCulloch CA. FAK, PIP5KIgamma and gelsolin cooperatively mediate force-induced expression of alpha-smooth muscle actin. J Cell Sci 2009; 122 (pt 15):2769–2781.
97. Aragona M, Panciera T, Manfrin A, Giulitti S, Michielin F, Elvassore N, Dupont S, Piccolo S. A mechanical checkpoint controls multicellular growth through YAP/TAZ regulation by actin-processing factors. Cell 2013; 154 5:1047–1059.
98. Chiu YJ, McBeath E, Fujiwara K. Mechanotransduction in an extracted cell model: Fyn drives stretch- and flow-elicited PECAM-1 phosphorylation. J Cell Biol 2008; 182 4:753–763.
99. Fujiwara K. Platelet endothelial cell adhesion molecule-1 and mechanotransduction in vascular endothelial cells. J Intern Med 2006; 259 4:373–380.
100. Chiu JJ, Chien S. Effects of disturbed flow on vascular endothelium: pathophysiological basis and clinical perspectives. Physiol Rev 2011; 91 1:327–387.
101. DePaola N, Davies PF, Pritchard WF Jr, Florez L, Harbeck N, Polacek DC. Spatial and temporal regulation of gap junction connexin43 in vascular endothelial cells exposed to controlled disturbed flows in vitro. Proc Natl Acad Sci U S A 1999; 96 6:3154–3159.
102. Jiang YZ, Manduchi E, Jimenez JM, Davies PF. Endothelial epigenetics in biomechanical stress: disturbed flow-mediated epigenomic plasticity in vivo and in vitro. Arterioscler Thromb Vasc Biol 2015; 35 6:1317–1326.
103. Birukov KG. Small GTPases in mechanosensitive regulation of endothelial barrier. Microvasc Res 2009; 77 1:46–52.
104. Shiomi H, Takahashi N, Kawashima Y, Ogawa S, Haga N, Kushida N, Nomiya M, Yanagida T, Ishibashi K, Aikawa K, et al. Involvement of stretch-induced Rho-kinase activation in the generation of bladder tone. Neurourol Urodyn 2013; 32 7:1019–1025.
105. Ali MH, Mungai PT, Schumacker PT. Stretch-induced phosphorylation of focal adhesion kinase in endothelial cells: role of mitochondrial oxidants. Am J Physiol Lung Cell Mol Physiol 2006; 291 1:L38–45.
106. Zebda N, Dubrovskyi O, Birukov KG. Focal adhesion kinase regulation of mechanotransduction and its impact on endothelial cell functions. Microvasc Res 2012; 83 1:71–81.
107. Thi MM, Tarbell JM, Weinbaum S, Spray DC. The role of the glycocalyx in reorganization of the actin cytoskeleton under fluid shear stress: a “bumper-car” model. Proc Natl Acad Sci U S A 2004; 101 47:16483–16488.
108. Tarbell JM, Pahakis MY. Mechanotransduction and the glycocalyx. J Intern Med 2006; 259 4:339–350.
109. Williams DA, Flood MH. Capillary tone: cyclooxygenase, shear stress, luminal glycocalyx, and hydraulic conductivity (Lp). Physiol Rep 2015; 3 4:
110. Hynes RO. The extracellular matrix: not just pretty fibrils. Science 2009; 326 5957:1216–1219.
111. Baranowsky A, Mokkapati S, Bechtel M, Krugel J, Miosge N, Wickenhauser C, Smyth N, Nischt R. Impaired wound healing in mice lacking the basement membrane protein nidogen 1. Matrix Biol 2010; 29 1:15–21.
112. Li J, Zhang YP, Kirsner RS. Angiogenesis in wound repair: angiogenic growth factors and the extracellular matrix. Microsc Res Tech 2003; 60 1:107–114.
113. Kirn-Safran C, Farach-Carson MC, Carson DD. Multifunctionality of extracellular and cell surface heparan sulfate proteoglycans. Cell Mol Life Sci 2009; 66 21:3421–3434.
114. Kruegel J, Miosge N. Basement membrane components are key players in specialized extracellular matrices. Cell Mol Life Sci 2010; 67 17:2879–2895.
115. McMillan JR, Akiyama M, Shimizu H. Epidermal basement membrane zone components: ultrastructural distribution and molecular interactions. J Dermatol Sci 2003; 31 3:169–177.
116. Yurchenco PD. Basement membranes: cell scaffoldings and signaling platforms. Cold Spring Harb Perspect Biol 2011; 3 2:
117. Wang S, Cao C, Chen Z, Bankaitis V, Tzima E, Sheibani N, Burridge K. Pericytes regulate vascular basement membrane remodeling and govern neutrophil extravasation during inflammation. PLoS One 2012; 7 9:e45499.
118. Voisin MB, Probstl D, Nourshargh S. Venular basement membranes ubiquitously express matrix protein low-expression regions: characterization in multiple tissues and remodeling during inflammation. Am J Pathol 2010; 176 1:482–495.
119. Kilo C, Vogler N, Williamson JR. Muscle capillary basement membrane changes related to aging and to diabetes mellitus. Diabetes 1972; 21 8:881–905.
120. Candiello J, Cole GJ, Halfter W. Age-dependent changes in the structure, composition and biophysical properties of a human basement membrane. Matrix Biol 2010; 29 5:402–410.
121. To M, Goz A, Camenzind L, Oertle P, Candiello J, Sullivan M, Henrich PB, Loparic M, Safi F, Eller A, et al. Diabetes-induced morphological, biomechanical, and compositional changes in ocular basement membranes. Exp Eye Res 2013; 116:298–307.
122. Halfter W, Oertle P, Monnier CA, Camenzind L, Reyes-Lua M, Hu H, Candiello J, Labilloy A, Balasubramani M, Henrich PB, et al. New concepts in basement membrane biology. FEBS J 2015; 282 23:4466–4479.
123. Thomopoulos GN, Spicer SS, Gratton MA, Schulte BA. Age-related thickening of basement membrane in stria vascularis capillaries. Hear Res 1997; 111 (1–2):31–41.
124. Farkas E, de Vos RA, Donka G, Jansen Steur EN, Mihaly A, Luiten PG. Age-related microvascular degeneration in the human cerebral periventricular white matter. Acta Neuropathol 2006; 111 2:150–157.
125. Halfter W, Candiello J, Hu H, Zhang P, Schreiber E, Balasubramani M. Protein composition and biomechanical properties of in vivo-derived basement membranes. Cell Adh Migr 2013; 7 1:64–71.
126. Streeten DHP. Orthostatic Disorders of the Circulation: Mechanisms, Manifestations, and Treatment. London, New York: Springer; 2012.
127. Castejon OJ. Ultrastructural alterations of human cortical capillary basement membrane in human brain oedema. Folia Neuropathol 2014; 52 1:10–21.
128. Kelley LC, Lohmer LL, Hagedorn EJ, Sherwood DR. Traversing the basement membrane in vivo: a diversity of strategies. J Cell Biol 2014; 204 3:291–302.
129. Li S, Edgar D, Fassler R, Wadsworth W, Yurchenco PD. The role of laminin in embryonic cell polarization and tissue organization. Dev Cell 2003; 4 5:613–624.
130. Bonnans C, Chou J, Werb Z. Remodelling the extracellular matrix in development and disease. Nat Rev Mol Cell Biol 2014; 15 12:786–801.
131. Pontenza B, Wilson WC, Greenberg M, Wong L, Dunkelman A, Tenenhaus M. Wilson WC, Grande CM, Hoyt DB. Burn injuries. Trauma Emergency Resuscitation Perioperative Anesthesia Surgical Management. New York: Informa; 2007. 655–666.Vol. 1.
132. Diaz-Flores L, Gutierrez R, Madrid JF, Varela H, Valladares F, Acosta E, Martin-Vasallo P, Diaz-Flores L Jr. Pericytes. Morphofunction, interactions and pathology in a quiescent and activated mesenchymal cell niche. Histol Histopathol 2009; 24 7:909–969.
133. Nakano M, Atobe Y, Goris RC, Yazama F, Ono M, Sawada H, Kadota T, Funakoshi K, Kishida R. Ultrastructure of the capillary pericytes and the expression of smooth muscle alpha-actin and desmin in the snake infrared sensory organs. Anat Rec 2000; 260 3:299–307.
134. Antonov AS, Antonova GN, Fujii M, ten Dijke P, Handa V, Catravas JD, Verin AD. Regulation of endothelial barrier function by TGF-beta type I receptor ALK5: potential role of contractile mechanisms and heat shock protein 90. J Cell Physiol 2012; 227 2:759–771.
135. Winkler EA, Bell RD, Zlokovic BV. Central nervous system pericytes in health and disease. Nat Neurosci 2011; 14 11:1398–1405.
136. Dominguez E, Raoul W, Calippe B, Sahel JA, Guillonneau X, Paques M, Sennlaub F. Experimental branch retinal vein occlusion induces upstream pericyte loss and vascular destabilization. PLoS One 2015; 10 7:e0132644.
137. von Tell D, Armulik A, Betsholtz C. Pericytes and vascular stability. Exp Cell Res 2006; 312 5:623–629.
138. Kutcher ME, Herman IM. The pericyte: cellular regulator of microvascular blood flow. Microvasc Res 2009; 77 3:235–246.
139. Kutcher ME, Kolyada AY, Surks HK, Herman IM. Pericyte Rho GTPase mediates both pericyte contractile phenotype and capillary endothelial growth state. Am J Pathol 2007; 171 2:693–701.
140. Durham JT, Surks HK, Dulmovits BM, Herman IM. Pericyte contractility controls endothelial cell cycle progression and sprouting: insights into angiogenic switch mechanics. Am J Physiol Cell Physiol 2014; 307 9:C878–C892.
141. Fuxe J, Tabruyn S, Colton K, Zaid H, Adams A, Baluk P, Lashnits E, Morisada T, Le T, O’Brien S, et al. Pericyte requirement for anti-leak action of angiopoietin-1 and vascular remodeling in sustained inflammation. Am J Pathol 2011; 178 6:2897–2909.
142. Hall CN, Reynell C, Gesslein B, Hamilton NB, Mishra A, Sutherland BA, O’Farrell FM, Buchan AM, Lauritzen M, Attwell D. Capillary pericytes regulate cerebral blood flow in health and disease. Nature 2014; 508 7494:55–60.
143. Crawford C, Wildman SS, Kelly MC, Kennedy-Lydon TM, Peppiatt-Wildman CM. Sympathetic nerve-derived ATP regulates renal medullary vasa recta diameter via pericyte cells: a role for regulating medullary blood flow? Front Physiol 2013; 4:307.
144. Garnacho-Montero J, Fernandez-Mondejar E, Ferrer-Roca R, Herrera-Gutierrez ME, Lorente JA, Ruiz-Santana S, Artigas A. Crystalloids and colloids in critical patient resuscitation. Med Intensiva 2015; 39 5:303–315.
145. Perel P, Roberts I. Colloids versus crystalloids for fluid resuscitation in critically ill patients. Cochrane Database Syst Rev 2012; 6:CD000567.
146. Chappell D, Bruegger D, Potzel J, Jacob M, Brettner F, Vogeser M, Conzen P, Becker BF, Rehm M. Hypervolemia increases release of atrial natriuretic peptide and shedding of the endothelial glycocalyx. Crit Care 2014; 18 5:538.
147. Chappell D, Jacob M. Role of the glycocalyx in fluid management: small things matter. Best Pract Res Clin Anaesthesiol 2014; 28 3:227–234.
148. Hess JR, Holcomb JB. Transfusion practice in military trauma. Transfus Med 2008; 18 3:143–150.
149. Holcomb JB, Tilley BC, Baraniuk S, Fox EE, Wade CE, Podbielski JM, del Junco DJ, Brasel KJ, Bulger EM, Callcut RA, et al. Transfusion of plasma, platelets, and red blood cells in a 1:1:1 vs a 1:1:2 ratio and mortality in patients with severe trauma: the PROPPR randomized clinical trial. JAMA 2015; 313 5:471–482.
150. Langan NR, Eckert M, Martin MJ. Changing patterns of in-hospital deaths following implementation of damage control resuscitation practices in US forward military treatment facilities. JAMA Surg 2014; 149 9:904–912.
151. Campion EM, Pritts TA, Dorlac WC, Nguyen AQ, Fraley SM, Hanseman D, Robinson BR. Implementation of a military-derived damage-control resuscitation strategy in a civilian trauma center decreases acute hypoxia in massively transfused patients. J Trauma Acute Care Surg 2013; 75 (2 suppl 2):S221–S227.
152. Pati S, Matijevic N, Doursout MF, Ko T, Cao Y, Deng X, Kozar RA, Hartwell E, Conyers J, Holcomb JB. Protective effects of fresh frozen plasma on vascular endothelial permeability, coagulation, and resuscitation after hemorrhagic shock are time dependent and diminish between days 0 and 5 after thaw. J Trauma 2010; 69 (Suppl 1):S55–S63.
153. Peng Z, Pati S, Potter D, Brown R, Holcomb JB, Grill R, Wataha K, Park PW, Xue H, Kozar RA. Fresh frozen plasma lessens pulmonary endothelial inflammation and hyperpermeability after hemorrhagic shock and is associated with loss of syndecan 1. Shock 2013; 40 3:195–202.
154. Pidcoke HF, Aden JK, Mora AG, Borgman MA, Spinella PC, Dubick MA, Blackbourne LH, Cap AP. Ten-year analysis of transfusion in Operation Iraqi Freedom and Operation Enduring Freedom: increased plasma and platelet use correlates with improved survival. J Trauma Acute Care Surg 2012; 73 (6 suppl 5):S445–S452.
155. Jenkins DH, Rappold JF, Badloe JF, Berseus O, Blackbourne L, Brohi KH, Butler FK, Cap AP, Cohen MJ, Davenport R, et al. Trauma hemostasis and oxygenation research position paper on remote damage control resuscitation: definitions, current practice, and knowledge gaps. Shock 2014; 41 (Suppl 1):3–12.
156. Hooper T, Nadler R, Butler FK, Badloe JF, Glassberg E. Implementation and execution of military forward resuscitation programs: reply. Shock 2014; 41 (Suppl 1):102–103.
157. Torres LN, Sondeen JL, Ji L, Dubick MA, Torres Filho I. Evaluation of resuscitation fluids on endothelial glycocalyx, venular blood flow, and coagulation function after hemorrhagic shock in rats. J Trauma Acute Care Surg 2013; 75 5:759–766.
158. Kozar RA, Peng Z, Zhang R, Holcomb JB, Pati S, Park P, Ko TC, Paredes A. Plasma restoration of endothelial glycocalyx in a rodent model of hemorrhagic shock. Anesth Analg 2011; 112 6:1289–1295.
159. Young PP, Cotton BA, Goodnough LT. Massive transfusion protocols for patients with substantial hemorrhage. Transfus Med Rev 2011; 25 4:293–303.
160. Dutton RP. Management of traumatic haemorrhage—the US perspective. Anaesthesia 2015; 70:108–138.
161. Chatrath V, Khetarpal R, Ahuja J. Fluid management in patients with trauma: restrictive versus liberal approach. J Anaesthesiol Clin Pharmacol 2015; 31 3:308–316.
162. Spinella PC, Doctor A. Role of transfused red blood cells for shock and coagulopathy within remote damage control resuscitation. Shock 2014; 41 (Suppl 1):30–34.
163. Becker BF, Jacob M, Leipert S, Salmon AH, Chappell D. Degradation of the endothelial glycocalyx in clinical settings: searching for the sheddases. Br J Clin Pharmacol 2015; 80 3:389–402.
164. Chappell D, Dorfler N, Jacob M, Rehm M, Welsch U, Conzen P, Becker BF. Glycocalyx protection reduces leukocyte adhesion after ischemia/reperfusion. Shock 2010; 34 2:133–139.
165. Zeng Y, Adamson RH, Curry FR, Tarbell JM. Sphingosine-1-phosphate protects endothelial glycocalyx by inhibiting syndecan-1 shedding. Am J Physiol Heart Circ Physiol 2014; 306 3:H363–H372.
166. Brower RG, Matthay MA, Morris A, Schoenfield D, Thompson T, Wheeler A. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. The Acute Respiratory Distress Syndrome Network. N Engl J Med 2000; 342 18:1301–1308.
167. Determann RM, Royakkers A, Wolthuis EK, Vlaar AP, Choi G, Paulus F, Hofstra JJ, de Graaff MJ, Korevaar JC, Schultz MJ. Ventilation with lower tidal volumes as compared with conventional tidal volumes for patients without acute lung injury: a preventive randomized controlled trial. Crit Care 2010; 14 1:R1.
168. Fuller BM, Mohr NM, Drewry AM, Carpenter CR. Lower tidal volume at initiation of mechanical ventilation may reduce progression to acute respiratory distress syndrome: a systematic review. Crit Care 2013; 17 1:R11.
169. Serpa Neto A, Simonis FD, Schultz MJ. How to ventilate patients without acute respiratory distress syndrome? Curr Opin Crit Care 2015; 21 1:65–73.
170. Serpa Neto A, Nagtzaam L, Schultz MJ. Ventilation with lower tidal volumes for critically ill patients without the acute respiratory distress syndrome: a systematic translational review and meta-analysis. Curr Opin Crit Care 2014; 20 1:25–32.
171. Hamanaka K, Jian MY, Townsley MI, King JA, Liedtke W, Weber DS, Eyal FG, Clapp MM, Parker JC. TRPV4 channels augment macrophage activation and ventilator-induced lung injury. Am J Physiol Lung Cell Mol Physiol 2010; 299 3:L353–L362.
172. Jurek SC, Hirano-Kobayashi M, Chiang H, Kohane DS, Matthews BD. Prevention of ventilator-induced lung edema by inhalation of nanoparticles releasing ruthenium red. Am J Respir Cell Mol Biol 2014; 50 6:1107–1117.
173. Birukova AA, Fu P, Xing J, Cokic I, Birukov KG. Lung endothelial barrier protection by iloprost in the 2-hit models of ventilator-induced lung injury (VILI) involves inhibition of Rho signaling. Transl Res 2010; 155 1:44–54.
174. de Prost N, Ricard JD, Saumon G, Dreyfuss D. Ventilator-induced lung injury: historical perspectives and clinical implications. Ann Intensive Care 2011; 1 1:28.
175. Rybalko V, Hsieh PL, Merscham-Banda M, Suggs LJ, Farrar RP. The development of macrophage-mediated cell therapy to improve skeletal muscle function after injury. PLoS One 2015; 10 12:e0145550.
176. Rowart P, Erpicum P, Detry O, Weekers L, Gregoire C, Lechanteur C, Briquet A, Beguin Y, Krzesinski JM, Jouret F. Mesenchymal stromal cell therapy in ischemia/reperfusion injury. J Immunol Res 2015; 2015:602597.
177. Ghieh F, Jurjus R, Ibrahim A, Geagea AG, Daouk H, El Baba B, Chams S, Matar M, Zein W, Jurjus A. The use of stem cells in burn wound healing: a review. Biomed Res Int 2015; 2015:684084.
178. Chimenti L, Luque T, Bonsignore MR, Ramirez J, Navajas D, Farre R. Pre-treatment with mesenchymal stem cells reduces ventilator-induced lung injury. Eur Respir J 2012; 40 4:939–948.
179. Gore AV, Bible LE, Livingston DH, Mohr AM, Sifri ZC. Mesenchymal stem cells enhance lung recovery after injury, shock, and chronic stress. Surgery 2016; 159 5:1430–1435.
180. Ranganath SH, Levy O, Inamdar MS, Karp JM. Harnessing the mesenchymal stem cell secretome for the treatment of cardiovascular disease. Cell Stem Cell 2012; 10 3:244–258.
181. Koizumi N, Okumura N, Ueno M, Kinoshita S. New therapeutic modality for corneal endothelial disease using Rho-associated kinase inhibitor eye drops. Cornea 2014; 33 (Suppl 11):S25–S31.
182. Yuan D, Xu S, He P. Enhanced permeability responses to inflammation in streptozotocin-induced diabetic rat venules: Rho-mediated alterations of actin cytoskeleton and VE-cadherin. Am J Physiol Heart Circ Physiol 2014; 307 1:H44–H53.
183. Kirchner C, Luer B, Efferz P, Wohlschlaeger J, Paul A, Minor T. Ex vivo use of a Rho-kinase inhibitor during renal preservation improves graft function upon reperfusion. Cryobiology 2015; 70 1:71–75.
184. Zheng HZ, Zhao KS, Zhou BY, Huang QB. Role of Rho kinase and actin filament in the increased vascular permeability of skin venules in rats after scalding. Burns 2003; 29 8:820–827.
185. Cui Q, Zhang Y, Chen H, Li J, Rho kinase. A new target for treatment of cerebral ischemia/reperfusion injury. Neural Regen Res 2013; 8 13:1180–1189.
186. Li T, Yang G, Xu J, Zhu Y, Liu L. Regulatory effect of Rac1 on vascular reactivity after hemorrhagic shock in rats. J Cardiovasc Pharmacol 2011; 57 6:656–665.
187. Childs EW, Tharakan B, Hunter FA, Smythe WR. 17beta-estradiol mediated protection against vascular leak after hemorrhagic shock: role of estrogen receptors and apoptotic signaling. Shock 2010; 34 3:229–235.
188. Hubbard W, Keith J, Berman J, Miller M, Scott C, Peck C, Chaudry IH. 17alpha-Ethynylestradiol-3-sulfate treatment of severe blood loss in rats. J Surg Res 2015; 193 1:355–360.
189. Gatson JW, Maass DL, Simpkins JW, Idris AH, Minei JP, Wigginton JG. Estrogen treatment following severe burn injury reduces brain inflammation and apoptotic signaling. J Neuroinflammation 2009; 6:30.
190. Evgenov OV, Pacher P, Williams W, Evgenov NV, Mabley JG, Cicila J, Siko ZB, Salzman AL, Szabo C. Parenteral administration of glipizide sodium salt, an inhibitor of adenosine triphosphate-sensitive potassium channels, prolongs short-term survival after severe controlled hemorrhage in rats. Crit Care Med 2003; 31 10:2429–2436.
191. Sordi R, Fernandes D, Heckert BT, Assreuy J. Early potassium channel blockade improves sepsis-induced organ damage and cardiovascular dysfunction. Br J Pharmacol 2011; 163 6:1289–1301.
192. Hu X, Yang Z, Yang M, Qian J, Cahoon J, Xu J, Sun S, Tang W. Remote ischemic preconditioning mitigates myocardial and neurological dysfunction via K(ATP) channel activation in a rat model of hemorrhagic shock. Shock 2014; 42 3:228–233.
193. Zhao G, Zhao Y, Pan B, Liu J, Huang X, Zhang X, Cao C, Hou N, Wu C, Zhao KS, et al. Hypersensitivity of BKCa to Ca2+ sparks underlies hyporeactivity of arterial smooth muscle in shock. Circ Res 2007; 101 5:493–502.
194. Lei Y, Peng X, Liu L, Dong Z, Li T. Beneficial effect of cyclosporine A on traumatic hemorrhagic shock. J Surg Res 2015; 195 2:529–540.
195. Tharakan B, Holder-Haynes JG, Hunter FA, Smythe WR, Childs EW. Cyclosporine A prevents vascular hyperpermeability after hemorrhagic shock by inhibiting apoptotic signaling. J Trauma 2009; 66 4:1033–1039.
196. Whaley JG, Tharakan B, Smith B, Hunter FA, Childs EW. (-)-Deprenyl inhibits thermal injury-induced apoptotic signaling and hyperpermeability in microvascular endothelial cells. J Burn Care Res 2009; 30 6:1018–1027.
197. Tharakan B, Whaley JG, Hunter FA, Smythe WR, Childs EW. (-)-Deprenyl inhibits vascular hyperpermeability after hemorrhagic shock. Shock 2010; 33 1:56–63.
198. Kim JH, Suk MH, Yoon DW, Lee SH, Hur GY, Jung KH, Jeong HC, Lee SY, Lee SY, Suh IB, et al. Inhibition of matrix metalloproteinase-9 prevents neutrophilic inflammation in ventilator-induced lung injury. Am J Physiol Lung Cell Mol Physiol 2006; 291 4:L580–L587.
199. Steinberg J, Halter J, Schiller HJ, Dasilva M, Landas S, Gatto LA, Maisi P, Sorsa T, Rajamaki M, Lee HM, et al. Metalloproteinase inhibition reduces lung injury and improves survival after cecal ligation and puncture in rats. J Surg Res 2003; 111 2:185–195.
200. Bae JS, Lee W, Son HN, Lee YM, Kim IS. Anti-transforming growth factor beta-induced protein antibody ameliorates vascular barrier dysfunction and improves survival in sepsis. Acta Physiol (Oxf) 2014; 212 4:306–315.
201. Stone ML, Sharma AK, Zhao Y, Charles EJ, Huerter ME, Johnston WF, Kron IL, Lynch KR, Laubach VE. Sphingosine-1-phosphate receptor 1 agonism attenuates lung ischemia-reperfusion injury. Am J Physiol Lung Cell Mol Physiol 2015; 308 12:L1245–L1252.
202. Bonitz JA, Son JY, Chandler B, Tomaio JN, Qin Y, Prescott LM, Feketeova E, Deitch EA. A sphingosine-1 phosphate agonist (FTY720) limits trauma/hemorrhagic shock-induced multiple organ dysfunction syndrome. Shock 2014; 42 5:448–455.
203. Lundblad C, Axelberg H, Grande PO. Treatment with the sphingosine-1-phosphate analogue FTY 720 reduces loss of plasma volume during experimental sepsis in the rat. Acta Anaesthesiol Scand 2013; 57 6:713–718.
204. Pedersen CM, Schmidt MR, Barnes G, Botker HE, Kharbanda RK, Newby DE, Cruden NL. Bradykinin does not mediate remote ischaemic preconditioning or ischaemia-reperfusion injury in vivo in man. Heart 2011; 97 22:1857–1861.
205. Pickkers P, Dorresteijn MJ, Bouw MP, van der Hoeven JG, Smits P. In vivo evidence for nitric oxide-mediated calcium-activated potassium-channel activation during human endotoxemia. Circulation 2006; 114 5:414–421.
206. Morelli A, Donati A, Ertmer C, Rehberg S, Lange M, Orecchioni A, Cecchini V, Landoni G, Pelaia P, Pietropaoli P, et al. Levosimendan for resuscitating the microcirculation in patients with septic shock: a randomized controlled study. Crit Care 2010; 14 6:R232.
207. Orme RM, Perkins GD, McAuley DF, Liu KD, Mason AJ, Morelli A, Singer M, Ashby D, Gordon AC. An efficacy and mechanism evaluation study of Levosimendan for the Prevention of Acute oRgan Dysfunction in Sepsis (LeoPARDS): protocol for a randomized controlled trial. Trials 2014; 15:199.
208. Piot C, Croisille P, Staat P, Thibault H, Rioufol G, Mewton N, Elbelghiti R, Cung TT, Bonnefoy E, Angoulvant D, et al. Effect of cyclosporine on reperfusion injury in acute myocardial infarction. N Engl J Med 2008; 359 5:473–481.
209. Wiewel MA, van der Meer AJ, Haddad J, Jacobson EW, Vlasuk GP, van der Poll T. SRT2379, a small-molecule SIRT1 activator, fails to reduce cytokine release in a human endotoxemia model. Crit Care 2013; 17 4:1–59.
210. Schulze CJ, Castro MM, Kandasamy AD, Cena J, Bryden C, Wang SH, Koshal A, Tsuyuki RT, Finegan BA, Schulz R. Doxycycline reduces cardiac matrix metalloproteinase-2 activity but does not ameliorate myocardial dysfunction during reperfusion in coronary artery bypass patients undergoing cardiopulmonary bypass. Crit Care Med 2013; 41 11:2512–2520.
211. Newby LK, Marber MS, Melloni C, Sarov-Blat L, Aberle LH, Aylward PE, Cai G, de Winter RJ, Hamm CW, Heitner JF, et al. Losmapimod, a novel p38 mitogen-activated protein kinase inhibitor, in non-ST-segment elevation myocardial infarction: a randomised phase 2 trial. Lancet 2014; 384 9949:1187–1195.
Keywords:

Barrier; basement membrane; edema; endothelial cell; glycocalyx; pericyte

© 2016 by the Shock Society