The June 2011 issue of Shock covers a wide range of excellent clinical and laboratory investigations. This issue of Shock has four articles focused on modulators of sepsis. Salgado et al. (1) focused on modulating microcirculatory dysfunction in a septic peritonitis sheep model using the angiotensin-converting enzyme inhibitor enalaprilat. They found that although sublingual microcirculatory disruption was improved, renal and lung functions were worsened in septic animals receiving enalaprilat. These data imply that the angiotensin-converting enzyme system may be playing a beneficial, as well as a detrimental, effect in sepsis.
Freitas et al. (2) tried ameliorating the reduction of neutrophil migration in a murine cecal ligation and puncture (CLP) model by modulating heme oxygenase (HO) products with the HO inhibitor zinc protoporphyrin IX (ZnPP IX). This study highlights the dichotomy of HO effects. Pretreatment of CLP mice with ZnPP IX reduced systemic inflammation, decreased bacterial count, and increased survival in severe CLP sepsis. In striking contrast, pre- plus post-ZnPP IX treatment actually increased mortality, tumor necrosis factor-α levels, and bacterial load. The authors suggest that early HO activity inhibition decreases carbon monoxide and biliverdin levels, and the fast elimination of administered ZnPP IX prevents a buildup of the HO substrate heme. However, combining pretreatment and posttreatment allows heme accumulation that inhibits neutrophil migration to infectious foci and increases free radical levels.
In another test of a modulator, Soriano et al. (3) focused on the deleterious effects of a reactive oxidant, peroxynitrite (nitric oxide [NO] + superoxide anion), in mediating increased mortality in a CLP or endotoxin model. These authors showed that a peroxynitrite decomposition catalyst (FP15) protected against CLP mortality. Interestingly, the FP15 effect seemed to primarily reduce liver and lung damage, with little effect on plasma nitrite/nitrate levels, implying that CLP mortality in this model was organ targeted rather than systemic.
Hasan et al. (4) also used the murine CLP model to assess the effect of administering an anti-CD44 antibody to decrease CLP-provoked neutrophil accumulation in the bronchoalveolar space. Interestingly, they demonstrated that direct targeting of neutrophil CD44 with the antibody was the mechanism behind blocking CLP-induced lung edema and tissue injury, rather than reducing the binding of the CD44 ligand hyaluronan or decreasing the induction of neutrophil macrophage inflammatory protein 1 expression, both of which have been previously linked to lung damage in septic models.
The theme of therapeutic intervention was continued in investigations of burn and hypotonia models. Lange et al. (5) assessed the ability of combined inducible and neuronal NO synthase (NOS) inhibitors (BBS-2 + 7-nitroindazole) to ameliorate pulmonary dysfunction in an ovine burn plus inhalation injury model. The simultaneous administration of the inducible NOS plus neuronal NOS inhibitors with the burn injury attenuated decreases in PaO2/FiO2 ratios, prevented elevation in lymph or plasma nitrate/nitrite levels, eliminated pulmonary shunting, and restored lung lymph flow. The deleterious effects of simultaneous NOS blockade on splanchnic perfusion and renal function previously reported were circumvented in this study by using half the dose administered in previous studies. These data suggest that combined NOS blockade may be beneficial for preventing organ damage in thermal injury patients.
Bhattacharjee et al. (6), working in a rat hemorrhage shock model, used resuscitation with a combination of a cannabinoid receptor agonist (tetrahydrocannabinol) and a cyclooxygenase 2 inhibitor (NS-398) to prolong postshock survival. The tetrahydrocannabinol-NS-398 drug combination also significantly reduced plasma IL-1, IFN-γ, and IL-10 levels, as well as leukocyte lung sequestration. The combination of this cannabinoid receptor antagonist and cyclooxygenase 2 inhibitor during isotonic sodium chloride solution resuscitation seemed to go beyond stabilizing the mean arterial pressure to inducing anti-inflammatory effects that protected from inflammation-mediated organ damage. These data suggest the potential for this combined therapy in the modulation of hemorrhagic shock.
Muir et al. (7) used a swine model of normovolemic replacement of blood to test a hemoglobin-based oxygen carrier (HBOC-201) consisting of a purified polymerized bovine hemoglobin solution as an improved treatment of hemorrhage. Their data showed that HBOC-201 maintained brain, heart, and kidney tissue oxygenation during exchange transfusion. The question of how to maintain tissue oxygenation and prevent hypoxia after blood loss is a major area of investigation. This study used 50% blood exchange transfusion with HBOC-201 and compared with transfusion with 6% human serum albumin. The heart tissue Po2 remains more stable with HBOC-201, with a minimum of histopathologic changes indicative of oxidative stress. These data indicate that HBOC-201 has potential benefits in organ preservation as a blood replacement in hemorrhage shock. The blood replacement product used in early hemorrhage treatment is only one factor that can affect outcome.
Bahrami et al. (8) investigated how the anesthesia used in experimental hemorrhage/trauma shock models might alter conclusions on the effectiveness of various experimental treatments. They compared ketamine/diazepam (KD), ketamine/xylazine (K/X), and isoflurane (ISO) in a hemorrhagic/traumatic shock rat model. Ketamine/diazepam increased mean arterial pressure and heart rate more than K/X while also inducing a higher systemic vascular resistance index than ISO. During hemorrhage shock, heart rate remained higher in K/D than K/X, whereas systemic vascular resistance index was increased in K/X and ISO groups. Most strikingly, damage to adrenals, kidney, and liver was detected in the K/D and K/X anesthetized hemorrhage/trauma groups, but not in ISO groups, demonstrating that choice of anesthetic could alter the amount of organ damage occurring in hemorrhage/trauma shock models.
Hypoxia is another major contributor to organ damage in hemorrhage shock and trauma. Three articles in this issue explore mechanisms behind hypoxia-mediated organ injury. Li et al. (9) investigated the role of hypoxia-induced P53, upregulated modulator of apoptosis (PUMA), in cardiomyocyte apoptosis. Using an in-vitro neonatal cardiomyocyte culture system, Li et al. (9) demonstrated that hypoxia-upregulated PUMA increased cardiomyocyte apoptosis by decreasing mitochondrial membrane potential, releasing cytochrome c, and activating caspases 3 and 8. Transfection of the cardiomyocytes with PUMA siRNA eliminated the hypoxia-induced cardiomyocyte apoptosis, suggesting a pivotal role for PUMA in hypoxia-induced cardiomyocyte apoptosis.
In another in-vitro culture system, Nevo-Caspi et al. (10) used an Epstein-Barr-transformed human lymphoblastoid line and mimicked hypoxia by treating with deferoxamine. This study focused on hypoxia-induced epigenetic changes. The data demonstrated that three genes related to cardiac pathophysiologies, MED13, STAT3, and F11R, are undergoing RNA editing, where the nucleotide adenosine undergoes deamination to create inosine (A to I RNA editing). This A to I RNA editing can result in gene alternative splicing and activation or gene nuclear retention and translation inhibition. In this study, MED13, STAT3, and F11R had increased expression in the deferoxamine-treated lymphoblastoid cell line. Generation of the STAT3B isoform was most prominently induced. The expression of the MED13 gene, which is a component of the thyroid hormone nuclear receptor, was also increased. These data suggest that A to I editing in response to hypoxic stress is part of the cellular response and may be involved in hypoxia's effects on cellular function.
The study by Dehne et al. (11) focuses on activation of hypoxia-inducible factor 1 (HIF-1) in skeletal muscle not by hypoxia but by exposure to muscle cell debris. When a murine muscle cell line was incubated with mechanically destroyed myotubes, the muscle cells upregulated their gene expression of adrenomedullin, insulin-like growth factors 1 and 2, metallopeptidase 9, and monocyte chemoattractant protein 1. All these genes are targets of HIF-1, and HIF-1 mRNA expression was also upregulated. The use of a gas-permeable system minimized the possibility that the cell debris reduced the Po2 in the cultured myoblasts and suggests that the damaged myofibers can directly activate HIF-1, independent of hypoxia. The data also suggest that trauma-mediated tissue damage, as well as postinjury hypoxia, might amplify the subsequent activation of phagocytes and innate immunity.
In another study on tissue damage-induced effects, Hoth et al. (12) investigated the contribution of neutrophil lung recruitment to lung injury in a murine pulmonary contusion model with tissue structural damage. Using antibody to block neutrophil migration or a gp91phox oxidant product knockout mouse, these authors showed that both neutrophil infiltration to the lung and neutrophil nicotinamide adenine dinucleotide phosphate oxidase function were required to produce lung injury in this model of pulmonary contusion injury.
Other mechanisms besides neutrophil infiltration may still be contributing to lung injury after pulmonary contusion. Interestingly, Seitz et al. (13) using a rat pulmonary contusion model implicated Fas and FasL interactions in the apoptosis of alveolar epithelial type 2 cells (AT2) and the release of IL-6 and depression of IL-10 in alveolar macrophages (AMΦ). The AMΦ were suggested as a source of increased soluble FasL after pulmonary contusion. Fas mRNA expression was increased in both AMΦ and AT2 after pulmonary contusion, and addition of soluble FasL increased the apoptosis of AT2 cells isolated after blunt chest trauma, whereas soluble FasL increased the AMΦ IL-6 release but decreased their IL-10 release. These data suggest that AMΦ-released soluble FasL can contribute to lung injury both directly by increasing lung epithelial cell apoptosis and indirectly by increasing autocrine release of AMΦ inflammatory mediators while decreasing their anti-inflammatory mediator release (IL-10).
The final article by Wu et al. (14) also assesses endothelial cell (EC) contributions to inflammatory activation and adhesion but in a burn sera model. Here, human dermal microvascular ECs were cultured with burn rat serum to investigate how various mitogen-activated protein kinases (MAPKs) modulated different EC functions. The p38 MAPK inhibitor decreased burn serum-induced EC tight junction damage as well as burn serum-induced stress fiber formation. The JNK MAPK inhibitor had neither effect in the in-vitro system. The extracellular signal-related kinase inhibitor significantly decreased burn serum-induced EC monocyte chemoattractant protein 1 release, thereby presumably decreasing inflammatory cell recruitment. In contrast, in the in-vivo studies of burned rat aorta where JNK or P38 was blocked by infusion of dominant-negative adenoviruses, JNK MAPK was implicated as involved in burn-induced P selectin and adhesion molecule 1 expression. The data imply that different MAPKs play differential roles in postburn alterations of EC inflammatory functions, and their specific inhibitors might be used to selectively modulate different inflammatory responses.
1. Salgado DR, He X, Su F, de Sousa DB, Penaccini L, Maciel LK, Taccone F, Rocco JR, Silva E, De Backer D, et al.: Sublingual microcirculatory effects of enalaprilat in an ovine model of septic shock. Shock
2. Freitas A, Alves-Filho JC, Trevelin SC, Spiller F, Suavinha MM, Nascimento DC, Pestana CR, Dal-Secco D, Sônego F, Czaikoski PG, et al.: Divergent role of heme oxygenase inhibition in the pathogenesis of sepsis. Shock
3. Soriano FG, Lorigados CB, Pacher P, Szabó C: Effects of a potent peroxynitrite decomposition catalyst in murine models of endotoxemia and sepsis. Shock
4. Hasan Z, Palani K, Rahman M, Thorlacius H: Targeting CD44 expressed on neutrophils inhibits lung damage in abdominal sepsis. Shock
5. Lange M, Hamahata A, Enkhbaatar P, Cox RA, Nakano Y, Westphal M, Traber LD, Herndon DN, Traber DL: Beneficial effects of concomitant neuronal and inducible nitric oxide synthase inhibition in ovine burn and inhalation injury. Shock
6. Bhattacharjee H, Nadipuram A, Kosanke S, Kiani MF, Moore BM II: Low-volume binary drug therapy for the treatment of hypovolemia. Shock
7. Muir WW, Ilangovan G, Zweier JL, Moon-Massat PF, Rentko VT: Vital organ tissue oxygenation after serial normovolemic exchange transfusion with HBOC-201 in anesthetized swine. Shock
8. Bahrami S, Benisch C, Zifko C, Jafarmadar M, Schöchl H, Redl H: Xylazine-/diazepam-ketamine and isoflurane differentially affect hemodynamics and organ injury under hemorrhagic/traumatic shock and resuscitation in rats. Shock
9. Li Y, Liu X, Rong F: PUMA mediates the apoptotic signal of hypoxia/reoxygenation in cardiomyocytes through mitochondrial pathway. Shock
10. Nevo-Caspi Y, Amariglio N, Rechavi G, Paret G: A-to-I RNA editing is induced upon hypoxia. Shock
11. Dehne N, Kerkweg U, Flohe SB, Brüne B, Fandrey J: Activation of hypoxia-inducible factor 1 in skeletal muscle cells after exposure to damaged muscle cell debris. Shock
12. Hoth JJ, Wells JD, Hiltbold EM, McCall CE, Yoza BK: Mechanism of neutrophil recruitment to the lung after pulmonary contusion. Shock
13. Seitz DH, Palmer A, Niesler U, Braumüller ST, Bauknecht S, Gebhard F, Knöferl MW: Altered expression of FAS receptor on alveolar macrophages and inflammatory effects of soluble FAS ligand following blunt chest trauma. Shock
14. Wu W, Huang Q, He F, Xiao M, Pang S, Guo X, Brunk UT, Zhao K, Zhao M: Roles of mitogen-activated protein kinases in the modulation of endothelial cell function following thermal injury. Shock