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What's New in Shock, January 2019?

Clemens, Mark G.

doi: 10.1097/SHK.0000000000001268
Commentaries

Department of Biological Sciences, University of North Carolina at Charlotte, Charlotte, North Carolina

E-mail: mgclemen@uncc.edu

The first issue of Shock for 2019 starts the year with a bang with 4 articles listed as “Editor's Choice” as well as outstanding additional articles addressing clinical and basic science aspects of shock, injury, inflammation, and sepsis. The first Editor's Choice sets the theme for the other 3. Over the past several decades, significant advances in sepsis research have been vitally dependent on animal models. Although variations on the cecal ligation and puncture model have been considered to be the gold standard for clinically relevant models, these many variations can have a significant impact on the outcomes. In a special commentary, Remick et al. (1) makes the case that establishing a standardized model of sepsis that is agreed upon by the sepsis research community would enable more valid comparisons of results from multiple laboratories. While it is uncertain that a completely standardized single model is feasible or even desirable, a systematic consideration of factors such as anesthesia, fluid resuscitation, antibiotic use, etc., would surely serve the sepsis research community well. As a first step in this process, a Wiggers–Bernard Conference was held in Vienna in May 2017 to bring together experts in the field. Rather than attempt to define a single standardized model, this group proposes a set of guidelines (minimum quality threshold in preclinical sepsis studies) for preclinical sepsis models. The results of this conference appear in 3 articles (2–4) in this month's issue which were also selected as Editor's Choice articles. An executive summary of these articles appeared in the October issue of Shock (5).

In the first article, Zingarelli et al. (2) provide recommendations for study design and humane endpoints. In their comprehensive review of the literature, these authors found consistency in the species (79% used mouse) only 9% defined humane endpoints. Recommendations include blinding, choice of follow-up monitoring to reflect clinical course and inclusion of biological variables and comorbidities as seen in clinical populations. Finally, they reiterate that the highest standards of humane treatment are essential. In the second article, Libert et al. (3) address the types of infections and organ dysfunction endpoints. They report that while the greatest number of studies surveyed used cecal ligation and puncture as a sepsis model, 40% used endotoxin injection. The recommendation was that infectious agents should duplicate as closely as possible, those seen in human sepsis. Endotoxinemia should not be considered to be an acceptable sepsis model. While many studies reported survival and specific biomarkers, relatively few reported organ dysfunction. Given that sepsis is defined as “... life-threatening organ dysfunction caused by a dysregulated host response to infection.” Reporting organ dysfunction is important. In particular, detailed assessment of organ dysfunction can often be done in animal models that is not possible to perform in human patients. In the final article of this series, Hellman et al. (4) provide recommendations for fluid resuscitation and antimicrobial therapy. Although guidelines for fluids and antimicrobials exist for clinical management of sepsis, no such guidelines exist for animal models. Given the importance of fluids and antibiotics in clinical treatment, these authors recommend their inclusion in the design of preclinical models. Overall, the recommendations suggest that fluid resuscitation and antimicrobial therapy need to be tailored to the needs of the specific model and designed to replicate as closely as possible clinical practice. This includes dynamic monitoring of hemodynamics to guide fluid replacement and consideration of infecting agent a pharmacokinetics in selecting antibiotic treatment. Taken together, these 3 reports provide an outstanding starting point for the development of standard “best practices” for the design of preclinical animal models of sepsis. In addition, conforming to agree upon best practices in sepsis models can be of enormous help in gaining approval of animal use protocols for sepsis studies.

Although the classic role of nucleic acids in regulation of gene expression has been studied in the context of shock, inflammation and ischemia has been studied for decades, other roles for both DNA and RNAs have been recently recognized. Two reviews in this month's issue address such roles. Hu et al. (6) provide an excellent summary of our current understanding of the role of mitochondrial DNA acting as an injury signal in ischemia and reperfusion in the context of the central role of mitochondria in determining cell injury. They provide a comprehensive overview of the mechanisms leading to release of mitochondrial DNA into the cytoplasm and then from the cell and how this DNA contributes to the systemic propagation of inflammation. This report should provide a valuable reference for this very active area of investigation. Another paper this month examines respiratory function in mitochondria in peripheral blood mononuclear cells (PBMCs). Clere-Jehl et al. (7) measured mitochondrial respiration in PBMCs from septic patients and compared that to respiration in a lymphoid cell line (CEM) exposed to septic plasma. PBMCs from septic patients showed increased basal respiration and total respiratory capacity but decreased ATP synthetic capacity. In contrast, CEM cells exposed to septic plasma showed decreased respiration which appeared to be related to the levels of high mobility group box 1 in the plasma. The authors conclude the increase in respiratory capacity in PBMCs is a compensatory response to the decrease in ATP synthetic capacity induced by factors in septic plasma.

In addition to DNA, the role of noncoding forms of RNA is now recognized to regulate protein translation. One of these noncoding RNAs is microRNA (miR). MiRs regulate families of proteins by either targeting mRNA for degradation or impairing translation. Kohns et al. (8) performed a systematic review of papers studying the potential role of miR expression in the development of remote ischemic preconditioning (RIPC) in the heart. They reviewed both animal and randomized clinical trial published papers reporting miR expression in RIPC. They provide an excellent table summarizing all miRs reported as being differentially expressed in RIPC; however, they found no good correlation between animal studies and clinical trials. This most likely represents the complexity of miR regulation and underscores the need for studies in this area. In another report related to miR expression, Wang et al. (9) studied the potential role of miR 34A in modulating endoplasmic reticulum (ER) stress following myocardial ischemia/reperfusion. They found that miR 34A was upregulated in cardiomyocytes following ischemia/reperfusion and that crocin, an active ingredient of saffron, downregulated miR 34A. This was associated with upregulation of the hypoxia-related protective proteins sirtuin, nuclear factor (erythroid-derived 2)-like 2, and heme oxygenase-1 (HO-1) and increased ER stress. Moreover, selective upregulation of miR 34A down-regulated sirtuin, nuclear factor (erythroid-derived 2)-like 2, and HO-1 and increased ER stress. These results indicate that miR 34A serves as a negative regulator expression of protective hypoxia-related genes and that modulation of miR34A by crocin can moderate ischemia/reperfusion injury.

Cardiac arrest leads to ischemia of all other organs with ensuing ER stress. Most sensitive to this ischemia is neuronal tissue. Qin et al. (10) examined the effect of an activator of the sigma 1 receptor (Sig-1R) on neuronal injury in rats resuscitated after cardiac arrest. Sig-1R is expressed in the mitochondria-associated ER membrane and helps regulate cellular calcium and attenuates ER stress. Treatment with a specific Sig-1R agonist SA4503 lowered cerebral hemisphere caspase-3 levels as well as markers of ER stress. In addition, SA4503 improved mitochondrial membrane potential and restored ATP levels as well as normalized Ca+ balance. These results suggest that activation of Sig-1R may have potential therapeutic benefit in preventing neurologic deficits in patients resuscitated following cardiac arrest.

The January issue of Shock also offers 2 papers related to aspects of hemorrhagic shock. Van Griensven et al. (11) used a nonhuman primate (cynomolgus monkey) model of hemorrhagic shock to study the therapeutic potential of complement (C3) inhibition. Treatment of monkeys with the C3 inhibitor Cp40 significantly improved kidney function and histological appearance, decreased intestinal edema, and improved markers of inflammation and coagulopathy. The testing of this intervention in a highly relevant nonhuman primate model is a very important step in supporting potential therapeutic use of Cp40 for inhibition of complement in human patients. It is now well recognized that comorbidities are important modulators of the response to injury. Hartmann et al. (12) provide a characterization of the effects of cigarette smoke (CS) on the acute response to trauma and hemorrhage. Mice were exposed to CS for 3 weeks followed by hemorrhagic shock (HS) with or without blunt chest trauma. CS alone produced maximal inflammation while HS and trauma increased organ injury and mortality without further increase in inflammation. These results show that CS is an important comorbidity that potentiates the inflammatory response to HS and trauma; however, there appears to be a dissociation between level of inflammation and degree of organ injury.

This month's issue also provides 3 articles related to cell signaling and control. Tao et al. (13) used endotoxin (lipopolysaccharide) to induce lung injury and examined the role of inhibition of the epithelial growth factor/toll like receptor4 pathway using erlotinib. They pretreated mice with erlotinib and then injected lipopolysaccharide. Peak phosphorylation of epithelial growth factor was found at 24 h and was associated with markers of lung injury such as inflammatory cell infiltration in bronchoalveolar lavage fluid. Erlotinib decreased inflammatory cytokine production, improved lung injury, and downregulated the NFkB pathway. Although the clinical relevance of this study is limited by the pretreatment and use of an endotoxemia model, the results provide mechanistic insights into the signaling pathways involved in the development of inflammation and injury in the lung.

Ischemia and inflammation are associated with increased reactive oxygen production that can lead to oxidation of membrane lipids. In addition, the production of hypochlorous acid via myeloperoxidase can lead to chlorination of membrane lipids. Yu et al. (14) tested whether these chlorinated lipids might contribute to microvascular activation leading to neutrophil activation and adhesion in the microcirculation. Addition of chlorinated lipids to human intestinal microvascular endothelial cells in vitro resulted in upregulation of endothelial cell adhesion molecules and increased neutrophil adhesion. In vivo, chlorinated lipids lead to neutrophil adhesion, increased reactive oxygen production, albumin leakage, and mast cell activation in rat mesenteric venules. These results provide proof of concept that chlorinated lipids might contribute to microvascular injury in vivo. Further studies will be required to define the relative importance of this mechanism. In addition to integrity of the microcirculation in the intestines, integrity of the epithelial barrier is of key importance in determining outcome in ischemia and sepsis. Meng et al. (15) used a cecal ligation and puncture model in mice to study factors involved in regulating migration and proliferation of intestinal epithelial cell in sepsis. In an elegant set of experiments, this group characterized multiple factors that give rise to decreased proliferation of crypt cells as well as decreased migration from the crypt to the villus tip in sepsis. These coupled with increased rates of apoptosis give rise to impaired barrier function of the intestine. Interestingly, decreasing apoptosis via overexpression of Bcl-2 decreased rate of migration and increasing permeability increased migration.

Effective elucidation of the mechanisms of clinically relevant shock and associated conditions requires a basic understanding of the etiology of shock in the real world. Holler et al. (16) make a contribution to this goal with their report in Shock this month. They categorized 1646 patients diagnosed with shock on admission to the emergency department over an 11 year period according to etiology. Hypovolemic and septic shock accounted for over half of the cases of shock with most of the remaining cases resulting from cardiogenic or nonseptic distributive shock. Interestingly, only septic shock showed a significant upward trend over the 11 year period. This information should help inform prioritization of shock models, at least with respect to emergency department patients.

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REFERENCES

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© 2019 by the Shock Society