The November 2019 issue of Shock is once again jam-packed with excellent research that encompasses all aspects of the shock research arena. As usual there are both clinically based and basic science-based manuscripts featured this month, and these manuscripts were submitted by investigators from across the world. The exciting findings showcased in this issue cover everything from sepsis, septic shock, and immune responses to bacteria, to work elucidating mechanisms of inflammation in burns, ischemia reperfusion, hemorrhagic shock, and acute pancreatitis. There will definitely be something to capture your interest this month!
In the November issue of Shock there are two clinically based and five basic science-based articles studying various aspects of sepsis. Sepsis remains a significant clinical problem associated with excessive inflammatory responses and organ failure in response to infection. Activation and recruitment of neutrophils and inflammatory monocytes are important mechanisms against microbial infection, and there are three studies published in this issue that focus on this particular aspect of sepsis responses.
The clinical science aspects article looks at the relationship between immunophenotype and functional changes of circulating leukocytes during sepsis. Flores-Mejía et al. (1) assess the activation-related immunophenotype (characterized as increased expression of CD64, CD69, CCR7, and TREM-1), cytokine production capacities, phagocytotic function, and bacterial clearance capacities with circulating leukocytes from 13 SIRS patients, 31 septic patients, and 14 healthy volunteers. They found that even with conversion to activation-related immunophenotypes and enhanced cytokine production capacities, the phagocytotic function and bacterial clearance capacities significantly decreased in peripheral neutrophils and monocytes from patients with SIRS/sepsis. These data suggest that the so called “activation” immunophenotype changes observed in circulating neutrophils and monocytes do not reflect the defect in other functions of leukocytes, such as phagocytosis. Further studies will be needed to determine how long the phagocytosis defect in leukocytes lasts, and if there are defects in other leukocyte functions to use this knowledge to help design new strategies for sepsis treatment.
As part of the basic science aspects articles Lee et al. (2) investigated the impact of hemorrhagic shock on neutrophil recruitment in response to secondary respiratory infection with P aeruginosa. Hemorrhagic shock is known to induce immune dysfunction that frequently results in secondary infection. Surprisingly, even with a 10-fold increase of circulating neutrophil chemokine after hemorrhagic shock and P aeruginosa infection, neutrophil numbers in the airway were significantly decreased compared with infected controls, and there was associated increased circulating IL-6 levels and mortality. The authors conclude that hemorrhagic shock leads to an attenuation of neutrophil recruitment into the lung after P aeruginosa infection. Further studies on the mechanisms of hemorrhagic shock on neutrophil recruitment will help to understand the balance between neutrophil-dependent host defense and neutrophil-mediated injury.
In addition to neutrophil recruitment, inflammatory monocyte recruitment is also an important mechanism of host defense during sepsis. First author, e Silva Castanheira et al. (3) explored mechanisms of inflammatory cell recruitment in a mouse model of cecal ligation and puncture (CLP). In this study they demonstrate that the expression of CCR5, a chemokine receptor, was induced in inflammatory monocytes, but not in neutrophils after CLP. Deficiency of CCR5 impaired monocyte recruitment into the infection site, and this was associated with increased bacterial burden and mortality. This study reveals an unrecognized role of CCR5 in specifically regulating inflammatory monocyte recruitment, suggesting CCR5 may be a potential therapeutic target for sepsis and other inflammatory diseases.
There is one clinically based and three basic science-based articles investigating aspects of sepsis other than immune cell activation and recruitment. Tilouche et al. (4) carried out a randomized controlled clinical trial to compare the therapeutic effect of bolus administration versus continuous infusion of hydrocortisone in septic patients in ICU (n=29/group). Treatment with hydrocortisone bolus significantly shortened the median time of shock reversal compared with continuous infusion treatment. The authors conclude that hydrocortisone administrated by intermittent bolus is associated with higher shock reversal at day 7 compared with a continuous infusion.
Although mouse models have been widely used for sepsis research, recent studies have highlighted the differences of immune responses observed in mice and humans in response to pathogen infection. Lin et al. (5) explored these differences by performing side-by-side experiments to compare the behavior of four strains of E coli and one strain of P aeruginosa, all clinical blood isolates cultured from patients with sepsis, when placed in fresh human or mouse blood. In this study, these human-derived gram-negative bacteria were phagocytosed and killed in the human blood but not in the mouse blood. There was also increased cytokine production in blood and plasma from healthy human volunteers in response to the bacteria compared with low cytokine levels measured in blood from female C57BL/6 mouse under the same conditions. The authors conclude that mouse bacteremia caused by these human gram-negative bacteria does not mimic human bacteremia caused by the same bacteria. There are several limitations in this study, including investigation of how mouse-derived bacteria are affected by culture in human or mouse blood. However, it would be useful to perform further studies to understand the differences of immune response during bacterial infection between mouse and human, so that we can create more representative models of sepsis, and have tools to more accurately interpret results from murine models of bacteremia so that we can develop new approaches for sepsis therapy.
Vascular hyporesponsiveness to vasopressors is another important mechanism in the pathogenesis of sepsis. Reactive nitrogen species (RNS), such as peroxynitrite, are important mediators contributing to vascular hyporesponsiveness during sepsis. Fukuda et al. (6) used a merino sheep “two-hit” injury model (smoke inhalation followed by live methicillin-resistant Staphylococcus aureus endotracheal inoculation to test the therapeutic efficacy of peroxynitrite decomposition catalyst (PDC) adjunct treatment in sepsis). Addition of PDC significantly reduced the total norepinephrine dose needed, the highest dose of norepinephrine warranted, the time on norepinephrine support, as well as reduced 24 h mortality compared with control, although sample size was small (n=7/group). No adverse effect was observed with PDC treatment. The authors conclude that modulation of RNS may be an effective adjunct therapy for sepsis-induced hyporesponsiveness to norepinephrine.
The final sepsis paper investigating mechanisms of sepsis is from Dr Zingarelli's laboratory at Cincinnati Children's Hospital. This research group has previously reported that activation of AMP-activated protein kinase (AMPK) by AICAR protects from organ injury during septic shock and hemorrhagic shock. In the current study (7), this research group demonstrate that activation of AMPK by A769662 ameliorated lung architecture changes, reduced bacterial load and circulating inflammatory cytokines levels, as well as increased 7-day survival after CLP in adult mice. Furthermore, the protective effect of A769662 was associated with activation of AMPK and increased autophagy. The current data together with their previous publication suggest that pharmacological activation of AMPK may be beneficial approaches for sepsis therapy in adults.
Switching gears now, the rest of the papers in this issue deal with topics related to inflammation (in multiple forms), hemorrhagic shock, and ischemia/reperfusion. There are two papers in this issue that tackle important aspects related to fluid resuscitation after hemorrhagic shock or after shock induced by acute pancreatitis. In their paper, Hofmann et al. (8) investigate the effect of adding coagulation factor concentrates to colloid fluid resuscitation protocols to assess if they are more protective of the endothelium than either colloid alone, or resuscitation with fresh frozen plasms. Interestingly, the authors found that although adding fibrinogen or prothrombin complexes improved endothelial dysfunction, this was no better than the protection afforded by resuscitating with plasma. Aggressive fluid resuscitation in severe pancreatitis is known to have disruptive effects on gut barrier and is associated with increased systemic inflammatory responses. Cui et al. (9) investigated whether adding an inhibitor of inflammatory necroptotic cell death was able to preserve gut barrier function during aggressive fluid management therapy in a rat model of severe acute pancreatitis. They found that necroptosis does play a pivotal role in the gut barrier dysfunction in their model, and that by adding necrostatin-1 the histological appearance of the gut was improved, and there was decreased inflammation and release of high mobility group box 1. Both these studies highlight the complex nature of fluid resuscitation in shock, and we are only just beginning to understand the inflammatory responses associated with protocols of resuscitation.
Circulating microparticles (MPs) are extracellular vesicles that have been shown to act as biomarkers and signaling mediators in multiple disease processes, as well as important mediators of cell communication under homeostatic conditions. In their current paper, Jian et al. (10) investigate the changes in protein composition of circulating MPs in patients with valvular heart disease, both before and at 72 h after cardiac surgery. This group recently demonstrated increased levels of circulating MPs in patients with valvular heart diseases subjected to cardiac surgery and associated impaired endothelial function and vasodilation. In this study they analyzed the protein composition of the MPs using mass spectrometry analysis and found that the protein make-up of MPs changes markedly after surgery. There were very high levels of pro-inflammatory proteins and complement after surgery compared with prior to surgery, suggesting that MPs are in part responsible for detrimental signaling in endothelium. Understanding signaling via extracellular vesicles is a burgeoning area of research, and it may be that these particles are the main signaling mediators between cells and drive inflammatory responses.
Staying with signaling pathways, there are two studies presented in the basic science aspects section looking at pathological effects of signaling pathways in shock. The first is a study by Obert et al. (11) investigating endoplasmic reticulum (ER) stress after hemorrhagic shock. ER stress initiates a series of signaling pathways that can induce inflammation, and ER stress has been shown to occur in hemorrhagic shock. Here, the investigators used chemical induction of ER stress with tunicamycin, or inhibition of ER stress with TUDCA, to identify its role in inflammatory responses and organ damage after hemorrhagic shock in mice. They found that modulation of ER stress could profoundly alter inflammation and in particular hepatocellular damage after hemorrhagic shock, although they do note that TUDCA is a non-specific ER stress inhibitor with multiple other functions that may be relevant. In contrast, Yu et al. (12) investigated the role of miRNA signaling, and specifically miR-190b, on skeletal muscle signaling, autophagy, and muscle wasting after burn. Recent studies have closely linked induction of autophagy in skeletal muscle after burn with skeletal muscle wasting, although how these pathways are regulated remains elusive. This current study identified decreased levels of miR-190b in muscle after burn, and that this had the effect of upregulating a signaling pathway involving PHLPP1/Akt/FOXO3A resulting in increased autophagic proteins and muscle wasting. Both these signaling papers highlight the importance of understanding the signaling and regulation behind vital pathways in shock and trauma to potentially identify novel treatment targets of potential interventions.
Understanding signaling is obviously equally important in other pathologies, and two papers in this month's issue investigate signaling pathways that contribute to organ protection in models of ischemia/reperfusion with remote ischemic pre- or post-conditioning (RIPC). Hong et al. (13) had previously noted cardioprotection in a model of acute myocardial ischemia using remote (femoral artery) ischemic post-conditioning, and this was associated with decreased PTEN/Akt/GSK3β signaling. In this study they investigated whether RIPC was able to protect hypercholesterolemic mice similarly. Many patients suffering from acute myocardial ischemia have hypercholesterolemia, along with multiple other risk factors for cardiovascular disease, so the investigators wanted to use a more clinically relevant model. They got some extremely interesting results. They found that hypercholesterolemic mice were not rescued by RIPC alone, as there was no inhibition of PTEN signaling. However, if they then added a PTEN inhibitor they were able to restore the cardioprotection. More work will need to be done to fully understand the pathways involved before PTEN inhibition would be useful in a clinical setting.
Ischemia/reperfusion injury also occurs in settings of organ transplantation, and remote ischemic pre and post-conditioning have been shown to be organ protective. Emontzpohl et al. (14) used an orthotopic liver transplant model in rats, together with RIPC (either pre or post-conditioning via caval clamping) and showed that RIPC was hepatoprotective, and associated with improved liver microcirculation. They also found that protection correlated with increased expression of macrophage migration inhibitory factor, a proinflammatory factor rapidly released after injury and suggested as an important mediator of RIPC protection.
The final two papers from the November issue involve studies that investigate the effects of using commonly available, clinically relevant drugs to try to modulate inflammatory responses to provide organ protection. In their paper, Geng et al. (15) use an interesting more of heatstroke in mice to investigate the protective effects of a commonly used ICU drug, dexmedetomidine, on lung injury. Dexmedetomidine is an alpha-adrenergic agonist and known sedative that has been shown recently to also have anti-inflammatory effects in multiple settings. In this current study the authors show treatment with dexmedetomidine after heatstroke decreased inflammatory cytokine production in the lung, as well as improved lung injury, without compromising respiratory function. This suggests using this drug in the ICU may be acutely beneficial in reducing inflammation, but the authors also point out that longer term treatment with dexmedetomidine can be detrimental. Kiyonaga et al. (16) investigate the protective effect of an ultra-short acting beta-1 adrenergic specific blocker, landiolol, on acute kidney injury in a model of lipopolysaccharide-induced inflammation. Landiolol has been shown previously to protect against sepsis-induced acute lung injury in mice, and appears to act via reduction of proinflammatory mediators. The investigators confirmed reduced proinflammatory cytokine levels in serum, as well as reduced markers of reactive oxygen species in urine, and histological evidence of renal protection after landiolol treatment in lipopolysaccharide-treated mice. Together these studies show how thoughtful use of already available pharmacological agents could help protect patients in settings of shock, sepsis, and inflammation.
As promised there is something to enthuse and amuse everyone in this latest issue of Shock. Keep up to date on the latest articles accepted for publication by signing up for the table of contents to be delivered directly to your email inbox, together with information on accepted articles available via our early publication system.
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1. Flores-Mejía LA, Cabrera-Rivera GL, Ferat-Osorio E, Mancilla-Herrera I, Torres-Rosas R, Boscó-Garate IB, López-Macías C, Isibasi A, Cérbulo-Vazquez A, Arriaga-Pizano LA. Function is dissociated from activation-related immunophenotype on phagocytes from patients with SIRS/sepsis syndrome. Shock
2. Lee K, Cohen JT, Wilson ZS, Zhao R, Lomas-Neira J, Chung C-S, Chen Y, Jamieson AM, Ayala A, Lefort CT. Hemorrhage attenuates neutrophil recruitment in response to secondary respiratory infection by pseudomonas aeruginosa
3. e Silva Castanheira FV, de Lima KA, Cebinelli GCM, Sônego F, Kanashiro A, Colon D-F, Borges V, Czaikoski PG, Mota JM, Cunha TM, et al. CCR5-positive inflammatory monocytes are crucial for control of sepsis. Shock
4. Tilouche N, Jaoued O, Ali HBS, Gharbi R, Fekih Hassen M, Elatrous S. Comparison between continuous and intermittent administration of hydrocortisone during septic shock: a randomized controlled clinical trial. Shock
5. Lin T, Moorlag SJCFM, Liu J, Ahmed MYH, Thundivalappil SR, Riley FE, Warren HS. Different bactericidal and inflammatory activities of human and mouse blood. Shock
6. Fukuda S, Ihara K, Andersen CR, Randolph AC, Nelson CL, Zeng Y, Kim J, DeWitt DS, Rojas JD, Koutrouvelis A, et al. Modulation of peroxynitrite reduces norepinephrine requirements in ovine MRSA septic shock. Shock
7. Kitzmiller L, Ledford JR, Hake PW, O’Connor M, Piraino G, Zingarelli B. Activation of AMP-activated protein kinase by A769662 ameliorates sepsis-induced acute lung injury in adult mice. Shock
8. Hofmann N, Zipperle J, Brettner F, Jafarmadar M, Ashmwe M, Keibl C, Ponschab M, Kipman U, Bahrami A, Redl H, et al. Effect of coagulation factor concentrates on markers of endothelial cell damage in experimental hemorrhagic shock. Shock
9. Cui Q-R, Ling Y-H, Wen S-H, Liu K-X, Xiang Y-K, Yang W-J, Shen J-T, Li Y-S, Yuan B-L, Huang W-Q. Gut barrier dysfunction induced by aggressive fluid resuscitation in severe acute pancreatitis is alleviated by necroptosis inhibition in rats. Shock
10. Jian Y-P, Yuan H-X, Hu K-H, Chen C, Li Y-Q, Li Y, Yang T-X, Ou Z-J, Ou J-S. Protein compositions changes of circulating microparticles in patients with valvular heart disease subjected to cardiac surgery contribute to systemic inflammatory response and disorder of coagulation. Shock
11. Obert DP, Wolpert AK, Korff S. Modulation of endoplasmic reticulum stress influences ischemia-reperfusion injury after hemorrhagic shock. Shock
12. Yu Y, Yang L, Han S, Wu Y, Liu L, Chang Y, Wang X, Chai J. MIR-190B alleviates cell autophagy and burn-induced skeletal muscle wasting via modulating PHLPP1/AKT/FOXO3A signaling pathway. Shock
13. Hong J, Ge H-W, Liu J-Q, Sun R-H, Kong F-J. Pharmacological inhibition of PTEN restores remote ischemic postconditioning cardioprotection in hypercholesterolemic mice: potential role of PTEN/Akt/GSK3β signals. Shock
14. Emontzpohl C, Stoppe C, Theißen A, Beckers C, Neumann UP, Lurje G, Ju C, Bernhagen J, Tolba RH, Czigany Z. The role of macrophage migration inhibitory factor in remote ischemic conditioning induced hepatoprotection in a rodent model of liver transplantation. Shock
15. Geng Y, Li R, He S-X, Yang H-H, Deng Q-t, Shao X-y, Wu Y-s, Xu W-w, Ma Q. Dexmedetomidine attenuates acute lung injury induced by heatstroke and improve outcome. Shock
16. Kiyonaga N, Moriyama T, Kanmura Y. Effects of landiolol in lipopolysaccharide-induced acute kidney injury in rats and in vitro