Human red blood cells express the RNA sensor TLR7.

Red blood cells (RBCs) express the nucleic acid-binding toll-like receptor 9 (TLR9) and bind CpG-containing DNA. However, whether human RBCs express other nucleic acid-binding TLRs is unknown. Here we show that human RBCs express the RNA sensor TLR7. TLR7 is present on the red cell membrane and is associated with the RBC membrane protein Band 3. In patients with SARS-CoV2-associated sepsis, TLR7-Band 3 interactions in the RBC membrane are increased when compared with healthy controls. In vitro, RBCs bind synthetic ssRNA and RNA from ssRNA viruses. Thus, RBCs may serve as a previously unrecognized sink for exogenous RNA, expanding the repertoire of non-gas exchanging functions performed by RBCs.

CTLA-4 Checkpoint Inhibition Improves Sepsis Survival in Alcohol-Exposed Mice.

Chronic alcohol use increases morbidity and mortality in the setting of sepsis. Both chronic alcohol use and sepsis are characterized by immune dysregulation, including overexpression of T cell coinhibitory molecules. We sought to characterize the role of CTLA-4 during sepsis in the setting of chronic alcohol exposure using a murine model of chronic alcohol ingestion followed by cecal ligation and puncture. Results indicated that CTLA-4 expression is increased on CD4+ T cells isolated from alcohol-drinking septic mice as compared with either alcohol-drinking sham controls or water-drinking septic mice. Moreover, checkpoint inhibition of CTLA-4 improved sepsis survival in alcohol-drinking septic mice, but not water-drinking septic mice. Interrogation of the T cell compartments in these animals following pharmacologic CTLA-4 blockade, as well as following conditional Ctla4 deletion in CD4+ T cells, revealed that CTLA-4 deficiency promoted the activation and proliferation of effector regulatory T cells and the generation of conventional effector memory CD4+ T cells. These data highlight an important role for CTLA-4 in mediating mortality during sepsis in the setting of chronic alcohol exposure and may inform future approaches to develop targeted therapies for this patient population.

CHRONIC ETHANOL USE WORSENS GUT PERMEABILITY AND ALTERS TIGHT JUNCTION EXPRESSION IN A MURINE SEPSIS MODEL.

ABSTRACT: Alcohol use disorder is associated with increased mortality in septic patients. Murine studies demonstrate that ethanol/sepsis is associated with changes in gut integrity. This study examined intestinal permeability after ethanol/sepsis and investigated mechanisms responsible for alterations in barrier function. Mice were randomized to drink either 20% ethanol or water for 12 weeks and then were subjected to either sham laparotomy or cecal ligation and puncture (CLP). Intestinal permeability was disproportionately increased in ethanol/septic mice via the pore, leak, and unrestricted pathways. Consistent with increased permeability in the leak pathway, jejunal myosin light chain (MLC) kinase (MLCK) expression and the ratio of phospho-MLC to total MLC were both increased in ethanol/CLP. Gut permeability was altered in MLCK -/- mice in water/CLP; however, permeability was not different between WT and MLCK -/- mice in ethanol/CLP. Similarly, jejunal IL-1ß levels were decreased while systemic IL-6 levels were increased in MLCK -/- mice in water/CLP but no differences were identified in ethanol/CLP. While we have previously shown that mortality is improved in MLCK -/- mice after water/CLP, mortality was significantly worse in MLCK -/- mice after ethanol/CLP. Consistent with an increase in the pore pathway, claudin 4 levels were also selectively decreased in ethanol/CLP WT mice. Furthermore, mRNA expression of jejunal TNF and IFN-γ were both significantly increased in ethanol/CLP. The frequency of CD4 + cells expressing TNF and IL-17A and the frequency of CD8 + cells expressing IFN-γ in Peyer's Patches were also increased in ethanol/CLP. Thus, there is an ethanol-specific worsening of gut barrier function after CLP that impacts all pathways of intestinal permeability, mediated, in part, via changes to the tight junction. Differences in the host response in the setting of chronic alcohol use may play a role in future precision medicine approaches toward the treatment of sepsis.

Rethinking protocolized completion angiography following extremity vascular trauma: A prospective observational multicenter trial.

BACKGROUND: Completion angiography (CA) is commonly used following repair of extremity vascular injury and is recommended by the Eastern Association for the Surgery of Trauma practice management guidelines for extremity trauma. However, it remains unclear which patients benefit from CA because only level 3 evidence exists. METHODS: This prospective observational multicenter (18LI, 2LII) analysis included patients 15 years or older with extremity vascular injuries requiring operative management. Clinical variables and outcomes were analyzed with respect to with our primary study endpoint, which is need for secondary vascular intervention. RESULTS: Of 438 patients, 296 patients required arterial repair, and 90 patients (30.4%) underwent CA following arterial repair. Institutional protocol (70.9%) was cited as the most common reason to perform CA compared with concern for inadequate repair (29.1%). No patients required a redo extremity vascular surgery if a CA was performed per institutional protocol; however, 26.7% required redo vascular surgery if the CA was performed because of a concern for inadequate repair. No differences were observed in hospital mortality, length of stay, extremity ischemia, or need for amputation between those who did and did not undergo CA. CONCLUSION: Completion angiogram following major extremity injury should be considered in a case-by-case basis. Limiting completion angiograms to those patients with concern for an inadequate vascular repair may limit unnecessary surgery and morbidity. LEVEL OF EVIDENCE: Therapeutic/Care Management; Level III.

Gut Microbiome in Sepsis.

Abstract The gut has been hypothesized to be the "motor" of multiple organ dysfunction in sepsis. Although there are multiple ways in which the gut can drive systemic inflammation, increasing evidence suggests that the intestinal microbiome plays a more substantial role than previously appreciated. An English language literature review was performed to summarize the current knowledge of sepsis-induced gut microbiome dysbiosis. Conversion of a normal microbiome to a pathobiome in the setting of sepsis is associated with worsened mortality. Changes in microbiome composition and diversity signal the intestinal epithelium and immune system resulting in increased intestinal permeability and a dysregulated immune response to sepsis. Clinical approaches to return to microbiome homeostasis may be theoretically possible through a variety of methods including probiotics, prebiotics, fecal microbial transplant, and selective decontamination of the digestive tract. However, more research is required to determine the efficacy (if any) of targeting the microbiome for therapeutic gain. The gut microbiome rapidly loses diversity with emergence of virulent bacteria in sepsis. Restoring normal commensal bacterial diversity through various therapies may be an avenue to improve sepsis mortality.

Junctional adhesion molecule-A deletion increases phagocytosis and improves survival in a murine model of sepsis.

Expression of the tight junction-associated protein junctional adhesion molecule-A (JAM-A) is increased in sepsis, although the significance of this is unknown. Here, we show that septic JAM-A -/- mice have increased gut permeability, yet paradoxically have decreased bacteremia and systemic TNF and IL-1ß expression. Survival is improved in JAM-A-/- mice. However, intestine-specific JAM-A-/- deletion does not alter mortality, suggesting that the mortality benefit conferred in mice lacking JAM-A is independent of the intestine. Septic JAM-A-/- mice have increased numbers of splenic CD44hiCD4+ T cells, decreased frequency of TNF+CD4+ cells, and elevated frequency of IL-2+CD4+ cells. Septic JAM-A-/- mice have increased numbers of B cells in mesenteric lymph nodes with elevated serum IgA and intraepithelial lymphocyte IgA production. JAM-A-/- × RAG-/- mice have improved survival compared with RAG-/- mice and identical mortality as WT mice. Gut neutrophil infiltration and neutrophil phagocytosis are increased in JAM-A-/- mice, while septic JAM-A-/- mice depleted of neutrophils lose their survival advantage. Therefore, increased bacterial clearance via neutrophils and an altered systemic inflammatory response with increased opsonizing IgA produced through the adaptive immune system results in improved survival in septic JAM-A-/- mice. JAM-A may be a therapeutic target in sepsis via immune mechanisms not related to its role in permeability.

Bullet Embolism into the Common Iliac Artery from a Gunshot Wound to the Heart.

We describe the management of bullet embolism from a penetrating cardiac injury, including the clinical, radiographic, and operative considerations in this challenging trauma scenario. Bullet embolism represents a rare but complex subset of ballistic penetrating trauma, and highlights the importance of radiographic correlation with intraoperative findings.

Superior Mesenteric Artery and Vein Injuries: Operative Strategies and Outcomes.

Traumatic injuries to the mesenteric vessels are rare and often lethal. Visceral vessels, such as the superior mesenteric artery (SMA) and vein (SMV), supply blood to the small and large bowel by a rich system of collaterals. Because fewer than 100 such injuries have been described in the literature, they pose challenges in both diagnosis and management and can unfortunately result in high mortality rates. Prompt diagnosis, surgical intervention, and resuscitation can lead to improved outcomes. Here, we review the literature surrounding traumatic injuries of the SMA/SMV and discuss management strategies.

Overexpression of BCL-2 in the Intestinal Epithelium Prevents Sepsis-Induced Gut Barrier Dysfunction via Altering Tight Junction Protein Expression.

Sepsis induces both intestinal hyperpermeability and epithelial apoptosis. While each has been implicated in mediating sepsis mortality, the relationship between these two processes is unclear. We hypothesized that preventing intestinal apoptosis would prevent gut barrier dysfunction. To test this hypothesis, transgenic mice that overexpress the anti-apoptotic protein Bcl-2 in the gut epithelium (Fabpl-Bcl-2 mice) and wild-type (WT) mice were subjected to sham laparotomy or cecal ligation and puncture and orally gavaged with fluorescein isothiocyanate conjugated-dextran (FD-4) 5 h before sacrifice. Serum FD-4 concentration was assayed to measure intestinal permeability, and jejunal tight junctions were assayed for mRNA and protein expression. Baseline FD-4 concentration was similar between WT and Fabpl-Bcl-2 mice. Intestinal permeability increased 6, 12, 24, and 48 h following sepsis in WT mice; however, FD-4 concentration was significantly lower at each timepoint in Fabpl-Bcl-2 mice. In addition, there were no statistically significant changes in permeability between septic and sham transgenic mice. Intestinal mRNA expression of claudin 3, claudin 5, and occludin was lower in septic Fabpl-Bcl-2 mice, while claudin 4 mRNA levels were higher in Fabpl-Bcl-2 mice. In contrast, no differences were detected in claudins 2, 7, 15, JAM-A, or ZO-1. Protein levels followed the same trend for all tight junction mediators different between WT and Fabpl-Bcl-2 mice except occludin was significantly higher in transgenic mice. Together these results demonstrate that decreasing intestinal epithelial apoptosis prevents hyperpermeability following sepsis via tight junction alterations which may be at least partially responsible for improved survival conferred by Bcl-2 overexpression.

The gut microbiome alters immunophenotype and survival from sepsis.

The microbiome is increasingly implicated in immune regulation and mortality from sepsis. Mice with identical genetic backgrounds but distinct microbiomes were obtained from different vendors and analyzed following cecal ligation and puncture (CLP). ß diversity of the microbiome measured from feces demonstrated significant differences between The Jackson Laboratory (Jax; Bar Harbor, ME, USA) and Charles River Laboratories (CR; Wilmington, MA, USA) C57/B6 mice. Jax mice had 7-d mortality of 90% following CLP, whereas CR mice had a mortality of 53%. Differences in vendor were associated with altered immunophenotype with increased splenic IFN-γ+CD4+ T cells, effector memory CD4+ T cells, and central memory CD4+ T cells and increased Peyer's patch effector memory CD4+ T cells in septic CR mice. To determine whether differences in the microbiome were responsible for these differences, Jax and CR mice were cohoused for 3 wk, after which they assumed a similar microbiota composition. Cohoused mice had improved survival following CLP compared to Jax mice and had similar survival regardless of their vendor of origin. All differences in immunophenotype between septic Jax and CR mice disappeared following cohousing. These findings suggest that the microbiome plays a crucial role in survival and the host immune response from sepsis and represents a potential target for therapeutic intervention.-Fay, K. T., Klingensmith, N. J., Chen, C.-W., Zhang, W., Sun, Y., Morrow, K. N., Liang, Z., Burd, E. M., Ford, M. L., Coopersmith, C. M. The gut microbiome alters immunophenotype and survival from sepsis.

Regulators of Intestinal Epithelial Migration in Sepsis.

The gut is a continuously renewing organ, with cell proliferation, migration, and death occurring rapidly under basal conditions. As the impact of critical illness on cell movement from crypt base to villus tip is poorly understood, the purpose of this study was to determine how sepsis alters enterocyte migration. Wild-type, transgenic, and knockout mice were injected with 5-bromo-2'deoxyuridine (BrdU) to label cells in S-phase before and after the onset of cecal ligation and puncture and were sacrificed at predetermined endpoints to determine distance proliferating cells migrated up the crypt-villus unit. Enterocyte migration rate was decreased from 24 to 96 h after sepsis. BrdU was not detectable on villi 6 days after sham laparotomy, meaning all cells had migrated the length of the gut and been exfoliated into its lumen. However, BrdU positive cells were detectable on villi 10 days after sepsis. Multiple components of gut integrity altered enterocyte migration. Sepsis decreased crypt proliferation, which further slowed enterocyte transit as mice injected with BrdU after the onset of sepsis (decreased proliferation) had slower migration than mice injected with BrdU before the onset of sepsis (normal proliferation). Decreasing intestinal apoptosis via gut-specific overexpression of Bcl-2 prevented sepsis-induced slowing of enterocyte migration. In contrast, worsened intestinal hyperpermeability by genetic deletion of JAM-A increased enterocyte migration. Sepsis therefore significantly slows enterocyte migration, and intestinal proliferation, apoptosis and permeability all affect migration time, which can potentially be targeted both genetically and pharmacologically.

Chronic Alcohol Ingestion Worsens Survival and Alters Gut Epithelial Apoptosis and CD8+ T Cell Function After Pseudomonas Aeruginosa Pneumonia-Induced Sepsis.

Mortality is higher in septic patients with a history of alcohol use disorder than in septic patients without a history of chronic alcohol usage. We have previously described a model of chronic alcohol ingestion followed by sepsis from cecal ligation and puncture in which alcohol-fed septic mice have higher mortality than water-fed septic mice, associated with altered gut integrity and increased production of TNF and IFNγ by splenic CD4 T cells without alterations in CD8 T cell function. The purpose of this study was to determine whether this represents a common host response to the combination of alcohol and sepsis by creating a new model in which mice with chronic alcohol ingestion were subjected to a different model of sepsis. C57Bl/6 mice were randomized to receive either alcohol or water for 12 weeks and then subjected to Pseudomonas aeruginosa pneumonia. Mice were sacrificed either 24 hours after the onset of sepsis or followed for survival. Alcohol-fed septic mice had significantly higher 7-day mortality than water-fed septic mice (96% vs 58%). This was associated with a 5-fold increase in intestinal apoptosis in alcohol-fed septic animals, accompanied by an increase in the pro-apoptotic protein Bax. Serum IL-6 levels were higher and IL-2 levels were lower in alcohol-fed septic mice. In contrast, CD8 T cell frequency was lower in alcohol-fed mice than water-fed septic mice, associated with increased production of IFNγ and TNF in stimulated splenocytes. No significant differences were noted in CD4 T cells, lung injury or bacteremia. Mice with chronic alcohol ingestion thus have increased mortality regardless of their septic insult, associated with changes in both the gut and the immune system.

Increased mortality in CD43-deficient mice during sepsis.

CD43 is a large transmembrane protein involved in T cell activation. Previous studies of CD43-/- mice in viral models have demonstrated a role for CD43 in Th1/Th2 skewing, activation of Foxp3+ Treg, and T cell apoptosis. However, the role of CD43 during sepsis has never been tested. Thus, we interrogated the role of CD43 during sepsis using a murine cecal ligation and puncture (CLP) model, and found that CD43-/- mice demonstrated significantly worsened mortality compared to B6 mice following CLP. Phenotypic analysis of splenocytes isolated 24 h after septic insult revealed significantly increased apoptosis of central memory cells in both CD4+ and CD8+ T cell compartments in CD43-/- septic mice compared to WT septic mice. Furthermore, CD43-/-septic mice exhibited a prominent Th2 skewing following sepsis relative to WT septic mice, as evidenced by a significant decrease in the frequency of IL-2+ CXCR3+ TH1 cells as a significant increase in the frequency of IL-4+ CCR4+ TH2 cells. Finally, septic CD43-/- animals contained significantly fewer CD25+ Foxp3+ TReg cells as compared to WT septic animals. Importantly, depleting CD25+ Treg eliminated the increased mortality observed in CD43-/- mice. Taken together, these data demonstrate an important role of CD43 in modulating immune dysregulation and mortality following sepsis.

Honokiol Increases CD4+ T Cell Activation and Decreases TNF but Fails to Improve Survival Following Sepsis.

Honokiol is a biphenolic isolate extracted from the bark of the magnolia tree that has been used in traditional Chinese and Japanese medicine, and has more recently been investigated for its anti-inflammatory and antibacterial properties. Honokiol has previously been demonstrated to improve survival in sepsis models that have rapid 100% lethality. The purpose of this study was to determine the impact of Honokiol on the host response in a model of sepsis that more closely approximates human disease. Male and female C57BL/6 mice underwent cecal ligation and puncture to induce polymicrobial intra-abdominal sepsis. Mice were then randomized to receive an injection of either Honokiol (120 mg/kg/day) or vehicle and were sacrificed after 24 h for functional studies or followed 7 days for survival. Honokiol treatment after sepsis increased the frequency of CD4 T cells and increased activation of CD4 T cells as measured by the activation marker CD69. Honokiol also increased splenic dendritic cells. Honokiol simultaneously decreased frequency and number of CD8 T cells. Honokiol decreased systemic tumor necrosis factor without impacting other systemic cytokines. Honokiol did not have a detectable effect on kidney function, lung physiology, liver function, or intestinal integrity. In contrast to prior studies of Honokiol in a lethal model of sepsis, Honokiol did not alter survival at 7 days (70% mortality for Honokiol vs. 60% mortality for vehicle). Honokiol is thus effective in modulating the host immune response and inflammation following a clinically relevant model of sepsis but is not sufficient to alter survival.

Effect of Remote Ischemic Preconditioning on Outcomes in Adult Cardiac Surgery: A Systematic Review and Meta-analysis of Randomized Controlled Studies.

BACKGROUND: Remote ischemic preconditioning (RIPC) has been demonstrated to prevent organ dysfunction in cardiac surgery patients. However, recent large, prospective, multicenter, randomized controlled trials (RCTs) had controversial results. Thus, a meta-analysis of RCTs was performed to investigate whether RIPC can reduce the incidence of acute myocardial infarction (AMI), acute kidney injury (AKI), and mortality in adult cardiac surgery patients. METHODS: Study data were collected from Medline, Elsevier, Cochrane Central Register of Controlled Trials and Web of Science databases. RCTs involving the effect of RIPC on organ protection in cardiac surgery patients, which reported the concentration or total release of creatine kinase-myocardial band, troponin I/troponin T (TNI/TNT) after operation, or the incidence of AMI, AKI, or mortality, were selected. Two reviewers independently extracted data using a standardized data extraction protocol where TNI or TNT concentrations; total TNI released after cardiac surgery; and the incidence of AKI, AMI, and mortality were recorded. Review Manager 5.3 software was used to analyze the data. RESULTS: Thirty trials, including 7036 patients were included in the analyses. RIPC significantly decreased the concentration of TNI/TNT (standard mean difference [SMD], -0.25 ng/mL; 95% confidence interval [CI], -0.41 to -0.048 ng/mL; P = .004), creatine kinase-myocardial band (SMD, -0.22; 95% CI, -0.07-0.35 ng/mL; P = .46), and the total TNI/TNT release (SMD, -0.49 ng/mL; 95% CI, -0.93 to -0.55 ng/mL; P = .03) in cardiac surgery patients after a procedure. However, RIPC could not reduce the incidence of AMI (relative risk, 0.89; 95% CI, 0.70-1.13; P = .34) and AKI (relative risk, 0.88; 95% CI, 0.72-1.06; P = .18), and there was also no effect of RIPC on mortality in adult cardiac surgery patients. Interestingly, subgroup analysis showed that RIPC reduced incidence of AKI and mortality of cardiac surgery patients who received volatile agent anesthesia. CONCLUSIONS: Our meta-analysis demonstrated that RIPC reduced TNI/TNT release after cardiac surgery. RIPC did not significantly reduce the incidence of AKI, AMI, and mortality. However, RIPC could reduce mortality in patients receiving volatile inhalational agent anesthesia.

CXCR4 blockade decreases CD4+ T cell exhaustion and improves survival in a murine model of polymicrobial sepsis.

Sepsis is a dysregulated systemic response to infection involving many inflammatory pathways and the induction of counter-regulatory anti-inflammatory processes that results in a state of immune incompetence and can lead to multi-organ failure. CXCR4 is a chemokine receptor that, following ligation by CXCL12, directs cells to bone marrow niches and also plays an important role in T cell cosignaling and formation of the immunological synapse. Here, we investigated the expression and function of CXCR4 in a murine model of polymicrobial sepsis. Results indicate that CXCR4 is selectively upregulated on naïve CD4+ and CD8+ T cells and CD4+ central memory T cells following the induction of sepsis, and that CXCR4 antagonism resulted in a significant decrease in sepsis-induced mortality. We probed the mechanistic basis for these findings and found that CXCR4 antagonism significantly increased the number of peripheral CD4+ and CD8+ T cells following sepsis. Moreover, mice treated with the CXCR4 antagonist contained fewer PD-1+ LAG-3+ 2B4+ cells, suggesting that blockade of CXCR4 mitigates CD4+ T cell exhaustion during sepsis. Taken together, these results characterize CXCR4 as an important pathway that modulates immune dysfunction and mortality following sepsis, which may hold promise as a target for future therapeutic intervention in septic patients.

Sepsis reveals compartment-specific responses in intestinal proliferation and apoptosis in transgenic mice whose enterocytes re-enter the cell cycle.

Cell production and death are tightly regulated in the rapidly renewing gut epithelium, with proliferation confined to crypts and apoptosis occurring in villi and crypts. This study sought to determine how stress alters these compartmentalized processes. Wild-type mice made septic via cecal ligation and puncture had decreased crypt proliferation and increased crypt and villus apoptosis. Fabpi-TAg mice expressing large T-antigen solely in villi had ectopic enterocyte proliferation with increased villus apoptosis in unmanipulated animals. Septic fabpi-TAg mice had an unexpected increase in villus proliferation compared with unmanipulated littermates, whereas crypt proliferation was decreased. Cell cycle regulators cyclin D1 and cyclin D2 were decreased in jejunal tissue in septic transgenic mice. In contrast, villus and crypt apoptosis were increased in septic fabpi-TAg mice. To examine the relationship between apoptosis and proliferation in a compartment-specific manner, fabpi-TAg mice were crossed with fabpl-Bcl-2 mice, resulting in expression of both genes in the villus but Bcl-2 alone in the crypt. Septic bi-transgenic animals had decreased crypt apoptosis but had a paradoxical increase in villus apoptosis compared with septic fabpi-TAg mice, associated with decreased proliferation in both compartments. Thus, sepsis unmasks compartment-specific proliferative and apoptotic regulation that is not present under homeostatic conditions.-Lyons, J. D., Klingensmith, N. J., Otani, S., Mittal, R., Liang, Z., Ford, M. L., Coopersmith, C. M. Sepsis reveals compartment-specific responses in intestinal proliferation and apoptosis in transgenic mice whose enterocytes re-enter the cell cycle.

Cutting Edge: 2B4-Mediated Coinhibition of CD4+ T Cells Underlies Mortality in Experimental Sepsis.

Sepsis is a leading cause of death in the United States, but the mechanisms underlying sepsis-induced immune dysregulation remain poorly understood. 2B4 (CD244, SLAM4) is a cosignaling molecule expressed predominantly on NK cells and memory CD8+ T cells that has been shown to regulate T cell function in models of viral infection and autoimmunity. In this article, we show that 2B4 signaling mediates sepsis lymphocyte dysfunction and mortality. 2B4 expression is increased on CD4+ T cells in septic animals and human patients at early time points. Importantly, genetic loss or pharmacologic inhibition of 2B4 significantly increased survival in a murine cecal ligation and puncture model. Further, CD4-specific conditional knockouts showed that 2B4 functions on CD4+ T cell populations in a cell-intrinsic manner and modulates adaptive and innate immune responses during sepsis. Our results illuminate a novel role for 2B4 coinhibitory signaling on CD4+ T cells in mediating immune dysregulation.

Myosin light chain kinase knockout improves gut barrier function and confers a survival advantage in polymicrobial sepsis.

Sepsis-induced intestinal hyperpermeability is mediated by disruption of the epithelial tight junction, which is closely associated with the peri-junctional actin-myosin ring. Myosin light chain kinase (MLCK) phosphorylates the myosin regulatory light chain, resulting in increased permeability. The purpose of this study was to determine whether genetic deletion of MLCK would alter gut barrier function and survival from sepsis. MLCK-/- and wild type (WT) mice were subjected to cecal ligation and puncture and assayed for both survival and mechanistic studies. Survival was significantly increased in MLCK-/- mice (95% vs. 24%, p<0.0001). Intestinal permeability increased in septic WT mice compared to unmanipulated mice. In contrast, permeability in septic MLCK-/- mice was similar to that seen in unmanipulated animals. Improved gut barrier function in MLCK-/- mice was associated with increases in the tight junction mediators ZO-1 and claudin 15 without alterations in claudin 1, 2, 3, 4, 5, 7, 8, 13, occludin or JAM-A. Other components of intestinal integrity (apoptosis, proliferation and villus length) were unaffected by MLCK deletion as were local peritoneal inflammation and distant lung injury. Systemic IL-10 was decreased greater than 10-fold in MLCK-/- mice; however, survival was similar between septic MLCK-/- mice given exogenous IL-10 or vehicle. These data demonstrate that deletion of MLCK improves survival following sepsis, associated with normalization of intestinal permeability and selected tight junction proteins.

New insights into the gut as the driver of critical illness and organ failure.

PURPOSE OF REVIEW: The gut has long been hypothesized to be the 'motor' of multiple organ dysfunction syndrome. This review serves as an update on new data elucidating the role of the gut as the propagator of organ failure in critical illness. RECENT FINDINGS: Under basal conditions, the gut absorbs nutrients and serves as a barrier that prevents approximately 40 trillion intraluminal microbes and their products from causing host injury. However, in critical illness, gut integrity is disrupted with hyperpermeability and increased epithelial apoptosis, allowing contamination of extraluminal sites that are ordinarily sterile. These alterations in gut integrity are further exacerbated in the setting of preexisting comorbidities. The normally commensal microflora is also altered in critical illness, with increases in microbial virulence and decreases in diversity, which leads to further pathologic responses within the host. SUMMARY: All components of the gut are adversely impacted by critical illness. Gut injury can not only propagate local damage, but can also cause distant injury and organ failure. Understanding how the multifaceted components of the gut interact and how these are perturbed in critical illness may play an important role in turning off the 'motor' of multiple organ dysfunction syndrome in the future.