Animal models of sepsis

Inflammatory CD11c+ B Cells Induced by the TREM2 Signal Accelerate Sepsis Development

CD11c+ B cells are an age-associated subset emerging in infections and autoimmune diseases. However, their role in sepsis is poorly clarified. This study identified a class of CD11c+ B cells with a proinflammatory phenotype that is expended in septic patients and mice. Notably, the transfer of these cells accelerates sepsis-induced lung injury and death in mice. Furthermore, the CD11c+ B cells were induced by the triggering receptor expressed on myeloid cells 2 (TREM2) signal, which promotes their generation via the interferon regulatory factor 4 (IRF4) pathway. Moreover, TREM2 directly participates in sepsis regulation mediated by CD11c+ B cells. This study reveals the proinflammatory role of CD11c+ B cells in sepsis and identifies TREM2 as a contributing factor in CD11c+ B-cell-mediated inflammatory injury during sepsis.

From Molecular Mechanisms to Clinical Therapy: Understanding Sepsis-Induced Multiple Organ Dysfunction

Sepsis-induced multiple organ dysfunction arises from the highly complex pathophysiology encompassing the interplay of inflammation, oxidative stress, endothelial dysfunction, mitochondrial damage, cellular energy failure, and dysbiosis. Over the past decades, numerous studies have been dedicated to elucidating the underlying molecular mechanisms of sepsis in order to develop effective treatments. Current research underscores liver and cardiac dysfunction, along with acute lung and kidney injuries, as predominant causes of mortality in sepsis patients. This understanding of sepsis-induced organ failure unveils potential therapeutic targets for sepsis treatment. Various novel therapeutics, including melatonin, metformin, palmitoylethanolamide (PEA), certain herbal extracts, and gut microbiota modulators, have demonstrated efficacy in different sepsis models. In recent years, the research focus has shifted from anti-inflammatory and antioxidative agents to exploring the modulation of energy metabolism and gut microbiota in sepsis. These approaches have shown a significant impact in preventing multiple organ damage and mortality in various animal sepsis models but require further clinical investigation. The accumulation of this knowledge enriches our understanding of sepsis and is anticipated to facilitate the development of effective therapeutic strategies in the future.

Heparin-Binding Protein Promotes Acute Lung Injury in Sepsis Mice by Blocking the Aryl Hydrocarbon Receptor Signaling Pathway

Purpose

This study aimed to explore the therapeutic effect and potential mechanism of heparin-binding protein (HBP) reduction on sepsis-related acute lung injury.

Methods

We utilized a murine model of sepsis-induced by intraperitoneal injection of lipopolysaccharides (LPS) in C57BL/6J mice divided into four groups: Control, LPS, Anti-HBP, and ceftriaxone (CEF). Following sepsis induction, Anti-HBP or CEF treatments were administered, and survival rates were monitored for 48 h. We then used reverse-transcription quantitative PCR to analyze the expression levels of HBP in lung tissues, immunohistochemistry for protein localization, and Western blotting for protein quantification. Pulmonary inflammation was assessed using enzyme-linked immunosorbent assays of proinflammatory cytokines (tumor necrosis factor-α, interleukin [IL]-1β, IL-6, and interferon-γ). The activation state of the aryl hydrocarbon receptor (AhR) signaling pathway was determined via Western blotting, evaluating both cytoplasmic and nuclear localization of AhR and the expression of cytochrome P450 1A1 protein by its target gene.

Results

Anti-HBP specifically reduced HBP levels. The survival rate of mice in the Anti-HBP and CEF groups was much higher than that in the LPS group. The severity of lung injury and pulmonary inflammatory response in the Anti-HBP and CEF groups was significantly lower than that in the LPS group. AhR signaling pathway activation was observed in the Anti-HBP and CEF groups. Additionally, there was no significant difference in the above indices between the Anti-HBP and CEF groups.

Conclusion

HBP downregulation in lung tissues significantly improved LPS-induced lung injury and the pulmonary inflammatory response, thereby prolonging the survival of sepsis mice, suggesting activation of the AhR signaling pathway. Moreover, the effect of lowering the HBP level was equivalent to that of the classical antibiotic CEF.

Trial Registration

Not applicable.

Pretreatment with Eupatilin Attenuates Inflammation and Coagulation in Sepsis by Suppressing JAK2/STAT3 Signaling Pathway

Purpose

Sepsis is an aggressive and life-threatening organ dysfunction induced by infection. Excessive inflammation and coagulation contribute to the negative outcomes for sepsis, resulting in high morbidity and mortality. In this study, we explored whether Eupatilin could alleviate lung injury, reduce inflammation and coagulation during sepsis.

Methods

We constructed an in vitro sepsis model by stimulating RAW264.7 cells with 1 μg/mL lipopolysaccharide (LPS) for 6 hours. The cells were divided into control group, LPS group, LPS+ Eupatilin (Eup) group, and Eup group to detect their cell activity and inflammatory cytokines and coagulation factor levels. Cells in LPS+Eup and Eup group were pretreated with Eupatilin (10μM) for 2 hours. In vivo, mice were divided into sham operation group, cecal ligation and puncture (CLP) group and Eup group. Mice in the CLP and Eup groups were pretreated with Eupatilin (10mg/kg) for 2 hours by gavage. Lung tissue and plasma were collected and inflammatory cytokines, coagulation factors and signaling were measured.

Results

In vitro, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and tissue factor (TF) expression in LPS-stimulated RAW264.7 cells was downregulated by Eupatilin (10μM). Furthermore, Eupatilin inhibited phosphorylation of the JAK2/STAT3 signaling pathway and suppressed p-STAT3 nuclear translocation. In vivo, Eupatilin increased the survival rate of the mice. In septic mice, plasma concentrations of TNF-α, IL-1β and IL-6, as well as TF, plasminogen activator inhibitor 1 (PAI-1), D-dimer, thrombin-antithrombin complex (TAT) and fibrinogen were improved by Eupatilin. Moreover, Eupatilin alleviated lung injury by improving the expression of inflammatory cytokines and TF, fibrin deposition and macrophage infiltration in lung tissue.

Conclusion

Our results revealed that Eupatilin may modulate inflammation and coagulation indicators as well as improve lung injury in sepsis via the JAK2/STAT3 signaling pathway.

Common Variables That Influence Sepsis Mortality in Mice

Introduction

Sepsis is characterized by a dysregulated host immune response to infection, leading to organ dysfunction and a high risk of death. The cecal ligation and puncture (CLP) mouse model is commonly used to study sepsis, but animal mortality rates vary between different studies. Technical factors and animal characteristics may affect this model in unanticipated ways, and if unaccounted for, may lead to serious biases in study findings. We sought to evaluate whether mouse sex, age, weight, surgeon, season of experiments, and timing of antibiotic administration influenced mortality in the CLP model.

Methods

We created a comprehensive dataset of C57BL/6J mice that had undergone CLP surgery within our lab during years 2015-2020 from published and unpublished studies. The primary outcome was defined as the time from sepsis induction to death or termination of study (14 days). The Log rank test and Cox regression models were used to analyze the dataset. The study included 119 mice, of which 43% were female, with an average age of 12.6 weeks, an average weight of 25.3 g. 38 (32%) of the animals died.

Results

In the unadjusted analyses, experiments performed in the summer and higher weight predicted a higher risk of mortality. In the stratified Cox model by sex, summer season (adjusted hazard ratio [aHR]=5.61, p=0.004) and delayed antibiotic administration (aHR=1.46, p=0.029) were associated with mortality in males, whereas higher weight (aHR=1.52, p=0.005) significantly affected mortality in females. In addition, delayed antibiotic administration (HR=1.42, p=0.025) was associated with mortality in the non-summer seasons, but not in the summer season.

Discussion

In conclusion, some factors specific to sex and season have a significant influence on sepsis mortality in the CLP model. Consideration of these factors along with appropriate group matching or adjusted analysis is critical to minimize variability beyond the experimental conditions within a study.

Pulsed Electromagnetic Field (PEMF) Treatment Reduces Lipopolysaccharide-Induced Septic Shock in Mice

Despite advances in medicine, mortality due to sepsis has not decreased. Pulsed electromagnetic field (PEMF) therapy is emerging as an alternative treatment in many inflammation-related diseases. However, there are few studies on the application of PEMF therapy to sepsis. In the current study, we examined the effect of PEMF therapy on a mouse model of lipopolysaccharide (LPS)-induced septic shock. Mice injected with LPS and treated with PEMF showed higher survival rates compared with the LPS group. The increased survival was correlated with decreased levels of pro-inflammatory cytokine mRNA expression and lower serum nitric oxide levels and nitric oxide synthase 2 mRNA expression in the liver compared with the LPS group. In the PEMF + LPS group, there was less organ damage in the liver, lungs, spleen, and kidneys compared to the LPS group. To identify potential gene targets of PEMF treatment, microarray analysis was performed, and the results showed that 136 genes were up-regulated, and 267 genes were down-regulated in the PEMF + LPS group compared to the LPS group. These results suggest that PEMF treatment can dramatically decrease septic shock through the reduction of pro-inflammatory cytokine gene expression. In a clinical setting, PEMF may provide a beneficial effect for patients with bacteria-induced sepsis and reduce septic shock-induced mortality.

Disruption of Kidney-Immune System Crosstalk in Sepsis with Acute Kidney Injury: Lessons Learned from Animal Models and Their Application to Human Health

In addition to being a leading cause of morbidity and mortality worldwide, sepsis is also the most common cause of acute kidney injury (AKI). When sepsis leads to the development of AKI, mortality increases dramatically. Since the cardinal feature of sepsis is a dysregulated host response to infection, a disruption of kidney-immune crosstalk is likely to be contributing to worsening prognosis in sepsis with acute kidney injury. Since immune-mediated injury to the kidney could disrupt its protein manufacturing capacity, an investigation of molecules mediating this crosstalk not only helps us understand the sepsis immune response, but also suggests that their supplementation could have a therapeutic effect. Erythropoietin, vitamin D and uromodulin are known to mediate kidney-immune crosstalk and their disrupted production could impact morbidity and mortality in sepsis with acute kidney injury.

Biochemical and Hematologic Reference Intervals for Anesthetized, Female, Juvenile Yorkshire Swine

Swine are widely used in biomedical research, translational research, xenotransplantation, and agriculture. For these uses, physiologic reference intervals are extremely important for assessing the health status of the swine and diagnosing disease. However, few biochemical and hematologic reference intervals that comply with guidelines from the Clinical and Laboratory Standards Institute and the American Society for Veterinary Clinical Pathology are available for swine. These guidelines state that reference intervals should be determined by using 120 subjects or more. The aim of this study was to generate hematologic and biochemical reference intervals for female, juvenile Yorkshire swine (Sus scrofa domesticus) and to compare these values with those for humans and baboons (Papio hamadryas). Blood samples were collected from the femoral artery or vein of female, juvenile Yorkshire swine, and standard hematologic and biochemical parameters were analyzed in multiple studies. Hematologic and biochemical reference intervals were calculated for arterial blood samples from Yorkshire swine (n = 121 to 124); human and baboon reference intervals were obtained from the literature. Arterial reference intervals for Yorkshire swine differed significantly from those for humans and baboons in all commonly measured parameters except platelet count, which did not differ significantly from the human value, and glucose, which was not significantly different from the baboon value. These data provide valuable information for investigators using female, juvenile Yorkshire swine for biomedical re- search, as disease models, and in xenotransplantation studies as well as useful physiologic information for veterinarians and livestock producers. Our findings highlight the need for caution when comparing data and study outcomes between species.

Recombinant Fasciola hepatica Fatty Acid Binding Protein as a Novel Anti-Inflammatory Biotherapeutic Drug in an Acute Gram-Negative Nonhuman Primate Sepsis Model

Due to their phylogenetic proximity to humans, nonhuman primates (NHPs) are considered an adequate choice for a basic and preclinical model of sepsis. Gram-negative bacteria are the primary causative of sepsis. During infection, bacteria continuously release the potent toxin lipopolysaccharide (LPS) into the bloodstream, which triggers an uncontrolled systemic inflammatory response leading to death. Our previous research has demonstrated in vitro and in vivo using a mouse model of septic shock that Fh15, a recombinant variant of the Fasciola hepatica fatty acid binding protein, acts as an antagonist of Toll-like receptor 4 (TLR4) suppressing the LPS-induced proinflammatory cytokine storm. The present communication is a proof-of concept study aimed to demonstrate that a low-dose of Fh15 suppresses the cytokine storm and other inflammatory markers during the early phase of sepsis induced in rhesus macaques by intravenous (i.v.) infusion with lethal doses of live Escherichia coli. Fh15 was administered as an isotonic infusion 30 min prior to the bacterial infusion. Among the novel findings reported in this communication, Fh15 (i) significantly prevented bacteremia, suppressed LPS levels in plasma, and the production of C-reactive protein and procalcitonin, which are key signatures of inflammation and bacterial infection, respectively; (ii) reduced the production of proinflammatory cytokines; and (iii) increased innate immune cell populations in blood, which suggests a role in promoting a prolonged steady state in rhesus macaques even in the presence of inflammatory stimuli. This report is the first to demonstrate that a F. hepatica-derived molecule possesses potential as an anti-inflammatory drug against sepsis in an NHP model.

IMPORTANCE Sepsis caused by Gram-negative bacteria affects 1.7 million adults annually in the United States and is one of the most important causes of death at intensive care units. Although the effective use of antibiotics has resulted in improved prognosis of sepsis, the pathological and deathly effects have been attributed to the persistent inflammatory cascade. There is a present need to develop anti-inflammatory agents that can suppress or neutralize the inflammatory responses and prevent the lethal consequences of sepsis. We demonstrated here that a small molecule of 14.5 kDa can suppress the bacteremia, endotoxemia, and many other inflammatory markers in an acute Gram-negative sepsis rhesus macaque model. These results reinforce the notion that Fh15 constitutes an excellent candidate for drug development against sepsis.

Dissect the immunity using cytokine profiling and NF-kB target gene analysis in systemic inflammatory minipig model

Minipigs have remarkably similar physiology to humans, therefore, they it can be a good animal model for inflammation study. Thus, the conventional (serum chemistry, histopathology) and novel analytic tools [immune cell identification in tissue, cytokine level in peripheral blood mononuclear cells (PBMC) and serum, NF-kB target gene analysis in tissue] were applied to determine inflammation in Chicago Miniature Swine (CMS) minipig. Lipopolysaccharide (LPS)-induced acute systemic inflammation caused liver and kidney damage in serum chemistry and histopathology. Immunohistochemistry (IHC) also showed an increase of immune cell distribution in spleen and lung during inflammation. Moreover, NF-kB-target gene expression was upregulated in lung and kidney in acute inflammation and in heart, liver, and intestine in chronic inflammation. Cytokine mRNA was elevated in PBMC under acute inflammation along with elevated absolute cytokine levels in serum. Overall, LPS-mediated systemic inflammation affects the various organs, and can be detected by IHC of immune cells, gene analysis in PBMC, and measuring the absolute cytokine in serum along with conventional inflammation analytic tools.

Development of a large animal model of lethal polytrauma and intra-abdominal sepsis with bacteremia

Background

Trauma and sepsis are individually two of the leading causes of death worldwide. When combined, the mortality is greater than 50%. Thus, it is imperative to have a reproducible and reliable animal model to study the effects of polytrauma and sepsis and test novel treatment options. Porcine models are more translatable to humans than rodent models due to the similarities in anatomy and physiological response. We embarked on a study to develop a reproducible model of lethal polytrauma and intra-abdominal sepsis, which was lethal, though potentially salvageable with treatment.

Methods

Our laboratory has a well-established porcine model that was used as the foundation. Animals were subjected to a rectus crush injury, long bone fracture, liver and spleen laceration, traumatic brain injury and hemorrhage that was used as a foundation. We tested various colon injuries to create intra-abdominal sepsis. All animals underwent injuries followed by a period of shock, then subsequent resuscitation.

Results

All animals had blood culture-proven sepsis. Attempts at long-term survival of animals after injury were ceased because of poor appetite and energy. We shifted to an 8-hour endpoint. The polytrauma injury pattern remained constant and the colon injury pattern changed with the intention of creating a model that was ultimately lethal but potentially salvageable with a therapeutic drug. An uncontrolled cecal injury (n=4) group resulted in very early deaths. A controlled cecal injury (CCI; n=4) group had prolonged time prior to mortality with one surviving to the endpoint. The sigmoid injury (n=5) produced a similar survival curve to CCI but no animals surviving to the endpoint.

Conclusion

We have described a porcine model of polytrauma and sepsis that is reproducible and may be used to investigate novel treatments for trauma and sepsis.

Level of evidence

Not applicable. Animal study.

Overexpression of Gilz Protects Mice Against Lethal Septic Peritonitis

Sepsis in humans and experimental animals is characterized by an acute inflammatory response. glucocorticoids (GCs) are widely used for the treatment of many inflammatory disorders, yet their effectiveness in sepsis is debatable. One of the major anti-inflammatory proteins induced by GCs is glucocorticoid-induced leucine zipper (GILZ, coded by the TSC22D3 gene). We found that TSC22D3 mRNA expression is downregulated in white blood cells of human sepsis patients. Interestingly, transgenic GILZ-overexpressing mice (GILZ-tg) showed better survival rates in the cecal ligation and puncture (CLP) model of mouse sepsis. To our surprise, GILZ had only mild anti-inflammatory effects in this model, as the systemic proinflammatory response was not significantly reduced in GILZ-tg mice compared with control mice. During CLP, we observed reduced bacterial counts in blood of GILZ-tg mice compared with control mice. We found increased expression of Tsc22d3 mRNA specifically in peritoneal exudate cells in the CLP model, as well as increased capacity for bacterial phagocytosis of CD45 GILZ-tg cells compared with CD45 GILZ-wt cells. Hence, we believe that the protective effects of GILZ in the CLP model can be linked to a more efficient phagocytosis.

Cardiorespiratory Alterations in a Newborn Ovine Model of Systemic Inflammation Induced by Lipopolysaccharide Injection

Although it is well known that neonatal sepsis can induce important alterations in cardiorespiratory control, their detailed early features and the mechanisms involved remain poorly understood. As a first step in resolving this issue, the main goal of this study was to characterize these alterations more extensively by setting up a full-term newborn lamb model of systemic inflammation using lipopolysaccharide (LPS) injection. Two 6-h polysomnographic recordings were performed on two consecutive days on eight full-term lambs: the first after an IV saline injection (control condition, CTRL); the second, after an IV injection of 2.5 μg/kg Escherichia coli LPS 0127:B8 (LPS condition). Rectal temperature, locomotor activity, state of alertness, arterial blood gases, respiratory frequency and heart rate, mean arterial blood pressure, apneas and cardiac decelerations, and heart-rate and respiratory-rate variability (HRV and RRV) were assessed. LPS injection decreased locomotor activity (p = 0.03) and active wakefulness (p = 0.01) compared to the CTRL. In addition, LPS injection led to a biphasic increase in rectal temperature (p = 0.01 at ∼30 and 180 min) and in respiratory frequency and heart rate (p = 0.0005 and 0.005, respectively), and to an increase in cardiac decelerations (p = 0.05). An overall decrease in HRV and RRV was also observed. Interestingly, the novel analysis of the representations of the horizontal and vertical visibility network yielded the most statistically significant alterations in HRV structure, suggesting its potential clinical importance for providing an earlier diagnosis of neonatal bacterial sepsis. A second goal was to assess whether the reflexivity of the autonomic nervous system was altered after LPS injection by studying the cardiorespiratory components of the laryngeal and pulmonary chemoreflexes. No difference was found. Lastly, preliminary results provide proof of principle that brainstem inflammation (increased IL-8 and TNF-α mRNA expression) can be shown 6 h after LPS injection. In conclusion, this full-term lamb model of systemic inflammation reproduces several important aspects of neonatal bacterial sepsis and paves the way for studies in preterm lambs aiming to assess both the effect of prematurity and the central neural mechanisms of cardiorespiratory control alterations observed during neonatal sepsis.

Eicosanoids derived from cytochrome P450 pathway of arachidonic acid and inflammatory shock

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection. Septic shock, the most common form of vasodilatory shock, is a subset of sepsis in which circulatory and cellular/metabolic abnormalities are severe enough to increase mortality. Inflammatory shock constitutes the hallmark of sepsis, but also a final common pathway of any form of severe long-term tissue hypoperfusion. The pathogenesis of inflammatory shock seems to be due to circulating substances released by pathogens (e.g., bacterial endotoxins) and host immuno-inflammatory responses (e.g., changes in the production of histamine, bradykinin, serotonin, nitric oxide [NO], reactive nitrogen and oxygen species, and arachidonic acid [AA]-derived eicosanoids mainly through NO synthase, cyclooxygenase, and cytochrome P450 [CYP] pathways, and proinflammatory cytokine formation). Therefore, refractory hypotension to vasoconstrictors with end-organ hypoperfusion is a life threatening feature of inflammatory shock. This review summarizes the current knowledge regarding the role of eicosanoids derived from CYP pathway of AA in animal models of inflammatory shock syndromes with an emphasis on septic shock in addition to potential therapeutic strategies targeting specific CYP isoforms responsible for proinflammatory/anti-inflammatory mediator production.

Increased expression of Toll-like receptors 2, 3, 4 and 7 mRNA in the kidney and intestine of a septic mouse model

Toll-like receptors (TLRs) are the key regulators of innate and adaptive immunity and are highly expressed during sepsis. Thus, studying the expression of TLRs in an animal septic model might indicate their possible association with acute kidney injury in sepsis. Seventy-two male C57BL/6J mice were used for this study. Randomly, these animals were divided into 6 groups (N = 12/group): 3 control and 3 septic groups depending on the euthanasia time (24 h, 48 h, 72 h). Septic groups underwent cecal ligation and puncture (CLP) to induce peritonitis, while control groups had a sham operation. Hematological tests were performed in serum for immune biomarkers; immunohistochemistry, morphometry and qRT-PCR analysis were used on both kidney and intestine tissues to evaluate the expression of TLR 2, 3, 4 and 7 in a septic process. At the end of each experimental period, we found that TLRs 2, 3, 4 and 7 were expressed in both tissues but there were differences between those at various time points. Also, we found that mRNA levels were significantly higher in qRT-PCR evaluation in septic groups than control groups in both kidney and intestinal tissues (p < 0.05); showing a steady increase in the septic groups as the time to euthanasia was prolonged (p < 0.05). Overall, our study provides a suggestion that TLRs 2, 3, 4 and 7 are highly expressed in the kidneys of septic mice and especially that these TLRs are sensitive and specific markers for sepsis. Finally, our study supports the diagnostic importance of TLRs in AKI and provides an insight on the contribution of septic mice models in the study of multi organ dysfunction syndrome in general.

Variability of mitochondrial respiration in relation to sepsis-induced multiple organ dysfunction

Ample experimental evidence suggests that sepsis could interfere with any mitochondrial function; however, the true role of mitochondrial dysfunction in the pathogenesis of sepsis-induced multiple organ dysfunction is still a matter of controversy. This review is primarily focused on mitochondrial oxygen consumption in various animal models of sepsis in relation to human disease and potential sources of variability in experimental results documenting decrease, increase or no change in mitochondrial respiration in various organs and species. To date, at least three possible explanations of sepsis-associated dysfunction of the mitochondrial respiratory system and consequently impaired energy production have been suggested: 1. Mitochondrial dysfunction is secondary to tissue hypoxia. 2. Mitochondria are challenged by various toxins or mediators of inflammation that impair oxygen utilization (cytopathic hypoxia). 3. Compromised mitochondrial respiration could be an active measure of survival strategy resembling stunning or hibernation. To reveal the true role of mitochondria in sepsis, sources of variability of experimental results based on animal species, models of sepsis, organs studied, or analytical approaches should be identified and minimized by the use of appropriate experimental models resembling human sepsis, wider use of larger animal species in preclinical studies, more detailed mapping of interspecies differences and organ-specific features of oxygen utilization in addition to use of complex and standardized protocols evaluating mitochondrial respiration.

Nonhuman primate species as models of human bacterial sepsis

Sepsis involves a disordered host response to systemic infection leading to high morbidity and mortality. Despite intense research, targeted sepsis therapies beyond antibiotics have remained elusive. The cornerstone of sepsis research is the development of animal models to mimic human bacterial infections and test novel pharmacologic targets. Nonhuman primates (NHPs) have served as an attractive, but expensive, animal to model human bacterial infections due to their nearly identical cardiopulmonary anatomy and physiology, as well as host response to infection. Several NHP species have provided substantial insight into sepsis-mediated inflammation, endothelial dysfunction, acute lung injury, and multi-organ failure. The use of NHPs has usually focused on translating therapies from early preclinical models to human clinical trials. However, despite successful sepsis interventions in NHP models, there are still no FDA-approved sepsis therapies. This review highlights major NHP models of bacterial sepsis and their relevance to clinical medicine.

Treatment for bacterial sepsis remains limited beyond the use of antibiotics. Lingye Chen, Karen Welty-Wolf, and Bryan Kraft review nonhuman primate models of sepsis and highlight their advantages and limitations compared to other preclinical models.

Toll-Like Receptors -2, -3, -4 and -7 Expression Patterns in the Liver of a CLP-Induced Sepsis Mouse Model

Objective: To investigate the expression of toll-like receptors (TLRs) in the liver of septic mouse model. Materials and methods: For this study seventy-two C57BL/6J mice were utilized. Sepsis was induced by cecal ligation and puncture (CLP) in the mice of the three septic (S) groups (euthanized at 24 hours, 48 hours and 72 hours). Sham (laparotomy)- operated mice constituted the control (C) groups (euthanized at 24, 48 and 72 hours). Blood samples were drawn and liver tissues were extracted and examined histologically. The expression of TLRs 2, 3, 4 and 7 was assessed via immunohistochemistry (IHC) and qrt-PCR (quantitative- Polymerase Chain Reaction). Results: Liver function tests were elevated in all S-groups in contrast to their time-equivalent control groups (S24 versus C24, S48 versus C48 and S72 versus C72) (p < 0.05). Liver histology displayed progressive deterioration in the septic groups. IHC and qrt-PCR both showed an increased expression of all TLRs in the septic mice in comparison to their analogous control ones (p < 0.05). Analysis of livers and intestines of the septic animals proved that all TLRs were significantly expressed in higher levels in the intestinal tissues at 24h and 48h (p < 0.05) except for TLR 3 in S48 (p > 0.05); whereas at 72 hours only TLR 4 levels were significantly elevated in the intestine (p < 0.05). Conclusion: TLRs seem to be expressed in significant levels in the livers of septic rodents, indicating that they have a possible role in the pathophysiology of liver damage in septic conditions.

Expression of Toll-like receptors (TLRs) in the lungs of an experimental sepsis mouse model

Background

Sepsis is a condition characterized by high mortality rates and often accompanied by multiple-organ dysfunction. During sepsis, respiratory system may be affected and possibly result in acute respiratory distress syndrome (ARDS). Toll-like receptors (TLRs), as a first line defense against invading pathogens, seem to be highly expressed in septic states. Therefore, expression of TLRs in the lungs of a sepsis animal model could indicate the involvement of the respiratory system and appear as a severity index of the clinical course.

Materials and methods

A total of 72 C57BL/6J mice, aged 12–14 weeks, were studied. The animals were divided into 3 sepsis (S) groups (24h, 48h and 72h) and 3 control (C) groups (24h, 48h and 72h), each consisting of 12 mice. The S-groups were subjected to cecal ligation and puncture (CLP) while the C-groups had a sham operation performed. Blood samples were drawn from all groups. Total blood count analysis was performed along with the measurement of certain biochemical markers. Additionally, lung tissues were harvested and the expression of TLRs, namely TLR 2, TLR 3, TLR 4 and TLR 7 were evaluated by means of immunofluorescence (IF) and qRT-PCR (quantitative-Polymerase Chain Reaction). Statistical analysis was performed by using one-way ANOVA followed by student t-test. Results were considered statistically significant when p<0.05.

Results

WBCs and lymphocytes were decreased in all S-groups compared to the corresponding C-groups (p<0.05), while RBCs showed a gradual decline in S-groups with the lowest levels appearing in the S72 group. Only, monocytes were higher in S-groups, especially between S48-C48 (p<0.05) and S72-C72 (p<0.05). Creatinine, IL-10 and IL-6 levels were significantly increased in the S-groups compared to the corresponding C-groups (S24 vs C24, S48 vs C48 and S72 vs C72, p<0.05). IF showed that expression of TLRs 2, 3, 4 and 7 was increased in all S-groups compared to the time-adjusted C-groups (p<0.05). Similarly, qRT-PCR revealed that expression of all TLRs was higher in all S-groups compared to their respective C-groups in both lungs and intestine (p<0.05). Comparing lung and intestinal tissues from S-groups, TLRs 2 and 4 were found increased in the lung at 24, 48 and 72 hours (p<0.05), whereas TLR 3 was higher in the intestine at all time points examined (p<0.05). Finally, TLR 7 levels were significantly higher in the intestinal tissues at 24 hours (p<0.0001), while lungs predominated at 48 hours (p<0.0001).

Conclusion

TLRs seem to be highly expressed in the lungs of septic mice, therefore suggesting a potential role in the pathogenesis of ARDS during sepsis. While more studies need to be conducted in order to completely understand the underlying mechanisms, TLRs may represent a promising target for establishing novel therapeutic strategies in the treatment of sepsis.

Ulinastatin inhibited sepsis-induced spinal inflammation to alleviate peripheral neuromuscular dysfunction in an experimental rat model of neuromyopathy

Sepsis initiates a neuroinflammatory cascade that contributes to spinal cord inflammation and behavioral impairment, and Toll-like receptor 4 (TLR4) is an important mediator of this cascade. In this study, we tested the hypothesis that ulinastatin (ULI) inhibits sepsis-induced spinal inflammation to alleviate peripheral neuromuscular dysfunction through the TLR4/myeloid differentiation factor 88 (MyD88)/NF-κB signaling pathway. Muscular function, spinal cord water content, and cytokine levels of spinal cord were tested in TLR4-inhibited rats subjected to cecal ligation and puncture (CLP). The normal rats were intrathecally injected with different concentrations of ULI or normal saline 60 min before CLP. At 24 h after CLP, the activation of microglia/macrophage was detected by immunofluorescence staining; and the cytokines were assayed by ELISA. The protein expression level of the TLR4 and its downstream effectors (MyD88 and NF-κB), the neuregulin-1, and the γ- and α7-nicotinic acetylcholine receptor was measured using western blotting. The protein expression of TLR4 in the spinal cord reached a maximum at 24 h post-CLP. Compared to the sham rats, the TLR4-inhibited rats showed attenuated functional impairment and cytokine release. ULI (5000 U/kg ) treatment pre-CLP significantly reduced the number of TLR4-positive microglia/macrophages as well as inflammatory mediator release in septic rats. Furthermore, the levels of TLR4, MyD88, and NF-κB and the expression level of γ-/α7-nicotinic acetylcholine receptors also decreased after ULI treatment. ULI administration may improve patient outcome by reducing the spinal inflammation through a mechanism involving the TLR4/MyD88/NF-κB signaling in sepsis.

Murine Models of Sepsis and Trauma: Can We Bridge the Gap?

Sepsis and trauma are both leading causes of death in the United States and represent major public health challenges. Murine models have largely been used in sepsis and trauma research to better understand the pathophysiological changes that occur after an insult and to develop potential life-saving therapeutic agents. Mice are favorable subjects for this type of research given the variety of readily available strains including inbred, outbred, and transgenic strains. In addition, they are relatively easy to maintain and have a high fecundity. However, pharmacological therapies demonstrating promise in preclinical mouse models of sepsis and trauma often fail to demonstrate similar efficacy in human clinical trials, prompting considerable criticism surrounding the capacity of murine models to recapitulate complex human diseases like sepsis and traumatic injury. Fundamental differences between the two species include, but are not limited to, the divergence of the transcriptomic response, the mismatch of temporal response patterns, differences in both innate and adaptive immunity, and heterogeneity within the human population in comparison to the homogeneity of highly inbred mouse strains. Given the ongoing controversy, this narrative review aims to not only highlight the historical importance of the mouse as an animal research model but also highlight the current benefits and limitations of the model as it pertains to sepsis and trauma. Lastly, this review will propose future directions that may promote further use of the model.

Improving animal welfare using continuous nalbuphine infusion in a long-term rat model of sepsis

Background

Sepsis research relies on animal models to investigate the mechanisms of the dysregulated host response to infection. Animal welfare concerns request the use of potent analgesics for the Refinement of existing sepsis models, according to the 3Rs principle. Nevertheless, adequate analgesia is often missing, partly because the effects of analgesics in this particular condition are unknown. We evaluated the use of nalbuphine, an opioid with kappa agonistic and mu antagonistic effects, in rats with and without experimental sepsis.

Methods

Male Wistar rats were anesthetized with isoflurane and instrumented with a venous line for drug administration. Arterial cannulation allowed for blood pressure measurements and blood sampling in short-term experiments of non-septic animals. Nalbuphine (or placebo) was administered intravenously at a dose of 1 mg/kg/h. Long-term (48 h) experiments in awake septic animals included repetitive clinical scoring with the Rat Grimace Scale and continuous heart rate monitoring by telemetry. Sepsis was induced by intraperitoneal injection of faecal slurry. Nalbuphine plasma levels were measured by liquid chromatography—high resolution mass spectrometry.

Results

In anesthetized healthy animals, nalbuphine led to a significant reduction of respiratory rate, heart rate, and mean arterial pressure during short-term experiments. In awake septic animals, a continuous nalbuphine infusion did not affect heart rate but significantly improved the values of the Rat Grimace Scale. Nalbuphine plasma concentrations remained stable between 4 and 24 h of continuous infusion in septic rats.

Conclusions

In anaesthetised rats, nalbuphine depresses respiratory rate, heart rate, and blood pressure. In awake animals, nalbuphine analgesia improves animal welfare during sepsis.

Could Biomarkers Direct Therapy for the Septic Patient?

Sepsis is a serious medical condition caused by a severe systemic inflammatory response to a bacterial, fungal, or viral infection that most commonly affects neonates and the elderly. Advances in understanding the pathophysiology of sepsis have resulted in guidelines for care that have helped reduce the risk of dying from sepsis for both children and older adults. Still, over the past three decades, a large number of clinical trials have been undertaken to evaluate pharmacological agents for sepsis. Unfortunately, all of these trials have failed, with the use of some agents even shown to be harmful. One key issue in these trials was the heterogeneity of the patient population that participated. What has emerged is the need to target therapeutic interventions to the specific patient's underlying pathophysiological processes, rather than looking for a universal therapy that would be effective in a "typical" septic patient, who does not exist. This review supports the concept that identification of the right biomarkers that can direct therapy and provide timely feedback on its effectiveness will enable critical care physicians to decrease mortality of patients with sepsis and improve the quality of life of survivors.

Effectiveness of Multiple Blood-Cleansing Interventions in Sepsis, Characterized in Rats

Sepsis is a serious, life-threatening condition that presents a growing problem in medicine, but there is still no satisfying solution for treating it. Several blood cleansing approaches recently gained attention as promising interventions that target the main site of problem development–the blood. The focus of this study is an evaluation of the theoretical effectiveness of hemoadsorption therapy and pathogen reduction therapy. This is evaluated using the mathematical model of Murine sepsis, and the results of over 2,200 configurations of single and multiple intervention therapies simulated on 5,000 virtual subjects suggest the advantage of pathogen reduction over hemoadsorption therapy. However, a combination of two approaches is found to take advantage of their complementary effects and outperform either therapy alone. The conducted computational experiments provide unprecedented evidence that the combination of two therapies synergistically enhances the positive effects beyond the simple superposition of the benefits of two approaches. Such a characteristic could have a profound influence on the way sepsis treatment is conducted.

The role of speckle tracking echocardiography in assessment of lipopolysaccharide-induced myocardial dysfunction in mice

BACKGROUND

Sepsis-induced myocardial dysfunction is a common and severe complication of septic shock. Conventional echocardiography often fails to reveal myocardial depression in severe sepsis due to hemodynamic changes; in contrast, decline of strain measurements by speckle tracking echocardiography (STE) may indicate impaired cardiac function. This study investigates the role of STE in detecting lipopolysaccharide (LPS)-induced cardiac dysfunction with mouse models.

METHODS

We evaluated cardiac function in 20 mice at baseline, 6 h (n=10) and 20 h (n=10) after LPS injection to monitor the development of heart failure induced by severe sepsis using 2-D and M-mode echocardiography. Ejection fraction (EF) and fractional shortening (FS) were measured with standard M-mode tracings, whereas circumferential and radial strain was derived from STE. Serum biochemical and cardiac histopathological examinations were performed to determine sepsis-induced myocardial injury.

RESULTS

Left ventricular (LV) myocardial function was significantly reduced at 6 h after LPS treatment assessed by circumferential strain (-14.65%±3.00% to -8.48%±1.72%, P=0.006), whereas there were no significant differences between 6 and 20 h group. Conversely, EF and FS were significantly increased at 20 h when comparing to 6 h (P<0.05) accompanied with marked decreases in EF and FS 6 h following LPS administration. Consistent with strain echocardiographic results, we showed that LPS injection leaded to elevated serum level of cardiac Troponin-T (cTnT), CK-MB and rising leucocytes infiltration into myocardium within 20 h.

CONCLUSIONS

Altogether, these results demonstrate that, circumferential strain by STE is a specific and reliable value for evaluating LPS-induced cardiac dysfunction in mice.

Refinement of animal models of sepsis and septic shock

This report aims to facilitate the implementation of the Three Rs (replacement, reduction, and refinement) in the use of animal models or procedures involving sepsis and septic shock, an area where there is the potential of high levels of suffering for animals. The emphasis is on refinement because this has the greatest potential for immediate implementation. Specific welfare issues are identified and discussed, and practical measures are proposed to reduce animal use and suffering as well as reducing experimental variability and increasing translatability. The report is based on discussions and submissions from a nonregulatory expert working group consisting of veterinarians, animal technologists, and scientists with expert knowledge relevant to the field.

IRAK4 as a Molecular Target in the Amelioration of Innate Immunity–Related Endotoxic Shock and Acute Liver Injury by Chlorogenic Acid

Mice lacking the IL-1R–associated kinase 4 (IRAK4) are completely resistant to LPS-induced endotoxic disorder or the TLR9 agonist CpG DNA plus d-galactosamine–induced acute liver injury (ALI), whereas wild-type strains succumb. However, translational drugs against sepsis or ALI remain elusive. Lonicerae flos extract is undergoing the clinical trial phase I in LPS-injected healthy human volunteers for sepsis treatment. In the current study, chlorogenic acid (CGA), a major anti-inflammatory constituent of lonicerae flos extract, rescued endotoxic mortality of LPS-intoxicated C57BL/6 mice, as well as ameliorated ALI of LPS/d-galactosamine–challenged C57BL/6 mice. As a mechanism, CGA inhibited various TLR agonist–, IL-1α–, or high-mobility group box-1–stimulated autophosphorylation (activation) of IRAK4 in peritoneal macrophages from C57BL/6 or C3H/HeJ mice via directly affecting the kinase activity of IRAK4, a proximal signal transducer in the MyD88-mediated innate immunity that enhances transcriptional activity of NF-κB or AP-1. CGA consequently attenuated protein or mRNA levels of NF-κB/AP-1 target genes encoding TNF-α, IL-1α, IL-6, and high-mobility group box-1 in vivo under endotoxemia or ALI. Finally, this study suggests IRAK4 as a molecular target of CGA in the treatment of innate immunity–related shock and organ dysfunction following insult of various TLR pathogens from bacteria and viruses.

Change of hemopexin level is associated with the severity of sepsis in endotoxemic rat model and the outcome of septic patients

PURPOSE

The purpose of the study is to uncover the role of hemopexin (HPX) as anti-inflammatory mediator in animals and humans.

MATERIALS AND METHODS

We injected rats with 5 and 10 mg/kg of lipopolysaccharide to induce low- and high-grade endotoxemia (LGE and HGE), respectively, and we measured serum levels of tumor necrosis factor α, interleukin 6, and HPX at 0, 1, 3, and 6 hours after the injection. In a clinical study, we measured the initial serum HPX concentrations of septic shock patients. We evaluated the correlation between HPX levels and sepsis severity in rats and the predictive value of the HPX level for 28-day mortality of patients.

RESULTS

In rats, serum interleukin 6 and tumor necrosis factor α concentrations were lower in LGE than in HGE, whereas the HPX level in HGE at 6 hours was significantly lower than in LGE (0.88, interquartile range [0.79-1.00] vs 1.33, interquartile range [1.29-1.49] mg/mL, P= .002). In patients, the initial serum HPX level in nonsurvivors was significantly lower than in survivors (0.75 vs 1.02 mg/mL, P< .001). Multivariate logistic regression analysis revealed that HPX exhibited independent prognostic value for 28-day mortality, and its levels were closely related to Acute Physiology and Chronic Health Evaluation II scores.

CONCLUSIONS

Low serum HPX levels are related to sepsis severity and could indicate poor prognosis for septic shock patients.

A new cecal slurry preparation protocol with improved long-term reproducibility for animal models of sepsis

Sepsis, a life-threatening systemic inflammatory response syndrome induced by infection, is widely studied using laboratory animal models. While cecal-ligation and puncture (CLP) is considered the gold standard model for sepsis research, it may not be preferable for experiments comparing animals of different size or under different dietary regimens. By comparing cecum size, shape, and cecal content characteristics in mice under different experimental conditions (aging, diabetes, pancreatitis), we show that cecum variability could be problematic for some CLP experiments. The cecal slurry (CS) injection model, in which the cecal contents of a laboratory animal are injected intraperitoneally to other animals, is an alternative method for inducing polymicrobial sepsis; however, the CS must be freshly prepared under conventional protocols, which is a major disadvantage with respect to reproducibility and convenience. The objective of this study was to develop an improved CS preparation protocol that allows for long-term storage of CS with reproducible results. Using our new CS preparation protocol we found that bacterial viability is maintained for at least 6 months when the CS is prepared in 15% glycerol-PBS and stored at -80°C. To test sepsis-inducing efficacy of stored CS stocks, various amounts of CS were injected to young (4-6 months old), middle-aged (12-14 months old), and aged (24-26 months old) male C57BL/6 mice. Dose- and age-dependent mortality was observed with high reproducibility. Circulating bacteria levels strongly correlated with mortality suggesting an infection-mediated death. Further, injection with heat-inactivated CS resulted in acute hypothermia without mortality, indicating that CS-mediated death is not due to endotoxic shock. This new CS preparation protocol results in CS stocks which are durable for freezing preservation without loss of bacterial viability, allowing experiments to be performed more conveniently and with higher reproducibility than before.

NLRC4 and TLR5 each contribute to host defense in respiratory melioidosis

Burkholderia pseudomallei causes the tropical infection melioidosis. Pneumonia is a common manifestation of melioidosis and is associated with high mortality. Understanding the key elements of host defense is essential to developing new therapeutics for melioidosis. As a flagellated bacterium encoding type III secretion systems, B. pseudomallei may trigger numerous host pathogen recognition receptors. TLR5 is a flagellin sensor located on the plasma membrane. NLRC4, along with NAIP proteins, assembles a canonical caspase-1-dependent inflammasome in the cytoplasm that responds to flagellin (in mice) and type III secretion system components (in mice and humans). In a murine model of respiratory melioidosis, Tlr5 and Nlrc4 each contributed to survival. Mice deficient in both Tlr5 and Nlrc4 were not more susceptible than single knockout animals. Deficiency of Casp1/Casp11 resulted in impaired bacterial control in the lung and spleen; in the lung much of this effect was attributable to Nlrc4, despite relative preservation of pulmonary IL-1β production in Nlrc4^−/− mice. Histologically, deficiency of Casp1/Casp11 imparted more severe pulmonary inflammation than deficiency of Nlrc4. The human NLRC4 region polymorphism rs6757121 was associated with survival in melioidosis patients with pulmonary involvement. Co-inheritance of rs6757121 and a functional TLR5 polymorphism had an additive effect on survival. Our results show that NLRC4 and TLR5, key components of two flagellin sensing pathways, each contribute to host defense in respiratory melioidosis.

Melioidosis is an infection caused by Burkholderia pseudomallei, a bacterium that is found in tropical soil and water. Melioidosis can present in a variety of ways, but lung involvement is common and usually severe. The host response to infection governs outcome. In this study, we examined the role of two host sensors of bacterial components–TLR5 and NLRC4–to determine their necessity in respiratory melioidosis. Although both proteins are involved in detection of bacterial flagellin, in mice we defined specific and individual roles for TLR5 and NLRC4 in protecting against death from melioidosis. In humans with melioidosis involving the lung, genetic variation in these receptors also had independent associations with survival. These results underscore the importance of these elements of host defense in respiratory melioidosis and support further studies of the underlying mechanisms.

Strategies to improve drug development for sepsis

Sepsis, a common and potentially fatal systemic illness, is triggered by microbial infection and often leads to impaired function of the lungs, kidneys or other vital organs. Since the early 1980s, a large number of therapeutic agents for the treatment of sepsis have been evaluated in randomized controlled clinical trials. With few exceptions, the results from these trials have been disappointing, and no specific therapeutic agent is currently approved for the treatment of sepsis. To improve upon this dismal record, investigators will need to identify more suitable therapeutic targets, improve their approaches for selecting candidate compounds for clinical development and adopt better designs for clinical trials.

A rabbit model of non-typhoidal Salmonella bacteremia

Bacteremia is an important cause of morbidity and mortality in humans. In this study, we focused on the development of an animal model of bacteremia induced by non-typhoidal Salmonella. New Zealand White rabbits were inoculated with a human isolate of non-typhoidal Salmonella strain CVD J73 via the intra-peritoneal route. Blood samples were collected at specific time points and at euthanasia from infected rabbits. Additionally, tissue samples from the heart, lungs, spleen, gastrointestinal tract, liver and kidneys were obtained at euthanasia. All experimentally infected rabbits displayed clinical signs of disease (fever, dehydration, weight loss and lethargy). Tissues collected at necropsy from the animals exhibited histopathological changes indicative of bacteremia. Non-typhoidal Salmonella bacteria were detected in the blood and tissue samples of infected rabbits by microbiological culture and real-time PCR assays. The development of this animal model of bacteremia could prove to be a useful tool for studying how non-typhoidal Salmonella infections disseminate and spread in humans.

Sepsis in old age: review of human and animal studies

Sepsis is a serious problem among the geriatric population as its incidence and mortality rates dramatically increase with advanced age. Despite a large number of ongoing clinical and basic research studies, there is currently no effective therapeutic strategy that rescues elderly patients with severe sepsis. Recognition of this problem is relatively low as compared to other age-associated diseases. The disparity between clinical and basic studies is a problem, and this is likely due, in part, to the fact that most laboratory animals used for sepsis research are not old while the majority of sepsis cases occur in the geriatric population. The objective of this article is to review recent epidemiological studies and clinical observations, and compare these with findings from basic laboratory studies which have used aged animals in experimental sepsis.

Survey of innate immune responses to Burkholderia pseudomallei in human blood identifies a central role for lipopolysaccharide

B. pseudomallei is a gram-negative bacterium that causes the tropical infection melioidosis. In northeast Thailand, mortality from melioidosis approaches 40%. As exemplified by the lipopolysaccharide-Toll-like receptor 4 interaction, innate immune responses to invading bacteria are precipitated by activation of host pathogen recognition receptors by pathogen associated molecular patterns. Human melioidosis is characterized by up-regulation of pathogen recognition receptors and pro-inflammatory cytokine release. In contrast to many gram-negative pathogens, however, the lipopolysaccharide of B. pseudomallei is considered only weakly inflammatory. We conducted a study in 300 healthy Thai subjects to investigate the ex vivo human blood response to various bacterial pathogen associated molecular patterns, including lipopolysaccharide from several bacteria, and to two heat-killed B. pseudomallei isolates. We measured cytokine levels after stimulation of fresh whole blood with a panel of stimuli. We found that age, sex, and white blood cell count modulate the innate immune response to B. pseudomallei. We further observed that, in comparison to other stimuli, the innate immune response to B. pseudomallei is most highly correlated with the response to lipopolysaccharide. The magnitude of cytokine responses induced by B. pseudomallei lipopolysaccharide was significantly greater than those induced by lipopolysaccharide from Escherichia coli and comparable to many responses induced by lipopolysaccharide from Salmonella minnesota despite lower amounts of lipid A in the B. pseudomallei lipopolysaccharide preparation. In human monocytes stimulated with B. pseudomallei, addition of polymyxin B or a TLR4/MD-2 neutralizing antibody inhibited the majority of TNF-α production. Challenging existing views, our data indicate that the innate immune response to B. pseudomallei in human blood is largely driven by lipopolysaccharide, and that the response to B. pseudomallei lipopolysaccharide in blood is greater than the response to other lipopolysaccharide expressing isolates. Our findings suggest that B. pseudomallei lipopolysaccharide may play a central role in stimulating the host response in melioidosis.

Inhibition of IRAK-4 activity for rescuing endotoxin LPS-induced septic mortality in mice by lonicerae flos extract

Lonicerae flos extract (HS-23) is a clinical candidate currently undergoing Phase I trial in lipopolysaccharide (LPS)-injected healthy human volunteers, but its molecular basis remains to be defined. Here, we investigated protective effects of HS-23 or its major constituents on Escherichia coli LPS-induced septic mortality in mice. Intravenous treatment with HS-23 rescued LPS-intoxicated C57BL/6J mice under septic conditions, and decreased the levels of cytokines such as tumor necrosis factor α (TNF-α), interleukin (IL)-1β and high-mobility group box-1 (HMGB-1) in the blood. Chlorogenic acid (CGA) and its isomers were assigned as major constituents of HS-23 in the protection against endotoxemia. As a molecular mechanism, HS-23 or CGA isomers inhibited endotoxin LPS-induced autophosphorylation of the IL-1 receptor-associated kinase 4 (IRAK-4) in mouse peritoneal macrophages as well as the kinase activity of IRAK-4 in cell-free reactions. HS-23 consequently suppressed downstream pathways critical for LPS-induced activation of nuclear factor (NF)-κB or activating protein 1 (AP-1) in the peritoneal macrophages. HS-23 also inhibited various toll-like receptor agonists-induced nitric oxide (NO) production, and down-regulated LPS-induced expression of NF-κB/AP-1-target inflammatory genes in the cells. Taken together, HS-23 or CGA isomers exhibited anti-inflammatory therapy against LPS-induced septic mortality in mice, at least in part, mediated through the inhibition of IRAK-4.

Animal models of sepsis

Sepsis remains a common, serious, and heterogeneous clinical entity that is difficult to define adequately. Despite its importance as a public health problem, efforts to develop and gain regulatory approval for a specific therapeutic agent for the adjuvant treatment of sepsis have been remarkably unsuccessful. One step in the critical pathway for the development of a new agent for adjuvant treatment of sepsis is evaluation in an appropriate animal model of the human condition. Unfortunately, the animal models that have been used for this purpose have often yielded misleading findings. It is likely that there are multiple reasons for the discrepancies between the results obtained in tests of pharmacological agents in animal models of sepsis and the outcomes of human clinical trials. One of important reason may be that the changes in gene expression, which are triggered by trauma or infection, are different in mice, a commonly used species for preclinical testing, and humans. Additionally, many species, including mice and baboons, are remarkably resistant to the toxic effects of bacterial lipopolysaccharide, whereas humans are exquisitely sensitive. New approaches toward the use of animals for sepsis research are being investigated. But, at present, results from preclinical studies of new therapeutic agents for sepsis must be viewed with a degree of skepticism.

New approaches to the study of sepsis

Models of sepsis have been instructive in understanding the sequence of events in animals and, to an extent, in humans with sepsis. Events developing early in sepsis suggest that a hyperinflammatory state exists, accompanied by a buildup of oxidants in tissues reflective of a redox imbalance. Development of immunosuppression and degraded innate and adaptive immune responses are well-established complications of sepsis. In addition, there is robust activation of the complement system, which contributes to the harmful effects of sepsis. These events appear to be associated with development of multiorgan failure. The relevance of animal models of sepsis to human sepsis and the failure of human clinical trials are discussed, together with suggestions as to how clinical trial design might be improved.

The inflammatory response in sepsis

The pathophysiology of sepsis and its accompanying systemic inflammatory response syndrome (SIRS) and the events that lead to multiorgan failure and death are poorly understood. It is known that, in septic humans and rodents, the development of SIRS is associated with a loss of the redox balance, but SIRS can also develop in noninfectious states. In addition, a hyperinflammatory state develops, together with impaired innate immune functions of phagocytes, immunosuppression, and complement activation, collectively leading to septic shock and lethality. Here, we discuss recent insights into the signaling pathways in immune and phagocytic cells that underlie sepsis and SIRS and consider how these might be targeted for therapeutic interventions to reverse or attenuate pathways that lead to lethality during sepsis.

Early course of microcirculatory perfusion in eye and digestive tract during hypodynamic sepsis

INTRODUCTION

The aim of the study was to evaluate and compare the microcirculatory perfusion during experimental sepsis in different potentially available parts of the body, such as sublingual mucosa, conjunctiva of the eye, and mucosa of jejunum and rectum.

METHODS

Pigs were randomly assigned to sepsis (n = 9) and sham (n = 4) groups. The sepsis group received a fixed dose of live Escherichia coli infusion over a 1-hour period (1.8 × 10(9)/kg colony-forming units). Animals were observed 5 hours after the start of E. coli infusion. In addition to systemic hemodynamic assessment, we performed conjunctival, sublingual, jejunal, and rectal evaluation of microcirculation by using Sidestream Dark Field (SDF) videomicroscopy at the same time points: at baseline, and at 3 and 5 hours after the start of live E. coli infusion. Assessment of microcirculatory parameters of convective oxygen transport (microvascular flow index (MFI) and proportion of perfused vessels (PPV)), and diffusion distance (perfused vessel density (PVD) and total vessel density (TVD)) was done by using a semiquantitative method.

RESULTS

Infusion of E. coli resulted in a hypodynamic state of sepsis associated with low cardiac output and increased systemic vascular resistance despite fluid administration. Significant decreases in MFI and PPV of small vessels were observed in sublingual, conjunctival, jejunal, and rectal locations 3 and 5 hours after the start of E. coli infusion in comparison with baseline variables. Correlation between sublingual and conjunctival (r = 0.80; P = 0.036), sublingual and jejunal (r = 0.80; P = 0.044), and sublingual and rectal (r = 0.79; P = 0.03) MFI was observed 3 hours after onset of sepsis. However, this strong correlation between the sublingual and other regions disappeared 5 hours after the start of E. coli infusion. Overall, the sublingual mucosa exhibited the most-pronounced alterations of microcirculatory flow in comparison with conjunctival, jejunal, and rectal microvasculature (P < 0.05).

CONCLUSIONS

In this pig model, a time-dependent correlation exists between sublingual and microvascular beds during the course of a hypodynamic state of sepsis.

Recombinant human Hsp70 protects against lipoteichoic acid-induced inflammation manifestations at the cellular and organismal levels

It has been previously reported that pretreatment with exogenous heat shock protein 70 (Hsp70) is able to protect cells and animals from the deleterious effects of bacterial lipopolysaccharide (LPS) produced by Gram-negative bacteria. However, the effects of Hsp70 pretreatment on lipoteichoic acid (LTA) challenge resulted from Gram-positive bacteria infection have not been fully elucidated. In this study, we demonstrated that preconditioning with human recombinant Hsp70 ameliorates various manifestations of systematic inflammation, including reactive oxygen species, TNFα, and CD11b/CD18 adhesion receptor expression induction observed in different myeloid cells after LTA addition. Therefore, exogenous Hsp70 may provide a mechanism for controlling excessive inflammatory responses after macrophage activation. Furthermore, in a rat model of LTA-induced sepsis, we demonstrated that prophylactic administration of exogenous human Hsp70 significantly exacerbated numerous homeostatic and hemodynamic disturbances induced by LTA challenge and partially normalized the coagulation system and multiple biochemical blood parameters, including albumin and bilirubin concentrations, which were severely disturbed after LTA injections. Importantly, prophylactic intravenous injection of Hsp70 before LTA challenge significantly reduced mortality rates. Thus, exogenous mammalian Hsp70 may serve as a powerful cellular defense agent against the deleterious effects of bacterial pathogens, such as LTA and LPS. Taken together, our findings reveal novel functions of this protein and establish exogenous Hsp70 as a promising pharmacological agent for the prophylactic treatment of various types of sepsis.