Essential role of gamma interferon in survival of colon ascendens stent peritonitis, a novel murine model of abdominal sepsis

An improved mouse model of sepsis based on intraperitoneal injections of the enriched culture of cecum slurry

AIM

Sepsis is a life-threatening clinical syndrome comprising multiorgan dysfunctions caused by a disproportionate body immune response. There are several animal sepsis models which are based on cecum ligation, cecal puncture, and cecum slurry injection. The major limitation of all current sepsis models is the high variability owing to the variable degree of ligation, puncture and inconsistent microbial composition used for sepsis initiation. The primary objective of this work is to demonstrate the feasibility of a standardized method for sepsis development.

MATERIALS AND METHODS

The cecal slurry bacterial culture was developed and preserved in glycerol stocks. Antibiotics aztreonam and vancomycin were used for generating several defined, enriched cecal slurry bacterial cultures. Mice survival was assessed until 48 hrs post injection, and the tissue samples were collected after 10 hrs from sepsis initiation.

KEY FINDINGS

The results indicate that increasing polymicrobial load resulted in lower survival rates and was associated with the higher number of infiltrating immune cells and necrosis. H&E (haematoxylin & eosin) staining & serum markers revealed that septic mice exhibited increased inflammation and significant damage to the liver and kidneys. The defined Gram-negative and Gram-positive specific cecal slurry bacterial cultures were developed and their efficiency in inducing sepsis was characterized.

SIGNIFICANCE

Enriched cecal slurry bacterial cultures can be stored in glycerol stocks at -80 °C. This has an ethical advantage of avoiding unnecessary animal euthanasia for each experiment and provides a standardization capability of sepsis development.

Multimodal nanoparticle-containing modified suberoylanilide hydroxamic acid polymer conjugates to mitigate immune dysfunction in severe inflammation

Excessive immune activation and immunosuppression are opposing factors that contribute to the dysregulated innate and adaptive immune responses seen in severe inflammation and sepsis. Here, a novel analog of the histone deacetylase inhibitor (HDACi), suberoylanilide hydroxamic acid (SAHA-OH), was incorporated into immunomodulatory poly(lactic acid)-based nanoparticles (iNP-SAHA) by employing a prodrug approach through the covalent modification of poly(lactic-co-glycolic acid) (PLGA) with SAHA-OH. iNP-SAHA formulation allowed for controlled incorporation and delivery of SAHA-OH from iNP-SAHA and treatment led to multimodal biological responses including significant reductions in proinflammatory cytokine secretions and gene expression, while increasing the survival of primary macrophages under lipopolysaccharide (LPS) challenge. Using a lethal LPS-induced endotoxemia mouse model of sepsis, iNP-SAHA administration improved the survival of mice in a dose-dependent manner and tended to improve survival at the lowest doses compared to iNP control. Further, iNP-SAHA reduced the levels of plasma proinflammatory cytokines and chemokines associated with sepsis more significantly than iNP and similarly improved inflammation-induced spleen and liver toxicity as iNP, supporting its potential polypharmacological activity. Collectively, iNP-SAHA offers a potential drug delivery approach to modulate the multifaceted inflammatory responses observed in diseases such as sepsis.

Advances in Rodent Experimental Models of Sepsis

In the development of therapeutic strategies for human diseases, preclinical experimental models have a key role. However, the preclinical immunomodulatory therapies developed using rodent sepsis were not successful in human clinical trials. Sepsis is characterized by a dysregulated inflammation and redox imbalance triggered by infection. Human sepsis is simulated in experimental models using methods that trigger inflammation or infection in the host animals, most often mice or rats. It remains unknown whether the characteristics of the host species, the methods used to induce sepsis, or the molecular processes focused upon need to be revisited in the development of treatment methods that will succeed in human clinical trials. Our goal in this review is to provide a survey of existing experimental models of sepsis, including the use of humanized mice and dirty mice, and to show how these models reflect the clinical course of sepsis. We will discuss the strengths and limitations of these models and present recent advances in this subject area. We maintain that rodent models continue to have an irreplaceable role in studies toward discovering treatment methods for human sepsis.

CASP-Model Sepsis Triggers Systemic Innate Immune Responses Revealed by the Systems-Level Signaling Pathways

Colon ascendens stent peritonitis (CASP) surgery induces a leakage of intestinal contents which may cause polymicrobial sepsis related to post-operative failure of remote multi-organs (including kidney, liver, lung and heart) and possible death from systemic syndromes. Mechanisms underlying such phenomena remain unclear. This article aims to elucidate the mechanisms underlying the CASP-model sepsis by analyzing real-world GEO data (GSE24327_A, B and C) generated from mice spleen 12 hours after a CASP-surgery in septic MyD88-deficient and wildtype mice, compared with untreated wildtype mice. Firstly, we identify and characterize 21 KO MyD88-associated signaling pathways, on which true key regulators (including ligands, receptors, adaptors, transducers, transcriptional factors and cytokines) are marked, which were coordinately, significantly, and differentially expressed at the systems-level, thus providing massive potential biomarkers that warrant experimental validations in the future. Secondly, we observe the full range of polymicrobial (viral, bacterial, and parasitic) sepsis triggered by the CASP-surgery by comparing the coordinated up- or down-regulations of true regulators among the experimental treatments born by the three data under study. Finally, we discuss the observed phenomena of “systemic syndrome”, “cytokine storm” and “KO MyD88 attenuation”, as well as the proposed hypothesis of “spleen-mediated immune-cell infiltration”. Together, our results provide novel insights into a better understanding of innate immune responses triggered by the CASP-model sepsis in both wildtype and MyD88-deficient mice at the systems-level in a broader vision. This may serve as a model for humans and ultimately guide formulating the research paradigms and composite strategies for the early diagnosis and prevention of sepsis.

A Toolbox to Investigate the Impact of Impaired Oxygen Delivery in Experimental Disease Models

Impaired oxygen utilization is the underlying pathophysiological process in different shock states. Clinically most important are septic and hemorrhagic shock, which comprise more than 75% of all clinical cases of shock. Both forms lead to severe dysfunction of the microcirculation and the mitochondria that can cause or further aggravate tissue damage and inflammation. However, the detailed mechanisms of acute and long-term effects of impaired oxygen utilization are still elusive. Importantly, a defective oxygen exploitation can impact multiple organs simultaneously and organ damage can be aggravated due to intense organ cross-talk or the presence of a systemic inflammatory response. Complexity is further increased through a large heterogeneity in the human population, differences in genetics, age and gender, comorbidities or disease history. To gain a deeper understanding of the principles, mechanisms, interconnections and consequences of impaired oxygen delivery and utilization, interdisciplinary preclinical as well as clinical research is required. In this review, we provide a "tool-box" that covers widely used animal disease models for septic and hemorrhagic shock and methods to determine the structure and function of the microcirculation as well as mitochondrial function. Furthermore, we suggest magnetic resonance imaging as a multimodal imaging platform to noninvasively assess the consequences of impaired oxygen delivery on organ function, cell metabolism, alterations in tissue textures or inflammation. Combining structural and functional analyses of oxygen delivery and utilization in animal models with additional data obtained by multiparametric MRI-based techniques can help to unravel mechanisms underlying immediate effects as well as long-term consequences of impaired oxygen delivery on multiple organs and may narrow the gap between experimental preclinical research and the human patient.

Protocol for a Sepsis Model Utilizing Fecal Suspension in Mice: Fecal Suspension Intraperitoneal Injection Model

Background

Various animal models of sepsis have been developed to optimize sepsis treatment. However, therapeutic agents that were successful in animal models were rarely effective in human clinical trials. The cecal ligation and puncture (CLP) model is currently the gold standard for sepsis studies. However, its limitations include the high variability among researchers and the difficulty in comparing animals with different cecum shapes and sizes. In this study, we established a protocol for the creation of a simple and accessible sepsis rodent model using fecal suspensions that minimized differences in technical effects among researchers and individual differences in animals.

Methods

A mouse model of sepsis using fecal suspension intraperitoneal injection (FSI) was created using fresh stool excreted within 24 h. The collected fresh stool was dissolved in saline solution and filtered. The obtained fecal suspension was injected intraperitoneally into the mice. Moreover, fecal suspensions with different concentrations were prepared, and the survival rates were compared among the fecal suspensions for each concentration. To assess the validity of the FSI as a sepsis model, CLP and FSI with similar mortality rates were compared pathologically, physiologically, immunologically, and bacteriologically. Histopathological comparison was evaluated by hematoxylin-eosin and Gram staining of the parenchymal organs. Physiological evaluation was performed by comparing the respiratory rate, body temperature, and blood gas analysis results. Immunological assessment was performed using multiplex analysis. Bacteriological comparisons were performed by culturing ascites fluid.

Results

The FSI model increased mortality in proportion to the fecal suspension concentration. The mortality rate was reduced with antibiotic administration. In various comparative experiments conducted using the FSI and CLP models, both models showed findings consistent with sepsis. Furthermore, the FSI model showed less variability among the individuals in each test.

Conclusion

This is the first detailed and accurate report of a protocol for creating a sepsis model using fecal suspension. The FSI model is a minimally invasive and accessible sepsis rodent model. Its clinical validity as a sepsis model was proven via histological, physiological, microbiological, and immunological evaluation methods. The FSI model minimizes individual differences between mice and helps to conduct accurate studies after the onset of sepsis.

Intestinal organoids in coculture: redefining the boundaries of gut mucosa ex vivo modeling

All-time preservation of an intact mucosal barrier is crucial to ensuring intestinal homeostasis and, hence, the organism's overall health maintenance. This complex process relies on an equilibrated signaling system between the intestinal epithelium and numerous cell populations inhabiting the gut mucosa. Any perturbations of this delicate cross talk, particularly regarding the immune cell compartment and microbiota, may sustainably debilitate the intestinal barrier function. As a final joint event, a critical rise in epithelial permeability facilitates the exposure of submucosal immunity to microbial antigens, resulting in uncontrolled inflammation, collateral tissue destruction, and dysbiosis. Organoid-derived intestinal coculture models have established themselves as convenient tools to reenact such pathophysiological events, explore interactions between selected cell populations, and assess their roles with a central focus on intestinal barrier recovery and stabilization.

Description of a rat model of polymicrobial abdominal sepsis mimicking human colon perforation

Objective

Standard rodent sepsis models as cecal ligation and puncture models (CLP) or cecal ligation and incision models (CLI) are frequently not suited experiments, mainly because they lack surgical repair, and they are difficult to control for severity. The colon ascendens stent peritonitis model (CASP) overcomes some of these limitations.

Result

Here we present our modification of the rodent CASP model, where severity of sepsis can be controlled by timing of surgical repair and treatment, and by diameter of the stent. Further, basic hemodynamic monitoring (blood pressure and heart rate) and frequent blood sampling can be achieved, which might guide further treatment.

The blood-brain barrier dysfunction in sepsis

Sepsis is a life-threatening organ dysfunction triggered by a dysregulated host immune response attempting to eliminate the infection. After hospital discharge, half of the sepsis survivors recover, one-third of the patients die the following year, and one-sixth have a long-term cognitive impairment, including memory dysfunction, anxiety, depression, and post-traumatic stress disorder. The infection triggers the host immune response, and both can cause vascular endothelial damage, interrupting tight junctions proteins; consequently, the blood-brain barrier (BBB) breaks down, allowing and facilitating the entry of peripheral immune cells into the brain, which triggers or exacerbates the activation of glial cells and neuroinflammation. The focus of this review is to identify biochemical abnormalities induced by sepsis, which is associated with BBB dysfunction; provide evidence of biomarkers involved in the tight junction disruption and BBB damage, and draw attention to the role of the BBB as a bridge between systemic infection and brain inflammation.

Colon Ascendens Stent Peritonitis (CASP )

Colon ascendens stent peritonitis (CASP) is one of the well-established models of experimental abdominal sepsis. In CASP surgery, an open link between the gut lumen and the abdominal cavity is created by placing a stent into the colon ascendens. This mimics well the insufficient intestinal anastomosis. It causes a continuous leakage of the gut contents into the peritoneum and leads therefore to peritonitis and sepsis. The abdominal cavity is opened under general anesthesia and a plastic stent is located through and sutured to the colonic wall. The septic severity in CASP models can be titrated by altering the size of the stent catheter. Therefore, CASP models with small stents sizes are suitable for long-term studies and studies with mild/moderate sepsis severity. Within 24 h, animals develop clinical signs of sepsis. Monitoring of the clinical state, sufficient analgesia, appropriate antibiotics and fluid resuscitation should be performed postoperatively.

Cecal Slurry Injection in Neonatal and Adult Mice

Studying the pathophysiology of sepsis still requires animal models, and the mouse remains the most commonly used species. Here we discuss the "cecal slurry" (CS) model of polymicrobial, peritoneal sepsis and compare and contrast it to other commonly used methods. Among the different murine models of sepsis, cecal ligation and puncture (CLP), and not the CS, is often considered the "gold standard" to induce polymicrobial sepsis in laboratory animals. CLP is a well-described model involving a simple surgical procedure that closely mimics the clinical course of intra-abdominal sepsis. However, CLP may not be an option for experiments involving newborn pups, where the cecum is indistinguishable from small bowel, where differences in microbiome content may affect the experiment, or where surgical procedures/anesthesia exposure needs to be limited. An important alternative method is the CS model, involving the intraperitoneal injection of cecal contents from a donor animal into the peritoneal cavity of a recipient animal to induce polymicrobial sepsis. Furthermore, CS is an effective alternative model of intraperitoneal polymicrobial sepsis in adult mice and can now be considered the "gold standard" for experiments in neonatal mice.

Nrf2-A Molecular Target for Sepsis Patients in Critical Care

The transcription factor NF-E2 p45-related factor 2 (Nrf2) is an established master regulator of the anti-oxidative and detoxifying cellular response. Thus, a role in inflammatory diseases associated with the generation of large amounts of reactive oxygen species (ROS) seems obvious. In line with this, data obtained in cell culture experiments and preclinical settings have shown that Nrf2 is important in regulating target genes that are necessary to ensure cellular redox balance. Additionally, Nrf2 is involved in the induction of phase II drug metabolizing enzymes, which are important both in degrading and converting drugs into active forms, and into putative carcinogens. Therefore, Nrf2 has also been implicated in tumorigenesis. This must be kept in mind when new therapy approaches are planned for the treatment of sepsis. Therefore, this review highlights the function of Nrf2 in sepsis with a special focus on the translation of rodent-based results into sepsis patients in the intensive care unit (ICU).

Oxidation-Specific Epitopes (OSEs) Dominate the B Cell Response in Murine Polymicrobial Sepsis

In murine abdominal sepsis by colon ascendens stent peritonitis (CASP), a strong increase in serum IgM and IgG antibodies was observed, which reached maximum values 14 days following sepsis induction. The specificity of this antibody response was studied in serum and at the single cell level using a broad panel of bacterial, sepsis-unrelated as well as self-antigens. Whereas an antibacterial IgM/IgG response was rarely observed, studies at the single-cell level revealed that IgM antibodies, in particular, were largely polyreactive. Interestingly, at least 16% of the IgM mAbs and 20% of the IgG mAbs derived from post-septic mice showed specificity for oxidation-specific epitopes (OSEs), which are known targets of the innate/adaptive immune response. This identifies those self-antigens as the main target of B cell responses in sepsis.

Intraperitoneal Neutrophil IL-10 production is promoted by interferon γ in a murine model of sepsis model in the acute phase of sepsis

The disease burden of sepsis continues to increase, with intraabdominal contamination being a significant source of infection. Sepsis is a syndrome involving both an increase in systemic inflammation as well as a regulatory component. We have previously demonstrated that neutrophils are significant IL-10 producers in the abdomen during sepsis. Here, we sought to further characterize these neutrophils and elucidate potential underlying mechanisms resulting in IL-10 generation. Using transcriptional reporter mice, we observed that IL-10 producing neutrophils were activated, non-apoptotic, and expressed C-X-C chemokine receptor type 4-expressing. Further, we observed that active Signal Transducer and Activator of Transcription 1 expression was significantly increased in IL-10 producing versus non-IL-10 producing neutrophils. During sepsis, IFN-γ blockade lead to a decrease of neutrophil IL-10 production, while peritoneal CD4 T cells were found to be the most numerous acute producers of IFN-γ. Altogether, this report demonstrates that during sepsis, mature neutrophils can potentially dampen local inflammation by IL-10 production and this can be orchestrated by CD4 T cells through an IFN-γ dependent manner.

Antibody Production in Murine Polymicrobial Sepsis-Kinetics and Key Players

Although antigen-specific priming of antibody responses is impaired during sepsis, there is nevertheless a strong increase in IgM and IgG serum concentrations. Using colon ascendens stent peritonitis (CASP), a mouse model of polymicrobial abdominal sepsis, we observed substantial increases in IgM as well as IgG of all subclasses, starting at day 3 and peaking 2 weeks after sepsis induction. The dominant source of antibody-secreting cells was by far the spleen, with a minor contribution of the mesenteric lymph nodes. Remarkably, sepsis induction in splenectomized mice did not change the dynamics of the serum IgM/IgG reaction, indicating that the marginal zone B cells, which almost exclusively reside in the spleen, are dispensable in such a setting. Hence, in systemic bacterial infection, the function of the spleen as dominant niche of antibody-producing cells can be compensated by extra-splenic B cell populations as well as other lymphoid organs. Depletion of CD4+ T cells did not affect the IgM response, while it impaired IgG generation of all subclasses with the exception of IgG3. Taken together, our data demonstrate that the robust class-switched antibody response in sepsis encompasses both T cell-dependent and -independent components.

Experimental Abdominal Sepsis: Sticking to an Awkward but Still Useful Translational Model

Animal models are widely used to replicate human intra-abdominal infections. Different methodologies have been described and proposed in the scientific literature, including injection and surgical models. The aim of this review is to recapitulate the advantages and disadvantages of each method to help choose the most appropriate model for individual experimental purposes.

Production of IFNβ by Conventional Dendritic Cells after Stimulation with Viral Compounds and IFNβ-Independent IFNAR1-Signaling Pathways are Associated with Aggravation of Polymicrobial Sepsis

Viral infections are associated with increased incidence of severe sepsis. Particularly during the early stages, type I interferons (IFNs) are known mediators of detrimental effects. However, the functional role of early interferon β (IFNβ) and its cellular source during sepsis in the context of preexisting viral infections has not been defined. Using the colon ascendens stent peritonitis (CASP) model, we demonstrate that IFNβ^−/− and type I IFN receptor (IFNAR1)^−/− mice were less susceptible to sepsis after pre-stimulation with the viral mimetic poly(I:C). Wild type (WT) mice treated with poly(I:C) exhibited altered expression patterns of TNF and IL-12p40 during CASP which were dependent on IFNβ or IFNAR1, suggesting a mechanism for the increased sepsis susceptibility of WT mice. Using a double cytokine reporter mouse model, we present novel data on the simultaneous expression of IFNβ and IL-12p40 on a single cell level during polymicrobial sepsis in vivo. Conventional dendritic cells (cDCs) were identified as primary source of IFNβ and the protective cytokine IL-12p40 after CASP surgery irrespective of poly(I:C) pre-stimulation. These data demonstrated that if polymicrobial sepsis is preceded by a viral infection, IFNβ and IL-12p40 are expressed by polyfunctional cDCs suggesting that these cells can play both detrimental and beneficial roles during sepsis development.

Targeting the Blood-Brain Barrier to Prevent Sepsis-Associated Cognitive Impairment

Sepsis is a systemic inflammatory disease resulting from an infection. This disorder affects 750 000 people annually in the United States and has a 62% rehospitalization rate. Septic symptoms range from typical flu-like symptoms (eg, headache, fever) to a multifactorial syndrome known as sepsis-associated encephalopathy (SAE). Patients with SAE exhibit an acute altered mental status and often have higher mortality and morbidity. In addition, many sepsis survivors are also burdened with long-term cognitive impairment. The mechanisms through which sepsis initiates SAE and promotes long-term cognitive impairment in septic survivors are poorly understood. Due to its unique role as an interface between the brain and the periphery, numerous studies support a regulatory role for the blood-brain barrier (BBB) in the progression of acute and chronic brain dysfunction. In this review, we discuss the current body of literature which supports the BBB as a nexus which integrates signals from the brain and the periphery in sepsis. We highlight key insights on the mechanisms that contribute to the BBB's role in sepsis which include neuroinflammation, increased barrier permeability, immune cell infiltration, mitochondrial dysfunction, and a potential barrier role for tissue non-specific alkaline phosphatase (TNAP). Finally, we address current drug treatments (eg, antimicrobials and intravenous immunoglobulins) for sepsis and their potential outcomes on brain function. A comprehensive understanding of these mechanisms may enable clinicians to target specific aspects of BBB function as a therapeutic tool to limit long-term cognitive impairment in sepsis survivors.

Evodiamine Augments NLRP3 Inflammasome Activation and Anti-bacterial Responses Through Inducing α-Tubulin Acetylation

Evodiamine is a major ingredient of the plant Evodia rutaecarpa, which has long been used for treating infection-related diseases including diarrhea, beriberi and oral ulcer, but the underlying mechanism is unclear. Here we aimed to explore whether evodiamine influenced NLRP3 (NLR family, pyrin containing domain 3) inflammasome activation in macrophages, which is a critical mechanism for defending the host against pathogenic infections. We uncovered that evodiamine dose-dependently enhanced NLRP3 inflammasome activation in lipopolysaccharide-primed macrophages, as indicated by increased interleukin (IL)-1β production and caspase-1 cleavage, accompanied by increased ASC speck formation and pyroptosis. Mechanistically, evodiamine induced acetylation of α-tubulin around the microtubule organization center (indicated by γ-tubulin) in lipopolysaccharide-primed macrophages. Such evodiamine-mediated increases in NLRP3 activation and pyroptosis were attenuated by activators of α-tubulin deacetylase, resveratrol and NAD⁺, or dynein-specific inhibitor ciliobrevin A. Small interfering RNA knockdown of αTAT1 (the gene encoding α-tubulin N-acetyltransferase) expression, which reduced α-tubulin acetylation, also diminished evodiamine-mediated augmentation of NLRP3 activation and pyroptosis. Evodiamine also enhanced NLRP3-mediated production of IL-1β and neutrophil recruitment in vivo. Moreover, evodiamine administration evidently improved survival of mice with lethal bacterial infection, accompanied by increased production of IL-1β and interferon-γ, decreased bacterial load, and dampened liver inflammation. Resveratrol treatment reversed evodiamine-induced increases of IL-1β and interferon-γ, and decreased bacterial clearance in mice. Collectively, our results indicated that evodiamine augmented the NLRP3 inflammasome activation through inducing α-tubulin acetylation, thereby conferring intensified innate immunity against bacterial infection.

Sepsis-Induced T Cell Immunoparalysis: The Ins and Outs of Impaired T Cell Immunity

Sepsis results in a deluge of pro- and anti-inflammatory cytokines, leading to lymphopenia and chronic immunoparalysis. Sepsis-induced long-lasting immunoparalysis is defined, in part, by impaired CD4 and CD8 αβ T cell responses in the postseptic environment. The dysfunction in T cell immunity affects naive, effector, and memory T cells and is not restricted to classical αβ T cells. Although sepsis-induced severe and transient lymphopenia is a contributory factor to diminished T cell immunity, T cell-intrinsic and -extrinsic factors/mechanisms also contribute to impaired T cell function. In this review, we summarize the current knowledge of how sepsis quantitatively and qualitatively impairs CD4 and CD8 T cell immunity of classical and nonclassical T cell subsets and discuss current therapeutic approaches being developed to boost the recovery of T cell immunity postsepsis induction.

Translational Sepsis Research: Spanning the Divide

OBJECTIVE

Our knowledge of the molecular mechanisms of sepsis has attained exponential growth. Yet, the pillars of its care remain antibiotics, fluid resuscitation, and physiologic support of failing organ systems. The inability to bring biologic breakthroughs to the bedside is not for lack of effort. Over 60 clinical trials of novel therapies, each heavily supported by the momentum of biologic data suggesting clinical utility, have been conducted and have failed to identify benefit. This mass of "negative" clinical data abut an equally towering mound of knowledge of sepsis biology, which collectively have led investigators to ask, "what happened?"

DATA SOURCES

Review of published scientific literature via MEDLINE searches using key terms related to the article topics.

STUDY SELECTION

Original articles, review articles, and systematic reviews were considered.

DATA EXTRACTION

Articles were selected for inclusion based upon author consensus.

DATA SYNTHESIS

Here, we present a synthetic review of some of the challenges in translating experimental animal models of sepsis to the bedside. We commence with the concept that the heterogeneity in the kinetics of the sepsis response serves as an important, often underappreciated but surmountable, source of translational impedance. Upon this groundwork, we discuss distinctions between animal experimentation and clinical trial design in the elements for hypothesis testing: cohort selection, power and sample size, randomization and blinding, and timing of intervention. From this concept, we develop a contextual framework for advancing the paradigm of animal-based investigations to facilitate science that transitions from molecule to medicine.

CONCLUSIONS

A persistent divide exists between the laboratory and clinical research arenas, which may be addressable via systematic targeting of identified translational gaps.

A New Venue of TNF Targeting

The first Food and Drug Administration-(FDA)-approved drugs were small, chemically-manufactured and highly active molecules with possible off-target effects, followed by protein-based medicines such as antibodies. Conventional antibodies bind a specific protein and are becoming increasingly important in the therapeutic landscape. A very prominent class of biologicals are the anti-tumor necrosis factor (TNF) drugs that are applied in several inflammatory diseases that are characterized by dysregulated TNF levels. Marketing of TNF inhibitors revolutionized the treatment of diseases such as Crohn’s disease. However, these inhibitors also have undesired effects, some of them directly associated with the inherent nature of this drug class, whereas others are linked with their mechanism of action, being pan-TNF inhibition. The effects of TNF can diverge at the level of TNF format or receptor, and we discuss the consequences of this in sepsis, autoimmunity and neurodegeneration. Recently, researchers tried to design drugs with reduced side effects. These include molecules with more specificity targeting one specific TNF format or receptor, or that neutralize TNF in specific cells. Alternatively, TNF-directed biologicals without the typical antibody structure are manufactured. Here, we review the complications related to the use of conventional TNF inhibitors, together with the anti-TNF alternatives and the benefits of selective approaches in different diseases.

Long-Term Cognitive Outcomes After Sepsis: a Translational Systematic Review

Sepsis is systemic inflammatory response syndrome with a life-threatening organ dysfunction that is caused by an unbalanced host immune response in an attempt to eliminate invasive microorganisms. We posed questions, "Does sepsis survivor patients have increased risk of neuropsychiatric manifestations?" and "What is the mechanism by which sepsis induces long-term neurological sequelae, particularly substantial cognitive function decline in survivor patients and in pre-clinical sepsis models?" The studies were identified by searching PubMed/MEDLINE (National Library of Medicine), PsycINFO, EMBASE (Ovid), LILACS (Latin American and Caribbean Health Sciences Literature), IBECS (Bibliographical Index in Spanish in Health Sciences), and Web of Science databases for peer-reviewed journals that were published until January 2018. A total of 3555 papers were included in the primary screening. After that, 130 articles were selected for the study. A number of pre-clinical studies have shown an auto amplification of pro-inflammatory cytokines such as tumor necrosis factor alpha (TNF-α), interleukin (IL)-1β, and IL-6 in the first few hours after sepsis induction, also increased blood-brain barrier permeability, elevated levels of matrix metalloproteinases, increased levels of damage-associated molecular patterns were demonstrated. In addition, the rodents presented long-term cognitive impairment in different behavioral tasks that were prevented by blocking the mechanism of action of these inflammatory mediators. Clinical studies have showed that sepsis survivors presented increased bodily symptoms such as fatigue, pain, visual disturbances, gastrointestinal problems, and neuropsychiatric problems compared to before sepsis. Sepsis leaves the survivors with an aftermath of physiological, neuropsychiatric, and functional impairment. Systematic review registration: CRD42017071755.

Polymicrobial sepsis and non-specific immunization induce adaptive immunosuppression to a similar degree

Sepsis is frequently complicated by a state of profound immunosuppression, in its extreme form known as immunoparalysis. We have studied the role of the adaptive immune system in the murine acute peritonitis model. To read out adaptive immunosuppression, we primed post-septic and control animals by immunization with the model antigen TNP-ovalbumin in alum, and measured the specific antibody-responses via ELISA and ELISpot assay as well as T-cell responses in a proliferation assay after restimulation. Specific antibody titers, antibody affinity and plasma cell counts in the bone marrow were reduced in post-septic animals. The antigen-induced splenic proliferation was also impaired. The adaptive immunosuppression was positively correlated with an overwhelming general antibody response to the septic insult. Remarkably, antigen “overload” by non-specific immunization induced a similar degree of adaptive immunosuppression in the absence of sepsis. In both settings, depletion of regulatory T cells before priming reversed some parameters of the immunosuppression. In conclusion, our data show that adaptive immunosuppression occurs independent of profound systemic inflammation and life-threatening illness.

Bench-to-Bedside: A Translational Perspective on Murine Models of Sepsis

BACKGROUND

Considerable research effort has focused on the development of novel therapies for the treatment of sepsis, yet after decades of clinical trials, few significant advances have been achieved. This limitation persists despite a wealth of data yielded by basic science that has expanded our knowledge of the biology of this disease exponentially.

METHOD

Review of the English-language literature.

RESULTS

Translational researchers may address the resultant gap between the basic science laboratory and clinical research worlds. Herein, we review potential causes for the challenges of translating basic laboratory discovery into clinical benefit.

CONCLUSION

We propose conceptual platforms to further the development of translational sepsis research efforts.

Methods to Study the Innate Immune Response to Sepsis

This chapter describes techniques to measure the innate immune response in the mouse cecal ligation and puncture model of sepsis. The reader will learn how to perform retro-orbital bleeds to harvest serum from mice and learn how to perform peritoneal lavage to harvest cells and inflammatory mediators from this compartment. The enzyme-linked immunosorbent assay (ELISA) technique is described as a method to measure the levels of cytokines and chemokines in these fluids. Additionally, this chapter describes techniques to stain the cellular fraction of the peritoneal lavage with fluorescently labeled antibodies, and perform fluorescence activated cell sorting (FACS) to quantify macrophages and neutrophils in this compartment.

Experimental Protocol for Cecal Ligation and Puncture Model of Polymicrobial Sepsis and Assessment of Vascular Functions in Mice

Sepsis is the systemic inflammatory response syndrome that occurs during infection and is exacerbated by the inappropriate immune response encountered by the affected individual. Despite extensive research, sepsis in humans is one of the biggest challenges for clinicians. The high mortality rate in sepsis is primarily due to hypoperfusion-induced multiorgan dysfunctions , resulting from a marked decrease in peripheral resistance. Vascular dysfunctions are further aggravated by sepsis-induced impairment in myocardial contractility. Circulatory failure in sepsis is characterized by refractory hypotension and vascular hyporeactivity (vasoplegia) to clinically used vasoconstrictors. To investigate the complex pathophysiology of sepsis and its associated multiple organ dysfunction, several animal models have been developed. However, cecal ligation and puncture (CLP) model of murine sepsis is still considered as 'gold standard' in sepsis research. In this protocol we have described the standard surgical procedure to induce polymicrobial sepsis by cecal ligation and puncture. Further, we have described the protocol to study the molecular mechanisms underlying vascular dysfunctions in sepsis.

Colon Ascendens Stent Peritonitis (CASP) Induces Excessive Inflammation and Systemic Metabolic Dysfunction in a Septic Rat Model

The colon ascendens stent peritonitis (CASP) surgery induces a leakage of gut contents, causing polymicrobial sepsis related to post-operative multiple organ failure and death in surgical patient. To evaluate the effects of CASP on multiple organs, we analyzed the systemic metabolic consequences in liver, kidney, lung, and heart of rats after CASP by employing a combination of metabolomics, clinical chemistry, and biological assays. We found that CASP surgery after 18 h resulted in striking elevations of lipid, amino acids, acetate, choline, PC, and GPC in rat liver together with significant depletion of glucose and glycogen. Marked elevations of organic acids including lactate, acetate, and creatine and amino acids accompanied by decline of glucose, betaine, TMAO, choline metabolites (PC and GPC) nucleotides, and a range of organic osmolytes such as myo-inositol are observed in the kidney of 18 h post-operative rat. Furthermore, 18 h post-operative rats exhibited accumulations of lipid, amino acids, and depletions of taurine, myo-inositol, choline, PC, and GPC and some nucleotides including uridine, inosine, and adenosine in the lung. In addition, significant elevations of some amino acids, uracil, betaine, and choline metabolites, together with depletion of inosine-5'-monophosphate, were only observed in the heart of 18 h post-operative rats. These results provide new insights into pathological consequences of CASP surgery, which are important for timely prognosis of sepsis.

Why Antibiotic Treatment Is Not Enough for Sepsis Resolution: an Evaluation in an Experimental Animal Model

Sepsis remains a major health problem at the levels of mortality, morbidity, and economic burden to the health care system, a condition that is aggravated by the development of secondary conditions such as septic shock and multiple-organ failure. Our current understanding of the etiology of human sepsis has advanced, at least in part, due to the use of experimental animal models, particularly the model of cecum ligation and puncture (CLP). Antibiotic treatment has been commonly used in this model to closely mirror the treatment of human septic patients. However, whether their use may obscure the elucidation of the cellular and molecular mechanisms involved in the septic response is questionable. The objective of the present study was to determine the effect of antibiotic treatment in the outcome of a fulminant model of CLP. Various dosing strategies were used for the administration of imipenem, which has broad-spectrum coverage of enteric bacteria. No statistically significant differences in the survival of mice were observed between the different antibiotic dosing strategies and no treatment, suggesting that live bacteria may not be the only factor inducing septic shock. To further investigate this hypothesis, mice were challenged with sterilized or unsterilized cecal contents. We found that exposure of mice to sterilized cecal contents also resulted in a high mortality rate. Therefore, it is possible that bacterial debris, apart from bacterial proliferation, triggers a septic response and contributes to mortality in this model, suggesting that additional factors are involved in the development of septic shock.

Deviation of the Fecal Stream in Colonic Bowel Segments Results in Increased Numbers of Isolated Lymphoid Follicles in the Submucosal Compartment in a Novel Murine Model of Diversion Colitis

INTRODUCTION

Diversion colitis is a significant health problem due to its high incidence in patients with diverting enterostomy. This mucosal inflammation presents characteristic histopathological features allowing for the differentiation of this entity from other inflammatory bowel diseases. The pathophysiology of this disease remains ill-defined, in part due to the lack of appropriate animal models. The present study was performed in order to develop and characterize a murine model of diversion colitis.

METHODS

A diverting loop colostomy was performed in C57BL/6 mice either in the ascending colon or in the transverse colon. Animals were assessed for clinical and histopathological parameters during short-term and long-term survival.

RESULTS

Animals with a colostomy in the transverse colon showed a good long-term survival and developed a mild colitis in the bypassed bowel closely resembling the human pathology on a histopathological level.

CONCLUSION

This model is a promising tool to further elucidate the pathomechanism leading to impaired mucosal homeostasis in bypassed colonic segments. Moreover, the establishment of the model in the C57BL/6 background allows the combination of this colitis model with various transgenic mouse strains to investigate the effect of locally deregulated mucosal immunity on systemic immune homeostasis and to develop specific therapeutic strategies.

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.

STING and TRIF Contribute to Mouse Sepsis, Depending on Severity of the Disease Model

IFN regulatory factor (IRF)3 plays a detrimental role in the cecal ligation and puncture (CLP) mouse model of sepsis. However, it is unclear which pathway activates IRF3 in this context. In this report, we investigate two pathways that activate IRF3: the Stimulator of Interferon Genes (STING) pathway (that senses cytosolic DNA) and the TIR-domain-containing adapter-inducing interferon-β (TRIF) pathway (that senses dsRNA and LPS via Toll-like receptor 3 and 4). Initially, we examine the impact of these pathways using a severe CLP model (∼90% mortality). Both STING-KO and TRIF-KO mice are protected from severe sepsis, exhibiting reduced mortality, disease score, hypothermia, and inflammatory cytokines relative to WT counterparts. STING/TRIF-DKO mice exhibit a similar phenotype to each of the single KO strains, suggesting that these pathways have an interrelated function. Subsequently, we examine the impact of these pathways using a moderate CLP model incorporating clinical treatments (Lactated Ringer Solution and antibiotics, ∼36% mortality). In this case, STING-KO mice show a similar phenotype to WT counterparts, while TRIF-KO mice show improved disease score and hypothermia. During sepsis, innate immune receptors recognize bacterial ligands and host-derived danger signals, including cell-free DNA released into the circulation. We show that IRF3 is activated in cultured macrophages treated with bacteria derived from the mouse cecum, dependent on TRIF, and in macrophages treated with mouse genomic DNA/Lipofectamine 2000, dependent on STING. Together, our data demonstrate that both the STING and TRIF pathways can promote sepsis pathogenesis; however, their contribution depends on the severity of the disease model. We show that bacteria are abundant in the peritoneum following both severe and moderate CLP, while cell-free DNA is more highly elevated in the serum following severe CLP compared with sham and moderate CLP. Hence, the presence of bacteria and cell-free DNA may explain the variable phenotypes in our severe CLP model (dependent on TRIF and STING) versus our moderate CLP model (dependent on TRIF only).

The potential efficacy of Survanta (r) and Seprafilm (r) on preventing intra-abdominal adhesions in rats

PURPOSE

To investigate the potential efficacy of beractant (Survanta(r)) and Seprafilm(r) on the prevention of postoperative adhesions.

METHODS

Forty Wistar-albino female rats were used. The rats were randomly allocated into four groups of 10 rats each as control group (CG), beractant group (BG), Seprafilm(r) group (SG), and combined group (COG). All rats underwent cecal abrasion via midline laparotomy. Before abdominal closure, isotonic saline, beractant, Seprafilm, and combined agents were intraperitoneally administered. Adhesions were classified macroscopically with Canbaz Scoring System on postoperative day 10. Ceacum was resected for histopathological assessment.

RESULTS

Macroscopic adhesion scores were significantly lower in BG, SG, and COG than CG (p<0.05); (45%, 15%, 25%, and 15%; respectively). Histopathological assessment revealed a reduced inflammation and fibrosis score in the study groups than CG (p<0.05). In BG, adhesion development, inflammation and fibrosis scores were lower than SG; however, it was not statistically significant.

CONCLUSIONS

Intra-abdominal application of beractant is significantly effective for the prevention of adhesion formation with no adverse effect by covering the whole peritoneal mesothelium with excellent gliding properties in a rat model. The combination of both agents is also effective in reducing adhesion formation, however, not superior to single beractant application.

Differential Paradigms in Animal Models of Sepsis

Sepsis is a serious clinical problem involving complex mechanisms which requires better understanding and insight. Animal models of sepsis have played a major role in providing insight into the complex pathophysiology of sepsis. There have been various animal models of sepsis with different paradigms. Endotoxin, bacterial infusion, cecal ligation and puncture, and colon ascendens stent peritonitis models are the commonly practiced methods at present. Each of these models has their own advantages and also confounding factors. We have discussed the underlying mechanisms regulating each of these models along with possible reasons why each model failed to translate into the clinic. In animal models, the timing of development of the hemodynamic phases and the varied cytokine patterns could not accurately resemble the progression of clinical sepsis. More often, the exuberant and transient pro-inflammatory cytokine response is only focused in most models. Immunosuppression and apoptosis in the later phase of sepsis have been found to cause more damage than the initial acute phase of sepsis. Likewise, better understanding of the existing models of sepsis could help us create a more relevant model which could provide solution to the currently failed clinical trials in sepsis.

TNF-related apoptosis-inducing ligand deficiency enhances survival in murine colon ascendens stent peritonitis

Background

Apart from inducing apoptosis in tumor cells, tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) influences inflammatory reactions. Murine colon ascendens stent peritonitis (CASP) represents a model of diffuse peritonitis. Recently, it has been demonstrated that administration of exogenous TRAIL not only induces apoptosis in neutrophils but also enhances survival in this model. The aim of this study was to examine the impact of genetic TRAIL deficiency on the course of CASP.

Methods

Peritonitis was induced in 6- to 8-week-old female TRAIL^−/− mice as well as in wild-type mice. The sepsis severity score and survival of mice were monitored. Bacterial loads in blood as well as in the lymphoid organs were examined. Additionally, the number of apoptotic cells within the lymphoid organs was determined.

Results

As early as 8 hours postinduction of CASP, TRAIL^−/− mice were significantly more affected by sepsis than wild-type mice, as measured by the sepsis severity score. However, during the further course of sepsis, TRAIL deficiency led to significantly decreased sepsis severity scores, resulting in an enhanced overall survival in TRAIL^−/− mice. The better survival of TRAIL^−/− mice was accompanied by a decreased bacterial load within the blood. In marked contrast, the number of apoptotic cells within the lymphoid organs was highly increased in TRAIL^−/− mice 20 hours after induction of CASP.

Conclusion

Hence, exogenous and endogenous TRAIL is protective during the early phase of sepsis, while endogenous TRAIL appears to be detrimental in the later course of this disease.

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.

Resuscitation with hydroxyethyl starch 130/0.4 attenuates intestinal injury in a rabbit model of sepsis

OBJECTIVE

Improvement of mucosal barrier function and reduction of bacterial translocation are important in the management of sepsis. The mechanisms that underlie the protective effects of colloids on the intestinal mucosal barrier are unclear. The study aims to investigate the effect of fluid resuscitation with hydroxyethyl starch (HES) 130/0.4 against intestinal mucosal barrier dysfunction in a rabbit model of sepsis.

MATERIALS AND METHODS

Thirty healthy rabbits were randomly and equally divided into a sham-operated control, a sepsis model, or a sepsis + HES treatment group. The sepsis model and sepsis + HES treatment groups were subjected to a modified colon ascendens stent peritonitis (CASP) procedure to induce sepsis. Four hours after the CASP procedure, fluid resuscitation was performed with 6% HES 130/0.4. Arterial and superior mesenteric vein blood samples were collected 4 and 8 h after the CASP procedure for blood gas analysis and measuring tumor necrosis factor-α, interleukin-10, and D-lactate levels. The rabbits were euthanized 8 h after CASP, and sections of the small intestine were stained to evaluate histopathological changes.

RESULTS

Respiratory rate and blood pressure were stable during the resuscitation period. Fluid resuscitation with 6% HES 130/0.4 alleviated pathological changes in the abdominal cavity, improved blood gas parameters and inflammatory mediator levels, decreased plasma D-lactate levels, and reduced intestinal mucosal injury compared with the non-treated sepsis model.

CONCLUSIONS

Fluid resuscitation with 6% HES 130/0.4 protects against intestinal mucosal barrier dysfunction in rabbits with sepsis, possibly via mechanisms associated with improving intestinal oxygen metabolism and reducing the release of inflammatory mediators.

Full activation of CD4+ T cells early during sepsis requires specific antigen

Supplemental digital content is available in the text.

During sepsis, CD4⁺ T cells express activation markers within the first 24 h. In the present study, the mechanisms of T-cell activation and its consequences were addressed in an acute peritonitis model in mice. The response of CD4⁺ T cells to sepsis induction was compared between OTII mice, characterized by ovalbumin-specific T-cell receptor–transgenic T cells, and C57BL/6 controls (wild type [WT] mice). Because ovalbumin was absent during peritonitis, the OTII CD4⁺ T cells could not be activated by canonical antigen recognition. In both OTII and WT control mice, CD4⁺ T effector cells and CD4⁺ Foxp3⁺ regulatory T cells (Tregs) expressed the activation marker CD69 early after sepsis onset. However, full activation with upregulation of CD25 and proliferation took place only in the presence of the antigen. Besides this, the fraction of Tregs was lower in OTII than that in WT mice. Sepsis mortality was increased in OTII mice. Our data show that, in sepsis, partial activation of CD4⁺ T cells is induced by a T-cell receptor–independent pathway, whereas full stimulation and proliferation require a specific antigen. Antigen-dependent T-cell effector functions as well as Treg activity may contribute to sepsis survival.

Myeloid-related protein 8 induces self-tolerance and cross-tolerance to bacterial infection via TLR4- and TLR2-mediated signal pathways

Myeloid-related protein 8 (Mrp8) is the active component of Mrp8/14 protein complex released by phagocytes at the site of infection and stimulates inflammatory responses. However, it is unclear whether Mrp8 could induce self-tolerance and cross-tolerance to bacterial infection. Here we report that Mrp8 triggered TNF-α and IL-6 release via a Toll-like receptor 4 (TLR4)-dependent manner. Pre-stimulation of murine macrophages and human monocytes with Mrp8 induced self-tolerance to Mrp8 re-stimulation and cross-tolerance to lipopolysaccharide (LPS), bacterial lipoprotein (BLP), gram-negative and gram-positive bacterial challenges, with substantially attenuated TNF-α and IL-6 release. Moreover, Mrp8 tolerisation significantly reduced serum TNF-α and IL-6, increased polymorphonuclear neutrophil (PMN) recruitment and accelerated bacterial clearance, thus protecting mice against LPS-induced lethality and cecal ligation and puncture (CLP)-induced polymicrobial sepsis. In addition to TLR4, TLR2 also contributed to Mrp8-induced inflammatory response and tolerance. Down-regulation of phosphorylated p38 by Mrp8 pre-stimulation was predominantly responsible for the intracellular mechanism of Mrp8-induced tolerance. Thus, our findings of Mrp8-induced self-tolerance and cross-tolerance may provide a potential strategy for attenuating an overwhelming proinflammatory cascade and enhancing antimicrobial responses during microbial sepsis.

CD1d- and MR1-Restricted T Cells in Sepsis

Dysregulated immune responses to infection, such as those encountered in sepsis, can be catastrophic. Sepsis is typically triggered by an overwhelming systemic response to an infectious agent(s) and is associated with high morbidity and mortality even under optimal critical care. Recent studies have implicated unconventional, innate-like T lymphocytes, including CD1d- and MR1-restricted T cells as effectors and/or regulators of inflammatory responses during sepsis. These cell types are typified by invariant natural killer T (iNKT) cells, variant NKT (vNKT) cells, and mucosa-associated invariant T (MAIT) cells. iNKT and vNKT cells are CD1d-restricted, lipid-reactive cells with remarkable immunoregulatory properties. MAIT cells participate in antimicrobial defense, and are restricted by major histocompatibility complex-related protein 1 (MR1), which displays microbe-derived vitamin B metabolites. Importantly, NKT and MAIT cells are rapid and potent producers of immunomodulatory cytokines. Therefore, they may be considered attractive targets during the early hyperinflammatory phase of sepsis when immediate interventions are urgently needed, and also in later phases when adjuvant immunotherapies could potentially reverse the dangerous state of immunosuppression. We will highlight recent findings that point to the significance or the therapeutic potentials of NKT and MAIT cells in sepsis and will also discuss what lies ahead in research in this area.

Phosphodiesterase 4 inhibition dose dependently stabilizes microvascular barrier functions and microcirculation in a rodent model of polymicrobial sepsis

BACKGROUND

Breakdown of microvascular endothelial barrier functions contributes to disturbed microcirculation, organ failure, and death in sepsis. Increased endothelial cAMP levels by systemic application of phosphodiesterase 4 inhibitors (PD-4-I) have previously been demonstrated to protect microvascular barrier properties in a model of systemic inflammation (systemic inflammatory response syndrome) suggesting a novel therapeutic option to overcome this problem. However, in a clinically relevant model of polymicrobial sepsis long-term effects, immunomodulatory effects and effectivity of PD-4-I to stabilize microvascular barrier functions and microcirculation remained unexplored.

METHODS

We induced polymicrobial sepsis using the colon ascendens stent peritonitis (CASP) model in which we performed macrohemodynamic and microhemodynamic monitoring with and without systemic intravenous application of different doses of PD-4-I rolipram in Sprague-Dawley rats over 26 h.

RESULTS

All animals with CASP showed clinical and laboratory signs of sepsis and peritonitis. Whereas macrohemodynamic adverse effects were not evident, application of PD-4-I led to stabilization of endothelial barrier properties as revealed by reduced extravasation of fluorescein isothiocyanate-albumin. However, only low-dose application of 1 mg/kg body weight per hour of PD-4-I improved microcirculatory flow in the CASP model, whereas high-dose therapy of 3 mg/kg BW per hour PDI-4-I had adverse effects. Accordingly, sepsis-induced acute kidney injury and lung edema were prevented by PD-4-I treatment. Furthermore, PD-4-I showed immunomodulatory effects as revealed by decreased interleukin 1α (IL-1α), IL-1β, IL-12, and tumor necrosis factor α levels following PD-4-I treatment, which appeared not to correlate with barrier-stabilizing effects of rolipram.

CONCLUSIONS

These data provide further evidence that systemic application of PD-4-I could be suitable for therapeutic microvascular barrier stabilization and improvement of microcirculatory flow in sepsis.

Sepsis-induced acute kidney injury by standardized colon ascendens stent peritonitis in rats - a simple, reproducible animal model

Background

Up to 50% of septic patients develop acute kidney injury (AKI). The pathomechanism of septic AKI is poorly understood. Therefore, we established an innovative rodent model to characterize sepsis-induced AKI by standardized colon ascendens stent peritonitis (sCASP). The model has a standardized focus of infection, an intensive care set up with monitoring of haemodynamics and oxygenation resulting in predictable impairment of renal function, AKI parameters as well as histopathology scoring.

Methods

Anaesthetized rats underwent the sCASP procedure, whereas sham animals were sham operated and control animals were just monitored invasively. Haemodynamic variables and blood gases were continuously measured. After 24 h, animals were reanesthetized; cardiac output (CO), inulin and PAH clearances were measured and later on kidneys were harvested; and creatinine, urea, cystatin C and neutrophil gelatinase-associated lipocalin (NGAL) were analysed. Additional sCASP-treated animals were investigated after 3 and 9 days.

Results

All sCASP-treated animals survived, whilst ubiquitous peritonitis and significantly deteriorated clinical and macrohaemodynamic sepsis signs after 24 h (MAP, CO, heart rate) were obvious. Blood analyses showed increased lactate and IL-6 levels as well as leucopenia. Urine output, inulin and PAH clearance were significantly decreased in sCASP compared to sham and control. Additionally, significant increase in cystatin C and NGAL was detected. Standard parameters like serum creatinine and urea were elevated and sCASP-induced sepsis increased significantly in a time-dependent manner. The renal histopathological score of sCASP-treated animals deteriorated after 3 and 9 days.

Conclusions

The presented sCASP method is a standardized, reliable and reproducible method to induce septic AKI. The intensive care set up, continuous macrohaemodynamic and gas exchange monitoring, low mortality rate as well as the opportunity of detailed analyses of kidney function and impairments are advantages of this setup. Thus, our described method may serve as a new standard for experimental investigations of septic AKI.

Differences between murine and human sepsis

Sepsis can be defined as a systemic inflammatory response syndrome occurring in the presence of an infectious source. Over the past 25 years, numerous guidelines have been established to clarify definitions and improve the overall management of clinical sepsis. In light of these multiple paradigm shifts, this review attempts to summarize the innate immunologic alterations that manifest during sepsis, establish and compare mouse models of sepsis with the clinical course, and discuss the authors' views on additional elements that should be considered in modeling and predicting clinical sepsis from the standpoint of a basic research setting.