Translational Sepsis Research: Spanning the Divide

Of mice and men: Laboratory murine models for recapitulating the immunosuppression of human sepsis

Prolonged immunosuppression is increasingly recognized as the major cause of late phase and long-term mortality in sepsis. Numerous murine models with different paradigms, such as lipopolysaccharide injection, bacterial inoculation, and barrier disruption, have been used to explore the pathogenesis of immunosuppression in sepsis or to test the efficacy of potential therapeutic agents. Nonetheless, the reproducibility and translational value of such models are often questioned, owing to a highly heterogeneric, complex, and dynamic nature of immunopathology in human sepsis, which cannot be consistently and stably recapitulated in mice. Despite of the inherent discrepancies that exist between mice and humans, we can increase the feasibility of murine models by minimizing inconsistency and increasing their clinical relevance. In this mini review, we summarize the current knowledge of murine models that are most commonly used to investigate sepsis-induced immunopathology, highlighting their strengths and limitations in mimicking the dysregulated immune response encountered in human sepsis. We also propose potential directions for refining murine sepsis models, such as reducing experimental inconsistencies, increasing the clinical relevance, and enhancing immunological similarities between mice and humans; such modifications may optimize the value of murine models in meeting research and translational demands when applied in studies of sepsis-induced immunosuppression.

Identification of cardiovascular and molecular prognostic factors for the morbidity and mortality in COVID-19-sepsis (ICROVID): Protocol for a prospective multi-centre cohort study

Introduction

Severe COVID-19 constitutes a form of viral sepsis. Part of the specific pathophysiological pattern of this condition is the occurrence of cardiovascular events. These include pulmonary embolism, arrhythmias and cardiomyopathy as manifestations of extra-pulmonary organ dysfunction. Hitherto, the prognostic impact of these cardiovascular events and their predisposing risk factors remains unclear. This study aims to explore this question in two cohorts of viral sepsis–COVID-19 and influenza–in order to identify new theragnostic strategies to improve the short- and long-term outcome of these two diseases.

Methods and analysis

In this prospective multi-centre cohort study, clinical assessment will take place during the acute and post-acute phase of sepsis and be complemented by molecular laboratory analyses. Specifically, echocardiography and cardiovascular risk factor documentation will be performed during the first two weeks after sepsis onset. Aside from routine haematological and biochemical laboratory tests, molecular phenotyping will comprise analyses of the metabolome, lipidome and immune status. The primary endpoint of this study is the difference in 3-month mortality of patients with and without septic cardiomyopathy in COVID-19 sepsis. Patients will be followed up until 6 months after onset of sepsis via telephone interviews and questionnaires. The results will be compared with a cohort of patients with influenza sepsis as well as previous cohorts of patients with bacterial sepsis and healthy controls.

Ethics and dissemination

Approval was obtained from the Ethics Committee of the Friedrich Schiller University Jena (2020-2052-BO). The results will be published in peer-reviewed journals and presented at appropriate conferences.

Trial registration

DRKS00024162.

Protective Effect of MicroRNA-23b on Kidney Injury in Septic Rats Through Regulation of Mothers Against Decapentaplegic Homolog 3 (Smad3)

Our study aims to investigate the mechanism whereby microRNA (miRNA)-23b alleviates kidney damage in septic rats. Herein, we set up septic rat model, control group and sham-operated model to evaluate the kidney tissue damage. The glomerular mesangial cells isolated from rats were transfected with plasmids expressing miR-23b followed by analysis of the expression of miR-23b, Smad3, TLR4, HMGB1 and expression of autophagy-related proteins (LC3, beclin-1) by western blot and RT-qPCR. The level of TNF-α, IL-6 and BUN and SCr were significantly elevated in the model group and decreased after overexpression of miR-23b with elevated LC3-II, Smad3 and Beclin-1 expression. miR-23b mimic group presented highest expression of miR-23b, followed by miR-23b NC group, and miR-23b inhibitor group. The levels of TLR4, and HMGB1 and positive rate of NF-κBp65 in miR-23b mimic group were significantly lower than those in miR-23b inhibitor group (p < 0.05). Importantly, miR-23b has a targeted relationship with Smad3. Overexpression of miR- 23b induces autophagy by promoting the Smad3 expression, alleviates kidney damage in septic rats, and reduces inflammation and inactivates NF-κB signaling pathway.

Croix C, Tyurina YY, Kagan VE, Mallampalli RK, Ray A, Ray P, Lee JS. Stressed erythrophagocytosis induces immunosuppression during sepsis through heme-mediated STAT1 dysregulation

Macrophages are main effectors of heme metabolism, increasing transiently in the liver during heightened disposal of damaged or senescent RBCs (sRBCs). Macrophages are also essential in defense against microbial threats, but pathological states of heme excess may be immunosuppressive. Herein, we uncovered a mechanism whereby an acute rise in sRBC disposal by macrophages led to an immunosuppressive phenotype after intrapulmonary Klebsiella pneumoniae infection characterized by increased extrapulmonary bacterial proliferation and reduced survival from sepsis in mice. The impaired immunity to K. pneumoniae during heightened sRBC disposal was independent of iron acquisition by bacterial siderophores, in that K. pneumoniae mutants lacking siderophore function recapitulated the findings observed with the WT strain. Rather, sRBC disposal induced a liver transcriptomic profile notable for suppression of Stat1 and IFN-related responses during K. pneumoniae sepsis. Excess heme handling by macrophages recapitulated STAT1 suppression during infection that required synergistic NRF1 and NRF2 activation but was independent of heme oxygenase-1 induction. Whereas iron was dispensable, the porphyrin moiety of heme was sufficient to mediate suppression of STAT1-dependent responses in human and mouse macrophages and promoted liver dissemination of K. pneumoniae in vivo. Thus, cellular heme metabolism dysfunction negatively regulated the STAT1 pathway, with implications in severe infection.

Checkpoint inhibitor therapy in preclinical sepsis models: a systematic review and meta-analysis

BACKGROUND

Animal studies reporting immune checkpoint inhibitors (CPIs) improved host defense and survival during bacterial sepsis provided one basis for phase I CPI sepsis trials. We performed a systematic review and meta-analysis examining the benefit of CPI therapy in preclinical studies, and whether variables potentially altering this clinical benefit were investigated. Studies were analyzed that compared survival following bacteria or lipopolysaccharide challenge in animals treated with inhibitors to programmed death-1 (PD-1), PD-ligand1 (PD-L1), cytotoxic T lymphocyte-associated protein-4 (CTLA-4), or B- and T-lymphocyte attenuator (BTLA) versus control.

RESULTS

Nineteen experiments from 11 studies (n = 709) were included. All experiments were in mice, and 10 of the 19 were published from a single research group. Sample size calculations and randomization were not reported in any studies, and blinding procedures were reported in just 1. Across all 19 experiments, CPIs increased the odds ratio for survival (OR, 95% CI) [3.37(1. 55, 7.31)] but with heterogeneity (I² = 59%, p < 0.01). After stratification by checkpoint molecule targeted, challenge site or type, or concurrent antibacterial treatment, CPIs had consistent effects over most experiments in the 9 that included antibacterial treatment [OR = 2.82 (1.60, 4.98), I² = 6%, p = 0.39 with versus 4.01 (0.89, 18.05), I² = 74%, p < 0.01 without]. All 9 antibiotic experiments employed cecal-ligation and puncture (CLP) bacterial challenge while 6 also included a Candida albicans challenge 3-4 days after CLP. In these six experiments (n = 322), CPIs were directed at the fungal challenge when CLP lethality had resolved, and were consistently beneficial [2.91 (2.41, 3.50), I² = 0%, p = 0.99]. In the three experiments (n = 66) providing antibiotics without fungal challenge, CPIs were administered within 1 day of CLP and had variable and non-significant effects [0.05 (0.00, 1.03); 7.86 (0.28, 217.11); and 8.50 (0.90, 80.03)]. No experiment examined pneumonia.

CONCLUSIONS

Preclinical studies showing that CPIs add benefit to antibiotic therapy for the common bacterial infections causing sepsis clinically are needed to support this therapeutic approach. Studies should be reproducible across multiple laboratories and include procedures to reduce the risk of bias.

Clinically relevant model of pneumococcal pneumonia, ARDS, and nonpulmonary organ dysfunction in mice

Pneumonia is responsible for more deaths in the United States than any other infectious disease. Severe pneumonia is a common cause of acute respiratory failure and acute respiratory distress syndrome (ARDS). Despite the introduction of effective antibiotics and intensive supportive care in the 20th century, death rates from community-acquired pneumonia among patients in the intensive care unit remain as high as 35%. Beyond antimicrobial treatment, no targeted molecular therapies have yet proven effective, highlighting the need for additional research. Despite some limitations, small animal models of pneumonia and the mechanistic insights they produce are likely to continue to play an important role in generating new therapeutic targets. Here we describe the development of an innovative mouse model of pneumococcal pneumonia developed for enhanced clinical relevance. We first reviewed the literature of small animal models of bacterial pneumonia that incorporated antibiotics. We then did a series of experiments in mice in which we systematically varied the pneumococcal inoculum and the timing of antibiotics while measuring systemic and lung-specific end points, producing a range of models that mirrors the spectrum of pneumococcal lung disease in patients, from mild self-resolving infection to severe pneumonia refractory to antibiotics. A delay in antibiotic treatment resulted in ongoing inflammation and renal and hepatic dysfunction despite effective bacterial killing. The addition of fluid resuscitation to the model improved renal function but worsened the severity of lung injury based on direct measurements of pulmonary edema and lung compliance, analogous to patients with pneumonia and sepsis who develop ARDS following fluid administration.

Mortality of septic old and adult male mice correlates with individual differences in premorbid behavioral phenotype and acute-phase sickness behavior

Individual differences in premorbid behaviors and in those exhibited in the course of an infection disease may be useful to explain the individual susceptibility to infections, the underlying neuroimmunological mechanisms and be helpful to design patient oriented treatments with better prediction of pharmacological reactivity/outcome. Age (old) and gender (male) are also considered vulnerability factors. In the present study, the motor, emotional, anxious-like and social phenotypes of adult (6-month-old) and old (18-month-old) male C57BL/6 × 129Sv mice were determined using both a transversal and longitudinal designs prior to the analysis of LPS (150 mg/kg, i.p.)-induced sickness behavior and mortality. The results show: i) Individual premorbid behavioral phenotype had short- and long-term predictive value of hours of survival; ii) Persistence of behavioral traits from adulthood to old age and predictive value on hours of survival; iii) First signs of sickness behavior were also predicting mortality, mostly in old animals; iv) LPS-sickness behavior was the same at both ages but adult animals were able to show attempts of motor recovery; v) The mortality rate over 96 h was 100% in both ages, but old animals showed shorter survival times. In summary, these results confirm the relevance of age/aging but also individual behavioral differences in the premorbid phenotype and the morbidity response to the LPS-induced-sepsis that correlate with the individual's mortality. Thus, this work supports the translational scenarios to study personalized evaluation of risks factors and psycho-neuro-immunological mechanisms relevant for better interventions and prognosis in the critically ill young but specially aged patient population.

Linagliptin Attenuates the Cardiac Dysfunction Associated With Experimental Sepsis in Mice With Pre-existing Type 2 Diabetes by Inhibiting NF-κB

The mortality rate of patients who develop sepsis-related cardiac dysfunction is high. Many disease conditions (e.g., diabetes) increase the susceptibility to infections and subsequently sepsis. Activation of the NF-κB pathway plays a crucial role in the pathophysiology of sepsis-associated cardiac dysfunction and diabetic cardiomyopathy. The effect of diabetes on outcomes in patients with sepsis is still highly controversial. We here hypothesized that type 2 diabetes (T2DM) augments the cardiac (organ) dysfunction associated with sepsis, and that inhibition of the NF-κB pathway with linagliptin attenuates the cardiac (organ) dysfunction in mice with T2DM/sepsis. To investigate this, 10-week old male C57BL/6 mice were randomized to receive normal chow or high fat diet (HFD), 60% of calories derived from fat). After 12 weeks, mice were subjected to sham surgery or cecal ligation and puncture (CLP) for 24 h. At 1 hour after surgery, mice were treated with linagliptin (10 mg/kg, i.v.), IKK-16 (1 mg/kg, i.v.), or vehicle (2% DMSO, 3 ml/kg, i.v.). Mice also received analgesia, fluids and antibiotics at 6 and 18 h after surgery. Mice that received HFD showed a significant increase in body weight, impairment in glucose tolerance, reduction in ejection fraction (%EF), and increase in alanine aminotransferase (ALT). Mice on HFD subjected to CLP showed further reduction in %EF, increase in ALT, developed acute kidney dysfunction and lung injury. They also showed significant increase in NF-κB pathway, iNOS expression, and serum inflammatory cytokines compared to sham surgery group. Treatment of HFD-CLP mice with linagliptin or IKK-16 resulted in significant reductions in (i) cardiac, liver, kidney, and lung injury associated with CLP-sepsis, (ii) NF-κB activation and iNOS expression in the heart, and (iii) serum inflammatory cytokine levels compared to HFD-CLP mice treated with vehicle. Our data show that pre-existing type 2 diabetes phenotype worsens the organ dysfunction/injury associated with CLP-sepsis in mice. Most notably, inhibition of NF-κB reduces the organ dysfunction/injury associated with sepsis in mice with pre-existing T2DM.