Common Variables That Influence Sepsis Mortality in Mice

Impact of thermoneutral acclimation on a murine model of polymicrobial peritonitis

To examine the effects of ambient temperature on the reproducibility and translation of a murine sepsis model, we hypothesized that acclimation of mice in temperatures within their thermoneutral zone would alter immune responses and outcomes compared to standard housing temperatures. Mice housed for one week in thermoneutral (30°C) as compared to standard (22°C) conditions displayed lower counts of circulating neutrophils (0.52 ± 0.20 vs. 1.10 ± 0.54 x103/μL; p = 0.011) and peritoneal macrophages (0.80 ± 0.57 vs. 1.62 ± 0.62 x 105/μL; p = 0.002) as well as reduced in vitro production of IFN-γ by stimulated splenocytes (0.38 ± 0.68 vs 2.55 ± 0.76 x104 pg/mL, respectively, p = 0.004). After one week of temperature acclimation followed by CLP, the 7-day mortality was significantly lower under thermoneutral as compared to standard temperatures (80% vs 30%, respectively; p = 0.012), although core body temperature was preserved (average for 24 hours: 36.4 ± 1.3°C vs 31.7 ± 4.7°C; p < 0.0001). The lower survival was accompanied by increased systemic IL-6 levels (3.8 ± 3.3 vs 1.9 ± 1.3 x103 pg/mL; p = 0.04) and less robust influx of neutrophils into the peritoneum (1.68 ± 1.07 vs. 4.20 ± 2.46 x105/μL, respectively; p = 0.0003). Overall, thermoneutral temperatures impacted innate immune parameters before and after CLP, producing distinctly different outcomes. Therefore, ambient temperature is an important variable that could impact model reproducibility and should be reported for the acclimation period and experimentation phases of murine sepsis studies.

Anserine reduces mortality in experimental sepsis by preventing methylglyoxal-induced capillary leakage

BACKGROUND

We previously identified methylglyoxal as a biomarker for early identification and outcome prediction in human sepsis. We hypothesised that methylglyoxal causally impacts disease severity, and the methylglyoxal-scavenging dipeptide anserine can attenuate the detrimental effects of methylglyoxal.

METHODS

Using a translational approach, secondary analyses of two observational trials were performed to test the initial hypotheses. Afterwards, these results were re-evaluated in different murine models of experimental sepsis in vivo. The detrimental effects of methylglyoxal as well as the underlying mechanisms were further assessed in vitro using transendothelial electrical resistance measurements, fluorescence-activated cell sorting analyses, cytokine assays, gene expression analyses, and enzyme activity assays, as well as immunofluorescence and immunohistochemistry staining.

FINDINGS

The secondary analyses confirmed methylglyoxal as an independent marker associated with increased mortality within the first 48 h after sepsis onset and high catecholamine and fluid requirements in the first 24 h after sepsis onset. In the sepsis models, methylglyoxal-derived carbonyl stress significantly contributed to the development of capillary leakage by disrupting endothelial barrier-forming proteins. Mechanistically, a pathway involving the receptor of advanced glycation end products and mitogen-activated protein kinase was identified. The methylglyoxal-scavenging dipeptide anserine (β-alanyl-N-methylhistidine) reduced methylglyoxal-induced advanced glycation end-product formation and disruptions of junctional complexes in vitro. Moreover, anserine reduced capillary leakage and mortality in vivo.

INTERPRETATION

Methylglyoxal causally contributes to capillary leak formation and mortality in experimental sepsis, which can be mitigated by anserine. Therefore, anserine represents an innovative therapeutic option for the treatment of septic shock.

FUNDING

German Research Foundation (grant number BR 4144/2-1).

CD5L as a promising biological therapeutic for treating sepsis

Sepsis results from systemic, dysregulated inflammatory responses to infection, culminating in multiple organ failure. Here, we demonstrate the utility of CD5L for treating experimental sepsis caused by cecal ligation and puncture (CLP). We show that CD5L's important features include its ability to enhance neutrophil recruitment and activation by increasing circulating levels of CXCL1, and to promote neutrophil phagocytosis. CD5L-deficient mice exhibit impaired neutrophil recruitment and compromised bacterial control, rendering them susceptible to attenuated CLP. CD5L-/- peritoneal cells from mice subjected to medium-grade CLP exhibit a heightened pro-inflammatory transcriptional profile, reflecting a loss of control of the immune response to the infection. Intravenous administration of recombinant CD5L (rCD5L) in immunocompetent C57BL/6 wild-type (WT) mice significantly ameliorates measures of disease in the setting of high-grade CLP-induced sepsis. Furthermore, rCD5L lowers endotoxin and damage-associated molecular pattern (DAMP) levels, and protects WT mice from LPS-induced endotoxic shock. These findings warrant the investigation of rCD5L as a possible treatment for sepsis in humans.

Sepsis sensitizes behavioural amphetamine responses while inducing inflammatory and neurotrophic vulnerability in the cecal ligation and puncture model

The present study aimed to evaluate if sepsis sensitizes behavioural and biochemical responses induced by m-amphetamine. For this, Wistar rats were submitted to the cecal ligation and puncture. After 30 days of cecal ligation and puncture procedure, the animals were submitted to a single intraperitoneal injection of saline or m-amphetamine (.25, .50, or 1.0 mg/kg). Locomotor behaviour was assessed 2 h after the administration. Interleukin (IL)-1β, IL-6, IL-10, tumour necrosis factor-α, dopamine-cAMP-regulated phosphoprotein of 32,000 kDa (DARPP-32) and neuronal calcium sensor (NCS-1) levels were evaluated in the frontal cortex, hippocampus and striatum. Also, brain-derived neurotrophic factor (BDNF), neuronal growth factor and glial-derived neurotrophic factor levels were assessed in the hippocampus. M-amphetamine alone (.25 and 1.0 mg/kg) increased rats' locomotion and exploratory behaviour compared with the Sham + Sal. Animals from the cecal ligation and puncture + m-amphetamine (.5 and/or 1.0 mg/kg) group showed an increase in locomotion, exploratory and risk-like behaviour when compared with the Sham + Saline group and with its respective Sham groups. Cecal ligation and puncture increased interleukin levels compared with the Sham + Sal. However, cecal ligation and puncture animals that received m-amphetamine (1 mg/kg) increased even more, these inflammatory parameters compared with the Sham + Sal and the cecal ligation and puncture + saline group. M-amphetamine at lower doses increased neurotrophic factors, but higher doses decreased these parameters in the brain of cecal ligation and puncture rats. M-amphetamine dose-dependently increased DARPP-32 and NCS-1 levels in cecal ligation and puncture rats in some structures. In conclusion, these results demonstrate that sepsis sensitizes behavioural amphetamine responses while inducing inflammatory and neurotrophic vulnerability in the cecal ligation and puncture model.

Tomatidine activates autophagy to improve lung injury and inflammation in sepsis by inhibiting NF-κB and MAPK pathways

Sepsis-induced acute lung injury (ALI) is a life-threatening medical condition with high mortality and morbidity. Autophagy is involved in the pathophysiological process of sepsis-induced ALI, including inflammation, which indicates that regulating autophagy may be beneficial for this disease. Tomatidine, a natural compound abundant in unripe tomatoes, has been reported to have anti-inflammatory, anti-tumorigenic, and lipid-lowering effects. However, the biological functions and mechanisms of tomatidine in sepsis-induced ALI remain unknown. The principal objective of this study was to investigate the effect of tomatidine on sepsis-induced ALI. Cecal ligation and puncture (CLP) was used to induce septic lung injury in mice, and 10 mg/kg tomatidine was intraperitoneally injected into mice 2 h after the operation. The results of hematoxylin and eosin staining and assessment of lung edema and total protein levels in bronchoalveolar lavage fluid (BALF) demonstrated that tomatidine alleviated CLP-induced severe lung injuries such as hemorrhage, infiltration of inflammatory cells, and interstitial and alveolar edema in mice. Additionally, the levels of proinflammatory cytokines in BALF and lung tissues were measured by enzyme-linked immunosorbent assay (ELISA), and the results showed that tomatidine inhibited CLP-induced inflammatory damage to lungs. Moreover, the results of western blotting showed that tomatidine promoted autophagy during CLP-induced ALI. Mechanistically, immunofluorescence staining and western blotting were used to measure the protein levels of TLR4, phosphorylated NF-κB, phosphorylated IκBα, and phosphorylated MAPKs, showing that tomatidine inactivated NF-κB and MAPK signaling in lung tissues of CLP-induced ALI mice. In conclusion, tomatidine exerts protective effects against sepsis-induced severe damage to the lungs by inhibiting inflammation and activating autophagy in CLP-treated mice through inactivating the NF-κB and MAPK pathways, which may be an effective candidate for treating septic ALI.

Sepsis and obesity: a scoping review of diet-induced obesity murine models

BACKGROUND

Sepsis, the life-threatening host response to infection, is a major cause of mortality. Obesity increases vulnerability to sepsis; however, some degree of obesity may be protective, called the "obesity paradox". This scoping review systematically maps the literature on outcomes associated with diet-induced obesity and sepsis-induced organ injury, focusing on non-transgenic murine models.

METHODS

A literature search of primary articles was conducted from database inception to June 2023. Eligible articles compared diet-induced obesity to non-obese mice in sepsis models involving live pathogens. Two reviewers screened articles and extracted data on obesogenic and sepsis models utilized, and organ injury outcomes, including physiological dysfunction, histological alterations, and biochemical changes.

RESULTS

Seventeen studies met eligibility criteria; 82% used male C57BL/6 mice, and 88% used cecal ligation and puncture to induce sepsis. Most studies used 60% high-fat diets compared to 10-16% fat in controls. Seven (64%) studies reported increased mortality in obese septic mice, one (9%) observed a decrease, and three (37%) found no significant difference. The liver, lungs, and kidneys were the most studied organs. Alanine transaminase results were inconclusive. Myeloperoxidase levels were increased in the livers of two studies and inconclusive in the lungs of obese septic mice. Creatinine and neutrophil gelatinase-associated lipocalin were elevated in obese septic mice.

CONCLUSIONS

There is variability in the methodology and measured outcomes in murine models of diet-induced obesity and sepsis and a lack of studies in female mice. The absence of standardized models has produced conflicting findings on the impact of obesity on sepsis outcomes.

Sepsis-Induced Inhibition of Contractile Function of Lymphatic Nodes

Inflammation accompanies most pathological processes, while the lymphatic system takes part in both the development and resolution of inflammation. We studied the contractile function of rat lymph nodes after cecal ligation and puncture (CLP). In 24 h after CLP, the mesenteric lymph nodes were removed and placed in the myograph chamber. After CLP, the lymph nodes showed lower tension than lymph nodes from sham-operated animals (control). The expression of inducible NO synthase, cyclooxygenase-2, and cystathionine-γ-lyase was observed in the lymph nodes of CLP rats. NO, prostaglandins, and H2S formed during inflammation inhibited contractile activity of smooth muscle cells in the capsule of the lymph nodes, which manifested itself in inhibition of phase contractions and a decrease in the tone of their capsule.

Targeting sting to reduce sepsis-induced acute intestinal injury

BACKGROUND

Sepsis is a dysregulated host response to infection syndrome leading to life-threatening organ dysfunction. Sepsis-induced intestinal dysfunction is a key element in the progression to multisystem organ failure. The stimulator of interferon genes is an intracellular protein implicated in intestinal injury in sepsis. H151, a small molecule inhibitor of stimulator of interferon genes, has not yet been studied as a potential therapeutic in sepsis. We hypothesize that H151 therapeutically reduces sepsis-induced acute intestinal injury.

METHODS

Male mice underwent cecal ligation and puncture and were treated with intraperitoneal H151 (10 mg/kg body weight) or vehicle. Intestines and serum were collected for analysis 20 hours after cecal ligation and puncture. Oral gavage of mice with FITC-dextran was performed 15 hours after cecal ligation and puncture. Five hours after gavage, serum was collected, and intestinal permeability was assessed. Mice were monitored for 10 days after cecal ligation and puncture to assess survival.

RESULTS

Zonula occludens 1 tight junctional protein expression was reduced after cecal ligation and puncture and recovered with H151 treatment. This was associated with a 62.3% reduction in intestinal permeability as assessed by fluorimetry. After cecal ligation and puncture, treatment with H151 was associated with a 58.7% reduction in intestinal histopathologic injury (P < .05) and a 56.6% reduction in intestinal apoptosis (P < .05). Intestinal myeloperoxidase activity was decreased by 70.8% after H151 treatment (P < .05). Finally, H151 improved 10-day survival from 33% to 80% after cecal ligation and puncture (P = .011).

CONCLUSION

H151, a novel stimulator of interferon genes inhibitor, reduces intestinal injury, inflammation, and permeability when administered as a treatment for cecal ligation and puncture-induced sepsis. Thus, targeting stimulator of interferon genes shows promise as a therapeutic strategy to ameliorate sepsis-induced acute intestinal injury.

EXTRACELLULAR CIRP INHIBITS NEUTROPHIL APOPTOSIS TO PROMOTE ITS AGING BY UPREGULATING SERPINB2 IN SEPSIS

ABSTRACT

Background: Sepsis reduces neutrophil apoptosis. As the result, neutrophils may become aged, exacerbating inflammation and tissue injury. Extracellular cold-inducible RNA-binding protein (eCIRP) acts as a damage-associated molecular pattern to promote inflammation and tissue injury in sepsis. SerpinB2, a serine protease inhibitor, has been shown to inhibit apoptosis. We hypothesize that eCIRP upregulates SerpinB2 to promote aged neutrophil subset by inhibiting apoptosis in sepsis. Methods: We stimulated bone marrow-derived neutrophils (BMDNs) of wild-type (WT) mice with 1 μg/mL of recombinant mouse CIRP (i.e., eCIRP) and assessed cleaved caspase-3 and SerpinB2 by western blotting. Apoptotic neutrophils were assessed by Annexin V/PI. Bone marrow-derived neutrophils were stimulated with 1 μg/mL eCIRP and treated with or without PAC-1 (caspase-3 activator) and aged neutrophils (CXCR4 hi CD62L lo ) were assessed by flow cytometry. To induce sepsis, we performed cecal ligation and puncture in WT or CIRP -/- mice. We determined the percentage of aged neutrophils and SerpinB2 + neutrophils in blood and spleen by flow cytometry. Results: We found that cleaved caspase-3 levels were increased at 4 h of PBS treatment compared with 0 h but decreased by eCIRP treatment. Extracellular cold-inducible RNA-binding protein reduced apoptotic cells after 20 h of treatment. Extracellular cold-inducible RNA-binding protein also increased the frequencies of aged neutrophils compared with PBS after 20 h, while PAC-1 treatment reduced aging in eCIRP-treated BMDNs. Extracellular cold-inducible RNA-binding protein significantly increased the expression of SerpinB2 at protein levels in BMDNs at 20 h. In WT mice, the frequencies of aged and SerpinB2 + neutrophils in blood and spleen were increased after 20 h of cecal ligation and puncture, while in CIRP -/- mice, aged and SerpinB2 + neutrophils were significantly decreased compared with WT mice. We also found that aged neutrophils expressed significantly higher levels of SerpinB2 compared with non-aged neutrophils. Conclusions: eCIRP inhibits neutrophil apoptosis to increase aged phenotype by increasing SerpinB2 expression in sepsis. Thus, targeting eCIRP could be a new therapeutic strategy to ameliorate inflammation caused by neutrophil aging in sepsis.