Exendin-4 Exacerbates Burn-Induced Morbidity in Mice by Activation of the Sympathetic Nervous System

Theabrownins improve burn-induced kidney injury by increasing the levels of guanidinoacetic acid and fumaric acid

BACKGROUND

Burns are a common and serious health issue, with severe burn-induced acute kidney injury (AKI) being a major factor contributing to poor recovery and increased mortality in patients. Theabrownins (TBs), bioactive compounds formed during tea leaf fermentation, have shown promising effects on reducing inflammation, combating oxidative stress, and enhancing metabolic function. However, the roles and mechanisms of TBs in burn-induced kidney injury are still not fully understood.

METHODS

The dorsal skin of 3-month-old mice was exposed to hot water for 10 s to induce burn-related renal injury. The mice were then orally administered TBs (40 mg/kg and 400 mg/kg). After 24 h of treatment, the mice were sacrificed for tissue collection. Transcriptomic and metabolomic analyses were performed to identify the pathways modulated by TBs. Metabolomics revealed TB-associated renal metabolites, such as guanidinoacetic acid (GAA) and fumaric acid (FA). Renal tubular epithelial (HK2) cells pretreated with GAA and FA were exposed to hydrogen peroxide (H2O2), cisplatin (CDDP) and erastin to establish a cell injury model. Changes in the levels of relevant molecules were assessed using quantitative RT-PCR, Western blotting, and fluorescence staining.

RESULTS

TB treatment significantly increased the survival rate and reduced kidney injury in mice with burn injury. Multiomics analyses and molecular experimental validation revealed that TB treatment downregulated the inflammation, apoptosis, and ferroptosis pathways in the kidneys of mice with burn injury and increased the levels of the renal metabolites GAA and FA. Cellular experiments confirmed that GAA and FA alleviated H2O2-, CDDP- and erastin-induced renal tubular epithelial cell injury by inhibiting apoptosis and ferroptosis.

CONCLUSIONS

Burns induce inflammation and kidney damage by upregulating the apoptosis and ferroptosis pathways in renal tissue. TBs alleviate burn-induced renal apoptosis and ferroptosis by increasing the levels of GAA and FA in the kidneys, thereby ameliorating kidney damage. This study innovatively and systematically evaluated the ability of TBs to ameliorate burn-induced kidney injury and, for the first time, identified the potential mechanism by which TBs ameliorate burn-induced kidney damage by increasing the levels of the metabolites GAA and FA in the kidneys.

Kinetics of Inflammatory Mediators in the Immune Response to Burn Injury: Systematic Review and Meta-Analysis of Animal Studies

Burns are often accompanied by a dysfunctional immune response, which can lead to systemic inflammation, shock, and excessive scarring. The objective of this study was to provide insight into inflammatory pathways associated with burn-related complications. Because detailed information on the various inflammatory mediators is scattered over individual studies, we systematically reviewed animal experimental data for all reported inflammatory mediators. Meta-analyses of 352 studies revealed a strong increase in cytokines, chemokines, and growth factors, particularly 19 mediators in blood and 12 in burn tissue. Temporal kinetics showed long-lasting surges of proinflammatory cytokines in blood and burn tissue. Significant time-dependent effects were seen for IL-1β, IL-6, TGF-β1, and CCL2. The response of anti-inflammatory mediators was limited. Burn technique had a profound impact on systemic response levels. Large burn size and scalds further increased systemic, but not local inflammation. Animal characteristics greatly affected inflammation, for example, IL-1β, IL-6, and TNF-α levels were highest in young, male rats. Time-dependent effects and dissimilarities in response demonstrate the importance of appropriate study design. Collectively, this review presents a general overview of the burn-induced immune response exposing inflammatory pathways that could be targeted through immunotherapy for burn patients and provides guidance for experimental set-ups to advance burn research.

Exendin-4 Exacerbates Burn-Induced Mortality in Mice by Switching to Th2 Response

INTRODUCTION

To determine if Exendin-4 could be a therapeutic agent for burn-induced hyperglycemia.

MATERIALS AND METHODS

Male Balb/c mice received a bolus of Exendin-4 intraperitoneally immediately after 15% total body surface area scald injury. Tail glucose levels were recorded and T-cell functions were analyzed at 4 h and 24 h postburn (pb). Pancreatic pathology was observed consecutively. The secretions of cytokines were detected in serum, spleen, and lung. Apoptosis of splenic CD3+ T-cells was examined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling and flow cytometry.

RESULTS

Although Exendin-4 could attenuate burn-induced hyperglycemia in mice at 4 h pb, it accelerated their survival dose dependently with progressive depletion of splenocyte number. T-cell function underwent two-phasic changes following Exendin-4 treatment. Compared to placebo mice, T-cell from Exendin-4-treated mice was manifested with increased proliferation, while decreased IL-2 secretion and lower ratio of IL-4/IFN-γ at 4 h pb. However, at 24 h pb, it showed decreased proliferation, while increased IL-2 secretion and higher ratio of IL-4/IFN-γ. Exendin-4 could elicit higher circulating IL-6 and IL-10 levels at 4 h pb, which were pronounced in the lung at 24 h pb. In the meanwhile, severe inflammation could be found in the pancreas. At 24 h pb, the numbers of terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling or caspase-3 positive cells and the apoptosis of CD3+ T-cells were significantly increased in the spleens of Exendin-4 mice relative to placebo mice.

CONCLUSIONS

These data support a pathogenic role of Exendin-4 signaling during thermal injury, warning against its clinical application in acute insults.

GLP-1 Receptor Signaling Differentially Modifies the Outcomes of Sterile vs Viral Pulmonary Inflammation in Male Mice

A number of disease states, including type 2 diabetes (T2D), are associated with an increased risk of pulmonary infection. Glucagon-like peptide-1 (GLP-1) receptor agonists are used to treat T2D and exert anti-inflammatory actions through a single, well-defined GLP-1 receptor (GLP-1R). Although highly expressed in the lung, little is known about the role of the GLP-1R in the context of pulmonary inflammation. Here we examined the consequences of gain or loss of GLP-1R activity in infectious and noninfectious lung inflammation. We studied wild-type mice treated with a GLP-1R agonist, and Glp1r-/- mice, in the setting of bleomycin-induced noninfectious lung injury and influenza virus infection. Loss of the GLP-1R attenuated the severity of bleomycin-induced lung injury, whereas activation of GLP-1R signaling increased pulmonary inflammation via the sympathetic nervous system. In contrast, GLP-1R agonism reduced the pathogen load in mice with experimental influenza virus infection in association with increased expression of intracellular interferon-inducible GTPases. Notably, the GLP-1 receptor agonist liraglutide improved the survival rate after influenza virus infection. Our results reveal context-dependent roles for the GLP-1 system in the response to lung injury. Notably, the therapeutic response of GLP-1R agonism in the setting of experimental influenza virus infection may have relevance for ongoing studies of GLP-1R agonism in people with T2D susceptible to viral lung injury.