Gut inflammation exacerbates hepatic injury in C57BL/6J mice via gut-vascular barrier dysfunction with high-fat-incorporated meat protein diets

AIM

Meat and its derivatives provide nutrients essential for human health. However, meat consumption, along with excessive fat intake, has been associated with gut inflammation, intestinal barrier dysfunction and alterations in gut microbiota. Herein, we investigated whether and how these changes in the intestinal barrier system affect the gut liver axis and hepatic injury and eventually lead to the progression of liver syndrome such as NAFLD.

METHODS

Mice were fed with high fat (60% kcal) or low fat (12% kcal) along with soybean (control), chicken and pork proteins (HFCH, HFP, LFCH, and LFP) for 12 weeks. The biomarkers for liver injury were investigated after meat protein intake along with the high fat.

FINDINGS

Greater amount of fat vacuoles visible in the H&E staining increased the inflammatory cell infiltration and disorganized liver structures were observed in the HFP-fed mice. Oil Red O staining revealed that the HFP-fed and HFCH-fed mice showed more lipid droplets, confirming the increased hepatic lipid accumulation. Potential serum markers for NAFLD, ALT and AST were increased in the HF meat diet groups. Key genes responsible for hepatic inflammation and lipogenesis, such as MCP-1, IL1-β and TNF-α were upregulated. HF meat protein diet-fed mice exhibited signs of compromised liver with increased levels of endotoxin in the liver and its binding protein in serum, upregulation of TLRs in the liver, and significant increase in TG, TC, LDL-C and HDL-C concentrations.

SIGNIFICANCE

Intestinal inflammation and barrier dysfunction aggravate liver injury and fibrosis due to the intake of HF meat protein diets in mice, which may contribute to the progress of liver injury and associated complications. Gut inflammation may directly contribute to the development of NAFLD, especially of the gut vascular barricade dysfunction.

Gut inflammation exacerbates hepatic injury in the high-fat diet induced NAFLD mouse: Attention to the gut-vascular barrier dysfunction

AIMS

Gut inflammation has been put forward to be associated with hepatic injury in the clinical practice. The dismantled intestinal barrier was highly concerned, however, largely unknown about the role of gut-vascular barrier (GVB) in this process. This study aimed to investigate if inflamed gut directly contributes to the progression of non-alcoholic steatohepatitis (NASH), especially attention to the GVB dysfunction.

MAIN METHODS

Male C57bl/6 mice were fed with a high-fat diet (HFD) and 1% DSS for 12 weeks. The colonic inflammatory injury as well as hepatic injury were evaluated. The GVB function was assessed via measuring the permeability to fluorescently-labeled dextran (70 kDa) and the expression of plasmalemma vesicle-associated protein-1 (PV1). Furthermore, the plasma endotoxin level and hepatic TLR4/TLR9 mRNA expression were detected.

KEY FINDINGS

There were evident colitis in DSS-exposed mice, which trend to be more apparent in HFD ones. The HFD + DSS mice exhibited more serious hepatic steatosis, inflammation and fibrosis than HFD groups. The downregulated tight junction protein in HFD + DSS mice indicated loss of epithelial barrier. The GVB disruption were also confirmed with increased permeability to macromolecules and high expression of endothelial PV1 in HFD + DSS mice. Accordingly, potentially elevated plasma endotoxin levels and markedly increased TLR4/TLR9 mRNA expression were demonstrated in HFD + DSS mice rather than HFD groups.

SIGNIFICANCE

Gut inflammation exacerbates liver injury and fibrosis in HFD mice, which may contribute to the development of NASH. Beyond the damaged intestinal epithelial barrier, GVB disruption with bacterial translocation into may play a key role in the pathogenesis of NASH.

Dysregulation of Systemic and Mucosal Humoral Responses to Microbial and Food Antigens as a Factor Contributing to Microbial Translocation and Chronic Inflammation in HIV-1 Infection

HIV-1 infection is associated with an early and profound depletion of mucosal memory CD4+ T cells, a population that plays an indispensable role in the regulation of isotype switching and transepithelial transport of antibodies. In this study, we addressed whether the depletion of CD4+ T cell in HIV-1-infected individuals results in altered humoral responses specific to antigens encountered at mucosal surfaces. Comprehensive protein microarray of systemic humoral responses to intestinal microbiota demonstrated reduced IgG responses to antigens derived from Proteobacteria and Firmicutes but not Bacteroidetes. Importantly, intestinal secretions of antiretroviral therapy-treated HIV-1-infected individuals exhibited a significant elevation of IgM levels and decreased IgA/IgM and IgG/IgM ratios of antibodies specific to a variety of microbial and food antigens. The presented findings indicate reduced competence of mucosal B cells for class switch recombination from IgM to other isotypes limiting their capacity to react to changing antigenic variety in the gut lumen. Decreased availability of microbiota-specific IgA and IgG may be an important factor contributing to the translocation of microbial antigens across the intestinal mucosal barrier and their systemic dissemination that drives chronic inflammation in HIV-1-infected individuals.