Nonalcoholic fatty liver disease (NAFLD) and its advanced stage, nonalcoholic steatohepatitis (NASH), are the most common causes of chronic liver disease in the United States. NASH features the metabolic syndrome, inflammation, and fibrosis. Probiotics exhibit immunoregulatory and anti-inflammatory activity. We tested the hypothesis that probiotic VSL#3 may ameliorate the methionine-choline-deficient (MCD) diet-induced mouse model of NASH. MCD diet resulted in NASH in C57BL/6 mice compared to methionine-choline-supplemented (MCS) diet feeding evidenced by liver steatosis, increased triglycerides, inflammatory cell accumulation, increased tumor necrosis factor α levels, and fibrosis. VSL#3 failed to prevent MCD-induced liver steatosis or inflammation. MCD diet, even in the presence of VSL#3, induced up-regulation of serum endotoxin and expression of the Toll-like receptor 4 signaling components, including CD14 and MD2, MyD88 adaptor, and nuclear factor κB activation. In contrast, VSL#3 treatment ameliorated MCD diet-induced liver fibrosis resulting in diminished accumulation of collagen and α-smooth muscle actin. We identified increased expression of liver peroxisome proliferator-activated receptors and decreased expression of procollagen and matrix metalloproteinases in mice fed MCD+VSL#3 compared to MCD diet alone. MCD diet triggered up-regulation of transforming growth factor beta (TGFβ), a known profibrotic agent. In the presence of VSL#3, the MCD diet-induced expression of TGFβ was maintained; however, the expression of Bambi, a TGFβ pseudoreceptor with negative regulatory function, was increased. In summary, our data indicate that VSL#3 modulates liver fibrosis but does not protect from inflammation and steatosis in NASH. The mechanisms of VSL#3-mediated protection from MCD diet-induced liver fibrosis likely include modulation of collagen expression and impaired TGFβ signaling.
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