Alcohol and a high-fat diet synergistically induce hepatic inflammation and fibrosis via TLR4

Aims: Alcoholic steatohepatitis (ASH) and non-alcoholic steatohepatitis (NASH) are the most frequent conditions leading to elevated liver enzymes and liver cirrhosis in the Western World. However and despite strong epidemiological evidence for combined effects on the progression of liver injury the mutual interaction of the pathophysiological mechanisms is incompletely understood. The aim of this study was to establish and analyze an experimental murine model, where we combined chronic alcohol administration in drinking water (increasing concentrations up to 5%) with a NASH inducing high-fat (HF) diet for six weeks. Results: HF-diet significantly induced hepatic triglyceride accumulation and expression of proinflammatory genes, while alcohol alone had only a slight effect on hepatic steatosis and inflammation compared to control mice or mice fed only HF-diet, respectively. In contrast, alcohol as well as HF-diet led to a marked increase of profibrogenic genes (collagen type I and transforming growth factor-beta), activation of hepatic stellate cells, and extracellular matrix deposition in the liver tissue, and noteworthy, the combination of both alcohol and HF-diet led to a further marked induction of hepatic fibrosis. Moreover, endotoxin levels in the portal circulation were significantly elevated in mice which received alcohol or HF-diet and were further significantly increased in those receiving both. Furthermore and surprisingly, HF-diet and its combination with alcohol led to a markedly increased hepatic expression of the endotoxin receptor Toll-like receptor 4 (TLR4), which is known to play a crucial role in hepatic fibrosis. Conclusion: This new model allows the investigation of isolated or joint effects of alcohol and HF-diet on hepatic injury including significant hepatic fibrosis in the histology, with alcohol and HF-diet acting synergistically on the development of hepatic fibrosis, potentially via enhanced TLR4 signaling.

ASH - Fibrosis - NASH - TLR4 - synergism