Coffee reduces liver damage in a rat model of steatohepatitis: the underlying mechanisms and the role of polyphenols and melanoidins

Epidemiological data associate coffee consumption with a lower prevalence of chronic liver disease and a reduced risk of elevated liver enzyme levels (gamma glutamyl transpeptidase and alanine aminotransferase), advanced liver disease and its complications, and hepatocellular carcinoma. Knowledge of the mechanisms underlying these effects and the coffee components responsible for these properties is still lacking. In this study, 1.5 mL/day of decaffeinated coffee or its polyphenols or melanoidins (corresponding to approximately 2 cups of filtered coffee or 6 cups of espresso coffee for a 70-kg person) were added for 8 weeks to the drinking water of rats who were being fed a high-fat, high-calorie solid diet (HFD) for the previous 4 weeks. At week 12, HFD + water rats showed a clinical picture typical of advanced nonalcoholic steatohepatitis compared with control rats (normal diet + water). In comparison, HFD + coffee rats showed: (1) reduced hepatic fat and collagen, as well as reduced serum alanine aminotransferase and triglycerides; (2) a two-fold reduced/oxidized glutathione ratio in both serum and liver; (3) reduced serum malondialdehyde (lipid peroxidation) and increased ferric reducing antioxidant power (reducing activity); (4) reduced expression of tumor necrosis factor alpha (TNF-alpha), tissue transglutaminase, and transforming growth factor beta and increased expression of adiponectin receptor and peroxisome proliferator-activated receptor alpha in liver tissue; and (5) reduced hepatic concentrations of proinflammatory TNF-alpha and interferon-gamma and increased anti-inflammatory interleukin-4 and interleukin-10. Conclusion: Our data demonstrate that coffee consumption protects the liver from damage caused by a high-fat diet. This effect was mediated by a reduction in hepatic fat accumulation (through increased fatty acid beta-oxidation); systemic and liver oxidative stress (through the glutathione system); liver inflammation (through modulation of genes); and expression and concentrations of proteins and cytokines related to inflammation.