Zinc and alcoholic liver disease

Zinc deficiency is one of the most consistent nutritional/biochemical observations in alcoholic liver disease (ALD). The objectives of our research are to determine how alcohol interferes with cellular zinc homeostasis and if zinc deficiency is a causal factor in the development of ALD. Metallothionein (MT) is a major protein responsible for cellular zinc homeostasis. MT-transgenic (MT-TG) mice with hepatic overexpression of MT and elevation of zinc level were resistant to ethanol-induced liver injury. MT-knockout (MT-KO) mice with a reduction of hepatic zinc were more susceptible to alcohol toxicity. However, zinc treatment also provided beneficial effects on alcohol hepatoxicity in MT-KO mice, suggesting a MT-independent action. Dietary zinc supplementation normalized hepatic zinc level and attenuated the pathological changes in the liver of mice chronically fed alcohol. Several mechanisms were involved in zinc action against alcoholic cytotoxicity. Zinc enhanced cellular antioxidant capacity and corrected alcohol metabolic switch from alcohol dehydrogenase to cytochrome P4502E1. Zinc attenuated cytokine production and TNF-α receptor- and Fas-mediated cell death pathways. Zinc restored activities of hepatocyte nuclear factor-4α (HNF-4α) and peroxisome proliferation activator-α (PPAR-α), and enhanced hepatic fatty acid β-oxidation and lipid secretion. Hepatoma cell cultures showed that zinc deprivation induces lipid accumulation via inactivating HNF-4α and PPAR-α. These results suggest that alcohol exposure interferes with hepatic zinc homeostasis, leading to cellular zinc deprivation. Inactivation of zinc proteins due to zinc release is likely an important molecular mechanism in the pathogenesis of ALD.