metallothionein and Liver-Diseases--Alcoholic

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.

Topics: Animals; Humans; Lipid Metabolism; Liver; Liver Diseases, Alcoholic; Metallothionein; Oxidative Stress; Zinc

Oxidative stress is implicated in pathogenesis of alcoholic liver disease (ALD). This study investigated the possible correlation among the erythrocyte indices of oxidative stress, the leukocyte panels of antioxidant proteins (metallothioneins), the serum biochemical parameters and the liver steatosis grade.. A total of 118 cases including 60 alcoholic subjects and 58 controls were enrolled. All the alcoholic subjects were screened for body mass index (BMI), liver steatosis, and blood chemistry and serology. The level of oxidative stress and oxidative stress-related parameters were measured in the blood and correlated with clinical findings.. Alcoholic subjects showed higher BMI, moderate/severe hepatic steatosis, increase in the levels of triglycerides, cholesterol, glucose, γ-glutamyl-transpeptidase (GGT), alanine aminotransferase (ALT), bilirubin, alpha 1 and beta 2 globulins, iron and a decrease in the levels of aspartate aminotransferase (AST) and beta 1 globulin with respect to the reference values. Moreover, alcoholic subjects showed: (i) an increase in Thiobarbituric Acid Reactive Substance (TBARS) content representing a good estimation of global oxidative stress; (ii) a stimulation of the activities of the antioxidant enzymes catalase and SOD; (iii) a modulation of expression of metallothioneins, with a down-regulation of MT-1A and an up-regulation of MT-1E isoforms.. Our data suggest that alcoholism is strongly associated with altered pattern of blood metallothioneins; this parameter combined with the score calculated by an ad hoc implemented algorithm (HePaTest) could offer a non-invasive alternative approach for evaluating alcohol-related damages and could be used in follow-up of alcoholic patients.

Topics: Adolescent; Adult; Alcoholism; Antioxidants; Case-Control Studies; Erythrocyte Indices; Fatty Liver; Humans; Leukocytes; Lipid Peroxidation; Liver Diseases, Alcoholic; Male; Metallothionein; Middle Aged; Oxidative Stress; Ultrasonography; Up-Regulation; Young Adult

Alcoholic liver disease is associated with zinc decrease in the liver. Therefore, we examined whether dietary zinc supplementation could provide protection from alcoholic liver injury. Metallothionein-knockout and wild-type 129/Sv mice were pair-fed an ethanol-containing liquid diet for 12 weeks, and the effects of zinc supplementation on ethanol-induced liver injury were analyzed. Zinc supplementation attenuated ethanol-induced hepatic zinc depletion and liver injury as measured by histopathological and ultrastructural changes, serum alanine transferase activity, and hepatic tumor necrosis factor-alpha in both metallothionein-knockout and wild-type mice, indicating a metallothionein-independent zinc protection. Zinc supplementation inhibited accumulation of reactive oxygen species, as indicated by dihydroethidium fluorescence, and the consequent oxidative damage, as assessed by immunohistochemical detection of 4-hydroxynonenal and nitrotyrosine and quantitative analysis of malondialdehyde and protein carbonyl in the liver. Zinc supplementation suppressed ethanol-elevated cytochrome P450 2E1 activity but increased the activity of alcohol dehydrogenase in the liver, without affecting the rate of blood ethanol elimination. Zinc supplementation also prevented ethanol-induced decreases in glutathione concentration and glutathione peroxidase activity and increased glutathione reductase activity in the liver. In conclusion, zinc supplementation prevents alcoholic liver injury in an metallothionein-independent manner by inhibiting the generation of reactive oxygen species (P450 2E1) and enhancing the activity of antioxidant pathways.

Topics: Animals; Central Nervous System Depressants; Cytochrome P-450 CYP2E1; Dietary Supplements; Ethanol; Glutathione; Glutathione Peroxidase; Glutathione Reductase; Liver; Liver Diseases, Alcoholic; Metallothionein; Mice; Mice, Knockout; Oxidative Stress; Zinc

Antioxidants are likely potential pharmaceutical agents for the treatment of alcoholic liver disease. Metallothionein (MT) is a cysteine-rich protein and functions as an antioxidant. This study was designed to determine whether MT confers resistance to acute alcohol-induced hepatotoxicity and to explore the mechanistic link between oxidative stress and alcoholic liver injury. MT-overexpressing transgenic and wild-type mice were administrated three gastric doses of alcohol at 5 g/kg. Liver injury, oxidative stress, and ethanol metabolism-associated changes were determined. Acute ethanol administration in the wild-type mice caused prominent microvesicular steatosis, along with necrosis and elevation of serum alanine aminotransferase. Ultrastructural changes of the hepatocytes include glycogen and fat accumulation, organelle abnormality, and focal cytoplasmic degeneration. This acute alcohol hepatotoxicity was significantly inhibited in the MT-transgenic mice. Furthermore, ethanol treatment decreased hepatic-reduced glutathione, but increased oxidized glutathione along with lipid peroxidation, protein oxidation, and superoxide generation in the wild-type mice. This hepatic oxidative stress was significantly suppressed in the MT-transgenic mice. However, MT did not affect the ethanol metabolism-associated decrease in NAD(+)/NADH ratio or increase in cytochrome P450 2E1. In conclusion, MT is an effective agent in cytoprotection against alcohol-induced liver injury, and hepatic protection by MT is likely through inhibition of alcohol-induced oxidative stress.

Topics: Animals; Antioxidants; Ethanol; Liver; Liver Diseases, Alcoholic; Metallothionein; Mice; Mice, Inbred C57BL; Mice, Transgenic; Microscopy, Electron; Oxidative Stress

Previous studies using metallothionein (MT)-overexpressing transgenic mice have demonstrated that MT protects the liver from oxidative injury induced by alcohol. The mechanism of action of MT is unknown. Because MT primarily binds to zinc under physiological conditions and releases zinc under oxidative stress and zinc is an antioxidant element, it is likely that zinc mediates the protective action of MT. The present study was undertaken to determine the distinct role of zinc in hepatic protection from alcoholic injury. MT I/II-knockout (MT-KO) mice along with their wild-type controls were treated with three gastric doses of ethanol at 5 g/kg at 12-hour intervals. Zinc sulfate was injected intraperitoneally in a dosage of 5 mg/kg/day for 3 days before ethanol treatment. MT concentrations in MT-KO mice were very low and zinc concentrations in MT-KO mice were lower than in wild-type mice. Zinc treatment significantly elevated hepatic MT concentrations only in wild-type mice and increased zinc concentrations in both MT-KO and wild-type mice. Ethanol treatment caused degenerative morphological changes and necrotic appearance in the livers of MT-KO mice. Microvesicular steatosis was the only ethanol-induced change in the liver of wild-type mice. Ethanol treatment decreased hepatic glutathione concentrations and increased hepatic lipid peroxidation, and the concentrations of lipid peroxide products in the wild-type mice were lower than in the MT-KO mice. All of these alcohol-induced toxic responses were significantly suppressed by zinc treatment in both MT-KO and wild-type mouse livers. These results demonstrate that zinc, independent of MT, plays an important role in protection from alcoholic liver injury. However, MT is required to maintain high levels of zinc in the liver, suggesting that the protective action of MT in the liver is likely mediated by zinc.

Topics: Animals; Ethanol; Lipid Peroxidation; Liver; Liver Cirrhosis, Alcoholic; Liver Diseases, Alcoholic; Metallothionein; Mice; Mice, Knockout; Thiobarbituric Acid Reactive Substances; Zinc; Zinc Sulfate