Search

Morphological and functional alterations of hepatic mitochondria have been docu- mented in patients with alcoholic liver disease (ALD). Our recent study demonstrated that zinc level was decreased in whole liver and mitochondria by chronic alcohol feeding. The present study was undertaken to determine whether zinc deficiency mediates alcohol- induced mitochondrial electron transport chain (ETC) defect and whether defective ETC function may lead to generation of reactive oxygen species (ROS). Male Wistar rats were pair fed with the Lieber-DeCarli control or ethanol diet for 5 mo. Chronic alcohol exposure increased hepatic triglyceride, free fatty acid, and 4-hy- droxynonenal (4HNE) levels; meanwhile hepatic mitochondrial 4HNE level was also increased. Moreover, hepatic mitochondrial respiratory complexes I, III, IV, and V and hepatic ATP production were decreased by chronic alcohol exposure. Chronic alcohol feeding decreased peroxisome proliferator-activated receptor gamma coacti- vator-1-alpha (PGC1a.), nuclear respiratory factor 1 (NRF1), mito- chondrial transcription factor A (TFAM), and mitochondrial DNA. HepG2 cells were treated with N,N,N=,N=-tetrakis (2-pyridylmethyl) ethylenediamine (TPEN) for 6 h. Zinc deficiency significantly de- creased mitochondrial respiratory complexes I, III, and IV. In addi- tion, PGC1a., NRF1, and TFAM levels as well as mitochondrial DNA were significantly decreased by TPEN treatment. Knockdown of mitochondrial respiratory complexes I, III, or IV by shRNA caused a decrease in mitochondrial membrane potential and an increase in ROS production. These results suggest that alcohol-induced hepatic zinc deficiency could inactivate mitochondrial biogenesis pathway and decrease mitochondrial DNA replication, which, in turn, decreases mitochondrial complex protein expression. The defect of mitochon- drial respiratory complexes may worsen alcohol-induced ROS pro- duction. [ABSTRACT FROM AUTHOR]

Hepatic zinc deficiency has been well documented in alcoholic patients, but the mechanisms by which zinc deficiency mediates cell death have not been well defined. The objectives of this study were to determine whether alcohol perturbs subcellular zinc homeostasis and how organelle zinc depletion may link with cell death pathways. Wistar rats were pair-fed with the Lieber-DeCarli control or ethanol diet for 5 mo. Chronic alcohol exposure significantly reduced zinc level in isolated hepatic endoplasmic reticulum (ER) and mitochondria. Among the detected zinc transporters, ER Zrt/Irt-like protein (ZIP)13 and mitochondrial ZIP8, which transport zinc from ER and mitochondria to cytosol, were significantly increased. Mitochondrial zinc transporter (ZnT) 4, which transports zinc from cytosol to mitochondria, was also increased. ER phosphorylated eukaryotic initiation factor 2α, activating transcription factor 4, and C/EBP homologous protein were significantly upregulated, and mitochondrial cytochrome c release and Bax insertion were detected in association with caspase-3 activation and apoptotic cell death. To define the role of zinc deficiency in ER and mitochondrial stress, H4IIEC3 cells were treated with 3 μM N,N,N'=,N'=-tetrakis (2-pyridylmethyl) ethylenediamine for 6 h with or without supplementation with zinc or N-acetylcysteine (NAC). The results demonstrated that zinc deprivation induced caspase-3 activation and apoptosis in association with ER and mitochondria dysfunction, which were inhibited by zinc as low as 10 μM but not by 2 mM NAC. These results suggest that chronic ethanol exposure induced in ER and mitochondrial zinc deficiency might activate intrinsic cell death signaling pathway, which could not be effectively rescued by antioxidant treatment. [ABSTRACT FROM AUTHOR]