Acetaldehyde does not inhibit glutathione peroxidase and glutathione reductase from mouse liver in vitro.

Acetaldehyde, the primary ethanol metabolite, has been implicated in the pathogenesis of alcoholic liver disease, but the mechanism involved is still under investigation. This study aims at the search for direct in vitro effects of different concentrations of acetaldehyde (30, 100 and 300microM) on the activities of glutathione reductase (GR), glutathione peroxidase (GPx) from liver supernatants, and the thiol-peroxidase activity of ebselen. They did not change after pre-incubation with acetaldehyde, which suggests that acetaldehyde does not have any direct effect. Nor were direct effects of acetaldehyde toward thiols, such as dithioerythritol and glutathione (GSH), observed either, even though GSH - measured as non-protein thiols from liver supernatants - were oxidized in the presence of acetaldehyde. In addition, acetaldehyde (up to 300microM) significantly oxidized GSH when incubated in the presence of commercially available gamma-glutamyltranspeptidase (GGT), but not in the presence of glutathione-S-transferase. The interaction between ebselen and GSH was also evaluated in an attempt to better understand the possible link between acetaldehyde and nucleophilic selenol groups. The formation and stability of ebselen intermediaries, produced in the chemical interaction between GSH and ebselen, were not affected by acetaldehyde either. Overall, the acetaldehyde oxidation of hepatic low-molecular thiols depends on mouse liver constituents and GGT is proposed as an important enzyme involved in this phenomenon. Thiol depletion, a phenomenon usually observed in the livers of alcoholic patients, can be related to GSH metabolism, and the involvement of GGT may reflect a molecular mechanism involved in thiol oxidation.

Effects of ethanol and diphenyl diselenide exposure on the activity of delta-aminolevulinate dehydratase from mouse liver and brain.

Ethanol toxicity is affected by both environmental and inherited features. Since oxidative stress is an important molecular mechanism for ethanol-induced cellular damage, the concomitant exposure to ethanol and pro-oxidative or antioxidant compounds can alter its toxicity. Here, we investigate the effects of exposure to ethanol and/or diphenyl diselenide, an organochalcogen with antioxidant properties, on parameters related to oxidative stress (thiobarbituric acid reactive species-TBARS-and delta-aminolevulinate dehydratase-delta-ALA-D activity) in mouse liver and brain. In addition, the in vitro effects of ethanol and acetaldehyde on the activity of delta-ALA-D from human erythrocytes were also investigated. Both ethanol and diphenyl diselenide decreased hepatic delta-ALA-D activity and DL-dithiothreitol (DTT) reactivated this enzyme only after ethanol-induced inhibition. Moreover, ethanol increased liver TBARS levels, independently of the presence of diphenyl diselenide treatment. Brain delta-ALA-D activity and TBARS levels were not changed by ethanol or diphenyl diselenide exposure. Under in vitro conditions, acetaldehyde was a more potent inhibitor of delta-ALA-D from human erythrocytes when compared to ethanol, demonstrating a dose-dependent effect. This study indicates that (1) hepatic delta-ALA-D is a molecular target for the damaging effect of ethanol under in vivo conditions; (2) diphenyl diselenide and ethanol seem to inhibit delta-ALA-D by different mechanisms; (3) acetaldehyde, a metabolite of ethanol, is probably the main molecule responsible for the inhibitory effects of the parent compound on delta-ALA-D.

Ethanol inhibits δ-aminolevulinate dehydratase and glutathione peroxidase activities in mice liver: Protective effects of ebselen and N-acetylcysteine.

Changes in sulfhydryl status have been shown to be involved with the ethanol-induced hepatotoxicity. In addition, evidence shows the importance of replenishing thiols in patients with alcoholic liver disease. This study was undertaken to examine the possible beneficial effects of the individual and simultaneous treatments with two antioxidant drugs (N-acetylcysteine and ebselen) against ethanol-induced changes in thiol status, as well as on the activities of δ-aminolevulinate dehydratase (δ-ALA-D) and glutathione peroxidase (GPx) in mice liver. Daily ethanol administrations (3g ethanol/kg, by gavage) decreased liver nonprotein thiols (NPSH) concentration after 30 days of treatment and N-acetylcysteine (300mg/kg once a day, i.p.) or ebselen (5mg/kg once a day, subcutaneously) treatment restored this variable to control levels. However, additive beneficial effects concerning NPSH levels were not observed after the simultaneous administration with both drugs. While liver GPx and δ-ALA-D activities were inhibited by ethanol exposure and these inhibitions were significantly blunted by N-acetylcysteine or ebselen treatment, the simultaneous administration with both drugs did not show additive beneficial effects in relation to the enzymes' activities. NPSH levels were positively correlated with GPx and δ-ALA-D activities. The results presented herein show that ebselen and N-acetylcysteine alone are able to restore ethanol-induced thiols as well as the inhibition of hepatic enzymes whose catalytic functions depend on their thiol (δ-ALA-D) and selenol (GPx) groups.