Corticosterone induces rat liver alcohol dehydrogenase mRNA but not enzyme protein or activity

Overview of the role of alcohol dehydrogenase and aldehyde dehydrogenase and their variants in the genesis of alcohol-related pathology

Alcohol dehydrogenase (ADH) and mitochondrial aldehyde dehydrogenase (ALDH2) are responsible for metabolizing the bulk of ethanol consumed as part of the diet and their activities contribute to the rate of ethanol elimination from the blood. They are expressed at highest levels in liver, but at lower levels in many tissues. This pathway probably evolved as a detoxification mechanism for environmental alcohols. However, with the consumption of large amounts of ethanol, the oxidation of ethanol can become a major energy source and, particularly in the liver, interferes with the metabolism of other nutrients. Polymorphic variants of the genes for these enzymes encode enzymes with altered kinetic properties. The pathophysiological effects of these variants may be mediated by accumulation of acetaldehyde; high-activity ADH variants are predicted to increase the rate of acetaldehyde generation, while the low-activity ALDH2 variant is associated with an inability to metabolize this compound. The effects of acetaldehyde may be expressed either in the cells generating it, or by delivery of acetaldehyde to various tissues by the bloodstream or even saliva. Inheritance of the high-activity ADH β2, encoded by theADH2*2gene, and the inactiveALDH2*2gene product have been conclusively associated with reduced risk of alcoholism. This association is influenced by gene–environment interactions, such as religion and national origin. The variants have also been studied for association with alcoholic liver disease, cancer, fetal alcohol syndrome, CVD, gout, asthma and clearance of xenobiotics. The strongest correlations found to date have been those between theALDH2*2allele and cancers of the oro-pharynx and oesophagus. It will be important to replicate other interesting associations between these variants and other cancers and heart disease, and to determine the biochemical mechanisms underlying the associations.

The class I alcohol dehydrogenase gene is glucocorticoid-responsive in the rat hepatoma microcell hybrid cell line, 11-3

Expression of the class I alcohol dehydrogenase (ADH) gene in the rat hepatoma microcell hybrid cell line, 11-3, was examined. The steady-state level of ADH mRNA in 11-3 was approximately 2-fold higher than that or rat liver and Fao, the parental cell line of 11-3. Removal of steroid hormones by activated charcoal from the serum in which 11-3 cells were maintained resulted in a significant decrease in the level of ADH transcript. Dexamethasone at a concentration of 1 muM increased the ADH mRNA content in 11-3 in a time-dependent fashion, up to 48 hr after its addition to cells that had first been deprived of steroid hormones. In addition, levels of ADH transcript in cells treated with dexamethasone increased in a dose-dependent manner, and the concentration of dexamethasone required to achieve half-maximal activation was 5 nM. By using the techniques of reverse transcription and polymerase chain reaction, and by taking advantage of a restriction polymorphism present between the rat and mouse ADH cDNA, we found that 11-3 contained both the rat and mouse class I ADH transcripts, although the rat sequence accounted for the great majority. Moreover, levels of both rat and mouse class I ADH transcripts increased in a similarly time-dependent manner in cells treated with dexamethasone. These results indicate that expression of class I ADH gene in 11-3 is high and is regulated by glucocorticoids, making the cell line an excellent model for the in vitro study of ADH expression.

Pharmacological aspects of gonadal alcohol and aldehyde-dehydrogenase

1. A brief overview of gonadal alcohol dehydrogenase (ADH) and aldehyde-dehydrogenase (ALDH) is presented and their relationships to gonadal toxicity of ethanol has been discussed. 2. The distributions of ADH and ALDH among major reproductive tissues of rodents, their subcellular localization and kinetic properties were summarized. 3. The sensitivity of testicular ADH and ALDH to ethanol intake, various psychoactive agents and steroidal compounds was assessed and the implication of these enzymes in gonadal ethanol-drug interaction has been suggested. 4. The possible role of testicular ALDH in tumorigenesis and in high altitude endocrine sensitivity to ethanol has been addressed.

Effects of thyroxine on the expression of alcohol dehydrogenase in rat liver and kidney

We studied the effect of thyroxine on alcohol dehydrogenase activity, immunoreactive protein levels and messenger RNA levels in the livers of thyroidectomized and sham-operated male rats. Effects on kidney alcohol dehydrogenase activity were also examined. Sham-operated rats injected with 100 micrograms thyroxine/kg/day, which induced hyperthyroidism, showed a 30% decrease in liver and a 40% decrease in kidney alcohol dehydrogenase activity compared with sham-operated rats injected with vehicle. Hypothyroid rats exhibited a 1.5-fold increase in alcohol dehydrogenase activity in liver and kidney compared with thyroidectomized rats injected with a replacement dose of 20 micrograms thyroxine/kg/day. We saw a twofold and a 2.5-fold higher level of alcohol dehydrogenase activity in liver and kidney, respectively, of hypothyroid rats compared with hyperthyroid rats. These effects were not accounted for by nutritional differences; daily food intake did not differ between groups. Immunoreactive protein levels as seen on Western blots varied in the same direction as enzyme activity. Northern-blot analysis showed higher levels of liver alcohol dehydrogenase messenger RNA in hypothyroid rats compared with euthyroid rats. These studies show that liver alcohol dehydrogenase activity and protein levels are modulated by thyroxine at pathophysiologically relevant levels and that this effect is not due to changes in food intake; kidney alcohol dehydrogenase activity is regulated in parallel. The change in alcohol dehydrogenase activity appears to be controlled in part by pretranslational mechanisms in hypothyroid animals and by posttranslational mechanisms in hyperthyroid animals.