Retinoids, ω-hydroxyfatty acids and cytotoxic aldehydes as physiological substrates, and H<inf>2</inf>-receptor antagonists as pharmacological inhibitors, of human class IV alcohol dehydrogenase

Kinetic constants of human class IV alcohol dehydrogenase (σσ-ADH) support a role of the enzyme in retinoid metabolism, fatty acid ω- oxidation, and elimination of cytotoxic aldehydes produced by lipid peroxidation. Class IV is the human ADH form most efficient in the reduction of 4-hydroxynonenal (k(cat)/K(m) : 39 500 mM-1 min-1). Class IV shows high activity with all-trans-retinol and 9-cis-retinol, while 13-cis-retinol is not a substrate but an inhibitor. Both all-trans-retinoic and 13-cis- retinoic acids are potent competitive inhibitors of retinol oxidation (K(i): 3-10 μM) which can be a basis for the regulation of the retinoic acid generation and of the pharmacological actions of the 13-cis-isomer. The inhibition of class IV retinol oxidation by ethanol (K(i) : 6-10 mM) may be the origin of toxic and teratogenic effects of ethanol. H2-receptor antagonists are poor inhibitors of human and rat classes I and IV (K(i) > 0.3 mM) suggesting a small interference in ethanol metabolism at the pharmacological doses of these common drugs.