Targeting of mouse alcohol dehydrogenase genes Adh1, Adh3, and Adh4 resulted in null mutant mice that all developed and reproduced apparently normally but differed markedly in clearance of ethanol and formaldehyde plus metabolism of retinol to the signaling molecule retinoic acid. Following administration of an intoxicating dose of ethanol, Adh1 ؊/؊ mice, and to a lesser extent Adh4 ؊/؊ mice, but not Adh3 ؊/؊ mice, displayed significant reductions in blood ethanol clearance. Ethanol-induced sleep was significantly longer only in Adh1 ؊/؊ mice. The incidence of embryonic resorption following ethanol administration was increased 3-fold in Adh1 ؊/؊ mice and 1.5-fold in Adh4 ؊/؊ mice but was unchanged in Adh3 ؊/؊ mice. Formaldehyde toxicity studies revealed that only Adh3 ؊/؊ mice had a significantly reduced LD 50 value. Retinoic acid production following retinol administration was reduced 4.8-fold in Adh1 ؊/؊ mice and 8.5-fold in Adh4 ؊/؊ mice. Thus, Adh1 and Adh4 demonstrate overlapping functions in ethanol and retinol metabolism in vivo, whereas Adh3 plays no role with these substrates but instead functions in formaldehyde metabolism. Redundant roles for Adh1 and Adh4 in retinoic acid production may explain the apparent normal development of mutant mice.
The alcohol dehydrogenase (ADH)1 family consists of numerous enzymes able to catalyze the reversible oxidation of a wide variety of xenobiotic and endogenous alcohols to the corresponding aldehydes (1). Several distinct classes of vertebrate ADH have been described, all of which are cytosolic and zincdependent but differ in substrate specificities and gene expression patterns (2, 3). Three forms that are highly conserved in mammals and other vertebrates are class I ADH (ADH1), class III ADH (ADH3), and class IV ADH (ADH4); see Ref. 1 for ADH nomenclature. Biochemical studies indicate that these three ADHs are able to utilize a wide variety of alcohol and aldehyde substrates in vitro ranging from ethanol to formaldehyde to retinol. However, the precise functions of these enzymes are not yet well established. In humans, ADH4 demonstrates higher retinol dehydrogenase activity than ADH1 with ADH1 having higher ethanol dehydrogenase activity than ADH4 and ADH3 having insignificant retinol or ethanol dehydrogenase activity (4 -6). Instead, ADH3 has glutathione-dependent formaldehyde dehydrogenase activity, i.e. upon reaction of formaldehyde with glutathione to produce S-hydroxymethylglutathione, ADH3 oxidizes the hydroxymethyl group to a formyl group to produce S-formylglutathione, which is then the substrate for a hydrolase that regenerates glutathione and produces formate (7).The potential role of ADH1 and ADH4 in retinol metabolism is particularly interesting because this pathway produces retinoic acid, which is a physiological ligand controlling numerous retinoic acid receptor signaling pathways (8). Also, the potential dual roles of ADH1 and ADH4 as ethanol and retinol dehydrogenases have led us to propose that alcohol abuse may lead to ethanol inhibition of ADH-c...