The alcohol dehydrogenase (ADH) family is involved in the metabolism of both ethanol and retinoids. To quantitatively assess the potential contributions to first-pass metabolism of ethanol and the ethanol interference with retinoid homeostasis, saturation kinetics for ethanol oxidation as well as inhibition kinetics by ethanol for all-trans-retinol oxidation of human class I AA, β 1 β 1 , β 2 β 2 , γ 1 γ 1 , class II ππ, class III χχ, and class IV µµ were evaluated and compared. Class I and class II ADHs exhibited substrate inhibition with inhibition constants ranging over 250Ϫ720 mM (except γ 1 γ 1 ) ethanol. Class IV ADH displayed no appreciable inhibition up to 1 M ethanol. Activity of the class III enzyme (190 nM subunit) was undetectable at 250 mM ethanol. The kinetic simulations indicate that the hepatic ππ and the gastric µµ can most effectively contribute to first-pass metabolism of alcohol. The Michaelis constant (K m ), turnover number (k cat ), and catalytic efficiency (k cat /K m ) for retinol oxidation relative to that for ethanol oxidation in class I, class II, and class IV ADHs ranged over 0.00022Ϫ1.3, 0.071Ϫ0.48, and 0.24Ϫ650, respectively. Ethanol was a competitive inhibitor against retinol for class I, II, and IV ADHs with apparent inhibition constants ranging over 0.037Ϫ11 mM, indicating that retinoic acid synthesis through the ADH pathways can be tremendously blocked during social/heavy drinking. These findings support the notion that first-pass metabolism of alcohol may occur mainly in the liver through class II ππ and that cellular retinoid signaling may be perturbed by ethanol via ADH pathways.Keywords : alcohol dehydrogenase ; retinol oxidation; first-pass metabolism; fetal alcohol syndrome ; alcohol-related disease.Alcohol dehydrogenase (ADH) constitutes a complex en-pass metabolism continues. It is difficult to measure directly the liver and gastric contribution to the metabolism of newly abzyme family [1]. Recently at least five classes of ADH have been categorized in humans on the basis of their structural and sorbed alcohol from the gastrointestinal tract. Dosage and the absorption rate, which can be influenced by gastric emptying, kinetic characteristics [2]. Class I homodimeric and heterodimeric A, β, and γ-ADHs are the low-K m forms for ethanol oxida-are among the major confounding factors [6Ϫ8, 11]. To assess the effective potential of ADHs to metabolize first-passed ethation ; class II ππ and class IV µµ (or denoted σσ), the high-K m forms. Class III χχ, a glutathione-dependent formaldehyde nol it is important to measure the magnitude of enzyme activity increase in the liver and stomach corresponding to the alcohol dehydrogenase, appears not to be saturable with ethanol. Kinetic features of class V ADH remain to be defined. Genetic polymor-concentration difference between organ and systemic blood during the period of first-pass metabolism. phism occurs in the class I isozymes among racial populations, which can affect the development of alcoholism [3,4]. Intraclass It is well ac...

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Recent in vivo and in vitro studies on corticosteroid metabolism in humans1,2 and hamsters1,3 have led to the conclusion that steroids with a 20-hydroxy 21-aldehyde (aldol) side chain are important intermediates in the metabolism of cortisol and other corticosteroids. Therefore, it was important to synthesize this class of metabolites for further biological studies.A procedure for the synthesis of the 20/3 epimer of the aldol side chain through a 20-keto 21-oxime intermediate was developed by Oh and Monder.4 By use of sodium borohydride as the reductant, the 20/3 steroids were produced preferentially. Generally, side chains of the pregnane and 21-hydroxypregnane series are readily reduced by hydride reagents to the 20/3 configuration.5 Reduction to the 20a form is more difficult. Chemical synthesis of these enantiomeric forms have been attempted, and several procedures appear in the literature. Fukushima et al.6 applied solvolysis to invert 17,20/3,21-triols via the 17aacetate 20/3-tosylate. Other approaches to the synthesis of the 20a-hydroxy steroid utilized the reduction by metal hydrides of 17a,20/3-epoxy-20-acetoxy steroids,7 16 20ones,8 and 16a,17a-oxido 20-ketone.9 The reduction by sodium borohydride at C-20 of 17,21-cyclic acetals and alkyl ortho esters to 17,20a,21-triols proceeded efficiently with 11-keto-substituted steroids and slowly with 11hydroxy or deoxy steroids.10 Other procedures utilized sodium in 1-propanol,11 hydrogenation with Raney nickel,12 and alkaline hydrolysis of 20/8-tosylates.13 Biological reductions of corticosteroids to 20a carbinols have also been reported.14,16The limitations of the available methods made it necessary to consider new approaches to the preparation of 20a-hydroxy steroids. Our goal was to develop broadly applicable methods for the synthesis of steroids with the 20a-hydroxy 21-aldehyde side chain. We now describe a novel method to obtain the 20a-hydroxy epimers of steroid aldols which utilizes many of the techniques we developed for the synthesis of the 20/3 isomers.The approach is outlined in Scheme I. Glyoxal 2 derived from ketol 1 by cupric acetate catalyzed oxidation is converted to oxime 3. Reduction of oxime in the cold in the presence of alkaline earth cations and under twophase conditions (ethyl acetate/water for 17-hydroxy steroids; chloroform/water for 17-deoxy steroids) yields a mixture of 20/3-hydroxy oxime 4 and 20a-hydroxy oxime 5. The protecting group is removed to afford the aldols 6 and 7. In early experiments, using a single-phase system, reduction of 10.6 µ of 3a with 5.3 or 79 µ of sodium borohydride in iV^V-dimethylformamide (DMF)-methanol (2/1 v/v) at 0 °C resulted in 20 /20/3 ratios of 0.17 and 0.42, respectively. The larger amount of sodium borohydride increased the proportion of the 20a isomer. Under these conditions, the production of the 20a isomer exceeded that obtained by known procedures, at -27 °C, the value with 5.3 µ of sodium borohydride was 0.32. The

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