AKR1B10 is a human aldo-keto reductase (AKR) found to be elevated in several cancer types and in precancerous lesions. In vitro, AKR1B10 exhibits a much higher retinaldehyde reductase activity than any other human AKR, including AKR1B1 (aldose reductase). We here demonstrate that AKR1B10 also acts as a retinaldehyde reductase in vivo. This activity may be relevant in controlling the first step of retinoic acid synthesis. Up-regulation of AKR1B10, resulting in retinoic acid depletion, may lead to cellular proliferation. Both in vitro and in vivo activities of AKR1B10 were inhibited by tolrestat, an AKR1B1 inhibitor developed for diabetes treatment. The crystal structure of the ternary complex AKR1B10 -NADP ؉ -tolrestat was determined at 1.25-Å resolution. Molecular dynamics models of AKR1B10 and AKR1B1 with retinaldehyde isomers and site-directed mutagenesis show that subtle differences at the entrance of the retinoid-binding site, especially at position 125, are determinant for the all-transretinaldehyde specificity of AKR1B10. Substitutions in the retinaldehyde cyclohexene ring also influence the specificity. These structural features should facilitate the design of specific inhibitors, with potential use in cancer and diabetes treatments.aldo-keto reductases ͉ aldose reductase ͉ protein structure ͉ retinoic acid ͉ tolrestat

Polymorphism at the ADH2 and ADH3 loci of alcohol dehydrogenase (ADH) has been shown to have an effect on the predisposition to alcoholism in Asian individuals. However, the results are not conclusive for white individuals. We have analyzed the ADH genotype of 876 white individuals from Spain (n ‫؍‬ 251), France (n ‫؍‬ 160), Germany (n ‫؍‬ 184), Sweden (n ‫؍‬ 88), and Poland (n ‫؍‬ 193). Peripheral blood samples from healthy controls and groups of patients with viral cirrhosis and alcohol-induced cirrhosis, as well as alcoholics with no liver disease, were collected on filter paper. Genotyping of the ADH2 and ADH3 loci was performed using polymerase chain reactionrestriction fragment length polymorphism methods on white cell DNA. In healthy controls, ADH2*2 frequencies ranged from 0% (France) to 5.4% (Spain), whereas ADH3*1 frequencies ranged from 47.6% (Germany) to 62.5% (Sweden). Statistically significant differences were not found, however, between controls from different countries, nor between patients with alcoholism and/or liver disease. When all individuals were grouped in nonalcoholics (n ‫؍‬ 451) and alcoholics (n ‫؍‬ 425), ADH2*2 frequency was higher in nonalcoholics (3.8%) than in alcoholics (1.3%) (P ‫؍‬ .0016), whereas the ADH3 alleles did not show differences. Linkage disequilibrium was found between ADH2 and ADH3, resulting in an association of the alleles ADH2*2 and ADH3*1, both coding for the most active enzymatic forms. In conclusion, the ADH2*2 allele decreases the risk for alcoholism, whereas the ADH2*2 and ADH3*1 alleles are found to be associated in the European population. (HEPATOLOGY 2000;31:984-989.)Ingested alcohol is mostly metabolized in the liver by the successive action of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). Both enzymes exhibit genetic polymorphisms that influence the rate of conversion of ethanol to acetaldehyde, and of acetaldehyde to acetate. It has been consistently reported that ALDH2 is the most important alcohol-metabolizing gene affecting predisposition to alcoholism in Asian populations. The prevalence of the ALDH2*2 allele, which codes for a physiologically inactive mitochondrial ALDH form, is lower in alcoholics than in nonalcoholics. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] However, this allele has not been found in white individuals. 21 Regarding ADH, polymorphism is detected at the ADH2 and ADH3 loci. Alleles of ADH2 found in whites and Asians are ADH2*1 and ADH2*2, which encode for the low activity (␤1) and high activity (␤2) subunits, respectively. The kcat values for the resulting dimeric isozymes are very different: 9.2 min Ϫ1 for ␤1␤1 and 400 min Ϫ1 for ␤2␤2. 22 The ADH2*2 frequency is much higher in Asians (60%-80%) than in whites (0%-10%). 21 ADH3 alleles are ADH3*1 and ADH3*2, which produce the ␥1 and ␥2 subunits. The ␥1␥1 isozyme (kcat ϭ 87 min Ϫ1 ) is moderately more active than the ␥2␥2 isozyme (kcat ϭ 35 min Ϫ1 ). 22 ADH3*1 frequency is about 50% to 60% in whites and higher than 90% in Asians. 3,23 ...

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Retinoic acid biosynthesis in vertebrates occurs in two consecutive steps: the oxidation of retinol to retinaldehyde followed by the oxidation of retinaldehyde to retinoic acid. Enzymes of the MDR (medium-chain dehydrogenase/reductase), SDR (short-chain dehydrogenase/reductase) and AKR (aldo-keto reductase) superfamilies have been reported to catalyse the conversion between retinol and retinaldehyde. Estimation of the relative contribution of enzymes of each type was difficult since kinetics were performed with different methodologies, but SDRs would supposedly play a major role because of their low K(m) values, and because they were found to be active with retinol bound to CRBPI (cellular retinol binding protein type I). In the present study we employed detergent-free assays and HPLC-based methodology to characterize side-by-side the retinoid-converting activities of human MDR [ADH (alcohol dehydrogenase) 1B2 and ADH4), SDR (RoDH (retinol dehydrogenase)-4 and RDH11] and AKR (AKR1B1 and AKR1B10) enzymes. Our results demonstrate that none of the enzymes, including the SDR members, are active with CRBPI-bound retinoids, which questions the previously suggested role of CRBPI as a retinol supplier in the retinoic acid synthesis pathway. The members of all three superfamilies exhibit similar and low K(m) values for retinoids (0.12-1.1 microM), whilst they strongly differ in their kcat values, which range from 0.35 min(-1) for AKR1B1 to 302 min(-1) for ADH4. ADHs appear to be more effective retinol dehydrogenases than SDRs because of their higher kcat values, whereas RDH11 and AKR1B10 are efficient retinaldehyde reductases. Cell culture studies support a role for RoDH-4 as a retinol dehydrogenase and for AKR1B1 as a retinaldehyde reductase in vivo.

Aldo-keto reductases (AKRs) are NAD(P)H-dependent oxidoreductases that catalyse the reduction of a variety of carbonyl compounds, such as carbohydrates, aliphatic and aromatic aldehydes and steroids. We have studied the retinal reductase activity of human aldose reductase (AR), human small-intestine (HSI) AR and pig aldehyde reductase. Human AR and HSI AR were very efficient in the reduction of all- trans -, 9- cis - and 13- cis -retinal ( k (cat)/ K (m)=1100-10300 mM(-1).min(-1)), constituting the first cytosolic NADP(H)-dependent retinal reductases described in humans. Aldehyde reductase showed no activity with these retinal isomers. Glucose was a poor inhibitor ( K (i)=80 mM) of retinal reductase activity of human AR, whereas tolrestat, a classical AKR inhibitor used pharmacologically to treat diabetes, inhibited retinal reduction by human AR and HSI AR. All- trans -retinoic acid failed to inhibit both enzymes. In this paper we present the AKRs as an emergent superfamily of retinal-active enzymes, putatively involved in the regulation of retinoid biological activity through the assimilation of retinoids from beta-carotene and the control of retinal bioavailability.

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Rat tissues contain three different isoenzymes of alcohol dehydrogenase (ADH) that we have named ADH-1, ADH-2 and ADH-3. ADH-1 is an anodic isoenzyme present in high amounts in the ocular tissues, stomach and lung. ADH-2 is also anodic and has been found in all the rat organs examined. ADH-3 is the group of cathodic ADH forms, mainly present in liver, that has been the subject of the majority of the previous studies on rat ADH. The three isoenzymes have been purified to homogeneity and characterized. All of them have similar physical characteristics: M , 80000, with two subunits of M, 40000; they contain four atoms of Zn per molecule, and prefer NAD' as cofactor. Isoelectric points are, however, different: 5.1 for ADH-1, 5.95-6.3 for ADH-2 and 8.25 -8.4 for ADH-3. ADH-3 exhibits a K , for ethanol of 1.4 mM, a broad substrate specificity and is strongly inhibited by pyrazole (Ki = 0.4 pM). ADH-2 shows substrate specificity toward long-chain alcohols and aldehydes, cannot be saturated by ethanol and is practically insensitive to pyrazole (Ki = 78.4 mM). ADH-I has intermediate properties, with a K , for ethanol of 340 mM, a broad substrate specificity and Ki for pyrazole of 0.56mM. Rat ADH-1, ADH-2 and ADH-3 exhibit many analogies with human ADH classes 11, 111 and I respectively. The specific localization and kinetic properties of rat ADH isoenzymes suggest that ADH-1 and ADH-3 may act as metabolic barriers to external alcohols and aldehydes whereas ADH-2 may have a function in the metabolism of the endogenous long-chain alcohols and aldehydes.Alcohol dehydrogenase (ADH ; alcohol : NAD + oxidoreductase) is a zinc-dependent metalloenzyme, principally responsible for ethanol oxidation in mammals. ADH catalyses the reversible interconversion of a variety of alcohols and their corresponding aldehydes and ketones, but the interest in studying this enzyme, in recent years, has been focused on its role in human ethanol metabolism. Human ADH has been extensively studied and is now well known. The human enzyme exhibits multiple isoenzymes that have been fully characterized and classified in three major classes (I, I1 and 111) on the basis of their electrophoretic mobility, kinetic properties and inhibition by pyrazole [l, 21. ADH from other species: monkey [3 -51, mouse [6], horse [7 -91, hamster [lo] and dog [ll], have been recently studied. In all cases different isoenzyme types, with some analogy with the human classes, have been recognized. Nevertheless a complete study on isoenzyme identification and characterization had not been performed in the rat. The enzymatic basis of alcohol metabolism is, therefore, only partially known for this species and, paradoxically, the rat has been the animal used most often in experimental studies on the pharmacological and metabolic effects of ethanol. Only the cathodic forms of rat ADH have been purified and characterized [12-171. These forms show a low K, for ethanol and are abundant in liver; therefore, they play a major role in ethanol metabolism. However, other ADH isoenzymes ...

Influence of vitamin A (retinol) on growth depends on its sequential oxidation to retinal and then to retinoic acid (RA), producing a ligand for RA receptors essential in development of specific tissues. Genetic studies have revealed that aldehyde dehydrogenases function as tissue-specific catalysts for oxidation of retinal to RA. However, enzymes catalyzing the first step of RA synthesis, oxidation of retinol to retinal, remain unclear because none of the present candidate enzymes have expression patterns that fully overlap with those of aldehyde dehydrogenases during development. Here, we provide genetic evidence that alcohol dehydrogenase (ADH) performs this function by demonstrating a role for Adh3, a ubiquitously expressed form. Adh3 null mutant mice exhibit reduced RA generation in vivo, growth deficiency that can be rescued by retinol supplementation, and completely penetrant postnatal lethality during vitamin A deficiency. ADH3 was also shown to have in vitro retinol oxidation activity. Unlike the second step, the first step of RA synthesis is not tissue-restricted because it is catalyzed by ADH3, a ubiquitous enzyme having an ancient origin.