Alcohol dehydrogenases: gene multiplicity and differential functions of five classes of isozymes

Prognostic value of alcohol dehydrogenase mRNA expression in gastric cancer

Previous studies have reported that alcohol dehydrogenase (ADH) isoenzymes possess diagnostic value in gastric cancer (GC). However, the prognostic value of ADH isoenzymes in GC remains unclear. The aim of the present study was to identify the prognostic value of ADH genes in patients with GC. The prognostic value of ADH genes was investigated in patients with GC using the Kaplan-Meier plotter tool. Kaplan-Meier plots were used to assess the difference between groups of patients with GC with different prognoses. Hazard ratios (HR) and 95% confidence intervals (CI) were used to assess the relative risk of GC survival. Overall, 593 patients with GC and 7 ADH genes were included in the survival analysis. High expression of ADH 1A (class 1), α polypeptide (ADH1A; log-rank P=0.043; HR=0.79; 95% CI: 0.64–0.99), ADH 1B (class 1), β polypeptide (ADH1B; log-rank P=1.9×10⁻⁰⁵; HR=0.65; 95% CI: 0.53–0.79) and ADH 5 (class III), χ polypeptide (ADH5; log-rank P=0.0011; HR=0.73; 95% CI: 0.6–0.88) resulted in a significantly decreased risk of mortality in all patients with GC compared with patients with low expression of those genes. Furthermore, protective effects may additionally be observed in patients with intestinal-type GC with high expression of ADH1B (log-rank P=0.031; HR=0.64; 95% CI: 0.43–0.96) and patients with diffuse-type GC with high expression of ADH1A (log-rank P=0.014; HR=0.51; 95% CI: 0.3–0.88), ADH1B (log-rank P=0.04; HR=0.53; 95% CI: 0.29–0.98), ADH 4 (class II), π polypeptide (log-rank P=0.033; HR=0.58; 95% CI: 0.35–0.96) and ADH 6 (class V) (log-rank P=0.037; HR=0.59; 95% CI: 0.35–0.97) resulting in a significantly decreased risk of mortality compared with patients with low expression of those genes. In contrast, patients with diffuse-type GC with high expression of ADH5 (log-rank P=0.044; HR=1.66; 95% CI: 1.01–2.74) were significantly correlated with a poor prognosis. The results of the present study suggest that ADH1A and ADH1B may be potential prognostic biomarkers of GC, whereas the prognostic value of other ADH genes requires further investigation.

Compound lipophilicity as a descriptor to predict binding affinity (1/K(m)) in mammals

In bioaccumulation models, biotransformation is one of the processes decreasing the concentration of chemicals in an organism. In order to be metabolized, a compound needs to bind to an enzyme. In this study, we derived relationships between binding affinity and lipophilicity, expressed as Log (1/K(m)) and Log K(ow), respectively. We focused on oxidations in mammals catalyzed by alcohol dehydrogenase (ADH), aldehyde dehydrogenase (ALDH), flavin-containing monooxygenase (FMO), and cytochrome P450 (CYP) enzymes. For all regressions, 1/K(m) increased with compound K(ow), which can be understood from the tendency to biotransform lipophilic compounds into more polar, thus more easily excretable metabolites. Lipophilicity was relevant to the binding of most of the substrate classes of ADH, ALDH, and CYP. The resulting slopes had 95% Confidence Intervals covering the value of 0.63, typically noted in protein-water distribution (Log K(pw)) and Log K(ow) regressions. A reduced slope (0.2-0.3) was found for FMO: this may be due to a different reaction mechanism involving a nucleophilic attack. The general patterns of metabolism were mechanistically interpreted in terms of partitioning theory. Information on the overall principles determining biotransformation may be helpful in predicting metabolic rates.

Alcohol dehydrogenases and aldehyde dehydrogenases among inbred strains of mice: multiplicity, development, genetic studies and metabolic roles

Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) are the major enzymes responsible for the metabolism of alcohols and aldehydes in the body. Both exist as a family of isozymes in mammals, and have been extensively studied in animal models, particularly among inbred strains of mice. Mouse ADH exists as at least three major classes, which are predominantly localized in liver (classes I and III), and in stomach/cornea (class IV). Mouse ALDH exhibits extensive multiplicity, several forms of which have been characterized, including ALDH1 (liver cytoplasmic/class 1 isozyme); ALDH2 (liver mitochondrial/class 2.); ALDH3 (stomach cytosolic/class 3); ALDH4 (liver microsomal/class 3); and ALDH5 (testis cytosolic/class 3). Biochemical, genetic and molecular genetic analyses have been performed on several of these enzymes, including studies on variant forms of ADH and ALDH. Distinct metabolic roles are proposed, based upon their tissue and subcellular distribution characteristics and the biochemical properties for these enzymes.

Human stomach class IV alcohol dehydrogenase: molecular genetic analysis

A partial human stomach alcohol dehydrogenase (ADH) encoding cDNA has been isolated, cloned, and sequenced, which contains 222 nucleotides encoding amino acid residues 227-299 of the ADH subunit. The amino acid sequence deduced from this cDNA was highly homologous with the rat stomach class IV ADH sequence recently reported (81.1% sequence identity). Homology with other human ADH classes was also observed: class I, 58.1% sequence identity; class II, 39.2% sequence identity; class III, 55.4% sequence identity; and class V, 50.0% sequence identity. These results support a proposal that the isolated cDNA encodes a partial sequence for human stomach class IV ADH. This sequence retains val294 for all other human ADH classes reported, as compared with an ala294 at this position reported for rat class IV ADH. This ala residue may contribute to the very high Km values with ethanol for the latter enzyme. In addition, three substitutions are reported for key residues in the coenzyme binding site: 251, gln/ser; 260, gly/asn; and 261, gly/asn, which may contribute to the weak coenzyme binding properties reported for human class IV ADH.