Molecular characterization of a class IV human alcohol dehydrogenase gene (ADH7)

Similarities in DSG1 and KRT3 Downregulation through Retinoic Acid Treatment and PAX6 Knockdown Related Expression Profiles: Does PAX6 Affect RA Signaling in Limbal Epithelial Cells?

Congenital PAX6-aniridia is a rare panocular disease resulting from limbal stem cell deficiency. In PAX6-aniridia, the downregulation of the retinol-metabolizing enzymes ADH7 (All-trans-retinol dehydrogenase 7) and ALDH1A1/A3 (Retinal dehydrogenase 1, Aldehyde dehydrogenase family 1 member A3) have been described in limbal epithelial cells (LECs) and conjunctival epithelial cells. The aim of this study was to identify the role of retinol derivates in the differentiation of human LEC and its potential impact on aniridia-associated keratopathy development. Human LEC were isolated from healthy donor corneas and were cultured with retinol, retinoic acid, or pan-retinoic acid receptor antagonist (AGN 193109) acting on RARα, β, γ (NR1B1, NR1B2 NR1B3) or were cultured with pan-retinoid X receptor antagonist (UVI 3003) acting on RXR α, β, γ (retinoid X receptor, NR2B1, NR2B2, BR2B3). Using qPCR, differentiation marker and retinoid-/fatty acid metabolism-related mRNA expression was analysed. DSG1 (Desmoglein 1), KRT3 (Keratin 3), and SPINK7 (Serine Peptidase Inhibitor Kazal Type 7) mRNA expression was downregulated when retinoid derivates were used. AGN 193109 treatment led to the upregulation of ADH7, KRT3, and DSG1 mRNA expression and to the downregulation of KRT12 (Keratin 12) and KRT19 (Keratin 19) mRNA expression. Retinol and all-trans retinoic acid affect some transcripts of corneal LEC in a similar way to what has been observed in the LEC of PAX6-aniridia patients with the altered expression of differentiation markers. An elevated concentration of retinol derivatives in LEC or an altered response to retinoids may contribute to this pattern. These initial findings help to explain ocular surface epithelia differentiation disorders in PAX6-aniridia and should be investigated in patient cells or in cell models in the future in more detail.

Role of alcohol metabolism in non-alcoholic steatohepatitis

Background

Non-alcoholic steatohepatitis (NASH) is a serious form of non-alcoholic fatty liver disease (NAFLD), associated with obesity and insulin resistance. Previous studies suggested that intestinal bacteria produced more alcohol in obese mice than lean animals.

Methodology/Principal Findings

To investigate whether alcohol is involved in the pathogenesis of NASH, the expression of inflammation, fibrosis and alcohol metabolism related genes in the liver tissues of NASH patients and normal controls (NCs) were examined by microarray (NASH, n = 7; NC, n = 4) and quantitative real-time PCR (NASH, n = 6; NC, n = 6). Genes related to liver inflammation and fibrosis were found to be elevated in NASH livers compared to normal livers. The most striking finding is the increased gene transcription of alcohol dehydrogenase (ADH) genes, genes for catalase and cytochrome P450 2E1, and aldehyde dehydrogenase genes. Immunoblot analysis confirmed the increased expression of ADH1 and ADH4 in NASH livers (NASH, n = 9; NC, n = 4).

Conclusions/Significance

The augmented activity of all the available genes of the pathways for alcohol catabolism suggest that 1) alcohol concentration was elevated in the circulation of NASH patients; 2) there was a high priority for the NASH livers to scavenge alcohol from the circulation. Our data is the first human evidence that suggests alcohol may contribute to the development of NAFLD.

Recommended nomenclature for the vertebrate alcohol dehydrogenase gene family

The alcohol dehydrogenase (ADH) gene family encodes enzymes that metabolize a wide variety of substrates, including ethanol, retinol, other aliphatic alcohols, hydroxysteroids, and lipid peroxidation products. Studies on 19 vertebrate animals have identified ADH orthologs across several species, and this has now led to questions of how best to name ADH proteins and genes. Seven distinct classes of vertebrate ADH encoded by non-orthologous genes have been defined based upon sequence homology as well as unique catalytic properties or gene expression patterns. Each class of vertebrate ADH shares <70% sequence identity with other classes of ADH in the same species. Classes may be further divided into multiple closely related isoenzymes sharing >80% sequence identity such as the case for class I ADH where humans have three class I ADH genes, horses have two, and mice have only one. Presented here is a nomenclature that uses the widely accepted vertebrate ADH class system as its basis. It follows the guidelines of human and mouse gene nomenclature committees, which recommend coordinating names across species boundaries and eliminating Roman numerals and Greek symbols. We recommend that enzyme subunits be referred to by the symbol "ADH" (alcohol dehydrogenase) followed by an Arabic number denoting the class; i.e. ADH1 for class I ADH. For genes we recommend the italicized root symbol "ADH" for human and "Adh" for mouse, followed by the appropriate Arabic number for the class; i.e. ADH1 or Adh1 for class I ADH genes. For organisms where multiple species-specific isoenzymes exist within a class, we recommend adding a capital letter after the Arabic number; i.e. ADH1A, ADH1B, and ADH1C for human alpha, beta, and gamma class I ADHs, respectively. This nomenclature will accommodate newly discovered members of the vertebrate ADH family, and will facilitate functional and evolutionary studies.

Regulation of human alcohol dehydrogenase gene ADH7: importance of an AP-1 site

The structure and function of the human alcohol dehydrogenase 7 (ADH7) promoter were analyzed. A promoter fragment extending to bp -232 functioned well in H4IIE-C3, CV-1, and HeLa cells, whereas the region extending further upstream to bp -799 had no significant effect on activity. We identified cis-acting elements in the proximal 232 bp and examined their effect on promoter activity. Mutation of site A, where c-Jun bound, caused a drastic decrease in the promoter activity in H4IIE-C3 and CV-1 cells, suggesting that AP-1 plays an important role in the regulation of ADH7. Mutation of site B also caused a large drop in promoter activity in both cell lines; C/EBPalpha can bind to this site, but because the site affects activity approximately equally in CV-1 cells that lack C/EBPalpha and in H4IIE-C3 cells that contain low levels, other proteins are likely to play the major roles in vivo. Mutation of site C, where C/EBP bound and c-Jun bound weakly, had different effects in the two cell lines: in H4IIE-C3 cells, the site C mutation did not significantly increase promoter activity, whereas in CV-1 cells, which lack C/EBPalpha, it led to a doubling of activity. Surprisingly, cotransfection of the wild-type promoter with C/EBPa or C/EBPbeta led to a decrease in promoter activity, which might in part explain the lack of activity of ADH7 in adult liver.

Ethnic differences in gastric sigma-alcohol dehydrogenase activity and ethanol first-pass metabolism

We assessed whether the low sigma-alcohol dehydrogenase (ADH) activity in Japanese (compared with Caucasians) affects the first-pass metabolism of ethanol. ADH isozyme activities were determined in endoscopic biopsies of the gastric corpus from 24 Japanese and 41 Caucasian men by starch gel electrophoresis and by comparing the reduction of m-nitrobenzaldehyde (a preferred substrate of sigma-ADH) with that of acetaldehyde (a preferred substrate of gamma-ADH) and the glutathione-dependent formaldehyde oxidation (a specific reaction of chi-ADH). Alcohol pharmacokinetics was compared in 10 Japanese and 10 Caucasians after administration of ethanol (300 mg/kg of body weight) intravenously or orally, using 5 and 40% oral solutions. Japanese exhibited lower sigma-ADH activity than Caucasians, with no difference in the other gastric isozymes. With 5% ethanol, first-pass metabolism was strikingly lower in Japanese than in Caucasians. Blood alcohol levels were similar because of the high elimination rate in Japanese due to the hepatic beta 2-ADH variant. With 40% ethanol, the first-pass metabolism increased in both groups to comparable levels, suggesting an additional contribution by chi-ADH at high ethanol concentrations. These results indicate that sigma-ADH activity contributes significantly to gastric ethanol oxidation and its lower activity in Japanese is associated with lesser first-pass metabolism.

Failure to find exon 7 polymorphism of the ADH7 gene in Chinese, Japanese, African-Americans, and Caucasians

Class IV alcohol dehydrogenase (sigma-ADH) activity has been found in high levels in the stomach and esophagus, but not in liver. Gastric ADH activity has been reported to influence blood alcohol levels after oral ethanol ingestion, suggesting that sigma-ADH activity plays a role in first-pass metabolism. It has also been reported that women have lower sigma-ADH activity than men and that Asians have lower sigma-ADH activity than Caucasians and African-Americans. A genetic basis for these gender and ethnic differences in sigma-ADH activity has been postulated. A recent study in a Japanese subject found a point mutation in the codon for amino acid 287 of the ADH7 gene (which encodes sigma-ADH), changing the amino acid from glycine to valine. A polymerase chain reaction-sequencing assay was established to determine the frequency of this polymorphism in the Asian, Caucasian, and African-American populations. The polymorphism was not present in the 21 Asians, 15 Caucasians, and 3 African-Americans we genotyped, suggesting that if this polymorphism exists, its frequency is low in these ethnic groups. It is therefore unlikely to be responsible for the absence of sigma-ADH activity in gastric specimens from Asians.

Effects of cimetidine on blood ethanol levels after alcohol ingestion and genetic polymorphisms of sigma-alcohol dehydrogenase in Japanese

Administration of cimetidine, an H2-receptor antagonist increases blood alcohol concentrations. This has been attributed to decreased gastric first-pass metabolism of ethanol caused by cimetidine's inhibitory effect on gastric alcohol dehydrogenase (sigma-ADH) activity. Molecular studies on sigma-ADH showed that a point mutation might occur at position 287 (G --> T) of the sigma-ADH gene in Japanese deficient type of sigma-ADH activity. To clarify the relationship between first-pass metabolism of ethanol and polymorphism of sigma-ADH, we analyzed the nucleotide sequence at positions 287 and 294 of sigma-ADH in 11 individuals who were administered ethanol orally before and after treatment with cimetidine. Higher blood ethanol levels after cimetidine administration were found in 4 of 11 cases (group A), whereas high blood ethanol levels were observed in 7 of 11 cases (B group), irrespective of cimetidine administration. Genetic polymorphisms at position 287 and 294 were not observed in all subjects. Even in 59 Japanese men with various alcoholic liver diseases, no polymorphisms at position 287 were observed by restriction-length polymorphisms with Avail digestion after polymerase chain reaction.

Cloning of the mouse class IV alcohol dehydrogenase (retinol dehydrogenase) cDNA and tissue-specific expression patterns of the murine ADH gene family

Humans possess five classes of alcohol dehydrogenase (ADH), including forms able to oxidize ethanol or formaldehyde as part of a defense mechanism, as well as forms acting as retinol dehydrogenases in the synthesis of the regulatory ligand retinoic acid. However, the mouse has previously been shown to possess only three forms of ADH. Hybridization analysis of mouse genomic DNA using cDNA probes specific for each of the five classes of human ADH has now indicated that mouse DNA cross-hybridizes to only classes I, III, and IV. With human class II or class V ADH cDNA probes, hybridization to mouse genomic DNA was very weak or undetectable, suggesting either a lack of these genes in the mouse or a high degree of mutational divergence relative to the human genes. cDNAs for murine ADH classes I and III have previously been cloned, and we now report the cloning of a full-length mouse class IV ADH cDNA. In Northern blot analyses, mouse class IV ADH mRNA was abundant in the stomach, eye, skin, and ovary, thus correlating with the expression pattern for the mouse Adh-3 gene previously determined by enzyme analysis. In situ hybridization studies on mouse stomach indicated that class IV ADH transcripts were abundant in the mucosal epithelium but absent from the muscular layer. Comparison of the expression patterns for all three mouse ADH genes indicated that class III was expressed ubiquitously, whereas classes I and IV were differentially expressed in an overlapping set of tissues that all contain a large component of epithelial cells. This expression pattern is consistent with the ability of classes I and IV to oxidize retinol for the synthesis of retinoic acid known to regulate epithelial cell differentiation. The results presented here indicate that the mouse has a simpler ADH gene family than the human but has conserved class IV ADH previously shown to be a very active retinol dehydrogenase in humans.