Protein expression changes in the nucleus accumbens and amygdala of inbred alcohol-preferring rats given either continuous or scheduled access to ethanol

Chronic ethanol (EtOH) drinking produces neuronal alterations within the limbic system. To investigate changes in protein expression levels associated with EtOH drinking, inbred alcohol-preferring (iP) rats were given one of three EtOH access conditions in their home-cages: continuous ethanol (CE: 24h/day, 7days/week access to EtOH), multiple scheduled access (MSA: four 1-h sessions during the dark cycle/day, 5 days/week) to EtOH, or remained EtOH-naïve. Both MSA and CE groups consumed between 6 and 6.5g of EtOH/kg/day after the 3rd week of access. On the first day of EtOH access for the seventh week, access was terminated at the end of the fourth MSA session for MSA rats and the corresponding time point (2300h) for CE rats. Ten h later, the rats were decapitated, brains extracted, the nucleus accumbens (NAcc) and amygdala (AMYG) microdissected, and protein isolated for 2-dimensional gel electrophoretic analyses. In the NAcc, MSA altered expression levels for 12 of the 14 identified proteins, compared with controls, with six of these proteins altered by CE access, as well. In the AMYG, CE access changed expression levels for 22 of the 27 identified proteins, compared with controls, with 8 of these proteins altered by MSA, as well. The proteins could be grouped into functional categories of chaperones, cytoskeleton, intracellular communication, membrane transport, metabolism, energy production, or neurotransmission. Overall, it appears that EtOH drinking and the conditions under which EtOH is consumed, differentially affect protein expression levels between the NAcc and AMYG. This may reflect differences in neuroanatomical and/or functional characteristics associated with EtOH self-administration and possibly withdrawal, between these two brain structures.

Antidiabetic thiazolidinediones inhibit invasiveness of pancreatic cancer cells via PPARgamma independent mechanisms

BACKGROUND/AIMS

Thiazolidinediones (TZD) are a new class of oral antidiabetic drugs that have been shown to inhibit growth of some epithelial cancer cells. Although TZD were found to be ligands for peroxisome proliferators activated receptor gamma (PPARgamma) the mechanism by which TZD exert their anticancer effect is currently unclear. Furthermore, the effect of TZD on local motility and metastatic potential of cancer cells is unknown. The authors analysed the effects of two TZD, rosiglitazone and pioglitazone, on invasiveness of human pancreatic carcinoma cell lines in order to evaluate the potential therapeutic use of these drugs in pancreatic adenocarcinoma.

METHODS

Expression of PPARgamma in human pancreatic adenocarcinomas and pancreatic carcinoma cell lines was measured by reverse transcription polymerase chain reaction and confirmed by western blot analysis. PPARgamma activity was evaluated by transient reporter gene assay. Invasion assay was performed in modified Boyden chambers. Gelatinolytic and fibrinolytic activity were evaluated by gel zymography.

RESULTS

TZD inhibited pancreatic cancer cells' invasiveness, affecting gelatinolytic and fibrinolytic activity with a mechanism independent of PPARgamma activation and involving MMP-2 and PAI-1 expression.

CONCLUSION

TZD treatment in pancreatic cancer cells has potent inhibitory effects on growth and invasiveness suggesting that these drugs may have application for prevention and treatment of pancreatic cancer in humans.

Alcohol and retinoids

This article represents the proceedings of a symposium at the 2000 ISBRA Meeting in Yokohama, Japan. The chairs were Hirokazu Yokoyama and David Crabb. The presentations were (1) Roles of vitamin A, retinoic acid, and retinoid receptors in the expression of liver ALDH2, by J. Pinaire, R. Hasanadka, M. Fang, and David W. Crabb; (2) Alcohol, vitamin A, and beta-carotene: Adverse interactions, by M. A. Leo and Charles S. Lieber; (3) Retinoic acid, hepatic stellate cells, and Kupffer cells, by Hidekazu Tsukamoto, K. Motomura, T. Miyahara, and M. Ohata; (4) Retinoid storage and metabolism in liver, by William Bosron, S. Sanghani, and N. Kedishvili; (5) Characterization of oxidation pathway from retinol to retinoic acid in esophageal mucosa, by Haruko Shiraishi, Hirokazu Yokoyama, Michiko Miyagi, and Hiromasa Ishii; and (6) Ethanol in an inhibitor of the cytosolic oxidation of retinol in the liver and the large intestine of rats as well as in the human colon mucosa, by Ina Bergheim, Ina Menzl, Alexandr Parlesak, and Christiane Bode.

Peroxisome proliferator-activated receptors (PPAR) and the mitochondrial aldehyde dehydrogenase (ALDH2) promoter in vitro and in vivo

BACKGROUND

The aldehyde dehydrogenase 2 (ALDH2) promoter contains a nuclear receptor response element (NRRE) that represents an overlapping direct repeat-1 (DR-1) and -5 (DR-5) element. Because DR-1 elements are preferred binding sites for peroxisome proliferator-activated receptors (PPARs), we tested the hypothesis that PPARs regulate ALDH2 expression.

METHODS

We examined the ability of PPAR isoforms to bind to the ALDH2 NRRE in electrophoretic mobility shift assays, their ability to activate the transcription of promoter-reporter constructs containing this NRRE, the effect of PPAR ligands on ALDH2 expression in liver, and the role of the PPARalpha on the expression of ALDH2 by using PPARalpha-null mice.

RESULTS

In vitro translated PPARs bound the ALDH NRRE with high affinity. Mutation of the NRRE indicated that binding was mediated by the DR-1 element. Cotransfection of PPAR expression plasmids showed that PPARalpha had no effect on expression of heterologous promoter constructs containing the NRRE. PPARgamma slightly induced expression, whereas PPARdelta repressed basal activity of the promoter and blocked induction by hepatocyte nuclear factor 4. Treatment of rats with the PPAR ligand clofibrate repressed expression of ALDH2 in rats fed either stock rodent chow or a low-protein diet. Consistent with the transfection data, expression of ALDH2 protein was not different in PPARalpha-null mice. Treatment of the mice with the PPARalpha agonist WY14643 slightly decreased the level of ALDH2 protein in both wild-type and PPARalpha-null mice, suggesting that the effect of WY14643 was not mediated by the receptor.

CONCLUSIONS

These data indicate that ALDH2 is not part of the battery of lipid metabolizing enzymes and proteins regulated by PPARalpha

Alcohol and retinoids

This article represents the proceedings of a symposium at the 2000 ISBRA Meeting in Yokohama, Japan. The chairs were Hirokazu Yokoyama and David Crabb. The presentations were (1) Roles of vitamin A, retinoic acid, and retinoid receptors in the expression of liver ALDH2, by J. Pinaire, R. Hasanadka, M. Fang, and David W. Crabb; (2) Alcohol, vitamin A, and beta-carotene: Adverse interactions, by M. A. Leo and Charles S. Lieber; (3) Retinoic acid, hepatic stellate cells, and Kupffer cells, by Hidekazu Tsukamoto, K. Motomura, T. Miyahara, and M. Ohata; (4) Retinoid storage and metabolism in liver, by William Bosron, S. Sanghani, and N. Kedishvili; (5) Characterization of oxidation pathway from retinol to retinoic acid in esophageal mucosa, by Haruko Shiraishi, Hirokazu Yokoyama, Michiko Miyagi, and Hiromasa Ishii; and (6) Ethanol in an inhibitor of the cytosolic oxidation of retinol in the liver and the large intestine of rats as well as in the human colon mucosa, by Ina Bergheim, Ina Menzl, Alexandr Parlesak, and Christiane Bode.

Alcoholic liver disease

Research has substantiated the role of several mechanisms responsible for alcohol-induced hepatotoxicity. These mechanisms include: oxidative stress and lipid peroxidation; immunogenic processes initiated by formation of protein adducts of acetaldehyde, other aldehydes and 1-hydroxyethyl radicals; and activation of Kupffer cells by endotoxin and subsequent cascade of events that involved cytokines, chemokines, and adhesion molecules. Increasing evidence implicates enhanced intestinal permeability caused by alcohol ingestion as the culprit that leads to endotoxemia. While oxidative stress is important, the principal source of reactive oxygen species that causes alcohol-induced liver injury is hotly debated. Potential sources may include cytochrome P450IIE1, activated Kupffer cells, and mitochondrial electron transfer chain. Apoptosis is likely an important pathway that culminates in hepatocyte cell death. Abstinence, corticosteroids, and enteral nutrition remain the cornerstones in the treatment of alcoholic hepatitis. The efficacies of medications such as S-adenosylmethionine and pentoxifylline will need further confirmation by additional randomized trials before they can be recommended as standard therapies for alcoholic hepatitis.

The transcriptional and DNA binding activity of peroxisome proliferator-activated receptor alpha is inhibited by ethanol metabolism. A novel mechanism for the development of ethanol-induced fatty liver

Fatty acids are ligands for the peroxisome proliferator-activated receptor alpha (PPAR alpha). Fatty acid levels are increased in liver during the metabolism of ethanol and might be expected to activate PPAR alpha. However, ethanol inhibited PPAR alpha activation of a reporter gene in H4IIEC3 hepatoma cells expressing alcohol-metabolizing enzymes but not in CV-1 cells, which lack these enzymes. Ethanol also reduced the ability of the PPAR alpha ligand WY14,643 to activate reporter constructs in the hepatoma cells or cultured rat hepatocytes. This effect of ethanol was abolished by the alcohol dehydrogenase inhibitor 4-methylpyrazole and augmented by the aldehyde dehydrogenase inhibitor cyanamide, indicating that acetaldehyde was responsible for the action of ethanol. PPAR alpha/retinoid X receptor extracted from hepatoma cells exposed to ethanol or acetaldehyde bound poorly to an oligonucleotide containing peroxisome proliferator response elements. This effect was also blocked by 4-methylpyrazole and augmented by cyanamide. Furthermore, in vitro translated PPAR alpha exposed to acetaldehyde failed to bind DNA. Thus, ethanol metabolism blocks transcriptional activation by PPAR alpha, in part due to impairment of its ability to bind DNA. This effect of ethanol may promote the development of alcoholic fatty liver and other hepatic consequences of alcohol abuse.

Genetic and environmental influences on alcohol metabolism in humans

This manuscript represents the proceedings of a symposium at the 2000 RSA Meeting in Denver, Colorado. The organizer/chair was Ting-Kai Li. The presentations were: (1) Introduction to the Symposium, by Ting-Kai Li; (2) ALDH2 polymorphism and alcohol metabolism, by Shih-Jiun Yin; (3) ALDH2 promoter polymorphism and alcohol metabolism, by David W. Crabb; (4) Use of BrAC clamping to estimate alcohol elimination rates: Application to studies of the influence of genetic and environmental determinants, by Sean O'Connor; and (5) Effect of food and food composition on alcohol elimination rates as determined by clamping, by Vijay A. Ramchandani.

Effects of vitamin A deficiency on rat liver alcohol dehydrogenase expression and alcohol elimination rate in rats

BACKGROUND

Vitamin A has been suggested to regulate the expression of liver alcohol dehydrogenase (ADH) in humans. There are few studies on the ability of retinoic acid to affect ADH expression in vivo and none on its effects on alcohol metabolic rate.

METHODS

Male Sprague Dawley rats were used for isolation of hepatocytes or were rendered vitamin A deficient by feeding a deficient diet for 7 weeks. ADH, retinoic acid receptor beta, and retinoid X receptor alpha protein levels were analyzed by Western blotting. Alcohol elimination rate was determined by following blood alcohol levels after administering a 1.5 g/kg dose of ethanol intraperitoneally.

RESULTS

Retinoic acid had no effect on ADH protein in cultured hepatocytes. In the vitamin A deficient rats, retinol was not detectable in serum or liver at the time animals were killed. ADH and retinoid X receptor alpha protein levels were unchanged in the deficient group compared with a vitamin A sufficient control group, whereas retinoic acid receptor beta levels increased 40%. The deficient rats had a reduced volume of distribution of alcohol, but this largely was accounted for by their smaller body size. The alcohol elimination rates were lower in the deficient animals, but this was accounted for by reduced body and liver weights.

CONCLUSIONS

Severe vitamin A deficiency did not alter liver ADH protein expression or rates of alcohol elimination when expressed per gram of body or liver weight.

Alcoholic liver disease

Important mechanisms responsible for alcohol-induced liver injury include mitochondrial damage and loss of ATP, formation of acetaldehyde-and other aldehyde-protein adducts, release of reactive oxygen species (ROS) from mitochondrial electron transfer chain, CYP2E1 , and activated Kupffer cells (KCs); weakening of antioxidant defense systems; and increased intestinal permeability with endotoxemia. Endotoxin interacts with ethanol and/or acetaldehyde, and such interaction leads to a complex cascade of autocrine and paracrine pathways that involve the release of cytokines (proinflammatory, anti-inflammatory, and mutagenic), chemokines, and eicosanoids. These pathways are mediated by activation of KCs, induction of proliferation, and other phenotype changes in hepatic stellate cells (HSCs) leading to transformation to myofibroblasts (the latter is responsible for fibrogenesis, chemotaxis, and contractility, therefore contributing to portal hypertension, angiogenic response, and release of additional cytokines), and stimulation of sinusoidal cells (SECs) to release adhesive molecules and cytokines. Recent data implicate a likely role of apoptosis as a mechanism of hepatocyte cell death in alcoholic liver disease.

Pathogenesis of alcoholic liver disease: newer mechanisms of injury

The understanding of how alcohol damages the liver has expanded substantially over the last decade. In particular, the genetics of alcoholism, the genesis of fatty liver, the role of oxidant stress, interactions between endotoxin and the Kupffer cell, and the factors that control activation of the hepatic stellate cell (HSC) have been the focus of a great deal of research. Genetic mechanisms for increasing the risk of alcoholism include alterations in alcohol metabolizing enzymes as well as neurobiological differences between individuals. The development of fatty liver may involve both redox forces, oxidative stress, and alterations in peroxisome proliferator activated receptor function. Oxidative stress is now known to involve both microsomal and mitochondrial systems. Recent studies implicate stimulation of Kupffer cells by portal vein endotoxin as a cause of release of cytokines and chemokines, hepatocyte hyper-metabolism, and activation of HSC. These actions appear to be in part gender-dependent and may explain the susceptibility of women to alcoholic liver disease. Activation of HSC underlies liver fibrosis and cirrhosis of all types; control of this activation might permit control of the progression of fibrosis. These advances suggest a number of new approaches as therapy for alcoholic liver injury.

Sensitivity of virally-driven luciferase reporter plasmids to members of the steroid/thyroid/retinoid family of nuclear receptors

During a series of transfection experiments, the pRSV-luc plasmid used as an internal control was found to be sensitive to cotransfection with expression vectors for several members of the steroid/thyroid/retinoid superfamily of nuclear receptors. Therefore, a survey of the effect of these expression vectors on the activity of four reporter plasmids was conducted. In CV-1 cells, the activity of pRSV-luc, which contains the P. pyralis luciferase gene, was repressed by co-transfection of PPARalpha and ARP-1 and was activated by COUP-TFI. Expression of pSV40-luc, containing the same luciferase gene, was repressed by PPARalpha and HNF-4 and activated by both COUP-TFI and ARP-1. All four of these expression vectors reduced the expression of the pRL-TK plasmid, which contains the luciferase gene from Renilla reniformis. RXR expression vectors had no effect on luciferase activity in CV-1 cells but induced luciferase activity in H4IIEC3 hepatoma cells. This activation was blocked by the addition of ligand, 9-cis retinoic acid. pSV2-CAT, which contains the chloramphenicol acetyltransferase gene, was insensitive to all receptor expression vectors tested. Both the P. pyralis and R. reniformis luciferase genes appear to contain sequences that render them responsive to steroid/thyroid/retinoid nuclear receptors.

An A/G polymorphism in the promoter of mitochondrial aldehyde dehydrogenase (ALDH2): effects of the sequence variant on transcription factor binding and promoter strength

INTRODUCTION

The strong protective effect of the ALDH2*2 mutation on risk of alcoholism suggests that other mutations that reduce mitochondrial aldehyde dehydrogenase (ALDH) activity in the liver might also deter drinking. This study describes a polymorphic locus found in the promoter of the ALDH2 gene that affects expression of reporter constructs.

METHODS

Polymerase chain reaction (PCR)-based sequencing was used to search for polymorphisms. The ability of the promoter variants to bind transcription factors apolipoprotein A regulatory protein 1 (ARP-1) and chicken ovalbumin upstream promoter-transcription factor (COUP-TF) was tested in gel retardation assays using in vitro synthesized transcription factors. The variant promoters were tested for transcriptional activity using a heterologous promoter system and transient transfection assays.

RESULTS

A common polymorphism (A or G) in the human ALDH2 promoter region was found at -361 base pair (bp) from the translation start site. This polymorphism was found at different frequencies in African Americans, Caucasians, and Asians. The polymorphism occurs adjacent to the core binding motif for the transcription factors COUP-TF and ARP-1. Competition and binding affinity determinations did not show differences in the ability of these two sequences to bind the factors. Reporter genes containing these elements upstream of a basal thymidine kinase promoter had similar activity when transfected into a fibroblast (CV-1) cell line. However, the reporter containing the G allele was more active than that containing the A allele in hepatoma (H4IIEC3) cells.

CONCLUSIONS

The -361 bp A/G polymorphism is common in all racial groups tested. The G allele was more active than the A allele in a transfection assay. The basis for this difference is not known. If the differences in activity of the promoter constructs were paralleled by differences in ALDH2 enzyme activity in the liver, this polymorphism could affect risk of alcoholism.

Alcohol and medication interactions

Many medications can interact with alcohol, thereby altering the metabolism or effects of alcohol and/or the medication. Some of these interactions can occur even at moderate drinking levels and result in adverse health effects for the drinker. Two types of alcohol-medication interactions exist: (1) pharmacokinetic interactions, in which alcohol interferes with the metabolism of the medication, and (2) pharmacodynamic interactions, in which alcohol enhances the effects of the medication, particularly in the central nervous system (e.g., sedation). Pharmacokinetic interactions generally occur in the liver, where both alcohol and many medications are metabolized, frequently by the same enzymes. Numerous classes of prescription medications can interact with alcohol, including antibiotics, antidepressants, antihistamines, barbiturates, benzodiazepines, histamine H2 receptor antagonists, muscle relaxants, nonnarcotic pain medications and anti-inflammatory agents, opioids, and warfarin. In addition, many over-the-counter and herbal medications can cause negative effects when taken with alcohol.

Binding and activation of the human aldehyde dehydrogenase 2 promoter by hepatocyte nuclear factor 4

Mitochondrial aldehyde dehydrogenase 2 (ALDH2) is expressed in a tissue-specific fashion with high levels in liver, heart, kidney, and muscle, and low levels in most other tissues. The ALDH2 promoter was found to bind nuclear proteins at a pair of adjacent sites approximately 300 bp upstream from the translation start site, each of which was contacted at motifs containing the hexamer A/GGGTCA. The 3' site was shown to bind in vitro translated HNF-4. It was also shown by electrophoretic mobility shift assay utilizing antibodies against nuclear factors and rat liver nuclear extracts to be bound by hepatocyte nuclear factor 4 (HNF-4), chicken ovalbumin upstream promoter transcription factor I and II, and retinoid X receptors. A reporter construct containing four copies of this promoter element was activated by co-transfection of an HNF-4 expression plasmid in COS-1 and hepatoma cell lines. These results suggest that the tissue specificity of ALDH2 expression is in part determined by its activation by HNF-4.

A direct repeat (DR-1) element in the first exon modulates transcription of the preproenkephalin A gene

The preproenkephalin A gene is regulated by upstream cis-acting elements which respond to various signals, such as cAMP, calcium, and phorbol esters. An additional regulatory element was detected downstream of the transcription start site of the human preproenkephalin A gene in transfection experiments. The element was localized by DNAse I footprinting and methylation interference assays to a direct repeat (DR-1) element in the first (untranslated) exon. Deletion or mutation of this site reduced transcriptional activity of promoter-reporter constructs by over 50%. Antibodies against COUP-TF beta/ARP-1 and RXR transcription factors altered the pattern seen on electrophoretic mobility shift assays using double-stranded oligonucleotide containing the exon 1 protein binding site. This suggests that the factors that bind this site and modulate transcription of the PPE gene include members of the COUP-TF and retinoid X receptor families.

The mutation in the mitochondrial aldehyde dehydrogenase (ALDH2) gene responsible for alcohol-induced flushing increases turnover of the enzyme tetramers in a dominant fashion

Deficiency in mitochondrial aldehyde dehydrogenase (ALDH2), a tetrameric enzyme, results from inheriting one or two ALDH2*2 alleles. This allele encodes a protein subunit with a lysine for glutamate substitution at position 487 and is dominant over the wild-type allele, ALDH2*1. The ALDH2*2-encoded subunit (ALDH2K) reduces the activity of ALDH2 enzyme in cell lines expressing the wild-type subunit (ALDH2E). In addition to this effect on the enzyme activity, we now report that ALDH2*2 heterozygotes had lower levels of ALDH2 immunoreactive protein in autopsy liver samples. The half-lives of ALDH2 protein in HeLa cell lines expressing ALDH2*1, ALDH2*2, or both were determined by the rate of loss of immunoreactive protein after inhibition of protein synthesis with puromycin and by pulse-chase experiments. By either measure, ALDH2E enzyme was very stable, with a half-life of at least 22 h. ALDH2K enzyme had an enzyme half-life of only 14 h. In cells expressing both subunits, most of the subunits assemble as heterotetramers, and these enzymes had a half-life of 13 h. Thus, the effect of ALDH2K on enzyme turnover is dominant. These studies indicate that the ALDH2*2 allele exerts its dominant effect both by interfering with the catalytic activity of the enzyme and by increasing its turnover. This represents the first example of a dominantly acting allele with this effect on a mitochondrial enzyme's turnover.

Dexamethasone represses phorbol ester-, forskolin-, and calcium-stimulated expression of a preproenkephalin A promoter-chloramphenicol acetyltransferase gene via a receptor-mediated mechanism

CV-1 cells were stably transfected with a preproenkephalin A (PPE) promoter-chloramphenicol acetyltransferase (CAT) reporter plasmid containing -176 to +171 bp of the human PPE gene. Low levels of CAT were expressed constitutively. The reporter enzyme activity was induced by treatment of the cells for 6 h with drugs that increased intracellular cAMP (forskolin and 8-bromo-cAMP), intracellular calcium (A23187), or protein kinase C activity (tetradecanoyl phorbol-4-acetate, TPA) in the presence of the phosphodiesterase inhibitor isobutylmethylxanthine. Co-administration of dexamethasone reduced the magnitude of phorbol ester-stimulated CAT activity by about 50%, while there were smaller but not significant effects on forskolin- or A23187-stimulated expression of this reporter construct. In transient transfections which included the PPE-CAT reporter gene and a glucocorticoid receptor expression plasmid, dexamethasone significantly reduced stimulated expression of the reporter by TPA, forskolin, and A23187. The effect was observed with 10(-8)-10(-6) M dexamethasone and was blocked by the presence of the glucocorticoid antagonist RU486, suggesting that the effect of dexamethasone was mediated by the glucocorticoid receptor. The promoter region contained in this construct lacks a classical glucocorticoid response element or known negative elements; thus, dexamethasone may reduce stimulated expression of the PPE promoter via indirect effects.

The role of nuclear factor NF-Y/CP1 in the transcriptional regulation of the human aldehyde dehydrogenase 2-encoding gene

Mitochondrial aldehyde dehydrogenase (ALDH2) activity is produced at low levels in many tissues, with highest production in liver. Transfection assays using the first 600 bp of upstream DNA provided evidence for both positive and negative regulatory elements in the proximal promoter. A region from -79 to -116 bp was protected in DNase I footprinting assays and bound in electrophoretic mobility shift assays (EMSA) by a nuclear factor found in all cell lines and tissues tested. This region, denoted FP160, contained the consensus recognition sites for Sp1 and AP2, and a CCAAT box. The CCAAT box was specifically protected by a nuclear factor in methylation interference assays. Mutagenesis of specific bp within the CCAAT box eliminated protein binding in vitro and decreased transcriptional activity from the ALDH2 promoter approximately 50% in reporter gene assays. Competition experiments showed that the nuclear factor binding to the FP160 oligodeoxyribonucleotide (oligo) was competed by oligos corresponding to an NY-Y/CP1-binding site to a greater extent than by those containing sites for CTF/NF1, C/EPB or CP2. The heat stability, resistance to proteinase K digestion, sensitivity to inhibition of DNA binding by o-phenanthroline, and immunological properties of the liver factor binding to FP160 were very similar to the corresponding properties of NF-Y/CP1. Thus, the proximal ALDH2 promoter was bound by NF-Y/CP1 and this transcription factor may be responsible for the basal expression of the gene observed in most tissues. The NFY-CP1 present in rat liver has similar properties to that previously characterized in M12 B-lymphoma cells and LMTK mouse fibroblasts.

Structural and mechanistic similarities of 6-phosphogluconate and 3-hydroxyisobutyrate dehydrogenases reveal a new enzyme family, the 3-hydroxyacid dehydrogenases

Rat 3-hydroxyisobutyrate dehydrogenase exhibits significant amino acid sequence homology with 6-phosphogluconate dehydrogenase, D-phenylserine dehydrogenase from Pseudomonas syringae, and a number of hypothetical proteins encoded by genes of microbial origin. Key residues previously proposed to have roles in substrate binding and catalysis in sheep 6-phosphogluconate dehydrogenase are highly conserved in this entire family of enzymes. Site-directed mutagenesis, chemical modification, and substrate specificity studies were used to compare possible mechanistic similarities of 3-hydroxyisobutyrate dehydrogenase with 6-phosphogluconate dehydrogenase. The data suggest that 3-hydroxyisobutyrate and 6-phosphogluconate dehydrogenases may comprise, in part, a previously unrecognized family of 3-hydroxyacid dehydrogenases.

Catabolism of isobutyrate by colonocytes

Isolated colonocytes have more capacity for the oxidation of isobutyrate and alpha-ketoisovalerate than isolated enterocytes. Both enterocytes and colonocytes express high levels of 3-hydroxyisobutyryl-CoA hydrolase, an enzyme activity important in maintaining low intracellular concentrations of methacrylyl-CoA, a common, potentially toxic intermediate in the catabolic pathways of these compounds. In spite of comparable 3-hydroxyisobutyryl-CoA hydrolase activities in both cell types, and much greater amounts of 3-hydroxyisobutyrate dehydrogenase in colonocytes than in enterocytes, only the colonocytes produced 3-hydroxyisobutyrate as an endproduct of alpha-ketoisovalerate and isobutyrate catabolism. Butyrate very effectively inhibits isobutyrate catabolism by colonocytes, most likely by competitively inhibiting activation of isobutyrate to its CoA ester. Oleate also inhibits isobutyrate catabolism, but at a site more distal than butyrate. Starvation of rats for 72 h decreased the capacity of colonocytes for butyrate but not isobutyrate catabolism. We conclude that isobutyrate could function as a carbon source for energy and anapleurosis in colonocytes under conditions of defective butyrate oxidation or low butyrate availability.

Distribution of messenger RNAs for aldehyde dehydrogenase 1, aldehyde dehydrogenase 2, and aldehyde dehydrogenase 5 in human tissues

BACKGROUND

The distribution of aldehyde dehydrogenases in human tissues is incompletely understood, in part because of technical limitations of gel electrophoretic and other enzyme assay methods used previously and because of the instability of the enzymes. Since these enzymes participate in detoxification of endogenous and exogenous compounds, including ethanol, their tissue distribution may be relevant to the toxicology of a number of substances and to the medical consequences of alcoholism.

METHODS

The abundance of mRNA for aldehyde dehydrogenase 1 (ALDH1), aldehyde dehydrogenase 2 (ALDH2), and aldehyde dehydrogenase 5 (ALDH5) was determined by Northern blotting using poly A+ RNA from 16 adult human tissues and 5 fetal tissues.

RESULTS

The highest levels of ALDH1 mRNA were found in liver, kidney, muscle, and pancreas. ALDH2 and ALDH5 were expressed in a larger number of tissues than ALDH1, with highest levels in liver, kidney, muscle, and heart. Fetal heart, brain, liver, lung, and kidney expressed ALDH2 and ALDH5, while ALDH1 was present mainly in fetal liver, kidney, and lung.

CONCLUSIONS

The results are in general agreement with the distribution of enzymes studied in a limited number of tissues in the past, with the exception that the ALDH1 activity reported to exist in heart and brain may, in fact, be ALDH5. The only mRNA detected in placenta was that for ALDH5. This study extends the knowledge of the expression of these enzymes to several tissues not previously studied and establishes the tissue distribution of the new enzyme ALDH5.

Hormonal and chemical influences on the expression of class 2 aldehyde dehydrogenases in rat H4IIEC3 and human HuH7 hepatoma cells

We studied the effect a variety of hormones and chemical stimuli on the activity of low Km aldehyde dehydrogenase (ALDH) in rat H4IIEC3 hepatoma cells and ALDH activity in human HuH7 hepatoma cells. The low Km enzyme in H4IIEC3 cells reflects ALDH2 activity, and the ALDH activity in HuH7 likely represents ALDH5. Of the steroid hormone family, thyroid hormone, progesterone, and dihydrotestosterone increased low Km ALDH activity approximately 50%, whereas dexamethasone and estradiol had little effect. Insulin decreased the activity of low Km ALDH. None of these hormones affected the activity of ALDH in HuH7 cells. Among second messengers, 8-bromo-cAMP and A23187 increased low Km ALDH activity; HuH7 ALDH activity again was unchanged. Exposure of the cells to 22 mM ethanol reduced low Km activity by approximately 20%, whereas hydrogen peroxide, tumor necrosis factor-alpha, and interleukin-1 beta had little effect. Ultraviolet light increased the HuH7 ALDH activity. Retinaldehyde or retinolc acid reduced the HuH7 ALDH activity, but had no effect on low Km ALDH activity. These data suggest that low Km ALDH2 can be regulated by hormones and may not be constitutive as previously thought, and that the HuH7 ALDH is regulated differently.

The aldehyde dehydrogenase ALDH2*2 allele exhibits dominance over ALDH2*1 in transduced HeLa cells

Individuals heterozygous or homozygous for the variant aldehyde dehydrogenase (ALDH2) allele (ALDH2*2), which encodes a protein differing only at residue 487 from the normal protein, have decreased ALDH2 activity in liver extracts and experience cutaneous flushing when they drink alcohol. The mechanisms by which this allele exerts its dominant effect is unknown. To study this effect, the human ALDH2*1 cDNA was cloned and the ALDH2*2 allele was generated by site-directed mutagenesis. These cDNAs were transduced using retroviral vectors into HeLa and CV1 cells, which do not express ALDH2. The normal allele directed synthesis of immunoreactive ALDH2 protein (ALDH2E) with the expected isoelectric point. Extracts of these cells contained increased aldehyde dehydrogenase activity with low Km for the aldehyde substrate. The ALDH2*2 allele directed synthesis of mRNA and immunoreactive protein (ALDH2K), but the protein lacked enzymatic activity. When ALDH2*1-expressing cells were transduced with ALDH2*2 vectors, both mRNAs were expressed and immunoreactive proteins with isoelectric points ranging between those of ALDH2E and ALDH2K were present, indicating that the subunits formed heteromers. ALDH2 activity in these cells was reduced below that of the parental ALDH2*1-expressing cells. Thus, the ALDH2*2 allele is sufficient to cause ALDH2 deficiency in vitro.

The novel aldehyde dehydrogenase gene, ALDH5, encodes an active aldehyde dehydrogenase enzyme

The mRNA for the novel aldehyde dehydrogenase 5 (ALDH5) gene was detected in HuH7 hepatoma cells. The cells also expressed cytosolic aldehyde dehydrogenase (ALDH1) mRNA, but no mitochondrial aldehyde dehydrogenase (ALDH2) mRNA. Extracts of the hepatoma cells contained an enzymatic activity with an isoelectric point similar to that of ALDH1. This enzyme activity was insensitive to inhibition by disulfiram, a potent inhibitor of ALDH1. The enzyme was active with short chain aldehydes (acetaldehyde and propionaldehyde) and NAD+, but not with NADP+, and the activity was higher in the mitochondrial pellet than other cell fractions. These studies demonstrate the expression of ALDH5 mRNA in a human hepatoma and suggest that the gene product is enzymatically active and probably resides in the mitochondria.

Chemical modification and site-directed mutagenesis studies of rat 3-hydroxyisobutyrate dehydrogenase

Rat 3-hydroxyisobutyrate dehydrogenase shares sequence homology with the short-chain alcohol dehydrogenases. Site-directed mutagenesis and chemical modifications were used to examine the roles of cysteine residues and other residues conserved in this family of enzymes. It was found that a highly conserved tyrosine residue, Y162 in 3-hydroxyisobutyrate dehydrogenase, does not function catalytically as it may in other short-chain alcohol dehydrogenases. Of the six cysteine residues present in 3-hydroxyisobutyrate dehydrogenase, only cysteine 215 was found to be critical to catalysis. C215A and C215D mutant enzymes were catalytically inactive but produced CD spectra identical to wild-type enzyme. C215S mutant enzyme displayed a lowered Vmax than wild-type enzyme, but Km values were similar to those of wild-type enzyme. The C215S mutant enzyme was inactivated by treatment with phenylmethanesulfonyl fluoride but was not inactivated by treatment with iodoacetate, whereas the wild-type enzyme was inactivated by treatment with iodoacetate but not inactivated by treatment with phenylmethanesulfonyl fluoride. The present data suggest that 3-hydroxyisobutyrate dehydrogenase differs in mechanism from other short-chain alcohol dehydrogenases studied to date and that cysteine 215 has a critical function in catalysis, possibly as a general base catalyst.

A new family of protein kinases--the mitochondrial protein kinases

Molecular cloning has provided evidence for a new family of protein kinases in eukaryotic cells. These kinases show no sequence similarity with other eukaryotic protein kinases, but are related by sequence to the histidine protein kinases found in prokaryotes. These protein kinases, responsible for phosphorylation and inactivation of the branched-chain alpha-ketoacid dehydrogenase and pyruvate dehydrogenase complexes, are located exclusively in mitochondrial matrix space and have most likely evolved from genes originally present in respiration-dependent bacteria endocytosed by primitive eukaryotic cells. Long-term regulatory mechanisms involved in the control of the activities of these two kinases are of considerable interest. Dietary protein deficiency increases the activity of branched-chain alpha-ketoacid dehydrogenase kinase associated with the branched-chain alpha-ketoacid dehydrogenase complex. The amount of branched-chain alpha-ketoacid dehydrogenase kinase protein associated with the branched-chain alpha-ketoacid dehydrogenase complex and the message level for branched-chain alpha-ketoacid dehydrogenase kinase are both greatly increased in the liver of rats starved for protein, suggesting increased expression of the gene encoding branched-chain alpha-ketoacid dehydrogenase kinase. The increase in branched-chain alpha-ketoacid dehydrogenase kinase activity results in greater phosphorylation and lower activity of the branched-chain alpha-ketoacid dehydrogenase complex. The metabolic consequence is conservation of branched chain amino acids for protein synthesis during periods of dietary protein deficiency. Two isoforms of pyruvate dehydrogenase kinase have been identified and cloned. Pyruvate dehydrogenase kinase 1, the first isoform cloned, corresponds to the 48 kDa subunit of the pyruvate dehydrogenase kinase isolated from rat heart tissue. Pyruvate dehydrogenase kinase 2, the second isoform cloned, corresponds to the 45 kDa subunit of this enzyme. In addition, it also appears to correspond to a possibly free or soluble form of pyruvate dehydrogenase kinase that was originally named kinase activator protein. Assuming that differences in kinetic and/or regulatory properties of these isoforms exist, tissue specific expression of these enzymes and/or control of their association with the complex will probably prove to be important for the long term regulation of the activity of the pyruvate dehydrogenase complex. Starvation and the diabetic state are known to greatly increase activity of the pyruvate dehydrogenase kinase in the liver, heart and muscle of the rat. This contributes in these states to the phosphorylation and inactivation of the pyruvate dehydrogenase complex and conservation of pyruvate and lactate for gluconeogenesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Ethanol oxidizing enzymes: roles in alcohol metabolism and alcoholic liver disease

The elucidation of nucleotide and amino acid sequences of the genes and enzymes involved in the metabolism of ethanol has led to the ability to genotype individuals simply and rapidly. Although the different isozymes were once thought to be a likely explanation for between individual differences in alcohol elimination rates, this has not been found to be the case. Other explanations that remain to be investigated include potential regulatory variants in the genes that alter the level of expression of the enzymes, and genetic influences on activity of the malateaspartate shuttle and rates of mitochondrial NADH reoxidation. However, the isozymes encoded by ADH2*2 and ALDH2*2 have been found to influence alcohol drinking behavior or alcoholism substantially. This supports the original premise that the metabolic disposition of ethanol affects individuals' responses to it. The results suggest that any additional variants might also contribute to the spectrum of individual drinking preferences. Among heavy drinkers, the influence of the isozymes on risk of alcoholic liver disease has not been found to be great, suggesting that many other factors, perhaps interacting with the enzyme polymorphisms, are involved in determining susceptibility.

Seven transmembrane domain receptor subtypes identified in NG108-15 cells by reverse transcription-polymerase chain reaction

NG108-15 neuroblastoma x glioma cells are widely used for the study of neurotransmitter receptors. We utilized reverse transcription-polymerase chain reaction to amplify members of the seven transmembrane domain class of G-protein linked receptors using RNA isolated from NG108-15 cells. Two complementary DNAs representing receptors were obtained; based upon comparison with the sequence database, they probably represent the murine dopamine D1A receptor and a receptor closely related to the serotonin 5HT1D receptor subtype. The finding of the 5HT receptor subtype is of interest, as only the 5HT3 subtype was previously identified in NG108-15 cells by pharmacological means. Certain responses of NG108-15 cells to serotonin have been described that do not appear to be mediated by known 5HT receptor subtypes. The cDNA we cloned may therefore represent an additional 5HT1D subclass.

Characterization of the 5'-flanking sequence of rat class I alcohol dehydrogenase gene

Expression of the rat class I alcohol dehydrogenase (ADH) gene is highest in the liver and regions of the intestine. We characterized over 3 kilobases of the gene's 5'-flanking region by sequencing and transient transfection. Alignment of the flanking sequence of the rat gene with those of the mouse and human class I genes revealed a cis-acting element, known to be a functional glucocorticoid response element in the human gene and conserved in the mouse, is interrupted in the rat promoter by a 490-base pair processed retropseudogene of the ribosomal protein S25. Southern analysis indicated that this inserted element is present in the class I ADH promoters of multiple strains of rat. Transfection analysis of the rat and mouse promoters showed that the mouse, but not the rat promoter, is inducible by dexamethasone. Electrophoretic mobility shift assays using nuclear extracts from dexamethasone-treated cells confirmed that the mouse's element interacts with the glucocorticoid receptor. Transient transfection of the 5'-flanking region of the rat gene linked to a human growth hormone reporter demonstrated the liver and intestinal specificity of the rat promoter. Two positive elements, one from nucleotides -1,327 to -977 and the other from -241 to -12, were shown to support high levels of reporter activity. In addition, a suppressive element was localized between nucleotides -403 and -241, a region of DNA situated within the domain of the S25 ribosomal protein pseudogene.

Genetic aspects and risk factors in alcoholism and alcoholic liver disease

There is a great deal of evidence for genetic predisposition to alcoholism; considerably less is known regarding predisposition to alcoholic liver disease. The specific genes involved in either disorder are not well understood, although the enzymes of alcohol metabolism appear to play some role. It will be interesting to determine whether genetic factors that alter the expression of these enzymes, in addition to altering the kinetics of the enzymes, could modify responses to drinking. Work in the next few years will include determination of which responses to alcohol are indeed genetically influenced in twin studies, testing additional candidate genes for alcohol-related traits in populations and families, as well as the application of genomic mapping methodologies to alcoholic pedigrees. The latter strategy will be integrated into the larger number of studies that will grow from the Human Genome Project. Animal studies with selectively bred lines of rodents that differ in voluntary alcohol consumption will lead the way to define the neuronal and behavioral substrates responsible for differences in alcohol-drinking behavior. The use of the quantitative trait locus (QTL) mapping approach in F2 intercross between two inbred strains of rodents with opposite alcohol-response characteristics and in recombinant inbred strains derived from F2 intercross already has and will continue to help identify chromosomal locations of genes relevant to voluntary alcohol consumption. Perhaps in the future selective breeding of rodents and QTL mapping strategies can also be used to determine the biology and genetics of alcohol-induced liver injury.

Site-directed mutagenesis of phosphorylation sites of the branched chain alpha-ketoacid dehydrogenase complex

Regulation of the branched chain alpha-ketoacid dehydrogenase complex, the rate-limiting enzyme of branched chain amino acid catabolism, involves phosphorylation of 2 amino acid residues (site 1, serine 293; site 2, serine 303). To directly assess the roles played by these sites, site-directed mutagenesis was used to convert these serines to glutamates and/or alanines. Functional E1 heterotetramers were expressed in Escherichia coli carrying genes for E1 alpha and E1 beta under control of separate T7 promoters in a dicistronic vector. Mutation of phosphorylation site 1 serine to glutamate inactivated E1 activity, i.e. mimicked the effect of phosphorylation of site 1. Replacement of the site 1 serine with alanine greatly increased Km for the alpha-ketoacid substrate but had no effect on maximum velocity. The site 1 serine to alanine mutant was phosphorylated at site 2, but phosphorylation had no effect upon enzyme activity. Mutation of site 2 serine to either glutamate or alanine also had no effect upon enzyme activity, but phosphorylation of these proteins at site 1 inhibited enzyme activity. E1 mutated to change both phosphorylation site serines to glutamates was without enzyme activity. The binding affinity of E1 to the E2 core was not affected by mutation of the phosphorylation sites to glutamates, suggesting no gross perturbation of the association of E1 with the E2 core. The results provide direct evidence that a negative charge at phosphorylation site 1 is responsible for kinase-mediated inactivation of E1. Site 2 is silent with respect to regulation of activity by phosphorylation.

Low frequency of the ADH2*2 allele among Atayal natives of Taiwan with alcohol use disorders

Genetic variation at two polymorphic alcohol dehydrogenase loci, ADH2 and ADH3, and at the polymorphic mitochondrial aldehyde dehydrogenase locus, ALDH2, may influence the risk of developing alcoholism by modulating the rate of elimination of ethanol and the rate of formation and elimination of acetaldehyde. Populations differ in allele frequencies at these loci. We determined the genotypes at all three of these loci in Atayal natives of Taiwan. The frequencies of ADH2*2, ADH3*1, and ALDH2*1 alleles (0.91, 0.99, and 0.95, respectively) were significantly higher among the Atayal than among a predominantly Han Chinese population from Taiwan. Among the Atayal, the group with alcohol use disorders (alcohol dependence and alcohol abuse) had a significantly lower frequency of the ADH2*2 allele (0.82) than those without alcohol use disorders (0.91). The ADH2*2 allele encodes the beta 2 subunit; isozymes containing beta 2 subunits oxidize alcohol faster in vitro than the beta 1 beta 1 isozyme encoded by ADH2*1. Thus, the simplest explanation for these data is that individuals with a beta 2 isozymes have a higher rate of ethanol oxidation, which is a deterrent to alcohol abuse and dependence in some individuals. The Atayal with alcohol use disorders also had a lower frequency of ALDH2*2 than the controls; this allele is known to be responsible for the alcohol-flush reaction among Asians, and thereby deters drinking.

Allele frequencies of the preproenkephalin A (PENK) gene CA repeat in Asians, African-Americans, and Caucasians: lack of evidence for different allele frequencies in alcoholics

Evidence from animal models and from recent reports on the efficacy of the opioid antagonist naltrexone in the treatment of alcoholism suggests that the endogenous opioid systems may play a role in alcohol seeking behavior. The gene encoding preproenkephalin A (PENK) is flanked at its 3' end by a polymorphic (CA)n repeat. We determined the allele frequencies for this locus in samples of Chinese and Atayal living in Taiwan, Caucasians living in the United States and Byelorussia, and African-Americans living in the United States. We compared the allele frequencies of nonalcoholics in each population with those of alcoholics with or without alcohol-induced organ pathology. There was no difference in allele frequencies within any racial group when alcoholics with or without organ pathology were compared; there was also no difference in allele frequency between nonalcoholics and alcoholics within the two Asian populations, Caucasians, or African-Americans. There were highly significant differences in the frequency of the various length polymorphisms between the Asian, Caucasian, and African-American samples.

Intrasplenic transplantation of isolated periportal and perivenous hepatocytes as a long-term system for study of liver-specific gene expression

Many hepatocyte-specific genes are expressed heterogeneously in the liver lobule depending on the location of the hepatocytes in relation to the inflow or outflow of portal blood (i.e., periportal or perivenous). For example, albumin is expressed in all hepatocytes but more so in the periportal zone, cytochrome P-450IIE1 is exclusively expressed in the perivenous zone and glutamine synthetase is limited to one or two cell layers next to the terminal hepatic venule. Additionally, hepatic damage caused by several xenobiotics, including carbon tetrachloride, is more severe in the perivenous zone. We have isolated highly enriched perivenous and periportal hepatocytes by means of a digitonin-collagenase perfusion method and transplanted them separately into the spleens of syngeneic rats. After transplantation, hepatocyte-specific gene expression in the transplanted perivenous and periportal cells was monitored for up to 13 mo with in situ hybridization to detect the specific gene transcripts (mRNAs). We also studied the effects of carbon tetrachloride administration on transplanted periportal cells by comparing them with intrasplenic transplanted periportal hepatocytes without carbon tetrachloride treatment. Our results showed that: (a) both transplanted perivenous and periportal hepatocytes could survive and proliferate in the splenic microenvironment for a prolonged period; (b) long-term-transplanted periportal hepatocytes in spleen could eventually express a high level of cytochrome P-450IIE1 mRNA in all transplanted hepatocytes and could express glutamine synthetase mRNA in only about 5% to 10% of them, specifically those hepatocytes located adjacent to splenic blood vessels. It is noteworthy that periportal hepatocytes in situ normally do not express the glutamine synthetase gene and express only a low level of cytochrome P-450IIE1 mRNA; and (c) carbon tetrachloride yielded different toxic effects on transplanted periportal hepatocytes at day 3 and mo 8. Necrosis was seen only when transplanted periportal hepatocytes expressed a high level of cytochrome P-450IIE1 mRNA by mo 8.

Primary structure of pyruvate dehydrogenase kinase establishes a new family of eukaryotic protein kinases

We recently reported molecular cloning of the branched chain alpha-ketoacid dehydrogenase kinase, the first mitochondrial protein kinase to be cloned (Popov, K. M., Zhao, Y., Shimomura, Y., Kuntz, M. J., and Harris, R. A. (1992) J. Biol. Chem. 267, 13127-13130). From a search for proteins related to the branched chain alpha-ketoacid dehydrogenase kinase, a cDNA encoding the 434 amino acid residues corresponding to pyruvate dehydrogenase kinase has been cloned from a rat heart cDNA library. Evidence that the clone codes for pyruvate dehydrogenase kinase includes: (a) the deduced amino acid sequence is identical to the partial sequence of the kinase determined by direct sequencing; (b) expression of the cDNA in Escherichia coli resulted in synthesis of a protein that phosphorylated and inactivated the pyruvate dehydrogenase complex; (c) kinase activity of the recombinant protein is sensitive to inhibition by a specific inhibitor of pyruvate dehydrogenase kinase; and (d) antiserum raised against the recombinant protein recognized the protein subunit known to correspond to pyruvate dehydrogenase kinase in a highly purified preparation of the pyruvate dehydrogenase complex. Like the branched chain alpha-ketoacid dehydrogenase kinase, pyruvate dehydrogenase kinase lacks motifs usually associated with eukaryotic Ser/Thr-protein kinases. Considerable sequence similarity exists between these mitochondrial protein kinases and members of the prokaryotic histidine kinase family, a diverse set of sensing and response systems important in the regulation of bacterial processes. Thus, molecular cloning of these proteins establishes a new eukaryotic family of protein kinases that is related to a prokaryotic family of protein kinases.

Effects of ethanol on urinary acidification and on gluconeogenesis by isolated renal tubules

Class I alcohol dehydrogenase (ADH) is present in the kidney of rats. Rats fed an alcohol-containing diet long-term had higher urinary pH and reduced titratable acidity compared with pair-fed controls; rates of ammonium excretion were unchanged. The effects of ethanol on the metabolism of isolated renal tubules were then studied. Gluconeogenesis from lactate, pyruvate, or glutamine was not inhibited by 10 mmol/L ethanol during 30- or 60-minute incubations, although there was a trend toward increased lactate/pyruvate ratios at 30 minutes in the presence of ethanol. When the medium was also supplemented with oleate, glucose synthesis from most substrates was decreased, and the addition of ethanol inhibited glucose synthesis dramatically. This interaction between oleate and ethanol was not abolished by 4-methylpyrazole, an inhibitor of ADH. This effect of ethanol was highly dependent on the concentration of oleate present in the medium and was not observed with palmitate or decanoate; the inhibition was reversed by increasing the medium concentration of albumin. We conclude that ethanol may mildly perturb the redox state of isolated kidney tubules without inhibiting glucose synthesis, and that ethanol and oleate interact to inhibit renal gluconeogenesis by a mechanism highly dependent on the fatty acid concentration. The mechanism by which ethanol in the diet reduces renal acid excretion remains unknown.

The mitochondrial aldehyde dehydrogenase gene resides in an HTF island but is expressed in a tissue-specific manner

The tissue distribution of mitochondrial aldehyde dehydrogenase (ALDH2) in rats was analyzed by activity assays, and by Western and Northern blotting. ALDH2 was expressed at highest levels in liver. The mRNA levels were intermediate in the kidney and lung, while lower levels were found in spleen and heart. The transcript was undetectable in other tissues tested. The human ALDH2 5' flanking region (-200 to +60) contains similar numbers of CpG and GpC dinucleotides and the rat ALDH2 gene was undermethylated in liver, kidney, and spleen. This suggests that the ALDH2 promoter resides in a Hpa II tiny fragment (HTF) island, unlike most genes expressed in a tissue-specific manner.

Effects of thyroxine on the expression of alcohol dehydrogenase in rat liver and kidney

We studied the effect of thyroxine on alcohol dehydrogenase activity, immunoreactive protein levels and messenger RNA levels in the livers of thyroidectomized and sham-operated male rats. Effects on kidney alcohol dehydrogenase activity were also examined. Sham-operated rats injected with 100 micrograms thyroxine/kg/day, which induced hyperthyroidism, showed a 30% decrease in liver and a 40% decrease in kidney alcohol dehydrogenase activity compared with sham-operated rats injected with vehicle. Hypothyroid rats exhibited a 1.5-fold increase in alcohol dehydrogenase activity in liver and kidney compared with thyroidectomized rats injected with a replacement dose of 20 micrograms thyroxine/kg/day. We saw a twofold and a 2.5-fold higher level of alcohol dehydrogenase activity in liver and kidney, respectively, of hypothyroid rats compared with hyperthyroid rats. These effects were not accounted for by nutritional differences; daily food intake did not differ between groups. Immunoreactive protein levels as seen on Western blots varied in the same direction as enzyme activity. Northern-blot analysis showed higher levels of liver alcohol dehydrogenase messenger RNA in hypothyroid rats compared with euthyroid rats. These studies show that liver alcohol dehydrogenase activity and protein levels are modulated by thyroxine at pathophysiologically relevant levels and that this effect is not due to changes in food intake; kidney alcohol dehydrogenase activity is regulated in parallel. The change in alcohol dehydrogenase activity appears to be controlled in part by pretranslational mechanisms in hypothyroid animals and by posttranslational mechanisms in hyperthyroid animals.

Alcohol and aldehyde dehydrogenase polymorphisms and alcoholism

The alcohol-flush reaction occurs in Asians who inherit the mutant ALDH2*2 allele that produces an inactive aldehyde dehydrogenase enzyme. In these individuals, high blood acetaldehyde levels are believed to be the cause of the unpleasant symptoms that follow drinking. We measured the alcohol elimination rates and intensity of flushing in Chinese subjects in whom the alcohol dehydrogenase ADH2 and ALDH2 genotypes were determined. We also correlated ADH2, ADH3, and ALDH2 genotypes with drinking behavior in 100 Chinese men. We discovered that ADH2*2 and ADH3*1, alleles that encode the high activity forms of alcohol dehydrogenase, as well as the mutant ALDH2*2 allele were less frequent in alcoholics than in controls. The presence of ALDH2*2 was associated with slower alcohol metabolism and the most intense flushing. In those homozygous for ALDH2*1, the presence of two ADH2*2 alleles correlated with slightly faster alcohol metabolism and more intense flushing, although a great deal of variability in the latter was noted.

Detection of a CA repeat polymorphism in the rat class I alcohol dehydrogenase gene

Differences in the amount of alcohol dehydrogenase (ADH) expressed in liver could play a role in altering ethanol metabolic rates and thus influence alcohol consumption. There is an alternating purine-pyrimidine repeat length polymorphism in the first intron of mouse Adh-1. Mouse strains that lack 101 basepairs of this 288 basepairs alternating sequence express only half as much ADH mRNA and have lower ADH-A2 activity, suggesting that this alternating sequence might modify transcription of the gene. The rat class I ADH gene also has a CA repeat in the first intron. A polymerase chain reaction (PCR) method was used to amplify the CA repeat region in different rat lines to determine whether this CA repeat is polymorphic in the rat and if so, if different length repeats correlate with the drinking behavior of rats selectively bred for high [preferring (P); high alcohol drinking (HAD); Alko, Alcohol (AA) lines] and low [non-preferring (NP); low alcohol drinking (LAD); Alko, Non-Alcohol (ANA) rat lines] alcohol drinking. A CA repeat polymorphism was detected in rat class I ADH of these different rat lines, but there was no difference in the length of the repeat between the high and low drinking rats in each line. Liver ADH activity was also not significantly different between two rat lines that have different CA repeat lengths. Thus, there is CA repeat length polymorphism in the first intron of rat class I ADH, which may be useful in genomic mapping, but it is not associated with differences in ADH activity or drinking behavior in these rat lines.

Molecular cloning of the branched-chain alpha-keto acid dehydrogenase kinase and the CoA-dependent methylmalonate semialdehyde dehydrogenase

The complete amino acid sequence of rat liver CoA-dependent methylmalonate semialdehyde dehydrogenase, the enzyme responsible for the oxidative decarboxylation of malonate- and methylmalonate semialdehydes to acetyl- and propionyl-CoA in the distal portions of the valine and pyrimidine catabolic pathways, has been deduced from overlapping cDNAs obtained by screening a lambda gt11 library with nondegenerate oligonucleotide probes synthesized according to PCR-amplified portions coding for the N-terminal amino acid sequence of the enzyme. Although unique because of its requirement for coenzyme A, the methylmalonate semialdehyde dehydrogenase clearly belongs to the aldehyde dehydrogenase superfamily of enzymes. Quantitation of mRNA and protein levels indicates tissue-specific expression of methylmalonate semialdehyde dehydrogenase. A large increase in expression of methylmalonate semialdehyde dehydrogenase occurs during 3T3-L1 preadipocyte differentiation into adipocytes. The complete amino acid sequence of rat liver branched-chain alpha-ketoacid dehydrogenase kinase, the enzyme responsible for phosphorylation and inactivation of the branched-chain alpha-ketoacid dehydrogenase complex, was deduced from a cDNA cloned by a procedure similar to that described above for the methylmalonate semialdehyde dehydrogenase. Expression of the cDNA in E. coli yielded a protein that phosphorylated and inactivated the branched-chain alpha-ketoacid dehydrogenase complex. Very little sequence similarity between branched-chain alpha-ketoacid dehydrogenase kinase and other eukaryotic protein kinases could be identified. However, a high degree of similarity within subdomains characteristic of prokaryotic histidine protein kinases was apparent. Thus, this first mitochondrial protein kinase to be cloned appears closer, evolutionarily, to the prokaryotic histidine protein kinases than eukaryotic ser/thr protein kinases.