Cloning and characterization of a new functional human aldehyde dehydrogenase gene

The Concept of Cancer Stem Cells: Elaborating on ALDH1B1 as an Emerging Marker of Cancer Progression

Cancer is a multifactorial, complex disease exhibiting extraordinary phenotypic plasticity and diversity. One of the greatest challenges in cancer treatment is intratumoral heterogeneity, which obstructs the efficient eradication of the tumor. Tumor heterogeneity is often associated with the presence of cancer stem cells (CSCs), a cancer cell sub-population possessing a panel of stem-like properties, such as a self-renewal ability and multipotency potential. CSCs are associated with enhanced chemoresistance due to the enhanced efflux of chemotherapeutic agents and the existence of powerful antioxidant and DNA damage repair mechanisms. The distinctive characteristics of CSCs make them ideal targets for clinical therapeutic approaches, and the identification of efficient and specific CSCs biomarkers is of utmost importance. Aldehyde dehydrogenases (ALDHs) comprise a wide superfamily of metabolic enzymes that, over the last years, have gained increasing attention due to their association with stem-related features in a wide panel of hematopoietic malignancies and solid cancers. Aldehyde dehydrogenase 1B1 (ALDH1B1) is an isoform that has been characterized as a marker of colon cancer progression, while various studies suggest its importance in additional malignancies. Here, we review the basic concepts related to CSCs and discuss the potential role of ALDH1B1 in cancer development and its contribution to the CSC phenotype.

Annotation of 1350 Common Genetic Variants of the 19 ALDH Multigene Family from Global Human Genome Aggregation Database (gnomAD)

Human aldehyde dehydrogenase (ALDH) is a multigene family with 19 functional members encoding a class of diverse but important enzymes for detoxification or biotransformation of different endogenous and exogenous aldehyde substrates. Genetic mutations in the ALDH genes can cause the accumulation of toxic aldehydes and abnormal carbonyl metabolism and serious human pathologies. However, the physiological functions and substrate specificity of many ALDH genes are still unknown. Although many genetic variants of the ALDH gene family exist in human populations, their phenotype or clinical consequences have not been determined. Using the most comprehensive global human Genome Aggregation Database, gnomAD, we annotated here 1350 common variants in the 19 ALDH genes. These 1350 common variants represent all known genetic polymorphisms with a variant allele frequency of ≥0.1% (or an expected occurrence of ≥1 carrier per 500 individuals) in any of the seven major ethnic groups recorded by gnomAD. We detailed 13 types of DNA sequence variants, their genomic positions, SNP ID numbers, and allele frequencies among the seven major ethnic groups worldwide for each of the 19 ALDH genes. For the 313 missense variants identified in the gnomAD, we used two software algorithms, Polymorphism Phenotyping (PolyPhen) and Sorting Intolerant From Tolerant (SIFT), to predict the consequences of the variants on the structure and function of the enzyme. Finally, gene constraint analysis was used to predict how well genetic mutations were tolerated by selection forces for each of the ALDH genes in humans. Based on the ratio of observed and expected variant numbers in gnomAD, the three ALDH1A gene members, ALDH1A1, ALDH1A2, and ALDH1A3, appeared to have the lowest tolerance for loss-of-function mutations as compared to the other ALDH genes (# observed/# expected ratio 0.15–0.26). These analyses suggest that the ALDH1A1, ALDH1A2, and ALDH1A3 enzymes may serve a more essential function as compared with the other ALDH enzymes; functional loss mutations are much less common in healthy human populations than expected. This informatic analysis may assist the research community in determining the physiological function of ALDH isozymes and associate common variants with clinical phenotypes.

Human ALDH1B1 polymorphisms may affect the metabolism of acetaldehyde and all-trans retinaldehyde--in vitro studies and computational modeling

PURPOSE

To elucidate additional substrate specificities of ALDH1B1 and determine the effect that human ALDH1B1 polymorphisms will have on substrate specificity.

METHODS

Computational-based molecular modeling was used to predict the binding of the substrates propionaldehyde, 4-hydroxynonenal, nitroglycerin, and all-trans retinaldehyde to ALDH1B1. Based on positive in silico results, the capacity of purified human recombinant ALDH1B1 to metabolize nitroglycerin and all-trans retinaldehyde was explored. Additionally, metabolism of 4-HNE by ALDH1B1 was revisited. Databases queried to find human polymorphisms of ALDH1B1 identified three major variants: ALDH1B1*2 (A86V), ALDH1B1*3 (L107R), and ALDH1B1*5 (M253V). Computational modeling was used to predict the binding of substrates and of cofactor (NAD(+)) to the variants. These human polymorphisms were created and expressed in a bacterial system and specific activity was determined.

RESULTS

ALDH1B1 metabolizes (and appears to be inhibited by) nitroglycerin and has favorable kinetics for the metabolism of all-trans retinaldehyde. ALDH1B1 metabolizes 4-HNE with higher apparent affinity than previously described, but with low throughput. Recombinant ALDH1B1*2 is catalytically inactive, whereas both ALDH1B1*3 and ALDH1B1*5 are catalytically active. Modeling indicated that the lack of activity in ALDH1B1*2 is likely due to poor NAD(+) binding. Modeling also suggests that ALDH1B1*3 may be less able to metabolize all-trans retinaldehyde and that ALDH1B1*5 may bind NAD(+) poorly.

CONCLUSIONS

ALDH1B1 metabolizes nitroglycerin and all-trans-retinaldehyde. One of the three human polymorphisms, ALDH1B1*2, is catalytically inactive, likely due to poor NAD(+) binding. Expression of this variant may affect ALDH1B1-dependent metabolic functions in stem cells and ethanol metabolism.

Genetic variation in alcohol metabolizing enzymes among Inuit and its relation to drinking patterns

BACKGROUND

Variation in genes involved in alcohol metabolism is associated with drinking patterns worldwide. We compared variation in these genes among the Inuit with published results from the general population of Denmark and, due to the Asian ancestry of the Inuit, with Han Chinese. We analyzed the association between gene variations and drinking patterns among the Inuit.

METHODS

We genotyped 4162 Inuit participants from two population health surveys. Information on drinking patterns was available for 3560. Seven single nucleotide polymorphisms (SNPs) were examined: ADH1B arg48his, ADH1C ile350val, ADH1C arg272gln, ALDH2 glu504lys, ALDH2 5'-UTR A-357G, ALDH1B1 ala86val and ALDH1B1 arg107leu.

RESULTS

The allele distribution differed significantly between Inuit and the general population of Denmark. A protective effect on heavy drinking was found for the TT genotype of the ALDH1B1 arg107leu SNP (OR=0.59; 95% CI 0.37-0.92), present in 3% of pure Inuit and 37% of Danes. The ADH1C GG genotype was associated with heavy drinking and a positive CAGE test (OR 1.34; 95% CI 1.05-1.72). It was present in 27% of Inuit and 18% of Danes. The Asian genotype pattern with a high frequency of the ADH1B A allele and an ALDH2 gene coding for an inactive enzyme was not present in Greenland.

CONCLUSIONS

ADH1C and ALDH1B1 arg107leu SNPs play a role in the shaping of drinking patterns among the Inuit in Greenland. A low frequency of the ALDH1B1 arg107leu TT genotype compared with the general population in Denmark deserves further study. This genotype was protective of heavy drinking among the Inuit.

Comparative genomics, molecular evolution and computational modeling of ALDH1B1 and ALDH2

Vertebrate ALDH2 genes encode mitochondrial enzymes capable of metabolizing acetaldehyde and other biological aldehydes in the body. Mammalian ALDH1B1, another mitochondrial enzyme sharing 72% identity with ALDH2, is also capable of metabolizing acetaldehyde but has a tissue distribution and pattern of activity distinct from that of ALDH2. Bioinformatic analyses of several vertebrate genomes were undertaken using known ALDH2 and ALDH1B1 amino acid sequences. Phylogenetic analysis of many representative vertebrate species (including fish, amphibians, birds and mammals) indicated the presence of ALDH1B1 in many mammalian species and in frogs (Xenopus tropicalis); no evidence was found for ALDH1B1 in the genomes of birds, reptiles or fish. Predicted vertebrate ALDH2 and ALDH1B1 subunit sequences and structures were highly conserved, including residues previously shown to be involved in catalysis and coenzyme binding for human ALDH2. Studies of ALDH1B1 sequences supported the hypothesis that the ALDH1B1 gene originated in early vertebrates from a retrotransposition of the vertebrate ALDH2 gene. Given the high degree of similarity between ALDH2 and ALDH1B1, it is surprising that individuals with an inactivating mutation in ALDH2 (ALDH2*2) do not exhibit a compensatory increase in ALDH1B1 activity. We hypothesized that the similarity between the two ALDHs would allow for dominant negative heterotetramerization between the inactive ALDH2 mutants and ALDH1B1. Computational-based molecular modeling studies examining predicted protein-protein interactions indicated that heterotetramerization between ALDH2 and ALDH1B1 subunits was highly probable and may partially explain a lack of compensation by ALDH1B1 in ALDH2(∗)2 individuals.

Differential metabolism of organic nitrates by aldehyde dehydrogenase 1a1 and 2: substrate selectivity, enzyme inactivation, and active cysteine sites

Organic nitrate vasodilators (ORN) exert their pharmacologic effects through the metabolic release of nitric oxide (NO). Mitochondrial aldehyde dehydrogenase (ALDH2) is the principal enzyme responsible for NO liberation from nitroglycerin (NTG), but lacks activity towards other ORN. Cytosolic aldehyde dehydrogenase (ALDH1a1) can produce NO from NTG, but its activity towards other ORN is unknown. Using purified enzymes, we showed that both isoforms could liberate NO from NTG, isosorbide dinitrate (ISDN), and nicrorandil, while only ALDH1a1 metabolized isosorbide-2-mononitrate and isosorbide-5-mononitrate (IS-5-MN). Following a 10-min incubation with purified enzyme, 0.1 mM NTG and 1 mM ISDN potently inactivated ALDH1a1 (to 21.9% ± 11.1% and 0.44% ± 1.04% of control activity, respectively) and ALDH2 (no activity remaining and 4.57% ± 7.92% of control activity, respectively), while 1 mM IS-5-MN exerted only modest inactivation of ALDH1a1 (reduced to 89% ± 4.3% of control). Cytosolic ALDH in hepatic homogenates incubated at the vascular EC(50) concentrations of ORN was inactivated by NTG (to 45.1% ± 8.1% of control activity) while mitochondrial ALDH was inactivated by NTG and nicorandil (to 68.2% ± 10.0% and 78.7% ± 19.8% of control, respectively). Via site-directed mutagenesis, the active sites of ORN metabolism of ALDH2 (Cys-319) and ALDH1a1 (Cys-303) were found to be identical to those responsible for their dehydrogenase activity. Cysteine-302 of ALDH1a1 and glutamate-504 of ALDH2 were found to modulate the rate of ORN metabolism. These studies provide further characterization of the substrate selectivity, inactivation, and active sites of ALDH2 and ALDH1a1 toward ORN.

The association of alcohol and alcohol metabolizing gene variants with diabetes and coronary heart disease risk factors in a white population

BACKGROUND

Epidemiological studies have shown a J- or U-shaped relation between alcohol and type 2 diabetes and coronary heart disease (CHD). The underlying mechanisms are not clear. The aim was to examine the association between alcohol intake and diabetes and intermediate CHD risk factors in relation to selected ADH and ALDH gene variants.

METHODOLOGY/PRINCIPAL FINDINGS

Cross-sectional study including 6,405 Northern European men and women aged 30-60 years from the general population of Copenhagen, Denmark. Data were collected with self-administered questionnaires, a physical examination, a 2 hour oral glucose tolerance test, and various blood tests. J shaped associations were observed between alcohol and diabetes, metabolic syndrome (MS), systolic and diastolic blood pressure, triglyceride, total cholesterol, and total homocysteine. Positive associations were observed with insulin sensitivity and HDL cholesterol, and a negative association with insulin release. Only a few of the selected ADH and ALDH gene variants was observed to have an effect. The ADH1c (rs1693482) fast metabolizing CC genotype was associated with an increased risk of impaired glucose tolerance (IGT)/diabetes compared to the CT and TT genotypes. Significant interactions were observed between alcohol and ADH1b (rs1229984) with respect to LDL and between alcohol and ALDH2 (rs886205) with respect to IGT/diabetes.

CONCLUSIONS/SIGNIFICANCE

The selected ADH and ALDH gene variants had only minor effects, and did not seem to markedly modify the health effects of alcohol drinking. The observed statistical significant associations would not be significant, if corrected for multiple testing.

Aldehyde dehydrogenase 1B1: molecular cloning and characterization of a novel mitochondrial acetaldehyde-metabolizing enzyme

Ethanol-induced damage is largely attributed to its toxic metabolite, acetaldehyde. Clearance of acetaldehyde is achieved by its oxidation, primarily catalyzed by the mitochondrial class II aldehyde dehydrogenase (ALDH2). ALDH1B1 is another mitochondrial aldehyde dehydrogenase (ALDH) that shares 75% peptide sequence homology with ALDH2. Recent population studies in whites suggest a role for ALDH1B1 in ethanol metabolism. However, to date, no formal documentation of the biochemical properties of ALDH1B1 has been forthcoming. In this current study, we cloned and expressed human recombinant ALDH1B1 in Sf9 insect cells. The resultant enzyme was purified by affinity chromatography to homogeneity. The kinetic properties of purified human ALDH1B1 were assessed using a wide range of aldehyde substrates. Human ALDH1B1 had an exclusive preference for NAD(+) as the cofactor and was catalytically active toward short- and medium-chain aliphatic aldehydes, aromatic aldehydes, and the products of lipid peroxidation, 4-hydroxynonenal and malondialdehyde. Most importantly, human ALDH1B1 exhibited an apparent K(m) of 55 μM for acetaldehyde, making it the second low K(m) ALDH for metabolism of this substrate. The dehydrogenase activity of ALDH1B1 was sensitive to disulfiram inhibition, a feature also shared with ALDH2. The tissue distribution of ALDH1B1 in C57BL/6J mice and humans was examined by quantitative polymerase chain reaction, Western blotting, and immunohistochemical analysis. The highest expression occurred in the liver, followed by the intestinal tract, implying a potential physiological role for ALDH1B1 in these tissues. The current study is the first report on the expression, purification, and biochemical characterization of human ALDH1B1 protein.

Genetic determinants of both ethanol and acetaldehyde metabolism influence alcohol hypersensitivity and drinking behaviour among Scandinavians

BACKGROUND

Although hypersensitivity reactions following intake of alcoholic drinks are common in Caucasians, the underlying mechanisms and clinical significance are not known. In contrast, in Asians, alcohol-induced asthma and flushing have been shown to be because of a single nucleotide polymorphism (SNP), the acetaldehyde dehydrogenase 2 (ALDH2) 487lys, causing decreased acetaldehyde (the metabolite of ethanol) metabolism and high levels of histamine. However, the ALDH2 487lys is absent in Caucasians.

OBJECTIVES

To investigate the genetic determinants of self-reported alcohol-induced hypersensitivity reactions in Caucasians.

METHODS

The study included two population-based studies of 1216 and 6784 adults living in Copenhagen. Assessment of alcohol consumption and hypersensitivity reactions (in a subgroup) was performed by a questionnaire and was related to common SNPs of genes encoding alcohol dehydrogenases (ADHs) and ALDHs.

RESULTS

In both populations, alcohol drinkers with a genetically determined fast metabolism of ethanol (the A allele of the ADH1b rs1229984) had an increased risk of alcohol-induced hypersensitivity reactions (odds ratio AA/AG vs. GG in combined populations: 1.82, 95% CI 1.04-3.17). In both populations, a common SNP encoding ALDH1b1 (rs2228093) was found to be significantly associated with alcohol-induced hypersensitivity (odds ratio TT vs. CC in combined populations: 2.53, 95% CI 1.31-4.90).

CONCLUSIONS

Our data support that alcohol sensitivity in Caucasians is genetically determined and suggest that a histamine-releasing effect of acetaldehyde represents a plausible biological mechanism. Furthermore, we present the first report of a clinically significant SNP within the acetaldehyde-metabolizing system in a Caucasian population.

Non-P450 aldehyde oxidizing enzymes: the aldehyde dehydrogenase superfamily

BACKGROUND

Aldehydes are highly reactive molecules. While several non-P450 enzyme systems participate in their metabolism, one of the most important is the aldehyde dehydrogenase (ALDH) superfamily, composed of NAD(P)+-dependent enzymes that catalyze aldehyde oxidation.

OBJECTIVE

This article presents a review of what is currently known about each member of the human ALDH superfamily including the pathophysiological significance of these enzymes.

METHODS

Relevant literature involving all members of the human ALDH family was extensively reviewed, with the primary focus on recent and novel findings.

CONCLUSION

To date, 19 ALDH genes have been identified in the human genome and mutations in these genes and subsequent inborn errors in aldehyde metabolism are the molecular basis of several diseases, including Sjögren-Larsson syndrome, type II hyperprolinemia, gamma-hydroxybutyric aciduria and pyridoxine-dependent seizures. ALDH enzymes also play important roles in embryogenesis and development, neurotransmission, oxidative stress and cancer. Finally, ALDH enzymes display multiple catalytic and non-catalytic functions including ester hydrolysis, antioxidant properties, xenobiotic bioactivation and UV light absorption.

The association of ADH and ALDH gene variants with alcohol drinking habits and cardiovascular disease risk factors

BACKGROUND

Genetic variation in ethanol metabolism may have an influence on both alcohol drinking habits and the susceptibility to health effects of alcohol drinking. Such influences are likely to bias exposure-disease associations in epidemiologic studies of health effects of alcohol drinking. In a Caucasian population, we examined the association of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) genetic variants with alcohol drinking habits, biomarkers of alcohol exposure, and risk factors for cardiovascular disease.

METHODS

The study population consisted of 1,216 Danish men and women aged 15-77 years participating in a health examination in 1998. The health examination included a self-administered questionnaire (alcohol drinking habits), a physical examination (blood pressure), and various blood tests [alanine aminotransferase (ALAT), erythrocyte mean corpuscular volume (E-MCV), and lipids]. ADH and ALDH gene variants were determined by standard techniques. Data were analyzed by regression analyses adjusted for relevant confounders.

RESULTS

Self-reported alcohol drinking was significantly associated with increasing levels of ALAT, E-MCV, high-density lipoprotein cholesterol, and blood pressure. The ALDH1b ala69val variant was associated with nondrinking and total alcohol intake. The ALDH2 promoter variant was associated with binge-drinking, and the ALDH1b1 ala69val polymorphism was associated with diastolic blood pressure. We did not find any statistically significant interactions between any of the gene variants and alcohol consumption in relation to the various outcomes.

CONCLUSIONS

In this Caucasian population sample, we found evidence to support that genetic variation in ethanol metabolism may influence drinking habits, but no statistically significant gene-environment interactions. More large-scale epidemiologic studies are needed to confirm theses results and to further investigate genetic susceptibility to the effects of alcohol drinking.

Tissue distribution, ontogeny, and regulation of aldehyde dehydrogenase (Aldh) enzymes mRNA by prototypical microsomal enzyme inducers in mice

Aldehyde dehydrogenases (Aldhs) are a group of nicotinamide adenine dinucleotide phosphate-dependent enzymes that catalyze the oxidation of a wide spectrum of aldehydes to carboxylic acids. Tissue distribution and developmental changes in the expression of the messenger RNA (mRNA) of 15 Aldh enzymes were quantified in male and female mice tissues using the branched DNA signal amplification assay. Furthermore, the regulation of the mRNA expression of Aldhs by 15 typical microsomal enzyme inducers (MEIs) was studied. Aldh1a1 mRNA expression was highest in ovary; 1a2 in testis; 1a3 in placenta; 1a7 in lung; 1b1 in small intestine; 2 in liver; 3a1 in stomach; 3a2 and 3b1 expression was ubiquitous; 4a1, 6a1, 7a1, and 8a1 in liver and kidney; 9a1 in liver, kidney, and small intestine; and 18a1 in ovary and small intestine. mRNAs of different Aldh enzymes were detected at lower levels in fetuses than adult mice and gradually increased after birth to reach adult levels between 15 and 45 days of age, when the gender difference began to appear. Aromatic hydrocarbon receptor (AhR) ligands induced the liver mRNA expression of Aldh1a7, 1b1, and 3a1, constitutive androstane receptor (CAR) activators induced Aldh1a1 and 1a7, whereas pregnane X receptor (PXR) ligands and NF-E2 related factor 2 (Nrf2) activators induced Aldh1a1, 1a7, and 1b1. Peroxisome proliferator activator receptor alpha (PPAR alpha) ligands induced the mRNA expression in liver of almost all Aldhs. The Aldh organ-specific distribution may be important in elucidating their role in metabolism, elimination, and organ-specific toxicity of xenobiotics. Finally, in contrast to other phase-I metabolic enzymes such as CYP450 enzymes, Aldh mRNA expression seems to be generally insensitive to typical microsomal inducers except PPAR alpha ligands.

Overview of the role of alcohol dehydrogenase and aldehyde dehydrogenase and their variants in the genesis of alcohol-related pathology

Alcohol dehydrogenase (ADH) and mitochondrial aldehyde dehydrogenase (ALDH2) are responsible for metabolizing the bulk of ethanol consumed as part of the diet and their activities contribute to the rate of ethanol elimination from the blood. They are expressed at highest levels in liver, but at lower levels in many tissues. This pathway probably evolved as a detoxification mechanism for environmental alcohols. However, with the consumption of large amounts of ethanol, the oxidation of ethanol can become a major energy source and, particularly in the liver, interferes with the metabolism of other nutrients. Polymorphic variants of the genes for these enzymes encode enzymes with altered kinetic properties. The pathophysiological effects of these variants may be mediated by accumulation of acetaldehyde; high-activity ADH variants are predicted to increase the rate of acetaldehyde generation, while the low-activity ALDH2 variant is associated with an inability to metabolize this compound. The effects of acetaldehyde may be expressed either in the cells generating it, or by delivery of acetaldehyde to various tissues by the bloodstream or even saliva. Inheritance of the high-activity ADH β2, encoded by theADH2*2gene, and the inactiveALDH2*2gene product have been conclusively associated with reduced risk of alcoholism. This association is influenced by gene–environment interactions, such as religion and national origin. The variants have also been studied for association with alcoholic liver disease, cancer, fetal alcohol syndrome, CVD, gout, asthma and clearance of xenobiotics. The strongest correlations found to date have been those between theALDH2*2allele and cancers of the oro-pharynx and oesophagus. It will be important to replicate other interesting associations between these variants and other cancers and heart disease, and to determine the biochemical mechanisms underlying the associations.

Is retinoic acid genetic machinery a chordate innovation?

Development of many chordate features depends on retinoic acid (RA). Because the action of RA during development seems to be restricted to chordates, it had been previously proposed that the "invention" of RA genetic machinery, including RA-binding nuclear hormone receptors (Rars), and the RA-synthesizing and RA-degrading enzymes Aldh1a (Raldh) and Cyp26, respectively, was an important step for the origin of developmental mechanisms leading to the chordate body plan. We tested this hypothesis by conducting an exhaustive survey of the RA machinery in genomic databases for twelve deuterostomes. We reconstructed the evolution of these genes in deuterostomes and showed for the first time that RA genetic machinery--that is Aldh1a, Cyp26, and Rar orthologs--is present in nonchordate deuterostomes. This finding implies that RA genetic machinery was already present during early deuterostome evolution, and therefore, is not a chordate innovation. This new evolutionary viewpoint argues against the hypothesis that the acquisition of gene families underlying RA metabolism and signaling was a key event for the origin of chordates. We propose a new hypothesis in which lineage-specific duplication and loss of RA machinery genes could be related to the morphological radiation of deuterostomes.

Human aldehyde dehydrogenases: potential pathological, pharmacological, and toxicological impact

Aldehyde dehydrogenases catalyze the pyridine nucleotide-dependent oxidation of aldehydes to acids. Seventeen enzymes are currently viewed as belonging to the human aldehyde dehydrogenase superfamily. Summarized herein, insofar as the information is available, are the structural composition, physical properties, tissue distribution, subcellular location, substrate specificity, and cofactor preference of each member of this superfamily. Also summarized are the chromosomal locations and organization of the genes that encode these enzymes and the biological consequences when enzyme activity is lost or substantially diminished. Broadly, aldehyde dehydrogenases can be categorized as critical for normal development and/or physiological homeostasis (1). even when the organism is in a friendly environment or (2). only when the organism finds itself in a hostile environment. The primary, if not sole, evolved raison d'être of first category aldehyde dehydrogenases appears to be to catalyze the biotransformation of a single endobiotic for which they are relatively specific and of which the resultant metabolite is essential to the organism. Most of the human aldehyde dehydrogenases for which the relevant information is available fall into this category. Second category aldehyde dehydrogenases are relatively substrate nonspecific and their evolved raison d'être seems to be to protect the organism from potentially harmful xenobiotics, specifically aldehydes or xenobiotics that give rise to aldehydes, by catalyzing their detoxification. Thus, the lack of a fully functional first category aldehyde dehydrogenase results in a gross pathological phenotype in the absence of any insult, whereas the lack of a functional second category aldehyde dehydrogenase is ordinarily of no consequence with respect to gross phenotype, but is of consequence in that regard when the organism is subjected to a relevant insult.

Role of aldehyde dehydrogenases in endogenous and xenobiotic metabolism

Aldehydes are highly reactive molecules that are intermediates or products involved in a broad spectrum of physiologic, biologic and pharmacologic processes. Aldehydes are generated from chemically diverse endogenous and exogenous precursors and aldehyde-mediated effects vary from homeostatic and therapeutic to cytotoxic, and genotoxic. One of the most important pathways for aldehyde metabolism is their oxidation to carboxylic acids by aldehyde dehydrogenases (ALDHs). Oxidation of the carbonyl functional group is considered a general detoxification process in that polymorphisms of several human ALDHs are associated a disease phenotypes or pathophysiologies. However, a number of ALDH-mediated oxidation form products that are known to possess significant biologic, therapeutic and/or toxic activities. These include the retinoic acid, an important element for vertebrate development, gamma-aminobutyric acid (GABA), an important neurotransmitter, and trichloroacetic acid, a potential toxicant. This review summarizes the ALDHs with an emphasis on catalytic properties and xenobiotic substrates of these enzymes.

Critical glutamic acid residues affecting the mechanism and nucleotide specificity of Vibrio harveyi aldehyde dehydrogenase

Fatty aldehyde dehydrogenase (ALDH) from the luminescent marine bacterium, Vibrio harveyi, differs from other ALDHs in its unique specificity and high affinity for NADP+. Two glutamic acid residues, Glu253 and Glu377, which are highly conserved in ALDHs, were investigated in the present study. Mutation of Glu253 to Ala decreased the kcat for ALDH activity by over four orders of magnitude without a significant change in the K(m) values for substrates or the ability to interact with nucleotides. Both thioesterase activity and a pre-steady-state burst of NAD(P)H were also eliminated, implicating Glu253 in promoting the nucleophilicity of the cysteine residue(Cys289) involved in forming the thiohemiacetal intermediate in the enzyme mechanism. Mutation of Glu377 to Gln (E377Q mutant) selectively decreased the kcat for NAD(+)-dependent ALDH activity (> 10(2)-fold) compared to only a 6-fold loss in NADP(+)-dependent activity without comparable changes to the K(m) values for substrates. Consequently, the E377Q mutant had a very high specificity for NADP+(kcat/K(m) > 10(3) of that for NAD+) which was over 20 times higher than that of the wild-type ALDH. Although a pre-steady-state burst of NAD(P)H was eliminated by this mutation, thioesterase activity was completely retained. Using [1-2H]acetaldehyde as a substrate, a significant deuterium isotope effect was observed, implicating Glu377 in the hydride transfer step and not in acylation or release of the acyl group from the cysteine nucleophile. The increase in specificity of the E377Q mutant for NADP+ is consistent with a change in the rate-limiting step determining kcat from nucleotide-dependent NAD(P)H dissociation to hydride transfer. The results provide biochemical evidence that the two highly conserved Glu residues are involved in different functions in the active site of V. harveyi ALDH.

The cytosolic aldehyde dehydrogenase gene (Aldh1) is developmentally expressed in Leydig cells

Cytosolic aldehyde dehydrogenase, ALDH1, participates in the oxidation of different aldehydes including that of all-trans retinal to retinoic acid. The accumulation of mouse Aldh1 transcripts is characterized by having different patterns in different tissues. This paper reports the greatest expression of Aldh1 in testis and liver. It was demonstrated that in testis, Aldh1 is specifically expressed in Leydig cells and is under developmental regulation. In vitro studies of cultured Leydig TM3 cells confirmed these results though such gene expression was found not to be mediated by LH regulation. Previous investigations have associated androgen receptors, and hence the androgen insensitivity syndrome in man, with the presence of ALDH1 in genital skin fibroblasts. However, this relationship was not established in a functional cell type, as is reported here for Leydig cells. These results could suggest a model for a molecular pathway from androgen receptor to retinoic acid biogenesis in Leydig cells via the mediation of ALDH.

Sequencing and expression of the human ALDH8 encoding a new member of the aldehyde dehydrogenase family

The human aldehyde dehydrogenase gene (ALDH) family is characterized by two major conserved DNA sequences encoding residues which are possibly involved in the catalytic function and the maintenance of the functional conformation of the ALDH enzyme. This property is the basis for synthesizing the degenerate primers to clone several cDNAs of the ALDH isozymes. In this report, we describe the cDNA sequence and the expression of a new member of this family, ALDH8. The human ALDH8 gene was identified during the process of the screening for the human ALDH7 genomic clones. Overlapping ALDH8 cDNA clones were isolated by polymerase chain reaction (PCR) amplification of human salivary gland total RNA or lambda gt11 cDNA library. When the ALDH8 cDNA sequence was aligned with that of the ALDH7 which encodes a polypeptide chain of 468 amino acid (aa) residues, it was found that a termination codon (TGA) is placed in frame at the ALDH8 sequence corresponding to the codon GCG for the seventeenth aa position of the ALDH7. Therefore, the human ALDH8 gene is a potential nonprocessed pseudogene in the ALDH multigene family which has no other pseudogenes reported so far. Alternatively, the ALDH8 gene is a functional gene if the premature stop codon is suppressed, or if the first downstream in-frame ATG serves as the initiator codon. This longest putative open reading frame (ORF) encodes a polypeptide chain of 385 aa residues, includes the two ALDH conserved regions, and demonstrates 86% identity with the corresponding ORF region of the human ALDH7. The expression of the ALDH8 transcripts is restricted to the salivary gland among the human tissues examined.

Localization of cytosolic aldehyde dehydrogenase in the developing chick retina: in situ hybridization and immunohistochemical analyses

Cytosolic aldehyde dehydrogenase (ALDH) mRNA is present at high levels in the undifferentiated chick retina. Tissue maturation is accompanied by a 20-25x decrease in transcript levels. To determine the spatial and temporal distribution pattern of the ALDH transcript and its encoded protein in the developing retina, in situ hybridization and immunohistochemical analyses were carried out using chick embryos at different stages of development. The ALDH transcript and protein were detected at the earliest stage tested, in the inner layer of the optic cup of stage 14 (day 2) embryos. Both the ALDH transcript and protein were found in the dorsal retina of chick embryos from stage 18 (day 3) to day 16 of incubation. Accumulation of the ALDH protein in the neurites of ganglion cells could readily be detected at early developmental stages. Staining of this ganglion fiber layer was strong in the dorsal retina and could be followed up to and into the optic nerve. By day 11, ALDH mRNA was located primarily in the ciliary margin and in the inner nuclear layer of the dorsal retina. In addition to these areas, the ALDH protein was also found in the inner plexiform and optic nerve fiber layers. These results suggest that environmental or transcriptional factors involved in the regulation of the ALDH gene are restricted to the dorsal retina at early developmental stages and that there is a requirement for the compartmentalization of the ALDH transcript/protein in the undifferentiated chick retina.

Mouse microsomal Class 3 aldehyde dehydrogenase: AHD3 cDNA sequence, inducibility by dioxin and clofibrate, and genetic mapping

We have cloned and sequenced the mouse AHD3 cDNA, which codes for the Class 3 microsomal aldehyde dehydrogenase (ALDH3m). The cDNA is 2,997 bp in length excluding the poly(A)+ tail, and has 5' and 3' non-translated regions of 113 bp and 1,429 bp, respectively. The deduced amino acid sequence consists of 484 amino acids, including the first methionine (Mr = 53,942), and contains a hydrophobic segment at the carboxyl terminus which is the putative membrane anchor. The mouse AHD3 protein was found to be: 95% similar to the rat microsomal ALDH3m protein, 65% identical to the mouse, rat and human cytosolic ALDH3c protein, and <28% similar to the rat Class 1 and Class 2 ALDH and methylmalonate-semialdehyde dehydrogenase proteins. Southern hybridization analysis of mouse cDNA probed with the full-length AHD3 cDNA revealed that the Ahd3 gene likely spans less than a total of 25 kb. The mouse Ahd3 gene is very tightly linked to the Ahd4 gene on chromosome 11. Mouse AHD3 mRNA levels are increased by dioxin in mouse Hepa-1c1c7 hepatoma wild-type (wt) cells but not in the Ah receptor nuclear translocator (ARNT)-defective (c4) mutant line, indicating that the induction process is mediated by the Ah (aromatic hydrocarbon) dioxin-binding receptor. AHD3 mRNA levels are also inducible by clofibrate in both the wt and c4 lines. AHD3 mRNA levels are not elevated in the CYP1A1 metabolism-deficient c37 mutant line or as part of the oxidative stress response found in the untreated 14CoS/14CoS mouse cell line. These data indicate that, although inducible by dioxin, the Ahd3 gene does not qualify as a member of the aromatic hydrocarbon [Ah] gene battery.

Constitutive expression of class 3 aldehyde dehydrogenase in cultured rat corneal epithelium

Mammalian Class 3 aldehyde dehydrogenase (ALDH) is normally associated with neoplastic transformation or xenobiotic induction by aromatic hydrocarbons in liver. However, Class 3 ALDH is constitutively expressed at it's highest specific activity in corneal epithelium. Tissue-specific, differential gene expression is often controlled by alternative, independent molecular pathways. We report here the development of an in vitro corneal epithelium culture system that retains constitutive high expression of the ALDH3 gene. This model system was used to establish, by enzymatic assays, Western and Northern analyses, histochemical and immunocytochemical staining, and 5'3' RACE methodologies that constitutive and xenobiotic induction of Class 3 ALDHs occurs from a single gene. Our results also provide a plausible explanation for the very high Class 3 ALDH activity in mammalian cornea, as the primary mechanism of oxidation of lipid peroxidation-derived aldehydes. Further studies with corneal epithelium suggest the presence of additional mechanisms, other than Ah-receptor-mediated, by which the ALDH3 gene can be differentially regulated in a tissue-specific manner.

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.

Chromosomal locations and modes of action of genes of the retinoid (vitamin A) system support their involvement in the etiology of schizophrenia

Vitamin A (retinoid), an essential nutrient for fetal and subsequent mammalian development, is involved in gene expression, cell differentiation, proliferation, migration, and death. Retinoic acid (RA) the morphogenic derivative of vitamin A is highly teratogenic. In humans retinoid excess or deficit can result in brain anomalies and psychosis. This review discusses chromosomal loci of genes that control the retinoid cascade in relation to some candidate genes in schizophrenia. The paper relates the knowledge about the transport, delivery, and action of retinoids to what is presently known about the pathology of schizophrenia, with particular reference to the dopamine hypothesis, neurotransmitters, the glutamate hypothesis, retinitis pigmentosa, dermatologic disorders, and craniofacial anomalies.

Cloning of a cDNA encoding human ALDH7, a new member of the aldehyde dehydrogenase family

Aldehyde dehydrogenases (ALDH; EC 1.2.1.3) are a family of isozymes which have been suggested to play a major role in the detoxification of aldehydes generated by alcohol metabolism and lipid peroxidation. Five non-allelic ALDH genes, encoding the ALDH1, 2, 3, 5 and 6 isozymes, have previously been identified and cloned in our laboratory. In this paper, we report the cloning and sequencing of a cDNA encoding a new human ALDH (ALDH7). Degenerate oligodeoxyribonucleotides derived from conserved regions of known ALDH cDNAs amplified a 408-bp product from human kidney total RNA by the reverse transcription-polymerase chain reaction (RT-PCR) procedures [Hsu et al., J. Biol. Chem. 266 (1992) 3030-3037]. This PCR product was subcloned, selected and used as a probe to screen a human kidney cDNA library. The full-length human kidney cDNA (ALDH7) is 2791 bp in length and contains an open reading frame encoding 468 amino acids (aa). The deduced sequence of ALDH7 is longer than that of the human stomach ALDH3 by 15 aa at the C terminus. The degree of identity between the two isozymes is 52% with a positional alignment of 453 aa. Northern blot analysis demonstrated that lung is another major tissue expressing ALDH7.

Gene structure and amino acid sequences of alcohol dehydrogenases of Bacillus stearothermophilus

Partial amino acid sequences of the two alcohol dehydrogenases of Bacillus stearothermophilus and the oligonucleotide sequence of a cloned fragment containing the gene for ADH 2334 were determined and compared with the known, derived ADH 1503 amino acid sequence. The two proteins are identical at 244 of 349 positions. ADH 2334 is encoded in a transcription unit containing an aldehyde dehydrogenase.

Human liver aldehyde dehydrogenases: new method of purification of the major mitochondrial and cytosolic enzymes and re-evaluation of their kinetic properties

A new purification procedure, based on dye-adsorption and affinity chromatography, has been developed for the isolation of the two major ALDH isozymes from human liver: ALDH-1 (cytosolic, pI 5.2) and ALDH-2 (mitochondrial, pI 4.9). The procedure affords milligram quantities of ALDH-1 and -2 at 850- and 275-fold purifications, respectively, from 50 g of liver in two days. Kinetic parameters for acetaldehyde oxidation were determined with these purified enzymes, because there is a wide discrepancy in the absolute magnitude of these parameters in the biochemical literature. The Michaelis constants for ALDH-1 and -2, determined from initial velocities (for ALDH-1) and single reaction progress curves (for ALDH-2), are 180 +/- 10 microM and 0.20 +/- 0.02 microM, respectively (pH 7.5 and 9.5, saturating NAD+ in both cases). This three orders of magnitude difference in Km values is much greater than that reported previously in all but one study.

Alcohol and acetaldehyde dehydrogenase gene polymorphism and alcoholism

Inherited variations in alcohol and aldehyde dehydrogenases, the principal enzymes of ethanol metabolism, have been implicated in determining susceptibility to alcoholism and alcohol-related organ damage. An association between an RFLP for the alcohol dehydrogenase-2 (ADH2) gene and alcohol-induced liver damage was demonstrated in a Caucasian population. Genotyping studies revealed an increase in the ADH3(2) allele in patients with alcohol-induced cirrhosis. PCR studies of the ALDH5 gene have demonstrated diverse polymorphism within a short segment of its coding region, with marked inter-racial variation in allele frequencies. In addition, the Caucasian alcohol-induced flushing reaction has been characterised and its relationship with phenotypic polymorphism of ALDH1 examined.

Diverse polymorphism within a short coding region of the human aldehyde dehydrogenase-5 (ALDH5) gene

Human aldehyde dehydrogenase-5 gene (originally named as ALDHX) is expressed in liver and testis. The ALDH5 does not contain introns in the coding sequence for 517 amino acid residues. Within a short nucleotide region of the gene, the following three nucleotide changes were found in high frequencies, i.e., a silent C<-->T at nucleotide (nt) 183, C<-->T at nt 257 associated with a Val<-->Ala substitution, and T<-->G at nt 320 associated with a Arg<-->Leu substitution. The frequency of C at nt 183 is 81% in Caucasians and 65% in Japanese, and the difference is statistically not significant. The frequency of C at nt 257 is 76% in Caucasians and 55% in Japanese, and the difference is statistically significant (P = 0.02). The frequency of T at nt 320 is 71% in Caucasians, while it is only 27% in Japanese. The racial difference at nt 320 is highly significant (P < 0.001). No significant difference was found in the genotypes of the three nucleotide positions between alcoholic and nonalcoholic Caucasians within the limited numbers of subjects examined.

Aldehyde dehydrogenases: widespread structural and functional diversity within a shared framework

Sequences of 16 NAD and/or NADP-linked aldehyde oxidoreductases are aligned, including representative examples of all aldehyde dehydrogenase forms with wide substrate preferences as well as additional types with distinct specificities for certain metabolic aldehyde intermediates, particularly semialdehydes, yielding pairwise identities from 15 to 83%. Eleven of 23 invariant residues are glycine and three are proline, indicating evolutionary restraint against alteration of peptide chain-bending points. Additionally, another 66 positions show high conservation of residue type, mostly hydrophobic residues. Ten of these occur in predicted beta-strands, suggesting important interior-packing interactions. A single invariant cysteine residue is found, further supporting its catalytic role. A previously identified essential glutamic acid residue is conserved in all but methyl malonyl semialdehyde dehydrogenase, which may relate to formation by that enzyme of a CoA ester as a product rather than a free carboxylate species. Earlier, similarity to a GXGXXG segment expected in the NAD-binding site was noted from alignments with fewer sequences. The same region continues to be indicated, although now only the first glycine residue is strictly conserved and the second (usually threonine) is not present at all, suggesting greater variance in coenzyme-binding interactions.

Alcohol and aldehyde dehydrogenases in human esophagus: comparison with the stomach enzyme activities

Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) isoenzymes from surgical esophageal and gastric mucosa were compared by agarose isoelectric focusing. Two prominent ADH forms, designated mu 1 (equivalent to the recently reported mu-form) and mu 2, were expressed in all the 15 esophagus specimens studied, whereas only four of seven examined gastric specimens exhibited a weak to moderately strong mu 1-ADH activity band on the isoelectric focusing gels. pI values of the esophageal mu 1-ADH and mu 2-ADH, and the liver pi-ADH were determined to be 8.61, 8.13, and 8.90, respectively. mu-ADHs exhibited high Km for ethanol (12 mM) and low sensitivity to 4-methylpyrazole inhibition. ALDH3 (BB form) and ALDH1 were the major high- and low-Km aldehyde dehydrogenase in the esophagus, respectively. The ADH and ALDH activities were determined at pH 7.5 to be 751 +/- 78 and 29.9 +/- 3.0 nmol/min/g tissue, respectively (measured at 500 mM ethanol or at 200 microM acetaldehyde; mean +/- SEM; N = 15). The esophageal ADH activity was approximately 4-fold and the ALDH activity 20% that of the stomach enzyme. Because the presence of high activity and high Km mu-ADHs as well as low-activity ALDH1 were found in human esophageal mucosa, it is suggested that there may exist an accumulation of intracellular acetaldehyde during alcohol ingestion. This reactive and toxic metabolite may be involved in the pathogenesis of alcohol-induced esophageal disorders.

Aldehyde dehydrogenases and their role in carcinogenesis

Aldehydes are highly reactive molecules that may have a variety of effects on biological systems. They can be generated from a virtually limitless number of endogenous and exogenous sources. Although some aldehyde-mediated effects such as vision are beneficial, many effects are deleterious, including cytotoxicity, mutagenicity, and carcinogenicity. A variety of enzymes have evolved to metabolize aldehydes to less reactive forms. Among the most effective pathways for aldehyde metabolism is their oxidation to carboxylic acids by aldehyde dehydrogenases (ALDHs). ALDHs are a family of NADP-dependent enzymes with common structural and functional features that catalyze the oxidation of a broad spectrum of aliphatic and aromatic aldehydes. Based on primary sequence analysis, three major classes of mammalian ALDHs--1, 2, and 3--have been identified. Classes 1 and 3 contain both constitutively expressed and inducible cytosolic forms. Class 2 consists of constitutive mitochondrial enzymes. Each class appears to oxidize a variety of substrates that may be derived either from endogenous sources such as amino acid, biogenic amine, or lipid metabolism or from exogenous sources, including aldehydes derived from xenobiotic metabolism. Changes in ALDH activity have been observed during experimental liver and urinary bladder carcinogenesis and in a number of human tumors, including some liver, colon, and mammary cancers. Changes in ALDH define at least one population of preneoplastic cells having a high probability of progressing to overt neoplasms. The most common change is the appearance of class 3 ALDH dehydrogenase activity in tumors arising in tissues that normally do not express this form. The changes in enzyme activity occur early in tumorigenesis and are the result of permanent changes in ALDH gene expression. This review discusses several aspects of ALDH expression during carcinogenesis. A brief introduction examines the variety of sources of aldehydes. This is followed by a discussion of the mammalian ALDHs. Because the ALDHs are a relatively understudied family of enzymes, this section presents what is currently known about the general structural and functional properties of the enzymes and the interrelationships of the various forms. The remainder of the review discusses various aspects of the ALDHs in relation to tumorigenesis. The expression of ALDH during experimental carcinogenesis and what is known about the molecular mechanisms underlying those changes are discussed. This is followed by an extended discussion of the potential roles for ALDH in tumorigenesis. The role of ALDH in the metabolism of cyclophosphamidelike chemotherapeutic agents is described. This work suggests that modulation of ALDH activity may an important determinant of the effectiveness of certain chemotherapeutic agents.(ABSTRACT TRUNCATED AT 400 WORDS)