Expression patterns of class I and class IV alcohol dehydrogenase genes in developing epithelia suggest a role for alcohol dehydrogenase in local retinoic acid synthesis

A common polymorphism in the retinoic acid pathway modifies adrenocortical carcinoma age-dependent incidence

BACKGROUND

Genome-wide association studies (GWASs) have enriched the fields of genomics and drug development. Adrenocortical carcinoma (ACC) is a rare cancer with a bimodal age distribution and inadequate treatment options. Paediatric ACC is frequently associated with TP53 mutations, with particularly high incidence in Southern Brazil due to the TP53 p.R337H (R337H) germline mutation. The heterogeneous risk among carriers suggests other genetic modifiers could exist.

METHODS

We analysed clinical, genotype and gene expression data derived from paediatric ACC, R337H carriers, and adult ACC patients. We restricted our analyses to single nucleotide polymorphisms (SNPs) previously identified in GWASs to associate with disease or human traits.

RESULTS

A SNP, rs971074, in the alcohol dehydrogenase 7 gene significantly and reproducibly associated with allelic differences in ACC age-of-onset in both cohorts. Patients homozygous for the minor allele were diagnosed up to 16 years earlier. This SNP resides in a gene involved in the retinoic acid (RA) pathway and patients with differing levels of RA pathway gene expression in their tumours associate with differential ACC progression.

CONCLUSIONS

These results identify a novel genetic component to ACC development that resides in the retinoic acid pathway, thereby informing strategies to develop management, preventive and therapeutic treatments for ACC.

The alterations in alcohol dehydrogenase and aldehyde dehydrogenase activities in the sera of patients with renal cell carcinoma

PURPOSE

In a previous study we showed that the total activity of alcohol dehydrogenase (ADH) and its isoenzyme class I was significantly higher in renal cancer (RCC) cells compared to normal kidney. The aim of this study was to compare the activities of ADH isoenzymes and aldehyde dehydrogenase (ALDH) in the sera of patients with different stages of RCC and healthy subjects.

MATERIALS AND METHODS

Serum samples were taken from 54 patients with clear cell RCC (17 patients in stage II, 22 in stage III and 15 in stage IV) and 52 healthy patients. Class III, IV of ADH and the total ADH activity was measured by the photometric method. For the measurement of ADH class I, II and the total ALDH activity we employed the fluorometric method.

RESULTS

The total activity of ADH and its isoenzyme class I were significantly higher in the sera of patients with every stage of RCC compared to healthy subjects. The analysis of ALDH activity did not indicate significant differences between tested groups.

CONCLUSIONS

The increased activity of total ADH and its isoenzyme class I in the sera of patients with RCC, seems to be caused by isoenzymes being released from cancerous cells and may be useful for diagnostics of renal cancer.

New insights and changing paradigms in the regulation of vitamin A metabolism in development

Vitamin A and its active metabolite retinoic acid are essential for embryonic development and adult homeostasis. Surprisingly, excess or deficiency of vitamin A and retinoic acid can cause similar developmental defects. Therefore, strict feedback and other mechanisms exist to regulate the levels of retinoic acid within a narrow physiological range. The oxidation of vitamin A to retinal has recently been established as a critical nodal point in the synthesis of retinoic acid, and over the past decade, RDH10 and DHRS3 have emerged as the predominant enzymes that regulate this reversible reaction. Together they form a codependent complex that facilitates negative feedback maintenance of retinoic acid levels and thus guard against the effects of dysregulated vitamin A metabolism and retinoic acid synthesis. This review focuses on advances in our understanding of the roles of Rdh10 and Dhrs3 and their impact on development and disease. WIREs Dev Biol 2017, 6:e264. doi: 10.1002/wdev.264 For further resources related to this article, please visit the WIREs website.

Altered expression of multiple genes involved in retinoic acid biosynthesis in human colorectal cancer

All-trans-retinoic acid (atRA), the oxidized form of vitamin A (retinol), regulates a wide variety of biological processes, such as cell proliferation and differentiation. Multiple alcohol, retinol and retinaldehyde dehydrogenases (ADHs, RDHs, RALDHs) as well as aldo-keto reductases (AKRs) catalyze atRA production. The reduced atRA biosynthesis has been observed in several human tumors, including colorectal cancer. However, subsets of atRA-synthesizing enzymes have not been determined in colorectal tumors. We investigated the expression patterns of genes involved in atRA biosynthesis in normal human colorectal tissues, primary carcinomas and cancer cell lines by RT-PCR. These genes were identified using transcriptomic data analysis (expressed sequence tags, RNA-sequencing, microarrays). Our results indicate that each step of the atRA biosynthesis pathway is dysregulated in colorectal cancer. Frequent and significant decreases in the mRNA levels of the ADH1B, ADH1C, RDHL, RDH5 and AKR1B10 genes were observed in a majority of colorectal carcinomas. The expression levels of the RALDH1 gene were reduced, and the expression levels of the cytochrome CYP26A1 gene increased. The human colon cancer cell lines showed a similar pattern of changes in the mRNA levels of these genes. A dramatic reduction in the expression of genes encoding the predominant retinol-oxidizing enzymes could impair atRA production. The most abundant of these genes, ADH1B and ADH1C, display decreased expression during progression from adenoma to early and more advanced stage of colorectal carcinomas. The diminished atRA biosynthesis may lead to alteration of cell growth and differentiation in the colon and rectum, thus contributing to the progression of colorectal cancer.

Perinatal exposure to alcohol: implications for lung development and disease

In utero alcohol exposure dramatically increases the risk of premature delivery. However, the majority of premature and term newborns exposed to alcohol remain undetected by medical caregivers. There is a desperate need for reliable and accurate biomarkers of alcohol exposure for the term and premature newborn population. The inability to identify the exposed newborn severely limits our understanding of alcohol's pathophysiological effects on developing organs such as the lung. This chapter will review potential advancements in future biomarkers of alcohol exposure for the newborn population. We will discuss alcohol's effects on redox homeostasis and cellular development of the neonatal lung. Finally, we will present the evidence describing in utero alcohol's derangement of innate and adaptive immunity and risk for infectious complications in the lung. Continued investigations into the identification and understanding of the mechanisms of alcohol-induced alterations in the premature lung will advance the care of this vulnerable patient population.

Relevance of xenobiotic enzymes in human skin in vitro models to activate pro-sensitizers

Skin exposure to sensitizing chemicals can induce allergic reactions. Certain chemicals, so called pro-sensitizers, need metabolic activation to become allergenic. Their metabolic activation occurs in skin cells such as keratinocytes or dendritic cells. These cell types are also incorporated into dermal in vitro test systems used to assess the sensitizing potential of chemicals for humans. In vitrosystems range from single cell cultures to organotypic multi-cellular reconstructed skin models. Until now, their metabolic competence to unmask sensitizing potential of pro-sensitizers was rarely investigated. This review aims to summarize current information on available skin in vitro models and the relevance of xenobiotic metabolizing enzymes for the activation of pro-sensitizers such as eugenol, 4-allylanisole, and ethylendiamine. Among others, these chemicals are discussed as performance standards to validate new coming in vitro systems for their potential to identify pro-sensitizers.

Analysis, occurrence, and function of 9-cis-retinoic acid

Metabolic conversion of vitamin A (retinol) into retinoic acid (RA) controls numerous physiological processes. 9-cis-retinoic acid (9cRA), an active metabolite of vitamin A, is a high affinity ligand for retinoid X receptor (RXR) and also activates retinoic acid receptor (RAR). Despite the identification of candidate enzymes that produce 9cRA and the importance of RXRs as established by knockout experiments, in vivo detection of 9cRA in tissue was elusive until recently when 9cRA was identified as an endogenous pancreas retinoid by validated liquid chromatography-tandem mass spectrometry (LC-MS/MS) methodology. This review will discuss the current status of the analysis, occurrence, and function of 9cRA. Understanding both the nuclear receptor-mediated and non-genomic mechanisms of 9cRA will aid in the elucidation of disease physiology and possibly lead to the development of new retinoid-based therapeutics. This article is part of a Special Issue entitled Retinoid and Lipid Metabolism.

RDH10 is the primary enzyme responsible for the first step of embryonic Vitamin A metabolism and retinoic acid synthesis

Retinoic acid (atRA) signaling is essential for regulating embryonic development, and atRA levels must be tightly controlled in order to prevent congenital abnormalities and fetal death which can result from both excessive and insufficient atRA signaling. Cellular enzymes synthesize atRA from Vitamin A, which is obtained from dietary sources. Embryos express multiple enzymes that are biochemically capable of catalyzing the initial step of Vitamin A oxidation, but the precise contribution of these enzymes to embryonic atRA synthesis remains unknown. Using Rdh10(trex)-mutant embryos, dietary supplementation of retinaldehyde, and retinol dehydrogenase (RDH) activity assays, we demonstrate that RDH10 is the primary RDH responsible for the first step of embryonic Vitamin A oxidation. Moreover, we show that this initial step of atRA synthesis occurs predominantly in a membrane-bound cellular compartment, which prevents inhibition by the cytosolic cellular retinol-binding protein (RBP1). These studies reveal that widely expressed cytosolic enzymes with RDH activity play a very limited role in embryonic atRA synthesis under normal dietary conditions. This provides a breakthrough in understanding the precise cellular mechanisms that regulate Vitamin A metabolism and the synthesis of the essential embryonic regulatory molecule atRA.

Alcohol and aldehyde dehydrogenases: retinoid metabolic effects in mouse knockout models

Retinoic acid (RA) is the active metabolite of vitamin A (retinol) that controls growth and development. The first step of RA synthesis is controlled by enzymes of the alcohol dehydrogenase (ADH) and retinol dehydrogenase (RDH) families that catalyze oxidation of retinol to retinaldehyde. The second step of RA synthesis is controlled by members of the aldehyde dehydrogenase (ALDH) family also known as retinaldehyde dehydrogenase (RALDH) that further oxidize retinaldehyde to produce RA. RA functions as a ligand for DNA-binding RA receptors that directly regulate transcription of specific target genes. Elucidation of the vitamin A metabolic pathway and investigation of the endogenous function of vitamin A metabolites has been greatly improved by development of mouse ADH, RDH, and RALDH loss-of-function models. ADH knockouts have demonstrated a postnatal role for this enzyme family in clearance of excess retinol to prevent vitamin A toxicity and in generation of RA for postnatal survival during vitamin A deficiency. A point mutation in Rdh10 generated by ethylnitrosourea has demonstrated that RDH10 generates much of the retinaldehyde needed for RA synthesis during embryonic development. Raldh1, Raldh2, and Raldh3 knockouts have demonstrated that RALDH1, RALDH2, and RALDH3 generate most of the RA needed during embryogenesis. These mouse models serve as instrumental tools for providing new insight into retinoid function. This article is part of a Special Issue entitled: Retinoid and Lipid Metabolism.

Vitamin A in reproduction and development

The requirement for vitamin A in reproduction was first recognized in the early 1900's, and its importance in the eyes of developing embryos was realized shortly after. A greater understanding of the large number of developmental processes that require vitamin A emerged first from nutritional deficiency studies in rat embryos, and later from genetic studies in mice. It is now generally believed that all-trans retinoic acid (RA) is the form of vitamin A that supports both male and female reproduction as well as embryonic development. This conclusion is based on the ability to reverse most reproductive and developmental blocks found in vitamin A deficiency induced either by nutritional or genetic means with RA, and the ability to recapitulate the majority of embryonic defects in retinoic acid receptor compound null mutants. The activity of the catabolic CYP26 enzymes in determining what tissues have access to RA has emerged as a key regulatory mechanism, and helps to explain why exogenous RA can rescue many vitamin A deficiency defects. In severely vitamin A-deficient (VAD) female rats, reproduction fails prior to implantation, whereas in VAD pregnant rats given small amounts of carotene or supported on limiting quantities of RA early in organogenesis, embryos form but show a collection of defects called the vitamin A deficiency syndrome or late vitamin A deficiency. Vitamin A is also essential for the maintenance of the male genital tract and spermatogenesis. Recent studies show that vitamin A participates in a signaling mechanism to initiate meiosis in the female gonad during embryogenesis, and in the male gonad postnatally. Both nutritional and genetic approaches are being used to elucidate the vitamin A-dependent pathways upon which these processes depend.

The activity of class I, II, III and IV of alcohol dehydrogenase (ADH) isoenzymes and aldehyde dehydrogenase (ALDH) in the wall of abdominal aortic aneurysms

OBJECTIVE

Human blood vessels contain a huge amount of alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH), which play a significant role in the metabolism of many biological substances and participate in various metabolic pathways. The aim of this study was the investigation of the differences between the activities of ADH and ALDH in the wall of aortic aneurysm and wall of healthy aorta, that can explain the pathological background of aneurysm development.

METHODS

For the measurement of the activity of class I and II ADH isoenzymes and ALDH activity the fluorometric methods was employed. The total ADH activity and activity of class III and IV isoenzymes was measured by the photometric method. The study material consisted of vessels wall samples obtained from 45 abdominal aortic aneurysm.

RESULTS

The activity of the class I ADH isoenzyme was significantly lower in the wall of aortic aneurysm than in healthy aorta. The other tested classes of ADH showed the tendency to lower level of the activity in aneurysm tissue than that in wall of unchanged aorta. The activities of total ADH and ALDH were also not significantly lower in the aneurysms.

CONCLUSION

The decrease of the activity of class I ADH isoenzymes in the wall of aortic aneurysm may be a factor of some disorders in metabolic pathways with participation of these isoenzymes.

Medium- and short-chain dehydrogenase/reductase gene and protein families : Medium-chain and short-chain dehydrogenases/reductases in retinoid metabolism

Retinoic acid (RA), the most active retinoid, is synthesized in two steps from retinol. The first step, oxidation of retinol to retinaldehyde, is catalyzed by cytosolic alcohol dehydrogenases (ADHs) of the medium-chain dehydrogenase/reductase (MDR) superfamily and microsomal retinol dehydrogenases (RDHs) of the short-chain dehydrogenase/reductase (SDR) superfamily. The second step, oxidation of retinaldehyde to RA, is catalyzed by several aldehyde dehydrogenases. ADH1 and ADH2 are the major MDR enzymes in liver retinol detoxification, while ADH3 (less active) and ADH4 (most active) participate in RA generation in tissues. Several NAD(+)- and NADP(+)-dependent SDRs are retinoid active. Their in vivo contribution has been demonstrated in the visual cycle (RDH5, RDH12), adult retinoid homeostasis (RDH1) and embryogenesis (RDH10). K(m) values for most retinoid-active ADHs and RDHs are close to 1 microM or lower, suggesting that they participate physiologically in retinol/retinaldehyde interconversion. Probably none of these enzymes uses retinoids bound to cellular retinol-binding protein, but only free retinoids. The large number of enzymes involved in the two directions of this step, also including aldo-keto reductases, suggests that retinaldehyde levels are strictly regulated.

ADH7 variation modulates extraversion and conscientiousness in substance-dependent subjects

Human personality traits have been closely linked to substance dependence (SD), and are partially genetically determined. Recently, associations between alcohol dehydrogenase 7 (ADH7) and SD have been reported, which led us to investigate the relationship between ADH7 variation and personality traits. We assessed dimensions of the five-factor model of personality and genotyped 4 ADH7 markers and 38 unlinked ancestry-informative markers in 244 subjects with SD [178 European-Americans (EAs) and 66 African-Americans (AAs)] and 293 healthy subjects (253 EAs and 40 AAs). The relationships between ADH7 markers and personality traits were comprehensively examined using multivariate analysis of covariance (MANCOVA), and then decomposed by Roy Bargmann Stepdown analysis of covariance (ANCOVA). Generally, older individuals, AAs, and males had significantly lower personality scores (4.7 x 10(-5) < or = P < or = 0.032), as reported previously. In SD subjects, Extraversion was most significantly associated with ADH7 haplotypes (3.7 x 10(-4) < or = P < or = 0.001), diplotypes (0.007 < or = P < or = 0.012), and genotypes (P = 0.001), followed by Conscientiousness (0.005 < or = P < or = 0.033). The contributory haplotype and diplotypes contained the alleles and genotypes of rs284786 (SNP1) and rs1154470 (SNP4). In healthy subjects, other personality factors (except Extraversion) were associated with ADH7 diplotypes (0.005 < or = P < or = 0.016) and genotypes (0.002 < or = P < or = 0.052). Some of the gene effects on personality factors were modified by sex. The present study demonstrated that the ADH7 variation may contribute to the genetic component of variation in personality traits, with the risk for SD and personality traits being partially shared.

Evidence for the expression of alcohol dehydrogenase class I gene in rat uterus and its up-regulation by progesterone

The endometrium is one of the target tissues of the ovarian steroid hormones, estrogen and progesterone. In order to elucidate the mechanism of gene regulation in the endometrium, suppressive subtraction hybridization was performed to isolate the candidate genes controlled by progesterone in rat uterus. Alcohol dehydrogenase (ADH) class I gene was one of the candidate genes. Here we investigated the expression and regulation of ADH class I gene in rat uterus. The mRNA of ADH class I was detected in uterus by RT-PCR using specific primers. Using specific probe for ADH class I, in situ hybridization was performed to investigate localization in rat uterus. Positive signals were detected in the endometrial stromal cells of rat uterus by in situ hybridization and were not detected in endometrial epithelial cells and myometrium in rat uterus. Ovariectomized rats were treated with 17-beta estradiol and progesterone and the uteri of these rats were used for Northern blot analysis and assay of the ADH activity. Northern blot analysis revealed that the expression of ADH class I mRNA in rat uteri was up-regulated approximately two-fold after progesterone treatment, but not estrogen. Likewise, ADH activity was approximately two-fold higher in progesterone-treated rat uteri compared with controls. This study demonstrated that ADH class I gene is progesterone-responsive in the uterus. This implies that progesterone might be involved with retinoic acid synthesis in the uterus, since ADH is the key enzyme for retinoic acid synthesis.

Disease gene candidates revealed by expression profiling of retinal ganglion cell development

To what extent do postmitotic neurons regulate gene expression during development or after injury? We took advantage of our ability to highly purify retinal ganglion cells (RGCs) to profile their pattern of gene expression at 13 ages from embryonic day 17 through postnatal day 21. We found that a large proportion of RGC genes are regulated dramatically throughout their postmitotic development, although the genes regulated through development in vivo generally are not regulated similarly by RGCs allowed to age in vitro. Interestingly, we found that genes regulated by developing RGCs are not generally correlated with genes regulated in RGCs stimulated to regenerate their axons. We unexpectedly found three genes associated with glaucoma, optineurin, cochlin, and CYP1B1 (cytochrome P450, family 1, subfamily B, polypeptide 1), previously thought to be primarily expressed in the trabecular meshwork, which are highly expressed by RGCs and regulated through their development. We also identified several other RGC genes that are encoded by loci linked to glaucoma. The expression of glaucoma-linked genes by RGCs suggests that, at least in some cases, RGCs may be directly involved in glaucoma pathogenesis rather than indirectly involved in response to increased intraocular pressure. Consistent with this hypothesis, we found that CYP1B1 overexpression potentiates RGC survival.

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.

High and complementary expression patterns of alcohol and aldehyde dehydrogenases in the gastrointestinal tract: implications for Parkinson's disease

Parkinson's disease (PD) is a heterogeneous movement disorder characterized by progressive degeneration of dopamine neurons in substantia nigra. We have previously presented genetic evidence for the possible involvement of alcohol and aldehyde dehydrogenases (ADH; ALDH) by identifying genetic variants in ADH1C and ADH4 that associate with PD. The absence of the corresponding mRNA species in the brain led us to the hypothesis that one cause of PD could be defects in the defense systems against toxic aldehydes in the gastrointestinal tract. We investigated cellular expression of Adh1, Adh3, Adh4 and Aldh1 mRNA along the rodent GI tract. Using oligonucleotide in situ hybridization probes, we were able to resolve the specific distribution patterns of closely related members of the ADH family. In both mice and rats, Adh4 is transcribed in the epithelium of tongue, esophagus and stomach, whereas Adh1 was active from stomach to rectum in mice, and in duodenum, colon and rectum in rats. Adh1 and Adh4 mRNAs were present in the mouse gastric mucosa in nonoverlapping patterns, with Adh1 in the gastric glands and Adh4 in the gastric pits. Aldh1 was found in epithelial cells from tongue to jejunum in rats and from esophagus to colon in mice. Adh3 hybridization revealed low mRNA levels in all tissues investigated. The distribution and known physiological functions of the investigated ADHs and Aldh1 are compatible with a role in a defense system, protecting against alcohols, aldehydes and formaldehydes as well as being involved in retinoid metabolism.

Gene induction during differentiation of human pulmonary type II cells in vitro

Mature alveolar type II cells that produce pulmonary surfactant are essential for adaptation to extrauterine life. We profiled gene expression in human fetal lung epithelial cells cultured in serum-free medium containing dexamethasone and cyclic AMP, a treatment that induces differentiation of type II cells. Microarray analysis identified 388 genes that were induced > 1.5-fold by 72 h of hormone treatment. Induced genes represented all categories of molecular function and subcellular location, with increased frequency in the categories of ionic channel, cell adhesion, surface film, lysosome, extracellular matrix, and basement membrane. In time-course experiments, self-organizing map analysis identified a cluster of 17 genes that were slowly but highly induced (5- to approximately 190-fold) and represented four functional categories: surfactant-related (SFTPC, SFTPA, PGC, SFTPB, LAMP3, LPL), regulatory (WIF2, IGF2, IL1RL1, NR4A2, HIF3A), metabolic (MAOA, ADH1B, SEPP1), and transport (SCNN1A, CLDN18, AQP4). Induction of both mRNA and protein for these genes, which included nine newly identified regulated genes, was confirmed, and cellular localization was determined in both fetal and postnatal tissue. Induction of lysosomal-associated membrane protein 3 required both hormones, and expression was localized to limiting membranes of lamellar bodies. Hormone-induced differentiation of human type II cells is associated with genome-wide increased expression of genes with diverse functions.

Expression of retinoic acid-synthesizing and -metabolizing enzymes during nephrogenesis in the rat

Vitamin A signaling through its active form retinoic acid (RA) plays a critical role during kidney development and vitamin A deficiency in the rat induces renal hypoplasia. Here, we describe the distribution of four enzymes of the RA synthetic pathway (aldehyde dehydrogenases ALDH1A1-3 and ALDH8A1) and two enzymes of the degradative pathway (CYP26A1 and CYP26B1) in the developing rat metanephros. We provide evidence that each enzyme displays a cell-type specific expression pattern that changes considerably in the course of renal organogenesis and nephron differentiation. ALDH1A2 expression was restricted to the cortical stroma cell population, whereas ALDH8A1 transcripts were present in emerging renal vesicles. CYP26A1 and CYP26B1 mRNAs were absent during this time. Following nephron induction, ALDH1A1 remained weakly expressed in the UB ends, but was highly expressed in the UB-connected tubule and in all differentiating tubular segments of the developing nephron. ALDH1A2 was strongly expressed in the visceral layer of the developing glomeruli, as well as in cortical collecting tubules. ALDH1A3 mRNAs were found in the developing papilla and ureter. During postnatal nephrogenesis, ALDH1A3 and ALDH8A1 were co-expressed in the ureteric bud ends. CYP26A1 and CYP26B1 were both expressed from E18.5 onwards in S-shaped bodies, in tubular and glomerular anlagen, respectively. On the last day of nephrogenesis in the rat, CYP26B1 expression extended to UB ends. Our results indicate that tubular and glomerular differentiation of the nephron relies upon precise control of the RA metabolic pathway.

Tissue- and species-specific expression patterns of class I, III, and IV Adh and Aldh1 mRNAs in rodent embryos

Alcohol and aldehyde dehydrogenases (ADHs and ALDHs) may be of interest in the pathology of Parkinson's disease (PD) because of their role in protection against toxins and in retinoid metabolism, which is required for growth and development of the mesencephalic dopamine system. In the present study, the spatial and temporal expression patterns of Adh 1, Adh 3, Adh 4, and Aldh 1 mRNAs in embryonic C57BL/6 mice (E 9.5-E19.5) and Sprague-Dawley rats (E12.5-P0) have been investigated by using radioactive oligonucleotide in situ hybridization. High expression of Aldh 1 mRNA was found in the developing mesencephalic dopamine neurons of both mice and rats. Expression of Adh 1 and Adh 4 mRNAs was observed in adrenal cortex and olfactory epithelium in mice. Additionally, Adh 1 was expressed in epidermis, liver, conjunctival, and intestinal epithelium. In rat embryos, expression was less extensive, with Adh 1 mRNA being found in liver and intestines. Adh 3 expression was ubiquitous in both mouse and rat embryos, suggesting a housekeeping function of the gene. Consistent with previous studies in adult rats and mice, our data suggest that Adh 3 is the only ADH class present in rodent brain. Adh and Aldh gene activity in mouse and rat embryos indicate the possible involvement of the respective enzymes in retinoid metabolism and participation in defense against toxic insults, including those that may be involved in the pathogenesis of PD.

Ethanol increases retinoic acid production in cerebellar astrocytes and in cerebellum

Several characteristics of fetal alcohol syndrome (FAS) are similar to the teratogenic effects of retinoic acid (RA) exposure. It has been suggested that FAS may result from ethanol-induced alteration in endogenous RA synthesis, leading to abnormal embryonic concentrations of this morphogen. We examined whether ethanol may interfere with RA synthesis in the postnatal cerebellum, as a region of the developing CNS particularly vulnerable to both ethanol and RA teratogenesis. It was found that astrocytes are the predominant source of postnatal RA synthesis in the cerebellum. They express both retinaldehyde dehydrogenase 1 and 2. In vitro cytosolic preparations of astrocytes, as well as live cell preparations, have an increased capacity to synthesize RA in the presence of ethanol. A mechanism by which ethanol could stimulate RA synthesis is via the ethanol-activated short-chain retinol dehydrogenases, which we show to be present in the postnatal cerebellum. To determine whether ethanol stimulated RA synthesis in vivo, a sensitive and highly specific HPLC/MSn technique was used to measure cerebellar RA after administration of ethanol to postnatal day 4 rat pups. Cerebellar RA levels climbed significantly after such treatment. These results suggest that the cerebellar pathology exerted by ethanol may occur, at least in part, through increased production of RA.

Fetal ADH2*3, maternal alcohol consumption, and fetal growth

There is some evidence suggesting the allele for alcohol dehydrogenase 2*3 (ADH2*3) is associated with a protective effect against alcohol-related intrauterine growth retardation (IUGR). This study was conducted to explore the affect of the ADH2*3 allele on fetal growth. Bloodspots (n = 1016) belonging to individual infants of a subgroup of the Baltimore-Washington Infant Study (BWIS) were assayed for the presence of the ADH2*3 allele by a polymerase chain reaction (PCR)-based method. Infants genotyped for ADH2*3 were those for whom bloodspots were identified and obtained from the Maryland Newborn Screening Program. The effect of ADH2*3 and maternal alcohol consumption on intrauterine growth was explored by multivariable linear regression analysis. Twenty-six percent of the 306 blood spots belonging to African-American infants were positive for ADH2*3 (4% were homozygous and 22% were heterozygous). Only a small percentage of bloodspots for Caucasian (1.3%) were positive for the ADH2*3 allele. Consequently, further analysis concentrated on gene-exposure interactions for African-American infants. It was found that the incidence of being small-for-gestation-age (SGA) was lower for ADH2*3-positive infants (2.5% versus 8.8%; p = .08). SGA infants had elevated odds for being ADH2*3 negative (OR: 3.15, 95% C.I.: 0.70-14.26) and for being born to mothers that consumed alcohol during pregnancy (OR: 2.31, 95% C.I.: 0.77-6.91). A negative trend between maternal alcohol consumption and mean offspring birthweight was found; however, ADH2*3 did not have a significant impact on mean birthweight for infants born to mothers that drank during pregnancy. These results could be interpreted as possible support for the hypothesis that ADH2 genotype in the infant may impact risk for alcohol-related IUGR. However, this study has limitations in that it is a "nested study of convenience" and involves a relatively small number of infants born to mothers reporting moderate to heavy alcohol use during pregnancy.

Two zebrafish alcohol dehydrogenases share common ancestry with mammalian class I, II, IV, and V alcohol dehydrogenase genes but have distinct functional characteristics

Ethanol is teratogenic to many vertebrates. We are utilizing zebrafish as a model system to determine whether there is an association between ethanol metabolism and ethanol-mediated developmental toxicity. Here we report the isolation and characterization of two cDNAs encoding zebrafish alcohol dehydrogenases (ADHs). Phylogenetic analysis of these zebrafish ADHs indicates that they share a common ancestor with mammalian class I, II, IV, and V ADHs. The genes encoding these zebrafish ADHs have been named Adh8a and Adh8b by the nomenclature committee. Both genes were genetically mapped to chromosome 13. The 1450-bp Adh8a is 82, 73, 72, and 72% similar at the amino acid level to the Baltic cod ADH8 (previously named ADH1), the human ADH1B2, the mouse ADH1, and the rat ADH1, respectively. Also, the 1484-bp Adh8b is 77, 68, 67, and 66% similar at the amino acid level to the Baltic cod ADH8, the human ADH1B2, the mouse ADH1, and the rat ADH1, respectively. ADH8A and ADH8B share 86% amino acid similarity. To characterize the functional properties of ADH8A and ADH8B, recombinant proteins were purified from SF-9 insect cells. Kinetic studies demonstrate that ADH8A metabolizes ethanol, with a V(max) of 13.4 nmol/min/mg protein, whereas ADH8B does not metabolize ethanol. The ADH8A K(m) for ethanol as a substrate is 0.7 mm. 4-Methyl pyrazole, a classical competitive inhibitor of class I ADH, failed to inhibit ADH8A. ADH8B has the capacity to efficiently biotransform longer chain primary alcohols (>/=5 carbons) and S-hydroxymethlyglutathione, whereas ADH8A does not efficiently metabolize these substrates. Finally, mRNA expression studies indicate that both ADH8A and ADH8B mRNA are expressed during early development and in the adult brain, fin, gill, heart, kidney, muscle, and liver. Together these results indicate that class I-like ADH is conserved in zebrafish, albeit with mixed functional properties.

The specificity of alcohol dehydrogenase with cis-retinoids. Activity with 11-cis-retinol and localization in retina

Studies in knockout mice support the involvement of alcohol dehydrogenases ADH1 and ADH4 in retinoid metabolism, although kinetics with retinoids are not known for the mouse enzymes. Moreover, a role of alcohol dehydrogenase (ADH) in the eye retinoid interconversions cannot be ascertained due to the lack of information on the kinetics with 11-cis-retinoids. We report here the kinetics of human ADH1B1, ADH1B2, ADH4, and mouse ADH1 and ADH4 with all-trans-, 7-cis-, 9-cis-, 11-cis- and 13-cis-isomers of retinol and retinal. These retinoids are substrates for all enzymes tested, except the 13-cis isomers which are not used by ADH1. In general, human and mouse ADH4 exhibit similar activity, higher than that of ADH1, while mouse ADH1 is more efficient than the homologous human enzymes. All tested ADHs use 11-cis-retinoids efficiently. ADH4 shows much higher k(cat)/K(m) values for 11-cis-retinol oxidation than for 11-cis-retinal reduction, a unique property among mammalian ADHs for any alcohol/aldehyde substrate pair. Docking simulations and the kinetic properties of the human ADH4 M141L mutant demonstrated that residue 141, in the middle region of the active site, is essential for such ADH4 specificity. The distinct kinetics of ADH4 with 11-cis-retinol, its wide specificity with retinol isomers and its immunolocalization in several retinal cell layers, including pigment epithelium, support a role of this enzyme in the various retinol oxidations that occur in the retina. Cytosolic ADH4 activity may complement the isomer-specific microsomal enzymes involved in photopigment regeneration and retinoic acid synthesis.

Spatio-temporal distribution of cellular retinol-binding protein gene transcripts (CRBPI and CRBPII) in the developing and adult zebrafish (Danio rerio)

We have cloned and determined the nucleotide sequence of the cDNA coding for a cellular retinol-binding protein type I (CRBPI) from zebrafish. The deduced amino acid sequence of the zebrafish CRBPI showed highest sequence identity ( approximately 59%) to the mammalian CRBPIs of the intracellular lipid-binding protein (iLBP) multigene family. Phylogenetic analysis clustered the zebrafish CRBPI to the CRBPI clade. The zebrafish CRBPI gene (rbp1) and CRBPII gene (rbp2) both consist of four exons separated by three introns, identical to all other iLBP genes in vertebrates. Two transcription start sites were identified in the rbp1 promoter and a single transcription start site was identified for rbp2. Radiation hybrid mapping assigned the zebrafish rbp1 gene to linkage group 16 and conserved syntenic genes were found by comparative analysis of mammalian orthologous rbp1 genes. RT-PCR detected mRNA transcripts in the adult intestine, liver, brain, ovary and testis for rbp1 gene and in the intestine and liver for rbp2 gene. Whole mount in situ hybridization of zebrafish embryos revealed rbp1 mRNA expression in the developing zebrafish central nervous system at specific sites that are known to have abundant retinoic acid distribution and significant retinoic acid action. Whole mount in situ hybridization also showed that the zebrafish rbp2 mRNA was localized specifically in the embryonic intestinal bulb and the developing intestine during the larval stage, implying a novel function for the rbp2 gene product during organogenesis and development of the zebrafish intestine.

Dexamethasone blocks the rapid biological effects of 17beta-estradiol in the rat uterus without antagonizing its global genomic actions

Estrogens and glucocorticoids have opposing effects on the female reproductive tract, but the molecular basis for this antagonism is poorly understood. We therefore examined the biological and transcriptional programs induced by estrogens and glucocorticoids in the uterus of immature female rats. Estradiol 17beta (E2) rapidly induced morphological changes reminiscent of an acute inflammatory response, including infiltration of eosinophils, edema in the stroma and myometrium, and a decrease in the height of luminal epithelial cells, whereas dexamethasone (Dex) only altered stromal cell morphology. When coadministered with E2, Dex completely blocked the proinflammatory effects of E2. Surprisingly, examination of E2 and Dex effects on gene expression using cDNA microarrays and real-time PCR revealed that these hormones had similar effects on the expression of many genes and that very few genes displayed antagonistic regulation. Together, these results indicate strong discord between the early biologic and genomic actions of estrogens and glucocorticoids and highlight a complex regulatory role for glucocorticoids and GR in the mammalian uterus.

Expression, localization and potential physiological significance of alcohol dehydrogenase in the gastrointestinal tract

ADH1 and ADH4 are the major alcohol dehydrogenases (ADH) in ethanol and retinol oxidation. ADH activity and protein expression were investigated in rat gastrointestinal tissue homogenates by enzymatic and Western blot analyses. In addition, sections of adult rat gastrointestinal tract were examined by in situ hybridization and immunohistochemistry. ADH1 and ADH4 were detected along the whole tract, changing their localization and relative content as a function of the area studied. While ADH4 was more abundant in the upper (esophagus and stomach) and lower (colorectal) regions, ADH1 was predominant in the intestine but also present in stomach. Both enzymes were detected in mucosa but, in general, ADH4 was found in outer cell layers, lining the lumen, while ADH1 was detected in the inner cell layers. Of interest were the sharp discontinuities in the expression found in the pyloric region (ADH1) and the gastroduodenal junction (ADH4), reflecting functional changes. The precise localization of ADH in the gut reveals the cell types where active alcohol oxidation occurs during ethanol ingestion, providing a molecular basis for the gastrointestinal alcohol pathology. Localization of ADH, acting as retinol dehydrogenase/retinal reductase, also indicates sites of active retinoid metabolism in the gut, essential for mucosa function and vitamin A absorption.

Species variations in cutaneous alcohol dehydrogenases and aldehyde dehydrogenases may impact on toxicological assessments of alcohols and aldehydes

Alcohol dehydrogenase (ADH; EC. 1.1.1.1) and aldehyde dehydrogenase (ALDH; EC 1.2.1.3) play important roles in the metabolism of both endogenous and exogenous alcohols and aldehydes. The expression and localisation patterns of ADH (1-3) and ALDH (1-3) were investigated in the skin and liver of the mouse (BALB/c and CBA/ca), rat (F344) and guinea-pig (Dunkin-Hartley), using Western blot analysis and immunohistochemistry with class-specific antisera. ALDH2 expression and localisation was also determined in human skin, while ethanol oxidation, catalysed by ADH, was investigated in the mouse, guinea-pig and human skin cytosol. Western blot analysis revealed that ADH1, ADH3, ALDH1 and ALDH2 were expressed, constitutively, in the skin and liver of the mouse, rat and guinea-pig. ADH2 was not detected in the skin of any rodent species/strain, but was present in all rodent livers. ALDH3 was expressed, constitutively, in the skin of both strains of mouse and rat, but was not detected in guinea-pig skin and was absent in all livers. Immunohistochemistry showed similar patterns of expression for ADH and ALDH in both strains of mouse, rat, guinea-pig and human skin sections, with localisation predominantly in the epidermis, sebaceous glands and hair follicles. ADH activity (apparent V(max), nmoles/mg protein/min) was higher in liver (6.02-16.67) compared to skin (0.32-1.21) and lower in human skin (0.32-0.41) compared to mouse skin (1.07-1.21). The ADH inhibitor 4-methyl pyrazole (4-MP) reduced ethanol oxidation in the skin and liver in a concentration dependent manner: activity was reduced to approximately 30-40% and approximately 2-10% of the control activity, in the skin and liver, respectively, using 1 mM 4-MP. The class-specific expression of ADH and ALDH enzymes, in the skin and liver and their variation between species, may have toxicological significance, with respect to the metabolism of endogenous and xenobiotic alcohols and aldehydes.

Distribution of class I, III and IV alcohol dehydrogenase mRNAs in the adult rat, mouse and human brain

The localization of different classes of alcohol dehydrogenases (ADH) in the brain is of great interest because of their role in both ethanol and retinoic acid metabolism. Conflicting data have been reported in the literature. By Northern blot and enzyme activity analyses only class III ADH has been detected in adult brain specimens, while results from riboprobe in situ hybridization indicate class I as well as class IV ADH expression in different regions of the rat brain. Here we have studied the expression patterns of three ADH classes in adult rat, mouse and human tissues using radioactive oligonucleotide in situ hybridization. Specificity of probes was tested on liver and stomach control tissue, as well as tissue from class IV ADH knock-out mice. Only class III ADH mRNA was found to be expressed in brain tissue of all three investigated species. Particularly high expression levels were found in neurons of the red nucleus in human tissue, while cortical neurons, pyramidal and granule cells of the hippocampus and dopamine neurons of substantia nigra showed moderate expression levels. Purkinje cells of cerebellum were positive for class III ADH mRNA in all species investigated, whereas granular layer neurons were positive only in rodents. The choroid plexus was highly positive for class III ADH, while no specific signal for class I or class IV ADH was detected. Our results thus support the notion that the only ADH expressed in adult mouse, rat and human brain is class III ADH.

Cytosolic retinoid dehydrogenases govern ubiquitous metabolism of retinol to retinaldehyde followed by tissue-specific metabolism to retinoic acid

The ability of vitamin A (retinol) to control growth and development depends upon tissue-specific metabolism of retinol to retinoic acid (RA). RA then functions as a ligand for retinoid receptor signaling. Mouse genetic studies support a role for cytosolic alcohol dehydrogenases (ADH) in the first step (oxidation of retinol to retinaldehyde) and a role for cytosolic retinaldehyde dehydrogenases (RALDH) in the second step (oxidation of retinaldehyde to RA). Mice lacking ADH3 have reduced survival and a growth defect that can be rescued by dietary retinol supplementation, whereas the effect of a loss of ADH1 or ADH4 is noticed only in mice subjected to vitamin A excess or deficiency, respectively. Also, genetic deficiency of both ADH1 and ADH4 does not have additive effects, verifying separate roles for these enzymes in retinoid metabolism. As for the second step of RA synthesis, a null mutation of RALDH2 is embryonic lethal, eliminating most mesodermal RA synthesis, whereas loss of RALDH1 eliminates RA synthesis only in the embryonic dorsal retina with no obvious effect on development. Analysis of RA-rescued RALDH2 mutants has also revealed that RALDH3 and at least one additional enzyme produce RA tissue-specifically in embryos. Collectively, these genetic findings indicate that metabolism of retinol to retinaldehyde is not tissue-restricted as it is catalyzed by ubiquitously-expressed ADH3 (a low activity form) as well as by tissue-specifically expressed ADH1 and ADH4 (high activity forms). In contrast, further metabolism of retinaldehyde to RA is tissue-restricted as all enzymes identified are tissue-specific. An important concept to emerge is that selective expression of enzymes catalyzing the second step is what limits the tissues that can completely metabolize retinol to RA to initiate retinoid signaling.

Human class IV alcohol dehydrogenase: kinetic mechanism, functional roles and medical relevance

Human alcohol dehydrogenase (ADH) constitutes a complex family. Class IV ADH (ADH4) is characteristic in its epithelial expression in the aerodigestive tract and high V(max) and K(m) for oxidation of ethanol. ADH4 exhibits the highest catalytic efficiency for retinol oxidation in human ADH family. Initial velocity, product inhibition, and dead-end inhibition studies indicate that ADH4, when functioning as ethanol dehydrogenase, conforms to an ordered sequential mechanism with coenzyme binding first and releasing last in catalytic cycle. When functioning as retinol dehydrogenase, the mechanism of ADH4 deduced from steady-state kinetic and equilibrium-binding studies is best described as a rapid equilibrium random mechanism with two dead-end ternary complex for retinol oxidation and a rapid equilibrium ordered mechanism with one dead-end ternary complex for retinal reduction, a unique mechanistic form for zinc-containing ADHs in the medium chain dehydrogenase/reductase superfamily. Kinetic and genetic studies support the proposal that ADH4 may play two important physiological roles, i.e., as a major contributor to first-pass metabolism of ethanol in stomach as well as involvement in the synthesis of retinoic acid, a hormonal ligand controlling a nuclear receptor signaling pathway that regulates growth, development, and epithelial maintenance. Quantitative simulation studies indicate that retinol metabolism through ADH pathway can be inhibited to a significant extent during alcohol consumption. The perturbation of retinoic acid synthesis by ethanol may underlie the pathogenesis of fetal alcohol syndrome and alcohol-related upper digestive tract cancer.

The role of vitamin A in mammalian reproduction and embryonic development

Since the late 1980s, there has been an explosion of information on the molecular mechanisms and functions of vitamin A. This review focuses on the essential role of vitamin A in female reproduction and embryonic development and the metabolism of vitamin A (retinol) that results in these functions. Evidence strongly supports that in situ-generated all-trans retinoic acid (atRA) is the functional form of vitamin A in female reproduction and embryonic development. This is supported by the ability to reverse most reproductive and developmental blocks found in vitamin A deficiency with atRA, the block in embryonic development that occurs in retinaldehyde dehydrogenase type 2 null mutant mice, and the essential roles of the retinoic acid receptors, at least in embryogenesis. Early studies of embryos from marginally vitamin A-deficient (VAD) pregnant rats revealed a collection of defects called the vitamin A-deficiency syndrome. The manipulation of all-trans retinoic acid (atRA) levels in the diet of VAD female rats undergoing a reproduction cycle has proved to be an important new tool in deciphering the points of atRA function in early embryos and has provided a means to generate large numbers of embryos at later stages of development with the vitamin A-deficiency syndrome. The essentiality of the retinoid receptors in mediating the activity of atRA is exemplified by the many compound null mutant embryos that now recapitulate both the original vitamin A-deficiency syndrome and exhibit a host of new defects, many of which can also be observed in the VAD-atRA-supported rat embryo model and in retinaldehyde dehydrogenase type 2 (RALDH2) mutant mice. A major task for the future is to elucidate the atRA-dependent pathways that are normally operational in vitamin A-sufficient animals and that are perturbed in deficiency, thus leading to the characteristic VAD phenotypes described above.

Differentiation of human pulmonary type II cells in vitro by glucocorticoid plus cAMP

Mature alveolar type II cells that produce pulmonary surfactant are essential for adaptation to extrauterine life and prevention of infant respiratory distress syndrome. We have developed a new in vitro model to further investigate regulation of type II cell differentiation. Epithelial cells isolated from human fetal lung were cultured in serum-free medium on plastic. Cells treated with dexamethasone + cAMP analog and isobutylmethylxanthine for 4 days exhibited increased phosphatidylcholine synthesis and content of disaturated phosphatidylcholine species, manyfold increases in all surfactant proteins with processing to mature forms, and abundant lamellar bodies. DNA microarray analysis identified approximately 3,100 expressed genes, including subsets of genes induced 2- to >100-fold (approximately 2.5%) or repressed 2- to 18-fold (approximately 1.2%) by hormone treatment. Of the highly regulated genes, most were coregulated in an additive or synergistic manner by dexamethasone and cAMP agents. Approximately 90% of the regulated genes identified by this initial microarray analysis have not been previously recognized as hormone responsive. One newly identified hormone-induced gene is Nkx2.1 (thyroid transcription factor-1), which has a critical role in surfactant protein gene expression. Our findings indicate that glucocorticoid + cAMP is sufficient and necessary for precocious induction of functional type II cells in this in vitro system and that these hormones act primarily in combination to regulate expression of a subset of specific genes.

Kinetic mechanism of human class IV alcohol dehydrogenase functioning as retinol dehydrogenase

Molecular genetic studies have indicated that alcohol dehydrogenase may be involved in the synthesis of retinoic acid, a hormonal molecule regulating diverse cellular functions at the transcriptional level. Class IV alcohol dehydrogenase (ADH) has been reported to be the most efficient enzyme catalyzing oxidation of retinol in human ADH family. Initial velocity, product inhibition, and dead-end inhibition experiments were performed with the recombinant human class IV ADH to elucidate kinetic mechanism with all-trans-retinol and all-trans-retinal as natural substrates. Fluorescence quenching was titrated in formation of the binary and abortive ternary enzyme complexes. The minimal mechanism deduced from steady-state kinetic and equilibrium binding studies is best described as an asymmetric rapid equilibrium random mechanism with two dead-end ternary complexes for retinol oxidation and a rapid equilibrium ordered mechanism with one dead-end ternary complex for retinal reduction, a unique mechanistic form for zinc-containing ADHs in the medium chain dehydrogenase/reductase superfamily. Dissociation constants for the binary complexes as well as the productive and abortive ternary complexes determined from different experimental approaches are in reasonable agreement. Kinetic isotope effect studies suggest rate-limiting isomerization of the central ternary complexes in both reaction directions. The potential interference of retinol metabolism by ethanol through the ADH pathway may play a significant role in the pathogenesis of fetal alcohol syndrome and alcohol-related upper digestive tract cancer.

Stimulation of retinoic acid production and growth by ubiquitously expressed alcohol dehydrogenase Adh3

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

Organization of six functional mouse alcohol dehydrogenase genes on two overlapping bacterial artificial chromosomes

Mammalian alcohol dehydrogenases (ADH) form a complex enzyme system based on amino-acid sequence, functional properties, and gene expression pattern. At least four mouse Adh genes are known to encode different enzyme classes that share less than 60% amino-acid sequence identity. Two ADH-containing and overlapping C57BL/6 bacterial artificial chromosome clones, RP23-393J8 and -463H24, were identified in a library screen, physically mapped, and sequenced. The gene order in the complex and two new mouse genes, Adh5a and Adh5b, and a pseudogene, Adh5ps, were obtained from the physical map and sequence. The mouse genes are all in the same transcriptional orientation in the order Adh4-Adh1-Adh5a-Adh5b-Adh5ps-Adh2-Adh3. A phylogenetic tree analysis shows that adjacent genes are most closely related suggesting a series of duplication events resulted in the gene complex. Although mouse and human ADH gene clusters contain at least one gene for ADH classes I-V, the human cluster contains 3 class I genes while the mouse cluster has two class V genes plus a class V pseudogene.

A vertebrate aldo-keto reductase active with retinoids and ethanol

Enzymes of the short chain and medium chain dehydrogenase/reductase families have been demonstrated to participate in the oxidoreduction of ethanol and retinoids. Mammals and amphibians contain, in the upper digestive tract mucosa, alcohol dehydrogenases of the medium chain dehydrogenase/reductase family, active with ethanol and retinol. In the present work, we searched for a similar enzyme in an avian species (Gallus domesticus). We found that chicken does not contain the homologous enzyme from the medium chain dehydrogenase/reductase family but an oxidoreductase from the aldo-keto reductase family, with retinal reductase and alcohol dehydrogenase activities. The amino acid sequence shows 66-69% residue identity with the aldose reductase and aldose reductase-like enzymes. Chicken aldo-keto reductase is a monomer of M(r) 36,000 expressed in eye, tongue, and esophagus. The enzyme can oxidize aliphatic alcohols, such as ethanol, and it is very efficient in all-trans- and 9-cis-retinal reduction (k(cat)/K(m) = 5,300 and 32,000 mm(-1).min(-1), respectively). This finding represents the inclusion of the aldo-keto reductase family, with the (alpha/beta)(8) barrel structure, into the scenario of retinoid metabolism and, therefore, of the regulation of vertebrate development and tissue differentiation.

Genetic dissection of retinoid dehydrogenases

Biochemical studies indicate that alcohol dehydrogenase (ADH) metabolizes retinol to retinal, and that aldehyde dehydrogenase (ALDH) metabolizes retinal to retinoic acid, a molecule essential for growth and development. Summarized herein are several genetic studies supporting in vivo functions for ADH and ALDH in retinoic acid synthesis. Gene targeting was used to create knockout mice for either Adh1 or Adh4. Both knockout mice were viable and fertile without obvious defects. However, when wild-type and Adh4 knockout mice were subjected to vitamin A deficiency during gestation, the survival rate at birth was 3.3-fold lower for Adh4 knockout mice. When adult mice were examined for production of retinoic acid following retinol administration, Adh1 knockout mice exhibited 10-fold lower retinoic acid levels in liver compared with wild-type, whereas Adh4 knockout mice differed from wild-type by less than 2-fold. Thus, Adh1 plays a major role in the metabolism of a large dose of retinol to retinoic acid in adults, whereas Adh4 plays a role in maintaining sufficient retinol metabolism for development during retinol deficiency. ALDHs were examined by overexpression studies in frog embryos. Injection of mRNAs for either mouse Raldh1 or Raldh2 stimulated retinoic acid synthesis in frog embryos at the blastula stage when retinoic acid is normally undetectable. Overexpression of human ALDH2, human ALDH3, and mouse Aldh-pb did not stimulate retinoic acid production. In addition, Raldh2 knockout mice exhibit embryonic lethality with defects in retinoid-dependent tissues. Overall, these studies provide genetic evidence that Adh1, Adh4, Raldh1, and Raldh2 encode retinoid dehydrogenases involved in retinoic acid synthesis in vivo.

Molecular basis for differential substrate specificity in class IV alcohol dehydrogenases: a conserved function in retinoid metabolism but not in ethanol oxidation

Mammalian class IV alcohol dehydrogenase enzymes are characteristic of epithelial tissues, exhibit moderate to high K(m) values for ethanol, and are very active in retinol oxidation. The human enzyme shows a K(m) value for ethanol which is 2 orders of magnitude lower than that of rat class IV. The uniquely significant difference in the substrate-binding pocket between the two enzymes appears to be at position 294, Val in the human enzyme and Ala in the rat enzyme. Moreover, a deletion at position 117 (Gly in class I) has been pointed out as probably responsible for class IV specificity toward retinoids. With the aim of establishing the role of these residues, we have studied the kinetics of the recombinant human and rat wild-type enzymes, the human G117ins and V294A mutants, and the rat A294V mutant toward aliphatic alcohols and retinoids. 9-cis-Retinol was the best retinoid substrate for both human and rat class IV, strongly supporting a role of class IV in the generation of 9-cis-retinoic acid. In contrast, 13-cis retinoids were not substrates. The G117ins mutant showed a decreased catalytic efficiency toward retinoids and toward three-carbon and longer primary aliphatic alcohols, a behavior that resembles that of the human class I enzyme, which has Gly(117). The K(m) values for ethanol dramatically changed in the 294 mutants, where the human V294A mutant showed a 280-fold increase, and the rat A294V mutant a 50-fold decrease, compared with those of the respective wild-type enzymes. This demonstrates that the Val/Ala exchange at position 294 is mostly responsible for the kinetic differences with ethanol between the human and rat class IV. In contrast, the kinetics toward retinoids was only slightly affected by the mutations at position 294, compatible with a more conserved function of mammalian class IV alcohol dehydrogenase in retinoid metabolism.

Changes in the activity of alcohol dehydrogenase isoenzymes during the estrus cycle in the vagina of the rat

In rodents, the vaginal epithelium undergoes cyclical changes with an alternating pattern of keratinization and mucification. It has been known for decades that vitamin A and its active form retinoic acid are responsible for normal epithelial homeostasis. However, it has not so far been certain which enzymes catalyze the first and rate-limiting step in retinoic acid synthesis. By means of microdissection and ultrathin-layer gel electrophoresis, alcohol dehydrogenase isoenzyme activity was determined quantitatively in the various layers of the vaginal mucous membrane. It was found that, in the rat, only alcohol dehydrogenase 3 and 4 are expressed. Marked cyclical changes of alcohol dehydrogenase 4 activity in the stratum germinativum of the vaginal epithelium strongly support the assumption that this isoenzyme is responsible for retinoic acid synthesis, and that it is essential for the changes accompanying keratinization and mucification.

Families of retinoid dehydrogenases regulating vitamin A function: production of visual pigment and retinoic acid

Vitamin A (retinol) and provitamin A (beta-carotene) are metabolized to specific retinoid derivatives which function in either vision or growth and development. The metabolite 11-cis-retinal functions in light absorption for vision in chordate and nonchordate animals, whereas all-trans-retinoic acid and 9-cis-retinoic acid function as ligands for nuclear retinoic acid receptors that regulate gene expression only in chordate animals. Investigation of retinoid metabolic pathways has resulted in the identification of numerous retinoid dehydrogenases that potentially contribute to metabolism of various retinoid isomers to produce active forms. These enzymes fall into three major families. Dehydrogenases catalyzing the reversible oxidation/reduction of retinol and retinal are members of either the alcohol dehydrogenase (ADH) or short-chain dehydrogenase/reductase (SDR) enzyme families, whereas dehydrogenases catalyzing the oxidation of retinal to retinoic acid are members of the aldehyde dehydrogenase (ALDH) family. Compilation of the known retinoid dehydrogenases indicates the existence of 17 nonorthologous forms: five ADHs, eight SDRs, and four ALDHs, eight of which are conserved in both mouse and human. Genetic studies indicate in vivo roles for two ADHs (ADH1 and ADH4), one SDR (RDH5), and two ALDHs (ALDH1 and RALDH2) all of which are conserved between humans and rodents. For several SDRs (RoDH1, RoDH4, CRAD1, and CRAD2) androgens rather than retinoids are the predominant substrates suggesting a function in androgen metabolism as well as retinoid metabolism.

Impaired retinol utilization in Adh4 alcohol dehydrogenase mutant mice

Adh4, a member of the mouse alcohol dehydrogenase (ADH) gene family, encodes an enzyme that functions in vitro as a retinol dehydrogenase in the conversion of retinol to retinoic acid, an important developmental signaling molecule. To explore the role of Adh4 in retinoid signaling in vivo, gene targeting was used to create a null mutation at the Adh4 locus. Homozygous Adh4 mutant mice were viable and fertile and demonstrated no obvious defects when maintained on a standard mouse diet. However, when subjected to vitamin A deficiency during gestation, Adh4 mutant mice demonstrated a higher number of stillbirths than did wild-type mice. The proportion of liveborn second generation vitamin A-deficient newborn mice was only 15% for Adh4 mutant mice but 49% for wild-type mice. After retinol administration to vitamin A-deficient dams in order to rescue embryonic development, Adh4 mutant mice demonstrated a higher resorption rate at stage E12.5 (69%), compared with wild-type mice (30%). The relative ability of Adh4 mutant and wild-type mice to metabolize retinol to retinoic acid was measured after administration of a 100-mg/kg dose of retinol. Whereas kidney retinoic acid levels were below the level of detection in all vehicle-treated mice (< 1 pmol/g), retinol treatment resulted in very high kidney retinoic acid levels in wild-type mice (273 pmol/g) but 8-fold lower levels in Adh4 mutant mice (32 pmol/g), indicating a defect in metabolism of retinol to retinoic acid. These findings demonstrate that another retinol dehydrogenase can compensate for a lack of Adh4 when vitamin A is sufficient, but that Adh4 helps optimize retinol utilization under conditions of both retinol deficiency and excess.

Retinoic acid: its biosynthesis and metabolism

This article presents a model that integrates the functions of retinoid-binding proteins with retinoid metabolism. One of these proteins, the widely expressed (throughout retinoid target tissues and in all vertebrates) and highly conserved cellular retinol-binding protein (CRBP), sequesters retinol in an internal binding pocket that segregates it from the intracellular milieu. The CRBP-retinol complex appears to be the quantitatively major form of retinol in vivo, and may protect the promiscuous substrate from nonenzymatic degradation and/or non-specific enzymes. For example, at least seven types of dehydrogenases catalyze retinal synthesis from unbound retinol in vitro (NAD+ vs. NADP+ dependent, cytosolic vs. microsomal, short-chain dehydrogenases/reductases vs. medium-chain alcohol dehydrogenases). But only a fraction of these (some of the short-chain de-hydrogenases/reductases) have the fascinating additional ability of catalyzing retinal synthesis from CRBP-bound retinol as well. Similarly, CRBP and/or other retinoid-binding proteins function in the synthesis of retinal esters, the reduction of retinal generated from intestinal beta-carotene metabolism, and retinoic acid metabolism. The discussion details the evidence supporting an integrated model of retinoid-binding protein/metabolism. Also addressed are retinoid-androgen interactions and evidence incompatible with ethanol causing fetal alcohol syndrome by competing directly with retinol dehydrogenation to impair retinoic acid biosynthesis.

Interactions of retinoid binding proteins and enzymes in retinoid metabolism

Naturally occurring retinoids (vitamin A or retinol and its active metabolites) are vital for vision, controlling the differentiation program of epithelial cells in the digestive tract and respiratory system, skin, bone, the nervous system, the immune system, and for hematopoiesis. Retinoids are essential for growth, reproduction (conception and embryonic development), and resistance to and recovery from infection. The functions of retinoids in the embryo begin soon after conception and continue throughout the lifespan of all vertebrates. Both naturally occurring and synthetic retinoids are used in the therapy of various skin diseases, especially acne, for augmenting the treatment of diabetes, and as cancer chemopreventive agents. Retinol metabolites serve as ligands that activate specific transcription factors in the superfamily of steroid/retinoid/thyroid/vitamin D/orphan receptors and thereby control gene expression. Additionally, retinoids may also function through non-genomic actions. Various retinoid binding proteins serve as partners in retinoid function. These binding proteins show high specificity and affinity for specific retinoids and seem to control retinoid metabolism in vivo qualitatively and quantitatively by reducing 'free' retinoid concentrations, protecting retinoids from non-specific interactions, and chaperoning access of metabolic enzymes to retinoids. Implementation of the physiological effects of retinoids depends on the spatial-temporal expressions of binding proteins, receptors and metabolic enzymes. This review will discuss current understanding of the enzymes that catalyze retinol and retinoic acid metabolism and their unique and integral relationship to retinoid binding proteins.

Recommended nomenclature for the vertebrate alcohol dehydrogenase gene family

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