Increased hepatic retinal dehydrogenase activity after phenobarbital and ethanol administration

Fetal Alcohol Spectrum Disorder: Embryogenesis Under Reduced Retinoic Acid Signaling Conditions

Fetal Alcohol Spectrum Disorder (FASD) is a complex set of developmental malformations, neurobehavioral anomalies and mental disabilities induced by exposing human embryos to alcohol during fetal development. Several experimental models and a series of developmental and biochemical approaches have established a strong link between FASD and reduced retinoic acid (RA) signaling. RA signaling is involved in the regulation of numerous developmental decisions from patterning of the anterior-posterior axis, starting at gastrulation, to the differentiation of specific cell types within developing organs, to adult tissue homeostasis. Being such an important regulatory signal during embryonic development, mutations or environmental perturbations that affect the level, timing or location of the RA signal can induce multiple and severe developmental malformations. The evidence connecting human syndromes to reduced RA signaling is presented here and the resulting phenotypes are compared to FASD. Available data suggest that competition between ethanol clearance and RA biosynthesis is a major etiological component in FASD.

The adverse effects of alcohol on vitamin A metabolism

The objective of this review is to explore the relationship between alcohol and the metabolism of the essential micronutrient, vitamin A; as well as the impact this interaction has on alcohol-induced disease in adults. Depleted hepatic vitamin A content has been reported in human alcoholics, an observation that has been confirmed in animal models of chronic alcohol consumption. Indeed, alcohol consumption has been associated with declines in hepatic levels of retinol (vitamin A), as well as retinyl ester and retinoic acid; collectively referred to as retinoids. Through the use of animal models, the complex interplay between alcohol metabolism and vitamin A homeostasis has been studied; the reviewed research supports the notion that chronic alcohol consumption precipitates a decline in hepatic retinoid levels through increased breakdown, as well as increased export to extra-hepatic tissues. While the precise biochemical mechanisms governing alcohol's effect remain to be elucidated, its profound effect on hepatic retinoid status is irrefutable. In addition to a review of the literature related to studies on tissue retinoid levels and the metabolic interactions between alcohol and retinoids, the significance of altered hepatic retinoid metabolism in the context of alcoholic liver disease is also considered.

Vitamin A and infancy. Biochemical, functional, and clinical aspects

Vitamin A is a very intriguing natural compound. The molecule not only has a complex array of physiological functions, but also represents the precursor of promising and powerful new pharmacological agents. Although several aspects of human retinol metabolism, including absorption and tissue delivery, have been clarified, the type and amounts of vitamin A derivatives that are intracellularly produced remain quite elusive. In addition, their precise function and targets still need to be identified. Retinoic acids, undoubtedly, play a major role in explaining activities of retinol, but, recently, a large number of physiological functions have been attributed to different retinoids and to vitamin A itself. One of the primary roles this vitamin plays is in embryogenesis. Almost all steps in organogenesis are controlled by retinoic acids, thus suggesting that retinol is necessary for proper development of embryonic tissues. These considerations point to the dramatic importance of a sufficient intake of vitamin A and explain the consequences if intake of retinol is deficient. However, hypervitaminosis A also has a number of remarkable negative consequences, which, in same cases, could be fatal. Thus, the use of large doses of retinol in the treatment of some human diseases and the use of megavitamin therapy for certain chronic disorders as well as the growing tendency toward vitamin faddism should alert physicians to the possibility of vitamin overdose.

Alcohol, vitamin A, and beta-carotene: adverse interactions, including hepatotoxicity and carcinogenicity

Isozymes of alcohol and other dehydrogenases convert ethanol and retinol to their corresponding aldehydes in vitro. In addition, new pathways of retinol metabolism have been described in hepatic microsomes that involve, in part, cytochrome P450s, which can also metabolize various drugs. In view of these overlapping metabolic pathways, it is not surprising that multiple interactions between retinol, ethanol, and other drugs occur. Accordingly, prolonged use of alcohol, drugs, or both, results not only in decreased dietary intake of retinoids and carotenoids, but also accelerates the breakdown of retinol through cross-induction of degradative enzymes. There is also competition between ethanol and retinoic acid precursors. Depletion ensues, with associated hepatic and extrahepatic pathology, including carcinogenesis and contribution to fetal defects. Correction of deficiency through vitamin A supplementation has been advocated. It is, however, complicated by the intrinsic hepatotoxicity of retinol, which is potentiated by concomitant alcohol consumption. By contrast, beta-carotene, a precursor of vitamin A, was considered innocuous until recently, when it was found to also interact with ethanol, which interferes with its conversion to retinol. Furthermore, the combination of beta-carotene with ethanol results in hepatotoxicity. Moreover, in smokers who also consume alcohol, beta-carotene supplementation promotes pulmonary cancer and, possibly, cardiovascular complications. Experimentally, beta-carotene toxicity was exacerbated when administered as part of beadlets. Thus ethanol, while promoting a deficiency of vitamin A also enhances its toxicity as well as that of beta-carotene. This narrowing of the therapeutic window for retinol and beta-carotene must be taken into account when formulating treatments aimed at correcting vitamin A deficiency, especially in drinking populations.

Chronic alcohol intake interferes with retinoid metabolism and signaling

Chronic and excessive ethanol consumption is associated with cellular proliferation, fibrosis, cirrhosis, and cancer of the liver. The critical event in early alcohol-induced hepatic injury is an alcohol-induced activation (cell proliferation and increased fibrogenesis) of hepatic stellate cells. However, the mechanisms by which alcohol causes proliferative activation in hepatic stellate cells have not been identified. An important characteristic of alcohol-induced injury is impaired vitamin A nutritional status. The demonstration that retinoic acid is the most physiologically active derivative of vitamin A and the discovery of retinoic acid receptors provide a mechanistic basis for understanding the actions of vitamin A and alcohol on hepatic cell proliferation. Recent studies have demonstrated that chronic alcohol intake can reduce hepatic retinoic acid concentrations, diminish retinoid signaling, and enhance activator protein-1 (AP-1 (c-Jun and c-Fos)) expression in rat liver. These are the possible biochemical and molecular mechanisms whereby ethanol ingestion results in hepatic stellate cell proliferative activation and hepatic fibrogenesis.

Class IV alcohol/retinol dehydrogenase localization in epidermal basal layer: potential site of retinoic acid synthesis during skin development

Vitamin A (retinol) plays a signaling role in the development of skin and other epithelial tissues. This is accomplished by a two-step metabolic pathway in which the rate-limiting step is oxidation of retinol to retinal, followed by oxidation of retinal to retinoic acid, which serves as the active ligand to activate nuclear retinoic acid receptors. Previous studies in mouse skin have shown that retinol oxidation is catalyzed by a cytosolic retinol dehydrogenase that may be a member of the alcohol dehydrogenase (ADH) enzyme family. Analysis of the ADH family has shown that class IV ADH is the most efficient isozyme for retinol oxidation but that other isozymes can catalyze this reaction. Here we have examined mouse skin for the expression of genes encoding class I ADH and class IV ADH, the only ADH isozymes in this species able to function as retinol dehydrogenases in vitro. In situ hybridization analysis of mouse skin revealed that class I ADH mRNA was absent, whereas class IV ADH mRNA was abundant and localized in the epidermal basal layer, providing evidence that the skin retinol dehydrogenase previously identified was class IV ADH. Immunohistochemical studies indicated that class I ADH protein was absent in the mouse skin, but class IV ADH protein was detected primarily in the basal layer of the epidermis, with less detection in the spinous layer and no detection in the cornified layer. This apparent down-regulation of class IV ADH expression during keratinocyte terminal differentiation provides evidence that the basal layer of the epidermis may be the primary site of local retinoic acid synthesis needed for retinoid signaling in the skin.

Purification and characterization of a novel cytosolic NADP(H)-dependent retinol oxidoreductase from rabbit liver

Rabbit liver cytosol exhibits very high retinol dehydrogenase activity. At least two retinol dehydrogenases were demonstrated to exist in rabbit liver cytosol, and the major one, a cytosolic NADP(H)-dependent retinol dehydrogenase (systematic name: retinol oxidoreductase) was purified about 1795-fold to electrophoretic and column chromatographic homogeneity by a procedure involving column chromatography on AF-Red Toyopearl twice and then hydroxyapatite. Its molecular mass was estimated to be 34 kDa by SDS-PAGE, and 144 kDa by HPLC gel filtration, suggesting that it is a homo-tetramer. The enzyme uses free retinol and retinal, and their complexes with CRBP as substrates in vitro. The optimum pH values for retinol oxidation of free retinol and CRBP-retinol were 8.8-9.2 and 8.0-9.0, respectively, and those for retinal reduction of free retinal and retinal-CRBP were the same, 7.0-7.6. Km for free retinol and Vmax for retinal formation were 2.8 microM and 2893 nmol/min per mg protein at 37 degrees C (pH 9.0) and the corresponding values with retinol-CRBP as a substrate were 2.5 microM and 2428 nmol/min per mg protein at 37 degrees C (pH 8.6); Km for free retinal and Vmax for retinol formation were 6.5 microM and 4108 nmol/min per mg protein, and the corresponding values with retinal-CRBP as a substrate were 5.1 microM and 3067 nmol/min per mg protein at 37 degrees C, pH 7.4. NAD(H) was not effective as a cofactor. 4-Methylpyrazole was a weak inhibitor (IC50 = 28 mM) of the enzyme, and ethanol was neither a substrate nor an inhibitor of the enzyme. This enzyme exhibits relatively broad aldehyde reductase activity and some ketone reductase activity, the activity for aromatic substitutive aldehydes being especially high and effective. Whereas, except in the case of retinol, oxidative activity toward the corresponding alcohols was not detected. This novel cytosolic enzyme may play an important role in vivo in maintaining the homeostasis of retinal, the substrate of retinoic acid synthesis, at least in rabbit liver, since a high concentration of retinol in liver and the lower Km of the enzyme for retinol force the oxidative reaction, while higher activity of retinal reductase at physiological pH forces the reductive reaction.

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

Vitamin A (retinol) regulates embryonic development and adult epithelial function via metabolism to retinoic acid, a pleiotrophic regulator of gene expression. Retinoic acid is synthesized locally and functions in an autocrine or paracrine fashion, but the enzymes involved remain obscure. Alcohol dehydrogenase (ADH) isozymes capable of metabolizing retinol include class I and class IV ADHs, with class III ADH unable to perform this function. ADHs also metabolize ethanol, and high levels of ethanol inhibit retinol metabolism, suggesting a possible mode of action for some of the medical complications of alcoholism. To explore whether any ADH isozymes are linked to retinoic acid synthesis, herein we have examined the expression patterns of all known classes of ADH in mouse embryonic and adult tissues, and also measured retinoic acid levels. Using in situ hybridization, class I ADH mRNA was localized in the embryo to the epithelia of the genitourinary tract, intestinal tract, adrenal gland, liver, conjunctival sac, epidermis, nasal epithelium, and lung, plus in the adult to epithelia within the testis, epididymis, uterus, kidney, intestine, adrenal cortex, and liver. Class IV ADH mRNA was localized in the embryo to the adrenal gland and nasal epithelium, plus in the adult to the epithelia of the esophagus, stomach, testis, epididymis, epidermis, and adrenal cortex. Class III ADH mRNA, in contrast, was present at low levels and not highly localized in the embryonic and adult tissues examined. We detected significant retinoic acid levels in the fetal kidney, fetal/adult intestine and adrenal gland, as well as the adult liver, lung, testis, epididymis, and uterus--all sites of class I and/or class IV ADH gene expression. These findings indicate that the expression patterns of class I ADH and class IV ADH, but not class III ADH, are consistent with a function in local retinoic acid synthesis needed for the development and maintenance of many specialized epithelial tissues.

Computational modeling of a putative fetal alcohol syndrome mechanism

Fetal alcohol syndrome (FAS) refers to a pattern of birth defects occurring in a subpopulation of children born to women who consume alcohol during pregnancy. The significant medical, social, and economic impact of FAS is increasing. Particularly hard-hit are African-American and native-American women and children. Over the past two decades, basic and clinical research produced voluminous data on ethanol effects on developing organisms. In 1991, Duester and Pullarkat proposed that competition of ethanol with retinol at the alcohol dehydrogenase (ADH) binding site formed the basis of the FAS mechanism. This competition adversely affects the developing fetus caused by deregulation of retinoic acid (RA) homeostasis essential for proper fetal tissue development. Stated concisely, the FAS hypothesis is: 1. Class I ADH catalyzes the rate-limiting step in oxidation of retinol (ROH) to RA, and ethanol (ETOH) to acetic acid, thus establishing competition for ADH between ROH and ETOH. 2. RA is required as a signal molecule for cell differentiation critical for normal fetal morphogenesis. 3. ADH binds ingested ETOH, thus deregulating RA homeostasis leading to improper RA signal transduction. Preliminary results from molecular modeling studies of ROH-ADH and ETOH-ADH structures, and physiologic pharmacokinetic modeling confirm the hypothesis with remarkable fidelity.

Characterization and localization of an aldehyde dehydrogenase to amacrine cells of bovine retina

An enzyme of bovine retina that catalyzes oxidation of retinaldehyde to retinoic acid was purified to homogeneity and a monoclonal antibody (mAb H-4) was generated. MAb H-4 recognized a single component (Mr = 55,000) in extracts of bovine retina and other bovine tissues. The antibody showed no cross-reactivity with extracts of rat, monkey, or human retinas. A 2067 bp cDNA was selected from a retina cDNA expression library using mAb H-4. The cDNA hybridized with a similarly sized, moderately abundant mRNA prepared from bovine retina. Nucleotide sequence analysis indicated that the cDNA contained a single open reading frame encoding 501 amino acids that have 88% sequence identity with the amino-acid sequence of human hepatic Class 1 aldehyde dehydrogenase. Amino-acid sequence analysis of purified enzyme demonstrated that the cDNA encodes the isolated enzyme. MAb H-4 specifically labeled the somata and processes of a subset of amacrine cells in bovine retinal sections. Labeled amacrine somata were located on both sides of the inner plexiform layer, and their processes ramified into two laminae within the inner plexiform layer. The inner radial processes of Müller (glial) cells were weakly reactive with mAb H-4. Weak immunostaining of amacrine cells was found in monkey retina with mAb H-4, but no signal was detected in rat or human retina. The results provide further evidence for metabolism and function of retinoids within cells of the inner retina and define a novel class of retinal amacrine cells.

Stage and tissue-specific expression of the alcohol dehydrogenase 1 (Adh-1) gene during mouse development

The Adh-1 gene product, ADH-A2, the only known murine class I alcohol dehydrogenase, is able to oxidize retinol (vitamin A) into retinaldehyde, the first enzymatic step in the conversion of retinol into its biologically active metabolite retinoic acid. We have investigated the developmental expression pattern of Adh-1 transcripts by in situ hybridization. Transcripts were first detected by embryonic day 10.5 in the mesonephros mesenchyme. During the following gestational days, Adh-1 transcripts were detected in several mesenchymal areas, such as nasal, laterocervical, and genital regions. Adh-1 transcripts were also detected in a small ectodermal domain at the anterior margins of both forelimbs and hindlimbs. During late fetal development. Adh-1 transcripts were found essentially in the epidermis and in a number of tissues which continue to express the gene after birth, such as liver, kidney, gut epithelium, adrenal cortex, testis interstitium, and ovarian stroma. In contrast, a strong expression of Adh-1 was found in the mesenchyme of developing lungs, but not in the adult organ. This highly regulated expression of Adh-1 is discussed with respect to the local synthesis of retinoic acid during development. Although the promoter of the human counterpart of Adh-1 contains a retinoic acid response element (Duester et al. [1991] Mol. Cell. Biol. 11:1638-1646), we report that this element is not conserved in the murine gene. Consistently, Adh-1 promoter-containing reporter constructs were not retinoic acid-inducible in cotransfections assays with RARs and/or RXRs, suggesting that retinoic acid regulation of Adh-1 differs from that of the human gene.

Characteristic properties of retinal oxidase (retinoic acid synthase) from rabbit hepatocytes

Retinal oxidase (retinoic acid synthase) (EC 1.2.3.11) was purified electrophoretically, as a single protein band, from rabbit liver cytosol. The characteristic properties, enzymatic reaction mechanism, substrate specificity and kinetic parameters for retinals and molecular oxygen of the retinal oxidase were investigated. The Km values for all-trans-retinal of the retinal oxidase was the lowest than those for the other retinal derivatives. The retinal oxidase is a metalloflavoenzyme containing 2 FADs as the coenzyme, and 8 irons, 2 molybdenums, 2 disulfide bonds and 8 inorganic sulfurs. Its relative molecular mass was determined to be 270 kDa by gel filtration HPLC on a TSKgel G3000swXL column. Its minimum molecular mass was estimated to be 135 kDa by SDS-PAGE. The optical spectrum of the retinal oxidase showed absorption peaks at 275, 340 and 450 nm, and shoulders at 420 and 473 nm, in the oxidized form. The molecular extinction coefficients of the oxidase at selected wavelengths were determined. Circular dichroism spectra of the retinal oxidase were measured in the ultraviolet and visible regions. These spectra showed positive absorption in the visible region. The amino-acid composition was determined. The activity of the oxidase was not affected by any cofactors, such as NADP+, NAD+, NADPH and NADH, and it did not occur under anaerobic conditions. The oxidase was not inhibited by BOF-4272, a potent inhibitor of xanthine dehydrogenase, or rat anti-xanthine dehydrogenase IgG. Experiments on retinoic acid formation under 18O2 or H2(18)O demonstrated that the oxygen of water was incorporated into retinoic acid by the retinal oxidase, but not molecular oxygen.

Differential depletion of carotenoids and tocopherol in liver disease

Carotenoids and tocopherols are major natural protective agents against free radical-mediated liver damage, but their levels in diseased liver are largely uncharted. Therefore we carried out measurements with high-pressure liquid chromatography of alpha- and beta-carotene, lycopene, cryptoxanthin, lutein and zeaxanthin, total retinoids and alpha- and gamma-tocopherol. Liver tissue was obtained from percutaneous needle biopsies, livers of transplant recipients or a donor bank. Compared with controls (transplant donors; n = 13), levels of all carotenoids and retinoids were extremely low at all stages of liver disease. Patients with alcoholic cirrhosis (n = 11) had 20- and 25-fold decreases of levels of lycopene (p < 0.001) and alpha- and beta-carotene (p < 0.005), respectively. Even in subjects with less severe alcoholic liver disease (steatosis, perivenular fibrosis, portal fibrosis; n = 14) and in patients with nonalcoholic liver disease (n = 13), levels were four to six times lower than those in normal subjects. By contrast, levels of alpha-tocopherol were decreased significantly only in patients with cirrhosis, who displayed a threefold reduction. In the serum of most patients, lycopene and tocopherol concentrations were not depressed, whereas one third of alpha- and beta-carotene levels were low, probably reflecting poor dietary intake. A significant correlation was observed between serum and liver alpha- and beta-carotene levels (p < 0.0001; r = 0.715). However, of the patients with extremely low liver alpha- and beta-carotene concentrations, more than half had blood levels in the normal range, suggesting that liver disease interferes with the uptake, excretion or, perhaps, metabolism of alpha- and beta-carotene. In the cirrhotic livers of eight candidates for liver transplantation, the ratios of alpha- and beta-carotene to total retinoids and of beta-carotene to retinoids were much higher than those in normal livers, suggesting some impairment in the conversion of alpha- and beta-carotene to retinoids. In most cases, even with high ratios, absolute levels of hepatic alpha- and beta-carotene and retinoids were severely depressed. We concluded that, even in the presence of normal serum levels alpha- and beta-carotene, tocopherol and lycopene, patients with cirrhosis have extremely low hepatic levels.

Kinetic evidence for the involvement of a common enzyme in the microsomal reduction of retinal and androstenedione in rat liver

Androst-4-ene-3,17-dione (androstenedione) was found to be a potent competitive inhibitor of the NADH-supported reduction of retinal in rat hepatic microsomes (Ki 42 microM, Km/Ki ratio 1.1). Similarly, the NADH-mediated reduction of androstenedione was inhibited in mixed fashion by retinal (Ki 12 microM, Km/Ki ratio 0.34). In subsequent experiments the cofactor NADH exhibited an identical Km (8 microM) in the microsomal reductions of both substrates. Acidic pH markedly stimulated the microsomal reduction of androstenedione to testosterone and was also found to enhance retinal reduction to retinol, although the latter reaction exhibited a distinct pH optimum between 6.0 and 6.5. These results suggest that a common enzyme may participate in the reduction of both substrates but at least one other enzyme probably participates in hepatic microsomal testosterone production.

Identification of human liver aldehyde dehydrogenases that catalyze the oxidation of aldophosphamide and retinaldehyde

Biotransformation of the biologically and pharmacologically important aldehydes, retinaldehyde and aldophosphamide, is mediated, in part, by NAD(P)-dependent aldehyde dehydrogenases catalyze the oxidation of the aldehydes to their respective acids, retinoic acid and carboxyphosphamide. Not known at the onset of this investigation was which of the several known human aldehyde dehydrogenases (ALDHs) catalyze these reactions. Thus, human liver aldehyde dehydrogenases were chromatographically resolved and the ability of each to catalyze the oxidation of retinaldehyde and aldophosphamide was assessed. Only one, namely ALDH-1, catalyzed the oxidation of retinaldehyde; the Km value was 0.3 microM. Three, namely ALDH-1, ALDH-2 and succinic semialdehyde dehydrogenase, catalyzed the oxidation of aldophosphamide; Km values were 52, 1193, and 560 microM, respectively. ALDH-4, ALDH-5 and betaine aldehyde dehydrogenase did not catalyze the oxidation of either aldophosphamide or retinaldehyde. ALDH-1 and succinic semialdehyde dehydrogenase accounted for 64 and 30%, respectively, of the total hepatic aldehyde dehydrogenase-catalyzed aldophosphamide (160 microM) oxidation. ALDH-1-catalyzed oxidation of aldophosphamide was noncompetitively inhibited by chloral hydrate; the Ki value was 13 microM. ALDH-2- and succinic semialdehyde dehydrogenase-catalyzed oxidation of aldophosphamide was relatively insensitive to inhibition by chloral hydrate. These observations strongly suggest an important in vivo role for ALDH-1 in the catalysis of retinaldehyde and aldophosphamide biotransformation. Succinic semialdehyde dehydrogenase-catalyzed biotransformation of aldophosphamide may also be of some in vivo importance.

Retinol forms retinoic acid via retinal

Hepatic cytosol from normal deermice having cytosolic alcohol dehydrogenase (ADH+) also displays retinol dehydrogenase activity and converts retinol to retinoic acid, whereas cytosol from ADH- deermice lacks these enzyme activities and does not produce retinoic acid. Furthermore, microsomes from either strain do not convert retinol to retinoic acid. However, when cytosol from ADH- animals is added to the microsomes, retinoic acid is produced. The obligatory role of retinal as an intermediary step in retinoic acid formation is further shown by isotopic dilution of retinoic acid formed from labeled retinol upon addition of unlabeled retinal. Microsomal retinol dehydrogenase also catalyzes the reduction of retinal to retinol, thereby explaining the decrease in retinoic acid production from retinol in liver cytosol of ADH+ deermice when microsomes are added. Thus, the results of this study indicate that retinal is an obligatory intermediate in the hepatic production of retinoic acid from retinol and that cytosolic and microsomal retinol dehydrogenases play a key role in this process.

Computed tomography of the brain, hepatotoxic drugs and high alcohol consumption in male alcoholic patients and a random sample from the general male population

Computed tomography (CT) of the brain was performed in a random sample of a total of 195 men and 211 male alcoholic patients admitted for the first time during a period of two years from the same geographically limited area of Greater Stockholm as the sample. The same medical, social and neuroradiological methods were used for examination of the alcoholic inpatients as for the random controls. Laboratory tests were performed, including liver and pancreatic tests. Toxicological screening was performed and the consumption of hepatotoxic drugs was also investigated and the following were the types of drugs used: antiarrhythmics, antiepileptics, antiphlogistics, mixed analgesics, barbiturates, sulphonamides, benzodiazepines, clomethiazole and phenothiazine derivatives, all of which are metabolised by the liver. The group of male alcoholic inpatients and the random sample were then subdivided with respect to alcohol consumption and use of hepatotoxic drugs: Group IA, men from the random sample with low or moderate alcohol consumption and no use of hepatotoxic drugs; IB, men from the random sample with low or moderate alcohol consumption with use of hepatotoxic drugs; IIA, alcoholic inpatients with use of alcohol and no drugs; and IIB, alcoholic inpatients with use of alcohol and drugs. Group IIB was found to have a higher incidence of cortical and subcortical changes than group IA. Group IB had a higher incidence of subcortical changes than group IA, and they differed only in drug use. Groups IIB and IIA only differed in drug use, and IIB had a higher incidence of brain damage except for anterior horn index and wide cerebellar sulci indicating vermian atrophy. Significantly higher serum (S) levels of bilirubin, gamma-glutamyl transpeptidase (GGT), aspartate aminotransferase (ASAT), alanine amino-transferase (ALAT), creatine kinase (CK), lactate dehydrogenase (LD) and amylase were found in IIB. The results indicate that drug use influences the incidence of cortical and subcortical aberrations, except anterior horn index. It is concluded that the groups with alcohol abuse who used hepatotoxic drugs showed a picture of cortical changes (wide transport sulci and clear-cut or high-grade cortical changes) and also of subcortical aberrations, expressed as an increased widening of the third ventricle.

Identification of mouse liver aldehyde dehydrogenases that catalyze the oxidation of retinaldehyde to retinoic acid

NAD(P)-linked aldehyde dehydrogenases catalyze the oxidation of a wide variety of aldehydes. Thirteen of these enzymes have been identified in mouse tissues; eleven are found in the liver. Some are substrate-nonspecific; others are relatively substrate-specific. The present investigation sought to determine which of these enzymes are operative in catalyzing the oxidation of retinaldehyde to retinoic acid, a metabolite of vitamin A that promotes the differentiation of epithelial and other cells. Spectrophotometric and HPLC assays were used for this purpose. Enzyme-catalyzed oxidation of retinaldehyde (25 microM) was restricted to the cytosol (105,000 g supernatant fraction) and occurred at a rate of 211 nmol/min/g liver; oxidation of acetaldehyde (4 mM) by this fraction proceeds about ten times faster. At least 90% of this activity was NAD dependent. Of the approximately 10% that was apparently NAD independent, two-thirds was inhibited by 1 mM pyridoxal, a known inhibitor of aldehyde oxidase. Of the six cytosolic aldehyde dehydrogenases, only two, viz. AHD-2 and AHD-7, catalyzed the oxidation of retinaldehyde to retinoic acid. An additional NAD-dependent enzyme, viz. xanthine oxidase (dehydrogenase form), also catalyzed the reaction. Catalysis by AHD-2 accounted for more than 90% of the total NAD-dependent activity. Km values were 0.7, 0.6 and 0.9 microM, respectively, for the AHD-2-, AHD-7- and xanthine oxidase (dehydrogenase form)-catalyzed reaction. AHD-4, an aldehyde dehydrogenase found in the cytosol of mouse stomach epithelium and cornea, did not catalyze the reaction.

A hypothetical mechanism for fetal alcohol syndrome involving ethanol inhibition of retinoic acid synthesis at the alcohol dehydrogenase step

Ethanol acts as a teratogen causing brain, craniofacial, and limb abnormalities in those suffering from fetal alcohol syndrome. Normal embryonic development of the vertebrate nervous system and limbs has recently been shown to be governed by retinoic acid, the active form of vitamin A. Retinol dehydrogenase is an enzyme needed to convert vitamin A (retinol) to retinoic acid, a molecule that specifies embryonic pattern formation by controlling gene expression. Ethanol acts as a competitive inhibitor of the retinol dehydrogenase activity attributed to mammalian alcohol dehydrogenase (ADH), an enzyme that uses both retinol and ethanol as substrates. An hypothesis is presented in which many of the abnormalities observed in fetal alcohol syndrome may be caused by high levels of ethanol acting as a competitive inhibitor of ADH-catalyzed retinol oxidation in the embryo or fetus. This would presumably result in a reduction of retinoic acid synthesis in embryonic tissues such as the nervous system and limbs that require critical levels of this molecule to specify spatial patterns.

Retinoic acid response element in the human alcohol dehydrogenase gene ADH3: implications for regulation of retinoic acid synthesis

Retinoic acid regulation of one member of the human class I alcohol dehydrogenase (ADH) gene family was demonstrated, suggesting that the retinol dehydrogenase function of ADH may play a regulatory role in the biosynthetic pathway for retinoic acid. Promoter activity of human ADH3, but not ADH1 or ADH2, was shown to be activated by retinoic acid in transient transfection assays of Hep3B human hepatoma cells. Deletion mapping experiments identified a region in the ADH3 promoter located between -328 and -272 bp which confers retinoic acid activation. This region was also demonstrated to confer retinoic acid responsiveness on the ADH1 and ADH2 genes in heterologous promoter fusions. Within a 34-bp stretch, the ADH3 retinoic acid response element (RARE) contains two TGACC motifs and one TGAAC motif, both of which exist in RAREs controlling other genes. A block mutation of the TGACC sequence located at -289 to -285 bp eliminated the retinoic acid response. As assayed by gel shift DNA binding studies, the RARE region (-328 to -272 bp) of ADH3 bound the human retinoic acid receptor beta (RAR beta) and was competed for by DNA containing a RARE present in the gene encoding RAR beta. Since ADH catalyzes the conversion of retinol to retinal, which can be further converted to retinoic acid by aldehyde dehydrogenase, these results suggest that retinoic acid activation of ADH3 constitutes a positive feedback loop regulating retinoic acid synthesis.

Retinoic acid response element in the human alcohol dehydrogenase gene ADH3: implications for regulation of retinoic acid synthesis

Retinoic acid regulation of one member of the human class I alcohol dehydrogenase (ADH) gene family was demonstrated, suggesting that the retinol dehydrogenase function of ADH may play a regulatory role in the biosynthetic pathway for retinoic acid. Promoter activity of human ADH3, but not ADH1 or ADH2, was shown to be activated by retinoic acid in transient transfection assays of Hep3B human hepatoma cells. Deletion mapping experiments identified a region in the ADH3 promoter located between -328 and -272 bp which confers retinoic acid activation. This region was also demonstrated to confer retinoic acid responsiveness on the ADH1 and ADH2 genes in heterologous promoter fusions. Within a 34-bp stretch, the ADH3 retinoic acid response element (RARE) contains two TGACC motifs and one TGAAC motif, both of which exist in RAREs controlling other genes. A block mutation of the TGACC sequence located at -289 to -285 bp eliminated the retinoic acid response. As assayed by gel shift DNA binding studies, the RARE region (-328 to -272 bp) of ADH3 bound the human retinoic acid receptor beta (RAR beta) and was competed for by DNA containing a RARE present in the gene encoding RAR beta. Since ADH catalyzes the conversion of retinol to retinal, which can be further converted to retinoic acid by aldehyde dehydrogenase, these results suggest that retinoic acid activation of ADH3 constitutes a positive feedback loop regulating retinoic acid synthesis.