Postnatal development of mouse alcohol dehydrogenases: agarose isoelectric focusing analyses of the liver, kidney, stomach and ocular isozymes

Ontogeny of mammalian metabolizing enzymes in humans and animals used in toxicological studies

It is well recognized that expression of enzymes varies during development and growth. However, an in-depth review of this acquired knowledge is needed to translate the understanding of enzyme expression and activity into the prediction of change in effects (e.g. kinetics and toxicity) of xenobiotics with age. Age-related changes in metabolic capacity are critical for understanding and predicting the potential differences resulting from exposure. Such information may be especially useful in the evaluation of the risk of exposure to very low (µg/kg/day or ng/kg/day) levels of environmental chemicals. This review is to better understand the ontogeny of metabolizing enzymes in converting chemicals to either less-toxic metabolite(s) or more toxic products (e.g. reactive intermediate[s]) during stages before birth and during early development (neonate/infant/child). In this review, we evaluated the ontogeny of major "phase I" and "phase II" metabolizing enzymes in humans and commonly used experimental animals (e.g. mouse, rat, and others) in order to fill the information gap.

Alcohol dehydrogenases and aldehyde dehydrogenases among inbred strains of mice: multiplicity, development, genetic studies and metabolic roles

Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) are the major enzymes responsible for the metabolism of alcohols and aldehydes in the body. Both exist as a family of isozymes in mammals, and have been extensively studied in animal models, particularly among inbred strains of mice. Mouse ADH exists as at least three major classes, which are predominantly localized in liver (classes I and III), and in stomach/cornea (class IV). Mouse ALDH exhibits extensive multiplicity, several forms of which have been characterized, including ALDH1 (liver cytoplasmic/class 1 isozyme); ALDH2 (liver mitochondrial/class 2.); ALDH3 (stomach cytosolic/class 3); ALDH4 (liver microsomal/class 3); and ALDH5 (testis cytosolic/class 3). Biochemical, genetic and molecular genetic analyses have been performed on several of these enzymes, including studies on variant forms of ADH and ALDH. Distinct metabolic roles are proposed, based upon their tissue and subcellular distribution characteristics and the biochemical properties for these enzymes.

Alcohol misuse and renal damage

Recent clinical and experimental studies have demonstrated that the habitual consumption of large amounts of ethanol has deleterious effects on the kidney. A variety of tubular defects have been described in patients with chronic alcoholism. Evidence is emerging that tubular dysfunction has an important pathophysiological role in a wide range of electrolyte and acid-base disturbances commonly observed in these patients, and possibly in alcohol-induced bone disease. These renal abnormalities are often reversible, disappearing with abstinence. However, since 1990 a few cases of a syndrome of acute tubular necrosis due to binge drinking of ethanol in the absence of other evident nephrotoxic mechanisms, or in association with the use of nonsteroidal anti-inflammatory drugs, have been reported. A link between glomerulonephritis and alcoholism has become evident. IgA nephropathy has been demonstrated at autopsy in 64% of chronic alcoholics and, more recently, the association between alcoholism and postinfectious glomerulonephritis has been described. Structural and functional abnormalities of the kidney are reported with increasing frequency in the fetal alcohol syndrome seen in children who have been prenatally exposed to ethanol. In addition, over the last few years experimental studies in vitro or in animal models have provided information about the biochemical and molecular basis of alcohol-induced injury to kidney. It is hoped that future experimental and clinical research will provide us with a more comprehensive knowledge of the mechanisms of renal damage in alcohol misuse.

Expression of genes for alcohol and aldehyde metabolizing enzymes in mouse oocytes and preimplantation embryos

Alcohols and aldehydes are metabolized primarily by alcohol (ADH) and aldehyde (ALDH) dehydrogenase isozymes. Although significant progress has been made towards understanding the involvement of these isozymes in the oxidation of alcohol and aldehydes in the body, it is not known how these compounds are handled during fertilization and preimplantation embryogenesis. In this study, reverse transcription and the polymerase chain reaction (RT-PCR) was used to determine which ADH and ALDH isozymes are expressed at the oocyte, zygote, morula, and blastocyst stages of preimplantation development in the mouse. Transcripts of beta-actin and vimentin, assayed as controls, were detected at all stages, as well as Class III ADH (Adh-2) and Class 3 ALDH (Ahd-4), involved in the detoxification of formaldehyde and aromatic aldehydes, respectively. In contrast, transcripts for the major ethanol oxidizing isozyme, Class I ADH (Adh-1) was not detected during preimplantation development. Cytosolic retinol dehydrogenase (Adh-3) transcripts were marginally detected in oocytes and zygotes. The mRNA for cytosolic retinal dehydrogenase (Ahd-2), microsomal short-chain retinol dehydrogenases (RoDH Type I), and the mitochondrial low-Km acetaldehyde dehydrogenase (Ahd-5) only appeared as maternal transcripts. Microsomal ALDH (Ahd-3), which is induced by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), was not expressed until the blastocyst stage. ADH and ALDH enzyme systems may guard mouse preimplantation embryos against the toxic effects of industrial pollutants, such as formaldehyde and TCDD, as well as peroxidatic aldehydes generated during lipid peroxidation. The absence of enzymes to convert ethanol to acetaldehyde, coupled with oocyte expression of the acetaldehyde-degrading enzyme, Ahd-5, may be protective for the early embryo.

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

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

Renal tubular dysfunction in chronic alcohol abuse--effects of abstinence

BACKGROUND

Alcohol abuse may be accompanied by a variety of disorders of electrolyte and acid-base metabolism. The role of the kidney in the pathogenesis of these disturbances is obscure. We sought to evaluate the alcohol-induced abnormalities of renal function and improvement during abstinence and to assess the relation between renal dysfunction and electrolyte and acid-base disorders.

METHODS

We measured biochemical constituents of blood and renal function before and after four weeks of abstinence in 61 patients with chronic alcoholism who had little or no liver disease.

RESULTS

On admission, 18 patients (30 percent) had hypophosphatemia and hypomagnesemia, 13 patients (21 percent) had hypocalcemia, and 8 patients (13 percent) had hypokalemia. Twenty-two patients (36 percent) had a variety of simple and mixed acid-base disorders. Twenty of these patients had metabolic acidosis, and among them, 80 percent had alcoholic acidosis. A wide range of defects in renal tubular function, with normal glomerular filtration rate, were detected in these patients. The defects included decreases in the threshold and maximal reabsorptive ability for glucose (38 percent of patients) and in the renal threshold for phosphate excretion (36 percent); increases in the fractional excretion of beta 2-microglobulin (38 percent), uric acid (12 percent), calcium (23 percent), and magnesium (21 percent); and aminoaciduria (38 percent). Seventeen patients (28 percent) had a defect in tubular acidification, and five an impairment in urinary concentrating ability. Urinary excretion of N-acetyl-beta-D-glucosaminidase and alanine aminopeptidase were increased in 41 and 34 percent of patients, respectively. The abnormalities of blood chemistry and renal tubular function disappeared after four weeks of abstinence.

CONCLUSIONS

Transient defects in renal tubular function are common in patients with chronic alcoholism and may contribute to their abnormalities of serum electrolyte and blood acid-base profiles.

Alcohol dehydrogenases in the brain of mice

Alcohol dehydrogenase (ADH) phenotypes were investigated in the brain of 15 different inbred mice by isoelectric focusing followed by staining of enzyme activities. The Class III ADH activity was detected in all the strains studied, whereas the Class II ADH activity was found only in few strains (including the alcohol-preferring strain--C57BL/6J) having the "a" allele (ADH-C2(2)) for this isozyme in stomach. The inbred strains having the "b" allele (ADH-C2(1)) for the Class II ADH in stomach (including the alcohol avoiding strains--BALB/c, CBA/H, C3H/He, DBA/2J, and SJL/J) demonstrated null variant for this phenotype in their brain. The Class I ADH activity was very low or absent in the brain extracts of all the strains studied. The ADH activities were confined to the cytosolic fractions of brain and were higher in the extracts of cerebral hemispheres than in cerebellum. The genetic linkage studies showed that the locus for the brain Class II ADH is closely linked to the "Adh gene complex" on chromosome 3 of mice.

Alcohol dehydrogenase isoenzymes in rat development. Effect of maternal ethanol consumption

The alcohol dehydrogenase (ADH) isoenzymes (alcohol:NAD oxidoreductase, EC 1.1.1.1) of classes I, III and IV were investigated by activity and starch gel electrophoresis analyses during rat ontogeny. Class I was studied in the liver, class III in the brain and class IV in the stomach and eyes. Classes I and IV exhibited very low activity during the fetal period, reaching 12% and 3%, respectively, of the adult value at birth. Class III was relatively more active in the fetus, with 38% of the adult activity at birth. In the three cases, activity increased after birth and adult values were found around day 20 (classes I and III), day 39 (stomach class IV) and after day 91 (eye class IV). The very low activity of the isoenzymes responsible for ethanol oxidation, i.e. liver class I and stomach class IV, in the fetus demonstrates that metabolism of ethanol during gestation is essentially performed by the maternal tissues. Development of ADH isoenzymes were also studied in the offspring of rats exposed to an alcoholic liquid diet. Activities of liver class I and stomach class IV were severely reduced: they were only 30% and 50%, respectively, of the control values. In contrast, eye class IV activity did not change and brain class III showed a 30% increase. Moreover, the concentration of liver soluble protein exhibited a 1.3-1.5-fold increase with respect to control animals. The effects on activities and liver protein were more pronounced in the adult than in the perinatal period, and they seem irreversible since normal values were not recovered after 6 weeks of feeding with a non-alcoholic diet. The low activities of the alcohol-oxidizing isoenzymes indicate tht maternal ethanol consumption results in an impaired ethanol metabolism of the offspring.