Subcellular aldehyde dehydrogenase activity and acetaldehyde oxidation by isolated intact mitochondria of rat brain and liver after acetaldehyde treatment

The effect of treatment of rats with acetaldehyde on the subcellular NAD⁺-aldehyde dehydrogenase (EC 1.2.1.3, ALDH) activities and acetaldehyde oxidation by isolated intact mitochondria of the liver and the brain was studied. Inhalation of acetaldehyde caused a significant decrease in the liver mitochondrial low K_m-ALDH activity, while brain mitochondrial ALDH activity remained unchanged. Acetaldehyde oxidation by isolated intact liver mitochondria decreased significantly but that by brain mitochondria remained unchanged after acetaldehyde inhalation. These findings raise the possibility that the brain enzyme may be exposed to lower concentration of acetaldehyde than the liver enzyme.     

Brain and liver aldehyde dehydrogenase activity and voluntary ethanol consumption by rats: Relations to strain,sex, and age

Voluntary ethanol consumption and brain and liver aldehyde dehydrogenase (ALDH) activity were measured in male and female rats of the Tryon Maze-Bright (S₁), Tryon Maze-Dull (S₃), and Wistar strains. The levels of brain ALDH measured in the different groups corresponded well to the levels of ethanol consumption, while differences in liver ALDH corresponded well to only the strain differences in ethanol intake. Within individual groups, levels of brain than liver aldehyde-oxidizing capacity. Age affected both voluntary ethanol intake and liver ALDH levels, but there were no systematic relations between the two effects. Age did not significantly affect the cerebral-aldehyde oxidizing capacity. It is argued that inherent variation in brain ALDH activity may be a principal biochemical counterpart of the differences in ethanol intake among different strains and sexes of laboratory rats.     

Electrical stimulation and lesions of the medial forebrain bundle of the rat: Changes in voluntary ethanol consumption and brain aldehyde dehydrogenase activity

Repeated sessions of electrical stimulation or lesions in the ventral aspect of the medial forebrain bundle (VMFB) region of the brain in rats resulted in a significant increase and a decrease in voluntary ethanol (10% v/v) intake, respectively. Whole brain and midbrain-diencephalon (MB-DE) aldehyde dehydrogenase (ALDH) were measured in different groups of experimental and control animals before, immediately after, and 30 days after the termination of the stimulation regimen, or 8 days and 30 days after the induction of the lesions. By the end of the stimulation regimen, the levels of MB-DE ALDH of the experimental (ethanol-drinking: stimulated) animals were significantly higher than those of control animals (ethanol-drinking: nonstimulated, water-drinking: stimulated, and water-drinking: nonstimulated). A marked decrease in MB-DE ALDH activity was noted in lesioned animals but not in cyanamide-treated or in implanted control animals. Neither the stimulation nor the lesions had any demonstrable effect on whole brain ALDH activity. Cyanamide administration caused a pronounced decrease in ethanol intake and in levels of liver ALDH activity. The increase in MB-DE ALDH activity in the ethanol-drinking, stimulated animals was attributed to the interaction between the VMFB activation and the ethanol drinking, while the reduction in ALDH activity was attributed to the degeneration of biogenic-amine-containing nerve fibers.     

Brain aldehyde dehydrogenase activity in rat strains with high and low ethanol preferences

The activity of aldehyde dehydrogenase in subcellular fractions of whole brain homogenates from the AA and ANA rat strains developed respectively for high and low ethanol preferences has been studied. No significant strain or sex differences between naive AA and ANA rats were found. In ethanol-experienced rats some strain and sex differences were found, the most consistent being higher enzyme activity in AA females than in males both with aliphatic and aromatic aldehyde substrates. However, contrary to previous findings no relation between brain aldehyde dehydrogenase activity and drinking behavior was found in the AA and ANA rat strains.     

Higher correlation of ethanol consumption with brain than liver aldehyde dehydrogenase in three strains of rats

Voluntary ethanol consumption and high K_m (mM range) brain and liver aldehyde dehydrogenase (ALDH) activity were measured in male rats of the Long-Evans, Wistar and Sprague-Dawley strains. The total amounts of ethanol consumed by the three strains did not differ significantly, nor did the levels of cerebral ALDH activity. Levels of brain ALDH did not differ as a function of ethanol exposure and across strains. Levels of ethanol consumption correlated better with levels of brain than liver aldehyde-oxidizing capacity, which were tested separately for each strain and also combining all the animals. Inherent variation in brain ALDH may be a biochemical counterpart of observed differences in voluntary ethanol intake within strains.     

Inhibition of rat hepatic mitochondrial aldehyde dehydrogenase isozymes by repeated cyanamide administration: Pharmacokinetic-pharmacodynamic relationships

The inhibition of rat hepatic mitochondrial aldehyde dehydrogenase (ALDH) isozymes was studied in apparent steady-state conditions after repeated intra-peritoneal cyanamide administration. The low-K_m mitochondrial ALDH isozyme was more susceptible to cyanamide-induced inhibition (DI₅₀ = 0.104 mg kg^?1) than the high-K_m isozyme (DI₅₀ = 8.52 mg kg^?1), with almost complete inhibition occurring at 0.35 mg kg^?1 total cyanamide administered for the low-K_m isozyme. The relationships between plasma and liver cyanamide concentrations and the inhibition of high-K_m ALDH were established by means of the sigmoid I_max model. The effect of dosing rate on the plasma concentration of cyanamide at apparent steady-state showed non-linearity, indicating that clearance or first-pass metabolism of cyanamide during its absorption after intraperitoneal administration did not remain constant throughout the range of doses studied.     

The potential of aldehyde dehydrogenase 2 as a therapeutic target in cardiovascular disease

Introduction: Mitochondrial aldehyde dehydrogenase (ALDH-2) plays a major role in the ethanol detoxification pathway by removing acetaldehyde. Therefore, ALDH-2 inhibitors such as disulfiram represent the first therapeutic targeting of ALDH-2 for alcoholism therapy.

Areas covered: Recently, ALDH-2 was identified as an essential bioactivating enzyme of the anti-ischemic organic nitrate nitroglycerin, bringing ALDH-2 again into the focus of clinical interest. Mechanistic studies on the nitroglycerin bioactivation process revealed that during bioconversion of nitroglycerin and in the presence of reactive oxygen and nitrogen species the active site thiols of ALDH-2 are oxidized and the enzyme activity is lost. Thus, ALDH-2 activity represents a useful marker for cardiovascular oxidative stress, a concept, which has been meanwhile supported by a number of animal disease models. Mechanistic studies on the protective role of ALDH-2 in different disease processes identified the detoxification of 4-hydroxynonenal by ALDH-2 as a fundamental process of cardiovascular, cerebral and antioxidant protection.

Expert opinion: The most recent therapeutic exploitation of ALDH-2 includes activators of the enzyme such as Alda-1 but also cell-based therapies (ALDH-bright cells) that deserve further clinical characterization in the future.     

The effects of the phytoestrogen genistein on the postnatal development of the rat.

The present studies report the effects on neonatal rats of oral exposure to genistein during the period from birth to postnatal day (PND) 21 to generate data for use in assessing human risk following oral ingestion of genistein. Failure to demonstrate significant exposure of the newborn pups via the mothers milk led us to subcutaneously inject genistein into the pups over the period PND 1-7, followed by daily gavage dosing to PND 21. The targeted doses throughout were 4 mg/kg/day genistein (equivalent to the average exposure of infants to total isoflavones in soy milk) and a dose 10 times higher than this (40 mg/kg genistein). The dose used during the injection phase of the experiment was based on plasma determinations of genistein and its major metabolites. Diethylstilbestrol (DES) at 10 micro g/kg was used as a positive control agent for assessment of changes in the sexually dimorphic nucleus of the preoptic area (SDN-POA). Administration of 40 mg/kg genistein increased uterus weights at day 22, advanced the mean day of vaginal opening, and induced permanent estrus in the developing female pups. Progesterone concentrations were also decreased in the mature females. There were no effects in females dosed with 4 mg/kg genistein, the predicted exposure level for infants drinking soy-based infant formulas. There were no consistent effects on male offspring at either dose level of genistein. Although genistein is estrogenic at 40 mg/kg/day, as illustrated by the effects described above, this dose does not have the same repercussions as DES in terms of the organizational effects on the SDN-POA.     

Genetic control of responsiveness of rat liver supernatant aldehyde dehydrogenase to phenobarbital and 3-methylcholanthrene

The responsiveness of the hepatic supernatant NAD⁺-dependent aldehyde dehydrogenase with a high Km value (high Km-AldDH) to phenobarbital (PB) and 3-methylcholanthrene (3-MC) treatment was studied in male rats of three strains; Wistar, Long-Evans, and Sprague-Dawley.A remarkable strain difference in the response of the enzyme to PB or 3-MC was observed. In rats of the Wistar strain the enzyme activity remained unchanged (non-responsive) in all rats after treatment with PB while it increased (responsive) 5- to 19-fold in all rats after treatment with 3-MC. The enzyme activity increased 8- to 20-fold and 2- to 8-fold respectively after treatment with PB and 3-MC in all rats of the Long-Evans strain. In rats of the Sprague-Dawley strain the enzyme activity remained unchanged in half of all the rats treated with PB or 3-MC and increased 2- to 7-fold over the basal level in half of the treated rats. The non-responsive rats to PB were all responsive to 3-MC treatment while the responsive rats to PB were responsive in 65% and non-responsive in 35% to 3-MC treatment.     

Role of aldehyde dehydrogenase in the biological activity of spermine dialdehyde, a novel immunosuppressive/purging agent

The antitumour and immunosuppressive activities of spermine dialdehyde (SDA), a synthetic, oxidized form of spermine, were examined using L1210 cell lines and murine bone marrow cells. SDA acted as a high affinity substrate for aldehyde dehydrogenase (ADH) derived from different sources, with kinetic profiles similar to other aldehyde substrates. The murine leukaemic, cyclophosphamide-resistant L1210/CPA cells, having high levels of intracellular ADH activity, were less sensitive to SDA compared to ADH deficient L1210/O cells as measured by [3H]-thymidine incorporation in proliferation studies. Furthermore, pretreatment of L1210/CPA cells with the ADH inhibitor, diethyl aminobenzaldehyde (DEAB), resulted in potentiation of the SDA response. Murine bone marrow cells were more resistant to SDA than splenic T cells. However, addition of DEAB to bone marrow cultures potentiated the sensitivity of progenitor cells to SDA, as measured by colony formation. The results indicate that levels of ADH in the target tissues would determine the potency of SDA and subsequently offer selectivity and specificity to the therapeutic potentials of this putative purging agent.     

Nitrate tolerance as a model of vascular dysfunction: Roles for mitochondrial aldehyde dehydrogenase and mitochondrial oxidative stress

Organic nitrates are a group of very effective anti-ischemic drugs. They are used for the treatment of patients with stable angina, acute myocardial infarction and chronic congestive heart failure. A major therapeutic limitation inherent to organic nitrates is the development of tolerance, which occurs during chronic treatment with these agents. The mechanisms underlying nitrate tolerance remain incompletely defined and are likely multifactorial. One mechanism seems to be a diminished bioconversion of nitroglycerin, another seems to be the induction of vascular oxidative stress, and a third may include neurohumoral adaptations. Recent studies have revealed that mitochondrial reactive oxygen species (ROS) formation and a subsequent oxidative inactivation of nitrate reductase, the mitochondrial aldehyde dehydrogenase (ALDH-2), play an important role in the development of nitrate and crosstolerance. The present review focus first on the role of oxidative stress and second on the role of ALDH-2 in organic nitrate bioactivation leading to the development of tolerance and cross-tolerance (endothelial dysfunction) in response to nitroglycerin treatment. Recently, the role of mitochondrial oxidative stress in the development of nitrate tolerance was demonstrated in a mouse model with a heterozygous deletion of manganese superoxide dismutase (MnSOD^+/?), which is the mitochondrial isoform of this enzyme. Studies from our own laboratory have provided evidence for cross-talk between mitochondrial and cytosolic (Nox-dependent) sources of ROS. We close this review by focusing on the protective properties of the organic nitrate pentaerithrityl tetranitrate, which upregulates enzymes that have strong antioxidative activity, such as heme oxygenase-1 and ferritin, thereby preventing the development of tolerance and endothelial dysfunction.     

Changes in the inducibility of a hepatic aldehyde dehydrogenase by various effectors

A hepatic soluble aldehyde dehydrogenase (ALDH), inducible by polycyclic aromatic hydrocarbons, was studied in Wistar rats in connection with substances known to affect drug metabolism or aldehyde dehydrogenase activity, such as phenobarbital (PB), disulfiram (DS), -diethylaminoethyl diphenylpropylacetate (SKF 525A) and calcium cyanamide (CC). 3-Methylcholanthrene (MC) was given as a model inducer of ALDH (100 mg/kg, i.p., as a single dose) and the animals were killed after 3 days. Pretreatment with PB (1 g/l drinking water, for 2 weeks) enhanced the inducing effect of MC. On the contrary, pretreatment with DS (100 mg/kg, i.p., daily x4) reduced by 70% the expected increase in ALDH activity. Neither SKF 525A (25 mg/kg, i.p., daily x4), nor CC (5 mg/kg, i.p., daily x4) could affect the action of the inducer. At the above doses, basal ALDH activity was inhibited by DS (30%) and CC (70%), but was not affected at all by PB or SKF 525A. The results were somewhat different when the various effectors tested were administered to animals already treated with MC (20 mg/kg, i.p., daily x6). In this case, DS did not affect the already induced ALDH activity. On the contrary, CC was still an effective inhibitor. Unexpectedly, post-treatment with SKF 525A further enhanced the initial induction brought about by MC. Our findings show that substances affecting microsomal drug metabolism can interfere with the process of ALDH induction by MC. The additive result of PB pretreatment is probably due to the enhanced accumulation of an active metabolite of MC. The opposite effect of DS on drug metabolism could explain the decreased ability of MC to induce ALDH activity. The MC-inducible ALDH isozyme can be effectively inhibited with CC, but not with DS.     

Aldehyde toxicity and metabolism: the role of aldehyde dehydrogenases in detoxification,drug resistance and carcinogenesis

Aldehydes are carbonyl compounds found ubiquitously in the environment, derived from both natural and anthropogenic sources. As the aldehydes are reactive species, therefore, they are generally toxic to the body. To reduce the toxicity and pathogenesis related to aldehydes, the human body contains several aldehyde metabolizing enzyme systems including aldehyde oxidases, cytochrome P450 enzymes, aldo-ketoreductases, alcohol dehydrogenases, short-chain dehydrogenases/reductases and aldehyde dehydrogenases (ALDHs). These enzyme systems maintain a low level of aldehydes in the body by catalytically converting them into less-harmful and easily excreted products. The human ALDH (hALDH) superfamily consists of 20 functional ALDH genes identified so far at distinct chromosomal locations, expressing 20 ALDH proteins, which belong to 11 different ALDH families. They are involved in the NAD(P)⁺-dependent oxidation of a wide range of exogenous and endogenous aldehydes to their corresponding carboxylic acids. The hALDHs are present in all sub-cellular locations and have a wide tissue distribution. This review gives an account of aldehydes; their source, toxicity and metabolism, different aldehyde metabolizing enzymes with special emphasis on ALDHs including their biochemical, physiological and pathophysiological roles in the body.     

Comparison of benzo(a)pyrene metabolism in isolated perfused rat lung and liver

The metabolism of 1 mM benzo(a)pyrene was studied in isolated perfused lung and liver of 5,6-benzoflavone-pretreated rats. Benzo(a)pyrene metabolism by the liver was more rapid than by the lung, but total metabolite formation in the lung at the end of a 120-min perfusion period was comparable to that in the liver. Lung perfusate was characterized by high concentrations of free metabolites, with diols outweighing phenols; in liver perfusate free metabolite concentrations were low, and large quantities of metabolites were found as conjugates in the bile at the end of perfusion. The tissue concentrations of free diols and phenols including the precursors of the main DNA-binding secondary metabolites were higher in the lung than in the liver. These findings explain the similar level of covalent binding in perfused lung and liver previously described (Klaus et al. 1982).Abbreviations Used BP benzo(a)pyrene - 9,10-diol 9,10-dihydro9,10-dihydroxy-benzo(a)pyrene - 4,5-diol 4,5-dihydro-4,5-dihydroxy-benzo(a)pyrene - 7,8-diol 7,8-dihydro-7,8-dihydroxy-benzo(a)pyrene - 9-OH 9-hydroxy-benzo(a)pyrene - 3-OH 3-hydroxybenzo(a)pyrene - tetrols 7,8,9,10-tetrahydro-7,8,9,10-tetrahydroxy-benzo(a)pyrenes - BF 5,6-benzoflavone - TLC thin-layer chromatography - HPLC high-pressure liquid chromatography     

Effects of long-term ethanol treatment on aldehyde and alcohol dehydrogenase activities in rat liver.

Administration of intoxicating doses of ethanol by gavage for 3 weeks caused weight loss and reduced hepatic aldehyde dehydrogenase activity in the soluble, mitochondrial and microsomal fractions. Rats receiving equivalent amounts of ethanol as a constituent of a liquid diet for 5 weeks gained weight and showed no changes in aldehyde dehydrogenase activity. Alcohol dehydrogenase activity was decreased in the rats treated by gavage and unchanged in those given ethanol in the diet, but in spite of this the rate of ethanol elimination was accelerated in both groups. In the livers of two strains of rats genetically selected for their difference in voluntary alcohol consumption, the mitochondrial and microsomal aldehyde dehydrogenase activities had previously been shown to be significantly higher in the alcohol-consuming (AA) than in the alcohol-avoiding (ANA) rats. Similar differences were now found after long-term intragastric ethanol administration, although in both strains the absolute levels of aldehyde dehydrogenase were reduced. Profound reduction of mitochondrial low-K_m aldehyde dehydrogenase activity and high blood acetaldehyde were observed, especially in the ANA rats. This suggests a possible connection between the low activity of this enzyme and the increased acetaldehyde level.     

Genetic alterations in cancer knowledge system: analysis of gene mutations in mouse and human liver and lung tumors.

Mutational incidence and spectra for genes examined in both human and mouse lung and liver tumors were analyzed using the National Institute of Environmental Health Sciences (NIEHS) Genetic Alterations in Cancer (GAC) knowledge system. GAC is a publicly available, web-based system for evaluating data obtained from peer-reviewed studies of genetic changes in tumors associated with exposure to chemical, physical, or biological agents, as well as spontaneous tumors. In mice, mutations in Kras2 and Hras-1 were the most common events reported for lung and liver tumors, respectively, whether chemically induced or spontaneous. There was a significant difference in Kras2 mutation incidence for spontaneous versus induced mouse lung tumors and in Hras-1 mutation incidence and spectrum for spontaneous versus induced mouse liver tumors. The major gene changes reported for human lung and liver tumors were in KRAS2 (lung only) and TP53. The KRAS2 mutation incidence was similar for spontaneous and asbestos-induced human lung tumors, while the TP53 mutation incidence differed significantly. Aflatoxin B1, hepatitis B virus, hepatitis C virus, and vinyl chloride all caused TP53 mutations in human liver tumors, but the mutation spectrum for each agent differed. The incidence of KRAS2 mutations in human compared to mouse lung tumors differed significantly, as did the incidence of Hras and p53 gene mutations in human compared to mouse liver tumors. Differences observed in the mutation spectra for agent-induced compared to spontaneous tumors and similarities in spectra for structurally similar agents support the concept that mutation spectra can serve as a "fingerprint" of exposure based on chemical structure.     

Characteristic expression profiles induced by genotoxic carcinogens in rat liver.

When applied in toxicological studies, the recently developed gene expression profiling techniques using microarrays, which brought forth the new field of toxicogenomics, facilitate the interpretation of a toxic compound's mechanism of action. In this study, we investigated whether genotoxic carcinogens at doses known to induce liver tumors in the 2-year rat bioassay deregulate a common set of genes in a short-term in vivo study and, if so, whether these deregulated genes represent defined biological pathways. Rats were dosed with the four genotoxic hepatocarcinogens dimethylnitrosamine (4 mg/kg/day), 2-nitrofluorene (44 mg/kg/day), aflatoxin B1 (0.24 mg/kg/day), and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK, 20 mg/kg/day). After treatment for up to 14 days, the expression profiles of the livers were analyzed on Affymetrix RG_U34A microarrays. Among the significantly upregulated genes were a set of target genes of the tumor suppressor protein p53, indicating a DNA damage response. Such a response was expected and, therefore, confirmed the validity of our approach. In addition, the gene expression changes suggest a specific detoxification response, the activation of proliferative and survival signaling pathways, and some cell structural changes. These responses were strong throughout the 14 day time course for 2-nitrofluorene and aflatoxin B1; in the case of dimethylnitrosamine and NNK, the effects were weakly detectable at day 1 and then increased with time. For dimethylnitrosamine and aflatoxin B1, which caused observable inflammation in vivo, we found a corresponding upregulation of inflammatory genes at the same time points. Thus, by the toxicogenomic analysis of short-term in vivo studies, we identified genes and pathways commonly deregulated by genotoxic carcinogens, which may be indicative for the early events in tumorigenesis and, thus, predictive of later tumor development.     

Effects of aldehyde dehydrogenase inhibitors on enzymes involved in the metabolism of biogenic aldehydes in rat liver and brain

The effects of the aldehyde dehydrogenase inhibitors disulfiram, coprine and cyanamide on enzymes involved in the metabolism of biogenic aldehydes in rat liver and brain were studied. Both liver and brain aldehyde dehydrogenase activities were significantly decreased in rats pretreated with these drugs. In the liver, the low-K_m aldehyde dehydrogenase activity was markedly decreased by all three drugs after 2 and 24 hr whereas only cyanamide inhibited the high-K_m enzymes. The brain ALDH-activity with a low acetaldehyde concentration was significantly decreased by coprine and cyanamide at both times tested, whereas disulfiram caused no change after 2 hr but an inhibition of 38% after 24 hr. The brain ALDH-activity with a high acetaldehyde concentration was significantly decreased by coprine and cyanamide but not by disulfiram. The activity of the substrate specific enzyme succinate semialdehyde dehydrogenase in brain was slightly but significantly decreased in rats pretreated with cyanamide but not in rats pretreated with disulfiram or coprine. None of the drugs caused any changes in the activities of aldehyde reductase and monoamine oxidase in brains in vivo. The activity of monoamine oxidase in liver was significantly decreased by coprine after 24 hr. In contrast to the effects obtained in vivo, disulfiram was found to be an inhibitor in vitro of brain succinate semialdehyde dehydrogenase and liver monoamine oxidase. Aldehyde reductase was slightly inhibited by both disulfiram and 1-aminocyclopropanol in vitro.     

Enzymology and subcellular localization of aldehyde oxidation in rat liver: Oxidation of 3,4-dihydroxyphenylacetaldehyde derived from dopamine to 3,4-dihydroxyphenylacetic acid

In the presence of ethanol, the metabolism of dopamine in rat liver slices is altered such that the major product is 3,4-dihydroxyphenylethanol, not 3,4-dihydroxyphenylacetic acid (DOPAC). It has been proposed that this metabolic alteration is due to the inhibition of the oxidation of 3,4-dihydroxyphenylacetaldehyde (DOPAL) by acetaldehyde, the first metabolite of ethanol. The oxidation of DOPAL in rat liver slices, however, is not inhibited dramatically by relatively high concentrations of acetaldehyde [A. W. Tank and H. Weiner, Biochem. Pharmac. 28, 3139 (1979)]. Thus, it is possible that acetaldehyde and DOPAL are oxidized by different isozymes of aldehyde dehydrogenase (ALDH) present in different subcellular compartments. Acetaldehyde is oxidized by isozymes of ALDH that are found in the matrix space of the mitochondria of rat liver. The subcellular site of the oxidation of most other aldehydes is not known. Mitochondrial, microsomal and cytosol fractions of the rat liver were isolated by differential centrifugation, and the isozymes of ALDH present in the cytosol and mitochondrial fractions were separated by column isoelectric focusing. Five isozymes of ALDH were isolated from the cytosol, and three isozymes were isolated from the mitochondria. The K_m values for acetaldehyde, p-nitrobenzaldehyde and DOPAL for each of the isolated isozymes were determined and were found to range from approximately 1 μM to 1 mM. Each subcellular fraction was incubated with [ethylamine-2-¹⁴C]dopamine to determine its ability to oxidize DOPAL. Partially purified monoamine oxidase was used to generate DOPAL for those incubations which did not contain mitochondria. Intact mitochondria were capable of oxidizing virtually all the DOPAL to DOPAC in the presence or absence of added pyridine nucleotide coenzymes. Cytosol and microsomal fractions were capable of oxidizing the aldehyde, but not to the same extent as the intact mitochondria. ALDH activity present in the mitochondrial matrix space was inhibited by the addition of rotenone. This treatment inhibited formation of DOPAC by 80 per cent in isolated intact mitochondria in the absence of added pyridine nucleotides. Inclusion of rotenone caused the inhibition of DOPAC formation by ca. 50 per cent when intact mitochondria, microsomes and cytosol were incubated together with dopamine. These results suggest that an isozyme of ALDH present in the mitochondrial matrix space is primarily responsible for the oxidation of DOPAL in rat liver, though nonmitochondrial enzymes can contribute to the oxidation.     

Comparing the role of glutathione-S-transferase and mitochondrial aldehyde dehydrogenase in nitroglycerin biotransformation and the correlation with calcitonin gene-related peptide

Both glutathione-S-transferase (GST) and mitochondrial aldehyde dehydrogenase (ALDH-2) have been reported to participate in the biotransformation of nitroglycerin. In this study, we explored which is the major player in nitroglycerin biotransformation. In vivo, rats were treated with nitroglycerin, the blood pressure and plasma calcitonin gene-related peptide (CGRP) were measured. The inhibitor of GST (ethacrynic acid) or ALDH-2 (cyanamide) was given before nitroglycerin treatment; In vitro, the isolated aorta rings were incubated with nitroglycerin to obtain the concentration–response curve. Ethacrynic acid or cyanamide was pre-incubated with the rings before nitroglycerin treatment. The release of CGRP from the aorta rings was determined. Both ethacrynic acid and cyanamide were able to reverse the depressant action of nitroglycerin while the inhibitory effect of cyanamide was more profound. However, combined administration of both inhibitors did not produce an additive effect. The change of plasma CGRP level positively correlated with the change of nitroglycerin-induced hypotensive effects. In the isolated aorta rings, vasodilator responses to nitroglycerin were reduced in the presence of ethacrynic acid or cyanamide while the inhibitory effect of cyanamide was more profound. However, combined administration of both inhibitors did not produce an additive effect. The change of CGRP release from the rings positively correlated with the nitroglycerin-induced vasodilator responses. The present results suggest that both GST and ALDH-2 are involved in nitroglycerin action while ALDH-2 plays a major role, and the change of CGRP contents closely correlates with the biotransformation of nitroglycerin.