Brain Aldehyde Dehydrogenase Research Articles

Enhanced 5-HT2A Receptors in Brain Stem and ALDH Activity in Brain Stem and Liver: 5-HT2A Regulation on ALDH in Primary Hepatocytes Cultures In Vitro

Brain serotonin (5-HT) modulates the neural effects of ethanol. In the present study, we investigated the changes in 5-HT level, 5-HT(2A) receptor binding and aldehyde dehydrogenase (ALDH) activity in brain stem and liver of ethanol treated rats and 5-HT(2A) regulation on ALDH in hepatocyte cultures in vitro. The 5-HT content in the brain stem and liver significantly decreased with an increased 5-HIAA/5-HT ratio in the ethanol treated rats compared to control. Scatchard analysis of [(3)H] (+/-)2,3-dimethoxyphenyl-1-[2-(-4-piperidine)-methanol] [(3)H] MDL 100907 against ketanserin in brain stem of ethanol treated rats showed a significant increase in B (max) without any change in K (d) compared to control. The competition curve for [(3)H] MDL 100907 against ketanserin fitted one-site model in both control and ethanol treated rats with unity as Hill slope value. A significant increase in V (max) of ALDH activity in liver and a significant decrease in K (m) in liver and brain stem of ethanol treated rats compared to control was observed. In 24 h culture studies, an increase in enzyme activity was observed in cells in medium with 10% ethanol. The elevated ALDH activity in ethanol treated cells was reversed to control level in presence of 10(-5) and 10(-7) M 5-HT. Ketanserin, an antagonist of 5-HT(2A), reversed the effect of 5HT on 10% ethanol induced ALDH activity in hepatocytes. Our results showed that there was a decreased 5-HT content with an enhanced 5-HT(2A) receptor and aldehyde dehydrogenase activity in the brain stem of alcohol treated rats and in vitro hepatocyte cultures. The enhanced ALDH activity in ethanol supplemented hepatocytes was reversed to control level in presence of 10(-5) and 10(-7) M 5-HT.

Decreased dopamine D2 receptor function in cerebral cortex and brain stem: their role in hepatic ALDH regulation in ethanol treated rats

Ethanol exerts numerous pharmacological effects through its interaction with various neurotransmitters. The dopaminergic pathway is associated with cognitive, endocrine, and motor functions, and reinforcement of addictive substances or behaviours. Aldehyde dehydrogenase (ALDH) is a vital enzyme involved with alcohol metabolism and detoxification. In the present study, we investigated the role of cerebral cortex and brain stem dopamine D(2) receptors in the functional regulation on ALDH enzyme activity, in ethanol administrated rats. Two groups of rats were selected viz. control and alcoholic. Cerebral cortex, brain stem and the liver dopamine content was decreased significantly (P < 0.05, 0.05, 0.001, respectively) and homovanillic acid/dopamine (HVA/DA) ratio has significantly increased (P < 0.05, 0.001 and 0.001), respectively in ethanol treated rats when compared to control. Scatchard analysis of [(3)H]YM-09151-2 binding to synaptic membrane preparations of cerebral cortex and brain stem showed a significant decrease (P < 0.001, 0.05, respectively) in B (max) in ethanol treated rats compared to control and the K (d) also decreased significantly (P < 0.05). The ALDH analysis showed a significant increase (P < 0.05) in V (max) in cerebral cortex, plasma and liver of experimental rats when compared with control without having significant change in brain stem but with decreased K (m) (P < 0.001). Our results suggest that decreased function of dopamine mediated through DA D(2) receptor in the cerebral cortex and brain stem enhanced the brain, plasma and liver ALDH activity in ethanol treated rats. This ALDH regulation has significance to correct alcoholics from addiction due to allergic reaction observed in aldehyde accumulation.

Effect of acetaldehyde on acute tolerance and ethanol consumption in drinker and nondrinker rats.

Acetaldehyde (AcH) has been shown to have aversive or reinforcing actions in relation to ethanol consumption. We have previously observed that a pharmacological dose of AcH (50-150 mg/kg) administered intraperitoneally (i.p.) produced a dose-dependent flavor aversion in low-ethanol drinker (UChA) rats, whereas high-ethanol drinker (UChB) rats appeared to be insensitive to AcH. Both strains of rats differ innately in their brain aldehyde dehydrogenase (ALDH) activity and in their capacity to develop acute tolerance to ethanol. The present study evaluates the effects of AcH, in UChA and UChB rats, on rats' behavior, their voluntary ethanol consumption and the development of acute functional tolerance to motor impairment induced by a dose of ethanol. Subjects were rats selectively bred for high (UChB; n = 48) and low (UChA; n = 40) voluntary ethanol consumption. Rats were treated with either saline or doses of AcH (50 or 100 mg/kg, i.p.), and examined for effects on motor activity, on voluntary alcohol consumption with free access to a 10% alcohol solution and on acute tolerance to motor impairment induced by an ethanol dose (2.3 g/kg, i.p.), using the tilting plane test. AcH, 50 or 100 mg/kg, caused a dose-dependent loss of the righting reflex in UChA rats, whereas in UChB rats with same dose, a slight excitement was observed. There was significant increase of voluntary ethanol consumption in UChB rats (p < .001) 17 hours after the AcH injection, compared with saline-treated and control rats; in UChA rats, no change in voluntary ethanol consumption was produced. AcH produced a faster acute tolerance-to-ethanol development in UChB rats (p < .001) as compared with saline-treated and control rats, and no change in acute tolerance in UChA rats. Acetaldehyde injection did not change total mitochondrial ALDH2 activity. These results show that, 17 hours later, treatment of rats with pharmacological doses of acetaldehyde alters the voluntary ethanol consumption and acute tolerance development in UChB but not UChA rats. One of the factors involved may be a different sensitivity to AcH in these rat strains.

Concurrent administration of diethyldithiocarbamate and 4-methylpyrazole enhances ethanol-induced locomotor activity: the role of brain ALDH.

It has been proposed that brain aldehyde dehydrogenase (ALDH) plays a role in the modulation of some psychopharmacological effects of ethanol. Diethyldithiocarbamate (DDTC), an ALDH inhibitor, elevates blood acetaldehyde levels in the presence of ethanol. Concurrent administration with 4-methylpyrazole (4-MP), an alcohol dehydrogenase inhibitor, prevents peripheral accumulation of acetaldehyde by DDTC. To investigate the effects of concurrent DDTC and 4-MP administration on ethanol-induced locomotor activity in mice. Mice were pretreated IP with saline (S+S) or 4-MP (10 mg/kg) (S+4-MP), then received IP injections of ethanol (0, 0.8, 1.6, 2.4, 3.2 and 4 g/kg) prior to testing in the open field. Pretreatment with 4-MP does not modify the spontaneous or ethanol-induced locomotor activity. In the second experiment, the DDTC (114, 228 and 456 mg/kg) and 4-MP (DDTC+4-MP) were administered 8 h prior to testing locomotor activity in the open field. Animals were then treated with ethanol (0, 0.8, 1.6, 2.4, 3.2 and 4 g/kg), and placed in open field chambers. The locomotor activity of animals pretreated with DDTC and 4-MP was significantly enhanced here compared to groups S+S and S+4-MP. These effects cannot be attributed to elevated blood acetaldehyde levels, as pretreatment with 4-MP prevented peripheral accumulation of acetaldehyde. These data suggest that brain ALDH may contribute to the effects of ethanol on locomotor activity. This role of the enzyme ALDH in some of the psychopharmacological effects of ethanol may be a result of its ability to regulate levels of acetaldehyde in brain.

Taurine modulates catalase, aldehyde dehydrogenase, and ethanol elimination rates in rat brain.

Chronic administration of either the sulphonated amino acid taurine (0.32 or 0.62 g/kg for 2 weeks) or the catalase inhibitor, 3-amino, 1,2,4-triazole (AT: 0.5 or 1.0 g/kg for 5 days) significantly reduced catalase activities both in the brain and liver of male Wistar rats. The total brain activity of aldehyde dehydrogenase was significantly increased after the lower dose of taurine and after administration of both doses of AT. Hepatic alcohol dehydrogenase activity was not altered by either AT or taurine administration. In taurine-supplemented rats, a significant increase in the ethanol elimination rates (EER) was discernible in the livers after a 2 g/kg dose of ethanol. In contrast, significant decreases in the EER were observed in both plasmas and livers of rats in which catalase was inhibited by AT. However, the brain EERs were comparable in both catalase-inhibited and taurine-supplemented rats, both showing a decrease by comparison to controls. The similar psychopharmacological effects induced by both of these compounds on ethanol-induced effects might indicate that this is mediated in part via the catalase pathway. Since both catalase and the EERs are diminished in the brain after the administration of either of these compounds, this may be an important factor in the moderation of ethanol-induced behaviour.

Effect of nicotinamide administration on ethanol consumption and on liver and brain acetaldehyde oxidation rate, by UChB rats

The activities of liver and brain aldehyde dehydrogenase, an NAD(+) dependent enzyme, which controls acetaldehyde oxidation have been reported to play a role in voluntary ethanol consumption. It has been reported that nicotinamide administration to rats increases NAD(+) levels, that may increase acetaldehyde oxidation rates if basal NAD(+) levels are not saturating for the enzyme. In the present paper the effect of nicotinamide administration on voluntary ethanol consumption by genetically high ethanol consumer UChB rats and brain and liver mitochondrial acetaldehyde oxidation were studied. Administration of nicotinamide 250 or 500 mg/kg i.p. to UChB rats, produced a significant reduction in their voluntary ethanol consumption and increased brain acetaldehyde oxidation in brain but not liver homogenates.These results suggest that basal NAD(+) levels are not saturating for brain aldehyde dehydrogenase and that the reduction of ethanol consumption by UChB rats may be the consequence of a change in the brain redox state, rather than the local level of acetaldehyde.

Genetic differences in alcohol drinking preference between inbred strains of mice.

Genetic factors are known to influence the preference for drinking alcohol-in humans as well as certain inbred strains of laboratory animals. Here we examined the possible role of the aromatic hydrocarbon receptor (AHR) in alcohol-preferring C57BL/6J (B6, high-affinity AHR) and alcohol-avoiding DBA/2J (D2, low-affinity AHR) inbred mouse strains, and in the two congenic lines B6.D2-Ahrd (> 99% B6 genome with the D2 low-affinity AHR) and D2.B6-Ahrb-1 (> 99% D2 genome with the B6 high-affinity AHR). This laboratory had previously shown an association between resistance to intraperitoneal ethanol-induced toxicity and the high-affinity AHR. Offering the choice between drinking water and 10% ethanol, we found that alcohol preference is three- to four-fold greater in B6 than D2 mice, as well as three- to four-fold greater in B6.D2-Ahrd than D2.B6-Ahrb-1 mice-indicating that alcohol preference is AHR-independent. The prototype AHR agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; dioxin) did not affect the rates of chronic alcohol consumption in B6 or D2 mice, suggesting that dioxin-inducible metabolism does not play a major role in alcohol drinking preference. In B6 mice, we found that oral treatment with the aldehyde dehydrogenase (ALDH) inhibitor disulfiram decreased alcohol preference by 50%, whereas oral treatment of the catalase inhibitor 3-amino-1,2,4-triazole increased alcohol drinking preference by 15-20%. Although liver and brain ALDH activities were both significantly higher in D2 than B6, these activities were not related to alcohol consumption. Hepatic and brain catalase activities, on the other hand, were two- to three-fold higher in D2 and D2.B6-Ahrb-1 mice, compared with that in B6 and B6.D2-Ahrd. Furthermore, brain acetaldehyde levels were inversely related to the quantity of alcohol voluntarily consumed. We conclude that the alcohol drinking preference between the B6 and D2 inbred mouse strains is independent of the Ah receptor-but is genetically determined, in part, by the level of brain catalase activity which, in turn, regulates brain acetaldehyde concentrations.

The regulation of alcohol consumption in rats: The role of alcohol-metabolizing enzymes—Catalase and aldehyde dehydrogenase

Aldehyde dehydrogenase (ALDH) and catalase enzymatic activities in brain were assayed and compared to measures of alcohol consumption in two groups of animals screened and maintained on free-choice alcohol access under different conditions. In the first group of Long-Evans rats screened and maintained in home cages, mean alcohol intake was 3.49 g/kg/day with a range of 1.69–5.33 g/kg/day. When alcohol intake (g/kg), total ALDH, low K m ALDH, and catalase activities were entered in a multiple regression, a significant correlation of r = 0.51 ( p < 0.05) was obtained. In the second group of rats consisting of Long-Evans, P, and NP rats screened using a drinkometer procedure, a multiple correlation between ALDH and catalase enzyme activities and alcohol intake of r = 0.42 ( p < 0.05) was obtained. There was a strong relationship between the frequency of alcohol drinking bouts and the activities of catalase and ALDH ( r = 0.68, p < 0.0001). The P rats had significantly higher catalase activities than either the NP or Long-Evans rats. The results of the present study confirmed earlier reports on the role of alcohol-metabolizing enzymes in the regulation of alcohol intake. The results also highlighted the fact that the activity of these alcohol-metabolizing enzymes may play a mediating role in patterns of alcohol intake displayed by animals selected for high and low alcohol drinking and also unselected animals.

Voluntary Alcohol Consumption in BXD Recombinant Inbred Mice: Relationship to Alcohol Metabolism

Studies were initiated to characterize behaviorally and biochemically C57BL/6J and DBA/2J inbred mice, as well as BXD Recombinant Inbred (RI) strains derived from them. The C57BL/6J, DBA/2J, and 7 BXD RI strains were tested for voluntary alcohol consumption (VAC) by receiving 4 days of forced exposure to a 10% (w/v) solution of alcohol, followed by 3 weeks of free choice between water and 10% alcohol. Measures of VAC included the absolute intake of alcohol (g/kg), as well as alcohol preference. A wide range of VAC was displayed by the various BXD RI strains with a continuous (rather than bimodal) distribution, indicating that there is likely to be additive effects of several genes involved in regulating alcohol-related behaviors. Kinetic characteristics of aldehyde dehydrogenase and catalase in liver and brain of the C57BL/6J, DBA/2J, and BXD strains of mice were determined to test the hypothesis that the genetic regulation of the levels of alcohol-metabolizing enzymes mediate differences in VAC. Aldehyde dehydrogenase activity was determined spectrophotometrically by observing the change in absorption at 340 nm. Catalase activity was determined by measuring oxygen production with a Yellow Springs Biological Oxygen monitor and oxygen electrode. There was a strong negative relationship between VAC and brain catalase activity in the BXD RI and parental strains. These data suggest that RI strains are likely to be useful genetic models in the examination of quantitative trait loci controlling VAC and other responses to alcohol.

Aldehyde Dehydrogenase Activities in the Brains of Rats and Mice Genetically Selected for Different Sensitivity to Alcohol

Aldehyde dehydrogenase activity in brain has been studied for many years. However, the question of its role in the actions of ethanol in the brain has not been resolved. We have utilized mice and rats selectively bred for sensitivity or resistance to the initial hypnotic effects of ethanol to gain some insight into the possible involvement of brain aldehyde dehydrogenase in the actions of ethanol. We compared the levels of aldehyde dehydrogenase activity in the brains of these selected lines of rodents by histochemical methods. It was found that, although aldehyde dehydrogenase activity was detected in many areas of the brain, only in the cerebellar Purkinje cells was there a difference between sensitive and resistant lines of mice or rats. The resistant lines (Short Sleep mice and Low Alcohol Sensitive rats) had statistically higher levels of aldehyde dehydrogenase than did the sensitive lines (Long Sleep mice and High Alcohol Sensitive rats). Although this does not prove that aldehyde dehydrogenase or aldehydes are involved in the central actions of ethanol, it provides another piece of evidence in this direction.

Purification and characterization of a rat brain aldehyde dehydrogenase able to metabolize γ-aminobutyraldehyde to γ-aminobutyric acid

An enzyme which catalyses dehydrogenation of gamma-aminobutyraldehyde (ABAL) to gamma-aminobutyric acid (GABA) was purified to homogeneity from rat brain tissues by using DEAE-cellulose and affinity chromatography on 5'-AMP-Sepharose, phosphocellulose and Blue Agarose, followed by gel filtration. Such an enzyme was first purified from mammalian brain tissues, and was identified as an isoenzyme of aldehyde dehydrogenase. It has an Mr of 210,000 determined by polyacrylamide-gradient-gel electrophoresis, and appeared to be composed of subunits of Mr 50,000. The close similarity of substrate specificity toward acetaldehyde, propionaldehyde and glycolaldehyde between the enzyme and other aldehyde dehydrogenases previously reported was observed. But substrate specificity of the enzyme toward ABAL was higher than those of aldehyde dehydrogenases from human liver (E1 and E2), and was lower than those of ABAL dehydrogenases from human liver (E3), Escherichia coli and Pseudomonas species. The Mr and relative amino acid composition of the enzyme are also similar to those of E1 and E2. The existence of this enzyme in mammalian brain seems to be related to a glutamate decarboxylase-independent pathway (alternative pathway) for GABA synthesis from putrescine.

Alterations in brain aldehyde dehydrogenase activity modify ethanol-induced conditioned taste aversion.

The role of peripherally and centrally acting acetaldehyde in ethanol-induced conditioned taste aversion (CTA) was investigated using various enzyme manipulations. Cyanamide, an aldehyde dehydrogenase inhibitor (ALDH) elevates blood acetaldehyde levels in the presence of ethanol. Concurrent administration with 4-methylpyrazole (4MP), an alcohol dehydrogenase inhibitor, prevents peripheral accumulation of acetaldehyde by cyanamide. Under both treatment conditions brain and liver ALDH activity is inhibited. Water-deprived rats were pretreated 4 hr prior to fluid presentation with intraperitoneal injections of saline (S+S), 4-methylpyrazole (4MP+S), cyanamide (S+C), or 4-methylpyrazole + cyanamide (4MP+C). Subsequently, animals were presented with a novel saccharin solution followed immediately by intraperitoneal injection of one of three doses of ethanol (0.4, 0.8, or 1.2 g/kg) or saline vehicle on four occasions. Results suggested that animals pretreated with cyanamide (groups S+C and 4MP+C) drank significantly less saccharin after conditioning with a subthreshold dose of ethanol (0.4 g/kg) in comparison to groups S+S and 4MP+S. Moreover, at the conditioning dose of 1.2 g/kg, cyanamide-treated animals demonstrated an attenuation of CTA compared to the other two groups. These effects cannot be attributed to elevated blood acetaldehyde levels since pretreatment with 4MP+C prevented peripheral acetaldehyde accumulation. A characteristic common to both cyanamide-treated groups was the inhibition of brain ALDH. It is therefore suggested that brain ALDH may play a role in the mediation of ethanol-induced CTAs. It is conceivable that ALDH plays this role by regulating the levels of acetaldehyde in brain.

Human brain aldehyde dehydrogenase: Activity with DOPAL and isozyme distribution

Aldehyde dehydrogenase (ALDH, EC 1.2.1.3), has been shown to be the most important enzyme for DOPAL metabolism in human brain (Agarwal et al. [2]). In the present investigation cerebellum, corpus striatum and pons showed the highest ALDH activity. Most of the enzyme activity was found in the mitochondrial and microsomal fractions. Two activity bands on IEF gels and dual Km values indicate the presence of two distinct isozymes in all the fractions. Two cerebella from alcoholics yielded the same results as the control group regarding their total ALDH activity, subcellular distribution pattern and protein content. The presence of DOPAC (acid metabolite of DOPAL), pargyline, pyrazole or ethanol in the assay mixture did not alter the ALDH activity significantly.

Assay of brain aldehyde dehydrogenase activity using high-performance liquid chromatography with electrochemical detection

A method has been developed for assay of aldehyde dehydrogenase (ALDH) in brain tissue or in other tissues containing low ALDH-activity. The aldehyde of dopamine was used as the substrate, and the 3,4-dihydroxyphenylacetic acid formed was measured using high-performance liquid chromatography (HPLC) with electrochemical detection. The aldehyde was prepared enzymatically by incubating dopamine with a monoamine-oxidase preparation from rat liver mitochondria in the presence of Na +-bisulfite in 10 m m K +-phosphate buffer (pH 7.5). Rat brain homogenates were incubated in 50 m m Na +-pyrophosphate buffer (pH 8.8) containing 0.5 m m NAD + and 5 μ m aldehyde. The reaction was terminated with perchloric acid containing Na +-bisulfite to trap excess of the aldehyde. The acid supernatants were injected on a reverse-phase HPLC column and elution was performed with citrate buffer, pH 2.50. The method permits assay with 1–10 mg of brain tissue with an overall precision of 3%. The assay rate was 5–6 samples per hour.

EFFECTS OF DIETS DECREASING ETHANOL CONSUMPTION ON ACETALDEHYDE METABOLISM IN UChA AND UChB RATS

It has previously been reported that the introduction of a new issue (D1) of a stock diet (D0) caused a significant decrease in voluntary ethanol consumption in rats of our UChA (low ethanol consumer) and UChB (high ethanol consumer) strains, and that, after changing to a diet lacking in animal products (D3), ethanol consumption reached the previous level attained in UChB rats and exhibited a bimodal distribution in UChA rats in such a way that about one-third of these consumed more than 2 ml of a 10% (v/v) ethanol solution per 100 g of body weight, as did UChB rats. When UChA rats exhibiting high ethanol consumption and also UChB rats were fed on the D3 diet with a brewer's yeast supplement, a significant decrease in ethanol intake was observed. Since significant correlations of voluntary ethanol intake to blood acetaldehyde levels, and to hepatic and brain aldehyde dehydrogenase (AldDH) activities, have been reported, the effects on these parameters of diet D1 and of supplements of brewer's yeast or disulfiram were studied. Results showed that rats of both strains fed on a D1 diet exhibited a significant increase in blood acetaldehyde level after ethanol administration, concomitant with an inhibition of hepatic and brain AldDH activities and a significant decrease in ethanol intake. Thus, this effect could be related to a disulfiram-like activity. The decrease in ethanol intake induced by brewer's yeast was not accompanied by changes of blood acetaldehyde level after ethanol, nor by inhibition of hepatic AldDH activity in either strain.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain ALDH as a possible modulator of voluntary ethanol intake

The relationship between voluntary ethanol intake and brain aldehyde dehydrogenase (ALDH) activity was investigated in the laboratory rat. Voluntary ethanol intake was compared to subcellular forms of brain ALDH. Mitochondrial, microsomal and cytosolic fractions were prepared and recovered ALDH activity of each form was compared to voluntary ethanol intake in Long Evans rats. Strong correlations were found between both mitochondrial and microsomal ALDH fractions and ethanol intake. No activity was observed in cytosolic fraction as measured with aromatic or aliphatic aldehydes. In addition, microsomal activity was detected with aromatic aldehydes only, whereas the mitochondrial form would oxidize both aromatic and aliphatic aldehydes.

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.

Subcellular distribution of human brain aldehyde dehydrogenase.

Two human brain surgery biopsies and one autopsy sample were subjected to subcellular fractionation. With either 0.12 or 6 mM-acetaldehyde as substrate, about half of the total aldehyde dehydrogenase activity was found in the mitochondrial (+ synaptosomal) fraction and less activity in the cytosolic, nuclear, and microsomal fractions. High-affinity activity was found only in the mitochondrial fraction. The enzyme in all fractions had a higher affinity for indole-3-acetaldehyde than for acetaldehyde. The kinetic data indicate the presence of several distinct aldehyde dehydrogenase isozymes that have ample capacity to oxidize both aliphatic and aromatic aldehydes in human brain.

Aldehyde dehydrogenases in rat brain. Subcellular distribution and properties.

Kinetic studies suggested the presence of several forms of NAD-dependent aldehyde dehydrogenase (ALDH) in rat brain. A subcellular distribution study showed that low- and high-Km activities with acetaldehyde as well as the substrate-specific enzyme succinate semialdehyde dehydrogenase were located mainly in the mitochondrial compartment. The low-Km activity was also present in the cytosol (less than 20%). The low-Km activity in the homogenate was only 10-15% of the total activity with acetaldehyde as the substrate. Two Km values were obtained with both acetaldehyde (0.2 and 2000 microM) and 3,4-dihydroxyphenylacetaldehyde (DOPAL) (0.3 and 31 microM), and one Km value with succinate semialdehyde (5 microM). The main part of the aldehyde dehydrogenase activities with acetaldehyde, DOPAL, and succinate semialdehyde, but only little activity of the marker enzyme for the outer membrane (monoamine oxidase, MAO), was released from a purified mitochondrial fraction subjected to sonication. Only small amounts of the ALDH activities were released from mitochondria subjected to swelling in a hypotonic buffer, whereas the main part of the marker enzyme for the intermembrane space (adenylate kinase) was released. These results indicate that the ALDH activities with acetaldehyde, DOPAL and succinate semialdehyde are located in the matrix compartment. The low-Km activity with acetaldehyde and DOPAL, but not the high-Km activities and succinate semialdehyde dehydrogenase, was markedly stimulated by Mg2+ and Ca2+ in phosphate buffer. The low- and high-Km activities with acetaldehyde showed different pH optima in pyrophosphate buffer.

P-72 - Alcohol preference and brain aldehyde dehydrogenase activity in mice

P-72 - Alcohol preference and brain aldehyde dehydrogenase activity in mice