Suppression of alcohol drinking with brain aldehyde dehydrogenase inhibition

Mystic Acetaldehyde: The Never-Ending Story on Alcoholism

After decades of uncertainties and drawbacks, the study on the role and significance of acetaldehyde in the effects of ethanol seemed to have found its main paths. Accordingly, the effects of acetaldehyde, after its systemic or central administration and as obtained following ethanol metabolism, looked as they were extensively characterized. However, almost 5 years after this research appeared at its highest momentum, the investigations on this topic have been revitalized on at least three main directions: (1) the role and the behavioral significance of acetaldehyde in different phases of ethanol self-administration and in voluntary ethanol consumption; (2) the distinction, in the central effects of ethanol, between those arising from its non-metabolized fraction and those attributable to ethanol-derived acetaldehyde; and (3) the role of the acetaldehyde-dopamine condensation product, salsolinol. The present review article aims at presenting and discussing prospectively the most recent data accumulated following these three research pathways on this never-ending story in order to offer the most up-to-date synoptic critical view on such still unresolved and exciting topic.

Glucagon-like peptide-1 (GLP-1) receptor agonist prevents development of tolerance to anti-anxiety effect of ethanol and withdrawal-induced anxiety in rats

Despite major advances in the understanding about ethanol actions, the precise underlying neurobiological mechanisms for ethanol dependence remain largely elusive. We recently reported that inhibition of dipeptidyl-peptidase IV (DPP-IV), an enzyme responsible for metabolism of endogenous glucagon-like peptide-1 (GLP-1), delays tolerance to anti-anxiety effect of ethanol and withdrawal-induced anxiety in rats. Intrigued with this report, present study examined the role of glucagon-like peptide-1 (GLP-1) receptor agonist, liraglutide in (1) acute anti-anxiety effect of ethanol; (2) tolerance to ethanol's anti-anxiety-effect and (3) ethanol withdrawal-induced anxiety using elevated plus maze (EPM) test in rats. Ethanol (2 g/kg, i.p.; 8 % w/v) and liraglutide (50 μg/kg, i.p.) treatments exhibited anti-anxiety effect in EPM test. Doses of ethanol (1.0 or 1.5 g/kg, i.p.) that were not effective per se elicited anti-anxiety when combined with sub-effective dose of liraglutide (25 μg/kg, i.p.). Rats consuming ethanol-diet (6 % v/v) exhibited tolerance to anti-anxiety effect of ethanol from day-7 of ethanol consumption. Peak ethanol withdrawal-induced anxiety was observed at 8-10 h upon abstinence from ethanol-diet after 15-days consumption. Rats on simultaneous once-daily liraglutide treatment (50 μg/kg, i.p.) neither had any signs of tolerance to anti-anxiety effect of ethanol nor did they exhibit withdrawal-induced anxiety.

IN CONCLUSION

(1) GLP-1 agonist, liraglutide exhibited anti-anxiety effect per se; (2) potentiated anti-anxiety effect of ethanol; (3) prevented development tolerance to anti-anxiety effect of ethanol and (4) prevented withdrawal-induced anxiety. Further studies examining intracellular cascade of events contributing to these effects may help to improve understanding about role of GLP-1 receptors in ethanol mediated behaviors.

Dipeptidyl-peptidase IV (DPP-IV) inhibitor delays tolerance to anxiolytic effect of ethanol and withdrawal-induced anxiety in rats

Dipeptidyl-peptidase IV (DPP-IV) is an enzyme responsible for the metabolism of endogenous gut-derived hormone, glucagon-like peptide-1 (GLP-1). DPP-IV is known for its role in energy homeostasis and pharmacological blockade of this enzyme is a recently approved clinical strategy for the management of type II diabetes. Accumulating evidences suggest that enzyme DPP-IV can affect spectrum of central nervous system (CNS) functions. However, little is known about the role of this enzyme in ethanol-mediated neurobehavioral complications. The objective of the present study was to examine the impact of DPP-IV inhibitor, sitagliptin on the development of tolerance to anxiolytic effect of ethanol and anxiety associated with ethanol withdrawal in rats. A dose-response study revealed that sitaglitpin (20 mg/kg, p.o.) per se exhibit anxiolytic effect in the elevated plus maze (EPM) test in rats. Tolerance to anxiolytic effect of ethanol (2 g/kg, i.p.; 8 % w/v) was observed from 7(th) day of ethanol-diet (6 % v/v) consumption. In contrast, tolerance to anxiolytic effect of ethanol was delayed in rats that were treated daily with sitagliptin (20 mg/kg, p.o.) as tolerance was observed from 13(th)day since commencement of ethanol-diet consumption. Discontinuation of rats from ethanol-diet after 15-days of ethanol consumption resulted in withdrawal anxiety between 8 h and 12 h post-abstinence. However, rats on 15-day ethanol-diet with concomitant sitagliptin (20 mg/kg, p.o.) treatment exhibited delay in appearance (24 h post-withdrawal) of withdrawal anxiety. In summary, DPP-IV inhibitors may prove as an attractive research strategy against ethanol tolerance and dependence.

Cyanamide-mediated Inhibition of N-acetyltransferase 1

Cyanamide has been used for decades for medical intentions in the treatment of alcoholism and for agricultural purposes as a plant growth regulator and bud-breaking agent. Its therapeutic effect is mediated by reversible inhibition of aldehyde dehydrogenase and it was reported to be metabolized in vivo mainly via coenzyme A dependent N-acetylation by N-acetyltransferases. Although described to be a substrate for N-acetyltransferases (NATs), cyanamide has a different molecular structure to arylamines and hydrazines, the preferred substrates for N-acetyltransferases. Therefore, a more detailed investigation of its interrelations with N-acetyltransferases was performed. We analyzed the impact of cyanamide on NAT1 activities of human monocytes (monocytic THP-1 cells) using the classical substrate p-aminobenzoic acid. We found that a 24h treatment with physiologically relevant concentrations of cyanamide decreased the NAT1 activity significantly. Based on this observation we performed additional experiments using recombinant human NAT1 and NAT2 to achieve further insights. In detail a significant dose- and time-dependent inhibition of NAT1 activity was observed for 100 and 1000μM cyanamide using recombinant human NAT1*4. However, cyanamide did not inhibit recombinant NAT2*4. Experiments testing cyanamide as substrate did not provide evidence that cyanamide is metabolized via coenzyme A dependent N-acetylation in vitro by human NAT1 or NAT2, THP-1 or human liver cytosol. Therefore we can conclude that the observed enzyme inhibition (around 50% and 25% after treatment with 0.5 and 0.25mM CA, respectively) is not based on substrate-dependent down-regulation of NAT1. Further mechanistic and kinetic studies indicated that cyanamide reacts with the active site cysteine residue of NAT1, leading to its rapid inhibition (significant inhibition after 30min and 2h for 1000 and 100μM CA, respectively). Addition of the reduction agent dithiothreitol (DTT) did not modify the effect, indicating that oxidative processes that can be reversed by 5mM DTT are not likely involved in the inhibition. Taken together our results show that cyanamide is able to inhibit NAT1 most likely via interaction with the active site cysteine residue. Thereby cyanamide might modulate NAT1 dependent detoxification and activation of arylamines.

The role of acetaldehyde in the neurobehavioral effects of ethanol: A comprehensive review of animal studies

Acetaldehyde has long been suggested to be involved in a number of ethanol's pharmacological and behavioral effects, such as its reinforcing, aversive, sedative, amnesic and stimulant properties. However, the role of acetaldehyde in ethanol's effects has been an extremely controversial topic during the past two decades. Opinions ranged from those virtually denying any role for acetaldehyde in ethanol's effects to those who claimed that alcoholism is in fact "acetaldehydism". Considering the possible key role of acetaldehyde in alcohol addiction, it is critical to clarify the respective functions of acetaldehyde and ethanol molecules in the pharmacological and behavioral effects of alcohol consumption. In the present paper, we review the animal studies reporting evidence that acetaldehyde is involved in the pharmacological and behavioral effects of ethanol. A number of studies demonstrated that acetaldehyde administration induces a range of behavioral effects. Other pharmacological studies indicated that acetaldehyde might be critically involved in several effects of ethanol consumption, including its reinforcing consequences. However, conflicting evidence has also been published. Furthermore, it remains to be shown whether pharmacologically relevant concentrations of acetaldehyde are achieved in the brain after alcohol consumption in order to induce significant effects. Finally, we review current evidence about the central mechanisms of action of acetaldehyde.

Genetic polymorphism in ethanol metabolism: acetaldehyde contribution to alcohol abuse and alcoholism

Acetaldehyde, the first product of ethanol metabolism, has been speculated to be involved in many pharmacological and behavioral effects of ethanol. In particular, acetaldehyde has been suggested to contribute to alcohol abuse and alcoholism. In the present paper, we review current data on the role of acetaldehyde and ethanol metabolism in alcohol consumption and abuse. Ethanol metabolism involves several enzymes. Whereas alcohol dehydrogenase metabolizes the bulk of ethanol within the liver, other enzymes, such as cytochrome P4502E1 and catalase, also contributes to the production of acetaldehyde from ethanol oxidation. In turn, acetaldehyde is metabolized by the enzyme aldehyde dehydrogenase. In animal studies, acetaldehyde is mainly reinforcing particularly when injected directly into the brain. In humans, genetic polymorphisms of the enzymes alcohol dehydrogenase and aldehyde dehydrogenase are also associated with alcohol drinking habits and the incidence of alcohol abuse. From these human genetic studies, it has been concluded that blood acetaldehyde accumulation induces unpleasant effects that prevent further alcohol drinking. It is therefore speculated that acetaldehyde exerts opposite hedonic effects depending on the localization of its accumulation. In the periphery, acetaldehyde is primarily aversive, whereas brain acetaldehyde is mainly reinforcing. However, the peripheral effects of acetaldehyde might also be dependent upon its peak blood concentrations and its rate of accumulation, with a narrow range of blood acetaldehyde concentrations being reinforcing.

Involvement of brain ethanol metabolism on acute tolerance development and on ethanol consumption in alcohol-drinker (UChB) and non-drinker (UChA) rats

Acute tolerance that develops in minutes of an ethanol exposure appears to influence voluntary ethanol consumption in our two selected bred lines, UChA (low ethanol drinker) and UChB (high ethanol drinker)rats. We have reported previously that an acute intraperitoneal (ip.) dose of ethanol (2.3 g/kg) induces both an increase in acute tolerance and a long-lasting increase in voluntary ethanol consumption in UChB rats. In the present paper we investigated the involvement of acetaldehyde produced centrally during ethanol oxidation by brain catalase and its oxidation by mitochondrial aldehyde dehydrogenase, on acute tolerance development and on voluntary ethanol consumption by rats. Acute tolerance developed to motor impairment induced by a dose of ethanol of 2.3 g/kg administered ip. was evaluated by the tilting plane test. Voluntary ethanol consumption by the rat with free access to a 10% v/v ethanol was measured daily. Both parameters were evaluated in controls,saline-pretreated and ethanol-injected rats. One group of rats that received the ethanol injection was pretreated with 3-amino-1,2,4-triazole (AT), a catalase inhibitor, and another group was pretreated with disulfiram, an aldehyde dehydrogenase inhibitor. Brain catalase and aldehyde dehydrogenase activities were measured in both groups of rats. Results show that acute tolerance to motor impairment, as well as ethanol consumption induced by ethanol, appears to be the consequence of acetaldehyde formed centrally during ethanol oxidation via the catalase system, because pretreatment of rats with the catalase inhibitor attenuated the increase in acute tolerance development and the increase in voluntary ethanol consumption in UChB rats that received the acute i.p. dose of ethanol. Moreover, the acetaldehyde metabolizing enzyme also appears to be an important factor in the modulation of acute tolerance development and voluntary ethanol consumption in UChA and UChB rats. The results lead us to propose that the possible mechanism by which the ip. injection of ethanol to UChB rats induces an increase in ethanol consumption is the development of acute tolerance, where acetaldehyde formed during brain ethanol metabolism via catalase and its subsequent oxidation via aldehyde dehydrogenase have an important role.

Mutations in mitochondrial aldehyde dehydrogenase (ALDH2) change cofactor affinity and segregate with voluntary alcohol consumption in rats

Genetic factors influence alcohol consumption and alcoholism. A number of groups have bred alcohol drinker and non drinker rat strains, but genetic determinants remain unknown. The University of Chile rat lines UChA (low drinkers) and UChB (high drinkers) display differences in the relative K(m) for NAD+ of mitochondrial aldehyde dehydrogenase (ALDH2) but no V(max) differences. The relative K(m) differences may be due to mitochondrial changes or to genetic differences coding for ALDH2. We investigated whether there are differences in the coding regions of ALDH2 cDNA in these lines and whether the Aldh2 genotype predicts the phenotype of alcohol consumption and the K(m) of ALDH2 for NAD+. Liver cDNA was prepared, and the Aldh2 transcript was amplified, cloned and sequenced. Genotyping was conducted by DNA amplification and restriction enzyme digestion. When compared to Aldh21 of Sprague-Dawley, 94% of the UChA (low drinker) rats (n = 61), presented a mutation that changes Gln67 to Arg in the mature enzyme (allele referred to as Aldh22). In UChB (high drinker) rats (n = 69), 58% presented the Aldh21 allele, while 42% presented the Gln67Arg change plus a second mutation that changed Glu479 to Lys (allele Aldh23). The Aldh22 allele was absent in high drinker rats. Rats of different Aldh2 genotypes displayed marked phenotypic differences in both ethanol consumption (g/kg/day; means +/- SE): (Aldh21/Aldh21) = 5.7 +/- 0.2, (Aldh22/Aldh22) = 0.9 +/- 0.2 and (Aldh23/Aldh23) = 4.6 +/- 0.2; and K(m)s for NAD+ of 43 +/- 3 microm, 132 +/- 13 microm and 41 +/- 2 microm, respectively (Aldh22 versus Aldh21 or Aldh23; P < 0.0001 for both phenotypes). Overall, the data show that alleles of Aldh2 strongly segregate with the phenotype of ethanol consumption and the relative K(m) for NAD+ of ALDH2. Bases mutated suggest that non drinker Aldh22 is ancestral with regard to the coding changes in either Aldh21 or Aldh23, variants which would allow ethanol consumption and may provide an evolutionary advantage by promoting calorie intake from fermented products along with carbohydrates.

In vivo study of salsolinol produced by a high concentration of acetaldehyde in the striatum and nucleus accumbens of free-moving rats

BACKGROUND

Salsolinol, a neuropharmacologically active compound, is formed by the condensation of acetaldehyde (AcH) with dopamine (DA) in the brain. The aim of our study was to examine the effect of a high concentration of AcH on salsolinol formation and to compare the release of DA, serotonin (5-HT), and salsolinol in the striatum and nucleus accumbens (NAc) in free-moving rats.

METHODS

After the insertion of a microdialysis probe, male Wistar rats (250-300 g) were treated with cyanamide (CY, a potent aldehyde dehydrogenase inhibitor) + ethanol (EtOH), CY + 4-methylpyrazole (4-MP, a strong alcohol dehydrogenase inhibitor) + EtOH, 4-MP + EtOH, CY, and 4-MP. Simultaneous quantitation of DA, 5-HT, and salsolinol in dialysates was performed by using in vivo microdialysis coupled with high-performance liquid chromatography with an electrochemical detector and blood EtOH and AcH by using a head-space gas chromatographic method.

RESULTS

Salsolinol was detected only in the CY + EtOH groups in both the striatum and NAc, and we also detected a high AcH concentration in the blood in those groups. A correlation was found between the dialysate levels of salsolinol and blood concentrations of AcH. The striatal levels of DA and 5-HT were approximately two times higher, whereas salsolinol levels were approximately three times higher compared with the usual level in the NAc. No significant difference of DA and 5-HT levels in the dialysates was observed in either the control or the other study groups.

CONCLUSION

Our observation suggested that the brain salsolinol formation may depend on the concentrations of DA and AcH in freely moving rats, and there is no effect of a high concentration of AcH on DA and 5-HT levels in the striatum and NAc.

Role of acetaldehyde in ethanol-induced conditioned taste aversion in rats

RATIONALE

In spite of many recent studies on the effects of acetaldehyde, it is still unclear whether acetaldehyde mediates the reinforcing and/or aversive effects of ethanol.

OBJECTIVES

The present study reexamined the role of acetaldehyde in ethanol-induced conditioned taste aversion (CTA). A first experiment compared ethanol- and acetaldehyde-induced CTA. In a second experiment, cyanamide, an aldehyde dehydrogenase inhibitor, was administered before conditioning with either ethanol or acetaldehyde to investigate the effects of acetaldehyde accumulation.

METHODS

A classic CTA protocol was used to associate the taste of a saccharin solution with either ethanol or acetaldehyde injections. In experiment 1, saccharin consumption was followed by injections of either ethanol (0, 0.5, 1.0, 1.5 or 2.0 g/kg) or acetaldehyde (0, 100, 170 or 300 mg/kg). In experiment 2, the rats were pretreated with either saline or cyanamide (25 mg/kg) before conditioning with either ethanol or acetaldehyde.

RESULTS

Both ethanol and acetaldehyde induced significant CTA. However, ethanol produced a very strong CTA relative to acetaldehyde that induced only a weak CTA even at toxic doses. Cyanamide pretreatments significantly potentiated ethanol- but not acetaldehyde-induced CTA.

CONCLUSIONS

The present results indicate that ethanol-induced CTA does not result from brain acetaldehyde effects. In contrast, it is suggested that the reinforcing effects of brain acetaldehyde might actually reduce ethanol-induced CTA. Our results also suggest that the inhibition of brain catalase activity may contribute to the potentiating effects of cyanamide on ethanol-induced CTA.

The effect of cyanamide and 4-methylpyrazole on the ethanol-induced locomotor activity in mice

To assess the role of cyanamide and 4-methylpyrazole (4-MP) in mediating ethanol-induced locomotor activity in mice, they were pretreated with cyanamide (12.5, 25, or 50 g/kg) prior to one ethanol injection (2.4 g/kg) and showed significantly depressed locomotor activity compared with control groups. Cyanamide (25 mg/kg) also cancelled out the biphasic action of ethanol (0, 0.8, 1.6, 2.4, 3.2, or 4 g/kg) on locomotor activity. The action of cyanamide and 4-MP in combined administration was also tested. Our data show that pretreatment with 4-MP alone does not change the spontaneous or ethanol-induced locomotor activity. Conversely, when mice were pretreated with cyanamide and 4-MP, the depressive effect of cyanamide on the locomotor activity induced by ethanol disappeared, and the locomotor activity rose to levels similar to those of the control group, recovering the biphasic ethanol effect. These effects cannot be attributed to peripheral elevated blood acetaldehyde levels, as pretreatment with 4-MP prevents accumulation of acetaldehyde. These data might suggest some influence of brain catalase and aldehyde dehydrogenase (ALDH) on the effects of ethanol.

The role of acetaldehyde in the actions of alcohol (update 2000)

BACKGROUND

Recent advances in the field of acetaldehyde (AcH) research have raised the need for a comprehensive review on the role of AcH in the actions of alcohol. This update is an attempt to summarize the available AcH research.

METHODS

The descriptive part of this article covers not only recent research but also the development of the field. Special emphasis is placed on mechanistic analyses, new hypotheses, and conclusions.

RESULTS

Elevated AcH during alcohol intoxication causes alcohol sensitivity, which involves vasodilation associated with increased skin temperature, subjective feelings of hotness and facial flushing, increased heart and respiration rate, lowered blood pressure, sensation of dry mouth or throat associated with bronchoconstriction and allergy reactions, nausea and headache, and also reinforcing reactions like euphoria. These effects seem to involve catecholamine, opiate peptide, prostaglandin, histamine, and/or kinin mechanisms. The contribution of AcH to the pathological consequences of chronic alcohol intake is well established for different forms of cancer in the digestive tract and the upper airways. AcH seems to play a role in the etiology of liver cirrhosis. AcH may have a role in other pathological developments, which include brain damage, cardiomyopathy, pancreatitis, and fetal alcohol syndrome. AcH creates both unpleasant aversive reactions that protect against excessive alcohol drinking and euphoric sensations that may reinforce alcohol drinking. The protective effect of AcH may be used in future treatments that involve gene therapy with or without liver transplantation.

CONCLUSIONS

AcH plays a role in most of the actions of alcohol. The individual variability in these AcH-mediated actions will depend on the genetic polymorphism, not only for the alcohol and AcH-metabolizing enzymes but also for the target sites for AcH actions. The subtle balance between aversive and reinforcing, protecting and promoting factors will determine the overall behavioral and pathological developments.

The role of acetaldehyde in the actions of alcohol (update 2000)

BACKGROUND

Recent advances in the field of acetaldehyde (AcH) research have raised the need for a comprehensive review on the role of AcH in the actions of alcohol. This update is an attempt to summarize the available AcH research.

METHODS

The descriptive part of this article covers not only recent research but also the development of the field. Special emphasis is placed on mechanistic analyses, new hypotheses, and conclusions.

RESULTS

Elevated AcH during alcohol intoxication causes alcohol sensitivity, which involves vasodilation associated with increased skin temperature, subjective feelings of hotness and facial flushing, increased heart and respiration rate, lowered blood pressure, sensation of dry mouth or throat associated with bronchoconstriction and allergy reactions, nausea and headache, and also reinforcing reactions like euphoria. These effects seem to involve catecholamine, opiate peptide, prostaglandin, histamine, and/or kinin mechanisms. The contribution of AcH to the pathological consequences of chronic alcohol intake is well established for different forms of cancer in the digestive tract and the upper airways. AcH seems to play a role in the etiology of liver cirrhosis. AcH may have a role in other pathological developments, which include brain damage, cardiomyopathy, pancreatitis, and fetal alcohol syndrome. AcH creates both unpleasant aversive reactions that protect against excessive alcohol drinking and euphoric sensations that may reinforce alcohol drinking. The protective effect of AcH may be used in future treatments that involve gene therapy with or without liver transplantation.

CONCLUSIONS

AcH plays a role in most of the actions of alcohol. The individual variability in these AcH-mediated actions will depend on the genetic polymorphism, not only for the alcohol and AcH-metabolizing enzymes but also for the target sites for AcH actions. The subtle balance between aversive and reinforcing, protecting and promoting factors will determine the overall behavioral and pathological developments.

Daidzin decreases ethanol consumption in rats

In a previous study, daidzin, a constituent of an ancient Chinese herbal treatment for alcoholism, decreased home-cage ethanol consumption in laboratory Syrian golden hamsters. The present study tested the generality of daidzin's antidipsotropic effects. Rats served as subjects in a two-lever choice procedure. At one lever, responses earned 10% ethanol, flavored with saccharin. At the other lever, responses earned an isocaloric starch solution. Daidzin decreased both ethanol and starch consumption, but the decreases in ethanol intake were larger. Changes in consumption were dose dependent, and differences in ethanol and food consumption increased slightly (but significantly) as dose increased. Daidzin produced a similar pattern of decreases in lever pressing. In baseline, there was an approximately equal distribution of responses between the two levers; at the highest daidzin dose, the relative number of responses at the ethanol lever decreased to 30%. These results replicate and extend earlier findings, and they encourage further research on daidzin's capacity to decrease ethanol consumption.

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.

Role of acetaldehyde in the actions of ethanol on the brain--a review

Over the last 30 years, acetaldehyde has been postulated to mediate various actions of ethanol on the brain. Experiments have studied ethanol consumption after acetaldehyde infusions into the brain, in rodents with high or low activities of hepatic and brain ethanol-metabolizing enzymes, and after treatment with drugs that alter the metabolism of acetaldehyde after ethanol ingestion. Evidence that acetaldehyde is involved in the actions of ethanol has been inconsistent because of the lack of knowledge of the brain acetaldehyde concentrations required to exert their effects, the lack of correlation between the activities of ethanol-metabolizing enzymes across strains of rodents and ethanol consumption, and the lack of specificity of drugs altering acetaldehyde metabolism. The formation of significant amounts of acetaldehyde the brain in vivo after ethanol ingestion and by what mechanism has not been clearly established, although catalase is a promising candidate. Future research needs to directly demonstrate in brain the formation of acetaldehyde in vivo, determine the concentrations in brain areas involved in ethanol consumption, and evaluate the possible actions of drugs other than an ability to block acetaldehyde metabolism.

Daidzin suppresses ethanol consumption by Syrian golden hamsters without blocking acetaldehyde metabolism

Daidzin is a potent, selective, and reversible inhibitor of human mitochondrial aldehyde dehydrogenase (ALDH) that suppresses free-choice ethanol intake by Syrian golden hamsters. Other ALDH inhibitors, such as disulfiram (Antabuse) and calcium citrate carbimide (Temposil), have also been shown to suppress ethanol intake of laboratory animals and are thought to act by inhibiting the metabolism of acetaldehyde produced from ingested ethanol. To determine whether or not daidzin inhibits acetaldehyde metabolism in vivo, plasma acetaldehyde in daidzin-treated hamsters was measured after the administration of a test dose of ethanol. Daidzin treatment (150 mg/kg per day i.p. for 6 days) significantly suppresses (> 70%) hamster ethanol intake but does not affect overall acetaldehyde metabolism. In contrast, after administration of the same ethanol dose, plasma acetaldehyde concentration in disulfiram-treated hamsters reaches 0.9 mM, 70 times higher than that of the control. In vitro, daidzin suppresses hamster liver mitochondria-catalyzed acetaldehyde oxidation very potently with an IC50 value of 0.4 microM, which is substantially lower than the daidzin concentration (70 microM) found in the liver mitochondria of daidzin-treated hamsters. These results indicate that (i) the action of daidzin differs from that proposed for the classic, broad-acting ALDH inhibitors (e.g., disulfiram), and (ii) the daidzin-sensitive mitochondrial ALDH is not the one and only enzyme that is essential for acetaldehyde metabolism in golden hamsters.

New drugs for the treatment of experimental alcoholism

This article presents a current overview of the efforts to suppress pharmacologically the craving, dependence, or other factors associated with the self-selection of alcohol in an experimental animal. The contemporary status of the pharmacotherapy of experimental alcoholism similarly is described for different animal models of alcohol drinking. An evaluation is presented of several classes of drug for their efficacy in ameliorating the volitional ingestion of alcohol in the presence of an alternative fluid. Currently, two main experimental animal models of alcoholism are being used in this endeavor: (a) genetic lines or substrains of high alcohol preferring or high drinking rats; and (b) strains of nondrinking or low alcohol preferring rats which are induced chemically to prefer alcohol. Because of technical, methodological, and other issues surrounding the procedures used to assess the efficacy of a drug in reducing alcohol intake, several of the newer findings remain controversial. For example, serious side effects on the intake of food, caloric regulation, motor activity, or other functions would preclude the clinical utility of the drug. However, several drugs which affect monoaminergic neurons as well as opioid systems in the brain now seem to offer promise as agents which do possess clinical benefits. Two of these drugs, FG5606 (amperozide) and FG 5893 are essentially "antialcoholic" or anticraving and are without any significant side effects on cerebral mechanisms responsible for hunger, caloric intake, motor activity, or other physiological process. Amperozide, a 5-HT2 receptor antagonist with dopamine releasing properties, is particularly notable because of its irreversible nature in attenuating alcohol preference for months after its administration. It is concluded that future pharmacological research on presently available and newly developed compounds will provide exciting opportunities to the clinician who can utilize a particular drug as an adjunctive tool in the therapeutic treatment of the alcoholic individual.

Potential gene therapy for alcoholism

Genes that have an actual or a potential relationship to alcoholism may be useful targets for therapy. Candidate genes are considered in relationship to family studies, differences in alcohol preferences in various rodent strains, biochemical reactions, physiologic response mechanisms, and alterations in brain pharmacology. Suggestions are made concerning the identification of candidate genes, design of gene antisense constructs, and techniques for their organ-specific delivery. The complexities surrounding alcoholism in humans make it likely that several simultaneous approaches may be required for effective therapy for alcoholism.

Age dependent development of ethanol drinking in rats after inhibition of aldehyde dehydrogenase

The purpose of this experiment was to determine the temporal characteristics associated with the age-related development of volitional consumption of ethanol induced by the pharmacological inhibition of aldehyde dehydrogenase (AlDH). To induce preference for ethanol, the AlDH inhibitor, cyanamide, was administered to male Sprague-Dawley rats which were 30 days of age. Cyanamide (n = 8) was injected subcutaneously twice daily in a dose of 10 mg/kg over a period of 3 days while the control group (n = 6) received the saline vehicle solution according to the same schedule. Then at 50, 70, 90, and 110 days of age, both groups of rats were given a standard 11-day test of preference for water versus ethanol offered in concentrations ranging from 3% through 30%. The results showed that at 70 days of age the preference for ethanol increased above the level of the 50-day test in terms of absolute g/kg intakes and proportion of ethanol to water consumed over the lower range of 3% through 15% concentrations. During the tests at 90 and 110 days of age, the cyanamide-treated rats further increased their preference for ethanol significantly over the levels at the 70-day test in terms of both g/kg and proportional intakes. The pattern of drinking of ethanol offered in the higher concentrations of 25% and 30% was unrelated to the age of the rats and the overall intakes were significantly higher than those of the lower concentrations. These findings demonstrate that the enzymatic inhibition of AlDH systematically acts in a delayed fashion to shift the pattern of preference for ethanol which is contingent on the maturation of the animal. In this instance, the volitional intake of ethanol in the cyanamide-treated rats reached its maximal level by 90-110 days of age. It is proposed that an endocrine mechanism involved in gonadal maturation may function in the intense shift in alcohol drinking.

Central action of an inhibitor of brain dopa-decarboxylase, NSD-1015, on cyanamide-induced alcohol drinking in rats

A cannula for repeated intracerebroventricular (ICV) infusion was implanted stereotaxically in 16 male Sprague-Dawley rats. Subsequently, an alcohol preference test was given to each animal to establish its preferred concentration in the presence of water. After the alcohol solution was removed, 15 mg/kg cyanamide was injected subcutaneously for 4 days to maximize volitional intake of the single preferred solution of alcohol, which ranged from 7-15% in these animals. The L-aromatic amino acid decarboxylase inhibitor, NSD-1015 (3-hydroxybenzylhydrazine dihydrochloride) was then given ICV twice daily in a volume of 5.0 microliters in the following doses: 0.005, 0.01, 0.1 and 1.0 micrograms. NSD-1015 in all doses attenuated the g/kg alcohol intake of the rats; however, this decline was significant only at the lowest dose, which was pharmacologically specific, since neither food nor water intakes were altered by the treatment. Following the ICV infusions of NSD-1015, alcohol drinking returned essentially to postcyanamide levels. Further, during the interval of administration of NSD-1015, the cyanamide-induced decline in food consumption was reversed. These observations are in agreement with previous findings obtained under similar experimental conditions with the L-aromatic amino acid decarboxylase inhibitor, benserazide (Ro4-4602). They suggest that central decarboxylation or other effects of this drug on limbic system structures involved in the intake of alcohol could comprise a part of the mechanism underlying the induction of drinking. Further support is also provided for the involvement of brain dopamine and/or serotonin in the specific pattern of alcohol consumption in the rat.

A histochemical study of the distribution of aldehyde dehydrogenase activity in brain structures of rats with genetically different alcohol-related behaviour

Brain samples from rats genetically selected for high or low voluntary alcohol intake (AA and ANA strains) or for differences in alcohol-induced motor incoordination (AT and ANT strains) were analyzed by histochemistry for aldehyde dehydrogenase (EC 1.2.1.3; ALDH) activity in various CNS structures. All strains exhibited the highest ALDH activities in neurons of the mesencephalic tract of trigeminal nerve nucleus and in spinal cord motoneurons, while the lowest activities were observed in the somatosensory cortex. Although the general distribution pattern of ALDH activity was similar in the genetically selected strains, some potentially important differences were observed. AA rats with high voluntary alcohol consumption had lower ALDH activity (with acetaldehyde as substrate) in the neuropil of the olfactory tubercle but higher activity (with benzaldehyde as substrate) in the spinal cord motoneurons, Purkinje cells and capillary endothelium of the cerebellum as compared to the corresponding structures from the alcohol avoiding ANA rats. Alcohol-resistant AT rats had higher ALDH activity, with benzaldehyde, in most CNS structures than did the alcohol-sensitive ANT's, significantly so in the lamina II of the somatosensory cortex and the neurons of the lateral hypothalamic area. This relationship was also found with acetaldehyde as substrate in the neurons of the hypothalamic arcuate nuclei and in cerebellar capillaries, but the ANT's had the higher activity in the neurons of the cerebral cortex V lamina. We suggest that some of the differences observed may relate to the differences between the rat strains with respect to voluntary alcohol intake and alcohol-induced motor incoordination.

Anatomical mapping of tetrahydropapaveroline-reactive sites in brain mediating suppression of alcohol drinking in the rat

In a previous study, anatomically circumscribed sites were identified within limbic-midbrain and limbic-forebrain structures of the rat in which injections of tetrahydropapaveroline (THP) evoked the drinking of alcohol even at aversive concentrations. The purpose of the second part of this study was to identify specific sites in the same limbic structures which also were reactive to THP but which mediated the suppression of alcohol consumption. Cannulae for repeated microinjection of THP were implanted stereotaxically in male Sprague-Dawley rats at sites extending from the ventral tegmental-substantia nigra complex rostrally to the region of the olfactory tubercle. Postoperatively, the rats were tested for their self-selection of water versus alcohol offered in solutions increased over 10 consecutive days in 10 concentrations from 3 to 30%. THP was dissolved in a CSF vehicle containing Na2S2O5 or ascorbate and microinjected in a dose of 25, 50 or 250 ng contained in a volume of 1.5-2.0 microliters. Following a sequence of 5 microinjections of THP, given over 3 days, the same 10-day alcohol drinking test was repeated. Ordinarily, sites at three depths 1.0-1.5 mm beneath the tip of the guide tube were tested for their reactivity to the amine-aldehyde adduct. When injected at 21 sites within coronal planes 1.0-10.5, THP attenuated the intake of alcohol significantly. Structures sensitive to the inhibitory action of the aldehyde adduct included the substantia nigra, reticular formation, medial lemniscus, preoptic area, nucleus accumbens, olfactory tubercle, cingulate gyrus and rostral hippocampus. Within 65 loci contained within the same AP planes, little or no effect of alcohol intake was exerted by THP independent of the dose microinjected. Nonreactive loci were identified within fiber pathways including the corpus callosum and optic tract, motor systems of the caudate nucleus, and both sensory and motor relay nuclei of the thalamus. An analysis of the critical part played by the dose of THP revealed that 81% of reactive sites given the 25 ng dose mediated enhanced drinking of alcohol, as demonstrated in the first study. Conversely, the 50 and 250 ng doses injected at THP-sensitive loci reduced alcohol consumption three to seven times more often than they augmented drinking. Anatomical sites mediating an attenuation of alcohol consumption in response to the higher doses of THP overlapped with both enkephalinergic and dopaminergic systems which project from the ventral tegmentum and substantia nigra to the rostral limbic-forebrain.(ABSTRACT TRUNCATED AT 400 WORDS)

Inhibition of brain dopa-decarboxylase by RO 4-4602 infused ICV blocks alcohol drinking induced in rats by cyanamide

Following the stereotaxic implantation of chronic cannulae for intracerebroventricular (ICV) infusion, rats were given an alcohol preference test to establish their preferred concentration in comparison with water. After alcohol was removed, 15 mg/kg cyanamide was then injected subcutaneously for 4 days in order to maximize volitional intake of single solutions of alcohol, which in these animals ranged from 7 to 15%. The L-dopa-decarboxylase inhibitor benserazide (Ro 4-4602) injected subcutaneously twice daily in doses of 50-100 mg/kg failed to alter the rats' alcohol consumption either in terms of g/kg or proportional values. However, when given ICV twice daily in concentrations of 10 ng-2.0 micrograms per 5.0 microliters volume, benserazide attenuated the rats' alcohol drinking significantly. This reduction occurred in a dose-dependent manner in terms of both absolute and proportional intakes of alcohol. Pre-treatment of the animals with 1.0 microgram benserazide given ICV, when alcohol was removed from the test situation, did not abolish the subsequent ingestion of alcohol but its peripheral administration (50 mg/kg) enhanced drinking. These results suggest that the interference with the metabolic pathway of dopamine or serotonin synthesis, possibly through the mechanism of reduced formation of aldehyde adducts in the brain, markedly alters the pattern of voluntary drinking in the rat. Alternatively, benserazide could act by its central inhibition of aldehyde dehydrogenase, which in turn would concomitantly elevate levels of acetaldehyde and thereby reduce alcohol drinking.

Protein, carbohydrate, and ethanol consumption: interactions in AA and ANA rats

Female rats of the alcohol-preferring AA line were given a choice between protein, carbohydrate, and fat sources. Subsequent free access to alcohol decreased their intake of carbohydrate but not of protein or fat. The individual alcohol intakes were negatively correlated with the carbohydrate intakes (-0.76) and with the alcohol-induced changes in carbohydrate intake (-0.83), but positively correlated with the concurrent protein intakes (0.78). The alcohol consumption and ethanol elimination rate of AA rats were subsequently found to vary directly with the protein content (5, 10, 20 and 40% by energy) of the premixed diet given to them--they drank more than 9 times more ethanol on the 40% than on the 5% protein diet--but the alcohol intake of the alcohol-avoiding ANA rats was not affected by protein intake. The results clearly indicate that the three macronutrients are related to alcohol consumption in different ways, suggesting that protein intake affects the selection of alcohol of AA rats through a factor correlated to ethanol elimination (but not through a ceiling effect from the rate of elimination) and that the alcohol in turn reduces carbohydrate consumption.

Depletion of hepatic glutathione by ethanol occurs independently of ethanol metabolism

The mechanism of ethanol-induced depletion of hepatic glutathione (GSH) was studied in vivo and in isolated hepatocytes. Neither inhibition of ethanol metabolism with 4-methylpyrazole, nor a 10-fold elevation of acetaldehyde levels by inhibition of aldehyde dehydrogenase with cyanamide or disulfiram, affected the magnitude of the GSH depletion observed in vivo. The rate of intracellular GSH accumulation by isolated hepatocytes incubated with cysteine or methionine was not inhibited by the addition of 80 mM ethanol. A significantly decreased rate of GSH accumulation was, however, found in hepatocytes isolated from ethanol-intoxicated animals. Neither the in vivo pretreatment with ethanol nor its in vitro addition to isolated hepatocytes affected the rate of GSH efflux. The results suggest that ethanol itself, rather than its metabolic products, causes depletion of liver GSH, and that events occurring in vivo are required for such an effect to be exerted.

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.

Cyanamide given ICV or systemically to the rat alters subsequent alcohol drinking

Cyanamide or disulfiram serves to suppress volitional intake of alcohol presumably because of the toxic build-up of acetaldehyde dehydrogenase (AIDH). However, the presence of acetaldehyde systemically favors the in vivo synthesis of addictive-like metabolites in the brain which in turn enhance alcohol drinking. The purpose of this investigation, therefore, was to determine whether cyanamide administered to the rat, which did not have access to alcohol during treatment, would nevertheless affect the subsequent preference for alcohol. In the first experiment, cannulae were implanted bilaterally above the cerebral ventricle of 33 adult male Sprague-Dawley rats so that an artificial CSF or a solution of cyanamide could be infused intracerebroventricularly (ICV). Following post-operative recovery, each rat was tested for its alcohol preference by offering it water and a solution of ethyl alcohol which was increased over 8 days from 3-20%. After a single test concentration of alcohol (range of 5-9%) was selected for each individual animal presented with water over a 5-day interval, cyanamide was infused in a volume of 2.5 microliters per side three times daily for 4 days in one of the following total doses: 0.03, 0.1, 0.3, 0.5 or 1.0 mg. A second five-day preference test was run, and 6 weeks following cyanamide infusions a final 3-20% alcohol preference screen was run over 8 days. The results showed that a long-term, dose-dependent increase or decrease in alcohol intake occurred in those rats reactive to the drug.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol-induced taste aversions: lack of involvement of acetaldehyde and the area postrema

Two experiments were run to evaluate the role of acetaldehyde and the area postrema in the acquisition of an ethanol-induced conditioned taste aversion. An ethanol-induced taste aversion was observed in male Sprague-Dawley rats with a dose of 4 g/kg. PO, but not after doses of 1 or 2 g/kg. Pretreatment with 4-methylpyrazole (8 mg/kg, IP), which itself did not induce an aversion as compared to pyrazole (68 mg/kg, IP) that did, and/or prior application of lesions of the area postrema had no influence on the development of an ethanol-induced taste aversion. The results indicate that ethanol-induced taste aversion learning does not result from the metabolism of ethanol to acetaldehyde and does not, like other toxins, involve the mediation of the area postrema.

Elevation by ethanol and its metabolites of liver adenosine monophosphate

Acute ethanol administration significantly increased the concentration of adenosine monophosphate (5'-AMP) in the intact freeze-clamped rat liver regardless of the ethanol dose administered. The increase was abolished by the alcohol dehydrogenase inhibitor 4-methylpyrazole, but was also seen after direct infusion of acetaldehyde into the portal vein. Administration of acetate to give hepatic levels similar to those seen during ethanol oxidation failed, however, to cause an increase in AMP. After ethanol administration there was a highly significant positive correlation between individual AMP levels and 3-OH-butyrate/acetoacetate ratios. The results suggest that the increase in liver AMP reflects activation of ethanol-derived acetate by acetothiokinase in the mitochondrial matrix. Ethanol, but not acetate inhibits the citric acid cycle, as reflected by the shift in the mitochondrial redox state. This could inhibit production of GTP needed for AMP phosphorylation by GTP-AMP phosphotransferase, thus explaining the accumulation of AMP by ethanol.

Voluntary consumption of ethanol and its consequences in C57 mice treated with 4-methylpyrazole

Daily injections of the alcohol dehydrogenase inhibitor 4-methylpyrazole (4MP) were administered to C57BL/6J mice offered continuous free access to food, water and 10% v/v ethanol. There was a significant correlation (r = -0.82) between the rate of ethanol consumption during pretreatment and the effect of 4MP on subsequent intake. Mice drinking more than 2.5 g/kg per day decreased their intake, while subjects drinking less than this amount increased the quantity of ethanol self-administered. The elevated concentrations of plasma ethanol which resulted from voluntary consumption were sufficient to produce intoxication but did not induce physical dependence. Presenting mice with 10% ethanol as their only fluid or offering them a choice of water and saccharin-sweetened ethanol increased intake but failed to raise plasma ethanol to the concentrations observed in mice offered unflavored ethanol and water, and treated with 4MP. The evidence suggests that plasma ethanol does not limit voluntary drinking in untreated mice and that concentrations of 135 to 250 mg/dl are not avoided by C57 mice in a free-choice situation.

Cyanamide injections during alcohol deprivation increase alcohol drinking

Long-Evans male rats were given 7 weeks of choice between 10% ethanol and water and then were divided into 6 matched groups, 3 of which were then deprived of alcohol for 6 days. Subcutaneous cyanamide injections (10 mg/kg, 3 times daily, for 4 days) during alcohol deprivation produced a long lasting, significant increase in subsequent alcohol selection, over and above the increase produced by alcohol deprivation alone. The same injections given to a group not deprived of alcohol caused a significant suppression of alcohol drinking during the treatment and had disappeared 4 days after the last injection. Thereafter the drinking remained at the control level and did not rise to that of the group given the injections during deprivation. The groups did not differ in their subsequent selection of saline solutions.

A correlation between voluntary ethanol consumption and brain catalase activity in the rat

The relationship between voluntary ethanol consumption and brain catalase activity was investigated in male Long Evans rats. In the first study, rats which were voluntarily consuming alcohol or water for 25 days were sacrificed by decapitation immediately (group A) or 15 days (group B) following withdrawal of alcohol and their brains analysed for catalase activity. Mean brain catalase activity did not differ among the two groups of rats exposed to ethanol and the ones exposed to water only. Furthermore, there were significant positive correlations between individual voluntary ethanol intake and catalase activity in both groups, (group A:r = .69, p less than or equal to 0.05; group B:r = .54, p less than or equal to 0.05). In the second study, rats were forced to drink high levels of ethanol presented as the only source of fluid for 25 days. Rats were sacrificed and brain, liver, muscle and heart tissue were extracted and analysed for catalase activity. There were no differences in mean brain catalase activity between water and forced ethanol drinking rats indicating that the enzyme was not inducible by high volume ethanol consumption. The results suggest that inherent differences in brain catalase activity may be one of the factors in determining an animal's propensity to voluntarily consume ethanol.

Ethanol preference in mice following acute or chronic ethanol administration

C57Bl mice, unlike LACG or BALB mice, show a significant preference for 12% (w/v) ethanol solution compared to water. C57Bl mice which have been rendered tolerant to but not dependent upon ethanol by a programme of enforced ethanol drinking lose this preference on withdrawal of compulsory ethanol. Loss of preference also occurs following one or more acute injections of ethanol ( 4ml /kg) and persists in mice 12 weeks following withdrawal. It is suggested that this long-lasting loss of preference has a CNS basis and is not due merely to taste aversion.

Elevated concentrations of ethanol in plasma do not suppress voluntary ethanol consumption in C57BL mice

The 24-hr patterns of ethanol intake and resulting concentrations of ethanol in plasma are described for male C57BL/6J mice given free access to water and a 10% v/v solution of ethanol. Animals treated with the alcohol dehydrogenase inhibitor 4-methylpyrazole developed peak plasma concentrations of 116 +/- 20 mg/100 ml, while controls given daily injections of saline exhibited peak plasma concentrations of 11 +/- 7 mg/100 ml. Ethanol consumption as measured by total daily intake and preference was not significantly different in the two groups of mice. The absence of an effect on ethanol consumption despite a tenfold difference in peak plasma levels suggests that concentrations of circulating ethanol within the range observed do not limit voluntary consumption of ethanol.

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-Km aldehyde dehydrogenase activity was markedly decreased by all three drugs after 2 and 24 hr whereas only cyanamide inhibited the high-Km 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.

Inhibition of aldehyde dehydrogenases in rat brain and liver by disulfiram and coprine

Rats were treated with either coprine or disulfiram and the inhibition of aldehyde dehydrogenase (ALDH) in liver and brain mitochondria was measured with acetaldehyde, 3,4-dihydroxyphenylacetaldehyde (DOPAL), and succinate semialdehyde at different concentrations. The inhibition pattern was similar for both inhibitors, but the degree of inhibition was lower with disulfiram. The ALDH activity both in the liver and the brain was inhibited at low concentrations of acetaldehyde and DOPAL, but not with succinate semialdehyde. The high-Km enzyme activities with acetaldehyde were not inhibited in liver and brain. The activity at high concentration of DOPAL was inhibited in the liver, but only slightly affected in the brain, suggesting the presence of a brain enzyme with an intermediate Km value for DOPAL. In contrast with the results observed in vivo, it was found that the high-Km activities with acetaldehyde and DOPAL in brain mitochondrial preparations were more sensitive to the inhibitors in vitro than the low-Km activities. Kinetic studies on ALDH preparations from brain and liver mitochondria suggested that acetaldehyde and DOPAL are metabolized by the same low-Km ALDH.