Effects of 3-amino-1,2,4-triazole on ethanol-induced open-field activity: evidence for brain catalase mediation of ethanol's effects

Orally administered zingerone does not mitigate alcohol-induced hepatic oxidative stress in growing Sprague Dawley rat pups

Neonatal alcohol exposure (NAE) can induce oxidative stress. We determined whether zingerone (ZO), a phytochemical with anti-oxidant activity, can mitigate the negative impact of neonatal alcohol-induced oxidative stress. Seventy ten-day-old Sprague-Dawley rat pups (35 male, 35 female) were randomly assigned and administered the following treatment regimens daily from postnatal day (PND) 12-21: group 1 - nutritive milk (NM), group 2 - NM +1 g/kg ethanol (Eth), group 3 - NM + 40 mg/kg ZO, group 4 - NM + Eth + ZO. Growth performance, blood glucose and plasma triglycerides (TGs), total cholesterol, HDL-cholesterol, leptin and insulin concentration were determined. Cytochrome p450E21(CYP2E1) and thiobarbituric acid (TBARS); markers of hepatic oxidative stress and catalase, superoxide dismutase (SOD) and total glutathione (GSH), anti-oxidant markers of the pups were determined. Oral administration of ethanol (NM + Eth), zingerone (NM + ZO) and combined ethanol and zingerone (NM + Eth + ZO) did not affect the growth performance and insulin and leptin concentration of the rats (p > 0.05). Ethanol significantly reduced plasma TGs concentration of female rats (p = 0.04 vs control). However, ethanol and/or its combination with zingerone decreased hepatic GSH (p = 0.02 vs control) and increased CYP2E1 (p = 0.0002 vs control) activity in male rat pups. Zingerone had no effect (p > 0.05 vs control) on the rats' CYP2E1, GSH, SOD and catalase activities. Neonatal alcohol administration elicited hepatic oxidative stress in male rat pups only, showing sexual dimorphism. Zingerone (NM + ZO) prevented an increase in CYP2E1 activity and a decrease in GSH concentration but did not prevent the alcohol-induced hepatic oxidative stress in the male rat pups.

Modulation of Ethanol-Metabolizing Enzymes by Developmental Lead Exposure: Effects in Voluntary Ethanol Consumption

This review article provides evidence of the impact of the environmental contaminant lead (Pb) on the pattern of the motivational effects of ethanol (EtOH). To find a mechanism that explains this interaction, the focus of this review article is on central EtOH metabolism and the participating enzymes, as key factors in the modulation of brain acetaldehyde (ACD) accumulation and resulting effect on EtOH intake. Catalase (CAT) seems a good candidate for the shared mechanism between Pb and EtOH due to both its antioxidant and its brain EtOH-metabolizing properties. CAT overactivation was reported to increase EtOH consumption, while CAT blockade reduced it, and both scenarios were modified by Pb exposure, probably as the result of elevated brain and blood CAT activity. Likewise, the motivational effects of EtOH were enhanced when brain ACD metabolism was prevented by ALDH2 inhibition, even in the Pb animals that evidenced reduced brain ALDH2 activity after chronic EtOH intake. Overall, these results suggest that brain EtOH metabolizing enzymes are modulated by Pb exposure with resultant central ACD accumulation and a prevalence of the reinforcing effects of the metabolite in brain against the aversive peripheral ACD accumulation. They also support the idea that early exposure to an environmental contaminant, even at low doses, predisposes at a later age to differential reactivity to challenging events, increasing, in this case, vulnerability to acquiring addictive behaviors, including excessive EtOH intake.

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.

Hydrogen inhalation ameliorated mast cell-mediated brain injury after intracerebral hemorrhage in mice

OBJECTIVE

Hydrogen inhalation was neuroprotective in several brain injury models. Its mechanisms are believed to be related to antioxidative stress. We investigated the potential neurovascular protective effect of hydrogen inhalation especially effect on mast cell activation in a mouse model of intracerebral hemorrhage.

DESIGN

Controlled in vivo laboratory study.

SETTING

Animal research laboratory.

SUBJECTS

One hundred seventy-one 8-week-old male CD-1 mice were used.

INTERVENTIONS

Collagenase-induced intracerebral hemorrhage model in 8-week-old male CD-1 mice was used. Hydrogen was administrated via spontaneous inhalation. The blood-brain barrier permeability and neurologic deficits were investigated at 24 and 72 hours after intracerebral hemorrhage. Mast cell activation was evaluated by Western blot and immuno-staining. The effects of hydrogen inhalation on mast cell activation were confirmed in an autologous blood injection model intracerebral hemorrhage.

MEASUREMENT AND MAIN RESULTS

At 24 and 72 hours post intracerebral hemorrhage, animals showed blood-brain barrier disruption, brain edema, and neurologic deficits, accompanied with phosphorylation of Lyn kinase and release of tryptase, indicating mast cell activation. Hydrogen treatment diminished phosphorylation of Lyn kinase and release of tryptase, decreased accumulation and degranulation of mast cells, attenuated blood-brain barrier disruption, and improved neurobehavioral function.

CONCLUSION

Activation of mast cells following intracerebral hemorrhage contributed to increase of blood-brain barrier permeability and brain edema. Hydrogen inhalation preserved blood-brain barrier disruption by prevention of mast cell activation after intracerebral hemorrhage.

Microinjections of acetaldehyde or salsolinol into the posterior ventral tegmental area increase dopamine release in the nucleus accumbens shell

BACKGROUND

Published findings indicate that acetaldehyde (ACD; the first metabolite of ethanol [EtOH]) and salsolinol (SAL; formed through the nonenzymatic condensation of ACD and dopamine [DA]) can be formed following EtOH consumption. Both ACD and SAL exhibit reinforcing properties within the posterior ventral tegmental area (pVTA) and both exhibit an inverted "U-shaped" dose-response curve. The current study was undertaken to examine the dose-response effects of microinjections of ACD or SAL into the pVTA on DA efflux in the nucleus accumbens shell (AcbSh).

METHODS

For the first experiment, separate groups of male Wistar rats received pulse microinjections of artificial cerebrospinal fluid (aCSF) or 12-, 23-, or 90-μM ACD into the pVTA, while extracellular DA levels were concurrently measured in the AcbSh. The second experiment was similarly conducted, except rats were given microinjections of aCSF or 0.03-, 0.3-, 1.0-, or 3.0-μM SAL, while extracellular levels of DA were measured in the AcbSh.

RESULTS

Both ACD and SAL produced a dose-dependent inverted "U-shaped" response on DA release in the AcbSh, with 23-μM ACD (200% baseline) and 0.3-μM SAL (300% baseline) producing maximal peak responses with higher concentrations of ACD (90 μM) and SAL (3.0 μM) producing significantly lower DA efflux.

CONCLUSIONS

The findings from the current study indicate that local application of intermediate concentrations of ACD and SAL stimulated DA neurons in the pVTA, whereas higher concentrations may be having secondary effects within the pVTA that inhibit DA neuronal activity. The present results parallel the studies on the reinforcing effects of ACD and SAL in the pVTA and support the idea that the reinforcing effects of ACD and SAL within the pVTA are mediated by activating DA neurons.

Ethanol injected into the hypothalamic arcuate nucleus induces behavioral stimulation in rats: an effect prevented by catalase inhibition and naltrexone

It is suggested that some of the behavioral effects of ethanol, including its psychomotor properties, are mediated by beta-endorphin and opioid receptors. Ethanol-induced increases in the release of hypothalamic beta-endorphin depend on the catalasemic conversion of ethanol to acetaldehyde. Here, we evaluated the locomotor activity in rats microinjected with ethanol directly into the hypothalamic arcuate nucleus (ArcN), the main site of beta-endorphin synthesis in the brain and a region with high levels of catalase expression. Intra-ArcN ethanol-induced changes in motor activity were also investigated in rats pretreated with the opioid receptor antagonist, naltrexone (0-2 mg/kg) or the catalase inhibitor 3-amino-1,2,4-triazole (AT; 0-1 g/kg). We found that ethanol microinjections of 64 or 128, but not 256 microg, produced locomotor stimulation. Intra-ArcN ethanol (128 microg)-induced activation was prevented by naltrexone and AT, whereas these compounds did not affect spontaneous activity. The present results support earlier evidence indicating that the ArcN and the beta-endorphinic neurons of this nucleus are necessary for ethanol to induce stimulation. In addition, our data suggest that brain structures that, as the ArcN, are rich in catalase may support the formation of ethanol-derived pharmacologically relevant concentrations of acetaldehyde and, thus be of particular importance for the behavioral effects of ethanol.

Infusions of acetaldehyde into the arcuate nucleus of the hypothalamus induce motor activity in rats

AIMS

The hypothalamic arcuate nucleus (ARH) is one of the brain regions with the highest levels of catalase expression. Acetaldehyde, metabolized from ethanol in the CNS through the actions of catalase, has a role in the behavioral effects observed after ethanol administration. In previous studies acetaldehyde injected in the lateral ventricles or in the substantia nigra reticulata (SNR) mimicked the behavioral stimulant effects of centrally administered ethanol.

MAIN METHODS

In the present study we assessed the effects of acetaldehyde administered either into the ARH into a dorsal control or into the third ventricle on locomotion and rearing observed in 30 min sessions in an open field.

KEY FINDINGS

Acetaldehyde injected into the ARH induced horizontal locomotion and rearing for 20 min. In contrast, administration of acetaldehyde into a control site dorsal to the ARH did not have any effect on locomotion. Although acetaldehyde administration into the third ventricle also induced locomotion, the time course for the effect in this area was different from the time course following ARH injections. Acetaldehyde in the ARH produced a long lasting induction of locomotion, while with intraventricular injections the effects disappeared after 5 min.

SIGNIFICANCE

The present results are consistent with previous studies demonstrating that acetaldehyde is an active metabolite of ethanol, which can have locomotor stimulant properties when administered in the ventricular system of the brain or into specific brain nuclei. Some brain nuclei rich in catalase (i.e.; SNR and ARH) could be mediating some of the locomotor stimulant effects of ethanol through its conversion to acetaldehyde.

Involvement of brain catalase activity in the acquisition of ethanol-induced conditioned place preference

It has been suggested that some of the behavioral effects produced by ethanol are mediated by its first metabolite, acetaldehyde. The present research addressed the hypothesis that catalase-dependent metabolism of ethanol to acetaldehyde in the brain is an important step in the production of ethanol-related affective properties. Firstly, we investigated the contribution of brain catalase in the acquisition of ethanol-induced conditioned place preference (CPP). Secondly, the specificity of the catalase inhibitor 3-amino-1,2,4-triazole (AT) was evaluated with morphine- and cocaine-induced CPP. Finally, to investigate the role of catalase in the process of relapse to ethanol seeking caused by re-exposure to ethanol, after an initial conditioning and extinction, mice were primed with saline and ethanol or AT and ethanol and tested for reinstatement of CPP. Conditioned place preference was blocked in animals treated with AT and ethanol. Morphine and cocaine CPP were unaffected by AT treatment. However, the reinstatement of place preference was not modified by catalase inhibition. Taken together, the results of the present study indicate that the brain catalase-H(2)O(2) system contributes to the acquisition of affective-dependent learning induced by ethanol, and support the involvement of centrally-formed acetaldehyde in the formation of positive affective memories produced by ethanol.

Comparison between multiple behavioral effects of peripheral ethanol administration in rats: Sedation, ataxia, and bradykinesia

Although low doses of systemic ethanol stimulate locomotion in mice, in rats the typical response to peripheral ethanol administration is a dose-dependent suppression of motor activity. In the present study, male rats received acute doses of ethanol IP (0.0, 0.25, 0.5, 1.0 or 2.0 g/kg) and were tested on several behavioral tasks related to the motor suppressive or sedative effects of the drug. This research design allowed for comparisons between the effects of ethanol on different behavioral tasks in order to determine which tasks were most sensitive to the drug (i.e., which tasks would yield deficits that appear at lower doses). In the first two experiments, rats were evaluated on a sedation rating scale, and ataxia/motor incoordination was assessed using the rotarod apparatus. Administration of 2.0 g/kg ethanol produced sedation as measured by the sedation scale, and also impaired performance on the rotarod. In a third experiment, ethanol reduced locomotion in the stabilimeter at several doses and times after IP injection, with 0.25 g/kg being the lowest dose that produced a significant decrease in locomotion. Finally, experiment four studied the effects of ethanol on operant lever pressing reinforced on a fixed ratio 5 (FR5) schedule for food reinforcement. Data showed suppressive effects on lever pressing at doses of 1.0, and 2.0 g/kg ethanol. Analysis of the interresponse time distribution showed that ethanol produced a modest slowing of operant responding, as well as fragmentation of the temporal pattern of responding and increases in pausing. Taken together, these results indicate that rats can demonstrate reduced locomotion and slowing of operant responding at doses lower than those that result in sedation or ataxia as measured by the rotarod. The detection of subtle changes in different motor test across a broad range of ethanol doses is important for understanding ethanol effects in other cognitive, motivational or sensory processes.

Motor stimulant effects of ethanol injected into the substantia nigra pars reticulata: importance of catalase-mediated metabolism and the role of acetaldehyde

A series of experiments was conducted to investigate the locomotor effects of local injections of ethanol and the ethanol metabolite, acetaldehyde, into substantia nigra pars reticulata (SNr). Infusions of ethanol into SNr resulted in a dose-related increase in locomotor activity, with maximal effects at a dose of 1.4 micromol. Ethanol injected into a control site dorsal to substantia nigra failed to stimulate locomotion, and another inactive site was identified in brainstem areas posterior to substantia nigra. The locomotor effects of intranigral ethanol (1.4 micromol) were reduced by coadministration of 10 mg/kg sodium azide, a catalase inhibitor that acts to reduce the metabolism of ethanol into acetaldehyde in the brain. SNr infusions of acetaldehyde, which is the first metabolite of ethanol, also increased locomotion. Taken together, these results indicate that SNr is one of the sites at which ethanol and acetaldehyde may be acting to induce locomotor activity. These results are consistent with the hypothesis that acetaldehyde is a centrally active metabolite of ethanol, and provide further support for the idea that catalase activity is a critical step in the regulation of ethanol-induced motor activity. These studies have implications for understanding the brain mechanisms involved in mediating the ascending limb of the biphasic dose-response curve for the effect of ethanol on locomotor activity.

Brain catalase activity inhibition as well as opioid receptor antagonism increases ethanol-induced HPA axis activation

BACKGROUND

Growing evidence indicates that brain catalase activity is involved in the psychopharmacological actions of ethanol. Recent data suggest that participation of this enzymatic system in some ethanol effects could be mediated by the endogenous opioid system. The present study assessed whether brain catalase has a role in ethanol-induced activation of the HPA axis, a neuroendocrine system modulated by the endogenous opioid neurotransmission.

METHODS

Swiss male mice received an intraperitoneal injection of the catalase inhibitor 3-amino-1,2,4-triazole (AT; 0-1 g/kg), and 0 to 20 hr after this administration, animals received an ethanol (0-4 g/kg; intraperitoneally) challenge. Thirty, 60, or 120 min after ethanol administration, plasma corticosterone levels were determined immunoenzymatically. In addition, we tested the effects of 45 mg/kg of cyanamide (another catalase inhibitor) and 0 to 2 mg/kg of naltrexone (nonselective opioid receptor antagonist) on ethanol-induced enhancement in plasma corticosterone values.

RESULTS

The present study revealed that AT boosts ethanol-induced increase in plasma corticosterone levels in a dose- and time-dependent manner. However, it did not affect corticosterone values when measured after administration of saline, cocaine (4 mg/kg, intraperitoneally), or morphine (30 mg/kg, intraperitoneally). The catalase inhibitor cyanamide (45 mg/kg, intraperitoneally) also increased ethanol-related plasma corticosterone levels. These effects of AT and cyanamide on ethanol-induced corticosterone values were observed under treatment conditions that decreased significantly brain catalase activity. Indeed, a significant correlation between effects of catalase manipulations on both variables was found. Finally, we found that the administration of naltrexone enhanced the levels of plasma corticosterone after the administration of saline or ethanol.

CONCLUSIONS

This study shows that the inhibition of brain catalase increases ethanol-induced plasma corticosterone levels. Results are discussed together with previous findings suggesting a putative linkage between brain ethanol metabolism and the endogenous opioid system to explain some of the neuroendocrine effects of ethanol.

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.

Catalase inhibition in the Arcuate nucleus blocks ethanol effects on the locomotor activity of rats

Previous studies have demonstrated that there is a bidirectional modulation of ethanol-induced locomotion produced by drugs that regulate brain catalase activity. In the present study we have assessed the effect in rats of intraperitoneal, intraventricular or intracraneal administration of the catalase inhibitor sodium azide in the locomotor changes observed after ethanol (1 g/kg) administration. Our results show that sodium azide prevents the effects of ethanol in rats locomotion not only when sodium azide was systemically administered but also when it was intraventricularly injected, then confirming that the interaction between catalase and ethanol takes place in Central Nervous System (CNS). Even more interestingly, the same results were observed when sodium azide administration was restricted to the hypothalamic Arcuate nucleus (ARC), a brain region which has one of the highest levels of expression of catalase. Therefore, the results of the present study not only confirm a role for brain catalase in the mediation of ethanol-induced locomotor changes in rodents but also point to the ARC as a major neuroanatomical location for this interaction. These results are in agreement with our reports showing that ethanol-induced locomotor changes are clearly dependent of the ARC integrity and, especially of the POMc-synthesising neurons of this nucleus. According to these data we propose a model in which ethanol oxidation via catalase could produce acetaldehyde into the ARC and to promote a release of beta-endorphins that would activate opioid receptors to produce locomotion and other ethanol-induced neurobehavioural changes.

Role of catalase in ethanol-induced conditioned taste aversion: a study with 3-amino-1,2,4-triazole

Recent studies involved acetaldehyde, the first ethanol metabolite, in both the rewarding and aversive effects of ethanol consumption. Brain acetaldehyde is believed to originate mainly from local brain metabolism of ethanol by the enzyme catalase. Therefore, the inhibition of catalase by 3-amino-1,2,4-triazole (aminotriazole) may help to clarify the involvement of acetaldehyde in ethanol's hedonic effects. In the present study, multiple doses of both ethanol and aminotriazole were used to investigate the effects of catalase inhibition on ethanol-induced conditioned taste aversion (CTA). A separate microdialysis experiment investigated the effects of aminotriazole pretreatment on the time course of brain ethanol concentrations. Ethanol induced a dose-dependent CTA with a maximal effect after conditioning with 2.0 g/kg ethanol. Aminotriazole pretreatments dose-dependently potentiated the CTA induced by 1.0 g/kg ethanol. However, aminotriazole pretreatments did not alter the CTA induced by higher ethanol doses (1.5 and 2.0 g/kg) probably because a maximal aversion for saccharin was already obtained without aminotriazole. The results of the microdialysis experiment confirmed that the effects of aminotriazole cannot be attributed to local alterations of brain ethanol levels. The present study argues against a role for brain acetaldehyde in ethanol's aversive effects but in favor of its involvement in ethanol rewarding properties.

N-acetylcysteine reduced the effect of ethanol on antioxidant system in rat plasma and brain tissue

Chronic ethanol administration is able to induce an oxidative stress in the central nervous system. N-Acetylcysteine (NAC) has antioxidant properties; as a sulphydryl donor, it contributes to the regeneration of glutathione and it acts through a direct reaction with hydroxyl radicals. In this study we investigated a possible beneficial effect of NAC on some of the free radical related parameters. Twenty four male Wistar rats were divided in to three groups and were given ethanol (Group 1), ethanol and NAC (Group 2) and isocaloric dextrose (Group 3). Ethanol and NAC were given intragastrically at doses of 6 g/kg/day and 1 g/kg/day, respectively. Our results show that chronic ethanol intake elicits statistically significant increase in MDA and NO levels and decrease in SOD and GSH levels in both plasma and brain (p < 0.001). GPx levels decreased in erythrocytes (p < 0.001). CAT activity showed significant decrease only in brain samples (p < 0.001). NAC administration effectively restores the above results to nearly normal levels. Therefore we suggest that reactive free radicals are, at least partly, involved in the ethanol-induced injury of brain cells and NAC mitigate the toxic effects of ethanol on the oxidant-antioxidant system of rat plasma and brain.

Behavioral consequences of the hypotaurine-ethanol interaction

In order to evaluate the effect of hypotaurine on ethanol-induced locomotion, different groups of mice received an injection of saline or 5.62, 8.45, 11.25, 16.87 or 33.75 mg/kg of hypotaurine 30 min prior to administering ethanol (2.4 g/kg). The duration of the effect of hypotaurine was explored by treating animals with ethanol 0, 30, 60 and 90 min after hypotaurine pretreatment. The effect of hypotaurine on acute stimulating ethanol locomotion was evaluated by pretreating animals with saline or 11.25 mg/kg of hypotaurine 30 or 60 min before ethanol (1.6, 2.4, 3.2 g/kg) or saline injections. Hypotaurine (11.25 mg/kg) required 30 min to boost, specifically ethanol-stimulated locomotion (2.4 g/kg). These results suggest a central locus for the interaction, firstly, because blood ethanol levels were not different between hypotaurine and saline pretreated mice, and, secondly, because a cotreatment with beta-alanine (22 mg/kg), a beta-amino acid that counteracts the transfer of hypotaurine across the blood-brain barrier (BBB), prevented the enhancement in ethanol-induced locomotion produced by hypotaurine.

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.

Measurement of inhibin A: a modification to an enzyme-linked immunosorbent assay

Inhibin A is a useful prenatal marker of Down syndrome. Currently, the available enzyme-linked immunosorbent assays (ELISAs) for inhibin A are based upon the same paired monoclonal antibodies. In the present study we have confirmed for one of those ELISAs that short-term sample storage as whole blood leads to a significant decline in detectable inhibin A and that this is most likely due to erythrocyte catalase interference with a critical oxidation step in the assay. While this interference can be eliminated by heating the samples pre-assay, this process is labour intensive. In the present study we have demonstrated that the addition of 3-amino-1,2,4-triazole (AT), a catalase 'suicide' inhibitor, also prevents the decline of inhibin A levels in samples stored as whole blood. We suggest that the addition of AT to samples prior to assay is a simple modification to the inhibin A ELISA that affords optimum performance.

Brain catalase activity is highly correlated with ethanol-induced locomotor activity in mice

It has been demonstrated that acute administration of lead to mice enhances brain catalase activity and ethanol-induced locomotion. These effects of lead seem to be related, since they show similar time courses and occur at similar doses. In the present study, in an attempt to further evaluate the relation between brain catalase activity and lead-induced changes in ethanol-stimulated locomotion, the interaction between lead acetate and 3-amino-1H,2,4-triazole (AT), a well-known catalase inhibitor, was assessed. In this study, lead acetate or saline was acutely injected intraperitoneally to Swiss mice at doses of 50 or 100 mg/kg 7 days before testing. On the test day, animals received an intraperitoneal injection of AT (0, 10, or 500 mg/kg). Five hours following AT treatment, ethanol (0.0 or 2.5 g/kg, ip) was injected and the animals were placed in open-field chambers, in which locomotion was measured for 10 min. Neither lead exposure nor AT administration, either alone or in combination, had any effect on spontaneous locomotor activity. AT treatment reduced ethanol-induced locomotion as well as brain catalase activity. On the other hand, ambulation and brain catalase activity were significantly increased by both doses of lead. Furthermore, AT significantly reduced the potentiation produced by lead acetate on brain catalase and on ethanol-induced locomotor activity in a dose-dependent manner. A significant correlation was found between locomotion and catalase activity across all test conditions. The results show that brain catalase activity is involved in the effects of lead acetate on ethanol-induced locomotion in mice. Thus, this study confirms the notion that brain catalase provides the molecular basis for understanding some of the mechanisms of the action of ethanol in the central nervous system.

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.

Conditioned stimulus preference after acetaldehyde but not ethanol injections

Acetaldehyde, the first ethanol metabolite, has been suggested to mediate some of the behavioral effects of ethanol and particularly its reinforcing properties, although this later hypothesis remains extremely controversial. While several studies demonstrated the reinforcing effects of brain acetaldehyde, blood acetaldehyde accumulation is believed to be primarily aversive. In the present study, a conditioned reinforcement procedure has been used to investigate the reinforcing and/or aversive effects of intraperitoneal injections of both acetaldehyde and ethanol in Wistar rats. An olfactory stimulus was paired with daily injections of either ethanol (0, 0.25, 0.5, 1 and 2 g/kg) or acetaldehyde (0, 10, 20, 100 and 150 mg/kg). After eight conditioning sessions, all rats were tested for their stimulus preference or aversion. The results show that conditioning with small, 0.25 and 0.5 g/kg, ethanol doses induced neither preference nor aversion for the olfactory cue. In contrast, higher ethanol doses (1.0 and 2.0 g/kg) resulted in significant stimulus aversions. Acetaldehyde conditioning led to a biphasic stimulus preference, with a maximal preference around 20 mg/kg acetaldehyde. No evidence of aversive effects was found with increasing doses of acetaldehyde, even with concentrations close to the lethal limit. The present study clearly shows that systemic acetaldehyde injections induced significant stimulus preferences. This suggests that acetaldehyde may be, at least in part, responsible for the reinforcing effects of alcohol intake.

Lead acetate potentiates brain catalase activity and enhances ethanol-induced locomotion in mice

Several reports have demonstrated that acute lead acetate administration enhances brain catalase activity in animals. Other reports have shown a role of brain catalase in ethanol-induced behaviors. In the present study we investigated the effect of acute lead acetate on brain catalase activity and on ethanol-induced locomotion, as well as whether mice treated with different doses of lead acetate, and therefore, with enhanced brain catalase activity, exhibit an increased ethanol-induced locomotor activity. Lead acetate or saline was injected IP in Swiss mice at doses of 50, 100, 150, or 200 mg/kg. At 7 days following this treatment, ethanol (0.0, 1.5, 2.0, 2.5, or 3.0 g/kg) was injected IP, and the animals were placed in the open-field chambers. Results indicated that the locomotor activity induced by ethanol was significantly increased in the groups treated with lead acetate. Maximum ethanol-induced locomotor activity increase was found in animals treated with 100 mg/kg of lead acetate and 2.5 g/kg of ethanol. Total brain catalase activity in lead-pretreated animals also showed a significant induction, which was maximum at 100 mg/kg of lead acetate treatment. No differences in blood ethanol levels were observed among treatment groups. The fact that brain catalase and ethanol-induced locomotor activity followed a similar pattern could suggest a relationship between both lead acetate effects and also a role for brain catalase in ethanol-induced behaviors.

Effects of chronic lead administration on ethanol-induced locomotor and brain catalase activity

Several reports have demonstrated that chronic lead administration decreases brain catalase activity in animals. Other reports have shown a role of brain catalase on ethanol-induced behaviors. In the present study, we questioned whether mice treated chronically with lead, and therefore functionally devoid of brain catalase activity, exhibit some alterations in ethanol-induced behaviors. Swiss-Webster mice were exposed to drinking fluid containing either 500 ppm lead acetate or sodium acetate (control group) for 0, 15, 30, or 60 days before an acute ethanol administration. Following ethanol injection (2.5 g/kg, i.p.), animals were placed in open field chambers and locomotor activity was measured. Lead exposure had no effect on spontaneous locomotor activity. However, a reduction in ethanol-induced locomotor activity was found at all periods of lead exposure. After 60 days of treatment, the lead group demonstrated 35% less activity than the control group. Brain catalase activity was significantly reduced in the lead group following 60 days of exposure. This reduction in ethanol-induced locomotor activity and in brain catalase activity persisted after 40 days of lead withdrawal. The fact that brain catalase and ethanol-induced locomotor activity followed a similar pattern could suggest a relationship between both lead acetate effects and also a role for brain catalase in ethanol-induced behaviors.

The catalase inhibitor sodium azide reduces ethanol-induced locomotor activity

The involvement of brain catalase in modulating the psychopharmacological effects of ethanol was investigated by examining ethanol-induced locomotor activity in sodium azide-treated mice. Mice were pretreated with i.p. injections of the catalase inhibitor sodium azide (5, 10, or 15 mg/kg) or saline. Following this treatment, animals received i.p. injections of ethanol (0.0, 1.6, 2.4, or 3.2 g/kg). Ten minutes after ethanol administration, locomotor activity was recorded during a 10-min testing period in open-field chambers. The time effect between the two treatments (0, 30, 60, or 90 min) was also evaluated. Results indicated that sodium azide alone did not change spontaneous locomotor activity. However, this catalase inhibitor significantly reduced ethanol-induced locomotor activity when it was injected simultaneously or 30 min before ethanol injections. Moreover, perfused brain homogenates of mice treated with sodium azide also showed a significant reduction of catalase activity. No differences in blood ethanol levels were observed between sodium azide and saline pretreated animals. Results of an additional experiment showed that sodium azide (10 mg/kg, at 30 min) did not produce an effect on d-amphetamine- (2 mg/kg) or tert-butanol- (0.5 g/kg) induced locomotor activities. A specific interaction between ethanol and sodium azide at the level of the central nervous system is suggested. These results provide further support for the involvement of brain catalase in ethanol-induced behavioral effects. They also support the notion that acetaldehyde may be produced directly in the brain by catalase and that it may be an important regulator of ethanol's locomotor effects.

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.

Ethanol metabolism in the brain

Acetaldehyde is suspected of being involved in the central mechanism of central nervous system depression and addiction to ethanol, but in contrast to ethanol, it can not penetrate easily from blood into the brain because of metabolic barriers. Therefore, the possibility of ethanol metabolism and acetaldehyde formation inside the brain has been one of the crucial questions in biomedical research of alcoholism. This article reviews the recent progress in this area and summarizes the evidence on the first stage of ethanol oxidation in the brain and the specific enzyme systems involved. The brain alcohol dehydrogenase and microsomal ethanol oxidizing systems, including cytochrome P450 II E1 and catalase are considered. Their physicochemical properties, the isoform composition, substrate specificity, the regional and subcellular distribution in CNS structures, their contribution to brain ethanol metabolism, induction under ethanol administration and the role in the neurochemical mechanisms of psychopharmacological and neurotoxic effects of ethanol are discussed. In addition, the nonoxidative pathway of ethanol metabolism with the formation of fatty acid ethyl esters and phosphatidylethanol in the brain is described.

Catalase and the production of brain acetaldehyde: a possible mediator of the psychopharmacological effects of ethanol

This review represents an attempt to assess the available data on the role of catalase in the mediation of the behavioral actions of ethanol and the regulation of voluntary ethanol consumption. It is argued that acetaldehyde may be formed in brain through the peroxidatic activity of catalase. Furthermore, acetaldehyde formed centrally through the activity of this enzyme, may be responsible, at least in part, for some of the motivational, behavioral and neurotoxic effects of ethanol.

Interaction of exercise and ethanol on antioxidant enzymes in brain regions of the rat

This study investigates the effect of ethanol ingestion on antioxidant enzymes (AOE) and lipid peroxidation (malondialdehyde, (MDA) in different brain regions of the rat after acute exercise. Acute exercise (100% VO2max) significantly increased glutathione peroxidase (GSH-Px) activity and decreased glutathione reductase (GR) activity in the cerebral cortex. Acute exercise significantly increased MDA level in the corpus striatum. Ethanol (20%) (1.6 g/kg, PO) significantly increased MDA level in the cerebral cortex. Ethanol also significantly increased superoxide dismutase (SOD) activity in the cortex and catalase (CAT), GSH-Px, and GR activities in the corpus striatum. Ethanol significantly augmented CAT activity in the medulla and GSH-Px activity in the hypothalamus. However, CAT activity significantly decreased in the hypothalamus after ethanol ingestion. The combination significantly increased GSH-Px activity in the hypothalamus, SOD activity in the cortex, GR activity in the striatum, and MDA level in the medulla. In conclusion, the cerebral cortex, striatum medulla, and hypothalamus reacted differentially in response to ethanol as well as to acute exercise-induced oxidative stress whereas the combination moderated the changes in AOE activity in specific brain regions.

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.

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.

Family history of alcoholism and the mediation of alcohol intake by catalase: further evidence for catalase as a marker of the propensity to ingest alcohol

Earlier studies have suggested that catalase activity (CA) may represent a biological marker of alcohol intake in animals and in humans. An initial study was designed to rule out the possibility that CA is induced as a function of acute alcohol intake. Subjects (n = 80) were presented with either an alcohol (0.5 g/kg of body weight) or control solution, and asked to provide four 100-microliters blood samples at 0.0, 0.5, 2.0, and 24.0 hr. Results showed no differences in CA between individuals who had received alcohol, and controls, even when the effects of previous drinking history were covaried out. This lack of effect of acute alcohol intake on the possible induction of CA further supported the notion that CA may be a viable marker of alcohol intake, rather than the converse. In the second study, the relation between CA and alcohol intake was investigated in individuals with a family history (FH) of alcoholism (FH+), and in those without a family history of alcoholism (FH-). Subjects (n = 607) completed the Michigan Alcoholism Screening Questionnaire, the MacAndrew Scale, and the Concordia University Alcohol Screening Questionnaire; answered questions concerning their FH for alcoholism; and provided a 100-microliters blood sample. Results showed that FH+ individuals had higher mean CA compared with FH- individuals. When individuals with FH+ were compared with those with FH-, differences in the pattern of relation between CA and alcohol intake were observed. Although a significant relation between CA and alcohol intake was obtained for both FH- and FH+ individuals, this relation was significantly higher (p < 0.001) for individuals with FH+.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of aminotriazole on ethanol, water, and food intake and on brain catalase in UChA and UChB rats

Aminotriazole (AT), a catalase inhibitor, was administered to UChA (low ethanol consumer) and UChB (high ethanol consumer) rats. Ethanol, water, and solid food intake were measured during basic, treatment, and posttreatment periods. The effects of AT on brain catalase activity and acetaldehyde recovered during incubation of brain homogenates with ethanol were also studied in rats of both strains. Results showed that AT decreased voluntary ethanol intake in UChB rats, and also diminished the consumption of food by rats of both strains. No strain difference in brain catalase activity and acetaldehyde recovered during ethanol incubation was observed. The results suggest that AT effect on ethanol consumption is secondary to a reduction in the appetite for calories and not related to its catalase blocking effect.

Low and moderate doses of ethanol produce distinct patterns of cerebral metabolic changes in rats

The quantitative autoradiographic 2-[14C]deoxyglucose method was used to measure the effects of the acute administration of ethanol on local rates of glucose utilization in male Sprague-Dawley rats. Rates of glucose utilization were measured 10 min after the intraperitoneal administration of 0.00, 0.25, 0.50, and 1.00 g/kg ethanol. The acute administration of the lowest dose of ethanol (0.25 g/kg) significantly increased rates of cerebral metabolism, as compared with vehicle-treated controls, in structures of the mesocorticolimbic and nigrostriatal dopaminergic systems. Among the affected regions were the nucleus accumbens, medial prefrontal cortex, olfactory tubercle, caudate, ventral tegmental area, and substantia nigra. Acute administration of 0.50 g/kg ethanol resulted in similar trends in increased functional activity; however, significant increases were limited to the somatosensory cortex, posterior nucleus accumbens, and the CA3 region of the hippocampus. In contrast, the administration of 1.00 g/kg ethanol produced widespread decreases in rates of glucose utilization in brain regions involved in processing of sensory and motor information, as well as in portions of the limbic system. These data indicate that the effects of acute ethanol administration on functional activity as reflected by rates of glucose utilization are dose-dependent. These cerebral metabolic effects parallel the dose-dependent effects of ethanol on motor behavior, with stimulatory effects generally observed at lower doses and depressive effects at higher doses. Moreover, each of the doses studied produced alterations in functional activity in a unique subset of structures. This suggests that different neuroanatomical circuits mediate the effects of each dose.

Effects of 3-amino-1,2,4-triazole on brain catalase in the mediation of ethanol consumption in mice

Research has suggested that catalase plays a role in mediating ethanol's psychopharmacological effects. It has been shown that acatalasemic (C3H-A) mice differing in the activity of this enzyme consume larger amounts of ethanol. It has also been reported that when catalase activity is pharmacologically reduced, via 3-amino-1,2,4-triazole (AT), rats reduce their intake and preference for ethanol. The present research attempted to investigate AT's effects in nonselected mice. Swiss Webster mice were randomly assigned to groups of four per cage and further assigned to either a 5%, a 10%, or a 15% ethanol exposure condition. Mice were given a choice between water and increasing 1% concentrations of ethanol starting with 2%. Following five days of baseline, mice were injected daily with either AT (0.5 g/kg) or saline for five days. Results showed that AT significantly reduced ethanol consumption across treatment, but not posttreatment days. Results could not be explained by differences in total fluid intake. These results suggest a role for brain catalase in ethanol consumption across a variety of strains and species and further support the involvement of centrally formed acetaldehyde in the mediation of ethanol's psychopharmacological effects.

Increase in catalase activity in developing rat brain cell reaggregation cultures in the presence of ethanol

The aim of this investigation was to study the effects of ethanol on antioxidant enzymes in the developing brain, using reaggregation cultures of fetal rat brain cells as a model. The cultures were grown in the presence of 20 and 40 mM ethanol from day 2 until day 44 of the culture period, corresponding to a period in vivo from gestational day 17 to postnatal day 37. The catalase (EC 1.11.1.6) activity was consistently increased at all observation periods, from culture day 11 to day 44, by both doses of ethanol, and an immunoblot showed that the amount of catalase protein was markedly increased. The activities of manganese and copper-zinc superoxide dismutase (EC 1.15.1.1) and glutathione peroxidase (EC 1.11.1.9) were largely unaffected.

Differences in ethanol-induced behaviors in normal and acatalasemic mice: systematic examination using a biobehavioral approach

In studies designed to further examine the previously reported involvement of catalase in ethanol-induced effects, we attempted to confirm earlier observations by using normal (C3H-N) and acatalasemic (C3H-A) mice. These mice are identical in every respect and differ only in their catalase activity. Data suggested that the application of 3-amino-1,2,4-triazole (AT), a catalase inhibitor, to both substrains of mice resulted in a proportional decrease in motor activity, thus supporting our earlier observations. We also showed that this effect was specific to ethanol because AT did not have any effect on cocaine-induced motor activity in both substrains. Contrary to the effects of ethanol, these substrains did not differ in motor activity in response to cocaine. In an additional study, we observed that acatalasemic mice differed from the normals in their pattern of voluntary ethanol consumption. Acatalasemic mice consumed more ethanol but only when it was presented in the range of concentrations between 12 and 18%. Finally, we also obtained data suggesting that acatalasemic mice have longer duration of sleep time following ethanol administration compared to normals. Catalase activity was measured in both substrains. Results, once again, confirmed earlier data that the substrains differ in this activity and that AT further decreases brain catalase activity in both mice. Finally, when brain homogenates derived from both substrains were incubated with ethanol significant differences in the amount of generated acetaldehyde were found between the two mice strains. Together, these results provide strong support for the involvement of brain catalase in a variety of ethanol-induced behavioral effects.

Ethanol toxicity and oxidative stress

The mechanisms underlying the toxicity of ethanol have been the subject of much study, but are not well understood. Unlike many selective pharmacological agents, ethanol clearly has several major loci of action. One deleterious factor in ethanol metabolism is the potential for generation of excess amounts of free radicals. The extent to which this activity accounts for the overall toxicity of ethanol is unknown. This review outlines the enzymic steps that have the capacity to generate reactive oxygen species. These steps are likely to differ in acute and extended exposures to ethanol. Acetaldehyde catabolism also has the likelihood of contributing to ethanol-related oxidative stress. The review focuses on the ethanol-induced production of excess amounts of pro-oxidant reactive species in both the liver and the central nervous system. The potential of various stages of ethanol catabolism to involve generation of free radicals is described.

Enzymatic production of acetaldehyde from ethanol in rat brain tissue

The capacity for the brain to produce acetaldehyde (AcHO) from ethanol was determined in rat brain homogenates. Rat brains were perfused with saline-heparin solution and homogenized in a phosphate buffer. Varying amounts of tissue were incubated with ethanol (0-100 mM) for periods of up to 60 min. The reaction was stopped by the addition of desferrioxamine and ice-cold perchloric acid. Supernatants were treated with dinitrophenylhydrazine reagent, extracted with isooctane in the presence of an internal standard, and the derivatives were separated by HPLC. The addition of 4-methyl pyrazole (an alcohol dehydrogenase inhibitor) or metyrapone (a cytochrome P450 inhibitor) had no effect on the amount of recovered AcHO. On the other hand, treatment with the catalase inhibitors sodium azide, cyanamide, or 3-amino-1,2,4-triazole blocked the production of AcHO while the addition of exogenous peroxide or a peroxide-generating system enhanced the production of AcHO. Overall, these results suggest that AcHO may be produced in the brain during alcohol intoxication, through the action of the enzyme catalase.

Ethanol metabolism in rat brain homogenates by a catalase-H2O2 system

Homogenates of perfused rat brains incubated in the presence of ethanol (50-100 mM) and glucose (10 mM) were found to oxidize ethanol to acetaldehyde. The addition of glucose oxidase, a known hydrogen peroxide generator, to the incubation medium, significantly (P less than 0.05) increased the generation of acetaldehyde. The presence in the incubation medium of metyrapone, an inhibitor of cytochrome P450, or pyrazole, an alcohol dehydrogenase inhibitor, did not affect the levels of acetaldehyde obtained. Conversely, the presence of 3-amino-1,2,4-triazole, a known catalase inhibitor, induced a concentration-dependent reduction of the amount of acetaldehyde generated after incubation, even in the presence of glucose oxidase. Homogenates of perfused brains of rats treated with 3-amino-1,2,4-triazole or cyanamide (another H2O2-dependent catalase blocker) also showed a dose-dependent reduction of the acetaldehyde obtained. These findings support the notion that a catalase-mediated oxidation of ethanol is present in rat brain homogenates. It is suggested that this local oxidation of ethanol may have important biological implications. The data of both studies increase support for the notion that acetaldehyde is produced directly in the brain and that it may be the agent mediating some of the psychopharmacological properties of ethanol and be one of the factors determining the propensity of an animal to voluntarily consume ethanol.

Ethanol-induced motor activity in normal and acatalasemic mice

The role of brain catalase in modulating the psychopharmacological effects of ethanol was investigated by examining ethanol induced motor activity in normal, C3H-N, and a corresponding group of acatalasemic C3H-A, mice. Following administration of one of three doses of ethanol (0.8, 1.6, and 3.2 g/kg) or saline, mice were placed in open field chambers and locomotor and rearing activity was measured during a 10-min testing period. A significant increase in locomotor activity was recorded in both groups of mice at lower doses of ethanol, while the higher dose produced a marked depression. Normal mice demonstrated more locomotor activity than acatalasemic mice at all ethanol doses. No differences between both groups of mice were observed in rearing activity. Also, no differences in blood ethanol levels were observed between the two substrains. Brain and liver residual catalase activity in the acatalasemic mice was found to be 40% and 50%, respectively, of normal mice. Furthermore, evidence for possible involvement of the peroxidatic activity in ethanol-induced motor activity is presented. These results suggest a role for centrally formed acetaldehyde as a factor mediating some of ethanol's psychopharmacological effects.

Implication of free radical mechanisms in ethanol-induced cellular injury

Numerous experimental data reviewed in the present article indicate that free radical mechanisms contribute to ethanol-induced liver injury. Increased generation of oxygen- and ethanol-derived free radicals has been observed at the microsomal level, especially through the intervention of the ethanol-inducible cytochrome P450 isoform (CYP2E1). Furthermore, an ethanol-linked enhancement in free radical generation can occur through the cytosolic xanthine and/or aldehyde oxidases, as well as through the mitochondrial respiratory chain. Ethanol administration also elicits hepatic disturbances in the availability of non-safely-sequestered iron derivatives and in the antioxidant defense. The resulting oxidative stress leads, in some experimental conditions, to enhanced lipid peroxidation and can also affect other important cellular components, such as proteins or DNA. The reported production of a chemoattractant for human neutrophils may be of special importance in the pathogenesis of alcoholic hepatitis. Free radical mechanisms also appear to be implicated in the toxicity of ethanol on various extrahepatic tissues. Most of the experimental data available concern the gastric mucosa, the central nervous system, the heart, and the testes. Clinical studies have not yet demonstrated the role of free radical mechanisms in the pathogenesis of ethanol-induced cellular injury in alcoholics. However, many data support the involvement of such mechanisms and suggest that dietary and/or pharmacological agents able to prevent an ethanol-induced oxidative stress may reduce the incidence of ethanol toxicity in humans.

Dose- and time-dependent effect of an acute 3-amino-1,2,4-triazole injection on rat brain catalase activity

The results presented in this study demonstrate a progressive inhibition of rat brain catalase activity by AT in vivo. Furthermore, the inhibition of brain catalase by AT demonstrates the presence of hydrogen peroxide in brain, since AT inhibits catalase in the presence of this compound. The rate of inhibition of catalase seems to be dependent upon the rate by which H2O2 is generated. A time course study showed slower onset of the inhibition of brain as compared to liver catalase, possibly reflecting tissue hydrogen peroxide levels or, alternatively, a rate-limiting penetration of AT into brain and into the catalase compartment. The presence of AT in brain was confirmed over the time period of the observed inhibition of brain catalase. Catalase inhibitors are of particular interest in the study of the physiological role of catalase. This study further supports the use of AT in investigations designed to further understand the role of brain catalase.

Effect of 3-amino-1,2,4-triazole on ethanol-induced narcosis, lethality and hypothermia in rats

It has been proposed that ethanol can be oxidized in brain via the peroxidatic activity of catalase and that centrally formed acetaldehyde may mediate several of the psychopharmacological actions of ethanol. The present study was designed to investigate the role of brain catalase in the mediation of ethanol-induced narcosis, hypothermia and lethality in rats. Rats were pretreated with the catalase inhibitor 3-amino-1,2,4-triazole (AT) or saline. Five hours later, animals in each pretreatment group received IP injections of ethanol (3 or 4 g/kg). Ethanol-induced narcosis was significantly attenuated in AT-pretreated rats compared to the saline control group. As well, AT pretreatments reduced significantly the lethal effect of these ethanol doses. However, AT-pretreated ethanol-injected animals significantly reduce their body temperature as compared to the saline-ethanol animals. Blood ethanol determinations revealed that AT did interfere with ethanol metabolism. AT inhibits significantly brain catalase activity at all doses used in this study. The results indicate a role for brain catalase in ethanol effects. Furthermore, they suggest that catalase may be involved in the oxidation of ethanol in brain and that centrally formed acetaldehyde may play a role in ethanol-induced narcosis and lethality, but not hypothermia.

Studies on ethanol-brain catalase interaction: evidence for central ethanol oxidation

The purpose of the present investigation was to further study the relationship between ethanol and brain catalase in vivo. Rats were pretreated intraperitoneally (ip) with varying doses of ethanol or saline 30 min prior to administration of cyanamide (0.68 mmol/kg; ip), 4-hydroxypyrazole (1 mmol/kg; ip) or saline. Rat tissues were perfused in situ under ether anaesthesia. Brain catalase activity was measured using the Clark electrode. Results confirmed inhibition of brain catalase activity by cyanamide and 4-hydroxypyrazole. Ethanol protected catalase from cyanamide and 4-hydroxypyrazole inactivation in a dose-related manner. In a second study, homogenates from perfused brains were incubated in the presence of glucose and glucose oxidase with ethanol or saline and cyanamide or saline. Cyanamide was shown to inhibit the catalase activity in vitro in a dose-related manner. Ethanol prevented this inhibition of catalase when added to the incubation medium prior to cyanamide. These data suggest a competition between ethanol and inhibitors for the H2O2-catalase compound. They also confirm the presence and generation of H2O2 in the rat brain in vivo, and overall seem to support the notion that centrally formed acetaldehyde via brain catalase may be responsible for some of the psychopharmacological actions of ethanol.

Involvement of endogenous opioid mechanisms in the interaction between stress and ethanol

The involvement of endogenous opioid mechanisms in the interaction between stress and ethanol was investigated in the rat. Animals were pretreated with naltrexone (10 mg/kg) or saline 3 h before a second injection consisting of ethanol (1.0 g/kg) or saline. They were then restrained for 15 or 60 min or left in home cages for an equivalent amount of time. After restraint, animals were either subjected to an open-field test or decapitated to collect blood for corticosterone determinations. Locomotor depression was found to be induced by 15 but not 60 min restraint. In naltrexone-treated animals, however, 60 min restraint was also found to induce locomotor depression. Ethanol pretreatment was found to block the locomotor depression induced by 15 min restraint. Such an interaction was in turn antagonized by naltrexone. In the 15 min condition, stress and ethanol were also found to interact in their effects on plasma levels of corticosterone. Naltrexone did not alter any effects of the stressors on corticosterone levels. These results provide support for the involvement of endogenous opioid mechanisms in the interaction of stress and ethanol at a behavioural level.