Distribution and kinetics of ethanol metabolism in rat brain

Stimulants and Depressor Drugs in the Sleep-Wake Cycle Modulation: The case of alcohol and cannabinoids

A complex neurobiological network drives the sleep-wake cycle. In addition, external stimuli, including stimulants or depressor drugs, also influence the control of sleep. Here we review the recent advances that contribute to the comprehensive understanding of the actions of stimulants and depressor compounds, such as alcohol and cannabis, in sleep regulation. The objective of this review is to highlight the neurobiological mechanism engaged by alcohol and cannabis in sleep control.

Alcohol induced impairment/abnormalities in brain: Role of MicroRNAs

Alcohol is a highly toxic substance and has teratogenic properties that can lead to a wide range of developmental disorders. Excessive use of alcohol can change the structural and functional aspects of developed brain and other organs. Which can further lead to significant health, social and economic implications in many countries of the world. Convincing evidence support the involvement of microRNAs (miRNAs) as important post-transcriptional regulators of gene expression in neurodevelopment and maintenance. They also show differential expression following an injury. MiRNAs are the special class of small non coding RNAs that can modify the gene by targeting the mRNA and fine tune the development of cells to organs. Numerous pieces of evidences have shown the relationship between miRNA, alcohol and brain damage. These studies also show how miRNA controls different cellular mechanisms involved in the development of alcohol use disorder. With the increasing number of research studies, the roles of miRNAs following alcohol-induced injury could help researchers to recognize alternative therapeutic methods to treat/cure alcohol-induced brain damage. The present review summarizes the available data and brings together the important miRNAs, that play a crucial role in alcohol-induced brain damage, which will help in better understanding complex mechanisms. Identifying these miRNAs will not only expand the current knowledge but can lead to the identification of better targets for the development of novel therapeutic interventions.

Molecular basis of alcoholic fatty liver disease: From incidence to treatment

Alcoholic liver diseases have complex and multiple pathogenic mechanisms but still no effective treatment. Steatosis or alcoholic fatty liver disease (AFLD) has a widespread incidence and is the first step in the progression to more severe stages of alcoholic liver disease, with concomitant increases in morbidity and mortality rates. The ways in which this progression occurs and why some individuals are susceptible are still unanswered scientific questions. Research with animal models and clinical evidence have shown that it is a multifactorial disease that involves interactions between lipid metabolism, inflammation, the immune response and oxidative stress. Each of these pathways provides a better understanding of the pathogenesis of AFLD and contributes to the development of therapeutic strategies. This review emphasizes the importance of research on alcoholic steatosis based on incidence data, key pathogenic mechanisms and therapeutic interventions, and discusses perspectives on the progression of this disease.

Acetaldehyde self-administration by a two-bottle choice paradigm: consequences on emotional reactivity, spatial learning, and memory

Acetaldehyde, the first alcohol metabolite, is responsible for many pharmacological effects that are not clearly distinguishable from those exerted by its parent compound. It alters motor performance, induces reinforced learning and motivated behavior, and produces different reactions according to the route of administration and the relative accumulation in the brain or in the periphery. The effective activity of oral acetaldehyde represents an unresolved field of inquiry that deserves further investigation. Thus, this study explores the acquisition and maintenance of acetaldehyde drinking behavior in adult male rats, employing a two-bottle choice paradigm for water and acetaldehyde solution (from 0.9% to 3.2% v/v), over 8 weeks. The behavioral consequences exerted by chronic acetaldehyde intake are assessed by a set of different tests: trials in an open-field arena and elevated-plus maze provided information on both general motor and explorative activity, and anxiety-driven behavioral responses. The Morris water maze allowed the exploration of cognitive processes such as spatial learning and memory. Determination of acetaldehyde levels in the brain was carried out at the end of the drinking paradigm. Our results indicate that rats exposed for the first time to acetaldehyde at 0.9% displayed a regular and stable daily drinking pattern that reached higher values and a "peaks and drops" shaped-trend when acetaldehyde concentration was increased to 3.2%. Accordingly, an increase in acetaldehyde levels in the brain was determined compared to non-acetaldehyde drinking rats. Acetaldehyde intake during the free-choice paradigm exerted an anxiogenic response in the open-field arena and elevated-plus maze, which in turn correlates with an enhancement in cognitive flexibility and spatial orientation skills, when an adaptive response to a stressful environmental challenge was required. These findings further support the idea that acetaldehyde is indeed a centrally active and behaviorally relevant metabolite of alcohol.

Pathogenesis of alcoholic liver disease: Role of oxidative metabolism

Alcohol consumption is a predominant etiological factor in the pathogenesis of chronic liver diseases, resulting in fatty liver, alcoholic hepatitis, fibrosis/cirrhosis, and hepatocellular carcinoma (HCC). Although the pathogenesis of alcoholic liver disease (ALD) involves complex and still unclear biological processes, the oxidative metabolites of ethanol such as acetaldehyde and reactive oxygen species (ROS) play a preeminent role in the clinical and pathological spectrum of ALD. Ethanol oxidative metabolism influences intracellular signaling pathways and deranges the transcriptional control of several genes, leading to fat accumulation, fibrogenesis and activation of innate and adaptive immunity. Acetaldehyde is known to be toxic to the liver and alters lipid homeostasis, decreasing peroxisome proliferator-activated receptors and increasing sterol regulatory element binding protein activity via an AMP-activated protein kinase (AMPK)-dependent mechanism. AMPK activation by ROS modulates autophagy, which has an important role in removing lipid droplets. Acetaldehyde and aldehydes generated from lipid peroxidation induce collagen synthesis by their ability to form protein adducts that activate transforming-growth-factor-β-dependent and independent profibrogenic pathways in activated hepatic stellate cells (HSCs). Furthermore, activation of innate and adaptive immunity in response to ethanol metabolism plays a key role in the development and progression of ALD. Acetaldehyde alters the intestinal barrier and promote lipopolysaccharide (LPS) translocation by disrupting tight and adherent junctions in human colonic mucosa. Acetaldehyde and LPS induce Kupffer cells to release ROS and proinflammatory cytokines and chemokines that contribute to neutrophils infiltration. In addition, alcohol consumption inhibits natural killer cells that are cytotoxic to HSCs and thus have an important antifibrotic function in the liver. Ethanol metabolism may also interfere with cell-mediated adaptive immunity by impairing proteasome function in macrophages and dendritic cells, and consequently alters allogenic antigen presentation. Finally, acetaldehyde and ROS have a role in alcohol-related carcinogenesis because they can form DNA adducts that are prone to mutagenesis, and they interfere with methylation, synthesis and repair of DNA, thereby increasing HCC susceptibility.

Sympathoexcitation and pressor responses induced by ethanol in the central nucleus of amygdala involves activation of NMDA receptors in rats

The central nervous system plays an important role in regulating sympathetic outflow and arterial pressure in response to ethanol exposure. However, the underlying neural mechanisms have not been fully understood. In the present study, we tested the hypothesis that injection of ethanol in the central nucleus of the amygdala (CeA) increases sympathetic outflow, which may require the activation of local ionotropic excitatory amino acid receptors. In anesthetized rats, CeA injection of ethanol (0, 0.17, and 1.7 μmol) increased splanchnic sympathetic nerve activity (SSNA), lumbar sympathetic nerve activity (LSNA), and mean arterial pressure (MAP) in a dose-dependent manner. A cocktail containing ethanol (1.7 μmol) and kynurenate (KYN), an ionotropic excitatory amino acid receptor blocker, showed significantly blunted sympathoexcitatory and pressor responses compared with those elicited by CeA-injected ethanol alone (P < 0.01). A cocktail containing ethanol and d-2-amino-5-phosphonovalerate, an N-methyl-d-aspartate (NMDA) receptor antagonist, elicited attenuated sympathoexcitatory and pressor responses that were significantly less than ethanol alone (P < 0.01). In addition, CeA injection of acetate (0.20 μmol, n = 7), an ethanol metabolite, consistently elicited sympathoexcitatory and pressor responses, which were effectively blocked by d-2-amino-5-phosphonovalerate (n = 9, P < 0.05). Inhibition of neuronal activity of the rostral ventrolateral medulla (RVLM) with KYN significantly (P < 0.01) attenuated sympathoexcitatory responses elicited by CeA-injected ethanol. Double labeling of immune fluorescence showed NMDA NR1 receptor expression in CeA neurons projecting to the RVLM. We conclude that ethanol and acetate increase sympathetic outflow and arterial pressure, which may involve the activation of NMDA receptors in CeA neurons projecting to the RVLM.

Induction of brain cytochrome P450 2E1 boosts the locomotor-stimulating effects of ethanol in mice

In the central nervous system ethanol (EtOH) is metabolized into acetaldehyde by different enzymes. Brain catalase accounts for 60% of the total production of EtOH-derived acetaldehyde, whereas cerebral cytochrome P450 2E1 (CYP 2E1) produces 20% of this metabolite. Acetaldehyde formed by the activity of central catalase has been implicated in some of the neurobehavioral properties of EtOH, yet the contribution of CYP 2E1 to the pharmacological actions of this drug has not been investigated. Here we assessed the possible participation of CYP 2E1 in the behavioral effects of EtOH. Thus, we induced CYP 2E1 activity and expression by exposing mice to chronic acetone intake (1% v/v for 10 days) and examined its consequences on the stimulating and uncoordinating effects of EtOH (0-3.2 g/kg) injected intraperitoneally. Our data showed that 24 h after withdrawal of acetone brain expression and activity of CYP 2E1 was induced. Furthermore, the locomotion produced by EtOH was boosted over the same interval of time. Locomotor stimulation produced by amphetamine or tert-butanol was unchanged by previous treatment with acetone. EtOH-induced motor impairment as evaluated in a Rota-Rod apparatus was unaffected by the preceding exposure to acetone. These results indicate that cerebral CYP 2E1 activity could contribute to the locomotor-stimulating effects of EtOH, and therefore we suggest that centrally produced acetaldehyde might be a possible mediator of some EtOH-induced pharmacological effects.

Metabolic products of [2-(13) C]ethanol in the rat brain after chronic ethanol exposure

Most ingested ethanol is metabolized in the liver to acetaldehyde and then to acetate, which can be oxidized by the brain. This project assessed whether chronic exposure to alcohol can increase cerebral oxidation of acetate. Through metabolism, acetate may contribute to long-term adaptation to drinking. Two groups of adult male Sprague-Dawley rats were studied, one treated with ethanol vapor and the other given room air. After 3 weeks the rats received an intravenous infusion of [2-(13) C]ethanol via a lateral tail vein for 2 h. As the liver converts ethanol to [2-(13) C]acetate, some of the acetate enters the brain. Through oxidation the (13) C is incorporated into the metabolic intermediate α-ketoglutarate, which is converted to glutamate (Glu), glutamine (Gln), and GABA. These were observed by magnetic resonance spectroscopy and found to be (13) C-labeled primarily through the consumption of ethanol-derived acetate. Brain Gln, Glu, and, GABA (13) C enrichments, normalized to (13) C-acetate enrichments in the plasma, were higher in the chronically treated rats than in the ethanol-naïve rats, suggesting increased cerebral uptake and oxidation of circulating acetate. Chronic ethanol exposure increased incorporation of systemically derived acetate into brain Gln, Glu, and GABA, key neurochemicals linked to brain energy metabolism and neurotransmission. The liver converts ethanol to acetate, which may contribute to long-term adaptation to drinking. Astroglia oxidize acetate and generate neurochemicals, while neurons and glia may also oxidize ethanol. When (13) C-ethanol is administered intravenously, (13) C-glutamine, glutamate, and GABA, normalized to (13) C-acetate, were higher in chronic ethanol-exposed rats than in control rats, suggesting that ethanol exposure increases cerebral oxidation of circulating acetate.

Oxidation of ethanol in the rat brain and effects associated with chronic ethanol exposure

It has been reported that chronic and acute alcohol exposure decreases cerebral glucose metabolism and increases acetate oxidation. However, it remains unknown how much ethanol the living brain can oxidize directly and whether such a process would be affected by alcohol exposure. The questions have implications for reward, oxidative damage, and long-term adaptation to drinking. One group of adult male Sprague-Dawley rats was treated with ethanol vapor and the other given room air. After 3 wk the rats received i.v. [2-(13)C]ethanol and [1, 2-(13)C2]acetate for 2 h, and then the brain was fixed, removed, and divided into neocortex and subcortical tissues for measurement of (13)C isotopic labeling of glutamate and glutamine by magnetic resonance spectroscopy. Ethanol oxidation was seen to occur both in the cortex and the subcortex. In ethanol-naïve rats, cortical oxidation of ethanol occurred at rates of 0.017 ± 0.002 µmol/min/g in astroglia and 0.014 ± 0.003 µmol/min/g in neurons, and chronic alcohol exposure increased the astroglial ethanol oxidation to 0.028 ± 0.002 µmol/min/g (P = 0.001) with an insignificant effect on neuronal ethanol oxidation. Compared with published rates of overall oxidative metabolism in astroglia and neurons, ethanol provided 12.3 ± 1.4% of cortical astroglial oxidation in ethanol-naïve rats and 20.2 ± 1.5% in ethanol-treated rats. For cortical astroglia and neurons combined, the ethanol oxidation for naïve and treated rats was 3.2 ± 0.3% and 3.8 ± 0.2% of total oxidation, respectively. (13)C labeling from subcortical oxidation of ethanol was similar to that seen in cortex but was not affected by chronic ethanol exposure.

Alcohol metabolism

This article describes the pathways and factors that modulate blood alcohol levels and metabolism and describes how the body disposes of alcohol. The various factors that play a role in the distribution of alcohol in the body, influence the absorption of alcohol, and contribute to first-pass metabolism of alcohol are described. Most alcohol is oxidized in the liver, and general principles and overall mechanisms for alcohol oxidation are summarized. The kinetics of alcohol elimination in-vivo and the various genetic and environmental factors that can modify the rate of alcohol metabolism are discussed.

DNA damage and neurotoxicity of chronic alcohol abuse

Chronic alcohol abuse results in a variety of pathological effects including damage to the brain. The causes of alcohol-induced brain pathology are presently unclear. Several mechanisms of pathogenicity of chronic alcoholism have been proposed, including accumulation of DNA damage in the absence of repair, resulting in genomic instability and death of neurons. Genomic instability is a unified genetic mechanism leading to a variety of neurodegenerative disorders. Ethanol also likely interacts with various metabolic pathways, including one-carbon metabolism (OCM). OCM is critical for the synthesis of DNA precursors, essential for DNA repair, and as a methyl donor for various methylation events, including DNA methylation. Both DNA repair and DNA methylation are critical for maintaining genomic stability. In this review, we outline the role of DNA damage and DNA repair dysfunction in chronic alcohol-induced neurodegeneration.

Acetaldehyde oral self-administration: evidence from the operant-conflict paradigm

BACKGROUND

Acetaldehyde (ACD), ethanol's first metabolite, has been reported to interact with the dopaminergic reward system, and with the neural circuits involved in stress response. Rats self-administer ACD directly into cerebral ventricles, and multiple intracerebroventricular infusions of ACD produce conditioned place preference. Self-administration has been largely employed to assess the reinforcing and addictive properties of most drugs of abuse. In particular, operant conditioning is a valid model to investigate drug-seeking and drug-taking behavior in rats.

METHODS

This study was aimed at the evaluation of (i) the motivational properties of oral ACD in the induction and maintenance of an operant-drinking behavior; (ii) ACD effect in a conflict situation employing the punishment-based Geller-Seifter procedure; and (iii) the onset of a relapse drinking behavior, following ACD deprivation. The lever-pressing procedure in a sound-attenuated operant-conditioning chamber was scheduled into 3 different periods: (i) training-rewarded responses with a fixed ratio 1; (ii) conflict-rewarded responses periodically associated with a 0.2 mA foot-shock; and (iii) relapse-rewarded lever presses following 1-week ACD abstinence.

RESULTS

Our results show that oral self-administrated ACD induced: a higher rate of punished responses in Geller-Seifter procedures; and the establishment of a relapse behavior following ACD deprivation.

CONCLUSIONS

In conclusion, our results indicate that ACD is able to induce an operant-drinking behavior, which is also maintained besides the conflict procedure and enhanced by the deprivation effect, supporting the hypothesis that ACD itself possesses motivational properties, such as alcohol and other substances of abuse.

Acetaldehyde elicits ERK phosphorylation in the rat nucleus accumbens and extended amygdala

Recent advances suggest that acetaldehyde mediates some of the neurobiological properties of ethanol. In a recent study, we have shown that ethanol elicits the phosphorylation of extracellular signal-regulated kinase (pERK) in the nucleus accumbens and extended amygdala, via a dopamine D(1) receptor-mediated mechanism. The aim of this study was to determine whether acetaldehyde and ethanol-derived acetaldehyde elicit the activation of ERK in the nucleus accumbens and extended amygdala. The effects of acetaldehyde (10 and 20 mg/kg) and ethanol (1 g/kg), administered to rats intragastrically, were assessed by pERK peroxidase immunohistochemistry. To establish the role of ethanol-derived acetaldehyde, the alcohol dehydrogenase inhibitor, 4-methylpyrazole (90 mg/kg), and the acetaldehyde-sequestering agent, D-penicillamine (50 mg/kg), were administered before ethanol. Acetaldehyde increased pERK immunoreactivity in the nucleus accumbens and extended amygdala. Inhibition of ethanol metabolism and sequestration of newly synthesized acetaldehyde completely prevented ERK activation by ethanol. In addition, to establish the role of D(1) receptors stimulation in acetaldehyde-elicited ERK phosphorylation, we studied the effect of the D(1) receptor antagonist, SCH 39166. Pretreatment with the D(1) receptor antagonist (50 μg/kg) fully prevented acetaldehyde-elicited ERK activation. Overall, these results indicate that ethanol activates ERK by means of its metabolic conversion into acetaldehyde and strengthen the view that acetaldehyde is a centrally acting compound with a pharmacological profile similar to ethanol.

Ethanol as a prodrug: brain metabolism of ethanol mediates its reinforcing effects

BACKGROUND

 While the molecular entity responsible for the rewarding effects of virtually all drugs of abuse is known, that for ethanol remains uncertain. Some lines of evidence suggest that the rewarding effects of alcohol are mediated not by ethanol per se but by acetaldehyde generated by catalase in the brain. However, the lack of specific inhibitors of catalase has not allowed strong conclusions to be drawn about its role on the rewarding properties of ethanol. The present studies determined the effect on voluntary alcohol consumption of two gene vectors, one designed to inhibit catalase synthesis and one designed to synthesize alcohol dehydrogenase (ADH), to respectively inhibit or increase brain acetaldehyde synthesis.

METHODS

 The lentiviral vectors, which incorporate the genes they carry into the cell genome, were (i) one encoding a shRNA anticatalase synthesis and (ii) one encoding alcohol dehydrogenase (rADH1). These were stereotaxically microinjected into the brain ventral tegmental area (VTA) of Wistar-derived rats bred for generations for their high alcohol preference (UChB), which were allowed access to an ethanol solution and water.

RESULTS

 Microinjection into the VTA of the lentiviral vector encoding the anticatalase shRNA virtually abolished (-94% p < 0.001) the voluntary consumption of alcohol by the rats. Conversely, injection into the VTA of the lentiviral vector coding for ADH greatly stimulated (2 to 3 fold p < 0.001) their voluntary ethanol consumption.

CONCLUSIONS

The study strongly suggests that to generate reward and reinforcement, ethanol must be metabolized into acetaldehyde in the brain. Data suggest novel targets for interventions aimed at reducing chronic alcohol intake.

Ethanol as a prodrug: brain metabolism of ethanol mediates its reinforcing effects--a commentary

BACKGROUND

This commentary discusses a study by Karahanian and colleagues (2011) on the role of central nervous system acetaldehyde in the reinforcing effects of ethanol. The goal is to emphasize the importance of the study and to discuss future directions.

RESULTS

This important paper solidifies the idea that the levels of acetaldehyde in the central nervous system have profound effects in mediating the reinforcing actions of ethanol. This is accomplished by manipulating the brain levels of acetaldehyde produced from ethanol by the injection of lentivirus containing either an anti-catalase shRNA construct or a rat liver alcohol dehydrogenase into the central nervous system and observing the effects on alcohol preference by high ethanol-consuming rats. A factor not directly considered is that acetaldehyde is further metabolized to acetate, which also has some behavioral actions.

CONCLUSIONS

The efficacy of lentivirus injections of enzyme inhibitors or enzymes themselves to alter a behavioral response to ethanol is clearly demonstrated here. The many other actions of ethanol that are postulated to be a result of the production of acetaldehyde in the brain remain to be investigated by similar techniques. Possible "therapeutic avenues to reduce chronic alcohol use" are envisioned.

Acetate causes alcohol hangover headache in rats

BACKGROUND

The mechanism of veisalgia cephalgia or hangover headache is unknown. Despite a lack of mechanistic studies, there are a number of theories positing congeners, dehydration, or the ethanol metabolite acetaldehyde as causes of hangover headache.

METHODS

We used a chronic headache model to examine how pure ethanol produces increased sensitivity for nociceptive behaviors in normally hydrated rats.

RESULTS

Ethanol initially decreased sensitivity to mechanical stimuli on the face (analgesia), followed 4 to 6 hours later by inflammatory pain. Inhibiting alcohol dehydrogenase extended the analgesia whereas inhibiting aldehyde dehydrogenase decreased analgesia. Neither treatment had nociceptive effects. Direct administration of acetate increased nociceptive behaviors suggesting that acetate, not acetaldehyde, accumulation results in hangover-like hypersensitivity in our model. Since adenosine accumulation is a result of acetate formation, we administered an adenosine antagonist that blocked hypersensitivity.

DISCUSSION

Our study shows that acetate contributes to hangover headache. These findings provide insight into the mechanism of hangover headache and the mechanism of headache induction.

Human catalase: looking for complete identity

Catalases are well studied enzymes that play critical roles in protecting cells against the toxic effects of hydrogen peroxide. The ubiquity of the enzyme and the availability of substrates made heme catalases the focus of many biochemical and molecular biology studies over 100 years. In human, this has been implicated in various physiological and pathological conditions. Advancement in proteomics revealed many of novel and previously unknown features of this mysterious enzyme, but some functional aspects are yet to be explained. Along with discussion on future research area, this mini-review compile the information available on the structure, function and mechanism of action of human catalase.

Prenatal and postnatal ethanol experiences modulate consumption of the drug in rat pups, without impairment in the granular cell layer of the main olfactory bulb

The effect of moderate exposure to ethanol during late gestation was studied in terms of its interaction with moderate exposure during nursing from an intoxicated dam. A further issue was whether behavioral effects of ethanol, especially the enhanced ethanol intake known to occur after moderate ethanol prenatally or during nursing, depend upon teratological effects that may include death of neurons in the main olfactory bulb (MOB). During gestational days 17-20 rats were given 0, 1 or 2g/kg ethanol doses intragastrically (i.g.). After parturition these dams were given a dose of 2.5g/kg ethanol i.g. each day and allowed to perform regular nursing activities. During postnatal days (PDs) 15 and 16, ethanol intake of pups was assessed along with aspects of their general activity. In a second experiment pups given the same prenatal treatment as above were tested for blood ethanol concentration (BEC) in response to an ethanol challenge on PD6. A third experiment (Experiment 2b) assessed stereologically the number of cells in the granular cell layer of the MOB on PD7, as a function of analogous pre- and postnatal ethanol exposures. Results revealed that ethanol intake during the third postnatal week was increased by prenatal as well as postnatal ethanol exposure, with a few interesting qualifications. For instance, pups given 1g/kg prenatally did not have increased ethanol intake unless they also had experienced ethanol during nursing. There were no effects of ethanol on either BECs or conventional teratology (cell number). This increases the viability of an explanation of the effects of prenatal and early postnatal ethanol on later ethanol intake in terms of learning and memory.

Systemic administration of D-penicillamine prevents the locomotor activation after intra-VTA ethanol administration in rats

Although recently published studies seem to confirm the important role displayed by acetaldehyde (ACH), the main metabolite of ethanol, in the behavioral effects of ethanol, the origin of ACH is still a matter of debate. While some authors confer more importance to the central (brain metabolism) origin of ACH, others indicate that the hepatic origin could be more relevant. In this study we have addressed this topic using an experimental approach that combines local microinjections of ethanol into the ventral tegmental area (VTA) (which guarantees the brain origin of the ACH) to induce motor activation in rats together with systemic administration (i.p.) of several doses (0, 12.5, 25 and 50 mg/kg) of D-penicillamine (DP), a sequestering agent of ACH with contrasted efficiency to abolish the behavioral effects of the drug. Our results clearly show that DP prevented in a dose-dependent manner the motor activation induced by intra-VTA ethanol, being the 50 mg/kg dose the most efficient. DP per se did not affect the basal activity of the rats. In order to determine the specificity of the DP action, we also studied the effects of DP 50 mg/kg on the DAMGO-induced motor activation after the intra-VTA administration of this mu-opioid receptors agonist. DP did not significantly modify the motor activation induced by DAMGO thus confirming the specificity of the DP effects. Our results clearly suggest that the brain-derived ACH is necessary to manifest the activating effects resulting from ethanol administration.

The role of acetaldehyde in human psychomotor function: a double-blind placebo-controlled crossover study

BACKGROUND

Acetaldehyde, the first product of ethanol metabolization, is a biologically active compound, but the behavioral properties of acetaldehyde in humans are largely undefined. We investigated the acute effects of both alcohol and acetaldehyde on psychomotor functions related to automobile driving skills.

METHODS

Twenty-four men were selected through genotyping; one-half had the ALDH2*1/*1 (active form) genotype and one-half had the ALDH2*1/*2 (inactive form) genotype. In a double-blind placebo-controlled crossover design, each subject was administered one of the following doses of alcohol: .25 g/kg, .5 g/kg, or .75 g/kg or a placebo in four trials that took place at 1-week intervals. Blood ethanol concentration (BEC) and blood acetaldehyde concentration (BAAC) were measured nine times, and psychomotor function tests (critical flicker fusion threshold, choice reaction time, compensatory tracking task, and digit symbol substitution test) were assessed seven times in total over 4 hours after study drug ingestion.

RESULTS

After the consumption of alcohol, BEC was comparable in the two subject groups, whereas BAAC was significantly higher in subjects with ALDH2 *1/*2 than in those with ALDH2 *1/*1. The psychomotor performance of subjects with ALDH2*1/*2 was significantly poorer than that of subjects with ALDH2*1/*1. Significant correlations between psychomotor performance and both BEC and BAAC were observed. However, in the linear regression analysis, BAAC significantly predicted poorer psychomotor performance, whereas BEC was not associated with any measure of psychomotor function.

CONCLUSIONS

Acetaldehyde might be more important than alcohol in determining the effects on human psychomotor function and skills.

Ethanol modulates corticotropin releasing hormone release from the rat hypothalamus: does acetaldehyde play a role?

BACKGROUND AND METHODS

Ethanol (EtOH) activates hypothalamic-pituitary-adrenal (HPA) axis, resulting in adrenocorticotropin hormone, glucocorticoid release, and in modifications of the response of the axis to other stressors. The initial site of EtOH action within the HPA system seems to be the hypothalamus. Thus, to determine the mechanisms responsible for these effects, we investigated: (i) whether EtOH was able to release corticotrophic releasing hormone (CRH) from incubated hypothalamic explants; (ii) whether acetaldehyde (ACD), its first metabolite formed in the brain by catalase activity, might play a role in EtOH activity. To this aim, rat hypothalamic explants were incubated with: (i) medium containing EtOH at 32.6 x 10(3) microM; (ii) different concentration of ACD (1, 3, 10, and 30 microM); (iii) EtOH plus 3amino-1,2,4-triazole (3AT, 32 x 10(3) microM) an inhibitor of cerebral catalase; (iv) ACD plus D-penicillamine (DP, 50.3 x 10(3) microM) an ACD-trapping agent. CRH levels were evaluated by a radioimmunoassay.

RESULTS

Incubation with EtOH induced a 7-fold increase in CRH secretion, with respect to basal levels; ACD was able to stimulate CRH release in a dose-dependent manner; the inhibition of cerebral catalase by 3AT blocked EtOH-induced CRH outflow; the inactivation of ACD by DP reverted the ACD-stimulating effect on CRH secretion.

CONCLUSIONS

These data show that both EtOH and acetaldehyde are able to increase hypothalamic CRH release from the rat hypothalamus and that acetaldehyde itself appears to be the mediator of EtOH activity.

The reinforcing properties of salsolinol in the ventral tegmental area: evidence for regional heterogeneity and the involvement of serotonin and dopamine

BACKGROUND

Salsolinol (SAL), the condensation product of acetaldehyde and dopamine, may be a factor contributing to alcohol abuse. Previous research indicated that both ethanol and acetaldehyde are self-administered into the posterior ventral tegmental area (VTA). The current study examined SAL self-infusions into the VTA, and determined the involvement of dopamine neurons and 5-HT3 receptors in this process.

METHODS

The intracranial self-administration technique was used to determine the self-infusion of SAL into the VTA of adult, male Wistar rats. The rats were placed in 2-lever (active and inactive) experimental chambers, and allowed to respond for the self-infusion of 0, 0.03, 0.1, 0.3, 1.0 or 3.0 microM SAL into the posterior or anterior VTA. In a second experiment, rats self-administered 0.3 microM SAL for the initial 4 sessions, co-administered SAL with ICS-205,930 (a 5-HT3 receptor antagonist) or quinpirole (a D(2,3) receptor agonist) for sessions 5 and 6, and then only 0.3 microM SAL for session 7.

RESULTS

Wistar rats, given 0.03 to 0.3 microM SAL, received more infusions per session than did the group given artificial cerebrospinal fluid (aCSF) alone (e.g., 41 infusions for 0.1 microM SAL versus 9 infusions for the aCSF group), and responded more on the active than inactive lever. These effects were observed in the posterior but not in anterior VTA. Co-infusion of 100 microM ICS-205,930, or quinpirole significantly reduced self-infusions and active lever responding.

CONCLUSIONS

SAL produces reinforcing effects in the posterior VTA of Wistar rats, and these effects are mediated by activation of DA neurons and local 5-HT3 receptors.

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.

Ethanol oxidation in the living brain

AIM

The examination of the possibility of ethanol oxidation in the brain in vivo and the evaluation of the enzyme catalase in this process.

METHODS

We anesthetized rats and perfused the brain with ethanol solutions through the lateral ventricle and collected the perfusate from the Cisterna magna. We determined ethanol and acetaldehyde in the perfusate by gas chromatography.

RESULTS

It was found that the passage of ethanol solution (85 and 90 mM) through the ventricular system of the rat brain (6-43 microl/min) results in the significant (up to 98%) elimination of ethanol from the perfusing fluid and in the appearance of acetaldehyde (up-to 60 microM) in the perfusate. The addition of the catalase inhibitor, aminotriazole, (10 mM) to the perfusing fluid decreased ethanol elimination significantly.

CONCLUSIONS

The ethanol oxidation and AA accumulation take place in the living brain. The enzyme catalase is involved in this process.

A novel method for evaluation of ethanol oxidation in living brain

We propose a method for intravital examination of ethanol metabolism in rat brain. Calipsol-anesthetized rats were fixed in stereotaxis and ethanol solution was infused into the lateral cerebral ventricle via an orifice in the skull at a constant rate with a syringe or micro-pump. Elimination of ethanol and production of acetaldehyde (ethanol metabolite) were measured in perfusate samples from the cisterna magna by gas chromatography. The method is highly sensitive, reliable, and reproducible and allows to study the kinetics and enzyme mechanisms of ethanol oxidation in the brain and regulation of this process.

Ethanol and acetaldehyde induce similar changes in extracellular levels of glutamate, taurine and GABA in rat anterior cingulate cortex

It is controversial regarding to the roles of acetaldehyde and ethanol in the central nervous system. In the present study, the effects of acetaldehyde and ethanol on extracellular levels of glutamate, taurine and GABA in the anterior cingulate cortex (ACC) of freely moving rats were investigated by using the microdialysis technique coupled to high performance liquid chromatography (HPLC) with fluorescent detection. The result showed that glutamate levels were significantly decreased after acute administration of acetaldehyde (AcH, 20 and 100 mg/kg, i.p.), while taurine levels were significantly increased after the higher dose of acetaldehyde (100 mg/kg, i.p.). GABA levels had no changes at any doses of acetaldehyde tested. Interestingly, similar changes of these amino acids were induced by ethanol (EtOH, 3 g/kg, i.p.) when sodium azide (NaN3, 10 mg/kg, i.p.), a catalase inhibitor that can reduce brain ethanol metabolism, was used simultaneously. These findings suggest that acetaldehyde and ethanol have the similar effects on the extracellular output of glutamate, taurine and GABA in the ACC.

Developing master keys to brain pathology, cancer and aging from the structural biology of proteins controlling reactive oxygen species and DNA repair

This review is focused on proteins with key roles in pathways controlling either reactive oxygen species or DNA damage responses, both of which are essential for preserving the nervous system. An imbalance of reactive oxygen species or inappropriate DNA damage response likely causes mutational or cytotoxic outcomes, which may lead to cancer and/or aging phenotypes. Moreover, individuals with hereditary disorders in proteins of these cellular pathways have significant neurological abnormalities. Mutations in a superoxide dismutase, which removes oxygen free radicals, may cause the neurodegenerative disease amyotrophic lateral sclerosis. Additionally, DNA repair disorders that affect the brain to various extents include ataxia-telangiectasia-like disorder, Cockayne syndrome or Werner syndrome. Here, we highlight recent advances gained through structural biochemistry studies on enzymes linked to these disorders and other related enzymes acting within the same cellular pathways. We describe the current understanding of how these vital proteins coordinate chemical steps and integrate cellular signaling and response events. Significantly, these structural studies may provide a set of master keys to developing a unified understanding of the survival mechanisms utilized after insults by reactive oxygen species and genotoxic agents, and also provide a basis for developing an informed intervention in brain tumor and neurodegenerative disease progression.

Enzymatic mechanisms of ethanol oxidation in the brain

BACKGROUND

The exact enzymatic mechanisms of ethanol oxidation in the brain are still unclear. The catalase-mediated oxidation of ethanol was demonstrated in rat brain using incubation of brain homogenates with catalase inhibitors. The role of the alcohol dehydrogenase (ADH) or cytochrome P450-dependent system in this process is possible, but has not been confirmed. The objective of the study was to determine the contribution of the different enzymatic pathways to ethanol oxidation in brain homogenates from mice and rats.

METHODS

Three approaches were used to investigate the enzymatic mechanisms of ethanol oxidation in the brain of rats and mice: (1) preincubation of brain homogenates with inhibitors of the ethanol-metabolizing enzymes (catalase, CYP2E1, ADH, and ALDH); (2) utilization of mice with genetic deficiency in ethanol-metabolizing enzymes (catalase, CYP2E1, or both enzymes); and (3) determination of ethanol oxidation in brain subcellular fractions known to have differential activity of ethanol-metabolizing enzymes. The ethanol-derived acetaldehyde (AC) and acetate were determined in brain samples by gas chromatography.

RESULTS

The catalase inhibitors sodium azide (5 mM) and aminotriazole (5 mM) as well as CYP2E1 inhibitors diallyl sulfide (2 mM) and beta-phenethyl isothiocyanate (0.1 mM) lowered significantly the accumulation of the ethanol-derived AC and acetate in brain homogenates. The ADH inhibitor 4-methyl pyrazole (5 mM) significantly decreased the acetate but not the AC accumulation. Ethanol-derived AC accumulation in brain homogenates of acatalasemic mice was 47% of the control value, 91% in CYP2E1-null mice, and 24% in double mutants (with deficiency of both catalase and CYP2E1). The highest levels of ethanol oxidation were found in microsomal and peroxisomal subcellular brain fractions, where CYP2E1 and catalase are located, respectively.

CONCLUSIONS

Catalase is the key enzyme of ethanol oxidation in the brain of rodents: it may be responsible for about 60% of the process. CYP2E1 plays an important role in ethanol oxidation in the rodent brains. Alcohol dehydrogenase plays a minor role, if any, in this process. Aldehyde dehydrogenase plays the crucial role in the further oxidation of ethanol-derived AC in the brain homogenates.

Does ascorbate/L-Cys/L-Met mixture protect different parts of the rat brain against chronic alcohol toxicity?

Chronic ingestion of high levels of alcohol may cause oxidative stress that results in the formation, through alcohol metabolism, of excess free radicals, acetaldehyde, lipid and protein oxidation, and their reactivity products. These harmful molecules may trigger oxidative damage to neurons and can cause cell death. It is hypothesized that cysteine-methionine and vitamin C may neutralize these harmful compounds while potentiating the antioxidant capacity of the cell or tissue. In the present study, rats were fed regular diets and were maintained for 90 days in (1) the control group, (2) the alcoholic group, which was given 2.5 g of 50% ethanol/kg body weight administered intragastrically every other day, or (3) the alcoholic with antioxidant supplement group, to whom 2.5 g of 50% ethanol/kg body weight + a solution that contained 200 mg vitamin C, 100 mg cysteine, and 100 mg methionine was administered intragastrically every other day. The mean blood alcohol level was raised by 40% in the alcoholic group compared with the control group, but, compared with the alcoholic group, the alcohol level was decreased by 30% in the antioxidant-supplemented group. In keeping with blood alcohol levels, oxidized protein and lipid content in the cerebrum, brain stem, and cerebellum were low in the control group, higher in the antioxidant-supplemented group, and highest in the alcoholic group. The mean total thiol level was higher in the antioxidant-supplemented group than in the alcoholic and control groups. It is interesting to note that the level of total glutathione in the cerebrum and cerebellum in the alcoholic group was lower than in the control and antioxidant-supplemented groups. In conclusion, long-term alcohol administration led to increased levels of oxidized protein and lipids in the cerebrum, brain stem, and cerebellum of rats. Simultaneous intake of ascorbate/l-cys/l-met and ethanol attenuated the amount of oxidation that occurred, which suggested that cysteine, methionine, and vitamin C may play a protective role in the central nervous system against oxidative damage caused by alcohol consumption. In addition, the mean alcohol level was increased in the alcoholic group compared with the control group. The level of total glutathione was significantly decreased in the cerebellum of the alcoholic group, and oxidative damage was noted in various parts of the brain in this group. These findings suggest that oxidative stress plays a pathogenetic role in brain damage related to chronic alcoholism.

The UChA and UChB rat lines: metabolic and genetic differences influencing ethanol intake

Ethanol non-drinker (UChA) and drinker (UChB) rat lines derived from an original Wistar colony have been selectively bred at the University of Chile for over 70 generations. Two main differences between these lines are clear. (1) Drinker rats display a markedly faster acute tolerance than non-drinker rats. In F2 UChA x UChB rats (in which all genes are 'shuffled'), a high acute tolerance of the offspring predicts higher drinking than a low acute tolerance. It is further shown that high-drinker animals 'learn' to drink, starting from consumption levels that are one half of the maximum consumptions reached after 1 month of unrestricted access to 10% ethanol and water. It is likely that acquired tolerance is at the basis of the increases in ethanol consumption over time. (2) Non-drinker rats carry a previously unreported allele of aldehyde dehydrogenase-2 (Aldh2) that encodes an enzyme with a low affinity for Nicotinamide-adenine-dinuclectide (NAD+) (Aldh2(2)), while drinker rats present two Aldh2 alleles (Aldh2(1) and Aldh2(3)) with four- to fivefold higher affinities for NAD+. Further, the ALDH2 encoded by Aldh2(1) also shows a 33% higher Vmax than those encoded by Aldh2(2) and Aldh2(3). Maximal voluntary ethanol intakes are the following: UChA Aldh2(2)/Aldh2(2) = 0.3-0.6 g/kg/day; UChB Aldh2(3)/Aldh2(3) = 4.5-5.0 g/kg/day; UChB Aldh2(1)/Aldh2(1) = 7.0-7.5 g/kg/day. In F2 offspring of UChA x UChB, the Aldh2(2)/Aldh2(2) genotype predicts a 40-60% of the alcohol consumption. Studies also show that the low alcohol consumption phenotype of Aldh2(2)/Aldh2(2) animals depends on the existence of a maternally derived low-activity mitochondrial reduced form of nicotinamide-adenine-dinucleotide (NADH)-ubiquinone complex I. The latter does not influence ethanol consumption of animals exhibiting an ALDH2 with a higher affinity for NAD+. An illuminating finding is the existence of an 'acetaldehyde burst' in animals with a low capacity to oxidize acetaldehyde, being fivefold higher in UChA than in UChB animals. We propose that such a burst results from a great generation of acetaldehyde by alcohol dehydrogenase in pre-steady-state conditions that is not met by the high rate of acetaldehyde oxidation in mitochondria. The acetaldehyde burst is seen despite the lack of differences between UChA and UChB rats in acetaldehyde levels or rates of alcohol metabolism in steady state. Inferences are drawn as to how these studies might explain the protection against alcoholism seen in humans that carry the high-activity alcohol dehydrogenase but metabolize ethanol at about normal rates.

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.

Voluntary ethanol consumption decreases after the inactivation of central acetaldehyde by d-penicillamine

Acetaldehyde, the first metabolite of ethanol, may mediate some ethanol-induced effects. Previous research in our laboratory has shown that D-penicillamine, an inactivation agent for acetaldehyde, is effective in decreasing locomotor stimulation and conditioned place preference induced by ethanol in mice. In the present study, the effects of D-penicillamine on the voluntary consumption of ethanol were assessed. Male rats were offered ethanol under restricted access, without food or water deprivation. Daily availability of ethanol was limited to a 15-min period in the home cages. When the response for 10% ethanol was stable, rats received an intraperitoneal (IP) injection of D-penicillamine (0, 25, 50 or 75 mg/kg) over a 5-day period, given 30 min before exposure to ethanol. In a second study we determined the specificity of D-penicillamine effects (50 mg/kg) on voluntary sucrose consumption (3%). Another study was conducted to evaluate whether IP D-penicillamine (50 mg/kg) alters taste reactivity responses. In the final experiment, rats were treated with intracerobroventricular (ICV) infusions of D-penicillamine (75 microg) for 5 days before drinking ethanol or sucrose. D-Penicillamine was found to reduce ethanol intake in a dose-dependent manner. Sucrose consumption was also affected by this thiol amino acid. We also demonstrated that D-penicillamine produced changes in the ingestive and flavor properties of sucrose and ethanol, measured by means of a taste reactivity test. When D-penicillamine was administered ICV, only voluntary ethanol consumption was modified. These findings indicate that the central inactivation of acetaldehyde blocks ethanol intake in rats, and suggest that acetaldehyde plays a key role in the motivational properties of ethanol.

Is ethanol a pro-drug? Acetaldehyde contribution to brain ethanol effects

This article presents the proceedings of a symposium at the 2004 meeting of the International Society for Biomedical Research on Alcoholism, held in Mannheim, Germany. The symposium was organized by Etienne Quertemont and chaired by C. J. Peter Eriksson. The presentations were (1) Brain ethanol metabolism and its behavior consequences, by Sergey M. Zimatkin and P. S. Pronko; (2) Acetaldehyde increases dopaminergic neuronal activity: a possible mechanism for acetaldehyde reinforcing effects, by Marco Diana and Milena Pisano; (3) Contrasting the reinforcing actions of acetaldehyde and ethanol within the ventral tegmental area (VTA) of alcohol-preferring (P) rats, by Zachary A. Rodd and Richard R. Bell; (4) Molecular and biochemical changes associated with acetaldehyde in human alcoholism and alcohol abuse, by C. J. Peter Eriksson.

Brain catalase mediates potentiation of social recognition memory produced by ethanol in mice

The involvement of catalase in ethanol-induced locomotion has been clearly proven. However, studies addressing the role of this enzyme in the effects that ethanol exerts on memory are lacking. In the present study, the social recognition test (SRT) was used to evaluate ethanol effects on memory. In this test, the reduction in investigation time of a juvenile conspecific, when this social stimulus is presented for the second time, is considered a reliable index of memory. Exploration ratios (ER) were calculated to evaluate the recognition capacity of mice. Ethanol (0.0, 0.5, 1.0 or 1.5g/kg, i.p.) was administered immediately after the first juvenile presentation, and 2h later the juvenile was re-exposed to the adult. Additionally, adult mice received aminotriazole (AT) or sodium azide (two catalase inhibitors) 5h or 30 min before juvenile presentation, respectively. Ethanol (1.0 and 1.5g/kg) was able to reduce ER, indicating an improving effect on memory. This improvement was prevented by either AT or sodium azide pre-treatment. However, neither AT nor sodium azide attenuated the memory-enhancing capacity of NMDA or nicotine, suggesting a specific interaction between catalase inhibitors and ethanol in their effects on memory. The present results suggest that brain catalase activity could mediate the memory-enhancing capacity of ethanol and add further support to the idea that this enzyme mediates some of the psychopharmacological effects produced by ethanol.

CHRONIC CONSUMPTION OF ETHANOL LEADS TO SUBSTANTIAL CELL DAMAGE IN CULTURED RAT ASTROCYTES IN CONDITIONS PROMOTING ACETALDEHYDE ACCUMULATION

AIMS

This study aimed at comparing the cerebral cytotoxicity of ethanol and its main metabolite acetaldehyde after acute or chronic exposures of rat astrocytes in primary culture.

METHODS

Cytotoxicity was evaluated on the cell reduction of viability (MTT reduction test) and on the characterization of DNA damage by single cell gel electrophoresis (or comet assay).

RESULTS

Changes in astrocyte survival and in DNA integrity only occurred when the astrocytes were chronically exposed to ethanol (20 mM; 3, 6 or 9 days). On the other hand, viability and DNA integrity were deeply affected by acute exposure to acetaldehyde. Both effects were dependent on the concentration of acetaldehyde. The cytotoxic effect of acetaldehyde was also indirectly evaluated after modifications of the normal ethanol metabolism by the use of different inducers or inhibitors. In presence of ethanol, the concomitant induction of catalase (i.e. by glucose oxidase) and inhibition of aldehyde dehydrogenase (i.e. by methylene blue) led to acetaldehyde accumulation within cells. It was followed by both a reduction in viability and a substantial increase in DNA strand breaks.

CONCLUSIONS

These data were thus consistent with a possible predominant role of acetaldehyde during brain ethanol metabolism. On the other hand, the effects observed after AMT could also suggest a possible direct ethanol effect and a role for free radical attacks. These data were thus consistent with a possible predominant role of acetaldehyde during brain ethanol metabolism. On the other hand, the effects observed after AMT could also suggest a possible direct ethanol effect and a role for free radical attacks.

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.

Inhibition of acetaldehyde metabolism decreases acetylcholine release in medial frontal cortex of freely moving rats

The effect of high acetaldehyde (ACe) on acetylcholine (ACh) release was studied in vivo in the medial frontal cortex (mfc) of freely moving rats using brain microdialysis coupled with high performance liquid chromatography and an electrochemical detector. Ethanol (EtOH) and ACe concentrations were quantified simultaneously in the mfc of awake rats by in vivo microdialysis followed by head-space gas chromatography. Rats were treated intraperitoneally with saline, EtOH (1 and 2 g/kg) or cyanamide (CY, 50 mg/kg, a potent aldehyde dehydrogenase inhibitor) plus EtOH (1 and 2 g/kg). No significant effect on ACh levels was observed in saline groups, as compared to baseline value. The basal level of ACh in the dialysate was about 0.30 +/- 0.04 pmol/20 microl, and this value was reduced significantly in the EtOH (1 and 2 g/kg) and CY + EtOH (1 and 2 g/kg) groups for 240 min after EtOH administration. The time courses of ACh release continued to decrease significantly after EtOH administration in the CY + EtOH (1 and 2 g/kg) groups compared to the values in the saline and EtOH (1 and 2 g/kg) groups. A significant decrease in ACh release was observed from 140 to 240 min after EtOH dosing in the EtOH (1 and 2 g/kg) groups, as compared to saline groups. EtOH and ACe concentrations in the mfc were first determined at 15 min after a dose of EtOH, reached a peak at 30 min and then gradually decreased in the CY + EtOH (1 and 2 g/kg) groups. The present study suggests that both EtOH and ACe concentration in the brain can decrease in vivo ACh release in the mfc of free-moving rats, and the ACe-induced decrease in ACh levels was significantly higher than EtOH.

Regional heterogeneity for the intracranial self-administration of ethanol and acetaldehyde within the ventral tegmental area of alcohol-preferring (P) rats: involvement of dopamine and serotonin

The meso-limbic dopamine (DA) system has an important role in regulating alcohol drinking. Previous findings from our laboratory indicated that Wistar rats self-administered ethanol (EtOH) directly into the posterior, but not anterior, ventral tegmental area (VTA), and that coadministration of a DA D(2,3) receptor agonist or a serotonin-3 (5-HT3) receptor antagonist blocked EtOH self-administration. In addition, we reported that alcohol-preferring (P) rats self-administered acetaldehyde (ACD), the first metabolite of EtOH, into the posterior VTA. The objectives of this study were to compare the reinforcing effects of EtOH and ACD within the VTA of P rats to examine the possibility that the reinforcing effects of EtOH within the VTA may be mediated by its conversion to ACD. Adult female P rats were stereotaxically implanted with guide cannulae aimed at either the posterior or anterior VTA. At 1 week after surgery, rats were placed in standard two-lever (active and inactive) experimental chambers for a total of seven to eight sessions. The 4-h sessions were conducted every other day. The results indicated that (a) 75-300 mg% (17-66 mM) EtOH and 6-90 microM ACD were self-administered into the posterior, but not anterior, VTA; (b) the self-administration of 150 mg% EtOH was not altered by coinfusion of a catalase inhibitor; (c) coadministration of the D(2/3) agonist quinpirole (100 microM) blocked the self-infusions of 150 mg% EtOH and 23 microM ACD into the posterior VTA; and (d) coadministration of 200 microM ICS205,930 (5-HT3 receptor antagonist) prevented the self-infusion of 150 mg% EtOH, whereas concentrations of ICS 205,930 up to 400 microM had no effect on the self-infusion of 23 microM ACD into the posterior VTA. Overall, the results of this study indicate that EtOH and ACD can independently produce reinforcing effects within the posterior VTA, and that activation of DA neurons mediates these effects. Furthermore, activation of 5-HT3 receptors within the posterior VTA is involved in the self-infusion of EtOH, but not ACD.

The Role of Acetaldehyde in the Central Effects of Ethanol

This article represents the proceedings of a symposium at the 2004 annual meeting of the Research Society on Alcoholism in Vancouver, Canada. The symposium was organized by Etienne Quertemont and chaired by Kathleen A. Grant. The presentations were (1) Behavioral stimulant effects of intracranial injections of ethanol and acetaldehyde in rats, by Mercè Correa, Maria N. Arizzi and John D. Salamone; (2) Behavioral characterization of acetaldehyde in mice, by Etienne Quertemont and Sophie Tambour; (3) Role of brain catalase and central formed acetaldehyde in ethanol's behavioral effects, by Carlos M.G. Aragon; (4) Contrasting the reinforcing actions of acetaldehyde and ethanol within the ventral tegmental area (VTA) of alcohol-preferring (P) rats, by William J. McBride, Zachary A. Rodd, Avram Goldstein, Alejandro Zaffaroni and Ting-Kai Li; and (5) Acetaldehyde increases dopaminergic transmission in the limbic system, by Milena Pisano and Marco Diana.

An Expanded Evaluation of the Relationship of Four Alleles to the Level of Response to Alcohol and the Alcoholism Risk

BACKGROUND

Alcoholism is a complex, genetically influenced disorder the cause of which may be better understood through the study of genetically influenced phenotypes that mediate the risk. One such intermediate phenotype is the low level of response (LR) to alcohol. This project used a case-control approach to search for genes that may contribute to LR.

METHODS

Data were available from alcohol challenges at approximately age 20 and regarding the development of alcohol use disorders over the subsequent 20 years for 85 men, including 40 reported in a previous genetic analysis. LR was evaluated using oral consumption of 0.75 ml/kg of alcohol, after which changes in subjective feelings of intoxication and body sway were measured. Alcohol abuse and dependence were diagnosed by DSM-III-R criteria through structured interviews administered to both the participant and an informant (usually the spouse) 10, 15, and 20 years after initial testing. Four polymorphisms were evaluated, including the serotonin transporter HTTLPR promoter ins/del, GABAAalpha6 Pro385Ser, NPY Leu7Pro, and catalase 262C>T. Two of these, HTTLPR and GABAAalpha6 Pro385Ser, had been previously associated with LR and alcoholism in a preliminary study.

RESULTS

The HTTLPR L allele was significantly related to both the LR and alcoholism in an allele-dosage (stepwise) manner. Furthermore, the association remained when L alleles were subdivided into recently reported functional subtypes: the lowest LR was associated with genotypes correlated with the highest serotonin transporter expression. The GABAAalpha6 Ser385 allele showed a nonsignificant trend for association to a low LR, as had been previously observed, although the Ser385 allele is uncommon, and only 18 heterozygotes were in the current group. However, the six men with both LL and Pro385/Ser385 genotypes had the lowest LR, and each had developed alcoholism during follow-up. Neither NPY nor catalase was associated with either LR or alcoholic outcomes, although the sample did not have sufficient power for definitive conclusions.

CONCLUSIONS

This report strengthens the support for a relationship between the HTTLPR L and GABAAalpha6 Ser385 alleles to low alcohol LR and to alcoholism in a prospectively studied cohort evaluated for LR in young adulthood and before the onset of alcohol dependence.

Behavioral characterization of acetaldehyde in C57BL/6J mice: locomotor, hypnotic, anxiolytic and amnesic effects

RATIONALE

Acetaldehyde, the first metabolite of ethanol, was recently suggested to contribute to many behavioral effects of ethanol, although few studies have directly investigated the behavioral effects of acetaldehyde itself.

OBJECTIVES

The aim of the present study was to characterize the locomotor, hypnotic, anxiolytic-like and amnesic effects of acetaldehyde in C57BL/6J mice.

METHODS

Increasing doses of acetaldehyde (0-300 mg/kg) were injected intraperitoneally and their effects on a series of representative behaviors were investigated. The locomotor effects of acetaldehyde were measured in activity boxes. The duration of the loss of righting reflex was used as an index of the hypnotic effects of acetaldehyde. The anxiolytic-like effects of acetaldehyde were tested with an elevated plus-maze and the amnesic effects with the one-trial passive avoidance test. Finally, brain and blood acetaldehyde concentrations were assessed.

RESULTS

Acetaldehyde induced a significant hypolocomotor effect at 170 mg/kg and higher doses. In addition, the hypnotic effects of acetaldehyde were demonstrated by a loss of righting reflex after the administration of 170 and 300 mg/kg acetaldehyde. The elevated plus-maze showed that acetaldehyde does not possess anxiolytic-like properties. Finally, acetaldehyde (100-300 mg/kg) dose-dependently altered memory consolidation as shown by a reduced performance in the passive avoidance test.

CONCLUSIONS

The present results show that acetaldehyde induces sedative, hypnotic and amnesic effects, whereas it is devoid of stimulant and anxiolytic-like properties in C57BL/6J mice. However, the behavioral effects of acetaldehyde after intraperitoneal administration were apparent at very high brain concentrations. The present results also indicate that acetaldehyde is unlikely to be involved in the anxiolytic properties of ethanol in mice.

The Search for Genes Contributing to the Low Level of Response to Alcohol: Patterns of Findings Across Studies

BACKGROUND

Alcoholism is a complex genetically influenced disorder in which multiple phenotypes [e.g., disinhibition, alcohol-metabolizing patterns, and the low level of response (LR) to alcohol] contribute to the risk. A low LR to alcohol is one of the more thoroughly studied risk phenotypes; data indicate that LR relates to the risk status, predicts future alcoholism, and has a heritability as high as 60%. This article reviews data from animal and human studies regarding the LR to alcohol, searching for a convergence of results that might lead to the identification of relevant genes.

METHODS

A literature search was performed regarding animal and human genetic studies focusing on genes that might affect the LR to alcohol as a risk factor for alcoholism. The goal was to synthesize these results and highlight potential patterns.

RESULTS

Focusing on both genetic linkage and association studies, a number of chromosomal regions and genes potentially relevant to findings across two or more sources were identified. The genes of potential interest fell into several categories, including second-messenger systems (e.g., G proteins, adenylyl cyclase, and protein kinases); neurotransmitters or drug-related receptors (e.g., gamma-aminobutyric acid-A, glutamate, serotonin, and cannabinoid and opioid receptors); genes that affect alcohol metabolism; and genes that might relate to an overlap in the risk for alcoholism and some psychiatric conditions (e.g., catechol-O-methyltransferase regarding schizophrenia and bipolar disorder).

CONCLUSIONS

The review identifies several genes that may contribute to a low LR to alcohol and, thus, to an increased risk for alcohol use disorders. The chromosomal regions and genes highlighted here may form the basis for more focused genetic studies of alcohol use disorders, with the goals of developing more specific and effective prevention and treatment approaches.

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.

The Unique Regulation of Brain Cytochrome P450 2 (CYP2) Family Enzymes by Drugs and Genetics

Cytochrome P450 (CYP) enzymes in the brain may have a role in the activation or inactivation of centrally acting drugs, in the metabolism of endogenous compounds, and in the generation of damaging toxic metabolites and/or oxygen stress. CYPs are distributed unevenly among brain regions, and are found in neurons, glial cells and at the blood-brain interface. They have been observed in mitochondrial membranes, in neuronal processes and in the plasma membrane, as well as in endoplastic reticulum. Brain CYPs are inducible by many common hepatic inducers, however many compounds affect liver and brain CYP expression differently, and some CYPs which are constitutively expressed in liver are inducible in brain. CYP induction is isozyme-, brain region-, cell type- and inducer-specific. While it is unlikely that brain CYPs contribute to overall clearance of xenobiotics, their punctate, region- and cell-specific expression suggests that CNS CYPs may create micro-environments in the brain with differing drug and metabolite levels (not detected or predicted by plasma drug monitoring). Coupled with the sensitivity of CNS CYPs to induction, this may in part account for inter-individual variation in response to centrally acting drugs and neurotoxins, and may have implications for individual variation in receptor adaptation and cross-tolerance to different drugs. In addition, genetic variation in brain CYPs, depending on the type of polymorphism (structural versus regulatory), will alter enzyme activity. These aspects of brain CYP expression regulation and genetic influences are illustrated in this review using mRNA, protein, and enzyme activity data for CYP2D1/6, CYP2E1 and CYP2B1/6 in rat and human brain. The role of CYP-mediated metabolism in the brain, a highly heterogeneous and complex organ, is a new and relatively unexplored field of scientific enquiry. It holds promise for furthering our undestanding of inter-individual variability in response to centrally acting drugs as well as risk for neurological diseases and pathogies.