Ethanol metabolism in the brain

A critical review of ethanol effects on neuronal firing: A metabolic perspective

Ethanol metabolism is relatively understudied in neurons, even though changes in neuronal metabolism are known to affect their activity. Recent work demonstrates that ethanol is preferentially metabolized over glucose as a source of carbon and energy, and it reprograms neurons to a state of reduced energy potential and diminished capacity to utilize glucose once ethanol is exhausted. Ethanol intake has been associated with changes in neuronal firing and specific brain activity (EEG) patterns have been linked with risk for alcohol use disorder (AUD). Furthermore, a haplotype of the inwardly rectifying potassium channel subunit, GIRK2, which plays a critical role in regulating excitability of neurons, has been linked with AUD and shown to be directly regulated by ethanol. At the same time, overexpression of GIRK2 prevents ethanol-induced metabolic changes. Based on the available evidence, we conclude that the mechanisms underlying the effects of ethanol on neuronal metabolism are a novel target for developing therapies for AUD.

Case-only exome variation analysis of severe alcohol dependence using a multivariate hierarchical gene clustering approach

BACKGROUND

Variation in genes involved in ethanol metabolism has been shown to influence risk for alcohol dependence (AD) including protective loss of function alleles in ethanol metabolizing genes. We therefore hypothesized that people with severe AD would exhibit different patterns of rare functional variation in genes with strong prior evidence for influencing ethanol metabolism and response when compared to genes not meeting these criteria.

OBJECTIVE

Leverage a novel case only design and Whole Exome Sequencing (WES) of severe AD cases from the island of Ireland to quantify differences in functional variation between genes associated with ethanol metabolism and/or response and their matched control genes.

METHODS

First, three sets of ethanol related genes were identified including those a) involved in alcohol metabolism in humans b) showing altered expression in mouse brain after alcohol exposure, and altering ethanol behavioral responses in invertebrate models. These genes of interest (GOI) sets were matched to control gene sets using multivariate hierarchical clustering of gene-level summary features from gnomAD. Using WES data from 190 individuals with severe AD, GOI were compared to matched control genes using logistic regression to detect aggregate differences in abundance of loss of function, missense, and synonymous variants, respectively.

RESULTS

Three non-independent sets of 10, 117, and 359 genes were queried against control gene sets of 139, 1522, and 3360 matched genes, respectively. Significant differences were not detected in the number of functional variants in the primary set of ethanol-metabolizing genes. In both the mouse expression and invertebrate sets, we observed an increased number of synonymous variants in GOI over matched control genes. Post-hoc simulations showed the estimated effects sizes observed are unlikely to be under-estimated.

CONCLUSION

The proposed method demonstrates a computationally viable and statistically appropriate approach for genetic analysis of case-only data for hypothesized gene sets supported by empirical evidence.

Alcohol-Related Liver Disease: An Overview on Pathophysiology, Diagnosis and Therapeutic Perspectives

Alcohol-related liver disease (ALD) refers to a spectrum of liver manifestations ranging from fatty liver diseases, steatohepatitis, and fibrosis/cirrhosis with chronic inflammation primarily due to excessive alcohol use. Currently, ALD is considered as one of the most prevalent causes of liver disease-associated mortality worldwide. Although the pathogenesis of ALD has been intensively investigated, the present understanding of its biomarkers in the context of early clinical diagnosis is not complete, and novel therapeutic targets that can significantly alleviate advanced forms of ALD are limited. While alcohol abstinence remains the primary therapeutic intervention for managing ALD, there are currently no approved medications for treating ALD. Furthermore, given the similarities and the differences between ALD and non-alcoholic fatty liver disease in terms of disease progression and underlying molecular mechanisms, numerous studies have demonstrated that many therapeutic interventions targeting several signaling pathways, including oxidative stress, inflammatory response, hormonal regulation, and hepatocyte death play a significant role in ALD treatment. Therefore, in this review, we summarized several key molecular targets and their modes of action in ALD progression. We also described the updated therapeutic options for ALD management with a particular emphasis on potentially novel signaling pathways.

Ethanol Metabolism in the Liver, the Induction of Oxidant Stress, and the Antioxidant Defense System

The liver metabolizes ethanol through three enzymatic pathways: alcohol dehydrogenase (ADH), cytochrome p450 (also called MEOS), and catalase. Alcohol dehydrogenase class I (ADH1) is considered the most important enzyme for the metabolism of ethanol, MEOS and catalase (CAT) are considered minor alternative pathways. However, contradicting experiments suggest that the non-ADH1 pathway may have a greater relevance for the metabolism of ethanol than previously thought. In some conditions, ethanol is predominately metabolized to acetaldehyde via cytochrome P450 family 2 (CYP2E1), which is involved in the generation of reactive oxygen species (ROS), mainly through electron leakage to oxygen to form the superoxide (O₂^•−) radical or in catalyzed lipid peroxidation. The CAT activity can also participate in the ethanol metabolism that produces ROS via ethanol directly reacting with the CAT-H₂O₂ complex, producing acetaldehyde and water and depending on the H₂O₂ availability, which is the rate-limiting component in ethanol peroxidation. We have shown that CAT actively participates in lactate-stimulated liver ethanol oxidation, where the addition of lactate generates H₂O₂, which is used by CAT to oxidize ethanol to acetaldehyde. Therefore, besides its known role as a catalytic antioxidant component, the primary role of CAT could be to function in the metabolism of xenobiotics in the liver.

Alcohol, inflammation, and blood-brain barrier function in health and disease across development

Alcohol is the most commonly used drug of abuse in the world and binge drinking is especially harmful to the brain, though the mechanisms by which alcohol compromises overall brain health remain somewhat elusive. A number of brain diseases and pathological states are accompanied by perturbations in Blood-Brain Barrier (BBB) function, ultimately exacerbating disease progression. The BBB is critical for coordinating activity between the peripheral immune system and the brain. Importantly, BBB integrity is responsive to circulating cytokines and other immune-related signaling molecules, which are powerfully modulated by alcohol exposure. This review will highlight key cellular components of the BBB; discuss mechanisms by which permeability is achieved; offer insight into methodological approaches for assessing BBB integrity; and forecast how alcohol-induced changes in the peripheral and central immune systems might influence BBB function in individuals with a history of binge drinking and ultimately Alcohol Use Disorders (AUD).

Activation of PPARα-catalase pathway reverses alcoholic liver injury via upregulating NAD synthesis and accelerating alcohol clearance

Alcohol metabolism in the liver simultaneously generates toxic metabolites and disrupts redox balance, but the regulatory mechanisms have not been fully elucidated. The study aimed to characterize the role of PPARα in alcohol detoxification. Hepatic PPARα and catalase levels were examined in patients with severe alcoholic hepatitis. Mouse studies were conducted to determine the effect of PPARα reactivation by Wy14,643 on alcoholic hepatotoxicity and how catalase is involved in mediating such effects. Cell culture study was conducted to determine the effect of hydrogen peroxide on cellular NAD levels. We found that the protein levels of PPARα and catalase were significantly reduced in the livers of patients with severe alcoholic hepatitis. PPARα reactivation by Wy14,643 effectively reversed alcohol-induced liver damage in mice. Global and targeted metabolites analysis revealed a fundamental role of PPARα in regulating the tryptophan-NAD pathway. Notably, PPARα activation completely switched alcohol metabolism from the CYP2E1 pathway to the catalase pathway along with accelerated alcohol clearance. Catalase knockout mice were incompetent in alcohol metabolism and hydrogen peroxide clearance and were more susceptible to alcohol-induced liver injury. Hydrogen peroxide-treated hepatocytes had a reduced size of cellular NAD pool. These data demonstrate a key role of PPARα in regulating hepatic alcohol detoxification. Catalase-mediated hydrogen peroxide removal represents an underlying mechanism of how PPARα preserves the NAD pool. The study provides a new angle of view about the PPARα-catalase pathway in combating alcohol toxicity.

Possible mechanisms of HIV neuro-infection in alcohol use: Interplay of oxidative stress, inflammation, and energy interruption

Alcohol use and HIV-1 infection have a pervasive impact on brain function, which extends to the requirement, distribution, and utilization of energy within the central nervous system. This effect on neuroenergetics may explain, in part, the exacerbation of HIV-1 disease under the influence of alcohol, particularly the persistence of HIV-associated neurological complications. The objective of this review article is to highlight the possible mechanisms of HIV/AIDS progression in alcohol users from the perspective of oxidative stress, neuroinflammation, and interruption of energy metabolism. These include the hallmark of sustained immune cell activation and high metabolic energy demand by HIV-1-infected cells in the central nervous system, with at-risk alcohol use. Here, we discussed the point that the increase in energy supply requirement by HIV-1-infected neuroimmune cells as well as the deterrence of nutrient uptake across the blood-brain barrier significantly depletes the energy source and neuro-environment homeostasis in the CNS. We also described the mechanistic idea that comorbidity of HIV-1 infection and alcohol use can cause a metabolic shift and redistribution of energy usage toward HIV-1-infected neuroimmune cells, as shown in neuropathological evidence. Under such an imbalanced neuro-environment, meaningless energy waste is expected in infected cells, along with unnecessary malnutrition in non-infected neuronal cells, which is likely to accelerate HIV neuro-infection progression in alcohol use. Thus, it will be important to consider the factor of nutrients/energy imbalance in formulating treatment strategies to help impede the progression of HIV-1 disease and associated neurological disorders in alcohol use.

Moderate Ethanol Pre-treatment Mitigates ICH-Induced Injury via ER Stress Modulation in Rats

Intracerebral hemorrhage (ICH) is a life-threatening type of stroke that disrupts the normal neurological function of the brain. Clinical studies have reported a non-linear J-shaped association between alcohol consumption levels and the occurrence of cerebral stroke. Specifically, alcohol intoxication increases stroke incidence, while moderate alcohol pre-conditioning decreases stroke frequency and improves outcomes. Although alcohol pre-consumption is likely a crucial player in ICH, the underlying mechanism remains unclear. We performed 1-h alcohol pre-conditioning followed by ICH induction in Sprague-Dawley (SD) rats to investigate the role of alcohol pre-conditioning in ICH. Interestingly, behavioral test analysis found that ethanol intoxication (3 g/kg) aggravated ICH-induced neurological deficits, but moderate ethanol pre-conditioning (0.75 g/kg) ameliorated ICH-induced neurological deficits by reducing the oxidative stress and proinflammatory cytokines release. Moreover, we found that moderate ethanol pretreatment improved the striatal endoplasmic reticulum (ER) homeostasis by increasing the chaperone protein expression and reducing oxidative stress and apoptosis caused by ICH. Our findings show that the mechanism regulated by moderate ethanol pre-conditioning might be beneficial for ICH, indicating the importance of ER homeostasis, oxidative stress, and differential cytokines release in ICH.

Ethanol metabolism: The good, the bad, and the ugly

Throughout the world, ethanol is both an important commercial commodity and a source of major medical and social problems. Ethanol readily passes through biological membranes and distributes throughout the body. It is oxidized, first to acetaldehyde and then to acetate, and finally by the citric acid cycle in virtually all tissues. The oxidation of ethanol is irreversible and unregulated, making the rate dependent only on local concentration and enzyme activity. This unregulated input of reducing equivalents increases reduction of both cytoplasmic and intramitochondrial NAD and, through the latter, cellular energy state {[ATP]/([ADP][Pi])}. In brain, this increase in energy state stimulates dopaminergic neural activity signalling reward and a sense of well being, while suppressing glutamatergic neural activity signalling anxiety and unease. These positive responses to ethanol ingestion are important to social alcohol consumption. Importantly, decreased free [AMP] decreases AMP-dependent protein kinase (AMPK) activity, an important regulator of cellular energy metabolism. Oxidation of substrates used for energy metabolism in the absence of ethanol is down regulated to accommodate the input from ethanol. In liver, chronic ethanol metabolism results in fatty liver and general metabolic dysfunction. In brain, transport of other oxidizable metabolites through the blood-brain barrier and the enzymes for their oxidation are both down regulated. For exposures of short duration, ethanol induced regulatory changes are rapid and reversible, recovering completely when the concentrations of ethanol and acetate fall again. Longer periods of ethanol exposure and associated chronic suppression of AMPK activity activates regulatory mechanisms, including gene expression, that operate over longer time scales, both in onset and reversal. If chronic alcohol consumption is abruptly ended, metabolism is no longer able to respond rapidly enough to compensate. Glutamatergic neural activity adapts to chronic dysregulation of glutamate metabolism and suppression of glutamatergic neural activity by increasing excitatory and decreasing inhibitory amino acid receptors. A point is reached (ethanol dependence) where withdrawal of ethanol results in significant metabolic energy depletion in neurons and other brain cells as well as hyperexcitation of the glutamatergic system. The extent and regional specificity of energy depletion in the brain, combined with hyperactivity of the glutamatergic neuronal system, largely determines the severity of withdrawal symptoms.

Effects of Acute Ethanol Administration on Brain Oxidative Status: The Role of Acetaldehyde

BACKGROUND

Ethanol (EtOH), one of the most widely consumed substances of abuse, can induce brain damage and neurodegeneration. EtOH is centrally metabolized into acetaldehyde, which has been shown to be responsible for some of the neurophysiological and cellular effects of EtOH. Although some of the consequences of chronic EtOH administration on cell oxidative status have been described, the mechanisms by which acute EtOH administration affects the brain's cellular oxidative status and the role of acetaldehyde remain to be elucidated in detail.

METHODS

Swiss CD-I mice were pretreated with the acetaldehyde-sequestering agent d-penicillamine (DP; 75 mg/kg, i.p.) or the antioxidant lipoic acid (LA; 50 mg/kg, i.p.) 30 minutes before EtOH (2.5 g/kg, i.p.) administration. Animals were sacrificed 30 minutes after EtOH injection. Glutathione peroxidase (GPx) mRNA levels; GPx and glutathione reductase (GR) enzymatic activities; reduced glutathione (GSH), glutathione disulfide (GSSG), glutamate, g-L-glutamyl-L-cysteine (Glut-Cys), and malondialdehyde (MDA) concentrations; and protein carbonyl group (CG) content were determined in whole-brain samples.

RESULTS

Acute EtOH administration enhanced GPx activity and the GSH/GSSG ratio, while it decreased GR activity and GSSG concentration. Pretreatment with DP or LA only prevented GPx activity changes induced by EtOH.

CONCLUSIONS

Altogether, these results show the capacity of a single dose of EtOH to unbalance cellular oxidative homeostasis.

Alcoholic Liver Disease: Alcohol Metabolism, Cascade of Molecular Mechanisms, Cellular Targets, and Clinical Aspects

Alcoholic liver disease is the result of cascade events, which clinically first lead to alcoholic fatty liver, and then mostly via alcoholic steatohepatitis or alcoholic hepatitis potentially to cirrhosis and hepatocellular carcinoma. Pathogenetic events are linked to the metabolism of ethanol and acetaldehyde as its first oxidation product generated via hepatic alcohol dehydrogenase (ADH) and the microsomal ethanol-oxidizing system (MEOS), which depends on cytochrome P450 2E1 (CYP 2E1), and is inducible by chronic alcohol use. MEOS induction accelerates the metabolism of ethanol to acetaldehyde that facilitates organ injury including the liver, and it produces via CYP 2E1 many reactive oxygen species (ROS) such as ethoxy radical, hydroxyethyl radical, acetyl radical, singlet radical, superoxide radical, hydrogen peroxide, hydroxyl radical, alkoxyl radical, and peroxyl radical. These attack hepatocytes, Kupffer cells, stellate cells, and liver sinusoidal endothelial cells, and their signaling mediators such as interleukins, interferons, and growth factors, help to initiate liver injury including fibrosis and cirrhosis in susceptible individuals with specific risk factors. Through CYP 2E1-dependent ROS, more evidence is emerging that alcohol generates lipid peroxides and modifies the intestinal microbiome, thereby stimulating actions of endotoxins produced by intestinal bacteria; lipid peroxides and endotoxins are potential causes that are involved in alcoholic liver injury. Alcohol modifies SIRT1 (Sirtuin-1; derived from Silent mating type Information Regulation) and SIRT2, and most importantly, the innate and adapted immune systems, which may explain the individual differences of injury susceptibility. Metabolic pathways are also influenced by circadian rhythms, specific conditions known from living organisms including plants. Open for discussion is a 5-hit working hypothesis, attempting to define key elements involved in injury progression. In essence, although abundant biochemical mechanisms are proposed for the initiation and perpetuation of liver injury, patients with an alcohol problem benefit from permanent alcohol abstinence alone.

Combined Catalase and ADH Inhibition Ameliorates Ethanol-Induced Myocardial Dysfunction Despite Causing Oxidative Stress in Conscious Female Rats

BACKGROUND

Ethanol (EtOH)-evoked oxidative stress, which contributes to myocardial dysfunction in proestrus rats, is mediated by increases in NADPH oxidase (Nox) activity, malondialdehyde (MDA), and ERK1/2 phosphorylation. Whether these biochemical responses, which are triggered by alcohol-derived acetaldehyde in noncardiac tissues, occur in proestrus rats' hearts remains unknown. Therefore, we elucidated the roles of alcohol dehydrogenase (ADH), cytochrome P4502E1 (CYP2E1), and catalase, which catalyze alcohol oxidation to acetaldehyde, in these alcohol-evoked biochemical and hemodynamic responses in proestrus rats.

METHODS

Conscious proestrus rats prepared for measurements of left ventricular (LV) function and blood pressure (BP) received EtOH (1.5 g/kg, intravenous [i.v.] infusion over 30 minutes) or saline 30 minutes after an ADH and CYP2E1 inhibitor, 4-methylpyrazole (4-MP) (82 mg/kg, intraperitoneal), a catalase inhibitor, 3-AT (0.5 g/kg, i.v.), their combination, or vehicle. LV function and BP were monitored for additional 60 minutes after EtOH or saline infusion before collecting the hearts for ex vivo measurements of LV reactive oxygen species (ROS), Nox activity, MDA, and ERK1/2 phosphorylation.

RESULTS

EtOH reduced LV function (dP/dt_max and LV developed pressure) and BP, and increased cardiac Nox activity, ROS and MDA levels, and ERK1/2 phosphorylation. Either inhibitor partially, and their combination significantly, attenuated these responses despite the substantially higher blood EtOH level, and the increased cardiac oxidative stress and reduced BP caused by 3-AT alone or with 4-MP. The inhibitors reduced cardiac MDA level and reversed EtOH effect on cardiac and plasma MDA.

CONCLUSIONS

EtOH oxidative metabolism plays a pivotal role in the EtOH-evoked LV oxidative stress and dysfunction in proestrus rats. Notably, catalase inhibition (3-AT) caused cardiac oxidative stress and hypotension.

Thirst sensation and oral dryness following alcohol intake

Substantial acute and chronic intakes of alcohol or ethanol (EtOH) severely influence oral sensations, such as thirst and oral dryness (dry mouth, xerostomia). Thirst sensation and oral dryness are primarily caused by the activation of neurons in brain regions, including the circumventricular organs and hypothalamus, which are referred to as the dipsogenic center, and by a decrease in salivary secretion, respectively. The sensation of thirst experienced after heavy-alcohol drinking is widely regarded as a consequence of EtOH-induced diuresis; however, EtOH in high doses induces anti-diuresis. Recently, it has been proposed that the ethanol metabolite acetaldehyde induces thirst via two distinct processes in the central nervous system from EtOH-induced diuresis, based on the results of animal experiments. The present review describes new insights regarding the induction mechanism of thirst sensation and oral dryness after drinking alcohol.

Effect of boric acid on oxidative stress in rats with fetal alcohol syndrome

To the best of our knowledge, this is the first study concerning the effect of boric acid (BA) administration on fetal alcohol syndrome (FAS). In this study, the aim was to investigate prenatal alcohol-induced oxidative stress on the cerebral cortex of newborn rat pups and assess the protective and beneficial effects of BA supplementation on rats with FAS. Pregnant rats were divided into three groups, namely the control, alcohol and alcohol + boric acid groups. As markers of alcohol-induced oxidative stress in the cerebral cortex of the newborn pups, malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) levels were measured. Although the MDA levels in the alcohol group were significantly increased compared with those in the control group (P<0.05), the MDA level in the alcohol + boric acid group was shown to be significantly decreased compared with that in the alcohol group (P<0.01). The CAT activity of the alcohol + boric acid group was significantly higher than that in the alcohol group (P<0.05). The GPx activity in the alcohol group was decreased compared with that in the control group (P<0.05). These results demonstrate that alcohol is capable of triggering damage to membranes of the cerebral cortex of rat pups and BA could be influential in antioxidant mechanisms against oxidative stress resulting from prenatal alcohol exposure.

Ethanol-induced oxidant stress modulates hepatic autophagy and proteasome activity

In this review, we describe research findings on the effects of alcohol exposure on two major catabolic systems in liver cells: the ubiquitin-proteasome system (UPS) and autophagy. These hydrolytic systems are not unique to liver cells; they exist in all eukaryotic tissues and cells. However, because the liver is the principal site of ethanol metabolism, it sustains the greatest damage from heavy drinking. Thus, the focus of this review is to specifically describe how ethanol oxidation modulates the activities of the UPS and autophagy and the mechanisms by which these changes contribute to the pathogenesis of alcohol-induced liver injury. Here, we describe the history and the importance of cellular hydrolytic systems, followed by a description of each catabolic pathway and the differential modulation of each by ethanol exposure. Overall, the evidence for an involvement of these catabolic systems in the pathogenesis of alcoholic liver disease is quite strong. It underscores their importance, not only as effective means of cellular recycling and eventual energy generation, but also as essential components of cellular defense.

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.

Modulation of ethanol-induced conditioned place preference in mice by 3-amino-1,2,4-triazole and D-penicillamine depends on ethanol dose and number of conditioning trials

Previous studies have shown that both 3-amino-1,2,4-triazole (AT), which inhibits metabolism of ethanol (EtOH) to acetaldehyde by inhibiting catalase, and D-penicillamine (D-P), an acetaldehyde-sequestering agent, modulate EtOH-conditioned place preference (CPP) in male albino Swiss (IOPS Orl) mice. These studies followed a reference-dose-like procedure, which involves comparing cues that have both been paired with EtOH. However, the role of EtOH-derived acetaldehyde has not been examined using a standard CPP method, and efficacy of these treatments could be different under the two circumstances. In the present investigation, we manipulated the strength of CPP across five separate studies and evaluated the effect of D-P and AT on EtOH-induced CPP following a standard unbiased CPP procedure. Mice received pairings with vehicle-saline injections with one cue and, alternatively, with AT- and D-P-EtOH with another cue. Our studies indicate that AT and D-P only disrupt CPP induced by EtOH in mice when the number of conditioning sessions and the dose of EtOH are low. These findings suggest that acquisition of EtOH-induced CPP may depend on the levels of acetaldehyde available during memory acquisition and the strength of the memory. Therefore, we propose that, at least when the memory processes are labile, brain acetaldehyde could participate in the formation of Pavlovian learning elicited by EtOH.

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.

Synthesis of fatty acid ethyl esters in mammalian tissues after ethanol exposure: a systematic review of the literature

The ability to undergo non-oxidative metabolism from ethanol to fatty acid ethyl esters (FAEEs) varies greatly among tissues and organs. To gain a greater understanding of non-oxidative ethanol metabolism to FAEE, we aimed to collect all published data on FAEE synthesis in mammalian organs and tissues to identify all tissues, organs, and enzymes that are known to, or likely possess FAEE-synthetic activity. A systematic search for relevant papers was performed and two independent reviewers examined potentially relevant abstracts (articles on FAEEs that pertain to ethanol exposure) to determine whether they met the inclusion criteria. Information on FAEE synthesis was retrieved from papers meeting the inclusion/exclusion criteria and summarized by organ/tissue/matrix examined. The systematic search through four databases yielded 78 articles that investigated FAEE synthesis by tissues, tissue fractions and cell lines, and 29 articles that attempted to purify and/or characterize the enzymes involved in FAEE synthesis. Two enzyme activities have been studied: FAEE synthase (FAEES, which conjugates ethanol and free fatty acid) and acyl-CoA: ethanol O-acyltransferase (AEAT, which conjugates ethanol and fatty acyl-CoA). Both activities are expressed by a variety of different enzymes. FAEES activity is the most widely studied and has been purified from several tissues and shown to be associated with several well-known enzymes, while the identity of enzymes possessing AEAT activity remains unknown. The organs and tissues that have been shown to synthesize FAEEs are discussed, with special emphasis on the studies that attempted to elucidate the enzymology of FAEE synthesis in those tissues.

Chronic-alcohol-abuse-induced oxidative stress in the development of acute respiratory distress syndrome

Chronic alcohol ingestion increases the risk of developing acute respiratory distress syndrome (ARDS), a severe form of acute lung injury, characterized by alveolar epithelial and endothelial barrier disruption and intense inflammation. Alcohol abuse is also associated with a higher incidence of sepsis or pneumonia resulting in a higher rate of admittance to intensive care, longer inpatient stays, higher healthcare costs, and a 2-4 times greater mortality rate. Chronic alcohol ingestion induced severe oxidative stress associated with increased ROS generation, depletion of the critical antioxidant glutathione (GSH), and oxidation of the thiol/disulfide redox potential in the alveolar epithelial lining fluid and exhaled breath condensate. Across intracellular and extracellular GSH pools in alveolar type II cells and alveolar macrophages, chronic alcohol ingestion consistently induced a 40-60 mV oxidation of GSH/GSSG suggesting that the redox potentials of different alveolar GSH pools are in equilibrium. Alcohol-induced GSH depletion or oxidation was associated with impaired functions of alveolar type II cells and alveolar macrophages but could be reversed by restoring GSH pools in the alveolar lining fluid. The aims of this paper are to address the mechanisms for alcohol-induced GSH depletion and oxidation and the subsequent effects in alveolar barrier integrity, modulation of the immune response, and apoptosis.

Curcuma comosa prevents the neuron loss and affects the antioxidative enzymes in hippocampus of ethanol-treated rats

Curcuma comosa Roxb. is widely used as a gynaecological traditional medicine in South-East Asia and recent behavioral studies have shown that C. comosa extract significantly improved the spatial memory in rats. The present study investigated the protective effects of Curcuma comosa hexane extract on the ethanol (EtOH)-induced oxidation in rat brains. Young female Wistar rats were given 20% of EtOH intraperitoneally to induce the oxidative stress. Subsequently, C. comosa hexane extract was intraperitoneally co-administered at the doses of 100 and 250 mg kg(-1) b.wt. to the EtOH-induced rats for 14 days. The neuron densities of CA1, CA3 and CA4 areas of the hippocampus were counted and the activities of hippocampal Catalase (CAT), Glutathione Peroxidase (GPx) and Superoxide Dismutase (SOD) were determined. EtOH significantly decreased the neuron densities in Cornu Ammonis (CA), including CA1 and CA3 areas; however, the decrease was prevented by C. comosa co-administration. EtOH administration also increased the CAT and GPx activities in the hippocampus which were reversed by C. comosa co-administration. Moreover, C. comosa administration increased the SOD activity in a dose-dependent manner in the EtOH treated groups. C. comosa prevented the neuron loss in the hippocampus caused by EtOH. The possible neural protective mechanism may involve with the changes in activities of the antioxidant enzymes in the hippocampus.

Anxiogenic and stress-inducing effects of peripherally administered acetaldehyde in mice: similarities with the disulfiram-ethanol reaction

Peripheral accumulation of acetaldehyde, the first metabolite of ethanol, produces autonomic responses in humans called "flushing". The aversive characteristics of flushing observed in some populations with an isoform of aldehyde dehydrogenase (ALDH2) less active, are the basis for treating alcoholics with disulfiram, an ALDH inhibitor. Although ethanol and centrally formed acetaldehyde have anxiolytic effects, peripheral accumulation of acetaldehyde may be aversive in part because it is anxiogenic.

OBJECTIVES

We investigated the effect of direct administration of acetaldehyde on behavioral measures of anxiety and on hormonal markers of stress in mice. The impact of disulfiram on the anxiolytic actions of ethanol was evaluated. Acetate (a metabolite of acetaldehyde) was also studied.

METHODS

CD1 male mice received acetaldehyde (0, 25, 50, 75 or 100 mg/kg) at different time intervals and were assessed in the elevated plus maze and in the dark-light box. Corticosterone release after acetaldehyde administration was also assessed. Additional experiments evaluated the impact of disulfiram on the anxiolytic effect of ethanol (0 or 1 mg/kg), and the effect of acetate on the plus maze.

RESULTS

Direct administration of acetaldehyde (100 mg/kg) had an anxiogenic effect at 1, 11 or 26 min after IP administration. Acetaldehyde was ten times more potent than ethanol at inducing corticosterone release. Disulfiram did not affect behavior on its own, but blocked the anxiolytic effect of ethanol at doses of 30 and 60 mg/kg, and had an anxiogenic effect at the highest dose (90 mg/kg) when co-administered with ethanol. Acetate did not affect any of the anxiety parameters.

CONCLUSIONS

Peripheral administration or accumulation of acetaldehyde produces anxiogenic effects and induces endocrine stress responses. This effect is not mediated by its metabolite acetate.

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.

Ethanol and acetaldehyde disturb TNF-alpha and IL-6 production in cultured astrocytes

Ethanol disturbs astroglial growth and differentiation and causes functional alterations. Furthermore, many signalling molecules produced by astrocytes contribute to these processes. The aim of the present study was to investigate the influence of ethanol and its primary metabolite, acetaldehyde, on TNF-alpha and IL-6 production in a rat cortical astrocyte primary culture. We are the first to report that both ethanol and acetaldehyde can modulate TNF-alpha and IL-6 secretion from cultured astrocytes. Long-term exposure (7 days) to ethanol and acetaldehyde was more toxic than an acute (24 hours) exposure. However, both compounds showed a biphasic, hormestic effect on the IL-6 secretion after the acute as well as the long-term exposure, and the maximum stimulation was reached for 50-mM ethanol and 1-mM acetaldehyde after 7-day exposure. In contrast, both compounds reduced the TNF-alpha secretion, where the effect was concentration-dependent. The catalase inhibitor 2-amino-1,2,4 triazole significantly reduced the ethanol toxicity in the cultured astrocytes after the acute as well as the long-term exposure. In conclusion, both ethanol and acetaldehyde affect the production of IL-6 and TNF-alpha in cultured astrocytes. The effect depends on the concentration of the compounds and the duration of the exposure. Acetaldehyde is a more potent toxin than ethanol, and ethanol's toxicity in the brain is at least partially due to its primary metabolite, acetaldehyde.

Comparison of ethanol and acetaldehyde toxicity in rat astrocytes in primary culture

This study compared the effects of toxicity of ethanol and its first metabolite acetaldehyde in rat astrocytes through cell viability and cell proliferation. The cells were treated with different concentrations of ethanol in the presence or absence of a catalase inhibitor 2-amino-1,2,4 triazole (AMT) or with different concentrations of acetaldehyde. Cell viability was assessed using the trypan blue test. Cell proliferation was assessed after 24 hours and after seven days of exposure to either ethanol or acetaldehyde.We showed that both ethanol and acetaldehyde decreased cell viability in a dose-dependent manner. In proliferation studies, after seven days of exposure to either ethanol or acetaldehyde, we observed a significant dose-dependent decrease in cell number. The protein content study showed biphasic dose-response curves, after 24 hours and seven days of exposure to either ethanol or acetaldehyde. Co-incubation in the presence of AMT significantly reduced the inhibitory effect of ethanol on cell proliferation.We concluded that long-term exposure of astrocytes to ethanol is more toxic than acute exposure. Acetaldehyde is a much more potent toxin than ethanol, and at least a part of ethanol toxicity is due to ethanol's first metabolite acetaldehyde.

Acetaldehyde and the hypothermic effects of ethanol in mice

BACKGROUND

Acetaldehyde, the first metabolite of ethanol, has been suggested to be involved in many behavioral effects of ethanol. However, few studies have investigated the hypothermic effects of acetaldehyde or the contribution of acetaldehyde to ethanol-induced hypothermia. The aim of the present study is to better understand the hypothermic effects of acetaldehyde and the possible contribution of acetaldehyde in ethanol-induced hypothermia, especially under conditions leading to acetaldehyde accumulation.

METHODS

Female Swiss mice were injected intraperitoneally with ethanol and acetaldehyde and their rectal temperatures were measured with a digital thermometer at various time points after the injections. Experiment 1 compared the hypothermic effects of various acetaldehyde doses (0 to 300 mg/kg) with a reference dose of ethanol (3 g/kg). Experiment 2 tested the effects of a pretreatment with the aldehyde dehydrogenase (ALDH) inhibitor cyanamide (25 mg/kg) on ethanol- and acetaldehyde-induced hypothermia. In experiments 3 and 4, mice received a combined pretreatment with cyanamide and the alcohol dehydrogenase (ADH) inhibitor 4-Methylpyrazole (10 mg/kg) before the injection of ethanol or acetaldehyde.

RESULTS

Acetaldehyde at doses between 100 and 300 mg/kg induced significant hypothermic effects, but of shorter duration than ethanol-induced hypothermia. The inhibition of ALDH enzymes by cyanamide induced a strong potentiation of both ethanol- and acetaldehyde-induced hypothermia. The pretreatment with 4-MP prevented the potentiation of ethanol-induced hypothermia by cyanamide, but slightly increased the potentiation of acetaldehyde-induced hypothermia by cyanamide.

CONCLUSIONS

The results of the present study clearly show that acetaldehyde has hypothermic properties in mice at least at relatively high concentrations. Furthermore, the accumulation of acetaldehyde following ALDH inhibition strongly enhanced the hypothermic effects of ethanol. These latter results confirm the hypothermic properties of acetaldehyde and show that acetate, the next step in ethanol metabolism, is not involved in these hypothermic effects. Finally, the experiment with 4-MP indicates that the potentiating effects of cyanamide are mediated by the peripheral accumulation of acetaldehyde, which then reaches the brain to induce a severe hypothermia.

Putative role of brain acetaldehyde in ethanol addiction

The putative contribution of brain acetaldehyde (AcH) to ethanol (EtOH) tolerance and dependence (addiction) is reviewed. Although the role of AcH in EtOH addiction has been controversial, there are data showing a relationship. AcH can be formed in the brain tissues through the peroxidatic activity of catalase and by oxidation via other oxidizing enzymes such as cytochrome P-4502E1. Significant formation of AcH occurs in vitro in brain tissue at concentrations of EtOH that can be achieved by voluntary consumption of EtOH by rodents. AcH itself possesses reinforcing properties, which suggests that some of the behavioral pharmacological effects attributed to EtOH may be a result of the formation of AcH, and supports the involvement of AcH in EtOH addiction. Modulation of aldehyde dehydrogenase (ALDH) and brain catalase activity can change EtOH-related addictive behaviors presumably by changing AcH levels. Moreover, some condensation reaction products of AcH may promote some actions of EtOH and its consumption. On the basis of the findings, it can be concluded that AcH may mediate some of the CNS actions of EtOH including tolerance and dependence, although further exploration the involvement of AcH in EtOH addiction is warranted.

Reduction in the anxiolytic effects of ethanol by centrally formed acetaldehyde: the role of catalase inhibitors and acetaldehyde-sequestering agents

RATIONALE

Considerable evidence indicates that brain ethanol metabolism mediated by catalase is involved in modulating some of the behavioral and physiological effects of this drug, which suggests that the first metabolite of ethanol, acetaldehyde, may have central actions. Previous results have shown that acetaldehyde administered into the lateral ventricles produced anxiolysis in a novel open arena in rats.

OBJECTIVES

The present studies investigate the effects of centrally formed acetaldehyde on ethanol-induced anxiolysis.

MATERIALS AND METHODS

The effects of the catalase inhibitor sodium azide (SA; 0 or 10 mg/kg, IP) on ethanol-induced anxiolysis (0.0, 0.5, or 1.0 g/kg, IP) were evaluated in CD1 mice in two anxiety paradigms, the elevated plus maze and the dark/light box. Additional studies assessed the effect of the noncompetitive catalase inhibitor 3-amino-1,2,4-triazole (AT; 0.5 g/kg, IP) and the acetaldehyde inactivation agent D: -penicillamine (50 mg/kg, IP) on the plus maze.

RESULTS

SA reduced the anxiolytic effects of ethanol on several parameters evaluated in the elevated plus maze and in the dark/light box. In the plus maze, AT completely blocked and D-penicillamine significantly reduced the anxiolytic properties of ethanol.

CONCLUSIONS

Thus, when cerebral metabolism of ethanol into acetaldehyde is blocked by catalase inhibitors, or acetaldehyde is inactivated, there is a suppressive effect on the anxiolytic actions of ethanol. These data provide further support for the idea that centrally formed or administered acetaldehyde can contribute to some of the psychopharmacological actions of ethanol, including its anxiolytic properties.

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.

Role of acetaldehyde in tobacco smoke addiction

This review evaluates the presumed contribution of acetaldehyde to tobacco smoke addiction. In rodents, acetaldehyde induces reinforcing effects, and acts in concert with nicotine. Harman and salsolinol, condensation products of acetaldehyde and biogenic amines, may be responsible for the observed reinforcing effect of acetaldehyde. Harman and salsolinol inhibit monoamine oxidase (MAO), and some MAO-inhibitors are known to increase nicotine self-administration and maintain behavioural sensitization to nicotine. Harman is formed in cigarette smoke, and blood harman levels appear to be 2-10 times higher compared to non-smokers. Since harman readily passes the blood-brain barrier and has sufficient MAO-inhibiting potency, it may contribute to the lower MAO-activity observed in the brain of smokers. In contrast, the minor amounts of salsolinol that can be formed in vivo most likely do not contribute to tobacco addiction. Thus, acetaldehyde may increase the addictive potential of tobacco products via the formation of acetaldehyde-biogenic amine adducts in cigarette smoke and/or in vivo, but further research is necessary to substantiate this hypothesis.

Effects of Chronic Ethanol Consumption on Brain Synaptosomes and Protective Role of Betaine

To evaluate the cytotoxic effects of chronic ethanol consumption on brain cerebral synaptosomes and preventive role of betaine as a methyl donor and S-adenosylmethionine precursor, 24 male Wistar rats were divided into three groups: control, ethanol (8 g/kg/day) and ethanol plus betaine(0.5% w/v) group. Animals were fed 60 ml/diet per day for two months, then sacrificed. Malondialdehyde (MDA), protein carbonyl contents and adenosine deaminase (ADA) activities were determined in synaptosomal/mitochondrial enriched fraction isolated from rat cerebral cortexes. When compared to controls, ethanol containing diet significantly increased MDA levels (P < 0.05), also increased protein carbonyl levels and adenosine deaminase activities. But these were not statistically significant (P > 0.05). However, adding betaine to ethanol containing diet caused a significant decrease in MDA, protein carbonyl levels and adenosine deaminase activities (P < 0.05). These results indicate that betaine may appear as a protective nutritional agent against cytotoxic brain damage induced by chronic ethanol consumption.

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.

Acute administration of 3-nitropropionic acid, a reactive oxygen species generator, boosts ethanol-induced locomotor stimulation. New support for the role of brain catalase in the behavioural effects of ethanol

The antioxidant enzyme catalase by reacting with H(2)O(2), forms the compound known as compound I (catalase-H(2)O(2)). This compound is able to oxidise ethanol to acetaldehyde in the CNS. It has been demonstrated that 3-nitropropionic acid (3-NPA) induces the activity of the brain catalase-H(2)O(2) system. In this study, we tested the effect of 3-NPA on both the brain catalase-H(2)O(2) system and on the acute locomotor effect of ethanol. To find the optimal interval for the 3-NPA-ethanol interaction mice were treated with 3-NPA 0, 45, 90 and 135min before an ethanol injection (2.4mg/kg). In a second study, 3-NPA (0, 15, 30 or 45mg/kg) was administered SC to animals 90min before saline or several doses of ethanol (1.6 or 2.4g/kg), and the open-field behaviour was registered. The specificity of the effect of 3-NPA (45mg/kg) was evaluated on caffeine (10mg/kg IP) and cocaine (4mg/kg)-induced locomotion. The prevention of 3-NPA effects on both ethanol-induced locomotion and brain catalase activity by L-carnitine, a potent antioxidant, was also studied. Nitropropionic acid boosted ethanol-induced locomotion and brain catalase activity after 90min. The effect of 3-NPA was prevented by l-carnitine administration. These results indicate that 3-NPA enhanced ethanol-induced locomotion by increasing the activity of the brain catalase system.

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.

Locomotor effects of ethanol and acetaldehyde after peripheral and intraventricular injections in Swiss and C57BL/6J mice

Several studies have suggested that acetaldehyde, the first product of ethanol metabolism, is involved in the locomotor stimulant effects of ethanol in mice, although it has never been formally tested whether acetaldehyde injected directly into the brain of mice has stimulant properties. Recently, it was also shown in rats that both ethanol and acetaldehyde can induce opposite locomotor effects according to the route of administration. Whereas peripheral administrations of ethanol and acetaldehyde induced locomotor depressant effects, their infusions directly into the brain produced locomotor stimulation. The aim of the present study was to characterize in mice the locomotor effects of ethanol and acetaldehyde injected either peripherally by the intraperitoneal route or centrally into the brain ventricles. Additionally, the effects of ethanol and acetaldehyde were compared in two strains of mice known for their differential sensitivity to the locomotor effects of ethanol, namely Swiss and C57BL/6J mice. Ethanol induced a biphasic effect on locomotor activity in Swiss mice, with stimulant effects at low to moderate doses and depressant effects at higher doses. Such a profile of effects was observed whatever the route of administration, peripheral or central. In C57BL/6J mice, ethanol only induced monophasic depressant effects. In this mouse strain, no evidence of the stimulant effects of ethanol was found after either an i.p. or an i.c.v. administration of ethanol. In contrast to ethanol, acetaldehyde yielded only depressant effects in both strains of mice after both peripheral and central administrations. These results indicate that the route of administration does not alter the locomotor effects of ethanol and acetaldehyde in mice. Additionally, the present study shows that the stimulant properties of acetaldehyde, even after direct infusion into the brain, are not as obvious as previously speculated.

Prevention of Ethanol-Induced Behavioral Stimulation by d-Penicillamine: A Sequestration Agent for Acetaldehyde

BACKGROUND

D-Penicillamine, a sulfhydryl amino acid derived from penicillin, is a highly selective agent for sequestering in vivo acetaldehyde, the first metabolic product of ethanol. A substantial amount of research supports the idea that brain acetaldehyde, produced by central ethanol metabolism, plays a key role in determining some of the behavioral effects of ethanol administration. This study addressed two questions. First, we tested if D-penicillamine was able to modify the depressant effects of acetaldehyde on behavior. Second, we studied the effect of D-penicillamine on ethanol-induced behavioral stimulation.

METHODS

Mice were pretreated with 75.00 mg/kg of D-penicillamine, and 30 min later, they received acetaldehyde at 0, 100, 200, or 300 mg/kg intraperitoneally. Different groups of animals were treated with 0.0, 37.5, 75, 150, or 300 mg/kg of D-penicillamine simultaneously 30, 90, 150, or 210 min before the intraperitoneal administration of saline or 1.2, 1.8, 2.4, 3.0, or 3.6 g/kg of ethanol, respectively. The specificity of D-penicillamine effects was addressed using two drugs: cocaine (4 mg/kg) and caffeine (15 mg/kg).

RESULTS

Our results revealed that behavioral depression caused by acetaldehyde (200 and 300 mg/kg) could be attenuated by D-penicillamine treatment. In addition, D-penicillamine was also effective in lowering behavioral locomotion induced by ethanol (1.8 and 2.4 g/kg), without altering spontaneous locomotor activity. This sulfhydryl amino acid specifically modified the effect of ethanol on locomotion because cocaine- or caffeine-induced locomotion was unaffected. In addition, blood ethanol levels were not different between D-penicillamine- and saline-pretreated mice.

CONCLUSIONS

Behavioral effects produced by acetaldehyde and ethanol are blocked when animals are treated with D-penicillamine, an effective sequestration agent for acetaldehyde. These results suggest that some of the psychopharmacological effects, classically attributed to ethanol, could be mediated by its first metabolite, acetaldehyde.

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.

Lead-induced catalase activity differentially modulates behaviors induced by short-chain alcohols

Acute lead administration produces a transient increase in brain catalase activity. This effect of lead has been used to assess the involvement of brain ethanol metabolism, and therefore centrally formed acetaldehyde, in the behavioral actions of ethanol. In mice, catalase is involved in ethanol and methanol metabolism, but not in the metabolism of other alcohols such as 1-propanol or tert-butanol. In the present study, we assessed the specificity of the effects of lead acetate on catalase-mediated metabolism of alcohols, and the ability of lead to modulate the locomotion and loss of the righting reflex (LRR) induced by 4 different short-chain alcohols. Animals were pretreated i.p. with lead acetate (100 mg/kg) or saline, and 7 days later were injected i.p. with ethanol (2.5 or 4.5 g/kg), methanol (2.5 or 6.0 g/kg), 1-propanol (0.5 or 2.5 g/kg) or tert-butanol (0.5 or 2.0 g/kg) for locomotion and LRR, respectively. Locomotion induced by ethanol was significantly potentiated in lead-treated mice, while methanol-induced locomotion was reduced by lead treatment. The loss of righting reflex induced by ethanol was shorter in lead-treated mice, and lead produced the opposite effect in methanol-treated mice. There was no effect of lead on 1-propanol or tert-butanol-induced behaviors. Lead treatment was effective in inducing catalase activity and protein both in liver and brain. These results support the hypothesis that the effects of lead treatment on ethanol-induced behaviors are related to changes in catalase activity, rather than some nonspecific effect that generalizes to all alcohols.

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.

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.

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.