Alcohol dehydrogenase activity in rat brain and liver

Ingested Ketone Ester Leads to a Rapid Rise of Acetyl-CoA and Competes with Glucose Metabolism in the Brain of Non-Fasted Mice

The role of ketone bodies in the cerebral energy homeostasis of neurological diseases has begun to attract recent attention particularly in acute neurological diseases. In ketogenic therapies, ketosis is achieved by either a ketogenic diet or by the administration of exogenous ketone bodies. The oral ingestion of the ketone ester (KE), (R)-3-hydroxybutyl (R)-3-hydroxybutyrate, is a new method to generate rapid and significant ketosis (i.e., above 6 mmol/L) in humans. KE is hydrolyzed into β-hydroxybutyrate (βHB) and its precursor 1,3-butanediol. Here, we investigate the effect of oral KE administration (3 mg KE/g of body weight) on brain metabolism of non-fasted mice using liquid chromatography in tandem with mass spectrometry. Ketosis (Cmax = 6.83 ± 0.19 mmol/L) was obtained at Tmax = 30 min after oral KE-gavage. We found that βHB uptake into the brain strongly correlated with the plasma βHB concentration and was preferentially distributed in the neocortex. We showed for the first time that oral KE led to an increase of acetyl-CoA and citric cycle intermediates in the brain of non-fasted mice. Furthermore, we found that the increased level of acetyl-CoA inhibited glycolysis by a feedback mechanism and thus competed with glucose under physiological conditions. The brain pharmacodynamics of this oral KE strongly suggest that this agent should be considered for acute neurological diseases.

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.

Binge ethanol administration enhances the MDMA-induced long-term 5-HT neurotoxicity in rat brain

RATIONALE

Ecstasy abuse commonly occurs in hot, overcrowded environments in combination with alcohol. Around 90% of ecstasy users take ethanol; over 70% of these users also often drink alcohol at hazardous levels.

OBJECTIVES

We wished to examine whether binge ethanol administration enhanced the long-lasting 5-HT neurotoxicity induced by 3,4-methylenedioxymethamphetamine (MDMA) in rats maintained at high ambient temperature and the role of acetaldehyde.

MATERIALS AND METHODS

Rats were treated with a 4-day ethanol regimen leading to plasma ethanol levels of around 450 mg/dl. On day 5, rats were placed at 30 degrees C and administered MDMA (5 mg/kg). Rectal temperature and hydroxyl radical formation were measured immediately before and up to 6 h after MDMA. 5-HT concentration and 5-HT transporter density were determined 7 days later. A group of rats received cyanamide (50 mg/kg) on days 1 and 3 of the 4-day-ethanol inhalation.

RESULTS

In ethanol treated rats, MDMA produced a hyperthermic response similar to that observed in controls but enhanced the loss of 5-HT concentration and 5-HT transporter density in the hippocampus. Cyanamide elevated the plasma acetaldehyde concentration fivefold to sevenfold, reduced the MDMA-induced hyperthermia and increased the neuronal damage with neurotoxicity also appearing in the cortex. MDMA increased hydroxyl radical production in the hippocampus, the effect being more marked in rats pre-exposed to ethanol.

CONCLUSIONS

Binge ethanol administration enhances the MDMA-induced long-term 5-HT neurotoxicity by a mechanism not related to changes in acute hyperthermia but probably involving hydroxyl radical formation. The magnitude of this effect is more pronounced after increasing plasma acetaldehyde levels by aldehyde dehydrogenase inhibition.

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.

A genetic polymorphism in the regulatory sequences of human CYP2E1: association with increased chlorzoxazone hydroxylation in the presence of obesity and ethanol intake

To pursue the hypothesis that differences in the regulatory region of CYP2E1 are partially responsible for the intersubject variation in in vivo CYP2E1 activity, restriction enzyme digestion and Southern blotting of 36 human DNA samples were performed. The fractionated DNA was hybridized with a genomic probe to the upstream region of CYP2E1 from positions -2710 to -580. After digestion with the restriction enzyme XbaI, most subjects (69%) were homozygous for the expected band representing the XbaI fragment from positions -2270 to -408, whereas 31% had an unexpected, slightly larger band. Analyses of Southern blots of the same DNA samples cut by other restriction enzymes were consistent with the larger band containing an estimated 100-bp insertion and localized the mutation to a region from positions -2270 to -1672. To determine the functional significance of this mutation, in vivo CYP2E1 metabolic ability was determined in the same subjects using the 6-hydroxylation of chlorzoxazone as a probe. The presence of the insertion mutation was associated with greater CYP2E1 metabolic ability, but only among individuals who either were obese or had recently consumed ethanol (p < 0.01, both). These data are consistent with a DNA insertion that is associated with altered CYP2E1 induction. The incidence of the mutation was 31% among 65 African Americans and 6.9% among 58 Caucasians (p < 0.01). Thus, this CYP2E1 regulatory polymorphism not only enhances CYP2E1 metabolic ability, but is sufficiently common to impact susceptibility to CYP2E1-related diseases in at least two ethnic groups.

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

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

Acetaldehyde-induced changes in monoamine and amino acid extracellular microdialysate content of the nucleus accumbens

The effect of an acute intraperitoneal (i.p.) injection of acetaldehyde, 20 mg/kg or 100 mg/kg, on the microdialysate content of both amino acids and monoamines was studies in the nucleus accumbens (NA) by a microdialysis technique. Acetaldehyde, ACH, which was detectable at levels of 50-130 mumol/g brain tissue 10 min after injection, evoked a significant decrease in the extracellular microdialysis dopamine content, which was sustained for the period of the study, i.e. 120 min. Homovanillic acid, HVA, decreased significantly when the lower dose of ACH was administered while dihydrophenylacetic acid, DOPAC, showed no significant change with either dose of ACH during the period of the study. Serotonin levels decreased significantly after both doses of acetaldehyde, with significant increases of its major metabolite, hydroxyindolacetic acid, 5-HIAA, with the higher acetaldehyde dose. Taurine increased significantly, only during the first twenty minutes, after both doses of acetaldehyde, although neither of the excitatory amino acids assayed, glutamate and aspartate, nor the inhibitory amino acid, GABA, showed any significant changes. Acetaldehyde clearly evokes significant perturbation in the monoamine content of the NA, such changes being the converse to those reported for monoamines after ethanol administration, which might indicate a negative reinforcement effect.

Effect of D- and L-1,3-butanediol isomers on glycolytic and citric acid cycle intermediates in the rat brain

DL-1,3-butanediol (DL-BD) is an ethanol dimer which affords cerebral protection in various experimental models of hypoxia and ischemia but its mechanism of action is unknown. DL-BD is a ketogenic alcohol and it has been proposed that its protective effect was accomplished through cerebral utilization of ketone bodies. Since DL-BD is a racemic, its metabolic effects could be due to D, L or both isomers. The effects of equimolar doses of DL-, D- and L-BD (25 mmol/Kg) on cerebral metabolism were studied by measuring the cortical levels of the main glycolytic (glycogen, glucose, glucose 6-phosphate, fructose 1,6-diphosphate, pyruvate and lactate) and citric acid cycle (citrate, alpha-ketoglutarate and L-malate) intermediates. The two BD isomers exerted different effects on cerebral metabolism. Unlike L-BD, D- and DL-BD treatments resulted in a slight (+10%) but significant increase in citrate level whereas L-BD treatment led to significant reduction in pyruvate (-12%) and lactate (-24%) levels. These effects were apparently not linked to hyperketonemia, since DL-BHB treatment, which mimicked hyperketonemia induced by DL-BD, had no effect on cerebral metabolites but might be due to intracerebral metabolism of BD.

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

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

Differential effects of alcohols on intracerebral arterioles. Ethanol alone causes vasoconstriction

We compared the effect of the acute application of ethanol, methanol, 1-propanol, 1-butanol, urea, and mannitol (1-100 mM) on the basal tone of isolated-cannulated rat intracerebral arterioles to determine if the response of these arterioles to ethanol could be attributed to alteration of membrane fluidity or changes in osmolality. These arterioles spontaneously developed tone to 62.0 +/- 8.4% of passive diameter (44.2 +/- 11.9 vs. 70.9 +/- 14.7 microns). Ethanol caused a dose-dependent reduction in arteriolar diameter starting at 3 mM (p = 0.03), reaching a diameter of 81.4 +/- 3.0% of basal tone at 100 mM. In comparison, all other agents tested caused the arterioles to dilate, with the exception of 1-propanol, which produced inconsistent vessel responses. At 100 mM concentration, methanol, 1-butanol, urea, and mannitol dilated intracerebral arterioles by 116.1 +/- 12.7, 151.5 +/- 12.4, 131.1 +/- 17.0, and 149.8 +/- 6.6%, respectively. Thus, in a concentration range associated with acute intoxication, ethanol causes constriction of isolated intracerebral arterioles. The mechanism of action of ethanol cannot be accounted for solely based upon its physicochemical characteristics of osmolality or lipid solubility, but rather may reflect a more specific action on one or more cellular mechanisms responsible for determining basal intracerebral arteriolar tone. The characterization of the response of intracerebral arterioles to ethanol is important in view of epidemiologic links between ethanol consumption and cerebrovascular disease.

Effect of 1,3-butanediol on cerebral energy metabolism. Comparison with beta-hydroxybutyrate

Previous studies have shown that 1,3-butanediol (BD) has beneficial effects in experimental models of hypoxia or ischemia but the mechanism by which it exerts its protective effects remains unknown. BD is converted in the body to beta-hydroxybutyrate (BHB) and it has been proposed that its effects were linked to its ketogenic effect. The effects of BD (25 and 50 mmol/kg) on cerebral energy metabolism of rats were studied by measuring the cerebral level of energy metabolites and by evaluating the cerebral metabolic rate according to the Lowry's method. BD induced an increase in [cortical glucose]/[plasma glucose] ratio which was associated with a decrease in lactate level and an increase in glucose and glycogen stores. In contrast, BHB treatment which mimicked hyperketonemia equivalent to BD did not modify cerebral glycolysis metabolites. Calculation of the energy reserve flux after decapitation showed that BD did not reduce the cerebral metabolic rate excluding a protective effect due to a depressant, barbiturate-like, action. These results suggest that BD induces a reduction of cerebral glycolytic rate. However, the effect is not linked to hyperketonemia but might be due to intracerebral conversion of BD to BHB.

Molecular mechanism of ethanol metabolism by human brain to fatty acid ethyl esters

Ethanol metabolism in the human brain has been documented to occur with the formation of fatty acid ethyl esters. These neutral lipids can disorder membranes and interrupt mitochondrial function. Their formation is under the control of three synthases, localized to grey matter and purified to homogeneity. cDNA cloning demonstrates two of these enzymes to be GSH S-transferases and has enabled initiation of genetic studies of alcohol-induced CNS injury.

Induction of brain cytochrome P-450IIE1 by chronic ethanol treatment

Cytochrome P-450 mediated metabolism is potentially involved in the expression of the pharmacological and/or toxicological effects of a wide variety of drugs and environmental chemicals upon tissues which contain this metabolic system. In the present investigation, the presence of cytochrome P-450IIE1 and associated mono-oxygenase activities in brain and the effect of chronic ethanol treatment on brain cytochrome P-450 (P-450) were studied. Aniline hydroxylase, N-nitroso-dimethylamine N-demethylase and p-nitrophenol hydroxylase activities (known to be mediated by P-450IIE1) were detectable in brain microsomes from untreated rats and were about 5%, 125% and 8.3%, respectively, of the corresponding hepatic levels. Chronic ethanol treatment resulted in induction of the above enzyme activities in brain microsomes by 243%, 496% and 155%, respectively. Intake of ethanol for a prolonged period also resulted in the induction of total P-450 in the brain (150% of the control). Addition of the antisera raised against rat liver cytochrome P-450IIE1 markedly inhibited brain microsomal p-nitrophenol hydroxylase activity. Immunoblot analysis of rat brain microsomes using the above antisera also revealed the induction of brain cytochrome P-450IIE1 following chronic ethanol administration. Immunocytochemical localization of cytochrome P-450IIE1 using the above antisera, revealed the preferential localization of the enzyme in the neuronal cell bodies in the cortex, hippocampus, basal ganglia, hypothalamic nuclei and reticular nuclei in the brainstem of rats treated chronically with ethanol. Based upon these studies, it is conceivable that chronic alcohol ingestion could enhance the sensitivity of certain regions of the brain to environmental chemicals that are metabolized to more toxic derivatives by the P-450 system.

Enzymatic production of acetaldehyde from ethanol in rat brain tissue

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

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

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

Ischemic brain damage is not ameliorated by 1,3-butanediol in hyperglycemic rats

BACKGROUND AND PURPOSE

Treatment with the ketone body precursor 1,3-butanediol has been suggested to ameliorate hypoxic/ischemic brain damage. Butanediol could provide an alternative energy substrate for the brain, thereby decreasing the amount of glycolytically produced lactate. Hyperglycemia aggravates brain damage after brain ischemia and causes fatal postischemic seizures, probably by increasing the production of lactate and decreasing the pH. We studied whether butanediol treatment altered the adverse consequences following ischemia complicated by hyperglycemia.

METHODS

Hyperglycemic adult male rats were given 25 or 50 mmol.kg-1 body wt butanediol intravenously 30 minutes before 10 minutes of transient forebrain ischemia. Morphological evaluation was performed following perfusion-fixation after 15 hours of recovery. Blood concentrations of beta-hydroxybutyrate, acetoacetate, glucose, and lactate and brain tissue concentrations of energy metabolites were measured before and after ischemia.

RESULTS

Blood levels of ketone bodies increased in the butanediol-treated rats. Ischemia decreased the blood levels of acetoacetate but increased the levels of beta-hydroxybutyrate by a similar amount, resulting in unchanged high levels of total ketone bodies in the animals that received butanediol. Brain tissue levels of glucose, energy metabolites, and lactate showed no difference between butanediol- and saline-treated rats. Furthermore, compared with saline-treated animals butanediol-treated rats showed no decrease in brain damage and no attenuation in the development of postischemic seizures.

CONCLUSIONS

The ketone body precursor 1,3-butanediol offers no protective effect in transient forebrain ischemia complicated by hyperglycemia.

Beneficial effect of 1,3-butanediol on cerebral energy metabolism and edema following brain embolization in rats

We assessed the effect of 1,3-butanediol on cerebral energy metabolism and edema after inducing multifocal brain infarcts in 108 rats by the intracarotid injection of 50-microns carbonized microspheres. An ethanol dimer that induces systemic ketosis, 25 mmol/kg i.p. butanediol was injected every 3 hours to produce a sustained increase in the plasma level of beta-hydroxybutyrate. Treatment significantly attenuated ischemia-induced metabolic changes by increasing the concentrations of phosphocreatine, adenosine triphosphate, and glycogen and by reducing the concentrations of pyruvate and lactate. Lactate concentration 2, 6, and 12 hours after embolization decreased by 13%, 44%, and 46%, respectively. Brain water content increased from 78.63% in six unembolized rats to 80.93% in 12 saline-treated and 79.57% in seven butanediol-treated rats 12 hours after embolization. (p less than 0.05). The decrease in water content was associated with significant decreases in the concentrations of sodium and chloride. The antiedema effect of butanediol could not be explained by an osmotic mechanism since equimolar doses of urea or ethanol were ineffective. Our results support the hypothesis that the beneficial effect of butanediol is mediated through cerebral utilization of ketone bodies arising from butanediol metabolism, reducing the rate of glycolysis and the deleterious accumulation of lactic acid during ischemia.

Immunocytochemistry of alcohol dehydrogenase in the rat central nervous system

A sensitive immunocytochemical method for the localization of alcohol dehydrogenase (ADH) in the rat brain is described. The method employs rat liver ADH isolated and purified with Cap-Gapp affinity chromatography. Antiserum to rat liver ADH is generated in rabbits, and used in the peroxidase-antiperoxidase immunocytochemical method. The method is compatible with both light and electron microscopic methods of tissue preparation. In the present report we describe the identification of ADH in neurons of the mammillary bodies, periaqueductal gray, and the cerebral and cerebellar cortices of normal adult rats. In all brain tissues examined, the enzyme is limited to neuronal cytoplasm, and only to some neurons. The restriction of the enzyme to a limited percentage of neurons in the central nervous system may help to account for the difficulty in demonstrating the enzyme in whole brain homogenates, as the dilution of enzyme-bearing cytoplasm with a large volume of enzymatically inactive tissue would reduce the specific activity of the enzyme to near the limit of detectability. In the cerebellar cortex, the enzyme is found only in Purkinje cell cytoplasm. In the other regions examined, we are unable to identify by other criteria a specific neuronal class that consistently displays ADH reactivity. The reactive cells seem to be generally midrange in size and bipolar or multipolar in configuration. The presence of ADH in certain neurons leads us to speculate that intraneuronal ethanol metabolism may lead to focal accumulation of acetaldehyde. The intracellular presence of this toxin may in turn help to account for brain dysfunction in acute ethanol intoxication, and the neuropathology of chronic alcohol abuse.

Distribution and possible metabolic role of class III alcohol dehydrogenase in the human brain

In human brain, the sole alcohol dehydrogenase (ADH) present in significant quantity has been shown to be Class III (chi) ADH and this ADH is ineffective in generating potentially toxic and reactive acetaldehyde from ethanol at concentrations attainable in living brain tissue. We have extended this finding to show that Class I ADH potentially present is undetectable even when concentrated several hundred-fold. Purified Class III ADH from human brain is identical in its pattern of tryptic peptides and in other properties to Class III ADH from human liver. Immunohistochemical staining and western immunoblots using polyclonal antibodies reveal that Class III ADH is widely distributed in brian and most concentrated in the subependymal layer and perivascular areas. Class III ADH closely resembles omega-hydroxyfatty acid dehydrogenase and a possible role for the brain enzyme is in the oxidation of long chain fatty alcohols and omega-hydroxyfatty acids.

Protective action of 1,3-butanediol in cerebral ischemia. A neurologic, histologic, and metabolic study

1,3-Butanediol (BD) is converted in the body to beta-hydroxybutyrate, and previous studies have shown that hyperketonemia had beneficial effects in experimental models of generalized hypoxia. The aim of this study was to determine if BD would reduce brain damage following cerebral ischemia. A transient forebrain ischemia of 30-min duration was induced by the four-vessel occlusion technique in control and BD-treated rats (25 mmol/kg, i.p.; 30 min prior to ischemia). BD treatment led to significant improvement of neurologic deficit during the 72-h recovery period and reduced neuronal damage in the striatum and cortex but not in the CA1 sector of the hippocampus. Evaluation of cerebral energy metabolism before and at the end of the ischemic period showed that the treatment did not change the preischemic glycolytic and energy metabolite levels but attenuated the ischemia-induced metabolic alterations. It increased energy charge, phosphocreatine, and glucose levels, and reduced lactate accumulation. The decrease in brain lactate concentration might account for the beneficial effects of BD by minimizing the neuropathological consequences of lactic acidosis.

Neuroglial and neuroblastoma cell lines are capable of metabolizing ethanol via an alcohol-dehydrogenase-independent pathway

Two neuroglial cell lines (U-251 MG and C6) had a substantial capacity to convert ethanol to acetate in vitro largely by an alcohol dehydrogenase (ADH)-independent mechanism and three neuroblastoma cell lines (IMR-32, NB41A3, and Neuro-2a) had a lesser but significant ethanol-metabolizing capacity which was also either partly or largely ADH-independent. The ADH-independent pathway of ethanol metabolism by neural cells appeared to be dependent on one or more isoenzymes of cytochrome P-450. The data emphasize the possibility that the neurotoxicity of ethanol may be related to a relatively high ethanol-metabolizing capability of neural tissue and particularly of neuroglial cells.

Chemical modification of human aldehyde dehydrogenase by physiological substrate

Employing 3,4-dihydroxyphenylacetaldehyde (dopal) as a substrate for human aldehyde dehydrogenase (aldehyde:NAD+ oxidoreductase, EC 1.2.1.3) in anaerobic conditions, inactivation of both cytoplasmic E1 and mitochondrial E2 isozymes during catalysis has been observed. Incorporation of 14C-labelled dopal has been demonstrated by retention of label following denaturation and exhaustive dialysis and by peptide mapping following tryptic digestion. Incorporation of label gave linear plots vs. activity remaining with up to two molecules incorporated per molecule of enzyme and 30% activity remaining. Further incorporation (up to 16 molecules) occurred, but was non-linear when plotted vs. activity remaining. Protection against activity loss during incorporation of the first two molecules was afforded by NAD, NADH, chloral, and by chloral and NAD together, the last being the most effective. Saturation kinetics gave y-axis intercepts, suggesting interaction at a specific point on the enzyme surface. The Ki value from saturation kinetics was the same as that from the slope replot in catalytic reaction. Peptide mapping of tryptic digests showed that a single peptide was labelled, confirming specificity of interaction. Even in the absence of complete inactivation, the results suggest that reaction with the first two molecules occurs at some point on the enzyme surface important for enzyme activity. The possibility of such a reaction occurring in vivo is discussed.

Blockade of ethanol induced conditioned taste aversion by 3-amino-1,2,4-triazole: evidence for catalase mediated synthesis of acetaldehyde in rat brain

This investigation seeks to present evidence for the oxidation of ethanol in the brain via the peroxidatic activity of catalase and simultaneously provide evidence for the role of central acetaldehyde (ACH) in the mediation of an ethanol-induced conditioned taste aversion (CTA). Ethanol is capable of inducing a conditioned taste aversion. Pretreatment with the catalase inhibitor, 3-amino-1,2,4-triazole (AT), shows an attenuation of this ethanol-induced CTA. Animals receiving ethanol injections showed a CTA to a novel solution paired with a drug administration, while ethanol injected animals pretreated with AT did not show a CTA to ethanol administration. This effect of AT appears to be specific to the effects of ethanol as CTA's to morphine and lithium chloride were not affected by AT pretreatment. Peripheral levels of ethanol were the same in all animals regardless of pretreatment indicating that AT had no effect on peripheral levels of ethanol. These data increase support for the notion that acetaldehyde is produced directly in the brain and that it may be the agent mediating some of the psychopharmacological properties of ethanol.

chi-ADH is the sole alcohol dehydrogenase isozyme of mammalian brains: implications and inferences

Class III (chi) is the only alcohol dehydrogenase (ADH) in human, equine, bovine, simian, canine, and rodent brain and is the first to be identified, purified, and characterized from the brain of humans or other vertebrates. Like the corresponding isozymes from human placenta and liver, the chi-ADH isozymes purified from mammalian brain are neither inhibited by nor do they bind to immobilized pyrazole, and they oxidize ethanol only very poorly (Km greater than 2.5 M). Indeed, it would be incorrect to classify them as "ethanol dehydrogenases." They contain 4 g.atom of zinc/mol, bind 2 moles of NAD, and readily oxidize long-chain aliphatic and aromatic primary alcohols. These findings appear to exclude the possibilities that ADH protects the brain of these vertebrates against ethanol or its metabolic products and that the brain can generate energy for cerebral function from ADH-monitored ethanol metabolism. Thus chi-ADH must serve a totally different but as yet unknown role. The failure to detect any ethanol dehydrogenase activity in brain creates an intellectual dilemma only if it is assumed that such an enzyme has evolved and developed as a protective mechanism for ethanol detoxification in that organ, as has been assumed. Tissue and substrate specificities of ADH isozymes are likely to give new insight regarding their physiological roles.

Biochemical basis of alcoholism: statements and hypotheses of present research

Experimental results and theoretical considerations on the biology of alcoholism are devoted to the following topics: genetically determined differences in metabolic tolerance; participation of the alternative alcohol metabolizing systems in chronic alcohol intake; genetically determined differences in functional tolerance of the CNS to the hypnotic effect of alcohol; cross tolerance between alcohol and centrally active drugs; dissociation of tolerance and cross tolerance from physical dependence; permanent effect of uncontrolled drinking behavior induced by alkaloid metabolites in the CNS; genetically determined alterations in the function of opiate receptors; and genetic predisposition to addiction due to innate endorphin deficiency. For the purpose of introducing the most important research teams and their main work, statements from selected publications of individual groups have been classified as to subject matter and summarized. Although the number for summary-quotations had to be restricted, the criterion for selection was the relevance to the etiology of alcoholism rather than consequences of alcohol drinking.

In vivo analysis of dopamine and its metabolites in the caudate nucleus during euthermia and hibernation

Golden-mantled ground squirrels (Citellus lateralis) were chronically implanted with a unilateral push-pull cannula in the caudate nucleus. Perfusates obtained in these unanesthetized, unrestrained animals during the euthermic (non-hibernating) and hibernating states were analyzed for dopamine (DA) and its metabolites (homovanillic acid (HVA), 3,4-dihydroxyphenylacetic acid (DOPAC), and 3-methoxy-4-hydroxyphenethanol (MOPET) using high performance liquid chromatography with electrochemical detection. The data revealed clear differences in the performance of the caudate DA system in the two states. During the euthermic state, DA metabolism was indicative of a constant and high turnover rate. Free DA was not detectable in the majority of samples, HVA was detected at consistently high levels, and DOPAC and conjugated DA were present at low levels. By contrast, DA metabolism was sharply altered during hibernation. Free DA was present at high concentrations and HVA concentrations were low. DOPAC was not detected in any sample whereas MOPET was present in all samples. Conjugated DA was present at high concentrations during the second half of the hibernation bout. The shift in the post-release disposition of DA could enhance the stability of DA receptors (i.e. prevent supersensitivity) during the prolonged periods of reduced neural activity typical of hibernation.

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

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

Temporal changes in plasma levels and metabolism of ketone bodies by liver and brain after ethanol and/or starvation in C57BL/6J mice

The effects of ethanol and starvation on ketone body production and utilization were investigated. In the first experiment, adult C57BL/6J mice were divided into four groups: (i) control (fed); (ii) starvation (up to 31 h); (iii) ethanol (acute 5 g/kg i.p.); (iv) ethanol (ETOH) + starvation. Plasma ketone body (KB) concentrations in control mice remained constant at approx. 0.37 mM. The levels of KBs in starved mice began to increase at about 7 h and rose to a peak of 2.5 mM at about 24 h, then fell to 1.8 mM at 31 h. The levels in mice treated with ETOH began to rise soon after injection, reached 1.5 mM at 10 h, and returned to control levels by 15 h. Although there was no difference in elevated levels of KBs between two groups of mice treated with ETOH plus starvation and ETOH alone at 7-10 h, the level continued to rise steadily to 2.0 mM through 31 h in the former group. At 10 h post ETOH, mice either fed ad lib. or fasted had increased hepatic capacity to synthesize acetoacetate (AcAc) from palmitate; this effect was prolonged and enhanced by continued fasting for 24 h. In the brain, the rate of AcAc oxidation was twice that for beta-hydroxybutyrate (beta OHB) and glucose. Neither ETOH nor starvation affected energy production from KB and glucose. AcAc was also utilized for fatty acid synthesis and the rate of synthesis was stimulated by ETOH at 10 h after injection. The rate of lipogenesis from beta OHB accounted for less than 10% of that from AcAc. Together these experiments demonstrate that ETOH increases both hepatic ketone production and plasma KB levels for at least 10 h. ETOH alone led to elevated KB levels long before the rise due to starvation. In brain, at 10 h, an increased capacity to utilize AcAc for lipogenesis was found. The results indicate that ETOH through the production of KBs could provide an important source of energy and lipid precursors for the brain of mice.

Higher correlation of ethanol consumption with brain than liver aldehyde dehydrogenase in three strains of rats

Voluntary ethanol consumption and high Km (mM range) brain and liver aldehyde dehydrogenase (ALDH) activity were measured in male rats of the Long-Evans, Wistar and Sprague-Dawley strains. The total amounts of ethanol consumed by the three strains did not differ significantly, nor did the levels of cerebral ALDH activity. Levels of brain ALDH did not differ as a function of ethanol exposure and across strains. Levels of ethanol consumption correlated better with levels of brain than liver aldehyde-oxidizing capacity, which were tested separately for each strain and also combining all the animals. Inherent variation in brain ALDH may be a biochemical counterpart of observed differences in voluntary ethanol intake within strains.

Alcohol-induced euphoria enhanced by disulfiram and calcium carbimide

In a double-blind study, subjects were treated with either disulfiram or calcium carbimide, inhibitors of acetaldehyde elimination, prior to consumption of low doses of alcohol. Self-rating scales, individual interviews, and observations by independent judges revealed that experimental subjects manifested enhanced changes in mood and euphoria compared to placebo control subjects.

Quantitation of alcohol dehydrogenase in human tissue and serum by an enzyme-linked immunosorbent assay (ELISA)

An enzyme-linked immunosorbent assay for human alcohol dehydrogenase (ADH) has been developed. The method is based on preventing anti-ADH antibodies from binding to ADH-coated polystyrene microtiter wells by preincubation with serial dilutions of ADH-containing samples. The test detects ADH below 50 ng/ml. The sensitivity of the assay is superior to the commonly used photometric method and is particularly useful to quantitate ADH in crude tissue homogenates and in serum. Enzymatically active as well as inactive ADH can be detected, shown by the longer half-life of the ADH antigenicity (6.5 months) as compared to the half-life of the enzymatic activity (3.5 months). Approximately 10% of the total soluble protein in liver homogenates was ADH protein. The specific activity was around 0.4 IU/mg. It was higher in "atypical" livers although the absolute amount of ADH protein in these livers was identical with that in normal livers. ADH protein paralleled ADH activity in liver, stomach, and kidney homogenates. Normal serum on the average contained 59 +/- 16 ng/ml ADH (n = 9). Activity at these levels lies beyond the limits of spectrophotometric detectability. Serum of patients with liver disease exhibited elevated ADH levels paralleled by increased gamma-glutamyl transpeptidase (GGT), glutamate oxalacetate transaminase (GOT), glutamate pyruvate transaminase (GPT), but not alkaline phosphatase (AP) activities.

Acute effect of ethanol on metabolite concentrations of dog pancreas in vivo

Sections of dog pancreas were freeze-clamped before and 1 hr after oral administration of 1 g/kg of ethanol in anesthetized, respirated, 24-hr-fasted animals, and multiple metabolites were determined in the perchloric acid extract of the frozen tissue. In spite of the fact that the pancreas contained little or no alcohol dehydrogenase activity (less than 0.01 IU/g of tissue), significant metabolite changes did occur. Although arterial oxygenation was constant and adequate (pO2 = 100 +/- 7 mM Hg) there was a significant 1.7-fold rise in L-lactate and fall in the cytoplasmic free [NAD+]/[NADH] ratio from 719 +/- 87 to 453 +/- 88 after ethanol. Except for a tendency for L-malate and L-alpha-glycerolphosphate to parallel the rise in L-lactate, there was little consistent disturbance in the remainder of the glycolytic metabolites (glucose, glucose 6-phosphate, pyruvate, 2-ketoglutarate, citrate, 3-phosphoglycerate, etc.) or in high energy intermediates and related compounds (ATP, creatine phosphate, ADP, Pi, creatine). There was, however, an unexpected and significant fall in the levels of the major transaminating amino acids, L-glutamate, L-aspartate, and L-alanine. The results can be only partially explained by an influence of blood-borne metabolites and imply significant effects of ethanol on the metabolism of the pancreas in vivo not directly mediated through alcohol dehydrogenase. Evidence is presented suggesting that both L-alanine and L-aspartate aminotransferases are functioning near equilibrium in the pancreas in vivo.

Aldehyde dehydrogenases in rat brain. Subcellular distribution and properties

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

Effect of ethanol on superoxide dismutase activity in cultured neural cells

Superoxide dismutase (EC 1.15.1.1) activity was investigated in several types of neural cells cultivated in the presence of 100 mM ethanol. Superoxide dismutase was inhibited by acute treatment with ethanol. Chronic treatment with ethanol specifically inhibited superoxide dismutase in glial cells. In all instances withdrawal of ethanol produced a quick return to control values. Inhibition of superoxide dismutase by ethanol may increase toxic oxygen radicals in nervous tissue.

Validity of cerebral blood flow measurements obtained with quantitative tracer techniques

A great number of results for the cerebral blood flow obtained in the animal with quantitative tracer techniques have been collected from the literature. They are exposed in order to compare both normal flow values in different laboratory species, and the characteristics, accuracy and sensitivity of each technique. A dramatic overall dispersion of flow values is observed, allowing neither the flow level particular to each species to be estimated, nor the average value provided by a given technique to be found. The physiological and technological causes of such a dispersion are discussed. Several techniques seem to have limitations which even alter the interpretation of their results, and especially the origin of the local or regional blood flow results. Other techniques may be criticized from the quantitative standpoint, but give more reliable results.

Ethanol oxidation by rat brain in vivo

Can brain metabolize ethanol? We present data demonstrating that brain catalase in conjunction with endogenous H2O2 will oxidize ethanol in vivo. The method is based on an H2O2-dependent inhibition of brain catalase in vivo by 3-amino-1,2,4-triazole and its prevention by ethanol. The irreversible inhibition of catalase by aminotriazole is known to proceed via the reaction of (catalase-H2O2) compound I with aminotriazole. Inhibition can be prevented by compounds that are oxidized by compound I. Ethanol is one such compound. Prevention of the inhibition of brain catalase in vivo by prior administration of ethanol constitutes indirect evidence for the oxidation of ethanol to acetaldehyde in rat brain. The catalase content of the tissues represented catalase in the brain parenchyma, from which erythrocytes and capillaries had been excluded. Ethanol did not alter the levels of aminotriazole in brain. These results constitute the first demonstration of ethanol oxidation by living brain.

Butanediol induced ketosis increases tolerance to hypoxia in the mouse

In previous studies from our laboratory a positive correlation between elevated blood ketone levels and the survival time (ST) during hypoxia (4-5% oxygen) was observed in fasted and alloxan diabetic mice. To test the hypothesis that ketosis was somehow increasing the tolerance of mice to hypoxia, we induced ketosis by either oral (PO), intraperitoneal (IP), or intravenous (IV) 1,3-butanediol (BD). Blood beta-hydroxbutyrate increased from 0.33 +/- 0.06 mM to 3.32 +/- 0.08 mM for PO, 1.2 +/- 0.2 mM for IV and 0.83 +/- 0.15 mM for IP. BD was associated with an increase in ST to 458% (n = 19) when given PO, 217% (n = 12) by IP route, and 560% (n = 13) by the IV route. The effect of ambient temperature (Ta) on this phenomenon was evaluated at 12, 22, 32, and 34 degrees C. At each Ta, IV BD at 1.4 mmole/mouse was associated with an increase in ST to 525, 559, 151, and 145% of control, respectively. The absolute ST of both control and treated mice was greater at Ta of 12 and 22 degrees C. Hypoxia, however, was associated with a decrease in body temperature in each group. It is concluded that the artificial induction of ketosis by BD is associated with an increase in ST of mice exposed to hypoxia.

[Effect of withdrawal from alcohol on extra-hepatic and alcohol- and aldehyde-dehydrogenasic activities in the rat (author's transl)]

Alcohol- and aldehyde-dehydrogenasic activities have been measured in different tissues; these activities are modified after chronic alcoholic intoxication and/or withdrawal in digestive tract, spleen, kidney and lung. The results underline the possible relationship between extra-hepatic ethyl-oxidation and withdrawal syndrome.

Paired helical filaments in rat spinal ganglia following chronic alcohol administration: an electron microscopic investigation

Young Wistar rats were given a 15% (v/v) ethanol solution ad libitum for at least 6 months, spinal ganglia (C6-7 and L1-2) in some of the experimental animals showed paired helical filaments. These curvilinear profiles consisted of 10 nm filaments with the twist every 35nm. There was also an increase in granular material and in nematosomes. Whether these features may be caused by an impaired cerebral protein biosynthesis is discussed.

Sources of energy for the brain and physical dependence on ethanol

This paper describes a proposed biochemical mechanism to account for physical dependence on ethanol. Long-term exposure to a continuous and plentiful supply of ethanol-derived hydrogens in NADH and ethanol-derived acetyl-CoA (AcCoA) may lead to a decreased rate of production of endogenous hydrogens in NADH and endogenous AcCoA in compensation. It is proposed that physical dependence on ethanol occurs when ketolytic- and glycolytic-based NADH and AcCoA synthetic rates fall below the rate of utilization by the brain; the brain then "depends" on alcohol-derived NADH and AcCoA for normal function.