Ethanol inhibits the activity of the B form of monoamine oxidase in human platelet and brain tissue

Use of illicit amphetamines is associated with long-lasting changes in hand circuitry and control

OBJECTIVE

The study aim was to determine if use of illicit amphetamines or ecstasy is associated with abnormal excitability of the corticomotoneuronal pathway and manipulation of novel objects with the hand.

METHODS

Three groups of adults aged 18-50 years were investigated: individuals with a history of illicit amphetamine use, individuals with a history of ecstasy use but minimal use of other stimulants, and non-drug users. Transcranial magnetic stimulation was delivered to the motor cortex and the electromyographic response (motor evoked potential; MEP) was recorded from a contralateral hand muscle. Participants also gripped and lifted a novel experimental object consisting of two strain gauges and an accelerometer.

RESULTS

Resting MEP amplitude was larger in the amphetamine group (6M, 6F) than the non-drug and ecstasy groups (p < 0.005) in males but not females. Overestimation of grip force during manipulation of a novel object was observed in the amphetamine group (p = 0.020) but not the ecstasy group.

CONCLUSIONS

History of illicit amphetamine use, in particular methamphetamine, is associated with abnormal motor cortical and/or corticomotoneuronal excitability in males and abnormal manipulation of novel objects in both males and females.

SIGNIFICANCE

Abnormal excitability and hand function is evident months to years after cessation of illicit amphetamine use.

Influence of chronic alcohol consumption on histaminergic neurons of the rat brain

AIMS

To clarify the effect of chronic alcohol consumption on the brain histaminergic neurons in rats.

METHODS

Male Wistar rats were given 20% ethanol as the only source of drinking during 6 months, control rats had a free access to water. The samples of hypothalamus were prepared for light and electron microscopy accompanied by morphometry to examine the brain histaminergic neurons of E2 group.

RESULTS

Chronic ethanol consumption increased the amount of histologically abnormal forms of histaminergic neurons and decreased the whole amount of E2 histaminergic neurons (for 5%). The neuron bodies and nuclei increased in size and sphericity, the nuclear/cytoplasmic ratio decreased by 15%. The ultrastructural changes in histaminergic neurons demonstrate the activation of their nuclear apparatus, both destruction and hypertrophy and hyperplasia of organelles, especially lysosomes. Chronic ethanol consumption induces the disturbances in cytoplasmic enzymes of neurons: increases the activity of type B monoamine oxidase, dehydrogenases of lactate and NADH and, especially, marker enzyme of lysosomes acid phosphatase as well as inhibits the activity of dehydrogenases of succinate and glucose-6-phosphate.

CONCLUSION

Chronic alcohol consumption affects significantly the structure and metabolism of the brain histaminergic neurons, demonstrating both the neurotoxic effect of ethanol and processes of adaptation in those neurons, necessary for their survival.

Polymorphisms in genes encoding dopamine signalling pathway and risk of alcohol dependence: a systematic review

BACKGROUND

Alcohol dependence (AD) is one of the major elements that significantly influence drinking pattern that provoke the alcohol-induced organ damage. The structural and neurophysiologic abnormalities in the frontal lobes of chronic alcoholics were revealed by magnetic resonance imaging scans. It is well known that candidate genes involved in dopaminergic pathway are of immense interest to the researchers engaged in a wide range of addictive disorders. Dopaminergic pathway gene polymorphisms are being extensively studied with respect to addictive and behavioral disorders.

METHODS

From the broad literature available, the current review summarizes the specific polymorphisms of dopaminergic genes that play a role in alcohol dependence.

RESULTS

No evidence indicating any strong association between AD and polymorphisms of dopamine pathway genes has emerged from the literature.

DISCUSSION

Further studies are warranted, considering a range of alcohol-related traits to determine the genes that influence alcohol dependence.

Effect of administered ethanol on protein kinase C in human platelets

There are numerous reports of the effect of ethanol on protein kinase C (PKC) in animals or with in vitro systems. However, the effect of ethanol on PKC in humans has not been extensively investigated despite the large number of studies involving PKC and human platelets. In this study, we administered ethanol to human volunteers and determined the level of PKC before and after a 0.4 g/kg dose of ethanol. We studied Native Americans and Caucasians of both sexes. There was an increases in PKC activity 60 min after ethanol administration. There were no ethnic, age, nor gender differences detected, nor was there any correlation between family history of alcoholism and the basal or stimulated platelet PKC levels. Neither was there any correlation of basal or stimulated PKC activity with the genotypes for ADH2, ADH3, ALDH2, CYP2E1, and CYP1A2.

Monoamine oxidase gene transcription in human cell lines: treatment with psychoactive drugs and ethanol

In the present study transcriptional activities has been measured with different fragments of the 5'-flanking sequence of the human monoamine oxidase (MAO) genes linked to human growth hormone which was used as a reporter gene. SH-SY5Y neuroblastoma cells and 1242 MG glioma cells were compared under basal conditions as well as after treatments with different drugs. Under basal conditions, the relative reporter activities of the different promoter fragments were similar for both cell lines. No changes in promoter activities, were observed when cells were treated with L-deprenyl, lithium chloride or raclopride. In contrast, increases (2-3-fold) in both reporter gene expression and enzyme activity were observed after ethanol treatment of cells transfected with MAO-B fragments. Gel retardation analysis showed that ethanol caused changes in transcription factor binding to the MAO-B core promoter in both the SH-SY5Y and 1242 MG cell lines in a cell-type specific fashion.

Monoamine oxidases and alcoholism. II. Studies in alcoholic families

Thirty-five alcoholic families have been studied to investigate the relationship between DNA markers at the monoamine oxidase (MAO) loci and 1) platelet activity levels and 2) alcoholism. A quantitative linkage analysis failed to reveal any evidence that the variation in activity levels cosegregates with the DNA markers. A sib-pair analysis did not reveal a significant excess of MAO haplotype sharing among alcoholic sibs, although the deviation from random sharing was in the direction consistent with an X-linked component. A reanalysis of platelet MAO activity levels in a subset of these families revealed that the lower levels previously found in alcoholics is more likely due to the differences between males and females. Only among males and only when a "broad" definition of alcoholism is used (and MAO activity levels are transformed to normality) does it appear that alcoholics have depressed activities compared to nonalcoholics. Finally, when the confounding due to gender difference is removed, no differences between type I and type II alcoholics are found in these families.

Monoamine oxidases and alcoholism. I. Studies in unrelated alcoholics and normal controls

Low platelet MAO activity has been associated with alcoholism. In order to evaluate the role of MAO genes in susceptibility to alcoholism, we have taken a biochemical and molecular genetic approach. The sample consisted of 133 alcoholic probands who were classified by subtypes of alcoholism and 92 normal controls. For those subjects typed for platelet MAO activity, alcoholics (N = 74) were found not to differ from the non-alcoholics controls (N = 34). Neither was there a significant difference between type I and type II alcoholics or between either subtype and normal controls. However, we do find significant differences between male and female alcoholics, but not between male and female controls. The allele frequency distribution for the MAO-A and MAO-B dinucleotide repeats is different between the alcoholic sample (N = 133) and the normal control sample (N = 92). In a two-way analysis of variance of MAO-B activity as a function of the allelic variation of each marker locus and diagnosis, there is no evidence for mean differences in activity levels for the different alleles. Our findings do not rule out a role for the MAO-B gene in controlling the enzyme activity because the dinucleotide repeats are located in introns.

Preliminary evidence for an association of a dinucleotide repeat polymorphism at the MAOA gene with early onset alcoholism/substance abuse

An association between the liability to early onset alcoholism/substance abuse and a recently discovered dinucleotide repeat length polymorphism at the MAOA gene (MAOCA-1) was examined using polymerase chain reaction (PCR). A significant correlation between the presence/absence of the disorder and the length of the MAOCA-1 repeat was found in males, but not females, with "long" alleles (repeat length above 115 bp) associated with both increased risk for the disorder and lower age of onset of substance abuse. These preliminary data suggest that further exploration of the relationship between the MAOA gene and behavioral traits in an expanded sample is warranted.

Longitudinal observations of monoamine oxidase B in alcoholics: differentiation of marker characteristics

The marker characteristics of monoamine oxidase B (MAO B) in human platelets were investigated in a clinical study of 59 alcoholics (diagnosed according to the criteria of ICD-10) observed over a period of 6 months. Demographic and family history were obtained by a structured interview, including the substance abuse section of CIDI (Composite International Diagnostic Interview). The patient's personality was assessed by Cloninger's Tridimensional Personality Questionnaire (TPQ). Blood samples were first drawn during chronic intoxication (day of admission to the hospital for detoxication), after short-term abstinence (8 days later), medium-term (3 months later), and long-term abstinence (6 months later). A group of 22 matched healthy nonalcoholics served as controls studied under sober conditions and during acute intoxication (4 hr after ingestion of 1 g ethanol/kg body weight). All platelet samples were investigated with 6 kynuramine concentrations as substrate (fluorometric assay) in the absence and presence of 200 mM ethanol (ETOH) in vitro. MAO B activity was significantly reduced in alcoholics during chronic intoxication (Vmax: 2.70 +/- 0.15 nmol/mg protein) compared with sober (Vmax: 3.25 +/- 0.23 nmol/min/mg protein) and acutely intoxicated controls that turned to normal during abstinence. However, MAO B activity obtained during medium- and long-term abstinence was significantly lowered in patients with high novelty-seeking and impulsiveness scores in the TPQ, a history of suicide attempts, or an alcoholic mother. The affinity of MAO B (Km values) was unchanged in alcoholics at any time investigated. Addition of ETOH in vitro reduced the affinity.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in brain MAO activity and glycogen levels upon chronic alcoholization of three successive generations of rats

Changes in neurobiological parameters were examined from early life (10 days post-natal) until late adulthood (8 months post-natal) in three successive generations of alcoholized rats. The mean daily consumption of alcohol by the 2nd and 3rd generation rats (7.40 +/- 0.22 and 7.70 +/- 0.20 g ethanol/kg body weight, respectively) was significantly greater than that of the 1st generation alcoholized group (4.26 +/- 0.33 g/kg). Brain/body weight ratios of alcoholized rats, 10 days post-natal, were significantly greater than controls, with 1st generation alcoholized rats presenting significantly greater brain/body weight ratios than those of the 2nd or 3rd generation, which tended toward control weights and ratios. This difference between alcoholized rats and controls persisted, although to a lesser extent, at 8 months post-natal. Glycogen content in the brains of rats of all alcoholized generations was significantly lower than in controls at 10 days post-natal, with a reversal of this situation in later life for 2nd and 3rd generation rats, which presented significantly greater cerebral glycogen levels than control or 1st generation alcoholized rats (which had an equivalent cerebral glycogen content). In 10-day-old rat pups, monoamine oxidase (MAO) activity in brain tissues had a tendency (mostly non-significant) to be greater in alcoholized rats than in controls, with a reversal of this situation, ie a statistically significant decrease in MAO activity in the 2nd and 3rd alcoholized generations with respect to controls, in 8-month-old rats. MAO activity in adrenal glands of alcoholized rats was greater than in controls at 10 days post-natal, and this difference persisted at 8 months.

Alterations in dopamine metabolism by intraperitoneal ethanol in rats selected for high and low ethanol preference: a 3-methoxytyramine study

Effects of an ethanol dose (1 g/kg, IP) on the metabolism of dopamine (DA) in the nucleus accumbens, striatum and hypothalamus of ethanol-naive alcohol-preferring (AA) and alcohol-avoiding (ANA) rats were studied. Rats were sacrificed by focused-beam microwave irradiation of the brain 20 minutes after ethanol administration, and the concentrations of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), assumed to reflect DA metabolism, and of 3-methoxytyramine (3-MT), assumed to reflect DA release, were measured using gas chromatography-mass spectrometry. Basal striatal DOPAC and HVA concentrations were higher in the AA rats in comparison with ANA rats. Ethanol increased HVA, but not DOPAC, concentration in the nucleus accumbens and striatum, but not in the hypothalamus. There was a significant rat line x ethanol treatment interaction with respect to HVA concentration in the nucleus accumbens. The increase in HVA was higher in the AA than ANA rats. Basal 3-MT concentration was not changed by ethanol, except in the nucleus accumbens, where a significant rat line x ethanol treatment interaction was found. A decrease in 3-MT concentration was only detected in the ANA rats. After inhibition of monoamine oxidase with pargyline hydrochloride (75 mg/kg, IP, 10 min before sacrifice), 3-MT accumulation was decreased by ethanol, especially in the nucleus accumbens of both AA and ANA rat lines as well as in that of nonselected Wistar rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Platelet MAO activity in type I and type II alcoholism

Lowered activity of the enzyme MAOB in the platelets and other tissues of alcoholics than of nonalcoholics is the most replicated biological finding in genetic research in alcoholism. Data presented here and elsewhere also indicate that the relationship between MAOB activity and alcoholism extends to the clinical subtypes referred to as Type I and Type II alcoholism. A detailed examination of the relationship between in vitro platelet MAOB activity levels, alcoholic subtype, and general mental health status among the relatives of the probands suggests that low MAOB activity is a marker of increased risk overall and that the families of Type II alcoholics have a higher genetic risk loading than do the families of Type I alcoholics. This increased genetic loading is probably due to the classification of Type II alcoholics on the basis of features related to severity of illness and additional psychiatric features such as personality disorders. Although the families of alcoholics tend to have higher levels of psychiatric illness compared to the general population, the overall risk is compounded in the families of Type II alcoholics, and these differences in underlying risk are reflected in the observed differences in MAOB activities. Thus, MAOB is not a biological/genetic marker of alcoholism sensu stricto but is rather a biological/genetic marker of an underlying pathophysiologic process leading to alcoholism and other psychiatric illness. The task now before us is to understand this process and how the activity of MAOB is involved.

Monoamine oxidase (MAO; E.C. 1.4.3.4) characteristics of platelets influenced by in vitro and in vivo ethanol on alcoholics and on control subjects

Ethanol (ETOH) in vitro displays a competitive inhibition of human platelet MAO-B with a Ki of 270 +/- 30 mM. Lineweaver-Burk analyses with 6 substrate concentrations (5-160 microM kynuramine) in the presence or absence of 200 mM ETOH were performed with platelets of alcoholics before withdrawal (Alc day 1), one week (Alc day 8) and 3 months (Alc mon 3) after withdrawal as well as in control subjects without and after ETOH intake. In all groups the Km increases highly significantly (p < 0.001) but the Vmax is unchanged by the presence of ETOH in vitro supporting the view of a competitive inhibition in each group. The Vmax of Alc day 1 is significantly 25% decreased, of Alc day 8 unchanged and of Alc mon 3 nonsignificantly 19% decreased in comparison with the controls. The increase of the Km in the presence of 200 mM ETOH is significantly 15% reduced in Alc day 1 and 9% in Alc day 8 but unchanged in Alc mon 3 compared with the controls.

The effects of ethanol on rat brain monoamine oxidase activities

In contrast to the reported behaviour of human platelet MAO-B, chronic ethanol feeding does not significantly affect the sensitivities of either MAO-A or -B from rat brain to inhibition by ethanol in vitro. The thermal stabilities of rat brain MAO-A and -B are not significantly affected by chronic ethanol feeding.

Low platelet gamma-aminobutyrate aminotransferase and monoamine oxidase activities in chronic alcoholic patients

The activities of gamma-aminobutyrate aminotransferase (GABA-T) and monoamine oxidase (MAO) were estimated in blood platelets from 25 male chronic alcoholics and from 27 healthy male volunteers without histories of alcohol abuse. Based on clinical criteria, the alcoholics were classified into type 1 or type 2 alcoholism. The activity of GABA-T was found to be lower both in type 1 and type 2 alcoholics than in healthy volunteers. With regard to MAO, the platelet activity was found to be significantly lower only in type 2 alcoholics in concordance with previous reports. No significant correlation was found between the activities of GABA-T and MAO in the blood platelets of healthy volunteers. The inhibitory effect of 400 mM ethanol on the platelet MAO activity increased with decreasing concentrations of the substrate phenylethylamine. The degree of inhibition of ethanol on the platelet MAO activity, however, did not differ significantly between alcoholics and controls.

Biological markers of alcoholism

Biological markers are biochemical or physiological characteristics which may help to classify a person according to the presence or absence of some disease or risk of disease, either with respect to their current status or future susceptibility. Many biological markers related to alcoholism have been described; this review suggests a classification of them and indicates areas where they are well-established and other areas where further investigation may be useful.

Platelet MAO in subtypes of alcoholism

A number of investigators have observed low platelet monoamine oxidase (MAO) activity in alcoholism. There is also preliminary evidence suggesting that low enzyme activity is principally associated with one of two putative subtypes of alcohol dependence, i.e., type II (male limited). The results of this study are consistent with two previous reports of reduced platelet MAO activity in type II male alcoholics as compared with type I male alcoholics and normal, healthy male controls. Type I (milieu-limited) alcoholics showed a smaller reduction in enzyme activity. The observed differences do not appear to be related to concurrent use of other psychoactive substances, characteristic differences in age between type I alcoholics and type II alcoholics, antisocial personality disorder, or variation in platelet size. Low platelet MAO activity in alcoholics is possibly related to both state and trait factors and may be a useful biochemical measure to assist with subtyping.

Differences in platelet enzyme activity between alcoholics and nonalcoholics

Blood platelets are an accessible tissue that reflects the activity of many enzymes found in the brain. To investigate the possible effect on such enzymes of long-term consumption of large quantities of ethanol, we assayed the activities of two enzymes, monoamine oxidase and adenylate cyclase, in platelet membranes of men with alcoholism and controls matched for sex and age. We also compared these two groups in terms of the inhibition of platelet monoamine oxidase activity by ethanol in vitro (400 mM), and in terms of the stimulation of adenylate cyclase activity by various agents. There was no significant difference in monoamine oxidase activity between the alcoholics and the controls. However, the inhibition of monoamine oxidase by ethanol was significantly higher in the platelets of alcoholics. The basal activity of adenylate cyclase was the same in platelets from the alcoholics and the controls, but the platelet adenylate cyclase activity after stimulation with guanine nucleotide, cesium fluoride, or prostaglandin E1 was significantly lower in alcoholics. These differences were not associated with age, race, smoking, or illicit drug use, and there was no significant correlation with the duration of problems with alcohol. The changes were long-lasting; cesium fluoride-stimulated adenylate cyclase activity was lower in alcoholic subjects who had abstained from alcohol for one to four years. Discriminant analysis showed that the use of values for the inhibition of monoamine oxidase activity by ethanol and cesium fluoride-stimulated adenylate cyclase activity correctly classified 75 percent of the alcoholics and 73 percent of the controls. These measures may be of value either as indexes of excessive alcohol consumption or as an indication of a predisposition to alcoholism.

In vivo relationship between monoamine oxidase type B and alcohol dehydrogenase: effects of ethanol and phenylethylamine

The role of acute ethanol (2.5 g/kg i.p.) and phenylethylamine (100 mg/kg i.p.) on the brain and platelet monoamine oxidase activities, hepatic cytosolic alcohol dehydrogenase, redox state and motor behaviour were studied in male rats. Ethanol on its own decreased the redox couple ratio, as well as, alcohol dehydrogenase activity in the liver whilst at the same time it increased brain and platelet monoamine oxidase activity due to lower Km with no change in Vmax. The elevation in both brain and platelet MAO activity was associated with ethanol-induced hypomotility in the rats. Co-administration of phenylethylamine and ethanol to the animals, caused antagonism of the ethanol-induced effects described above. The effects of phenylethylamine alone, on the above mentioned biochemical and behavioural indices, are more complex. Phenylethylamine on its own, like ethanol, caused reduction of the cytosolic redox ratio and elevation of monoamine oxidase activity in the brain and platelets. However, in contrast to ethanol, this monoamine produced hypermotility and activation of the hepatic cytosolic alcohol dehydrogenase activity in the animals. The results suggest that some of the toxic actions of ethanol in rats may be mediated through the activation of monoamine oxidase type B, with the consequent depletion of the endogenous levels of phenylethylamine. The data appear to support the concept of phenylethylamine involvement in affective disorders.

Effects of beta-phenylethylamine on locomotor activity, body temperature and ethanol blood concentrations during acute ethanol intoxication

Beta-phenylethylamine (PEA) is an endogenous amine which is metabolised by MAO B. The function of this enzyme is known to be modified by ethanol so we have studied the interactions of PEA with ethanol. Rectal temperatures of rats were determined and animals pretreated with ethanol (2.5 g kg-1 IP) 90 min before PEA 20, 40, 100 mg kg-1 IP). Spontaneous locomotor activity (SLA) was then recorded, for 30 min, temperatures redetermined and blood ethanol levels evaluated. PEA increased SLA but did not alter rectal temperatures, and at 40 mg kg-1 it not only attenuated ethanol hypothermia and blood levels but also modified ethanol hypomotility. The highest dose of PEA (100 mg kg-1) decreased blood ethanol concentration and sedation but did not counteract the hypothermia. Thus PEA increased ethanol clearance, though the underlying mechanism is not totally clear. This finding is discussed in relation to its catecholaminergic and enzyme inducing characteristics.

Potentiation by deprenyl of the autoreceptor-mediated inhibition of [3H]-5-hydroxytryptamine release by 5-methoxytryptamine

The 5-hydroxytryptamine (5HT) receptor agonist, 5-methoxytryptamine, inhibited in a concentration-dependent manner the electrically-evoked release of 3H-5HT from superfused rat hypothalamic slices, with an IC50 of 560 nmol/l, without affecting the spontaneous outflow of radioactivity. In the presence of the selective monoamine oxidase B (MAO B) inhibitor, (-)-deprenyl (1 mumol/l), the concentration-effect curve for 5-methoxytryptamine was shifted significantly to the left, and the IC50 was decreased to 25 nmol/l. Under the same experimental conditions, the potency of the 5HT receptor agonist lysergic acid diethylamide (LSD) at inhibiting the electrically-evoked release of 3H-5HT was the same in the presence as well as in the absence of (-)-deprenyl. The IC50 values for LSD were 34 nmol/l in the absence of deprenyl, and 31 nmol/l in the presence of the MAO B inhibitor. It is concluded that deprenyl potentiates the inhibition by 5-methoxytryptamine of 3H-5HT release, by preventing its inactivation through MAO B. Since 5-methoxytryptamine may be present in the pineal gland of some species, the potent effects of this 5-HT receptor agonist on serotoninergic neurotransmission may be of physiological relevance.