Platelet MAO during the alcohol withdrawal syndrome

The role of MAO in personality and drug use

Monoamine oxidases, both MAO-A and MAO-B, have been implicated in personality traits and complex behaviour, including drug use. Findings supporting the involvement of MAO-A and MAO-B in shaping personality and in the development of strategies of making behavioural choices come from a variety of studies that have examined either prevalence of gene variants in clinical groups or population-derived samples, estimates of enzyme activity in blood or, by positron emission tomography, in the brain and, most recently, measurement of methylation of the gene. Most of the studies converge in associating MAO-A and MAO-B with impulsive, aggressive or antisocial personality traits or behaviours, including alcohol-related problems, and for MAO-A available evidence strongly supports interaction with adverse environmental exposures in childhood. What is known about genotype effects, and on expression and activity of the enzyme in the brain and in blood has not yet been possible to unite into a mechanistic model of the role of monoamine systems, but the reason for this low degree of generalization is likely caused by the cross-sectional nature of investigation that has not incorporated the developmental effects of MAO-s in critical time windows, including the foetal period. The "risk variants" of both MAO-s appear to increase behavioural plasticity, as supportive environments may particularly well enhance the hidden potential of their carriers. Importantly, male and female brain and behaviours have been found very different with regard to MAO×life events interaction. Future studies need to take into consideration these developmental aspects and sex/gender, as well as to specify the role of different types of environmental factors.

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.

Neuropsychological function and platelet monoamine oxidase activity levels in type I alcoholic patients

AIMS

To explore neuropsychological function in two differentiated patterns of platelet monoamine oxidase B (MAO B) activity in alcoholic patients.

METHODS

Neuropsychological examination and platelet MAO B activity extracted from blood were collected from 42 alcohol-dependent patients recruited in the alcoholism unit (NETER) of the Psychiatric Service of Santa Maria University Hospital.

RESULTS

Alcoholics presented significantly low levels of platelet MAO B activity, when compared with control subjects; platelet MAO B activity in alcoholics classified as "under average subgroup" showed significant lower scores in the Raven Progressive Matrix and higher scores in hostility dimension, when compared with platelet MAO B activity in "above average subgroup."

CONCLUSIONS

Results suggested platelet MAO B as a trait marker also to type I alcohol-dependent patients and the two observed associations between platelet MAO B activity with neurocognitive measures of executive functions (nonverbal reasoning) and psychopathological dimension such as hostility may support the notion about the effect of platelet MAO B activity in the further development of an impulsive cognitive style.

Changes in platelet monoamine oxidase activity, cholesterol levels and hyperactive behaviour in adolescents over a period of three years

Platelet monoamine oxidase (MAO) activity is a peripheral marker of central serotonergic activity, and has been associated with aggressive, impulsive and hyperactive behaviour, alcohol and drug abuse. Central serotonergic activity has also been associated with plasma cholesterol levels. In the present longitudinal investigation in adolescents (n = 320) changes in platelet MAO activity and in plasma cholesterol levels over three years were measured, and their possible association with changes in aggressive and hyperactive behaviour, smoking, alcohol and drug use was studied. The measures were taken at age 15 and 18 years. Psychological data were obtained from teachers by using the Hyperactivity Scale [B. af Klinteberg, Studies on Sex-related Psychological and Biological Indicators of Psychosocial Vulnerability: A Developmental Perspective, University of Stockholm, Department of Psychology, 1988]. The results of the study show that in most of the tested individuals, platelet MAO activity is a relatively stable measure, however, there was a significant number of subjects with a noticeable change in MAO activity. In subjects with decreased platelet MAO activity, total and HDL cholesterol levels were significantly increased. Also, changes in HDL cholesterol and in platelet MAO activity were inversely associated with changes in the score of Concentration Difficulties. The changes in platelet MAO activity and cholesterol level were not associated with alcohol and drug use among the subjects. This longitudinal analysis provides preliminary evidence that changes in platelet MAO activity and cholesterol, which may reflect changes in central serotonergic activity are associated with attention deficit in adolescents.

Platelet monoamine oxidase activity in subgroups of alcoholics and controls: results from the Collaborative Study on the Genetics of Alcoholism

OBJECTIVE

Platelet monoamine oxidase (MAO) B activity levels were evaluated to determine whether low platelet MAO activity is a marker for alcoholism, correlates of alcoholism (e.g., cigarette smoking), or a subtype of alcoholism.

METHODS

Adult women (n = 788) and men (n = 685) participating in the Collaborative Study on the Genetics of Alcoholism study were evaluated with a semistructured interview, and blood samples were obtained for determination of platelet MAO activity using tryptamine (0.1 mM) as substrate. DSM-III-R alcohol-dependent individuals were subgrouped using four currently available methods (e.g., two variations of the type 1/type 2 scheme, primary versus secondary typology, type A/type B dichotomy).

RESULTS

In the overall sample, subjects' gender, cigarette smoking status, and the Collaborative Study on the Genetics of Alcoholism site at which their platelets were prepared explained 22% of the variance in platelet MAO activity levels, and multivariate analysis showed that carrying a broad diagnosis of alcohol dependence did not uniquely explain any additional variance in platelet MAO activity levels. Furthermore, within each of the alcoholic subgrouping methods tested, there were no significant differences in platelet MAO activity for type 1 versus type 2, type A versus type B, or primary versus secondary alcoholics.

CONCLUSIONS

Cigarette smoking and male gender are associated with decreased platelet MAO activity levels. After considering these factors, a diagnosis of alcohol dependence does not predict any additional variance in MAO-B activity. Phenotypes of alcoholics (e.g., type 1 versus type 2, type A versus type B, primary versus secondary) do not differ in platelet MAO activity. The results suggest that decreased platelet MAO activity is not a trait marker of alcoholism or one of its subtypes; but, rather, is a state marker of cigarette smoking.

Platelet MAO activity in subtypes of alcoholics and controls in a homogenous population

The level of platelet monoamine oxidase (MAO) activity has been found to vary between alcoholics and healthy controls and between subtypes of alcoholics, in different populations. This study measured the MAO activity in a group of 46 abstinent alcohol dependent subjects and 22 healthy non-alcoholic controls, male and female, in an ethnically homogenous Irish population. The healthy control subjects had a mean MAO activity of 0.27 pmol/hr/10(5) platelets (+/- SEM 0.03), while the alcoholics overall had a mean activity of 0.34 pmol/hr/10(5) platelets (+/- 0.03) and this difference was not significant, P = 0.2. When the alcoholic group was divided into subtypes of alcoholism, (type 1 and type 2) there was no difference between subtypes of alcoholics nor between each subtype and the controls in their MAO activity. There was no correlation between MAO activity and the age of the subjects, the duration of abstinence from alcohol, the severity of alcoholism, smoking status or the gender of the subjects. These data are discussed in the context of the current literature on alcoholism and platelet MAO in different ethnic populations and the status of platelet MAO as a potential marker for alcoholism.

Platelet monoamine oxidase (MAO) activity and alcoholism: is there a genuine association?

Monoamine oxidase (MAO) is a particle-bound flavoenzyme principally located in the outer mitochondrial membrane, which catalyzes the oxidative deamination of a variety of the amine transmitters in the central nervous system. There have been many reports from different groups around the world over the last 20 years that indicated a lower platelet MAO activity was associated with alcoholism. As there are multiple influences upon measured MAO activity, this article attempts to address each of the issues in turn for potential confounding of the reported association. These issues include: the duration of abstinence from alcohol, the substrate used for analysis, gender issues, association with different subtypes of alcoholics, the influence of other psychopathology, personality traits of alcoholics, the question of smoking, and proposed modes of transmission of MAO activity. The initial promise about MAO activity being a possible marker for alcoholism or a least a genetically predisposed subgroup has receded as the number of negative typology-based studies increases. The failure to account for a major confounding variable, e.g. smoking and other minor but possibly vital confounds in almost all these studies leaves the whole hypothesis open to criticism. However, the possible association between personality traits that might predispose to some if not all substances of addiction to low MAO activity may make it possible to reframe the hypothesized association in the setting of a generalized predisposition to addictions in particular, and to psychopathology in general. Nonetheless the association remains of great interest and may yet yield vital genetic and clinical information.

Genetic markers of alcohol abuse

In this paper, we review the current status of genetic markers for the development of alcohol abuse. Family, twin, half-sibling and adoption studies of alcoholic subjects suggest that the heritability of liability to alcoholism is at least 50%. These findings have fuelled intensive investigation in the fields of neurology, biochemistry, genetics and molecular biology aimed at the identification of markers for the risk of alcoholism. The most promising of these are discussed in detail. Alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) polymorphisms, specifically the ADH3*1, ADH2*2, and ALDH2*2 genotypes appear to confer a protective effect against alcoholism, most notably in Oriental subjects. Caucasian alcohol abusers and their first-degree relatives exhibit depressed platelet monoamine oxidase activity, the degree of which is greater in Type II than Type I alcoholics. Electrophysiological characteristics of alcoholics and those at risk for developing alcoholism have also been identified, including the reduced amplitude of the event-related brain potential and, after ethanol ingestion, characteristic EEG alpha-wave activity. Lower platelet adenylate cyclase activity is seen in alcoholics compared to controls, presumably as a result of over-expression of an inhibitory G-protein. Markers related to other signal transduction pathways of the central nervous system including the serotoninergic, muscarinic and dopaminergic systems are also discussed. In this group of markers, the putative association between the inheritance of the AI allele of the D2 dopamine receptor and the susceptibility to alcoholism provides the most dramatic illustration of the challenges presently existing in this field of scientific investigation. Current limitations in the definition, diagnosis and classification of alcoholism, the confounding influences of race and gender on association studies, as well as the statistical approach of linkage studies are discussed as they relate to the endeavor to uncover valid genetic markers for the risk of alcoholism.

Platelet monoamine oxidase activity levels in subgroups of alcoholics: diagnostic, temporal, and clinical correlates

Platelet monoamine oxidase (MAO) activity levels were measured in 47 male inpatient alcoholics to determine whether this biological marker might be useful in differentiating subtypes of alcoholics. Of the subgrouping methods tested, only type 2 alcoholics defined by the criteria of Gilligan et al had significantly lower platelet MAO activity than type 1 alcoholics at intake, but this finding was not stable over time in a subset of subjects. Neither separating male veteran alcoholics into either of two other variations of the type 1/type 2 subtypes, nor classifying the sample into primary alcoholics versus primary ASPD with secondary alcoholism categories, yielded significant differences between subgroups. Generally, enzyme activity levels (Vmax) were higher about 10 days after stopping drinking compared to platelet MAO values determined in thrombocytes obtained after approximately 4 weeks abstinence; these levels remained relatively stable 3 months later in a cohort of subjects. Tobacco smoking was significantly negatively correlated to platelet MAO activity levels.

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.

Association of monoamine oxidase (MAO) activity with alcoholism and alcoholic subtypes

A familial/genetic study of platelet monoamine oxidase (MAO) activity in alcoholics was carried out. MAO activities were determined using phenylethylamine (PEA) as substrate at Km concentration (1.2 microM) and at saturating concentration (12.0 microM). Complex segregation analysis of familial data indicated a single major gene mode of transmission of activity at both substrate concentrations. In addition, the present sample size (13 families, 108 members) proved sufficient to allow correlation analysis of enzyme activity with affection status and clinical subtypes of affecteds. MAO activity was significantly correlated with alcoholism at both Km and saturating substrate concentrations and a significant correlation between low MAO activity and Cloninger Type II alcoholism was seen at Km substrate concentration. These results confirm a hierarchical cosegregation of platelet MAO activity and alcoholism suggesting that MAO activity warrants continued status as a marker in alcoholism.

Why there is no gene for alcoholism

The search for and recognition of biological and genetic markers of alcoholism are discussed in the context of a heuristic model of human alcoholism as a complex, multilocus, heterogeneous disorder. Implications of this model for the interpretation of results from both linkage and association studies are presented.

Platelet monoamine oxidase, plasma dopamine beta-hydroxylase activity, dementia and family history of alcoholism in chronic alcoholics

The authors measured platelet monoamine oxidase (MAO) activity and plasma dopamine beta-hydroxylase activity in 36 male chronic alcoholics during a period of non-abstinence, and in 29 normal controls. The influence of family history, dementia, chronicity of drinking and liver injury on the enzyme activities was also examined by multiple regression analysis. Platelet MAO was significantly lower in the alcoholic group. Both enzyme activities were negatively related to the presence of dementia, while low MAO activity was associated with positive family history (parents, sibs) of alcoholism.

Platelet monoamine oxidase in alcoholism

We studied platelet monamine oxidase (MAO) activity using 14C-tyramine as substrate in hospitalized alcoholic patients in the early phases of abstinence and in nonhospitalized normal control volunteers. Platelet MAO was determined in 75 patients (67 men, 8 women) with alcoholism and 123 normal control volunteers (52 men, 71 women). The platelet MAO activity in alcoholic patients was significantly lower than in normal control volunteers. We also observed that the mean platelet MAO activity in male alcoholics was significantly lower than in normal males. The analysis of platelet MAO in alcoholics revealed a mixture of two normal distributions. Alcoholic patients falling into the low MAO component were younger in age, with a lower age of onset of alcoholism, and had higher frequencies of family history of alcoholism. They thus resembled type II alcoholics described by other investigators. Platelet MAO may thus serve as a useful biological marker for subtyping alcoholism and identifying high-risk groups at an early stage. The findings of this study are consistent with previous reports of low platelet MAO activity in alcoholic patients.

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.

Platelet monoamine oxidase and plasma dopamine-beta-hydroxylase activities in non-abstinent chronic alcoholics. Relation to clinical parameters

Platelet monoamine oxidase (MAO) and plasma dopamine-beta-hydroxylase (DBH) activities were determined in 27 male non-abstinent chronic alcoholics. Compared to 24 normals, no significant difference in both enzyme activities was found. Alcoholics with at least one alcoholic first degree relative had a trend toward lower platelet MAO activity compared to those without such a history. Matched pair analysis showed that alcoholics of the former subgroup had significantly lower MAO activity than controls. Demented alcoholics had significantly reduced plasma DBH activity compared with the non-demented subgroup and with age, and sex, matched controls.