Platelet monoamine oxidase activity in alcoholics, alcoholics with drug dependence, and cocaine addicts

Association between platelet MAO activity and lifetime drug use in a longitudinal birth cohort study

RATIONALE

Platelet monoamine oxidase (MAO) activity, a marker of central serotonergic capacity, has been associated with a variety of problem behaviours. However, studies on platelet MAO activity and addictive drugs have not consistently linked MAO activity with addiction or reported to predict illicit substance use initiation or frequency.

OBJECTIVES

Platelet MAO activity and illicit drug use was examined in a longitudinal birth cohort study.

METHODS

The sample included both birth cohorts (original n = 1238) of the Estonian Children Personality Behaviour and Health Study. Longitudinal association from age 15 to 25 years between platelet MAO activity and lifetime drug use was analysed by mixed-effects regression models. Differences at ages 15, 18 and 25 were analysed by t-test. Cox proportional hazard regression analysis was used to assess the association between platelet MAO activity and the age of drug use initiation.

RESULTS

Male subjects who reported at least one drug use event had lower platelet MAO activity compared to nonusers, both in cross-sectional and longitudinal analyses. Males with low platelet MAO activity had started to use drugs at a younger age. Moreover, in male subjects who had experimented with illicit drugs only once in lifetime, low platelet MAO activity was also associated with higher risk at a younger age. In females, platelet MAO activity was not associated with drug use.

CONCLUSION

In males, low platelet MAO activity is associated with drug abuse primarily owing to risk-taking at early age.

Gene polymorphisms associated with temperament

When individuals are exposed to stressful environmental challenges, the response varies widely in one or more of three components: psychology, behavior and physiology. This variability among individuals can be defined as temperament. In recent years, an increasing large body of evidence suggests that the dimensions of temperament, as well as personality, psychological disorders and behavioral traits, are influenced by genetic factors, and much of the variation appears to involve variation in genes or gene polymorphisms in the hypothalamic-pituitary-adrenocortical (HPA) axis and the behavior-controlling neurotransmitter networks. Here, we review our current understanding of the probabilistic impact of a number of candidate gene polymorphisms that control temperament, psychological disorders and behavioral traits in animals and human, including the gene polymorphisms related to corticotrophin-releasing hormone (CRH) production and adrenal cortisol production involved in the HPA axis, and a large number of gene polymorphisms in the dopaminergic and serotonergic neurotransmitter networks. It will very likely to assist in diagnosis and treatment of human relevant disorders, and provide useful contributions to our understanding of evolution, welfare and conservation, for animals in the wild and in production systems. Additionally, investigations of gene-gene and gene-environment complex interactions in humans and animals need further clear illustration.

Selective MAO-B inhibitors: a lesson from natural products

Monoamine oxidases (MAOs) are mitochondrial bound enzymes, which catalyze the oxidative deamination of monoamine neurotransmitters. Inside the brain, MAOs are present in two isoforms: MAO-A and MAO-B. The activity of MAO-B is generally higher in patients affected by neurodegenerative diseases like Alzheimer's and Parkinson's. Therefore, the search for potent and selective MAO-B inhibitors is still a challenge for medicinal chemists. Nature has always been a source of inspiration for the discovery of new lead compounds. Moreover, natural medicine is a major component in all traditional medicine systems. In this review, we present the latest discoveries in the search for selective MAO-B inhibitors from natural sources. For clarity, compounds have been classified on the basis of structural analogy or source: flavonoids, xanthones, tannins, proanthocyanidins, iridoid glucosides, curcumin, alkaloids, cannabinoids, and natural sources extracts. MAO inhibition values reported in the text are not always consistent due to the high variability of MAO sources (bovine, pig, rat brain or liver, and human) and to the heterogeneity of the experimental protocols used.

From depression to neurodegeneration and heart failure: re-examining the potential of MAO inhibitors

Initially introduced in the 1950s for treating depression, monoamine oxidase (MAO) inhibitors were gradually abandoned, mainly owing to their potential for drug-drug and drug-food interactions, the most widely known being with tyramine-containing food (the 'cheese' effect). Since then, more selective MAO-A or MAO-B inhibitors have been developed with substantially reduced risks, and have been approved for the treatment of depression and Parkinson's disease, respectively. Recent research suggests that some of these drugs also have neuroprotective properties, while preclinical evidence expands the spectrum of potential indications to heart failure, renal diseases and multiple sclerosis. In this article, the authors review the relevance of MAO isoforms to disease, and they also outline current research and development efforts in this class of drugs, including newer multipotent compounds.

Cannabinoids and monoamine neurotransmission with focus on monoamine oxidase

Progress in understanding the mechanisms of action of cannabinoids was made after discovery of cannabinoid receptors and finding their endogenous ligands. New findings are obtained using both endogenous cannabinoids and plant or synthetic cannabinoids. Activation of cannabinoid receptors on synaptic terminals results in regulation of ion channels, neurotransmitter release and synaptic plasticity. Neuromodulation of synapses by cannabinoids is proving to have a wide range of functional effects, making them potential targets as medical preparations in a variety of illnesses, including some neurodegenerative and mental disorders. Brain monoamines are involved in many of the same processes affected by neuropsychiatric disorders and by different psychotropic drugs, including cannabinoids. Basic information is summarized in the paper about mechanisms of action of cannabinoids on monoaminergic systems, with a view to inhibition of monoamine oxidase.

The biometric measurement of alcohol consumption

BACKGROUND

Proper ascertainment of the history of alcohol consumption by an individual is an important component of medical diagnosis of disease and influences the implementation of appropriate treatment strategies that include prescription of medication, as well as intervention for the negative physical and social consequences of hazardous/harmful levels of alcohol consumption. Biological (biometric) diagnostic tests that provide information on current and past quantity and frequency of alcohol consumption by an individual, prior to onset of organ damage, continue to be sought.

METHODS

Platelet monoamine oxidase B (MAO-B) protein was quantitated in 2 populations of subjects who had histories of different levels of alcohol consumption. Levels were assayed by immunoblotting or by ELISA. The development and evaluation of the new ELISA-based measure of platelet MAO-B protein levels is described.

RESULTS

One subject population constituted a nontreatment-seeking, cross-sectional subject sample, and the other population was a longitudinally followed, hospitalized group of subjects. An algorithm combining measures of platelet MAO-B protein with the plasma levels of carbohydrate-deficient transferrin (CDT) and with liver enzymes (aspartate aminotransferase or γ-glutamyltransferase [GGT]) can detect hazardous/harmful alcohol use (HHAU) with the highest sensitivity and specificity in the cross-sectional nontreatment-seeking population. In the treatment-seeking population, low MAO-B protein levels at admission are associated with heavy drinking prior to admission, and these protein levels increase over a period of abstinence from alcohol.

CONCLUSIONS

The platelet MAO-B protein measurement is particularly effective for male alcohol consumers. The combined use of MAO-B protein measures together with measures of CDT and GGT does, however, improve the diagnostic utility of both markers for ascertaining HHAU in women. Furthermore, measurement of changes in platelet MAO-B protein levels during treatment for alcohol dependence may help monitor the success of the treatment program.

Transcriptional regulation and multiple functions of MAO genes

Monoamine oxidase (MAO) A and MAO B are a crucial pair of isoenzymes, which oxidatively deaminate monoamine neurotransmitters and dietary amines with a production of hydrogen peroxide. These two isoenzymes have different but overlapping substrate and inhibitor specificities. MAO A and MAO B share 70% amino acid sequence identity and show different temporal and spatial expressions in both humans and mice. Abnormal MAO A or MAO B activity has been implicated in numerous neurological and psychiatric disorders. A better understanding of the transcriptional regulation of MAO A and MAO B genes may help explain the differential tissue-specific expression of these two isoenzymes and provide insights into the molecular basis of the disorders associated with MAO dysfunction. This review discusses the recent progress in the transcriptional regulation and multiple functions of MAO A and MAO B genes.

Inhibition of monoamine oxidase activity by cannabinoids

Brain monoamines are involved in many of the same processes affected by neuropsychiatric disorders and psychotropic drugs, including cannabinoids. This study investigated in vitro effects of cannabinoids on the activity of monoamine oxidase (MAO), the enzyme responsible for metabolism of monoamine neurotransmitters and affecting brain development and function. The effects of the phytocannabinoid Delta(9)-tetrahydrocannabinol (THC), the endocannabinoid anandamide (N-arachidonoylethanolamide [AEA]), and the synthetic cannabinoid receptor agonist WIN 55,212-2 (WIN) on the activity of MAO were measured in a crude mitochondrial fraction isolated from pig brain cortex. Monoamine oxidase activity was inhibited by the cannabinoids; however, higher half maximal inhibitory concentrations (IC(50)) of cannabinoids were required compared to the known MAO inhibitor iproniazid. The IC(50) was 24.7 micromol/l for THC, 751 micromol/l for AEA, and 17.9 micromol/l for WIN when serotonin was used as substrate (MAO-A), and 22.6 micromol/l for THC, 1,668 micromol/l for AEA, and 21.2 micromol/l for WIN when phenylethylamine was used as substrate (MAO-B). The inhibition of MAOs by THC was noncompetitive. N-Arachidonoylethanolamide was a competitive inhibitor of MAO-A and a noncompetitive inhibitor of MAO-B. WIN was a noncompetitive inhibitor of MAO-A and an uncompetitive inhibitor of MAO-B. Monoamine oxidase activity is affected by cannabinoids at relatively high drug concentrations, and this effect is inhibitory. Decrease of MAO activity may play a role in some effects of cannabinoids on serotonergic, noradrenergic, and dopaminergic neurotransmission.

Retinoic acid activates monoamine oxidase B promoter in human neuronal cells

Monoamine oxidase (MAO) B deaminates a number of biogenic and dietary amines and plays an important role in many biological processes. Among hormonal regulations of MAO B, we have recently found that retinoic acid (RA) significantly activates both MAO B promoter activity and mRNA expression in a human neuroblastoma BE(2)C cell line. RA activates MAO B promoter in both concentration- and time-dependent manners, which is mediated through retinoic acid receptor alpha (RARalpha) and retinoid X receptor alpha (RXRalpha). There are four retinoic acid response elements (RAREs) as identified in the MAO B 2-kb promoter, and mutation of the third RARE reduced RA-induced MAO B promoter activation by 50%, suggesting this element is important. Electrophoretic mobility shift analysis and chromatin immunoprecipitation assay demonstrated that RARalpha specifically binds to the third RARE both in vitro and in vivo. Moreover, transient transfection and luciferase assays revealed that Sp1 enhances but not essentially required for the RA activation of MAO B through two clusters of Sp1-binding sites in the MAO B promoter. RARalpha physically interacts with Sp1 via zinc finger domains in Sp1 as determined by co-immunoprecipitation assay. Further, RARalpha was shown to be recruited by Sp1 and to form a transcriptional regulation complex with Sp1 in the Sp1-binding sites of natural MAO B promoter. Taken together, this study provides evidence for the first time showing the stimulating effect of RA on MAO B and new insight into the molecular mechanisms of MAO B regulation by hormones.

Contribution of monoamine oxidase (MAO) inhibition to tobacco and alcohol addiction

Whole-body PET-scan studies in brains of tobacco smokers have shown a decrease in monoamine oxidase (MAO) activity, which reverts to control level when they quit smoking. The observed decrease in MAO activity in smokers is presumably due to their exposure to tobacco constituents that possess MAO-inhibiting properties. The inhibition of MAO activity seems, however, not to be a unique feature of tobacco smoking as subjects with Type II alcoholism have been reported to show a similar decrease in MAO activity that reverses when they cease to use alcohol. The present review summarizes the data on MAO-inhibiting tobacco constituents and explains that the decrease in MAO activity observed in alcoholics is probably due to concomitant tobacco use. It is concluded that the inhibition of MAO by constituents contained in tobacco and tobacco smoke, enhances the addiction induced by tobacco smoking.

Assessing effects of neurotoxic pollutants by biochemical markers

Neurotoxins cause biochemical and molecular events which indicate early stage effects in exposed persons well before or well below the induction of overt disease. Monitoring these early events may represent a valid approach to developing markers of neurotoxicity in individuals exposed to environmental chemicals. In neurotoxicology, the use of biochemical markers is more problematic compared to other fields due to the complexity of central nervous system function, the multistage nature of neurotoxic events, and the inaccessibility of target tissue. Nevertheless, new biochemical assays have been developed in recent years to assess exposure, subclinical effects, and susceptibility to neurotoxic disorders. This paper reviews novel biomarkers of neurotoxicity and discusses perspectives and limitations of their use in occupational and environmental medicine.

Association between polymorphisms in dopamine metabolic enzymes and tobacco consumption in smokers

Central dopaminergic reward pathways give rise to dependence and are activated by nicotine. Allelic variants in genes involved in dopamine metabolism may therefore influence the amount of tobacco consumed by smokers. We developed assays for polymorphisms in dopamine beta-hydroxylase (DBH), monoamine oxidase (MAO) and catechol O-methyl transferase (COMT) using the polymerase chain reaction with sequence specific primers (PCR-SSP). We then typed 225 cigarette smokers to assess whether genotype was related to the number of cigarettes smoked a day. Smokers with DBH 1368 GG genotype smoked fewer cigarettes than those with GA/AA [mean difference -2.9 cigarettes, 95% confidence interval (CI) -5.5, -0.4; P = 0.022]. The effect reached statistical significance in women (-3.8, 95% CI -6.4, -1.0, P = 0.007) but not in men (-1.5, 95% CI -6.0, 3.0, P = 0.498). Overall, the effect was greater when analysis was confined to Caucasians (-3.8, 95% CI -6.6, -1.1, P = 0.007). Smokers with MAO-A 1460 TT/TO smoked more cigarettes than those with CC/CT/CO (2.9, 95% CI 0.6, 5.1, P = 0.013). Within each sex group, the trend was similar but not statistically significant (difference for men 2.9, 95% CI -1.0, 6.7; for women 2.0, 95% CI -0.7, 4.8). The effect of the allele was greater in smokers with a high body mass index (> 26) (difference 5.1, 95% CI 1.4, 8.8, P = 0.008). More heavy smokers (> 20 a day) had the DBH 1368A allele when compared to light smokers (< 10 a day). (Relative risk 2.3, 95% CI 1.1, 5.0, P = 0.024.) The trend for increasing prevalence of the DBH A allele in heavy smokers was greater when analysis was restricted to Caucasians (relative risk 3.2, 95% CI 1.3, 8.2, P = 0.004). Conversely, heavy smokers were less likely to have the MAO-A 1460C allele (relative risk 0.3, 95% CI 0.1, 0.7, P = 0.012). Variations in DBH and MAO predict whether a person is a heavy smoker and how many cigarettes they consume. Our results support the view that these enzymes help to determine a smoker's requirement for nicotine and may explain why some people are predisposed to tobacco addiction and why some find it very difficult to stop smoking. This finding has important implications for smoking prevention and offers potential for developing patient-specific therapy for smoking cessation.

Monoamine oxidase: from genes to behavior

Cloning of MAO (monoamine oxidase) A and B has demonstrated unequivocally that these enzymes are made up of different polypeptides, and our understanding of MAO structure, regulation, and function has been significantly advanced by studies using their cDNA. MAO A and B genes are located on the X-chromosome (Xp11.23) and comprise 15 exons with identical intron-exon organization, which suggests that they are derived from the same ancestral gene. MAO A and B knock-out mice exhibit distinct differences in neurotransmitter metabolism and behavior. MAO A knock-out mice have elevated brain levels of serotonin, norephinephrine, and dopamine and manifest aggressive behavior similar to human males with a deletion of MAO A. In contrast, MAO B knock-out mice do not exhibit aggression and only levels of phenylethylamine are increased. Mice lacking MAO B are resistant to the Parkinsongenic neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetra-hydropyridine. Both MAO A and B knock-out mice show increased reactivity to stress. These knock-out mice are valuable models for investigating the role of monoamines in psychoses and neurodegenerative and stress-related disorders.

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.

Serotonin in early-onset alcoholism

This chapter examines current, common schemes to subgroup alcoholics to arrive at relatively homogeneous groups of patients to facilitate psychobiological and molecular genetic studies. Early-onset, male-limited alcoholism is commonly associated with antisocial personality disorder or antisocial behavioral traits. It is often preceded by early-onset aggressiveness, which is followed by conduct disorder. Early-onset alcoholism among men is associated with low central serotonin turnover rate. The data concerning platelet MAO activity and serotonin uptake to platelets among early-onset alcoholics are conflicting. Recent molecular genetic and brain imaging studies on early-onset alcoholics are preliminary but appear very promising.

Association of monoamine oxidase A alleles with alcoholism among male Chinese in Taiwan

OBJECTIVE

The role of monoamine oxidase (MAO) in alcoholism was assessed by genetic association studies separately in five ethnic groups in Taiwan.

METHOD

Restriction fragment length polymorphisms (RFLP) and dinucleotide repeat polymorphisms (DNRP) were used to determine MAOA and MAOB alleles in male alcoholic patients and nonalcoholic comparison subjects among Han Chinese and four aboriginal groups.

RESULTS

Significant associations of alcohol dependence with MAOA alleles (RFLP and DNRP) were found among the Han Chinese, but not among the aboriginal groups. No significant association with MAOB DNRP alleles was found in any group.

CONCLUSIONS

Genetic heterogeneity may underlie alcoholism among different ethnic groups in Taiwan, and MAOA mutations may play a role in susceptibility to alcoholism among Han Chinese.

Tridimensional personality traits in sons of alcoholic and nonalcoholic fathers

Sons of alcoholics (SOAs; n = 27) and sons of nonalcoholics (SONAs; n = 23) were compared across Tridimensional Personality Questionnaire (TPQ) and Sensation Seeking scales and measures of plasma homovanillic acid and platelet monoamine oxidase activity. SOAs and SONAs did not differ significantly on any measure. The pattern of correlations between TPQ and Sensation Seeking scales provided some support for the construct validity of TPQ measures. Scores on the TPQ Novelty Seeking scale and platelet monoamine oxidase activity were significantly inversely associated (r = -0.52, p < 0.02) among SOAs, but not among SONAs (r = -0.06).