Inhibition of monoamine oxidase B in the brains of smokers

Cigarette smoking and incidence of first depressive episode: an 11-year, population-based follow-up study

Smoking has been found to be associated with depression. Biologic hypotheses support causation in both directions. This study examined the association between cigarette smoking and a subsequent first depression. In 1990, 2,014 adults in Norway were interviewed about their lifestyle and mental health. A 2001 reinterview by trained interviewers defined the study cohort of 1,190 participants. The cases were those who experienced a first depression whose onset was estimated to occur during the follow-up period, based on retrospective assessment by the Composite International Diagnostic Interview (International Classification of Diseases, Tenth Revision). Cox regression was used to estimate the hazard rate of depression during follow-up. Alternative explanations for a direct causal influence from smoking on subsequent depression were assessed, and a sensitivity analysis was performed. The risk of depression was four times as high for heavy smokers compared with never smokers. A dose-response relation with an increasing hazard for past smokers and for an increasing number of cigarettes smoked per day for current smokers was found. Similarly, increasing smoking time was associated with increasing risk. Failure of other plausible alternatives to explain the observed association between smoking and depression might reflect a direct causal influence of smoking on depression.

Striatal dopamine D2/D3 receptor availability in male smokers

It has been reported that the activation of the nicotine receptor evokes central endogenous dopamine release. However, whether smoking affects striatal dopamine D(2)/D(3) availability over the long run has not been well established in vivo. Fifteen male smokers and their matching controls were recruited. Striatal dopamine D(2)/D(3) receptor availability was assessed by single photon emission computed tomography with [(123)]IBZM Iodo-benzaimide. There was no significant difference in striatal D(2)/D(3) receptor availability between smokers and controls.

Molecular mechanism of the relation of monoamine oxidase B and its inhibitors to Parkinson's disease: possible implications of glial cells

Monoamine oxidases A and B (MAO A and MAO B) are the major enzymes that catalyze the oxidative deamination of monoamine neurotaransmitters such as dopamine (DA), noradrenaline, and serotonin in the central and peripheral nervous systems. MAO B is mainly localized in glial cells. MAO B also oxidizes the xenobiotic 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to a parkinsonism-producing neurotoxin, 1-methyl-4-phenyl-pyridinium (MPP+). MAO B may be closely related to the pathogenesis of Parkinson's disease (PD), in which neuromelanin-containing DA neurons in the substantia nigra projecting to the striatum in the brain selectively degenerate. MAO B degrades the neurotransmitter DA that is deficient in the nigro-striatal region in PD, and forms H2O2 and toxic aldehyde metabolites of DA. H2O2 produces highly toxic reactive oxygen species (ROS) by Fenton reaction that is catalyzed by iron and neuromelanin. MAO B inhibitors such as L-(-)-deprenyl (selegiline) and rasagiline are effective for the treatment of PD. Concerning the mechanism of the clinical efficacy of MAO B inhibitors in PD, the inhibition of DA degradation (a symptomatic effect) and also the prevention of the formation of neurotoxic DA metabolites, i.e., ROS and dopamine derived aldehydes have been speculated. As another mechanism of clinical efficacy, MAO B inhibitors such as selegiline are speculated to have neuroprotective effects to prevent progress of PD. The possible mechanism of neuroprotection of MAO B inhibitors may be related not only to MAO B inhibition but also to induction and activation of multiple factors for anti-oxidative stress and anti-apoptosis: i.e., catalase, superoxide dismutase 1 and 2, thioredoxin, Bcl-2, the cellular poly(ADP-ribosyl)ation, and binding to glyceraldehydes-3-phosphate dehydrogenase (GAPDH). Furthermore, it should be noted that selegiline increases production of neurotrophins such as nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and glial cell line-derived neurotrphic factor (GDNF), possibly from glial cells, to protect neurons from inflammatory process.

Human monoamine oxidase enzyme inhibition by coffee and β-carbolines norharman and harman isolated from coffee

Monoamine oxidase (MAO) is a mitochondrial outer-membrane flavoenzyme involved in brain and peripheral oxidative catabolism of neurotransmitters and xenobiotic amines, including neurotoxic amines, and a well-known target for antidepressant and neuroprotective drugs. Recent epidemiological studies have consistently shown that coffee drinkers have an apparently lower incidence of Parkinson's disease (PD), suggesting that coffee might somehow act as a purported neuroprotectant. In this paper, "ready to drink" coffee brews exhibited inhibitory properties on recombinant human MAO A and B isozymes catalyzing the oxidative deamination of kynuramine, suggesting that coffee contains compounds acting as MAO inhibitors. MAO inhibition was reversible and competitive for MAO A and MAO B. Subsequently, the pyrido-indole (beta-carboline) alkaloids, norharman and harman, were identified and isolated from MAO-inhibiting coffee, and were good inhibitors on MAO A (harman and norharman) and MAO B (norharman) isozymes. beta-carbolines isolated from ready-to-drink coffee were competitive and reversible inhibitors and appeared up to 210 microg/L, confirming that coffee is the most important exogenous source of these alkaloids in addition to cigarette smoking. Inhibition of MAO enzymes by coffee and the presence of MAO inhibitors that are also neuroactive, such as beta-carbolines and eventually others, might play a role in the neuroactive actions including a purported neuroprotection associated with coffee consumption.

Effect of monoamine oxidase inhibition on amphetamine-evoked changes in dopamine receptor availability in the living pig: A dual tracer PET study with [11C]harmine and [11C]raclopride

The activity of both isozymes of monoamine oxidase (MAO) is reduced by 50% in the brain of human smokers. We hypothesized that this is not an epiphenomenon, but should bring about potentiation of the action of psychostimulant drugs. To test this hypothesis, we carried out serial positron emission tomography (PET) studies in Göttingen miniature pigs to measure the binding of the MAO-A ligand [11C]harmine and to measure the changes in [11C]raclopride binding evoked by a low dose of amphetamine (0.7 mg/kg as free base, i.v.), first in a baseline condition, and, one month later, after acute treatment with pargyline (2 x 3 mg/kg as free base, i.m.). In the baseline, the distribution volume of [11C]harmine relative to the arterial input (V(d), ml g(-1)) ranged from 74 ml g(-1) in cerebellum to 139 ml g(-1) in the medial hypothalamus. Pargyline treatment reduced the magnitude of V(d) globally to 34-54 ml g(-1). Nearly complete displacement of [11C]harmine binding was detected in neocortex and striatum, but there was evidence for pargyline-resistant binding in the pituitary gland and diencephalon. In the baseline condition, the low dose of amphetamine evoked a 14% decline in the binding potential (BP) (pB) of [11C]raclopride in striatum (P = 0.026). After pargyline treatment, the amphetamine effect was of similar magnitude (-11%), although not statistically significant (P = 0.054). However, the second amphetamine challenge evoked a 24% reduction in [11C]raclopride pB relative to the original baseline condition (P = 0.018). Present results do not strongly support our hypothesis that MAO inhibition should potentiate the amphetamine-evoked dopamine release as measured in the [11C]raclopride competition paradigm.

Nicotine normalizes increased prefrontal cortical dopamine D1 receptor binding and decreased working memory performance produced by repeated pretreatment with MK-801: a PET study in conscious monkeys

The effects of acute nicotine were determined on dopamine (DA) D(1) (D(1)R) and D(2) (D(2)R) receptor binding in the neocortex of conscious monkeys under control conditions as well as after chronic pretreatment with MK-801 (dizocilpine), a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist. Extrastriatal neocortical D(1)R and D(2)R binding was evaluated with [(11)C]NNC112 and [(11)C]FLB457 with high-specific radioactivity using positron emission tomography (PET). Acute administration of nicotine bitartrate, given as an intravenous (i.v.) bolus plus infusion for 30 min at doses of 32 microg/kg+0.8 microg/kg/min or 100 microg/kg+2.53 microg/kg/min as base, induced slight but significant dose-dependent increases of DA in the extracellular fluid of prefrontal cortex (PFC) as determined by microdialysis. However, acute nicotine did not affect either [(11)C]NNC112 or [(11)C]FLB457 binding to D(1)R or D(2)R, respectively, in any cortical region. Chronic MK-801 (0.03 mg/kg, intramuscularly (i.m.), twice daily for 13 days) increased [(11)C]NNC112 binding to D(1)R in PFC. No significant changes were detected in [(11)C]FLB457 binding to PFC D(2)R. Although chronic MK-801 lowered baseline DA and glutamate levels in PFC, acute nicotine normalized reduced DA to control levels. Acute nicotine dose-dependently normalized the increased binding of [(11)C]NNC112 to D(1)R produced by chronic MK-801 but [(11)C]FLB457 binding to PFC D(2)R did not change. Working memory performance, impaired after chronic MK-801, was partially improved by acute nicotine. These results demonstrate that acute nicotine normalizes MK-801-induced PFC abnormality of D(1)R in PFC.

Harmane inhibits serotonergic dorsal raphe neurons in the rat

RATIONALE

Harmane and norharmane (two beta-carbolines) are tobacco components or products. The effects of harmane and norharmane on serotonergic raphe neurons remain unknown. Harmane and norharmane are inhibitors of the monoamine oxidases A (MAO-A) and B (MAO-B), respectively.

OBJECTIVES

To study the effects of harmane, norharmane, befloxatone (MAOI-A), and selegiline (MAOI-B) on the firing of serotonergic neurons. To compare the effects of these compounds to those of nicotine (whose inhibitory action on serotonergic neurons has been previously described). The effects of cotinine, a metabolite of nicotine known to interact with serotonergic systems, are also tested.

METHODS

In vivo electrophysiological recordings of serotonergic dorsal raphe neurons in the anaesthetized rat.

RESULTS

Nicotine, harmane, and befloxatone inhibited serotonergic dorsal raphe neurons. The other compounds had no effects. The inhibitory effect of harmane (rapid and long-lasting inhibition) differed from that of nicotine (short and rapidly reversed inhibition) and from that of befloxatone (slow, progressive, and long-lasting inhibition). The inhibitory effects of harmane and befloxatone were reversed by the 5-HT1A antagonist WAY 100 635. Pretreatment of animals with p-chlorophenylalanine abolished the inhibitory effect of befloxatone, but not that of harmane.

CONCLUSIONS

Nicotine, harmane, and befloxatone inhibit the activity of raphe serotonergic neurons. Therefore, at least two tobacco compounds, nicotine and harmane, inhibit the activity of serotonergic neurons. The mechanism by which harmane inhibits serotonergic dorsal raphe neurons is likely unrelated to a MAO-A inhibitory effect.

Science and society: applications of behavioural genetics: outpacing the science?

Human behavioural genetics is an established research discipline of the genomic age, and applications for behavioural genetic information are most likely to emerge in areas such as criminal justice, education, employment and insurance. However, behavioural genetic research into personality traits and antisocial behaviour poses several risks; for example, tentative or preliminary research findings might be misused in legal and commercial settings. Scientific caution, public and media education, expert consultation and confidentiality protection are essential for the responsible use of behavioural genetics.

Genotype combinations for monoamine oxidase-B intron 13 polymorphism and dopamine D2 receptor TaqIB polymorphism are associated with ever-smoking status among men

Tobacco smoke inhibits monoamine oxidase-B (MAO-B) activity in vitro and in vivo, suggesting that MAO-B inhibition is a possible contributing factor to tobacco smoke addiction. Thus, MAO-B is a possible candidate gene for predisposition to smoking. The TaqIB polymorphism for the Dopamine D2 Receptor gene (DRD2) has been previously associated with smoking status, although with some contradictory results. We investigated whether genetic variants of MAO-B intron 13 and DRD2 TaqIB polymorphism could be associated with smoking status among control subjects. There was no association of the intron 13 polymorphism itself with smoking status in either men or women. Similarly, no association with smoking status was observed for the TaqIB polymorphism of DRD2 itself. However, among men, there was an interaction between MAO-B intron 13 polymorphism and the DRD2 TaqIB polymorphisms, in which subjects carrying MAO-B allele A and genotype B12 of DRD2 were 2.50 times (95% CI=1.05-5.95) more likely to be ever-smokers than the pool of men carrying all other genotype combinations. These results demonstrate that particular combinations of genotypes for MAO-B and DRD2 genes are associated with significantly higher risk for smoking behavior in men, but not in women.

Effects of depression, cigarette smoking, and age on monoamine oxidase B in amygdaloid nuclei

Altered concentrations of dopamine transporter and D2/D3 receptors have been observed in the amygdaloid complex of subjects with major depression. These findings are suggestive of neurochemical abnormalities in the limbic dopamine system in depression. Monoamine oxidase-B (MAO-B) is a key enzyme in the catabolism of biogenic amines, including dopamine, and alterations in this enzyme may underlie dopaminergic abnormalities associated with depression. The specific binding of [(3)H]lazabemide to MAO-B was measured in the right amygdaloid complex of 15 major depressive subjects and 16 psychiatrically normal controls. Subjects of the two study groups were matched as close as possible for age, sex, and postmortem interval. Examination of the regional distribution of MAO-B revealed lower [(3)H]lazabemide binding to MAO-B in the lateral and basal nuclei of the amygdala and higher binding in the medial nucleus. A modest elevation in binding to MAO-B observed in all amygdaloid nuclei in major depressive subjects as compared to control subjects failed to reach statistical significance. A significant decrease in binding to MAO-B was observed when cigarette smokers were compared to nonsmoking subjects. The amount of MAO-B binding positively correlated with the age of subjects in all nuclei investigated. A decreased amount of MAO-B in smokers further validates the pharmacological effect of tobacco smoke on this enzyme.

Acute inhibition of cardiac monoamine oxidase A after tobacco smoke inhalation: validation study of [11C]befloxatone in rats followed by a positron emission tomography application in baboons

The in vivo characteristics of [11C]befloxatone were assessed in myocardium of rats and monkeys. A complete multicompartmental model was developed to quantify monkey cardiac monoamine oxidase A (MAO-A) binding sites using positron emission tomography (PET) and was applied to assess the acute effects of inhalation of tobacco smoke. Unknown compounds contained in tobacco smoke inhibit brain MAO. In vitro, befloxatone inhibits selectively, competitively, and reversibly MAO-A in human tissues. [11C]Befloxatone (1.85 MBq) was i.v. injected into rats. Animals were sacrificed, dissected, and samples were assessed for radioactivity. Another group of rats was pretreated with clorgyline (10 mg/kg i.v.). Monkeys were injected with [11C]befloxatone (222-370 MBq), and the chest was imaged with PET for 2 h. Presaturation and displacement experiments were performed using unlabeled befloxatone. For quantification of myocardial binding sites (Bmax), [11C]befloxatone was first injected as a tracer dose (2.7-9.3 nmol) and 20 min later injected as a mixture of labeled and unlabeled befloxatone (labeled, 10.3-41.9 nmol; unlabeled, 407-765 nmol). In rodents, cardiac uptake was high (3.39 +/- 0.5% injected dose/g tissue) and strongly inhibited (80%) by clorgyline. In monkeys, administration of unlabeled befloxatone displaced 85% of cardiac radioactivity. Bmax was found to be 208 +/- 13 pmol ml(-1) tissue. Inhalation of tobacco smoke decreased Bmax: 150 +/- 6.2 pmol ml(-1), whereas nicotine did not. [11C]Befloxatone allows a good visualization of the heart. Cardiac MAO-A Bmax was quantified and a clear effect of acute inhalation of tobacco smoke was evidenced. Therefore, a single cigarette can interfere with the cardiac turnover of catecholamines.

Evidence for reduced arterial plasma input, prolonged lung retention and reduced lung monoamine oxidase in smokers

We have previously found that smokers have reduced brain monoamine oxidase (MAO) A and B using positron emission tomography (PET) and the irreversible mechanism-based radiotracers [(11)C]-labeled clorgyline (CLG) and deprenyl (DEP) and their deuterated analogs (D CLG, D DEP). More recently, we have estimated MAO A and B activity in other organs using the deuterium isotope effect to determine binding specificity for MAO and a three-compartment model to estimate k(3), the model term proportional to MAO A activity. Here, we have investigated the robustness of the model term k(3) for estimating lung MAO A and B in light of our unexpected finding that lung MAO activity (k(3)) was reduced for smokers relative to nonsmokers, although radiotracer uptake in the lungs was similar at peak and plateau for the two groups.

METHODS

Time-activity data from lung and arterial plasma were used from seven nonsmokers and seven smokers scanned previously with CLG and D CLG, and five nonsmokers and nine smokers scanned previously with DEP and D DEP. The measured time-activity curves for lung and plasma and the integrals for the arterial plasma time-activity curves were compared at an early time point (2.5 min) and at the end of the study (55 min). A three-compartment irreversible model was used to estimate the differences between smokers and nonsmokers, and the stability of the parameter (k(3)) while varying model assumptions for the relative fractions of lung tissue, blood and air in the PET voxel.

RESULTS

The peak in the arterial plasma input function and the integral of the arterial plasma time-activity curve over the first 2.5 min after radiotracer injection were significantly lower for smokers relative to nonsmokers for all four tracers. However, although the peak and plateau of the lung time-activity curves were similar for smokers and nonsmokers, the decline in radioactivity from peak to plateau was slower for smokers for all tracers. Using a three-compartment irreversible model, we estimated the ratio of MAO subtypes A and B in normal lung tissue to be on the order of 3 to 1 (MAO A to B) and that smokers have reduced MAO levels for both subtypes as measured by the model parameter, k(3). The values of k(3) are insensitive to model assumptions of variations in air and tissue fraction in the PET voxel. Most of the effects of changes in these fractions are absorbed into the parameter K(1), which governs the plasma-to-tissue transfer of tracer and is a function of blood flow. K(1) was found to be larger in smokers, although the values depend upon model assumptions of air and tissue fractions. k(3) was found to be significantly lower in smokers; for CLG, a 50% reduction in MAO A for both CLG and D CLG was observed. For DEP, k(3) was also significantly lower in smokers with a reduction of approximately 80% in lung MAO B, although there was a very large coefficient of variation in the smoker's k(3). We also found larger values of lambda (K(1)/k(2)) for smokers relative to nonsmokers for all tracers consistent with a longer lung retention of the nonenzyme-bound tracer, which explains the slower decline in uptake from peak radioactivity for smokers.

CONCLUSIONS

The measured arterial input function values for smokers and nonsmokers are significantly different for these two tracer pairs for nonsmokers and smokers particularly for the first few minutes after radiotracer injection. Model estimates of k(3) that indicate that smokers have lower lung MAO A and B activity than nonsmokers are robust and insensitive to variations in model assumptions for relative fractions of lung tissue, blood and air in the PET voxel. Although we have only investigated the behavior of [(11)C]clorgyline and [(11)C]l-deprenyl and their deuterium-substituted analogs in this report, the extent to which reduced arterial input and longer lung retention also hold for other tracers for subjects who smoke merits investigation.

Nicotinic receptor mechanisms and cognition in normal states and neuropsychiatric disorders

Cigarette smoking rates in the American population are approximately 23%, whereas rates of smoking in clinical and population studies of individuals with neuropsychiatric disorders are typically two- to four-fold higher. Studies conducted in a variety of neuropsychiatric populations [e.g. attention-deficit hyperactivity disorder (ADHD), Alzheimer's disease, schizophrenia] have collectively suggested that nicotine may be efficacious in remediating selected cognitive deficits associated with these disorders, thus providing a framework for understanding the specific vulnerability of these patients to smoking initiation and maintenance. However, the specific gain in cognitive performance produced by nicotine administration in healthy subjects with normal cognitive function is less clear. This article reviews our current understanding of central nicotinic acetylcholine receptor (nAChRs) systems in normal and neuropsychiatric disease states and, specifically, their role with respect to cognitive dysfunction and clinical symptoms in several specific neuropsychiatric populations, including ADHD, Alzheimer's disease, Parkinson's disease, Tourette's Disorder, schizophrenia and affective disorders. The potential benefits of nicotinic agents for therapeutic use in neuropsychiatric disorders is discussed, as well as directions for further research in this area.

Bases genéticas del hábito tabáquico

Dependence on tobacco is one of the most important health problems in our society due to the direct relationship with lung cancer. Early studies in twins revealed that genetic factors modify the susceptibility to develop tobacco dependence. Different studies are underway to try to find an association between polymorphisms of genes involved either in nicotine metabolization or in neural transmission and the initiation and maintenance of the dependence on tobacco. Here we review the studies performed so far and discuss new perspectives for future studies.

Human monoamine oxidase is inhibited by tobacco smoke: beta-carboline alkaloids act as potent and reversible inhibitors

Monoamine oxidase (MAO) is a mitochondrial outer-membrane flavoenzyme involved in brain and peripheral oxidative catabolism of neurotransmitters and xenobiotic amines, including neurotoxic amines, and a well-known target for antidepressant and neuroprotective drugs. Recently, positron emission tomography imaging has shown that smokers have a much lower activity of peripheral and brain MAO-A (30%) and -B (40%) isozymes compared to non-smokers. This MAO inhibition results from a pharmacological effect of smoke, but little is known about its mechanism. Working with mainstream smoke collected from commercial cigarettes we confirmed that cigarette smoke is a potent inhibitor of human MAO-A and -B isozymes. MAO inhibition was partly reversible, competitive for MAO-A, and a mixed-type inhibition for MAO-B. Two beta-carboline alkaloids, norharman (beta-carboline) and harman (1-methyl-beta-carboline), were identified by GC-MS, quantified, and isolated from the mainstream smoke by solid phase extraction and HPLC. Kinetics analysis revealed that beta-carbolines from cigarette smoke were competitive, reversible, and potent inhibitors of MAO enzymes. Norharman was an inhibitor of MAO-A (K(i)=1.2+/-0.18 microM) and MAO-B (K(i)=1.12+/-0.19 microM), and harman of MAO-A (K(i)=55.54+/-5.3nM). Beta-carboline alkaloids are psychopharmacologically active compounds that may occur endogenously in human tissues, including the brain. These results suggest that beta-carboline alkaloids from cigarette smoke acting as potent reversible inhibitors of MAO enzymes may contribute to the MAO-reduced activity produced by tobacco smoke in smokers. The presence of MAO inhibitors in smoke like beta-carbolines and others may help us to understand some of the purported neuropharmacological effects associated with smoking.

Iminium metabolite mechanism for nicotine toxicity and addiction: Oxidative stress and electron transfer

The mechanism of nicotine toxicity is not completely delineated. Considerable evidence points to involvement of oxidative stress (OS), reactive oxygen species, lipid peroxidation, DNA damage, and beneficial effect of antioxidants. Previously, a suggestion was advanced for participation of iminium metabolites which might operate, via electron transfer (ET) with redox cycling, to produce radical entities. The conjugated iminium functionality is one of the less well-known ET types. The cationic metabolites arise from several routes, including oxidation of nicotine itself, and protonation of myosmine which originates from nornicotine via demethylation of nicotine. Reduction potentials, which are in the range amenable to ET in vivo, lend credence to the theoretical framework. An alternate metabolic route entails hydrolysis of nicotine iminium to an open-chain ketoamine that, in turn, undergoes nitrosation to form a toxic nitrosamine. Subsequently, the nitrosamine serves as a DNA alkylator which can also generate conjugated iminiums by attack on certain nitrogens of DNA bases. During the past 14 years, the hypothesis has enjoyed substantial support. Increasing evidence points to a role for OS in toxicity by nicotine entailing major body organs, including the lung, cardiovascular system, central nervous system, liver, kidney, testes, ovary, pancreas, and esophagus. The mechanism of addiction is also addressed based on interaction of iminiums with normal electron transport chains or electrical phenomena in the brain. The process might occur with or without participation of reactive oxygen species. Evidence indicates that free radicals are widely involved in cell signaling entailing redox processes in the categories of ion transport, neuromodulation, and transcription. Low levels of radicals appear to participate since high concentrations are associated with toxicity. Various possibilities for future work based on the hypothetical approach are addressed, including some that may have practical utility in relation to health improvement, toxicity, and addiction. Insight should be gained from computational studies on the energetics of electron uptake by metabolic iminiums, and on stability of the resultant delocalized radicals. Additional large-scale investigations of antioxidant effects are needed in order to resolve prior conflicting reports. Other proposals are based on interference with metabolism to iminiums and nitrosamines, and destruction of harmful metabolites. Since the iminium entities are proposed to play crucial, adverse roles, it would be worthwhile to explore them with regard to receptors, physiological activities, possible generation of reactive oxygen species, and effect of antioxidants.

Anti-nicotine vaccination: where are we?

Nicotine is the main substance responsible for dependence on tobacco-containing, products, which have a heavy impact on the public health of developed as well as non-developed countries by being a main etiologic factor for the induction of cardiovascular diseases and tobacco-related cancer. A vaccine against nicotine induces antibodies against the molecule, intercepting the nicotine on its way to its specific receptors. The binding of the antibody to nicotine in turn significantly diminishes the nicotine concentration in the brain shortly after smoking. This approach therefore interrupts the vicious circle between smoking and nicotine-related gratification. The preclinical data of our animal experiments are briefly summarized. At the end of 2003, three companies were in early clinical development of an anti-nicotine vaccine: Xenova (TA-NIC), Nabi (NicVAX) and Cytos (Nicotine-Qbeta). The carrier molecules are recombinant cholera toxin B (TA-NIC), an especially selected carrier protein (Nabi) and a virus-like particle VLP (Cytos). Another carrier is additionally used by Chilka in an advanced preclinical model, which showed superiority to cholera toxin B carrier. Cytos has successfully completed a phase I study with 40 healthy non-smoking volunteers. So far, results of a phase I trial by Cytos have shown no unexpected toxicities and phase II trials have now started in Switzerland (Cytos).

Oxygen as a therapy for reducing nicotine withdrawal symptoms

Nicotine addiction leads to withdrawal symptoms in many persons who quit smoking. In addition to craving, the most commonly experienced symptoms are: depression; difficulty sleeping; irritability, frustration, or anger; anxiety; difficulty concentrating; restlessness; decreased heart rate; and increased appetite or weight gain. The severity of withdrawal symptoms are variable, and often lead to relapse. By altering the course of withdrawal symptoms it is possible to improve the chances of the quit attempt and reduce the risk of relapse. There is strong evidence that dopamine is the primary neurotransmitter in the reward pathway in addiction. The use of nicotine replacement therapies and Zyban (sustained release bupropion hydrochloride), both of which are suspected of exploiting dopamine's role in addiction, enhance the likelihood of long-term smoking cessation. Anecdotal reports of oxygen's capacity to reduce both the desire for nicotine and withdrawal symptoms suggest that this may be a therapeutic possibility for those who do not experience success with more traditional cessation approaches. Oxygen may have a favorable effect on nicotine withdrawal, as it appears to alter the balance of central neurotransmitters such as dopamine.

Platelet MAO-B, personality, and psychopathology

The article investigates the relationships between platelet monoamine oxidase-B (MAO-B) activity, personality, and psychopathology (Diagnostic and Statistical Manual of Mental Disorders [4th ed.; American Psychiatric Association, 1994] diagnoses. These relationships were assessed in 178 incarcerated male juvenile delinquents. Even after controlling for smoking, the authors found that both Internalizing and Externalizing Psychopathology were negatively related to MAO-B activity. In the final reduced model, novelty seeking fully mediated the relationships between MAO-B and Externalizing Psychopathology but not between MAO-B and Internalizing Psychopathology. It was hypothesized that low platelet MAO-B activity does not directly predispose individuals to psychopathology but is related to specific personality traits, which in turn represent a vulnerability factor for psychopathology. Future studies should help clarify the nature of the relationships between personality, biological markers, and psychopathology.

Nicotinic receptor mechanisms and cognition in normal states and neuropsychiatric disorders

Cigarette smoking rates in the American population are approximately 23%, whereas rates of smoking in clinical and population studies of individuals with neuropsychiatric disorders are typically two- to four-fold higher. Studies conducted in a variety of neuropsychiatric populations [e.g. attention-deficit hyperactivity disorder (ADHD), Alzheimer's disease, schizophrenia] have collectively suggested that nicotine may be efficacious in remediating selected cognitive deficits associated with these disorders, thus providing a framework for understanding the specific vulnerability of these patients to smoking initiation and maintenance. However, the specific gain in cognitive performance produced by nicotine administration in healthy subjects with normal cognitive function is less clear. This article reviews our current understanding of central nicotinic acetylcholine receptor (nAChRs) systems in normal and neuropsychiatric disease states and, specifically, their role with respect to cognitive dysfunction and clinical symptoms in several specific neuropsychiatric populations, including ADHD, Alzheimer's disease, Parkinson's disease, Tourette's Disorder, schizophrenia and affective disorders. The potential benefits of nicotinic agents for therapeutic use in neuropsychiatric disorders is discussed, as well as directions for further research in this area.

[Neuroimaging in substance abuse disorders]

The use of neuroimaging techniques in research on substance abuse disorders has advanced our understanding of the underlying pathophysiological and neuropsychological mechanisms. While initial structural imaging techniques were applied to investigate substance abuse-related cerebral atrophy, the functional techniques of SPECT, PET, and later fMRT and MRS provide a much broader range of possible research in this field. Besides their use in characterizing the pharmacology of abused substances and their relations to the pathophysiology of substance abuse disorders, they have also played an essential role in examining the neuropsychiatric underpinnings of the illness and their manifestation in changes of cerebral metabolism. Here, the influence of these techniques on the developing picture of substance abuse disorders is discussed by examining areas of particular scientific interest and reviewing exemplary findings.

Smoking and Parkinson's disease: systematic review of prospective studies

We estimated the pooled risk of tobacco smoking for Parkinson's disease (PD). Inclusion criteria included systematic searches of MedLine, PsycLIT, Embase, Current Contents, previously published reviews, examination of cited reference sources, and personal contact and discussion with several investigators expert in the field. Published prospective studies on PD and cigarette smoking. When two or more studies were based on an identical study, the study that principally investigated the relationship or the study that was published last was used. Seven prospective studies were carried out between 1959 and 1997, of which six reported risk estimates. Four cohorts were based on standardised mortality rates, which were exclusively of male. Only one study included risk estimates for both males and females separately. The risk of ever smoker was 0.51 (95% confidence interval, 0.43 to 0.61). There was an obvious protective effect of current smoking in the pooled estimate (relative risk, 0.35; 95% CI, 0.26-0.47). Former smokers had lower risk compared with never smokers (relative risk, 0.66; 95% CI, 0.49-0.88). Although our pooled estimates show that smoking is inversely associated with the risk of PD, the four prospective studies that were based on follow-up of mortality of smokers had many limitations. Further studies evaluating the association between smoking and PD in women are strongly needed.

Inhibition of human MAO-A and MAO-B by a compound isolated from flue-cured tobacco leaves and its neuroprotective properties in the MPTP mouse model of neurodegeneration

Prompted by the findings that smokers have lowered brain and blood platelet monoamine oxidase-A and -B activities compared to non-smokers and that smokers have a lowered incidence of Parkinson's disease, we have examined the neuroprotective properties of an MAO inhibitor, 2,3,6-trimethyl-1,4-naphthoquinone (TMN), which is present in the tobacco plant and smoke in the MPTP C57BL/6 mouse model of neurodegeneration. Dopamine (DA) levels in the striata of mice treated with TMN prior to the administration of MPTP were significantly higher than DA levels in the striata of mice receiving MPTP only, thus indicating a degree of neuroprotection in this model of Parkinson's disease. The potential consequences on MAO activity of long term exposure to this compound need to be evaluated. Furthermore, there is evidence for the presence of other inhibitors in the tobacco leaf and smoke, including compounds with irreversible MAO inhibitory properties. Although there is no evidence to link the lowered activities of MAO to the lowered incidence of Parkinson's disease in smokers, the neuroprotective effects of TMN in the MPTP mouse model suggest that such a relationship is worthy of further evaluation.

MAOB : un gène modificateur dans la phénylcétonurie ?

Phenylketonuria (PKU), the most frequent inborn error of metabolism (1/15,000 live births), is an autosomal recessive condition caused by phenylalanine hydroxylase deficiency. Despite early and strict dietary control, some PKU children still exhibit behavioral and cognitive difficulties suggestive of a partly prenatal brain injury. The reported variability between the cognitive and clinical phenotypes within the same family raises the question of modifying genes in PKU. We suggest here that monoamine oxidase type B, MAOB, an enzyme degrading phenylethylamine, a very toxic metabolite of phenylalanine, could act as a modifying gene since a variant enzymatic activity of MAOB in PKU patients with similar phenylalanine levels would result in different phenylethylamine levels and different clinical outcomes. Finally the report of low MAOB, and consequently expectedly high phenylethylamine levels in neonates is consistent with a phenylethylamine-mediated brain injury possibly causing irreversible damages in PKU newborns prior to onset of the low protein diet.

Perspectives on MAO-B in aging and neurological disease: where do we go from here?

The catecholamine-oxidizing enzyme monoamine oxidase-B (MAO-B) has been hypothesized to be an important determining factor in the etiology of both normal aging and age-related neurological disorders such as Parkinson's disease (PD). Catalysis of substrate by the enzyme produces H2O2 which is a primary originator of oxidative stress which in turn can lead to cellular damage. MAO-B increases with age as does predisposition towards PD which has also been linked to increased oxidative stress. Inhibition of MAO-B, along with supplementation of lost dopamine via L-DOPA, is one of the major antiparkinsonian therapies currently in use. In this review, we address several factors contributing to a possible role for MAO-B in normal brain aging and neurological disease and also discuss the use of MAO-B inhibitors as drug therapy for these conditions.

Long-Term Exposure to Nicotine Modulates the Level and Activity of Acetylcholine Receptors in White Blood Cells of Smokers and Model Mice

Long-term consumption of tobacco by smokers causes addiction and increases the level of neuronal nicotinic acetylcholine receptors (nAChRs) in the brain, a phenomenon known as up-regulation. Here, we show that up-regulation of specific nAChR subunits takes place in white blood cells (WBCs) of smokers and mice subjected to long-term administration of nicotine. The basal level of alpha-bungarotoxin binding site, which corresponds to the homomeric alpha7 nAChR subtype, was not affected in WBCs of both smokers and mice administered nicotine. In contrast, epibatidine (EB) binding sites, which correspond to heteromeric nAChR subtypes, were detected in WBCs of smokers but not in WBCs of nonsmokers. The number of EB binding sites significantly decreased after incubation of the smokers' WBCs for 3 days in nicotine-free culture medium. In WBCs of wild-type mice, basal level of EB binding sites was detected before nicotine administration. This basal level is reduced by approximately 60% in knockout mice lacking the genes encoding either the beta2 or the alpha4 receptor subunits. Additional analysis of knockout mice revealed that the remaining approximately 40% do not undergo up-regulation, indicating that the alpha4/beta2 subunits comprise the up-regulated nAChRs. We further found that upregulation in mouse WBCs is accompanied by a significant decrease in the capacity of the up-regulated receptor channels to convey calcium ions. The phenomenon of nAChR up-regulation in WBCs provides a simple tool to evaluate and study tobacco addiction.

Neuroendocrinological and neuropsychological correlates of dopaminergic function in nicotine dependence

RATIONALE

There is multiple evidence that nicotine--as with ethanol and other drugs of abuse--stimulates dopamine release in the ventral striatum as a central part of the brain reward circuits. Chronic nicotine exposure leads to changes in these dopaminergic reward circuits. During nicotine withdrawal, an impaired dopaminergic function has been reported. On the behavioral level, this seems to result in motivational disturbances in abstaining smokers.

OBJECTIVES

To investigate the impact of smoking on dopaminergic function in humans both on a neuroendocrinological and on a neuropsychological level.

METHODS

Thirty-seven healthy smokers were assessed whilst smoking (test 1) and after abstaining overnight for 12 h (test 2). A control group of 18 non-smokers was also examined twice. Severity of nicotine dependence, incentive motivation, digit span and verbal fluency were assessed. The sensitivity of central dopamine (DA) D2 receptors was assessed with the apomorphine-induced growth hormone (GH) secretion.

RESULTS

ANOVA revealed that GH response was significantly lower in smokers than in non-smokers (P=0.04). The GH response was significantly inversely correlated with severity of nicotine dependence (r=-0.39). Neuropsychological performance was not influenced by smoking status. After overnight abstinence from nicotine GH response, digit span and verbal fluency were not affected, whereas incentive motivation was significantly impaired in smokers (P=0.04).

CONCLUSIONS

Smoking is significantly associated with a reduced sensitivity of central DA D2 receptors. This alteration of dopaminergic sensitivity is stable even after 12 h of abstinence from nicotine. Therefore, the hypothesis that the motivational impairment during withdrawal from nicotine is associated with an altered sensitivity of central DA D2 receptors cannot be supported.

Smoking, nicotine and Parkinson's disease

Epidemiological studies show that smoking is associated with a lower incidence of Parkinson's disease (PD). This finding is important because it could provide clues about therapeutic strategies for protection against this debilitating movement disorder. Smoke contains numerous chemicals that could be responsible for the apparent protective effect. Here, a role for nicotine is considered, because this chemical stimulates brain dopaminergic systems and provides some symptomatic benefit in PD. Nicotine also has a neuroprotective action. Putative factors and signaling pathways involved in the actions of nicotine are discussed. An understanding of the molecular basis for the reduced occurrence of PD in tobacco users is crucial for the development of intervention strategies to reduce or halt disease progression.

Imaging localised dynamic changes in the nucleus accumbens following nicotine withdrawal in rats

This study utilises pharmacological functional magnetic resonance imaging (fMRI) to examine the neurobiological mechanisms through which nicotine produces dependence. Using an established regime to induce physical dependence to nicotine in rats (osmotic minipumps delivering 3.16 mg/kg/day nicotine for 7 days SC), animals were subsequently anaesthetised under urethane and positioned in a stereotaxic frame to allow collection of gradient echo whole brain images with a 4.7-T MRI spectrometer. Rats were initially scanned for 34 min (40 baseline image volumes, 1 volume per 51 s) then challenged with mecamylamine (1.0 mg/kg SC) or saline (1 ml/kg) and scanned for a further 68 min (80 image volumes). Mecamylamine precipitated highly significant positive changes in fMRI blood oxygen level dependent (BOLD) contrast that were predominantly localised to the NAc of nicotine-dependent rats. Saline-treated rats challenged with the same dose of mecamylamine exhibited similar but smaller increases in BOLD contrast although such changes were less defined around the NAc. Precipitated withdrawal also elicited statistically significant negative BOLD contrast changes in widespread cortical regions. These findings are consistent with previous neurochemical reports on decreases in dopamine in the NAc during nicotine withdrawal. This fMRI study further highlights the potential and power to image the neurobiological events during nicotine dependence.

Phencyclidine-induced changes in rat cortical gene expression identified by microarray analysis: implications for schizophrenia

Acute phencyclidine induces schizophrenia-like symptoms in healthy humans and psychotic episodes in schizophrenics. Although phencyclidine is known as a N-methyl d-aspartate receptor antagonist (NMDA-R), the molecular events underlying the behavioral symptoms remain largely unknown. Statistical analysis of oligonucleotide microarray data was used to identify phencyclidine-induced alterations in rat cortical gene expression. Acute phencyclidine produced a statistically significant change in 477 genes in rat prefrontal cortex (PFC), a brain area associated with cognitive dysfunction in schizophrenics. Real-time quantitative PCR (RTQ-PCR) confirmed a subset of these changes ranging from -59% to 255% (smallest confirmation: -19%). Subsequent time-course and dose-response studies using RTQ-PCR confirmed and extended the original microarray results. At the molecular level, genes altered by phencyclidine are related to diverse biological processes including stress, inflammatory response, growth and development, neural plasticity and signal transduction. Further analysis, aimed at assessing the relevance of our results to schizophrenia, revealed dysregulation of genes related to: (i) thalamocortical projections, (ii) neurotransmission and neuromodulation, (iii) thyroid hormone activity, (iv) oligodendrocyte linage, (v) brain lipid metabolism, (vi) sleep architecture and (viii) the velocardiofacial syndrome.

N-methyl-D-aspartate antagonists as drug models of schizophrenia: a surprising link to tobacco smoking

The pros and cons of N-methyl-D-aspartate (NMDA) antagonists as drug models of schizophrenia are discussed in relation to the neuropathology of this complex mental spectrum of diseases. The role of acetylcholine, dopamine, gamma aminobutyric acid, glutamic acid, and serotonin emphasizes that multiple neurotransmitter system abnormalities are involved, even though current drug therapy involves primarily dopamine (D(2))/serotonin (5 HT(2)) antagonists. Only some of the fundamental aspects of schizophrenia are replicated by NMDA receptor antagonists of glutamic acid. Subchronic NMDA antagonism in an animal model results in decreased levels of dopamine in prefrontal cortex and increased D(1) receptor binding. The results of PET studies of schizophrenic patients imply decreased dopamine levels in their prefrontal cortex. Tobacco-smoking schizophrenic patients transiently normalize prepulse inhibition. Nicotine appears to be one factor that may help explain some of these phenomena.

Addressing tobacco among individuals with a mental illness or an addiction

Tobacco dependence among individuals with a mental illness or an addiction is a tremendous problem that goes largely ignored. Studies of genetics, neuroimaging, and nicotinic receptors support a neurobiological link between tobacco use and alcohol dependence, drug dependence, schizophrenia, depression, attention-deficit hyperactivity disorder (ADHD), and anxiety disorders. This paper summarizes the recent literature on this topic and discusses how treatment for tobacco can no longer be ignored in mental-health and addiction-treatment settings. More research is needed as well as a national organized effort to address tobacco in this large segment of smokers.

Bupropion (Zyban, Wellbutrin) inhibits nicotine-induced viral reactivation in herpes simplex virus type 1 latent rabbits

We reported that nicotine applied via a transdermal patch (21 mg/day) induced viral reactivation and ocular shedding in herpes simplex virus type 1 (HSV-1) latent rabbits. One possible mechanism of action involves the release of catecholamines and other similar agents, triggering HSV reactivation. Bupropion (Zyban, Wellbutrin), a non-nicotine aid to smoking cessation, inhibits neuronal uptake of norepinephrine, serotonin, and dopamine. To determine whether bupropion inhibits HSV reactivation, rabbits latent with HSV-1 were grouped (at least 10 rabbits/group) and treated as follows: nicotine patch (transdermal delivery) and bupropion [Zyban sustained-release tablets (150 mg) twice a day (oral)], nicotine patch only, Zyban tablets only [twice a day (oral)], nicotine patch with oral placebo [twice a day (oral)], or no drug treatment. Eyes were swabbed for 22 consecutive days. The appearance of HSV-1 in the tear film was significantly less frequent in the bupropion-treated rabbits, in terms of positive rabbits/total rabbits, positive eyes/total eyes, and positive swabs/total swabs. Nicotine-treated rabbits had 78/440 (17.7%) positive/total swabs, and nicotine/placebo-treated rabbits had 149/792 (18.8%) positive/total swabs, whereas bupropion-treated rabbits had 23/440 (5.2%), and nicotine/bupropion-treated rabbits had 47/792 (5.9%) positive/total swabs. Thus, bupropion significantly reduces nicotine-induced HSV reactivation in latent rabbits.

Genetics of tobacco use

The worldwide prevalence of tobacco use is widespread, resulting in nearly 4.5 million deaths every year. Nicotine is addictive and has psychopharmacological effects that maintain the use of tobacco products. Several studies have documented a strong hereditary component to tobacco use. The present article reviews results from twin and adoption studies and proceeds to present association studies of specific genes that may be involved in tobacco use. Cholinergic receptor nicotinic beta polypeptide 2, serotonin receptor and transporter genes, dopamine receptor and transporter genes, and the cytochrome P450A6 gene are reviewed. Linkage studies help to identify regions of the genome that may be worth further investigation. The paper concludes with a discussion of the limitations of genetic research and the future of genetic epidemiology in this domain.

Neuroprotective strategies for Parkinson's disease: conceptual limits of animal models and clinical trials

Parkinson's disease (PD) is a progressive neurodegenerative disorder. Although therapies that treat the symptoms of the disease have proven efficacy, strategies that slow or stop the neurodegenerative process are currently not available. Recently, the National Institute of Neurological Disorders and Stroke (NINDS) conducted a systematic assessment of candidate pharmacological agents with putative neuroprotective properties. Twelve agents have been selected as potential candidates for upcoming clinical trials. However, the data resulting from the use of these agents in animal models of PD using a clinically driven design have not been published. Furthermore, the selection of interesting candidates should be based on the soundest clinically driven preclinical validation. This lack of published data, associated with the conceptual limits of the current way of testing drugs in clinical trials, prompts us to argue for further preclinical validation of the 12 candidates.

Measures and models of nicotine dependence: positive reinforcement

This paper addresses the problem of assessing nicotine dependence. The main objective is to develop theory-led suggestions for measures that will be relevant in the early phases of tobacco use, as well as in established smokers. Theoretical models of addiction falling into the general class of 'positive reinforcement theories' were identified and reviewed. From this review a number of drug effects and patterns of behaviour were distilled and categorized as either vulnerability or dependence indicators. A comparison of those features with the International Classification of Diseases (ICD-10) and Diagnostic and Statistical Manual (DSM-IV) diagnostic systems shows that neither system includes detailed assessment of vulnerability indicators. It is argued that measurement of vulnerability indicators, in addition to dependence indicators, may add to the predictive validity of assessments carried out in early career tobacco users, especially where there is limited evidence of established dependence. In addition, it is suggested that examination of measures that differentiate a subgroup of early career smokers termed 'rapid accelerators' may prove profitable and enable identification of the key parameters of nicotine reinforcement.

2-deoxy-2-[18F]fluoro-d-glucose and alternative radiotracers for positron emission tomography imaging using the human brain as a model

2-deoxy-2-[18F]fluoro-D-glucose (18FDG) is now routinely available in many hospitals and other institutions either via on-site production or from one of the dozens of regional radiopharmacies worldwide. Its reliable production has opened the possibility for use in both basic and clinical investigations and also in pairing it with other more biologically specific positron emission tomography tracers to provide an important functional perspective to the measurement. In this article, we highlight examples in which 18FDG is paired with another carbon-11- or fluorine-18-labeled radiotracer in the same subject to correlate neurotransmitter-specific effects with regional metabolic effects using the human brain as a model. We describe studies that fall into three major areas: normal aging, neuropsychiatric disorders, and drug action.

Current pharmacological treatments for nicotine dependence

There are nearly 1.1 billion users of nicotine and tobacco products worldwide. Tobacco use through cigarette smoking is the leading preventable cause of death in the world and kills nearly four million people annually. However, although some cigarette smokers are able to quit, many are not, and standard medications to assist in smoking cessation (e.g. nicotine-replacement therapies and sustained-release bupropion) are ineffective in many remaining smokers. Recent developments in our understanding of the neurobiology of nicotine dependence have identified several neurotransmitter systems that might contribute to the process of smoking maintenance and relapse, including dopamine, noradrenaline, 5-hydroxytryptamine, acetylcholine, endogenous opioids, GABA, glutamate and endocannabinoids. Several existing medications are being tested as treatments for nicotine dependence and novel investigational agents are under development as effective treatments for nicotine dependence in the 'hard to treat' tobacco user.

Both low and high activities of platelet monoamine oxidase increase the probability of becoming a smoker

Platelet monoamine oxidase (MAO) activity is a marker of personality and psychiatric vulnerability, but the direct inhibitory action of tobacco constituents on the enzyme distorts the association. In the present investigation, data from a prospective longitudinal study of smoking behaviour and platelet MAO activity in adolescents at ages 15 and 18 years were sequentially analysed using a second-order multiple logistic regression analysis. The odds of regular smoking at 18 years increased significantly with increasing absolute deviation of platelet MAO activity at 15 years from the mean. That is, both low and high platelet MAO activity at 15 years predicted a higher probability of becoming a smoker. These data suggest that smoking is associated with low platelet MAO activity not only because of the direct inhibitory effect of tobacco constituents on the enzyme, but also because subjects with low platelet MAO activity are more likely to become smokers. Furthermore, the possible association between above-average platelet MAO activity and behavioural phenotypes should be reexamined.

A randomized controlled trial of oral selegiline plus nicotine skin patch compared with placebo plus nicotine skin patch for smoking cessation

OBJECTIVES

To compare the effect of oral selegiline plus nicotine patch with placebo plus nicotine patch on smoking cessation rates.

DESIGN

Randomized double-blind placebo-controlled trial.

SETTING

Three community-based clinics.

PARTICIPANTS

One hundred and nine male and female smokers aged 18-55 years, who smoked at least 15 cigarettes/day.

INTERVENTIONS

Oral selegiline, 2.5 mg, or placebo twice/day initiated 1 week before the quit day, followed by 5 mg oral selegiline or placebo twice daily for 26 weeks, plus active nicotine skin patch to all participants for the first 8 weeks only. Measures of continuous abstinence rates up to 52 weeks, withdrawal symptoms, blood pressure and adverse events incidence.

FINDINGS

Twenty-five per cent (14 of 56) were continuously abstinent for 52 weeks in the selegiline plus nicotine group compared with 11% (6 of 53) in the placebo plus nicotine group (P = 0.08). Craving for cigarettes was lower in the selegiline plus nicotine group 4 weeks after quit day (P = 0.02).

CONCLUSIONS

Adding selegiline to nicotine patch was associated with a doubling of the 52-week continuous abstinence rate, but this difference was not statistically significant. Selegiline significantly reduced craving for cigarettes and appeared to mitigate the need for nicotine replacement therapy. The results suggest that selegiline is a promising drug for future smoking cessation research.

Low monoamine oxidase B in peripheral organs in smokers

One of the major mechanisms for terminating the actions of catecholamines and vasoactive dietary amines is oxidation by monoamine oxidase (MAO). Smokers have been shown to have reduced levels of brain MAO, leading to speculation that MAO inhibition by tobacco smoke may underlie some of the behavioral and epidemiological features of smoking. Because smoking exposes peripheral organs as well as the brain to MAO-inhibitory compounds, we questioned whether smokers would also have reduced MAO levels in peripheral organs. Here we compared MAO B in peripheral organs in nonsmokers and smokers by using positron emission tomography and serial scans with the MAO B-specific radiotracers,l-[11C]deprenyl and deuterium-substituted l-[11C]deprenyl (l-[11C]deprenyl-D2). Binding specificity was assessed by using the deuterium isotope effect. We found that smokers have significantly reduced MAO B in peripheral organs, particularly in the heart, lungs, and kidneys, when compared with nonsmokers. Reductions ranged from 33% to 46%. Because MAO B breaks down catecholamines and other physiologically active amines, including those released by nicotine, its inhibition may alter sympathetic tone as well as central neurotransmitter activity, which could contribute to the medical consequences of smoking. In addition, although most of the emphases on the carcinogenic properties of smoke have been placed on the lungs and the upper airways, this finding highlights the fact that multiple organs in the body are also exposed to pharmacologically significant quantities of chemical compounds in tobacco smoke.

DNA sequence analysis of monoamine oxidase B gene coding and promoter regions in Parkinson's disease cases and unrelated controls

The allele G of the intron 13 G/A polymorphism of the monoamine oxidase B gene (MAO-B) has been associated with Parkinson's disease (PD) in several studies. Apart from a potential direct effect on splicing processes, the association of this intronic polymorphism with PD is due possibly to linkage disequilibrium with other mutations in the coding or promoter regions of the gene. We addressed this latter hypothesis by determining the DNA sequence of the entire MAO-B coding region comprising 15 exons and partial intronic sequences flanking each exon, in 33 cases with idiopathic PD and 38 unrelated controls. The promoter region of MAO-B gene up to base -1,369 from ATG (start point of mRNA translation) was also sequenced to identify variants with potential functional effects on gene transcription. In the promoter region, a new polymorphism consisting of a C to T single base change was detected in position -1,114 from ATG, with an allelic frequency of 3.5%, but it was not associated with PD risk. No commonly occurring (>10%) polymorphisms were found in the exons or the intronic sequences flanking the exons, although several rare variants were detected in the coding and promoter regions.

Cigarette smoke and nicotine protect dopaminergic neurons against the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine Parkinsonian toxin

Epidemiological studies have found a negative association between cigarette smoking and Parkinson's disease (PD). In order to analyze the putative neuroprotective effect of cigarette smoke and nicotine, one of its major constituents, we examined their effects in an animal model of PD provoked by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) intoxication. Two groups of mice were chronically exposed to cigarette smoke (a low exposure subgroup and a high exposure subgroup; 5 exposures per day at 2-h intervals), two other groups received nicotine treatment (two doses tested 0.2 and 2 mg/kg, 5 injections i.p. per day at 2-h intervals) and one group placebo. On day 8 after the beginning of the treatment, 4 injections of MPTP hydrochloride (15 mg/kg, i.p., at 2-h intervals) or saline were administered to these animals. Nicotine and cotinine plasmatic concentration was quantified by the HPLC method, and degeneration of the nigrostriatal system was assessed by tyrosine hydroxylase (TH) immunohistochemistry. The loss of dopaminergic neurons induced by MPTP in the substantia nigra was significantly less severe in the chronic nicotine treatment groups (at 0.2 and 2 mg/kg) and the low exposure to cigarette smoke group than in the high exposure to cigarette smoke subgroup and the placebo treated subgroup. In contrast, no preservation of TH immunostaining of nerve terminals was observed in the striatum in any group. This suggests that nicotine and low exposure to cigarette smoke may have a neuroprotective effect on the dopaminergic nigrostriatal system by an as yet unknown mechanism.

The environment and Parkinson's disease: is the nigrostriatal system preferentially targeted by neurotoxins?

Recent epidemiological and experimental studies have renewed interest in the hypothesis that the environment has a role in the pathogenesis of Parkinson's disease (PD). Epidemiological studies have identified protective associations (eg, smoking) as well as adverse risk factors (eg, pesticide exposure) for PD. The concordance rate of PD in pairs of dizygotic twins is similar to that in pairs of monozygotic twins, supporting a role of non-genetic risk factors. New models of selective nigrostriatal damage--such as neurotoxicity induced by rotenone or paraquat--have emphasised that environmental agents may contribute to the neurodegenerative process in PD. Toxins interact, in vitro and in vivo, with alpha-synuclein, an endogenous protein that is implicated in pathology of PD. Similarities between clinical and experimental findings, such as the role of pesticide exposure as a potential environmental risk factor, highlight the importance of a multidisciplinary approach to the aetiology of PD.

Monoamine oxidase A imaging in peripheral organs in healthy human subjects

Monoamine oxidase (MAO) catalyzes the oxidative deamination of many biogenic and dietary amines. Though studies of MAO have focused mainly on its regulatory role in the brain, MAO in peripheral organs also represents a vast mechanism for detoxifying vasoactive compounds as well as for terminating the action of physiologically active amines, which can cross the blood brain barrier. Indeed, robust central and peripheral MAO activity is a major requirement in the safe use of many CNS drugs, particularly antidepressants, and thus an awareness of the MAO inhibitory potential of drugs is essential in therapeutics. In this study, we examined the feasibility of quantifying MAO A in peripheral organs in healthy human subjects using comparative positron emission tomography (PET) imaging with carbon-11 (t(1/2): 20.4 min) labeled clorgyline ([(11)C]clorgyline) a suicide inactivator of MAO A and its deuterium labeled counterpart ([(11)C]clorgyline-D2). Heart, lungs, kidneys, thyroid, and spleen showed a robust deuterium isotope effect characteristic of MAO and the magnitude of the effect was similar to that of trancylcypromine, an irreversible MAO inhibitor used in the treatment of depression. Liver time-activity curves were not affected by deuterium substitution precluding the estimation of liver MAO in vivo. In organs showing an isotope effect, MAO A is greatest in the lungs and kidneys followed by the thyroid and heart. This method, which has been previously applied in the human brain, opens the possibility to also directly assess the effects of different variables including smoking, dietary substances, drugs, disease, and genetics on peripheral MAO A in humans.

Monoamine oxidase B polymorphism, cigarette smoking and risk of Parkinson's disease: a study in an Asian population

Cigarette smoking is associated with reduced monoamine oxidase B (MAO B) activity. Polymorphisms of the MAO B gene may modify the relationship between smoking and Parkinson's Disease (PD). We examined the association of MAO B intron 13 G/A polymorphism and risk of PD, and the modulation of the polymorphism on smoking and PD in an Asian study population in Singapore. Two hundred and thirty PD patients (mean age 66.0 +/- 9.4 years, 63% men) and 241 age, gender, and race matched controls (mean age 64 +/- 9.2 years, 58.9% males) were studied. The frequency of G and A alleles in PD and controls was; 66/315 (21.0%) vs. 73/340 (21.5%) and 249/315 (79.0%) vs. 267/340 (78.5%). For women, the genotype frequency in PD and controls was; GG: 7/85 (8.2%) vs. 8/99 (8.1%); GA: 25/85 (29.4%) vs. 27/99 (27.3%); AA: 53/85 (62.4%) vs. 64/99 (64.6%). For men, allele frequency in PD and controls was; A: 118/145 (81.4%) vs. 112/142 (78.9%) and G: 27/145 (18.6%) vs. 30/142 (21.1%). The allele and genotype frequencies were not significantly different between young and late onset PD. The frequency of "ever" smokers in PD and controls was 31/230 (13.5%) vs. 52/241 (21.6%), P = 0.02. A stepwise logistic regression analysis did not reveal any interaction of smoking and the G allele and risk of PD. The MAO B G/A genotype frequency in our Asian population was quite different from Caucasians suggesting that ethnicity specific effects need to be considered in evaluating gene-environmental interaction.