Platelet monoamine oxidase, smoking cessation, and tobacco withdrawal symptoms

Association between tobacco smoke exposure and depression: the NHANES 2005-2018 and Mendelian randomization study

OBJECTIVE

The relationship between tobacco smoke exposure (TSE) and depression is controversial. This study combined observational research and Mendelian randomization (MR) to explore the relationship of depression with both smoking status and cotinine levels.

METHOD

We collected relevant data from the National Health and Nutrition Examination Survey (NHANES) database from 2005 to 2018, and used weighted multifactorial logistic regression modelling to assess the correlation between TSE and depression, and assessed the causal relationship of depression with both smoking status and cotinine levels by MR.

RESULT

Current smokers had the highest risk of depression (OR 1.94; P < 0.01); there was a positive trend for correlation between daily smoking and depression (OR 1.66; P for trend < 0.01). Serum ketamine levels above 3.00 ng/ml had a higher risk of depression (OR 2.13; P < 0.001). MR results showed that current smoking (OR = 4.66; P < 0.001) and previous smoking (OR 2.09; P < 0.01) were risk factors for the onset of depression, and that there was no causal association between cotinine levels and depression.

CONCLUSION

Smoking is significantly associated with depression and plays a potential causal role in the development of depression. Cotinine was significantly associated with depression, however MR results showed no causal relationship between cotinine and depression.

The longitudinal analysis for the association between smoking and the risk of depressive symptoms

BACKGROUND

Despite high smoking rate in people with depressive symptoms, there is ongoing debate about relationship between smoking and depressive symptoms.

METHODS

Study participants were 57,441 Korean men. We collected their baseline data between 2011 and 2012, and conducted follow-up from 2013 to 2019. They were categorized by smoking status (never: < 100 cigarettes smoking in life time, former: currently quitting smoking, and current smoker: currently smoking), smoking amount (pack/day and pack-year) and urine cotinine excretion. The development of depressive symptoms was determined in CES-D score ≥ 16. Cox proportional hazards model was used to analyze the multivariable-adjusted hazard ratio (HR) and 95% confidence intervals (CI) for depressive symptoms in relation to smoking status, smoking amount, and urine cotinine excretion.

RESULTS

During 6.7 years of median follow-up, the risk of depressive symptoms increased in order of never (reference), former (HR = 1.08, 95% CI: 1.01-1.15) and current smoker (HR = 1.24, 95% CI: 1.16-1.32). Among current smoker, the risk of depressive symptoms increased proportionally to daily smoking amount (< 1 pack; HR = 1.21, 95% CI: 1.13-1.29, and ≥ 1 pack; HR = 1.34, 95% CI: 1.23 - 1.45). This pattern of relationship was consistently observed for pack-year in former smoker and current smoker. Additionally, urine cotinine excretion was proportionally associated with the risk of depressive symptoms.

CONCLUSION

Exposure to smoking was associated with the increased risk of depressive symptoms. Dose dependent relationship was observed between smoking amount and the risk of depressive symptoms.

The HINT1 Gene rs2526303 Polymorphism and Its Association with Personality Traits in Cigarette Smokers

The development of a substance use disorder (SUD) is a multifaceted process influenced by both genetic and environmental factors. Recent research has suggested the potential involvement of the HINT1 gene in various aspects of plasticity, mood regulation, anxiety-like behaviour, and stress-coping mechanisms. Moreover, personality traits are also recognised to be instrumental in developing substance dependency. Given these considerations, our study investigated the associations among cigarette smoking, personality traits, and the rs2526303 polymorphism. Additionally, we investigated the interactions between personality traits and rs2526303 in the HINT1 gene. The study group comprised 531 volunteers: 375 cigarette users (mean age = 29.42 ± 10.72; F = 49%, M = 51%) and 156 never-smokers (mean age = 26.93 ± 10.09; F = 79%, M = 21%). Genotyping was conducted using the real-time PCR method, and the NEO Five-Factor Personality Inventory and State-Trait Anxiety Inventory were administered. There were no statistically significant differences in the frequency of rs2526303 genotypes and alleles in the cigarette user group compared to the control group. Compared to the control group, the cigarette users obtained higher scores in the assessment of the NEO-FFI Extraversion scale and lower results for the NEO-FFI Openness, Agreeableness, and Conscientiousness scales. Additionally, there was a statistically significant effect of rs2526303 genotype interaction and cigarette-using status on the conscientiousness scale. These outcomes collectively suggest a notable association between cigarette smoking and specific dimensions of personality, particularly highlighting differences in extraversion, openness, agreeableness, and conscientiousness. Furthermore, the detected interaction effect involving rs2526303 concerning conscientiousness signifies a complex interplay between genetic factors and smoking behaviour.

Concurrent changes in dental anxiety and smoking in parents of the FinnBrain Birth Cohort Study

We evaluated associations between changes in dental anxiety and tobacco use, adjusted for general anxiety and depressive symptoms. The FinnBrain Birth Cohort Study data, collected at gestational weeks 14 and 34 and at 3 months postpartum, were used. Questionnaires included the Modified Dental Anxiety Scale (MDAS), the Edinburgh Postnatal Depression Scale (EPDS), and the anxiety subscale of the Symptom Checklist-90 (SCL). Smoking was categorized as "stable non-smoking", "started smoking", "quit smoking", and "stable smoking". Changes in smoking and dental anxiety were evaluated "during pregnancy" (i.e., from gestational week 14 to gestational week 34) in 2442 women and 1346 men and "after pregnancy" (i.e., from gestational week 34 to 3 months postpartum) in 2008 women and 1095 men. Changes were evaluated in three smoking categories (stable non-smoking, fluctuating, and stable smoking), using data from all three time-points (1979 women and 1049 men). Modeling used repeated measures analysis of covariance. Stable smoking mothers had statistically significantly higher levels of dental anxiety (mean MDAS 12.3-12.6) than non-smoking mothers (mean MDAS 10.1-10.7) or mothers who smoked at some point during pregnancy (mean MDAS 10.8-11.5). A similar tendency was observed in fathers. However, no systematic change in dental anxiety by changes in smoking habits was observed. Those smoking during pregnancy and with high dental anxiety may need special support for smoking cessation.

A review of monoamine oxidase (MAO) inhibitors in tobacco or tobacco smoke

Tobacco smoking is reputed to be the most difficult addiction of all to give up, and nicotine has been noted as the major addictive agent in tobacco smoke. However, research shows that nicotine addiction is due to more than nicotine alone. One hypothesis is that monoamine oxidase (MAO) inhibition from non-nicotinic components in, or derived from, tobacco smoke contributes to nicotine addiction. Harman and norharman, have been recognised as major and potent MAO inhibitors in tobacco smoke, but these two inhibitors together comprise perhaps less than 10% of the total MAO A inhibitory activity in cigarette smoke suggesting other unidentified components may make significant contributions to total inhibitory activity. Therefore, we reviewed an index of the chemical components of tobacco and tobacco smoke and identified those known to be MAO inhibitors. Amongst these inhibitors, phenols and phenolic acids with MAO inhibitory activity are commonly reversible and selective MAO A inhibitors, whereas trans,trans-farnesol, 2-methyl-1,4-naphthoquinone (menadione), 1,4-naphthoquinone, scopoletin, and diosmetin with MAO inhibitory activity are reversible and selective MAO B inhibitors. The compound, 1,4-benzoquinone is an irreversible MAO A inhibitor and to the best of our knowledge, this is the first irreversible MAO A inhibitor to be reported in tobacco smoke. MAO inhibitors have been used clinically to treat depression, anxiety, and Parkinson's disease. The MAO inhibitors identified from tobacco and tobacco smoke and summarized in this review, are potential pharmacological candidates to be investigated further. This review will enhance our knowledge of the way tobacco smoke affects MAO activity in smokers and will also be important in helping to understand nicotine addiction.

Monoamine oxidase inhibition in cigarette smokers: From preclinical studies to tobacco product regulation

Monoamine oxidase (MAO) activity is reduced in cigarette smokers and this may promote the reinforcing actions of nicotine, thereby enhancing the addictive properties of cigarettes. At present, it is unclear how cigarette smoking leads to MAO inhibition, but preclinical studies in rodents show that MAO inhibition increases nicotine self-administration, especially at low doses of nicotine. This effect of MAO inhibition develops slowly, likely due to plasticity of brain monoamine systems; studies relying on acute MAO inhibition are unlikely to replicate what happens with smoking. Given that MAO inhibition may reduce the threshold level at which nicotine becomes reinforcing, it is important to consider this in the context of very low nicotine content (VLNC) cigarettes and potential tobacco product regulation. It is also important to consider how this interaction between MAO inhibition and the reinforcing actions of nicotine may be modified in populations that are particularly vulnerable to nicotine dependence. In the context of these issues, we show that the MAO-inhibiting action of cigarette smoke extract (CSE) is similar in VLNC cigarettes and cigarettes with a standard nicotine content. In addition, we present evidence that in a rodent model of schizophrenia the effect of MAO inhibition to enhance nicotine self-administration is absent, and speculate how this may relate to brain serotonin systems. These issues are relevant to the MAO-inhibiting effect of cigarette smoking and its implications to tobacco product regulation.

Behavioral risk factors for noncommunicable diseases associated with depression and suicide risk in adolescence

Noncommunicable diseases (NCDs) and mental disorders cooccur in adulthood, which is why their determinants and common risk factors should be addressed at an early age. Therefore, we estimated the association of the major risk factors for NCDs with depression and suicide risk by structural equation modeling considering pathways triggered by social vulnerability or mediated by obesity. This population-based study included 2,515 Brazilian adolescents. The following exposures were the major risk factors for NCDs: substance use behaviors (variable deduced from alcohol, tobacco, and drug use), physical inactivity, and components of unhealthy eating markers (added sugar and saturated fat). Obesity was assessed using the fat mass index. The outcomes were depression and suicide risk. Depression was associated with substance use behaviors (SC = 0.304; p < 0.001), added sugar (SC = 0.094; p = 0.005), and females (SC = 0.310; p < 0.001). Suicide risk was also associated with substance use behaviors (SC = 0.356; p < 0.001), added sugar (SC = 0.100; p = 0.012), and females (SC = 0.207; p < 0.001). In adolescents, these associations may help explain the cluster of NCDs and mental disorders in adulthood.

Prenatal tobacco use and the risk of mood disorders in offspring: a systematic review and meta-analysis

PURPOSE

It is plausible that offspring born to mothers using tobacco during pregnancy may have increased risk of mood disorders (depression and bipolar disorders); however, mixed results have been reported. We conducted a systematic review and meta-analysis to investigate the magnitude and consistency of associations reported between prenatal tobacco use and mood disorders in offspring.

METHODS

We systematically searched EMBASE, SCOPUS, PubMed and Psych-INFO for studies on mood disorders and prenatal tobacco use. Methodological quality of studies was assessed with the revised Newcastle-Ottawa Scale. We estimated pooled relative risk (RR) with inverse variance weighted random-effects meta-analysis. We performed leave-one-out analyses, and stratified analyses by a subgroup (depression and bipolar disorder). Potential publication bias was assessed by inspection of the funnel plot and Egger's test for regression asymmetry. This study protocol was prospectively registered in PROSPERO (CRD42017060037).

RESULTS

Eight cohort and two case-control studies were included in the final meta-analysis. We found an increased pooled relative risk of mood disorders in offspring exposed to maternal prenatal tobacco use RRs 1.43 (95% CI 1.27-1.60) compared to no prenatal tobacco use. Similarly, the pooled relative risks of bipolar and depressive disorders in offspring were 1.44, (95% CI 1.15-1.80) and 1.44, (95% CI 1.21-1.71), respectively. Moreover, the pooled estimated risk of mood disorders was not significantly attenuated in the studies that reported sibling comparison results [RR = 1.21 (95% CI 1.04-1.41)].

CONCLUSION

Taken together, there was strong evidence for a small (RR < 2) association between prenatal tobacco use and mood disorders in offspring.

Randomized Clinical Trials Investigating Innovative Interventions for Smoking Cessation in the Last Decade

Every year, billions of dollars are spent treating smoking and related conditions, yet smoking-related morbidity and mortality continue to rise. There are currently only three FDA-approved medications for smoking cessation: nicotine replacement therapy, bupropion, and varenicline. Although these medications increase abstinence rates, most individuals relapse following treatment. This chapter reviews clinical trials published within the past 10 years investigating novel smoking cessation pharmacotherapies. Among these pharmacotherapies, some showed promising results, such as cytisine and endocannabinoid modulators, whereas others failed to produce significant effects. More research is needed to develop drugs that produce higher rates of long-term abstinence and to determine which subgroups of patients benefit from a given treatment.

Monoamine oxidase inhibitory activity in tobacco particulate matter: Are harman and norharman the only physiologically relevant inhibitors?

Monoamine oxidase inhibition is significant in smokers, but it is still unclear how the inhibition that is seen in the brains and bodies of smokers is brought about. Our aim was to test the contribution of the harman and norharman in tobacco smoke to MAO-A inhibition from tobacco smoke preparations, as part of a re-examination of harman and norharman as the cause of the inhibition of MAO-A inhibition in the brain. Tobacco smoke particulate matter and cigarette smoke particulate matter were prepared and the amounts of harman and norharman measured. The results were compared with the total monoamine oxidase-A inhibitory activity. At a nicotine concentration of 0.6μM (a "physiological" concentration in blood) the total monoamine oxidase-A inhibitory activity measured in these samples was sufficient to inhibit the enzyme by approximately 10%. Of this inhibitory activity, only a small proportion of the total was found to be due to harman and norharman. These results show that harman and norharman provide only a moderate contribution to the total monoamine oxidase-A inhibitory activity of tobacco smoke, perhaps under 10%. This suggests that other inhibitors (either known or unknown) may be more significant contributors to total inhibitory activity than has yet been established, and deserve closer examination.

The Association of Cigarette Smoking With Depression and Anxiety: A Systematic Review

BACKGROUND

Many studies report a positive association between smoking and mental illness. However, the literature remains mixed regarding the direction of this association. We therefore conducted a systematic review evaluating the association of smoking and depression and/or anxiety in longitudinal studies.

METHODS

Studies were identified by searching PubMed, Scopus, and Web of Science and were included if they: (1) used human participants, (2) were longitudinal, (3) reported primary data, (4) had smoking as an exposure and depression and/or anxiety as an outcome, or (5) had depression and/or anxiety as the exposure and smoking as an outcome.

RESULTS

Outcomes from 148 studies were categorized into: smoking onset, smoking status, smoking heaviness, tobacco dependence, and smoking trajectory. The results for each category varied substantially, with evidence for positive associations in both directions (smoking to later mental health and mental health to later smoking) as well as null findings. Overall, nearly half the studies reported that baseline depression/anxiety was associated with some type of later smoking behavior, while over a third found evidence that a smoking exposure was associated with later depression/anxiety. However, there were few studies directly supporting a bidirectional model of smoking and anxiety, and very few studies reporting null results.

CONCLUSIONS

The literature on the prospective association between smoking and depression and anxiety is inconsistent in terms of the direction of association most strongly supported. This suggests the need for future studies that employ different methodologies, such as Mendelian randomization (MR), which will allow us to draw stronger causal inferences.

IMPLICATIONS

We systematically reviewed longitudinal studies on the association of different aspects of smoking behavior with depression and anxiety. The results varied considerably, with evidence for smoking both associated with subsequent depression and anxiety, and vice versa. Few studies supported a bidirectional relationship, or reported null results, and no clear patterns by gender, ethnicity, clinical status, length to follow-up, or diagnostic test. Suggesting that despite advantages of longitudinal studies, they cannot alone provide strong evidence of causality. Therefore, future studies investigating this association should employ different methods allowing for stronger causal inferences to be made, such as MR.

Contribution of Monoamine Oxidase Inhibition to Tobacco Dependence: A Review of the Evidence

BACKGROUND

There is a hypothesis that substances present in, or derived from, tobacco smoke inhibit monoamine oxidase (MAO) in the brains of smokers, reducing the degradation of catecholamine neurotransmitters involved in central reward pathways and acting synergistically with nicotine to increase its addictive effects.

OBJECTIVE

The objective of this review was to evaluate the evidence for a role of MAO inhibition by tobacco-derived substances in tobacco dependence.

INVESTIGATIONAL PLAN

Relevant studies on the effects of tobacco use on MAO levels or activity in humans were identified by electronic searches.

RESULTS

The identified data show a clear association between smoking and lower density of MAO-A and MAO-B binding sites in the brains of smokers and strong evidence that MAO is inhibited by a substance or substances in, or derived from, tobacco smoke. There was little evidence to support the hypothesis that low MAO levels/activity is a predictive factor for tobacco use. Substances that inhibit MAO in in vitro assays have been isolated from tobacco leaves and tobacco smoke; however, no single substance has been shown to be absorbed from tobacco smoke and to inhibit MAO in the brains of human smokers. Nevertheless, it is possible that MAO inhibition in smokers could result from additive or synergistic effects of several tobacco-derived substances. MAO inhibition potentiates the reinforcing effects of intravenous nicotine in rodents; however, no data were identified to support the hypothesis that MAO inhibitors in or derived from tobacco or tobacco additives affect tobacco dependence in human smokers.

IMPLICATIONS

This comprehensive review describes the available evidence for the role of MAO inhibition in tobacco dependence and points the way for further research in this field. In view of the large number of MAO inhibitors identified in tobacco and tobacco smoke, identification of the putative inhibitors responsible for the lower level/activity of MAO in smokers may be impractical. Future studies must address whether the lower level/activity of MAO observed in smokers is also seen in users of other tobacco products and if this change is implicated in their dependence-inducing effects.

Association between monoamine oxidase gene polymorphisms and smoking behavior: A meta-analysis

BACKGROUND

A number of studies have researched the association between monoamine oxidase gene (MAO) polymorphisms and smoking behavior, but the conclusion is quite inconsistent. A meta-analysis was conducted to assess the association of MAO-A C1460T, MAO-A VNTR and MAO-B G644A polymorphisms with smoking behavior.

METHODS

A comprehensive search was performed to identify all eligible studies. Meta-analysis was applied to calculate the pooled effect values and their 95% confidence intervals. Meta-regression and the 'leave one out' sensitivity analysis were used to explore potential sources of heterogeneity. The risk of bias was assessed by the Egger regression asymmetry test.

RESULTS

11 articles conformed to the inclusion criteria. The meta-analysis showed T allele in MAO-A C1460T reduced the risk of heavy smoking (OR=0.66, 95% CI: 0.52-0.84; I(2)=0.0%), especially in Caucasians; the active group in MAO-A VNTR increased the likelihood of failed smoking cessation in males (OR=1.49, 95% CI: 1.01-2.22; I(2)=0.0%); A allele in MAO-B G644A reduced the risk of heavy smoking in males (OR=0.20, 95% CI: 0.04-0.98).

CONCLUSION

Our findings indicate that the low activity of monoamine oxidase gene polymorphisms has a protective effect on smoking cessation and heaviness. Some associations and applications should be further confirmed.

The separate and combined effects of monoamine oxidase A inhibition and nicotine on the mismatch negativity event related potential

The mismatch negativity (MMN) auditory event-related potential (ERP) has been extensively studied as a potential biomarker for abnormal auditory processing in schizophrenia (SZ), a population which exhibits abnormally high smoking rates. The relationship between nicotinic activation and cognition in SZ may be related to underlying nicotinic and NMDA receptor dysfunction within the disease. However, transient cognitive improvements via smoking in patients may also result from monoamine oxidase (MAO) inhibition, achieved through tobacco smoke. In 24 healthy non-smoking males, we investigated the separate and combined effects of nicotine and MAO-A inhibition via moclobemide (75mg) on the optimal-5 variation of the MMN paradigm. No significant drug effects were observed in our total sample, however, stratification of individuals into low (N=12) and high (N=12) baseline MMN amplitude groups revealed increases in duration MMN amplitude relative to placebo by nicotine, as well as moclobemide, but not after the combination of the two. Because previous research has shown there was no effect of monoamine modulation on MMN, this study shows an unexpected effect of moclobemide on duration MMN.

The separate and combined effects of monoamine oxidase inhibition and nicotine on P50 sensory gating

INTRODUCTION

The cognitive effects of nicotine in humans remain a topic of great interest, due to the continued prevalence of cigarette smoking in society as well as the hypothesis that cognitively impaired populations such as schizophrenia patients use nicotine as a means of self-medicating against deficits of sensory gating. However, chronic smoking can predispose individuals to robust monoamine oxidase (MAO) inhibition, and thus far, the effect of MAO inhibition on human sensory gating is unknown.

METHODS

In this study, we investigated the effects of both nicotine (6-mg gum) and pharmacologically induced MAO-A inhibition via moclobemide (75 mg) on P50 event-related potential-indexed sensory gating in a sample of 24 healthy non-smoking males.

RESULTS

Ratio score (rP50) measured gating revealed significant improvement in auditory stimulus suppression after combined nicotine and MAO-A inhibition compared to placebo and to the nicotine-alone condition. This nicotine + MAO-A inhibition-induced efficient gating was consistent regardless of participants' baseline (placebo) gating efficiency, despite the observation that nicotine in the absence of MAO-A inhibition exhibited a detrimental effect on gating in participants with high baseline suppression ratios.

CONCLUSION

Nicotine and monoamine oxidase-inhibiting agents in tobacco smoke appear to exert a synergistic effect on sensory gating, which may contribute to the elevated dependence rates seen in populations with cognitive deficits such as schizophrenia.

Inhibition effects of Vernonia cinerea active compounds against cytochrome P450 2A6 and human monoamine oxidases, possible targets for reduction of tobacco dependence

The human cytochrome P450 2A6 (CYP2A6) and monoamine oxidases (MAO-A and MAO-B), catalyzing nicotine and dopamine metabolisms, respectively, are two therapeutic targets of nicotine dependence. Vernonia cinerea, a medicinal plant commonly used for treatment of diseases such as asthma and bronchitis, has been shown reducing tobacco dependence effect among tobacco users. In the present study, we found eight active compounds isolated from V. cinerea that comprise inhibitory activity toward CYP2A6 and MAO-A and MAO-B enzymes using activity-guided assays, with coumarin as substrate of CYP2A6 and kynuramine of MAOs. These compounds were three flavones (apigenin, chrysoeriol, luteolin), one flavonol (quercetin), and four hirsutinolide-type sesquiterpene lactones (8α-(2-methylacryloyloxy)-hirsutinolide-13-O-acetate, 8α-(4-hydroxymethacryloyloxy)-hirsutinolide-13-O-acetate, 8α-tigloyloxyhirsutinolide-13-O-acetate, and 8α-(4-hydroxytigloyloxy)-hirsutinolide-13-O-acetate). Modes and kinetics of inhibition against the three enzymes were determined. Flavonoids possessed strong inhibitory effect on CYP2A6 in reversible mode, while inhibition by hirsutinolides was mechanism-based (NADPH-, concentration-, and time-dependence) and irreversible. Inhibition by hirsutinolides could not be reversed by dialysis and by addition of trapping agents or potassium ferricyanide. Flavonoids inhibited MAOs with variable degrees and were more prominent in inhibition toward MAO-A than hirsutinolides, while two of hirsutinolides inhibited MAO-B approximately comparable to two flavonoids. These results could have implications in combination of drug therapy for smoking cessation.

Investigating the possible causal association of smoking with depression and anxiety using Mendelian randomisation meta-analysis: the CARTA consortium

OBJECTIVES

To investigate whether associations of smoking with depression and anxiety are likely to be causal, using a Mendelian randomisation approach.

DESIGN

Mendelian randomisation meta-analyses using a genetic variant (rs16969968/rs1051730) as a proxy for smoking heaviness, and observational meta-analyses of the associations of smoking status and smoking heaviness with depression, anxiety and psychological distress.

PARTICIPANTS

Current, former and never smokers of European ancestry aged ≥16 years from 25 studies in the Consortium for Causal Analysis Research in Tobacco and Alcohol (CARTA).

PRIMARY OUTCOME MEASURES

Binary definitions of depression, anxiety and psychological distress assessed by clinical interview, symptom scales or self-reported recall of clinician diagnosis.

RESULTS

The analytic sample included up to 58 176 never smokers, 37 428 former smokers and 32 028 current smokers (total N=127 632). In observational analyses, current smokers had 1.85 times greater odds of depression (95% CI 1.65 to 2.07), 1.71 times greater odds of anxiety (95% CI 1.54 to 1.90) and 1.69 times greater odds of psychological distress (95% CI 1.56 to 1.83) than never smokers. Former smokers also had greater odds of depression, anxiety and psychological distress than never smokers. There was evidence for positive associations of smoking heaviness with depression, anxiety and psychological distress (ORs per cigarette per day: 1.03 (95% CI 1.02 to 1.04), 1.03 (95% CI 1.02 to 1.04) and 1.02 (95% CI 1.02 to 1.03) respectively). In Mendelian randomisation analyses, there was no strong evidence that the minor allele of rs16969968/rs1051730 was associated with depression (OR=1.00, 95% CI 0.95 to 1.05), anxiety (OR=1.02, 95% CI 0.97 to 1.07) or psychological distress (OR=1.02, 95% CI 0.98 to 1.06) in current smokers. Results were similar for former smokers.

CONCLUSIONS

Findings from Mendelian randomisation analyses do not support a causal role of smoking heaviness in the development of depression and anxiety.

Using Mendelian randomisation to infer causality in depression and anxiety research

Depression and anxiety co-occur with substance use and abuse at a high rate. Ascertaining whether substance use plays a causal role in depression and anxiety is difficult or impossible with conventional observational epidemiology. Mendelian randomisation uses genetic variants as a proxy for environmental exposures, such as substance use, which can address problems of reverse causation and residual confounding, providing stronger evidence about causality. Genetic variants can be used instead of directly measuring exposure levels, in order to gain an unbiased estimate of the effect of various exposures on depression and anxiety. The suitability of the genetic variant as a proxy can be ascertained by confirming that there is no relationship between variant and outcome in those who do not use the substance. At present, there are suitable instruments for tobacco use, so we use that as a case study. Proof-of-principle Mendelian randomisation studies using these variants have found evidence for a causal effect of smoking on body mass index. Two studies have investigated tobacco and depression using this method, but neither found strong evidence that smoking causes depression or anxiety; evidence is more consistent with a self-medication hypothesis. Mendelian randomisation represents a technique that can aid understanding of exposures that may or may not be causally related to depression and anxiety. As more suitable instruments emerge (including the use of allelic risk scores rather than individual single nucleotide polymorphisms), the effect of other substances can be investigated. Linkage disequilibrium, pleiotropy, and population stratification, which can distort Mendelian randomisation studies, are also discussed.

Inhibition of monoamine oxidase isoforms modulates nicotine withdrawal syndrome in the rat

AIMS

There have been many reports of monoamine oxidase (MAO) inhibition by non-nicotine ingredients in tobacco smoke, persisting for days after smoking cessation. This study determined the effect of inhibiting MAO and its isoforms on nicotine withdrawal syndrome.

MAIN METHODS

Rats were rendered nicotine-dependent by seven days of subcutaneous (s.c.) 9 mg/kg/day infusion of nicotine bitartrate. Twenty-two hours after termination of infusion, they were observed over 20 min for somatically expressed nicotine withdrawal signs. Three hours before observation, rats were injected intraperitoneally (i.p.) with 4 mg/kg each of the MAO A antagonist clorgyline and the MAO B antagonist deprenyl, or with saline alone. A similar experiment was performed with non-dependent, saline-infused rats. Another experiment compared nicotine-dependent rats that received injections of either saline or 4 mg/kg clorgyline alone. A further experiment compared rats receiving either saline or 4 mg/kg deprenyl alone.

KEY FINDINGS

Combined treatment with both MAO inhibitors markedly and significantly exacerbated somatically expressed nicotine withdrawal signs in nicotine infused rats, while having no significant effects in saline-infused rats. Rats injected s.c. with 4 mg/kg clorgyline alone had significantly more withdrawal signs than saline-injected rats, while deprenyl-injected rats had significantly fewer signs than saline controls. Assays confirmed that clorgyline thoroughly reduced MAO A enzymatic activity and deprenyl thoroughly reduced MAO B activity.

SIGNIFICANCE

The results suggest that inhibition of MAO A may contribute to the intensity of withdrawal syndrome in smoking cessation.

A selective reversible monoamine oxidase B inhibitor in smoking cessation: effects on its own and in association with transdermal nicotine patch

RATIONALE

Monoamine oxidase B (MAO-B) activity is reduced in smokers. A MAO-B inhibitor alone or co-administered with nicotine may mimic the effects of smoking and be a candidate drug for smoking cessation.

OBJECTIVE

This study aims to determine the efficacy and safety of EVT302, a selective reversible MAO-B inhibitor, alone and on top of nicotine patch (NP) in smoking cessation.

METHODS

This was a randomised, double blind, placebo-controlled phase II, multicentre trial. Smokers (≥10 cigarettes/day) received either EVT302 (N = 145) or placebo (N = 145), or EVT302 (N = 61) or placebo (N = 61) on top of open label NP 21 mg/day for 8 weeks. The main comparison was between EVT302 and placebo without NP. The primary outcome measure was end-of-treatment 4-week continuous abstinence rate (CAR).

SECONDARY OUTCOME MEASURES

point prevalence abstinence rate, saliva cotinine concentrations in the groups without NP, urge to smoke, nicotine withdrawal symptoms and assessment of subjective effects of cigarettes.

RESULTS

The 4-week CAR was 15.2 % in the placebo, 17.2 % in the EVT302, 26.8 % in the NP + placebo and 32.8 % in the NP + EVT302 groups, respectively. There was no difference between EVT302 and placebo either alone (adjusted OR: 1.45, 95 % CI: 0.65-3.26) or when co-administered with NP. No statistically significant difference occurred for the secondary outcome measures.

CONCLUSIONS

The selective, reversible MAO-B inhibitor EVT302 was not superior to placebo in helping smokers quit, in line with data with selegiline and confirms that MAO-B inhibitors are not effective in smoking cessation. Co-administration of NP does not provide a supplementary benefit.

Biological basis of tobacco addiction: Implications for smoking-cessation treatment

Tobacco use became common all over the world after discovery of Americas. Tobacco, a plant carries in its leaves an alkaloid called nicotine, which is responsible not only for several pathophysiological changes in the body but also develops tolerance to its own action with repeated use. Studies suggest that the alpha-4 beta-2 nicotine acetylcholine receptor subtype is the main receptor that mediates nicotine dependence. Nicotine acts on these receptors to facilitate neurotransmitter release (dopamine and others), producing pleasure and mood modulation. Repeated exposure to nicotine develops neuroadaptation of the receptors, resulting in tolerance to many of the effects of nicotine. Withdrawal symptoms appear on stoppage of tobacco use, which are characterized by irritability, anxiety, increased eating, dysphoria, and hedonic dysregulation, among others. Smoking is also reinforced by conditioning. Pharmacotherapies for smoking cessation should reduce withdrawal symptoms and block the reinforcing effects of nicotine obtained from smoking without causing excessive adverse effects.

A systematic review of longitudinal studies on the association between depression and smoking in adolescents

Background

It is well-established that smoking and depression are associated in adolescents, but the temporal ordering of the association is subject to debate.

Methods

Longitudinal studies in English language which reported the onset of smoking on depression in non clinical populations (age 13-19) published between January 1990 and July 2008 were selected from PubMed, OVID, and PsychInfo databases. Study characteristics were extracted. Meta-analytic pooling procedures with random effects were used.

Results

Fifteen studies were retained for analysis. The pooled estimate for smoking predicting depression in 6 studies was 1.73 (95% CI: 1.32, 2.40; p < 0.001). The pooled estimate for depression predicting smoking in 12 studies was 1.41 (95% CI: 1.21, 1.63; p < 0.001). Studies that used clinical measures of depression were more likely to report a bidirectional effect, with a stronger effect of depression predicting smoking.

Conclusion

Evidence from longitudinal studies suggests that the association between smoking and depression is bidirectional. To better estimate these effects, future research should consider the potential utility of: (a) shorter intervals between surveys with longer follow-up time, (b) more accurate measurement of depression, and (c) adequate control of confounding.

A community-based study of cigarette smoking behavior in relation to variation in three genes involved in dopamine metabolism: Catechol-O-methyltransferase (COMT), dopamine beta-hydroxylase (DBH) and monoamine oxidase-A (MAO-A)

OBJECTIVE

Cigarette smoking behavior may be influenced by catechol-O-methlyltransferase (COMT), dopamine beta-hydroxylase (DBH), and monamine oxidase-A (MAO-A), genes that play roles in dopamine metabolism. The association between common polymorphisms of these genes and smoking behavior was assessed among 10,059 Caucasian volunteers in Washington County, MD in 1989.

METHODS

Age-adjusted logistic regression was used to measure the association between variants of these single nucleotide polymorphisms and smoking initiation and persistent smoking.

RESULTS

Overall, no association was seen between each genotype and smoking behavior. However, among younger (<54 years) women, the COMT GG genotype was positively associated with smoking initiation (OR=1.3; 95% CI: 1.0 1.5), and the MAO-A TT genotype was inversely associated with persistent smoking (OR=0.7; 95% CI: 0.4, 1.0). Men who smoked fewer than 10 cigarettes per day were more likely to be persistent smokers if they had the COMT GG (OR=1.7; 95% CI: 1.0, 2.9) or the DBH GG (OR=1.6; 95% CI: 1.0, 2.5) genotypes.

CONCLUSION

Overall the results of this large community-based study do not provide evidence to support the presence of important associations between variants of COMT, DBH, or MAO-A and smoking initiation or persistent smoking.

Smoking predicts posttraumatic stress symptoms among rescue workers: a prospective study of ambulance personnel involved in the Enschede Fireworks Disaster

BACKGROUND

Examining whether smoking is a risk factor for posttraumatic stress disorder (PTSD) symptoms among rescue workers affected by a disaster.

METHODS

Ambulance personnel (N=66) participated in surveys 2-3 weeks (T1) and 18 months after a fireworks disaster (T2). Hierarchical multiple regression analyses were conducted with cigarette consumption at T1 as a predictor of PTSD symptoms at T2. Demographic characteristics, disaster experiences, peritraumatic dissociation, intrusions and avoidance, psychological distress and alcohol consumption assessed at T1 were included as covariates.

RESULTS

Regression analyses showed that smoking at T1 independently predicted intrusions, avoidance, hostility, and depression symptoms at T2. Results were not affected by controlling for post-disaster critical incidents at work.

CONCLUSIONS

This is the first prospective study among rescue workers demonstrating that smoking soon after a disaster predicts PTSD symptoms in the intermediate term. Findings substantiate results of previous studies indicating that smoking is a relevant risk factor. Future research on how changes in cigarettes consumption post-trauma affect risk of PTSD is required.

The monoamine oxidase inhibitor phenelzine enhances the discriminative stimulus effect of nicotine in rats

In addition to delivering nicotine, tobacco smoke also inhibits monoamine oxidase (MAO). Although MAO inhibitors (MAOIs) can increase nicotine self-administration in rodents, the effects of MAOIs on the discriminative stimulus effect of nicotine are not known. This study examined the effects of three MAOIs (phenelzine, clorgyline and pargyline) with varying selectivity for MAOA and MAOB in the nicotine drug discrimination procedure in rats. Adult male Sprague-Dawley rats were trained to discriminate nicotine (0.3 mg/kg, subcutaneously) from saline in a standard, two-lever food-reinforced operant task. Once the discrimination was acquired, the ability of each MAOI to substitute for or alter the discriminative stimulus effect of nicotine was determined. In substitution tests, nicotine (0.03-0.3 mg/kg) produced full, dose-dependent substitution. Although the selective MAOA inhibitor clorgyline (3-56 mg/kg) and the selective MAOB inhibitor pargyline (3-56 mg/kg) did not elicit any nicotine-appropriate responding, partial substitution was obtained with the nonselective MAO inhibitor phenelzine (1-17 mg/kg). Phenelzine (10 mg/kg) also enhanced the discriminative stimulus effect of a low dose of nicotine (0.056 mg/kg) and prolonged the time course effect of the nicotine-training dose. These findings indicate that concomitant inhibition of MAOA and MAOB can enhance the discriminative stimulus effect of nicotine in rats.

Monoamine oxidase inhibition dramatically prolongs the duration of nicotine withdrawal-induced place aversion

BACKGROUND

Long-lasting effects of withdrawal from nicotine are hypothesized to contribute to relapse and persistence of tobacco habits, and significant evidence supports a role of monoamine oxidase inhibitors (MAOI) contained in cigarette smoke as potent modulators of the rewarding effects of tobacco.

METHODS

With quantification of somatic signs of withdrawal and the place aversion conditioning paradigm, we assessed the effects of MAOI pretreatment on both somatic and aversive motivational components of mecamylamine-induced nicotine withdrawal in rats rendered dependent on nicotine by the subcutaneous implantation of osmotic minipumps (vehicle or nicotine tartrate 9 mg/kg/day).

RESULTS

In nicotine-infused rats, mecamylamine induced a place aversion that lasted 6 weeks. When nicotine-infused rats were also treated with a MAOI, mecamylamine-induced conditioned place aversion persisted for at least 8 months of abstinence. The MAOI treatment slightly decreased ratings of somatic signs induced by mecamylamine administration but had no effect on the threshold or the magnitude of mecamylamine-induced conditioned place aversion.

CONCLUSIONS

These results show that MAOI pretreatment induces a long-lasting conditioned placed aversion associated with nicotine withdrawal, possibly through a potentiation of learning and memory process, and provides some indications on protracted abstinence that might be useful for delineating the neurobiological substrate of relapse.

Effects of progression to cigarette smoking on depressed mood in adolescents: evidence from the National Longitudinal Study of Adolescent Health

AIMS

To investigate the relationship between smoking status and continuously distributed depressed mood among a cohort of adolescents.

DESIGN

Quasi-experimental design, selecting the subset of adolescents who reported never having smoked a cigarette at baseline, some of whom progressed subsequently to smoking at follow-up approximately 1 year later.

SETTING

Data were drawn from the National Longitudinal Study of Adolescent Health, an ongoing study designed to assess the health status of adolescents, and explore the causes of adolescent health-related behaviours.

PARTICIPANTS

Nationally representative sample of adolescents from the USA (n = 12 149), including a subsample who reported never having smoked a cigarette at baseline (n = 5475), aged on average 15 years at baseline and of predominantly European ancestry.

MEASUREMENTS

Logistic and linear regression models controlling for potential confounders to explore the relationship between smoking status and depressed mood measured using the Centers for Epidemiological Studies Depression Scale (CES-D).

FINDINGS

Various relationships between smoking status and depressed mood were observed, with a general trend for these effects to be greater among females. Smoking status at baseline did not significantly predict CES-D score at follow-up, although this effect approached significance in females (P = 0.077). Among never smokers at baseline, level of depressed mood at baseline predicted subsequent progression to smoking initiation (P = 0.022) but not progression to regular smoking (P = 0.229). Among never smokers at baseline, progression to smoking initiation during the follow-up period was associated with higher CES-D scores at follow-up, even after adjusting for baseline depressed mood (P < 0.001), with this effect greater for females than for males. Among those who initiated smoking, progression to regular smoking was associated with higher CES-D score at follow-up among females (P = 0.001), but not males (P = 0.966).

CONCLUSIONS

These data appear to support a complex model of the relationship between depressed mood and smoking status which includes elements of both confounding and causal models. The relationship between cigarette smoking and depression may be a factor in the development of subsequent dependence.

A biopsychosocial approach to examining tobacco-related health disparities among racially classified social groups

AIMS

To articulate a broader, multi-causal model that incorporates psychosocial and environmental factors that can differ systematically across racially classified social groups (RCSGs) and impact biological pathways related to the development of tobacco-related diseases.

METHODS

This paper is built upon a review of the existing scientific literature on selected biopsychosocial factors (diet/nutrition, obesity, alcoholic intake, psychosocial stress, occupational/environmental exposures and exposure to other diseases and illnesses) and tobacco use in examining the biological contributions to differences in tobacco-related health outcomes among RCSGs.

FINDINGS

Recent work has focused on RCSG genetic variations as a possible explanation for differences in tobacco-related health disparities. It is argued in this paper that, given the genetic heterogeneity 'within' RCSGs, it is unlikely that across RCSG genetic variations are likely to be the major source of differences impacting biological pathways in tobacco-related health outcomes. The evidence shows that results, even at the level of within-population genetic variations, have been limited and often inconsistent. A conceptual framework is proposed to account for biological pathways related to the development of tobacco-related diseases.

CONCLUSIONS

Determinants of tobacco-related health disparities are not understood clearly. The contribution of biological factors may be important. Current efforts to determine biological differences in tobacco use and related diseases among RCSGs have focused primarily on genetic variations. However, this approach has limitations. An alternative biopsychosocial framework that examines the potential biological mechanisms through which life experiences and behavior might affect tobacco use and health outcomes in these population groups is needed, including those of life-style (e.g. diet/nutrition, obesity, physical exercise, alcohol consumption), psychosocial (e.g. stress and coping), occupational/environmental exposures and the presence of other diseases/illnesses.

Role of acetaldehyde in tobacco smoke addiction

This review evaluates the presumed contribution of acetaldehyde to tobacco smoke addiction. In rodents, acetaldehyde induces reinforcing effects, and acts in concert with nicotine. Harman and salsolinol, condensation products of acetaldehyde and biogenic amines, may be responsible for the observed reinforcing effect of acetaldehyde. Harman and salsolinol inhibit monoamine oxidase (MAO), and some MAO-inhibitors are known to increase nicotine self-administration and maintain behavioural sensitization to nicotine. Harman is formed in cigarette smoke, and blood harman levels appear to be 2-10 times higher compared to non-smokers. Since harman readily passes the blood-brain barrier and has sufficient MAO-inhibiting potency, it may contribute to the lower MAO-activity observed in the brain of smokers. In contrast, the minor amounts of salsolinol that can be formed in vivo most likely do not contribute to tobacco addiction. Thus, acetaldehyde may increase the addictive potential of tobacco products via the formation of acetaldehyde-biogenic amine adducts in cigarette smoke and/or in vivo, but further research is necessary to substantiate this hypothesis.

Monoamine oxidase and tobacco dependence

Tobacco smoking is a leading cause of preventable death around the world, and there are major public health and research efforts in many countries aimed at reducing its usage. However, the molecular mechanisms underlying tobacco dependence are still not completely understood. Nicotine's action on nicotinic acetylcholine receptors, and the downstream release of dopamine, is believed to be the major pathway underlying tobacco dependence. However there is mounting evidence indicating that non-nicotinic components of tobacco smoke also play a role by inhibiting monoamine oxidase (MAO) and subsequently altering neurotransmitter levels. This article provides a review of the current knowledge of the association between MAO and tobacco dependence and suggests that further research into this topic is likely to lead to more effective pharmacotherapies for smoking cessation.

Monoamine oxidase A rather than monoamine oxidase B inhibition increases nicotine reinforcement in rats

Although nicotine is considered to be responsible for the addictive properties of tobacco, growing evidence underlines the importance of non-nicotine components in smoking reinforcement. It has been shown that tobacco smoke contains monoamine oxidase (MAO) A and B inhibitors and decreases MAO-A and MAO-B activity in smokers. Here, we investigated the effects of clorgyline hydrochloride (irreversible MAO-A inhibitor; 2 mg/kg/day), selegiline (irreversible MAO-B inhibitor; 4 mg/kg) and the beta-carboline norharmane hydrochloride (reversible MAO-B inhibitor; 5 mg/kg/day) treatments on nicotine self-administration (30 microg/kg/infusion, free base) in rats. Independent of the responsiveness to novelty and locomotor activity stimulation, only clorgyline hydrochloride treatment increased the intake of nicotine in a fixed-ratio schedule (FR5) of reinforcement. When a progressive-ratio schedule was implemented, both clorgyline hydrochloride and norharmane hydrochloride treatments potentiated the reinforcing effects of nicotine, whereas selegiline had no effect. Taken together, these results indicate that MAO-A inhibition interacts with nicotine to enhance its rewarding effects in rats and suggest that other compounds present in tobacco, such as beta-carboline, may also play an important role in sustaining smoking behavior in humans.

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.

Isolation and characterization of a monoamine oxidase B selective inhibitor from tobacco smoke

It is well established that tobacco smokers have reduced levels of monoamine oxidase activities both in the brain and peripheral organs. Furthermore, extensive evidence suggests that smokers are less prone to develop Parkinson's disease. These facts, plus the observation that inhibition of monoamine oxidase B protects against the parkinsonian inducing effects of the nigrostriatal neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, have prompted studies to identify monoamine oxidase inhibitors in the tobacco plant and tobacco cigarette smoke. Our previous efforts on cured tobacco leaf extracts have led to the characterization of 2,3,6-trimethyl-1,4-naphthoquinone, a non-selective monoamine oxidase inhibitor, and farnesylacetone, a selective monoamine oxidase B inhibitor. We now have extended these studies to tobacco smoke constituents. Fractionation of the smoke extracts has confirmed and extended the qualitative results of an earlier report [J. Korean Soc. Tob. Sci.1997, 19, 136] demonstrating the inhibitory activity of the terpene trans,trans-farnesol on rat brain MAO-B. In the present study, K(i) values for the inhibition of human, baboon, monkey, dog, rat, and mouse liver MAO-B have been determined. Noteworthy is the absence of inhibitory effects on human placental MAO-A and beef liver MAO-B. A limited structure-activity relationship study of analogs of trans,trans-farnesol is reported. Although the health hazards associated with the use of tobacco products preclude any therapeutic opportunities linked to smoking, these results suggest the possibility of identifying novel structures of compounds that could lead to the development of neuroprotective agents.

Nicotine and nonnicotine factors in cigarette addiction

RATIONALE

A great deal of research supports the role of nicotine in cigarette addiction. However, the effectiveness of nicotine replacement therapy (NRT) as a smoking cessation treatment has fallen short of initial hopes. A key reason may be that NRT does not address nonnicotine components of smoking reinforcement. These include constituents that provide reinforcing sensory stimulation, components that minimize excessive irritation from inhaled nicotine and other pharmacologically active compounds in cigarette smoke.

OBJECTIVE

Studies using various paradigms to dissociate nicotine from other components of smoking are summarized.

RESULTS

Nonnicotine components provide many rewarding effects, often surpassing the direct effects of nicotine. Substitutes for the sensory effects of smoking may be effective in relieving craving for cigarettes and in facilitating smoking cessation. Moreover, techniques for devaluing smoking-related cues may decrease craving and enhance subsequent abstinence. Promising approaches for devaluing smoke cues include extinction-based treatments employing denicotinized cigarettes and the use of nicotinic agonist and/or antagonist treatment during the weeks leading up to a quit attempt. Recent studies suggest that incorporating these approaches into a treatment program may significantly increase smoking abstinence rates. Preliminary findings also suggest that replacement of the effects of monoamine oxidase inhibitors contained in cigarette smoke may enhance quit rates.

CONCLUSIONS

While current NRT methods have been the mainstay of smoking cessation treatment and will likely continue to serve a useful role, the next stage of progress will likely entail the development of tools designed with recognition of the importance of nonnicotine components of cigarette smoking.

Expanding treatment of tobacco dependence

Nicotine dependence is the leading preventable cause of adult morbidity and mortality in the world. New research on the treatment of this disorder ranges from studies evaluating access to treatment to studies elucidating the molecular mechanisms of nicotine addiction. As our understanding of the neurobiology of tobacco addiction grows, the number of potential therapeutic targets by which we can intervene in this pernicious disorder also increases. This paper presents an overview of recent research trends in the treatment of tobacco dependence. We review several novel mechanisms of action that may serve as therapeutic targets for the pharmacologic treatment of tobacco dependence, including drugs that affect monamine oxidase, selective nicotinic receptors, glutamate and gamma-aminobutyric acid receptors, and the endocannabinoid system. For each of these therapeutic targets, we discuss medications in development that affect these pathophysiologic mechanisms.

Biomonitoring of inhaled complex mixtures--ambient air, diesel exhaust and cigarette smoke

Human biomonitoring comprises the determination of biomarkers in body-fluids, cells and tissues. Biomarkers are generally assigned to one of three classes, namely, biomarkers of exposure, effect or susceptibility. Since biomarkers represent steps in an exposure-disease continuum, their application in epidemiological studies ('molecular epidemiology') shows promise. However, to be a predictor of disease, a biomarker has to be validated. Validation criteria for a biomarker include intrinsic qualities such as specificity, sensitivity, knowledge of background in the population, existence of dose-response relationships, degree of inter- and intra-individual variability, knowledge of the kinetics, confounding and modifying factors. In addition, properties of the sampling and analytical procedures are of relevance, including constraints and non-invasiveness of sampling, stability of sample as well as simplicity, high sensitivity, specificity and speed of the analytical method. It is of particular importance to prove by suitable studies that the biomarker of exposure indicates the actual exposure, the biomarker of effect strongly predicts the actual risk of disease and the biomarker of susceptibility actually modifies the risk. Biomonitoring of the exposure to complex mixtures such as polluted ambient air, diesel exhaust or tobacco smoke is a particular challenge since these exposures have many constituents in common and many people were exposed to more than one of these mixtures. Data on the exposure to polycyclic aromatic hydrocarbons (PAH) and benzene from ambient air, diesel exhaust and tobacco smoke will be presented. In addition, some source-specific biomarkers such as nitro-arenes and nicotine metabolites as well as their application in population groups will be discussed. The second part of the presentation addresses the application of biomarkers for assessing so called 'potentially reduced exposure products' (PREPs). According to a recent report of the Institute of Medicine (USA), "reducing risk of disease by reducing exposure to tobacco toxicants is feasible" and "surrogate biological markers that are associated with tobacco-related diseases could be used to offer guidance as to whether or not PREPs are likely to be risk-reducing." In general, the same validation criteria apply as discussed above. In addition, it is suggested that a panel of biomarkers should be used, representing both smoke phases (gas and particulate phase) and the various chemical classes of smoke constituents (e.g., carbonyls, benzene, PAH, tobacco-specific nitrosamines, aromatic amines). Also, a panel of biomarkers of effect should cover the major known adverse effects of smoking (e.g., oxidative stress, inflammatory processes, lipid peroxidation, lipometabolic disorders, mutagenic effects). Biomarkers of nicotine and carbon monoxide uptake are of interest for evaluating the smoking and inhalation behavior, respectively. Finally, suitable study designs for evaluating PREPs are discussed. It is concluded that suitable biomarkers for assessing the exposure to complex mixtures such as ambient air, diesel exhaust and tobacco smoke as well as for evaluating the exposure-reducing properties of PREPs are already available. Future efforts should focus on the development and validation of biomarkers of effect.

Reduced nicotine reward in obesity: cross-comparison in human and mouse

RATIONALE

Tobacco use and obesity lead to significant morbidity and mortality.

OBJECTIVE

This study was conducted to investigate the factors maintaining smoking behavior in lean and obese individuals by utilizing a mouse/human cross-validation model of nicotine reward.

METHODS

In humans, a cigarette choice paradigm was used to examine the relative reinforcing value of nicotine in obese and non-obese smokers. Conditioned place preference (CPP) for nicotine was assessed in mice fed standard low fat rodent chow and mice rendered obese by a high fat diet.

RESULTS

In humans, obese smokers self-administered nicotine via cigarettes significantly less often than non-obese smokers and showed attenuated hedonic effects of nicotine-containing cigarettes compared to denicotinized cigarettes. Similarly, mice exposed to a high fat diet did not exhibit nicotine CPP, relative to control mice. mRNA levels for mu-opiate and leptin receptors were also downregulated in the ventral tegmental area of these mice.

CONCLUSIONS

Together, these studies provide the first evidence for reduced nicotine reward in obese subjects and suggest that this may be mediated by dietary influences on the endogenous opioid system.

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.

The Austrian multicentre study on smoking: subgroups of nicotine dependence and their craving

BACKGROUND

The misconception of tobacco smoking as a 'bad habit' has been replaced by a diagnosis of addiction. Although help to quit is offered by nicotine replacement, antidepressants and psychotherapeutic support, there is no cure yet. One cause of impediment might be psychiatric comorbidity. Therefore, we searched for smoker subgroups, needing different treatments.

AIM OF THE STUDY

The study aimed at subtyping smokers in an attempt to better understand the phenomenon of resistant smokers and provide more information that could potentially become useful to treatment centres assuming the subtypes correlate directly with outcomes of different smoking cessation treatments, tailor-made according to subtypes.

METHODS

330 out of 430 recruited smokers were classified as nicotine dependent (ICD-10) and tobacco dependent (DSM-IV) and remained in the study. They were investigated with different diagnostic assessments: Fagerström Test (FT), Lübeck Craving Risk Relapse Questionnaire and Lesch Typology Questionnaire (the last two being modified for smoking).

RESULTS

Dependence severity degree is reflected by the FT. FT scores >/=5 indicated higher conspicuousness. Four clusters for nicotine craving were found: (1) 'depressed', (2) 'stimulated', (3) 'relaxed mood state' and (4) 'socially triggered tensed mood'. In contrast to alcoholism, 'stimulation' was one of the major craving conditions in smokers. The decision tree, consisting of the FT and the Lesch Typology Questionnaire, distinguishes four subgroups of nicotine-dependent persons.

CONCLUSION

The subgroups reflect different reinforcement and psychosocial disturbances. They match treatment and can be applied as outcome predictors in controlled treatment and relapse prevention studies.

Genetics and drug use as a complex phenotype

Drug use is a complex behavior influenced by multiple biological, family, and sociocultural factors. The concurrent use/misuse of multiple drugs is often seen and drug use also co-occurs with other psychiatric conditions. Behavior and molecular genetic studies support an important posited role of genes in drug use. This posited genetic risk does not appear to be conferred by one or two major genes manifesting large effects, but rather by a number of genes manifesting smaller effects. Genetic factors explain, on average, only about half of the total variability in drug use, with the remaining variability influenced by environmental factors. Also, genetic risk may be differentially expressed in the presence vs. absence of particular environmental conditions. Thus, investigation of environmental factors and their interaction with genetic risk is a necessary component of genetic research. While the full potential of genetic investigations for the prevention of drug misuse has yet to be realized, an example of the impact of risk factor modification under various conditions of gene-environment interaction is provided, and the implications for use of genetic information in drug-misuse prevention are discussed. The multifactorial nature of drug use necessitates coordinated investigation from multiple disciplines and timely dissemination of scientific findings. In addition, this work demands adherence to the highest standards of confidentiality and ethical use of genetic information to best inform future prevention efforts.

Positron emission tomography and single-photon emission computed tomography in substance abuse research

Many advances in the conceptualization of addiction as a disease of the brain have come from the application of imaging technologies directly in the human drug abuser. New knowledge has been driven by advances in radiotracer design and chemistry and positron emission tomography (PET) and single-photon emission computed tomography (SPECT) instrumentation and the integration of these scientific tools with the tools of biochemistry, pharmacology, and medicine. This topic cuts across the medical specialties of neurology, psychiatry, oncology, and cardiology because of the high medical, social, and economic toll that drugs of abuse, including the legal drugs, cigarettes and alcohol, take on society. This article highlights recent advances in the use of PET and SPECT imaging to measure the pharmacokinetic and pharmacodynamic effects of drugs of abuse on the human brain.

Monoamine oxidase and cigarette smoking

Current cigarette smokers have reduced monoamine oxidase (MAO) and there is evidence that this is a pharmacological effect of tobacco smoke exposure rather than a biological characteristic of smokers. This article summarizes human and animal studies documenting the inhibitory effects of tobacco smoke on MAO and discusses MAO inhibition in the context of smoking epidemiology, MAO inhibitor compounds in tobacco, reinvestigations of low platelet MAO in psychiatric disorders and smoking cessation.

Radiotracers for positron emission tomography imaging

Over the past 30 years, advances in radiotracer chemistry and positron emission tomography instrumentation have merged to make positron emission tomography a powerful scientific tool in the biomedical sciences. However, despite the increasing reliance of the biomedical sciences on imaging and the new needs for functional information created by the sequencing of the human genome, the development of new radiotracers with the specificity and kinetic characteristics for quantitative analysis in vivo remains a slow process. In this article, we focus on advances in the development of the radiotracers involved in neurotransmission, amino acid transport, protein synthesis, and DNA synthesis. We conclude with a brief section on newer radiotracers that image other molecular targets and conclude with a summary of some of the scientific and infrastructure needs that would expedite the development and introduction of new radiotracers into biomedical research and the practice of medicine.