Activation of AMPK by metformin improves withdrawal signs precipitated by nicotine withdrawal.

Cigarette smoking is the leading cause of preventable disease and death in the United States, with more persons dying from nicotine addiction than any other preventable cause of death. Even though smoking cessation incurs multiple health benefits, the abstinence rate remains low with current medications. Here we show that the AMP-activated protein kinase (AMPK) pathway in the hippocampus is activated following chronic nicotine use, an effect that is rapidly reversed by nicotine withdrawal. Increasing pAMPK levels and, consequently, downstream AMPK signaling pharmacologically attenuate anxiety-like behavior following nicotine withdrawal. We show that metformin, a known AMPK activator in the periphery, reduces withdrawal symptoms through a mechanism dependent on the presence of the AMPKα subunits within the hippocampus. This study provides evidence of a direct effect of AMPK modulation on nicotine withdrawal symptoms and suggests central AMPK activation as a therapeutic target for smoking cessation.

Optimization of a nicotine degrading enzyme for potential use in treatment of nicotine addiction.

BACKGROUND: Smoking and tobacco use continue to be the largest preventable causes of death globally. A novel therapeutic approach has recently been proposed: administration of an enzyme that degrades nicotine, the main addictive component of tobacco, minimizing brain exposure and reducing its reinforcing effects. Pre-clinical proof of concept has been previously established through dosing the amine oxidase NicA2 from Pseudomonas putida in rat nicotine self-administration models of addiction. RESULTS: This paper describes efforts towards optimizing NicA2 for potential therapeutic use: enhancing potency, improving its pharmacokinetic profile, and attenuating immunogenicity. Libraries randomizing residues located in all 22 active site positions of NicA2 were screened. 58 single mutations with 2- to 19-fold enhanced catalytic activity compared to wt at 10 µM nicotine were identified. A novel nicotine biosensor assay allowed efficient screening of the many primary hits for activity at nicotine concentrations typically found in smokers. 10 mutants with improved activity in rat serum at or below 250 nM were identified. These catalytic improvements translated to increased potency in vivo in the form of further lowering of nicotine blood levels and nicotine accumulation in the brains of Sprague-Dawley rats. Examination of the X-ray crystal structure suggests that these mutants may accelerate the rate limiting re-oxidation of the flavin adenine dinucleotide cofactor by enhancing molecular oxygen's access. PEGylation of NicA2 led to prolonged serum half-life and lowered immunogenicity observed in a human HLA DR4 transgenic mouse model, without impacting nicotine degrading activity. CONCLUSIONS: Systematic mutational analysis of the active site of the nicotine-degrading enzyme NicA2 has yielded 10 variants that increase the catalytic activity and its effects on nicotine distribution in vivo at nicotine plasma concentrations found in smokers. In addition, PEGylation substantially increases circulating half-life and reduces the enzyme's immunogenic potential. Taken together, these results provide a viable path towards generation of a drug candidate suitable for human therapeutic use in treating nicotine addiction.

Inhibition of Nicotine Dependence by Curcuminoid Is Associated with Reduced Acetylcholinesterase Activity in the Mouse Brain.

Nicotine is a stimulatory component in tobacco that activates the central nervous system reward pathway and causes nicotine dependence. We found that the anti-inflammatory agent, curcuminoid, prevents nicotine dependence and relapse, as assessed by the conditioned placed preference test. Curcuminoid (1, 3.2, and 10 mg·kg-1, oral) dose-dependently inhibited nicotine dependence and enhanced nicotine extinction when administrated 30 min prior to nicotine administration (0.5 mg·kg-1, i.p.) for 7 days. In addition, curcuminoid significantly suppressed the priming effects of nicotine and inhibited acetylcholinesterase (AChE) activity. Taken together, curcuminoid ameliorates nicotine dependence and relapse, in part via the inhibition of the AChE activity in the brain.

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.

CYP2A6 Effects on Subjective Reactions to Initial Smoking Attempt.

INTRODUCTION: In very novice smokers, CYP2A6 genotypes that reduce nicotine metabolism to an intermediate rate may increase smoking risk, relative to both normal and slow rates. The present study examined the hypothesis that intermediate metabolism variants are associated with greater pleasurable effects of the initial smoking attempt than either normal or slow metabolism variants. METHODS: Participants were novice smokers (N = 261, 65% female) of European descent. Predicted nicotine metabolic rate based on CYP2A6 diplotypes (CYP2A6 Diplotype Predicted Rate [CDPR]) was partitioned into Normal, Intermediate, and Slow categories using a metabolism metric. Subjective reactions to the initial smoking attempt were assessed by the Pleasurable Smoking Experiences (PSE) scale, which was collected within 3 years of the initial smoking attempt. The effect of CDPR on PSE was tested using a generalized linear model in which CDPR was dummy coded and Intermediate CDPR was the reference condition. Gender was included in the model as a control for higher PSE scores by males. RESULTS: Lower PSE scores were associated with Normal CDPR, ß = -0.34, P = .008, and Slow CDPR, ß = -0.52, P = .001, relative to Intermediate CDPR. CONCLUSIONS: Intermediate CDPR-enhanced pleasurable effects of the initial smoking attempt relative to other CYP2A6 variants. This finding is consistent with the hypothesis that the risk effect of Intermediate CDPR on early smoking is a function of optimal pleasurable effects. IMPLICATIONS: This study supports our recent hypothesis that CYP2A6 diplotypes that encode intermediate nicotine metabolism rate are associated with enhanced pleasurable events following the initial smoking attempt, compared with diplotypes that encode either normal or slow metabolism. This hypothesis was offered to account for our unexpected previous finding of enhanced smoking risk in very novice smokers associated with intermediate metabolism rate. Our new finding encourages further investigation of time-dependent relations between CYP2A6 effects and smoking motives, and it encourages laboratory study of the mechanisms underlying the initial smoking enhancement in novice smokers associated with intermediate metabolism.

Effect of genotype and methylation of CYP2D6 on smoking behaviour.

OBJECTIVE: Cigarette smoking is one of the most influential environmental factors affecting the DNA methylation patterns. The addiction-causing substance of tobacco smoke, nicotine, has also shown the potential to alter DNA methylation patterns. However, genetics has a strong influence on DNA methylation patterns, which in turn may affect an individual's smoking behaviour. MATERIALS AND METHODS: We studied eight functional gene variants of one of the most important drug-metabolizing enzymes, CYP2D6, in relation to smoking behaviour in our well-characterized study population consisting of 1230 Whites of Russian origin. In addition, potential associations between methylation levels in a CpG island in the CYP2D6 gene and sex, age, different smoking-related phenotypes and CYP2D6 genotypes were studied. RESULTS: Both age and sex were found to be associated with the methylation level of the CYP2D6 gene. The CYP2D6 methylation pattern also showed high genotype dependence; compared with the extensive metabolizer genotype, the poor metabolizer genotype occurred notably more frequently with higher methylation status (odds ratio 5.05, 95% confidence interval 2.14-11.90). Moreover, higher methylation levels were found to be related inversely to heavier smoking (odds ratio 0.56, 95% confidence interval 0.35-0.91). We also found associations between the CYP2D6 genotype and smoking habits; the poor metabolizer genotype tended to decrease the risk of becoming a heavy smoker compared with the extensive metabolizers, whereas the ultrarapid metabolism-related genotypes tended to increase the risk. CONCLUSION: The CYP2D6-related metabolic capacity seems to be related to cigarette consumption both through genetic and through epigenetic mechanisms.

Cytochrome P450-mediated drug metabolism in the brain.

Cytochrome P450 enzymes (CYPs) metabolize many drugs that act on the central nervous system (CNS), such as antidepressants and antipsychotics; drugs of abuse; endogenous neurochemicals, such as serotonin and dopamine; neurotoxins; and carcinogens. This takes place primarily in the liver, but metabolism can also occur in extrahepatic organs, including the brain. This is important for CNS-acting drugs, as variation in brain CYP-mediated metabolism may be a contributing factor when plasma levels do not predict drug response. This review summarizes the characterization of CYPs in the brain, using examples from the CYP2 subfamily, and discusses sources of variation in brain CYP levels and metabolism. Some recent experiments are described that demonstrate how changes in brain CYP metabolism can influence drug response, toxicity and drug-induced behaviours. Advancing knowledge of brain CYP-mediated metabolism may help us understand why patients respond differently to drugs used in psychiatry and predict risk for psychiatric disorders, including neurodegenerative diseases and substance abuse.

The activity of serum beta-galactosidase in colon cancer patients with a history of alcohol and nicotine dependence: preliminary data.

INTRODUCTION: Beta-galactosidase (GAL) is a lysosomal exoglycosidase involved in the catabolism of glycoconjugates through the sequential release of beta-linked terminal galactosyl residues. The stimulation of activity of exoglycosidases and other degradative enzymes has been noted in cancers as well as in alcohol and nicotine addiction separately. This is the first study to evaluate the activity of the serum senescence marker GAL in colon cancer patients with a history of alcohol and nicotine dependence, as a potential factor of worse cancer prognosis. MATERIAL AND METHODS: The material was serum of 18 colon cancer patients and 10 healthy volunteers. Ten colon cancer patients met alcohol and nicotine dependence criteria. The activity of beta-galactosidase (pkat/ml) was determined by the colorimetric method. Comparisons between groups were made using the Kruskal-Wallis analysis and differences evaluated using the Mann-Whitney U test. Spearman's rank correlation coefficient was used to measure the statistical dependence between two variables. RESULTS: The activity of serum GAL was significantly higher in colon cancer patients with a history of alcohol and nicotine dependence, in comparison to colon cancer patients without a history of drinking/smoking (p=0.015; 46% increase), and the controls (p=0.0002; 81% increase). The activity of serum GAL in colon cancer patients without a history of alcohol/nicotine dependence was higher than the activity in the controls (p = 0.043; 24% increase). DISCUSSION/CONCLUSION: Higher activity of beta-galactosidase may potentially reflect the accelerated growth of the cancer, invasion, metastases, and maturation, when alcohol and nicotine dependence coincide with colon cancer. For a better prognosis of colon cancer, alcohol and nicotine withdrawal seems to be required.

Common polymorphisms in FMO1 are associated with nicotine dependence.

BACKGROUND: Cigarette smoking and other forms of tobacco use are the leading cause of preventable mortality in the world. A better understanding of the etiology of nicotine addiction may help to increase the success rate of cessation and to decrease the massive morbidity and mortality associated with smoking. METHODS: To identify genetic polymorphisms that contribute to nicotine dependence, our group undertook a genetic association study including three enzyme families that potentially influence nicotine metabolism: cytochrome P450 enzymes, flavin monooxygenases (FMOs), and UDP-glucuronosyl transferases. RESULTS: Several polymorphisms in FMO1 showed association in a discovery sample, and were tested in an independent replication sample. One polymorphism, rs10912765, showed an association that remained significant after Bonferroni correction (nominal P=0.0067, corrected P=0.0134). Several additional polymorphisms in linkage disequilibrium with this single nucleotide polymorphism also showed association. Subsequent in-vitro experiments characterized FMO1 as a more efficient catalyst of nicotine N-oxidation than FMO3. In adult humans, FMO1 is primarily expressed in the kidney and is likely to be a major contributor to the renal metabolism and clearance of therapeutic drugs. FMO1 is also expressed in the brain and could contribute to the nicotine concentration in this tissue. CONCLUSION: These findings suggest that polymorphisms in FMO1 are significant risk factors in the development of nicotine dependence and that the mechanism may involve variation in nicotine pharmacology.

Nicotine metabolism in African Americans and European Americans: variation in glucuronidation by ethnicity and UGT2B10 haplotype.

Nicotine is the major addictive agent in tobacco smoke, and it is metabolized extensively by oxidation and glucuronide conjugation. The contributions of ethnicity and UGT2B10 haplotype on variation in nicotine metabolism were investigated. Nicotine metabolism was evaluated in two populations of smokers. In one population of African American and European American smokers (n = 93), nicotine and its metabolites were analyzed in plasma and 24-h urine over 3 days while participants were abstinent and at steady state on the nicotine patch. In a second study of smokers (n = 84), the relationship of a UGT2B10 haplotype linked with D67Y to nicotine and cotinine glucuronidation levels was determined. We observed that both African American ethnicity and the UGT2B10 D67Y allele were associated with a low glucuronidation phenotype. African Americans excreted less nicotine and cotinine as their glucuronide conjugates compared with European Americans; percentage of nicotine glucuronidation, 18.1 versus 29.3 (p < 0.002) and percentage of cotinine glucuronidation, 41.4 versus 61.7 (p < 0.0001). In smokers with a UGT2B10 Tyr67 allele, glucuronide conjugation of nicotine and cotinine was decreased by 20% compared with smokers without this allele. Two key outcomes are reported here. First, the observation that African Americans have lower nicotine and cotinine glucuronidation was confirmed in a population of abstinent smokers on the nicotine patch. Second, we provide the first convincing evidence that UGT2B10 is a key catalyst of these glucuronidation pathways in vivo.

[Electrophoretic pattern of alpha-amylase isoenzymes in serum of non-smoking and smoking normal persons and patients with pancreatitis]. / Rozdzial elektroforetyczny izoenzymów alpha-amylazy w surowicy niepalacych i palacych zdrowych osób oraz pacjentów ze stanem zapalnym trzustki.

Recent epidemiological studies have shown the significant role of tobacco smoking in the development of chronic pancreatitis. It has been demonstrated that nicotine may also alter normal exocrine pancreatic function. However, the mechanism of development of these changes has not been fully recognised. In this pilot study we used a electrophoresis to compare the serum amylase patterns of healthy smokers and non-smokers. Amylase isoenzymes, separated into the pancreatic types by electrophoresis in agarose gel. Sample volume was 20 mL. The electrophoresis was at 4 degrees C temperature for 2 to 2.5 h. Amylase isoenzymes on agarose gels was localized by staining using the visualization system Phadebas Amylase Test. In serum normal non-smokers, I and II-type isoenzymes were predominant. III type izoenzyme was found in serum of smoking patients with pancreatitis. Total amylase activity in serum of smokers was slightly above normal. The isoenzymogram shows the presence of II and III-type isoenzyme, increase of isoenzymes activity. Earlier study III-type isoenzyme was found only in serum from cases of acute pancreatitis. In electrophoretic pattern of alpha-amylase isoenzymes in serum of smoking normal persons and patients with pancreatitis was affirmed the additional form of izoenzmes of amylase, that provide damaging influence tobacco smoking on pancreas.

Inhibition of anandamide hydrolysis by cyclohexyl carbamic acid 3'-carbamoyl-3-yl ester (URB597) reverses abuse-related behavioral and neurochemical effects of nicotine in rats.

Emerging evidence suggests that the rewarding, abuse-related effects of nicotine are modulated by the endocannabinoid system of the brain. For example, pharmacological blockade or genetic deletion of cannabinoid CB(1) receptors can reduce or eliminate many abuse-related behavioral and neurochemical effects of nicotine. Furthermore, doses of Delta(9)-tetrahydrocannabinol and nicotine that are ineffective when given alone can induce conditioned place preference when given together. These previous studies have used systemically administered CB(1) receptor agonists and antagonists and gene deletion techniques, which affect cannabinoid CB(1) receptors throughout the brain. A more functionally selective way to alter endocannabinoid activity is to inhibit fatty acid amide hydrolase (FAAH), thereby magnifying and prolonging the effects of the endocannabinoid anandamide only when and where it is synthesized and released on demand. Here, we combined behavioral and neurochemical approaches to evaluate whether the FAAH inhibitor URB597 (cyclohexyl carbamic acid 3'-carbamoyl-3-yl ester) could alter the abuse-related effects of nicotine in rats. We found that URB597, at a dose (0.3 mg/kg) that had no behavioral effects by itself, prevented development of nicotine-induced conditioned place preference (CPP) and acquisition of nicotine self-administration. URB597 also reduced nicotine-induced reinstatement in both CPP and self-administration models of relapse. Furthermore, in vivo microdialysis showed that URB597 reduced nicotine-induced dopamine elevations in the nucleus accumbens shell, the terminal area of the brain's mesolimbic reward system. These findings suggest that FAAH inhibition can counteract the addictive properties of nicotine and that FAAH may serve as a new target for development of medications for treatment of tobacco dependence.

Smoking behavior and related cancers: the role of CYP2A6 polymorphisms.

Smoking exerts complex central and peripheral nervous system, behavioral, cardiovascular, and endocrine effects in humans and is a primary risk factor for various cancers. Nicotine, a major constituent of tobacco, is the compound that is responsible for the development and maintenance of tobacco dependence. The absorbed nicotine is rapidly and extensively metabolized to inactive cotinine by CYP2A6 in human livers, which has a major impact on nicotine clearance. Progress has been made in understanding the relationship between the inter-individual variability in nicotine metabolism and genetic polymorphisms of CYP2A6. Recent findings have increased our knowledge concerning ethnic differences in the allele frequencies of the CYP2A6 variants, nicotine metabolism, and cancer risk. In this review, the potential associations between the CYP2A6 polymorphisms and smoking behavior or the risk of cancer are also discussed.

Association of functional catechol O-methyl transferase (COMT) Val108Met polymorphism with smoking severity and age of smoking initiation in Chinese male smokers.

RATIONALE: Catechol-O-methyltransferase (COMT) is an enzyme involved in the degradation and inactivation of the neurotransmitter dopamine, which is important in mediating drug reward such as nicotine in tobacco smoke. Different COMT alleles encode enzyme whose activity varies from three- to fourfold that may affect dopamine levels and alter subjective effects of nicotine. Recent evidence also suggests that a COMT polymorphism may be especially important in determining an individual's predisposition to developing nicotine dependence. SUBJECTS AND METHODS: We studied the COMT Val108Met polymorphism in a male population of 203 current smokers, 66 former smokers, and 102 non-smokers. The age-adjusted odds ratios were estimated by multiple logistic regression models. RESULTS: The results showed no significant association of the COMT Val108Met with initiation, persistent smoking, or smoking cessation. However, current smokers with the Met allele had significantly higher Fagerstrom Test for Nicotine Dependence scores (7.5 +/- 2.1 vs 6.8 +/- 1.8, p = 0.018) and started smoking significantly earlier (18.4 +/- 4.9 vs 20.1 +/- 5.9 years, p = 0.036). CONCLUSIONS: These results suggest that the COMT Val108Met polymorphism may not influence smoking status in a Chinese male population but may influence the age at which smoking started and smoking severity among smokers. However, the findings must be regarded as preliminary because of the relatively small sample size and marginal associations and should be replicated in a larger cohort.

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.

Targeted sequencing identifies genetic polymorphisms of flavin-containing monooxygenase genes contributing to susceptibility of nicotine dependence in European American and African American.

BACKGROUND: Smoking is a leading cause of preventable death. Early studies based on samples of twins have linked the lifetime smoking practices to genetic predisposition. The flavin-containing monooxygenase (FMO) protein family consists of a group of enzymes that metabolize drugs and xenobiotics. Both FMO1 and FMO3 were potentially susceptible genes for nicotine metabolism process. METHODS: In this study, we investigated the potential of FMO genes to confer risk of nicotine dependence via deep targeted sequencing in 2,820 study subjects comprising 1,583 nicotine dependents and 1,237 controls from European American and African American. Specifically, we focused on the two genomic segments including FMO1,FMO3, and pseudo gene FMO6P, and aimed to investigate the potential association between FMO genes and nicotine dependence. Both common and low-frequency/rare variants were analyzed using different algorithms. The potential functional significance of SNPs with association signal was investigated with relevant bioinformatics tools. RESULTS: We identified different clusters of significant common variants in European (with most significant SNP rs6674596, p = .0004, OR = 0.67, MAF_EA = 0.14, FMO1) and African Americans (with the most significant SNP rs6608453, p = .001, OR = 0.64, MAF_AA = 0.1, FMO6P). No significant signals were identified through haplotype-based analyses. Gene network investigation indicated that both FMO1 and FMO3 have a strong relation with a variety of genes belonging to CYP gene families (with combined score greater than 0.9). Most of the significant variants identified were SNPs located within intron regions or with unknown functional significance, indicating a need for future work to understand the underlying functional significance of these signals. CONCLUSIONS: Our findings indicated significant association between FMO genes and nicotine dependence. Replications of our findings in other ethnic groups were needed in the future. Most of the significant variants identified were SNPs located within intronic regions or with unknown functional significance, indicating a need for future work to understand the underlying functional significance of these signals.

Significant association of catechol-O-methyltransferase (COMT) haplotypes with nicotine dependence in male and female smokers of two ethnic populations.

The catechol-O-methyltransferase (COMT) gene plays a prominent role in dopaminergic circuits central to drug reward. Allelic variants within the COMT gene are therefore potential candidates for examining interindividual differences in vulnerability to nicotine dependence (ND). We analyzed five single nucleotide polymorphisms (SNPs), including the Val/Met variant (rs4680), which results in a three- to four-fold difference in enzyme activity within COMT, for association with the three ND measures, SQ, HSI, and FTND, in 602 nuclear families of African-American (AA) or European-American (EA) origin. The Val/Met variant showed a significant association with the three ND measures in the pooled and EA samples and with FTND in the AA sample. Haplotype analysis revealed a major protective A-G-T haplotype (frequency 23.6%) for rs740603-rs4680-rs174699 in the AA sample (minimum Z=-3.35; P=0.0005 for FTND), a major protective T-G-T haplotype (frequency 15.2%; minimum Z=-2.92; P=0.003 for FTND) in the EA sample, and a high-risk C-A-T haplotype (frequency 16.9%; minimum Z=3.16; P=0.002 for SQ) in the AA sample for rs933271-rs4680-rs174699. Furthermore, we found that the significant haplotypes within COMT were gender-specific and the significantly associated A-G-T is protective in AA females only, whereas T-G-T is protective in EA males only. Moreover, we found a major high-risk T-A-T haplotype (frequency 56.7%) that showed significant association with the three ND measures in EA males. Further examination of two protective haplotypes, A-G-T in AAs and T-G-T in EAs, indicated that the low COMT enzyme activity Met allele is protective to become nicotine dependent. In summary, our results provide evidence for a role of COMT in the susceptibility to ND and further confirm that its effect is ethnic and gender specific.

DOPA decarboxylase gene is associated with nicotine dependence.

INTRODUCTION: Cigarette smoking is a prevalent and harmful behavior. Although the heritability of nicotine dependence (ND) is well documented and many candidate genetic regions have been identified, few of them were confirmed. This may be, in part, due to analytic methods that sacrifice power. METHODS: Using a recently developed, more powerful method for testing association between a genetic marker and an ordinal trait, we analyzed data from 1879 smokers and nonsmokers from 600 nuclear families of African- or European-American (AA or EA) ancestry. This method increases power principally by accounting for differences in severity between affected subjects. RESULTS: To demonstrate the more powerful method, we re-analyzed an existing dataset, which confirmed the association of the DOPA decarboxylase (DDC) gene on chromosome 7p11 with measures of nicotine dependence. Although none of the eight single nucleotide polymorphisms (SNPs) studied were found to be significantly associated with nicotine dependence (unadjusted p-value > 0.01), we identified haplotypes from those SNPs that were significantly associated with nicotine dependence in both AA and EA samples. CONCLUSION: The associated haplotypes differed in the AA and EA samples. The strongest association (p-value = 0.003) was identified between the 'heaviness of smoking index' and haplotype C-A-T-G in SNPs rs921451-rs3735273-rs1451371-rs2060762. However, this association was not found significant in a previous report (p-value = 0.19) that used the same sample, underscoring the importance of using the statistical methods that use more of the available phenotypic information, and thereby better reflect the distribution of the phenotypes.

Antagonism of ethanol ataxia by intracerebellar nicotine: possible modulation by mouse cerebellar nitric oxide and cGMP.

We have reported previously that intracerebellar nicotine attenuates ethanol ataxia via nicotinic-cholinergic receptors. We report now that attenuation of ethanol ataxia by intracerebellar nicotine is modulated by cerebellar nitric oxide-guanylyl cyclase (GC) messenger system. Intracerebellar microinfusion of SNP (sodium nitroprusside, a nitric oxide donor; 15, 30, and 60 pg) and SMT (S-methylisothiourea; 70, 140, and 280 fg; an inhibitor of inducible nitric oxide synthase), significantly enhanced and reduced, respectively, intracerebellar nicotine-induced attenuation of ethanol ataxia in a dose-related manner. Similarly, intracerebellar isoliquiritigenin (an activator of GC; 1, 2, and 4 pg) and ODQ (1H [1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one, an inhibitor of GC; 375, 750, and 1500 fg), significantly enhanced and reduced, respectively, intracerebellar nicotine-induced attenuation of ethanol ataxia in a dose-related fashion. These results suggest that the functional interaction between nicotine and ethanol may involve modulation by cerebellar nitric oxide and cGMP. Intracerebellar microinfusion of isoliquiritigenin (4, 8, and 16 pg) in the absence of nicotine significantly attenuated ethanol ataxia dose-dependently indicating a tonic involvement of cGMP in ethanol ataxia. Finally, intracerebellar nicotine (5 ng) significantly increased and ethanol 2 g/kg i.p. decreased levels of total cerebellar nitrite+nitrate (NOx) which were functionally correlated with ethanol ataxia and its attenuation by intracerebellar nicotine. The ethanol-induced decrease in NOx was significantly antagonized by intracerebellar nicotine. The NOx data further supported an involvement of nitric oxide in the behavioral interaction between nicotine and ethanol. Overall, the results of the present investigation demonstrate a functional correlation between cerebellar nitric oxide messenger system and the behavioral interaction between nicotine and ethanol.

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.