Pharmacogenetic association of the galanin receptor (GALR1) SNP rs2717162 with smoking cessation.

Galanin modulates dopaminergic neurotransmission in the mesolimbic dopamine system, thereby influencing the rewarding effects of nicotine. Variants in the galanin receptor 1 (GALR1) gene have been associated with retrospective craving severity and heaviness of smoking in prior research. We investigated pharmacogenetic associations of the previously studied GALR1 polymorphism, rs2717162, in 1217 smokers of European ancestry who participated in one of three pharmacogenetic smoking cessation clinical trials and were treated with nicotine patch (n=623), nicotine nasal spray (n=189), bupropion (n=213), or placebo (n=192). The primary endpoint was abstinence (7-day point prevalence, biochemically confirmed) at the end of treatment. Cravings to smoke were assessed on the target quit day (TQD). The longitudinal regression model revealed a significant genotype by treatment interaction (P=0.03). There was a reduced odds of quitting success with the presence of at least one minor (C) allele in the bupropion-treated group (OR=0.43; 95% CI=0.22-0.77; P=0.005) but equivalent quit rates by genotype in the nicotine-replacement therapy groups. This genotype by treatment interaction was reproduced in a Cox regression model of time to relapse (P=0.04). In the bupropion trial, smokers carrying the C allele also reported more severe TQD cravings. Further research to identify functional variants in GALR1 and to replicate pharmacogenetic associations is warranted.

µ-Opioid receptor availability in the amygdala is associated with smoking for negative affect relief.

RATIONALE: The perception that smoking relieves negative affect contributes to smoking persistence. Endogenous opioid neurotransmission, and the µ-opioid receptor (MOR) in particular, plays a role in affective regulation and is modulated by nicotine. OBJECTIVES: We examined the relationship of MOR binding availability in the amygdala to the motivation to smoke for negative affect relief and to the acute effects of smoking on affective responses. METHODS: Twenty-two smokers were scanned on two separate occasions after overnight abstinence using [¹¹C]carfentanil positron emission tomography imaging: after smoking a nicotine-containing cigarette and after smoking a denicotinized cigarette. Self-reports of smoking motives were collected at baseline, and measures of positive and negative affect were collected pre- and post- cigarette smoking. RESULTS: Higher MOR availability in the amygdala was associated with motivation to smoke to relieve negative affect. However, MOR availability was unrelated to changes in affect after smoking either cigarette. CONCLUSIONS: Increased MOR availability in amygdala may underlie the motivation to smoke for negative affective relief. These results are consistent with previous data highlighting the role of MOR neurotransmission in smoking behavior.

Pharmacogenetics of smoking cessation: role of nicotine target and metabolism genes.

Many smokers attempt to quit smoking but few are successful in the long term. The heritability of nicotine addiction and smoking relapse have been documented, and research is focused on identifying specific genetic influences on the ability to quit smoking and response to specific medications. Research in genetically modified cell lines and mice has identified nicotine acetylcholine receptor subtypes that mediate the pharmacological and behavioral effects of nicotine sensitivity and withdrawal. Human genetic association studies have identified single nucleotide polymorphisms (SNPs) in genes encoding nicotine acetylcholine receptor subunits and nicotine metabolizing enzymes that influence smoking cessation phenotypes. There is initial promising evidence for a role in smoking cessation for SNPs in the ß2 and α5/α3/ß4 nAChR subunit genes; however, effects are small and not consistently replicated. There are reproducible and clinically significant associations of genotypic and phenotypic measures of CYP2A6 enzyme activity and nicotine metabolic rate with smoking cessation as well as response to nicotine replacement therapies and bupropion. Prospective clinical trials to identify associations of genetic variants and gene-gene interactions on smoking cessation are needed to generate the evidence base for both medication development and targeted therapy approaches based on genotype.

The relationship between indoleamine 2,3-dioxygenase activity and post-stroke cognitive impairment.

BACKGROUND: Activation of indoleamine 2,3-dioxygenase (IDO) and higher concentrations of several kynurenine metabolites have been observed post-stroke, where they have been associated with increased mortality. While lower tryptophan or a higher ratio of kynurenine/tryptophan (K/T) in peripheral blood have been associated with dementia and the severity of cognitive symptoms in Alzheimer's disease, the association between K/T ratios and post-stroke cognitive impairment (PSCI) has not been investigated. METHODS: Patients were recruited from the acute stroke unit of a general hospital within 1 month post-stroke. Assessments included the Standardized Mini-Mental State Examination (sMMSE) for cognition, the National Institutes of Health Stroke Scale (NIHSS) for stroke severity, and the Center for Epidemiological Studies-Depression Scale (CES-D) for depressive symptoms. Tryptophan and kynurenine concentrations were determined by high-performance liquid chromatography. RESULTS: A total of 41 patients with ischemic stroke ([mean ± SD] age 72.3 ± 12.2 years, 53.7% male, sMMSE 25.6 ± 4.1, NIHSS 7.27 ± 5.55) were recruited. Higher K/T ratios were associated with lower post-stroke global cognition (i.e. sMMSE scores; ß = -.327, P = .037). A backward stepwise elimination linear regression (F1,40=6.15, P=.005, adjusted R2=.205) showed that the highest K/T ratio tertile (ß = -.412, P = .006) predicted lower sMMSE scores, controlling for age (ß = -.253, p = .081), with NIHSS (ß = -.027, P = 0.859), and lesion volume (ß = -.066, P = 0.659) removed from the model. In receiver operating characteristic analysis, a K/T ratio of 78.3 µmol/mmol (top tertile) predicted significant cognitive impairment (sMMSE score ≤ 24) with 67% sensitivity and 86% specificity (area under the curve = 0.730, p = .022). CONCLUSIONS: These data suggest an inflammatory response characterized by IDO activation may be relevant to the development of PSCI. Since the neuroactivity of kynurenine metabolites may be amenable to pharmacotherapeutic intervention, the K/T ratio may be a clinically important biomarker.

Prenatal exposure of rats to nicotine causes persistent alterations of nicotinic cholinergic receptors.

We examined for immediate and persistent changes in nAChRs in cerebral cortex, thalamus and striatum of male rats caused by prenatal exposure to nicotine from gestational day 3 to postnatal day 10 (PN10), and how such exposure affected the responses of adolescents to subsequent nicotine challenge. Receptor numbers were assessed by [(3)H]epibatidine binding and receptor function was measured by acetylcholine-stimulated (86)Rb efflux (cerebral cortex and thalamus) and nicotine-stimulated dopamine release (striatum). Immediate effects of prenatal nicotine, assessed in PN10 animals, were not detected for any parameter. A subsequent 14 day nicotine exposure in adolescence revealed persistent changes caused by prenatal nicotine exposure. Nicotine exposure in adolescents caused up-regulation of binding in all three regions; however, this up-regulation was lost in thalamus from animals prenatally exposed to nicotine. Nicotine exposure in adolescents caused decreased nicotine-stimulated dopamine release in striatum; this effect was lost in animals prenatally exposed to nicotine. Comparison of parameters in PN10 and PN42 rats revealed developmental changes in the CNS cholinergic system. In thalamus, binding increased with age, as did the proportion of (86)Rb efflux with high sensitivity to acetylcholine. In cortex, binding also increased with age, but there was no change in total (86)Rb efflux, and the proportion of high to low sensitivity efflux declined with age. Nicotine-stimulated striatal dopamine release (both total and alpha-conotoxin MII-resistant release) increased with age in naïve animals, but not in those prenatally exposed to nicotine. These findings demonstrate that prenatal exposure to nicotine causes alterations in nAChRs and in their regulation by nicotine that persist into adolescence. These changes may play a role in the increased risk for nicotine addiction observed in adolescent offspring of smoking mothers.

Adult and periadolescent rats differ in expression of nicotinic cholinergic receptor subtypes and in the response of these subtypes to chronic nicotine exposure.

Adolescence is a time of significant brain development, and exposure to nicotine during this period is associated with higher subsequent rates of dependence. Chronic nicotine exposure alters expression of nicotinic acetylcholine receptors (nAChRs), changing the pattern of nicotine responsiveness. We used quantitative autoradiography to measure three major subtypes of nAChRs after chronic nicotine exposure by osmotic minipump in adult and periadolescent rats. Comparison of control animals at the two different ages revealed that periadolescents express consistently greater numbers of alpha4beta2* nAChRs compared to the same brain regions of adults. Similar but less pronounced increases in alpha7 nAChRs were found in control periadolescent rats compared to adults. Binding of [(125)I]alpha-conotoxin MII (largely to alpha6* nAChRs) did not systematically differ between adults and periadolescents. The response to chronic nicotine exposure also differed by age. Up-regulation of alpha4beta2* nAChRs was prominent and widespread in adult animals; in periadolescents, alpha4beta2* up-regulation also occurred, but in fewer regions and to a lesser extent. A similar pattern of response was seen with alpha7 receptors: adults were more responsive than periadolescents to nicotine-induced up-regulation. In adult animals, chronic nicotine exposure did not cause up-regulation of alpha6* nAChRs; binding was down-regulated in three regions. Unlike the other subtypes, the response of alpha6* nAChRs to chronic nicotine was greater in periadolescents, with more regions showing greater down-regulation compared to adults. These differences in receptor expression and regulation between age groups are likely to be important given the unique vulnerability of adolescents to nicotine-induced behavioral changes and susceptibility to drug abuse.

Chronic nicotine differentially regulates alpha6- and beta3-containing nicotinic cholinergic receptors in rat brain.

We investigated the effects of chronic nicotine on alpha6- and beta3-containing nicotinic acetylcholine receptors (nAChRs) in two rat brain regions using three methodological approaches: radioligand binding, immunoprecipitation, and nicotine-stimulated synaptosomal release of dopamine. Nicotine was administered by osmotic minipumps for 2 weeks. Quantitative autoradiography with [(125)I]alpha-conotoxin MII to selectively label alpha6(*) nAChRs showed a 28% decrease in binding in the striatum but no change in the superior colliculus. Immunoprecipitation of nAChRs labeled by [(3)H]epibatidine in these two regions showed that chronic nicotine increased alpha4- and beta2-containing nAChRs by 39 to 67%. In contrast, chronic nicotine caused a 39% decrease in alpha6-containing nAChRs in striatum but no change in superior colliculus. No changes in beta3-containing nAChRs were seen in either region after chronic nicotine. The decreased expression of alpha6-containing nAChRs persisted for at least 3 days, recovering to baseline by 7 days after removal of the pumps. There was a small but significant decrease in total nicotine-stimulated dopamine release in striatal synaptosomes after nicotine exposure. However, the component of dopamine release that was resistant to alpha-conotoxin MII blockade was unaffected, whereas dopamine release that was sensitive to blockade by alpha-conotoxin MII was decreased by 56%. These findings indicate that the alpha6(*) nAChR is regulated differently from other nAChR subtypes, and they suggest that the inclusion of a beta3 subunit with alpha6 may serve to inhibit nicotine-induced down-regulation of these receptors.