Tobacco dependence dramatically increases health burdens and financial costs. Limitations of current smoking cessation therapies indicate the need for improved molecular targets. Nicotine, the main addictive component of tobacco, exerts its dependency effects via nicotinic acetylcholine receptors (nAChRs). The homomeric α7 nAChR is one of the most abundant receptors found in the brain and has unique features in comparison to other nAChR subtypes such as high calcium permeability, low probability of channel opening, and a rapid desensitization rate. α7 nAChR agonists reduce nicotine's rewarding properties in the conditioned place preference (CPP) test and i.v. self-administration. Recently, the peroxisome proliferator-activated receptor type-α (PPARα) has been implicated as a downstream signaling target of the α7 nAChR in ventral tegmental area dopamine cells. It is unknown whether the intrinsic characteristics of the α7 nAChR and PPARα are involved in its attenuation of nicotine reward. Therefore, this dissertation sought to investigate the role of α7 nAChRs in a mouse model of nicotine CPP and nicotine withdrawal by 1) investigating the impact of pharmacological modulation of α7 nAChR function in nicotine dependence and 2) evaluating a possible role for PPARα as a downstream mediator of α7 nAChRs in nicotine dependence. Positive allosteric modulators (PAMs) and a silent agonist were used to investigate the role of α7 nAChR conformations. The utilization of the α7 nAChR Type I PAM NS1738, Type II PAM PNU120596, and silent agonist NS6740 provided insight about the probability of channel opening (NS1738, PNU120596), desensitization (PNU120596, NS6740), and modulation of the endogenous acetylcholine/ choline tone (NS1738, PNU120596) as it relates to the α7 nAChR in nicotine CPP and withdrawal. In addition, this dissertation sought to elucidate the role of the α7 nAChR and PPARα in nicotine dependence using pharmacological interventions. The results suggest that the role of the α7 nAChR in nicotine dependence is conformation-dependent and PPARα-mediated. This dissertation is the first to report PPARα-mediation of the effects of α7 nAChR in nicotine reward and attenuation of nicotine withdrawal signs by PPARα activation. This data supports the development of α7 nAChR agonists and PPARα activators as possible smoking cessation aids.

In an effort to search for a more selective, less toxic neuronal nicotinic acetylcholine receptor analgesic agent in comparison to epibatidine, a series of analogs with hybrid structures of epibatidine and ABT-594 were designed and synthesized. The 1-(pyridyloxymethyl)-7-azabicyclo[2.2.1]heptane ring systems were furnished via an intramolecular cyclization from a trans 1, 4 disubstitituted amino-cyclohexane derivative. The functionalized cyclohexane ring was formed via a [4+2] Diels-Alder cyclization reaction between the acetamidoacrylate and Danishefsky's diene. These 1- (pyridyloxymethyl)-7-azabicyclo[2.2.1]heptane ring systems were then tested in vitro as potential á4â2 nicotinic acetylcholine receptor ligands with high potency and selectivity. In addition, a series of rigid acetylcholine analogs were synthesized from cocaine to study the conformation of acetylcholine, the endogenous neurotransmitter at the nicotinic acetylcholine receptor. A stereoselective reduction of 2-tropinone led to the enantioselective synthesis of the desired acetoxytropane systems. These compounds were also tested in in vivo models for binding affinity and efficacy responses. Anabasamine, an alkaloid isolated from the Central Asian shrub, Anabasis aphylla, was synthesized for the first time. It was targeted due to interesting preliminary biological activity such as exhibiting anticholinesterase activity, anti-inflammatory activity, and facilitated an increase in hepatic alcohol dehydrogenase levels. Only preliminary studies were performed as anabasamine is limited in quantity due to its difficult isolation. A versatile synthetic methodology was developed for the synthesis of anabasamine and related nicotine analogs. This new methodology employed a pyridyl anion addition to valerolactone, for anabasamine, or butyrolactone for the nicotine analog, to afford 5-hydroxy-1-(6-methoxy-pyridin-3-yl)-pentan-1-one or 4-hydroxy-1-(6- methoxy-pyridin-3-yl)-butan-1-one, respectively. A reductive amination provided the piperidine ring moiety and a Suzuki coupling reaction introduced the bipyridyl moiety to anabasamine in five steps and 23% overall yield. In addition, this methodology was applied successfully to the synthesis of nicotine and other related analogs. In particular the synthesis of 6-methoxynicotine, a useful drug intermediate, was generated improving the yield from 16% over five steps to 54% over three steps.

Nicotine is the primary substance in tobacco causing addiction. In humans the majority (70-80%) of nicotine is inactivated to cotinine in a reaction predominantly catalyzed by CYP2A6 (80-90%), with a minor possible role for CYP2B6. Substantial interindividual variability is observed in the rate of nicotine’s inactivation to cotinine and this variation contributes to differences in smoking behaviors (e.g. cigarette consumption). Twin studies suggest an important genetic contribution to the variability in nicotine metabolism. However in 2004, genetic variation in CYP2A6 and CYP2B6 accounted for only a small portion of the variability suggesting gaps in our knowledge. Our objective was to identify additional genetic and non-genetic sources of variability in CYP2A6 expression/activity, CYP2B6 expression, and nicotine to cotinine metabolism in vivo and/or in vitro. Participants included individuals from different world populations phenotyped for CYP2A6 activity either following oral nicotine administration or using metabolite ratios derived from baseline smoking. Genotyping and sequencing were utilized to identify and characterize multiple new CYP2A6 alleles. In total 17 novel CYP2A6 alleles were identified, many of which were found predominantly among individuals of black African descent and exhibited lower CYP2A6 activity. In addition, human livers were assessed for CYP2A6 and CYP2B6 expression and nicotine to cotinine metabolism. The mechanisms underlying the lower CYP2A6 activity associated with some of the variant CYP2A6 alleles included either a reduction in hepatic CYP2A6 protein expression, an alteration of CYP2A6’s structural property, or a combination of both. DNA methylation was not associated with altered hepatic CYP2A6 expression/activity. Livers from female donors were associated with higher CYP2A6 and CYP2B6 protein expression compared to male livers, while age did not influence the expression of either CYP. Finally, CYP2B6 and its prevalent altered function genetic variant (CYP2B6*6) did not influence nicotine to cotinine metabolism. Identification of factors that contribute to the variability in CYP2A6 and nicotine metabolism is important to improve future association studies between CYP2A6 genotype, nicotine metabolism, and smoking behaviors. In addition, this information could provide the potential to personalize therapy in order to improve the clinical efficacy of nicotine, particularly as a smoking cessation aid.

Nicotine is the primary substance in tobacco causing addiction. In humans the majority (70-80%) of nicotine is inactivated to cotinine in a reaction predominantly catalyzed by CYP2A6 (80-90%), with a minor possible role for CYP2B6. Substantial interindividual variability is observed in the rate of nicotine’s inactivation to cotinine and this variation contributes to differences in smoking behaviors (e.g. cigarette consumption). Twin studies suggest an important genetic contribution to the variability in nicotine metabolism. However in 2004, genetic variation in CYP2A6 and CYP2B6 accounted for only a small portion of the variability suggesting gaps in our knowledge. Our objective was to identify additional genetic and non-genetic sources of variability in CYP2A6 expression/activity, CYP2B6 expression, and nicotine to cotinine metabolism in vivo and/or in vitro. Participants included individuals from different world populations phenotyped for CYP2A6 activity either following oral nicotine administration or using metabolite ratios derived from baseline smoking. Genotyping and sequencing were utilized to identify and characterize multiple new CYP2A6 alleles. In total 17 novel CYP2A6 alleles were identified, many of which were found predominantly among individuals of black African descent and exhibited lower CYP2A6 activity. In addition, human livers were assessed for CYP2A6 and CYP2B6 expression and nicotine to cotinine metabolism. The mechanisms underlying the lower CYP2A6 activity associated with some of the variant CYP2A6 alleles included either a reduction in hepatic CYP2A6 protein expression, an alteration of CYP2A6’s structural property, or a combination of both. DNA methylation was not associated with altered hepatic CYP2A6 expression/activity. Livers from female donors were associated with higher CYP2A6 and CYP2B6 protein expression compared to male livers, while age did not influence the expression of either CYP. Finally, CYP2B6 and its prevalent altered function genetic variant (CYP2B6*6) did not influence nicotine to cotinine metabolism. Identification of factors that contribute to the variability in CYP2A6 and nicotine metabolism is important to improve future association studies between CYP2A6 genotype, nicotine metabolism, and smoking behaviors. In addition, this information could provide the potential to personalize therapy in order to improve the clinical efficacy of nicotine, particularly as a smoking cessation aid.

Thèse de doctorat : Neurosciences : Paris 12 : 2006. / Titre provenant de l'écran-titre. Pagination : 218 f. Bibliogr. f. 203-218.

Title from title page of PDF (University of Missouri--St. Louis, viewed February 9, 2010). Includes bibliographical references (p. 107-119).

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Ghrelin is a 28 amino acid peptide that interacts with ghrelin receptors (GHS-Rs) to modulate brain reinforcement circuits. Systemic ghrelin infusions augment cocaine (COC) stimulated locomotion and conditioned place preference (CPP) in rats, whereas genetic or pharmacological ablation of GHS-Rs has been shown to attenuate the acute locomotor-enhancing effects of nicotine (NIC) and COC, and to blunt the CPP induced by food, alcohol, amphetamine and COC in mice. The stimulant NIC can induce CPP and like COC, repeated administration of NIC induces locomotor sensitization in rats. In experiment 1, we examined the effects of GHS-R antagonism with JMV 2959 on COC-induced locomotion and found that JMV 2959 suppresses COC-induced locomotor sensitization. In experiment 2, we examined the effects of GHS-R antagonism with JMV 2959 on NIC-induced locomotion and found that JMV 2959 suppresses NIC-induced locomotor sensitization. In experiment 3, we examined the effects of GHS-R knockout on COC-induced locomotion and found that animals sustaining GHS-R knockout display a suppression of COC-induced locomotor sensitization. In experiment 4, we examined the effects of GHS-R knockout on COC-induced locomotion and found that animals sustaining GHS-R knockout display a suppression of COC-induced locomotor sensitization. In experiment 5, we examined the effects of JMV 2959 on NIC-enhanced intracranial self-stimulation (ICSS) responding and found that JMV 2959 alone had no effect, but when combined with NIC,JMV 2959 pretreatment reversed the enhancement of responding produced by NIC. In experiment 6, we examined the effects of GHS-R knockout on ICSS responding and found that animals sustaining GHS-R knockout were unable to acquire ICSS at current intensity levels that would support responding by WT animals. It was not until the intensity was ramped up four fold that these knockout rats were able to acquire responding. These results show that antagonism of GHS-Rs diminishes the reinforcing effects of NIC and COC. This provides evidence that antagonists of GHS-Rs could be useful in the treatment of drug addiction, particularly that involving nicotine.

Thesis (M.D.S.) -- Dept. of Dental Health, University of Adelaide, 1981. / Typescript (photocopy).