Variants in nicotine receptors and pharmacogenetics

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DESCRIPTION (provided by applicant): Tobacco smoking is addictive and data from epidemiological studies have suggested that genetic factors play an important role in smoking and nicotine addiction. Multiple recent studies indicate that variants in the CHRNA5/CHRNA3/ CHRNB4 locus on chromosome 15q25 are associated with heavy smoking and nicotine dependence (ND). One of the variants, SNP rs16969968, changes the 398th amino acid from aspartic acid (D) to asparagine (N) (D398N) in the CHRNA5 gene. This finding gives us an opportunity to test whether this functional D398N polymorphism and/or other variants in the locus change the pharmacological and physiological responses to nicotine administration in humans. We hypothesize that this D398N and/or other variants in the CHRNA5/CHRNA3/CHRNB4 genes may change the functional properties of nAChRs, ultimately altering the responses to nicotine administration. To test this hypothesis, we propose the following: 1. To measure the nicotine response phenotypes of 400 non-smoking volunteers. In a single laboratory session, each participant will receive 0, 2 and 4 mg of nicotine gum doses in ascending order. Outcome measures include responses to a battery of questionnaires administered before and after nicotine dosing, as well as skin temperature, heart rate and blood pressure measured before and during nicotine dosing. These questionnaires include the Profile of Mood and States (POMS), the Direct Effects of Nicotine Scale (DENS) and the Positive and Negative Affect Schedule (PANAS). 2. To evaluate whether genotypes at the D398N site and other polymorphisms in the CHRNA5/CHRNA3/CHRNB4 locus affect the pharmacological and physiological responses of nicotine gum administration. We will genotype all subjects for the D398N polymorphism and other SNPs in the locus and use the UNPHASED and PLINK programs to test whether genotypes are associated with the phenotypes obtained from aim 1 above. There is evidence that genetic factors influence humans' subjective experience and physiological responses to nicotine administration. Since regular smokers develop nicotine tolerance, which confounds human responses to nicotine, we propose to use non-smokers in this application. Humans' subjective experience is correlated to smoking behaviors, therefore, understanding the influence of genetic variants on subjective experience provides a new approach to understand the genetic mechanisms of smoking and nicotine addiction. PUBLIC HEALTH RELEVANCE: Multiple recent studies have shown that variants in the CHRNA5, CHRNA3 and CHRNB4 genes increase risks for tobacco smoking and nicotine dependence. In this application, we propose to test the hypothesis whether variants in these genes mediate humans' subjective experience and physiological responses to nicotine administration. The plan includes two specific aims. The first is to recruit 400 non- smokers to participate an experiment that measures their subjective and physiological responses to nicotine gum administration. The reason to use only non-smokers is to avoid nicotine tolerance and brain adaptation observed in regular smokers. The second aim is to analyze genetic variations at the CHRNA5, CHRNA3 and CHRNB4 genes and to correlate these variations with the response data obtained from the first aim. The overall goal is to evaluate whether and how genetic variants at particular genes affect humans' responses to nicotine administration. Knowledge obtained from this study can be used to guide future genetic studies of smoking and nicotine addiction and to help development of strategies for smoking cessation and prevention treatments.