The main focus is to understand the pharmacological basis for differences in individual susceptibility to tobacco addiction and adverse health and consequences of smoking, and to advance the science base relevant to tobacco harm reduction. Clinical studies will investigate genetic and environmental factors that influence nicotine metabolism and questions of the cardiovascular safety of nicotine. Using stable isotope methodology, we will characterize nicotine clearance and metabolism phenotype in African-Americans, Asian-Americans, and whites, and we will identify gene polymorphisms that underlie racial differences in nicotine metabolism. To examine the possible contribution of smoking mentholated cigarettes to tobacco-related disease, we will study exposure to tobacco smoke carcinogens and patterns of nicotine and tobacco-specific nitrosamine metabolism in African-Americans and whites, comparing those who smoke mentholated vs. regular cigarettes. To explore the mechanism of our prior observation that smoking mentholated cigarettes inhibits nicotine metabolism, we will examine the effects of dietary menthol on nicotine metabolism. To further our understanding of the observation that cigarette smoking inhibits nicotine metabolism, we will examine the effects of nicotine itself on nicotine metabolism (CYP2A6), and the effects on the metabolism of other drugs. We will examine the hypothesis that nicotine itself is metabolized in the body to the tobacco-specific nitrosamine NNAL. To examine nicotine cardiovascular safety issues, we will examine the effects of nicotine on various biomarkers of cardiovascular disease, including studies of transdermal nicotine vs. cigarette smoking, studies of the effects of smoking cigarettes with different nicotine content, and studies of the effects of concomitant transdermal nicotine and cigarette smoking. Chemistry studies will include: a) developing and executing GC-MS and LC-MS/MS assays for nicotine metabolites, tobacco smoke carcinogens, and various cardiovascular biomarkers for studies of nicotine metabolism and nicotine safety; b) synthesis of tobacco alkaloids, metabolites and deuterium-labeled analogs for pharmacological and metabolic studies. Our research program will help further define the role of nicotine and metabolites in the dependence process and will aid in the development of harm reduction approaches for tobacco addiction.