Nicotine metabolism in three ethnic/racial groups with different risks of lung cancer

Previously, we documented that smoking-associated lung cancer risk is greater in Hawaiians and lower in Japanese compared with Whites. Nicotine metabolism by cytochrome P450 2A6 (CYP2A6) varies across ethnicity/race and is hypothesized to affect smoking behavior. We investigated whether higher CYP2A6 activity results in the smoker extracting more nicotine (adjusting for cigarettes per day) and being exposed to higher levels of tobacco-specific nitrosamine [4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)] and pyrene, a representative polycyclic aromatic hydrocarbon. We conducted a cross-sectional study of 585 smokers among the three main ethnic/racial groups in Hawaii and examined whether differences in CYP2A6 activity correlate with the ethnic/racial differences in lung cancer risk. We assessed CYP2A6 activity by nicotine metabolite ratio (total trans-3-hydroxycotinine/total cotinine) and caffeine metabolite ratio (1,7-dimethyl uric acid/1,7-dimethylxanthine) in 12 h urine. We also measured urinary nicotine equivalents (sum of nicotine, cotinine, and trans-3-hydroxycotinine and their respective glucuronides), a marker of nicotine dose, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol and its glucuronide, markers of NNK exposure, and 1-hydroxypyrene, a marker of pyrene exposure. The nicotine metabolite ratio was higher in Whites than in Japanese and intermediate in Hawaiians (P values < 0.05). Cigarettes per day-adjusted nicotine equivalents were lower in Japanese compared with Hawaiians or Whites (P = 0.005 and P < 0.0001, respectively) and greater in men than women (P < 0.0001). Nicotine equivalents and total 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol increased with CYP2A6 activity, indicating that smokers with greater nicotine metabolism smoke more extensively and have a higher internal NNK dose. The particularly low nicotine metabolism of Japanese smokers may contribute to their previously described decreased lung cancer risk.