FREQUENCIES OF HPRT MUTANT LYMPHOCYTES IN SMOKERS, NONSMOKERS, AND FORMER SMOKERS

Previous work with the autoradiographic mutant lymphocyte assay has pr ovided information about the time-course of development of hprt mutati ons and the persistence of detectable mutant cells in human subjects f ollowing therapeutic exposures to genotoxic agents. These early studie s also revealed elevations in Frequencies of mutant cells in pretreatm ent blood samples from patients who were current tobacco smokers, but no information was available on former smokers. In the present study, blood samples were obtained from 21 healthy former tobacco smokers who had quit smoking at least 1 year before sampling, 42 subjects who had never smoked, and 23 tobacco smokers. Plasma from all samples was tes ted for cotinine, a metabolite of nicotine. Current smokers were categ orized as heavy smokers (greater than or equal to 10 cigarettes per da y, cotinine greater than or equal to 90 ng/ml plasma) and light smoker s (<10/day, cotinine < 90 ng/ml). Lymphocytes from the blood samples w ere isolated, cryopreserved, and later thawed and assayed with the aut oradiographic hprt assay. The 21 former tobacco smokers had a mean var iant (mutant) frequency (Vf+/-standard error) of 1.97 (+/-0.13) per mi llion evaluatable cells. The Vf of 42 subjects who had never smoked wa s 1.74 (+/-0.13) x 10(-6), not significantly different from the former smokers. The smokers had Vfs of 8.09 (+/-0.78) x 10(-6) for 18 heavy smokers and 5.22 (+/-1.02) x 10(-6) for five light smokers. The two ca tegories of smokers had frequencies of mutant cells significantly diff erent from each other, and each was significantly higher than non-smok ers and former smokers (P < 0.05). Vfs were significantly correlated w ith both cotinine concentrations and the number of cigarettes smoked p er day, P < 0.001. This study demonstrates the sensitivity of the auto radiographic hprt assay for detecting mutagenic effects related to chr onic low-level exposures to genotoxins, and indicates that this essay is more likely to detect the effects of recent rather than past exposu res. (C) 1997 Wiley-Liss, Inc.