University of Minnesota cancer researchers have shown for the first time that a chemical derived from a cancer-causing agent in tobacco products can be found in the toenails of smokers as well as nonsmokers exposed to secondhand smoke.
Irina Stepanov, Ph.D., a research associate at the University of Minnesota Cancer Center, led the research team on this study, which was published in the December issue of the journal Cancer Epidemiology, Biomarkers and Prevention.
"Our findings demonstrate that toenail clippings and the sensitive testing methods we developed could be useful in studies about the role of chronic tobacco smoke exposure in human cancer," Stepanov noted.
NNK is a cancer-causing agent in tobacco products, and nicotine is the main known addictive component of tobacco. In the human body, NNK is converted to NNAL, while nicotine is converted to cotinine, both chemical compounds.
"Numerous studies have quantified cotinine and NNAL in the urine and blood of smokers, smokeless tobacco users, and nonsmokers exposed to secondhand tobacco smoke," Stepanov said. "Our study is the first to show these agents also become part of the toenail composition."
Stepanov and her colleagues developed a testing method, involving chromatography coupled with mass spectrometry, to quantify nicotine, cotinine, and NNAL in human toenails.
The study participants included 35 active smokers who smoked at least 10 cigarettes per day for one year or more, and six non-smokers.
All of the smokers in the study had nicotine, cotinine and NNAL in their toenails. The samples taken from the nonsmokers were negative for NNAL. However, nicotine and cotinine were found in the toenails of nonsmokers who were exposed to secondhand smoke.
Stepanov sees using toenails as another method for determining the negative effects of secondhand smoke in nonsmokers. Fingernails and toenails are already commonly used for detection of drugs of abuse, in studies of arsenic intoxication, and occupational exposures to toxins.
She said toenails are more suitable than fingernails because toenails grow more slowly, thus clippings better reflect cumulative exposure over a relatively long period. Toenails also are less likely than fingernails to become environmentally contaminated. Further, analysis of toenails has several advantages over blood and urine testing, including accumulations of chemicals during long-term exposure, ease of collection and storage, and indefinite stability of samples.
This research was supported with a grant from the National Cancer Institute. Stepanov worked with these researchers on this study: Rachel Feuer, Joni Jensen, Dorothy Hatsukami, and Stephen Hecht.
