Affiliations: Ludwig-Maximilians University of Munich, Walther Straub Institute of Pharmacology and Toxicology, Munich, Germany,
University of Cincinnati, Cincinnati, OH,
Cincinnati Children’s Hospital Medical Center, Cincinnati, OH
Correspondence to: Elmar Richter, DVM, Ludwig-Maximilians University of Munich, Walther Straub Institute of Pharmacology and Toxicology, Goethestrasse 33, D-80336 Munich, Germany; e-mail: firstname.lastname@example.org
Although very interesting and well documented, the result presented by Wilson and colleagues1deserves some comments. The authors wonder that the racial differences are much higher for hair cotinine as compared to cotinine in serum samples. However, it is well known that melanin binds cotinine.2In animal experiments,3–4 pigmented mice and rats clearly had higher amounts of cotinine accumulating in melanin-rich tissues including hair. On average, African-American children have higher melanin concentrations in their hair as compared to white children. Therefore, hair concentrations of tobacco alkaloids are not expected to correlate closely with serum concentrations. As discussed by Yerger and Malone,5 “… the sequestering of nicotine in melanin-containing tissues [could] prolong its half-life… ” Differential use of various hair products1 are much less likely to impact hair cotinine concentrations.
The author has no conflicts of interest to disclose.
The authors have no conflicts of interest to disclose.
We appreciate Dr. Richter’s interest in our recent article in CHEST (March 2007)1on racial differences in serum and hair cotinine levels. We also want to thank him for sharing potential explanations for the racial differences in hair cotinine levels. The article by Dehn et al2provided compelling evidence that cotinine irreversibly binds to melanin in in vitro studies. To the extent that African-American children have higher hair melanin levels, this may explain in part why racial differences in cotinine levels were greater in hair than in serum. Previous studies also have noted that there are significant interindividual differences in cotinine levels based on hair color. A review of the literature by Yerger and Malone3 found that darker hair has significantly higher cotinine levels than lighter hair even when they were sampled from the same individual. Knight et al4 observed a similar phenomenon in their cohort. Unfortunately, we did not record hair color for the subjects in our cohort. However, we think it remains plausible that the more pronounced racial differences in cotinine levels may also reflect cumulative differences. Since hair follicles are supplied through the bulb artery, cotinine may be deposited in hair at greater levels in African Americans than in whites.4–5
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