SMOKING AND ESTROGEN METABOLISM RELATED TO CANCER RISK

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Several epidemiological studies indicate that cigarette smoking is associated with a significant anti-estrogenic effect, and this fact is related to the recent finding of decreased endometrial cancer among postmenopausal female smokers. Other estrogen-related physiological processes affected include earlier menopause, increased osteoporosis, and possibly, decreased breast cancer among female smokers. Elucidation of the underlying mechanism whereby smoking affects estrogen disposition and pathophysiology may prove useful in developing strategies toward the prevention of endometrial and breast cancer. We have demonstrated a powerful induction of estradiol 2-hydroxylation measured in vivo with the radiometric procedure in premenopausal females smoking at least 15 cigarettes per day, possibly accounting for the decreased estrogen bioavailability at hormone target tissues. Several constituents of cigarette smoke are known to be powerful inducers of the hepatic microsomal P-450 enzymes participating in estradiol metabolism. This laboratory has extensive experience using radiometric procedures for studying the three principal oxidative transformations of estradiol at the C-2, C-16yield, and C-17 position in humans. The C-2 hydroxylation of estradiol is unique among these metabolic steps in that the catecholestrogens formed in the reaction are virtually devoid of peripheral estrogenic activity. Thus, induction in this metabolic pathway would be expected to have a significant anti-estrogenic effect, and may explain the reduced risk of endometrial cancer in smokers. We will use the radiometric method to further explore the effect of smoking on estradiol 2-hydroxylation in the following groups: postmenopausal smokers versus controls; male smokers versus controls; and, female smokers with different levels of tobacco consumption. We will correlate changes in estradiol 2-hydroxylation with serum nicotine (or continine) levels, and attempt to induce changes in estrogen metabolism by administering nicotine transdermally. We will follow esstradiol 2-hydroxylation in female smokers who have stopped smoking for various periods of time. Finally, we will examine other metabolic pathways of estrogen metabolism, including the irreversible C-16yield hydroxylation step, and the aromatization of androstenedione to estrone, for further evidence of induction by cigarette smoking.