Induction of cytochrome P-450 enzymes via tobacco smoke: a potential mechanism for developing resistance to environmental toxins as related to parkinsonism and other neurologic diseases.

Case-control studies have consistently demonstrated a reduced risk of Parkinsonism in smokers. A potential mechanism of protection is based on the 'induction' of cytochrome P-450 enzymes by polyaromatic hydrocarbons in tobacco smoke. Cytochrome P-450 enzymes are responsible for biomodification and detoxification of foreign substances. Stimulation of these enzymes in the olfactory epithelium and in the liver may lead to increased metabolism of xenobiotics, thereby preventing environmental neurotoxins from reaching target organs. Polymorphic expression of this family of isozymes may confer a unique susceptibility to some neurologic diseases.