[Cytochromes P450: toxicologic importance of determination of levels].

Drug-metabolizing enzymes, especially cytochrome P450-dependent monooxygenases, are involved in the metabolic activation of the majority of xenobiotics and in the production of oxygen radicals. The most significant are cytochromes P450IA1 and IA2, but also P450IIB, IIE and IIIA are involved. Various classes of xenobiotics induce levels of distinct P450 forms. Their key position in the expression of toxic, mutagenic, carcinogenic and other adverse effects of reactive metabolites and oxygen radicals allows us: 1. to estimate the tetrachlorodibenzo-p-dioxin-like toxicity in both environmental mixtures and individual contaminants by the measurement of induction of P450IA1; 2. to monitor the contamination of ecosystems by the measurement of P450 induction in selected species; 3. to determine toxicity potentials of drugs, agrochemicals, industrial contaminants and other xenobiotics by the measurement of P450IA, IIB, IIE, IIIA and/or IVA levels in model systems.