Characterization of the human cytochrome P450 isozymes responsible for styrene metabolism.

The rate of formation of styrene glycol from styrene was compared in human, rat and mouse liver microsomes. At a low styrene concentration (0.085 mM), the rates decreased in the order, mouse > rat > human; at a high concentration (1.85 mM), the order was rat > mouse > human. The forms of cytochrome P450 that are responsible for transforming styrene to styrene glycol were determined by vaccinia virus-mediated cDNA expression of individual P450 forms in cultured cells. Of the 10 human P450 forms studied, CYP2B6 was the most effective in forming of styrene glycol, followed by CYP1A2, CYP2E1 and CYP2C8; the human P450s CYP3A3, CYP3A4 and CYP3A5 also catalysed metabolism, but were much less active; and CYP2A6, CYP2C9 and CYP2D6 had little detectable activity. CYP1A1 from mouse liver was more active in forming styrene glycol than mouse CYP1A2; the latter was less active than human CYP1A2. CYP2B1 from rat liver was more active than rat CYP2B2 or CYP2B6 from human liver. The rate of styrene glycol formation was higher in lung microsomes from smokers than in those from current nonsmokers.