ABSTRACT
Oxidative metabolism mediated by the superfamily of heme enzymes known as the cytochromes P450 represents an important elimination pathway for the majority of drugs prescribed today [1]. In general, the enzymes catalyze the oxidative metabolism of a wide range of drugs and endogenous compounds to yield products (e.g., metabolites) that are usually more hydrophilic through the addition of a polar functional group, which may then serve as a reactive site for conjugating enzymes to enhance the rate of clearance and excretion of the products further by the addition of a yet more polar moiety [1]. For the most part, cytochrome P450–mediated reactions are typically considered to reflect detoxification pathways of xenobiotics as the hydrophilic metabolites are rapidly excreted from the body. In some instances, however, P450 metabolism results in the formation of reactive intermediates that can react with cellular macromolecules, such as DNA, RNA, and proteins, and lead to toxicity [2]. Given the chemical nature of these reactive intermediates, it is not surprising then that the same enzymes responsible for their formation are also susceptible to modification by these bioactivated species [3]. Compounds that are transformed by the P450 enzymes into reactive intermediates, which then react with active-site moieties leading to inactivation of the enzyme, are referred to as mechanism-based inactivators [4].
