Oxidative metabolism of BDE-99 by rat liver microsomes: metabolites formed and CYP enzymes involved

Introduction 2,2ʹ,4,4ʹ,5-Pentabromodiphenyl ether (BDE-99) is the major congener in the widely-used commercial penta-brominated diphenyl ether (BDE) mixture and has become a widely distributed environmental contaminant (Hites 2004). Hydroxy-BDEs have been identified in humans and other vertebrate species (Athanasiadou et al. 2008, Marsh et al. 2004, McKinney et al. 2006, Qiu et al. 2009) but the oxidative metabolism of BDE-99 has not been thoroughly investigated in vivo or in vitro. Recent studies showed that hydroxy metabolites of BDE-99 are formed in rats, mice and humans (Chen et al. 2006, Hakk et al. 2002, Lupton et al. 2009, Stapleton et al. 2009, Staskal et al. 2006). Structural characterization of all the hydroxy metabolites of BDE-99 formed, the identification of the enzymes involved in BDE-99 oxidative metabolism and the characterization of enzyme kinetics (i.e. Km and Vmax) have not been undertaken yet. The objectives of the present study were to use rat liver microsomal preparations to investigate the oxidative metabolism of BDE-99, to identify the hydroxy metabolites produced, to determine rates of metabolite formation and apparent Km and Vmax values. Ultimately, a panel of recombinant enzymes will be used to determine the degree of participation of individual CYP enzymes in the metabolism of BDE-99.