In vitro metabolism and interaction of profenofos by human, mouse and rat liver preparations

Biotransformations of profenofos were studied in vitro. Two metabolites, desthiopropylprofenofos and hydroxyprofenofos, were detected by LC–MS after incubation of profenofos with human liver homogenates and different mammalian liver microsomes. The rank order of desthiopropylprofenofos formation in liver microsomes based on intrinsic clearance (Vmax/Km) was mouse > human > rat, while for profenofos hydroxylation it was mouse > rat > human. In view of the ratio between desthiopropylation and hydroxylation intrinsic clearance rates, human liver microsomes were most active in profenofos bioactivation. The interspecies differences and interindividual variation were within range of the default uncertainty/safety factors for chemical risk assessment. CYP3A4, CYP2B6 and CYP2C19 were identified as profenofos-oxidizing enzymes in human liver on the basis of recombinant expressed enzymes and correlation with CYP model activities. The rank order of CYPs in profenofos activation was CYP3A4 > CYP2B6 > CYP2C19, whereas it was the contrary for profenofos hydroxylation. Profenofos inhibited relatively potently several human liver microsomal activities: the lowest IC50 values were about 3 μM for CYP1A1/2 and CYP2B-associated activities. Profenofos is extensively metabolized by liver microsomal CYP enzymes and its interaction potential with several CYP activities is considerable.