Pyrethroids, a common class of insecticide used in both commercial and household products, are neurotoxic to many environmentally significant insects, can affect aquatic animals including fish, and developmental exposures have exhibited neurological and behavioral changes in mice. In vivo metabolism of pyrethroids has not been well studied in humans, therefore the potential health effects of these commonly used insecticides is constructed primarily from animal-based research. Research has demonstrated the potential for negative health outcomes due to pyrethroid exposure. Additionally, previous animal studies suggest pyrethroids are metabolized via phase I oxidation and hydrolysis followed by phase II glucuronidation. 3-Phenoxybenzoic Acid (3-PBA) is the primary phase II metabolite of pyrethroids. In this study, we examine the metabolism and inhibition of 3-PBA in vitro, using UDP-glucuronosyltransferase (UGT) isoenzymes. Previous studies suggest that 3-PBA undergoes glucuronidation exclusively by UGT1A9 and is expected to fit the Michaelis-Menten kinetic model, with known inhibitors decreasing enzymatic activity. Kinetic models in this study are constructed from data acquired via high-pressure liquid chromatography coupled with ultraviolet detection (HPLC-UV) analysis of in vitro enzymatic assays. For this analysis, a 4.6 mm x 150 mm 3 micron C-18 column served as the stationary phase with an H2O/Acetonitrile gradient mobile phase. The resulting retention time of 3-PBA was found to be 13.7 min. Detection was measured as UV absorbance at 210 nm. For the enzymatic portion of the study, human recombinant DNA isoenzymes were incubated at 37ºC with 3-PBA and buffer solutions. Initial assays allowed for determination of the optimal incubation time. These initial assays were followed by variable substrate concentration assays to yield data on the kinetics of the enzyme-substate interaction. In future work, known inhibitors will be also be investigated. The results of this study will improve our understanding of pyrethroid metabolism and the effects that inhibitors have on 3-PBA glucuronidation as well as improving our understanding of the effects these compounds could have in relation to human health. Any determined inhibitory activity could mean an increased half-life of this metabolite in vivo, which could result in negative human health outcomes.
