The contribution of human small intestine to chlorpyrifos biotransformation

Despite the oral intake is the major route of exposure to chlorpyrifos for the general population, few data are available on human intestine biotransformation. In this study the contribution of chlorpyrifos (CPF) metabolism in human small intestine was investigated in microsomes from duodenum (HDM) and ileum/jejunum (HS2M) from 11 individual donors. Samples were characterized for testosterone hydroxylated metabolite formation and CYP content quantification by means of Western blotting. The two methods gave consistent results, evidencing the presence of CY3A4 and its-related activity in 10/11 samples, among which one showed also the presence of CYP2C9. Analogously, although with high interindividual variability (about 10 fold), CPF bioactivation to chlorpyrifos-oxon (CPFO) was observed in 10/11 HDM: intrinsic clearance highest value was 0.75 pmolCPFO/(mgproteinminμM). Detoxication to 3,5,6-trichloropyrin-2-ol formation was negligible. The comparison between HDM and HS2M indicates that most CPF bioactivation was confined in the duodenum, declining toward the distal ileum. Results suggest that following oral exposure, the small intestine CPF bioactivation, although much lower when compared to the total hepatic metabolism, could play a role in the pre-systemic CPF clearance, with CPFO transported into the lumen by the efflux P-glycoprotein and further metabolized by esterases.