In vitro intestinal and hepatic metabolism of Di(2-ethylhexyl) phthalate (DEHP) in human and rat

- The clearance via DEHP hydrolysis in human intestine was higher than in human liver.
- The clearance via DEHP hydrolysis in rat liver was higher than in rat intestine.
- Hepatic CYP-mediated metabolism of MEHP in human was more predominant than in rat.
- Human CYP2C9*1/3A4 have higher binding affinity and clearances than rat CYP2C6/3A2.
- CYP2C9 polymorphism has qualitative and quantitative variability in MEHP metabolism.

Species and organ differences in the intrinsic clearance and the enzymes involved in the metabolism of DEHP were examined in subcellular fractions of the intestine and liver as well as by recombinant cytochrome P450 (CYP) isoforms of human and rat. Estimated clearance (CLint) of DEHP via esterase-mediated pathway in human intestine was 2.4-fold greater than that in human liver while its value in rat intestine was 1.7-fold less than that in rat liver. Ranks of CLint for CYP-mediated oxidation/dealkylation of MEHP were human liver > rat liver > human intestine > rat intestine. Estimates of CLint for the production of mono(2-ethyl-5-hydroxyhexyl) phthalate and mono(2-ethyl-5-oxohexyl) phthalate by human CYP2C9*1 were 4.2- and 2.6-fold greater than those by rat CYP2C6, respectively. Total CLint via hCYP2C9*3-mediated oxidation was 1.9- and 2.6-fold less than those by hCYP2C9*2 and 2C9*1, respectively. Estimated CLint for phthalic acid production by hCYP3A4 was 24.5 μL nmol CYP−1 min−1 while it was continuously produced by rCYP2C6 and 3A2 via passive mechanism. These species/organ differences in major metabolic pathway and CYP isoforms should be considered for appraisal of the potential adverse health effects of DEHP.