Impact of Species and Tissue Differences on In Vitro Glucuronidation of Diclofenac

Background: The aim of this study is to determine the impact of species and tissue differences on the glucuronidation of diclofenac in vitro.

Method: Microsomes from different species (rat, monkey, mouse, dog, and human) and rat and human tissues (liver, intestine, and kidney) were used to assess the rate of glucuronidation reaction of diclofenac. The metabolites were quantified using ultra high-performance liquid chromatography (UHPLC) and fitted into a Michaelis-Menten model to determine the metabolic kinetic parameters.

Results: The results showed higher rates of metabolism in the liver as compared to that of the intestine and kidney by both human and rat tissues microsomes. There were also differences in the rate of metabolism in the liver across the tested species, with mouse liver microsome having the highest maximum reaction rate (V_max) at 7.22 nmol/min/mg followed by human liver microsome at 6.66 ± 0.33 nmol/min/mg, dog liver microsome at 5.05 ± 0.42 nmol/min/mg, monkey liver microsome at 3.88 ± 0.15 nmol/min/mg, and rat liver microsome at 0.83 ± 0.04 nmol/min/mg.

Conclusions: This study demonstrated that the liver is the major organ for the glucuronidation of diclofenac. In addition, glucuronidation of diclofenac was different across the tested species; therefore, the influence of species should be taken into consideration in the pharmacological, pharmaceutical, and toxicological study of diclofenac.