Identification and kinetics of microsomal and recombinant equine liver cytochrome P450 enzymes responsible for in vitro metabolism of omeprazole.

The research explores how the drug omeprazole is metabolised in horses, establishing that the process differs from that in humans, with most of the work being done by the CYP3A family of enzymes. The researchers’ findings have potential implications for how omeprazole is used therapeutically in horses.

Objective and Methodology of the Study

• This research focuses on the drug omeprazole, commonly used in horses but with varying degrees of therapeutic efficiency. The goal is to learn more about how this drug is metabolised at an enzymatic level within horses.
• The study used both liver microsomes and a set of equine recombinant cytochrome P450 enzymes (eq-rCYPs) and analyzed the kinetic behavior of omeprazole metabolism in vitro.
• After the omeprazole was incubated with the microsomes and eq-rCYPs, the concentrations of metabolites were measured using liquid chromatography–mass spectrometry (LC-MS) and non-linear regression analysis was used to understand the kinetics of metabolite formation.

Results of the Metabolism Study

• The in vitro study produced three metabolites: 5-hydroxy-omeprazole, 5-O-desmethyl-omeprazole, and omeprazole-sulfone. The most prevalent of these was 5-hydroxy-omeprazole.
• Two different kinetics models were found to fit the formation of the metabolites best: a two enzyme Michaelis-Menten model for 5-O-desmesthyl-omeprazole and a one enzyme Michaelis-Menten model for 5-hydroxy-omeprazole.
• The enzymes CYP3A89 and CYP3A97 were found to produce significant amounts of 5-hydroxy-omeprazole while other eq-rCYPs from the CYP2C and CYP3A family produced lesser amounts of the other two metabolites.

Implications and Future Research

• The research indicates that the metabolism of omeprazole in horses is different from humans, primarily involving the CYP3A family of enzymes. This deviates from the metabolism in humans where CYP2C19 and CYP3A4 play a larger role.
• The findings serve as a basis for further studies seeking to understand single nucleotide polymorphisms (SNPs) of the CYP450 enzymes as these could be linked to the varying treatment efficacy of omeprazole in horses.