Investigating the bioavailabilities of olerciamide A via the rat's hepatic, gastric and intestinal first-pass effect models

Olerciamide A (OA) is a new alkaloid isolated from Portulaca oleracea L. that has been proved to possess a low bioavailability (F) after oral administration in rats in our previous study. Hence, to clarify the reasons for its low bioavailability, hepatic, gastric and intestinal first-pass effect models were established, and a rapid, sensitive UHPLC method was validated and applied for the determination after dosing via the femoral, portal, gastric and intestinal routes. As inhibitors of CYP3A and P-gp, verapamil, midazolam and borneol in low and high dose groups were selected to improve the low bioavailability of olerciamide A. Moreover, a rectal administration method was also carried out to improve the bioavailability of olerciamide A. The results showed that the bioavailability of olerciamide A using hepatic, gastric and intestinal routes were 92.16%, 84.88% and 5.76%, respectively. The areas under the plasma concentration-time curve from zero to infinity (AUC(0 -> infinity)) were increased a little after being dosed with 10 and 30 mg/kg verapamil (p > 0.05), but markedly increased after being dosed with 0.4 and 1.2 mg/kg midazolam as well as 8 and 24 mg/kg borneol (p < 0.05). Besides, the AUC(0 -> infinity) values after the lower and upper rectal administrations were separately similar to the intravenous and intraportal administrations. Our study showed that the intestinal first-pass effect mainly contributed to the low bioavailability of olerciamide A in rats due to it being a substrate of CYP3A and P-gp as well as to its poor intestinal absorption.