Improved Pharmacokinetic Characteristics of Ursolic Acid in Rats Following Intratracheal Instillation and Nose-Only Inhalation Exposure

Ursolic acid (UA) is a common pentacyclic triterpene phytochemical with various pharmacological activities. However, UA is classified as a class IV drug in BCS system and its development as an oral drug is limited. Pulmonary delivery is an effective way to improve the bioavailability of drugs with low absorption. In this study, the differences in pharmacokinetic behaviors of UA after pulmonary and oral administration was explored in rats. Compared with oral administration, the plasma concentration of UA increased rapidly after pulmonary administration, and the bioavailability increased about 80 times. UA instantly accumulated in the lungs after pulmonary administration, and the pulmonary AUC0-t/dose increased by 114 times compared to oral dosing. Incubation experiments showed that the metabolism of UA in rat lung microsomes was significantly reduced compared with that in liver microsomes, in which the clearance rate of phase I and phase II metabolism was reduced by 14.7 times and 1.4 times respectively. These results indicated that pulmonary administration could improve the bioavailability of UA and reduce its metabolism. This study not only provides a preferable route of administration for the application of UA but also offers new insights for the development of phytochemical drug candidates with poor pharmacokinetic properties.