Intestinal Transport of Pure Diester-type Alkaloids from an Aconite Extract across the Caco-2 Cell Monolayer Model

Aconitine (AC), mesaconitine (MA), and hypaconitine (HA) are the active alkaloids identified in aconite tuber, an important traditional Chinese medicine. The study is aimed to investigate their intestinal transport profiles and potential interaction during the intestinal absorption using the Caco-2 cell monolayer model. All three alkaloids had good permeability with P-app values greater than 1 x 10(-6) cm.s(-1). However, AC, MA, and HA in a mixture and as an extract, in both cases with the same content of alkaloids, showed higher transport efficiency in the apical to basolateral, and lower transport efficiency in the basolateral to apical directions. Digoxin, as a P-glycoprotein (P-gp) substrate, was substantially effluxed in the basolateral to apical direction but inhibited by the three alkaloids. Furthermore, the backwards transport of MA and HA was inhibited by the P-gp inhibitor verapamil. These observations indicated that the three alkaloids may not only be P-gp inhibitors but also its substrates; they interact with each other and can potentially enhance their own bioavailability when taken concomitantly.