Elucidation of the Intestinal Absorption Mechanism of Celastrol Using the Caco-2 Cell Transwell Model

Celastrol, a triterpenoid isolated from stem (caulis) of Celastrus orbiculatus Thunb. (Celastraceae), has been known to have various pharmacological effects, including anti-inflammatory, anticancer, and antioxidant activities. However, the mechanism of the intestinal absorption of celastrol is unknown. The aim of this study was to investigate the intestinal absorption of celastrol using the Caco-2 cell transwell model. First, the bidirectional transport of celastrol in Caco-2 cell monolayers was observed. Then, the effects of time, concentration, temperature, paracellular pathway, and efflux transport inhibition on the transport of celastrol across the Caco-2 cell monolayers were investigated. The P-glycoprotein inhibitor verapamil and cyclosporin A, the multidrug resistance protein 2 inhibitor MK571, and the breast cancer resistance protein inhibitor reserpine were used. Additionally, the effects of celastrol on the activity of P-glycoprotein were evaluated using the rhodamine 123 uptake assay. In this study, we found that the intestinal transport of celastrol was a time- and concentration-dependent active transport. The paracellular pathway was not involved in the transport of celastrol, and the efflux of celastrol was energy dependent. The results indicated that celastrol is a substrate of P-glycoprotein but not multidrug resistance protein 2 or the breast cancer resistance protein. In addition, celastrol could not affect the uptake of rhodamine 123 in Caco-2 cells, which indicated that celastrol could not inhibit or induce the activity of P-glycoprotein.