Effects of ECa-233 and asiaticoside on P-glycoprotein function

Abstract

In the present study, standardized extract of Centella asiatica (ECa-233) and asiaticoside (ATS) were tested for their effects on P-gp function as well as their potentiative effect on vinblastine (VBL)-induced cytotoxicity in the in vitro cell culture models of Caco-2 and LLC-GA5-COL300 (human P-gp overexpressed-LLC-PK1) cell lines. In this study, the P-gp activity was determined by calcein-AM accumulation assay whereas the cytotoxic activity was evaluated by an MTT assay. The results revealed that ECa-233 (1000 µg/mL) was able to increase the intracellular level of calcein in LLC-GA5-COL300 by 84 % and Caco-2 cells by 42%. In addition, ECa-233 also increased calcein accumulation in LLC-PK1 by 55%. Because the expression of P-gp is significant lower in LLC-PK1 cells than in LLC-GA5-COL300 cells, it was unlikely that P-gp was a major target of ECa-233 action. It was possible that ECa-233 could affect other membrane efflux pumps involving with calcein transport. Furthermore, the presence of ECa-233 (1000 µg/mL) in the co-treatment study with VBL in Caco-2 cells resulted in significant higher number of VBL-induced cell death. The apparent IC50 of VBL decreased by 5 folds in the presence of ECa-233. Moreover, ATS could also significantly enhance the cytotoxicity of VBL in caco-2 cells (by 2 folds) without any modulating effects on efflux pumps. Taken together, the cytotoxic effects of VBL may be enhanced by ECa-233 and ATS through mechanisms other than P-gp modulations.