Inhibitory effect of clemastine on P-glycoprotein expression and function: an in vitro and in situ study

Objective(s): Transporters have an important role in pharmacokinetics of drugs. Inhibition or induction of drug transporters activity can affect drug absorption, safety, and efficacy. P-glycoprotein (P-gp) is the most important membrane transporter that is responsible for active efflux of drugs. It is important to understand which drugs are substrates, inhibitors, or inducers of P-gp to minimize or avoid unwanted interactions. The aim of this study was to investigate the effects of clemastine on the expression and function of P-gp. Materials and Methods: The effect of clemastine on P-gp function and expression was evaluated in vitro byrhodamine-123 (Rho(123)) efflux assay in Caco-2 cells and Western blot analysis. Rat in situ single pass intestinal permeability model was used to investigate the clemastine effect on digoxin P-eff, as a known P-gp substrate. Digoxin levels in intestinal perfusates were assayed by high performance liquid chromatography (HPLC) method. Results: The Caco-2 intracellular accumulation of Rho123 in clemastine and verapamil treated cells was 90.8 +/- 9.8 and 420.6 +/- 25.4 pg/mg protein, respectively which was significantly higher than that in control cells (50.2 +/- 6.0; P<0.05). Immunoblotting results indicated that clemastine decreased expression of P-gp in Caco-2 cells in vitro. More over effective intestinal permeability (P-eff) of digoxin in the presence of clemastine, was significantly increased compare to control group. Conclusion: Findings of our study suggested dose dependent P-gp inhibition activity for clemastine in vitro and in situ. Therefore co-administration of clemastine with P-gp substrates may result in unwanted interactions and side effects.