The prevention of cyclosporin A adsorption to Transwell® surfaces by human plasma

Prevention of cyclosporin A (CsA) adsorption onto the inner surface of Transwell® during transport experiments, by the addition of human plasma to the receiver compartment (basolateral side), was investigated. The addition of plasma to a level of 50% (v/v) of the transport medium led to a reduction in the adsorption of CsA (0.1 μM) down to a level of 5%. As a result, the apical to basolateral flux of CsA across the Caco-2 cell monolayer in the presence of 50% (v/v) plasma was estimated to be 2.7-fold higher than that obtained in the absence of plasma. Thus, the adsorption problem can be overcome simply by the addition of an appropriate volume of human plasma to the transport medium. This method appears to be applicable to the routine estimation of CsA flux across epithelial cell monolayers using Transwell®.