Mechanisms of transport and structure-permeability relationship of sulfasalazine and its analogs in Caco-2 cell monolayers

Purpose. To investigate the mechanisms involved in transport of sulfasalazine in Caco-2 cells. Methods. Permeability coefficients of sulfasalazine and its analogs across Caco-2 cell monolayers were measured as a function of direction of transport, energy and concentration dependence, and in the presence of inhibitors of various cellular efflux pumps and transporters. Results. Permeability coefficients of sulfasalazine across Caco-2 cell monolayers were approximately 342-, 261-, and 176-ford higher from basolateral to apical direction (BL-->AP) than from apical to basolateral direction (AP-->BL) at 100, 200, and 500 muM, respectively. Carrier permeability coefficient, non-saturable membrane permeability coefficient, and Michaelis constant were estimated to be 1.4x10(-5) cm/s, 1.9x10(-8) cm/s, and 369 muM, respectively. The efflux of sulfasalazine was completely blocked at CC and in the presence of an uncoupler of oxidative phosphorylation. Using cellular egfflux inhibitors, the permeability of sulfasalazine was shown to depend on multidrug resistance-associated protein and anion sensitive transport mechanisms. Structure-permeability studies showed that the affinity of sulfasalazine for the cellular efflux pumps and transporters in Caco-2 cells depended strongly on the carboxylic acid functional group. Conclusions. The permeability of sulfasalazine across Caco-2 cell monolayer is very low due to its strong interaction with multiple celular efflux pumps and transporters. This may partially explain its low absorption in vivo.