Involvement of P-glycoprotein in the transport of saquinavir and indinavir in rat brain microvessel endothelial and microglia cell lines

Membrane-bound efflux transporters, such as P-glycoprotein (P-gp), may limit the brain entry and distribution of HIV-1 protease inhibitors and be in part responsible for HIV-1-associated dementia treatment failure. The purpose of this study was to characterize the transport properties of saquinavir and indinavir in a brain microvessel endothelial cell line and in microglia, the immune cells of the brain and primary HIV-1 cellular target. Biochemical and transport studies were performed in an immortalized rat brain endothelial cell line (RBE4), a rat microglia cell line (MLS-9), and a P-gp overexpressing Chinese hamster ovary cell line (CHRC5). Western blot analysis using the P-gp monoclonal antibody C219 detected a single band at approximately 170 to 180 kDa (a size previously reported for P-gp) in all cell lines. Cellular accumulation of [14C]saquinavir and [3H]indinavir by RBE4, MLS-9, and CHRC5 monolayers was significantly enhanced in the presence of P-gp inhibitors, HIV-1 protease inhibitors, the ATPase inhibitor sodium azide, and the ATP depleting agent 2',4'-dinitrophenol respectively. [14C]Saquinavir and [3H]indinavir efflux from both cell systems was rapid and significantly reduced in the presence of PSC833. These results provide evidence for P-gp mediated transport of saquinavir and indinavir in RBE4 and MLS-9 and suggest that this transporter can restrict, at least in part, the permeation of HIV-1 protease inhibitors at both the brain barrier site and in brain parenchyma.