Role of the arachnoid mater organic anion and cation transporters in the clearance of prostaglandin D2 and metformin from the cerebrospinal fluid in rats.

The arachnoid mater-forming cells, which exhibit expressions of organic anion and cation transporters, as well as tight junction proteins, form the blood-arachnoid barrier. The purpose of the present study was to clarify the roles of the arachnoid mater transporters in the cerebrospinal fluid (CSF) clearance of prostaglandin D2 (PGD2) and metformin by using an intracisternal administration method for evaluating arachnoid mater-mediated transport in rats. Global proteomics of rat leptomeninges showed the transporter expression of Slc22a6/Oat1, Slc22a8/Oat3, Slco2a1/Oatp2a1, Slc22a2/Oct2, and Slco2b1/Oatp2b1. The CSF clearance of PGD2 and metformin was greater than that of FITC-inulin, which is a marker of CSF bulk flow and parenchymal diffusion. The CSF elimination of PGD2 was significantly inhibited by p-aminohippuric acid, diclofenac (substrates/inhibitors of Slc22a6/Oat1 and Slc22a8/Oat3), and taurocholate (a broad substrate/inhibitor of Slco family transporters), whereas that of metformin was blocked by cimetidine, tetraethylammonium, and thiamine (substrates/inhibitors of Slc22a2/Oct2). The CSF-to-circulating blood transfer of metformin was inhibited by tetraethylammonium. These results suggested that the PGD2 clearance from the CSF most likely occurred via Slc22a6/Oat1, Slc22a8/Oat3, Slco2a1/Oatp2a1, and Slco2b1/Oatp2b1, while the metformin clearance was primarily mediated by Slc22a2/Oct2, in the arachnoid mater. These transporters would regulate the CSF concentrations of pharmacologically active substances and drugs.