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INFLUX AND EFFLUX TRANSPORT OF H1-ANTAGONIST EPINASTINE ACROSS THE BLOOD-BRAIN BARRIER

Faculty of Pharmaceutical Sciences, Tokyo University of Science, Chiba, Japan (N.I., T.N., T.Y., I.T.); Department of Drug Metabolism and Pharmacokinetics, Kawanishi Pharma Research Institute, Nippon Boehringer Ingelheim Co., Ltd., Hyogo, Japan (N.I., A.T., A.S., W.K., K.Y., K.S., T.I.); CREST, Japan Science and Technology Cooperation, Kawaguchi, Japan (I.T.)

We investigated influx and efflux transporters involved in blood-brain barrier transport of the nonsedative H1-antagonist epinastine. The basal-to-apical transport of [¹⁴C]epinastine was markedly higher than that in the opposite direction in LLC-GA5-COL150 cells stably transfected with human multidrug resistance (MDR)1 gene. The brain-to-plasma concentration ratio of [¹⁴C]epinastine in mdr1a/b(-/-) mice was 3.2 times higher than that in wild-type mice. The uptake of both [³H]mepyramine and [¹⁴C]epinastine into immortalized rat brain capillary endothelial cells (RBEC)1 showed temperature and concentration dependence. The kinetic parameters, K_m, V_max, and uptake clearance (V_max/K_m), of the initial uptake of [³H]mepyramine and [¹⁴C]epinastine by RBEC1 were 150 µM, 41.8 nmol/min/mg protein, and 279 µl/min/mg protein for mepyramine and 10.0 mM, 339 nmol/min/mg protein, and 33.9 µl/min/mg protein for epinastine, respectively. The uptake of [³H]mepyramine and [¹⁴C]epinastine by RBEC1 was inhibited by organic cations such as quinidine, amantadine, and verapamil, but not by other organic cations, tetraethyl ammonium, guanidine, and carnitine. Organic anions such as benzoic acid, estrone-3-sulfate, taurocholate, and neutral digoxin were not inhibitory. Furthermore, some cationic H1 antagonists (chlorpheniramine, cyproheptadine, ketotifen, and desloratadine) inhibited the [³H]mepyramine and [¹⁴C]epinastine uptake into RBEC1. In conclusion, the present study demonstrated that the combination of efficient efflux transport by P-glycoprotein and poor uptake by the influx transporter, which is identical with that responsible for the uptake of mepyramine, account for the low brain distribution of epinastine.

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