Diphenhydramine as a selective probe to study H+-antiporter function at the blood-brain barrier: Application to [C-11]diphenhydramine positron emission tomography imaging

摘要

Diphenhydramine, a sedative histamine H-1-receptor (H1R) antagonist, was evaluated as a probe to measure drug/H+-antiporter function at the blood-brain barrier. In situ brain perfusion experiments in mice and rats showed that diphenhydramine transport at the blood-brain barrier was saturable, following Michaelis-Menten kinetics with a K-m=2.99mM and V-max=179.5nmols(-1)g(-1). In the pharmacological plasma concentration range the carrier-mediated component accounted for 77% of diphenhydramine influx while passive diffusion accounted for only 23%. [C-14]Diphenhydramine blood-brain barrier transport was proton and clonidine sensitive but was influenced by neither tetraethylammonium, a MATE1 (SLC47A1), and OCT/OCTN (SLC22A1-5) modulator, nor P-gp/Bcrp (ABCB(1a/1b)/ABCG2) deficiency. Brain and plasma kinetics of [C-11]diphenhydramine were measured by positron emission tomography imaging in rats. [C-11]Diphenhydramine kinetics in different brain regions were not influenced by displacement with 1mgkg(-1) unlabeled diphenhydramine, indicating the specificity of the brain positron emission tomography signal for blood-brain barrier transport activity over binding to any central nervous system target invivo. [C-11]Diphenhydramine radiometabolites were not detected in the brain 15min after injection, allowing for the reliable calculation of [C-11]diphenhydramine brain uptake clearance (Cl-up=0.99 +/- 0.18mLmin(-1)cm(-3)). Diphenhydramine is a selective and specific H+-antiporter substrate. [C-11]Diphenhydramine positron emission tomography imaging offers a reliable and noninvasive method to evaluate H+-antiporter function at the blood-brain barrier.