Clobenpropit, a histamine H3 receptor antagonist/inverse agonist, inhibits [3H]-dopamine uptake by human neuroblastoma SH-SY5Y cells and rat brain synaptosomes

Background: Clobenpropit, a potent antagonist/inverse agonist at the histamine H-3 receptor (H3R), reduced the cytotoxic action of 6-hydroxydopamine (6-OHDA) in neuroblastoma SH-SY5Y cells transfected with the human H3R. We therefore set out to study whether this effect involved a receptor-independent action on dopamine transport. Methods: The uptake of [H-3]-dopamine was assayed in SH-SY5Y cells and rat striatal or cerebro-cortical isolated nerve terminals (synaptosomes). Clobenpropit binding to the human norepinephrine (NET) and dopamine (DAT) transporters was analyzed by molecular modeling. Results: In SH-SY5Y cells, [H-3]-dopamine uptake was inhibited by desipramine (selective NET inhibitor), GBR-12909 (selective DAT inhibitor), and fluoxetine (selective inhibitor of the serotonin transporter, SERT) with IC50 values 37, 537, and 2800 nM, respectively. The potency rank order indicates that [H-3]-dopamine uptake is primarily performed by NET. Clobenpropit inhibited [H-3]-dopamine uptake (maximum inhibition 82.7 +/- 2.8%, IC50 490 nM), and the effect was reproduced by the H3R antagonist/inverse agonist iodophenpropit, but not by the agonists R-alpha-methylhistamine and immepip or the antagonists/inverse agonists ciproxifan and A-331440. Clobenpropit also inhibited [H-3]-dopamine uptake by rat striatal and cerebro-cortical synaptosomes (-54.6 +/- 11.3% and -46.3 +/- 9.6%, respectively, at 10 mu M). Modeling of the human NET and DAT obtained by homology from the crystal of Drosophila melanogaster DAT showed that clobenpropit can bind to a site also recognized in both transporters by nisoxetine, a potent NET inhibitor. Conclusion: These data indicate a direct inhibitory effect of clobenpropit on catecholamine transport. (c) 2017 Institute of Pharmacology, Polish Academy of Sciences. Published by Elsevier Sp. z o.o. All rights reserved.