Inhibition of choline transport by redox-active cholinomimetic bis-catechol reagents

Both N,N'-(2,3-dihydroxybenzyl)-N,N,N',N'-tetramethyl-1,6-hexanediamine dibromide (DTH, 6) and N,N'-(2,3-dihydroxybenzyl)-N,N,N',N'-tetramethyl-1,10-decanediamine dibromide (DTD, 7), which are symmetrical bis-catechol substituted hexamethonium and decamethonium analogues, respectively, were found to inhibit high-affinity choline transport in mouse brain synaptosomes. Inhibitory properties were evaluated using an extraordinarily sensitive capillary electrophoresis method employing electrochemical detection at an enzyme-modified microelectrode. Dose-response curves were generated for each inhibitor and IC(50) values were determined to be 76 microM for 6 and 21 microM for 7. Lineweaver-Burk analysis revealed that both molecules inhibit high-affinity choline uptake by a mixed inhibition mechanism. The K(I) values for 6 and 7 were determined to be 73+/-1 and 31+/-2 microM, respectively. The inhibition properties were further compared to a series of mono-catechol analogues, 3-[(trimethylammonio)methyl]catechol (1), N,N-dimethylepinephrine (4) and 6-hydroxy-N,N-dimethylepinephrine (5), as well as the well-characterized hemicholinium inhibitors, hemicholinium-15 (HC-15, 8) and hemicholinum-3 (HC-3, 9).