Benzophenanthridine alkaloid, piperonyl butoxide and (S)-methoprene action at the cannabinoid-1 receptor (CB1-receptor) pathway of mouse brain: Interference with [3H]CP55940 and [3H]SR141716A binding and miodification of WIN55212-2-dependent inhibition of synaptosomal L-glutamate release

Benzophenanthridine alkaloids (chelerythrine and sanguinarine) inhibited binding of [H-3]SR141716A to mouse brain membranes (IC(50)s: < 1 mu M). Piperonyl butoxide and (S)-methoprene were less potent (IC(50)s: 21 and 63 mu M respectively). Benzophenanthridines and piperonyl butoxicle were more selective towards brain CB1 receptors versus spleen CB2 receptors. All compounds reduced B-max of [H-3]SR141716A binding to CB1 receptors, but only methoprene and piperonyl butoxide increased K-d (3-5-fold). Benzophenanthridines increased the K-d of [H-3]CP55940 binding (6-fold), but did not alter B-max. (S)methoprene increased the K-d of [H-3]CP55940 binding (by almost 4-fold) and reduced B-max by 60%. Piperonyl butoxicle lowered the B-max of [H-3]CP55940 binding by 50%, but did not influence K-d. All compounds reduced [H-3]SR141716A and [H-3]CP55940 association with CBI receptors. Combined with a saturating concentration of SR141716A, only piperonyl butoxide and (S)-methoprene increased dissociation of [H-3]SR141716A above that of SR141716A alone. Only piperonyl butoxicle increased dissociation of [H-3]CP55940 to a level greater than CP55940 alone. Binding results indicate predominantly allosteric components to the study compounds action. 4-Aminopyridine-(4-AP-) evoked release of L-glutamate from synaptosomes was partially inhibited by WIN55212-2, an effect completely neutralized by AM251, (s) methoprene and piperonyl butoxide. With WIN55212-2 present, benzophenanthridines enhanced 4-AP-evoked L-glutamaterelease above 4-AP alone. Modulatory patterns of L-glutamate release (with WIN-55212-2 present) align with previous antagonist/inverse agonist profiling based on [S-35]GTP gamma S binding. Although these compounds exhibit lower potencies compared to many classical CB1 receptor inhibitors, they may have potential to modify CB1-receptor-dependent behavioral/physiological outcomes in the whole animal. (C) 2013 Elsevier B.V. All rights reserved