Therapeutic concentrations of varenicline increase exocytotic release of catecholamines from human chromaffin cells in the presence of nicotine

Abstract

Background and Purpose: Cardiovascular side effects from varenicline, and a case report of a hypertensive crisis event in a patient with pheochromocytoma being treated with varenicline, have been reported. The goal of the present study was to determine if such side effects might derive, in part, from increased exocytosis of secretory vesicles and subsequent catecholamine release triggered by varenicline in chromaffin cells of the adrenal gland. Experimental Approach: We performed electrophysiological plasma membrane capacitance (Cm) and carbon fiber amperometry experiments to evaluate the effect of varenicline on exocytosis and catecholamine release, respectively, at concentrations reached during varenicline therapy (100 nM). Experiments were conducted in the absence or presence of nicotine, at plasma concentrations achieved right after smoking (250 nM) or steady-state concentrations (110 nM), in chromaffin cells of the adrenal gland obtained from human organ donors or rats. Key Results: Varenicline increased the exocytosis of secretory vesicles and the release of catecholamines from human chromaffin cells in the presence of nicotine. Comparable results were found using rat chromaffin cells; varenicline alone or in the presence of acute or steady-state concentrations of nicotine found in human plasma increased exocytosis. These effects were not due to an increase of Cm or currents triggered by the nicotinic agonists alone. Conclusion and Implications: Therapeutic concentrations of varenicline in the presence of nicotine increased exocytosis and catecholamine release from human chromaffin cells. These results should be taken into account in nicotine addiction therapies when varenicline is used.