Evidence that Melanocortin Receptor Agonist Melanotan-II Synergistically Augments the Ability of Naltrexone to Blunt Binge-Like Ethanol Intake in Male C57BL/6J Mice

Abstract

Background—The non-selective opioid receptor antagonist, naltrexone (NAL), reduces alcohol (ethanol) consumption in animals and humans and is an approved medication for treating alcohol abuse disorders. Proopiomelanocortin (POMC)-derived melanocortin (MC) and opioid peptides are produced in the same neurons in the brain, and recent pre-clinical evidence shows that MC receptor (MCR) agonists reduce excessive ethanol drinking in animal models. Interestingly, there is a growing body of literature revealing interactions between the MC and opioid systems in the modulation of pain, drug tolerance, and food intake. Method—In the present report, a mouse model of binge ethanol drinking was employed to determine if the MCR agonist, melanotan-II (MTII), would improve the effectiveness of NAL in reducing excessive binge-like ethanol drinking when these drugs were co-administered prior to ethanol access. Results—Both NAL and MTII blunt binge-like ethanol drinking and associated blood ethanol levels, and when administered together, a low dose of MTII (0.26 mg/kg) produces a 7.6-fold increase in the effectiveness of NAL in reducing binge-like ethanol drinking. Using isobolographic analysis, it is demonstrated that MTII increases the effectiveness of NAL in a synergistic manner. Conclusions—The current observations suggest that activators of MC signaling may represent a new approach to treating alcohol abuse disorders, and a way to potentially improve existing NAL-based therapies.