The melanocortin system as a therapeutic treatment target for adiposity and adiposopathy.
The melanocortin system is an important treatment target towards improving both adiposity (excessive body fat) and adiposopathy (dysfunctional body fat). Melanocortin agonism can be achieved by increasing CNS leptin and/or insulin activity, which is dependent upon peripheral leptin/insulin production, transport across the blood-brain barrier (potentially relevant to inhaled/nasal insulin), and effects upon CNS target receptors. Melanocortin agonism may also be achieved through inhibiting inverse agonists of melanocortin receptors (such as inhibition of agouti-related peptide), and directly through selective melanocortin receptor ligands such as piperazine, piperidine, pyridazinone, tetrahydropyran, thiadiazole and diazole derivatives. While the development of most (but not all) neuropeptide Y inhibitors as monotherapy interventions have demonstrated limited efficacy thus far, it is possible that the combination of a neuropeptide Y inhibitor with a selective melanocortin receptor ligand may provide improved weight loss over that of either agent alone. In general, melanocortin system agonism promotes weight loss through decreasing appetite, increasing sympathetic nervous system activity, and modulating thyroid-releasing hormone, corticotropin-releasing hormone, brain-derived neurotrophic factor, melanin-concentrating hormone and orexin. Of particular interest, given the development of cannabinoid receptor antagonists as weight loss agents, is the fact that receptors in the endocannabinoid system are also affected by the melanocortin system. It will only be through the conduct of human clinical trials that melanocortin agonists will be proven to reduce adiposity to a meaningful degree, and, as importantly, be proven to improve adiposopathy, and thus effectively treat excessive fat-related metabolic diseases.