Biased signaling at neural melanocortin receptors in regulation of energy homeostasis

The global prevalence of obesity highlights the importance of understanding on regulation of energy homeostasis. The central melanocortin system is an important intersection connecting the neural pathways controlling satiety and energy expenditure to regulate energy homeostasis by sensing and integrating the signals of external stimuli. In this system, neural melanocortin receptors (MCRs), melanocortin-3 and -4 receptors (MC3R and MC4R), play crucial roles in the regulation of energy homeostasis. Recently, multiple intracellular signaling pathways and biased signaling at neural MCRs have been discovered, providing new insights into neural MCR signaling. This review attempts to summarize biased signaling including biased receptor mutants (both naturally occurring and lab-generated) and biased ligands at neural MCRs, and to provide a better understanding of obesity pathogenesis and new therapeutic implications for obesity treatment.

Endocrinologic Control of Men's Sexual Desire and Arousal/Erection

INTRODUCTION

Several hormones and neurotransmitters orchestrate men's sexual response, including the appetitive (sexual desire) and consummative (arousal and penile erection) phases.

AIM

To provide an overview and recommendations regarding endocrinologic control of sexual desire and arousal and erection and their disturbances.

METHODS

Medical literature was reviewed by the subcommittee of the International Consultation of Sexual Medicine, followed by extensive internal discussion, and then public presentation and discussion with other experts. The role of pituitary (prolactin, oxytocin, growth hormone, and α-melanocyte-stimulating hormone), thyroid, and testicular hormones was scrutinized and discussed.

MAIN OUTCOME MEASURES

Recommendations were based on grading of evidence-based medical literature, followed by interactive discussion.

RESULTS

Testosterone has a primary role in controlling and synchronizing male sexual desire and arousal, acting at multiple levels. Accordingly, meta-analysis indicates that testosterone therapy for hypogonadal individuals can improve low desire and erectile dysfunction. Hyperprolactinemia is associated with low desire that can be successfully corrected by appropriate treatments. Oxytocin and α-melanocyte-stimulating hormone are important in eliciting sexual arousal; however, use of these peptides, or their analogs, for stimulating sexual arousal is still under investigation. Evaluation and treatment of other endocrine disorders are suggested only in selected cases.

CONCLUSION

Endocrine abnormalities are common in patients with sexual dysfunction. Their identification and treatment is strongly encouraged in disturbances of sexual desire and arousal.

Melanocortin-4 receptor modulators for the treatment of obesity: a patent analysis (2008–2014)

The central melanocortin system and particularly the melanocortin-4 receptor (MC4R) subtype, plays an important role in the regulation of body weight. The discovery of orally active MC4R agonists suitable for evaluation in human clinical trials as weight loss agents has attracted considerable interest over the past decade, but has proved challenging, in part because of cardiovascular and behavioral side effects. Currently, the only MC4R agonist in clinical trials is a peptide identified as RM-493. To avoid some of the undesirable side effects associated with MC4R activation, new pharmacological approaches for modulating the MC system have been investigated. In this article, we provide a review of the MC4R patent landscape from 2008 to 2014 and analyze the physicochemical properties of compounds described herein.

Investigation of safety, tolerability, pharmacokinetics, and pharmacodynamics of single and multiple doses of a long-acting α-MSH analog in healthy overweight and obese subjects

MC4-NN2-0453 is a novel, long-acting, selective, melanocortin-4-receptor agonist developed for treatment of obesity. This first-human-dose, randomized, double-blind, placebo-controlled trial investigated the safety, tolerability, pharmacokinetics, and pharmacodynamics of single and multiple doses of MC4-NN2-0453 in overweight to obese but otherwise healthy subjects. The trial included a single-dose part of ascending subcutaneous 0.03-1.50 mg/kg doses in overweight to obese but otherwise healthy men, and a multiple-dose part of ascending subcutaneous 0.75-3.0 mg/day doses in obese but otherwise healthy men/women. The single-dose part included 7 cohorts of 8 subjects, randomized 6:2 to active drug/placebo; the multiple-dose part included 4 cohorts of 20 subjects, randomized 16:4 to active drug/placebo. MC4-NN2-0453 was well tolerated and raised no safety concerns except for nonserious skin-related adverse events, this along with lack of weight loss effect led to premature termination of the trial. Headache, sexual-arousal disturbance, and penile erection were also reported. Single-dose pharmacokinetics showed dose-linearity and dose-proportionality. Maximum plasma concentration was observed after 50-100 hours, which then declined with a of approximately 250 hours. Plasma concentration reached steady state after 4 weeks for 0.75 and 1.5 mg/day multiple-dose cohorts, and the was similar to single dose. There were no significant pharmacodynamic effects, including effect on body weight.

The melanocortin-4 receptor: physiology, pharmacology, and pathophysiology

The melanocortin-4 receptor (MC4R) was cloned in 1993 by degenerate PCR; however, its function was unknown. Subsequent studies suggest that the MC4R might be involved in regulating energy homeostasis. This hypothesis was confirmed in 1997 by a series of seminal studies in mice. In 1998, human genetic studies demonstrated that mutations in the MC4R gene can cause monogenic obesity. We now know that mutations in the MC4R are the most common monogenic form of obesity, with more than 150 distinct mutations reported thus far. This review will summarize the studies on the MC4R, from its cloning and tissue distribution to its physiological roles in regulating energy homeostasis, cachexia, cardiovascular function, glucose and lipid homeostasis, reproduction and sexual function, drug abuse, pain perception, brain inflammation, and anxiety. I will then review the studies on the pharmacology of the receptor, including ligand binding and receptor activation, signaling pathways, as well as its regulation. Finally, the pathophysiology of the MC4R in obesity pathogenesis will be reviewed. Functional studies of the mutant MC4Rs and the therapeutic implications, including small molecules in correcting binding and signaling defect, and their potential as pharmacological chaperones in rescuing intracellularly retained mutants, will be highlighted.