Behavioural characterization of ghrelin ligands, anamorelin and HM01: Appetite and reward-motivated effects in rodents. (15th May 2020)

• Record Type: Journal Article
• Authors: Howick, Ken; Chruscicka, Barbara; Felice, Daniela; Ramirez, Valerie T.; van Leuven, Lucas; Pietra, Claudio; Cryan, John F.; Griffin, Brendan T.; Schellekens, Harriët
• Is Part Of: Neuropharmacology. Volume 168(2020)
• Publication Date: 2020-05-15
• Subjects: Neuropsychopharmacology -- Periodicals; Autonomic Agents -- Periodicals; Neuropsychopharmacologie -- Périodiques; Neuropsychopharmacology; Periodicals; Electronic journals; 615.78
• DOI: 10.1016/j.neuropharm.2020.108011
• Languages: English
• ISSNs: 0028-3908

Abstract

Abstract: The ghrelinergic system has been steadily investigated as a therapeutic target in the treatment of metabolic disorders and modulation of appetite. While endogenous ghrelin activates the full complement of the growth hormone secretagogue receptor (GHSR-1a) pathways, synthetic GHSR-1a ligands display biased signalling and functional selectivity, which have a significant impact on the intended and indeed, unintended, therapeutic effects. The widespread expression of the GHSR-1a receptor in vivo also necessitates an imperative consideration of the biodistribution of GHSR-1a ligands. Here, we investigate anamorelin and HM01, two recently described synthetic GHSR-1a ligands which have shown promising effects on food intake in preclinical and clinical studies. We compare the downstream signalling pathways in cellular in vitro assays, including calcium mobilization, IP-one, internalization and β-arrestin recruitment assays. We describe a novel divergent activation of central reward circuitry by anamorelin and HM01 using c-Fos immunostaining as well as behavioural effects in food intake and reward paradigms. Interestingly, we found a paradoxical reduction in reward-related behaviour for anamorelin and HM01 treated animals in our chosen paradigms. The work highlights the critical importance to consider signalling bias in relation to future ghrelin-based therapies. In addition, central access of GHSR-1a ligands, particularly to reward areas of the brain, remains a crucial factor in eliciting potent appetite-stimulating effects. The precise characterization of downstream ghrelinergic signalling and biodistribution of novel GHSR-1a ligands will be decisive in their successful development and will allow predictive modelling and design of future synthetic ligands to combat metabolic and appetite disorders involving the ghrelinergic system. This article is part of the special issue on 'Neuropeptides'. Highlights: Anamorelin and HM01, have enhanced in vitro potency for GHSR-1a signalling. HM01 enhances hypothalamic neuronal activation and increases cumulative food intake more compared to ghrelin and anamorelin. HM01 increases neuronal activation in reward circuitry but shows a paradoxical reduction in reward-related behaviour. Signalling bias and central access of GHSR-1a ligands are crucial factors to consider for future ghrelin-based therapies.