Lack of Protection with a Novel, Selective Melanocortin Receptor Subtype-4 Agonist RY767 in a Rat Transient Middle Cerebral Artery Occlusion Stroke Model

Abstract

Previous studies utilizing α-melanocyte-stimulating hormone (α-MSH) or the synthetic analog [Nle⁴, D-Phe⁷] α-MSH have reported beneficial effects in animal models of ischemic stroke, with the latter studies suggesting melanocortin receptor subtype-4 (MC4R) activation as a protective mechanism. The present study directly addresses the hypothesis that MC4R activation may ameliorate ischemic brain injury by assessing the efficacy of a novel small molecule MC4R agonist RY767, administered in a pharmacokinetically guided and pharmacologically validated dosing regimen, in a rat stroke model of transient middle cerebral artery occlusion (tMCAO). Male Wistar rats were subjected to 90-min tMCAO followed by 72 h of reperfusion. Treatments were i.p. pretreatment with MK-801 (15 min prior to occlusion, positive control), or combined i.v. and p.o. daily administrations of vehicle, dextrose (negative control) or RY767 in blinded fashion initiated 2 h after occlusion. Infarct volume in MK-801-treated rats (158.7 ± 22.3 mm³) was reduced significantly compared to vehicle infarct volume (243.4 ± 12.5 mm³), whereas infarct volumes in dextrose- (224.3 ± 16.5 mm³) and RY767- (262.1 ± 19.2 mm³) treated rats did not differ from vehicle infarct volume. These results indicate that selective MC4R activation provides no significant neuroprotection, as reflected by infarct volume, in a rat stroke model utilizing a 90-min ischemic insult.

Multiple beneficial effects of melanocortin MC4 receptor agonists in experimental neurodegenerative disorders: Therapeutic perspectives

“…As a matter of fact, this compound does not bear the common core sequence (6-9) of MSH, necessary for binding to all MC receptor and for agonist activity (Brzoska et al, 2008;Catania et al, 2004;Getting, 2006;Oosterom et al, 1999;Schiöth, 2001;Versteeg et al, 1998); thus it may be that the mechanism of action of this molecule differs from that of melanocortin peptides. Finally, the MC 4 receptor agonist RY767 (a small non peptide molecule) did not induce neuroprotection in a rat model of ischemic stroke (Regan et al, 2009); however, this research only assessed indirect infarct volume at day 3 after stroke, but pathophysiological pathways, neuron viability and functional recovery were not investigated.…”

Evidence for the Use of Isoflurane as a Replacement for Chloral Hydrate Anesthesia in Experimental Stroke: An Ethical Issue

“…No significant difference was observed in terms of infarct volume and mortality in different groups. In addition, we wanted to investigate the modulation of the neuroprotection induced by MK801, an antagonist of NMDA receptor, extensively studied in stroke animal models [14–16]. Whatever the anesthetic agent used here was, the infarct volume was reduced when animals were treated with MK801.…”

“…To assess the ability of isoflurane and chloral hydrate to interfere with pharmacologically induced neuroprotection, we used MK801, a well-described NMDA receptor antagonist, used as a reference compound for experimental neuroprotection in rodents [14–16]. Since animal pain is centrally considered in the ethical issues of experimental studies, and therefore in the requirements for anesthetics, a pain assessment was included in the study in order to check for the postoperative analgesic potential of both compared anesthetics.…”

Neither nefopam nor acetaminophen can be used as postoperative analgesics in a rat model of ischemic stroke

“…In the second protocol, the effect of the neuroprotective compound MK801 was assessed when nefopam was administered or not as an analgesic procedure. For this purpose, MK801 (3 mg/kg), dose frequently used in experimental neuroprotective research , or its vehicle (saline 0.9%) was administered intravenously 3 min before MCAO to rats receiving or not nefopam (20 mg/kg, IM) at the end of the MCAO. Control rats received vehicles of MK801 (saline 0.9%) and nefopam at the same time and route.…”