An Acyl-Ghrelin-Specific Neutralizing Antibody Inhibits the Acute Ghrelin-Mediated Orexigenic Effects in Mice

Abstract

Ghrelin is a 28-amino acid peptide secreted mainly by the stomach. Acyl-ghrelin, which binds to and activates the growth hormone secretagogue receptor type 1a (GHS-R1a), is considered to be the active form for its orexigenic effects. It has been demonstrated that peripheral administration of ghrelin stimulates food intake and adiposity in rodents and humans. Accordingly, different approaches to antagonize ghrelin/GHS-R1a signaling have been pursued for the treatment of obesity. In the present study, we generated and characterized high-affinity anti-acyl ghrelin-specific monoclonal antibodies (mAbs). In vitro, the lead mAb (33A) displayed specific binding to acyl-ghrelin, with an estimated K d value Ͻ 100 pM. In recombinant receptor cell-based assays, 33A dose-dependently inhibited the ghrelin-mediated calcium signal, with an IC 50 of ϳ3.5 nM. In vivo, ghrelin dose-dependently stimulated food intake in mice, and this effect was fully blocked by a single injection of 33A. In a 4-week chronic study, 33A was shown to effectively bind to endogenous acyl-ghrelin; however, long-term administration of 33A did not affect food intake or body weight gain in a mouse model of diet-induced obesity. Our results indicate that peripheral neutralization of ghrelin can suppress appetite stimulated by a transient surge in ghrelin levels. The lack of longterm effects on body weight control by 33A suggests that compensatory mechanisms may contribute to the regulation of energy balance.

Ghrelin’s Orexigenic Effect Is Modulated via a Serotonin 2C Receptor Interaction

“…Ghrelin is the only known gut-peptide exerting an orexigenic effect via the activation of the centrally expressed GHS-R1a receptor [3][4][5][6] and has thus received much attention as an antiobesity drug target [7][8][9][10][11][12][13][14][15][16] . However, despite previous and ongoing drug development efforts, no weight-loss drugs that target the ghrelin receptor are currently on the market.…”

Anti-ghrelin Therapeutic Vaccine: A Novel Approach for Obesity Treatment

“…As a proof of this concept, it was demonstrated that inoculation of monoclonal anti-ghrelin antibodies in mice inhibited acute ghrelin-mediated orexigenic effects, but it was unable to change long-term food intake [ 41 ]. More recently, another study suggested that the use of a mixture of monoclonal antibodies targeting different haptens, but not the antibodies individually, promotes not only an increase in energy expenditure but also reduced deprivation-induced food intake [ 42 ].…”

“…Several research groups have previously attempted ghrelin neutralization. Passive transfer of monoclonal anti-ghrelin antibodies was unable to change long-term food intake in mice [ 41 ]. Antibodies targeted to hydrolyze the octanoyl moiety of ghrelin to form desacyl ghrelin, which has no biological activity, resulted in increased metabolic rate and suppressed 6 h refeeding after 24 h of food deprivation in mice, but this approach would imply the need of periodic antibodies administration [ 53 ].…”

Obesity vaccines

“…Since this antighrelin antibody was shown to increase the ratio of acylated to des-acylated ghrelin, compensatory mechanisms might have been activated to counteract the blockage of peripheral ghrelin which suggests that blocking the peripheral ghrelin pathway alone may not be sufficient in the long-term. 71 More recently, a mixture of monoclonal antibodies targeting different ghrelin haptens was shown to be required to maintain increased energy expenditure during fasting and deprivationinduced food intake, as well as to reduce overall food intake upon re-feeding. Passive immunization with a single high-affinity monoclonal antibody that targeted specifically the ghrelin N-terminus (JG4) did not in alter energy expenditure, fuel substrate utilization, or food intake in fasted mice.…”

“…71 The inoculation of this monoclonal anti-ghrelin antibody inhibited acute ghrelin-mediated orexigenic effects, but was unable to change long-term food intake in mice. The antibody demonstrated to prevent the increase in food intake induced by exogenous administration of acyl-ghrelin, showing that 33A specifically blocked the activity of acylated ghrelin, however was unable to prevent the increase in food intake after a fast-refeeding challenge that is mediated by endogenous ghrelin.…”