Abstract
Part of circulating ghrelin is bound to immunoglobulins (Ig) protecting it from degradation and preserving its functional activity. This review summarizes the data on ghrelin- and desacyl-ghrelin-reactive IgG in conditions of altered appetite and energy balance. Plasma levels and affinity kinetics of such IgG were compared in patients with obesity and anorexia nervosa (AN) and in animal models of obesity including ob/ob mice, high-fat diet-induced obese mice, and obese Zucker rats as well as in mice after chronic food restriction and activity-based anorexia and in rats with methotrexate-induced anorexia. We show that plasmatic IgG in both obese humans and animals are characterized by increased affinity for ghrelin. In contrast, patients with AN and anorectic rodents all show lower affinity of ghrelin- and desacyl-ghrelin-reactive IgG, respectively, the changes which were not observed in non-anorectic, chronically starved mice. We also show that affinity of ghrelin-reactive IgG correlate with plasma levels of ghrelin. These data point to common mechanisms underlying modifications of affinity kinetics properties of ghrelin-reactive IgG during chronic alterations of energy balance in humans and rodents and support a functional role of such autoantibodies in ghrelin-mediated regulation of appetite.
Highlights
Ghrelin is a 28 amino acid acylated enteroendocrine peptide produced mainly in the stomach, which has been isolated and named based on its ability to stimulate growth hormone secretion [1]
The active, acylated form of ghrelin is unstable in the circulation and is degraded to desacyl-ghrelin [9, 10]
Data analysis from patients and several animal models of altered energy balance shows that both obese humans and animals display lower levels of ghrelin-reactive IgG characterized by increased affinity
Summary
Ghrelin is a 28 amino acid acylated enteroendocrine peptide produced mainly in the stomach, which has been isolated and named based on its ability to stimulate growth hormone secretion [1]. One of the main properties of ghrelin, independent from growth hormone secretagogue activity, is stimulation of feeding and body weight gain [2,3,4]. Acylation of the serine 3 residue in the ghrelin’s N-terminal by octanoic acid is necessary for binding of the growth hormone secretagogue receptor 1 (GHSR1), designated as ghrelin receptor [5] and biological activity including stimulation of food intake [6,7,8]. The preservation of the acylated ghrelin form in the circulation appears, as a key factor for maintaining its role in regulation of appetite and energy balance. This review is the first attempt to summarize the data on ghrelin-reactive IgG obtained since their initial identification and the following studies in animal models of altered appetite and energy balance
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