Oligoclonal Antibody Targeting Ghrelin Increases Energy Expenditure and Reduces Food Intake in Fasted Mice

Abstract

Ghrelin, an enteric peptide hormone linked to the pathophysiology of obesity has been a therapeutic target of great interest over the past decade. Many research efforts have focused on the antagonism of ghrelin’s endogenous receptor GHSR1a, which is found along ascending vagal afferent fibers, as well as in the arcuate nucleus of the hypothalamus. Additionally, peptidic inhibitors against ghrelin O-acyltransferase, the enzyme responsible for the paracrine activation of ghrelin, have recently been studied. Our research has taken an alternative immunological approach, studying both active and passive vaccination as a means to sequester ghrelin in the periphery, with the original discovery in rat of decreased feed efficiency and adiposity, as well as increased metabolic activity. Using our previous hapten designs as a stepping-stone, three monoclonal antibodies (JG2, JG3, and JG4) were procured against ghrelin and tested in vivo. While mAb JG4 had the highest affinity for ghrelin, it failed to attenuate the orexigenic effects of food deprivation on energy metabolism or food intake in mice. However, animals that were administered a combination of JG3:JG4, (termed a doublet), or JG2:JG3:JG4, (termed a triplet), demonstrated higher heat dispersion and rate of respiration (higher CO2 emission and O2 consumption) during a 24-hr fast refeed. Mice administered the triplet cocktail of JG2:JG3:JG4 also demonstrated decreased food intake upon refeeding as compared to control animals. Recently, Lu and colleagues reported that a passive approach using a single, high affinity N-terminally directed monoclonal antibody did not abrogate the effects of endogenous ghrelin. Our current report corroborates this finding, yet, refutes that a monoclonal antibody approach cannot be efficacious. Rather, we find that a multiple monoclonal antibody (oligoclonal) approach can reproduce the underlying logic to previously reported efficacies using active vaccinations.

Ghrelin

“…Ghrelin signaling has increasingly been recognized as a key regulator of obesity, insulin resistance and diabetes; intriguingly, many of these regulatory functions appear to be independent of ghrelin's effect on food intake (4–8). This current review is focused on the most recent findings of ghrelin in glucose homeostasis (9–11), energy-homeostasis (7, 12), heart disease (13–16), muscular atrophy (17, 18), bone metabolism (8, 19, 20), and cancer development/progression (21, 22). …”

“…It was recently reported that administration of ghrelin antibody to mice increases fasting energy expenditure (12). This study suggests that ghrelin can regulate energy balance in addition to energy intake.…”

Obesity vaccines

“…Thus, suggesting that an oligoclonal response is necessary to maintain an increased whole body energy expenditure during fasting and re-feeding over a 24-h period, as well as to reduce overall food intake after fasting. 72 The main limitations of passive immunization approaches include development of acquired tolerance and lack of long-term effectiveness, due to the reduced half-lives of the antibodies and need of periodic administration, as well as the possibility of activation of compensatory pathways of ghrelin production in common with the other methods used for ghrelin inactivation.…”

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 ]. Ghrelin receptor antagonists, GSH-R1, demonstrated improved glucose tolerance, suppressed appetite and promoted weight loss [ 43 ], thus confi rming the potential of ghrelin blocking as a potential treatment target for obesity.…”

“…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 ]. More recently, another study concluded that an oligoclonal response is required to maintain increased energy expenditure during fasting and deprivation-induced food intake as well as to reduce overall food intake upon refeeding [ 42 ]. Ghrelin receptor antagonists have also been tested, and GSH-R1a decreased food intake and body weight and improved glucose tolerance due to increased glucose-dependent insulin secretion [ 43 ].…”