Antagonism of ghrelin receptor reduces food intake and body weight gain in mice

Abstract

Background and aims: Ghrelin, an endogenous ligand for growth hormone secretagogue receptor (GHS-R), is an appetite stimulatory signal from the stomach with structural resemblance to motilin. We examined the effects of the gastric peptide ghrelin and GHS-R antagonists on energy balance and glycaemic control in mice.

Materials and methods: Body weight, fat mass, glucose, insulin, and gene expression of leptin, adiponectin, and resistin in white adipose tissue (WAT) were measured after repeated administrations of ghrelin under a high fat diet. Gastric ghrelin gene expression was assessed by northern blot analysis. Energy intake and gastric emptying were measured after administration of GHS-R antagonists. Repeated administration of GHS-R antagonist was continued for six days in ob/ob obese mice.

Results: Ghrelin induced remarkable adiposity and worsened glycaemic control under a high fat diet. Pair feeding inhibited this effect. Ghrelin elevated leptin mRNA expression and reduced resistin mRNA expression. Gastric ghrelin mRNA expression during fasting was increased by a high fat diet. GHS-R antagonists decreased energy intake in lean mice, in mice with diet induced obesity, and in ob/ob obese mice; it also reduced the rate of gastric emptying. Repeated administration of GHS-R antagonist decreased body weight gain and improved glycaemic control in ob/ob obese mice.

Conclusions: Ghrelin appears to be closely related to excess weight gain, adiposity, and insulin resistance, particularly under a high fat diet and in the dynamic stage. Gastric peptide ghrelin and GHS-R may be promising therapeutic targets not only for anorexia-cachexia but also for obesity and type 2 diabetes, which are becoming increasingly prevalent worldwide.

Figure 1

(A) Chronic effects of ghrelin administered intraperitoneally (3 nmol/mouse every 12 hours for five days) on resistin gene expression in the epididymal fat mass under a high fat (HF) diet, as assessed by northern blot analysis, expressed as a percentage of physiological saline treated controls under a standard (LF) diet. Results are expressed as mean (SEM): n indicates the number of mice used, *p<0.05 between saline treated mice fed a high fat diet and ghrelin treated mice fed a high fat diet. (B) Stimulatory effects of a high fat diet for two weeks on ghrelin gene expression in the stomach of food deprived mice, as assessed by northern blot analysis, expressed as a percentage of standard diet fed controls. (Top) A representative northern blot analysis showing gastric ghrelin mRNA during fasting after a high fat diet for two weeks; *p<0.05 compared with the control group by Bonferroni’s t test. G3PDH, glyceraldehyde 3-phosphate dehydrogenase.

Figure 2

(A) Effects of intraperitoneally administered [D-Lys-3]-GHRP-6 (2–200 nmol/mouse) on cumulative food intake in food deprived lean mice: *p<0.05, **p<0.01 compared with the control group by Bonferroni’s t test. (B) Effects of intracerebroventricularly administered [D-Lys-3]-GHRP-6 (0.2–20 nmol/mouse) on cumulative food intake in food deprived lean mice. ACSF, artificial cerebrospinal fluid. (C) Antagonistic effects of [D-Lys-3]-GHRP-6 administered intracerebroventricularly (20 nmol/mouse) on feeding induced by intraperitoneal injection of ghrelin (3 nmol/mouse) in non-food deprived lean mice. (D) Inhibitory effects of intraperitoneally administered [D-Lys- 3]-GHRP-6 (20–200 nmol/mouse) on the gastric emptying rate one and two hours after injection in lean mice. (E) Effects of intraperitoneally administered [D-Arg-1, D-Phe-5, D- Trp-7, 9, Leu-11] substance P (10–100 nmol/mouse) on cumulative food intake in food deprived lean mice. (F) Effects of intraperitoneally administered [D-Lys-3]-GHRP-6 (20–200 nmol/mouse) on cumulative food intake in mice with diet induced obesity who received a high fat diet for two weeks.

Figure 3

(A) Acute effects of intraperitoneally administered [D-Lys-3]-GHRP-6 (200 nmol/mouse) on cumulative food intake in food deprived ob/ob obese mice: *p<0.05, **p<0.01 compared with physiological saline treated controls. (B) Chronic effects of [D-Lys- 3]-GHRP-6 administered intraperitoneally (20–200 nmol/mouse every 12 hours for six days) on body weight gain in non-food deprived ob/ob obese mice.