Dual melanocortin-4 receptor and GLP-1 receptor agonism amplifies metabolic benefits in diet-induced obese mice

Abstract

We assessed the efficacy of simultaneous agonism at the glucagon-like peptide-1 receptor (GLP-1R) and the melanocortin-4 receptor (MC4R) for the treatment of obesity and diabetes in rodents. Diet-induced obese (DIO) mice were chronically treated with either the long-acting GLP-1R agonist liraglutide, the MC4R agonist RM-493 or a combination of RM-493 and liraglutide. Co-treatment of DIO mice with RM-493 and liraglutide improves body weight loss and enhances glycemic control and cholesterol metabolism beyond what can be achieved with either mono-therapy. The superior metabolic efficacy of this combination therapy is attributed to the anorectic and glycemic actions of both drugs, along with the ability of RM-493 to increase energy expenditure. Interestingly, compared to mice treated with liraglutide alone, hypothalamic Glp-1r expression was higher in mice treated with the combination therapy after both acute and chronic treatment. Further, RM-493 enhanced hypothalamic Mc4r expression. Hence, co-dosing with MC4R and GLP-1R agonists increases expression of each receptor, indicative of minimized receptor desensitization. Together, these findings suggest potential opportunities for employing combination treatments that comprise parallel MC4R and GLP-1R agonism for the treatment of obesity and diabetes.

Keywords: Glp‐1r; Mc4r; diabetes; liraglutide; obesity.

Figure 1

Effect of liraglutide and RM-493 co-treatment on body weight and body composition in DIO mice

1. A-C Five-day treatment of DIO male mice with vehicle (white), liraglutide (10 nmol/kg) (gray), RM-493 (3.6 μmol/kg) (black), or liraglutide (10 nmol/kg) and RM-493 (3.6 μmol/kg) (checkered). Effects on (A) body weight and (B, C) body composition. Compounds were administered by daily subcutaneous injections. Data represent means ± SEM;n = 8; *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 2

Effect of liraglutide and RM-493 co-treatment on energy metabolic parameters in DIO mice

1. A-G Five-day treatment of DIO male mice with vehicle (white), liraglutide (10 nmol/kg) (gray), RM-493 (3.6 μmol/kg) (black), or liraglutide (10 nmol/kg) and RM-493 (3.6 μmol/kg) (checkered). Effects on (A, B) energy expenditure, (C) respiratory exchange ratio (RER), (D) locomotor activity, (E) cumulative food intake, (F) meal number and (G) meal size. Compounds were administered by daily subcutaneous injections. Data represent means ± SEM;n = 8; *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 3

Effect of liraglutide and RM-493 co-treatment on hypothalamic gene expression in DIO mice

1. A, B Treatment-induced changes in hypothalamic gene expression in DIO mice treated for 2 (A) or 5 (B) days with vehicle (white), liraglutide (10 nmol/kg) (gray), RM-493 (3.6 μmol/kg) (black), or liraglutide (10 nmol/kg) and RM-493 (3.6 μmol/kg) (checkered). Compounds were administered by daily subcutaneous injections, and the last injection was provided 2 h prior to tissues sampling. Data represent means ± SEM;n = 8; *P < 0.05, **P < 0.01, ^§P < 0,001, comparison between treatment and vehicle control. ^#P < 0.05, ^##P < 0.01, ^###P < 0.001, comparison to liraglutide. ⁺P < 0.05, comparison to RM-493.

Figure 4

Effect of liraglutide and RM-493 co-treatment on glucose metabolism in DIO mice

1. A-I Glucose metabolic parameters were assessed following 5 days of treatment of DIO male mice with vehicle (white), liraglutide (10 nmol/kg) (gray), RM-493 (3.6 μmol/kg) (black), or liraglutide (10 nmol/kg) and RM-493 (3.6 μmol/kg) (checkered). (A) Fasted blood glucose levels, (B, C) glucose tolerance, (D) fasted insulin levels, (E, F) glucose-induced insulin secretion, (G) HOMA-IR, (H) insulin sensitivity and (I) hepatic phosphorylation of AKT (p-AKT^Ser473) were analyzed. Compounds were administered by daily subcutaneous injections. To assess insulin-stimulated p-AKT^Ser473, insulin (n = 5) or saline (n = 3) was injected 10 min prior to liver sampling. Data represent means ± SEM;n = 8 in (A–H); *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 5

Effect of liraglutide and RM-493 co-treatment on cholesterol metabolism in DIO mice

1. A-D Cholesterol metabolic parameters were assessed following 5 days of treatment of DIO male mice with vehicle (white), liraglutide (10 nmol/kg) (gray), RM-493 (3.6 μmol/kg) (black), or liraglutide (10 nmol/kg) and RM-493 (3.6 μmol/kg) (checkered). (A) Plasma lipoprotein fractions, (B) liver cholesterol levels, (C) expression of genes implicated in hepatic cholesterol and lipoprotein uptake and (D) expression of genes implicated in cholesterol and bile acid metabolism and excretion were analyzed. Data represent means ± SEM;n = 8; *P < 0.05, **P < 0.01, ***P < 0.001.

Figure 6

Effect of long-term liraglutide and RM-493 co-treatment on obesity and glucose metabolism in DIO mice

1. A-F 22 days of treatment of DIO male mice with vehicle (white), liraglutide (10 nmol/kg) (gray), RM-493 (3.6 μmol/kg) (black), or liraglutide (10 nmol/kg) and RM-493 (3.6 μmol/kg) (checkered). Effects on (A) body weight, (B) cumulative food intake, (C, D) body composition and (E, F) glucose tolerance. Compounds were administered by daily subcutaneous injections. Data represent means ± SEM;n = 8; *P < 0.05, **P < 0.01, ***P < 0.001.