The Chimeric Peptide (GEP44) Reduces Body Weight and Both Energy Intake and Energy Expenditure in Diet-Induced Obese Rats

Abstract

We recently reported that a chimeric peptide (GEP44) targeting the glucagon-like peptide-1 receptor (GLP-1R) and neuropeptide Y1- and Y2- receptors decreased body weight (BW), energy intake, and core temperature in diet-induced obese (DIO) male and female mice. In the current study, we tested the hypothesis that the strong reduction in body weight in response to GEP44 is partially related to the stimulation of energy expenditure (EE). To test this, rats were maintained on a high fat diet (HFD) for at least 4 months to elicit DIO prior to undergoing a sequential 2-day vehicle period, 2-day GEP44 (50 nmol/kg) period, and a minimum 2-day washout period, and detailed measures of energy homeostasis. GEP44 (50 nmol/kg) reduced EE (indirect calorimetry), respiratory exchange ratio (RER), core temperature, activity, energy intake, and BW in male and female rats. As in our previous study in mice, GEP44 reduced BW in male and female HFD-fed rats by 3.8 ± 0.2% and 2.3 ± 0.4%, respectively. These effects appear to be mediated by increased lipid oxidation and reductions in energy intake as GEP44 reduced RER and cumulative energy intake in male and female HFD-fed rats. The strong reduction in body weight in response to GEP44 is related to a robust reduction in energy intake, but not to the stimulation of EE. The paradoxical finding that GEP44 reduced EE might be secondary to a reduction in diet-induced thermogenesis or might indicate an important mechanism to limit the overall efficacy of GEP44 to prevent further weight loss.

Keywords: GLP-1; PYY; iBAT; iWAT; multi-agonist; obesity.

Figure 1

(A–D) Effects of the chimeric peptide, GEP44, or selective GLP-1R agonist, exendin-4, on body weight and energy intake in male and female HFD-fed rats. Male (n = 19/group) and female (n = 22/group) rats were maintained on HFD (60% kcal from fat) for at least 4 months prior to being implanted with PDT-4000 telemetry devices into the abdominal cavity. During this study, animals remained in their home cages and were maintained on a 1-h fast. Animals received SC injections of vehicle (sterile saline/water) followed by GEP44 (50 nmol/kg; 1 mL/kg injection volume) or exendin-4 within 15 min prior to the start of the dark cycle in a counterbalanced design. (A) Effect of GEP44 on change in body weight in male and female HFD-fed rats; (B) Effect of exendin-4 on change in body weight in male and female HFD-fed rats; (C) Effect of GEP44 on energy intake in male and female HFD-fed rats; (D) Effect of exendin-4 on energy intake in male and female HFD-fed rats. The change in body weight and cumulative energy intake reflects the total change in both measurements over the sequential 2-day vehicle and 2-day drug treatment period. Data are expressed as mean ± SEM. * p < 0.05 GEP44 or exendin-4 vs. vehicle.

Figure 2

(A–D) Effects of the chimeric peptide, GEP44, or selective GLP-1R agonist, exendin-4, on core temperature in male and female HFD-fed rats. Male (n = 15/group) and female (n = 7/group) rats were maintained on HFD (60% kcal from fat) for at least 4 months prior to being implanted with PDT-4000 telemetry devices into the abdominal cavity. During this study, animals remained in their home cages and were maintained on a 1-h fast. Animals received SC injections of vehicle (sterile saline/water) followed by GEP44 (50 nmol/kg; 1 mL/kg injection volume) or exendin-4 within 15 min prior to the start of the dark cycle in a counterbalanced design. (A) Effect of GEP44 on 6-h core temperature in male and female HFD-fed rats. (B) Effect of GEP44 on daily (23 h) core temperature in male and female HFD-fed rats. (C) Effect of exendin-4 on 6-h core temperature in male and female HFD-fed rats. (D) Effect of exendin-4 on daily (23 h) core temperature in male and female HFD-fed rats. Core temperature was averaged at 6-h and 23-h post-treatment periods over the 2-day vehicle and 2-day drug treatment period. Data are expressed as mean ± SEM. * p < 0.05 GEP44 or exendin-4 vs. vehicle.

Figure 3

(A–D) Effects of the chimeric peptide, GEP44, or selective GLP-1R agonist, exendin-4, on ambulatory activity in male and female HFD-fed rats. Male (n = 16/group) and female (n = 16/group) rats were maintained on HFD (60% kcal from fat) for at least 4 months prior to being implanted with PDT-4000 telemetry devices into the abdominal cavity. During this study, animals remained in their home cages and were maintained on a 1-h fast. Animals received SC injections of vehicle (sterile saline/water) followed by GEP44 (50 nmol/kg; 1 mL/kg injection volume) or exendin-4 within 15 min prior to the start of the dark cycle in a counterbalanced design. (A/B) Effect of GEP44 on ambulatory activity during the light and dark cycle periods in (A) male and (B) female HFD-fed rats. (C/D) Effect of exendin-4 on ambulatory activity during the light and dark cycle periods in (C) male and (D) female HFD-fed rats. Ambulatory activity was averaged over the light (11 h) and dark (12 h) cycles across the 2-day vehicle and 2-day drug treatment periods. Data are expressed as mean ± SEM. * p < 0.05 GEP44 or exendin-4 vs. vehicle.

Figure 4

(A–D) Effects of the chimeric peptide, GEP44, or selective GLP-1R agonist, exendin-4, on EE (indirect calorimetry) in male and female HFD-fed rats. Male (n = 16/group) and female (n = 16/group) rats were maintained on HFD (60% kcal from fat) for at least 4 months prior to being implanted with PDT-4000 telemetry devices into the abdominal cavity. Animals were transferred to individual metabolic cages that were part of the CLAMS-HC indirect calorimetry system prior to receiving SC injections of vehicle (sterile saline/water) followed by GEP44 (50 nmol/kg; 1 mL/kg injection volume) or exendin-4 within 1.5 h prior to the start of the dark cycle in a counterbalanced design. (A/B) Effect of GEP44 on EE during the light and dark cycle periods in (A) male and (B) female HFD-fed rats. (C/D) Effect of exendin-4 on EE during the light and dark cycle periods in (C) male and (D) female HFD-fed rats. EE was averaged over the light (11 h) and dark (12 h) cycles across the 2-day vehicle and 2-day drug treatment periods. Data are expressed as mean ± SEM. * p < 0.05 GEP44 or exendin-4 vs. vehicle.

Figure 5

(A–D) Effects of the chimeric peptide, GEP44, or selective GLP-1R agonist, exendin-4, on RER (indirect calorimetry) in male and female HFD-fed rats. Male (n = 16/group) and female (n = 16/group) rats were maintained on HFD (60% kcal from fat) for at least 4 months prior to being implanted with PDT-4000 telemetry devices into the abdominal cavity. Animals were transferred to individual metabolic cages that were part of the CLAMS-HC indirect calorimetry system prior to receiving SC injections of vehicle (sterile saline/water) followed by GEP44 (50 nmol/kg; 1 mL/kg injection volume) or exendin-4 within 1.5 h prior to the start of the dark cycle in a counterbalanced design. (A/B) Effect of GEP44 on RER during the light and dark cycle periods in (A) male and (B) female HFD-fed rats. (C/D) Effect of exendin-4 on RER during the light and dark cycle periods in (C) male and (D) female HFD-fed rats. RER was averaged over the light (11 h) and dark (12 h) cycles across the 2-day vehicle and 2-day drug treatment periods. Data are expressed as mean ± SEM. * p < 0.05 GEP44 or exendin-4 vs. vehicle.