Investigating the Glucagon Receptor and Glucagon-Like Peptide 1 Receptor Activity of Oxyntomodulin-Like Analogues in Male Wistar Rats

• Main Authors: Samantha L. Price, MRes, James S. Minnion, PhD, Stephen R. Bloom, MD
• Format: Article
• Language: English
• Published: Elsevier 2015-12-01
• Series: Current Therapeutic Research
• Subjects: analogue; body weight; glucagons; oxyntomodulin
• Online Access: http://www.sciencedirect.com/science/article/pii/S0011393X15000156

Aims: To investigate the effect of Glu-3 OXM-like analogues on food intake and bodyweight in male rats. Background: Oxyntomodulin (OXM) is a natural agonist at both the glucagon receptor (GCGr) and the glucagon-like peptide 1 receptor (GLP-1r), and peripheral administration reduces food intake and increases energy expenditure in rodents and humans. Substituting the native glutamine (Gln) at amino acid position 3 of OXM for glutamate (Glu) has previously been shown to diminish GCGr activity without affecting GLP-1r activity. The effects of Glu-3 OXM analogues have not been investigated in rats. Methods: The effect of 2 Glu-3-substituted OXM-like analogues (eg, OXM14E3 and OXM15E3) on food intake and body weight was investigated in male Wistar rats during 6 days of daily subcutaneous (SC) administration. The effects of Glu-3 substitution on analogue binding and activity at the rat GCGr and rat GLP-1 receptor were investigated in vitro using Chinese hamster ovary or Chinese hamster lung cells. Results: We report the novel finding that 2 5-nmol/kg Glu-3 OXM-like analogues (OXM14E3 and OXM15E3) significantly increased rat body weight by up to 4% compared with the equivalent non-Glu-3 analogues (OXM14 and OXM15), without affecting food intake. The effect of OXM15E3 on body weight was dose–dependent. Glu-3 analogues, including Glu-3 OXM, decreased glucagon-mediated cyclic adenosine monophosphate accumulation in Chinese hamster ovary cells expressing the rat GCGr, suggesting they may be acting as antagonists. Conclusions: The results indicate Glu-3 OXM-like analogues might not be suitable tools to investigate the mechanism of OXM analogue action in a rat model because they significantly increase body weight independent of food intake. Glu-3 OXM analogues are partial agonists at the rat GCGr and may also act as antagonists, possibly resulting in the observed increase in body weight.