Introduction: The effect of dual GLP-1 and glucagon analogues on insulin secretion remains unclear. Here, we investigated the effect of novel GLP-1 / glucagon receptor (GLP-1R/GCGR) co-agonists on beta cell lines, finding augmented insulin release compared to reference agonist Exendin-4. This effect was related to signalling bias at the GLP-1R.
Methods: GLP-1R/GCGR co-agonists were designed, based on the sequence of oxyntomodulin. INS-1 832/3 beta cells and MIN6B1 beta cells were used to perform 24 hour insulin secretion assays. Ligand-directed signal bias was determined from cyclic adenosine monophosphate (cAMP) and β arrestin-1/2 responses measured by enzyme fragment complementation in CHO-K1 cells expressing GLP-1R or GCGR.
Results: Several co-agonists show enhanced maximal insulin release compared to Exendin-4 (representative co-agonist Peptide A vs. Exendin-4 fold insulin release, normalized to 11mM glucose: INS-1 823/3 cells 4.45 ± 0.24 vs. 2.55 ± 0.22, p = 0.0002; MIN6B1 cells 2.28 ± 0.22 vs. 1.57 ± 0.08, p = 0.002). At the GLP-1 receptor, co-agonists were biased towards cAMP generation, compared to the β arrestin-2 pathway (delta log (τ/KA) -0.70 ± 0.11 [Peptide A], vs. 0.29 ± 0.11 [Exendin-4], p= <0.0001). At the GCGR, no significant change in bias was seen relative to native glucagon.
Conclusion: GLP-1R/GCGR co-agonists show enhanced insulin release in vitro compared to exendin-4. As canonical effects of β arrestin recruitment include desensitisation and loss of cell surface receptors via endocytosis, the observed signal bias with these peptides may be linked to their insulinotropic effect. These findings may inform the design of more potent insulinotropic compounds for therapeutic use in type 2 diabetes.
G. Farooq: None. B. Jones: None. J.S. Minnion: None. S.R. Bloom: None.