Sustained glucagon receptor antagonism in insulin-deficient high-fat-fed mice

Abstract

Discerning modification to the amino acid sequence of native glucagon can generate specific glucagon receptor (GCGR) antagonists, that include desHis1Pro4Glu9-glucagon and the acylated form desHis1Pro4Glu9(Lys12PAL)-glucagon. In the current study, we have evaluated the metabolic benefits of once daily injection of these peptide-based GCGR antagonists for 18 days in insulin-resistant high fat fed (HFF) mice with streptozotocin (STZ)-induced insulin deficiency, namely HFF-STZ mice. Administration of desHis1Pro4Glu9-glucagon moderately (P<0.05) decreased STZ-induced elevations of food intake. Body weight was not different between groups of HFF-STZ mice and both treatment interventions delayed (P<0.05) the onset of hyperglycaemia. The treatments reduced (P<0.05 - P<0.001) circulating and pancreatic glucagon, whilst desHis1Pro4Glu9(Lys12PAL)-glucagon also substantially increased (P<0.001) pancreatic insulin stores. Oral glucose tolerance was appreciably improved (P<0.05) by both antagonists, despite lack of augmentation of glucose-stimulated insulin release. Interestingly, positive effects on intraperitoneal glucose tolerance were less obvious suggesting important beneficial effects on gut function. Metabolic benefits were accompanied by decreased (P<0.05 - P<0.01) locomotor activity and increases (P<0.001) in energy expenditure and respiratory exchange ratio in both treatment groups. In addition, desHis1Pro4Glu9-glucagon increased (P<0.01 - P<0.001) O2 consumption and CO2 production. Together, these data provide further evidence that peptidic GCGR antagonists are effective treatment options for obesity-driven forms of diabetes, even when accompanied by insulin deficiency.

The Glucagon Receptor Antagonist desHis1Pro4Glu9-Glucagon(Lys12PAL) Alters Alpha-Cell Turnover and Lineage in Mice, But Does Not Cause Alpha-Cell Hyperplasia

“…This was confirmed in the current study, that employed a rodent model of insulin deficiency through multiple low-dose STZ administration and subsequent twice daily injection of the characterised and long-acting GCGR antagonist, desHis 1 Pro 4 Glu 9 -glucagon (Lys 12 PAL) (O'Harte et al, 2013), at either 25 or 100 nmol/kg. Accordingly, our observations correspond well with previous investigations of chronic peptide-based GCGR antagonism in high-fat-fed mice (McShane et al, 2014), obese diabetic (ob/ob) mice (O'Harte et al, 2014) and in mice given a single high dose of STZ (Lafferty et al, 2022). Furthermore, while previous studies documenting antihyperglycaemic efficacy of peptidic GCGR antagonists employed male mice (O'Harte et al, 2013;Lafferty et al, 2022;Franklin et al, 2022), the current work extends these findings to female mice.…”

“…Accordingly, our observations correspond well with previous investigations of chronic peptide-based GCGR antagonism in high-fat-fed mice (McShane et al, 2014), obese diabetic (ob/ob) mice (O'Harte et al, 2014) and in mice given a single high dose of STZ (Lafferty et al, 2022). Furthermore, while previous studies documenting antihyperglycaemic efficacy of peptidic GCGR antagonists employed male mice (O'Harte et al, 2013;Lafferty et al, 2022;Franklin et al, 2022), the current work extends these findings to female mice.…”

“…for 5 consecutive days) streptozotocin (STZ) injection, and for a subsequent 10 days. Twice-daily 25 nmol/kg treatment was selected based on previous studies showing positive metabolic effects of desHis 1 Pro 4 Glu 9 -glucagon (Lys 12 PAL) at this dose in normal and diabetic rodents (Franklin et al, 2014;Lafferty et al, 2022;McShane et al, 2016;O'Harte et al, 2014). The twice-daily 100 nmol/kg dose was then employed as a high dose regimen, with the current study representing the first observations with desHis 1 Pro 4 Glu 9 -glucagon (Lys 12 PAL) at this dosage.…”

“…In that regard, our previous preclinical work highlights the potential of peptide-based agents as a safe and effective method of GCGR blockade in diabetic rodents (Irwin et al, 2013;O'Harte et al, 2013;Franklin et al, 2014;McShane et al, 2014;Lafferty et al, 2022), in agreement with others (Yang et al, 2021). For example, desHis 1 Pro 4 Glu 9 -glucagon, which incorporates removal of the His 1 residue as well as Gly 4 to Pro 4 and Asp 9 to Glu 9 amino acid substitutions of native glucagon, residues known to be essential for GCGR activation (Unson et al, 1989;Ahn et al, 2001;Hruby, 1982), annuls glucagon signalling in vitro and in vivo (O'Harte et al, 2013).…”

Sustained metabolic benefits of ΔTRTX‐Ac1, a tarantula venom‐derived peptide, when administered together with exenatide in high‐fat fed mice

“…injections of STZ (4-h fast, 50 mg/kg BW, freshly dissolved in citrate buffer, pH 4.5) while still being maintained on 45% high-fat diet throughout, with peptide administration commencing 1 week after the final STZ injection when mice were 15 weeks of age. Notably, as might be expected, STZ-induced insulin deficiency resulted in some weight loss in HFF mice, 16 with HFF/STZ mice having similar BW as lean controls (31.3 ± 0.9 vs. 30.2 ± 0.3 g; respectively) at the start of the experiment.…”