Glucagon and energy expenditure; Revisiting amino acid metabolism and implications for weight loss therapy

Glucagon receptor (GCGR)-targeted multi-agonists are being developed for the treatment of obesity and metabolic disease. GCGR activity is utilised for its favourable weight loss and metabolic properties, including increased energy expenditure (EE) and hepatic lipid metabolism. GLP1R and GIPR activities are increasingly present in a multi-agonist strategy. Due to the compound effect of increased satiety, reduced food intake and increased energy expenditure, the striking weight loss effects of these multi-agonists has been demonstrated in pre-clinical models of obesity. The precise contribution and mechanism of GCGR activity to enhanced energy expenditure and weight loss in both rodents and humans is not fully understood. In this review, our understanding of glucagon-mediated EE is explored, and an amino acid-centric paradigm contributing to this phenomenon is presented. The current progress of GCGR-targeted multi-agonists in development is also highlighted with a focus on the implications of glucagon-stimulated hypoaminoacidemia.

Unusual presentation of phaeochromocytoma

A 44-year-old woman, with a background of heart, lung and renal transplantation secondary to cystic fibrosis and type 1 diabetes, presented with tachycardia, hyperglycaemia, nausea and vomiting. She was initially managed for diabetic ketoacidosis with severe dehydration. However, persistent episodic hypertension and tachycardia led the investigating team to identify significantly raised urinary metanephrines and a left-sided adrenal mass; Iodine-123-meta-iodobenzylguanidine single photon emission computer tomography scan (MIBG SPECT/CT) showed avid uptake of tracer, confirming a left-sided phaeochromocytoma. She was started on medical management and is awaiting an elective laparoscopic procedure. This case describes the presentation of a unilateral phaeochromocytoma as ketoacidosis in a patient with type 1 diabetes with no other apparent precipitant. This highlights the metabolic counter-regulatory effect of excess catecholamines in addition to the inotropic/chronotropic effects that are associated with this adrenal tumour. Recognition of atypical signs and symptoms may point towards an atypical precipitant of diabetic ketoacidosis-a medical emergency presenting to front-line clinicians.

Effect of high-fat diet on glucose homeostasis and gene expression in glucokinase knockout mice

AIM

We have generated a heterozygous glucokinase knockout mouse (gk(del/wt)), upon which we investigated the effect of high-fat diet (HFD) with respect to metabolic control and both hepatic and beta-cell gene expression. We also investigated the in vitro efficacy of a glucokinase activator (GKA) on glucose-stimulated insulin secretion (GSIS) in gk(del/wt)mouse islets.

METHODS

Male gk(del/wt)and gk(wt/wt)mice were grouped (n = 8-10) at 10 weeks of age and fed HFD or chow diet (CD) for 10 weeks. Multiple parameters including blood glucose, plasma insulin and glucose tolerance were assessed. Further animal groups were used for in vitro GSIS and islet and liver gene expression analysis.

RESULTS AND CONCLUSIONS

gk(del/wt)mice showed early-onset persistent hyperglycaemia, raised glycated haemoglobin levels, impaired GSIS and glucose tolerance but no change in plasma cholesterol, non-esterified fatty acids or triglyceride levels. After HFD feeding, insulin levels of gk(del/wt)mice were less than half that of gk(wt/wt)mice, although they were equivalent to gk(wt/wt)mice on CD. While gk(wt/wt)mice maintained moderate hyperglycaemia, gk(del/wt)mice became overtly diabetic, with worsened glucose tolerance. A GKA (GKA50) increased GSIS, at 10 mM glucose, in gk(del/wt)mice to an extent at least as great as that seen in gk(wt/wt)mice on both CD and HFD. gk(del/wt)mice showed only a small number of changes in gene expression compared with gk(wt/wt)mice. We propose the high fat-fed gk(del/wt)mouse as a model of type 2 diabetes and report retained efficacy of a GKA on in vitro GSIS.