Dual treatment with a fixed ratio of glucagon and insulin increases the therapeutic window of insulin in diabetic rats

Abstract

The current available insulin therapies decrease blood glucose but are associated with the risk of developing hypoglycemia. Glucagon is a counter regulatory hormone and we hypothesize that a fixed ratio of insulin and a long‐acting glucagon‐analogue can reduce the risk of hypoglycemia. To define an appropriate ratio we tested two fixed glucagon doses (3.5 and 10 nmol/kg) in combination with increasing doses of insulin in diabetic rats. We observed a plateau in blood glucose at 15.2 mmol/L with 10 nmol/kg of the glucagon‐analogue. The mechanism behind this plateau, protecting against hypoglycemia, was investigated by measuring the glucose output, cAMP production, and hormone binding in primary rat hepatocytes. While glucose output could contribute to the observed plateau in blood glucose, cAMP response or hormone binding did not explain the observation. Though such plateau indicated decreased risk of hypoglycemia a full normalization of blood glucose was still needed. Based on the data obtained with 3.5 nmol/kg of the glucagon‐analogue, a 1:23 (glucagon‐analogue:insulin) ratio was chosen and a dose‐response was performed in diabetic rats. At low doses (≤20 nmol/kg), insulin and the 1:23 ratio showed similar efficacy of lowering blood glucose. Interestingly, the insulin‐dose resulting in hypoglycemia was increased from 40 nmol/kg insulin alone to 160 nmol/kg insulin in the 1:23 ratio. Analysis of the liver glycogen content at the end of the experiment showed that the highest dose in the 1:23 ratio almost emptied the liver from glycogen. Thus, liver glycogen is essential for the protective effect of glucagon in hypoglycemia.

Glucagon lowers glycemia when β cells are active

“…We propose that the interaction of glucagon and insulin in the prandial state is responsible for the modest state of relative hyperglycemia that defines normal glucose tolerance. Although insulin has some effects to blunt glucagon-stimulated glycogenolysis in cultured hepatocytes (29)(30)(31), there is evidence that this response is maintained (32), or even amplified (33), following coadministration of the 2 hormones. In the prandial setting, the role of glucagon may be to shunt glucose absorbed from the GI tract past the liver, and promote glucose use and disposal by peripheral tissues, similar to the incretins.…”

Sustained effect of glucagon on body weight and blood glucose: Assessed by continuous glucose monitoring in diabetic rats

“…Regardless of mechanism, glucagon has been shown to both decrease food intake [ 6 – 8 ] and increase energy expenditure [ 9 , 10 ]. In addition, we have recently shown that treatment with a fixed 1:23 ratio of a long-acting glucagon analog and insulin reduced the acute risk of hypoglycemia in streptozotocin (STZ) induced diabetic rats [ 11 ]. The insulin dose causing hypoglycemia was increased from 40 nmol/kg insulin alone to 160 nmol/kg insulin in the fixed ratio.…”

Ultra-stable insulin-glucagon fusion protein exploits an endogenous hepatic switch to mitigate hypoglycemic risk

“…3B and Table S1), and decrease potency to better match insulin. The latter emulates preferred molar ratios in prior co-administration studies, which favored reduced relative glucagon activity (31).…”

“…4B; Table 1). Fortuitously, this degree of impairment would predict a favorable balance of respective glucagon-and insulin signaling activities in a FP, as extrapolated from the prior co-infusion studies (30)(31)(32) and assuming functional independence of the constituent domains (below). To provide a broader context for assessment of the selected lc-glucagon, alternative positions for the lactam-bond formation [residues 9-13, 12-16, 16-20, 20-24, or 24-28] were evaluated without achieving the desired functional properties (Table S6).…”