The counterregulatory response to hypoglycaemia in the pig

Combining Celiac and Hepatic Vagus Nerve Neuromodulation Reverses Glucose Intolerance and Improves Glycemic Control in Pre- and Overt-Type 2 Diabetes Mellitus

Neurological disorders and type 2 diabetes mellitus (T2DM) are deeply intertwined. For example, autonomic neuropathy contributes to the development of T2DM and continued unmanaged T2DM causes further progression of nerve damage. Increasing glycemic control has been shown to prevent the onset and progression of diabetic autonomic neuropathies. Neuromodulation consisting of combined stimulation of celiac vagal fibers innervating the pancreas with concurrent electrical blockade of neuronal hepatic vagal fibers innervating the liver has been shown to increase glycemic control in animal models of T2DM. The present study demonstrated that the neuromodulation reversed glucose intolerance in alloxan-treated swine in both pre- and overt stages of T2DM. This was demonstrated by improved performance on oral glucose tolerance tests (OGTTs), as assessed by area under the curve (AUC). In prediabetic swine (fasting plasma glucose (FPG) range: 101-119 mg/dL) the median AUC decreased from 31.9 AUs (IQR = 28.6, 35.5) to 15.9 AUs (IQR = 15.1, 18.3) p = 0.004. In diabetic swine (FPG range: 133-207 mg/dL) the median AUC decreased from 54.2 AUs (IQR = 41.5, 56.6) to 16.0 AUs (IQR = 15.4, 21.5) p = 0.003. This neuromodulation technique may offer a new treatment for T2DM and reverse glycemic dysregulation at multiple states of T2DM involved in diabetic neuropathy including at its development and during progression.

Hyperpolarized [1-13 C]pyruvate combined with the hyperinsulinaemic euglycaemic and hypoglycaemic clamp technique in skeletal muscle in a large animal model

New Findings

What is the central question of this study?

Is it possible to combine the hyperpolarized magnetic resonance technique and the hyperinsulinaemic clamp method in order to evaluate skeletal muscle metabolism in a large animal model?

What is the main finding and its importance?

The logistical set‐up is possible, and we found substantial increments in glucose infusion rates representing skeletal muscle glucose uptake but no differences in ratios of [1‐¹³C]lactate to [1‐¹³C]pyruvate, [1‐¹³C]alanine to [1‐¹³C]pyruvate, and ¹³C‐bicarbonate to [1‐¹³C]pyruvate, implying that the hyperpolarization technique might not be optimal for detecting effects of insulin in skeletal muscle of anaesthetized animals, which is of significance for future studies.

Abstract

In skeletal muscle, glucose metabolism is tightly regulated by the reciprocal relationship between insulin and adrenaline, with pyruvate being at the intersection of both pathways. Hyperpolarized magnetic resonance (hMR) is a new approach to gain insights into these pathways, and human trials involving hMR and skeletal muscle metabolism are imminent. We aimed to combine the hyperinsulinaemic clamp technique and hMR in a large animal model resembling human physiology. Fifteen anaesthetized pigs were randomized to saline (control group), hyperinsulinaemic euglycaemic clamp technique (HE group) or hyperinsulinaemic hypoglycaemic clamp technique (HH group). Skeletal muscle metabolism was evaluated by hyperpolarized [1‐¹³C]pyruvate injection and hMR at baseline and after intervention. The glucose infusion rate per kilogram increased by a statistically significant amount in the HE and HH groups (P < 0.001). Hyperpolarized magnetic resonance showed no statistically significant changes in metabolite ratios: [1‐¹³C]lactate to [1‐¹³C]pyruvate in the HH group versus control group (P = 0.19); and ¹³C‐bicarbonate to [1‐¹³C]pyruvate ratio in the HE group versus the control group (P = 0.12). We found evidence of profound increments in glucose infusion rates representing skeletal muscle glucose uptake, but interestingly, no signs of significant changes in aerobic and anaerobic metabolism using hMR. These results imply that hyperpolarized [1‐¹³C]pyruvate might not be optimally suited to detect effects of insulin in anaesthetized resting skeletal muscle, which is of significance for future studies.

Hyperinsulinaemic hypoglycaemia in non-anaesthetized Göttingen minipigs induces a counter-regulatory endocrine response and electrocardiographic changes

The potentially fatal cardiovascular effects of hypoglycaemia are not well understood and large animal models of the counter-regulatory responses and cardiovascular consequences of insulin-induced hypoglycaemia are needed to understand the mechanisms in humans. The aim of this study was to develop a human-like minipig model of hypoglycaemia including healthy and diabetic pigs to investigate endocrine, electrocardiographic and platelet effects. Hypoglycaemia was induced using a hyperinsulinaemic, hypoglycaemic clamp and an insulin bolus protocol. Plasma glucose, glucagon, C-peptide, insulin, epinephrine and platelet aggregation responses were measured before, during and after hypoglycaemia. Continuous electrocardiographic recordings were obtained. Hypoglycaemia at a plasma glucose concentration of 0.8–1.0 mM in the clamp induced 25-fold increase in epinephrine and sixfold and threefold increase in glucagon for healthy and diabetic pigs, respectively. The hypoglycaemic clamp induced QTc-interval prolongation and increase in cardiac arrhythmias. In the bolus approach, the non-diabetic group reached plasma glucose target of 1.5 mM and QTc-interval was prolonged after insulin injection, but before glucose nadir. The diabetic group did not reach hypoglycaemic target, but still demonstrated QTc-interval prolongation. These results demonstrate effects of hyperinsulinaemic hypoglycaemia closely resembling human physiology, indicating the minipig as a translational animal model of counter-regulatory endocrine and myocardial effects of hypoglycaemia.

Food intake rather than blood glucose levels affects the pharmacokinetic profile of insulin aspart in pigs

In humans, food intake and glucose infusion have been reported to increase subcutaneous blood flow. Since local blood flow influences the rate of insulin absorption from the subcutaneous tissue, we hypothesised that an increase in blood glucose levels-occurring as the result of glucose infusion or food intake-could modulate the pharmacokinetic properties of subcutaneously administered insulin. The pharmacokinetic profile of insulin aspart was assessed in 29 domestic pigs that were examined in a fed and fasted state or included in hyperinsulinaemic clamp studies of 4 vs. 10 mmol/L glucose prior to subcutaneous (30 nmol) or intravenous (0.1 nmol/kg) insulin administration. Results showed that food intake compared to fasting accelerated absorption and decreased clearance of insulin aspart (P < 0.05). Furthermore, higher c-peptide but also glucagon levels were observed in fed compared to fasted pigs (P < 0.05). The pharmacokinetic profile of insulin aspart did not differ between pigs clamped at 4 vs. 10 mmol/L glucose. Hence, food intake rather than blood glucose levels within normal range modulates the pharmacokinetic properties of insulin aspart upon subcutaneous and intravenous administration in pigs.