Reduced insulin clearance in normal subjects due to extreme hyperinsulinemia

Insulin Clearance in Obesity and Type 2 Diabetes

Plasma insulin clearance is an important determinant of plasma insulin concentration. In this review, we provide an overview of the factors that regulate insulin removal from plasma and discuss the interrelationships among plasma insulin clearance, excess adiposity, insulin sensitivity, and type 2 diabetes (T2D). We conclude with the perspective that the commonly observed lower insulin clearance rate in people with obesity, compared with lean people, is not a compensatory response to insulin resistance but occurs because insulin sensitivity and insulin clearance are mechanistically, directly linked. Furthermore, insulin clearance decreases postprandially because of the marked increase in insulin delivery to tissues that clear insulin. The commonly observed high postprandial insulin clearance in people with obesity and T2D likely results from the relatively low insulin secretion rate, not an impaired adaptation of tissues that clear insulin.

Endurance training inhibits insulin clearance and IDE expression in Swiss mice

INTRODUCTION

Endurance training improves peripheral insulin sensitivity in the liver and the skeletal muscle, but the mechanism for this effect is poorly understood. Recently, it was proposed that insulin clearance plays a major role in both glucose homeostasis and insulin sensitivity. Therefore, our goal was to determine the mechanism by which endurance training improves insulin sensitivity and how it regulates insulin clearance in mice.

METHODS

Mice were treadmill-trained for 4 weeks at 70-80% of maximal oxygen consumption (VO2 max) for 60 min, 5 days a week. The glucose tolerance and the insulin resistance were determined using an IPGTT and an IPITT, respectively, and the insulin decay rate was calculated from the insulin clearance. Protein expression and phosphorylation in the liver and the skeletal muscle were ascertained by Western blot.

RESULTS

Trained mice exhibited an increased VO2 max, time to exhaustion, glucose tolerance and insulin sensitivity. They had smaller fat pads and lower plasma concentrations of insulin and glucose. Endurance training inhibited insulin clearance and reduced expression of IDE in the liver, while also inhibiting insulin secretion by pancreatic islets. There was increased phosphorylation of both the canonical (IR-AKT) and the non-canonical (CaMKII-AMPK-ACC) insulin pathways in the liver of trained mice, whereas only the CaMKII-AMPK pathway was increased in the skeletal muscle.

CONCLUSION

Endurance training improved glucose homeostasis not only by increasing peripheral insulin sensitivity but also by decreasing insulin clearance and reducing IDE expression in the liver.

Ciliary neurotrophic factor (CNTF) protects non-obese Swiss mice against type 2 diabetes by increasing beta cell mass and reducing insulin clearance

AIMS/HYPOTHESIS

Ciliary neurotrophic factor (CNTF) improves metabolic variables of obese animals with characteristics of type 2 diabetes, mainly by reducing insulin resistance. We evaluated whether CNTF was able to improve other metabolic variables in mouse models of type 2 diabetes, such as beta cell mass and insulin clearance, and whether CNTF has any effect on non-obese mice with characteristics of type 2 diabetes.

METHODS

Neonatal mice were treated with 0.1 mg/kg CNTF or citrate buffer via intraperitoneal injections, before injection of 250 mg/kg alloxan. HEPG2 cells were cultured for 3 days in the presence of citrate buffer, 1 nmol/l CNTF or 50 mmol/l alloxan or a combination of CNTF and alloxan. Twenty-one days after treatment, we determined body weight, epididymal fat weight, blood glucose, plasma insulin, NEFA, glucose tolerance, insulin resistance, insulin clearance and beta cell mass. Finally, we assessed insulin receptor and protein kinase B phosphorylation in peripheral organs, as well as insulin-degrading enzyme (IDE) protein production and alternative splicing in the liver and HEPG2 cells.

RESULTS

CNTF improved insulin sensitivity and beta cell mass, while reducing glucose-stimulated insulin secretion and insulin clearance in Swiss mice, improving glucose handling in a non-obese type 2 diabetes model. This effect was associated with lower IDE production and activity in liver cells. All these effects were observed even at 21 days after CNTF treatment.

CONCLUSIONS/INTERPRETATION

CNTF protection against type 2 diabetes is partially independent of the anti-obesity actions of CNTF, requiring a reduction in insulin clearance and increased beta cell mass, besides increased insulin sensitivity. Furthermore, knowledge of the long-term effects of CNTF expands its pharmacological relevance.

Insulin therapy in diabetes mellitus: how can the currently available injectable insulins be most prudently and efficaciously utilised?

The era of animal source insulins has passed and human recombinant DNA insulins are gradually being replaced because of the superior efficacy of insulin analogues. Analogue insulins are available in both rapid- and long-acting preparations. Currently available rapid-acting insulins are lispro, aspart and glulisine, and the currently available long-acting analogue basal insulins are detemir and glargine. The rapid-acting insulin analogues are also available in combination with protamine in fixed-dose pre-mixed insulins to provide a more sustained action. The chemical structure, subcutaneous behaviour, time of onset, maximal effect and duration of action of both analogue and human insulins, and how these actions can be best utilised in the diabetic patient are discussed in this review. In addition, strategies where efficacy of the available analogue insulins can be maximally utilised in both type 1 and type 2 diabetes mellitus are described. Maximal utilisation of analogue insulins will result not only in better glycaemic control, but will also minimise the frequency and severity of hypoglycaemic episodes. In addition, maximisation of glycaemic control will result in prevention, delay of onset or amelioration of both the microvascular and perhaps the macrovascular complications of diabetes.

A novel mechanism of glipizide sulfonylurea action: decreased metabolic clearance rate of insulin

To examine whether sulfonylureas inhibit the metabolic clearance rate (MCR) of insulin, 19 healthy young subjects participated in two experiments. In the first protocol (n = 10), a 3-h oral glucose load was performed with and without 2 mg of glipizide given 30 min before glucose ingestion. The total insulin response was 60% greater with than without glipizide (5.9 +/- 0.6 vs 3.7 +/- 0.5 microU/ml; P < 0.001). However, the total C-peptide responses were virtually identical (4.7 +/- 0.5 vs 4.8 +/- 0.4 nmol/l) in both studies. In the second protocol (n = 9), the MCR of insulin was measured during 4-h euglycemic insulin clamps performed with and without glipizide. In the study with glipizide, the subjects ingested 5 mg of glipizide at 120 min. The steady-state plasma insulin concentration during the 4th h, i.e., 1-2 h after glipizide ingestion, was significantly higher than during the 2nd h, i.e., before glipizide ingestion (99 +/- 22 vs 78 +/- 17 microU/ml; P < 0.01). In addition, glucose uptake during the 4th h was greater (8.0 +/- 1.6 vs 6.4 +/- 1.5 mg/kg.min) and the MCR of insulin was reduced (503 +/- 126 vs 621 +/- 176 ml/m2.min; P < 0.01). We conclude that glipizide augments plasma insulin levels both by enhancing its secretion and by decreasing the MCR of insulin.

Does glibenclamide influence the clearance of insulin and glucose uptake in patients with type 2 diabetes mellitus?

Sulphonylureas have been proposed to decrease the clearance of insulin based on the finding that they increase peripheral insulin concentrations more than C-peptide concentrations. However, direct evidence for such an effect has so far been lacking. The aim of this study was to investigate whether glibenclamide affects clearance of insulin in Type 2 diabetic patients. Nine patients with Type-2 diabetes participated in the study. Insulin clearance and glucose metabolism was assessed with a 240 min euglycaemic insulin clamp in combination with infusion of somatostatin (400 micrograms h-1) to completely suppress endogenous insulin secretion. Either saline or glibenclamide was infused throughout the clamp in random order. During both the glibenclamide and the saline protocol the C-peptide level declined to < 0.07 nmol l-1 within 150 min, indicating that insulin secretion was completely suppressed. However, peripheral clamp insulin concentrations remained similar during both saline and glibenclamide protocols (3374 +/- 258 vs. 3350 +/- 265 pmol l-1 x 240 min, p = NS). There was no significant difference in the metabolic clearance rate of insulin during the glibenclamide compared to the saline experiment neither during the first 120 min (796 +/- 36 vs. 757 +/- 34 ml m-2min-1) nor during the last 2 h of the clamp (780 +/- 43 vs. 724 +/- 35 ml m-2min-1). Total glucose metabolism during the first two (14 +/- 2 vs. 15 +/- 2 mumol kg-1 min-1) and the last 2 h of the clamp was similar both during saline and glibenclamide infusions (27 +/- 4 vs. 28 +/- 4 mumol kg-1min-1).(ABSTRACT TRUNCATED AT 250 WORDS)