Improved Postprandial Glucose Control Using the InsuPad Device in Insulin-Treated Type 2 Diabetes: Injection Site Warming to Improve Glycemic Control

Effect of Injection Site Cooling and Warming on Insulin Glargine Pharmacokinetics and Pharmacodynamics

BACKGROUND

In type 1 diabetes (T1D), closed-loop systems provide excellent overnight fasting blood glucose control by adjusting the insulin infusion rate based on corresponding changes in sensor glucose levels. In patients on multiple daily insulin (MDI) injections, such control in overnight glucose levels has not been possible due to the inability to alter the absorption rate of long-acting insulin after injection. In this study, we tested the hypothesis that increases/decreases of fasting glucose levels could be achieved by cooling/warming the skin around the injection site, which would result in lower/higher Glargine absorption rates from its subcutaneous depot.

METHODS

Fourteen subjects with T1D (4 females; age 39.6 ± 16.7 years, HbA1c 7.8 ± 1.1%, BMI 25.4 ± 2.8 kg/m²) on MDI therapy underwent fasting pharmacokinetic and pharmacodynamic studies that started at ~8 am and lasted 240 min on 3 separate days in random order: a control day without warming or cooling of the injection site and two experimental days, one day with injection site warming and the other with cooling.

RESULTS

Cooling the skin around the glargine injection site reduced insulin concentrations by >40% (P < .01 versus the warming study, P = .21 versus the control study), accompanied by a 55 mg/dL increase in serum glucose (P < .01 versus the control study). Conversely, skin warming prevented the fall in serum insulin (P = .2 versus the control study; P < .01 versus the cooling study), resulting in a 40 mg/dL reduction in serum glucose (P < .001 versus the cooling study, P = .11 versus the control study).

CONCLUSIONS

This proof of concept study has shown that cooling and warming the skin around the injection site provides a means to decrease and increase the rate of absorption and action of insulin glargine from its subcutaneous depot.

Modeling the acute effects of exercise on insulin kinetics in type 1 diabetes

Our objective is to develop a physiology-based model of insulin kinetics to understand how exercise alters insulin concentrations in those with type 1 diabetes (T1D). We reveal the relationship between the insulin absorption rate ([Formula: see text]) from subcutaneous tissue, the insulin delivery rate ([Formula: see text]) to skeletal muscle, and two physiological parameters that characterize the tissue: the perfusion rate (Q) and the capillary permeability surface area (PS), both of which increase during exercise because of capillary recruitment. We compare model predictions to experimental observations from two pump-wearing T1D cohorts [resting subjects ([Formula: see text]) and exercising subjects ([Formula: see text])] who were each given a mixed-meal tolerance test and a bolus of insulin. Using independently measured values of Q and PS from literature, the model predicts that during exercise insulin concentration increases by 30% in plasma and by 60% in skeletal muscle. Predictions reasonably agree with experimental observations from the two cohorts, without the need for parameter estimation by curve fitting. The insulin kinetics model suggests that the increase in surface area associated with exercise-induced capillary recruitment significantly increases [Formula: see text] and [Formula: see text], which explains why insulin concentrations in plasma and skeletal muscle increase during exercise, ultimately enhancing insulin-dependent glucose uptake. Preventing hypoglycemia is of paramount importance in determining the proper insulin dose during exercise. The presented model provides mechanistic insight into how exercise affects insulin kinetics, which could be useful in guiding the design of decision support systems and artificial pancreas control algorithms.

Towards a Physiological Prandial Insulin Profile: Enhancement of Subcutaneously Injected Prandial Insulin Using Local Warming Devices

The need to develop an insulin delivery system that can closely mimic physiologically induced changes in prandial insulin release has been a major research target since the discovery of insulin. The challenges facing existing insulin delivery systems, related to relatively slow pharmacokinetics and pharmacodynamics, have been further highlighted by rapid advances in diabetes technology and progress in artificial pancreas research. Despite the growing interest in alternative routes of insulin administration, the subcutaneous route remains-at least for now-the preferred route for insulin administration. In this article, we review efforts aimed at developing subcutaneously injected ultrafast-acting insulin and measures aimed at enhancing insulin absorption, focusing on local warming devices.