Continuous Monitoring of Biomarkers in Diabetic Rat Models under Stress Conditions
Purpose: Diabetes is a chronic disease involving elevated blood glucose levels and is one of the leading causes of death in the United States. In type 1-diabetic patients, the pancreas produces little or no insulin, and accordingly patients usually rely on insulin treatment. Glucose levels may vary as a result of different conditions and activities, such as meals, exercise and stress. It is essential to monitor appropriate biomarkers of these natural physiological perturbations and achieve a holistic understanding of patient’s metabolism for successful diabetes management. The purpose of the current work was to investigate the effect of stress on pH and different metabolic analytes (including glucose, lactate and glycerol). Methods: A type 1 diabetic rat model was established by inducing diabetes in healthy Sprague Dawley rats using streptozocin (STZ) (60 mg/kg, IP). The diabetic rats were then divided into two groups, and one group was injected subcutaneously with insulin (insulin-treated diabetic model). A tail suspension test was optimized and used as the stress model for the different groups of rats (normal healthy rats, diabetic rats and insulin-treated diabetic rats). pH and multiple metabolic analytes (glucose, lactate and glycerol) were continuously monitored in the subcutaneous (s.c.) tissue of the normal healthy rats, diabetic rats and insulin-treated diabetic rats during stress experiments (30 minutes equilibration, 8 minutes tail suspension and 60 minutes recovery) using implantable pH sensors and s.c. microdialysis analysis. Glucose, lactate and glycerol levels in the microdialysis samples were measured using commercial assay kits. Results: Changes in analyte levels were shown to be more pronounced in the diabetic rats compared to the healthy rats during and after the stress experiments. As shown in Figure 1, the onset of stress was correlated with change in the pH levels and was very significant in both the diabetic rats and the insulin-treated diabetic groups, where the pH levels increased during tail suspension, then decreased shortly after tail suspension. Conclusion: Continuous multi-biomarker monitoring was successfully designed and optimized to monitor metabolic changes in the s.c. tissue under stress conditions. Monitoring of biomarkers is useful for detection of stress onset and duration. These results demonstrate that changes in s.c. pH levels of diabetic and insulin treated diabetic rats were more affected under stress compared to normal animals. The results provide valuable information that will help in future studies to facilitate accurate insulin dosing of diabetic patients and in the eventual automation of an artificial pancreas.