Pancreas and liver uptake of new radiolabeled incretins (GLP-1 and Exendin-4) in models of diet-induced and diet-restricted obesity

Abstract Introduction Radiolabeled GLP-1 and its analog Exendin-4, have been employed in diabetes and insulinoma. No protocol in conventional Diet-Induced Obesity (DIO), and Diet-Restricted Obesity (DRO), has been identified. Aiming to assess pancreatic beta cell uptake in DIO and DRO, a protocol was designed. Methods GLP-1-βAla-HYNIC and HYNIC-βAla-Exendin-4 were labeled with technetium-99m. Four Swiss mouse models were adopted: Controls (C), Alloxan Diabetes Controls (ADC), DIO and DRO. Biodistribution and ex-vivo planar imaging were documented. Results Radiolabeling yield was in the range of 97% and both agents were hydrophilic. Fasting Blood Glucose (FBG) was 79.2±8.2mg/dl in C, 590.4±23.3mg/dl in ADC, 234.3±66.7mg/dl in DIO, and 96.6±9.3 in DRO (p=0.010). Biodistribution confirmed predominantly urinary excretion. DIO mice exhibited depressed uptake in liver and pancreas, for both radiomarkers, in the range of ADC. DRO only partially restored such values. 99m Tc-HYNIC-βAla-Exendin-4 demonstrated better results than GLP-1-βAla-HYNIC- 99m Tc. Conclusions 1) Diet-induced obesity remarkably depressed beta cell uptake; 2) Restriction of obesity failed to normalize uptake, despite robust improvement of FBG; 3) HYNIC-βAla-Exendin-4 was the most useful marker; 4) Further studies are recommended in obesity and dieting, including bariatric surgery.