Evaluation of hepatic glucose metabolism via gluconeogenesis and glycogenolysis after oral administration of insulin nanoparticles

Abstract

Nanoparticles were designed to promote insulin intestinal absorption via the oral route, to increase portal insulin levels to better mimic the physiological pathway, providing enhanced glucose control through glycogenolysis and gluconeogenesis. Nanoparticles were formulated with insulin encapsulated in the core material consisting of alginate and dextran sulfate, associated with poloxamer and subsequently coated with chitosan then albumin. A spherical and slightly rough core was observed in electron micrographs with the appearance of a concentration gradient of the polysaccharide structure toward the periphery of the nanoparticle. Atomic force microscopy showed that the fully formed nanoparticles are about 200 nm in diameter with smooth and spherical morphology. Histopathological analysis of organs and tissues of diabetic rats dosed daily for 15 days with insulin nanoparticles was used to evaluate toxicological issues. No morphological or pathological alterations were observed in rat liver, spleen, pancreas, kidney or intestinal sections. Following, the effect of nanoencapsulated insulin on inhibiting hepatic gluconeogenesis was evaluated after a single insulin administration and oral glucose tolerance test, which represents a significant metabolic challenge to the liver. Alterations in the hepatic glucose metabolism of fasted streptozotocin-diabetic rats were determined by the percent contribution of glycogenolysis and gluconeogenesis, measured by using metabolic tracers, however similar gluconeogenesis contribution to the hepatic metabolism was observed between diabetic rats receiving nanoencapsulated insulin or insulin solution. The metabolic results may be explained by the inability of a single dose in shifting the gluconeogenesis/glycogenolysis contributions, sampling time, fasting period or by influence of the kidney enzymes and impairment in insulin signaling observed in stz-diabetic rats.

Keywords::

• Insulin
• nanoparticles
• oral delivery
• histopathological analysis
• hepatic metabolism

Acknowledgements

The authors thank Rede Nacional de RMN for access to the facilities for the NMR analyses. The authors also thank Dr. António Silverio Cabrita from the Institute of Experimental Pathology at the Faculty of Medicine, University of Coimbra for assistance with the histopathological analyses.

Declaration of interest

This work was funded by Fundação para a Ciência e Tecnologia of Portugal (SFRH/BD/30644/2006), the Natural Sciences and Engineering Research Council of Canada and LNLS – Brazilian Synchroton Light Laboratory/MCT. The Varian VNMRS 600 MHz spectrometer is part of the National NMR Network and was purchased in the framework of the National Program for Scientific Re-equipment, contract REDE/1517/RMN/2005, with funds from POCI 2010 (FEDER) and Fundação para a Ciência e a Tecnologia (FCT).