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Stimulation of VEGF secretion in rat pancreatic islets using Liraglutide

Allan Langlois¹, Kevin Vivot¹, Nathalie Jeandidier^2,3, William Bietiger¹, Camille Dollinger¹, Michel Pinget^1,2,3, Severine Sigrist¹

¹Centre européen d’étude du Diabète; ²Service d’endocrinologie, diabète, maladies métaboliques, Pôle NUDE, Hôpitaux Universitaires de Strasbourg; ³Université de Strasbourg, Strasbourg, France

Introduction: The formation of microvascularization by capillary sprouting at the site of islet transplantation is crucial for survival of the graft. Vascular Endothelial Growth Factor (VEGF), a major angiogenic factor, may be a key protein in modulating the angiogenesis of islets after transplantation. Development of a pharmacological approach enhancing VEGF synthesis could improve islet graft survival.

Liraglutide has been shown to decrease islets apoptosis and increase survival in cultured or transplanted islets. The mechanisms of its role in islets viability in culture and during transplantation have to be identified. The aim of this work was to study in vitro the effects of liraglutide on islet viability and its relation to angiogenesis via VEGF secretion.

Materials and methods: Previous studies have determined a protocol allowing the systematic evaluation of pharmacological molecules. Following this protocol, cultures of rats islets were incubated in presence of 1 and 10 µM of liraglutide (50 fold higher than pharmacological concentrations used) during 12, 24 and 48h. The islet viability was evaluated using fluorescein diacetate/propidium iodure dying and functionality was determined by glucose test stimulation. Islets insulin-secretion was expressed as an index of stimulation (IS). VEGF secretion was determined by ELISA assay.

Results: Islets viability was 100% in controls and with liraglutide. Ten µM of liraglutide induced a significant stimulation of VEGF secretion as early as 24h with 10.57 ± 3.55 vs control with 4.42 ± 1.09 pg of VEGF/µg of protein (p< 0.05, n=4), and was maintained after 48h. It only appeared after 48h with 1 µM liraglutide. Levels of secretion were respectively: 39.28 ± 14.81 with 1 µM, 53.60 ± 25.03 with 10 µM; 13.63 ± 4.48 pg of VEGF/µg of protein with controls, p< 0.05, n=4). At the same time, a significant stimulation of the insulin-secretion was observed at 24h of culture with 1 and 10 µM of liraglutide and controls with respectively 7.86 ± 1.78 and 8.17 ± 2.43 vs 4.27 ± 1.46 µg of insulin/g of protein (n=4, p< 0.05). The effect was maintained after 48h with 1 µM: 2.63 ± 1.64 and 10 µM: 6.28 ± 4.74 for liraglutide vs controls: 2.29 ± 1.05 µg insulin/g of protein, n=4).

Conclusion: In vitro, suprapharmacological concentrations of liraglutide had no toxicity and significantly stimulated VEGF secretion in islets. Also, insulin-secretion increased during the first 24h of culture. VEGF secretion could be one of the mechanisms involved in the improvement of islet viability during transplantation. Increased angiogenesis remains to be assessed.