Mechanisms by which glucagon-like peptide-1 analogue exenatide reduces amyloid toxicity in cultured human islets: Implications for clinical islet transplantation

Z. Ao¹, Y.J. Park², L. Jew², M. Meloche², N. Safikhan², Y. Zhang², D. Thompson¹, G.L. Warnock², L. Marzban^2
1 University of British Columbia, Medicine, Vancouver, Canada; ² University of British Columbia, Surgery, Vancouver, Canada

Introduction: Islet transplantation is a feasible approach for treatment of type 1 diabetes (T1D) but is limited by islet loss during pre-transplant incubation and post-transplant which eventually leads to graft failure in most recipients. Islet amyloid is a pathologic lesion of T2D that also forms in cultured and transplanted islets associated with beta-cell death. Preliminary studies show that ~40% of islet donors have pre-existing amyloid pre-transplant which may potentially contribute to graft failure. Impaired processing of islet amyloid polypeptide (IAPP), the major component of amyloid deposits, has been implicated in amyloid formation. We previously showed that treatment with exenatide, a long-acting analogue of glucagon-like peptide-1 (GLP-1), reduces amyloid formation. In this study, we tested whether exenetide treatment: 1. Protects human islets from amyloid toxicity following its formation; 2. Improves impaired processing of the IAPP precursor, proIAPP.

Methods: Freshly isolated amyloid-negative (n=3) or positive human islets (n=3) were cultured in CMRL (5 mM glucose) without or with exenatide (10 nM, 7 days). In parallel studies, islets were cultured in 11.1 mM glucose (3 days) to potentiate amyloid formation and then treated similarly with exenatide. Amyloid formation, proIAPP processing, beta-cell apoptosis, and function were assessed.

Results: As expected, amyloid-negative islets formed amyloid during culture. Treatment with exenatide markedly enhanced proIAPP processing (70%) and reduced amyloid formation (40%) in cultured islets associated with decreased beta-cell apoptosis (30%), increased islet insulin content (27%), and insulin response to elevated glucose (32%). Interestingly, the proportion of active caspase-3 and TUNEL-positive (apoptotic) beta-cells were reduced by 25% in exenatide treated islets with pre-existing amyloid compared to corresponding untreated islets.

Conclusion: These studies suggest that treatment with GLP-1 analogues such as exenatide protects islets from amyloid toxicity during pre-transplant culture by: 1. improving proIAPP processing; 2. reducing amyloid formation; 3. decreasing amyloid toxicity in islets with pre-exisitng amyloid.