Rosiglitazone Treatment Does Not Decrease Amyloid Deposition in Transplanted Islets From Transgenic Mice Expressing Human Islet Amyloid Polypeptide.
ABSTRACT In human islet transplantation, insulin independence decreases over time. We previously showed that amyloid deposition following transplantation of islets from human islet amyloid polypeptide (hIAPP) transgenic mice resulted in ß-cell loss and that rosiglitazone treatment decreased islet amyloid deposition and preserved ß-cell area in the endogenous pancreas of hIAPP transgenic mice. Thus, we sought to determine if rosiglitazone treatment decreases islet amyloid deposition and the associated ß-cell loss after islet transplantation. Streptozocin-diabetic mice were transplanted with 100 islets from hIAPP transgenic (T) mice or nontransgenic (NT) littermates under the kidney capsule and received either rosiglitazone (R) in drinking water or plain drinking water (C). The resultant groups (NTC [n = 11], NTR [n = 9], TC [n = 14], and TR [n = 10]) were followed for 12 weeks after which the graft was removed and processed for histology. Amyloid was detected in nearly all T islet grafts (TC = 13/14, TR = 10/10) but not in NT grafts. Rosiglitazone did not alter amyloid deposition (% graft area occupied by amyloid; TC: 2.15 ± 0.7, TR: 1.72 ± 0.66; P = .86). % ß-cell/graft area was decreased in the TC grafts compared to NTC (56.2 ± 3.1 vs 73.8 ± 1.4; P < .0001) but was not different between TC and TR groups (56.2 ± 3.1 vs 61.0 ± 2.9; P = .34). Plasma glucose levels before and after transplantation did not differ between NTC and TC groups and rosiglitazone did not affect plasma glucose levels post-islet transplantation. Rosiglitazone did not decrease amyloid deposition in hIAPP transgenic islet grafts. Therefore, rosiglitazone treatment of recipients of amyloid forming islets may not improve transplantation outcomes.
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ABSTRACT: Deposition of islet amyloid has been associated with beta-cell death, thereby furthering diabetes progression. Several hypoglycemic agents, such as thiazolidinediones, biguanide and dipeptidyl peptidase-4 inhibitors, have been known to preserve beta-cell mass, possibly by direct inhibition of islet amyloid formation. The general objective of this study was to evaluate the impact of the major representatives of hypoglycemic agents on amyloid formation by using in vitro molecular screening approaches. Ten prototypical representatives of hypoglycemic agents were evaluated for the inhibition of amyloid formation in vitro using thioflavin fluorescence assays, far-ultraviolet circular dichroism, photo-induced cross linking assays and cell viability assays. Glyburide, repaglinide and troglitazone showed the highest potency in delaying and reducing fibril formation. Troglitazone, a thiazolidinedione, was the most effective agent abrogating amyloid fibril formation. Troglitazone affected the secondary structures of incubated human islet amyloid polypeptide (hIAPP). The circular dichroism spectra showed a delayed transition to the beta sheet conformation. A photo-induced cross-linking-based oligomerization assay demonstrated that repaglinide supressed the formation of hIAPP oligomers, whereas glyburide and troglitazone were ineffective in inhibiting oligomerization. Cell toxicity induced by hIAPP was reduced by all 3 compounds. This study provides new insights that could potentially identify new therapeutic strategies to impede the progression of pancreatic amyloidosis in human patients with type 2 diabetes. Copyright © 2015 Canadian Diabetes Association. Published by Elsevier Inc. All rights reserved.Canadian Journal of Diabetes 04/2015; DOI:10.1016/j.jcjd.2015.01.291 · 0.46 Impact Factor