Glucose-responsive beta cells in islets isolated from a patient with long-standing type 1 diabetes mellitus

Abstract

To the Editor: The heterogeneous nature of the autoimmune process in type 1 diabetes mellitus can, on occasion, result in the preservation of beta cells in patients with longstanding disease [1]. The detection of low levels of basal C-peptide secretion in these patients suggests some beta cell secretory capacity [2]. Whether these residual beta cells are functionally intact, however, remains unanswered. Here we report in vitro observations on islets isolated from a cadaveric donor who had had type 1 diabetes mellitus for 13 years. The objectives were to isolate islets from the pancreas to determine islet hormone secretion profiles and cellular electrophysiological responses, and to compare these variables with data from islets from non-diabetic donors. In addition, we compared the pancreatic histology of this donor pancreas with that of other type 1 diabetic mellitus donors with established or newly diagnosed disease. The donor, a white female, was 19 years old at diagnosis, weighed 73.8 kg (BMI 28 kg/m) and had no family history of diabetes. She was treated with gliclazide and metformin. Seven weeks after diagnosis, despite maximal doses of oral therapy, she developed ketonuria and had a fasting blood glucose of 24 mmol/l. She therefore started insulin treatment (0.27 U/kg insulin twice daily). This was increased to 0.6 U/kg using a basal bolus regimen over a 6 month period. She underwent four admissions for severe diabetic ketoacidosis. Unfortunately no serum samples were taken for determination of C-peptide or antibody status at any time. Samples taken at the time of death showed HLA-DR3 and -4 positivity. The donor’s pancreas was retrieved for research with the informed consent of the family and with the approval of the local ethics committee. Islets were isolated using established protocols [3]. An islet count was omitted as poor dithizone uptake was predicted. Islets that were visibly structurally intact were hand-picked from the purified digest for the secretion experiments and the residual islets were retained for morphological analysis. The islets used for the functional experiments were therefore not a true representation of the whole isolated population. Insulin and glucagon secretion was measured from batches of 15 islets (in quadruplicates) pre-incubated in 1 mmol/l glucose for 1 h followed by incubation for 1 h at 1, 6 or 20 mmol/l glucose. The hormone contents of islets and supernatant fractions were determined by radioimmunoassay [4]. Membrane capacitance, as a measure of insulin granule exocytosis, was recorded from isolated alpha and beta cells using the patch-clamp technique [5]. Pancreatic tissue samples taken from the body and tail regions of this donor pancreas and from the donor pancreases of three additional type 1 diabetic patients (diabetes duration >10 years, n=2; diabetes duration <48 h, n=1; tissue retrieval at post mortem was approved by the local ethics committee) were prepared for light and electron microscopy [6]; they were J. N. Walker : P. R. V. Johnson : S. J. Hughes Nuffield Department of Surgery, University of Oxford, John Radcliffe Hospital, Oxford, UK