IN-SITU CHARACTERIZATION OF ISLETS IN DIABETES WITH A MITOCHONDRIAL-DNA MUTATION AT NUCLEOTIDE POSITION-3243

Changes in the pancreas of diabetic patients with the A-to-G mitochond rial DNA (mtDNA) mutation at nucleotide position 3243 base pair (bp) h ave not previously been described. The clinical phenotypes of diabetes associated with the mtDNA 3243 mutation range from NIDDM to IDDM. We sought the presence of the mutation and studied volume of beta-, alpha -, and delta-cells, mitochondrial enzyme activity, and presence of apo ptosis in diabetic pancreases obtained at autopsy. Pancreases were obt ained from 16 patients with IDDM, from 18 patients with NIDDM, and fro m 11 nondiabetic patients. Mitochondrial enzyme activity was determine d for cytochrome c oxidase (COX), the subunits of which are partially encoded by mtDNA, and for succinate dehydrogenase (SDH), the subunits of which are solely encoded by nuclear DNA. The volumes of islet beta- , alpha-, and delta-cells were estimated by computerized morphometry. Pancreatic cells were examined for apoptosis by an in situ end-labelin g procedure. The mtDNA 3243 mutation was detected in 1 of 16 (6%) panc reases from the IDDM patients; none of the pancreases from 18 NIDDM pa tients and 11 nondiabetic patients had the mutation. The single patien t with the mtDNA 3243 mutation was a 56-year-old woman with IDDM, aged 39 years at diabetes onset, whose mother was diagnosed with NIDDM. Th e patient had a history of secondary failure of oral hypoglycemic agen ts and had a marked decrease in the number of beta-cells. The islet be ta-cells and non-beta-cells of the patient showed extremely decreased COX enzyme activity. The islet cells in the patient showed a high acti vity when examined for SDH. Some pancreatic exocrine cells also showed decreased COX activity with high SDH activity. In IDDM, NIDDM, and no ndiabetic patients without the mtDNA 3243 mutation, only weak staining for SDH of the islet cells showed. The percentage of heteroplasmy of the mtDNA 3243 mutation in pancreatic micropunched islet specimens was 63 +/- 5% (mean +/- SD) in the islets, 32 +/- 3% in the exocrine panc reas, and 8 +/- 1% in peripheral polymorphonuclear cells. Apoptotic ce lls were not observed in the IDDM pancreas in the patient with the mtD NA 3243 mutation. The fact that higher levels of mutated mtDNA at 3243 bp were found in affected islets rather than in other tissue suggests that the distribution of the mutant may determine the effect on islet function. A characteristic decrease in the mitochondrial enzyme with COX activity and accelerated SDH activity of the affected islets may p rovide new insights into the pathogenesis of mitochondrial diabetes.