Expression of key antioxidant enzymes as markers of early beta cell stress in pancreatic islets: Studies in human donor pancreas with newly diagnosed and long-term type 1 diabetes and without the disease

Abstract

Type 1 diabetes (T1D) is a multifactorial disorder, involving complex genetic and environmental interactions, leading to immune-mediated beta cell destruction. Whether beta cells play a pathogenic role in early disease is poorly understood. Studies in rodents indicate beta cells harbour the lowest level of antioxidant enzymes, including glutathione peroxidase1 (GPX1), superoxide dismutase 2 (SOD2) and catalase and thus, clear excess free radicals inefficiently. This defect may confer beta cell injury, predisposing beta cells to self-immune reactivity and T1D. However, antioxidant enzyme deficiency has not been demonstrated in beta cells of human cases with and without T1D. The major aim of this study was to develop and apply reliable immunohistochemical techniques for the detection of the three antioxidant enzymes, GPX1, SOD2 and catalase, co-stained for insulin and glucagon, to rare pancreatic sections from new-onset T1D donors (group 1), non-diabetic autoantibody-negative (group 2), non-diabetic-autoantibody-positive (group 3) and long-term diabetic donors (group 4). The cellular origins of antioxidant enzymes, their frequencies, graded overall cellular intensities in islets and in beta and alpha cells were determined. The mean number of antioxidant enzyme immunoreactive cells in random exocrine regions was also determined. Although a larger number of cases were analysed for GPX1 than for SOD2 and catalase, donors from all four groups showed various intensities of staining for the enzymes in islet cells, without significant differences. Staining intensities in alpha and beta cells within an islet from various donors were heterogeneous, ranging from negative, weak, moderate and strong. In several diabetic cases, the remaining beta cells showed strong expression of all three enzymes. More detailed analysis demonstrated that the staining intensity for GPX1 per defined islet area was lower in beta cells from diabetic than non-diabetic cases. GPX1, SOD2 and catalase immunoreactive cells in the exocrine regions were distributed randomly in all study groups. The present research shows that although the staining intensities of the three enzymes in islets were variable, a significant lower staining intensity for GPX1 was observed in diabetic donors when extrapolated per unit islet area. This research requires examination in a larger number of donors, by applying yet to be developed more sophisticated quantifiable imaging tools for estimating differential antioxidant enzyme levels in specific islet cells of T1D and whether such deficits play a predisposing role during disease.