Alloxan cytotoxicity in vitro. Microscope photometric analyses of Trypan Blue uptake by pancreatic islet cells in suspension.

Suspensions of islet cells were prepared by shaking pancreatic islets from non-inbred ob/ob mice in a Ca2+-free buffer. The cells were incubated with or without 20 mM-alloxan, and subsequently with Trypan Blue. The uptake of Trypan Blue by cell nuclei was analysed by microscope photometry and by counting the frequency of cells appearing stained on visual inspection. Cells classified as stained or unstained by inspection showed no overlap in nuclear absorbance. Suspensions not exposed to alloxan contained 70-80% of unstained cells. Alloxan markedly decreased the frequency of unstained cells, an effect counteracted by 5 or 20 mM-D-glucose. The spectrum of Trypan Blue in islet-cell nuclei was red-shifted by about 20 nm. A similar red-shift was observed on adding the dye to solutions of albumin or histones, but not on mixing the dye with DNA. Binding to basic proteins may explain the concentrative uptake of Trypan Blue in dead cells and contribute to the oncogenic transformation of phagocytotically active cells. Beta-Cells in vitro are killed by alloxan and hence represent a valid model for studying the diabetogenic action of the drug.