A novel method for the detection of viable human pancreatic beta cells by flow cytometry using fluorophores that selectively detect labile zinc, mitochondrial membrane potential and protein thiols

Abstract

Improvement over current methods of beta cell viability assessment is highly warranted in order to efficiently predict the viability and function of beta cells prior to transplantation into type 1 diabetes patients. Dispersed human islet cells were stained with the cell-permeable zinc-selective dye, FluoZin-3-AM, along with the mitochondrial membrane potential indicator [(tetramethylrhodamine ethylester (TMRE)] and the thiol-binding dye, monochlorobimane (mBcl), and analyzed by flow cytometry. Islets were subjected to various experimental conditions to validate the usefulness of this method to accurately determine the viability and function of beta cells. Staining with FluoZin-3 revealed the presence of higher amounts of chelatable zinc ions in beta cells than in lymphoid cells and fibroblasts. An intracellular zinc chelator competitively inhibited the binding of FluoZin-3 to zinc ions. Mitochondrial depolarization or oxidative stress minimally affected the binding of mBcl and FluoZin-3, respectively, to thiols and zinc ions. The combination of FluoZin-3, TMRE, and mBcl was sufficient and necessary for the determination of the viability and function of beta cells. The data demonstrate the usefulness of the zinc-specific dye and the indicators of mitochondrial function and thiol levels, to accurately estimate the beta cell viability and function. This novel flow cytometry method has implications for islet transplantation in type 1 diabetes patients.