S U M M A R Y Pancreatic ␤ -cells contain large amounts of zinc. We took advantage of this to try to localize, quantify, and isolate insulin-producing cells from islet preparations. Our study was designed to identify a non-toxic zinc-sensitive fluorescent probe able to selectively label labile zinc in viable ␤ -cells and to exhibit excitation and emission wavelengths in the visible spectrum, making this technique exploitable by most instruments. We tested Newport Green, a probe excitable at 485 nm with a dissociation constant in the micromolar range corresponding to a low affinity for zinc. The loading of the lipophilic esterified form of Newport Green was easy, rapid, specific, and non-toxic to cells. Confocal microscopy highlighted an intense fluorescence associated with secretory granules. Regression analyses showed a good relationship between zinc fluorescence and islet number ( r ϭ 0.98) and between zinc fluorescence and insulin content ( r ϭ 0.81). The determination of Zn fluorescence per DNA enabled us to assess the quality of the different islet preparations intended for islet allografting in terms of both purity and viability. Cell sorting of dissociated Newport Green-labeled cells resulted in a clear separation of ␤ -cells, as judged by insulin content per DNA and immunocytochemical analysis. This zinc probe, the first able to specifically label living cells in the visible spectrum, appears very promising for ␤ -cell experimentation, both clinically and for basic research. P ancreatic islets contain a much higher concentration of zinc than other tissues. Zinc plays an important role in packaging insulin because it is firmly established as an integral part of the insulin crystal as a 2-Zn-insulin hexamer. In addition, free ionized zinc is found in the extragranular space of ␤ -cells, where it may act as a reservoir for granular zinc (Figlewicz et al. 1984). These pools of free and loosely bound zinc can be visualized histochemically by most cytological stains, unlike zinc tightly complexed to proteins such as metalloproteins, including transcription factors and metalloenzymes. Our study was designed to search for a new non-toxic probe that was able to specifically stain living ␤ -cells. Our aim was threefold: (a) to visualize ␤ -cells in pancreatic islets by confocal microscopy or image analysis; (b) to isolate these ␤ -cells for physiological studies; and (c) to rapidly estimate, in allograft management, the amount of viable ␤ -cells in semipurified preparations containing contaminating exocrine cells. The latter pretransplantation evaluation of the quality of the graft has become a crucial prerequisite to ensure successful engraftment. Here we describe the use of Newport Green, a new zinc-sensitive probe with an excitation wavelength in the visible spectrum, which fulfills all the criteria required for efficient staining of human ␤ -cells in clinical and research applications. Materials and Methods Human Islet ProcessingHuman pancreata ( n ϭ 11; mean age 35 Ϯ 12 years) were harvested from adult brain-...

Transplantation of islets of Langerhans is a potential cure for type 1 diabetes, but its success is hampered by destruction of the islets. The data presented herein suggest that the active metabolite of vitamin D3 [1,25-(OH)2D3] may promote islet cell survival by modulating the effects of inflammatory cytokines, which contribute to beta-cell demise. We investigated some of the mechanisms triggering the apoptotic machinery in rat insulinoma RINm5F cells and human islets treated with IL-1beta plus interferon-gamma plus TNFalpha and assessed the effects of 1,25-(OH)2D3 in these processes. Mitochondrial transmembrane permeability and apoptotic features, determined by percentage of sub-G1 cells, quantitation of DNA strand breaks, and Hoechst staining, were significantly increased by cytokines and reverted toward control values by 1,25-(OH)2D3 cotreatment. The cytoprotection of cells correlated with the abrogation of cytokine-induced nitric oxide production. The activation of nuclear factor-kappaB plays a key role in the different pathways implicated in nitric oxide generation. We demonstrated for the first time, in both RINm5F cells and human islets, that 1,25-(OH)2D3 was able to induce and maintain high levels of A20, an antiapoptotic protein known to block nuclear factor-kappaB activation. Our study showed a clear efficiency of 1,25-(OH)2D3 on the apoptotic machinery triggered by cytokines in beta-cells and suggests that 1,25-(OH)2D3 could help overcome a major obstacle encountered in the cellular therapy of diabetes, such as nonfunction in the immediate posttransplantation period.

Beta cell loss occurs at the onset of type 1 diabetes and after islet graft. It results from the dysfunction and destruction of beta cells mainly achieved by apoptosis. One of the mediators believed to be involved in beta cell apoptosis is Fas, a transmembrane cell surface receptor transducing an apoptotic death signal and contributing to the pathogenesis of several autoimmune diseases. Fas expression is particularly induced in beta cells by inflammatory cytokines secreted by islet-infiltrating mononuclear cells and makes cells susceptible to apoptosis by interaction with Fas-ligand expressing cells. We have previously demonstrated that 1,25(OH)2D3, the active metabolite of vitamin D, known to exhibit immunomodulatory properties and prevent the development of type 1 diabetes in NOD mice, is efficient against apoptosis induced by cytokines in human pancreatic islets in vitro. The effects were mainly mediated by the inactivation of NF-kappa-B. In this study we demonstrated that 1,25(OH)2D3 was also able to counteract cytokine-induced Fas expression in human islets both at the mRNA and protein levels. These results were reinforced by our microarray analysis highlighting the beneficial effects of 1,25(OH)2D3 on death signals induced by Fas activation. Our results provides additional evidence that 1,25(OH)2D3 may be an interesting tool to help prevent the onset of type 1 diabetes and improve islet graft survival.