EARLY ASSESSMENT OF APOPTOSIS IN ISOLATED ISLETS OF LANGERHANS1

Development and characterization of simulant pancreatic islets

Insulin is stored in pancreatic islets as a zinc-insulin complex, and stimulating the islets results in the release of insulin and zinc. Simulant pancreatic islet beads have been developed using agarose beads (50-250 micro m diameter) derivatized with iminodiacetic acid that have been loaded with zinc. A qualitative comparison of the simulant beads with pancreatic islets has been made by staining with dithizone and a zinc-binding fluorescent dye, TSQ. The binding capacity of simulant beads was determined to be 34 micro mol Zn(2+)/g of dried beads using anodic stripping voltammetry. Hydrochloric acid was used to release zinc from beads to mimic the secretion of insulin from pancreatic islets and a release profile was established. The simulant beads can be used to optimize the islet isolation process and reduce the use of real islets in method development.

Occurance of apoptosis during ischemia in porcine pancreas islet cells

PURPOSE

Pancreas islet transplantation is a potential treatment of diabetes mellitus and porcine organs provide an easily available source of cells. Unfortunately quality and quantity of isolated islets are still not satisfactory. Apoptosis occurs in freshly isolated islets and plays a significant role in early graft loss. We evaluated the influence of four storage solutions on porcine pancreas islets.

METHOD

After warm ischemia of 15-20 minutes 12 organs were stored in 4 cold preservation solutions: Histidine-Tryptophan-Ketoglutarate solution (HTK), Hank's buffered saline solution (HBSS), University of Wisconsin (UW) solution and Ringer-Lactate (R). After cold ischemia for 100 minutes, organs were fixed in 3% formalin. Apoptotic cells were counted on hematocylin-eosin stainings.

RESULTS

Most apoptotic cells were found in organs stored in R. Low numbers were found in the other groups. The difference between organs stored in R and organs stored in UW, HTK, or HBSS was highly significant. No significant difference could be found between UW, HTK and HBSS.

CONCLUSION

Cold and warm ischemia of the pancreas seems to induce apoptosis in islet cells. Preservation solutions cause less apoptosis than electrolyte solution. No significant differences could be found among the preservation solutions.

A novel approach to increase human islet cell mass while preserving beta-cell function

Human islet expansion in monolayer culture leads to loss of function and senescence. By maintaining the 3-D configuration of islets in fibrin gels, it is feasible to expand beta-cells in response to hepatocyte growth factor (HGF) while preserving physiologic glucose responsiveness both in vitro and in vivo after transplantation into nude mice. Islets were cultured free floating with or without growth factors and nicotinamide and in fibrin gels with the same conditions. Proliferation was observed only in islets cultured in fibrin gels and the cocktail; total insulin increased by threefold, with a concomitant increase in beta-cell mass by morphometry. Insulin release after glucose challenge was also preserved. Islets in fibrin gels gave rise in vivo to large grafts rich in insulin and glucagon, and grafts from free-floating islets were smaller with fewer endocrine cells. Circulating human C-peptide levels were higher than in the mice receiving free-floating islets. In summary, fibrin allows for HGF-mediated cell proliferation while preserving glucose responsiveness in an environment that preserves cell-cell contacts. Limited islet ex vivo expansion under these conditions may improve recipient-donor tissue ratios to equal the functional results of whole-organ transplants.

17beta-Estradiol protects isolated human pancreatic islets against proinflammatory cytokine-induced cell death: molecular mechanisms and islet functionality

INTRODUCTION

Proinflammatory cytokines (PIC) (interleukin-1beta, interferon-gamma, and tumor necrosis factor alpha) are released after intraportal islet transplantation lead to functional suppression and islet apoptosis. Estradiol has been shown to promote survival of cells undergoing PIC-induced apoptosis. In this study, we evaluated the effects of estradiol on isolated human pancreatic islet (IHPI) survival after exposure to PIC and analyzed potential mechanisms of action.

METHODS

Hand-picked, freshly isolated IHPI were incubated with PIC and estradiol. Viability was analyzed from single islet cells stained with ethidium bromide and acridine orange, apoptosis using a quantitative kit, NF-kappaB nuclear translocation using a promoter-Luciferase NF-kappaB responsive construct, mitochondrial permeability transition using the ApoAlert Mitochondrial kit, and caspase 9 by a fluorometric assay. In vitro functionality was examined by static incubation, and a limited number of islets were transplanted in nonobese diabetic, severe combined immunodeficient mice.

RESULTS

17beta-Estradiol induced a dose-dependent increase in islet viability, an effect partially reversed by the estrogen receptor antagonist ICI 182,780. In vitro, islets treated with estradiol presented higher stimulation index. Euglycemia was achieved in 6 of 12 animals that received estradiol-treated islets compared with 1 of 12 control animals. Lower NF-kappaB nuclear translocation, cytochrome release, and caspase 9 activation occurred in islets treated with estradiol.

CONCLUSIONS

Estradiol promoted IHPI survival and improved functionality after PIC exposure in vitro and in vivo after transplantation. The molecular mechanisms involved included a decrease in NF-kappaB nuclear translocation, decrease in mitochondrial cytochrome release, and caspase 9 activation. The use of estradiol might be beneficial in clinical islet transplantation.

Continuous measurement of oxygen consumption by pancreatic islets

The rate of oxygen consumption is an important measure of mitochondrial function in all aerobic cells. In pancreatic beta cells, it is linked to the transduction mechanism that mediates glucose-stimulated insulin secretion. However, measurement of oxygen consumption over long periods of time is technically difficult owing to the error resulting from baseline drift and the challenge of measuring small changes in oxygen tension. We have adapted an ultrastable oxygen sensor based on the detection of the decay of the phosphorescent emission from an oxygen-sensitive dye to a previously developed islet flow culture system. The drift of the sensor is approximately 0.3%/24 h, allowing for the continuous measurement of oxygen consumption by 300 islets (or about 6 x 10(5) cells) for hours or days. Rat islets placed in the perifusion chamber for 24 h were well maintained as reflected by membrane integrity, insulin secretion, and oxygen consumption. Both acute changes in oxygen consumption as induced by glucose and chronic changes as induced by sequential pulses of azide were resolved. The features of the flow culture system--aseptic conditions, fine temporal control of the composition of the media, and the collection of outflow fractions for measurement of insulin, and other products--facilitate a systematic approach to assessing metabolic and functional viability in responses to a variety of stimuli. Applications to the measurement of effects of hypoxia on insulin secretion, membrane integrity, and the redox state of cytochromes are demonstrated. The system has particular application to the field of human islet transplantation, where assessment and the study of islet viability have been hampered by a lack of experimental methods.

Proteins linked to a protein transduction domain efficiently transduce pancreatic islets

The resounding success of a new immunosuppressive regimen known as the Edmonton protocol demonstrates that islet cell transplantation is becoming a therapeutic reality for diabetes. However, under the Edmonton protocol, a single donor does not provide enough islets to attain the insulin independence of a transplant recipient. This limitation is mainly caused by islet apoptosis triggered during isolation. In this study, we describe a highly efficient system of transiently transferring anti-apoptotic proteins into pancreatic islets, thus opening an exciting new therapeutic opportunity to improve the viability of transplantable islets. We fused beta-galactosidase to the 11-amino acid residues that constitute the protein transduction domain (PTD) of the HIV/TAT protein and transduced pancreatic islets ex vivo with this fusion protein in a dose-dependent manner with >80% efficiency. We observed that transduction of the anti-apoptotic proteins Bcl-X(L) and PEA-15 fused to TAT/PTD prevented apoptosis induced by tumor necrosis factor-alpha in a pancreatic beta-cell line, indicating that TAT/PTD anti-apoptotic proteins retained their biological activity. Finally, we demonstrated that TAT-fusion proteins did not affect the insulin secretion capability of islets, as determined by glucose static incubation and by reversion of hyperglycemia in diabetic immunodeficient mice.