Human Islet Function Research Articles

Effects of nicotinamide supplementation on human pancreatic islet function in tissue culture

Effects of nicotinamide supplementation on human pancreatic islet function in tissue culture

Effects of nicotinamide supplementation on human pancreatic islet function in tissue culture.

Nicotinamide currently attracts considerable interest as a compound that might prevent the development of human insulin-dependent diabetes mellitus. The present study investigated the direct actions of nicotinamide on human pancreatic beta-cells. For this purpose, islets were isolated from 11 adult cadaveric donors. The human islets were subsequently precultured in RPMI-1640 (5.6 mmol/L glucose) and 10% fetal calf serum for 3-4 days. The islets were cultured for another 6 days in the same medium in either the presence or absence of 10 mmol/L nicotinamide, and subsequently, islet function was examined. After culture, both groups of islets contained similar amounts of DNA, and DNA synthesis, determined by the tritiated thymidine incorporation rate, was unchanged. The insulin content both on a per islet basis and per DNA was similar in both groups as was the islet glucose oxidation rate. Insulin accumulation into the culture medium was sustained over the entire culture period and did not differ at any time point between the nicotinamide and the control group. Nicotinamide affected neither basal and glucose-stimulated insulin secretion nor (pro)insulin and total protein biosynthesis rates after culture. The insulin response to glucose of the human islets was about 5-fold. In conclusion, the present study shows that nicotinamide does not directly affect human beta-cell function or the cell replicatory rate. This would suggest that any potential beneficial effects observed after treatment with nicotinamide in patients with insulin-dependent diabetes mellitus may not necessarily reflect an action at the beta-cell level.

NICOTINAMIDE AND INTERLEUKIN-1 (IL-1) EFFECTS ON HUMAN PANCREATIC ISLET FUNCTION

The cytokine IL-1β inhibits rodent β-cell function in a time- and dose-dependent manner and has been implicated as effector molecule in the IDDM pathogenesis. In isolated rat islets IL-1 toxicity to β-cells is dependent on generation of free nitric oxide radicals. Nicotinamide (NA), a free radical scavenger and inhibitor of poly-ADP-ribose synthetase prevents macrophage mediated islet cell destruction and autoimmune diabetes in the NOD mouse, and NA shows promising preventive effects in prediabetic humans. Here we studied IL-1 sensitivity and NA protection of isolated human islets using a completely intra-species in vitro system: A 24 hr human islet exposure to authentic recombinant human IL-1β (150pg/ml) reduces 16.7 mM glucose-challenged islet insulin release to 0.19±0.08ng/islet/2hrs vs 0.41±0.14 in controls (p<0.05). Coincubation with 10 mM NA counteracts the IL-1 effect to 0.38±0.13ng/islet/2hrs (ns vs controls) without showing any intrinsic effect on β-cell function by itself. A 6 hr human islet IL-1 exposure already leads to a 30% decrease of insulin accumulation while in rat islets functional inhibition is seen only after 24 hrs of IL-1 exposure. In conclusion isolated human islets are most sensitive to IL-1 induced β-cell suppression and NA protects human islet function against the IL-1 attack.

Prolonged exposure of human pancreatic islets to high glucose concentrations in vitro impairs the beta-cell function.

The aim of the present study was to clarify whether prolonged in vitro exposure of human pancreatic islets to high glucose concentrations impairs the function of these cells. For this purpose, islets isolated from adult cadaveric organ donors were cultured for seven days in RPMI 1640 medium supplemented with 10% fetal calf serum and containing either 5.6, 11, or 28 mM glucose. There was no glucose-induced decrease in islet DNA content or signs of morphological damage. However, islets cultured at 11 or 28 mM glucose showed a 45 or 60% decrease in insulin content, as compared to islets cultured at 5.6 mM glucose. Moreover, when such islets were submitted to a 60-min stimulation with a low (1.7 mM) followed by a high (16.7 mM) concentration of glucose, the islets cultured at 5.6 mM glucose showed a higher insulin response to glucose than those of the two other groups. Islets cultured at the two higher glucose concentrations showed increased rates of insulin release in the presence of low glucose, and a failure to enhance further the release in response to an elevated glucose level. Islets cultured at 28 mM glucose showed an absolute decrease in insulin release after stimulation with 16.7 mM glucose, as compared to islets cultured at 5.6 mM glucose. The rates of glucose oxidation, proinsulin biosynthesis, and total protein biosynthesis were similar in islets cultured at 5.6 or 11 mM glucose, but they were decreased in islets cultured at 28 mM glucose. These combined results suggest that lasting exposure to high glucose concentrations impairs the function of human pancreatic islets.

Xenotransplantation of microencapsulated pancreatic islets contained in a vascular prosthesis: preliminary results

Abstract. Porcine and human pancreatic islets were microencapsulated in an alginate-polylysine biomembrane and put in a chamber of a new vascular prosthesis composed of an inner tubing of Dacron mesh and an outer tubing of expanded polytetrafluorethylene material. The vascular prosthesis was anastomized between the iliac artery and the contralateral vein of diabetic dogs. The recipients did not receive any immunosuppressive therapy. Function of porcine and human islets was monitored by measuring serum glucose levels and human C-peptide concentrations. After transplantation, serum glucose levels were maintained at values lower than 200 mg/dl, and C-peptide concentrations were between 0.8 and 3.2 ng/ml. Injected insulin requirements decreased by 50%-60%. Four to 8 weeks after transplantation, histologic examination showed well-preserved and functioning islets in the majority of intact microcapsules. Fibrin and inflammatory cells were not observed in the chamber. These data suggest long-term survival and function of microencapsulated pancreatic islets in the vascular prosthesis.

Lack of glucose-induced functional maturation during long-term culture of human fetal islet cells

To investigate the long-term effects of glucose on the function of human fetal islets we cultured islet-like cell clusters (ICC) obtained from 12 human fetuses with a mean age of 16.1 weeks in media containing 2.8, 11.1 or 16.7 mM glucose. On the 8th day of culture, the ICC that had been maintained in 16.7 mM glucose contained 60% less insulin than the ICC cultured in 2.8 mM glucose. However, insulin release was similar in both groups, and was not affected by a 24-h incubation in high vs. low glucose. Also (pro)insulin biosynthesis was not significantly affected. During a 24-day culture period, the total release of insulin and glucagon was similar in all glucose concentrations. The ICC released about 75 % of their insulin content but only 15 % of their glucagon content during the last 48 h of the 24-day culture period, again regardless of glucose concentration in media. Insulin release was insensitive to acute glucose and leucine challenges in perifusion experiments after culture for 1, 5, 8 or 16 days in 11.1 mM glucose, whereas glucagon was always a potent stimulus. In conclusion, the function of cultured young human fetal islet cells is remarkably independent of glucose, even during prolonged exposure. Moreover, the primary role of glucagon in fetal life may be that of a paracrine stimulator of β-cell function.

Xenotransplantation of microencapsulated pancreatic islets contained in a vascular prosthesis: preliminary results

Porcine and human pancreatic islets were microencapsulated in an alginate-polylysine biomembrane and put in a chamber of a new vascular prosthesis composed of an inner tubing of Dacron mesh and an outer tubing of expanded polytetrafluorethylene material. The vascular prosthesis was anastomized between the iliac artery and the contralateral vein of diabetic dogs. The recipients did not receive any immunosuppressive therapy. Function of porcine and human islets was monitored by measuring serum glucose levels and human C-peptide concentrations. After transplantation, serum glucose levels were maintained at values lower than 200 mg/dl, and C-peptide concentrations were between 0.8 and 3.2 ng/ml. Injected insulin requirements decreased by 50%-60%. Four to 8 weeks after transplantation, histologic examination showed well-preserved and functioning islets in the majority of intact microcapsules. Fibrin and inflammatory cells were not observed in the chamber. These data suggest long-term survival and function of microencapsulated pancreatic islets in the vascular prosthesis.

Effects of glucose and D-3-hydroxybutyrate on human pancreatic islet cell function.

Beta-Cell function in human islets derived from a number of kidney donors was investigated by using various types of islet preparations. With fresh islets, both insulin release and biosynthesis were increased by raising glucose concentrations, although the response was a variable one. In fresh islets, the effects of 5 mmol of glucose/l on release were potentiated by 10 mmol of D-3-hydroxybutyrate/l. Insulin release at 20 mmol of glucose/l was inhibited by adrenaline (0.1 mmol/l), and potentiated by theophylline (10 mmol/l) in the presence of 5 mmol of glucose/l, in islets cultured for 4 days. After culture for 8 days, islets still showed an increase in insulin release and biosynthesis in response to glucose. Pancreas slices derived from fresh human tissue also responded to increasing concentrations of glucose with a sigmoidal curve for insulin release.

Role of circulating somatostatin in regulation of gastric acid secretion, gastrin release, and islet cell function. Studies in healthy subjects and duodenal ulcer patients.

Studies were designed (a) to determine whether somatostatin is released into the circulation after meals in sufficient amounts to regulate gastric or pancreatic islet function in humans and (b) to investigate the possible role of somatostatin in the pathogenesis of duodenal ulcer disease. Mean plasma somatostatin-like immunoreactivity (SLI) increased from 6.2 +/- 1.5 pg/ml to a peak level of 13.8 +/- 1.3 pg/ml in eight healthy subjects after a 1,440-cal steak meal (P less than 0.005). When somatostatin-14 was infused intravenously, basal and food-stimulated gastric acid secretion and also basal and food-simulated plasma insulin and glucagon concentrations were reduced significantly at mean plasma SLI concentrations within the range seen after a meal. Thus, the amount of somatostatin reaching the systemic circulation after a steak meal was sufficient to inhibit gastric acid secretion and islet cell function. On the other hand, basal and food-stimulated plasma gastrin concentrations were reduced by intravenous somatostatin only at plasma SLI concentrations that were several-fold greater than post-prandial SLI concentrations. Although duodenal ulcer patients had significantly higher basal, food-stimulated, and peak pentagastrin-stimulated gastric acid secretion rates than healthy controls, duodenal ulcer patients and controls had nearly identical basal and food-stimulated SLI concentrations. Moreover, food-stimulated gastric acid secretion and gastrin release were inhibited by intravenous somatostatin to the same extent in ulcer patients and controls. These studies suggest that duodenal ulcer patients release normal amounts of somatostatin into the circulation and that target cells controlling acid secretion and gastrin release are normally sensitive to somatostatin in these patients.

Preservation of Beta cell function in adult human pancreatic islets for several months in vitro

Islets of Langerhans were isolated from four human kidney donors, aged 16 to 21 years by the collagenase method described for isolation of rodent islets. So far the human islets have been kept in tissue culture, without attachment, in medium RPMI 1640 supplemented with 10% calf serum for more than 9 months, with preservation of the ability to release insulin in response to glucose stimulation. Replacement of calf serum with serum from normal human subjects did not affect B-cell survival, but resulted in elevated insulin values partly due to lower insulin degrading activity. Thus the described technique presents a valuable tool for studying chronic effects of metabolites and hormones on islet function, as well as for islet storage prior to transplantation into humans.