SEARCH · PubMed Health

Results for “Islet”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 55 records · Page 3Linked to original sources

PubMed2001

Effect of liver transplantation on islet allografts: up-regulation of Fas ligand and apoptosis of T lymphocytes are associated with islet graft tolerance.

BACKGROUND: Liver allografts in spontaneously tolerant strain combinations can protect other organs of the same donor origin from rejection and reverse ongoing rejection in previously placed grafts. The aims of this study were to examine whether liver allografts have the same protective effect on islet allografts and to investigate the underlying mechanisms. METHODS: PVG islets were transplanted beneath the kidney capsule of streptozotocin-induced diabetic DA rats with or without liver allografting. The cellular infiltrate, and the extent of apoptosis and of Fas ligand (FasL) expression in the islet grafts were evaluated on days 2, 4, and 7 after transplantation by means of immunostaining and the in situ terminal deoxynucleotide transferase-mediated dUTP nick end labeling assay. Donor and recipient mixed lymphocyte reactions (MLR) were determined at 7 days or 100 days after islet transplantation. RESULTS: Islet allografts transplanted alone were rapidly rejected within 5-8 days. Rejection was delayed, but not prevented, when islets were transplanted simultaneously with the liver. Liver transplantation 1 month before islet transplantation resulted in long-term survival (>100 days) of islet grafts in three of seven animals, whereas the other four died of liver rejection with functional islet grafts. Liver transplantation on day 4 after islet grafting reversed ongoing islet rejection and led to indefinite islet graft survival in three of seven cases. There was a progressive increase of cellular infiltration in all of the islet allografts, but the intensity of the infiltrate did not correlate with the outcome of the islet allografts. Islet rejection was characterized by an early dominance of monocytes/macrophages and CD25+ T cells in the infiltrates, a high incidence of apoptotic beta cells in grafts, and a sensitized status in the MLR. Tolerance of islet allografts was associated with increased numbers of dendritic cells in the graft infiltrates, up-regulation of FasL, and prominent apoptosis of alloreactive leukocytes in the islet grafts, as well as donor-specific MLR suppression in long-term survivors. CONCLUSIONS: These results demonstrate that the extent of the protective effect of liver transplantation on islet allografts varies with the time of liver grafting, ranging from delay in islet rejection to complete islet acceptance. Islet graft tolerance induced by liver transplantation is the result of an immune process that involves up-regulation of Fas ligand expression on, and apoptosis of, islet graft infiltrating lymphocytes.

Animals↗

PubMed1999

Glutamic acid decarboxylase antibodies are more frequent than islet cell antibodies in islet transplanted IDDM patients and persist or occur despite immunosuppression.

Pancreatic islet grafts transplanted into patients with autoimmune diabetes are potentially threatened by two immune responses, allograft rejection and the recurrence of autoimmune insulitis. In the present study we investigated the humoral autoimmune response directed to islet autoantigens by studying islet cell antibodies and glutamic acid decarboxylase (GAD 65) antibodies in twenty-one insulin-dependent diabetes-mellitus (IDDM) patients undergoing intraportal islet allotransplantation. Islet transplantation was performed according to the following recipient categories: Islet after kidney transplantation (n=10), simultaneous islet and kidney transplantation (n=6) and islet transplant alone (n=5). GAD 65 antibodies were detected in a radioligand GAD 65 antibody assay using recombinant, in vitro translated, human 35S-methionin labelled GAD 65 as tracer. Islet cell antibodies were determined by indirect immunofluorescence technique on human pancreas. In six out of twenty-one patients we observed GAD 65 antibodies before islet transplantation and the GAD 65 antibodies persisted despite immunosuppression. In contrast only two subjects were concordantly islet cell antibody positive and the titre decreased post transplantation. In addition we observed occurrence of GAD 65 antibodies in five subjects that were shown to be antibody negative before islet transplantation with three of them subsequently becoming positive for islet cell antibodies. The remaining ten patients were GAD 65 antibody and islet cell antibody negative before islet transplantation and remained negative thereafter. Interestingly none of the patients was exclusively positive for islet cell antibodies without being positive for GAD 65 antibodies. In summary we have demonstrated in twenty-one islet grafted individuals that humoral autoimmunity to islet antigens can persist or occur despite immunosuppression. Islet cell antibodies appear to be less frequent (5 out of 21, 23%) compared to GAD 65 antibodies (11 out of 21, 52%) suggesting that they are more affected by immunosuppressive therapy. We conclude that GAD 65 antibodies are a useful tool to further evaluate a possible link between persistent autoimmunity and early or late graft failure after islet transplantation.

Autoantibodies↗

PubMed2004

Islet amyloid: a complication of islet dysfunction or an aetiological factor in Type 2 diabetes?

The role of islet amyloidosis in the onset and progression of Type 2 diabetes remains obscure. Islet amyloid polypeptide is a 37 amino-acid, beta-cell peptide which is co-stored and co-released with insulin. Human islet amyloid polypeptide refolds to a beta-conformation and oligomerises to form insoluble fibrils; proline substitutions in rodent islet amyloid polypeptide prevent this molecular transition. Pro-islet amyloid polypeptide (67 amino acids in man) is processed in secretory granules. Refolding of islet amyloid polypeptide may be prevented by intragranular heterodimer formation with insulin (but not proinsulin). Diabetes-associated abnormal proinsulin processing could contribute to de-stabilisation of granular islet amyloid polypeptide. Increased pro-islet amyloid polypeptide secretion as a consequence of islet dysfunction could promote fibrillogenesis; the propeptide forms fibrils and binds to basement membrane glycosamino-glycans. Islet amyloid polypeptide gene polymorphisms are not universally associated with Type 2 diabetes. Transgenic mice expressing human islet amyloid polypeptide gene have increased islet amyloid polypeptide concentrations but develop islet amyloid only against a background of obesity and/or high fat diet. In transgenic mice, obese monkeys and cats, initially small perivascular deposits progressively increase to occupy 80% islet mass; the severity of amyloidosis in animal models is related to the onset of hyperglycaemia, suggesting that islet amyloid and the associated destruction of islet cells cause diabetes. In human diabetes, islet amyloid can affect less than 1% or up to 80% of islets indicating that islet amyloidosis largely results from diabetes-related pathologies and is not an aetiological factor for hyperglycaemia. However, the associated progressive beta-cell destruction leads to severe islet dysfunction and insulin requirement.

Amino Acid Sequence↗

PubMed2001

Islet amyloid polypeptide promotes beta-cell proliferation in neonatal rat pancreatic islets.

AIMS/HYPOTHESIS: We aimed to clarify the role of islet amyloid polypeptide, which is expressed at early embryonic onset, in the proliferation and cell death of neonatal islet cells. METHODS: Fetal islets were prepared from pregnant rats on gestational day 21. Islets were cultured in RPMI 1640 (11.1 mmol/l glucose) + 10 % fetal calf serum (FCS) for 48 h, followed by a 24-h culture period in RPMI 1640 (5.6 mmol/l glucose) + 1 % FCS. The islets were then exposed to rat islet amyloid polypeptide (1-10 nmol/l) for 24 h. RESULTS: Islet amyloid polypeptide increased islet DNA synthesis (dpm/microg of DNA. 6 h) (control 1 % FCS: 3634 +/- 662; 1 nmol/l 6347 +/- 1535; 10 nmol/l 5157 +/- 769; p < 0.05 islet amyloid polypeptide vs control). In accordance with this, a doubling of the autoradiographic labelling index was seen in immunocytochemically stained islet beta cells after exposure to 1 and 10 nmol/l islet amyloid polypeptide. Islet amyloid polypeptide at 1 nmol/l increased the islet insulin content (202 +/- 25 % of control; p < 0.01) and the 24-h medium insulin concentration (1 nmol/l islet amyloid polypeptide: 143 +/- 19 % of control; p < 0.05) but at 10 nmol/l islet amyloid polypeptide these changes did not attain statistical difference. Islet amyloid polypeptide did not have any marked effect on the islet cell death frequency, suggesting that islet amyloid polypeptide is a more potent promoter of proliferation than of programmed cell death. CONCLUSION/INTERPRETATION: Our data indicate islet amyloid polypeptide is a potential regulator of proliferation in neonatal pancreatic islet cells, an effect which can partly be attributed to the proliferation of beta cells.

Amyloid↗

PubMed2006

Protection of human islets from induction of apoptosis and improved islet function with HO-1 gene transduction.

BACKGROUND: Islet transplantation represents an ideal therapeutic approach for treatment of type 1 diabetes but islet function and regeneration may be influenced by necrosis or apoptosis induced by oxidative stress and other insults. Heme oxygenase-1 (HO-1) is the rate-limiting enzyme in the catabolism of heme into biliverdin, releasing free iron and carbon monoxide. It has also been reported to be an antioxidant enzyme which can improve the function of grafted islets by cytoprotection via free radical scavenging and apoptosis prevention. In the present study, we investigated whether transduction of HO-1 genes into human islets with an adenovirus vector has cytoprotective action on islets cultured in vitro and discuss this method of gene therapy for clinical islet transplantation. METHODS: Cadaveric pancreatic islets were isolated and purified in vitro. Transduction efficiency of islets was determined by infecting islets with adenovirus vector containing the enhanced green fluorescent protein gene (Ad-EGFP) at multiplicities of infection (MOI) of 2, 5, 10, or 20. Newly isolated islets were divided into three groups: EGFP group, islets transduced with Ad-EGFP using MOI = 20; HO-1 group, transduced with adenovirus vectors containing the human HO-1 gene using MOI = 20; and control group, mock transduced islets. Insulin release after glucose stimulation of the cell lines was determined by a radioimmunoassay kit and the stimulation index was calculated. Flow cytometry was used to detect apoptotic cells in the HO-1 group and in the control group after induction by recombinant human tumor necrosis factor-alpha (rTNFalpha) and cycloheximide (CHX) for 48 hours. RESULTS: Adenovirus vectors have a high efficiency of gene transduction into adult islet cells. Transduction of islets with the Ad-EGFP was most successful at MOI 20, at which MOI fluorescence was very intense on day 7 after transduction and EGFP was expressed in cultured islet cells for more than four weeks in vitro. The insulin release in the control group was (182.36 +/- 58.96) mIU/L after stimulation by high glucose media (16.7 mmol/L), while insulin release from the HO-1 group and the EGFP group were (270.09 +/- 89.37) mIU/L and (175.95 +/- 75.05) mIU/L respectively. Compared to the control group and the EGFP group, insulin release in the HO-1 group increased significantly (P < 0.05). After treatment with rTNFalpha and CHX the apoptotic ratio of islet cells was (63.09 +/- 10.86)% in the HO-1 group, significantly lower than (90.86 +/- 11.25)% in the control group (P < 0.05). CONCLUSIONS: Transduction of human islets with Ad-HO-1 can protect against TNF-alpha and CHX mediated cytotoxicity. The HO-1 gene also appears to facilitate insulin release from human islets. Transduction of donor islets with the adenovirus vector containing an HO-1 gene might have potential value in clinical islet transplantation.

Adenoviridae↗

PubMed1990

Purified canine islet autografts. Functional outcome as influenced by islet number and implantation site.

Using a modification of the basic principles of pancreatic intraductal collagenase digestion and density gradient purification to isolate canine islets, in conjunction with simultaneous fluorogenic and dithizone islet staining, we quantified the yield, purity, and viability of the isolated islets. We then determined the combined influences of total and weight-corrected islet counts and implantation site on immediate and long-term functional outcome of purified canine islet autografts. Weight-corrected islet counts were 100% sensitive and specific in differentiating successful and unsuccessful islet autografts implanted to the liver (n = 10) and spleen (n = 10) of pancreatectomized dogs. The threshold number of islets required to achieve normoglycemia in the liver (4400 islets/kg) and spleen (4650 islets/kg) were nearly identical. Islet autografts failed to ameliorate hyperglycemia when implanted to the renal subcapsular space (n = 5) at counts of 4400 to 5500 islets/kg. The mean one- and three-month intravenous glucose tolerance test K-values of dogs with purified islet autografts to the liver (-1.43 +/- 0.27 and -1.69 +/- 0.27, respectively) and spleen (-1.78 +/- 0.36 and -1.64 +/- 0.3, respectively) were also similar. Time needed to achieve normoglycemia , however, was significantly (P less than 0.02) shorter for intrahepatic islets (1.0 +/- 0.0 days posttransplant) than intrasplenic islets (6.8 +/- 2.3 days posttransplant). The long-term durability of islet autograft function was not unlimited. Overall, thirteen canine islet autograft recipients have been followed for greater than or equal to 12 months posttransplant (range 12-18 months), seven canine islet autograft recipients (five intrahepatic and two intrasplenic) have had spontaneous recurrence of hyperglycemia at 2, 6, 11, 13, 14, 8, and 16 months, respectively. The phenomenon depended only on the number of islets implanted. The data underscore the significance of quantitatively defined islet preparations and the importance of islet number and implantation site on immediate and long-term functional outcome of canine islet autografts.

Animals↗

PubMed2005

Simple evaluation of engraftment by secretory unit of islet transplant objects for living donor and cadaveric donor fresh or cultured islet transplantation.

BACKGROUND: Evaluation of engraftment is important to assess the success of islet transplantation. Recently we developed secretory unit of islet transplant objects (SUITO) index for simple evaluation of engraftment. Assuming that normal subjects aged <40 years have 100% pancreatic beta-cell function, SUITO index was calculated by the formula: 1500 x fasting C-peptide immunoreactivity [ng/dL]/(fasting blood glucose [mg/dL] - 63). In this study, we compared the efficacy of islet transplantation from cadaveric and living donors using the SUITO index. METHODS: We performed eight islet transplantations with non-heart-beating donors (NHBDs) into five patients. Two patients received fresh islets once, one patient received fresh islets twice, one patient received cultured islets once, and one patient received cultured islets twice plus fresh islets once. In addition, one patient received fresh islets from a living donor. We calculated the SUITO index from postoperative days 3 to 30 for each case. RESULTS: Mean SUITO index after one fresh islet transplant was 11.7 +/- 1.0, after two fresh islet transplants was 28.5 +/- 3.4, after one cultured islet transplant was 2.1 +/- 0.4, after two cultured islet transplant was 12.1 +/- 1.9, and after two cultured islet transplant plus one fresh islet transplant was 26.7 +/- 1.7. The mean SUITO index after single living donor islet transplant was 40.7 +/- 2.6, which was significantly higher compared with all other groups. Insulin independence was obtained when the SUITO index was >26, which might reflect that 26% beta-cell mass was required for insulin independence. CONCLUSION: SUITO index is useful to evaluate islet engraftment and to predict the possibility of insulin independence.

Blood Glucose↗

PubMed2001

Improved in vivo pancreatic islet function after prolonged in vitro islet culture.

BACKGROUND: Difficulties with recovering and preserving pancreatic islets have hampered progress in islet transplantation. In previous in vitro studies, our laboratory successfully demonstrated that using serum-free medium for prolonged pancreatic islet culture allows postculture recovery ratios greater than those obtained with standard media with sustained in vitro islet function. The goal of this study was to determine whether culturing of islets in a modified serum-free medium (M-SFM) would sustain function in vivo. METHODS: Islets were isolated from pancreata procured from 12 cadaveric organ donors and cultured in the M-SFM for up to 2 months, cryopreserved at -70 degrees C within 1-3 days of isolation for 2 months, or placed in short-term culture (3-5 days) before their transplantation under the kidney capsule of nonobese diabetic-severe combined immunodeficient mice (n=4-7 per group/time point). In vivo islet function was assessed by measuring the production of human insulin and C-peptide over a period of 3-15 months. RESULTS: After extended culture of islets in M-SFM for 1 or 2 months, transplanted islets maintained their viability, and in some instances in vivo function improved when compared with short-term cultured islets transplanted from the same preparation (P<0.01). Improvement was particularly evident for islets cultured for 1 month. Furthermore, when compared with cryopreserved preparations, early function (postoperative day 7) of islets from 1-month culture preparations was statistically better (P<0.05). Prolonged culture in M-SFM had no significant impact on long-term function, inasmuch as cultured islets functioned for more than 120 days. CONCLUSION: These data demonstrate that prolonged islet culture in M-SFM sustained viability and function, and in some instances had a positive effect on in vivo islet function, particularly in the 1-month cultures. No negative effect on long-term in vivo function was demonstrated in this study. Confirmation in clinical models utilizing extended (1-2 months) islet culture in M-SFM could significantly enhance islet transplantation by allowing the identification of best-matched recipients, pretransplantation recipient conditioning, and possible pretransplantation islet modifications to promote engraftment and prolonged graft function.

Animals↗

PubMedDate not supplied

Reduced NO production improves early canine islet xenograft function: a role for nitric oxide in islet xenograft primary nonfunction.

Isolated canine islets transplanted to hyperglycemic rats fail to restore euglycemia in almost all cases, although the grafted islet tissue appears to be morphologically intact for up to 48 h following transplantation. Cytokines typically produced in the xenograft environment (e.g., IL-1 and TNF) inhibit insulin biosynthesis and secretion from isolated pancreatic islets, and are associated with the production of nitric oxide (NO). To further define the relationship between NO production and islet xenotransplantation, the inhibition of NO in a splenocyte/islet coculture system, and the in vivo effect of this inhibition on canine islet xenotransplantation, was investigated. Splenocytes (SPLC) from Lewis rats were cocultured with canine islets (freshly isolated or cultured 7 days), supernatant removed, and NO concentration (NO2) determined by optical density (Griess reaction, 550 nm, expressed as nmol nitrite/10(6) cells/18 h). Lipopolysaccharide (LPS) was used as a positive control of SPLC production of NO. Stimulation by LPS resulted in maximal NO production (2.20 +/- 0.16 nmol/10(6) cells/18 h, p < 0.001 compared to baseline values of 0.73 +/- 0.04 nmol/10(6) cells/18 h). In the presence of NO inhibitors (NMA, polymyxin B, hydrocortisone, aminoguanidine, DMSO), nitrite levels did not significantly rise above unstimulated values. Freshly isolated canine islets did stimulate NO production (1.26 +/- 0.12 nmol/10(6) cells/18 h, p < 0.001). In contrast, cultured canine islets did not stimulate NO production (0.84 +/- 0.09 nmol/10(6) cells/18 h). Transplantation of freshly isolated canine islets to STZ-diabetic recipient Lewis rats resulted in amelioration of hyperglycemia in only 50% (n = 6) of recipients 12 h posttransplant, with a return to hyperglycemia at all subsequent time points. Transplantation of 7-day cultured canine islets resulted in amelioration of hyperglycemia in 88% of recipients 12 h posttransplant and 63% of recipients 24 h posttransplant [p = 0.028, mean survival time (MST) = 1.0 days, n = 8]. Transplantation of canine islet xenografts with aminoguanidine therapy (BID, n = 11) resulted in amelioration of hyperglycemia in 100% of recipients at 12 h posttransplant, decreasing to 82% by 24 h following transplantation (p = 0.002, MST = 0.9 days). These results demonstrate that freshly isolated canine islets are potent stimulators of NO production by rat SPLC in vitro, and that culture of canine islets, or addition of NO inhibitors, abrogates stimulated NO production. These results also demonstrate a statistically significant improvement (p < 0.001) in early function of canine islet xenografts following 7 days of islet culture prior to transplant, and following recipient treatment with aminoguanidine. These studies suggest that the production of NO in the microenvironment of the graft site may adversely affect engraftment and function of canine islets, and suggest that the abrogation of islet-stimulated NO production may improve engraftment following islet xenotransplantation.

Animals↗

PubMed1993

Chronic overproduction of islet amyloid polypeptide/amylin in transgenic mice: lysosomal localization of human islet amyloid polypeptide and lack of marked hyperglycaemia or hyperinsulinaemia.

Type 2 (non-insulin-dependent) diabetes mellitus is characterised by hyperglycaemia, peripheral insulin resistance, impaired insulin secretion and pancreatic islet amyloid formation. The major constituent of islet amyloid is islet amyloid polypeptide (amylin). Islet amyloid polypeptide is synthesized by islet beta cells and co-secreted with insulin. The ability of islet amyloid polypeptide to form amyloid fibrils is related to its species-specific amino acid sequence. Islet amyloid associated with diabetes is only found in man, monkeys, cats and racoons. Pharmacological doses of islet amyloid polypeptide have been shown to inhibit insulin secretion as well as insulin action on peripheral tissues (insulin resistance). To examine the role of islet amyloid polypeptide in the pathogenesis of Type 2 diabetes, we have generated transgenic mice with the gene encoding either human islet amyloid polypeptide (which can form amyloid) or rat islet amyloid polypeptide, under control of an insulin promoter. Transgenic islet amyloid polypeptide mRNA was detected in the pancreas in all transgenic mice. Plasma islet amyloid polypeptide levels were significantly elevated (up to 15-fold) in three out of five transgenic lines, but elevated glucose levels, hyperinsulinaemia and obesity were not observed. This suggests that insulin resistance is not induced by chronic hypersecretion of islet amyloid polypeptide. Islet amyloid polypeptide immunoreactivity was localized to beta-cell secretory granules in all mice. Islet amyloid polypeptide immunoreactivity in beta-cell lysosomes was seen only in mice with the human islet amyloid polypeptide gene, as in human beta cells, and might represent an initial step in intracellular formation of amyloid fibrils.(ABSTRACT TRUNCATED AT 250 WORDS)

Amyloid↗

PubMed2005

Pretransplant islet culture: a comparison of four serum-free media using a murine model of islet transplantation.

INTRODUCTION: Human islet transplant protocols frequently incorporate a brief period of islet culture before transplantation. The optimal medium for pretransplant islet culture is unknown. METHODS: We compared four serum-free media formulated for human islets: Miami (MM1), Memphis (M-SFM), Edmonton (EDM), and hCell OCZEM-SF/AF (hCell). Islets isolated from a single human pancreas with purity >80% were cultured in 2500-islet-equivalent (IE) fractions using the media listed. After 7 days, each 2500-IE fraction was grafted under the kidney capsule of a streptozocin-diabetic rag1 mouse (n = 4 per group). Mice were evaluated with serum glucose monitoring, stimulated C-peptide release, and glucose tolerance tests. Islet fractions transplanted immediately after isolation (n = 4 mice) served as controls. In vitro islet function was assessed on days 0 and 3 and included insulin release (after static glucose stimulation), total cellular C-peptide content, cell count, and viability. RESULTS: Glucose control was improved in all cohorts of mice after transplant, but only islet grafts cultured in MM1 were statistically indistinguishable from fresh islets. MM1- and hCell-cultured islet grafts showed improved glucose tolerance compared with fresh islets; C-peptide release was similar among the four cohorts. In vitro, only islets cultured in MM1 had similar stimulation index to fresh islets, whereas only hCell- and MM1-cultured islets demonstrated recovery of C-peptide content and insulin release. CONCLUSIONS: Media choice before transplant can influence islet quality, even when culture periods are short. Miami MM1 and hCell media may provide better islet protection than alternative media.

Animals↗

PubMed2002

The interaction between primate blood and mouse islets induces accelerated clotting with islet destruction.

BACKGROUND: Mouse islets transplanted under the renal subcapsular space of cynomolgus monkeys are subject to a form of hyperacute rejection, the mechanism of which is unclear. As islets are in contact with whole blood at the time of transplantation, the effect of platelets and the coagulation cascade on islet destruction was assessed. METHODS: Coagulation was assessed using thromboelastography on citrated/recalcified human blood samples with freshly isolated C57/Bl6 mouse islets. A dynamic islet perifusion system was used to assess the effect of islets on blood cells and coagulation factors. Cytotoxicity was evaluated using (51)Cr labelled islets incubated with human blood and islet destruction was also evaluated using a histological grading system. Continuous PO(2) measurements were made in a static incubation system to assess the role of hypoxia in islet destruction. RESULTS: Mouse islets incubated in human blood induced accelerated coagulation and rapid consumption of platelets within 15 min. Within 1 h of incubation, 52% of mouse islets exposed to xenogeneic human blood showed features of severe damage with necrosis when compared with islets incubated in syngeneic blood. Specific lysis of the xenogeneic islets was demonstrable (Mean percentage lysis: 48%, P < 0.05 vs. control) after 4 h incubation in human blood. Oxygen levels remained constant at a level adequate to maintain islet viability in separate experiments. CONCLUSION: Mouse islets induce rapid activation of the clotting cascade and platelet consumption in vitro when exposed to human blood, which correlated with histological evidence of significant destruction demonstrable within 1 h of exposure to human or non-human primate blood. This in vitro model has features which appear to correlate with the islet destruction seen in vivo and could be a useful model for the study of the mechanisms underlying the rapid destruction of xenogeneic islets in primate recipients.

Animals↗

PubMed1997

Assessment of insulin secretion in vitro from microencapsulated fetal porcine islet-like cell clusters and rat, mouse, and human pancreatic islets.

BACKGROUND: The possibility of transplanting microencapsulated pancreatic islets into patients with insulin-dependent diabetes mellitus, either as allografts or xenografts, has attracted great interest. A critical evaluation of the results obtained reveals that the success has been very limited. The aim of the present study was to compare the in vitro function of microencapsulated islets obtained from adult humans, adult mice, adult rats, and fetal pigs. METHODS: Human pancreatic islets were isolated at beta-Cell Transplant in Brussels, Belgium, and sent to the Department of Medical Cell Biology, Uppsala University in Uppsala, Sweden. Rat and mouse pancreatic islets and fetal porcine islet-like cell clusters (ICC) were prepared in Uppsala. All groups of islets were subsequently sent to the Department of Biotechnology, Norwegian Institute of Biotechnology, University of Trondheim, Trondheim, Norway. After 1 day in tissue culture, the islets were microencapsulated in alginate then cultured and sent back to Uppsala the next day. After either overnight culture (day 1) or 6 days of culture (day 6), the microencapsulated islets were examined for their insulin content and insulin release. Nonencapsulated islets from the same isolations were used as controls. RESULTS: The insulin content of rodent and human islets was not affected by microencapsulation, whereas porcine ICC showed a diminished insulin content. Microencapsulated porcine ICC also had a marked reduction in their insulin secretion in response to stimulation with glucose or glucose + theophylline both on days 1 and 6 in tissue culture. Mouse islets showed a reduced insulin response at both time points. Rat islets exhibited an inhibition of insulin secretion on day 1, but this had been restored by day 6. Human islets had well-preserved insulin secretion after both days 1 and 6. Microencapsulated human islets showed a normal morphology 3-4 weeks after intraperitoneal transplantation to nude mice. CONCLUSIONS: Pancreatic islets isolated from human, rat, and mouse donors show a glucose-stimulated insulin release in vitro after microencapsulation and repeated transports between laboratories. The insulin secretory capacity of microencapsulated human and rat islets was preserved best, whereas mouse islets and particularly fetal porcine ICC were impaired by microencapsulation.

Adult↗

PubMed1992

The effect of transplantation site and islet mass on long-term survival and metabolic and hormonal function of canine purified islet autografts.

Determination of the long-term function of islet transplantation in relation to the implantation site and the numbers of islets is of scientific interest and, with human islet transplant trials in progress, is a pressing clinical question. In this study, highly purified canine islets were isolated by collagenase digestion and Ficoll purification, and autotransplanted into either the spleen (in 10 dogs) or the liver (in 12 dogs). Dogs transplanted with islets into the spleen or liver received 264,300 +/- 20,300 (mean +/- SEM) and 158,600 +/- 15,000 islet equivalents (150-microns-sized islets) respectively. Graft survival at 1 yr was 86% in intrasplenic islet autografts (ISTx) and 50% in intraportal islet autografts (IPTx). Intravenous glucose tolerance tests and mixed meal-oral glucose tests were performed 1-12 mo from islet transplantation. Compared to controls, ISTx and IPTx dogs showed a similar decrease of glucose tolerance after both intravenous glucose tolerance tests and mixed meal-oral glucose tests. On intravenous glucose tolerance tests, plasma insulin levels were lower in ISTx than in IPTx dogs and controls. On mixed meal-oral glucose tests, insulin values were higher in IPTx dogs than in controls. There was a positive correlation (r = .56, p < 0.05) between the number of transplanted islet equivalents and the K values. These results demonstrate that, in dogs with islet transplant: 1) long-term islet survival can be achieved in the spleen better than in the liver; 2) islet survival is related to the mass of transplanted islets in the spleen, but not in the liver, where other factors probably affect islet survival; 3) the ability of metabolizing glucose is reduced after both intrasplenic and intraportal islet autografts; 4) both reduced insulin secretion (predominant in ISTx dogs on intravenous glucose tolerance testing) and insulin resistance (predominant in IPTx dogs on mixed meal-oral glucose tests) are the probable causes of the decreased glucose tolerance.

Animals↗

PubMed1999

Incompatibility between human blood and isolated islets of Langerhans: a finding with implications for clinical intraportal islet transplantation?

The remarkable difference in success rates between clinical pancreas transplantation and islet transplantation is poorly understood. Despite the same histocompatibility barrier and similar immunosuppressive treatments in both transplantation procedures, human intraportal islet transplantation has a much inferior success rate than does vascularized pancreas transplantation. Thus far, little attention has been directed to the possibility that islets transplanted into the blood stream may elicit an injurious incompatibility reaction. We have tested this hypothesis in vitro with human islets and in vivo with porcine islets. Human islets were exposed to nonanticoagulated human ABO-compatible blood in surface-heparinized polyvinyl chloride tubing loops. Heparin and/or the soluble complement receptor 1 (sCR1) TP10 were tested as additives. Adult porcine islets were transplanted intraportally into pigs, and the liver was recovered after 60 min for immunohistochemical staining. Human islets induced a rapid consumption and activation of platelets. Neutrophils and monocytes were also consumed, and the coagulation and complement systems were activated. Upon histological examination, islets were found to be embedded in clots and infiltrated with CD11+ leukocytes. Furthermore, the cellular morphology was disrupted. When heparin and sCR1 were added to the blood, these events were avoided. Porcine islets retrieved in liver biopsies after intraportal islet allotransplantation showed a morphology similar to that of human islets perifused in vitro. Thus, exposure of isolated islets of Langerhans to allogenic blood resulted in significant damage to the islets, a finding that could explain the unsatisfactory clinical results obtained with intraportal islet transplantation. Because administration of heparin in combination with a soluble complement receptor abrogated these events, such treatment would presumably improve the outcome of clinical islet transplantation by reducing both initial islet loss and subsequent specific immune responses.

Adult↗

PubMed2005

Donor islet endothelial cells participate in formation of functional vessels within pancreatic islet grafts.

Pancreatic islet transplantation has emerged as a therapy for type 1 diabetes and is today performed using both freshly isolated and cultured islets. Islet blood vessels are disrupted during islet isolation; therefore, proper revascularization of the transplanted islets is of great importance for islet graft function and survival. We have studied intraislet endothelial cells after islet isolation, during islet culture, and following islet transplantation. By isolating islets from the transgenic Tie2-GFP (green fluorescent protein) mouse, characterized by an endothelial cell-specific expression of GFP, living endothelial cells could be studied in intact islets utilizing two-photon laser-scanning microscopy (TPLSM). Intraislet endothelial cells were found to survive islet transplantation but to rapidly disappear during islet culture. By transplanting freshly isolated Tie2-GFP islets and applying a novel ex vivo model for simultaneous perfusion and TPLSM imaging of the graft-bearing kidneys, GFP fluorescent endothelial cells were found to extensively contribute to vessels within the islet graft vasculature. Real-time imaging of the flow through the islet graft vasculature confirmed that the donor-derived vessels were functionally integrated. Hence, intraislet endothelial cells have the capability of participating in revascularization of pancreatic islets subsequent to transplantation. Therefore, preservation of intraislet endothelial cell mass may improve long-term graft function.

Animals↗

PubMed1988

Heterogeneities of the islets in the rabbit pancreas and the problem of "paracrine" regulation of islet cells.

In addition to "external" signals conveyed by the circulation or the nervous system, the pancreatic islets obviously are regulated also by "internal" (intra-islet) signals, e.g. by the islet hormones: insulin (B-), glucagon (A-), and somatostatin (D-) cells are able to affect the secretion of the heterologous cell types. It is, however, unclear whether this functional cooperation between islet cells occurs by an intercellular route (paracrinia sensu strictore), by intra-islet "portal" vessels, or by the systemic circulation. These likely interactions are limited by islet anatomy. To identify the anatomical basis for the mutual functional relationships between the islet cells, islets of Langerhans in the rabbit pancreas were completely analyzed in immunostained serial semithin (0.5 micron) sections. The islets were found to be largely heterogenous. They were classified in three basic types: a) polycellular islets, composed of all established endocrine cells, and including two subtypes of islets, b) bicellular islets, containing only B- and A-cells or B- and D-cells, and c) monocellular islets, exclusively made up of B-cells. Concerning the modes of paracrine regulation of islet cells, the findings suggest primarily an endocrinous route of transport of the islet peptides to heterologous endocrine cells. The corresponding functional cooperation between islet cells probably is mediated rather by the systemic circulation than by intra-islet portal vessels.

Aging↗

PubMed1999

Pancreatic islet cell survival following islet isolation: the role of cellular interactions in the pancreas.

The purpose of this study was to characterize the trophic effect of pancreatic duct cells on the islets of Langerhans. Ductal epithelium and islets were isolated from hamster pancreata. In addition, duct-conditioned medium (DCM) was prepared from primary duct cultures that had been passaged twice to remove other cellular elements. Three experimental groups were then established: Group 1, 100 islets alone; Group 2, 100 islets+80 duct fragments; and Group 3, 100 islets in 25% DCM. All tissues were embedded in rat tail collagen for up to 12 days and the influence of pancreatic ductal epithelium on islet cell survival was examined. By day 12, 20.6+/-3. 0% (S.E.M.) of the islets cultured alone developed central necrosis, compared with 6.7+/-2.0% of the islets co-cultured with ducts and 5.6+/-1.5% of the islets cultured in DCM (P<0.05). The presence of apoptotic cell death was determined by a TdT-mediated dUTP-biotin nick end labelling (TUNEL) assay and by a specific cell death ELISA. DNA fragmentation in islets cultured alone was significantly increased compared with islets cultured either in the presence of duct epithelium or in DCM (P<0.05). More than 80% of TUNEL-positive cells were situated in the inner 80% of the islet area, suggesting that most were beta-cells. DCM was analysed for known growth factors. The presence of a large amount of IGF-II (34 ng/ml) and a much smaller quantity of nerve growth factor (4 ng/ml) was identified. When the apoptosis studies were repeated to compare islets alone, islets+DCM and islets+IGF-II, the cell death ELISA indicated that IGF-II produced the same beneficial result as DCM when compared with islets cultured alone. We conclude that pancreatic ductal epithelium promotes islet cell survival. This effect appears to be mediated in a paracrine manner by the release of IGF-II from cells in the ductal epithelium.

Animals↗