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 271 records · Page 15Linked to original sources

PubMed1984

In vitro lymphocyte recognition of islet cells following in vivo priming with allogeneic murine pancreatic islets.

Lymphocytes from patients with insulin-dependent diabetes have been shown to be sensitized to pancreatic tissue antigens. Mice immunized with homologous pancreatic islets have been found to develop glucose intolerance and insulitis. Since lymphocytes may be involved in diabetogenesis, we wished to determine if lymph node cells from islet-immunized mice can recognize and respond to islet cells in vitro. A.TL female mice were immunized with an emulsion of BALB/c islet homogenate and complete Freund's adjuvant (CFA); sham-treated A.TL mice were injected with adjuvant and water. Mice were sacrificed 7-8 days later and the draining lymph nodes were removed. The lymph node cells were co-cultured with freshly prepared irradiated BALB/c islet cell, which served as stimulator cells. The co-cultures were incubated for 24-26 h at 37 degrees C, followed by a 16 h [3H]thymidine (TdR) pulse. A significant proliferation of lymph node cells from islet-primed mice was induced during the in vitro stimulation with irradiated islet cells when compared with lymph node cells from sham-treated mice (P less than 0.001). The response may be islet-cell-specific, since irradiated lymph node cells from BALB/c mice failed to elicit a proliferative response under the same culture conditions (P greater than 0.80).

Animals↗

PubMed1999

Maintenance of beta-cell function and survival following islet isolation requires re-establishment of the islet-matrix relationship.

Islet transplantation is associated with a high rate of early graft failure, a problem that remains poorly understood. It is probable that the destruction of the islet microenvironment and loss of tropic support that occur during isolation lead to compromised survival. The purpose of this study was to determine the role of matrix-integrin interactions on beta-cell survival and function following islet isolation. Canine islets were obtained by conventional methods. Immediately after isolation, the peri-insular basement membrane (BM) was absent. The ability of islets maintained in suspension culture to attach to a collagen matrix declined progressively over 6 days. Attachment could be blocked by an arginine-glycine-aspartate (RGD) motif-presenting synthetic peptide, thereby implicating an integrin-mediated process. Characterization of cell surface integrins by immunocytochemistry (ICC) demonstrated that the expression of integrins alpha3, alpha5 and alphaV diminished during the culture period. This change was coincident with both a decrease in beta-cell function (proinsulin gene expression, islet insulin content and stimulated insulin release) and a rise in beta-cell death from apoptosis, as determined by in situ cell death detection (TUNEL) assay. These adverse events were prevented or delayed by exposure of islets to matrix proteins. In conclusion, routine islet isolation disrupts the cell-matrix relationship leading to a variety of structural and functional abnormalities, including apoptotic cell death. These alterations can be diminished by restoration of a culture microenvironment that includes matrix proteins.

Animals↗

PubMed1991

Transplantation of purified islet cells in diabetic rats. I. Standardization of islet cell grafts.

A standardized procedure was developed for the preparation of rat islet cell grafts with selected cell number and composition. After collagenase digestion of pancreases and elutriation of tissue fragments, islets were isolated and dissociated, and cells were purified by autofluorescence-activated cell sorting. Approximately 30% of the initial beta-cell mass was lost during digestion and elimination of small mostly exocrine particles. Fifty percent was recovered in isolated islet preparations and 30% in the purified beta-cell suspensions of greater than 95% purity and viability. Sorting according to cellular flavin adenine dinucleotide content discriminated islet beta-cells from islet endocrine non-beta-cells, fibroblasts, leukocytes, and exocrine cells. Purified endocrine islet cell grafts were prepared by aggregating 10(6) pure beta-cells with or without 8 x 10(5) pure endocrine non-beta-cells. In contrast to intact islets, the purified aggregates were devoid of nonendocrine and damaged cells. Intraportal implantation of a pure beta-cell graft rapidly and permanently normalized the diabetic state of streptozocin-administered animals. The standardized preparation of purified beta-cell grafts allows us to address several metabolic and immunological questions concerning islet cell transplantation in diabetes.

Animals↗

PubMed2001

Transgenic overexpression of hepatocyte growth factor in the beta-cell markedly improves islet function and islet transplant outcomes in mice.

Recent advances in human islet transplantation have highlighted the need for expanding the pool of beta-cells available for transplantation. We have developed three transgenic models in which growth factors (hepatocyte growth factor [HGF], placental lactogen, or parathyroid hormone-related protein) have been targeted to the beta-cell using rat insulin promoter (RIP). Each displays an increase in islet size and islet number, and each displays insulin-mediated hypoglycemia. Of these three models, the RIP-HGF mouse displays the least impressive phenotype under basal conditions. In this study, we show that this mild basal phenotype is misleading and that RIP-HGF mice have a unique and salutary phenotype. Compared with normal islets, RIP-HGF islets contain more insulin per beta-cell (50 +/- 5 vs. 78 +/- 9 ng/islet equivalent [IE] in normal vs. RIP-HGF islets, P < 0.025), secrete more insulin in response to glucose in vivo (0.66 +/- 0.06 vs. 0.91 +/- 0.10 ng/ml in normal vs. RIP-HGF mice, P < 0.05) and in vitro (at 22.2 mmol/l glucose: 640 +/- 120.1 vs. 1,615 +/- 196.9 pg. microg protein(-1). 30 min(-1) in normal vs. RIP-HGF islets, P < 0.01), have two- to threefold higher GLUT2 and glucokinase steady-state mRNA levels, take up and metabolize glucose more effectively, and most importantly, function at least twice as effectively after transplantation. These findings indicate that HGF has surprisingly positive effects on beta-cell mitogenesis, glucose sensing, beta-cell markers of differentiation, and transplant survival. It appears to have a unique and unanticipated effective profile as an islet mass- and function-enhancing agent in vivo.

Animals↗

PubMed1999

Structural and functional changes resulting from islet isolation lead to islet cell death.

BACKGROUND: Islet isolation exposes the islet to a variety of cellular stresses and disrupts the cell-matrix relationship--events known to be associated with apoptosis. The purpose of this study was to determine whether islet isolation leads invariably to islet cell death and to specify the mechanisms involved. METHODS: Canine islets were isolated using Liberase CI and purified using a centrifuge. Islets were sampled for up to 5 days in culture and analyzed by routine histology, electron microscopy, immunocytochemistry, and reticulin staining for basement membrane. Apoptosis was assessed by cell death enzyme-linked immunosorbent assay and terminal deoxynucleotidyl transferase-mediated decoxyuridine triphosphate nick and labeling (TUNEL) assay. Activation of the prosurvival ERK1/2 and proapoptotic p38 and JNK were determined by immunoblotting. RESULTS: Immediately after isolation, the peri-insular basement membrane was absent, and integrin-alpha 5 expression diminished. DNA fragmentation rose from 2.5 +/- 1.8 (arbitrary units) on the day of isolation to 42.4 +/- 6.7 48 hours later (P < .05), coinciding with the appearance of pyknotic nuclei and apoptotic bodies. The apoptotic index determined by TUNEL assay increased from 5% +/- 1% on the day of isolation to 60% +/- 2% on day 5 (P < .01), and most of the affected cells were beta-cells. Finally, the p38 and JNK activity were elevated relative to ERK1/2. CONCLUSIONS: During isolation, islet cells undergo profound changes in structure and function, resulting in beta-cell apoptosis. These findings suggest that strategies directed to the manipulation of the cell-matrix relationship and the modulation of mitogen-activated protein kinase signal transduction may offer a valuable new approach to improving islet transplant outcome.

Animals↗

PubMed1989

Trophic factors from pancreatic islets in combined hepatocyte-islet allografts enhance hepatocellular survival.

The purpose of this study was to determine the effect of pancreatic islets on the survival of clusters of rat hepatocytes transplanted across a major histocompatibility barrier into an ectopic site. Aggregates of hepatocytes and pancreatic islets were obtained from Wistar-Furth rats by an automated method of collagenase digestion. Approximately 8000 Wistar-Furth hepatocyte clusters (100 to 300 micron diameter) were transplanted beneath the renal capsule of Lewis rats with or without the addition of 800 pancreatic islets. Recipients received subcutaneous injections of cyclosporine A (CsA): 30 mg/kg on days 0, 1, and 2, 10 mg/kg on days 3 to 7, and 10 mg/kg every other day for days 8 to 28. In the absence of CsA recipient treatment, all the allografts were rejected within 7 days. The combined hepatocyte-islet allografts in recipients treated with CsA showed maintenance of morphologic integrity of both hepatocytes and islet cells 1, 2, and 4 weeks after transplantation, whereas in the absence of pancreatic islets, the hepatocellular aggregates degenerated despite CsA treatment, leaving only a thin rim of hepatocytes immediately adjacent to the renal parenchyma. It can be concluded that in immunosuppressed recipients hepatocyte-islet renal subcapsular allografts survived despite the presence of an intact liver, which indicates a possible role of trophic factors released locally from the islets.

Animals↗

PubMed1989

Induction of Ia antigen expression on murine islet parenchymal cells does not diminish islet allograft survival.

Aberrant Ia antigen expression has been implicated in the pathogenesis of type 1 diabetes. Ia antigen expression was induced on isolated B10.BR murine islet parenchymal cells by culturing them for 5 days with lymphokine supernatants containing interferon-gamma (IFN-gamma) or with recombinant murine IFN-gamma + recombinant tumor necrosis factor. Ia positivity was confirmed by indirect immunofluorescence. Islets cultured for 5 days without cytokines were Ia-negative. Purified B10.BR islets allografted into the portal veins of C57BL/6J mice do not reject, which allowed the authors to determine whether aberrant expression of Ia on parenchymal cells has a deleterious effect on allograft survival. Ia-positive or Ia-negative islets were transplanted via the portal vein into diabetic C57BL/6J mice. All mice remained normoglycemic until they were killed at 30 to 60 days. Well-granulated islet allografts were identified histologically in all mice. The experiment was repeated using Balb/cJ mice as donors. Purified Balb/cJ islets are rapidly rejected by C57BL/6J mice. Induction of Ia expression on Balb/cJ islets significantly improved allograft survival. These findings indicate that Ia-positive islet cells do not induce rejection in these allograft models but may actually have a protective effect.

Animals↗

PubMed1985

Evidence for a direct action of exogenous insulin on the pancreatic islets of diabetic mice: islet response to insulin pre-incubation.

Pancreatic islets were isolated by collagenase digest from normal (+/+) and severely diabetic (db/db) mice of the C57BL/Ks strain. Batches of islets from the diabetic mice were incubated for 1 h at 37 degrees C in Krebs-Ringer medium containing glucose (3 mmol/l), with or without mouse insulin (50 mU/l), before perifusion. When compared with untreated islets from the same digest, pre-incubation of islets from diabetic mice with insulin elicited a restoration of the biphasic insulin response to a glucose challenge which was indistinguishable from the response of the untreated, control islets from non-diabetic mice. Untreated diabetic islets showed no insulin response to glucose challenge, insulin values being very significantly lower than those of either non-diabetic or treated diabetic mouse islets (p = less than 0.005). The restoration of secretion in treated islets of diabetic mice was shown not to be an artefact. These observations provide evidence for a direct, as yet undefined, action of insulin on the beta cell of the diabetic mouse.

Animals↗

PubMed1989

Co-localization of islet amyloid polypeptide and insulin in the B cell secretory granules of the human pancreatic islets.

Islet amyloid polypeptide is a novel 37 amino-acid-residues polypeptide which has been isolated from amyloid deposits in an insulinoma, and in human and cat islets of Langerhans. The molecule has 46% homology with the calcitonin gene-related peptide. Light microscopy examination of the pancreas shows that islet amyloid polypeptide immunoreactivity is restricted to the islet B cells. The present study utilized a rabbit antiserum against a synthetic peptide corresponding to positions 20-29 of islet amyloid polypeptide, a sequence without any amino-acid identity with calcitonin gene-related peptide. By applying the immunogold technique at the ultrastructural level, it was shown that both insulin and islet amyloid polypeptide immunoreactivity occurs in the central granular core of the human B cell secretory granules, while the A cells remain unlabelled. The demonstration that islet amyloid polypeptide is a granular protein of the B cells may indicate that it is released together with insulin. Further studies are necessary to evaluate the functional role of islet amyloid polypeptide.

Aged↗

PubMed2005

Increased expression of cyclooxygenase-2 in human pancreatic islets treated with high glucose or ligands of the advanced glycation endproduct-specific receptor (AGER), and in islets from diabetic mice.

AIMS/HYPOTHESIS: The cyclooxygenase-2 (PTGS2, previously known as COX2) enzyme and its products, such as prostaglandin E(2) (PGE(2)), have been implicated in the pathogenesis of several inflammatory diseases including islet dysfunction under diabetic conditions. In this study we evaluated whether diabetic conditions in vitro, such as high-glucose (HG) culture or AGE, or in vivo in animal models of diabetes can induce PTGS2 expression and activity in pancreatic islets. MATERIALS AND METHODS: Isolated human pancreatic islets were treated for 24 h with HG (25 mmol/l) or with S100b (5 mg/l), a specific ligand for the AGE-specific receptor. PTGS2 and cyclooxygenase-1 (PTGS1, previously known as COX1) mRNA, protein expression and product PGE(2) were analysed by RT-PCR, Western blots and specific enzyme immunoassay respectively. Islet PTGS2 production in animal models was assessed by immunofluorescence. RESULTS: Treatment of human pancreatic islets with HG and S100b led to a three-five-fold induction of PTGS2 mRNA (p<0.001). PTGS2 protein and its product PGE(2) (351.4+/-13.05 fg/ml vs control 39.4+/-0.11 fg/ml) were also increased (p<0.001). Pretreatment with specific inhibitors demonstrated the involvement of protein kinase C and oxidant stress in S100b- and HG-induced PTGS2 expression. However, insulin secretion was not significantly altered by S100b. Double immunofluorescent staining showed increased PTGS2 production in pancreatic islets from diabetic mice relative to corresponding controls. CONCLUSION/INTERPRETATION: These results show for the first time that diabetes as well as diabetic conditions such as AGE and HG in vitro can directly upregulate the expression of the inflammatory PTGS2 gene in pancreatic islets. This might contribute to the pathogenesis of islet dysfunction in diabetes.

Animals↗

PubMed2001

Monocyte chemoattractant protein-1 is expressed in pancreatic islets from prediabetic NOD mice and in interleukin-1 beta-exposed human and rat islet cells.

AIMS/HYPOTHESIS: Monocyte chemoattractant protein-1 (MCP-1) attracts monocytes and T lymphocytes, and could thus contribute to mononuclear cell infiltration in Type I (insulin-dependent) diabetes mellitus. Cytokines induce MCP-1 mRNA expression in pancreatic rat beta cells. To investigate this issue, we analysed the signal transduction for IL-1 beta-induced MCP-1 expression in rat beta cells and in vitro MCP-1 mRNA expression and protein release by human islets as well as in vivo islet MCP-1 mRNA expression in prediabetic non-obese diabetic mice. METHODS: Fluorescence-activated cell sorting-purified rat beta cells were cultured for 6 h with IL-1 beta (30 U/ml) or MAPK inhibitors or both. Human islets were cultured for 6-72 h with the cytokines IL-1 beta, IFN-gamma or the inducible nitric oxide synthase (iNOS) inhibitor NG-methyl-L-arginine or both. We measured MCP-1 mRNA by RT-PCR and protein by ELISA. The MCP-1 mRNA expression in islets from male and female non-obese diabetic mice (2-12 weeks of age) was measured by real time reverse transcription-polymerase chain reaction (RT-PCR). RESULTS: Interleukin-1 beta induced MCP-1 mRNA expression in rat beta cells, with a maximum induction after 6 h. A combination of p38 and ERK1/2 inhibitors decreased MCP-1 expression by 70%. IL-1 beta induced both MCP-1 mRNA expression and a threefold increase in medium MCP-1 protein accumulation in human islet cells. This effect was not prevented by iNOS blockers. In vivo there was an age-related increase in MCP-1 mRNA expression in islets from male and female non-obese diabetic mice, reaching a peak at 8 weeks. CONCLUSIONS/INTERPRETATION: In rat and human islet cells MCP-1 mRNA is induced by IL-1 beta. Both ERK1/2 and p38 MAPK, but not nitric oxide, contribute to MCP-1 expression. In non-obese diabetic mice MCP-1 mRNA expression increases with age, peaking at the early phases of insulitis. The production of MCP-1 by pancreatic beta cells could contribute to the recruitment of mononuclear cells into pancreatic islets in early Type I diabetes.

1-Methyl-3-isobutylxanthine↗

PubMed2007

Differential susceptibility of chick and mouse islets to streptozotocin and its co-relation with islet antioxidant status.

Species differences in susceptibility of islets to STZ in different mammals have been well documented. Likewise, failure of diabetes induction in birds by streptozotocin has been reported. We hypothesized that the susceptibility of islets to STZ treatment may be related to generation of reactive oxygen species (ROS) and their antioxidant defense mechanisms. To test this hypothesis, we measured the total ROS generated and estimated the damage caused to the chick islets due to STZ treatment, in terms of lipid peroxidation, protein carbonyl formation and DNA strand breaks and compared it with that of mouse islets. We also compared the activities of antioxidant enzymes like catalase, superoxide dismutase (SOD), glutathione peroxidase (GPX), glutathione reductase (GR) and amount of antioxidant molecules like reduced glutathione (GSH) and uric acid under control and STZ-treated conditions. These studies coupled with viability, functionality and presence of glucose transporter GLUT2 in chick and mouse islets clearly indicated that STZ treatment neither affects viability nor functionality of chick islets whereas those of mouse islets are affected significantly. Here we demonstrate for the first time a correlation between the generation of ROS on STZ treatment and antioxidant status with insensitivity of chick islets to STZ resulting into failure of diabetes induction in chick.

Animals↗

PubMed1985

Arachidonic acid metabolism in isolated pancreatic islets. IV. Negative ion-mass spectrometric quantitation of monooxygenase product synthesis by liver and islets.

Deuterium-labelled standards of four regionally isomeric epoxyeicosatrienoic acids (EETs) and their hydrolysis products, the dihydroxyeicosatrienoic acids (DHETs), have been prepared and analyzed by capillary column gas chromatography (GC)-negative ion (NI)-methane chemical ionization (MCI)-mass spectrometry (MS) as the pentafluorobenzyl esters. As little as 40 pg of these compounds were readily visualized by these methods, and the deuterium-labelled standards were used in a stable isotope dilution mass spectrometric assay which was linear from near the detection limit over several orders of magnitude. NADPH-dependent synthesis of both EETs and DHETs from arachidonate by hepatic microsomal cytochrome P-450-mono-oxygenase activity was demonstrable with these methods and was significantly suppressed by the compound BW755C (500 microM), but not by eicosa-5,8,11,14-tetraynoic acid (ETYA, 20 microM) or by nordihydroguaiaretic acid (NDGA, 50 microM). All three compounds suppress glucose-induced insulin secretion and 12-hydroxyeicosatetraenoic acid (12-HETE) synthesis by isolated pancreatic islets with similar concentration dependence. Microsomes derived from isolated pancreatic islets synthesized less than 3% of the EET and DHET compounds as a comparable amount of hepatic microsomes. Intact islets synthesized less than 3% by mass of the EET and DHET compounds compared to the mass of 12-HETE produced by the islets. Islets also failed to convert 3H-labelled arachidonate to 3H-labelled EETs or DHETs under conditions where conversion to [3H]12-HETE and to [3H]prostaglandin E2 (but not to [3H]leukotriene C4, D4, or E4) was clearly demonstrable. Neither exogenous EETs nor leukotriene C4 stimulated insulin secretion from the isolated islets or reversed the suppression of glucose-induced secretion by the lipoxygenase inhibitor BW755C. The cytochrome P-450-monooxygenase inhibitor, metyrapone (50 microM), did not influence insulin secretion from the isolated islets under conditions where the lipoxygenase inhibitor, NDGA, suppressed glucose-induced secretion. These observations argue against the recently suggested hypothesis that EETs derived from arachidonate by monooxygenase action participate in glucose-induced insulin secretion by isolated pancreatic islets.

4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyraz↗

PubMed1989

Effects of lactate on pancreatic islets. Lactate efflux as a possible determinant of islet-cell depolarization by glucose.

The secretion of insulin from perifused rat pancreatic islets was stimulated by raising the glucose concentration from 5.6 to 20 mM or by exposure to tolbutamide. The addition of sodium lactate (40 mM) to islets perifused in the presence of glucose (5.6 mM) resulted in a small, transient, rise in the rate of secretion. The subsequent removal of lactate, but not glucose or tolbutamide, from the perifusate produced a dramatic potentiation of insulin release. The rate of efflux of 45Ca2+ was also increased when islets were exposed to a high concentration of glucose or lactate or to tolbutamide, and again subsequently upon withdrawal of lactate. Efflux of 86Rb+ was modestly inhibited upon addition of lactate and markedly enhanced by the subsequent withdrawal of lactate from islets. The output of [14C]lactate from islets incubated in the presence of [U-14C]glucose increased linearly with increasing concentrations of glucose (1-25 mM). It is proposed that the activation of islets by the addition or withdrawal of lactate is not due to increased oxidative flux, but occurs as a result of the electrogenic passage of lactate ions across the plasma membrane, resulting in islet-cell depolarization, Ca2+ entry and insulin secretion. The production of lactate via the glycolytic pathway, and the subsequent efflux of lactate from the islet cells with concomitant exchange of H+ for Na+, could be a major determinant of depolarization and hence insulin secretion, in response to glucose.

Animals↗

PubMed1992

Nitric oxide and cyclic GMP formation induced by interleukin 1 beta in islets of Langerhans. Evidence for an effector role of nitric oxide in islet dysfunction.

Treatment of pancreatic islets with interleukin 1 (IL-1) results in a time-dependent inhibition of glucose-stimulated insulin secretion which has recently been demonstrated to be dependent on the metabolism of L-arginine to nitric oxide. In this report IL-1 beta is shown to induce the accumulation of cyclic GMP (cGMP) in a time-dependent fashion that mimics the time-dependent inhibition of insulin secretion by IL-1 beta. The accumulation of cGMP is dependent on nitric oxide synthase activity, since NG-monomethyl-L-arginine (a competitive inhibitor of nitric oxide synthase) prevents IL-1 beta-induced cGMP accumulation. cGMP formation and nitrite production induced by IL-1 beta pretreatment of islets are also blocked by the protein synthesis inhibitor, cycloheximide. The formation of cGMP does not appear to mediate the inhibitory effects of IL-1 beta on insulin secretion since a concentration of cycloheximide (1 microM) that blocks IL-1 beta-induced inhibition of glucose-stimulated insulin secretion and nitric oxide formation does not prevent cGMP accumulation, thus dissociating the two events. By using e.p.r. spectroscopy, IL-1 beta is shown to induce the formation of a g = 2.04 iron-nitrosyl feature in islets which is prevented by cycloheximide, demonstrating the requirement of protein synthesis for IL-1 beta-induced nitric oxide formation. Iron-nitrosyl complex-formation by islets confirms that IL-1 beta induces the generation of nitric oxide by islets, and provides evidence indicating that nitric oxide mediates destruction of iron-sulphur clusters of iron-containing enzymes. Consistent with the destruction of iron-sulphur centres is the finding that pretreatment of islets with IL-1 beta results in an approx. 60% inhibition of mitochondrial oxidation of D-glucose to CO2. Inhibition of islet glucose oxidation appears to be mediated by nitric oxide since both NMMA and cycloheximide prevent IL-1 beta-induced inhibition of glucose oxidation. These results show that IL-1 beta-induced nitric oxide formation parallels the ability of IL-1 beta to inhibit glucose-stimulated insulin secretion by islets, and that protein synthesis is required for IL-1 beta-induced nitric oxide formation. These results also suggest that nitric oxide mediates IL-1 beta-induced inhibitory effects on the pancreatic beta-cell by functioning as an effector molecule responsible for the destruction of iron-sulphur centres of iron-containing proteins, resulting in an impairment of mitochondrial function.

Amino Acid Oxidoreductases↗

PubMed1990

Humoral-mediated anti-islet cytotoxicity in diabetes-prone BB/OK rats--effect on beta-cell function and autologous islets.

The present study investigates whether sera from diabetic BB/OK rats impair beta-cell-specific functions of rat pancreatic islets and whether humoral-mediated cytotoxicity in BB rat sera also affects the autologous islets of normoglycaemic serum donors. Exposure of neonatal rat islets of Langerhans for 20 h to sera from diabetic BB rats and rabbit complement resulted in a decrease in insulin content and in insulin release upon glucose stimulation. However, the extent of islet alterations caused by sera from various BB rats was different as revealed by comparison of the ability of beta-cells to restore their functions during a 48 h recovery period. While the effect of some of the sera was completely reversible, in other cases the insulin content and/or the secretory capacity of the islets could not be fully restored indicating partially irreversible islet alterations due to pretreatment with cytotoxic BB rat serum. The potential effect of anti-islet cytotoxicity in BB rat sera against autologous islets of the serum donor indicated by enhanced 51Cr-release in the presence of rabbit complement was proven in 50% (6/12) of the investigated normoglycaemic BB/OK rats. These results suggest that humoral-mediated cytotoxicity may contribute to beta-cell alteration in this model of diabetes.

Animals↗

PubMed1984

Comparison of prohormone-processing activities in islet microsomes and secretory granules: evidence for distinct converting enzymes for separate islet prosomatostatins.

In previous work we have examined the nature of converting enzymes for proinsulin, proglucagon, and prosomatostatin-I (PSS-I) in secretory granules isolated from anglerfish islets. The purpose of the present study was to extend the examination of precursor conversion to islet microsomes and to compare prohormone processing, including that of PSS-I and prosomatostatin-II (PSS-II), in islet secretory granules and microsomes. Microsomes (rough endoplasmic reticulum [RER] and Golgi complex) and secretory granules were prepared from anglerfish islets by differential and discontinuous density-gradient centrifugation. Microsomes were further fractionated into Golgi- and RER-enriched subfractions. Lysed secretory granule or microsome preparations were incubated in the presence of a mixture of radioactively labeled islet prohormones. Extracts of products generated were subjected to analysis by gel filtration and high-pressure liquid chromatography. Accuracy of product cleavage was monitored by comparing high-pressure liquid chromatography retention times from the radiolabeled in vitro conversion products with the retention times of labeled products from tissue extracts. All converting activity in microsomes was found to be similar to that in granules in that it had a pH optimum near pH 5 and was inhibited by p-chloromercuribenzoate. No significant differences in the converting activity of Golgi complex- and RER-enriched subfractions of microsomes was observed. The proinsulin, proglucagon, and PSS-II converting-enzymes, which were found in islet secretory granules, were also present and membrane-associated in islet microsomes. However, converting activity for PSS-I was displayed only in secretory granules. This suggests that two or more separate enzymes are involved in processing PSS-I and PSS-II, and that these enzymes have either differential distribution or differential activity in RER/Golgi complex and secretory granules. The demonstration of converting enzyme activity in islet microsomes supports the proposal that these enzymes may be synthesized at the RER and are internalized along with the prohormones.

Animals↗

PubMedDate not supplied

Influence of pancreatic islets on spheroid formation and functions of hepatocytes in hepatocyte-pancreatic islet spheroid culture.

Hepatotrophic stimulation of hepatocytes is necessary to preserve long-term function of hepatocytes in hepatocyte transplantation and bioartificial liver system. The main source of hepatotrophic factors in portal venous blood seems to be the pancreatic islets. It was also reported that hepatocyte spheroids, tightly packed multicellular aggregates, showed enhanced liver-specific activities and a prolonged differentiated state compared with cells that were maintained as a monolayer. On the basis of these two facts, the authors tried to form hepatocyte-pancreatic islet spheroids and to evaluate the influence of pancreatic islets on spheroid formation and functions of hepatocytes in spheroid culture. Hepatocytes and pancreatic islet cells were harvested from adult male Sprague-Dawley rats weighing 200-250 g. Hepatocytes were cultured in spinner flasks with either basic nonstimulated medium (hepatocytes only [group BH] and cocultures with islet cells [group BI]) or hormone-stimulated medium (hepatocytes only [group HH] and cocultures with islet cells [group HI]). The size and morphology of spheroids, as determined by phase-contrast microscopy, and liver-specific functions, such as albumin secretion, urea synthesis, and ammonia removal, were compared among groups. The results were as follows: the size of spheroids, 66 +/- 53.4 microm, in group BH on day 2 was smaller than in group BI (179 +/- 66.2 microm on day 2, p < 0.05). In group BI, group HH, and group HI, smooth spheroids were observed on culture day 2. However, in group BH rugged incomplete aggregates were observed on the same day. In groups with basal medium, group BI showed better results in terms of hepatocyte-specific function such as albumin secretion, urea synthesis, and ammonia removal compared with group BH on days 2 and 3 (p < 0.05). In groups with hormone-defined medium, cocultures had no impact on albumin secretion rate, urea synthetic rate, and ammonia removal rate. In conclusion, we made a new type of hepatocyte-pancreatic islet spheroid, using a rotational culture method. Pancreatic islets in a spheroid culture system stimulated hepatocyte spheroid formation and some hepatocyte-specific functions in vitro.

Animals↗