Biomedical subjects

S Sandler

Publications and source records attributed to S Sandler.

At least 37 records · Page 2Linked to original sources

PubMed2000

Expression of pancreatic islet MHC class I, insulin, and ICA 512 tyrosine phosphatase in low-dose streptozotocin-induced diabetes in mice.

Activated immune cells contribute to the development of diabetes mellitus in multiple low-dose streptozotocin-treated mice. However, a role in the process for MHC Class I restricted T-cells remains a matter of debate. In this study, we examined by confocal microscopy the pancreatic expression of MHC Class I protein, insulin, and ICA 512 protein tyrosine phosphatase in C57BL/Ks mice given 40 mg/kg bw streptozotocin IP on 5 consecutive days. All animals were hyperglycemic from Day 7 and onwards. A loss of ICA 512 from the central portions of the islets was noted on Day 3. On Day 7, an increase in MHC Class I expression, confined primarily to immune cells in the exocrine pancreas and the periinsular areas, was detected. Later, several MHC class I/glucagon and some MHC class I/insulin double-positive cells were found. The insulitis was maximal on Day 14 and declined thereafter. The induction of MHC Class I expression in endocrine cells, occuring only after the cellular infiltration and when the animals were diabetic, indicates that the immune component of the disease does not depend on MHC Class I-restricted cytotoxic T-cells but rather comprises a non-antigen-specific process. (J Histochem Cytochem 48:761-767, 2000)

Animals↗

PubMed2000

Islet blood flow in multiple low dose streptozotocin-treated wild-type and inducible nitric oxide synthase-deficient mice.

The present study tested the hypothesis that changes in islet blood perfusion occur during the development of diabetes in the multiple low dose streptozotocin-treated mouse. Streptozotocin (40 mg/kg) or citrate buffer was given ip once daily for 5 consecutive days to wild-type and inducible nitric oxide synthase (iNOS)-deficient C57BL/6 x 129 SvEv hybrid mice. The blood flows were then determined by a microsphere technique. The islet blood perfusion was almost 2-fold higher in wild-type mice treated with streptozotocin than in those given vehicle. Whole pancreatic blood flow was also increased in the streptozotocin-treated wild-type mice. In iNOS-deficient mice, neither islet blood flow nor whole pancreatic blood flow was affected by repeated streptozotocin treatment. These combined findings suggest an increased islet blood perfusion in the prediabetic stage mediated by an iNOS-dependent mechanism. In combination with increased vasopermeability and expression of adhesion molecules on the islet endothelium, as previously described, this increased islet blood flow may be of crucial importance for the recruitment of inflammatory cells into the islets during the development of diabetes in this animal model. Indeed, an increased degree of insulitis was observed in wild-type mice compared with mice deficient in iNOS as well as a more rapid decrease in islet volume and an earlier debut of manifest diabetes. We also describe altered islet blood perfusion in the iNOS-deficient mice during basal conditions due to a compensatory increase in constitutive NOS activity.

Animals↗

PubMed2000

Novel experimental strategies to prevent the development of type 1 diabetes mellitus.

Type 1 diabetes is an autoimmune disease leading to extensive destruction of the pancreatic beta-cells. Our research focusses on the role of beta-cells during the course of the disease, aiming at finding novel strategies to enhance beta-cell resistance against the cytotoxic damage inflicted by the immune system. Special attention has been paid to the possibility that cytokines released by the immune cells infiltrating the pancreatic islets can directly suppress and kill beta-cells. Certain cytokines (interleukin-1beta, tumor necrosis factor-alpha and interferon-gamma) either alone or in combination, are able to activate signal transduction pathways in beta-cells leading to transcription factor activation and de novo gene expression. In this context, it has been found that induction of inducible nitric oxide synthase mediates an elevated production of nitric oxide, which impairs mitochondrial function and causes DNA damage eventually leading to apoptosis and necrosis. However, other induced proteins SUCH AS heat shock protein 70 and superoxide dismutase may reflect a defense reaction elicited in the beta-cells by the cytokines. Our strategy is to further seek for proteins involved in both destruction and protection of beta-cells. Based on this knowledge, we plan to apply gene therapeutic approaches to increase expression of protective genes in beta-cells. If this is feasible we will then evaluate the function and survival of such modified beta-cells in animal models of type 1 diabetes such as the NOD mouse. The long-term goal for this research line is to find novel approaches to influence beta-cell resistance in humans at risk of developing type 1 diabetes.

Cytokines↗

PubMed2000

Engraftment and growth of transplanted pancreatic islets.

Transplantation of pancreatic islets may provide a cure for type 1 diabetes. However, this treatment can currently be offered only to very few patients. To improve transplantation success we need to understand better the mechanisms of how the implanted islets survive, grow and/or maintain adequate function. We herein report on our studies to evaluate the factors responsible for the engraftment, i.e. revascularization, reinnervation etc., of transplanted islets and relate these factors to the metabolism and growth of the islets. Graft metabolism can be monitored by microdialysis probes that allow for the measurement of minute amounts of islet metabolites and hormonal products. Growth of the endocrine cells can be stimulated both in vitro before implantation and in vivo post-transplantation. Another problem is rejection of transplanted islets, which may be overcome by the microencapsulation of islets. The knowledge gained by the present studies will enable us to elucidate the optimal treatment of islets to ensure a maximal survival of the transplanted islets, and may be applied also to clinical islet transplantation.

Animals↗

PubMed2000

Islet loss and alpha cell expansion in type 1 diabetes induced by multiple low-dose streptozotocin administration in mice.

The aim of this study was to investigate the alpha cell population during the development of type 1 diabetes following multiple low-dose streptozotocin administration in mice. For this purpose C57BL/Ks male mice were injected with streptozotocin (40 mg/kg body weight for 5 days). Development of hyperglycemia was monitored over 28 days and a morphometric analysis of islet endocrine cells was performed. A reduction of islet cell area was observed after two injections of streptozotocin. The subsequent decrease of the area throughout the study period averaged 35%. Insulin-positive beta cells gradually disappeared from the identified islets. Hyperglycemia was present from day 7 onwards and in parallel with hyperglycemia, insulitis developed. An analysis of the alpha cell number per islet area revealed a 2- to 3-fold increase in this cell population, with the highest value on day 21. Confocal microscopy analysis of the ICA 512 protein tyrosine phosphatase revealed strong expression in the alpha cells at day 21, suggesting high secretory activity in the diabetic state. It is concluded that multiple low-dose streptozotocin treatment of C57BL/Ks male mice causes the disappearance of a fraction of the islets of Langerhans. In the remaining islet tissue an expansion of alpha cells occurs, reflecting a loss of intraislet beta cells as well as a regeneration of alpha cells.

Animals↗

PubMed2000

Cytokines induce apoptosis in beta-cells isolated from mice lacking the inducible isoform of nitric oxide synthase (iNOS-/-).

Prolonged exposure of rodent beta-cells to combinations of cytokines induces the inducible form of nitric oxide synthase (iNOS) expression and Fas expression, nitric oxide (NO) production, and cell death. It also induces the expression of potential "defense" genes, such as manganese superoxide dismutase (MnSOD) and heat shock protein (hsp) 70. NO is a radical with multifaceted actions. Recent studies have shown that NO, in addition to having cytotoxic actions, may regulate gene transcription. It remains unclear whether NO mediates cytokine-induced gene expression and subsequent beta-cell death. Previous studies using NO synthase blockers yielded conflicting results, which may be due to nonspecific effects of these agents. In this study, we examined the effects of cytokines on gene expression, determined by reverse transcriptase-polymerase chain reaction (RT-PCR), and viability, determined by nuclear dyes, of pancreatic islets or fluorescence-activated cell sorter (FACS)-purified beta-cells isolated from iNOS knockout mice (iNOS-/-, background C57BL/6x129SvEv) or their respective controls (C57BL/6x129SvEv). The combination of cytokines used was interleukin-1beta (50 U/ml) plus gamma-interferon (1,000 U/ml) plus tumor necrosis factor-alpha (1,000 U/ml). The lack of cytokine-induced iNOS activity in the iNOS-/- islet cells was confirmed by RT-PCR and nitrite determination. Cytokines induced a >3-fold increase in Fas and MnSOD mRNA expression in wild-type (WT) and iNOS-/- islets. On the other hand, hsp 70 was induced in WT but not in iNOS-/- islets. Prolonged (6-9 days) exposure of WT islets to cytokines leads to an 80-90% decrease in islet cell viability, whereas viability decreased by only 10-30% in iNOS-/- islet cells. To determine the mode of cytokine-induced cell death, FACS-purified beta-cells were exposed to the same cytokines. After 9 days, the apoptosis index was similarly increased in WT (39 +/- 3%) and iNOS4-/- (33 +/- 4%) beta-cells. On the other hand, cytokines increased necrosis in WT (20 +/- 4%) but not in iNOS-/- (7 +/- 3%) beta-cells. From these data, we concluded that 1) NO is required for cytokine-induced hsp 70 mRNA expression but not for Fas and MnSOD expression, 2) cytokines induce both apoptosis and necrosis in mouse beta-cells, and 3) cytokine-induced apoptosis is mostly NO-independent, whereas necrosis requires NO formation.

Adult↗

PubMed2000

K(ATP) channel openers protect rat islets against the toxic effect of streptozotocin.

We examined the influence of two K(ATP) channel openers, diazoxide and an analog (NNC 55-0118), on experimental beta-cell damage induced by streptozotocin (STZ; 0.5 mmol/l). Rat pancreatic islets were exposed to diazoxide or NNC 55-0118 for 30 min and were further incubated for 30 min after the addition of STZ. The islets were then washed and cultured for 24 h. Islets exposed to STZ alone showed extensive morphological damage, reduced glucose oxidation, low insulin content, and severely impaired glucose-stimulated insulin secretion and proinsulin biosynthesis. Islets treated with STZ in the presence of the channel openers (0.03-0.30 mmol/l) showed dose-dependent preservation of the morphology and improved glucose oxidation rates, insulin content, and secretion. NNC 55-0118 was capable of fully counteracting the STZ impairment, whereas diazoxide had a less protective effect. NNC 55-0118 did not counteract STZ-induced depression of islet NAD levels when examined 2 h after STZ exposure, which suggests that the mechanism of action by NNC 55-0118 is not through an inhibition of poly(ADP-ribose) polymerase. The results illustrate that K(ATP) channel openers can protect insulin-producing cells against toxic damage, an effect that may be of use in subjects with ongoing insulitis.

Animals↗

PubMed1999

Effects of TNF-alpha, IFN-gamma and IL-beta on normal human bronchial epithelial cells.

Several diseases affecting the airways such as asthma are associated with both epithelial damage and increased levels of pro-inflammatory cytokines. To investigate the possible relation between cytokines and epithelial damage, the effects of tumour necrosis factor-alpha (TNF)-alpha, interferon gamma (IFN-gamma) and interleukin-1 beta (IL-1beta) on normal human bronchial epithelial cells in vitro were studied. The cells were exposed to these cytokines for 48 or 72 h, followed by morphological, immunohistochemical and metabolic studies. Transmission and scanning electron microscopical analyses demonstrated damage to the mitochondria and an increase in cell processes induced by the cytokines. The use of antibodies against desmosomal cytokeratin showed a decrease in desmosome formation in IFN-gamma-exposed cells. Decreased glucose oxidation rate and increased accumulation of nitric oxide were found in cytokine-exposed cells. Nomega-monomethyl-L-arginine (L-NMMA) reduced nitrite production. X-ray microanalysis showed an increase in the intracellular sodium/potassium ratio of the cells after exposure to cytokines, which is an indication of cell damage. The cytokines induced both necrosis and apoptosis to varying degrees. IFN-gamma and TNF-alpha generally potentiate each other's effects. In conclusion tumour necrosis factor-alpha and interferon gamma, and to a lesser extent interleukin-1beta, can cause damage to epithelial cells, which may be a factor involved in epithelial shedding in airway diseases.

Adolescent↗

PubMed1999

Preserved pulsatile insulin release from prediabetic mouse islets.

During the development of type I diabetes, the plasma insulin pattern changes. Because the islet secretory pattern has been implicated in this phenomenon, insulin release was measured from female nonobese diabetic (NOD) mouse islets isolated at different ages. Islets from 5-week-old mice were used as controls because they had no infiltrating mononuclear cells and insulin release rose almost 9-fold with maintained oscillatory frequency when the glucose concentration was raised from 3 to 11 mM. Islets isolated from 13- and 25-week-old mice were infiltrated with mononuclear cells. In these islets, increase in the glucose concentration from 3 to 11 mM only doubled insulin release. However, despite the cellular infiltration, insulin release was pulsatile. Islets from 13-week-old mice had reduced glucose oxidation rate. Culture of such islets for 7 days at 11.1 mM glucose causes a decrease in the number of mononuclear cells infiltrating the islets, which in the present study was accompanied by a normalization of both glucose oxidation and glucose-induced insulin release. In the presence of the mitochondrial substrate alpha-keto-isocaproate (5 mM) both control and infiltrated islets responded with pronounced insulin pulses with similar amplitudes. The results suggest that the deranged plasma insulin pattern observed during the development of type I diabetes may be related to decrease in the insulin pulse amplitude rather than loss of the pulsatile release from the islets.

Aging↗

PubMed1999

Prolactin protects against diabetes induced by multiple low doses of streptozotocin in mice.

In earlier studies it has been shown that prolactin (PRL) is a stimulating factor for the immune system, and it has been suggested that PRL might antagonize immunosuppressive effects of glucocorticoids. PRL has been reported to affect the cytokine secretion pattern, by elevating cytokine gene expression in macrophages, after the onset of sepsis. It also promotes the antibody response in mice where it increases the production of interferon-gamma (IFN-gamma) and inhibits interleukin-1 (IL-1) production. Due to these properties, PRL might influence the development of autoimmune type 1 diabetes. The aim of the present study was to examine the effects of two drugs; PRL and bromocriptine (BC) in vivo on the development of hyperglycemia and pancreatic insulitis in mice treated with multiple doses of streptozotocin (STZ) (40 mg/kg body weight, i.p.). The dopaminergic agonist BC is known to inhibit PRL secretion. In another set of experiments, the direct effects of PRL on the function of pancreatic islets exposed to STZ in vitro were studied. Mice treated with STZ became gradually hyperglycemic, and concomitant treatment with PRL (4 mg/kg body weight) for 21 days significantly reduced the elevation in blood glucose levels from day 10 onwards (P<0.05). Morphologic examinations of the pancreas on day 21 of mice receiving STZ injections revealed a marked insulitis, but only moderate insulitis in the STZ treated animals given PRL. BC administration (10 mg/kg body weight) in combination with STZ did not significantly affect the elevation in blood glucose levels or the insulitis. PRL or BC administration alone did not change the serum glucose concentration. This study indicates that PRL may affect hyperglycemia in the early phase of autoimmune diabetes. We suggest that it might be due to counteraction of autoimmune immunologic mechanisms and/or enhancement of beta-cell regeneration.

Animals↗

PubMed1999

Early prophylaxis with recombinant human interleukin-11 prevents spontaneous diabetes in NOD mice.

We evaluated the effects of recombinant human (rh) interleukin (IL)-11 on the development of spontaneous and cyclophosphamide-induced diabetes in female NOD mice. Prolonged treatment with rhIL-11 10 microg i.p. five consecutive times a week between the 4th and 22nd weeks of age significantly suppressed both development and cumulative incidence of type 1 diabetes. Disease protection was transient because most of the animals developed type 1 diabetes within 3 months of treatment withdrawal. In contrast, rhIL-11 failed to prevent type 1 diabetes when administered for the first time to euglycemic 18-week-old NOD mice. Most likely, this discrepancy was not due to age-dependent differences in the immunological responses of NOD mice to rhIL-11 because staphylococcus aureus enterotoxin B-induced tumor necrosis factor (TNF) and IL-12 production were equally suppressed by rhIL-11 in 12- and 25-week-old NOD mice. Relative to controls, NOD mice pretreated with rhIL-11 also showed significantly diminished blood levels of TNF, interferon-gamma, and IL-12 induced by anti-CD3 antibody and/or lipopolysaccharide. The results demonstrate that rhIL-11 has powerful anti-inflammatory effects that are capable of down-regulating early immunodiabetogenic pathways in NOD mice.

Aging↗

PubMed1999

Reduced sensitivity of inducible nitric oxide synthase-deficient mice to multiple low-dose streptozotocin-induced diabetes.

Nitric oxide (NO), synthesized by the inducible isoform of nitric oxide synthase (iNOS), has been proposed as a mediator of immune-induced beta-cell destruction in type 1 diabetes. To evaluate the role of iNOS for beta-cell dysfunction and death, we investigated the sensitivity of beta-cells from mice genetically deficient in this enzyme (iNOS-/-, background C57BL/6x129SvEv, H-2b) both to interleukin (IL)-1beta-induced beta-cell dysfunction in vitro and to multiple low-dose streptozotocin (MLDS)-induced diabetes in vivo. Exposure of islets isolated from C57BL/6 mice to IL-1beta for 24 h in vitro resulted in an induction of iNOS mRNA expression, an increase in nitrite formation, and a decrease in insulin release and proinsulin biosynthesis as compared with untreated C57BL/6 islets. IL-1beta failed to induce iNOS mRNA expression and increase nitrite formation by islets isolated from iNOS knockout mice (iNOS-/-), and no impairment in islet function was observed. The iNOS-/- mice showed a reduced incidence of hyperglycemia after treatment with MLDS as compared with wild-type C57BL/6 (H-2b) and 129 SvEv (H-2b) mice. On day 21 after the first streptozotocin (STZ) injection, 75% of the C57BL/6 mice and 100% of the 129SvEv mice had blood glucose levels >11 mmol/l, whereas the corresponding number for iNOS-/- mice was only 23%. This protection was not due to a delay in the onset of hyperglycemia, since no increase in number of hyperglycemic iNOS-/- mice was observed when the animals were followed up to 42 days. Moreover, islets isolated from iNOS-/- mice were susceptible to the in vitro deleterious effects of STZ. In conclusion, the present study provides evidence that iNOS may contribute to beta-cell damage after exposure to IL-1beta in vitro and treatment with MLDS in vivo.

Animals↗

PubMed1999

Function of rat pancreatic islets exposed to interleukin-18 in vitro.

The recently cloned cytokine interleukin-18 (IL-18) has been shown to promote a Th1-cell immune response, which may be a prerequisite for development of Type 1 diabetes. In this study we examined the effects of IL-18 on the function of isolated rat pancreatic islets. The islets were cultured in medium RPMI 1640 + 10% fetal calf serum and exposed for 48 h to recombinant human IL-18 (0, 0.1, 1 and 10 nM). In some experiments IL-18 (l0 nM) was combined with interleukin-12 (10 ng/ml), since these cytokines may act synergistically. IL-18 alone, or in combination, with IL-12 did not affect the islet DNA content suggesting absence of cytotoxicity. However, both cytokines induced an increased islet insulin content compared to non-cytokine exposed control islets. A slight increase in the medium insulin accumulation was observed when 1.0 nM IL-18 was added, but not in other experimental groups. Glucose-stimulated insulin release, glucose oxidation and (pro)insulin biosynthesis rates were not affected by the cytokines after culture. In acute experiments IL-18 had a small stimulatory effect on glucose-stimulated insulin secretion. It was also tested if IL-18 (10 nM) could affect IL-1beta (25 U/ml) induced suppression of the glucose oxidation rate, but this was not the case. We conclude that IL-18 has minor stimulatory effects on beta-cell function, and no clear synergistic effect is observed when IL-12 is added together with IL-18. If IL-18 is involved in beta-cell destruction in Type 1 diabetes, it is likely that this effect is secondary to an influence on the action of other cytokines.

Animals↗

PubMed1999

Glucose metabolism in vitro of cultured and transplanted mouse pancreatic islets microencapsulated by means of a high-voltage electrostatic field.

The aim of this study was to assess the function of mouse pancreatic islets microencapsulated using a high-voltage electrostatic field. Islets were microencapsulated in alginate/poly-L-lysine/alginate (APA) capsules and maintained in tissue culture. Rates of glucose oxidation and insulin release were then assessed. Glucose metabolism was also measured in microencapsulated islets retrieved after transplantation to normal syngeneic mice. The high-voltage electrostatic system made possible the production of uniformly sized microcapsules, which were smaller than those produced by co-axial air-jet systems. Nonencapsulated islets were used as controls. Empty microcapsules or islet-containing microcapsules were transplanted intraperitoneally and retrieved after 2 weeks for assessment of foreign-body reactions and glucose oxidation rates. After 1 day and 2 weeks in tissue culture, both control islets and microencapsulated islets increased their rates of glucose oxidation and insulin release 7- to 10-fold in response to an increase in glucose concentration from 1.7 to 16.7 mmol/l. Both empty and islet-containing microcapsules, retrieved 2 weeks after transplantation, showed high rates of glucose oxidation at both low and high glucose concentrations, suggesting overgrowth with metabolically active fibroblasts. Morphological studies indicated a marked foreign-body reaction on the surface of all transplanted microcapsules. The islets in cultured microcapsules had a normal histological appearance, whereas the islets within transplanted microcapsules showed a range of morphological appearances, from intact islets to cell debris. In conclusion, this study shows that mouse pancreatic islets survive and remain functionally competent for at least 2 weeks in vitro after microencapsulation in APA capsules generated in an electrostatic field. However, a foreign-body reaction with cellular growth on the capsular surface was present after intraperitoneal syngeneic transplantation.

Animals↗

PubMed1999

Transgenic mice expressing Shb adaptor protein under the control of rat insulin promoter exhibit altered viability of pancreatic islet cells.

BACKGROUND: The Src-homology 2 domain-containing adaptor protein Shb was recently cloned as a serum-inducible gene in the insulin-producing beta-TC1 cell line. Subsequent studies have revealed an involvement of Shb for apoptosis in NIH3T3 fibroblasts and differentiation in the neuronal PC12 cells. To assess a role of Shb for beta-cell function, transgenic mice utilizing the rat insulin promoter to drive expression of Shb were generated. MATERIALS AND METHODS: A gene construct allowing the Shb cDNA to be expressed from the rat insulin 2 promoter was microinjected into fertilized mouse oocytes and implanted into pseudopregnant mice. Mice containing a low copy number of this transgene were bred and used for further experimentation. Shb expression was determined by Western blot analysis. The insulin-positive area of whole pancreas, insulin secretion of isolated islets and islet cell apoptosis, glucose tolerance tests, and in vivo sensitivity to multiple injections of the beta-cell toxin streptozotocin were determined in control CBA and Shb-transgenic mice. RESULTS: Western blot analysis revealed elevated islet content of the Shb protein. Shb-transgenic mice displayed enhanced glucose-disappearance rates in response to an intravenous glucose injection. The relative pancreatic beta-cell area neonatally and at 6 months of age were increased in the Shb-transgenic mice. Islets isolated from Shb-transgenic mice showed enhanced insulin secretion in response to glucose and increased insulin and DNA content. Apoptosis was increased in islets isolated from Shb-transgenic mice compared with control islets both under basal conditions and after incubation with IL-1 beta + IFN-gamma. Rat insulinoma RINm5F cells overexpressing Shb displayed decreased viability during culture in 0.1% serum and after exposure to a cytotoxic dose of nicotinamide. Shb-transgenic mice injected with multiple doses of streptozotocin showed increased blood glucose values compared with the corresponding controls, suggesting increased in vivo susceptibility to this toxin. CONCLUSION: The results suggest that Shb has dual effects on beta-cell growth: whereas Shb increases beta-cell formation during late embryonal stages, Shb also enhances beta-cell death under certain stressful conditions and may thus contribute to beta-cell destruction in type 1 diabetes.

Animals↗

PubMed1998

Leptin regulation of islet amyloid polypeptide secretion from mouse pancreatic islets.

Leptin receptors are expressed in pancreatic beta-cells. However, leptin's role in islet hormone secretion is essentially unknown. In the present study, we aimed to elucidate leptin's effect on isolated pancreatic NMRI mouse islets by examining islet amyloid polypeptide (IAPP) and insulin secretion in acute experiments and after 48-hr exposure to leptin (1-100 nM). It was also examined whether a putative effect of leptin was affected by the glucose concentration. Islets were cultured in medium RPMI 1640 + 10% fetal calf serum, and the effects of leptin on islet cell replication, glucose metabolism, and hormone content were subsequently examined. Glucose-stimulated IAPP secretion was reduced both acutely and after 48-hr exposure to leptin, whereas only minor effects were found on insulin release, i.e. an inhibition in islets cultured with 1 nM leptin. An acute inhibitory effect by 10 nM leptin was observed on the ratio of IAPP/insulin release at 5.6-11.1 mM glucose, but this was overcome by 16.7 mM glucose. The islet glucose oxidation rate was enhanced by 1 nM leptin, but decreased at higher concentrations of leptin in acute experiments. In contrast, glucose metabolism was not affected in long-term experiments. Moreover, leptin did not influence islet (pro)insulin synthesis or the cell replication rate after culture. In conclusion, we show that islet IAPP release seems to be more sensitive to leptin than is insulin release. The effect of leptin on islet hormone secretion is dependent on the glucose concentration. The regulation of hormone secretion seems to be dissociated from glucose metabolism, an effect previously described in islets after exposure to certain cytokines. Our data necessarily suggest that a previously proposed negative feedback loop between leptin and insulin can be counteracted by IAPP.

Amyloid↗

PubMed1998

Pancreatic islet blood perfusion in the nonobese diabetic mouse: diabetes-prone female mice exhibit a higher blood flow compared with male mice in the prediabetic phase.

The present study tested the hypothesis that changes in pancreatic islet blood flow correlate with the difference in diabetes incidence between male and female nonobese diabetic (NOD) mice. The blood flows were determined by a microsphere technique. In animals aged 10 and 14 weeks, the islet blood perfusion was 3-fold higher in female NOD mice compared with that in either age-matched male NOD mice or age- and sex-matched control ICR mice. At 5 weeks of age islet blood flow was similar in all groups. No differences between male and female NOD mice in whole pancreatic, duodenal, ileal, or colonic blood flows were observed at any time point. Administration of a bolus dose of aminoguanidine (a blocker of inducible nitric oxide synthase) to 10-week-old animals selectively and markedly decreased islet blood flow in female NOD mice, whereas islet blood flow in ICR mice and male NOD mice remained unaffected. Aminoguanidine did not affect mean arterial blood pressure or whole pancreatic blood flow in any of the groups. Injection of N(G)-methyl-L-arginine, an unspecific inhibitor of both constitutive and inducible nitric oxide synthase, markedly decreased whole pancreatic and islet blood flow to the same level in both male and female NOD mice. These combined findings suggest that diabetes-prone female NOD mice have an increased islet blood flow, which is mediated by an excessive production of nitric oxide formed by inducible nitric oxide synthase. The islet blood hyperperfusion may augment homing to the pancreatic islets of inflammatory cells and soluble factors involved in beta-cell destruction during the development of insulin-dependent diabetes mellitus in this animal model. The presently observed gender difference in the blood flow response could, therefore, at least partially explain why female NOD mice are more prone to develop hyperglycemia than the males.

Aging↗

PubMed1998

Effects of interleukin-12 in vitro on pancreatic islets isolated from normal rodents and from non-obese diabetic mice.

Administration of the T-helper 1 (Th 1) cell promoting cytokine interleukin-12 (IL-12) accelerates the development of autoimmune diabetes in non-obese diabetic (NOD) mice. In this study we examined the effects of IL-12 on isolated islets from NMRI (Naval Medical Research Institute-established) mice, Sprague-Dawley (S-D) rats and NOD mice. NMRI and S-D islets were cultured in medium RPMI 1640 + 10% fetal calf serum and exposed for 48 h to recombinant mouse IL-12 (0, 0.1, 1 and 10 ng/ml). Islet glucose metabolism, as measured by glucose oxidation rate, was suppressed by about 25% in NMRI islets exposed to 10 ng/ml IL-12. In rat islets 0.1 ng/ml IL-12 induced a 20% decrease in glucose oxidation rate. Islets cultured with 10 ng/ml IL-12 showed a decrease in medium insulin accumulation both in mouse and rat. Glucose-stimulated insulin release was lowered in rat islets exposed to 10 ng/ml IL-12, but not affected in NMRI islets. In NMRI islets IL-12 did not influence nitric oxide production as measured by nitrite formation. In rat islets IL-12 induced a decrease in nitrite formation compared with control islets. Islets were isolated from female NOD mice (age 5, 12, 20 and 26 weeks) and examined either immediately or cultured for 7 days with 10 ng/ml IL-12 alone or in combination with 4 ng/ml of the T-cell stimulating cytokine interleukin-2 (IL-2). In the age groups > 5 weeks of age the glucose-stimulated insulin release was lower in freshly isolated compared with cultured control islets. IL-2 + IL-12 addition induced a small decrease in glucose-stimulated insulin release in islets from 12-week-old animals. With increasing age the DNA content in freshly isolated islets increased due to immune cell infiltration. The DNA content in cultured islets was decreased by 40-60% compared with freshly isolated islets in the age groups over 5 weeks. Islet insulin content was similar in both freshly isolated and cultured islets. None of the cytokines, either alone or in combination, affected islet DNA or insulin content. We conclude that IL-12 has minor suppressive effects in vitro on normal rodent islets. It is likely that the reported accelerated diabetes development of IL-12 administration to NOD mice in vivo is not mediated by a direct toxic effect to the islets. The suppressed insulin release in NOD mouse islets treated with IL-2 + IL-12 suggests, however, that the accelerating effect might partly be attributed to stimulation of immune cells present in the insulitic lesion.

Aging↗