Biomedical subjects

S Sandler

Publications and source records attributed to S Sandler.

At least 55 records · Page 3Linked to original sources

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↗

PubMed1997

Effects of vascular endothelial growth factor on pancreatic duct cell replication and the insulin production of fetal islet-like cell clusters in vitro.

We have previously shown that the tyrosine kinase receptor Flk-1 and its ligand, vascular endothelial growth factor (VEGF), may play a role in the development of fetal rat islet-like structures in vitro, possibly by stimulating the maturation of endocrine precursor cells in the pancreatic ductal epithelium. In order to further assess this, adult rat pancreatic ducts and fetal porcine islet-like cell clusters (ICC) were cultured in the presence of VEGF. In ducts, VEGF stimulated the mitogenesis in the epithelium. Culture of ICC in the presence of VEGF significantly enhanced their insulin content, but decreased the insulin accumulation to the culture medium. Glucose-stimulated acute insulin release was not affected by VEGF. Northern blot analysis after partial pancreatectomy in adult rats revealed induction of VEGF mRNA 3 days after the operation. Immunohistochemistry of fetal rat pancreas showed staining mainly in the islets of Langerhans. We conclude that VEGF directly stimulates the replication of the ductal epithelium, a possible prerequisite for beta-cell formation. This could require local production of VEGF, which may alter in response to physiological demands.

Animals↗

PubMed1997

S-methyl-L-thiocitrulline counteracts interleukin 1 beta induced suppression of pancreatic islet function in vitro, but does not protect against multiple low-dose streptozotocin-induced diabetes in vivo.

Nitric oxide, induced by pancreatic islet exposure to cytokines, has been implicated in beta-cell destruction in insulin-dependent diabetes mellitus. In this context it could be worthwhile to characterize inhibitors of the nitric oxide generating enzyme. For this purpose rat pancreatic islets were cultured for 48 h in medium supplemented without or with 10, 100 or 500 microM of S-methyl-L-thiocitrulline, in the absence or presence of 25 U/ml of interleukin 1 beta (IL-1 beta). S-methyl-L-thiocitrulline alone did not affect the islet glucose oxidation rate, but all concentrations of S-methyl-L-thiocitrulline prevented IL-1 beta induced suppression of the islet glucose metabolism. Moreover, S-methyl-L-thiocitrulline (100 microM) completely protected against cytokine mediated inhibition of medium insulin accumulation, glucose-stimulated insulin release and (pro)insulin biosynthesis. IL-1 beta caused a more than 10-fold increase in medium nitrite production, an indication of nitric oxide production, which was blocked by S-methyl-L-thiocitrulline. Acutely in the absence of IL-1 beta, islet glucose-stimulated insulin release was enhanced by S-methyl-L-thiocitrulline (100 microM). The efficacy of S-methyl-L-thiocitrulline, NG-monomethyl-L-arginine and aminoguanidine in counteracting IL-1 beta induced nitrite formation was also compared. When estimating the half-maximal inhibitory concentration for this effect, it was approximately 10 microM for S-methyl-L-thiocitrulline and about 1000 microM for NG-monomethyl-L-arginine and aminoguanidine. Next, the efficacy of S-methyl-L-thiocitrulline was tested in an animal model of insulin-dependent diabetes mellitus i.e. multiple low-dose streptozotocin-induced diabetes in male C57BL/Ks mice (40 mg/kg body weight/day for 5 days). It was found that all groups of mice treated with streptozotocin injections gradually developed hyperglycaemia. Administration of S-methyl-L-thiocitrulline (15 mg/kg body weight/day) either for 6-13 days or for 5-11 days after the first STZ injection could not prevent this effect. Moreover, S-methyl-L-thiocitrulline did not appear to influence the evolution of mononuclear cell infiltration and pancreatic insulitis. Thus the present study shows that S-methyl-L-thiocitrulline can potently block cytokine induced activation of nitric oxide synthase in pancreatic islets, but using the presently adopted administration protocol failed to protect against development of insulin-dependent diabetes mellitus in vivo.

Animals↗

PubMed1997

Inhibition of nitric oxide formation by aminoguanidine: an attempt to prevent insulin-dependent diabetes mellitus.

1. Insulin-dependent diabetes mellitus is an autoimmune disease leading to pancreatic beta-cell destruction, an event that may, at least partially, be induced by the formation of nitric oxide. 2. Under the influence of cytokines, the enzyme nitric oxide synthase is induced. 3. Blockage of the inducible form of nitric oxide synthase has been found to protect against insulin-dependent diabetes mellitus in some animal models. 4. Aminoguanidine has been found to be a fairly specific inhibitor of cytokine-inducible nitric oxide synthase. 5. Aminoguanidine may reduce the blood flow to the pancreatic islets in vivo and, at higher concentrations, also impair insulin secretion by the beta-cells,--which may make the compound less useful in attempts to prevent insulin-dependent diabetes mellitus.

Animals↗

PubMed1997

IL-1 receptor antagonist inhibits recurrence of disease after syngeneic pancreatic islet transplantation to spontaneously diabetic non-obese diabetic (NOD) mice.

The effect of an IL-1 receptor antagonist on recurrence of hyperglycaemia after syngeneic pancreatic islet transplantation to spontaneously diabetic female NOD mice was investigated. The transplanted animals were treated with either the receptor antagonist (8.0 mg/kg body weight per day for 12-14 days) or PBS, delivered by subcutaneously implanted osmotic pumps. In the control animals, a transient normoglycaemia was achieved, but hyperglycaemia was generally observed 6 days after islet transplantation. Administration of IL-1 receptor antagonist had a clear protective effect against recurrence of hyperglycaemia until day 14, but after cessation of drug delivery hyperglycaemia re-appeared. The results indicate that continuous administration of the IL-1 receptor antagonist can prevent recurrence of the diabetogenic process in NOD mice. IL-1 receptor antagonist may therefore become a useful adjuvant immunomodulating therapy after human islet transplantation in insulin-dependent diabetes mellitus.

Animals↗

PubMed1997

In vitro response to interleukin-1 beta and streptozotocin in pancreatic islets isolated from male and female nonobese diabetic mice.

The aim of the present study was to examine if the islet donor gender influences the beta-cell sensitivity to possible mediators of beta-cell destruction in insulin-dependent diabetes mellitus (IDDM). We have currently addressed this issue by comparing the action of the cytokine interleukin-1 beta (IL-1 beta) and the alkylating agent streptozotocin (STZ), on isolated pancreatic islets derived from prediabetic female and male nonobese diabetic (NOD) mice. In this mouse strain the females have a much higher incidence of spontaneous IDDM than the males. Pancreatic islets were isolated from female and male mice of the same litter, cultured for 6 days and thereafter either 5-50 U/ml IL-1 beta were added for 48 h or 1.8 mM STZ for 30 min. The cytokine exposure caused a strong increase in the medium insulin accumulation in the cultures of islets obtained from both males and females. The insulin and DNA contents were similar when comparing female and male islets before and after cytokine exposure. The male pancreatic islets exhibited a higher rate of islet glucose oxidation than islets obtained from females after IL-1 beta addition. Non-cytokine treated islets from males showed a higher insulin content compared with corresponding female islets. After IL-1 beta addition male and female islets had a similar inhibition of insulin secretion following stimulation by glucose. On the other hand, islets of both genders were equally sensitive to the inhibitory action of STZ, when studied 6 days after STZ incubation, as assessed by glucose oxidation and insulin release experiments. In conclusion the data of the present study did not demonstrate a clear gender difference in the islet beta-cell sensitivity to immune mediated suppression by IL-1 beta or alkylation damage in IDDM-prone NOD mice. However, it cannot be excluded that in vivo, under the influence of sex hormones, a decisive alteration in beta-cell sensitivity to damage might develop.

Alkylating Agents↗

PubMed1997

Interleukin-13 counteracts suppression induced by interleukin-1beta of glucose metabolism but not of insulin secretion in rat pancreatic islets.

The cytokine interleukin-1beta (IL-1beta) has been postulated to be involved in beta-cell destruction in IDDM. It has also been suggested that this action by IL-1beta is mediated by nitric oxide (NO) generation. Recently it has been reported that Th2-cell promoting cytokines e.g. interleukin-4 (IL-4) and interleukin-13 (IL-13) can reduce NO formation from activated macrophaghes after cytokine activation. In the present study we examined the effect of IL-13 on IL-1beta suppression of islet function. For this purpose rat pancreatic islets were cultured in medium RPMI 1640 + 10% fetal calf serum and exposed for 42 h to human IL-13 (0. 0.1, 1 and 10 ng/ml) in the presence or absence of human IL-1beta (25 U/ml) during the last 24 h of culture. IL-13 alone did not affect any islet functions during prolonged exposure. The highest concentration of IL-13 counteracted IL-1beta suppression of islet glucose oxidation, but not insulin release. Moreover, IL-13 failed to reduce IL-1beta stimulated NO production, as measured by medium nitrite levels. Acute exposure to IL-13 caused a slight stimulation of islet insulin secretion. When IL-4 (10 ng/ml) was combined with IL-13 no synergistic action of the two cytokines was observed in the counteraction of IL-1beta mediated changes. In conclusion, the present study showed that IL-13 could partially prevent IL-1beta induced inhibition of the glucose metabolism, and this effect appeared to be unrelated to NO levels. So far it has not been possible to demonstrate in vitro that Th2-cell promoting cytokines such as IL-4 and IL-13 can effectively reduce cytokine-induced NO from islet cells, as has been reported for macrophages. However, it cannot be excluded that Th2-cell promoting cytokines can be effective in reducing a Th1-cell mediated anti-beta-cell response in vivo.

Animals↗

PubMed1996

Influence of the neurotoxin capsaicin on rat pancreatic islets in culture, and on the pancreatic islet blood flow of rats.

The importance of peptidergic nerve fibres for the regulation of whole pancreatic and islet blood flow was studied by administration of the neurotoxin capsaicin. Administration of capsaicin induces an acute release and depletion of mainly substance P and calcitonin gene-related peptide from sensory nerve fibres. When given repeatedly to adult rats for several days, the neuropeptides are irreversibly depleted from the nerve endings. Depletion of substance P was confirmed by immunohistochemical stainings in the present study. A bolus dose of capsaicin (4 micrograms/kg body weight) reduced both whole pancreatic and islet blood flow in anesthetized rats, whereas repeated treatment with capsaicin led to an increase in both pancreatic and islet blood flow. In vitro experiments on isolated islets exposed to capsaicin (0.25 and 2.5 microM) for 4 days showed no effect on beta-cell function. We conclude that peptidergic nerves have an important role for the maintenance of basal vascular tone in both the endocrine and exocrine parts of the pancreas, and may thereby influence the regulation of insulin secretion in rats.

Animals↗

PubMed1996

Effects of aminoguanidine on rat pancreatic islets in culture and on the pancreatic islet blood flow of anaesthetized rats.

Aminoguanidine (AG; < or =0.5 mM) is a potent inhibitor of the inducible form of nitric oxide synthase (iNOS) and, at higher concentrations, is also able to prevent advanced glycosylation of proteins. Due to these properties, AG might be an interesting therapeutic compound for prevention of the development of diabetes and for prevention of diabetes complications. In the present study, we examined the effect of AG (0.1, 0.5, 1.0, 5.0, or 10 mM) on prolonged in vitro culture of isolated rat pancreatic islets. Furthermore, the acute effect of AG on pancreatic and islet blood flow in anaesthetized rats was studied with a microsphere technique. Culture for 6 days of pancreatic islets at either 11.1 mM or 28 mM glucose, in the presence of 0.1-1.0 mM AG, was not toxic to the islet cells or impaired insulin secretion. However, when islets were cultured for 8 days with the addition of 5 mM AG at 11.1 mM or 28 mM glucose, a 50% inhibition of glucose-stimulated insulin release was observed. Rats injected intravenously with AG (1, 10, or 50 mg/kg body weight) had a decreased pancreatic blood flow 30 min later. Glucose injection (1 g/kg body weight) increased the islet blood flow, and this effect was not attenuated by AG. The present data suggest that AG, when used in concentrations that inhibit iNOS, can affect pancreatic blood flow, but appears not to be directly harmful to beta-cell function.

Animals↗

PubMed1996

Islet amyloid polypeptide (IAPP) secretion from pancreatic islets isolated from non-obese diabetic (NOD) mice.

The secretion of islet amyloid polypeptide (IAPP) during the course of insulin-dependent diabetes mellitus (IDDM) is essentially unknown. In the present study we elucidated this issue by examining IAPP and insulin secretion from isolated pancreatic islets obtained from IDDM-prone female NOD mice aged 6-9 weeks and 12-15 weeks and from non-IDDM-prone male NMRI mice. Basal islet hormone secretion at 1.7 mM glucose and after stimulation with 17 mM glucose or with 17 mM glucose + 5 mM theophylline was studied acutely or after 1 week of tissue culture. The levels of glucose-stimulated insulin release from NOD mouse islets increased after tissue culture, whereas it remained unchanged in NMRI mouse islets. Overall changes in islet insulin secretion were accompanied by similar changes in IAPP secretion. Acute after isolation, islets from NMRI mice displayed a reduced IAPP/insulin secretion ratio in response to the stimulation, which could reflect a destabilized hormone release. When the NOD mouse islets at 6-9 weeks of age were exposed to secretory stimuli the molar ratio of IAPP/insulin secretion declined. At a later stage of advanced insulitis (12-15 weeks) also the basal IAPP/insulin secretory ratio at low glucose tended to decline. If extrapolated to the early prediabetic phase of human IDDM, this would mean that a relative hypersecretion of insulin in relation to IAPP might occur, due to an increased secretory demand for insulin or due to an intrinsic change in the biology of the secretory cells.

Amyloid↗

PubMed1995

The blood flow in pancreatico-duodenal grafts in rats: inhibition of nitric oxide synthase preferentially decreases islet blood flow.

In this study normoglycemic inbred Wistar-Furth rats were implanted with a syngeneic pancreatico-duodenal graft, i.e. a denervated pancreas. The blood flow to the intact native pancreas and to the transplanted gland was measured with a microsphere technique in anesthetized rats 2 weeks after transplantation. The animals were given an intravenous injection with saline alone, NG-nitro-L-arginine (25 mg/kg body weight) or sodium nitroprusside (10 micrograms/kg body weight) 10 min before blood flow measurements. Administration of NG-nitro-L-arginine increased mean arterial blood pressure and caused a pronounced decrease in whole pancreatic blood flow in both the native and transplanted gland. The islet blood flow was more markedly decreased by NG-nitro-L-arginine in both the native and transplanted pancreas, and constituted about 4% of whole pancreatic blood flow compared with 10% in the control animals. Sodium nitroprusside markedly decreased mean arterial blood pressure, but did not affect pancreatic or islet blood flow in any of the glands. It is concluded that inhibition of nitric oxide synthase causes a preferential decrease in islet blood flow both in the native pancreas and in the transplanted pancreas. This suggests that nitric oxide which affects islet blood flow is mainly endothelial-derived, and does not emanate from external nervous fibers.

Amino Acid Oxidoreductases↗

PubMed1995

Interleukin 4 impairs rat pancreatic islet function in vitro by an action different to that of interleukin 1.

Cytokines, in particular interleukin 1 beta (IL-1 beta), have been implicated in pancreatic beta-cell destruction in insulin-dependent diabetes mellitus. In the rat prolonged exposure in vitro of islets of IL-1 beta leads to nitric oxide formation, impaired glucose metabolism and inhibition of insulin secretion. Interleukin 4 (IL-4) has been shown to be able to modulate nitric oxide formation in other cell systems. In the present study we have investigated the effect of IL-4 alone and in combination with IL-1 beta on islet cells. For this purpose isolated rat pancreatic islets were cultured for 42 h in medium supplemented with 0, 0.1, 1.0 or 10 ng/ml of human IL-4 in the absence or presence of 25 U/ml of IL-1 beta during the last 24 h of culture. IL-4 alone dose-dependently decreased the islet glucose oxidation rate and the glucose-stimulated insulin release. Furthermore, the cytokine potentiated IL-1 beta-induced reduction in the islet DNA content and (pro)insulin biosynthesis rate. The medium nitrite accumulation, as an index of nitric oxide formation, was not influenced by IL-4 (10 ng/ml) alone, whilst IL-1 beta stimulation of medium nitrite was partly reduced by IL-4. Compared to the action exerted by IL-1 beta the inhibitory action of IL-4 on rat islet function was moderate, and the latter action seems to be independent on nitric oxide production.

Animals↗

PubMed1995

Comparison of mRNA contents of interleukin-1 beta and nitric oxide synthase in pancreatic islets isolated from female and male nonobese diabetic mice.

Interleukin-1 beta (IL-1 beta) has been suggested to mediate beta-cell destruction in insulin-dependent diabetes mellitus (IDDM) by inducing nitric oxide production. In this study, we assessed the levels of IL-1 beta and the inducible form of nitric oxide synthase (iNOS), using a semi-quantitative polymerase chain reaction assay, and performed determinations of nitrite accumulation and IL-1 beta bioactivity, on pancreatic islets isolated from 5- and 16-week-old female and male nonobese diabetic (NOD) mice and from nondiabetes prone NMRI mice. NOD mouse islets contained notable amounts of IL-1 beta mRNA. At 5 weeks of age, but not at 16 weeks, the values were higher in islets isolated from NOD females compared to males. The IL-1 beta bioactivity showed differences roughly reflecting the mRNA levels in the NOD mouse islets. In the NMRI mouse islets the IL-1 beta bioactivity was very low. The expression of iNOS mRNA increased in both male and female islets between 5 and 16 weeks of age. Immunocytochemistry of pancreatic sections indicated the presence of macrophages especially in the peri-insular area of the NOD mice which suggests that IL-1 beta was produced by macrophages. The levels of IL-1 beta activity and mRNA in freshly isolated islets from NOD 5-weeks-old females did not correlate to the iNOS mRNA content or to the nitrite production. However, after incubation with IL-1 beta in vitro, both NOD and NMRI islets responded with a marked increase in nitric oxide production.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Oxidoreductases↗

PubMed1995

Interleukin-1 beta-induced stimulation of insulin release in mouse pancreatic islets is related to diacylglycerol production and protein kinase C activation.

The aim of the present study was to investigate the mechanisms responsible for the acute, stimulatory effects of interleukin-1 beta (rIL-1 beta; 1 ng/ml) on insulin release from mouse pancreatic islets. For this purpose, mouse islets were exposed for 60-120 min to rIL-1 beta and their function and metabolism characterized during this period. The cytokine did not increase insulin release in the presence of 1.7 mM glucose, but both in the presence of 5.6 or 16.7 mM glucose, or 10 mM leucine + 2 mM glutamine, it induced a 60-100% increase in insulin release. Moreover, rIL-1 beta also enhanced the effects of 1 mu/ml glipizide on insulin release, but failed to increase insulin release induced by 30 mM KCl or by glucose plus phorbol ester (TPA; 100 nM). These early stimulatory effects of rIL-1 beta on insulin release were neither accompanied by major increases in glucose or amino acid metabolism, nor by modifications in islet cAMP content, and they were prevented by mannoheptulose, diazoxide or verapamil. rIL-1 beta potentiation of glucose-induced insulin release was not accompanied by modifications in [Ca2+]i, but the cytokine increased diacylglycerol production and induced protein kinase C (PKC) activation. Down-regulation of PKC completely prevented the stimulatory effects of rIL-1 beta on glucose-induced insulin release. In conclusion, rIL-1 beta induces an early stimulation of insulin release in mouse beta-cells by a mechanism independent of glucose metabolism, cAMP generation or modifications in [Ca2+]i. This effect is probably related to diacylglycerol formation and stimulation of PKC.

Animals↗

PubMed1995

Long-term effects of nicotinamide-induced inhibition of poly(adenosine diphosphate-ribose) polymerase activity in rat pancreatic islets exposed to interleukin-1 beta.

Nicotinamide (NIC) is presently extensively studied as a potential agent that might prevent the development of insulin-dependent diabetes mellitus. This study aimed to examine the consequence of exposing isolated rat pancreatic islets to various concentrations of NIC (0, 0.5, 1.0, 5.0, 10, and 25 mM) over a prolonged period (6 days) in tissue culture and also to assess the efficacy of NIC to counteract interleukin-1 beta (IL-1; 25 U/ml)-induced beta-cell dysfunction. Except for a 30-40% increase at 5.0 mM NIC, the insulin content of islets was not affected by NIC. Also, the islet DNA content remained essentially unchanged. The insulin accumulation in the culture medium declined at 5-25 mM NIC between days 4-6. The insulin release in response to 16.7 mM glucose on day 6 was enhanced after culture with the addition of 0.5 mM NIC, but 25 mM NIC caused a strong inhibition of insulin secretion. However, neither the (pro)insulin nor the total protein biosynthesis rate of the islets was affected by NIC. A significant inhibition of the islet poly(ADP-ribose) polymerase activity by 40-80% was observed at 5-25 mM NIC. IL-1 was then tested together with 1.0 and 10 mM NIC. The islet DNA content was markedly reduced in all groups treated with IL-1, as was the medium insulin accumulation. Moreover, NIC failed to prevent IL-1 induced impairment of islet insulin release on day 6. The cytokine induced a very pronounced and sustained increase in the medium nitrite accumulation, and NIC could not influence this elevation. Thus, these data show that prolonged exposure to elevated NIC levels impaired the function of rat beta-cells, and NIC failed to counteract IL-1 actions. Whether these events are mimicked in the ongoing clinical trials with NIC remain to be established.

Animals↗

PubMed1995

Effects of prolonged exposure in vitro to interferon-gamma and tumour necrosis factor-alpha on nitric oxide and insulin production of rat pancreatic islets.

It has been postulated that cytokines may mediate the beta-cell destructive process causing insulin-dependent diabetes mellitus. The aim of this investigation was to study cytokine effects on pancreatic islet functions in vitro. For this purpose 5-7 days precultured (medium RPMI 1640 +/- 10% fetal calf serum) rat pancreatic islets were exposed for another 48 h to either culture medium alone or with addition of rat interferon-gamma (IFN-gamma; 1000 U/ml), or human tumor necrosis factor-alpha (TNF-alpha; 1000 U/ml) or a combination of the cytokines. After the culture period the islets were subjected to short-term experiments in the absence of cytokines. Neither the DNA nor the insulin content of the islets were affected by the cytokines alone or by the combination. The combination IFN-gamma + TNF-alpha caused a 5-fold increase in the medium nitrite accumulation, indicating induction of nitric oxide formation. It was found that IFN-gamma reduced medium insulin accumulation and basal insulin secretion at 1.7 mM glucose, without affecting the medium nitrite level. On the other hand, the islet glucose oxidation rate at 16.7 mM glucose and the insulin secretory response to 16.7 mM glucose was normal or even increased when examined after 48 h. TNF-alpha alone had no significant effects. In conclusion, a combination of the cytokines can induce nitric oxide formation and inhibition of insulin production in rat pancreatic islets. However, this effect appears not to be sustained. Moreover, IFN-gamma alone seems to induce changes not related to nitric oxide.

Animals↗

PubMed1995

Age-dependent sensitivity to streptozotocin of pancreatic islets isolated from female NOD mice.

Streptozotocin (STZ), a selective beta-cell cytotoxin, given in multiple low doses to susceptible mouse strains causes insulin-dependent diabetes mellitus (IDDM) with an autoimmune pathology. Studies in the human suggest that environmental factors such as viruses and certain toxins may modulate the expression of the disease in genetically-prone individuals and the effect may also be age-dependent. Here we have examined the effects of graded, low doses of STZ on beta-cell function and insulin and DNA contents in vitro in cultured islets isolated from female IDDM-prone NOD mice at 4 weeks and at 8 weeks. Results were compared with islets from age and sex-matched non-diabetes prone C57BL/Ks mice. No changes in islet DNA or insulin contents were observed after an acute 30 min exposure to STZ (0, 1.1, 2.2 and 4.4 mM) in the two strains at each of the age groups. However, the DNA content in the NOD mouse islets tended to be lower at 8 weeks, being significant at 1.1 mM STZ. At 4 weeks, islets from NOD mice had a higher insulin content than the control mice but this declined at 8 weeks when it became comparable to the control strain. STZ caused a dose-dependent inhibition of islet glucose oxidation rates in all groups. However, at 4 weeks, exposure to 2.2 mM STZ resulted in a significantly greater inhibition in NOD mice than in age-matched control mice. This was reversed at 8 weeks when the islets from NOD mice showed a greater resistance to oxidative impairment than from C57BL/Ks mice. In the presence of 16.7 mM glucose, an inhibitory pattern, similar to the glucose oxidation rate, was also observed for insulin release. In the control mice the relative inhibition of insulin release and glucose oxidation rate was similar at 4 and 8 weeks. These results suggest that islets from the NOD mouse at 4 weeks and prior to insulitis are more sensitive to STZ-induced functional impairment. This enhanced sensitivity suggests that cumulative exposure of diabetes-prone islets to low doses of selective beta cell toxins may be a determinant for later development of IDDM.

Aging↗

PubMed1994

Dissociation between interleukin-1 beta-induced expression of mRNA for superoxide dismutase and nitric oxide synthase in insulin-producing cells.

We presently investigated the induction of manganese superoxide dismutase (MnSOD) and nitric oxide synthase (iNOS) mRNA by interleukin-1 beta (IL-1 beta) in insulin-producing RINm5F cells. IL-1 beta induced both mRNAs in parallel, with increased levels detectable after 4 h and further increase at 6 h. Aminoguanidine, a blocker of NO production, did not prevent IL-1 beta-induced MnSOD mRNA expression, and SNP, a NO releasing agent, did not induce MnSOD mRNA. Actinomycin D, an inhibitor of gene transcription, prevented IL-1 beta induction of both MnSOD and iNOS mRNA. Cycloheximide, an inhibitor of protein synthesis, prevented IL-1 beta-induced expression of iNOS mRNA, but not MnSOD mRNA. These data suggest that induction of MnSOD mRNA by IL-1 beta is independent of iNOS expression and NO production. Moreover, while expression of iNOS mRNA depends on protein synthesis, MnSOD mRNA induction does not necessarily require this step. Thus, it seems that IL-1 induces genes potentially involved in cell damage (iNOS) and defense (MnSOD) by different mechanisms.

Amino Acid Oxidoreductases↗