Jesper I. Reimers

On the pathogenesis of IDDM.

SummaryA model of the pathogenesis of insulin-dependent diabetes mellitus, i.e. the initial phase of beta-cell destruction, is proposed: in a cascade-like fashion efficient antigen presentation, unbalanced cytokine, secretion and poor beta-cell defence result in beta-cell destruction by toxic free radicals (O2− and nitric oxide) produced by the beta cells themselves. This entire process is under polygenetic control.

Involvement of interleukin 1 and interleukin 1 antagonist in pancreatic β-cell destruction in insulin-dependent diabetes mellitus

In this review we propose that the balance between the action of interleukin 1 (IL-1) and its natural antagonist IL-1ra on the level of the insulin-producing pancreatic beta-cell may play a decisive role in the pathogenesis of insulin-dependent diabetes mellitus (IDDM). We argue that IL-1 potentiated by other cytokines (tumor necrosis factor alpha, interferon gamma) is an important effector molecule involved in both early and late events in the immune-mediated process that leads to beta-cell destruction and IDDM. We also point out that surprisingly high molar excesses of IL-1ra over IL-1 are necessary to block the action of IL-1 on islet beta-cells compared to islet alpha-cells in vitro and in animals. We suggest that the selectivity of beta-cell destruction in IDDM may be conferred on several levels: (1) homing of beta-cell antigen specific T cells, (2) targeted delivery of cytokines by lymphocytic and monocytic cells beta-cells, (3) high molar excesses of IL-1ra over IL-1 needed to prevent IL-1 mediated beta-cell toxicity, (4) increased beta-cell sensitivity to free nitric oxide and oxygen radical formation induced by IL-1 and (5) inadequate oxidative stress response by beta-cells to cytokines. Further studies are needed to establish the in vivo role of an imbalance between the amounts of IL-1 and IL-1ra produced relative to their action in the pathogenesis of IDDM.

Interleukin 1β induces diabetes and fever in normal rats by nitric oxide via induction of different nitric oxide synthases

Substantial in vitro evidence suggests that nitric oxide may be a major mediator of interleukin 1 (IL-1) induced pancreatic beta-cell inhibition and destruction in the initial events leading to insulin-dependent diabetes mellitus. Using NG-nitro-L-arginine methyl ester, an inhibitor of both the constitutive and the cytokine inducible forms of nitric oxide synthase, and aminoguanidine, a preferential inhibitor of the inducible form of nitric oxide synthase, we investigated the impact of inhibiting nitric oxide production on food-intake, body weight and temperature, blood glucose, plasma insulin, glucagon, corticosterone and leukocyte- and differential-counts in normal rats injected once daily for 5 days with interleukin 1 beta (IL-1 beta) (0.8 microgram/rat = 4.0 micrograms/kg). Inhibition of both the constitutive and the inducible forms of nitric oxide synthase prevented IL-1 beta-induced fever, hyperglycaemia, hypoinsulinemia, and hyperglucagonemia, and partially prevented lymphopenia and neutrophilia, but had no effect on IL-1 beta-induced anorexia and changes in plasma corticosterone. Preferential inhibition of the inducible form of nitric oxide synthase using two daily injections of 5 mg/rat of aminoguanidine prevented IL-1 beta-induced hyperglycaemia and hypoinsulinaemia, and slightly reduced the pyrogenicity of IL-1 on 3 out of 5 days. Higher doses of aminoguanidine (100 mg/rat) prevented lymphopenia and neutrophilia. We conclude that nitric oxide produced by the inducible form of nitric oxide synthase, mediates the IL-1 beta-induced inhibition of insulin release and that the effect of IL-1 beta on temperature, pancreatic alpha-cells, and leukocyte differential counts seems to be mediated by nitric oxide produced by the constitutive form of nitric oxide synthase.

Differential interleukin-1 receptor antagonism on pancreatic beta and alpha cells. Studies in rodent and human islets and in normal rats

SummaryThe monokines interleukin-1α and -β have been implicated as effector molecules in the immune-mediated pancreatic beta-cell destruction leading to insulin-dependent diabetes mellitus. Here we investigated the effects of interleukin-1 receptor antagonism on insulin and glucagon release of rat, mouse and human islets exposed to recombinant human interleukin-1β, and on interleukin-1β induced changes in blood glucose, serum insulin and serum glucagon levels in Wistar Kyoto rats. The interleukin-1 receptor antagonist reduced the co-mitogenic effect of interleukin-1β on mouse and rat thymocytes with a 50% inhibitory concentration of 10- and 100-fold molar excess, respectively. Complete inhibition was obtained with a 100–1,000-fold molar excess. However, at a 100-fold molar excess the interleukin-1 receptor antagonist did not antagonise the potentiating effect of interleukin-1βon rat islet insulin accumulation during 3 and 6 h of exposure or of interleukin-1β-induced inhibition of insulin release after 24 h. In contrast, interleukin-1β-stimulated islet glucagon release was completely antagonised by a 100-fold molar excess of interleukin-1 receptor antagonist. A 10,000-fold molar excess of interleukin-1 receptor antagonist was needed to antagonise interleukin-1β stimulatory and inhibitory effects on rat beta-cell function in vitro. A 100-fold excess of interleukin-1 receptor antagonist could not counteract interleukin-1β effects on mouse and human beta cells, excluding species difference in the efficacy of the human interleukin-1 receptor antagonist. An anti-mouse interleukin-1 receptor type I antibody completely abolished interleukin-1β effects on isolated mouse islets. A 10–100-fold molar excess of interleukin-1 receptor antagonist antagonised interleukin-1β-induced fever, hypercorticosteronaemia and hyperglucagonaemia, but not interleukin-1β-induced reduction in insulin/glucose ratio in normal rats. In conclusion, our results suggest that antagonism of interleukin-1β effects on beta cells requires higher concentrations of interleukin-1 receptor antagonist than those necessary to block interleukin-1 action on islet alpha cells and other interleukin-1 targets in vitro and in vivo. This may contribute to the understanding of the specificity of the immunological beta-cell destruction leading to insulin-dependent diabetes.

Strain-Dependent Differences in Sensitivity of Rat β-Cells to Interleukin 1β In Vitro and In Vivo

The aim of this study was to investigate whether straindependent differences in β-cell sensitivity to interleukin (IL) 1β exist in vitro and in vivo and if so, whether these differences correlate to variations in IL-1β-induced islet inducible nitric oxide synthase (iNOS) mRNA expression and nitrite production in vitro and islet iNOS protein content in vivo. Isolated islets of Langerhans in vitro from Wistar-Kyoto/Møllegården (WK/Mol) rats were sensitive to the inhibitory effect of IL-1β on accumulated and acute insulin secretion, whereas islets from Brown Norway/Charles River (BN/CR) rats were resistant. Furthermore, IL-1β induced higher islet iNOS mRNA expression and nitric oxide production from WK/Mol islets compared with BN/CR islets. WK/Mol, WK/CR, BN/Mol, BN/CR, and Lewis-Scripps/Mol (LS/Mol) rats received one daily injection of recombinant human IL-1β (4.0 μg/kg) or vehicle for 5 days. All the strains investigated were susceptible to IL-1β–induced changes in body weight, food intake, temperature, and plasma glucagon and corticosterone. However, IL-1β induced hyperglycemia and impairment of β-cell glucose responsiveness in WK/Mol and LS/Mol rats, but not in BN rats. Furthermore, IL-1β–induced islet iNOS expression in vivo determined by immunostaining was greater in WK/Mol rats compared with WK/CR and BN/CR rats. No restriction fragment length polymorphisms, using 20 restriction enzymes, were identified in the iNOS gene in six rat strains including BioBreeding rats. In conclusion, the relative resistance of BN rat islets to IL-1β–induced inhibition of β-cell function in vitro was associated with lower islet iNOS mRNA expression and nitrite production in this strain. Further, the resistance of BN rats to IL-1β–induced hyperglycemia was associated with a lower islet iNOS expression in vivo.

Interleukin-1β (IL-1) Does Not Reduce the Diabetes Incidence in Diabetes-Prone Bb Rats

The cytokine interleukin 1 beta (IL-1) has been implicated as a pathogenetic factor in the initial events leading to insulin-dependent diabetes mellitus. Previous studies investigating the impact of IL-1 on diabetes incidence in spontaneously diabetic rodent models have been conflicting. IL-1 induces anorexia and previous studies are hampered by the lack of pair-fed controls to the IL-1 treated animals. We report that daily injections of 4.0 micrograms/kg/day of recombinant human IL-1 (rhIL-1) for 13 weeks from 25-30 days of age did not alter the incidence of diabetes in the diabetes-prone (DP) BB rats (75%) when compared to pair-fed, vehicle treated controls (55%, p = 0.18), or to unhandled DP BB rats (80%, p = 0.71). However, IL-1 induced significantly higher blood glucose concentrations in the prediabetic period (p < 0.00005) and at diabetes onset (p < 0.00005) in the DP BB rats and caused episodes of blood glucose concentrations > 11 mmol/l in the prediabetic period in 11/20 DP BB rats compared to 4/27 diabetes-resistant (DR) BB rats and 4/28 Wistar Furth (WF) rats (both p < 0.004), compared to DP BB). Further, rhIL-1 induced fever in 11 weeks in the DP BB rats compared to 3 weeks in the DR BB and 6 weeks in the WF rats. Using high performance size exclusion chromatography specific anti-rhIL-1-antibodies were demonstrated in DR BB and WF, but not in DP BB rats. These antibodies neutralized the inhibitory effect of rhIL-1 on insulin secretion from isolated islets of Langerhans in vitro. The reduced pyrogenic and endocrine effect of rhIL-1 in the DR BB and WF rats compared to the DP BB rats could be explained by the impaired ability of the DP BB rats to produce anti-rhIL-1-antibodies. In conclusion, administration of rhIL-1 modulated the prediabetic period, and produced higher blood glucose concentrations at diagnosis, but did not change the diabetes incidence in DP BB rats. The results are not in conflict with the hypothesis that IL-1 is a pathogenetic factor in IDDM, caused by high local concentrations of rat IL-1 in the islets during early insulitis. The results also show the necessity of pair-feeding of the control group to the rhIL-1 group when interpreting data from experiments investigating rhIL-1 effects on diabetes development in animal models.

Linomide increases plasma corticosterone in normal rats, but does not prevent the inhibitory action of IL-1 on β-cells in vivo or ex vivo

Recently, the synthetic immunomodulator Linomide (quinoline-3-carboxamide, LS 2616) was reported to prevent IDDM and insulitis in NOD mice. The mechanism for this protective effect is not known. The cytokine interleukin 1 (IL-1) may be a pathogenetic factor in the initial destruction of the beta-cells leading to IDDM. This study was undertaken to investigate the influence of Linomide on IL-1beta induced diabetogenic and hormonal changes in the rat in vivo, and on IL-1beta mediated synthesis of NO and inhibition of insulin secretion in isolated islets of Langerhans ex vivo. Normal male Wistar Kyoto rats received 4.0 microg/kg of recombinant human IL-1beta (rhIL-1beta) i.p. daily for 5 days with or without Linomide (8-9 mg/kg/day) in the drinking water. Litters of neonatal Wistar rats were pretreated for 3 days with injections of 10 mg/kg of Linomide i.p., and pancreatic islets of Langerhans were isolated for ex vivo studies. Linomide alone caused significant hypercorticosteronemia, hypoglucagonemia, lymphopenia and neutrophilia. Linomide had no effect on IL-1beta induced hyperglycemia, hyperglucagonemia, lymphopenia, neutrocytosis, or hypercorticosteronemia on day three and hypocorticosteronemia on day five. Further, Linomide did not prevent rhIL-1beta mediated reduction in insulin secretion or increase in NO synthesis ex vivo. In conclusion, Linomide does not seem to exert its protective effect on IDDM development via inhibition of interleukin 1 action on islet insulin release or NO production, but the increase in plasma corticosterone may contribute to the understanding of the immunomodulatory effects of Linomide.