Interleukin 1 inhibits insulin secretion from isolated rat pancreatic islets by a process that requires gene transcription and mRNA translation

Interleukin-1 beta effects on cyclic GMP and cyclic AMP in cultured rat islets of Langerhans-arginine-dependence and relationship to insulin secretion

When islets were cultured with interleukin-1 beta (1 or 100 pmol/l) for 12 h in arginine-containing medium, cyclic GMP levels were increased 1.6- and 4.5-fold respectively. The arginine analogue, N-omega-nitro-L-arginine methyl ester, which blocks nitric oxide formation and partially reverses inhibition of insulin secretion by 100 pmol/l interleukin-1 beta, largely, but not completely, blocked generation of cyclic GMP. Treatment of islets with 100 pmol/l interleukin-1 beta for 12 h significantly decreased islet cyclic AMP generation in the absence of isobutylmethylxanthine (from 13.1 +/- 0.7 to 9.3 +/- 0.8 fmol/micrograms islet protein), this fall was arginine-dependent and may have resulted from an effect on a cyclic AMP phosphodiesterase, since it was masked if isobutylmethylxanthine was present. Isobutylmethylxanthine (0.4 mmol/l) reduced the inhibitory potency of interleukin-1 beta in 15 h slightly but significantly from 80.5 to 59.0%. The morpholinosydnonimine SIN-1, which is a nitric oxide donor, inhibited insulin secretion, raised islet cyclic GMP and lowered cyclic AMP; its effects were similar to those of interleukin-1 beta. However, 6-anilinoquinoline-5,8-quinone, [LY83583 (1-10 mumol/l)], inhibited insulin secretion, and significantly decreased cyclic GMP while 8-bromocyclic GMP stimulated insulin secretion. Both low- and high-dose interleukin-1 beta treatment give a large arginine-dependent and a small, yet significant, arginine-independent increase in cyclic GMP. The inhibitory effect of SIN-1 or interleukin-1 beta on insulin secretion seems to depend to a small extent on decreased islet cyclic AMP, though sustained increases in nitric oxide or depleted islet GTP may directly affect the secretory process.

Interleukin 1 beta induces the formation of nitric oxide by beta-cells purified from rodent islets of Langerhans. Evidence for the beta-cell as a source and site of action of nitric oxide

Nitric oxide has recently been implicated as the effector molecule that mediates IL-1 beta-induced inhibition of glucose-stimulated insulin secretion and beta-cell specific destruction. The pancreatic islet represents a heterogeneous cell population containing both endocrine cells (beta-[insulin], alpha-]glucagon], gamma[somatostatin], and PP-[polypeptide] secreting cells) and non-endocrine cells (fibroblast, macrophage, endothelial, and dendritic cells). The purpose of this investigation was to determine if the beta-cell, which is selectively destroyed during insulin-dependent diabetes mellitus, is both a source of IL-1 beta-induced nitric oxide production and also a site of action of this free radical. Pretreatment of beta-cells, purified by FACS with IL-1 beta results in a 40% inhibition of glucose-stimulated insulin secretion that is prevented by the nitric oxide synthase inhibitor, NG-monomethyl-L-arginine (NMMA). IL-1 beta induces the formation of nitric oxide by purified beta-cells as evidenced by the accumulation of cGMP, which is blocked by NMMA. IL-1 beta also induces the accumulation of cGMP by the insulinoma cell line Rin-m5F, and both NMMA as well as the protein synthesis inhibitor cycloheximide prevent this cGMP accumulation. Iron-sulfur proteins appear to be intracellular targets of nitric oxide. IL-1 beta induces the formation of an iron-dinitrosyl complex by Rin-m5F cells indicating that nitric oxide mediates the destruction of iron-sulfur clusters of iron containing enzymes. This is further demonstrated by IL-1 beta-induced inhibition of glucose oxidation by purified beta-cells, mitochondrial aconitase activity of dispersed islet cells, and mitochondrial aconitase activity of Rin-m5F cells, all of which are prevented by NMMA. IL-1 beta does not appear to affect FACS-purified alpha-cell metabolic activity or intracellular cGMP levels, suggesting that IL-1 beta does not exert any effect on alpha-cells. These results demonstrate that the islet beta-cell is a source of IL-1 beta-induced nitric oxide production, and that beta-cell mitochondrial iron-sulfur containing enzymes are one site of action of nitric oxide.

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.

Pulsatile hormone secretion during severe sepsis: accuracy of different blood sampling regimens

The metabolic response to sepsis is dependent on the hormonal status. However, reported plasma hormone levels vary widely among studies. The persistence of pulsatile secretion, as occurs normally, may explain the observed variability. To study whether pulsatile hormone secretion persists during sepsis and how it affects assessment of the hormonal status from single measurements, we measured growth hormone (GH), prolactin, cortisol, insulin, and C-peptide at 20-minute intervals for 24 hours in eight consecutive patients with severe sepsis. Twenty-four-hour averages (mean +/- SD) were 3.3 +/- 2.5 ng/mL for GH, 640 +/- 461 nmol/L for cortisol, 18.2 +/- 4.8 mU/L for insulin, and 3.4 +/- 2.9 U/L for C-peptide, at a pulse frequency between 3.3 +/- 2.7 for C-peptide and 10.2 +/- 3.4 for insulin, and an increase of the maximal value in a pulse above the preceding nadir of 131% +/- 13% for cortisol and 376% +/- 386% for GH, as assessed with Cluster analysis. Prolactin levels were below the detection limit in all but one patient, probably due to the administration of dopamine. To determine the accuracy of less frequent blood sampling regimens, we simulated different sampling strategies and compared them with the 24-hour averages. The accuracy of single samples proved inadequate for all hormones. Sampling every 20 minutes for periods of 4, 8, or 12 hours improved accuracy, but intermittent sampling every 1, 2, 4, or 6 hours during a 24-hour period yielded even more accurate results.(ABSTRACT TRUNCATED AT 250 WORDS)

Interleukin-1 beta induces the expression of an isoform of nitric oxide synthase in insulin-producing cells, which is similar to that observed in activated macrophages

The suppressive and cytotoxic effects of interleukin-1 beta (IL-1 beta) on rodent insulin-producing cells observed in vitro are probably mediated through formation of nitric oxide (NO). In this study we demonstrate that IL-1-induced NO formation in isolated rat islets and insulin-producing HIT cells is more sensitive to inhibition by NG-monomethyl-L-arginine than to inhibition by NG-nitro-L-arginine, thus suggesting that IL-1-exposed insulin-producing cells express an isoform of nitric oxide synthase similar to that present in activated macrophages. Furthermore, IL-1 beta markedly increased the mRNA levels of the inducible macrophage form of nitric oxide synthase in HIT cells.

Exogenous administration of IL-1 alpha inhibits active and adoptive transfer autoimmune diabetes in NOD mice

Diabetes susceptibility in non-obese diabetic (NOD) mice may involve immune dysregulation resulting from cytokine deficiencies. The cytokine IL-1 plays a role in various immune as well as endocrine responses and may be hypoexpressed in NOD mice. Treatment with low levels of exogenous IL-1 alpha for 22 weeks prevented the naturally occurring insulitis and diabetogenic process in NOD mice during and at least 33 weeks after cessation of IL-1 alpha treatment. Treatment with IL-1 alpha also inhibited insulitis and hyperglycemia induced by adoptive transfer of pathogenic, polyclonal CD4+8- T cells. Even after islet-cell destruction, IL-1 alpha injections in diabetic NOD mice normalized plasma glucose levels when administered in combination with insulin, whereas equivalent levels of IL-1 alpha alone did not. Our studies support the hypothesis that IL-1 alpha suppresses autoimmune diabetes and hyperglycemia in NOD mice by pleiotropic effects on both immune and metabolic systems. Thus, IL-1 treatment could clinically be an effective immunotherapeutic modality for autoimmune diabetes mellitus by suppressing early disease progression or normalize plasma glucose levels when insulin is present.

Role of receptor binding and gene transcription for both the stimulatory and inhibitory effects of interleukin-1 in pancreatic beta-cells

A brief exposure of pancreatic islets to the cytokine interleukin-1 beta (IL-1 beta) induces an initial stimulatory phase, which is followed by inhibition of islet function and eventually beta-cell damage. In the present study we have investigated the effects of IRAP, a blocker of type I IL-1 receptor and actinomycin D, an inhibitor of DNA transcription, on both the stimulatory and inhibitory effects of IL-1 beta on rat pancreatic islets in vitro. The two test agents counteracted the initial stimulatory actions of IL-1 beta on both islet glucose-induced insulin release and glucose oxidation rates. Furthermore, cycloheximide, an inhibitor of protein synthesis, could also prevent the early IL-1 beta-induced stimulation of insulin release. When islets were exposed for 1 hr to IL-1 beta and studied after 12 hr, there was a 75% inhibition of glucose induced insulin release, a 50% decrease in glucose oxidation rates and a 30% decrease in (pro)insulin biosynthesis. These effects were completely counteracted by coincubation with IRAP or actinomycin D, but were not affected by coincubation with pertussis toxin. Islet exposure to IL-1 alpha also induced a 60-80% inhibition of glucose-induced insulin release after 12 hr. As observed with rIL-1 beta, IRAP was also able to block the suppressive effects of IL-1 alpha on islet function. Mouse islets exposed for 2 hr to IL-1 beta and studied after 12 hr presented a 50% decrease in the glucose-induced insulin release. This effect was completely blocked by coincubation with a rat monoclonal antibody generated against the type I mouse IL-1 receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytokines inhibit proliferation and insulin secretion by clonal rat insulinoma cells (RINm5F) non-synergistically and in a pertussis toxin-insensitive manner

It has been proposed that certain cytokines secreted by islet-infiltrating leukocytes may be involved in the pathogenesis of insulin-dependent diabetes mellitus. Since the cytotoxic actions by the cytokines may reflect interactions with islet cell types other than the beta-cell, in this work I have investigated the effects of different combinations of various cytokines on the proliferation and hormone content and secretion by a pure insulin-producing cell population, i.e., the clonal rat insulinoma cell line RINm5F. For this purpose RINm5F cells were exposed in culture for 1-2 days to interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6), tumor necrosis factor alpha (TNF-alpha), interferon gamma (IFN-gamma) and interferon alpha (IFN-alpha) at different concentrations. It was found that IL-1 beta markedly decreased the cellular content of insulin and secretion of the hormone into the culture medium, while causing a very slight inhibition of RINm5F cell proliferation. On the other hand, IFN-gamma and IFN-alpha both elicited marked decreases in proliferation and insulin content and secretion by the insulinoma cells. IL-6 and TNF-alpha were found not to affect these parameters. No additive or synergistic effects were observed when the cytokines were added in various combinations. There was no protection against the cytotoxicity of IL-1 beta, IFN-gamma or IFN-alpha by pre-treatment with pertussis toxin. From these findings it is concluded that the cytokines IL-1 beta, IFN-gamma and IFN-alpha act in a non-synergistic fashion in suppressing RINm5F cell proliferation and hormone secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

An interleukin-1 receptor antagonist protein protects insulin-producing beta cells against suppressive effects of interleukin-1 beta

The cytokine interleukin-1 beta may have an important role in the autoimmune mediated damage of pancreatic Beta cells in insulin-dependent diabetes mellitus. In the present study we have investigated the effects of an interleukin-1 receptor antagonist protein, a blocker of the type I interleukin-1 receptor, on the suppressive actions of recombinant interleukin-1 beta on insulin-producing cells. Brief exposure (1-2 h) of rat and mouse pancreatic islets to 10 ng/ml recombinant interleukin-1 beta induced an 70-80% inhibition of insulin response to glucose after 12 h. These effects were completely counteracted by co-incubation with 100 ng/ml interleukin-1 receptor antagonist protein. When rat islets were cultured for 48 h in the presence of recombinant interleukin-1 beta (5 ng/ml) higher concentrations of interleukin-1 receptor antagonist protein (5000 ng/ml) were required to protect Beta-cell function. Interleukin-1 receptor antagonist protein also counteracted the inhibitory effects of recombinant interleukin-1 beta on the growth of the rat insulinoma cell line RINm5F. These data suggest that interleukin-1 receptor antagonist protein can protect insulin-producing cells from the deleterious effects of recombinant interleukin-1 beta, and that these cells possess type I interleukin-1 receptors.

Interleukin-1 beta induces an early decrease in insulin release, (pro)insulin biosynthesis and insulin mRNA in mouse pancreatic islets by a mechanism dependent on gene transcription and protein synthesis

In an attempt to further characterize the mechanisms of action of recombinant interleukin-1 beta (rIL-1 beta) on mouse pancreatic islets, islets were exposed for different periods of time (6, 12 and 24 h) to 50 U/ml rIL-1 beta. After 6 h there was already a significant decrease in glucose (16.7 mM)-induced insulin release. This was followed at 12 h by a decrease in insulin mRNA contents and (pro)insulin biosynthesis and, after 24 h, by a decrease in islet insulin contents. There was no decrease in total protein biosynthesis or DNA contents in any of the studied time points and the glucose oxidation rates were not affected by rIL-1 beta after 12 h of exposure. A similar inhibition of insulin release, (pro)insulin biosynthesis and insulin mRNA content was observed 12 h after a short (2 h) exposure of the islets to rIL-beta, suggesting that a brief exposure of mouse islets to the cytokine can modify their function for several hours. When islets were exposed for 12 h to 50 U/ml rIL-1 beta in the presence of either an inhibitor of gene transcription (actinomycin D) or an inhibitor of mRNA translation (cycloheximide) there was a complete protection against the suppressive effects of rIL-1 beta on insulin release, (pro)insulin biosynthesis and insulin mRNA contents. However, when islets were exposed for 2 h to rIL-1 beta in the presence of actinomycin D, and studied 12 h later, actinomycin counteracted the inhibitory effects of rIL-1 beta on insulin release, but not on (pro)insulin biosynthesis.(ABSTRACT TRUNCATED AT 250 WORDS)