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Reversibility of interleukin-1 beta-induced islet destruction and dysfunction by the inhibition of nitric oxide synthase.

ABSTRACT: We have examined the reversibility of NO-mediated islet dysfunction and destruction induced by interleukin-1 beta (IL-1 beta). Previous studies have shown that pretreatment of islets for 18 h with IL-1 beta results in an inhibition of glucose-stimulated insulin secretion that requires 4 days incubation in the absence of IL-1 beta to restore islet secretory function. In this study we use a sequential experimental design in which islets are first exposed to IL-1 beta for 18 h, and then treated with the NO synthase inhibitor NG-monomethyl-L-arginine (NMMA). Insulin secretion is inhibited by 98% after the 18 h incubation with IL-1 beta, and this inhibition is reversed in a time-dependent fashion by NMMA, with complete recovery of insulin secretion observed 8 h after the inhibition of NO synthase. Inhibition of NO synthase also restores IL-1 beta-induced inhibition of mitochondrial aconitase activity in a time-dependent fashion that mimics the recovery of glucose-stimulated insulin secretion by islets. Ferrous iron and the reducing agents cysteine and thiosulphate accelerate the rate of recovery of insulin secretion, and ferrous iron and thiosulphate stimulate the recovery of islet aconitase activity, suggesting that iron-sulphurcentre reconstitution may be involved in the recovery process. The recovery process also appears to require mRNA transcription, because the transcriptional inhibitor actinomycin D prevents the recovery of insulin secretion by islets after the inhibition of NO synthase. Although IL-1 beta induces the co-expression of NO synthase and cyclo-oxygenase by islets, cyclo-oxygenase is not involved in the recovery of glucose-stimulated insulin secretion. Inhibition of NO synthase also prevents IL-1 beta-induced islet destruction, which otherwise occurs during a 96 h continuous exposure to this cytokine. The destructive effects of IL-1 beta on islet viability are prevented if NMMA is added to islet cultures during the first 24 h of exposure to IL-1 beta, but islet destruction is not prevented if NMMA is added after the first 48 h exposure to IL-1 beta. These results show that IL-1 beta-induced islet dysfunction is reversed by the inhibition of NO synthase, that recovery of insulin secretion is stimulated by iron and reducing agents, and that the recovery process appears to require mRNA transcription. We also show that it is possible to rescue islets from the destructive effects of IL-1 beta if NO synthase is inhibited early after its induction.

SUBMITTER: Corbett JA

PROVIDER: S-EPMC1138079 | biostudies-other | 1994 May

REPOSITORIES: biostudies-other

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Project description: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.

Project description:BackgroundAltered nitric oxide synthase (NOS) has been implicated in the pathophysiology of heart failure (HF). Recent evidence links hypothyroidism to the pathology of HF. However, the precise mechanisms are incompletely understood. The alterations and functional effects of cardiac NOS in hypothyroidism are unknown. We tested the hypothesis that hypothyroidism increases cardiomyocyte inducible NOS (iNOS) expression, which plays an important role in hypothyroidism-induced depression of cardiomyocyte contractile properties, [Ca(2+)]i transient ([Ca(2+)]iT), and β-adrenergic hyporesponsiveness.Methods and resultsWe simultaneously evaluated LV functional performance and compared myocyte three NOS, β-adrenergic receptors (AR) and SERCA2a expressions and assessed cardiomyocyte contractile and [Ca(2+)]iT responses to β-AR stimulation with and without pretreatment of iNOS inhibitor (1400 W, 10(-5)mol/L) in 26 controls and 26 rats with hypothyroidism induced by methimazole (~30 mg/kg/day for 8 weeks in the drinking water). Compared with controls, in hypothyroidism, total serum T3 and T4 were significantly reduced followed by significantly decreased LV contractility (EES) with increased LV time constant of relaxation. These LV abnormalities were accompanied by concomitant significant decreases in myocyte contraction (dL/dtmax), relaxation (dR/dtmax), and [Ca(2+)]iT. In hypothyroidism, isoproterenol (10(-8)M) produced significantly smaller increases in dL/dtmax, dR/dtmax and [Ca(2+)]iT. These changes were associated with decreased β1-AR and SERCA2a, but significantly increased iNOS. Moreover, only in hypothyroidism, pretreatment with iNOS inhibitor significantly improved basal and isoproterenol-stimulated myocyte contraction, relaxation and [Ca(2+)]iT.ConclusionsHypothyroidism produces intrinsic defects of LV myocyte force-generating capacity and relaxation with β-AR desensitization. Up-regulation of cardiomyocyte iNOS may promote progressive cardiac dysfunction in hypothyroidism.

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Reversibility of interleukin-1 beta-induced islet destruction and dysfunction by the inhibition of nitric oxide synthase.

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