Prevention of spontaneous and experimentally induced diabetes in mice with zinc sulfate-enriched drinking water is associated with activation and reduction of NF-kappa B and AP-1 in islets, respectively.

Recently, we reported that zinc sulfate-enriched (25 mM) drinking water (Zn(2+)) protected male C57BL/6 mice from diabetes induced by multiple low doses of streptozotocin (MLD-STZ) and that MLD-STZ activates the transcription factors nuclear factor (NF)-kappa B and activator protein (AP)-1 in islets of these mice. Therefore, we studied the effect of Zn(2+) on spontaneous diabetes in female nonobese diabetic (NOD) mice and on the activity of NF-kappa B and AP-1 in islets of NOD and MLD-STZ-injected male C57BL/6 mice. We hypothesized that Zn(2+) may affect NF-kappa B, which may play a key role in immune-mediated diabetogenesis. Here we continuously administered Zn(2+) to NOD mice, to both parents and their F(1) offspring, and treated C57BL/6 male mice with MLD-STZ either alone or in addition to Zn(2+) . We assessed effects of Zn(2+) on insulitis and peri-insulitis in 8-week-old NOD mice and analyzed NF-kappa B and AP-1 activities in islets. Zn(2+) significantly prevented diabetes in female F(1) offspring and significantly reduced insulitis and peri-insulitis. Zn(2+) significantly stimulated NF-kappa B and AP-1 activation in NOD mice, in contrast, in C57BL/6 mice, Zn(2+) significantly reduced their activation by MLD-STZ. These data demonstrate that NF-kappa B may play a critical role in immune-mediated diabetes. Depending on the mode of beta-cell destruction, Zn(2+) may prevent apoptosis through activation of NF-kappa B in NOD mice or prevent inflammatory immune destruction through inhibition of NF-kappa B in MLD-STZ-treated C57BL/6 mice.

Interleukin-11 inhibits NF-kappaB and AP-1 activation in islets and prevents diabetes induced with streptozotocin in mice.

This laboratory has reported that multiple low doses of streptozotocin (MLD-STZ) similarly upregulate the T helper (Th)1-type proinflammatory cytokines tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma in islets of both the diabetes-susceptible male and the diabetes-resistant female C57BL/6 mice and that MLD-STZ downregulates the anti-inflammatory Th2-type cytokines interleukin (IL)-4 and IL-10, as well as the anti-inflammatory Th3-type cytokine-transforming growth factor (TGF)-ss1 in islets of male, but not female, mice. Thus, diabetes is associated with a relative preponderance of local proinflammatory cytokines. Here, we investigated the effects of MLD-STZ on the anti-inflammatory cytokine IL-11 and the transcription factors nuclear factor (NF)-kappaB and activator protein (AP)-1, which are involved in gene activation of proinflammatory cytokines, and on the cytosolic kinase (IKK-alpha) of NF-kappaB inhibitor (IkappaB). Furthermore, the effect of recombinant human (rh)IL-11 on MLD-STZ diabetes, insulitis, cytokines, IKK-alpha, NF-kappaB, and AP-1 was analyzed in islets. Interleukin-11 prevented diabetes without affecting insulitis; attenuated TNF-alpha and IFN-gamma response; and stimulated IL-4 production and inhibited activation of IKK-alpha, NF-kappaB, and AP-1. The results demonstrated the potential of rhIL-11 in preventing MLD-STZ diabetes through enhancement of anti-inflammatory responses in islets. In this process, the transcription factors NF-kappaB and AP-1 might play a key role.

Generation of hydroxyl radicals mediated by streptozotocin in pancreatic islets of mice in vitro.

Type I diabetes is considered a multifactorial autoimmune process initiated by an environmental factor. There is evidence that reactive oxygen species are involved in destructing insulin-producing beta-cells. In mice, reactive oxygen species and nitric monoxide contribute to beta-cell damage in the non-obese diabetic strain developing spontaneously diabetes and in diabetes induced with multiple low doses of streptozotocin. Previously, we found that zinc sulfate induced metallothionein in pancreatic islets, protected beta-cells against streptozotocin toxicity in vitro, and prevented diabetes induced with multiple low doses of streptozotocin. Since metallothionein is known to scavenge hydroxyl radicals in cell-free systems, we hypothesize that the protective effect of zinc sulfate results from metallothionein induction scavenging hydroxyl radicals generated by multiple low doses of streptozotocin. Therefore, we studied whether levels of hydroxyl radicals are increased by streptozotocin in isolated islets in vitro. Here, we demonstrate basal and streptozotocin-stimulated hydroxyl radicals by electron spin resonance spectroscopy in combination with hydroxyl radical-specific spin trapping in islet homogenates. Furthermore, in islet cultures, streptozotocin augmented generation of reactive oxygen species as determined by fluorescence. Of the group of reactive oxygen species, the streptozotocin-augmented generation of hydrogen peroxide was also specifically determined. We conclude that streptozotocin-mediated hydroxyl radicals and generation of reactive oxygen species may be crucial effectors in beta-cell damage.

Molecular target structures in alloxan-induced diabetes in mice.

Type 1 diabetes results from irreversible damage of insulin-producing beta-cells. In laboratory animals, diabetes can be induced with alloxan (ALX), a 2,4,5,6-tetraoxopyrimidine. ALX is a potent generator of reactive oxygen species (ROS), which can mediate beta-cell toxicity. However, the initial lesions on essential beta-cell structures are not known. In this study, we report that the glucose transporter 2 (GLUT2) and glucokinase (GK) are target molecules for ALX. Ex vivo, a gradual decrement of both GLUT2 and GK mRNA expression was found in islets isolated from ALX-treated C57BL/6 mice. This reduction was more pronounced for GLUT2 than for GK. The mRNA expression of beta-actin was also slightly affected with time after ALX exposure, the proinsulin mRNA, however, remained unaffected as well as the pancreatic total insulin content. Pretreatment with D-glucose (D-G) protected the mRNA expression of GLUT2 and GK against ALX toxicity and prevented diabetes. Yet, in these euglycemic mice, an impaired oral glucose tolerance persisted. Pretreatment with 5-thio-D-glucose (5-T-G) failed to prevent ALX diabetes, administration of zinc sulfate (Zn(2+))-enriched drinking water, however, reduced ALX-induced hyperglycemia. In conclusion, ALX exerted differential toxicity on beta-cell structures similar to in vitro results reported from this laboratory. Furthermore, the present results differ from those reported for the diabetogen streptozotocin (STZ). Injections of multiple low doses (MLD) of STZ reduced GLUT2 expression only, but failed to affect expression of GK and proinsulin as well as beta-actin as internal control. MLD-STZ diabetes was prevented by pretreatment with both D-G and 5-T-G and administration of Zn(2+)-enriched drinking water. Apparently, ALX and MLD-STZ exert diabetogenicity by different pathways requiring different interventional schedules for prevention.

Differential regulation of Th1-type and Th2-type cytokine profiles in pancreatic islets of C57BL/6 and BALB/c mice by multiple low doses of streptozotocin.

In the nonobese diabetic (NOD) mouse, the T helper (Th)1-type inflammatory cytokines interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha play a critical role in the development of type 1 diabetes, whereas the Th2-type anti-inflammatory cytokines interleukin (IL)-4 and IL-10 operate counterregulatory. There are no comprehensive analyses on cytokine profiles in the mouse model of diabetes induced with multiple low doses of streptozotocin (MLD-STZ). Therefore, we used islets to study ex vivo effects of MLD-STZ and in vitro effects of STZ on IFN-gamma, TNF-alpha, IL-4, and IL-10 on both levels of protein-producing cells and the mRNA expression, as well as the mRNA expression of the Th3-type cytokine transforming growth factor TGF-beta1. C57BL/6 and BALB/c mice of both genders were injected intraperitoneally with 40 mg/kg body wt STZ on five consecutive days and islets were isolated on day I and 3 after the fifth STZ-injection. Control mice received the solvent of STZ. In islets of C57BL/6 mice of both genders MLD-STZ similarly stimulated production of IFN-gamma and TNF-alpha, but significantly reduced IL-4 and IL-10 levels in male mice only. Opposite results were obtained in islets of BALB/c mice of both genders. Here, MLD-STZ markedly decreased the levels of IFN-gamma and TNF-alpha, but significantly increased the levels of IL-4 and IL-10. The functional results were in line with MLD-STZ effects on the mRNA expression of the cytokines. Moreover, MLD-STZ effects on the TGF-beta1 mRNA expression were reversed to the effects on IFN-gamma and TNF-alpha. The in vitro effects of STZ in islets, in general, were similar to those exerted by MLD-STZ. Apparently, reduction and upregulation of Th2-type cytokines was more associated with susceptibility and resistance, respectively, to MLD-STZ-induced diabetes than upregulation of Th1-type cytokine levels.