Low dose streptozotocin-induced diabetes in rat insulin promoter-mCD80-transgenic mice is T cell autoantigen-specific and CD28 dependent

CTLA-4-Ig internalizes CD80 in fibroblast-like synoviocytes from chronic inflammatory arthritis mouse model

CD80 interact with CD28 and CTLA-4 on antigen-presenting cells, and function in the co-stimulatory signaling that regulates T cell activity. CTLA-4-Ig is used to treat RA by blocking co-stimulatory signaling. Chronic inflammatory arthritis was induced in D1BC mice using low-dose arthritogenic antigens and treated with CTLA-4-Ig. We performed histopathology of the joints and lymph nodes, serological examination for rheumatoid factors, and flow cytometric analysis of isolated synovial cells, including CD45- FLSs and CD45+ synovial macrophages. CTLA-4-Ig treatment ameliorated the chronic inflammatory polyarthritis. There was a decrease in the number of infiltrating lymphoid cells in the joints as well as in the levels of RF-IgG associated with a decrease in the number of B cells in the lymph nodes; more than 15% of CD45- FLSs expressed CD80, and a small number of them expressed PD-L1, indicating the presence of PD-L1/CD80 cis-heterodimers in these cells. CTLA-4-Ig internalized CD80, but not PD-L1, in isolated synovial cells. Gene ontology analysis revealed that CTLA-4-Ig internalization did not significantly alter the expression of inflammation-related genes. The therapeutic effect of CTLA-4-Ig appears to extend beyond the lymph nodes into the inflamed synovial compartment through the synergistic inactivation of T cells by the CD80 and PD-L1 axes.

Pam3CSK(4) enhanced beta cell loss and diabetogenesis: the roles of IFN-gamma and IL-17

Toll like receptors are primary sensors of both innate and adaptive immune systems. They activate APCs and influence T-cell function in inflammatory autoimmune response. Studies have shown that TLR manipulation may lead to either tolerance or trigger autoimmunity. Using diabetogenic and subdiabetogenic multiple low doses of streptozotocin, we demonstrate here that Pam3 CYS-CK4 a TLR-2 agonist, enhances and promotes diabetes in C57BL/6 male mice following increased apoptosis of β islet cells. FACS analysis of isolated pancreatic lymph node cells revealed significant increased number of macrophages, dendritic cells, CD4(+) TNF-α(+), CD4(+) IFN-γ(+) and most significantly, CD4(+) IL-17(+) and reduced number of CD25(+)Fox p3(+) T cells after Pam3CSK4 treatment. Genetic deletion of IFN-γ prevents whereas deletion of IL-17 reduced severity of Pam3CSK4-induced enhancement of diabetes. TLR-2 agonist-enhanced diabetogenesis is also influenced by enhanced influx of antigen presenting cells and suppression of regulatory T cell activity.

β Cell Protecting and Immunomodulatory Activities of Paecilomyces Hepiali Chen Mycelium in STZ Induced T1DM Mice

The anti-hyperglycemic and immunomodulatory activities of the ethanol extract from Paecilomyces Hepiali Chen (PHC), a Chinese medicine, were investigated in streptozotocin-induced type 1 diabetic (T1DM) mice. Male Balb/c mice, which were i.p. injected with streptozotocin (STZ, 50 mg/kg, for 5 consecutive days) on Day 7, were orally administered saline (the normal control and diabetic control group), Metformin (60 mg/kg, b.w., positive group), or the extract (100 mg/kg, b.w., PHC prevention group) from Day 1 to Day 28, Mice i.p. injected with streptozotocin (STZ, 50 mg/kg, b.w.) for 5 consecutive days prior to PHC treatment (100 mg/kg, b.w.) were used as the PHC treatment group. The effects of PHC on postprandial blood glucose concentrations, plasmatic insulin levels, morphology of pancreatic β cells and CD4+ T cells proliferation after 28-day treatment were monitored. Results showed that PHC administered 6 days before STZ induction of diabetes in mice significantly decreased blood glucose level (p < 0.01). An increase of insulin level was also observed as compared to those in the diabetic control group (p < 0.01). In addition, fewer inflammatory cells infiltrated the pancreatic islet and fewer β cells death by apoptosis within the inflamed islets were observed. More importantly, the CD4+ T cell proliferation was remarkably attenuated ex vivo in mice preventively treated with PHC (p < 0.01). In comparison to the PHC prevention group, no significant hypoglycemia, changes of insulin level and β cell protection were observed in mice treated with PHC after STZ administration. Our findings demonstrated that preventive administration of PHC protected β cells from apoptosis in type 1 diabetes induced by STZ, and the underlying mechanism may be involved in suppressing CD4+ T cells reaction, reducing inflammatory cells infiltration and protecting beta cell apoptosis in pancreatic islet.

Induction of diabetes with signs of autoimmunity in primates by the injection of multiple-low-dose streptozotocin

AIM

To develop a preclinical large animal model of autoimmune diabetes to facilitate the translational research of autoimmune diabetes in human.

MATERIALS AND METHODS

Nine young rhesus monkeys received multiple-low-dose (MLD) intravenous injections of streptozotocin for five consecutive days, followed by two additional boosting injections of STZ given 1 week apart. The induction of autoimmune diabetes was evaluated by regular metabolic testing, serological assessment of islet-reactive autoantibodies and histological examination of pancreatic tissues.

RESULTS

Seven of nine treated animals became diabetic with moderate hyperglycemia initially and more severe hyperglycemia thereafter. All diabetic animals exhibited severely impaired glucose tolerance, limited islet function, and required insulin therapy to maintain relatively normal glucose metabolism and healthy status. Serological tests showed that all diabetic monkeys developed autoantibodies specifically against insulin and islet antigens. Furthermore, histological examination of the pancreata from diabetic animals revealed evidence of specific destruction of islet β cells and islets infiltrated with T lymphocytes. Overt and persistent diabetes can be induced in young rhesus monkeys by the injection of MLD-STZ, and autoimmune responses to pancreatic islet cells seem to be involved in the development of glucose intolerance and diabetes.

CONCLUSION

These data indicate for the first time that autoimmune diabetes can be induced in primates; this may serve as a valuable preclinical model for studying the pathogenesis of and potential therapies for autoimmune diabetes in humans.

Streptozotocin, type I diabetes severity and bone

As many as 50% of adults with type I (T1) diabetes exhibit bone loss and are at increased risk for fractures. Therapeutic development to prevent bone loss and/or restore lost bone in T1 diabetic patients requires knowledge of the molecular mechanisms accounting for the bone pathology. Because cell culture models alone cannot fully address the systemic/metabolic complexity of T1 diabetes, animal models are critical. A variety of models exist including spontaneous and pharmacologically induced T1 diabetic rodents. In this paper, we discuss the streptozotocin (STZ)-induced T1 diabetic mouse model and examine dose-dependent effects on disease severity and bone. Five daily injections of either 40 or 60 mg/kg STZ induce bone pathologies similar to spontaneously diabetic mouse and rat models and to human T1 diabetic bone pathology. Specifically, bone volume, mineral apposition rate, and osteocalcin serum and tibia messenger RNA levels are decreased. In contrast, bone marrow adiposity and aP2 expression are increased with either dose. However, high-dose STZ caused a more rapid elevation of blood glucose levels and a greater magnitude of change in body mass, fat pad mass, and bone gene expression (osteocalcin, aP2). An increase in cathepsin K and in the ratio of RANKL/OPG was noted in high-dose STZ mice, suggesting the possibility that severe diabetes could increase osteoclast activity, something not seen with lower doses. This may contribute to some of the disparity between existing studies regarding the role of osteoclasts in diabetic bone pathology. Examination of kidney and liver toxicity indicate that the high STZ dose causes some liver inflammation. In summary, the multiple low-dose STZ mouse model exhibits a similar bone phenotype to spontaneous models, has low toxicity, and serves as a useful tool for examining mechanisms of T1 diabetic bone loss.

Bone inflammation and altered gene expression with type I diabetes early onset

Type I diabetes is associated with bone loss and marrow adiposity. To identify early events involved in the etiology of diabetic bone loss, diabetes was induced in mice by multiple low dose streptozotocin injections. Serum markers of bone metabolism and inflammation as well as tibial gene expression were examined between 1 and 17 days post-injection (dpi). At 3 dpi, when blood glucose levels were significantly elevated, body, fat pad and muscle mass were decreased. Serum markers of bone resorption and formation significantly decreased at 5 dpi in diabetic mice and remained suppressed throughout the time course. An osteoclast gene, TRAP5 mRNA, was suppressed at early and late time points. Suppression of osteogenic genes (runx2 and osteocalcin) and induction of adipogenic genes (PPARgamma2 and aP2) were evident as early as 5 dpi. These changes were associated with an elevation of serum cytokines, but more importantly we observed an increase in the expression of cytokines in bone, supporting the idea that bone, itself, exhibits an inflammatory response during diabetes induction. This inflammation could in turn contribute to diabetic bone pathology. IFN-gamma (one of the key cytokines elevated in bone and known to be involved in bone regulation) deficiency did not prevent diabetic bone pathology. Taken together, our findings indicate that bone becomes inflamed with the onset of T1-diabetes and during this time bone phenotype markers become altered. However, inhibition of one cytokine, IFN-gamma was not sufficient to prevent the rapid bone phenotype changes.

Hyperglycemia enhances adipogenic induction of lipid accumulation: involvement of extracellular signal-regulated protein kinase 1/2, phosphoinositide 3-kinase/Akt, and peroxisome proliferator-activated receptor gamma signaling

The molecular events of hyperglycemia-triggered increase in adipogenic induction of lipid accumulation remain unclear. We examined the effects of hyperglycemia on adipogenic induction of lipid accumulation and its involved signaling molecules, such as phosphoinositide 3-kinase (PI3K), ERKs, and peroxisome proliferator-activated receptor gamma (PPAR gamma). Bone marrow-derived mesenchymal stem cells (MSCs) isolated from FVB/N mice were capable of differentiating into adipocytes in adipogenic medium. The effects of high glucose (HG) (25.5 mm) were assessed in vitro by RT-PCR, ELISA, flow cytometry, immunostaining, and immunoblotting. The in vivo effect of hyperglycemia was further studied in streptozotocin (STZ)-induced diabetic FVB/N mice. Exposure of MSCs to HG enhanced adipogenic induction of lipid accumulation as compared with 5.5 mm glucose. HG increased PPAR gamma expression and PI3K activity and its downstream effector Akt phosphorylation during adipogenesis. Inhibition of PI3K/Akt activity with PI3K inhibitor LY294002 or by expressing the dominant negative p85 or Akt prevented the HG-enhanced PPAR gamma-dependent adipogenic induction of lipid accumulation. Moreover, HG increased the phosphorylation of ERK1/2 during adipogenesis. MAPK/ERK inhibitor PD98059 inhibited the PI3K activity, Akt phosphorylation, and lipid accumulation triggered by HG. PI3K inhibitor LY294002 did not affect the HG-increased ERK1/2 phosphorylation during adipogenesis. We next observed that adipogenic induction of lipid accumulation of MSCs isolated from STZ-induced diabetic mice is enhanced. Moreover, triglyceride, PPAR gamma expression, phosphorylated Akt and ERK1/2, and marrow fat in bones of STZ-diabetic mice were also increased. These results suggest that hyperglycemia enhances the adipogenic induction of lipid accumulation through an ERK1/2-activated PI3K/Akt-regulated PPAR gamma pathway.

Type I diabetic bone phenotype is location but not gender dependent

Bone is highly dynamic and responsive. Bone location, bone type and gender can influence bone responses (positive, negative or none) and magnitude. Type I diabetes induces bone loss and increased marrow adiposity in the tibia. We tested if this response exhibits gender and location dependency by examining femur, vertebrae and calvaria of male and female, control and diabetic BALB/c mice. Non-diabetic male mice exhibited larger body, muscle, and fat mass, and increased femur BMD compared to female mice, while vertebrae and calvarial bone parameters did not exhibit gender differences. Streptozotocin-induced diabetes caused a reduction in BMD at all sites examined irrespective of gender. Increased marrow adiposity was evident in diabetic femurs and calvaria (endochondrial and intramembranous formed bones, respectively), but not in vertebrae. Leptin-deficient mice also exhibit location dependent bone responses and we found that serum leptin levels were significantly lower in diabetic compared to control mice. However, in contrast to leptin-deficient mice, the vertebrae of T1-diabetic mice exhibit bone loss, not gain. Taken together, our findings indicate that TI-diabetic bone loss in mice is not gender, bone location or bone type dependent, while increased marrow adiposity is location dependent.

Cytotoxic T cell-mediated diabetes in RIP-CD80 transgenic mice: autoantigen peptide sensitivity and fine specificity

Rodent immune-mediated diabetes model studies have advanced understanding of beta cell-specific T cell responses, and the testing of therapeutic approaches. We have used an inducible diabetes model based on rat insulin promotor (RIP)-driven expression of CD80 (B7-1) on pancreatic beta cells. Using these mice, we have established that immunizing with a single autoantigen can promote progressive islet inflammation and eventually T cell-mediated diabetes. We now describe a potent immunization protocol using peptide-pulsed mature dendritic cells (DCs) to examine peptide epitopes derived from endogenous (preproinsulin) and transgenically expressed beta cell antigens, namely lymphocytic choriomeningitis virus glycoprotein (LCMV-GP). LCMV-GP epitopes efficiently promote beta cell destruction, and the autoantigenic peptide concentration used to load the DCs correlates directly with diabetes onset. The system allowed us to assess cytotoxic T cell (CTL) fine specificity by immunizing with DCs presenting altered peptide ligands (APLs) of the dominant LCMV-GP epitope, gp33. Finally, using an adoptive transfer system, we tested alternative in vitro T cell activation conditions, including APLs and mitogens, for their impact on T cell effector function and diabetes onset. Our studies revealed a marked discrepancy between (inflammatory) effector functions and diabetes progression, thus emphasizing the importance of structural identity between sensitizing and target epitope and the context of initial T cell activation.

Inhibition of PPARgamma prevents type I diabetic bone marrow adiposity but not bone loss

Diabetes type I is associated with bone loss and increased bone adiposity. Osteoblasts and adipocytes are both derived from mesenchymal stem cells located in the bone marrow, therefore we hypothesized that if we could block adipocyte differentiation we might prevent bone loss in diabetic mice. Control and insulin-deficient diabetic BALB/c mice were chronically treated with a peroxisomal proliferator-activated receptor gamma (PPARgamma) antagonist, bisphenol-A-diglycidyl ether (BADGE), to block adipocyte differentiation. Effects on bone density, adiposity, and gene expression were measured. BADGE treatment did not prevent diabetes-associated hyperglycemia or weight loss, but did prevent diabetes-induced hyperlipidemia and effectively blocked diabetes type I-induced bone adiposity. Despite this, BADGE treatment did not prevent diabetes type I suppression of osteoblast markers (runx2 and osteocalcin) and bone loss (as determined by micro-computed tomography). BADGE did not suppress osteoblast gene expression or bone mineral density in control mice, however, chronic (but not acute) BADGE treatment did suppress osteocalcin expression in osteoblasts in vitro. Taken together, our findings suggest that BADGE treatment is an effective approach to reduce serum triglyceride and free fatty acid levels as well as bone adiposity associated with type I diabetes. The inability of BADGE treatment to prevent bone loss in diabetic mice suggests that marrow adiposity is not linked to bone density status in type I diabetes, but we cannot exclude the possibility of additional BADGE effects on osteoblasts or other bone cells, which could contribute to preventing the rescue of the bone phenotype.

Immune tolerance induced by adoptive transfer of dendritic cells in an insulin-dependent diabetes mellitus murine model

AIM

To investigate the effect and underlying mechanisms of immune-tolerance induced by the adoptive transfer of bone marrow (BM)-derived dendritic cells (DC) in insulin-dependent diabetes mellitus (IDDM) mice.

METHODS

The IDDM model was established by a low dose of streptozotocin (STZ) in Balb/c mice. Two DC subpopulations were generated from the BM cells with granulocyte-macrophage colony-stimulating factor with or without interleukin-4. The purity and the T cell stimulatory capability of DC were identified. These cells were used to modulate autoimmune response in pre-diabetic mice. Blood glucose was examined weekly; pancreas tissues were taken for histopathological analysis, and CD4(+) T cells were isolated to detect lymphocyte proliferation by MTT assay and the ratio of CD4(+)CD25(+) T cells by fluorescence-activated cell sorting (FACS). The cytokine secretion was determined by ELISA analysis.

RESULTS

Two DC subsets were generated from BM, which have phenotypes of mature DC (mDC) and immature DC (iDC), respectively. The level of blood glucose decreased significantly by transferring iDC (P< 0.01) rather than mDC. Less lymphocyte infiltration was observed in the islets, and pancreatic structure was intact. In vitro, proliferation of lymphocytes decreased and the proportion of CD4(+)CD25(+) T cells increased remarkably, compared with the mDC-treated groups (P< 0.05), which were associated with increased level of the Th2 cytokine and reduced level of the Th1 cytokine after iDC transfer.

CONCLUSION

Our data showed that iDC transfer was able to confer protection to mice from STZ-induced IDDM. The immune-tolerance to IDDM may be associated with promoting the production of CD4(+)CD25(+) T cells and inducing regulatory Th2 responses in vivo.

Bone loss and increased bone adiposity in spontaneous and pharmacologically induced diabetic mice

Insulin-dependent diabetes mellitus (IDDM) is associated with increased risk of osteopenia/osteoporosis in humans. The mechanisms accounting for diabetic bone loss remain unclear. Pharmacologic inducers of IDDM, such as streptozotocin, mimic key aspects of diabetes in rodents, allow analysis at the onset of diabetes, and induce diabetes in genetically modified mice. However, side effects of streptozotocin, unrelated to diabetes, can complicate data interpretation. The nonobese diabetic (NOD) mouse model develops diabetes spontaneously without external influences, negating side effects of inducing agents. Unfortunately, in this model the onset of diabetes is unpredictable, occurs in a minority of male mice, and can only be studied in a single mouse strain. To validate the relevance of the more flexible streptozotocin-induced diabetes model for studying diabetes-associated bone loss, we compared its phenotype to the spontaneously diabetic NOD model. Both models exhibited hyperglycemia and loss of body, fat pad, and muscle weight. Furthermore, these genetically different and distinct models of diabetes induction demonstrated similar bone phenotypes marked by significant trabecular bone loss and increased bone marrow adiposity. Correspondingly, both diabetic models exhibited decreased osteocalcin mRNA and increased adipocyte fatty acid-binding protein 2 mRNA levels in isolated tibias and calvaria. Taken together, multiple streptozotocin injection-induced diabetes is a valid model for understanding the acute and chronic pathophysiologic responses to diabetes and their mechanisms in bone.

Chronic hyperglycemia modulates osteoblast gene expression through osmotic and non-osmotic pathways

Insulin dependent diabetes mellitus (IDDM; type I) is a chronic disease stemming from little or no insulin production and elevated blood glucose levels. IDDM is associated with osteoporosis and increased fracture rates. The mechanisms underlying IDDM associated bone loss are not known. Previously we demonstrated that osteoblasts exhibit a response to acute (1 and 24 h) hyperglycemia and hyperosmolality. Here we examined the influence of chronic hyperglycemia (30 mM) and its associated hyperosmolality on osteoblast phenotype. Our findings demonstrate that osteoblasts respond to chronic hyperglycemia through modulated gene expression. Specifically, chronic hyperglycemia increases alkaline phosphatase activity and expression and decreases osteocalcin, MMP-13, VEGF and GAPDH expression. Of these genes, only MMP-13 mRNA levels exhibit a similar suppression in response to hyperosmotic conditions (mannitol treatment). Acute hyperglycemia for a 48-h period was also capable of inducing alkaline phosphatase and suppressing osteocalcin, MMP-13, VEGF, and GAPDH expression in differentiated osteoblasts. This suggests that acute responses in differentiated cells are maintained chronically. In addition, hyperglycemic and hyperosmotic conditions increased PPARgamma2 expression, although this increase reached significance only in 21 days chronic glucose treated cultures. Given that osteocalcin is suppressed and PPARgamma2 expression is increased in type I diabetic mouse model bones, these findings suggest that diabetes-associated hyperglycemia may modulate osteoblast gene expression, function and bone formation and thereby contribute to type I diabetic bone loss.

IL-23 leads to diabetes induction after subdiabetogenic treatment with multiple low doses of streptozotocin

IL-23, a proximal regulator of IL-17, may be a major driving force in the induction of autoimmune inflammation. We have used a model of subdiabetogenic treatment with multiple low doses of streptozotocin (MLD-STZ; 4 x 40 mg/kg body weight) in male C57BL/6 mice to study the effect of IL-23 on immune-mediated beta cell damage and the development of diabetes, as evaluated by blood glucose, quantitative histology, immunohistochemistry and expression of relevant cytokines in the islets. Ten daily injections of 400 ng IL-23, starting on the first day of MLD-STZ administration led to significant and sustained hyperglycemia along with weight loss compared with controls (no IL-23), and a significant increase in the number of infiltrating cells, a lower insulin content, enhanced apoptosis, expression of IFN-gamma and IL-17 (not seen in the controls) and a significant increase in the expression of TNF-alpha and IL-18 in the pancreatic islets. IL-23 treatment started 5 days prior to MLD-STZ administration had no effect on diabetogenesis or cytokines expression in the pancreatic islets. We provide the first evidence in an animal model that IL-23 is involved in the development of type-1 diabetes, by inducing IL-17 and possibly IFN-gamma production in the target tissue.

Increased bone adiposity and peroxisomal proliferator-activated receptor-gamma2 expression in type I diabetic mice

Decreased bone mass, osteoporosis, and increased fracture rates are common skeletal complications in patients with insulin-dependent diabetes mellitus (IDDM; type I diabetes). IDDM develops from little or no insulin production and is marked by elevated blood glucose levels and weight loss. In this study we use a streptozotocin-induced diabetic mouse model to examine the effect of type I diabetes on bone. Histology and microcomputed tomography demonstrate that adult diabetic mice, exhibiting increased plasma glucose and osmolality, have decreased trabecular bone mineral content compared with controls. Bone resorption could not completely account for this effect, because resorption markers (tartrate-resistant acid phosphatase 5b, urinary deoxypyridinoline excretion, and tartrate-resistant acid phosphatase 5 mRNA) are unchanged or reduced at 2 and/or 4 wk after diabetes induction. However, osteocalcin mRNA (a marker of late-stage osteoblast differentiation) and dynamic parameters of bone formation were decreased in diabetic tibias, whereas osteoblast number and runx2 and alkaline phosphatase mRNA levels did not differ. These findings suggest that the final stages of osteoblast maturation and function are suppressed. We also propose a second mechanism contributing to diabetic bone loss: increased marrow adiposity. This is supported by increased expression of adipocyte markers [peroxisome proliferator-activated receptor gamma2, resistin, and adipocyte fatty acid binding protein (alphaP2)] and the appearance of lipid-dense adipocytes in diabetic tibias. In contrast to bone marrow, adipose stores at other sites are depleted in diabetic mice, as indicated by decreased body, liver, and peripheral adipose tissue weights. These findings suggest that IDDM contributes to bone loss through changes in marrow composition resulting in decreased mature osteoblasts and increased adipose accumulation.

The Reactive d-Glucopyranose Moiety of Streptozotocin Is Responsible for Activation of Macrophages and Subsequent Stimulation of CD8+ T Cells

The antitumor drug streptozotocin (STZ) is commonly used as a diabetogenic compound in animal models. At relatively low doses, STZ-induced beta cell destruction is associated with Th1-driven type 1 immune reactions, including macrophages (MPhi) and IFN-gamma-producing CD8(+) T cells. STZ induces similar Th1-dependent effects in the popliteal lymph node assay (PLNA), and because this assay allows straightforward examination of early immunostimulating processes, the PLNA was used to further examine the importance of MPhi and structural properties of STZ in relation to the induction of type 1 immune responses. Results show that elimination of MPhi with clodronate-containing liposomes prior to exposure to STZ prevents the occurrence of some (CD8(+) T cell activation, IFN-gamma production, and tissue destruction) but not all (IgG2a formation) type 1 immune responses. It appeared that stimulation of MPhi depends on the d-glucopyranose moiety of STZ, as well as on the intact reactive N-methyl-N-nitrosourea (MNU) moiety. However, the MNU moiety suffices to induce IgG2a formation. In addition, STZ-derived nitric oxide may have modulating effects on the elicitation of STZ-induced immune responses. Present results support the idea that MPhi activation is indispensable for the STZ-induced tissue destructive type 1 responses and that various STZ-induced type 1 immune responses are differently regulated.

Immunosuppressive and anti-inflammatory action of antioxidants in rat autoimmune diabetes

Oxidative stress makes an important contribution to the development of autoimmune diabetes. We therefore tested the possible therapeutic value of two anti-oxidants, butylated hydroxyanisole (BHA) and pyrrolidine dithiocarbamate (PDTC), in the animal model of diabetes induced in susceptible DA rats by multiple low doses of streptozotocin (MLD-SZ, 20 mg/kg/day for 5 days). Administration of either BHA, or PDTC (50 mg/kg/day for 7 days), after finishing MLD-SZ injections, attenuated both the development of hyperglycemia and insulitis. Ex vivo analysis revealed that BHA treatment reduced the proliferation of autoreactive lymphocytes and down-regulated their adhesion to endothelium. In addition, BHA markedly attenuated the production of proinflammatory cytokines IL-1beta and TNF-alpha by both islets of pancreas and peritoneal macrophages. In parallel, macrophage release of cytotoxic oxygen and nitrogen intermediates superoxide anion (O(2)*(-)) and nitric oxide (NO*), respectively, was significantly inhibited. Finally, BHA treatment reduced intrapancreatic expression of inducible NO synthase (iNOS) and consequent production of NO* by pancreatic islets. Together, these data indicate that antioxidant agents might be a feasible therapeutic tools to interfere with development of autoimmune diabetes at multiple levels, including lymphocyte proliferation and adhesion, as well as the production of proinflammatory and cytotoxic mediators.

Lack of the mediators of innate immunity attenuate the development of autoimmune diabetes in mice

Interleukin 15 (IL-15) and Interleukin 18 (IL-18) are key cytokines produced by macrophages during innate immune response. These cytokines can profoundly affect subsequent adaptive immune responses including autoimmunity. We have investigated the role of IL-15 and IL-18 in the development of autoimmune diabetes in mice induced by multiple low dose streptozotocin (MLD-STZ). To analyze the role of IL-15, we tested the effects of a soluble murine IL-15 receptor alpha-chain (smIL-15Ralpha), on the development of MLD-STZ in C57BL/6 mice. Animals were treated with 10 daily injections of 32 microg of smIL-15Ralpha starting on the first day of diabetes induction. This treatment significantly attenuated the development of diabetes as evaluated by significantly lower glycemia compared with control mice treated with an inactive mutant form of sIL-15Ra. To directly address the role of IL-18 in MLD-STZ we used IL-18 knockout (KO) mice on DBA/1 background. IL-18 deficient mice were significantly more resistant to the induction of diabetes compared with the wild-type controls and did not develop the typical mononuclear cell infiltrates in the islets. Taken together our data suggest that the innate mediators, IL-15 and IL-18, are essential for the development of diabetes and may be important targets in prevention and early treatment of autoimmune diabetes.

Defective thymocyte apoptosis and accelerated autoimmune diseases in TRAIL-/- mice

TRAIL, the tumor necrosis factor-related apoptosis-inducing ligand, selectively induces apoptosis of tumor cells, but not most normal cells. Its role in normal, nontransformed tissues is not clear. We report here that mice deficient in TRAIL have a severe defect in thymocyte apoptosis-thus, thymic deletion induced by T cell receptor ligation is severely impaired. TRAIL-deficient mice are also hypersensitive to collagen-induced arthritis and streptozotocin-induced diabetes and develop heightened autoimmune responses. Thus, TRAIL mediates thymocyte apoptosis and is important in the induction of autoimmune diseases.

Induction of autoimmune diabetes through insulin (but not GAD65) DNA vaccination in nonobese diabetic and in RIP-B7.1 mice

Insulin has been used to modify T-cell autoimmunity in experimental models of type 1 diabetes. In a large clinical trial, the effect of insulin to prevent type 1 diabetes is currently investigated. We here show that insulin can adversely trigger autoimmune diabetes in two mouse models of type 1 diabetes, using intramuscular DNA vaccination for antigen administration. In female nonobese diabetic (NOD) mice, diabetes development was enhanced after preproinsulin (ppIns) DNA treatment, and natural diabetes resistance in male NOD mice was diminished by ppIns DNA vaccination. In contrast, GAD65 DNA conferred partial diabetes protection, and empty DNA plasmid was without effect. In RIP-B7.1 C57BL/6 mice (expressing the T-cell costimulatory molecule B7.1 in pancreatic beta-cells), autoimmune diabetes occurred in 70% of animals after ppIns vaccination, whereas diabetes did not develop spontaneously in RIP-B7.1 mice or after GAD65 or control DNA treatment. Diabetes was characterized by diffuse CD4(+)CD8(+) T-cell infiltration of pancreatic islets and severe insulin deficiency, and ppIns, proinsulin, and insulin DNA were equally effective for disease induction. Our work provides a new model of experimental autoimmune diabetes suitable to study mechanisms and outcomes of insulin-specific T-cell reactivity. In antigen-based prevention of type 1 diabetes, diabetes acceleration should be considered as a potential adverse result.

Downregulation of apoptosis in the target tissue prevents low-dose streptozotocin-induced autoimmune diabetes

3,7-dimethyl-1-(5-oxohexyl) xanthine, pentoxifylline (PTX) is shown to affect cytokine-induced apoptosis in several experimental models and clinical conditions. It had been also shown to prevent insulitis and hyperglycemia in non-obese diabetic (NOD) mice, and mice and rats susceptible to diabetes induction with multiple low-doses of streptozotocin (MLD-STZ). We therefore analysed the development of diabetes and apoptosis of pancreatic beta islet cells in CBA/mice after diabetes induction with MLD-STZ. We have evaluated the effect of PTX on the level of apoptosis in the islet at different time intervals after diabetes induction. Complementary histological and immunohistochemical studies and analyses of the expression of cytokines and nitric oxide have also been done. It was concluded that PTX significantly attenuated apoptosis of the beta-cells in the islet and suppressed the induction of diabetes. Our data are compatible with the notion that interferon-gamma (IFN-gamma)/tumor necrosis factor (TNF)/nitric oxide (NO)-induced apoptosis of beta-cells in experimental diabetes is attenuated by PTX.

In situ beta cell death promotes priming of diabetogenic CD8 T lymphocytes

CTLs are important mediators of pancreatic beta cell destruction in the nonobese diabetic mouse model of type 1 diabetes. Cross-presentation of Ag is one means of priming CTLs. The death of Ag-bearing cells has been implicated in facilitating this mode of priming. The role of beta cell death in facilitating the onset of spontaneous autoimmune diabetes is unknown. Here, we used an adoptive transfer system to determine the time course of islet-derived Ag presentation to naive beta cell-specific CD8 T cells in nonobese diabetic mice and to test the hypothesis that beta cell death enhances the presentation of beta cell autoantigen. We have determined that beta cell death enhances autoantigen presentation. Priming of diabetogenic CD8 T cells in the pancreatic lymph nodes was negligible before 4 wk, progressively increased until 8 wk of age, and was not influenced by gender. Administration of multiple low doses of the beta cell toxin streptozotocin augmented in situ beta cell apoptosis and accelerated the onset and magnitude of autoantigen presentation to naive CD8 T cells. Increasing doses of streptozotocin resulted in both increased pancreatic beta cell death and significantly enhanced T cell priming. These results indicate that in situ beta cell death facilitates autoantigen-specific CD8 T cell priming and can contribute to both the initiation and the ongoing amplification of an autoimmune response.