Type 1 diabetes: Islet inflammation – the contribution of cytokines and beta cells

Layer-by-Layer Cerium Oxide Nanoparticle Coating for Antioxidant Protection of Encapsulated Beta Cells

In type 1 diabetes, the replacement of the destroyed beta cells could restore physiological glucose regulation and eliminate the need for exogenous insulin. Immunoisolation of these foreign cellular transplants via biomaterial encapsulation is widely used to prevent graft rejection. While highly effective in blocking direct cell-to-cell contact, nonspecific inflammatory reactions to the implant lead to the overproduction of reactive oxygen species, which contribute to foreign body reaction and encapsulated cell loss. For antioxidant protection, cerium oxide nanoparticles (CONPs) are a self-renewable, ubiquitous, free radical scavenger currently explored in several biomedical applications. Herein, 2-12 alternating layers of CONP/alginate are assembled onto alginate microbeads containing beta cells using a layer-by-layer (LbL) technique. The resulting nanocomposite coatings demonstrate robust antioxidant activity. The degree of cytoprotection correlates with layer number, indicating tunable antioxidant protection. Coating of alginate beads with 12 layers of CONP/alginate provides complete protection to the entrapped beta cells from exposure to 100 × 10-6 m H2 O2 , with no significant changes in cellular metabolic activity, oxidant capacity, or insulin secretion dynamics, when compared to untreated controls. The flexibility of this LbL method, as well as its nanoscale profile, provides a versatile approach for imparting antioxidant protection to numerous biomedical implants, including beta cell transplantation.

1,25-dihydroxyvitamin D3 down-modulates the production of proinflammatory cytokines and nitric oxide and enhances the phosphorylation of monocyte-expressed STAT6 at the recent-onset type 1 diabetes

BACKGROUND

Type 1 diabetes (T1D) is associated with an imbalance between inflammation and repair. Recently, the biologically active form of vitamin D₃, i.e. 1,25(OH)₂D₃, has been reported to have potent immunomodulatory effects on both innate and adaptive immune cells, as well as on the production of their specific cytokines.

METHODS

We examined the effect of 1,25(OH)₂D₃ on the production of proinflammatory Th1/Th17 and anti-inflammatory Th2/Treg related cytokines, as well as on the phosphorylation of monocyte-expressed STAT4 and STAT6 at the recent-onset human T1D.

RESULTS

The levels of IFN-γ, IL-17 and nitric oxide (NO) production were significantly increased in peripheral blood mononuclear cells (PBMCs) from patients with T1D compared to controls. Similarly, STAT4 tyrosine phosphorylation (p-STAT4, Tyr693) levels were significantly increased in monocytes from patients when compared to controls. Conversely, the levels of IL-4, IL-10 and p-STAT6 (Tyr641) were significantly decreased in type 1 diabetic patients than in controls. Treatment with 1,25(OH)₂D₃ resulted in significant up-regulation of IL-4, IL-10, arginase activity, and p-STAT6 and, conversely, down-regulation of IFN-γ, IL-17 and NO production levels, as well as p-STAT4. Additionally, 1,25(OH)₂D₃ significantly enhanced Treg-to-Th17 ratio, and induced a significant decrease in Th1-to-Th2, NO production-to-arginase activity and p-STAT4-to-p-STAT6 ratios.

CONCLUSIONS

Our study suggests that the biologically active form of vitamin D can reverse the activation of inflammatory pathways at the onset of T1D. Additionally, its immunomodulation properties may vary depending on the overall patterns of cytokines. From a therapeutic point of view, vitamin D may potentially be suggested as an immunological adjuvant and a potential anti-inflammatory agent in individuals at risk of T1D.

Oral Magnesium Treatment Reduces Anemia and Levels of Inflammatory Markers in Experimental Diabetes

Magnesium has been reported to improve glucose utilization in diabetes mellitus. However, information on its effects on anemic and inflammatory markers in diabetes mellitus is limited. This study investigated the effect of oral magnesium (Mg) treatment on some markers of anemia and inflammation in 25 male Wistar rats. Rats (200 ± 15 g) were randomly divided into five groups (n = 5). Group 1 was control (received orally 0.2 mL distilled water daily), group 2 (Diabetic Untreated), group 3 (Diabetic Mg treated-100 mg/kg bw), group 4 (Diabetic Mg treated-250 mg/kg bw), group 5 (Diabetic Insulin treated-1 IU/kg bw). Diabetes was induced with a single dose of alloxan (100 mg/kg intraperitoneal (i.p.)). All treatments were done for 14 days. Anemic and inflammatory markers were investigated on blood samples obtained from each animal using standard laboratory methods. Significant increase (p < 0.05) in total white blood cell (WBC) count was observed in diabetic untreated rats (7.67 ± 0.397 × 10⁹/L) compared to control (5.88 ± 0.25 × 10⁹/L), DMg 100 (5.86 ± 0.74 × 10⁹/L) and DMg 250 (5.06 ± 0.78 × 10⁹/L). Hemoglobin concentration, packed cell volume (PCV) and red blood cell (RBC) count was decreased (p < 0.05) in DU compared to control, DMg 100, and DI rats. Erythrocyte sedimentation rate (ESR) was significantly increased (p < 0.05) in DU compared to control, DMg 100, DMg 250, and DI groups. Fibrinogen level was increased (p < 0.05) in DU rats (0.44 ± 0.02 g/dL) compared to control(0.26 ± 0.02 g/dL). Values obtained in DMg 100 (0.30 ± 0.03 g/dL), DMg 250 (0.22 ± 0.04 g/dL), and DI (0.36 ± 0.02 g/dL) rats were comparable to control (0.26 ± 0.02 g/dL). Total protein, albumin, and globulin levels were decreased in DU rats compared to normal control, DMg 100, DMg 250, and DI rats. In conclusion, anemia and increased hematologic and metabolic inflammatory markers may be associated with untreated diabetes mellitus. Treatment of alloxan-induced diabetic rats with magnesium improved the anemic state and reduced hematologic and metabolic inflammatory markers.

Do β-cells generate peroxynitrite in response to cytokine treatment?

The purpose of this study was to determine the reactive species that is responsible for cytokine-mediated β-cell death. Inhibitors of inducible nitric oxide synthase prevent this death, and addition of exogenous nitric oxide using donors induces β-cell death. The reaction of nitric oxide with superoxide results in the generation of peroxynitrite, and this powerful oxidant has been suggested to be the mediator of β-cell death in response to cytokine treatment. Recently, coumarin-7-boronate has been developed as a probe for the selective detection of peroxynitrite. Using this reagent, we show that addition of the NADPH oxidase activator phorbol 12-myristate 13-acetate to nitric oxide-producing macrophages results in peroxynitrite generation. Using a similar approach, we demonstrate that cytokines fail to stimulate peroxynitrite generation by rat islets and insulinoma cells, either with or without phorbol 12-myristate 13-acetate treatment. When forced to produce superoxide using redox cyclers, this generation is associated with protection from nitric oxide toxicity. These findings indicate that: (i) nitric oxide is the likely mediator of the toxic effects of cytokines, (ii) β-cells do not produce peroxynitrite in response to cytokines, and (iii) when forced to produce superoxide, the scavenging of nitric oxide by superoxide is associated with protection of β-cells from nitric oxide-mediated toxicity.

Immune-mediated β-cell death in type 1 diabetes: lessons from human β-cell lines

Type 1 diabetes (T1D) is a chronic, multifactorial disorder that results from a contretemps of genetic and environmental factors. Autoimmune attack and functional inhibition of the insulin-producing β cells in the pancreas lead to the inability of β cells to metabolize glucose, and thus results the hallmark clinical symptom of diabetes: abnormally high blood glucose levels. Treatment and protection from T1D require a detailed knowledge of the molecular effectors and the mechanism(s) of cell death leading to β-cell demise. Primary islets and surrogate β cells have been utilized in vitro to investigate in isolation-specific mechanisms associated with progression to T1D in vivo. This review focuses on the data obtained from these experiments. Studies using transformed β cells of human sources are described.

Dysregulated TLR3-dependent signaling and innate immune activation in superoxide-deficient macrophages from nonobese diabetic mice

In type 1 diabetes (T1D), reactive oxygen species (ROS) and proinflammatory cytokines produced by macrophages and other innate immune cells destroy pancreatic β cells while promoting autoreactive T cell maturation. Superoxide-deficient nonobese diabetic mice (NOD.Ncf1(m1J)) are resistant to spontaneous diabetes, revealing the integral role of ROS signaling in T1D. Here, we evaluate the innate immune activation state of bone marrow-derived macrophages (BM-Mϕ) from NOD and NOD.Ncf1(m1J) mice after poly(I:C)-induced Toll-like receptor 3 (TLR3) signaling. We show that ROS synthesis is required for efficient activation of the NF-κB signaling pathway and concomitant expression of TLR3 and the cognate adaptor molecule, TRIF. Poly(I:C)-stimulated NOD.Ncf1(m1J) BM-Mϕ exhibited a 2- and 10-fold decrease in TNF-α and IFN-β proinflammatory cytokine synthesis, respectively, in contrast to NOD BM-Mϕ. Optimal expression of IFN-α/β is not solely dependent on superoxide synthesis, but requires p47(phox) to function in a NOX-independent manner to mediate type I interferon synthesis. Interestingly, MHC-II I-A(g7) expression necessary for CD4 T cell activation is increased 2-fold relative to NOD, implicating a role for superoxide in I-A(g7) downregulation. These findings suggest that defective innate immune-pattern-recognition receptor activation and subsequent decrease in TNF-α and IFN-β proinflammatory cytokine synthesis necessary for autoreactive T cell maturation may contribute to the T1D protection observed in NOD.Ncf1(m1J) mice.

NADPH oxidase deficiency regulates Th lineage commitment and modulates autoimmunity

Reactive oxygen species are used by the immune system to eliminate infections; however, they may also serve as signaling intermediates to coordinate the efforts of the innate and adaptive immune systems. In this study, we show that by eliminating macrophage and T cell superoxide production through the NADPH oxidase (NOX), T cell polarization was altered. After stimulation with immobilized anti-CD3 and anti-CD28 or priming recall, T cells from NOX-deficient mice exhibited a skewed Th17 phenotype, whereas NOX-intact cells produced cytokines indicative of a Th1 response. These findings were corroborated in vivo by studying two different autoimmune diseases mediated by Th17 or Th1 pathogenic T cell responses. NOX-deficient NOD mice were Th17 prone with a concomitant susceptibility to experimental allergic encephalomyelitis and significant protection against type 1 diabetes. These data validate the role of superoxide in shaping Th responses and as a signaling intermediate to modulate Th17 and Th1 T cell responses.