Mechanisms underlying type 1 diabetes

Immunoprotection of cellular transplants for autoimmune type 1 diabetes through local drug delivery

Type 1 diabetes mellitus (T1DM) is an autoimmune condition that results in the destruction of insulin-secreting β cells of the islets of Langerhans. Allogeneic islet transplantation could be a successful treatment for T1DM; however, it is limited by the need for effective, permanent immunosuppression to prevent graft rejection. Upon transplantation, islets are rejected through non-specific, alloantigen specific, and recurring autoimmune pathways. Immunosuppressive agents used for islet transplantation are generally successful in inhibiting alloantigen rejection, but they are suboptimal in hindering non-specific and autoimmune pathways. In this review, we summarize the challenges with cellular immunological rejection and therapeutics used for islet transplantation. We highlight agents that target these three immune rejection pathways and how to package them for controlled, local delivery via biomaterials. Exploring macro-, micro-, and nano-scale immunomodulatory biomaterial platforms, we summarize their advantages, challenges, and future directions. We hypothesize that understanding their key features will help identify effective platforms to prevent islet graft rejection. Outcomes can further be translated to other cellular therapies beyond T1DM.

Insights in diabetes: Molecular mechanisms-Protectin DX, an anti-inflammatory and a stimulator of inflammation resolution metabolite of docosahexaenoic acid, protects against the development of streptozotocin-induced type 1 and type 2 diabetes mellitus in male Swiss albino mice

Our previous studies revealed that certain endogenous low molecular weight lipids have potent anti-diabetic actions. Of all, arachidonic acid (AA) and its anti-inflammatory and inflammation resolving metabolite lipoxin A4 (LXA4) are the most potent anti-diabetic molecules. Similar anti-diabetic action is also shown by resolvins. In our efforts to identify other similar lipid based anti-diabetic molecules, we investigated potential anti-diabetic action of protectin DX that also has anti-inflammatory and inducer of inflammation resolution action(s) like LXA4. Protectin DX {10(S),17(S)-dihydroxy-4Z,7Z,11E,13Z,15E,19Z-docosahexaenoic acid, also called as 10(S),17(S)-DiHDoHE)} prevented the development of streptozotocin-induced type 1 and type 2 diabetes mellitus in Swiss male albino mice. Protectin DX showed potent anti-inflammatory, antioxidant and anti-apoptotic actions that could explain its anti-diabetic action. In view of these beneficial actions, efforts need to be developed to exploit PDX and other similar compounds as potential anti-diabetic molecule in humans.

Immunomodulatory effects of mesenchymal stem cell-derived exosomes on experimental type-1 autoimmune diabetes

Exosomes derived from adipose tissue-derived mesenchymal stem cells (AD-MSCs) have immunomodulatory effects of T-cell inflammatory response and reduction of clinical symptoms on streptozotocin-induced of the type-1 diabetes mellitus (T1DM). Beside control group and untreated T1DM mice, a group of T1DM mice was treated with intraperitoneal injections of characterized exosomes derived from autologous AD-MSCs. Body weight and blood glucose levels were measured during the procedure. Histopathology and immunohistochemistry were used for evaluation of pancreatic islets using hemotoxylin and eosin (H&E) staining and anti-insulin antibody. Isolated splenic mononuclear cells (MNCs) were subjected to splenocytes proliferation assay using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, immunophenotyping of regulatory T cells and cytokines. A significant increase in the levels of interleukin-4 (IL-4), IL-10, and transforming growth factor-β, and a decrease in the levels of IL-17 and interferon-γ in concordance with the significant increase in the Treg cell ratio in splenic MNCs (P < 0.05) was shown in T1DM mice treated with AD-MSC's exosomes as compared to T1DM untreated mice. This amelioration of autoimmune reaction after treatment of T1DM mice with the AD-MSC exosomes was confirmed with a significant increase in islets using H&E staining and Immunohistochemistry analyses. As expected, body weight, blood glucose levels in a survival of T1DM mice treated with AD-MSC's exosomes were maintained stable in comparison to untreated T1DM mice. It can be concluded that AD-MSC's exosomes exert ameliorative effects on autoimmune T1DM through increasing regulatory T-cell population and their products without a change in the proliferation index of lymphocytes, which makes them more effective and practical candidates.

Nonviral delivery of small interfering RNA into pancreas-associated immune cells prevents autoimmune diabetes

The development of small interfering RNA (siRNA) for the treatment of human disorders has been often hampered by their low transfection efficiency in vivo. In order to overcome this major drawback, various in vivo siRNA transfection methods have been developed. However, their capacity to transfect immune or insulin-producing β-cells within the pancreas for the treatment of autoimmune diabetes remains undetermined. We found that lipid- or polyethylenimine-based delivery agents were efficient to address siRNA molecules within pancreas-associated antigen-presenting cells (APCs) (but not β-cells) and particularly a CD11b(+) cell population comprising both CD11b(+)CD11c(neg) macrophages and CD11b(+)CD11c(+) dendritic cells. However, the route of administration and the carrier composition greatly affected the transfection efficacy. Therapeutically, we showed that early (starting at 6-week-old) short-course treatment with lipid/Alox15-specific siRNA complex promoted long-term protection from type 1 diabetes (T1D) in wild-type (WT) nonobese diabetic (NOD) mice. Alox15 downregulation in pancreas-associated CD11b(+) cells significantly upregulated a variety of costimulatory molecules and particularly the programmed death 1 ligand 1 (PD-L1) pathway involved in tolerance induction. Concomitantly, we found that regulatory T cells were increased in the pancreas of lipid/Alox15 siRNA-treated NOD mice. Collectively, our data provide new insights into the development of siRNA-based therapeutics for T1D.

Preimplantation factor (PIF) analog prevents type I diabetes mellitus (TIDM) development by preserving pancreatic function in NOD mice

Preimplantation factor (PIF) is a novel embryo-secreted immunomodulatory peptide. Its synthetic analog (sPIF) modulates maternal immunity without suppression. There is an urgent need to develop agents that could prevent the development of type 1 diabetes mellitus (TIDM). Herein, we examine sPIF's preventive effect on TIDM development by using acute adoptive-transfer (ATDM) and spontaneously developing (SDM) in non-obese diabetic (NOD) murine models. Diabetes was evaluated by urinary and plasma glucose, intraperitoneal glucose tolerance test (IPGTT), pancreatic islets insulin staining by immunohistochemistry and by pancreatic proteome evaluation using mass spectrometry, followed by signal pathway analysis. Continuous administration of sPIF for 4-weeks prevents diabetes development in ATDM model in >90% of recipients demonstrated by normal IPGTT, preserved islets architecture, number, and insulin staining. (P < 0.01). sPIF effect was specific; its protective effects are not replicated by scrambled PIF (χ(2) = 0.009) control. sPIF led also to increased circulating Th2 and Th1 cytokines. In SDM model, 4-week continuous sPIF administration prevented onset of diabetes for 21 weeks post-therapy (P < 0.01). Low-dose sPIF administration for 16 weeks prevented diabetes development up to 14 weeks post-therapy, evidenced by preserved islets architecture and insulin staining. In SDM model, pancreatic proteome pathway analysis demonstrated that sPIF regulates protein traffic, prevents protein misfolding and aggregation, and reduces oxidative stress and islets apoptosis, leading to preserved insulin staining. sPIF further increased insulin receptor expression and reduced actin and tubulin proteins, thereby blocking neutrophil invasion and inflammation. Exocrine pancreatic function was also preserved. sPIF administration results in marked prevention of spontaneous and induced adoptive-transfer diabetes suggesting its potential effectiveness in treating early-stage TIDM.

Genetic-induced variations in the GAD65 T-cell repertoire governs efficacy of anti-CD3/GAD65 combination therapy in new-onset type 1 diabetes

To enhance efficacy of forthcoming type 1 diabetes (T1D) clinical trials, combination therapies (CTs) are envisaged. In this study, we showed that efficacy of a CT, using anti-CD3 antibody and glutamic acid decarboxylase of 65 kd (GAD65)-expressing plasmid, to reverse new-onset T1D was dependent upon the genetic background. Synergism between both treatments was only observed in the RIP-LCMV-GP but not in the nonobese diabetic (NOD) or RIP-LCMV-NOD models. Efficacy was associated with an expansion of bystander suppressor regulatory T cells (Tregs) recognizing the C-terminal region of GAD65 and secreting interleukin-10 (IL-10), transforming growth factor-beta (TGF-beta), and interferon-gamma (IFN-gamma). In addition, we found that frequency and epitope specificity of GAD65-reactive CD4(+) T cells during antigen priming at diabetes onset and Tregs detected after CT correlated. Consequently, NOD mice harbored significantly lower levels of GAD65-reactive CD4(+) T cells than RIP-LCMV-GP before and after treatment. Our results demonstrate that antigen-specific T cells available at treatment may differ between various major histocompatibility complex (MHC) and genetic backgrounds. These cells play a major role in shaping T-cell responses following antigen-specific immune intervention and determine whether a beneficial Tregs response is generated. Our findings hold important implications to understand and predict the success of antigen-based clinical trials, where responsiveness to immunotherapy might vary from patient to patient.

Intracytoplasmic cytokine levels and neutrophil functions in early clinical stage of type 1 diabetes

Studies indicate that both CD4(+) and CD8(+) T lymphocytes and their cytokines play a critical role in different clinical stages of type 1 diabetes (T1D). Disturbances of oxidative burst and phagocytic activities in neutrophils of diabetic patients compared to uncontrolled disease support the importance of neutrophil functions in the treatment and follow up of diabetic patients. This study is designed in order to investigate Th1 and Th2 cytokine profiles and neutrophil functions in early clinical stage of T1D. Patients diagnosed as T1D but not yet under insulin therapy (Group 1; n=15) and T1D patients with disease duration of <3 months (Group 2; n=20) were compared to healthy subjects (Group 3; n=15). All subjects with T1D were positive for islet cell antibody (ICA) and glutamic acid decarboxylase antibody (GADA), their fasting glucose levels were >126 mg/dl and A1(c) levels were >8. Intracytoplasmic interleukin (IL)-2, IL-10, interferon (IFN)-gamma and tumour necrosis factor (TNF)-alpha levels of isolated CD4(+) and CD8(+) T cells, and neutrophil functions were determined by flow cytometry. Intracellular TNF-alpha level of CD4(+) T lymphocytes was significantly decreased in Group 1 compared to Group 2 and healthy subjects. In contrast, TNF-alpha in CD8(+) T lymphocytes was higher in Group 1 compared to Group 2. Increased TNF-alpha content of CD8(+) T lymphocytes was also obtained in Groups 1 and 2 compared to healthy subjects. Increased TNF-alpha secretion of CD8(+) T cells might reflect the role of CD8(+) T cells in beta cell destruction. Similar to cytokine content, phagocytic and oxidative burst activities in Group 1 were significantly lower compared to Group 2 and healthy subjects. Impaired neutrophil functions could be recovered by the treatment of the disease.