Type 1 Diabetes Prevention in NOD Mice by Targeting DPPIV/CD26 Is Associated with Changes in CD8⁺T Effector Memory Subset

Crosstalk between incretin hormones, Th17 and Treg cells in inflammatory diseases

Intestinal epithelial cells constantly crosstalk with the gut microbiota and immune cells of the gut lamina propria. Enteroendocrine cells, secrete hormones, such as incretin hormones, which participate in host physiological events, such as stimulating insulin secretion, satiety, and glucose homeostasis. Interestingly, evidence suggests that the incretin pathway may influence immune cell activation. Consequently, drugs targeting the incretin hormone signaling pathway may ameliorate inflammatory diseases such as inflammatory bowel diseases, cancer, and autoimmune diseases. In this review, we discuss how these hormones may modulate two subsets of CD4 + T cells, the regulatory T cells (Treg)/Th17 axis important for gut homeostasis: thus, preventing the development and progression of inflammatory diseases. We also summarize the main experimental and clinical findings using drugs targeting the glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide (GLP-1) signaling pathways and their great impact on conditions in which the Treg/Th17 axis is disturbed such as inflammatory diseases and cancer. Understanding the role of incretin stimulation in immune cell activation and function, might contribute to new therapeutic designs for the treatment of inflammatory diseases, autoimmunity, and tumors.

Combination of vitamin D and dipeptidyl peptidase-4 inhibitors (VIDPP-4i) as an immunomodulation therapy for autoimmune diabetes

Type 1 diabetes (T1D) and latent autoimmune diabetes in adults (LADA) represent the most common types of autoimmune diabetes and are characterized by different age of onset, degrees of immune-mediated destruction of pancreatic beta cells and rates of disease progression towards insulin dependence. Several immunotherapies aimed to counteract autoimmune responses against beta cells and preserve beta-cell function are currently being investigated, particularly in T1D. Preliminary findings suggest a potential role of combination therapy with vitamin D and dipeptidyl peptidase-4 (DPP-4) inhibitors (VIDPP-4i) in preserving beta-cell function in autoimmune diabetes. This manuscript aims to provide a comprehensive overview of the immunomodulatory properties of vitamin D and DPP-4 inhibitors, as well as the rationale for investigation of their combined use as an immunomodulation therapy for autoimmune diabetes.

DPP-4 Inhibition Leads to Decreased Pancreatic Inflammatory Profile and Increased Frequency of Regulatory T Cells in Experimental Type 1 Diabetes

Sitagliptin is a dipeptidyl peptidase-4 inhibitor (iDPP-4), which has been used for type 2 diabetes treatment. Recently, iDPP-4 has been described as a promising treatment of type 1 diabetes (T1D) but is still necessary to evaluate immune effects of sitagliptin. C57BL/6 mice were induced by multiple low doses of streptozotocin. Diabetes incidence, insulin, glucagon, glucagon-like peptide-1 (GLP-1) serum levels, and inflammatory cytokine levels were quantified in pancreas homogenate after 30 and 90 days of treatment. In addition, frequencies of inflammatory and regulatory T cell subsets were determined in the spleen and in the pancreatic lymph nodes. iDPP-4 decreased blood glucose level while increased GLP-1 and insulin levels. After long-term treatment, treated diabetic mice presented decreased frequency of CD4⁺CD26⁺ T cells and increased percentage of CD4⁺CD25^hiFoxp3⁺ T cells in the spleen. Besides, pancreatic lymph nodes from diabetic mice treated with iDPP-4 presented lower percentage of CD11b⁺ cells and decreased levels of inflammatory cytokines in the pancreas. Treatment of type 1 diabetic mice with iDPP-4 improved metabolic control, decreased inflammatory profile in the pancreatic microenvironment, and increased systemic regulatory T cell frequency. Therefore, we suggest the long-term use of sitagliptin as a feasible and effective therapy for T1D.

CD26 in autoimmune diseases: The other side of "moonlight protein"

Dipeptidyl peptidase 4 (DPP-4) is a serine protease, which has enzymatic activity to selectively clean the N-terminal dipeptide of peptides and proteins with proline or alanine in the second position. DPP-4 inhibitor has been widely used for the treatment of type 2 diabetes by increasing the level of the glucagon-like peptide-1 and decreasing the glucose level. DPP-4, also known as lymphocyte cell surface protein CD26, plays a core role of T cell immunity. Many roles of CD26 in other immune cells have been found. As a "moonlight protein", the effect of CD26 in autoimmune diseases has attracted more and more attention. The paper reviewed the function and potential effect of CD26 in autoimmune diseases, which shows CD26 may be a new target of autoimmune diseases deserved further study.

Dipeptidyl peptidase-4(DPP-4) inhibitors: promising new agents for autoimmune diabetes

Dipeptidyl peptidase-4 (DPP-4) inhibitors constitute a novel class of anti-diabetic agents confirmed to improve glycemic control and preserve β-cell function in type 2 diabetes. Three major large-scale studies, EXAMINE, SAVOR-TIMI 53, and TECOS, have confirmed the cardiovascular safety profile of DPP-4 inhibitors. Based on these results, DPP-4 inhibitors have gained widespread use in type 2 diabetes treatment. It is currently unknown, however, whether DPP-4 inhibitors have similar therapeutic efficacy against autoimmune diabetes. Several in vitro and in vivo studies have addressed this issue, but the results remain controversial. In this review, we summarize experimental findings and preliminary clinical trial results, and identify potentially effective immune modulation targets of DPP-4 inhibitors for autoimmune diabetes.

Possible Long-Term Efficacy of Sitagliptin, a Dipeptidyl Peptidase-4 Inhibitor, for Slowly Progressive Type 1 Diabetes (SPIDDM) in the Stage of Non-Insulin-Dependency: An Open-Label Randomized Controlled Pilot Trial (SPAN-S)

INTRODUCTION

We tested the hypothesis that dipeptidyl peptidase-4 (DPP-4) inhibitors are effective in preserving the β-cell function for long-term periods in patients with slowly progressive type 1 diabetes (SPIDDM) or latent autoimmune diabetes in adults (LADA).

METHODS

In the present open-label, randomized, controlled trial, 14 non-insulin-requiring diabetic patients with glutamic acid decarboxylase autoantibodies (GADAb) were randomly assigned to receive either sitagliptin (S group) or pioglitazone (P group). As a historical control, the Tokyo Study, in which non-insulin-dependent patients with SPIDDM were assigned to receive treatment by either insulin or sulfonylurea (SU), was used.

RESULTS

On average, the ∑C-peptide values during the oral glucose tolerance test through the follow-up periods showed a nonsignificant increase in the S group (n = 6, n = 5 at 48 months) compared to the P group (n = 5, n = 2 at 48 months). In comparison to the data in the Tokyo Study, treatment by sitagliptin significantly influenced the longitudinal changes in the ∑C-peptide values with a more increased direction than insulin or SU, especially in patients with 48 months of follow-up (p = 0.014 and p = 0.007, respectively). Although the titers of GADAb were not significantly different between the S and P groups during the study, the change ratio of the GADAb titers from baseline was significantly inversely correlated with the change ratio of the ∑C-peptide values from baseline in the S group (p = 0.003); in particular, when the GADAb titers decreased from baseline, the ∑C-peptide values frequently increased.

CONCLUSION

The present pilot trial suggests that treatment of SPIDDM/LADA by sitagliptin, a DPP-4 inhibitor, may be more effective in preserving the β-cell function than insulin treatment for at least 4 years, possibly through the immune modulatory effects of DPP-4 inhibitors.

CLINICAL TRIAL REGISTRATION

Japanese Clinical Trials Registry UMIN000003693.

CD26/DPPIV inhibition alters the expression of immune response-related genes in the thymi of NOD mice

The transmembrane glycoprotein CD26 or dipeptidyl peptidase IV (DPPIV) is a multifunctional protein. In immune system, CD26 plays a role in T-cell function and is also involved in thymic maturation and emigration patterns. In preclinical studies, treatment with DPPIV inhibitors reduces insulitis and delays or even reverses the new -onset of type 1 diabetes (T1D) in non-obese diabetic (NOD) mice. However, the specific mechanisms involved in these effects remain unknown. The aim of the present study was to investigate how DPPIV inhibition modifies the expression of genes in the thymus of NOD mice by microarray analysis. Changes in the gene expression of β-cell autoantigens and Aire in thymic epithelial cells (TECs) were also evaluated by using qRT-PCR. A DPPIV inhibitor, MK626, was orally administered in the diet for 4 and 6 weeks starting at 6-8 weeks of age. Thymic glands from treated and control mice were obtained for each study checkpoint. Thymus transcriptome analysis revealed that 58 genes were significantly over-expressed in MK626-treated mice after 6 weeks of treatment. Changes in gene expression in the thymus were confined mainly to the immune system, including innate immunity, chemotaxis, antigen presentation and immunoregulation. Most of the genes are implicated in central tolerance mechanisms through several pathways. No differences were observed in the expression of Aire and β-cell autoantigens in TECs. In the current study, we demonstrate that treatment with the DPPIV inhibitor MK626 in NOD mice alters the expression of the immune response-related genes in the thymus, especially those related to immunological central tolerance, and may contribute to the prevention of T1D.