Higher Serum DPP-4 Enzyme Activity and Decreased Lymphocyte CD26 Expression in Type 1 Diabetes

Increased Thyroid DPP4 Expression Is Associated With Inflammatory Process in Patients With Hashimoto Thyroiditis

CONTEXT

Dipeptidyl peptidase-4 (DPP4) is originally described as a surface protein in lymphocytes. Lymphocyte infiltration and subsequent destruction of thyroid tissue have been considered as the central pathological mechanism in Hashimoto thyroiditis (HT).

OBJECTIVE

The present study aimed to investigate DPP4 expression in peripheral blood and thyroid tissue in HT patients, and explore the role of DPP4 in the pathophysiological process of HT.

METHODS

This case-control study recruited 40 drug-naive HT patients and 81 control individuals. Peripheral blood and thyroid specimens were collected for assessing the expression and activity of DPP4. Moreover, single-cell RNA sequencing (scRNA-seq) analysis of 6 "para-tumor tissues" samples from scRNA-seq data set GSE184362 and in vitro cell experiments were also conducted.

RESULTS

The HT patients had similar DPP4 serum concentration and activity as the controls. However, the expression and activity of DPP4 was significantly increased in the thyroid of the HT group than in the control group. The scRNA-seq analysis showed that DPP4 expression was significantly increased in the HT group, and mainly expressed in T cells. Further in vitro studies showed that inhibition of lymphocyte DPP4 activity with sitagliptin downregulated the production of inflammatory factors in co-cultured thyroid cells.

CONCLUSION

DPP4 expression was significantly increased in the thyroid of the HT group compared with the control group, and was mainly localized in the lymphocytes. Inhibition of lymphocyte DPP4 activity reduced the production of inflammatory factors in co-cultured thyroid cells. Therefore, inhibition of DPP4 may have a beneficial effect by alleviating inflammatory reactions in HT patients.

PRE1BRAZIL Protocol: A Randomized Controlled Trial to Evaluate the Effectiveness and Safety of the DPP-4 Inhibitor Alogliptin in Delaying the Progression of Stage 2 Type 1 Diabetes

Background

The incidence of Type 1 Diabetes Mellitus (T1DM) is on the rise. Since there is no curative treatment, it is urgent to look for therapies that can delay disease progression and protect pancreatic β-cells. Dipeptidyl peptidase-4 inhibitors (DPP-4i) have shown potential in modulating inflammation and preventing β-cell destruction. This protocol describes an upcoming trial to evaluate the effectiveness of the DPP-4i alogliptin in delaying the progression of stage 2 (presymptomatic) to stage 3 (symptomatic) T1DM.

Patients and Methods

We propose a two-year, two-arm, multicenter, randomized, open-label clinical trial targeting Brazilian patients aged 18 to 35 with stage 2 T1DM. The study, facilitated by the custom-developed "PRE1BRAZIL" web application, aims to enroll 130 participants. They will be randomly assigned in a 1:1 ratio to either a treatment group (alogliptin 25 mg daily plus regular clinical and laboratory assessments) or a control group (regular assessments only). The primary outcome is the rate of progression to stage 3 T1DM. Secondary outcomes include changes in A1c levels, glucose levels during a 2-hour oral glucose tolerance test (OGTT), C-peptide levels, exogenous insulin requirements, Insulin-Dose Adjusted A1c (IDAA1c), and the incidence of diabetic ketoacidosis (DKA) in those advancing to stage 3.

Discussion

This protocol outlines the first randomized clinical trial (RCT) to investigate the impact of a DPP-4i in the presymptomatic stage of T1DM. The trial is designed to provide critical insights into the role of DPP-4i in the secondary prevention of T1DM. Utilizing the "PRE1BRAZIL" web application is expected to enhance participant enrollment and reduce operational costs.

Registration

Brazilian Registry of Clinical Trials.

The serum concentration and activity of DPP4 is positively related with the severity of hyperthyroidism in patients with Graves' disease

OBJECTIVE

Graves' disease (GD) is an organ-specific autoimmune disease. The production of anti-thyrotropin receptor antibodies (TRAb) is associated with a loss of immune tolerance. Dipeptidyl peptidase-4 (DPP-4) is expressed on multiple immune cells. This study aimed to investigate the relationship between serum concentration/activity of DPP4 and the severity of hyperthyroidism in GD patients.

METHODS

A total of 82 newly diagnosed drug-naive patients with GD hyperthyroidism, 20 patients with non-autoimmune thyrotoxicosis and 122 age- and sex- matched healthy controls were enrolled. The clinical parameters and serum concentration and activity of DPP4 were measured.

RESULTS

The GD group had increased serum concentration and activity of DPP4 than the healthy controls and patients with non-autoimmune thyrotoxicosis, while no significant difference was observed in the latter two groups. Multivariate linear regression indicated that the serum concentration/activity of DPP4 were positively associated with FT3, FT4 and TRAb levels in the GD patients. And the positive association between serum concentration/activity of DPP4 and TRAb was remained even after adjustment for confounding factors (all p < 0.05).

CONCLUSIONS

The GD patients had significantly increased serum concentration/activity of DPP4. And the serum concentration/activity of DPP4 was positively associated with the severity of hyperthyroidism in GD patients.Key messagesThe activity and concentration of DPP4 in patients with Graves' disease were higher than those in healthy controls.There was a significant positive correlation between serum DPP4 concentration and TRAb levels in patients with Graves' disease.In patients with Graves 'disease, serum DPP4 activity was positively correlated with TRAb levels.

Hepatocyte-derived DPP4 regulates portal GLP-1 bioactivity, modulates glucose production, and when absent influences NAFLD progression

Elevated circulating dipeptidyl peptidase-4 (DPP4) is a biomarker for liver disease, but its involvement in gluconeogenesis and metabolic associated fatty liver disease progression remains unclear. Here, we identified that DPP4 in hepatocytes but not TEK receptor tyrosine kinase-positive endothelial cells regulates the local bioactivity of incretin hormones and gluconeogenesis. However, the complete absence of DPP4 (Dpp4-/-) in aged mice with metabolic syndrome accelerates liver fibrosis without altering dyslipidemia and steatosis. Analysis of transcripts from the livers of Dpp4-/- mice displayed enrichment for inflammasome, p53, and senescence programs compared with littermate controls. High-fat, high-cholesterol feeding decreased Dpp4 expression in F4/80+ cells, with only minor changes in immune signaling. Moreover, in a lean mouse model of severe nonalcoholic fatty liver disease, phosphatidylethanolamine N-methyltransferase mice, we observed a 4-fold increase in circulating DPP4, in contrast with previous findings connecting DPP4 release and obesity. Last, we evaluated DPP4 levels in patients with hepatitis C infection with dysglycemia (Homeostatic Model Assessment of Insulin Resistance > 2) who underwent direct antiviral treatment (with/without ribavirin). DPP4 protein levels decreased with viral clearance; DPP4 activity levels were reduced at long-term follow-up in ribavirin-treated patients; but metabolic factors did not improve. These data suggest elevations in DPP4 during hepatitis C infection are not primarily regulated by metabolic disturbances.

Emerging Role of Dipeptidyl Peptidase-4 in Autoimmune Disease

Dipeptidyl-peptidase IV (DPP4), originally identified as an aminopeptidase in 1960s, is an ubiquitously expressed protease presented as either a membrane-bound or soluble form. DPP4 cleaves dipeptide off from the N-terminal of its substrates, altering the bioactivity of its substrates. Subsequent studies reveal that DPP4 is also involved in various cellular processes by directly binding to a number of ligands, including adenosine deaminase, CD45, fibronectin, plasminogen, and caveolin-1. In recent years, many novel functions of DPP4, such as promoting fibrosis and mediating virus entry, have been discovered. Due to its implication in fibrotic response and immunoregulation, increasing studies are focusing on the potential role of DPP4 in inflammatory disorders. As a moonlighting protein, DPP4 possesses multiple functions in different types of cells, including both enzymatic and non-enzymatic functions. However, most of the review articles on the role of DPP4 in autoimmune disease were focused on the association between DPP4 enzymatic inhibitors and the risk of autoimmune disease. An updated comprehensive summary of DPP4’s immunoregulatory actions including both enzymatic dependent and independent functions is needed. In this article, we will review the recent advances of DPP4 in immune regulation and autoimmune rheumatic disease.

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.

Effect of stevia aqueous extract on the antidiabetic activity of saxagliptin in diabetic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Stevia rebaudiana Bertoni is a perennial herb that belongs to the Asteraceae family. It is a natural sweetener plant known as "Sweet Leaf", "Sweet Herbs" and "Honey Leaf", which is estimated to be 300 times more sweetening than sugar cane. Stevia has been used as a traditional treatment for diabetes in many countries for hundreds of years. Several animal studies referred to the antihyperglycemic activity of stevia. However, the combined use of stevia with saxagliptin has not been studied so far, so this study has been done. The aim of the present study was to evaluate the antihyperglycemic effect of stevia alone and in combination with saxagliptin.

MATERIALS AND METHODS

Diabetes was induced in rats by i.p. injection of streptozotocin and nicotinamide. Animals were divided into five groups, each contains eight rats. Group I: included negative controland group II: included diabetic control that received saline. Group III: included diabetic rats that received 400 mg/kg/day stevia aqueous extract. Group IV: included diabetic rats that received saxagliptin 10 mg/kg/day. Group V: included diabetic rats that received stevia 400 mg/kg + saxagliptin 10 mg/kg. Food and water intake were measured daily while body weight was measured weekly. After 3 weeks animals were sacrificed and blood and tissue samples were collected. Fasting blood glucose (FBG), serum insulin, serum dipeptidylepeptidase-4 (DPP-4), TC, TGs, LDL, HDL, GSH and MDA were measured in treated and control rats by colorimetric and ELISA methods.

RESULTS

Both stevia and saxagliptin significantly reduced food, water intake, body weight and FBG. Stevia with saxagliptin produced more significant decrease in FBG. While serum insulin increased significantly in stevia, saxagliptin treated groups and their combination. Serum DPP-4 decreased significantly in all treated groups, concerning lipid profile, stevia and saxagliptin notably lowered TC, TGs, and LDL and increased HDL. Both stevia and saxagliptin remarkably decreased MDA and increased GSH compared to diabetic rats. In addition, stevia significantly improved the antidiabetic effects of saxagliptin.

CONCLUSION

Stevia has an antihyperglycemic effect and could enhance the antidiabetic activity of saxagliptin. DPP-4 attenuation, antihyperlipidemic and antioxidant activity as well as improvement of insulin sensitivity may be involved in the antidiabetic action of stevia.

Emerging Roles of Dipeptidyl Peptidase-4 Inhibitors in Delaying the Progression of Type 1 Diabetes Mellitus

Type 1 diabetes mellitus (T1DM) results from the immune cell-mediated destruction of functional pancreatic β-cells. In the presymptomatic period, T1DM is characterized by the presence of two or more autoantibodies against the islet cells in patients without glycemic decompensation. Therapeutic strategies that can modify the autoimmune process could slow the progression of T1DM. Dipeptidyl peptidase-4 (DPP-4) or CD26, a multifunctional serine protease with a dual function (regulatory protease and binding protein), can modulate inflammation and immune cell-mediated β-cell destruction. CD26 is involved in T-cell co-stimulation, migration, memory development, thymic maturation, and emigration patterns. DPP-4 degrades the peptide hormones GLP-1 and GIP. In addition to regulating glucose metabolism, DPP-4 exerts anti-apoptotic, regenerative, and proliferative effects to promote β-cell mass expansion. GLP-1 receptor signaling may regulate murine lymphocyte proliferation and maintenance of peripheral regulatory T-cells. In patients with T1DM, the serum DPP-4 activity is upregulated. Several studies have suggested that the upregulated DPP-4 activity is correlated with T1DM pathophysiology. DPP-4, which is preferentially expressed on the Th1 surface, can promote the polarization of Th1 immunity, a prerequisite for T1DM development. CD26 inhibition can suppress T-cell proliferation and Th1 cytokine production and stimulate tumor growth factor beta-1 (TGF-β1) secretion, which plays an important role in the regulation of autoimmunity in T1DM. Studies on humans or animal models of T1DM have suggested that DPP-4 inhibitors can improve β-cell function and attenuate autoimmunity in addition to decreasing insulin dependence. This review summarizes the emerging roles of DPP-4 inhibitors in potentially delaying the progression of T1DM.

Serum Dipeptidyl peptidase-4 level is related to adiposity in type 1 diabetic adolescents

BACKGROUND

Insulin resistance (IR) plays a great role in type 1 diabetes (T1DM) disease process than is commonly recognized. Dipeptidyl peptidase-4 (DPP-4) is an enzyme that deactivates many bioactive peptides involved in glucose regulation.

AIMS

This study evaluates DPP-4 level in adolescent patients with T1DM compared to controls and investigates the relationship between DPP-4 level and IR in these patients.

MATERIALS AND METHODS

We measured serum DPP-4 level in 50 patients with T1DM recruited from the Diabetes Endocrine Metabolism Pediatric Unit, and in 80 healthy controls. IR was assessed by the equation for estimated glucose disposal rate (eGDR). Biochemical evaluation including glycated haemoglobin (HbA1C) and lipid profile were included.

RESULTS

IR was found in 80% of patients with T1DM. DPP-4 was significantly higher in control group than patients with T1DM. Patients with T1DM were classified into 3 groups according to DPP-4 tertiles showing significant increase in BMI SDS and total cholesterol across the 3 groups. Significant correlation was found between DPP-4 levels and insulin dose. DPP-4 was significantly higher in patients with T1DM with good glycemic control.

CONCLUSION

In sample of individuals researched by us, serum DPP-4 was related to adiposity and not to the hyperglycemia in patients with T1DM. Larger sample should be researched to make firm conclusions.

Reduced GLP-1 response to a meal is associated with the CTLA4 rs3087243 G/G genotype

Although insulitis is the characteristic main feature of type 1 diabetes mellitus (T1DM), many aspects of β cell loss still remain elusive. Immune dysregulation and alterations in the dipeptidyl-peptidase-4-incretin system might have a role in disease development, but their connection is poorly understood. We assessed the associations of a few selected, immunologically relevant single nucleotide gene variants with the DPP-4-incretin system in individuals with T1DM and in healthy controls. Prandial plasma (total, active) GLP-1 levels, serum DPP-4 activity, CD25 and CTLA-4 expression of T cells and DPP4 rs6741949, CTLA4 rs3087243, CD25 rs61839660 and PTPN2 rs2476601 SNPs were assessed in 33 T1DM patients and 34 age-, gender-, BMI-matched non-diabetic controls without a family history of T1DM. CTLA-4 expression was lower in the Foxp3+CD25+ regulatory T cells from individuals homozygous for the CTLA4 rs3087243-G variant compared to those who carry an A allele. Prandial plasma total GLP-1 levels 45 min after a standardized meal were reduced in individuals homozygous for the CTLA4 rs3087243 G major allele compared to A allele carriers both in the entire study population (with statistical power over 90%) and within the T1DM group. Here we report for the first time a reduced total prandial GLP-1 plasma concentration in individuals with the CTLA4 rs3087243 G/G genotype. One may speculate that immune response-related L cell damage might possibly explain this novel association.

The dipeptidyl peptidase 4 inhibitor sitagliptin improves oxidative stress and ameliorates glomerular lesions in a rat model of type 1 diabetes

AIMS

Oxidative stress has been linked to the development and progression of diabetic nephropathy (DN). The present study evaluated whether the dipeptidyl peptidase-4 inhibitor sitagliptin attenuates glomerular lesions and oxidative stress evoked by chronic hyperglycemia, by a mechanism independent of insulin secretion and glycemia normalization.

MAIN METHODS

A rat model of DN caused by streptozotocin injection was established and the effects of sitagliptin (5 mg/kg/day) were evaluated after two weeks of treatment.

KEY FINDINGS

Sitagliptin treatment did not change body weight, glycemic and lipid profiles. However, histopathological observation revealed that sitagliptin attenuates diabetes-induced glomerular lesions on diabetic rats. Sitagliptin also ameliorated the increase in DPP-4 content and promoted the stabilization of GLP-1 in the diabetic kidney. Furthermore, sitagliptin treatment significantly attenuated the increase of free-radical formation and the decrease of antioxidant defenses, attenuating therefore the oxidative stress in the kidneys of diabetic animals.

SIGNIFICANCE

The results suggest that sitagliptin treatment alleviates kidney oxidative stress in type 1 diabetic rats, which could play a key role in reducing the progression of DN.

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.

Slowly Progressive Type 1 Diabetes Mellitus: Current Knowledge And Future Perspectives

Slowly progressive type 1 insulin-dependent diabetes mellitus (SPIDDM), sometimes referred to as latent autoimmune diabetes in adults (LADA), is a heterogeneous disease that is often confused with type 1 and type 2 diabetes. As a result, there were few diagnostic criteria for this disorder until 2012, when the Japan Diabetes Society established criteria that could be used in clinical practice. A primary question is whether pathologic markers for type 1 or type 2 diabetes are present in the pancreas of patients with SPIDDM, because the phenotype of SPIDDM is similar to both type 1 and type 2 diabetes. Recent studies clarified pathologic findings in the pancreas of patients with SPIDDM, which included T-cell-mediated insulitis, a marker of type 1 diabetes; pseudoatrophic islets (islets specifically devoid of beta cells), another hallmark of type 1 diabetes; and a lack of amylin (ie, islet amyloid polypeptide) deposition to the islet cells, a pathologic marker of type 2 diabetes. In terms of preventing the loss of beta-cell function in patients with SPIDDM, several studies have shown that some drugs, including dipeptidyl peptidase-4 inhibitors, are effective. There is an increased need for early diagnosis of SPIDDM to preserve beta-cell function. This review presents updated findings on the pathogenesis and immunologic findings of the affected pancreas, diagnostic markers, risk factors for progression of beta-cell dysfunction, epidemiology, clinical features, diagnostic strategies, prevention strategies, and clinical options for patients with SPIDDM.

Increased Plasma Dipeptidyl Peptidase-4 (DPP4) Activity Is an Obesity-Independent Parameter for Glycemic Deregulation in Type 2 Diabetes Patients

Background: Increase in circulating dipeptidyl peptidase-4 (DPP4) activity and levels has been reported to associate both with hyperglycemia and obesity. Here we aim to decipher the role of enhanced plasma DPP4 activity in obese type 2 diabetes (T2DM) patients. Materials and methods: Plasma DPP4 levels and activity were measured in obese and non-obese newly diagnosed T2DM patients (n = 123). Visceral and subcutaneous adipose tissue DPP4 expression and activity were determined in 43 obese subjects (T2DM = 21 and non-T2DM = 22). 20 subjects undergoing Mini-Gastric Bypass (MGB) surgery were followed up over 4-6 weeks for plasma DPP4. Results: Plasma DPP4 levels and activity both were increased in T2DM patients compared to control group. However, DPP4 levels and not DPP4 activity were increased in obese T2DM patients compared to non-obese T2DM (62.49 ± 26.27 μg/ml vs. 48.4 ± 30.98 μg/ml, respectively, p = 0.028). DPP4 activity in visceral adipose tissue (VAT) from obese T2DM and obese non-T2DM groups were similar (5.05 ± 3.96 nmol/min/ml vs. 5.83 ± 4.13 nmol/min/ml respectively, p = 0.548) in spite of having increased DPP4 expression in the obese T2DM group. Moreover, in obese patients, plasma DPP4 levels and activity did not show any significant change after weight reduction and glycemic control following MGB surgery. Conclusion: Enhanced plasma DPP4 activity in T2DM occurs independently of obesity. Thus, adipose derived DPP4 may not be playing any significant role in glycemic deregulation in obese T2DM patients.

Activatable Near-Infrared Fluorescent Probe for Dipeptidyl Peptidase IV and Its Bioimaging Applications in Living Cells and Animals

Visualization of endogenous disease-associated enzymes is of great clinical significance, as it could allow earlier clinical diagnosis and timely intervention. Herein, we first synthesized and characterized an enzyme-activatable near-infrared fluorescent probe, GP-DM, for determining the activity of dipeptidyl peptidase IV (DPP IV), which is associated with various pathological processes, especially in diabetes and malignant tumors. GP-DM emitted significant turn-on NIR fluorescent signals simultaneously in response to DPP IV, making it favorable for accurately and dynamically monitoring DPP IV activity in vitro and in vivo. GP-DM exhibited excellent specificity and sensitivity in DPP IV imaging, as indicated by its higher catalytic activity than other human serine hydrolases and by its strong anti-interference ability to a complex biological matrix, which was fully characterized in a series of phenotyping reactions and inhibition assays. Encouraged by the advantages mentioned above, we successfully used GP-DM to evaluate endogenous DPP IV activity in various biological samples (plasma and tissue preparations) and living tumor cells and performed real-time in vivo bioimaging of DPP IV in zebrafish and tumor-bearing nude mice. All of the results reflected and highlighted the potential application value of GP-DM in the early detection of pathologies, individual tailoring of drug therapy, and image-guided tumor resection. Furthermore, our results revealed that DPP IV, a key target enzyme, is closely associated with the migration and proliferation of cancer cells and regulating the biological activity of DPP IV may be a useful approach for cancer therapy.

DPP-4 Inhibitors as Treatments for Type 1 Diabetes Mellitus: A Systematic Review and Meta-Analysis

OBJECTIVE

Several clinical studies have reported the application of dipeptidyl peptidase-4 (DPP-4) inhibitors as treatments for type 1 diabetes mellitus (T1DM). This study aims to review the outcomes of these existing studies and to discuss the therapeutic effects of DPP-4 inhibitors on T1DM.

METHODS

We thoroughly searched the Medline, Embase, PubMed, and Cochrane Library databases and ClinicalTrials.gov for studies concerning the use of DPP-4 inhibitors in patients with T1DM.

RESULTS

In preclinical trials, DPP-4 inhibitors improved the pathogenesis of T1DM. However, only a portion of the studies showed potential efficacy regarding clinical glycemic control and other clinical parameters. From this meta-analysis, pooled data from 5 randomized controlled trials revealed that the additional use of DPP-4 inhibitors resulted in a greater decrease in glycated hemoglobin A1c (HbA1c) levels (0.07%, 95% CI (-0.37%-0.23%)) than insulin monotherapy, although the decrease was not significant. A small decrease in postprandial glucose or insulin consumption was confirmed.

CONCLUSION

Although DPP-4 inhibitors may be beneficial for T1DM, existing studies do not strongly support these positive effects in clinical practice. Further optimized clinical trials are needed.

Hepatic Dipeptidyl Peptidase-4 Controls Pharmacokinetics of Vildagliptin In Vivo

The main route of elimination of vildagliptin, which is an inhibitor of dipeptidyl peptidase-4 (DPP-4), in humans is cyano group hydrolysis to produce a carboxylic acid metabolite M20.7. Our in vitro study previously demonstrated that DPP-4 itself greatly contributed to the hydrolysis of vildagliptin in mouse, rat, and human livers. To investigate whether hepatic DPP-4 contributes to the hydrolysis of vildagliptin in vivo, in the present study, we conducted in vivo pharmacokinetics studies of vildagliptin in mice coadministered with vildagliptin and sitagliptin, which is another DPP-4 inhibitor, and also in streptozotocin (STZ)-induced diabetic mice. The area under the plasma concentration-time curve (AUC) value of M20.7 in mice coadministered with vildagliptin and sitagliptin was significantly lower than that in mice administered vildagliptin alone (P < 0.01). Although plasma DPP-4 expression level was increased 1.9-fold, hepatic DPP-4 activity was decreased in STZ-induced diabetic mice. The AUC values of M20.7 in STZ-induced diabetic mice were lower than those in control mice (P < 0.01). Additionally, the AUC values of M20.7 significantly positively correlated with hepatic DPP-4 activities in the individual mice (Rs = 0.943, P < 0.05). These findings indicated that DPP-4 greatly contributed to the hydrolysis of vildagliptin in vivo and that not plasma, but hepatic DPP-4 controlled pharmacokinetics of vildagliptin. Furthermore, enzyme assays of 23 individual human liver samples showed that there was a 3.6-fold interindividual variability in vildagliptin-hydrolyzing activities. Predetermination of the interindividual variability of hepatic vildagliptin-hydrolyzing activity might be useful for the prediction of blood vildagliptin concentrations in vivo.

Persons with latent autoimmune diabetes in adults express higher dipeptidyl peptidase-4 activity compared to persons with type 2 and type 1 diabetes

AIMS

We aimed to determine serum dipeptidyl peptidase-4 (DPP-4) activity in a group of persons with latent autoimmune diabetes in adults (LADA) and to compare it with persons with type 1, type 2 diabetes and healthy controls.

METHODS

DPP-4 activity measurement was performed in 67 persons (21 with type 1, 26 type 2 and 19 with LADA) and 13 healthy age and gender matched controls.

RESULTS

Persons with LADA showed highest DPP-4 activity among the study groups (32.71±3.55 vs 25.37±2.84 vs 18.57±2.54 vs 18.57±2.61U/L p<0.001). Mean glutamic acid autoantibody in persons with LADA was 164.32±86.28IU/mL. It correlated with DPP-4 activity (r=0.484, p=0.013). Furthermore, DPP-4 activity correlated with waist circumference (r=0.279, p=0.034) and glycated haemoglobin A1c (r=0.483, p<0.001), as well as with LDL cholesterol (r=0.854, p<0.001) and total daily insulin dose (r=0.397, p=0.001). In the multinomial regression analysis DPP-4 activity remained associated with both LADA (prevalence ratio 1.058 (1.012-1.287), p=0.001) and type 1 diabetes (prevalence ratio 1.506 (1.335-1.765), p<0.001) while it did not show an association with type 2 diabetes (prevalence ratio 0.942 (0.713-1.988), p=0.564).

CONCLUSIONS

Persons with LADA express higher DPP-4 activity compared to persons with both type 1 and type 2 diabetes. The possible pathophysiological role of DPP-4 in the LADA pathogenesis needs to be further evaluated.

Dipeptidyl peptidase-4 activity might be a link between tumour necrosis factor alpha and insulin resistance in type 1 diabetes

Tumour necrosis factor alpha (TNF α) leads to β cell damage in type 1 diabetes (T1DM) but also causes insulin resistance (IR). It modulates dipeptidyl peptidase-4 (DPP-4) activity, adipokine linked with both IR and T1DM. We were interested if there is an association of TNF α in conjunction with DPP-4 and IR in T1DM. DPP-4 activity, TNF α concentration measurements, and insulin sensitivity calculation using estimated glucose disposal rate (eGDR) equation were performed in 70 T1DM patients. They were divided into two groups according to eGDR median. The group with higher IR had higher value of DPP-4 activity (27.57 ± 1.77 vs. 18.33 ± 1.14, p < 0.001) and TNF α concentration (12.91 ± 0.83 vs. 6.72 ± 0.36, p < 0.001). TNF α concentration and DPP-4 activity negatively correlated with eGDR (r = -0.616, p < 0.001 and r = -0.643, p < 0.001) while correlating positively with each other (r = 0.422; p = 0.001). The linear regression showed that eGDR decreases for 0.166 mg kg(-1) min(-1) by TNF α concentration increase of 1 pg/mL (p < 0.001) and for 0.090 mg kg(-1) min(-1) by DPP-4 activity increase of 1 U/L (p = 0.001) when adjusted for age, gender disease duration, glycated haemoglobin, body mass index and waist-to-hip ratio. eGDR decreased by additional 0.60 mg kg(-1) min(-1) (B = -0.150, p < 0.001) when DPP-4 activity was additionally adjusted for TNF α. TNF α concentration is associated with IR, correlates with its severity and increases the drop in insulin sensitivity modulated by DPP-4 activity. Whether TNF α involvement in the insulin signalling pathway is mediated by DPP-4 activity needs to be further evaluated.

Significant elevation of serum dipeptidyl peptidase-4 activity in young-adult type 1 diabetes

AIMS

Currently, inhibition of dipeptidyl peptidase-4 (DPP-4) is widely used in the treatment of type 2 diabetes. Application of this strategy is awaited as a new therapeutic approach for type 1 diabetes, but the scientific basis is still lacking. This report describes the evaluation of serum DPP-4 activity in type 1 diabetes compared with control subjects, and assessment of relationships between DPP-4 activity and diabetic complication markers and metabolic variables in type 1 diabetes.

METHODS

We examined serum DPP-4 activity in Japanese young-adult type 1 diabetes (n=76, females 69.7%, age 30.9 ± 6.2 years, duration of diabetes 16.5 ± 11.1 years; mean ± SD) and healthy controls (n=22). Association of the enzymatic activity with diabetic micro- and macro- vascular complication markers and clinical parameters was also assessed.

RESULTS

Subjects with type 1 diabetes displayed significantly higher serum DPP-4 activity than healthy controls (relative value, control: 1.00 ± 0.28, T1D, 1.29 ± 0.38; p=0.0011) independent of other clinical parameters. In type 1 diabetes, DPP-4 activity was positively correlated with duration of diabetes (r=0.248, p=0.031), while not correlated with HbA1c level. In univariate correlation analysis of diabetic complication markers and other metabolic parameters, coefficient of variation of R-R intervals (CVR-R) and gamma (γ)-glutamyltransferase (GGT) levels were correlated with DPP-4 activity. GGT was extracted as an independent variable of DPP-4 activity in multivariate analysis (β=0.213, p=0.035).

CONCLUSIONS

Serum DPP-4 activity is significantly elevated in Japanese type 1 diabetes, suggesting pathophysiological significance of the enzyme in type 1 diabetes.

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

CD26 is a T cell activation marker consisting in a type II transmembrane glycoprotein with dipeptidyl peptidase IV (DPPIV) activity in its extracellular domain. It has been described that DPPIV inhibition delays the onset of type 1 diabetes and reverses the disease in non-obese diabetic (NOD) mice. The aim of the present study was to assess the effect of MK626, a DPPIV inhibitor, in type 1 diabetes incidence and in T lymphocyte subsets at central and peripheral compartments. Pre-diabetic NOD mice were treated with MK626. Diabetes incidence, insulitis score, and phenotyping of T lymphocytes in the thymus, spleen and pancreatic lymph nodes were determined after 4 and 6 weeks of treatment, as well as alterations in the expression of genes encoding β-cell autoantigens in the islets. The effect of MK626 was also assessed in two in vitro assays to determine proliferative and immunosuppressive effects. Results show that MK626 treatment reduces type 1 diabetes incidence and after 6 weeks of treatment reduces insulitis. No differences were observed in the percentage of T lymphocyte subsets from central and peripheral compartments between treated and control mice. MK626 increased the expression of CD26 in CD8+ T effector memory (TEM) from spleen and pancreatic lymph nodes and in CD8+ T cells from islet infiltration. CD8+TEM cells showed an increased proliferation rate and cytokine secretion in the presence of MK626. Moreover, the combination of CD8+ TEM cells and MK626 induces an immunosuppressive response. In conclusion, treatment with the DPPIV inhibitor MK626 prevents experimental type 1 diabetes in association to increase expression of CD26 in the CD8+ TEM lymphocyte subset. In vitro assays suggest an immunoregulatory role of CD8+ TEM cells that may be involved in the protection against autoimmunity to β pancreatic islets associated to DPPIV inhibitor treatment.

Altered crosstalk in the dipeptidyl peptidase-4-incretin-immune system in type 1 diabetes: A hypothesis generating pilot study

Both GLP1(7)(-)(36) (via GLP1 receptor) and the dipeptidyl peptidase-4 (DPP4) cleaved form of GLP1 (GLP1(9)(-)(36), independently of GLP1R) may modulate the response of lymphocytes to cytokine stimuli. The incretin axis, CXCR3 (receptor of DPP4 ligand cytokines CXCL9-11) expression on T(reg)s and hematologic parameters were assessed in 34 patients with long standing type 1 diabetes (T1DM) and in 35 healthy controls. Serum DPP4 (sDPP4) activity, plasma total GLP1 and GLP1(7)(-)(36) concentrations were determined. GLP1(9)(-)(36) concentrations were calculated. CXCR3 expression (flow cytometry) was higher on the CD25(-/)(low)Foxp3(+) than on the CD25(+)Foxp3(+) T(reg)s independently from T1DM, suggesting that CD25(-/)(low)Foxp3(+) T(reg)s are possibly waiting for orientational chemotactic stimuli in a "standby mode". The higher sDPP4 activities in T1DM were inversely correlated with GLP1(7)(-)(36) levels and GLP1(9)(-)(36) levels directly with lymphocyte counts in controls. Our results might indicate an altered DPP4-incretin system and altered immunoregulation including a potentially dysfunctional GLP1(9)(-)(36) signaling in T1DM.

Saxagliptin: a novel antiparkinsonian approach

The emergence of glucagon-like peptide-1 as a crucial contender in modifying neurodegenerative diseases in the preclinical studies has instigated interest in investigating the antiparkinsonian effect of dipeptidyl peptidase (DPP)-4 inhibition. Notably, saxagliptin (SAX), the DPP-4 inhibitor, recently showed efficacy in ameliorating streptozotocin-induced Alzheimer's disease; however, its effect on Parkinson's disease (PD) has not yet been elucidated. In a rat rotenone (ROT) model, SAX prominently improved motor performance as well as muscle coordination and corrected akinesia. Moreover, SAX preserved substantia nigra pars compacta tyrosine hydroxylase (TH) immunoreactivity while halting the reduction in the striatal TH, dopamine (DA) and complex I. Meanwhile, SAX prevented the ROT-induced increment of striatal DPP-4 and the decline in cAMP, ATP/ADP and brain-derived neurotropic factor levels. Improvement in striatal energy level was associated with partial hindrance of ROT-induced body weight reduction. In addition, through its anti-inflammatory potential, SAX decreased the ROT-induced nuclear factor-κΒ, inducible nitric oxide synthase, tumor necrosis factor-α, intracellular adhesion molecule-1 and myeloperoxidase. The antiapoptotic marker B-cell lymphoma-2 was enhanced by SAX, versus reduction in caspase-3 and its intrinsic apoptotic activator cytochrome C. Furthermore, SAX amended alterations induced by ROT in the thiobarbituric acid reactive substances and the transcriptional factor Nrf-2 level. In conclusion, SAX can be introduced as a novel approach for the management of PD based on the remarkable improvement in motor functions denoting antiparkinsonian efficacy via antioxidant, anti-inflammatory, antiapoptotic, neuroprotective and neurorestorative mechanisms. These effects were linked to DPP-4 inhibition, reduced neurodegeneration and enhanced DA synthesis.

Circulating dipeptidyl peptidase-4 activity is associated with insulin resistance in type 1 diabetic patients

AIM

The pathophysiology of insulin resistance (IR) comprises a complex adipokine mediated cross-talk between white adipose tissue and other organs. Dipeptidyl peptidase-4 (DPP4) is protease recently proposed as a novel adipokine linked to IR. We aimed to assess the relationship between fasting serum DPP4 activityand IR in type 1 diabetic (T1DM) patients.

METHODS

A cross-sectional study comprised 44 T1DM patients aged >18 and <65years. IR was esimated using the equation for insulin sensitivity derived from euglycemic-hyperinsulinemic clamp studies-estimated glucose disposal rate (eGDR). DPP4 serum activity was determined spectrophotometrically as a rate of cleavage of 7-Amino-4-Methyl Coumarin (AMC) from H-Gly-Pro-AMC.

RESULTS

Patients were divided according to DPP4 activity tertiles (<25.40; ≥36.54 U/L). Fasting serum DPP4 activity was related to disease duration (p=0.012), systolic (p=0.009) and diastolic (p=0.047) blood pressure, waist circumference (p=0.037), urine albumin excretion (p=0.022) and conversely related to eGDR (p=0.004). The linear regression has shown that eGDR decreases for 0.203 mgkg(-1)min(-1) by each increase of serum DPP4 activity of 1 U/L (p<0.001) after adjustment for adjusted for age, gender, disease duration, albuminuria and the use of antihypertensives and statins.

CONCLUSION

Serum DPP4 activity is associated with IR in T1DM patients and it might play an important role in its pathophysiology.

Potential role of dipeptidyl peptidase IV in the pathophysiology of heart failure

Dipeptidyl peptidase IV (DPPIV) is a widely expressed multifunctional serine peptidase that exists as a membrane-anchored cell surface protein or in a soluble form in the plasma and other body fluids. Numerous substrates are cleaved at the penultimate amino acid by DPPIV, including glucagon-like peptide-1 (GLP-1), brain natriuretic peptide (BNP) and stromal cell-derived factor-1 (SDF-α), all of which play important roles in the cardiovascular system. In this regard, recent reports have documented that circulating DPPIV activity correlates with poorer cardiovascular outcomes in human and experimental heart failure (HF). Moreover, emerging evidence indicates that DPPIV inhibitors exert cardioprotective and renoprotective actions in a variety of experimental models of cardiac dysfunction. On the other hand, conflicting results have been found when translating these promising findings from preclinical animal models to clinical therapy. In this review, we discuss how DPPIV might be involved in the cardio-renal axis in HF. In addition, the potential role for DPPIV inhibitors in ameliorating heart disease is revised, focusing on the effects of the main DPPIV substrates on cardiac remodeling and renal handling of salt and water.

Cord serum dipeptidyl-peptidase 4 activity in gestational diabetes

BACKGROUND

Tissue-specific dipeptidyl-peptidase 4 (DPP4) dysregulation has been described in adults with diabetes mellitus. The DPP4 -incretin system has not been studied in foetal life. In this study, DPP4 activity and glucagon-like peptide-1 (GLP-1) levels were assessed in cord blood of neonates born to women with gestational diabetes mellitus (GDM) and nondiabetic controls.

MATERIAL AND METHODS

This study has been conducted in two Hungarian and one Austrian centres.

PATIENTS

A total of 568 pregnant women were enrolled in the study after their OGTT between the 24th and 28th gestational week. Cord blood samplings with DPP4 activity and GLP-1 level measurements were possible in 270 (DPP4: 159 control, 111 GDM) and 112 (GLP-1: 72 control, 40 GDM) cases. OGTT (24-28th gestational week) and cord blood sampling at delivery were performed. Cord serum DPP4 activity was determined in a continuous monitoring microplate-based kinetic assay, and cord plasma GLP-1 was measured using a fluorescence ELISA method.

RESULTS

Cord serum DPP4 activity was lower in GDM [mean (95% CI): 28.07 U/L (26.32-29.82 U/L)] than in controls [31.61 U/L (29.93-33.29 U/L), MWU P = 0.0015]. Cord plasma active GLP-1 levels were close to the lower detection limit and were not altered in GDM (control: mean = 3.43 pM, 95% CI: 3.04-3.82 pM, GDM: mean = 3.61 pM, 95% CI: 2.96-4.28 pM - MWU test P = 0.6).

CONCLUSIONS

Decreased cord serum DPP4 activity in gestational diabetes mellitus might be the result of an adaptive foetal response or an early dysregulation in the entero-insular axis with consequences beyond the incretin system. Cord plasma GLP-1 levels may reflect the missing oral intake with a limited glucose sensing of L cells via the circulation in foetal life.

Circulating Dipeptidyl Peptidase-4 Activity is Associated with Diabetic Retinopathy in Type 1 Diabetic Patients

Purpose

Diabetic retinopathy (DR) is the most frequent complication among patients with type 1 diabetes mellitus (T1DM). Dipeptidyl peptidase–4 (DPP4) is a protease with elevated activity in patients with T1DM. Several studies indicate that DPP4 inhibitors might have beneficial effect on nonproliferative retinopathy (NPR) development as well as on its progression to proliferative retinopathy (PR). We aimed to explore the relationship between serum DPP4 activity and DR in patients with T1DM.

Methods

This cross-sectional study recruited 44 patients with T1DM. The DPP4 activity was measured by colorimetric assay in a microplate reader. Photodocumented retinopathy status was made according to the EURODIAB protocol.

Results

A total of 28 (63.6%) patients were men, mean age 45.36 years, diabetes duration 23.71 years, glycated hemoglobin A1c (HbA1c) 7.4%. Patients were stratified into 2 groups according to retinopathy prevalence. Group 1 comprised 14 (31.85%) patients with DR absence while the second group consisted of 30 (68.15%) patients with both PR and NPR. Group 1 had lower fasting serum DPP4 activity (25.85 vs 33.84 U/L, p<0.001) when compared to the second group. In the binary logistic regression model adjusted for age, sex, diabetes duration, and HbA1c level, DPP4 activity was associated with DR prevalence (odds ratio 1.887 [1.073-3.321]).

Conclusions

Serum DPP4 activity may be independently associated with both DR types in patients with T1DM. Further study is warranted to elucidate whether there is an association between DPP4 activity and DR severity and/or progression.

Extension of the CD4⁺Foxp3⁺CD25(-/low) regulatory T-cell subpopulation in type 1 diabetes mellitus

Regulatory T-cells (Treg) have a crucial role in limiting physiologic autoreactivity. Foxp3 is a master regulator transcription factor of Treg differentiation and active Treg cells express high levels of IL-2 receptor α-chain (CD25). The aim of our study was to assess the key markers of Treg cell function in type 1 diabetic (T1DM) and control subjects by flow cytometry. The proportion of CD25(-/low) cells among CD4(+)Foxp3(+) Treg cells was higher in T1DM patients that might suggest a shifted proportion of the incomplete/reserve and the fully active (CD4(+)Foxp3(+)CD25(+)) Treg cell subpopulations in T1DM, similarly to other Th1-mediated autoimmune diseases. In addition to the decreased expression of CD25 and CTLA-4 in T1DM patients, a positive correlation was observed between the CD25 expression on CD4(+) and the CTLA-4 expression in CD8(-) T-lymphocytes both in the T1DM and in the healthy control group. Our results suggest an impaired balance of CD25(+) and CD25(-/low) Treg cells in T1DM which might reflect a decreased late phase peripheral Treg activation even in patients with a mean disease duration of more than a decade.

Emerging roles of dipeptidyl peptidase 4 inhibitors: anti-inflammatory and immunomodulatory effect and its application in diabetes mellitus

Dipeptidyl peptidase 4 (DPP4) inhibitors have been widely used in the treatment of type 2 diabetes mellitus. It is well known that DPP4 inhibitors exert their antidiabetes effects mainly by inhibiting the enzymatic degradation of glucagon-like peptide-1 and glucose-dependent insulinotropic peptide. The anti-inflammatory effect of DPP4 inhibitors was proved by preclinical and clinical studies of type 2 diabetes and coronary artery disease. Preclinical data using DPP4 inhibitors-based therapies in studies of nonobese diabetic mice demonstrated additional effects, including immunomodulation, preserving beta-cell mass, promoting beta-cell regeneration and reversing newly diagnosed diabetes. Thus, these data show that DPP4 inhibitors may be effective for type 1 diabetes mellitus. However, their potential clinical benefits for type 1 diabetes remain to be evaluated. This paper will provide an overview of the progress of the anti-inflammatory and immunomodulatory effects of DPP4 inhibitors in treating both type 1 and type 2 diabetes.

Dipeptidyl peptidase-IV inhibition prevents blood-retinal barrier breakdown, inflammation and neuronal cell death in the retina of type 1 diabetic rats

Diabetic retinopathy, a leading cause of vision loss in working-age population, is often associated with inflammation and apoptosis. We have previously reported that sitagliptin, a DPP-IV inhibitor, exerts beneficial effects in the retina of type 2 diabetic animals. The present study aimed to evaluate whether sitagliptin can exert protective effects in the retina of type 1 diabetic animals by a mechanism independent of insulin secretion and glycemia normalization. Streptozotocin-induced diabetic rats were treated orally with sitagliptin (5mg/kg/day) for the last two weeks of 4 weeks of diabetes. Sitagliptin treatment did not change the weight and glucose, HbA1c or insulin levels. However, it prevented the diabetes-induced increase in DPP-IV/CD26 activity and levels in serum and retina. Sitagliptin also prevented the increase in blood-retinal barrier (BRB) permeability and inhibited the changes in immunoreactivity and endothelial subcellular distribution of occludin, claudin-5 and ZO-1 proteins induced by diabetes. Furthermore, sitagliptin decreased the retinal inflammatory state and neuronal apoptosis. Sitagliptin inhibited the BRB breakdown in a type 1 diabetic animal model, by a mechanism independent of normalization of glycemia, by preventing changes in tight junctions (TJs) organization. Sitagliptin also exerted protective effects against inflammation and pro-apoptotic state in the retina of diabetic rats. Altogether, these results suggest that sitagliptin might be envisaged to be used to prevent or delay some of the alterations associated with the development of diabetic retinopathy.

Identification of the catalytic triad of family S46 exopeptidases, closely related to clan PA endopeptidases

The exopeptidases of family S46 are exceptional, as the closest homologs of these enzymes are the endopeptidases of clan PA. The three-dimensional structure of S46 enzymes is unknown and only one of the catalytic residues, the serine, has been identified. The catalytic histidine and aspartate residues are not experimentally identified. Here we present phylogenetic and experimental data that identify all residues of the catalytic triad of S46 peptidase, dipeptidyl aminopeptidase BII (DAP BII) from Pseudoxanthomonas mexicana WO24. Phylogenetic comparison with the protein and S46 peptidases, revealed His-86, Ser-657, and five aspartate residues as possible catalytic residues. Mutation studies identified the catalytic triad of DAP BII as His-86, Asp-224, and Ser-657, while secondary structure analysis predicted an extended alpha-helical domain in between Asp-224 and Ser-657. This domain is unique for family S46 exopeptidases and its absence from the endopeptidases of clan PA might be key to their different hydrolysis activities.

Regulation of dipeptidyl peptidase 4 production in adipocytes by glucose

OBJECTIVE

Type 1 and 2 diabetes are characterized by elevated blood glucose levels and increased dipeptidyl peptidase 4 (DPP4) activity levels in the serum. However, previous studies reported a negative correlation between glucose concentrations and DPP4 levels. The purpose of this study was to elucidate the connection between glucose and DPP4 in adipocytes under physiological and diabetic conditions, because DPP4 is an adipokine.

METHODS

Blood glucose and serum DPP4 levels were measured, and adipocytes were collected from mice under normal, high-fat diet fed, and diabetic conditions. The adipocytes obtained were incubated for 24 hours in medium containing 5.5 or 25 mM glucose, and 3T3-L1 preadipocytes were differentiated under 5.5 or 25 mM glucose. Adipocytes from mice and 3T3-L1 were stimulated by tumor necrosis factor-α (TNF-α) for 24 hours. The levels of released and intracellular DPP4 were determined by enzyme-linked immunosorbent assay.

RESULTS

Mice fed high-fat diet had lower serum DPP4 levels in the first and second week than controls. However, this difference gradually disappeared over 6 weeks. The differentiation of 3T3-L1 adipocytes under 25 mM glucose produced lower DPP4 levels than those differentiated under 5.5 mM; this was also observed in isolated adipocytes from mice. However, these effects of glucose were lost in adipocytes from diabetic mice, and an increase in total DPP4 levels was observed. The stimulation of adipocytes with TNF-α increased the release of DPP4 irrespective of glucose concentration.

CONCLUSION

The production of DPP4 in adipocytes was negatively regulated by 25 mM glucose under physiological conditions, but not in diabetic mice. Our results suggest that the observed increase in serum DPP4 levels may be attributed to increased production of DPP4 in adipocytes and an enhancement in TNF-α-induced release.

The ameliorative effect of Cetraria islandica against diabetes-induced genetic and oxidative damage in human blood

CONTEXT

The aqueous extracts of Cetraria islandica (L.) Ach. (Parmeliaceae) is traditionally used in many countries against a number of conditions, including inflammatory conditions.

OBJECTIVE

The present study aimed to assess, for the first time, the effectiveness of C. islandica in cultured primary blood cells of Type 1 diabetes subjects.

MATERIALS AND METHODS

Diabetic and control blood samples were treated with or without aqueous lichen extract (5 and 10 μg mL(-1)) for 48 h. The activity of antioxidant enzymes in erythrocytes and also malondialdehyde levels in plasma were determined to evaluate the oxidative status. DNA damages were analyzed by SCE, MN and comet assays in cultured human lymphocytes. Additionally, proliferation index (PI) was evaluated in peripheral blood lymphocytes.

RESULTS

There were significant increases in observed total DNA damage (comet assay) (240.2%) and SCE (168.8%), but not in MN frequencies of cultures with diabetes as compared (p > 0.05) to controls. Whereas, the significant reductions of total DNA damage (69.2 and 65.3%) and SCE frequencies (17.7 and 12.3%) were determined when the 5 and 10 mg mL(-1) lichen extract was added to the cell culture medium, respectively. However, lichen extract did not completely inhibit the induction of SCEs in lymphocytes of patients with diabetes. C. islandica extract was also useful on PI rates.

DISCUSSION

In conclusion, the antioxidant role of C. islandica in alleviating diabetes-induced genomic instability and for increasing cell viability was firstly indicated in the present study.

Altered immune regulation in type 1 diabetes

Research in genetics and immunology was going on separate strands for a long time. Type 1 diabetes mellitus might not be characterized with a single pathogenetic factor. It develops when a susceptible individual is exposed to potential triggers in a given sequence and timeframe that eventually disarranges the fine-tuned immune mechanisms that keep autoimmunity under control in health. Genomewide association studies have helped to understand the congenital susceptibility, and hand-in-hand with the immunological research novel paths of immune dysregulation were described in central tolerance, apoptotic pathways, or peripheral tolerance mediated by regulatory T-cells. Epigenetic factors are contributing to the immune dysregulation. The interplay between genetic susceptibility and potential triggers is likely to play a role at a very early age and gradually results in the loss of balanced autotolerance and subsequently in the development of the clinical disease. Genetic susceptibility, the impaired elimination of apoptotic β-cell remnants, altered immune regulatory functions, and environmental factors such as viral infections determine the outcome. Autoreactivity might exist under physiologic conditions and when the integrity of the complex regulatory process is damaged the disease might develop. We summarized the immune regulatory mechanisms that might have a crucial role in disease pathology and development.

Evaluation of insulin secretion and sensitivity in a patient with slowly progressive type 1 diabetes mellitus

We herein report the case of a patient with slowly progressive type 1 diabetes and insulin independence lasting for >10 years despite the detection of continuously elevated glutamic acid decarboxylase autoantibody titers. We monitored the patient's clinical course and analyzed his endogenous insulin secretion and sensitivity using an intravenous glucose tolerance test (IVGTT) and oral glucose tolerance test (OGTT). His body mass index remained at approximately 22, while his serum C-peptide immunoreactivity level gradually decreased. The level of insulin secretion was significantly higher on the OGTT than the IVGTT. The patient's insulin sensitivity was within the normal limits. These results suggest that maintaining a lifestyle sufficient to preserve insulin secretion and/or normal insulin sensitivity is important and that β-cell responsiveness to incretins may, in part, contribute to insulin independence.

[Type 1 diabetes mellitus: most recent advances in its pathogenesis and treatment]

The incidence and prevalence of diabetes mellitus is globally increasing. The causes of this trend are relatively obvious in the case of type 2 diabetes. In contrast, in case of type 1 diabetes the amount of available data is continuously growing, but the causes are not so well defined. The genetic risk, especially related to the MHC genes is well known, and the increasing amount of data underlines the role of additional risks due to non-MHC genetic polimorphisms. Hopefully, they will provide the basis for future diagnostic and therapeutic approaches. There is increasing knowledge about the pathophysiological aspects including the role of immunological disregulation (balance of autotolerance, role of regulatory T-cells) and environmental triggers (nutrients, viruses). Information on the entero-insular axis and the β-cell protective role of incretin hormones might offer an opportunity for new therapeutic strategies. In this paper, the authors try to summarize some current aspects of the pathomechanism and related therapeutic approaches.