Reduction of both beta cell death and alpha cell proliferation by dipeptidyl peptidase-4 inhibition in a streptozotocin-induced model of diabetes in mice

Fabrication of a Near-Infrared-Emissive Probe for Detecting Dipeptidyl Peptidase 4 in the Liver of Diabetic Mice and Clinical Serum

Dipeptidyl peptidase 4 (DPP4) plays a key role in glucose metabolism, which has been a close target for diabetes pathology and treatment. It is significant for the evaluation of cellular DPP4 activity in various biological systems. Fluorescence imaging technology is currently a popular method for detecting enzymes in living cells due to its advantages of high selectivity, high sensitivity, high spatiotemporal resolution, and real-time visualization. Herein, a near-infrared (NIR)-emissive probe NEDP with a large Stokes shift (153 nm) was developed for the assay of DPP4 activity. Upon addition of DPP4, NEDP can emit a significant turn-on NIR fluorescence signal (673 nm) with high sensitivity and specificity. Moreover, NEDP can successfully be used for imaging of intracellular DPP4, confirming the regulation of DPP4 expression in hyperglucose and its treatment in living cells. Most importantly, NEDP can not only monitor the changes of DPP4 in vivo but also show that DPP4 in diabetes is mainly up-regulated in the liver, and the level of DPP4 is positively correlated with the pathological damage of the liver. In addition, NEDP can identify the serum of diabetic patients from healthy people through the fluorescence response to DPP4. These results demonstrated that the designed probe NEDP provides a prospective visual tool to explore the relationship between DPP4 and diabetes and would be applied for detecting serum of diabetes in the clinic.

Lithium and exercise ameliorate insulin-deficient hyperglycemia by independently attenuating pancreatic α-cell mass and hepatic gluconeogenesis

As in type 1 diabetes, the loss of pancreatic β-cells leads to insulin deficiency and the subsequent development of hyperglycemia. Exercise has been proposed as a viable remedy for hyperglycemia. Lithium, which has been used as a treatment for bipolar disorder, has also been shown to improve glucose homeostasis under the conditions of obesity and type 2 diabetes by enhancing the effects of exercise on the skeletal muscles. In this study, we demonstrated that unlike in obesity and type 2 diabetic conditions, under the condition of insulin-deficient type 1 diabetes, lithium administration attenuated pancreatic a-cell mass without altering insulin-secreting β-cell mass, implying a selective impact on glucagon production. Additionally, we also documented that lithium downregulated the hepatic gluconeogenic program by decreasing G6Pase protein levels and upregulating AMPK activity. These findings suggest that lithium's effect on glucose metabolism in type 1 diabetes is mediated through a different mechanism than those associated with exerciseinduced metabolic changes in the muscle. Therefore, our research presents the novel therapeutic potential of lithium in the treatment of type 1 diabetes, which can be utilized along with insulin and independently of exercise.

Food contaminants and potential risk of diabetes development: A narrative review

The number of people diagnosed with diabetes continues to increase, especially among younger populations. Apart from genetic predisposition and lifestyle, there is increasing scientific and public concern that environmental agents may also contribute to diabetes. Food contamination by chemical substances that originate from packaging materials, or are the result of chemical reactions during food processing, is generally recognized as a worldwide problem with potential health hazards. Phthalates, bisphenol A (BPA) and acrylamide (AA) have been the focus of attention in recent years, due to the numerous adverse health effects associated with their exposure. This paper summarizes the available data about the association between phthalates, BPA and AA exposure and diabetes. Although their mechanism of action has not been fully clarified, in vitro, in vivo and epidemiological studies have made significant progress toward identifying the potential roles of phthalates, BPA and AA in diabetes development and progression. These chemicals interfere with multiple signaling pathways involved in glucose and lipid homeostasis and can aggravate the symptoms of diabetes. Especially concerning are the effects of exposure during early stages and the gestational period. Well-designed prospective studies are needed in order to better establish prevention strategies against the harmful effects of these food contaminants.

Improvement effect of a next-generation probiotic L. plantarum-pMG36e-GLP-1 on type 2 diabetes mellitus via the gut-pancreas-liver axis

Next-generation probiotics (NGPs) are currently being investigated as therapeutic agents that impact the gut microbiota and disease development. Glucagon-like peptide-1 (GLP-1) shows an excellent therapeutic effect on diabetes, but has an extremely short half-life in vivo. Here, we constructed a novel and diabetes-specific NGP, the genetically engineered strain Lactobacillus plantarum (L. plantarum)-pMG36e-GLP-1, and evaluated its ameliorative effect on type 2 diabetes mellitus (T2DM) in artificially induced mice and transgenic mice. In vitro, L. plantarum-pMG36e-GLP-1 showed good genetic stability and probiotic characteristics. In the high-fat diet combined with streptozotocin (HFD/STZ)-induced T2DM mice, L. plantarum-pMG36e-GLP-1 relieved the diabetic symptoms, regulated the intestinal microbiota, and reduced the inflammatory reaction in the pancreatic tissue. Meanwhile, the apoptosis of pancreatic islet cells was inhibited, while islet tissue morphology repairs, islet β-cell proliferation, and insulin secretion were all promoted by L. plantarum-pMG36e-GLP-1. Furthermore, a similar effect of the engineered strain on diabetic symptoms and the pancreas was observed in db/db mice, and the metabolism of lipids in the liver was regulated. Together, the findings of this study confirmed the anti-hyperglycemic effect of the engineered strain L. plantarum-pMG36e-GLP-1, providing a promising approach for T2DM treatment.

Age-related hearing loss was accelerated by apoptosis of spiral ganglion and stria vascularis cells in ApoE KO mice with hyperglycemia and hyperlipidemia

Age-related hearing loss (ARHL) is associated with diabetes and/or dyslipidemia in humans. However, the detailed mechanism for the development of ARHL by diabetes and/or dyslipidemia has not been elucidated. In this study, we investigated the etiology of ARHL in apolipoprotein E (ApoE)-deficient mice with diabetes and dyslipidemia. The atherosclerotic CD-STZ (mice fed with a control diet and received an STZ injection), WD-con (mice fed with a western diet), and WD-STZ (mice fed with a western diet and received an STZ injection) mice showed a 2.4-, 4.9-, and 6.8-fold larger area, respectively, occupied by lesions throughout the aorta compared with the CD-con mice. A significantly larger area under the curve (AUC) was observed in the STZ-treated groups than in the non-treated groups based on the oral glucose tolerance test (OGTT). At 20 weeks of age, HbA_1c levels were significantly higher in the CD-STZ and WD-STZ mice than in the CD-con and WD-con mice. In all the groups, the auditory brainstem response (ABR) thresholds of the 16-week-old mice were significantly higher compared with those of the 8-week-old mice. In particular, in the WD-STZ mice, the ABR thresholds of the left and right ears reached the maximum decibel peak equivalent sound pressure levels (130 dBpeSPL), which is a sign of deafness. The apoptotic spiral ganglion neurons (SGNs) of the WD-STZ mice were significantly increased compared with those of the other three groups, indicating that SGN apoptosis resulted in hearing loss in STZ-induced diabetic ApoE KO mice fed with a WD. A significant loss of the stria vascularis cells was observed in the WD-STZ group compared with the CD-con mice. In the organ of Corti, few apoptotic hair cells were found in all the groups; however, no significant difference was observed. Therefore, we consider that the reduced hearing ability in the STZ-treated and WD-fed groups was attributed to the damage to the SGN and stria vascularis in the cochlea. Thus, our results indicated that ototoxicity by diabetes and/or dyslipidemia accelerated ARHL in ApoE KO mice, thereby suggesting the importance of appropriate treatment of patients with diabetes and/or dyslipidemia to prevent ARHL.

Acrylamide and Potential Risk of Diabetes Mellitus: Effects on Human Population, Glucose Metabolism and Beta-Cell Toxicity

Diabetes mellitus is a frequent endocrine disorder characterized by hyperglycemia. Acrylamide (AA) is food contaminant formed during the high-temperature processing of food rich in carbohydrates and low in proteins. Recent human epidemiological studies have shown a potential association between AA exposure and the prevalence of diabetes in the general population. In male rats, AA treatment promoted pancreatic islet remodeling, which was determined by alpha-cell expansion and beta-cell reduction, while in female rats AA caused hyperglycemia and histopathological changes in pancreatic islets. In vitro and in vivo rodent model systems have revealed that AA induces oxidative stress in beta cells and that AA impairs glucose metabolism and the insulin signaling pathway. Animal studies have shown that diabetic rodents are more sensitive to acrylamide and that AA aggravates the diabetic state. In this review, we provide an overview of human epidemiological studies that examined the relation between AA exposure and glucose disorders. In addition, the effects of AA treatment on pancreatic islet structure, beta-cell function and glucose metabolism in animal models are comprehensively analyzed with an emphasis on sex-related responses. Furthermore, oxidative stress as a putative mechanism of AA-induced toxicity in beta cells is explored. Finally, we discuss the effects of AA on diabetics in a rodent model system.

CD26 expression on donor harvest as a risk predictive biomarker for developing graft-versus-host disease post-allogeneic hematopoietic stem cell transplantation: A ten-year follow-up study

BACKGROUND

Allogeneic hematopoietic stem cell transplantation (ASCT) is the preferred treatment option for patients with several hematologic disorders and immunodeficiency syndromes. Graft-versus-host disease (GVHD) is an immune mediated post-transplant complication which has a major impact on long-term transplant outcomes.

OBJECTIVE

Current efforts are focused on identification of new markers that serve as potential predictors of GVHD and other post-transplant clinical outcomes.

METHODS

This study includes donor harvests collected from twenty-three allogeneic donors during period 2008-2009 and respective transplant recipients followed for clinical outcomes till March 2019. Percent CD26+ and CD34+ cells in donor harvest were analyzed using flow cytometry. Percent expression and infused dose of CD26+ and CD34+ cells were evaluated for association with various clinical outcomes.

RESULTS

Total 23 healthy donors with median age of 28 years (13 males), and transplant recipients with median age of 24 years (17 males) formed the study cohort. The diagnosis included malignant (n= 13) and non-malignant (n= 10) hematological disorders. Median CD34brCD45lo HSC expression was 0.57% (IQR 0.24-1.03) while median CD26 expression was 19.64% (IQR 8.96-33.56) of all nucleated cells. CD26 expression was associated with donor age (P= 0.037). CD26 percent expression correlated with WBC engraftment (P= 0.015) and with acute GVHD (P= 0.023) whereas infused CD26 cell dose correlated with WBC engraftment (P= 0.004) and risk of CMV reactivation (P= 0.020). There was no statistically significant correlation of either CD26 expression or cell dose with chronic GVHD, EFS or OS.

CONCLUSIONS

Our findings suggest a role of CD26 expression on human donor harvest as a potential predictor of acute GVHD. This association warrants further exploration.

Triple drug therapy with GABA, sitagliptin, and omeprazole prevents type 1 diabetes onset and promotes its reversal in non-obese diabetic mice

Previous studies have reported that dual drug combinations consisting of γ-aminobutyric acid (GABA) together with a dipeptidyl-peptidase-4 inhibitor (DPP-4i), also a DPP-4i with a proton pump inhibitor (PPI), could improve pancreatic β-cell function and ameliorate diabetes in diabetic mice. In this study, we sought to determine if a triple drug combination of GABA, a DPP-4i and a PPI might have superior therapeutic effects compared with double drug therapies in the prevention and reversal of diabetes in the non-obese diabetic (NOD) mouse model of human type 1 diabetes (T1D). In a diabetes prevention arm of the study, the triple drug combination of GABA, a DPP-4i, and a PPI exhibited superior therapeutic effects in preventing the onset of diabetes compared with all the double drug combinations and placebo. Also, the triple drug combination significantly increased circulating C-peptide and serum insulin levels in the mice. In a diabetes reversal arm of the study, the triple drug combination was superior to all of the double drug combinations in reducing hyperglycemia in the mice. In addition, the triple drug combination was the most effective in increasing circulating levels of C-peptide and serum insulin, thereby significantly reducing exogenous insulin needs. The combination of GABA, a DPP-4i and a PPI appears to be a promising and easily scalable therapy for the treatment and prevention of T1D.

Models of nonalcoholic steatohepatitis potentiated by chemical inducers leading to hepatocellular carcinoma

Hepatocellular carcinoma (HCC), the most common primary liver cancer, arises after a long period of exposure to etiological factors. Nonalcoholic steatohepatitis (NASH) is ranked as the main risk factor for developing HCC; hence, experimental models of NASH leading to HCC have become key tools both to investigate the molecular mechanisms underlying the pathophysiology and to evaluate new putative drugs for treating chronic liver diseases in humans. Animal models of NASH induced by a high-fat diet (HFD) plus chemical inducers, such as the NASH-HCC (STAM), high-fat diet/diethylnitrosamine (HFD/DEN), choline-deficient high-fat diet/DEN (CDHFD/DEN), and Western diet/carbon tetrachloride (WD/CCl₄) models, are promising because they exacerbate liver damage and significantly shorten the experimental time. In this review, we critically summarize and discuss the ability of these models to recapitulate the liver alterations that precede and lead to HCC progression, as well as the impact of the diet in promoting liver injury progression. We also emphasize the strengths and weaknesses of the models' ability to closely mimic the stages of liver injury development that occur in humans. Based on the molecular mechanisms induced by the currently available NASH models leading to HCC, we argue that although several NASH models have importantly contributed to describing the disease chronology, the progress in emulating the progression from NASH to HCC has been partial. Thus, the development of novel NASH/HCC models remains an unmet need.

Pancreatic β-Cell O-GlcNAc Transferase Overexpression Increases Susceptibility to Metabolic Stressors in Female Mice

The nutrient-sensor O-GlcNAc transferase (Ogt), the sole enzyme that adds an O-GlcNAc-modification onto proteins, plays a critical role for pancreatic β-cell survival and insulin secretion. We hypothesized that β-cell Ogt overexpression would confer protection from β-cell failure in response to metabolic stressors, such as high-fat diet (HFD) and streptozocin (STZ). Here, we generated a β-cell-specific Ogt in overexpressing (βOgtOE) mice, where a significant increase in Ogt protein level and O-GlcNAc-modification of proteins were observed in islets under a normal chow diet. We uncovered that βOgtOE mice show normal peripheral insulin sensitivity and glucose tolerance with a regular chow diet. However, when challenged with an HFD, only female βOgtOE (homozygous) Hz mice developed a mild glucose intolerance, despite increased insulin secretion and normal β-cell mass. While female mice are normally resistant to low-dose STZ treatments, the βOgtOE Hz mice developed hyperglycemia and glucose intolerance post-STZ treatment. Transcriptome analysis between islets with loss or gain of Ogt by RNA sequencing shows common altered pathways involving pro-survival Erk and Akt and inflammatory regulators IL1β and NFkβ. Together, these data show a possible gene dosage effect of Ogt and the importance O-GlcNAc cycling in β-cell survival and function to regulate glucose homeostasis.

Prolonged Honeymoon Period in a Thai Patient with Adult-Onset Type 1 Diabetes Mellitus

Objective

To describe a usual case of adult-onset T1DM with prolonged honeymoon period for more than 5 years.

Methods

Repeated mixed meal stimulation tests for a period of 6–12 months together with monitoring pancreatic autoantibodies and laboratory data were followed following the onset of diagnosis.

Results

We report a 24-year-old Thai patient with T1DM with sustained remission without antidiabetic medication for more than 5 years while maintaining low-carbohydrate intake and regular exercise. Repeated mixed meal stimulation tests for a period of 6–12 months revealed preserved beta-cell functions. Interestingly, repeated pancreatic autoantibodies at 5 years after diagnosis still showed positive anti-GAD, anti-IA2, and anti-ZnT8.

Conclusion

Restored beta-cell function with complete insulin withdrawal in new-onset T1DM has been reported in very few cases with some common factors as in our patient (low-carbohydrate intake with regular exercise). Delaying autoimmune activity by reducing metabolic load in newly diagnosed T1DM might play a role in maintaining the honeymoon period and could lead to an innovative therapeutic option in new-onset T1DM.

Stage-specific transcriptomic changes in pancreatic α-cells after massive β-cell loss

Background

Loss of pancreatic insulin-secreting β-cells due to metabolic or autoimmune damage leads to the development of diabetes. The discovery that α-cells can be efficiently reprogrammed into insulin-secreting cells in mice and humans has opened promising avenues for innovative diabetes therapies. β-cell loss triggers spontaneous reprogramming of only 1–2% of α-cells, limiting the extent of regeneration. Most α-cells are refractory to conversion and their global transcriptomic response to severe β-cell loss as well as the mechanisms opposing their reprogramming into insulin producers are largely unknown. Here, we performed RNA-seq on FAC-sorted α-cells to characterize their global transcriptional responses at different time points after massive β-cell ablation.

Results

Our results show that α-cells undergo stage-specific transcriptional changes 5- and 15-days post-diphtheria toxin (DT)-mediated β-cell ablation. At 5 days, α-cells transiently upregulate various genes associated with interferon signaling and proliferation, including Interferon Induced Protein with Tetratricopeptide Repeats 3 (Ifit3). Subsequently, at 15 days post β-cell ablation, α-cells undergo a transient downregulation of genes from several pathways including Insulin receptor, mTOR and MET signaling.

Conclusions

The results presented here pinpoint novel markers discriminating α-cells at different stages after acute β-cell loss, and highlight additional signaling pathways that are modulated in α-cells in this context.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07812-x.

Lactobacillus paracasei modulates the gut microbiota and improves inflammation in type 2 diabetic rats

This study aimed to investigate the effects of probiotic Lactobacillus paracasei NL41 on inflammation and the gut microbiota of type 2 diabetic (T2D) rats induced by high-fat diet (HFD) and low-dose streptozotocin (STZ). A T2D rat model was established by inducing Sprague-Dawley rats with HFD/STZ, followed by 12-weeks L. paracasei NL41 gavage. The blood, colonic tissues, and feces samples of these rats were collected for inflammation, histology, and intestinal microbiota profiling. L. paracasei NL41 treatment induced remarkable improvement in the inflammatory status by decreasing the levels of serum lipopolysaccharides (LPS), free fatty acids (FFA), tumor necrosis factor-α (TNF-α), interleukin (IL)-6, and IL-8 and increasing the level of IL-10. Gut barrier function was significantly protected in NL41-treated rats. Moreover, the strain NL41 induced changes in the microbiota structure and influenced the relative abundance of the key species. Specifically, Bacteroides, Clostridia (specifically, Ruminococcus torques), and Parasutterella were significantly reduced, while some beneficial microorganisms (Bacteroidales_S24-7_group and the families Lachnospiraceae and Ruminococcaceae) were enriched by NL41. The correlational analyses indicated that L. paracasei NL41 ameliorating inflammation was closely related to the key species of the gut microbiota. The present study indicates that probiotic L. paracasei NL41 decreases LPS-induced inflammation by improving the gut microbiota and preserving intestinal integrity.

A Comprehensive Review and Perspective on Natural Sources as Dipeptidyl Peptidase-4 Inhibitors for Management of Diabetes

Type 2 diabetes mellitus (T2DM) is an increasing global public health problem, and its prevalence is expected to rise in coming decades. Dipeptidyl peptidase-4 (DPP-4) is a therapeutic target for the management of T2DM, and its inhibitors prevent the degradation of glucose-dependent insulinotropic peptide and glucagon-like peptide 1, and thus, maintain their endogenous levels and lower blood glucose levels. Various medicinal plant extracts and isolated bioactive compounds exhibit DPP-4 inhibitory activity. In this review, we discussed different natural sources that have been shown to have anti-diabetic efficacy with a particular emphasis on DPP-4 inhibition. Furthermore, the effect of DPP-4 inhibition on pancreatic beta cell function, skeletal muscle function, and the glucose-lowering mechanisms were also discussed. We believe that scientists looking for novel compounds with therapeutic promise against T2DM will be able to develop antidiabetic drugs using these natural sources.

Mechanisms of Beta-Cell Apoptosis in Type 2 Diabetes-Prone Situations and Potential Protection by GLP-1-Based Therapies

Type 2 diabetes (T2D) is characterized by chronic hyperglycemia secondary to the decline of functional beta-cells and is usually accompanied by a reduced sensitivity to insulin. Whereas altered beta-cell function plays a key role in T2D onset, a decreased beta-cell mass was also reported to contribute to the pathophysiology of this metabolic disease. The decreased beta-cell mass in T2D is, at least in part, attributed to beta-cell apoptosis that is triggered by diabetogenic situations such as amyloid deposits, lipotoxicity and glucotoxicity. In this review, we discussed the molecular mechanisms involved in pancreatic beta-cell apoptosis under such diabetes-prone situations. Finally, we considered the molecular signaling pathways recruited by glucagon-like peptide-1-based therapies to potentially protect beta-cells from death under diabetogenic situations.

Lactobacillus paracasei modulates the gut microbiota and improves inflammation in type 2 diabetic rats

L. paracasei NL41 maintained the gut microecosystem, which led to improvement of the gut barrier function and reduction of the permeation of LPS, thereby inhibiting inflammation.

Implanted islet mass influences the effects of dipeptidyl peptidase-IV inhibitor LAF237 on transplantation outcomes in diabetic mice

Background

Previous studies showed inconsistent Results of the effects of dipeptidyl peptidase (DPP)-IV inhibitors on syngeneic mouse islet transplantation. We hypothesized that the implanted islet numbers are critical for the effects of DPP-IV inhibitors on the outcomes of transplantation.

Methods

One hundred and fifty or three hundred islets were syngeneically transplanted under the renal capsule of each streptozocin-diabetic C57BL/6 mouse and recipients were then treated without or with LAF237 (10 mg/kg/day, po) for 6 weeks. After transplantation, recipients’ blood glucose, body weight and intraperitoneal glucose tolerance test (IPGTT) were followed-up periodically. The graft was removed for the measurement of β-cell mass at 6 weeks.

Results

In recipients with 150 islets, it was not significantly different between the LAF237- treated group (n = 14) and control group (n = 14) in terms of the blood glucose, body weight, glucose tolerance at 2, 4 and 6 weeks or the graft β-cell mass at 6 weeks. In contrast, in recipients with 300 islets, the LAF237-treated group (n = 24) did have a lower area under the curve of the IPGTT at 4 weeks (p = 0.0237) and 6 weeks (p = 0.0113) as well as more graft β-cell mass at 6 weeks (0.655 ± 0.008 mg vs. 0.435 ± 0.006 mg, p = 0.0463) than controls (n = 24).

Conclusions

Our findings revealed 6-week treatment of LAF237 improves glucose tolerance and increases graft β-cell mass in diabetic mice transplanted with a sufficient number but not a marginal number of islets. These indicate that the effects of DPP-IV inhibitors are influenced by the implanted islet mass.

Prevention of Type 1 Diabetes: Past Experiences and Future Opportunities

Type 1 diabetes (T1D) results from autoimmune destruction of insulin-producing beta-cells in the pancreas, caused by the interplay of genetic and environmental factors. Despite the introduction of advanced technologies for diabetes management, most patients fail to achieve target glycemic control, and T1D still has a high burden of long-term end-organ complications. Over several decades, multiple clinical trials have attempted to find prevention for T1D in at-risk individuals or to stabilize, ultimately reverse, the disease in those with T1D. To date, T1D remains yet incurable condition; however, recently improved understanding of the natural history of the disease may lead to new strategies to preserve or improve beta-cell function in those at increased risk and T1D patients. This publication aims to provide an overview of past experiences and recent findings in the prevention of T1D.

Latest Evidence on Sulfonylureas: What's New?

This review addresses the question of the cardiovascular (CV) safety of sulfonylureas (SUs) in patients with type 2 diabetes mellitus (T2DM) when directly tested against comparator agents in CV outcome trials. Presented at a recent symposium entitled "SUs in the treatment of T2DM: a fresh look and new insights" held on Wednesday September 18, 2019 during the 55th Annual Meeting of the European Association for the Study of Diabetes (EASD) in Barcelona Spain, this review discusses the initial evidence that sparked concerns over the CV safety of SUs as well as more recent findings from large studies of SUs (i.e. ADVANCE, TOSCA.IT and CAROLINA trials), highlighting the differences in CV and hypoglycaemia risks among the various SUs. Finally, the impact of glycaemic control on CV outcomes is also discussed, where the data suggest that the recent positive CV outcomes with some antihyperglycaemic agents may have been driven in part by improved glycaemic control.

Metformin Delays the Development of Atherosclerosis in Type 1 Diabetes Mellitus via the Methylglyoxal Pathway

INTRODUCTION

The aim of our study was to determine the effect of metformin administration on juvenile type 1 diabetes mellitus and atherosclerosis in apolipoprotein E null (ApoE^-/-) mice and to explore the mechanism involved.

METHODS

Eighteen male ApoE^-/- mice were injected with streptozotocin to induce diabetes (diabetic group) and 18 mice who received no streptozotocin injection were assigned to the control (non-diabetic) group. Six mice in each group were then orally administered metformin, simvastatin, or vehicle, respectively, following which the mice were euthanized and tissue samples collected.

RESULTS

Fasting plasma glucose, low-density lipoprotein-cholesterol, and triglyceride concentrations were significantly higher in the three diabetic groups than in the three non-diabetic groups. Plasma N^∈-(carboxymethyl)lysine and N^∈-(carboxyethyl)lysine concentrations were higher in the diabetic mice than in the non-diabetic mice, but metformin treatment reduced these concentrations more effectively than simvastatin. All three diabetic groups demonstrated obvious arterial plaques, but these were largest in the vehicle-treated diabetic group. The expression of extracellular nitric oxide synthase was highest in the simvastatin-treated non-diabetic group, and in diabetic mice it was higher in the simvastatin-treated group than in the other two groups. No significant expression of AMP-activated protein kinase (AMPK) was measured in the three diabetic groups, but a low level of AMPK expression was detected in the non-diabetic groups.

CONCLUSIONS

Metformin can limit the development of atherosclerosis secondary to diabetes in young diabetic mice. A possible mechanism is the removal of methylglyoxal, thereby reducing the formation of advanced glycation endproducts, rather than by lowering the blood glucose level.

FUNDING

This work was supported by the National Natural Science Foundation of China (81901106) and Jinan clinical medical science and technology innovation plan (201907002).

Dipeptidyl peptidase 4 inhibitors and their potential immune modulatory functions

Dipeptidyl peptidase 4 (DPP4) inhibitors (DPP4is) are oral anti-diabetic drugs (OADs) for the treatment of type 2 diabetes mellitus (T2DM) through inhibiting the degradation of incretin peptides. Numerous investigations have been focused on the effects of DPP4is on glucose homeostasis. However, there are limited evidences demonstrating their Potential modulatory functions in the immune system. DPP4, originally known as the lymphocyte cell surface protein CD26, is widely expressed in many types of immune cells including CD4(+) and CD8(+) T cells, B cells, NK cells, dendritic cells, and macrophages; and regulate the functions of these cells. In addition, DPP4 is capable of modulating plenty of cytokines, chemokines and peptide hormones. Accordingly, DPP4/CD26 is speculated to be involved in various immune/inflammatory diseases and DPP4is may become a new drug class applied in these diseases. This review focuses on the regulatory effects of DPP4is on immune functions and their possible underlying mechanisms. Further clinical studies will be necessitated to fully evaluate the administration of DPP4is in diabetic patients with or without immune diseases.

A Low-Carbohydrate Diet Improves Glucose Metabolism in Lean Insulinopenic Akita Mice Along With Sodium-Glucose Cotransporter 2 Inhibitor

OBJECTIVE

A low-carbohydrate diet (LC) can be beneficial to obese subjects with type2 diabetes mellitus (T2DM). Sodium-glucose cotransporter 2 inhibitor (SGLT2i) presents prompt glucose-lowering effects in subjects with T2DM. We investigated how LC and SGLT2i could similarly or differently influence on the metabolic changes, including glucose, lipid, and ketone metabolism in lean insulinopenic Akita mice. We also examined the impacts of the combination.

METHODS

Male Akita mice were fed ad libitum normal-carbohydrate diet (NC) as a control or low-carbohydrate diet (LC) as an intervention for 8 weeks with or without SGLT2i treatment. Body weight and casual bold glucose levels were monitored during the study, in addition to measuring TG, NEFA, and ketone levels. We quantified gene expressions involved in gluconeogenesis, lipid metabolism and ketogenesis in the liver and the kidney. We also investigated the immunostaining analysis of pancreatic islets to assess the effect of islet protection.

RESULTS

Both LC and SGLT2i treatment reduced chronic hyperglycemia. Moreover, the combination therapy additionally ameliorated glycemic levels and preserved the islet morphology in part. LC but not SGLT2i increased body weight accompanied by epididymal fat accumulation. In contrast, SGLT2i, not LC potentiated four-fold ketone production with higher ketogenic gene expression, in comparison with the non-treated Akita mice. Besides, the combination did not enhance further ketone production compared to the SGLT2i alone.

CONCLUSIONS

Our results indicated that both LC and SGLT2i reduced chronic hyperglycemia, and the combination presented synergistic favorable effects concomitantly with amelioration of islet morphology, while the combination did not enhance further ketosis in Akita mice.

Ameliorative Effects of Probiotic Lactobacillus paracasei NL41 on Insulin Sensitivity, Oxidative Stress, and Beta-Cell Function in a Type 2 Diabetes Mellitus Rat Model

SCOPE

The present study aims to assess the antidiabetic effect of Lactobacillus paracasei strain NL41 and its potential mechanisms in rats with type 2 diabetes mellitus (T2DM) induced by a high-fat diet and low-dose streptozotocin administration (HFD/STZ).

METHODS AND RESULTS

Eighteen Sprague-Dawley (SD) rats are randomly assigned to three groups: one control, one HFD/STZ model, and one HFD/STZ-Lactobacillus protection group with administration of strain NL41 for 12 weeks. Blood is collected for biochemical parameters analysis and tissue samples for histological analysis. Treatment with strain NL41 results in excellent blood glucose regulation and significantly decreases insulin resistance, and HbA1c, glucagon, and leptin levels, accompanied by remarkable improvement of dyslipidemia and oxidative stress status in the animals. Islets of Langerhans, liver, and kidney are significantly protected in the NL41-treated rats compared to the HFD/STZ-T2DM model rats. Histochemistry shows that strain NL41 inhibits beta-cell loss and alpha-cell expansion, indicating pancreatic islets as the targeted tissues for the primary ameliorative effect of the probiotic strain on HFD/STZ-T2DM rats. Crosstalk between the gut-liver and liver-pancreas endocrine axes is discussed.

CONCLUSION

Probiotic strain NL41 prevents HFD/STZ-T2DM by decreasing insulin resistance and oxidative stress status, and protecting beta-cell function.

Leucine-glycine and carnosine dipeptides prevent diabetes induced by multiple low-doses of streptozotocin in an experimental model of adult mice

AIMS/INTRODUCTION

Peptides are considered to be quasi-hormones and effective molecules for regulation of the cells function and prevention of metabolic disorders. Di- and tripeptides gastrointestinal absorption ability have been proposed to prevent diabetes progression.

MATERIALS AND METHODS

Small peptides with different sequences of specific amino acids were synthesized based on a solid phase peptide synthesis protocol, and carnosine (A) and glutathione were examined for the prevention of diabetes induced by multiple low-doses of streptozotocin in mice.

RESULTS

The peptides A, Leu-Gly (D) and Pro-Pro showed preventive effects on blood glucose elevation and impairment of the signaling and performance of β-cells. The β-cell function assessed by immunofluorescence and blood glucose level in mice exposed to diabetes treated by the peptides A and D was similar to the normal mice. The peptide D prevented bodyweight loss caused by diabetes induction. The use of D and A peptides dramatically prevented the incidence of disruption in β-cells signaling by maintaining the natural balance of intracellular Akt-2 and cyclic adenosine monophosphate.

CONCLUSIONS

The results proved that peptide D (Leu-Gly), named Hannaneh, inhibits the bodyweight loss caused by diabetes induction. The Hannaneh and carnosine dipeptides, with preservation of normal β-cell signaling and anti dipeptidyl peptidase-4 activity, prevented blood glucose increases in mice at risk of diabetes. These dipeptides might be regarded as the pharmaceutical agents for the prevention of diabetes.

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.

Pancreatic alpha-cell mass in the early-onset and advanced stage of a mouse model of experimental autoimmune diabetes

Most studies in type 1 diabetes (T1D) have focused on the loss of the pancreatic beta-cell population. However, despite the involvement of the alpha-cell in the aetiology and complications of T1D, little is known about the regulation of the pancreatic alpha-cell mass in this disease. The need for a better understanding of this process is further emphasized by recent findings suggesting that alpha-cells may constitute a potential reservoir for beta-cell regeneration. In this study, we characterized the pancreatic alpha-cell mass and its regulatory processes in the transgenic RIP-B7.1 mice model of experimental autoimmune diabetes (EAD). Diabetic mice presented insulitis, hyperglycaemia, hypoinsulinemia and hyperglucagonemia along with lower pancreatic insulin content. While alpha-cell mass and pancreatic glucagon content were preserved at the early-onset of EAD, both parameters were reduced in the advanced phase. At both stages, alpha-cell size, proliferation and ductal neogenesis were up-regulated, whereas apoptosis was almost negligible. Interestingly, we found an increase in the proportion of glucagon-containing cells positive for insulin or the beta-cell transcription factor PDX1. Our findings suggest that pancreatic alpha-cell renewal mechanisms are boosted during the natural course of EAD, possibly as an attempt to maintain the alpha-cell population and/or to increase beta-cell regeneration via alpha-cell transdifferentiation.

Alogliptin improves survival and health of mice on a high-fat diet

Alogliptin is a commonly prescribed drug treating patients with type 2 diabetes. Here, we show that long‐term intervention with alogliptin (0.03% w/w in diet) improves survival and health of mice on a high‐fat diet. Alogliptin intervention takes beneficial effects associated with longevity, including increased insulin sensitivity, attenuated functionality decline, decreased organ pathology, preserved mitochondrial function, and reduced oxidative stress. Autophagy activation is proposed as an underlying mechanism of these beneficial effects. We conclude that alogliptin intervention could be considered as a potential strategy for extending lifespan and healthspan in obesity and overweight.

Lymphocyte-Derived Exosomal MicroRNAs Promote Pancreatic β Cell Death and May Contribute to Type 1 Diabetes Development

Type 1 diabetes is an autoimmune disease initiated by the invasion of pancreatic islets by immune cells that selectively kill the β cells. We found that rodent and human T lymphocytes release exosomes containing the microRNAs (miRNAs) miR-142-3p, miR-142-5p, and miR-155, which can be transferred in active form to β cells favoring apoptosis. Inactivation of these miRNAs in recipient β cells prevents exosome-mediated apoptosis and protects non-obese diabetic (NOD) mice from diabetes development. Islets from protected NOD mice display higher insulin levels, lower insulitis scores, and reduced inflammation. Looking at the mechanisms underlying exosome action, we found that T lymphocyte exosomes trigger apoptosis and the expression of genes involved in chemokine signaling, including Ccl2, Ccl7, and Cxcl10, exclusively in β cells. The induction of these genes may promote the recruitment of immune cells and exacerbate β cell death during the autoimmune attack. Our data point to exosomal-miRNA transfer as a communication mode between immune and insulin-secreting cells.

Pharmacology of dipeptidyl peptidase-4 inhibitors and its use in the management of metabolic syndrome: a comprehensive review on drug repositioning

OBJECTIVES

Despite advances in our understanding of metabolic syndrome (MetS) and the treatment of each of its components separately, currently there is no single therapy approved to manage it as a single condition. Since multi-drug treatment increases drug interactions, decreases patient compliance and increases health costs, it is important to introduce single therapies that improve all of the MetS components.

EVIDENCE ACQUISITION

We conducted a PubMed, Scopus, Google Scholar, Web of Science, US FDA, utdo.ir and clinicaltrial.gov search, gathered the most relevant preclinical and clinical studies that have been published since 2010, and discussed the beneficial effects of dipeptidyl peptidase (DPP)-4 inhibitors to prevent and treat different constituent of the MetS as a single therapy. Furthermore, the pharmacology of DPP-4 inhibitors, focusing on pharmacodynamics, pharmacokinetics, drug interactions and their side effects are also reviewed.

RESULTS

DPP-4 inhibitors or gliptins are a new class of oral anti-diabetic drugs that seem safe drugs with no severe side effects, commonly GI disturbance, infection and inflammatory bowel disease. They increase mass and function of pancreatic β-cells, and insulin sensitivity in liver, muscle and adipose tissue. It has been noted that gliptin therapy decreases dyslipidemia. DPP-4 inhibitors increase fatty oxidation, and cholesterol efflux, and decrease hepatic triglyceride synthase and de novo lipogenesis. They delay gastric emptying time and lead to satiety. Besides, gliptin therapy has anti-inflammatory and anti-atherogenic impacts, and improves endothelial function and reduces vascular stiffness.

CONCLUSION

The gathered data prove the efficacy of DPP-4 inhibitors in managing MetS in some levels beyond anti-diabetic effects. This review could be a lead for designing new DPP-4 inhibitors with greatest effects on MetS in future. Introducing drugs with polypharmacologic effects could increase the patient's compliance and decrease the health cost that there is not in multi-drug therapy. Graphical abstract ᅟ.

A Novel Dipeptidyl Peptidase IV Inhibitory Tea Peptide Improves Pancreatic β-Cell Function and Reduces α-Cell Proliferation in Streptozotocin-Induced Diabetic Mice

Dipeptidyl peptidase IV (DPP-IV) inhibitors occupy a growing place in the drugs used for the management of type 2 diabetes. Recently, food components, including food-derived bioactive peptides, have been suggested as sources of DPP-IV inhibitors without side effects. Chinese black tea is a traditional health beverage, and it was used for finding DPP-IV inhibitory peptides in this study. The ultra-filtrated fractions isolated from the aqueous extracts of black tea revealed DPP-IV inhibitory activity in vitro. Four peptides under 1 kDa were identified by SDS-PAGE and LC-MS/MS (Liquid Chromatography-Mass Spectrometry-Mass Spectrometry) from the ultra-filtrate. The peptide II (sequence: AGFAGDDAPR), with a molecular mass of 976 Da, showed the greatest DPP-IV inhibitory activity (in vitro) among the four peptides. After administration of peptide II (400 mg/day) for 57 days to streptozotocin (STZ)-induced hyperglycemic mice, the concentration of glucagon-like peptide-1 (GLP-1) in the blood increased from 9.85 ± 1.96 pmol/L to 19.22 ± 6.79 pmol/L, and the insulin level was increased 4.3-fold compared to that in STZ control mice. Immunohistochemistry revealed the improved function of pancreatic beta-cells and suppressed proliferation of pancreatic alpha-cells. This study provides new insight into the use of black tea as a potential resource of food-derived DPP-IV inhibitory peptides for the management of type 2 diabetes.

NLRP3 inflammasome promotes diabetes-induced endothelial inflammation and atherosclerosis

BACKGROUND

NLRP3 inflammasome can be activated by high glucose and links inflammation and metabolic disease. This study aimed to investigate the role of NLRP3 inflammasome in hyperglycemia-induced endothelial inflammation and diabetic atherosclerosis.

METHODS

NLRP3 levels in peripheral blood mononuclear cell (PBMC) and plasma IL-1β level were measured in diabetes patients. The activation of NLPR3 was detected in diabetic ApoE-/- mice and human umbilical vein endothelial cells (HUVECs).

RESULTS

Compared with healthy controls, NLRP3 expression levels in PBMC and plasma IL-1β level were significantly higher in diabetes patients but considerably decreased after lifestyle interventions and medicine. Moreover, carotid atherosclerosis was significantly related to plasma IL-1β level in diabetes patients. In diabetic atherosclerosis mouse model, NLRP3 knockdown suppressed NLRP3 inflammasome activation, inhibited the expression of adhesion molecules ICAM-1 and VCAM-1 in intima, reduced atherosclerosis and stabilized atherosclerotic plaque. In vitro, the expression of NLRP3 inflammasome components and the secretion of IL-1β were augmented by high glucose in HUVECs. Moreover, either high glucose or IL-1β promoted the expression of adhesion molecules, which were suppressed by NLRP3 knockdown or IL-1β receptor antagonist.

CONCLUSION

These findings provide novel insights into pathological mechanisms of diabetic atherosclerosis and have potential therapeutic implications for cardiovascular complications in diabetes.

Prion protein modulates glucose homeostasis by altering intracellular iron

The prion protein (PrP^C), a mainly neuronal protein, is known to modulate glucose homeostasis in mouse models. We explored the underlying mechanism in mouse models and the human pancreatic β-cell line 1.1B4. We report expression of PrP^C on mouse pancreatic β-cells, where it promoted uptake of iron through divalent-metal-transporters. Accordingly, pancreatic iron stores in PrP knockout mice (PrP^-/-) were significantly lower than wild type (PrP^+/+) controls. Silencing of PrP^C in 1.1B4 cells resulted in significant depletion of intracellular (IC) iron, and remarkably, upregulation of glucose transporter GLUT2 and insulin. Iron overloading, on the other hand, resulted in downregulation of GLUT2 and insulin in a PrP^C-dependent manner. Similar observations were noted in the brain, liver, and neuroretina of iron overloaded PrP^+/+ but not PrP^-/- mice, indicating PrP^C-mediated modulation of insulin and glucose homeostasis through iron. Peripheral challenge with glucose and insulin revealed blunting of the response in iron-overloaded PrP^+/+ relative to PrP^-/- mice, suggesting that PrP^C-mediated modulation of IC iron influences both secretion and sensitivity of peripheral organs to insulin. These observations have implications for Alzheimer's disease and diabetic retinopathy, known complications of type-2-diabetes associated with brain and ocular iron-dyshomeostasis.

Practical strategies for improving outcomes in T2DM: The potential role of pioglitazone and DPP4 inhibitors

T2DM is a complex disease underlined by multiple pathogenic defects responsible for the development and progression of hyperglycaemia. Each of these factors can now be tackled in a more targeted manner thanks to glucose-lowering drugs that have been made available in the past 2 to 3 decades. Recognition of the multiplicity of the mechanisms underlying hyperglycaemia calls for treatments that address more than 1 of these mechanisms, with more emphasis placed on the earlier use of combination therapies. Although chronic hyperglycaemia contributes to and amplifies cardiovascular risk, several trials have failed to show a marked effect from intensive glycaemic control. During the past 10 years, the effect of specific glucose-lowering agents on cardiovascular risk has been explored with dedicated trials. Overall, the cardiovascular safety of the new glucose-lowering agents has been proven with some of the trials summarized in this review, showing significant reduction of cardiovascular risk. Against this background, pioglitazone, in addition to exerting a sustained glucose-lowering effect, also has ancillary metabolic actions of potential interest in addressing the cardiovascular risk of T2DM, such as preservation of beta-cell mass and function. As such, it seems a logical agent to combine with other oral anti-hyperglycaemic agents, including dipeptidyl peptidase-4 inhibitors (DPP4i). DPP4i, which may also have a potential to preserve beta-cell function, is available as a fixed-dose combination with pioglitazone, and could, potentially, attenuate some of the side effects of pioglitazone, particularly if a lower dose of the thiazolidinedione is used. This review critically discusses the potential for early combination of pioglitazone and DPP4i.

Subchronic exposure to acrylamide leads to pancreatic islet remodeling determined by alpha cell expansion and beta cell mass reduction in adult rats

Acrylamide (AA) is a toxic substance, used to synthesize polymers for industrial and laboratory processes. Also, AA is a food contaminant formed during the high temperature preparation of carbohydrate-rich food. The main subject of this study was to examine effects of subchronic AA treatment on the islets of Langerhans of adult rats. Adult male Wistar rats were orally treated with 25 or 50 mg/kg bw of AA for 3 weeks. Qualitative and quantitative immunohistochemical evaluation of glucagon and insulin expression and stereological analyses of pancreatic alpha and beta cells were performed. Serum insulin and glucose levels were measured. Analysis of glucagon-immunostained sections revealed a dose-dependent increase of intensity of glucagon immunopositive signal, alpha cell surface and numerical densities, volume density of alpha cell nuclei and nucleocytoplasmic ratio in AA-treated groups compared to the control. In insulin-immunolabeled pancreatic sections in AA-treated animals was observed decrease of intensity of insulin immunopositive signal, beta cell surface, numerical and volume densities and volume density of beta cell cytoplasm. Serum insulin and glucose concentrations remained unchanged after both AA treatments. The number of islets of Langerhans was not affected by AA treatment. Our results suggest that AA subchronic treatment of adult rats leads to remodeling of islet of Langerhans characterized by alpha cell expansion and beta cell mass reduction.

Tissue expression of DPP-IV in obesity-diabetes and modulatory effects on peptide regulation of insulin secretion

Dipeptidyl peptidase type 4 (DPP-4) inhibitors represent an important class of glucose-lowering drug for type 2 diabetes. DPP-4 enzyme activity has been observed to be significantly altered in type 2 diabetes. Here, the role of DPP-4 was examined in a high fat fed (HFF) mouse model of insulin resistance. HFF mice had an increased bodyweight (p < .01), were hyperglycaemic (p < .01) and hyperinsulinaemic (p < .05). Compared to normal diet, HFF mice exhibited increased plasma DPP-4 activity (p < .01). Tissue distribution patterns in lean and HFF mice demonstrated highest levels of DPP-4 activity in lung (20-26 μmol/min/mg protein) and small intestine (13-14 μmol/min/mg protein), and lowest activity in the spleen (3.8 μmol/min/mg protein). Modulation of DPP-4 activity by high fat feeding was observed in several tissues with increases in the lung (p < .05), liver (p < .05), kidney (p < .05) and pancreas (p < .05). With a high fat diet, DPP-4 gene expression was upregulated in the liver (p < .001) and downregulated in the pancreas (p < 0.001) and small intestine (p < .001). Immunohistochemical analysis revealed increased DPP-4 immunostaining localised primarily in the pancreatic islets of HFF mice (p < .01) with no change in islet GLP-1 expression. Treatment of HFF mice with metformin for 21-days resulted in inhibition of circulating DPP-4 activity (p < .05), decreased blood glucose (p < .05) and increased GLP-1 gene expression (p < .001). These data indicate that DPP-4 is modulated in a tissue specific manner and is dependent on physiological conditions such as hyperglycaemia and insulin resistance, suggesting a significant role in disorders such as diabetes.

Effects of subchronic acrylamide treatment on the endocrine pancreas of juvenile male Wistar rats

Acrylamide (AA) is a well-known industrial monomer with carcinogenic, mutagenic, neurotoxic and endocrine disruptive effects on living organisms. AA has been the subject of renewed interest owing to its presence in various food products. We investigated the potential adverse effects of oral AA treatment on the endocrine pancreas of juvenile rats using histochemical, immunohistochemical, stereological and biochemical methods. Thirty juvenile male Wistar rats were divided into one control and two AA treatment groups: one treated with 25 mg/kg AA and the other treated with 50 mg/kg AA for 21 days. We found a significant decrease in β-cell mass. The significant decrease in β-cell optical density and unchanged blood glucose levels indicate that normoglycemia in AA treated rats may result from intensive exocytosis of insulin-containing secretory granules. By contrast with β-cells, we observed increased α-cell mass. The slight increase in α-cell cytoplasmic volume suggests retention of glucagon in α-cells, which is consistent with the significant increase in α-cell optical density for AA treated animals. The number of islets of Langerhans did not change significantly in AA treated groups. Our findings suggest that AA treatment causes decreased β-cell mass and moderate α-cell mass increase in the islets of Langerhans of juvenile male Wistar rats.

The Myokine Irisin Is Released in Response to Saturated Fatty Acids and Promotes Pancreatic β-Cell Survival and Insulin Secretion

This study explored the role of irisin as a new pancreatic β-cell secretagogue and survival factor and its potential role in the communication between skeletal muscle and pancreatic β-cells under lipotoxic conditions. Recombinant irisin stimulated insulin biosynthesis and glucose-stimulated insulin secretion (GSIS) in a PKA-dependent manner and prevented saturated fatty acid-induced apoptosis in human and rat pancreatic β-cells, as well as in human and murine pancreatic islets, via AKT/BCL2 signaling. Treatment of myotubes with 0.5 mmol/L palmitate for 4 h, but not with oleate, promoted an increase in irisin release in the culture medium. Moreover, increased serum levels of irisin were observed in mice fed with a high-fat diet. Mouse serum rich in irisin and the conditioned medium from myotubes exposed to palmitate for 4 h significantly reduced apoptosis of murine pancreatic islets and insulin-secreting INS-1E cells, respectively, and this was abrogated in the presence of an irisin-neutralizing antibody. Finally, in vivo administration of irisin improved GSIS and increased β-cell proliferation. In conclusion, irisin can promote β-cell survival and enhance GSIS and may thus participate in the communication between skeletal muscle and β-cells under conditions of excess saturated fatty acids.

Renoprotective Effects of the Dipeptidyl Peptidase-4 Inhibitor Sitagliptin: A Review in Type 2 Diabetes

Diabetic nephropathy (DN) is now the single commonest cause of end-stage renal disease (ESRD) worldwide and one of the main causes of death in diabetic patients. It is also acknowledged as an independent risk factor for cardiovascular disease (CVD). Since sitagliptin was approved, many studies have been carried out revealing its ability to not only improve metabolic control but also ameliorate dysfunction in various diabetes-targeted organs, especially the kidney, due to putative underlying cytoprotective properties, namely, its antiapoptotic, antioxidant, anti-inflammatory, and antifibrotic properties. Despite overall recommendations, many patients spend a long time well outside the recommended glycaemic range and, therefore, have an increased risk for developing micro- and macrovascular complications. Currently, it is becoming clearer that type 2 diabetes mellitus (T2DM) management must envision not only the improvement in glycaemic control but also, and particularly, the prevention of pancreatic deterioration and the evolution of complications, such as DN. This review aims to provide an overview of the current knowledge in the field of renoprotective actions of sitagliptin, namely, improvement in diabetic dysmetabolism, hemodynamic factors, renal function, diabetic kidney lesions, and cytoprotective properties.

GDF11 Attenuates Development of Type 2 Diabetes via Improvement of Islet β-Cell Function and Survival

Growth differentiation factor 11 (GDF11) has been implicated in the regulation of islet development and a variety of aging conditions, but little is known about the physiological functions of GDF11 in adult pancreatic islets. Here, we showed that systematic replenishment of GDF11 not only preserved insulin secretion but also improved the survival and morphology of β-cells and improved glucose metabolism in both nongenetic and genetic mouse models of type 2 diabetes (T2D). Conversely, anti-GDF11 monoclonal antibody treatment caused β-cell failure and lethal T2D. In vitro treatment of isolated murine islets and MIN6 cells with recombinant GDF11 attenuated glucotoxicity-induced β-cell dysfunction and apoptosis. Mechanistically, the GDF11-mediated protective effects could be attributed to the activation of transforming growth factor-β/Smad2 and phosphatidylinositol-4,5-bisphosphate 3-kinase-AKT-FoxO1 signaling. These findings suggest that GDF11 repletion may improve β-cell function and mass and thus may lead to a new therapeutic approach for T2D.

Combined Oral Administration of GABA and DPP-4 Inhibitor Prevents Beta Cell Damage and Promotes Beta Cell Regeneration in Mice

γ-aminobutyric acid (GABA) or glucagon-like peptide-1 based drugs, such as sitagliptin (a dipeptidyl peptidase-4 inhibitor), were shown to induce beta cell regenerative effects in various diabetic mouse models. We propose that their combined administration can bring forth an additive therapeutic effect. We tested this hypothesis in a multiple low-dose streptozotocin (STZ)-induced beta cell injury mouse model (MDSD). Male C57BL/6J mice were assigned randomly into four groups: non-treatment diabetic control, GABA, sitagliptin, or GABA plus sitagliptin. Oral drug administration was initiated 1 week before STZ injection and maintained for 6 weeks. GABA or sitagliptin administration decreased ambient blood glucose levels and improved the glucose excursion rate. This was associated with elevated plasma insulin and reduced plasma glucagon levels. Importantly, combined use of GABA and sitagliptin significantly enhanced these effects as compared with each of the monotherapies. An additive effect on reducing water consumption was also observed. Immunohistochemical analyses revealed that combined GABA and sitagliptin therapy was superior in increasing beta cell mass, associated with increased small-size islet numbers, Ki67⁺ and PDX-1⁺ beta cell counts; and reduced Tunel⁺ beta cell counts. Thus, beta cell proliferation was increased, whereas apoptosis was reduced. We also noticed a suppressive effect of GABA or sitagliptin on alpha cell mass, which was not significantly altered by combining the two agents. Although either GABA or sitagliptin administration delays the onset of MDSD, our study indicates that combined use of them produces superior therapeutic outcomes. This is likely due to an amelioration of beta cell proliferation and a decrease of beta cell apoptosis.

The regulatory role of DPP4 in atherosclerotic disease

The increasing prevalence of atherosclerosis has become a worldwide health concern. Although significant progress has been made in the understanding of atherosclerosis pathogenesis, the underlying mechanisms are not fully understood. Recent studies suggest dipeptidyl peptidase-4 (DPP4), a regulator of inflammation and metabolism, may be involved in the development of atherosclerotic diseases. There has been increasing clinical and pre-clinical evidence showing DPP4-incretin axis is involved in cardiovascular disease. Although the cardiovascular outcome of DPP4 inhibition or incretin analogues has been or being evaluated by several large scale clinical trials, the exact role of DPP4 in atherosclerotic diseases is not completely understood. In the current review, we will summarize the recent advances in direct and indirect regulatory role of DPP4 in atherosclerosis.

Inhibition of DPP-4 Activity and Neuronal Atrophy with Genistein Attenuates Neurological Deficits Induced by Transient Global Cerebral Ischemia and Reperfusion in Streptozotocin-Induced Diabetic Mice

Genistein, an isoflavonoid phytoestrogen, has been known for its potential pharmacological properties especially for neuroprotection and treating diabetes. The present study aims to determine the neuroprotective efficacy of genistein against global cerebral ischemia-reperfusion-induced neuronal injury in streptozotocin-induced diabetic mice and explore the underlying mechanisms. Streptozotocin-induced diabetic mice were subjected to transient cerebral ischemia by occluding both common carotid arteries for 30 min followed by 24 h reperfusion to induce neuronal injury. Effect of genistein (2.5, 5.0, and 10.0 mg/kg, i.p., o.d.) treatment on ischemia-reperfusion-induced neuronal injury in diabetic mice was evaluated in terms of cerebral infarct size, oxidative damage, mitochondrial activity in terms of neuronal apoptosis and cellular viability, dipeptidyl peptidase-4 activity and active glucagon-like peptide-1 concentration, and neurological functions measured as short-term memory and motor performance. Genistein administration following transient cerebral ischemia significantly (p ˂ 0.0001) counteracted cognitive impairment and re-established (p ˂ 0.001) motor performance in diabetic mice. Ischemia-reperfusion increased the infarct size, genistein administration prevented the increase in cerebral infarct size (p ˂ 0.0001) and significantly suppressed (p ˂ 0.001) the increase in cerebral oxidative stress in transient cerebral ischemia-reperfusion subjected diabetic mice. Genistein treatment significantly (p ˂ 0.001) reduced neuronal apoptosis and increased cellular viability (p ˂ 0.0001), almost completely suppressed (p ˂ 0.0001) the circulating dipeptidyl peptidase-4 activity, and enhanced (p ˂ 0.0001) glucagon-like peptide-1 concentration in diabetic mice with cerebral ischemia-reperfusion. This study suggests that genistein has potent neuroprotective activity against global cerebral ischemia-reperfusion-induced neuronal injury and consequent neurological deficits in streptozotocin-induced diabetic mice.

Efficacy and Safety of the Dipeptidyl Peptidase-4 Inhibitor Sitagliptin on Atherosclerosis, β-Cell Function, and Glycemic Control in Japanese Patients with Type 2 Diabetes Mellitus Who are Treatment Naïve or Poorly Responsive to Antidiabetes Agents: A Multicenter, Prospective Observational, Uncontrolled Study

BACKGROUND

Sitagliptin, a dipeptidyl peptidase-4 inhibitor, is widely used in patients with type 2 diabetes. However, the pleiotropic effects of sitagliptin is not well understood.

OBJECTIVE

To assess the clinical efficacy and safety of sitagliptin on atherosclerosis, β-cell function, and glycemic control in Japanese patients with type 2 diabetes.

METHODS

A prospective observational study of 270 patients with type 2 diabetes mellitus was carried out. Patients (aged 64.3 [12.4] years, body mas index 25.2 [4.3]) with glycated hemoglobin >6.9% (52 mmol/mol) or fasting plasma glucose >130 mg/dL were treated with sitagliptin for 12 months. The primary end point was glycated hemoglobin level changes from baseline to 3 months. The secondary end points included changes in several biomarkers related to inflammation and β-cell function from baseline to 3 months, as well as changes in glycated hemoglobin level from baseline to 12 months.

RESULTS

Glycated hemoglobin levels were significantly lower in patients treated with sitagliptin for 3 months than at baseline (8.1% [1.4%]-7.3% [1.2%]) (65 [16.9]-56 [13.1] mmol/mol]) (P < 0.0001), which continued after 12 months (7.4% [1.3%]) (56 [15.2] mmol/mol) (P < 0.0001). In addition, a marker of vascular-specific inflammation, pentraxin-3, and a marker of β-cell function (proinsulin/insulin ratio), respectively, were lower after treatment with sitagliptin for 3 months than at baseline (1.88 [0.78]-1.65 [0.63] ng/mL [P = 0.0038] and 0.20 [0.14]-0.17 [0.11] [P = 0.01], respectively). On the other hand, a biomarker reflecting whole body inflammation; that is, high-sensitivity C-reactive protein level, was unchanged. Adverse events occurred in 14 patients (5.18%).

CONCLUSIONS

Sitagliptin may have beneficial effects on vascular inflammation and β-cell function in Japanese patients with type 2 diabetes. Pentraxin-3 may be an early predictive marker for detecting the antiatherosclerotic effects of dipeptidyl peptidase-4.

Saxagliptin Induces β-Cell Proliferation through Increasing Stromal Cell-Derived Factor-1α In Vivo and In Vitro

Dipeptidyl peptidase-4 inhibitors, such as saxagliptin, have been reported to have beneficial effects on β-cell function, but the specific underlying mechanism remains unclear. Stromal cell-derived factor-1α (SDF-1α), a chemokine produced in multiple organs, has been considered as a crucial regulator in promoting β-cell survival. Here, we speculate that SDF-1α might mediate the effect of saxagliptin on improving β-cell function. After 12-week saxagliptin treatment in high-fat diet/streptozotocin-induced diabetic rats, significant improvement in pancreas insulin secretion capacity evaluated by hyperglycemia clamp and increased β-cell to α-cell areas ratio were observed. Saxagliptin significantly induced β-cell proliferation and upregulated the expression of proliferation-related factors including c-myc and cyclind D1 determined with western blotting from the isolated islets. The expression/activity of DPP-4 was significantly reduced and paralleled with the restoration of SDF-1α levels in the saxagliptin-treated diabetic rats, subsequently the key WNT-signaling regulators, β-catenin, and AKT were activated. However, the effect of saxagliptin inducing β-cell proliferation was attenuated when we silenced the SDF-1α receptor (CXCR4) with RNAi in INS cell lines. Collectively, our data indicate that SDF-1α mediates the protective effect of saxagliptin on β-cell proliferation, suggesting that DPP-4 inhibitors have the potential role on delaying β-cell failure and SDF-1α could be a therapeutic target of β-cell regeneration.

TSC1-mTOR signaling determines the differentiation of islet cells

Neurogenin3-driven deletion of tuberous sclerosis complex 1 (Tsc1) activated mechanistic target of rapamycin complex 1 (mTORC1) measured by the upregulation of mTOR and S6 phosphorylation in islet cells. Neurogenin3-Tsc1-/- mice demonstrated a significant increase in average islet size and mean area of individual islet cell. Insulin mRNA and plasma insulin levels increased significantly after weaning. Glucagon mRNA and plasma levels increased in neonate followed by modest reduction in adult. Somatostatin mRNA and plasma levels markedly increased. Neurogenin3-Tsc1-/- mice fed standard chow demonstrated a significant improvement in glucose tolerance and no alteration in insulin sensitivity. In Neurogenin3-Tsc1-/- mice fed 45% high-fat diets, both glucose tolerance and insulin sensitivity were significantly impaired. Rapamycin reversed the activation of mTORC1, attenuated β cells hypertrophy and abolished the improvement of glucose tolerance. TSC1-mTORC1 signaling plays an important role in the development of pancreatic endocrine cells and in the regulation of glucose metabolism.

Four-year clinical remission of type 1 diabetes mellitus in two patients treated with sitagliptin and vitamin D3

Type 1 diabetes mellitus (T1DM) is a chronic disease characterized by autoimmune destruction of pancreatic beta cells and inadequate insulin production. Remission criteria in T1DM take into account serum levels of C-peptide and glycosylated hemoglobin, as well as the dose of insulin administered to the patient. However, remission of T1DM lasting longer than 1 year is rare. We describe here the cases of two young women who presented with positive glutamic acid decarboxylase (GAD) antibody and classic clinical manifestations of T1DM. Both patients had a prior history of Hashimoto’s thyroiditis. They were initially treated with a basal-bolus regimen of insulin (glargine and lispro/glulisine). Once their blood glucose levels were controlled, they were started on oral sitagliptin 100 mg and vitamin D3 5000 IU daily. After this therapy, both patients achieved clinical diabetes remission for 4 years, along with a decrease in anti-GAD antibody levels. These benefits were probably associated with immunological effects of these medications. Inhibition of dipeptidyl peptidase 4 (DPP-4) in animal models deregulates Th1 immune response, increases secretion of Th2 cytokines, activates CD4⁺CD25⁺FoxP3⁺ regulatory T-cells and prevents IL-17 production. Vitamin D3 also activates CD4⁺CD25⁺FoxP3⁺ regulatory T-cells, and these medications combined can improve the immune response in patients with new-onset T1DM and probably promote sustained clinical remission.

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.

A murine model of type 2 diabetes mellitus developed using a combination of high fat diet and multiple low doses of streptozotocin treatment mimics the metabolic characteristics of type 2 diabetes mellitus in humans

INTRODUCTION

A murine model of type 2 diabetes mellitus was used to compare the antidiabetic effects of the dipeptidyl peptidase-4 (DPP4) inhibitor vildagliptin and biguanide, metformin.

METHODS

Swiss albino mice (n=20 males; n=25 females) were given high fat diet (HFD) ad libitum for 3weeks followed by low dose (40mgkg^-1 body weight, bw daily) of streptozotocin (STZ) intraperitoneally five times from the 22nd day of treatment onwards, with HFD continued up to 26th day. Controls (n=15 males; n=15 females) were fed normal balanced diet without administration of STZ. Successful induction of diabetes mellitus was confirmed by testing for fasting blood glucose, intraperitoneal glucose tolerance and intraperitoneal insulin sensitivity. Diabetic mice were administered vildagliptin (10mgkg^-1 bw daily) and metformin (50mgkg^-1 bw daily) orally for 4weeks. Control, diabetic, vildagliptin and metformin-treated diabetic mice were evaluated for alterations in lipid profile using blood serum and histopathology and oxidative stress using tissues including liver, kidney and heart.

RESULTS

Diabetic mice showed significant alterations in lipid profile, tissue histopathology, impaired glucose tolerance, lower insulin sensitivity and elevated lipid peroxidation and protein carbonylation, with depressed catalase activity, when compared to age and gender-matched controls. Metformin and vildagliptin ameliorated the abovementioned diabetic conditions, with vildagliptin found to be more effective.

DISCUSSION

A murine model developed by the combination of HFD and multiple low dose of STZ mimics the metabolic characteristics of type 2 diabetes mellitus in humans, and may be useful for antidiabetic drug screening.