Effects of saxagliptin and sitagliptin on glycaemic control and pancreatic β-cell mass in a streptozotocin-induced mouse model of type 2 diabetes

A novel combination of sitagliptin and melatonin ameliorates T2D manifestations: studies on experimental diabetic models

INTRODUCTION

Type 2 diabetes (T2D) is an endocrine disorder characterized by hyperglycemia, insulin resistance, dysregulated glucose and lipid metabolism, reduced pancreatic β-cell function and mass, and a reduced incretin effect. Circadian rhythm disruption is associated with increased T2D risk. We have investigated the therapeutic potential of a combination of melatonin (M) and sitagliptin (S), a dipeptidyl peptidase IV (DPP-IV) inhibitor, in the amelioration of T2D manifestations in high-fat diet (HFD) induced T2D mouse model and also on β-cell proliferation under gluco-lipotoxicity stress in vitro.

METHODS

For in vivo study, mice were fed with HFD for 25 weeks to induce T2D and were treated with monotherapies and S + M for four weeks. For the in vitro study, primary mouse islets were exposed to normal glucose and high glucose + palmitate to induce gluco-lipotoxic stress.

RESULTS

Our results suggest that monotherapies and S + M improve metabolic parameters and glyco-lipid metabolism in the liver and adipose tissue, respectively, and improve mitochondrial function in the skeletal muscle. Moreover, it increases peripheral insulin sensitivity. Our in vitro and in vivo studies suggest that β-cell mass was preserved in all the drug-treated groups.

CONCLUSION

The combination treatment is superior to monotherapies in the management of T2D.

Dipeptidyl Peptidase 4 (DPP4) as A Novel Adipokine: Role in Metabolism and Fat Homeostasis

Dipeptidyl peptidase 4 (DPP4) is a molecule implicated in the regulation of metabolic homeostasis and inflammatory processes, and it exerts its main action through its enzymatic activity. DPP4 represents the enzyme most involved in the catabolism of incretin hormones; thus, its activity impacts appetite, energy balance, and the fine regulation of glucose homeostasis. Indeed, DPP4 inhibitors represent a class of antidiabetic agents widely used for the treatment of Type 2 diabetes mellitus (T2DM). DPP4 also acts as an adipokine and is mainly secreted by the adipose tissue, mostly from mature adipocytes of the visceral compartment, where it exerts autocrine and paracrine activities. DPP4 can disrupt insulin signaling within the adipocyte and in other target cells and tissues, where it also favors the development of a proinflammatory environment. This is likely at the basis of the presence of elevated circulating DPP4 levels in several metabolic diseases. In this review, we summarize the most recent evidence of the role of the DPP4 as an adipokine-regulating glucose/insulin metabolism and fat homeostasis, with a particular focus on clinical outcomes associated with its increased secretion in the presence of adipose tissue accumulation and dysfunction.

A ROCK1 Inhibitior Fasudil Alleviates Cardiomyocyte Apoptosis in Diabetic Cardiomyopathy by Inhibiting Mitochondrial Fission in a Type 2 Diabetes Mouse Model

Diabetes mellitus (DM) often involves cardiovascular complications; however, treatment regimens are limited. ROCK1 (rho-associated coiled-coil containing protein kinase 1) serves as a pathological factor in several diabetic complications. Herein, we aimed to explore the effect of Fasudil (a ROCK1 inhibitor) on the progress of cardiac dysfunction in type 2 DM (T2DM), and to explore the possible mechanisms. Type II diabetic mice models were established by inducing insulin resistance through a high-fat diet combined with low-dose streptozotocin (STZ) injection. NMCMs (neonatal mouse ventricular cardiac myocytes) in the control group were treated with 5.5 mM glucose, while those in the High Glucose (HG) group were treated with 33 mM glucose and 10 nmol/L insulin. In vivo, we found that type 2 diabetes enhanced the expression and activation of ROCK1 (p < 0.05). The ROCK1 inhibitor, Fasudil, prevented cardiac dysfunction, fibrosis, oxidative stress and myocardial ultrastructural disorders (p < 0.05) in the diabetic mice. In vitro, ROCK1 was upregulated in HG-induced cardiomyocytes, and ROCK1 inhibition using Fasudil reversed the increased apoptosis, consistent with in vivo results. Mechanistically, ROCK1 inhibition abrogated apoptosis, relieved mitochondrial fission, and efficiently attenuated the escalated production of reactive oxygen species in vitro and in vivo. The content of Ser616-phosphorylated dynamin-related protein 1 (Drp1) increased while ROCK1 led to apoptosis in HG-treated cardiomyocytes, which could be partly neutralized by ROCK1 inhibition with Fasudil, consistent with the in vivo results. Fasudil attenuated the cardiac dysfunction in diabetes by decreasing excessive mitochondrial fission via inhibiting Drp1 phosphorylation at serine 616.

Positive regulation of endothelial Tom70 by metformin as a new mechanism against cardiac microvascular injury in diabetes

Microvascular protection is the main mechanism of metformin against diabetic complications. Cardiac microvascular endothelial cells (CMECs) are the basic component of cardiac microvessels, and they suffer from oxidative stress and mitochondrial dysfunction under type 2 diabetes mellitus (T2DM). Translocase of the outer mitochondrial membrane 70 (Tom70) improves mitochondrial dysfunction, but its role in the hearts of T2DM patients remains unclear. The purpose of this study was to demonstrate the protective effect of metformin on diabetic cardiac microvascular injury and to identify the role of Tom70 in this effect. T2DM mice were established by multiple intraperitoneal injections of low-dose streptozotocin and 12-week high-fat feeding. CMECs were isolated and cultured with normal glucose (NG), high glucose (HG), and HG plus high fat (HG-HF) media. The results indicated that long-term metformin treatment partly reversed cardiovascular complication and mitigated cardiac microvascular injury in T2DM. In addition, exposure to HG-HF led to CMEC damage, aggravated oxidative stress, aggravated mitochondrial dysfunction, and reduced mitochondrial Tom70 expression, whereas upregulation of Tom70 significantly ameliorated these injuries. Furthermore, metformin treatment promoted Tom70 expression and effectively reversed CMEC injury induced by HG-HF. However, all of these effects were interrupted after Tom70 was knocked down. In conclusion, T2DM damages microvascular integrity by activating a cycle of decreased Tom70 expression, mitochondrial dysfunction, and reactive oxygen species (ROS) overload in CMECs. However, metformin suppresses oxidative stress, relieves mitochondrial dysfunction, and promotes the expression of Tom70, ultimately ameliorating diabetic microvascular injury and heart complications.

Exacerbated post-infarct pathological myocardial remodelling in diabetes is associated with impaired autophagy and aggravated NLRP3 inflammasome activation

Background

Diabetes mellitus (DM) patients surviving myocardial infarction (MI) have substantially higher mortality due to the more frequent development of subsequent pathological myocardial remodelling and concomitant functional deterioration. This study investigates the molecular pathways underlying accelerated cardiac remodelling in a well‐established mouse model of diabetes exposed to MI.

Methods and results

Myocardial infarction in DM mice was established by ligating the left anterior descending coronary artery. Cardiac function was assessed by echocardiography. Myocardial hypertrophy and cardiac fibrosis were determined histologically 6 weeks post‐MI or sham operation. Autophagy, the NLRP3 inflammasome, and caspase‐1 were evaluated by western blotting or immunofluorescence. Echocardiographic imaging revealed significantly increased left ventricular dilation in parallel with increased mortality after MI in DM mice (53.33%) compared with control mice (26.67%, P < 0.05). Immunoblotting, electron microscopy, and immunofluorescence staining for LC3 and p62 indicated impaired autophagy in DM + MI mice compared with control mice (P < 0.05). Furthermore, defective autophagy was associated with increased NLRP3 inflammasome and caspase‐1 hyperactivation in DM + MI mouse cardiomyocytes (P < 0.05). Consistent with NLRP3 inflammasome and caspase‐I hyperactivation, cardiomyocyte death and IL‐1β and IL‐18 secretion were increased in DM + MI mice (P < 0.05). Importantly, the autophagy inducer and the NLRP3 inhibitor attenuated the cardiac remodelling of DM mice after MI.

Conclusion

In summary, our results indicate that DM aggravates cardiac remodelling after MI through defective autophagy and associated exaggerated NLRP3 inflammasome activation, proinflammatory cytokine secretion, suggesting that restoring autophagy and inhibiting NLRP3 inflammasome activation may serve as novel targets for the prevention and treatment of post‐infarct remodelling in DM.

A new mouse model of type 2 diabetes mellitus established through combination of high-fat diet, streptozotocin and glucocorticoid

AIM

A stable induced type 2 diabetes model (T2DM) still needs to be explored for basic and clinical research, due to nonuniform model methods and unstable consequences. Our aims were to explore and establish an optimized induced T2DM model in mice that exhibits insulin resistance and β-cell damage.

MATERIALS AND METHODS

C57BL/6 mice were treated with a high-fat diet (HFD), streptozotocin (STZ) and dexamethasone (DEX) at different doses and in combination. The general growth status, blood glucose and fasting insulin were detected, and the success rate and insulin sensitivity indices were calculated.

KEY FINDING

Low-dose STZ injection multiple times was more secure in the process of T2DM model production. Combined intervention was more efficient in reducing insulin sensitivity and improving the success rate of T2DM model construction.

SIGNIFICANCE

Combined with a high-fat diet, glucocorticoids and streptozotocin, a new mouse model of T2DM with insulin resistance and β-cell damage could be established. The optimized experimental method can serve as a stable model for further studies on the mechanisms and therapy of T2DM.

Ameliorative effect of white tea from 50-year-old tree of Camellia sinensis L. (Theaceae) on kidney damage in diabetic mice via SIRT1/AMPK pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Diabetic kidney damage (DKD) is one of the most common complications of diabetes, which is known as a chronic inflammatory kidney disease caused by persistent hyperglycemia. White tea was originally used as a folk medicine to treat measles in ancient China. What arouses our interest is that there is a traditional method to treat diabetes with white tea taken from over 30-year-old tree of Camellia sinensis L. However, there are few reports on the renal protection of white tea.

AIM OF THE STUDY

This present study was designed to study the potential protective effects of white tea (WT) and old tree white tea (OTWT) on high-fat-diet (HFD) combined with streptozotocin (STZ)-induced type 2 diabetic mice to explore the possible mechanism of WT/OTWT against DKD.

MATERIALS AND METHODS

C57BL/6 mice were randomly divided into four groups: NC, T2D, WT (400 mg/kg·b.w, p.o.), OTWT (400 mg/kg·b.w, p.o.). Diabetes was established in all groups except NC group, by six weeks of HFD feeding combined with STZ (50 mg/kg, i.p.) for 3 times, treatments were administered for six weeks and then all the animals were decapitated; kidney tissues and blood samples were collected for the further analysis, including: levels of insulin, lipid metabolism (TG, TC, HDL, LDL, FFA), antioxidative enzymes (catalase (CAT), super oxide dismutase (SOD), glutathione peroxidase (GPx)), blood urea nitrogen (BUN) and creatine, inflammatory cytokines (TNF-α, IL-1β, COX-2, iNOS, MCP-1), advanced glycation end products (AGE), receptor of AGE (RAGE), Nrf2, AMPK, SIRT1, and PGC-1α. H&E, PAS and Masson staining were performed to examine the histopathological alterations of the kidneys.

RESULTS

Our data showed that WT and OTWT reversed the abnormal serum lipids (TG, TC, HDL, LDL, FFA) in T2D mice, upregulated antioxidative enzymes levels (CAT, SOD, GPx) and inhibit the excessive production of proinflammatory mediators (including MCP-1, TNF-α, IL1β, COX-2 and iNOS) by varying degrees, and OTWT was more effective. In histopathology, OTWT could significantly alleviate the accumulation of renal AGE in T2D mice, thereby improving the structural changes of the kidneys, such as glomerular hypertrophy, glomerular basement membrane thickening and kidney FIbrosis.

CONCLUSIONS

Both WT and OTWT could alleviate the diabetic changes in T2D mice via hypoglycemic, hypolipidemic, anti-oxidative and anti-inflammatory effects, while OTWT was more evident. OTWT could prominently alleviate the accumulation of AGE in the kidneys of T2D mice, thereby ameliorating the renal oxidative stress and inflammatory damage, which was associated with the activation of SIRT1/AMPK pathway.

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.

Targeting AGE-RAGE signaling pathway by Saxagliptin prevents myocardial injury in isoproterenol challenged diabetic rats

The role of Saxagliptin in diabetes-associated cardiovascular complications is controversial. This study aimed to investigate whether Saxagliptin could prevent Isoproterenol-induced myocardial changes in diabetic rats and to identify the possible mechanism as well. The high-fat diet/low-dose Streptozotocin-induced type 2 diabetic rats were divided into 3 groups: the control group (0.25% CMC for 28 days), the Isoproterenol group (85 mg/kg Isoproterenol for the last 2 days plus 0.25% CMC for 28 days), and the treatment group (10 mg/kg Saxagliptin for 28 days plus 85 mg/kg Isoproterenol for the last 2 days). Hemodynamic measurements were performed, and samples were examined for RAGE and NF-κB expressions, histopathological and ultrastructural changes, AGEs level, myocardial injury markers, oxidative stress, and apoptosis. Saxagliptin significantly recovered cardiac function (p < .001), reverted myocardial injury and oxidative stress levels back to the control value (p < .05 to p < .001). Saxagliptin alleviates Isoproterenol-induced myocardial injury in diabetic rats by suppressing AGE-RAGE pathway.

Dietary Ginsenoside T19 Supplementation Regulates Glucose and Lipid Metabolism via AMPK and PI3K Pathways and Its Effect on Intestinal Microbiota

Ginseng, as a functional food, is widely used worldwide because of its multifarious benefits. Studies have verified that 25-hydroxyl-protopanaxatriol (T19) is a new ginsenoside from ginseng, which had an important inhibitory effect on α-glucosidase and protein tyrosine phosphatase 1B in vitro. This study aims to assess the regulation of T19 against glycolipid metabolism by insulin-resistant HepG2 cells and diabetes mice induced with high-fat diet combined with streptozotocin (STZ). T19 effectively lowered the levels of blood glucose and lipid, alleviated insulin resistance, and improved histological pathology of liver and pancreas. Further study demonstrated that regulation of AMP-activated protein kinase- and phosphoinositide-3-kinase-signaling pathways was involved in the potential mechanism of T19 efficiency. Simultaneously, high-throughput sequencing of 16S rDNA revealed that T19 remarkably ameliorated the high-fat diet/STZ-induced disorders of intestinal microbiota by decreasing the value of Firmicutes/Bacteroidetes, and remarkably raised the relative abundance of the Lachnospiraceae family, which are the beneficial bacteria that can regulate glucose and lipid metabolism. The results may provide clues for further understanding the mechanism of T19 in regulating glycolipid metabolism, and may provide a scientific basis for ginseng as a potential dietary food to prevent metabolic diseases.

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.

Dipeptidyl Peptidase-IV Inhibitory Activity and Related Molecular Mechanism of Bovine α-Lactalbumin-Derived Peptides

Identifying DPP-IV inhibitory peptides from dietary protein has attracted increased attention. In the present study, bovine α-lactalbumin hydrolysates were generated by alcalase for various hydrolysis times, and DPP-IV inhibitory activity of these hydrolysates was determined. The 4 h hydrolysates displayed the most potent DPP-IV inhibitory activity, with DPP-IV inhibition rate of 82.30 ± 1.39% at concentration of 1.0 mg/mL. DPP-IV inhibitory peptides were isolated from the 4 h-hydrolysates with gel filtration chromatography and reversed-phase high-performance liquid chromatography (RP-HPLC). Using liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI MS/MS), two DPP-IV inhibitory peptides were identified, and their amino acid sequences were Glu-Leu-Lys-Asp-Leu-Lys-Gly-Tyr (ELKDLKGY) and Ile-Leu-Asp-Lys-Val-Gly-Ile-Asn-Tyr (ILDKVGINY), respectively. Furthermore, molecular docking analysis showed that peptides ELKDLKGY and ILDKVGINY could form hydrogen bonds, pi-cation interactions, and salt bridges with DPP-IV. These findings indicated that bovine α-lactalbumin may be a potential source of natural DPP-IV inhibitor.

Systemic Delivery of siRNA Specific for Silencing TLR4 Gene Expression Reduces Diabetic Cardiomyopathy in a Mouse Model of Streptozotocin-Induced Type 1 Diabetes

INTRODUCTION

Diabetic cardiomyopathy is a cardiac dysfunction in patients with diabetes which may lead to overt heart failure and death. Toll-like receptor (TLR) signaling triggers diabetic cardiomyopathy through various mechanisms, one of which is the upregulation of TLR4 expression. The aim of this study was to delineate the role of TLR4 in diabetic cardiomyopathy.

METHODS

C57BL/6 mice were injected with streptozotocin to induce diabetes. The experimental and control groups were treated with 5 μg of TLR4 small interfering RNA (siRNA) or scrambled siRNA. Cardiac histopathology was evaluated by hematoxylin and eosin, Sirius red, and immunofluorescence staining after treatment with TLR4 siRNA. The myocardial fibrosis and inflammatory factors were detected by quantitative real-time polymerase chain reaction after treatment with TLR4 siRNA. The myocardial function was evaluated by echocardiography after treatment with TLR4 siRNA.

RESULTS

Compared with non-diabetic mouse hearts, hypertrophy, fibrosis, inflammation of cardiomyocytes, and myocardial dysfunction were significantly increased in diabetic mice (p < 0.05). Knockdown of TLR4 decreased hypertrophy, fibrosis, inflammation of cardiomyocytes, and myocardial dysfunction (p < 0.05). Cardiomyocytic cross-sectional areas in hearts of TLR4 siRNA-treated diabetic mice were similar to those of the sham-treated mice (p > 0.05). The induction of expression of cardiac fetal genes, beta-myosin heavy chain (β-MHC) and atrial natriuretic peptide (ANP), which are two markers of cardiac hypertrophy, was significantly reduced in TLR4 siRNA-treated hearts compared with controls (p < 0.05). Moreover, siRNA-mediated silencing of TLR4 reduced diabetes-induced collagen deposition (p < 0.05). Paralleled with changes in collagen deposition and the expression of collagen I and collagen III, knockdown of TLR4 also reduced the expression of transforming growth factor-β1 (TGFβ1) mRNA (p < 0.05). The increased expression of intercellular cell adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) was significantly attenuated by TLR4 siRNA treatment in the hearts of diabetic mice (p < 0.05). Furthermore, both fractional shortening (FS) and ejection fraction (EF) values were preserved in TLR4 siRNA-treated diabetic mice compared with control siRNA-treated mice (31.80% ± 2.82% vs. 28.50% ± 5.83% for FS, p < 0.05) (57.95% ± 6.48% vs. 45.34% ± 4.25% for EF, p < 0.05).

CONCLUSION

Our study used siRNA to specifically silence TLR4 gene expression in the diabetic mouse heart in vivo and to investigate the role that TLR4 plays in diabetic cardiomyopathy. It is likely that silencing of the TLR4 gene through siRNA could prevent the development of diabetic cardiomyopathy.

Distinct cardiac energy metabolism and oxidative stress adaptations between obese and non-obese type 2 diabetes mellitus

Background: Little is known about the pathophysiological diversity of myocardial injury in type 2 diabetes mellitus (T2DM), but analyzing these differences is important for the accurate diagnosis and precise treatment of diabetic cardiomyopathy. This study aimed to elucidate the key cardiac pathophysiological differences in myocardial injury between obese and non-obese T2DM from mice to humans.

Methods: Obese and non-obese T2DM mouse models were successfully constructed and observed until systolic dysfunction occurred. Changes in cardiac structure, function, energy metabolism and oxidative stress were assessed by biochemical and pathological tests, echocardiography, free fatty acids (FFAs) uptake fluorescence imaging, transmission electron microscopy, etc. Key molecule changes were screened and verified by RNA sequencing, quantitative real-time polymerase chain reaction and western blotting. Further, 28 human heart samples of healthy population and T2DM patients were collected to observe the cardiac remodeling, energy metabolism and oxidative stress adaptations as measured by pathological and immunohistochemistry tests.

Results: Obese T2DM mice exhibited more severe cardiac structure remodeling and earlier systolic dysfunction than non-obese mice. Moreover, obese T2DM mice exhibited severe and persistent myocardial lipotoxicity, mainly manifested by increased FFAs uptake, accumulation of lipid droplets and glycogen, accompanied by continuous activation of the peroxisome proliferator activated receptor alpha (PPARα) pathway and phosphorylated glycogen synthase kinase 3 beta (p-GSK-3β), and sustained inhibition of glucose transport protein 4 (GLUT4) and adipose triglyceride lipase (ATGL), whereas non-obese mice showed no myocardial lipotoxicity characteristics at systolic dysfunction stage, accompanied by the restored PPARα pathway and GLUT4, sustained inhibition of p-GSK-3β and activation of ATGL. Additionally, both obese and non-obese T2DM mice showed significant accumulation of reactive oxygen species (ROS) when systolic dysfunction occurred, but the NF-E2-related factor 2 (Nrf2) pathway was significantly activated in obese mice, while was significantly inhibited in non-obese mice. Furthermore, the key differences found in animals were reliably verified in human samples.

Conclusion: Myocardial injury in obese and non-obese T2DM may represent two different types of complications. Obese T2DM individuals, compared to non-obese individuals, are more prone to develop cardiac systolic dysfunction due to severe and persistent myocardial lipotoxicity. Additionally, anti-oxidative dysfunction may be a key factor leading to myocardial injury in non-obese T2DM.

Hyperbaric Oxygen Ameliorates Insulin Sensitivity by Increasing GLUT4 Expression in Skeletal Muscle and Stimulating UCP1 in Brown Adipose Tissue in T2DM Mice

Hyperbaric oxygen (HBO) therapy is a treatment modality useful for diseases. Hypoxia could stimulate the induction of insulin resistance. Therefore, we sought to determine whether hyperbaric oxygen would ameliorate insulin sensitivity by promoting glucose transporter type 4 (GLUT4) expression in muscle and by stimulating UCP1 in brown adipose tissue (BAT) in a streptozocin (STZ)-induced type 2 diabetes mellitus (T2DM) mouse model. Male C57BL/6J mice were treated three times with low-dose of streptozocin (60 mg/kg, i.p.) and were fed with high-fat diets (HFD) to establish the T2DM model. HBO was administered daily as 100% oxygen at 2.0 atmosphere absolute (ATA) for 1 h for a week. We found that HBO significantly reduced blood glucose levels and attenuated insulin resistance in T2DM mice. HBO modulated food intake by influencing the activity of neuropeptide Y (NPY)-positive neurons in the arcuate nucleus (Arc). HBO treatment increased GLUT4 amount and level of phosphorylated Akt (p-Akt) in muscles of T2DM mice whereas this treatment stimulated the phosphorylation of AMPK in muscles of both T2DM and HFD mice. The morphological staining of BAT and the increased expression of uncoupling of protein 1 (UCP1) demonstrated the promotion of metabolism after HBO treatment. These findings suggest that HBO ameliorates insulin sensitivity of T2DM mice by stimulating the Akt signaling pathway and by promoting GLUT4 expression in muscle, and by increasing UCP1 expression in BAT.

Jiaogulan tea (Gpostemma pentaphyllum) potentiates the antidiabetic effect of white tea via the AMPK and PI3K pathways in C57BL/6 mice

The use of plant-based beverages to interfere with the onset of diabetes may be a promising approach towards type 2 diabetes mellitus (T2DM).

Dipeptidyl Peptidase-4 (DPP-4) Inhibitor Saxagliptin Alleviates Lipopolysaccharide-Induced Acute Lung Injury via Regulating the Nrf-2/HO-1 and NF-B Pathways

PURPOSE

We aimed at investigating the effects of Dipeptidyl peptidase-4 (DPP-4) inhibitor saxagliptin (Saxa) on mouse acute lung injury (ALI)-induced by lipopolysaccharide (LPS) and the potential mechanisms.

MATERIALS/METHODS

Animals were divided into four groups: control, Saxa, LPS, and LPS + Saxa. Histopathology changes of lung tissues were assessed by hematoxylin and eosin staining and periodic acid-Schiff staining. The degree of edema was determined by wet/dry ratio. The levels of oxidative stress markers and inflammatory cytokines in lung homogenate and bronchoalveolar lavage fluid were detected using kits. Terminal deoxynucleotidyl transferase dUTP nick end labeling assay was used to test apoptosis and Western blotting was applied to measure the expression of apoptosis-associated proteins. The expression of nuclear factor erythroid 2-related factor 2 (Nrf-2)/heme oxygenase-1 (HO-1) and nuclear factor-kappa B (NF-κB) pathways were detected by Western blotting.

RESULTS

The results revealed that Saxa attenuated LPS-induced pathological injury and edema. Saxa decreased the levels of reactive oxygen species (ROS), malondialdehyde (MDA), myeloperoxidase (MPO) and increased the levels of superoxide dismutase (SOD) and catalase (CAT). The contents of inflammatory cytokines were reduced in the Saxa intervention group. Saxa attenuated apoptosis accompanied by alterations in the expression of apoptosis-associated proteins. Furthermore, the expression of Nrf-2 and HO-1 were upregulated whereas phospho (p)-NF-κB p65 and phospho-inhibitory subunit of NF-κB alpha (p-IκB-α) were downregulated after Saxa treatment.

CONCLUSION

These findings concluded that Saxa alleviates oxidative stress, inflammation and apoptosis in ALI induced by LPS via modulating the Nrf-2/HO-1 and NF-κB pathways, which provides evidence for employing Saxa in ALI treatment.

Dendrobium huoshanense polysaccharide regulates hepatic glucose homeostasis and pancreatic β-cell function in type 2 diabetic mice

In the present study, the hypoglycemic mechanism of a homogeneous Dendrobium huoshanense polysaccharide (GXG) was investigated using type 2 diabetic (T2D) mouse model. With a 5-week oral administration of GXG, the levels of fasting blood glucose, glycosylated serum protein and serum insulin in T2D mice were decreased, and the glucose tolerance and the insulin sensitivity were improved. The histological analysis, the periodic acid-schiff staining and the immunofluorescence staining of insulin, glucagon and apoptosis showed that the hypoglycemic effect of GXG was related to the improvement of pancreatic β-cell quantity and function and the regulation of hepatic glucose metabolism. Western blot analysis indicated that the up-regulated IRS1-PI3K-Akt phosphorylation followed by the down-regulated FoxO1/GSK 3β phosphorylation contributed to the enhanced glycogen synthesis and the decreased gluconeogenesis by GXG, suggesting that the response of insulin-mediated IRS1-PI3K-Akt-FoxO1/GSK 3β signaling to GXG might be the required mechanism for GXG-ameliorated development of type 2 diabetes.

Identification of novel uracil derivatives incorporating benzoic acid moieties as highly potent Dipeptidyl Peptidase-IV inhibitors

Dipeptidyl Peptidase-IV (DPP-4) is a validated therapeutic target for type 2 diabetes. Aiming to interact with both residues Try629 and Lys554 in S₂' site, a series of novel uracil derivatives 1a-l and 2a-i incorporating benzoic acid moieties at the N₃ position were designed and evaluated for their DPP-4 inhibitory activity. Structure-activity relationships (SAR) study led to the identification of the optimal compound 2b as a potent and selective DPP-4 inhibitor (IC₅₀ = 1.7 nM). Docking study revealed the additional salt bridge formed between the carboxylic acid and primary amine of Lys554 has a key role in the enhancement of the activity. Furthermore, compound 2b exhibited no cytotoxicity in human hepatocyte LO2 cells up to 50 μM. Subsequent in vivo evaluations revealed that the ester of 2b robustly improves the glucose tolerance in normal mice. The overall results have shown that compound 2b has the potential to a safe and efficacious treatment for T2DM.

Hypoglycemic Mechanism of the Berberine Organic Acid Salt under the Synergistic Effect of Intestinal Flora and Oxidative Stress

Both alterations to the intestinal microflora and chronic systemic inflammation predispose towards type 2 diabetes (T2D). Changes in the composition of the intestinal microflora are associated with glucose metabolism changes in rats with T2D. Here, we demonstrate that a berberine fumarate (BF) has a hypoglycemic effect by regulating the intestinal microflora and metabolism of diabetic rats. The T2D rats had disorders of glucose and lipid metabolism, an abnormal intestinal microflora, fewer butyrate-producing and probiotic-type bacteria, larger numbers of potentially pathogenic and sulfate-reducing bacteria, and tissue inflammation. Administration of berberine fumarate significantly ameliorated the metabolic disorder; increased the populations of Bacteroidetes, Clostridia, Lactobacillales, Prevotellaceae, and Alloprevotella; and reduced those of Bacteroidales, Lachnospiraceae, Rikenellaceae, and Desulfovibrio. In addition, it reduced inflammation, inhibiting the overexpression of TLR4 and p-JNK and increasing the expression of PI3K, GLUT2, and other proteins, which are closely related to oxidative stress, thereby promoting the metabolism of glucose.

Sitagliptin attenuates myocardial apoptosis via activating LKB-1/AMPK/Akt pathway and suppressing the activity of GSK-3β and p38α/MAPK in a rat model of diabetic cardiomyopathy

The present study aimed to investigate the protective effect of sitagliptin, a dipeptidyl peptidase-4 inhibitor, on diabetic cardiomyopathy (DCM)-associated apoptosis and if this effect is mediated via modulating the activity of the survival kinases; AMP-activated protein kinase (AMPK) and Akt & the apoptotic kinases; glycogen synthase kinase-3 β (GSK-3β) and p38 mitogen-activated protein kinase (p38MAPK). Diabetes was induced by a single intraperitoneal injection of streptozotocin (55 mg/kg). Diabetic rats were treated with sitagliptin (10 mg/kg/day, p.o.) and metformin (200 mg/kg/day, p.o. as positive control) for six weeks. Chronic hyperglycemia resulted in elevation of serum cardiac biomarkers reflecting cardiac damage which was supported by H&E stain. The mRNA levels of collagen types I and III were augmented reflecting cardiac fibrosis and hypertrophy which was supported by Masson trichome stain and enhanced phosphorylation of p38MAPK. Cardiac protein levels of cleaved casapse-3, BAX were elevated, whereas, the levels of Bcl-2 and p-BAD were reduced indicating cardiac apoptosis which could be attributed to the diabetes-induced reduced phosphorylation of Akt and AMPK with concomitant augmented activation of GSK-3β and p38MAPK. Protein levels of liver kinase B-1, the upstream kinase of AMPK were also supressed. Sitagliptin administration alleviated the decreased phosphorylation of AMPK and Akt, inactivated the GSK-3β and p38 AMPK, therefore, attenuating the apoptosis and hypertrophy induced by hyperglycemia in the diabetic heart. In conclusion, sitagliptin exhibits valuable therapeutic potential in the management of DCM by attenuating apoptosis. The underlying mechanism may involve the modulating activity of AMPK, Akt, GSK-3β and p38MAPK.

A Mouse Model of Beta-Cell Dysfunction as Seen in Human Type 2 Diabetes

Loss of first-phase insulin release is an early pathogenic feature of type 2 diabetes (T2D). Various mouse models exist to study T2D; however, few recapitulate the early β-cell defects seen in humans. We sought to develop a nongenetic mouse model of T2D that exhibits reduced first-phase insulin secretion without a significant deficit in pancreatic insulin content. C57BL/6J mice were fed 10% or 60% fat diet for three weeks, followed by three consecutive, once-daily intraperitoneal injections of the β-cell toxin streptozotocin (STZ; 30, 50, or 75 mg/kg) or vehicle. Four weeks after injections, the first-phase insulin response to glucose was reduced in mice when high-fat diet was combined with 30, 50, or 75 mg/kg STZ. This was accompanied by diminished second-phase insulin release and elevated fed glucose levels. Further, body weight gain, pancreatic insulin content, and β-cell area were decreased in high fat-fed mice treated with 50 and 75 mg/kg STZ, but not 30 mg/kg STZ. Low fat-fed mice were relatively resistant to STZ, with the exception of reduced pancreatic insulin content and β-cell area. Together, these data demonstrate that in high fat-fed mice, three once-daily injections of 30 mg/kg STZ produces a model of β-cell failure without insulin deficiency that may be useful in studies investigating the etiology and progression of human T2D.

Saxagliptin Attenuates Albuminuria by Inhibiting Podocyte Epithelial- to-Mesenchymal Transition via SDF-1α in Diabetic Nephropathy

The dipeptidyl peptidase-4 (DPP-4) inhibitor saxagliptin has been found to reduce progressive albuminuria, but the exact mechanism of inhibition is unclear. Podocyte epithelial-to-mesenchymal transition (EMT) has emerged as a potential pathway leading to proteinuria in diabetic nephropathy (DN). Stromal cell–derived factor-1α (SDF-1α), one of the substrates of DPP-4, can activate the protein kinase A pathway and subsequently inhibit its downstream effector, transforming growth factor-β1 (TGF-β1), which induces podocyte EMT. Thus, this study was designed to test the hypothesis that saxagliptin reduces progressive albuminuria by preventing podocyte EMT through inhibition of SDF-1α cleavage in DN. The results of a series of assays, including ELISA, western blotting, and immunochemistry/immunofluorescence, showed that saxagliptin treatment obviously ameliorated urinary microalbumin excretion and renal histological changes in high-fat diet/streptozotocin-induced diabetic rats. Furthermore, saxagliptin-treated diabetic rats presented with suppression of DPP-4 activity/protein expression accompanied by restoration of SDF-1α levels, which subsequently hindered NOX2 expression and podocyte EMT. In vitro, we consistently observed that saxagliptin significantly inhibited increased DPP-4 activity/expression, oxidative stress and podocyte EMT. Application of an SDF-1α receptor inhibitor (AMD3100) to cultured podocytes further confirmed the essential role of SDF-1α in podocyte EMT inhibition. In sum, we demonstrated for the first time that saxagliptin treatment plays an essential role in ameliorating progressive DN by preventing podocyte EMT through a SDF-1α-related pathway, suggesting that saxagliptin could offer renoprotection and that SDF-1α might be a potential therapeutic target for DN.

Assessment of Saxagliptin Efficacy: Meta-Analysis of 14 Phase 2 and 3 Clinical Trials

INTRODUCTION

This meta-analysis of data from 14 phase 2 and 3, double-blind, randomized, controlled 12- and 24-week studies (N = 4632) summarizes saxagliptin efficacy in patients with type 2 diabetes (T2D) across treatment regimens.

METHODS

Patients received saxagliptin 5 mg/d or control as either monotherapy (n = 1196 vs placebo), add-on therapy (n = 2139 vs placebo and n = 514 vs uptitrated sulfonylurea), or initial combination therapy (n = 619 vs control monotherapy). Patients with renal impairment received saxagliptin 2.5 mg/d or placebo (n = 164).

RESULTS

Mean baseline glycated hemoglobin (A1C) ranged from 8.07% to 9.43% for the saxagliptin and control groups across treatment regimens. A1C reduction from baseline was greater with saxagliptin versus control for all studies combined (mean treatment difference [95% CI]: -0.55% [-0.63%, -0.47%]) and when used as monotherapy (-0.52% [-0.63, -0.40%]), add-on (-0.55% [-0.69%, -0.40%] vs placebo; -0.72% [-0.88%, -0.56%] vs uptitrated sulfonylurea), initial combination therapy (-0.54% [-0.73%, -0.35%] vs control monotherapy), and in patients with renal impairment (-0.42% [-0.75%, -0.09%]). Similar reductions in A1C versus control were noted for patients <65 years (-0.55% [-0.67%, -0.43%]) and ≥65 years (-0.54% [-0.69%, -0.38%]) and for men (-0.54% [-0.69%, -0.40%]) and women (-0.55% [-0.64%, -0.47%]) across treatment regimens. More patients achieved A1C <7% (39% vs 23%) and A1C ≤6.5% (24% vs 14%) with saxagliptin than with placebo or active-control treatment. Saxagliptin versus control was associated with a reduction in glucagon area under the curve (AUC) from baseline and increases in insulin AUC, C-peptide AUC, and the homeostasis model assessment of β-cell function.

CONCLUSION

Results of this meta-analysis demonstrate the consistency of saxagliptin efficacy in different subgroups of patients with T2D across treatment regimens.

FUNDING

AstraZeneca.

Incretin Therapies Do Not Expand β-Cell Mass or Alter Pancreatic Histology in Young Male Mice

The impact of incretins upon pancreatic β-cell expansion remains extremely controversial. Multiple studies indicate that incretin-based therapies can increase β-cell proliferation, and incretins have been hypothesized to expand β-cell mass. However, disagreement exists on whether incretins increase β-cell mass. Moreover, some reports indicate that incretins may cause metaplastic changes in pancreatic histology. To resolve these questions, we treated a large cohort of mice with incretin-based therapies and carried out a rigorous analysis of β-cell turnover and pancreatic histology using high-throughput imaging. Young mice received exenatide via osmotic pump, des-fluoro-sitagliptin, or glipizide compounded in diet for 2 weeks (short-term) on a low-fat diet (LFD) or 4.5 months (long-term) on a LFD or high-fat diet (HFD). Pancreata were quantified for β-cell turnover and mass. Slides were examined for gross anatomical and microscopic changes to exocrine pancreas. Short-term des-fluoro-sitagliptin increased serum insulin and induced modest β-cell proliferation but no change in β-cell mass. Long-term incretin therapy in HFD-fed mice resulted in reduced weight gain, improved glucose homeostasis, and abrogated β-cell mass expansion. No evidence for rapidly dividing progenitor cells was found in islets or pancreatic parenchyma, indicating that incretins do not induce islet neogenesis or pancreatic metaplasia. Contrasting prior reports, we found no evidence of β-cell mass expansion after acute or chronic incretin therapy. Chronic incretin administration was not associated with histological abnormalities in pancreatic parenchyma; mice did not develop tumors, pancreatitis, or ductal hyperplasia. We conclude that incretin therapies do not generate β-cells or alter pancreatic histology in young mice.

Improvement of glycemic control in streptozotocin-induced diabetic rats by Atlantic salmon skin gelatin hydrolysate as the dipeptidyl-peptidase IV inhibitor

In our previous study, Atlantic salmon skin gelatin hydrolysed with flavourzyme possessed 42.5% dipeptidyl-peptidase (DPP)-IV inhibitory activity at a concentration of 5 mg mL(-1). The oral administration of the hydrolysate (FSGH) at a single dose of 300 mg per day in streptozotocin (STZ)-induced diabetic rats for 5 weeks was evaluated for its antidiabetic effect. During the 5-week experiment, body weight increased, and the food and water intake was reduced by FSGH in diabetic rats. The daily administration of FSGH for 5 weeks was effective for lowering the blood glucose levels of diabetic rats during an oral glucose tolerance test (OGTT). After the 5-week treatment, plasma DPP-IV activity was inhibited; the plasma activity of glucagon-like peptide-1 (GLP-1), insulin, and the insulin-to-glucagon ratio were increased by FSGH in diabetic rats. The results indicate that FSGH has the function of inhibiting GLP-1 degradation by DPP-IV, resulting in the enhancement of insulin secretion and improvement of glycemic control in STZ-induced diabetic rats.

Sitagliptin protects proliferation of neural progenitor cells in diabetic mice

Sitagliptin (SIT) is a dipeptidyl peptidase-4 (DPP-4) inhibitor that enhances the effects of incretin hormones, such as Glucose-dependent Insulinotropic Peptide (also known as Gastric Inhibitory Polypeptide, GIP) and Glucagon-Like Peptide 1 (GLP-1). We have now evaluated the effect of SIT on proliferation of neural progenitors in diabetic mice. A condition resembling the non-obese type 2 diabetes mellitus (D2) was achieved by a combination of streptozotocin and nicotinamide (NA-STZ), whereas a type 1-like disease (D1) was provoked by STZ without NA. Non-diabetic mice received vehicle injections. Cell proliferation was estimated by bromodeoxyuridine (BrdU) incorporation in two different regions of the subventricular zone (SVZ), the largest reserve of neural stem cells in the adult brain. SIT treatment did not modify the high fasting blood glucose (BG) levels and intraperitoneal glucose tolerance test (IPGTT) of D1 mice. By contrast, in D2 mice, SIT treatment significantly reduced BG and IPGTT. Both D1 and D2 mice showed a substantial reduction of BrdU labeling in the SVZ. Remarkably, SIT treatment improved BrdU labeling in both conditions. Our findings suggest that SIT would protect proliferation of neural progenitor cells even in the presence of non-controlled diabetic alterations.

A Novel TGR5 Activator WB403 Promotes GLP-1 Secretion and Preserves Pancreatic β-Cells in Type 2 Diabetic Mice

The G protein-coupled receptor TGR5 is a membrane receptor for bile acids. Its agonism increases energy expenditure and controls blood glucose through secretion of glucagon-like peptide-1 in enteroendocrine cells. In this study, we explored the therapeutic potential of WB403, a small compound activating TGR5 which was identified by combining TGR5 targeted luciferase assay and active GLP-1 assay, in treating type 2 diabetes. After confirmation of TGR5 and GLP-1 stimulating activities in various cell systems, WB403 was examined in oral glucose tolerance test, and tested on different mouse models of type 2 diabetes for glycemic control and pancreatic β-cell protection effect. As a result, WB403 exhibited a moderate TGR5 activation effect while promoting GLP-1 secretion efficiently. Interestingly, gallbladder filling effect, which was reported for some known TGR5 agonists, was not detected in this novel compound. In vivo results showed that WB403 significantly improved glucose tolerance and decreased fasting blood glucose, postprandial blood glucose and HbA1c in type 2 diabetic mice. Further analysis revealed that WB403 increased pancreatic β-cells and restored the normal distribution pattern of α-cell and β-cell in islets. These findings demonstrated that TGR5 activator WB403 effectively promoted GLP-1 release, improved hyperglycemia and preserved the mass and function of pancreatic β-cells, whereas it did not show a significant side effect on gallbladder. It may represent a promising approach for future type 2 diabetes mellitus drug development.

Clinical use of dipeptidyl peptidase-4 and sodium-glucose cotransporter 2 inhibitors in combination therapy for type 2 diabetes mellitus

OBJECTIVE

To review the efficacy, safety, and tolerability of combination treatment regimens including a dipeptidyl peptidase-4 (DPP-4) inhibitor and/or sodium-glucose cotransporter 2 (SGLT2) inhibitor for type 2 diabetes mellitus (T2DM).

METHODS

Clinical trials of combination therapies including a DPP-4 and/or SGLT2 inhibitor were identified through a PubMed database search. To be included, studies had to have a primary end point of change from baseline to ≥24 weeks in glycated hemoglobin, include ≥1 other oral antidiabetic drug (OAD), and have randomized more than 200 patients. Results were limited to medications approved by the US Food and Drug Administration at the time of the search (March 2015).

RESULTS

A total of 1534 articles for the DPP-4 inhibitor class and 434 articles for the SGLT2 inhibitor class were retrieved from PubMed. Of these, 33 articles from the DPP-4 inhibitor class and 24 articles from the SGLT2 inhibitor class were included for review. In each study, the addition of a DPP-4 or SGLT2 inhibitor as a second or third agent resulted in improved glycemic control versus comparator arms. Reductions in weight or lack of weight gain were consistently observed, as were low rates of hypoglycemic events, particularly when the combination regimen also included metformin. Overall, the pattern of adverse events observed in combination treatment groups was consistent with the known effects of the individual agents.

CONCLUSION

Combination treatment with a DPP-4 and/or SGLT2 inhibitor is an efficacious option for patients with T2DM starting pharmacological therapy, or for patients who have received treatment but require additional glycemic control. Study findings indicate that the underlying mechanisms of action of DPP-4 inhibitors and SGLT2 inhibitors complement a variety of OADs.

Combination immunotherapies for type 1 diabetes mellitus

Immunotherapies for type 1 diabetes mellitus (T1DM) have been the focus of intense basic and clinical research over the past few decades. Restoring β-cell function is the ultimate goal of intervention trials that target the immune system in T1DM. In an attempt to achieve this aim, different combination therapies have been proposed over the past few years that are based on treatments tackling the various mechanisms involved in the destruction of β cells. The results of clinical trials have not matched expectations based on the positive results from preclinical studies. The heterogeneity of T1DM might explain the negative results obtained, but previous trials have not addressed this issue. However, novel promising combination therapies are being developed, including those that couple immunomodulators with drugs that stimulate β-cell regeneration in order to restore normoglycaemia. This strategy is an encouraging one to pursue the goal of finding a cure for T1DM. This Review summarizes the available data about combination immunotherapies in T1DM, particularly addressing their clinical importance. The available data supporting the use of registered drugs, such as proton pump inhibitors and incretin-based agents, that have been shown to induce β-cell regeneration will also be discussed.

Sitagliptin, a dipeptidyl peptidase-4 inhibitor, improves recognition memory, oxidative stress and hippocampal neurogenesis and upregulates key genes involved in cognitive decline

AIM

To examine whether prolonged dipeptidyl peptidase-4 (DPP-4) inhibition can reverse learning and memory impairment in high-fat-fed mice.

METHODS

High-fat-fed mice received oral sitagliptin (50 mg/kg body weight) once daily or saline vehicle over 21 days. An additional group of mice on standard chow received saline vehicle. Energy intake, body weight, glucose and insulin concentrations were measured at regular intervals. Glucose tolerance, insulin sensitivity, novel object recognition, DPP-4 activity, hormone analysis, hippocampal gene expression and histology were performed.

RESULTS

Sitagliptin decreased circulating DPP-4 activity and improved glucose tolerance, glucose-stimulated insulin secretion and insulin sensitivity, and reduced plasma triglycerides and cholesterol levels. DPP-4 inhibition improved recognition memory (1.2-fold increase) without affecting hypermoteric activity or anxiety levels. Improvement in memory and learning was linked to reduced immunostaining for 8-oxoguanine and increased doublecortin staining in the hippocampus, which were indicative of reduced brain oxidative stress and increased hippocampal neurogenesis, respectively. These effects were associated with significant upregulation of hippocampal gene expression of glucagon-like peptide-1 (GLP-1) receptor, glucose-dependent insulinotropic polypeptide receptor, synaptophysin, sirtuin 1, glycogen synthase kinase 3β, superdioxide mutase 2, nuclear factor (erythroid-derived 2)-like 2 and vascular endothelial growth factor. Total plasma and brain GLP-1 concentrations were significantly increased after sitagliptin therapy, whereas DPP-4 activity in brain tissue was not altered.

CONCLUSION

These studies show that sitagliptin can reverse memory impairment in high-fat-fed mice and is also associated with improved insulin sensitivity, enhanced hippocampal neurogenesis and reduced oxidative stress. DPP-4 inhibitors may therefore exhibit dual benefits by improving metabolic control and reducing the decline in cognitive function.

Clinical utility and patient considerations in the use of the sitagliptin-metformin combination in Chinese patients

The prevalence of diabetes mellitus (DM) continues to increase each year. However, the efficacy of glucose-lowering therapies remains unsatisfactory. Moreover, the clinical characteristics and manifestations of DM in Chinese patients are different from those in Western patients. Thus, it is imperative to develop an optimal treatment protocol for lowering blood glucose levels in Chinese patients with DM. Sitagliptin has been used in People's Republic of China, and sitagliptin and metformin combination therapy may not alter their individual pharmacokinetics. To date, several clinical trials undertaken to investigate the efficacy of sitagliptin and metformin combination therapy have revealed that it effectively controlled glycated hemoglobin, fasting plasma glucose, and postprandial plasma glucose levels to a greater extent than sitagliptin or metformin alone. In addition, the combined therapy was well tolerated and induced few side effects, which were largely mild. Furthermore, the combined therapy was easy to administer, and the patients receiving this therapy showed good compliance. Therefore, for Chinese patients with type 2 DM, sitagliptin and metformin combination therapy is preferred.

Characterisation of pain responses in the high fat diet/streptozotocin model of diabetes and the analgesic effects of antidiabetic treatments

Chronic pain is a common complication of diabetes. The aim of the present study was to characterise pain behaviour in a high fat diet/streptozotocin (HFD/STZ) model of diabetes in the rat, investigate spinal mechanisms, and determine the effects of antidiabetic interventions. Three-week consumption of a high fat diet followed by single injection of STZ (45 mgkg(-1)) produced sustained changes in plasma insulin and glucose until day 120. Hindpaw mechanical withdrawal thresholds were significantly lowered in the model, but mechanically evoked responses of spinal neurones were unaltered, compared to HFD/vehicle rats. HFD/STZ rats had significantly lower numbers of spinal Iba-1 positive cells (morphologically identified as activated microglia) and spinal GFAP immunofluorescence (a marker of astrogliosis) in the spinal cord at day 50, compared to time-matched controls. The PPARγ ligand pioglitazone (10 mgkg(-1)) did not alter HFD/STZ induced metabolic changes or hindpaw withdrawal thresholds of HFD/STZ rats. Daily linagliptin (3 mgkg(-1)) and metformin (200 mgkg(-1)) from day 4 after model induction did not alter plasma glucose or insulin in HFD/STZ rats but significantly prevented changes in the mechanical withdrawal thresholds. The demonstration that currently prescribed antidiabetic drugs prevent aberrant pain behaviour supports the use of this model to investigate pain mechanisms associated with diabetes.

Divergent effects of liraglutide, exendin-4, and sitagliptin on beta-cell mass and indicators of pancreatitis in a mouse model of hyperglycaemia

Aims

Glucagon-like peptide-1 (GLP-1) receptor agonists and dipeptidyl peptidase-4 (DPP4) inhibitors improve glucose tolerance by still incompletely understood mechanisms. Each class of antihyperglycemic drugs has also been proposed to increase pancreatitis risk. Here, we compare systematically the effects of two widely-used GLP-1 analogues, liraglutide and exendin-4, and the DPP4 inhibitor, sitagliptin, in the mouse.

Methods

C57BL6 mice were maintained for 131 days on a normal diet (ND) or a diet comprising 60% fat (HFD) before measurements of fasting blood glucose and insulin, and intraperitoneal glucose tolerance. Beta- and alpha- cell volume, and Reg3b immunoreactivity, were measured by immunohistochemical analysis of pancreatic slices.

Results

Whereas liraglutide (200 µg/kg) and exendin-4 (10 µg/kg) treatment reduced body weight and/or improved glucose tolerance, sitagliptin (10 mg/kg) was without effect on either parameter. Liraglutide caused a sharp reduction in beta-cell mass in both ND and HFD mice, whereas exendin-4 exerted no effect. By contrast, sitagliptin unmasked an action of high fat diet to increase beta-cell mass. Reg3B positive area was augmented by all three agents in normal chow-fed mice, whilst sitagliptin and exendin-4, but not liraglutide, affected this parameter in HFD animals. Correspondingly sitagliptin, but not the GLP-1 analogues, increased circulating amylase levels in ND and HFD mice.

Conclusions

Liraglutide improves glucose tolerance in the mouse whilst exerting relatively modest effects on pancreatitis risk. Conversely, exendin-4 and sitagliptin, at doses which exert, respectively, minor or no effects on metabolic parameters, lead to signs of pancreatitis.

BMP-7 attenuates adverse cardiac remodeling mediated through M2 macrophages in prediabetic cardiomyopathy

The main objective of this study was to determine whether or not monocyte infiltration occurs in the prediabetic (PD) heart and its role in PD cardiomyopathy. We hypothesized that the PD heart is significantly populated with monocytes and that bone morphogenetic protein (BMP)-7, a novel mediator of monocyte polarization, activates infiltrated monocytes into anti-inflammatory M2 macrophages, thereby inhibiting apoptosis and fibrosis and improving cardiac function. C57Bl6 mice were assigned to control, PD, or PD + BMP-7 groups. PD and PD + BMP-7 groups were administered streptozotocin (50 mg/kg), whereas control animals received sodium citrate buffer. Afterward, the PD + BMP-7 group was administered BMP-7 (200 μg/kg) for 3 days. Our data showed significantly increased infiltrated monocytes and associated pro-inflammatory cytokines, adverse cardiac remodeling, and heart dysfunction in the PD group (P < 0.05). Interestingly, M2 macrophage differentiation and associated anti-inflammatory cytokines were enhanced and there were reduced adverse cardiac remodeling and improved cardiac function in the PD + BMP-7 group (P < 0.05). In conclusion, our data suggest that PD cardiomyopathy is associated with increased monocyte infiltration and released proinflammatory cytokines, which contributes to adverse cardiac remodeling and cardiac dysfunction. Moreover, we report that BMP-7 possesses novel therapeutic potential in its ability to differentiate monocytes into M2 macrophages and confer cardiac protection in the PD heart.

Efficacy and safety of vildagliptin in new-onset diabetes after kidney transplantation--a randomized, double-blind, placebo-controlled trial

New-onset diabetes after transplantation (NODAT) is a serious complication after kidney transplantation, but therapeutic strategies remain underexplored. Dipeptidyl peptidase-4 (DPP-4) inhibitors selectively foster insulin secretion without inducing hypoglycemia, which might be advantageous in kidney transplant recipients (KTRs) with NODAT. We conducted a randomized, double-blind, placebo-controlled, phase II trial to assess safety and efficacy of the DPP-4 inhibitor vildagliptin. Intraindividual differences in oral glucose tolerance test (OGTT)-derived 2-h plasma glucose (2HPG) from baseline to 3 months after treatment served as primary endpoint. Among secondary outcomes, we evaluated HbA1c, metabolic and safety parameters, as well as OGTTs at 1 month after drug discontinuation. Of 509 stable KTRs who were screened in our outpatient clinic, 63 (12.4%) had 2HPG ≥ 200 mg/dL, 33 of them were randomized and 32 completed the study. In the vildagliptin group 2HPG and HbA1c were profoundly reduced in comparison to placebo (vildagliptin: 2HPG = 182.7 mg/dL, HbA1c = 6.1%; placebo: 2HPG = 231.2 mg/dL, HbA1c = 6.5%; both p ≤ 0.05), and statistical significance was achieved for the primary endpoint (vildagliptin: 2HPG-difference -73.7 ± 51.3 mg/dL; placebo: -5.7 ± 41.4 mg/dL; p < 0.01). Adverse events were generally mild and occurred at similar rates in both groups. In conclusion, DPP-4 inhibition in KTRs with overt NODAT was safe and efficient, providing a novel treatment alternative for this specific form of diabetes.

Nesfatin-1 stimulates fatty-acid oxidation by activating AMP-activated protein kinase in STZ-induced type 2 diabetic mice

Nesfatin-1 is an anorexigenic peptide involved in energy homeostasis. Recently, nesfatin-1 was reported to decrease blood glucose level and improve insulin sensitivity in high-fat diet-fed rats. However, little information is known about the influence of nesfatin-1 on lipid metabolism either in physiological or diabetic condition. This study undertook whether nesfatin-1 was involved in the pathophysiology in Streptozotocin-induced type 2 diabetic mice (T2DM), which was induced by a combination of high-calorie diet and two low-doses Streptozotocin. We observed that plasma nesfatin-1 was significantly increased while expression of nesfatin-1 neurons were decreased in hypothalamus in diabetes group compared to only high-calorie diet control group; intravenous injection of nesfatin-1 decreased 0–1h, 0–2h, 0–3h cumulative food intake in T2DM, but 0–24h total food intake had no difference between groups. Body weight and plasma FFA were normalized after nesfatin-1(10 µg/Kg) administration for 6 days. These results suggested that nesfatin-1 improved lipid disorder in T2DM. It was found that blood glucose and insulin resistance coefficient decreased with treatment of nesfatin-1 (both in 1 µg/Kg and 10 µg/Kg doses) in diabetes mice. For further understanding the role of nesfatin-1 on lipid metabolism, we detected p-AMPK and p-ACC of skeletal muscle in T2DM using western blotting. The expression of p-AMPK and p-ACC increased when nesfatin-1 was given with doses 1 µg/Kg but not in doses 10 µg/Kg. Taken together, nesfatin-1 participated in the development of T2DM and stimulated free fatty acid utilization via AMPK-ACC pathway in skeletal muscle in T2DM.