The role of oxidative stress in the pathogenesis of diabetic vascular complications

Rhodanine-benzamides as potential hits for α-amylase enzyme inhibitors and radical (DPPH and ABTS) scavengers

A series of 3-substituted and 3,5-disubstituted rhodanine-based derivatives were synthesized from 3-aminorhodanine and examined for α-amylase inhibitory, DPPH (1,1-diphenyl-2-picrylhydrazyl) and ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging activities in vitro. These derivatives displayed significant α-amylase inhibitory potential with IC50 values of 11.01-56.04 µM in comparison to standard acarbose (IC50 = 9.08 ± 0.07 µM). Especially, compounds 7 (IC50 = 11.01 ± 0.07 µM) and 8 (IC50 = 12.01 ± 0.07 µM) showed highest α-amylase inhibitory activities among the whole series. In addition to α-amylase inhibitory activity, all compounds also demonstrated significant scavenging activities against DPPH and ABTS radicals, with IC50 values ranging from 12.24 to 57.33 and 13.29-59.09 µM, respectively, as compared to the standard ascorbic acid (IC50 = 15.08 ± 0.03 µM for DPPH; IC50 = 16.09 ± 0.17 µM for ABTS). These findings reveal that the nature and position of the substituents on the phenyl ring(s) are crucial for variation in the activities. The structure-activity relationship (SAR) revealed that the compounds bearing an electron-withdrawing group (EWG) at para substitution possessed the highest activity. In kinetic studies, only the km value was changed, with no observed changes in Vmax, indicating a competitive inhibition. Molecular docking studies revealed important interactions between compounds and the α-amylase active pocket. Further advanced research needs to perform on the identified compounds in order to obtain potential antidiabetic agents.

Pathophysiologic Mechanisms and Potential Biomarkers in Diabetic Kidney Disease

Although diabetic kidney disease (DKD) remains the leading cause of end-stage kidney disease eventually requiring chronic kidney replacement therapy, the prevalence of DKD has failed to decline over the past 30 years. In order to reduce disease prevalence, extensive research has been ongoing to improve prediction of DKD onset and progression. Although the most commonly used markers of DKD are albuminuria and estimated glomerular filtration rate, their limitations have encouraged researchers to search for novel biomarkers that could improve risk stratification. Considering that DKD is a complex disease process that involves several pathophysiologic mechanisms such as hyperglycemia induced inflammation, oxidative stress, tubular damage, eventually leading to kidney damage and fibrosis, many novel biomarkers that capture one specific mechanism of the disease have been developed. Moreover, the increasing use of high-throughput omic approaches to analyze biological samples that include proteomics, metabolomics, and transcriptomics has emerged as a strong tool in biomarker discovery. This review will first describe recent advances in the understanding of the pathophysiology of DKD, and second, describe the current clinical biomarkers for DKD, as well as the current status of multiple potential novel biomarkers with respect to protein biomarkers, proteomics, metabolomics, and transcriptomics.

Chronically Elevated Exogenous Glucose Elicits Antipodal Effects on the Proteome Signature of Differentiating Human iPSC-Derived Pancreatic Progenitors

The past decade revealed that cell identity changes, such as dedifferentiation or transdifferentiation, accompany the insulin-producing β-cell decay in most diabetes conditions. Mapping and controlling the mechanisms governing these processes is, thus, extremely valuable for managing the disease progression. Extracellular glucose is known to influence cell identity by impacting the redox balance. Here, we use global proteomics and pathway analysis to map the response of differentiating human pancreatic progenitors to chronically increased in vitro glucose levels. We show that exogenous high glucose levels impact different protein subsets in a concentration-dependent manner. In contrast, regardless of concentration, glucose elicits an antipodal effect on the proteome landscape, inducing both beneficial and detrimental changes in regard to achieving the desired islet cell fingerprint. Furthermore, we identified that only a subgroup of these effects and pathways are regulated by changes in redox balance. Our study highlights a complex effect of exogenous glucose on differentiating pancreas progenitors characterized by a distinct proteome signature.

Resveratrol-Elicited PKC Inhibition Counteracts NOX-Mediated Endothelial to Mesenchymal Transition in Human Retinal Endothelial Cells Exposed to High Glucose

Diabetes-associated long-term hyperglycaemia leads to oxidative stress-mediated fibrosis in different tissues and organs. Endothelial-to-mesenchymal-transition (EndMT) appears to play a role in diabetes-associated fibrotic conditions. Here, we investigate whether EndMT is implicated in the diabetic retinopathy fibrotic process and evaluate the possibility that resveratrol could counteract EndMT by inhibiting high glucose (HG)-induced increases in ROS. Primary Human Retinal Endothelial Cells (HRECs) were either pre-treated for 24 h with 1 µM resveratrol or left untreated, then glucose (30 mM) was applied at 3-day intervals for 10 days. qRT-PCR and ELISA were used to detect mRNA or protein expression of endothelial markers (CD31, CDH5, vWF) or mesenchymal markers (VIM, αSMA and collagen I), respectively. Intracellular ROS levels were measured with carboxy-DCFDA, while NOX-associated ROS levels were evaluated using the NADPH-specific redox biosensor p47-roGFP. Treatment of HRECs with HG increased intracellular ROS levels and promoted phenotype shifting towards EndMT, evidenced by decreased expression of endothelial markers concomitant with increased expression of mesenchymal ones. HG-induced EndMT appears to be mediated by NADPH-associated ROS generation as pre-treatment of HRECs with resveratrol or the NADPH inhibitor, diphenyleneiodonium chloride (DPI), attenuated ROS production and EndMT transition, suggesting that the effect of resveratrol on HG-induced ROS occurs via down-regulation of NADPH oxidase. It is worth noting that resveratrol or Chelerythrine, a Protein kinase C (PKC) inhibitor, reduce ROS and EndMT in HG-exposed cells, suggesting that NADPH activation occurs via a PKC-dependent mechanism. Taken together, our results provide the basis for a resveratrol-based potential protective therapy to prevent diabetic-associated complications.

Imbalance in the antioxidant defence system and pro-genotoxic status induced by high glucose concentrations: In vitro testing in human liver cells

It has been hypothesized that high glucose concentrations might contribute to the overall intracellular oxidative stress either by the direct generation of reactive oxygen species (ROS) or by altering the redox balance. Moreover, it has also been suggested that high glucose concentration can increase the susceptibility of DNA to genotoxic effects of xenobiotics. The aim of this approach was to test high glucose concentrations for pro-genotoxicity in human liver cells by setting up an in vitro model for hyperglycaemia. The experimental design included performing of tests on both human HepG2 tumour cells and HepaRG immortalized cells. Increased cell susceptibility to genotoxic xenobiotics was tested by challenging cell cultures with 4-nitroquinoline-N-oxide (4NQO) and evaluating the extent of primary DNA damage by comet assay. Moreover, we evaluated the relationship between glucose concentration and intracellular ROS, as well as the effects of glucose concentration on the induction of Nrf2-dependent genes such as Glutathione S-transferases, Heme‑oxygenase-1, and Glutathione peroxidase-4. To investigate the involvement of ROS in the induced pro-genotoxic activity, parallel experimental sets were set up by considering co-treatment of cells with the model mutagen 4NQO and the antioxidant, glutathione precursor N-acetyl-L-cysteine. High glucose concentrations caused a significant increase in the levels of primary DNA damage, with a pro-genotoxic condition closely related to the concentration of glucose in the culture medium when cells were exposed to 4NQO. High glucose concentrations also stimulated the production of ROS and down-regulated genes involved in contrasting of the effects of oxidative stress. In conclusion, in the presence of high concentrations of glucose, the cells are in unfavourable conditions for the maintenance of genome integrity.

Analysis of long non-coding RNA expression profiles in high-glucose treated vascular endothelial cells

BACKGROUND

Diabetes mellitus is often associated with microvascular and macrovascular lesions, and hyperglycemia-induced vascular endothelial cell damage is a key factor.

METHODS

We investigated long non-coding RNAs (lncRNAs) and mRNAs that are affected by hyperglycemia-induced damage using human umbilical vein endothelial cells (HUVECs) as a model. HUVECs were cultured under high (25 mmol/L) or normal (5 mmol/L) glucose conditions for 6 d, and then lncRNAs and protein-coding transcripts were profiled by RNA-seq.

RESULT

Among 40,379 lncRNAs screened, 214 were upregulated (log2 [fold-change] > 1, FDR < 0.05) and 197 were downregulated (log2 [fold-change] < - 1, FDR < 0.05) in response to high-glucose. Furthermore, among 28,431 protein-coding genes screened, 778 were upregulated and 998 were downregulated. A total of 945 lncRNA/mRNA pairs were identified, including 126 differentially expressed lncRNAs predicted to target 201 mRNAs, among which 26 were cis-regulatory interactions. The corresponding lncRNA-mRNA network was composed of 354 lncRNA nodes, 1167 mRNA nodes and 9735 edges. Dozens of lncRNAs with high degree may play important roles in high-glucose-induced HUVEC damage, including ENST00000600527, NONHSAT037576.2, NONHSAT135706.2, ENST00000602127, NONHSAT200243.1, NONHSAT217282.1, NONHSAT176260.1, NONHSAT199075.1, NONHSAT067063.2, NONHSAT058417.2.

CONCLUSION

These observations may provide novel insights into the regulatory molecules and pathways of hyperglycemia-related endothelial dysfunction in diabetes-associated vascular disease.

A review of fibroblast growth factor 21 in diabetic cardiomyopathy

FGF21 (fibroblast growth factor 21) is a regulator of metabolism and performs an important role in glucose and lipid metabolism and the maintenance of energy balance. FGF21 is principally expressed in the liver, but it can also be found in the pancreas, skeletal muscle, and adipose tissue. It is known that levels of serum FGF21 are significantly elevated in obese, insulin-resistant patients, and those with metabolic syndrome. Elevated levels of FGF21 in serum during the early stages of various metabolic diseases are considered a compensatory response by the organism. Therefore, FGF21 is considered a hormone in response to stress and an early diagnostic marker of disease. Diabetic cardiomyopathy is a special type of cardiac complication, characterized as a chronic myocardial disorder caused by diabetes. The pathological process includes increased oxidative stress, energy metabolism in myocardial cells, an inflammatory response, and myocardial cell apoptosis. A growing body of evidence suggests that FGF21 has the potential to be an effective drug for the treatment of diabetic cardiomyopathy. Here, we review recent progress on the characteristics of FGF21 in its protective role, especially in pathological processes such as suppressing apoptosis in the myocardium, reducing inflammation in cardiomyocytes, reducing oxidative stress, and promoting fatty acid oxidation. In addition, we explore the possibility that diabetic cardiomyopathy can be delayed through the application of FGF21, providing possible therapeutic targets of the disease.

Ameliorative effects of Hydrolea zeylanica in streptozotocin-induced oxidative stress and metabolic changes in diabetic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Hydrolea zeylanica L. Vahl. (Hydroleaceae) is an aquatic medicinal plant used as leafy vegetable in some parts of India. In south Odisha and Hazaribag district of Jharkhand, India, decoction of leaves is used as household remedy for diabetes. To our knowledge, no prior studies have examined the antidiabetic activity of H. zeylanica to validate its ethnomedicinal claim.

PURPOSE

With this aim in mind, we examined the bioactivity of hydroalcohol fraction of leaves of H. zeylanica (HAHZ) in streptozotocin-induced oxidative stress in diabetic rats.

MATERIALS AND METHODS

In vitro antidiabetic and free radical scavenging activities of different fractions of H. zeylanica were performed. The most effective bioactive fraction e.g. HAHZ was considered for kinetic studies to understand the mode of inhibition of α-glucosidase and α-amylase. To understand the chemical composition, GC-MS/MS and LC-MS/MS analysis of HAHZ were performed. To find out the molecular mechanism of action of HAHZ, streptozotocin-induced oxidative stress and metabolic changes in diabetic rats were studied.

RESULTS

HAHZ demonstrated significantly higher radical scavenging and antidiabetic activities. Kinetic analysis revealed that HAHZ inhibited α-glucosidase competitively, and α-amylase mixed competitively. To understand the chemical composition, GC-MS/MS and LC-MS/MS analysis of HAHZ identified 32 compounds and among which R-limonene (0.52%), perillartine (0.41%), N-formyl-L-lysine (1.49%), limonen-6-ol, pivalate (1.43%), lidocaine (1.70%) and gamolenic acid (2.80%) were reported to have antioxidant and antidiabetic activities. HAHZ-400 mg/kg showed significant (p < 0.001) improvement in serum markers (SGOT, SGPT, ALP, total bilirubin, total protein, triglycerides, total cholesterol, HDL-C, LDL-C) and oxidative markers (MDA, SOD, CAT, GSH) in serum, liver and pancreas at effective dose dependent manner. In histopathological observation, HAHZ-400 mg/kg showed marked improvement in restoring cellular architecture of liver and pancreas.

CONCLUSION

In diabetic rats, the improvement in glycemic control mechanism was achieved upon stimulating insulin secretion by R-limonene, perillartine, N-formyl-L-lysine, limonen-6-ol, pivalate, lidocaine and gamolenic acid of HAHZ.

Recent advances in the pathogenesis of microvascular complications in diabetes

Millions of people worldwide have diabetes, which is diagnosed by fasting blood glucose levels exceeding 126 mg/dL. Regardless of the type of diabetes, prolonged hyperglycemia is damaging to several organs including eyes, kidneys, nerve, and/or heart. The damages are associated with a high risk of morbidity and mortality. Diabetes has been implicated in ischemia in the microvasculature of the target tissues, which occurs due to the insufficient perfusion of tissues. The resulting occlusion and pain affect the quality of life. Multiple therapeutic approaches have been proposed for a long time to overcome these vascular complications. Apart from systemically controlling high glucose levels, other therapeutic strategies are not well understood. In this review, we summarize the recent literature for biochemical/cellular targets that are being utilized for the treatment of diabetic microvascular diseases. These targets, which are closely associated with mitochondrial dysfunction, include the polyol and diacylglycerol-protein kinase C pathways, oxidative stress, non-enzymatic glycation and the formation of advanced glycation end products, and immune dysregulation/inflammation.

p38 MAPK Inhibitor (SB203580) and Metformin Reduces Aortic Protein Carbonyl and Inflammation in Non-obese Type 2 Diabetic Rats

Microvascular and macrovascular diseases are the main causes of morbidity in type 2 diabetes patients through chronic hyperglycaemic condition via oxidative stress and inflammation. Reactive oxygen species (ROS) activate p38 MAPK phosphorylation and inflammation which enhances protein modification by carbonylation. The use of metformin and a p38 MAPK inhibitor is hypothesised to reduce ROS production and inflammation but effects of metformin and p38 MAPK inhibitor (SB203580) on ROS production and inflammation in vascular type 2 diabetes mellitus non-obese (T2DM) have not been investigated. The Goto-Kakizaki rat T2DM model was divided into three groups as T2DM, T2DM treated with 15 mg/kg bw metformin and T2DM treated with 2 mg/kg bw SB203580 for 4 weeks. Rat aortas were isolated and protein carbonyl (PC) contents were measured by spectrophotometric DNPH assay. Aortic IL-1ß level was determined by ELISA. Results showed that aortic PC contents in the T2DM group were significantly higher than in non-diabetic rats. Treatment with metformin or SB203580 significantly reduced PC contents while only metformin significantly reduced IL-1ß levels. Findings indicated that metformin reduced ROS production and inflammation in diabetic vessels and possibly reduce vascular complications in non-obese T2DM.

Metabolic syndrome status over 2 years predicts incident chronic kidney disease in mid-life adults: a 10-year prospective cohort study

We investigated whether changes in MetS status over two years modify the 10-year risk of CKD and proteinuria. A prospective cohort study was conducted in 7,251 subjects without CKD at baseline. We categorized subjects according to MetS status over two years: non-MetS (no MetS at either visit), intermittent MetS (positive for MetS at one assessment), and persistent MetS (positive for MetS at two assessments). The hazard ratio (HR) of new-onset CKD over 10-year was calculated using Cox models. During the 10-year follow-up period, 923 (12.7%) developed CKD. Compared to the non-MetS group, the fully adjusted HR for new-onset CKD was the highest in the persistent MetS group (HR, 1.53; 95% CI, 1.23-1.90), followed by the intermittent MetS group (HR, 1.29; 95% CI, 1.04-1.59) (P for trend <0.001). The HR for developing proteinuria was 1.79 (95% CI, 1.15-2.79) in the persistent MetS group and 0.70 (95% CI, 0.42-1.19) in the intermittent MetS group when the non-MetS group was considered as the reference group. Temporal changes in MetS status over two years influenced the 10-year risk of incident CKD and proteinuria. Our findings suggest that monitoring and strictly controlling MetS are important in preventing renal function decline.

Antioxidant effects of vitamins in type 2 diabetes: a meta-analysis of randomized controlled trials

BACKGROUND

Vitamins are essential micronutrients with antioxidant potential that may provide a complementary treatment for patients with chronic diseases. Our aim was to assess the effect of vitamin supplementation on the antioxidant status and glycemic index of type 2 diabetes mellitus patients.

METHODS

We performed a systematic review with meta-analyses. Electronic searches were conducted in PubMed, Scopus, and Web of Science (December 2017). Randomized controlled trials evaluating the effect of any vitamin or vitamin complex supplementation on antioxidant status as primary outcome were included. The outcomes considered were: reduction of malondialdehyde (MDA); augmentation of glutathione peroxidase (GPx); changes in total antioxidant capacity (TAC), enhance in superoxide dismutase enzyme-SOD, and thiobarbituric acid reactive substances (TBARS). Outcomes of glycemic control were also evaluated. Pairwise meta-analyses were performed using software Review Manager 5.3.

RESULTS

Thirty trials fulfilled the inclusion criteria, but only 12 could be included in the meta-analyses of antioxidant outcomes. The most commonly studied vitamins were B, C, D and E. Vitamin E was related to significant reduction of blood glucose as well as glycated hemoglobin compared to placebo, while both vitamins C and E were mainly associated with reducing MDA and TBARS and elevating GPx, SOD and TAC, compared to placebo. However, outcome reports in this field are still inconsistent (e.g. because of a lack of standard measures).

CONCLUSIONS

Supplementation of vitamin E may be a valuable strategy for controlling diabetes complications and enhancing antioxidant capacity. The effects of other micronutrients should be further investigated in larger and well-designed trials to properly place these complementary therapies in clinical practice.

Liraglutide ameliorates early renal injury by the activation of renal FoxO1 in a type 2 diabetic kidney disease rat model

AIMS

The aim of this study was to investigate the effects of liraglutide on renal injury and the renal expression of FoxO1 in type 2 diabetic rats.

METHODS

Type 2 diabetic rats model was induced by a high-sugar and high-fat diet and intraperitoneal injection of low-dose Streptozotocin (STZ) (30 mg/kg). Five weeks after STZ injection, diabetic rats were randomly treated with or without subcutaneous injection of liraglutide (0.2 mg/kg/12 h) for eight weeks. Diabetes-related physical and biochemical indicators, renal histopathological and ultrastructural changes, the expression of renal transforming growth factor beta-1 (TGF-β1), fibronectin (FN), type IV collagen (Col IV), protein kinase B (Akt), forkhead box protein O1 (FoxO1) and manganese superoxide dismutase (MnSOD) were measured.

RESULTS

Rats in DN group showed a significant increase in fasting blood glucose, HbA1c, kidney to body weight index, serum creatinine (Scr), blood urea nitrogen (BUN), urinary albumin excretion, mesangial matrix index, glomerular basement membrane (GBM) thickening, podocyte foot process fusion, the mRNA and protein levels of renal TGF-β1, FN and Col IV and a dramatic decrease in the mRNA and protein levels of renal MnSOD, all of which were significantly ameliorated by liraglutide. In addition, liraglutide also increased the expression of FoxO1 mRNA and reduced renal phosphorylation levels of Akt and FoxO1 protein.

CONCLUSIONS

These results suggest that liraglutide may exert a renoprotective effect by a FoxO1-mediated upregulation of renal MnSOD expression in the early DKD.

Role of peroxisome proliferator-activated receptor-gamma activation on visfatin, advanced glycation end products, and renal oxidative stress in obesity-induced type 2 diabetes mellitus

The present study focused on the role of peroxisome proliferator-activated receptor-gamma (PPAR-γ) activation on renal oxidative damages, serum visfatin, and advanced glycation end products (AGEs) in high-fat diet (HFD)-induced type 2 diabetes mellitus. Following the institutional animal ethics committee guidelines, Wistar rats were categorized into five groups: group 1: fed on a normal rat diet; group 2: HFD-induced obese rats (HFD for 8 weeks); group 3: HFD-fed rats treated with rosiglitazone (RSG; 3 mg/kg orally for 7 days); group 4: T2DM rats induced by HFD and low dose of streptozotocin (i.p. 35 mg/kg); group 5: T2DM rats treated with RSG (3 mg/kg orally for 7 days). Serum levels of AGEs and visfatin, renal damage, and oxidative stress were analyzed. Results showed that HFD-induced obesity and T2DM caused an elevated blood glucose, serum AGEs, visfatin, insulin, urea, creatinine, and tissue malondialdehyde, whereas a decreased catalase and superoxide dismutase activity were observed. The PPAR-γ activation via agonist restored these changes. Our findings suggest that AGEs and visfatin possess an important role in the progression of renal oxidative stress, which can be reduced by the PPAR-γ agonist that impede deleterious effects of HFD and HFD-induced T2DM on renal damage.

Gilbert syndrome in patients with type 1 diabetes-Prevalence, glycemic control, and microalbuminuria

BACKGROUND

Gilbert syndrome (GS) is a common hereditary condition, characterized by intermittent unconjugated hyperbilirubinemia. In adults with type 2 diabetes and GS, a markedly lower prevalence of nephropathy was documented, suggesting a beneficial effect of hyperbilirubinemia. We investigated the prevalence of GS among individuals with type 1 diabetes mellitus (T1DM), and the prevalence of microalbuminuria.

METHODS

The prevalence of GS was assessed in 401 (204 female) patients with T1DM, median age 21.0 years, (interquartile range [IQR], 15.7-27.9), median disease duration 10.8 years (IQR, 5.7-15.8); and was compared with GS prevalence in 181 children (control). The prevalence of microalbuminuria was assessed in patients with T1DM and GS (group I) and compared with that of patients with T1DM alone (group II), in a ratio of 1:2 matched by gender, age, and duration of diabetes.

RESULTS

The prevalence of GS in TIDM patients was significantly higher than in the control group (10.7% vs 3.3% respectively, p = .004), with no gender difference. Patients with T1DM and GS had significantly lower HbA1c levels than did those with T1DM alone 7.3 ± 1.2 vs 7.9 ± 1.3% respectively (56 ± 13 vs 63 ± 14 mmol/mol), p = .02. The rate of microalbuminuria was 14.0% vs 11.0% for patients with T1DM and GS, compared with those with T1DM alone (p = .6).

CONCLUSIONS

The occurrence of GS was 3-fold higher among individuals with T1DM than in a healthy control group. Despite better glycemic control, the rate of microalbuminuria was similar among young individuals with T1DM and GS, and those with T1DM alone, suggesting no protective value to elevated bilirubin.

Low serum bilirubin level predicts the development of chronic kidney disease in patients with type 2 diabetes mellitus

BACKGROUND/AIMS

We evaluated whether serum bilirubin levels can predict the development of chronic kidney disease (CKD) in patients with type 2 diabetes mellitus (T2DM).

METHODS

This was a retrospective observational longitudinal study of patients presenting at the Pusan National University Hospital. A total of 349 patients with T2DM and preserved kidney function (estimated glomerular filtration rate ≥ 60 mL/min/1.73 m²) were enrolled. The main outcome was the development of CKD stage 3 or greater. The patients were divided into four groups according to the quartiles of the total serum bilirubin levels at baseline.

RESULTS

The group with the lowest range of total serum bilirubin level (Q1) showed the highest cumulative incidence of CKD stage 3 or greater than that of the other lower quartiles (Q1 vs. Q4; hazard ratio [HR], 6.75; 95% confidence interval [CI], 1.54 to 29.47; p = 0.011). In multivariate analysis, the risk of developing CKD stage 3 or greater was higher in the second lowest quartile of the serum bilirubin level than that in the highest quartile of the serum bilirubin level (Q2 vs. Q4; HR, 9.36; 95% CI, 1.33 to 65.73; p = 0.024). In the normoalbuminuria subgroup (n = 236), multivariate analysis showed that the risk of developing CKD stage 3 or greater was higher in the lowest quartile of the serum bilirubin level than that in the highest quartile of the serum bilirubin level (Q1 vs. Q4; HR, 7.36; 95% CI, 1.24 to 35.82; p = 0.019).

CONCLUSIONS

Serum bilirubin might be an early clinical marker for predicting the progression of CKD in patients with T2DM and preserved renal function.

Protective effects of 6-Gingerol on vascular endothelial cell injury induced by high glucose via activation of PI3K-AKT-eNOS pathway in human umbilical vein endothelial cells

6-Gingerol (6-Gin), an active constituent of Zingiber officinale, has been reported to have anti-inflammatory, anti-oxidative, anti-cancerous etc. bioactivities. However, little is known about its endothelial protective effects and the underlying mechanisms. In this study, our purpose was to investigate the protective effects of 6-Gin and its underlying mechanisms. HUVECs were exposed to high glucose (HG, 33mM glucose) for 48h, followed by 50μM 6-Gin with or without LY294002 (10μM), AKT inhibitor IV (0.5μM) or L-NAME (5mM) for another 24h. Cell viability, levels of NO, LDH and ROS were detected. In addition, the expression levels of IKK, IRS-1, PI3K, AKT, eNOS and their phosphorylated proteins were measured by western blots. Compared with the control, HUVECs were significantly impaired by HG, characterized by decreased levels of the cell viability, NO, pY458-PI3K, pS473-AKT and pS1177-eNOS while increased levels of LDH, pS176-IKK, and p-S312-IRS-1. Conversely, 6-Gin remarkably protected HUVECs against HG-induced injury in a concentration- and time-dependent manner. However, the protective effects of 6-Gin were abolished by co-treatment with LY294002, AKT inhibitor IV or L-NAME at the HG state. Collectively, 6-Gin attenuated the injury of HUVECs induced by HG through the activation of PI3K-AKT-eNOS signal pathway. The findings provide a novel potential for 6-Gin to prevent and treat the angiopathy resulting from diabetes mellitus.

Agkistrodon acutus-purified protein C activator protects human umbilical vein endothelial cells against H2O2-induced apoptosis

CONTEXT

Recent studies show that the Agkistrodon acutus (Viperidae) (syn. Deinagkistrodon acutus) protein C activator (PCA) treats acute myocardial infarction and ischaemia-reperfusion animal models effectively, while the underlying mechanism remains unknown.

OBJECTIVE

To study the effect of PCA on the injury of human umbilical vein endothelial cells (HUVECs) induced by H₂O₂ and the underlying mechanism.

MATERIALS AND METHODS

Primary cultured HUVECs were pretreated with PCA (20, 40 and 80 μg/mL) for 1 h, then HUVEC apoptosis was induced by 300 μmol/mL H₂O₂. Apoptosis was analyzed by AnnexinV-FITC/PI, and reactive oxygen species (ROS) level was tested by flow cytometry. Colorimetric methods were used to detect the levels of NO and IL-1. In addition, real-time PCR and western blot analyses were used to detect the expression of eNOS and phospho-p38/MAPK.

RESULTS

Morphological changes were induced by H₂O₂ in HUVECs. The cell survival rate was increased by 43.9, 64.0 and 80.6% in each PCA pretreated group (20, 40 and 80 μg/mL) compared to the model group. In each PCA pretreated group, oxidative stress level was also decreased to 54.7, 42.7 and 25.1%. Moreover, the level of IL-1 was decreased to 83.3, 62.2 and 30.7%. The level of NO was increased by 155.9, 232.4 and 317.6%. Apoptosis rate was decreased to 59.0, 47.7 and 32.7%. Phospho-p38 expression was downregulated, but eNOS expression was upregulated.

DISCUSSION AND CONCLUSION

The results suggest that PCA can effectively protect the endothelial cells from injury induced by H₂O₂, which may be associated with antioxidation, upregulation of eNOS and downregulation of p38-MAPK.

Diabetes and increased lipid peroxidation are associated with systemic inflammation even in well-controlled patients

BACKGROUND

The effect of the interaction between type 2 diabetes and dyslipidemia on inflammation and lipid peroxidation (LPO) has not been assessed.

AIM

To investigate whether diabetes coupled with dyslipidemia alters oxidative metabolism leading to increased LPO products and inflammatory status.

METHODS

100 patients were divided into four groups based upon diabetic and dyslipidemic status: poorly controlled diabetes with dyslipidemia (DM-PC/D), well-controlled diabetes with dyslipidemia (DM-WC/D), normoglycemic individuals with dyslipidemia (NG/D), and normoglycemic individuals without dyslipidemia (NG/ND). Plasma was evaluated for an LPO product (MDA), antioxidant levels and inflammatory cytokines.

RESULTS

Diabetics presented significantly higher levels of LPO (p<0.05) and the DM-PC/D had higher levels of proinflammatory cytokines and MDA in the plasma in comparison with normoglycemics (p<0.05). Interestingly IL1-β, IL-6, and TNF-α in DM-WC/D were not statistically different from those in DM-PC/D. Normoglycemic individuals with dyslipidemia presented significantly increased levels of IL-6 and TNF-α when compared to normoglycemic without dyslipidemia (p<0.05). MDA levels were also positively correlated with the presence of DM complications (r=0.42, p<0.01).

CONCLUSIONS

These findings show that dyslipidemia is associated with an increased inflammatory status, even in well-controlled diabetics and in normoglycemics. Our results suggest that lipid metabolism and peroxidation are important for the development of inflammation, which is elevated in several complications associated with diabetes.

Comparison of acarbose and metformin therapy in newly diagnosed type 2 diabetic patients with overweight and/or obesity

OBJECTIVE

To compare the efficacy of acarbose and metformin in overweight and/or obese patients with newly diagnosed type 2 diabetes mellitus (T2DM).

METHODS

A total of 108 drug-naïve patients with newly diagnosed T2DM, whose hemoglobin A1c (HbA1c) was between 7% and 10% and body mass index was greater than 24 kg/m(2), were enrolled in the First People's Hospital and Municipal Central Hospital of Xiangtan City, Xiangtan, China, from 1 February 2010 to 1 August 2011. Patients were randomly assigned to acarbose (100 mg three times a day) and metformin (1.5 g/day) groups for a predictive follow-up period of 24 weeks. Plasma glucose, insulin, and glucagons at 0, 0.5, and 2 hours after a standardized meal, and HbA1c were measured at baseline and 24 weeks.

RESULTS

Baseline characteristics of the acarbose and metformin groups were similar. Glucose control improved significantly in both groups at 24 weeks. The percentage of patients achieving HbA1C <6.5% was comparable for acarbose and metformin therapy at 24 weeks. Body weight reduction from baseline to 24 weeks was 3.3 kg in the acarbose group and 2.7 kg in the metformin group, whereas the change in HbA1c and body weight was similar in both groups. The early-phase insulin secretion index improved only in the acarbose group at 24 weeks. After 24 weeks of therapy, fasting glucagon and 0.5 hour postprandial glucagon levels decreased markedly in the acarbose group compared to the metformin group.

CONCLUSIONS

Twenty-four weeks of therapy with acarbose and metformin induced similar reductions in HbA1c and body weight, but acarbose showed superior efficacy in improving islet α-cell function compared with metformin in overweight/obese patients with newly diagnosed T2DM. However, more large-sample, multicenter, randomized controlled trials are needed to evaluate the efficacy, safety, cost-effectiveness, and glycemic variability of the two drugs.

Mechanisms for the cardiovascular effects of glucagon-like peptide-1

Over the past three decades, at least 10 hormones secreted by the enteroendocrine cells have been discovered, which directly affect the cardiovascular system through their innate receptors expressed in the heart and blood vessels or through a neural mechanism. Glucagon-like peptide-1 (GLP-1), an important incretin, is perhaps best studied of these gut-derived hormones with important cardiovascular effects. In this review, I have discussed the mechanism of GLP-1 release from the enteroendocrine L-cells and its physiological effects on the cardiovascular system. Current evidence suggests that GLP-1 has positive inotropic and chronotropic effects on the heart and may be important in preserving left ventricular structure and function by direct and indirect mechanisms. The direct effects of GLP-1 in the heart may be mediated through GLP-1R expressed in atria as well as arteries and arterioles in the left ventricle and mainly involve in the activation of multiple pro-survival kinases and enhanced energy utilization. There is also good evidence to support the involvement of a second, yet to be identified, GLP-1 receptor. Further, GLP-1(9-36)amide, which was previously thought to be the inactive metabolite of the active GLP-1(7-36)amide, may also have direct cardioprotective effects. GLP-1's action on GLP-1R expressed in the central nervous system, kidney, vasculature and the pancreas may indirectly contribute to its cardioprotective effects.

Clinical implications of carotid artery intima media thickness assessment on cardiovascular risk stratification in hyperlipidemic Korean adults with diabetes: the ALTO study

BACKGROUND

The primary objective was to investigate prevalence of subclinical atherosclerosis in Korean individuals with diabetes and hyperlipidemia. Association of subclinical atherosclerosis with cardiovascular risk was assessed.

METHODS

Assessments of carotid artery intima media thickness (cIMT) and atheromatous plaque were done using B-mode ultrasonography. Subclinical atherosclerosis was diagnosed based on presence of plaque, and/or increased cIMT versus mean cIMT reference values for Korean healthy controls. Atherosclerosis risk factors were analyzed using United Kingdom Prospective Diabetes Study (UKPDS) risk engine and Framingham Risk Score.

RESULTS

In total, 355 patients were included; increased mean cIMT was observed in 15.3 % of patients, 69 % had >1 carotid artery plaque, and 72.7 % were diagnosed with subclinical atherosclerosis. In total, 60 % of subjects were taking statins, with low-density lipoprotein cholesterol level maintained ~80 mg/dL at enrollment. Carotid artery measures were well correlated with UKPDS and Framingham risk scores. Prevalence of subclinical atherosclerosis in the low risk group (<15 % 10-year UKPDS-predicted coronary heart disease risk) was 64.7 %; higher than predicted in previous studies. In multivariate analysis, advanced age was a significant risk factor for subclinical atherosclerosis in men and women, while increased waist circumference and longer diabetes duration were independent predictors only in women.

CONCLUSION

Subclinical atherosclerosis is more prevalent among individuals with both diabetes and hyperlipidemia than in diabetic patients without additional cardiovascular risk factors. As conventional risk engines, based on modifiable risk factors may underestimate cardiovascular risk, early non-invasive carotid artery imaging screening may be warranted for patients with diabetes and hyperlipidemia, especially if they are elderly, have central obesity or have long duration of diabetes.

TRIAL REGISTRATION

www.clinicaltrials.gov NCT01264263.

Serum Total Bilirubin Levels Provide Additive Risk Information over the Framingham Risk Score for Identifying Asymptomatic Diabetic Patients at Higher Risk for Coronary Artery Stenosis

BACKGROUND

The diagnosis of coronary artery disease (CAD) is often delayed in patients with type 2 diabetes. Serum total bilirubin levels are inversely associated with CAD. However, no studies have examined whether this can be used as a biochemical marker for identifying asymptomatic diabetic patients at higher risk for having obstructive CAD.

METHODS

We performed a cross-sectional study of 460 consecutive asymptomatic patients with type 2 diabetes. All patients underwent coronary computed tomographic angiography, and their serum total bilirubin levels were measured. Obstructive CAD was defined as ≥50% diameter stenosis in at least one coronary artery.

RESULTS

Serum total bilirubin tertiles showed an inverse association with the prevalence of obstructive CAD. In multivariate logistic regression analysis, the odds ratio for the highest versus the lowest tertile of total bilirubin was 0.227 (95% confidence interval [CI], 0.130 to 0.398), and an increment of 1 µmol/L in serum total bilirubin level was associated with a 14.6% decrease in obstructive CAD after adjustment for confounding variables. Receiver operating characteristic curve analysis showed that the area under the curve for the Framingham Risk Score (FRS) plus serum total bilirubin level was 0.712 (95% CI, 0.668 to 0.753), which is significantly greater than that of the FRS alone (P=0.0028).

CONCLUSION

Serum total bilirubin level is inversely associated with obstructive CAD and provides additive risk information over the FRS. Serum total bilirubin may be helpful for identifying asymptomatic patients with type 2 diabetes who are at higher risk for obstructive CAD.

Undiagnosed diabetes is prevalent in younger adults and associated with a higher risk cardiometabolic profile compared to diagnosed diabetes

BACKGROUND

A substantial percentage of patients have undiagnosed diabetes. We investigated the demographic characteristics and cardiometabolic profiles of subjects with undiagnosed diabetes.

METHODS

A cross-sectional study with nationally representative samples of 25490 subjects aged ≥ 20 years from the KHNANES 2008 to 2011, which applied a complex, multistage, probability proportional to size sampling design. Subjects were categorized as having normal glucose (n = 16880), impaired fasting glucose (n = 5771), undiagnosed diabetes (n = 713), or diagnosed diabetes (n = 2126). Hyper low-density lipoprotein cholesterolemia was individually evaluated by the 2004 Adult Treatment Panel III guidelines and predicted risk of cardiovascular disease was estimated from the Framingham model.

RESULTS

Among overall subjects with diabetes, the prevalence of undiagnosed diabetes was markedly increased in younger adults compared to older adults (49% in diabetic subjects <50 years vs 23% in diabetic subjects ≥50 years, P < .001), suggesting significant discrepancies in age-based screening. Patients with undiagnosed diabetes were also more likely to have undiagnosed or uncontrolled hypertension and hyper-low-density lipoprotein cholesterolemia. Individuals with undiagnosed diabetes had a significantly higher predicted 10-year Framingham cardiovascular disease risk than those with diagnosed diabetes (11% vs 8% in <50 years, 33% vs 30% in ≥50 years; both P < .001). Patients with undiagnosed diabetes were also more likely to have multiple cardiovascular risk factors including obesity, smoking and uncontrolled hypertension.

CONCLUSIONS

People with undiagnosed diabetes have a higher predicted risk for cardiovascular disease compared to those with diagnosed diabetes. Intensive screening for diabetes in younger adults should be stressed in public healthcare to reduce the burden of modifiable cardiometabolic risk among individuals with undiagnosed diabetes.

Roles of oxidative stress, adiponectin, and nuclear hormone receptors in obesity-associated insulin resistance and cardiovascular risk

Obesity leads to the development of type 2 diabetes mellitus, which is a strong risk factor for cardiovascular disease. A better understanding of the molecular basis of obesity will lead to the establishment of effective prevention strategies for cardiovascular diseases. Adipocytes have been shown to generate a variety of endocrine factors termed adipokines/adipocytokines. Obesity-associated changes to these adipocytokines contribute to the development of cardiovascular diseases. Adiponectin, which is one of the most well-characterized adipocytokines, is produced exclusively by adipocytes and exerts insulin-sensitizing and anti-atherogenic effects. Obese subjects have lower levels of circulating adiponectin, and this is recognized as one of the factors involved in obesity-induced insulin resistance and atherosclerosis. Another pathophysiological feature of obesity may involve the low-grade chronic inflammation in adipose tissue. This inflammatory process increases oxidative stress in adipose tissue, which may affect remote organs, leading to the development of diabetes, hypertension, and atherosclerosis. Nuclear hormone receptors (NRs) regulate the transcription of the target genes in response to binding with their ligands, which include metabolic and nutritional substrates. Among the various NRs, peroxisome proliferator-activated receptor γ promotes the transcription of adiponectin and antioxidative enzymes, whereas mineralocorticoid receptor mediates the effects of aldosterone and glucocorticoid to induce oxidative stress in adipocytes. It is hypothesized that both play crucial roles in the pathophysiology of obesity-associated insulin resistance and cardiovascular diseases. Thus, reduced adiponectin and increased oxidative stress play pathological roles in obesity-associated insulin resistance to increase the cardiovascular disease risk, and various NRs may be involved in this pathogenesis.

Common polymorphisms in antioxidant genes are associated with diabetic nephropathy in Type 2 diabetes patients

AIM

To investigate if antioxidative genes' polymorphisms influence the risk for Type 2 diabetes (T2D) complications.

MATERIALS & METHODS

In total, 181 T2D patients were genotyped for SOD2, CAT, GPX1, GSTP1, GSTM1*0, GSTT1*0, GCLC and GCLM.

RESULTS

After adjustment for duration of T2D, CAT rs1001179 and GSTP1 rs1138272 showed strongest association with risk for end-stage kidney failure (p = 0.005 and p = 0.049, respectively). In patients without end-stage kidney failure CAT rs1001179 influenced urea levels (p = 0.003), while GSTP1 rs1695 and GSTP1 haplotypes influenced the risk of moderately increased albuminuria (p = 0.024 and p = 0.014, respectively).

CONCLUSION

Common CAT and GSTP1 polymorphisms could be used to identify T2D patients at an increased risk for developing end-stage kidney failure.

The impact of mast cells on cardiovascular diseases

Mast cells comprise an innate immune cell population, which accumulates in tissues proximal to the outside environment and, upon activation, augments the progression of immunological reactions through the release and diffusion of either pre-formed or newly generated mediators. The released products of mast cells include histamine, proteases, as well as a variety of cytokines, chemokines and growth factors, which act on the surrounding microenvironment thereby shaping the immune responses triggered in various diseased states. Mast cells have also been detected in the arterial wall and are implicated in the onset and progression of numerous cardiovascular diseases. Notably, modulation of distinct mast cell actions using genetic and pharmacological approaches highlights the crucial role of this cell type in cardiovascular syndromes. The acquired evidence renders mast cells and their mediators as potential prognostic markers and therapeutic targets in a broad spectrum of pathophysiological conditions related to cardiovascular diseases.

Evidence-based practice use of incretin-based therapy in the natural history of diabetes

The incretin class of anti-hyperglycemic agents, including glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-inhibitors, is an important addition to the therapeutic armamentarium for the management of appropriate patients with type 2 diabetes mellitus as an adjunct to diet and exercise and/or with the agents metformin, sulfonylureas, thiazolidinediones, or any combination thereof. More recently, US Food and Drug Administration (FDA)-approved indications for incretins were expanded to include use with basal insulin. This review article takes an evidence-based practice approach in discussing the importance of aggressive treatment for diabetes, the principles of incretin physiology and pathophysiology, use of glucagon-like peptide-1 receptor agonists and dipeptidyl peptidase-4 inhibitors, and patient types and contexts where incretin therapy has been found beneficial, from metabolic syndrome to overt diabetes.

Antioxidant effects of statins in the management of cardiometabolic disorders

Redox systems are key players in vascular health. A shift in redox homeostasis-that results in an imbalance between reactive oxygen species (ROS) generation and endogenous antioxidant defenses has the potential to create a state of oxidative stress that subsequently plays a role in the pathogenesis of a number of diseases, including those of the cardiovascular and metabolic system. Statins, which are primarily used to reduce the concentration of low-density lipoprotein cholesterol, have also been shown to reduce oxidative stress by modulating redox systems. Studies conducted both in vitro and in vivo support the role of oxidative stress in the development of atherosclerosis and cardiovascular diseases. Oxidative stress may also be responsible for various diabetic complications and the development of fatty liver. Statins reduce oxidative stress by blocking the generation of ROS and reducing the NAD+/NADH ratio. These drugs also have effects on nitric oxide synthase, lipid peroxidation and the adiponectin levels. It is possible that the antioxidant properties of statins contribute to their protective cardiovascular effects, independent of the lipid-lowering actions of these agents. However, possible adverse effects of statins on glucose homeostasis may be related to the redox system. Therefore, studies investigating the modulation of redox signaling by statins are warranted.

Increased oxidative stress in obesity: implications for metabolic syndrome, diabetes, hypertension, dyslipidemia, atherosclerosis, and cancer

Obesity, especially of the abdominal type, is a health problem that constitutes metabolic syndrome and increases the incidence of various diseases, including diabetes, hypertension, dyslipidemia, atherosclerosis, and cancer. Various mechanisms linking obesity to these associated diseases have been postulated. One candidate is oxidative stress, which has been implicated in vascular complications of diabetes and in pancreatic -cell failure in diabetes. Notably, obese people without diabetes also display elevated levels of systemic oxidative stress. In addition, levels of oxidative stress are increased in the adipose tissue in obese mice. Treating obese mice with antioxidant agents attenuates the development of diabetes. In 3T3-L1 adipocytes, increases in reactive oxygen species (ROS) occur with lipid accumulation; the addition of free fatty acids elevates ROS generation further. Thus, adipose tissue represents an important source of ROS; ROS may contribute to the development of obesity-associated insulin resistance and type 2 diabetes. Moreover, the levels of oxidative stress present in several other types of cells or tis-sues, including those in the brain, arterial walls, and tumors, have been implicated in the pathogenesis associated with hypertension, atherosclerosis, and cancer. The increased levels of systemic oxidative stress that occur in obesity may contribute to the obesity-associated development of these diseases.

Serum total bilirubin levels and prevalence of diabetic retinopathy in a Chinese population

BACKGROUND

Patients with type 2 diabetes (T2D) are at a high risk of developing microvascular complications, such as diabetic retinopathy (DR). Previous studies have shown that low serum bilirubin concentrations in T2D patients may increase the risk of diabetic complications. Thus, the aim of the present was to investigate the association between the prevalence of DR and serum concentrations of total bilirubin in a Chinese population.

METHODS

The present study was a population-based cross-sectional study on 1761 T2D patients aged ≥40 years from the Jiading district of Shanghai, China. Fundus photographs were taken to confirm the presence and severity of DR. Subjects were assigned to quartiles based on serum total bilirubin concentrations (Quartile (Q) 1 <0.60 mg/dL; Q2 0.60-0.76 mg/dL; Q3 0.77-0.99 mg/dL; Q4 >0.99 mg/dL). Logistic regression models were used to explore the association between bilirubin concentrations and the prevalence of DR.

RESULTS

The prevalence of DR in the entire study population was 9.6%. The prevalence of DR was significantly lower in Q4 compared with the other three quartiles (Ptrend  = 0.004). After adjustment for multiple confounding factors, T2D patients in Q4 (i.e. serum bilirubin >0.99 mg/dL) were less likely (odds ratio 0.55; 95% confidence interval 0.33-0.91) to suffer from DR than patients in Q1 (i.e. serum bilirubin <0.60 mg/dL).

CONCLUSION

Serum bilirubin concentrations were inversely associated with DR in an elderly Chinese population, independent of traditional risk factors for microvascular complications.

Roles of adiponectin and oxidative stress in obesity-associated metabolic and cardiovascular diseases

The recent increase in populations with obesity is a worldwide social problem, and the enhanced susceptibility of obese people to metabolic and cardiovascular diseases has become a growing health threat. An understanding of the molecular basis for obesity-associated disease development is required to prevent these diseases. Many studies have revealed that the mechanism involves various bioactive molecules that are released from adipose tissues and designated as adipocytokines/adipokines. Adiponectin is an adipocytokine that exerts insulin-sensitizing effects in the liver and skeletal muscle via adenosine monophosphate-activated protein kinase and proliferator-activated receptor α activation. Additionally, adiponectin can suppress atherosclerosis development in vascular walls via various anti-inflammatory effects. In contrast, oxidative stress is a harmful factor that systemically increases during obesity and promotes the development of diabetes, atherosclerosis, and various other diseases. In obese mice, oxidative stress is enhanced in adipose tissue before diabetes development, but not in the liver, skeletal muscle, and aorta, suggesting that in obesity, adipose tissue may be a major source of reactive oxygen species (ROS). ROS suppress adiponectin production in adipocytes. Treatment of obese mice with anti-oxidative agents improves insulin resistance and restores adiponectin production. Recent studies have demonstrated that adiponectin protects against oxidative stress-induced damage in the vascular endothelium and myocardium. Thus, decreased circulating adiponectin levels and increased oxidative stress, which are closely linked to each other, should be deeply involved in obesity-associated metabolic and cardiovascular disease pathogenesis.

Low serum bilirubin concentration is a novel risk factor for the development of albuminuria in patients with type 2 diabetes

OBJECTIVE

Bilirubin has been recognized as an important endogeneous antioxidant. Previous studies reported that bilirubin could prevent atherosclerosis. The aim of this study was to investigate if serum bilirubin concentration could be a predictor for the development of albuminuria in patients with type 2 diabetes.

MATERIALS AND METHODS

We measured serum bilirubin in 320 consecutive patients with normoalbuminuria. We performed follow-up study to assess the development of albuminuria, mean interval of which was 3.2±0.9years. Cox proportional hazards regression was used to examine the relationship between serum bilirubin concentration and the development of albuminuria.

RESULTS

During follow-up duration, 43 patients have developed albuminuria. In multivariate analysis, after adjusting for comprehensive risk factors, the risk of developing albuminuria was higher in the lowest quartile of serum bilirubin concentrations than that in the highest quartile of serum bilirubin concentrations (Hazard ratio, 5.76; 95% CI, 1.65 to 24.93).

CONCLUSIONS

Low serum bilirubin concentration could be a novel risk factor for the development of albuminuria in patients with type 2 diabetes.

Pathogenesis of chronic hyperglycemia: from reductive stress to oxidative stress

Chronic overnutrition creates chronic hyperglycemia that can gradually induce insulin resistance and insulin secretion impairment. These disorders, if not intervened, will eventually be followed by appearance of frank diabetes. The mechanisms of this chronic pathogenic process are complex but have been suggested to involve production of reactive oxygen species (ROS) and oxidative stress. In this review, I highlight evidence that reductive stress imposed by overflux of NADH through the mitochondrial electron transport chain is the source of oxidative stress, which is based on establishments that more NADH recycling by mitochondrial complex I leads to more electron leakage and thus more ROS production. The elevated levels of both NADH and ROS can inhibit and inactivate glyceraldehyde 3-phosphate dehydrogenase (GAPDH), respectively, resulting in blockage of the glycolytic pathway and accumulation of glycerol 3-phospate and its prior metabolites along the pathway. This accumulation then initiates all those alternative glucose metabolic pathways such as the polyol pathway and the advanced glycation pathways that otherwise are minor and insignificant under euglycemic conditions. Importantly, all these alternative pathways lead to ROS production, thus aggravating cellular oxidative stress. Therefore, reductive stress followed by oxidative stress comprises a major mechanism of hyperglycemia-induced metabolic syndrome.

Role of angiotensin-converting enzyme 2 (ACE2) in diabetic cardiovascular complications

Diabetes mellitus results in severe cardiovascular complications, and heart disease and failure remain the major causes of death in patients with diabetes. Given the increasing global tide of obesity and diabetes, the clinical burden of diabetes-induced cardiovascular disease is reaching epidemic proportions. Therefore urgent actions are needed to stem the tide of diabetes which entails new prevention and treatment tools. Clinical and pharmacological studies have demonstrated that AngII (angiotensin II), the major effector peptide of the RAS (renin–angiotensin system), is a critical promoter of insulin resistance and diabetes mellitus. The role of RAS and AngII has been implicated in the progression of diabetic cardiovascular complications and AT1R (AngII type 1 receptor) blockers and ACE (angiotensin-converting enzyme) inhibitors have shown clinical benefits. ACE2, the recently discovered homologue of ACE, is a monocarboxypeptidase which converts AngII into Ang-(1–7) [angiotensin-(1–7)] which, by virtue of its actions on the MasR (Mas receptor), opposes the effects of AngII. In animal models of diabetes, an early increase in ACE2 expression and activity occurs, whereas ACE2 mRNA and protein levels have been found to decrease in older STZ (streptozotocin)-induced diabetic rats. Using the Akita mouse model of Type 1 diabetes, we have recently shown that loss of ACE2 disrupts the balance of the RAS in a diabetic state and leads to AngII/AT1R-dependent systolic dysfunction and impaired vascular function. In the present review, we will discuss the role of the RAS in the pathophysiology and treatment of diabetes and its complications with particular emphasis on potential benefits of the ACE2/Ang-(1–7)/MasR axis activation.

Clinical marker of platelet hyperreactivity in diabetes mellitus

Atherothrombotic complications are important causes of morbidity and mortality in diabetic patients. Diabetes has been considered to be a prothrombotic status. Several factors contribute to the prothrombotic condition, such as increasing coagulation, impaired fibrinolysis, endothelial dysfunction, and platelet hyperreactivity. Among the factors that contribute to the prothrombotic status in diabetes, altered platelet function plays a crucial role. Although understanding platelet function abnormalities in diabetes still remains as a challenge, more attention should be focused on platelet function for effective management and the prediction of atherothrombotic events in diabetic patients. This review will provide an overview on the current status of knowledge of platelet function abnormalities and clinical marker of platelet hyperreactivity in patients with diabetes.

Role of TRPM7 channels in hyperglycemia-mediated injury of vascular endothelial cells

This study investigated the change of transient receptor potential melastatin 7 (TRPM7) expression by high glucose and its role in hyperglycemia induced injury of vascular endothelial cells. Human umbilical vein endothelial cells (HUVECs) were incubated in the presence or absence of high concentrations of D-glucose (HG) for 72h. RT-PCR, Real-time PCR, Western blotting, Immunofluorescence staining and whole-cell patch-clamp recordings showed that TRPM7 mRNA, TRPM7 protein expression and TRPM7-like currents were increased in HUVECs following exposure to HG. In contrast to D-glucose, exposure of HUVECs to high concentrations of L-glucose had no effect. HG increased reactive oxygen species (ROS) generation, cytotoxicity and decreased endothelial nitric oxide synthase protein expression, which could be attenuated by knockdown of TRPM7 with TRPM7 siRNA. The protective effect of silencing TRPM7 against HG induced endothelial injury was abolished by U0126, an inhibitor of the extracellular signal-regulated kinase signaling pathway. These observations suggest that TRPM7 channels play an important role in hyperglycemia-induced injury of vascular endothelial cells.

Toxicological and pharmacological concerns on oxidative stress and related diseases

Although reactive oxygen species (ROS) such as superoxide, hydrogen peroxide and hydroxyl radical are generated as the natural byproduct of normal oxygen metabolism, they can create oxidative damage via interaction with bio-molecules. The role of oxidative stress as a remarkable upstream part is frequently reported in the signaling cascade of inflammation as well as chemo attractant production. Even though hydrogen peroxide can control cell signaling and stimulate cell proliferation at low levels, in higher concentrations it can initiate apoptosis and in very high levels may create necrosis. So far, the role of ROS in cellular damage and death is well documented with implicating in a broad range of degenerative alterations e.g. carcinogenesis, aging and other oxidative stress related diseases (OSRDs). Reversely, it is cleared that antioxidants are potentially able to suppress (at least in part) the immune system and to enhance the normal cellular protective responses to tissue damage. In this review, we aimed to provide insights on diverse OSRDs, which are correlated with the concept of oxidative stress as well as its cellular effects that can be inhibited by antioxidants. Resveratrol, angiotensin converting enzyme inhibitors, angiotensin receptor blockers, statins, nebivolol and carvedilol, pentaerythritol tetranitrate, mitochondria-targeted antioxidants, and plant-derived drugs (alone or combined) are the potential medicines that can be used to control OSRD.

Daily intake of vitamin D- or calcium-vitamin D-fortified Persian yogurt drink (doogh) attenuates diabetes-induced oxidative stress: evidence for antioxidative properties of vitamin D

BACKGROUND

Both poor vitamin D status and oxidative stress (OS) have been independently associated with late diabetic complications, including cardiovascular disease (CVD). The present study aimed to examine the effect of daily intake of vitamin D alone or in combination with calcium as a fortified Persian yogurt drink (doogh) on OS over 12 weeks.

METHODS

Ninety patients with type 2 diabetes aged 30-50 years from both sexes were randomly allocated to one of the three groups to receive two 250-mL bottles of doogh a day, which was either plain (PD; containing 150 mg per 250 mL of calcium and no detectable vitamin D), vitamin D-fortified (DD; containing 150 mg of calcium + 500 IU vitamin D per 250 mL) or calcium-vitamin D-fortified (CDD; 250 mg od calcium + 500 IU vitamin D per 250 mL).

RESULTS

Although mean (SD) serum concentrations of protein carbonyl significantly decreased in both DD and CDD groups [-2.07 (4.39) nm, P = 0.015 and -4.4 (7.64) nm, P = 0.003, respectively], the change in PD group was not significant [-0.54 (6.96) nm, P = 0.674]. A similar pattern was observed for cardiac myeloperoxidase [PD: -19.4 (75.9) μg L(-1) , P = 0.173; DD: -21.8 (54.2) μg L(-1) , P = 0.035, CDD: -48.5 (76.9) μg L(-1) , P = 0.002]. Superoxide dismutase increased significantly only in DD and CDD [56.9 (74.0) U L(-1) , P < 0.001 and 51.6 (119.9) U L(-1) , P = 0.025, respectively]. Changes of serum advanced glycation end-products showed a significant between-group difference among PD, DD and CDD [239.4 (388.4) U L(-1) , -58.1 (147.6) U L(-1) and -143.7 (475.9) U L(-1)  × 10(3) , respectively, P = 0.003], which remained significant after controlling for changes of fasting serum glucose (P = 0.013) and glycated haemoglobin (P = 0.015).

CONCLUSIONS

The findings of the present study demonstrated an OS attenuating effect of vitamin D. However, extra calcium did not convey additional benefit.