Advanced glycation end products induce apoptosis and procoagulant activity in cultured human umbilical vein endothelial cells

Thrombin Generation Is Associated With Extracellular Vesicle and Leukocyte Lipid Membranes in Atherosclerotic Cardiovascular Disease

BACKGROUND

Clotting, leading to thrombosis, requires interactions of coagulation factors with the membrane aminophospholipids (aPLs) phosphatidylserine and phosphatidylethanolamine. Atherosclerotic cardiovascular disease (ASCVD) is associated with elevated thrombotic risk, which is not fully preventable using current therapies. Currently, the contribution of aPL to thrombotic risk in ASCVD is not known. Here, the aPL composition of circulating membranes in ASCVD of varying severity will be characterized along with the contribution of external facing aPL to plasma thrombin generation in patient samples.

METHODS

Thrombin generation was measured using a purified factor assay on platelet, leukocyte, and extracellular vesicles (EVs) from patients with acute coronary syndrome (n=24), stable coronary artery disease (n=18), and positive risk factor (n=23) and compared with healthy controls (n=24). aPL composition of resting/activated platelet and leukocytes and EV membranes was determined using lipidomics.

RESULTS

External facing aPLs were detected on EVs, platelets, and leukocytes, elevating significantly following cell activation. Thrombin generation was higher on the surface of EVs from patients with acute coronary syndrome than healthy controls, along with increased circulating EV counts. Thrombin generation correlated significantly with externalized EV phosphatidylserine, plasma EV counts, and total EV membrane surface area. In contrast, aPL levels and thrombin generation from leukocytes and platelets were not impacted by disease, although circulating leukocyte counts were higher in patients.

CONCLUSIONS

The aPL membrane of EV supports an elevated level of thrombin generation in patient plasma in ASCVD. Leukocytes may also play a role although the platelet membrane did not seem to contribute. Targeting EV formation/clearance and developing strategies to prevent the aPL surface of EV interacting with coagulation factors represents a novel antithrombotic target in ASCVD.

Subcutaneous advanced glycation end products, cardiovascular risk factors and vascular health during childhood development in a Swiss population

Background

Skin-derived advanced glycation end products (sAGEs) have been associated with cardiovascular (CV) risk and mortality in adults. We hypothesize that cardiorespiratory fitness (CRF), body mass index (BMI) and vascular health are associated with development of sAGEs during childhood.

Methods

In our prospective cohort study, 1171 children aged 6-8 years were screened for sAGEs, BMI, retinal arteriolar diameters (CRAE) and pulse wave velocity (PWV), using standardized procedures. To determine CRF a 20 m shuttle run was performed. After four 4 years, all parameters were assessed in 675 children using the same protocols.

Results

Higher initial CRF levels were significantly associated with lower sAGEs (β [95 CI] -0.02 [-0.03 to -0.002] au, p = 0.022) levels at follow-up, although they showed a greater change from baseline to follow-up (β [95 CI] 0.02 [0.002 to 0.03] au, p = 0.027). Moreover, individuals with higher sAGEs at baseline showed narrower CRAE (β [95% CI] -5.42 [-8.76 to -2.08] μm, p = 0.001) at follow-up and showed a greater change in CRAE (β [95% CI] -3.99 [-7.03 to -0.96] μm, p = 0.010) from baseline to follow-up.

Conclusion

Exercise and higher CRF may help mitigate the formation of AGEs during childhood, thereby reducing the risk for development of CV disease associated with AGEs-induced damage. Preventive strategies may need to target CRF early in life to achieve improvement of CV risk factors and may counteract the development of CV disease later in life.

The Phosphodiesterase-5 Inhibitor Vardenafil Improves the Activation of BMP Signaling in Response to Hydrogen Peroxide

PURPOSE

The pleiotropic roles of phosphodiesterase-5 inhibitors (PDE5is) in cardiovascular diseases have attracted attention. The effect of vardenafil (a PDE5i) is partly mediated through reduced oxidative stress, but it is unclear whether vardenafil protects against hydrogen peroxide (H₂O₂)-induced endothelial cell injury, and the molecular mechanisms that are involved remain unknown. We determined the protective role of vardenafil on H₂O₂-induced endothelial cell injury in cultured human umbilical vein endothelial cells (HUVECs).

METHODS AND RESULTS

Vardenafil decreased the number of TUNEL-positive cells, increased the Bcl2/Bax ratio, and ameliorated the numbers of BrdU-positive cells in H₂O₂-treated HUVECs. The bone morphogenetic protein receptor (BMPR)/p-Smad/MSX2 pathway was enhanced in response to H₂O₂, and vardenafil treatment could normalize this pathway. To determine whether the BMP pathway is involved, we blocked the BMP pathway using dorsomorphin, which abolished the protective effects of vardenafil. We found that vardenafil improved the H₂O₂-induced downregulation of BMP-binding endothelial regulator protein (BMPER), which possibly intersects with the BMP pathway in the regulation of endothelial cell injury in response to oxidative stress.

CONCLUSIONS

We demonstrated for the first time that exogenous H₂O₂ activates BMPR expression and promotes Smad1/5/8 phosphorylation. Additionally, vardenafil can attenuate H₂O₂-induced endothelial cell injury in HUVECs. Vardenafil decreases apoptosis through an improved Bcl-2/Bax ratio and increases cell proliferation. Vardenafil protects against endothelial cell injury through ameliorating the intracellular oxidative stress level and BMPER expression. The protective role of vardenafil on H₂O₂-induced endothelial cell injury is mediated through BMPR/p-Smad/MSX2 in HUVECs.

AGE-RAGE synergy influences programmed cell death signaling to promote cancer

Advanced glycation end products (AGEs) are formed as a result of non-enzymatic reaction between the free reducing sugars and proteins, lipids, or nucleic acids. AGEs are predominantly synthesized during chronic hyperglycemic conditions or aging. AGEs interact with their receptor RAGE and activate various sets of genes and proteins of the signal transduction pathway. Accumulation of AGEs and upregulated expression of RAGE is associated with various pathological conditions including diabetes, cardiovascular diseases, neurodegenerative disorders, and cancer. The role of AGE-RAGE signaling has been demonstrated in the progression of various types of cancer and other pathological disorders. The expression of RAGE increases manifold during cancer progression. The activation of AGE-RAGE signaling also perturbs the cellular redox balance and modulates various cell death pathways. The programmed cell death signaling often altered during the progression of malignancies. The cellular reprogramming of AGE-RAGE signaling with cell death machinery during tumorigenesis is interesting to understand the complex signaling mechanism of cancer cells. The present review focus on multiple molecular paradigms relevant to cell death particularly Apoptosis, Autophagy, and Necroptosis that are considerably influenced by the AGE-RAGE signaling in the cancer cells. Furthermore, the review also attempts to shed light on the provenience of AGE-RAGE signaling on oxidative stress and consequences of cell survival mechanism of cancer cells.

Glycation With Fructose: The Bitter Side of Nature's Own Sweetener

Fructose is a ketohexose and sweetest among all the natural sugars. Like other reducing sugars, it reacts readily with the amino- and nucleophilic groups of proteins, nucleic acids and other biomolecules resulting in glycation reactions. The non-enzymatic glycation reactions comprise Schiff base formation, their Amadori rearrangement followed by complex and partly incompletely understood reactions culminating in the formation of Advance Glycation End products (AGEs). The AGEs are implicated in complications associated with diabetes, cardiovascular disorders, Parkinson's disease, etc. Fructose is highly reactive and forms glycation products that differ both in structure and reactivity as compared to those formed from glucose. Nearly all tissues of higher organisms utilize fructose but only a few like the ocular lens, peripheral nerves erythrocytes and testis have polyol pathway active for the synthesis of fructose. Fructose levels rarely exceed those of glucose but, in tissues that operate the polyol pathway, its concentration may rise remarkably during diabetes and related disorders. Diet contributes significantly to the body fructose levels however, availability of technologies for the large scale and inexpensive production of fructose, popularity of high fructose syrups as well as the promotion of vegetarianism have resulted in a remarkable increase in the consumption of fructose. In vivo glycation reactions by fructose, therefore, assume remarkable significance. The review, therefore, aims to highlight the uniqueness of glycation reactions with fructose and its role in some pathophysiological situations.

The link between advanced glycation end products and apoptosis in delayed wound healing

Advanced glycation end products (AGEs) are naturally occurring molecules that start to accumulate from embryonic developmental stages and form as part of normal ageing. When reducing sugars interact with and modify proteins or lipids, AGE production occurs. AGE formation accelerates in chronic hyperglycemic conditions, and high AGE levels have been associated with the pathogenesis of various diseases. In addition, enhanced levels of AGEs have been linked to delayed wound healing as seen in patients with diabetes mellitus. Research has provided numerous ways in which a high AGE concentration results in impaired wound healing, including oxidative stress, structural and functional changes to proteins important in wound repair, an enhanced inflammatory response by activation of transcription factors, and possible exaggerated apoptosis of cells necessary to the wound repair process. Apoptosis is a naturally occurring cell death process that is significant for normal tissue functioning and plays an important role in wound repair by preventing a prolonged inflammatory response and excessive scar formation. Abnormal apoptosis affects wound healing, resulting in slow healing wounds. This review will summarize the role of AGEs in wound healing, focusing on the mechanisms by which AGEs lead to apoptosis in various cell types. The review provides the way forward for medical research and molecular studies as it focuses on the mechanisms by which AGEs induce apoptosis in various cell types, including fibroblasts, osteoblasts, neuronal cells, and endothelial cells. Reviewing the mechanisms of AGE-linked apoptosis is important in understanding the impact of high AGE levels in delayed wound healing in diabetic patients due to abnormal apoptosis of cells necessary to the wound healing process.

The receptor for advanced glycation endproducts is a mediator of toxicity by IAPP and other proteotoxic aggregates: Establishing and exploiting common ground for novel amyloidosis therapies

Proteotoxicity plays a key role in many devastating human disorders, including Alzheimer's, Huntington's and Parkinson's diseases; type 2 diabetes; systemic amyloidosis; and cardiac dysfunction, to name a few. The cellular mechanisms of proteotoxicity in these disorders have been the focus of considerable research, but their role in prevalent and morbid disorders, such as diabetes, is less appreciated. There is a large body of literature on the impact of glucotoxicity and lipotoxicity on insulin-producing pancreatic β-cells, and there is increasing recognition that proteotoxicty plays a key role. Pancreatic islet amyloidosis by the hormone IAPP, the production of advanced glycation endproducts (AGE), and insulin misprocessing into cytotoxic aggregates are all sources of β-cell proteotoxicity in diabetes. AGE, produced by the reaction of reducing sugars with proteins and lipids are ligands for the receptor for AGE (RAGE), as are the toxic pre-fibrillar aggregates of IAPP produced during amyloid formation. The mechanisms of amyloid formation by IAPP in vivo or in vitro are not well understood, and the cellular mechanisms of IAPP-induced β-cell death are not fully defined. Here, we review recent findings that illuminate the factors and mechanisms involved in β-cell proteotoxicity in diabetes. Together, these new insights have far-reaching implications for the establishment of unifying mechanisms by which pathological amyloidoses imbue their injurious effects in vivo.

Pre-existing diabetes is a risk factor for increased rates of cellular rejection after kidney transplantation: an observational cohort study

AIM

To investigate whether people with diabetes have an elevated risk of kidney allograft rejection in a well characterized clinical cohort in the setting of contemporary immunosuppression.

METHODS

We conducted a retrospective cohort study including all kidney allograft recipients at a single centre between 2007 and 2015, linking clinical, biochemical and histopathological data from electronic patient records.

RESULTS

Data were analysed for 1140 kidney transplant recipients. The median follow-up was 4.4 years post-transplantation, and 117 of the kidney transplant recipients (10.2%) had diabetes at time of transplantation. Kidney allograft recipients with vs without diabetes were older (53 vs 45 years; P<0.001) and more likely to be non-white (41.0% vs 26.4%; P=0.001). Kidney allograft recipients with vs without diabetes had a higher risk of cellular rejection (19.7% vs 12.4%; P=0.024), but not of antibody-mediated rejection (3.4% vs 3.7%; P=0.564). Graft function and risk of death-censored graft loss were similar in the two groups, but kidney allograft recipients with diabetes had a higher risk of death and overall graft loss than those without diabetes. In a Cox regression model of non-modifiable risk factors at time of transplantation, diabetes was found to be an independent risk factor for cellular rejection (hazard ratio 1.445, 95% CI 1.023-1.945; P=0.042).

CONCLUSIONS

Kidney allograft recipients with diabetes at transplantation should be counselled regarding their increased risk of cellular rejection but reassured regarding the lack of any adverse impact on short-to-medium term allograft function or survival.

SOCS3 overexpression inhibits advanced glycation end product-induced EMT in proximal tubule epithelial cells

Diabetic nephropathy (DN) is among the most severe complications of diabetes mellitus, and may lead to end-stage renal disease. Sustained exposure to advanced glycation end products (AGEs) typically causes renal tubular epithelial cells (TECs) to suffer from an epithelial-to-mesenchymal transition (EMT). However, there remains no consensus regarding the mechanism underlying the cause of EMT in TECs as induced by AGEs. In the present study, we investigated the promotion of EMT in TECs by AGEs, and the activation of Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling. In addition, we constructed a recombinant adenovirus (Ad) that overexpressed suppressor of cytokine signaling 3 (SOCS3), and examined the regulatory role of SOCS3 in the activation of JAK/STAT signaling and the promotion of EMT in TECs. The results demonstrated that AGE-bovine serum albumin (BSA) treatment significantly promoted the expression of EMT-associated proteins, while reducing the expression of the epithelial cell marker, E-cadherin. Furthermore, the Ad-mediated SOCS3 overexpression markedly inhibited the AGE-BSA-induced JAK2/STAT3 activation; phosphorylated JAK2 and phosphorylated STAT3 expression levels were reduced by the Ad-SOCS3 infection, compared with the control Ad (Ad-con) infection, in HK-2 cells subject to AGE-BSA. Moreover, the overexpression of SOCS3 markedly inhibited the AGE-BSA-promoted EMT in HK-2 cells. AGE-BSA-promoted EMT-associated proteins, such as α-smooth muscle actin and collagen I, were reduced by the Ad-SOCS3 virus infection, in contrast to the Ad-con virus infection. Furthermore, reduced E-cadherin expression was reversed by the Ad-SOCS3 virus infection, in contrast to the Ad-con virus infection, in epithelial HK-2 cells. In conclusion, the present study confirmed the inhibitory role of SOCS3 in the AGE-induced EMT in renal TECs, implying the protective role of SOCS3 in DN.

Central Role of Metabolism in Endothelial Cell Function and Vascular Disease

The importance of endothelial cell (EC) metabolism and its regulatory role in the angiogenic behavior of ECs during vessel formation and in the function of different EC subtypes determined by different vascular beds has been recognized only in the last few years. Even more importantly, apart from a role of nitric oxide and reactive oxygen species in EC dysfunction, deregulations of EC metabolism in disease only recently received increasing attention. Although comprehensive metabolic characterization of ECs still needs further investigation, the concept of targeting EC metabolism to treat vascular disease is emerging. In this overview, we summarize EC-specific metabolic pathways, describe the current knowledge on their deregulation in vascular diseases, and give an outlook on how vascular endothelial metabolism can serve as a target to normalize deregulated endothelium.

Protective effects of physiological testosterone on advanced glycation end product‑induced injury in human endothelial cells

The effect of testosterone, a sex steroid, on endothelial cells is controversial as it is uncertain if it has a protective effect on them. Whether physiological testosterone can inhibit the deleterious effects of advanced glycation end products (AGEs) on endothelial cells remains to be elucidated. The present study focused on elucidating the effect of testosterone on the injury of endothelial cells induced by AGEs. Human umbilical vein endothelial cells (HUVECs) were cultured in vitro and treated with AGEs in the presence or absence of various concentrations of testosterone. The cell viability in each group was measured using an MTS assay. Early-stage apoptosis was detected using flow cytometry with Annexin V-fluorescein isothiocyanate/propidium iodide double staining, and the expression levels of apoptosis-associated proteins, B cell lymphoma-2 (Bcl-2), Bcl-2-associated X protein (Bax) and caspase-3, were determined using western blot analysis. Oxidative stress and pro-inflammatory parameters in the medium were evaluated using an enzyme-linked immunosorbent assay. The MTS results showed that AGEs significantly decreased the proliferation of HUVECs, whereas a physiological concentration of testosterone alleviated this damage. Physiological concentrations of testosterone protected the HUVECs from AGE-induced apoptosis, mediated by caspase-3 and Bax/Bcl-2. In addition, treatment of the HUVECs with AGEs caused a significant decrease in anti-oxidative parameters, but increased the concentrations of malondialdehyde and tumor necrosis factor-α. The activation of Janus kinase 2 and signal transducer and activator of transcription 3 was significantly increased by incubation with AGEs. However, pre-incubation with a physiological concentration of testosterone attenuated these changes. Therefore, the data obtained in the present study established the potential role of physiological testosterone in ameliorating AGE-induced damage in HUVECs.

miR-223 contributes to the AGE-promoted apoptosis via down-regulating insulin-like growth factor 1 receptor in osteoblasts

miR-223 inhibits the advanced glycation end product (AGE)-promoted apoptosis in osteoblasts.

Advanced glycation end products (AGEs) have been confirmed to induce bone quality deterioration in diabetes mellitus (DM), and to associate with abnormal expression of miRNAs in DM patients or in vitro. Recently, miRNAs have been recognized to mediate the onset or progression of DM. In the present study, we investigated the regulation on miR-223 level by AGE-BSA treatment in osteoblast-like MC3T3-E1 cells, with real-time quantitative PCR assay. And then we examined the inhibition of insulin-like growth factor 1 receptor (IGF-1R) expression by miR-223, via targeting of the 3′ UTR of IGF-1R with real-time quantitative PCR, western blotting and luciferase reporter assay. Then we explored the regulation of miR-223 and IGF-1R levels, via the lentivirus-mediated miR-223 inhibition and IGF-1R overexpression in the AGE-BSA-induced apoptosis in MC3T3-E1 cells. It was demonstrated that AGE-BSA treatment with more than 100 μg/ml significantly up-regulated miR-223 level, whereas down-regulated IGF-1R level in MC3T3-E1 cells. And the up-regulated miR-223 down-regulated IGF-1R expression in both mRNA and protein levels, via targeting the 3′ UTR of IGF-1R. Moreover, though the AGE-BSA treatment promoted apoptosis in MC3T3-E1 cells, the IGF-1R overexpression or the miR-223 inhibition significantly attenuated the AGE-BSA-promoted apoptosis in MC3T3-E1 cells. In summary, our study recognized the promotion of miR-223 level by AGE-BSA treatment in osteoblast-like MC3T3-E1 cells. The promoted miR-223 targeted IGF-1R and mediated the AGE-BSA-induced apoptosis in MC3T3-E1 cells. It implies that miR-223 might be an effective therapeutic target to antagonize the AGE-induced damage to osteoblasts in DM.

Principles of targeting endothelial cell metabolism to treat angiogenesis and endothelial cell dysfunction in disease

The endothelium is the orchestral conductor of blood vessel function. Pathological blood vessel formation (a process termed pathological angiogenesis) or the inability of endothelial cells (ECs) to perform their physiological function (a condition known as EC dysfunction) are defining features of various diseases. Therapeutic intervention to inhibit aberrant angiogenesis or ameliorate EC dysfunction could be beneficial in diseases such as cancer and cardiovascular disease, respectively, but current strategies have limited efficacy. Based on recent findings that pathological angiogenesis and EC dysfunction are accompanied by EC-specific metabolic alterations, targeting EC metabolism is emerging as a novel therapeutic strategy. Here, we review recent progress in our understanding of how EC metabolism is altered in disease and discuss potential metabolic targets and strategies to reverse EC dysfunction and inhibit pathological angiogenesis.

Advanced glycation end products induce endothelial-to-mesenchymal transition via downregulating Sirt 1 and upregulating TGF-β in human endothelial cells

In the present study, we examined the advanced glycation end products- (AGEs-) induced endothelial-to-mesenchymal transition (EndMT) in human umbilical vein endothelial cells (HUVECs). Results demonstrated that AGE-BSAs significantly reduced the cluster of differentiation 31 (CD 31) expression, whereas they promoted the expression of fibroblast-specific protein-1 (FSP-1), α-smooth muscle antibody (α-SMA), and collagen I at both mRNA and protein levels in HUVECs. And the AGE-BSAs also promoted the receptors for AGEs (RAGEs) and receptor I for TGF-β (TGFR I) markedly with a dose dependence, whereas the Sirt 1 was significantly downregulated by the AGE-BSA at both mRNA and protein levels. Moreover, the Sirt 1 activity manipulation with its activator, resveratrol (RSV), or its inhibitor, EX527, markedly inhibited or ameliorated the AGE-mediated TGF-β upregulation. And the manipulated Sirt 1 activity positively regulated the AGE-induced CD31, whereas it negatively regulated the AGE-induced FSP-1. Thus, Sirt 1 was confirmed to regulate the AGE-induced EndMT via TGF-β. In summary, we found that AGE-BSA induced EndMT in HUVECs via upregulating TGF-β and downregulating Sirt 1, which also negatively regulated TGF-β in the cell. This study implied the EndMT probably as an important mechanism of AGE-induced cardiovascular injury.

Mechanisms of PEDF-mediated protection against reactive oxygen species damage in diabetic retinopathy and neuropathy

Pigment epithelium-derived factor (PEDF) is a pluripotent glycoprotein belonging to the serpin family. PEDF can stimulate several physiological processes such as angiogenesis, cell proliferation, and survival. Oxidative stress plays an important role in the occurrence of diabetic retinopathy (DR), which is the major cause of blindness in young diabetic adults. PEDF plays a protective role in DR and there is accumulating evidence of the neuroprotective effect of PEDF. In this paper, we review the role of PEDF and the mechanisms involved in its antioxidative, anti-inflammatory, and neuroprotective properties.

Methylglyoxal-induced cytotoxicity in neonatal rat brain: a role for oxidative stress and MAP kinases

Carbonyl compounds such as methylglyoxal (MGO) seem to play an important role in complications resulting from diabetes mellitus, in aging and neurodegenerative disorders. In this study, we are showing, that MGO is able to suppress cell viability and induce apoptosis in the cerebral cortex and hippocampus of neonatal rats ex-vivo. These effects are partially related with ROS production, evaluated by DCFH-DA assay. Coincubation of MGO and reduced glutathione (GSH) or Trolox (vitamin E) totally prevented ROS production but only partially prevented the MGO-induced decreased cell viability in the two brain structures, as evaluated by the MTT assay. Otherwise, L-NAME, a nitric oxide (NO) inhibitor, partially prevented ROS production in the two structures but partially prevented cytotoxicity in the hippocampus. Pharmacological inhibition of Erk, has totally attenuated MGO-induced ROS production and cytotoxicity, suggesting that MEK/Erk pathway could be upstream of ROS generation and cell survival. Otherwise, p38MAPK and JNK failed to prevent ROS generation but induced decreased cell survival consistent with ROS-independent mechanisms. We can propose that Erk, p38MAPK and JNK are involved in the cytotoxicity induced by MGO through different signaling pathways. While Erk could be an upstream effector of ROS generation, p38MAPK and JNK seem to be associated with ROS-independent cytotoxicity in neonatal rat brain. The cytotoxic damage progressed to apoptotic cell death at MGO concentration higher than those described for adult brain, suggesting that the neonatal brain is resistant to MGO-induced cell death. The consequences of MGO-induced brain damage early in life, remains to be clarified. However, it is feasible that high MGO levels during cortical and hippocampal development could be, at least in part, responsible for the impairment of cognitive functions in adulthood.

Diabetes, Obesity and Atrial Fibrillation: Epidemiology, Mechanisms and Interventions

Body mass index (BMI) is a powerful predictor of death, type 2 diabetes (T2DM) and cardiovascular (CV) morbidity and mortality. Over the last few decades, we have witnessed a global rise in adult obesity of epidemic proportions. Similarly, there has been a parallel increase in the incidence of atrial fibrillation (AF), itself a significant cause of cardiovascular morbidity and mortality. This may be partly attributable to advances in the treatment of coronary heart disease (CHD) and heart failure (HF) improving life expectancy, however, epidemiological studies have demonstrated an independent association between obesity, diabetes and AF, suggesting possible common pathophysiological mechanisms and risk factors. Indeed, cardiac remodeling, haemodynamic alterations, autonomic dysfunction, and diastolic dysfunction have been reported in obese and diabetic cohorts. Moreover, diabetic cardiomyopathy is characterized by an adverse structural and functional cardiac phenotype, which may predispose to the development of AF. In this review, we discuss the pathophysiological and mechanistic relationships between obesity, diabetes and AF, and some of the challenges posed in the management of this high-risk group of individuals.

Obesity, diabetes and atrial fibrillation; epidemiology, mechanisms and interventions

The last few decades have witnessed a global rise in adult obesity of epidemic proportions. The potential impact of this is emphasized when one considers that body mass index (BMI) is a powerful predictor of death, type 2 diabetes (T2DM) and cardiovascular (CV) morbidity and mortality [1, 2]. Similarly we have witnessed a parallel rise in the incidence of atrial fibrillation (AF), the commonest sustained cardiac arrhythmia, which is also a significant cause of cardiovascular morbidity and mortality. Part of this increase is attributable to advances in the treatment of coronary heart disease (CHD) and heart failure (HF) improving life expectancy and consequently the prevalence of AF. However, epidemiological studies have demonstrated an independent association between obesity and AF, possibly reflecting common pathophysiology and risk factors for both conditions. Indeed, weight gain and obesity are associated with structural and functional changes of the cardiovascular system including left atrial and ventricular remodeling, haemodynamic alterations, autonomic dysfunction, and diastolic dysfunction. Moreover, diabetic cardiomyopathy is characterized by an adverse structural and functional cardiac phenotype which may predispose to the development of AF [3]. In this review, we discuss the pathophysiological and mechanistic relationships between obesity, diabetes and AF, and the challenges posed in the management of this high-risk group of individuals.

Parainflammation associated with advanced glycation endproduct stimulation of RPE in vitro: implications for age-related degenerative diseases of the eye

Age related macular degeneration (AMD) is one of the leading causes of blindness in Western society. A hallmark of early stage AMD are drusen, extracellular deposits that accumulate in the outer retina. Advanced glycation endproducts (AGE) accumulate with aging and are linked to several age-related diseases such as Alzheimer's disease, osteoarthritis, atherosclerosis and AMD. AGE deposits are found in drusen and in Bruch's membrane of the eye and several studies have suggested its role in promoting oxidative stress, apoptosis and lipofuscin accumulation. Recently, complement activation and chronic inflammation have been implicated in the pathogenesis of AMD. While AGEs have been shown to promote inflammation in other diseases, whether it plays a similar role in AMD is not known. This study investigates the effects of AGE stimulation on pro- and anti-inflammatory pathways in primary culture of human retinal pigment epithelial cells (RPE). Differential gene expression studies revealed a total of 41 up- and 18 down-regulated RPE genes in response to AGE stimulation. These genes fell into three categories as assessed by gene set enrichment analysis (GSEA). The main categories were inflammation (interferon-induced, immune response) and proteasome degradation, followed by caspase signaling. Using suspension array technology, protein levels of secreted cytokines and growth factors were also examined. Anti-inflammatory cytokines including IL10, IL1ra and IL9 were all overexpressed. Pro-inflammatory cytokines including IL4, IL15 and IFN-γ were overexpressed, while other pro-inflammatory cytokines including IL8, MCP1, IP10 were underexpressed after AGE stimulation, suggesting a para-inflammation state of the RPE under these conditions. Levels of mRNA of chemokine, CXCL11, and viperin, RSAD2, were up-regulated and may play a role in driving the inflammatory response via the NF-kB and JAK-STAT pathways. CXCL11 was strongly immunoreactive and associated with drusen in the AMD eye. The pathways and novel genes identified here highlight inflammation as a key response to AGE stimulation in primary culture of human RPE, and identify chemokine CXCL11 as putative novel agent associated with the pathogenesis of AMD.

Plasma glycation levels are associated with severity in sepsis

BACKGROUND

Advanced glycation end-products (AGE) have been involved in inflammatory diseases and may have an important role in the progression of symptoms. However, few studies have analysed the levels of glycated proteins in sepsis. In this study, we evaluated the levels of the well-known AGE (N(ε) -(carboxymethyl)lysine (CML) and N(ε) -(carboxyethyl)lysine (CEL)) in the plasma of septic patients.

MATERIAL AND METHODS

Plasma from 36 patients admitted to an adult intensive care unit and 6 healthy controls had the levels of CML/CEL measured by ELISA.

RESULTS

The level of AGE in plasma decreased with the increase of severity (1·40±0·46 nmol/mg of protein in sepsis, 0·58±0·23 nmol/mg of protein in severe sepsis and 0·31±0·12 nmol/mg of protein in septic shock). Control plasma presented low AGE concentration (0·06±0·01 nmol/mg protein). Also, we found a decrease in plasma AGE in those patients that died at the end of 28 days follow-up (0·80±0·50 nmol/mg of protein in survivors vs. 0·31±0·10 nmol/mg of protein in nonsurvivors), being associated with the renal component of sequential organ failure assessment (SOFA) score. In the same line, there was a decrease in plasma AGE with the increase in SOFA.

CONCLUSIONS

Our data demonstrate that plasma AGE levels are inversely associated with the severity of sepsis and may be associated with kidney dysfunction.

Role of advanced glycation end products in cardiovascular disease

Advanced glycation end products (AGEs) are produced through the non enzymatic glycation and oxidation of proteins, lipids and nucleic acids. Enhanced formation of AGEs occurs particularly in conditions associated with hyperglycaemia such as diabetes mellitus (DM). AGEs are believed to have a key role in the development and progression of cardiovascular disease in patients with DM through the modification of the structure, function and mechanical properties of tissues through crosslinking intracellular as well as extracellular matrix proteins and through modulating cellular processes through binding to cell surface receptors [receptor for AGEs (RAGE)]. A number of studies have shown a correlation between serum AGE levels and the development and severity of heart failure (HF). Moreover, some studies have suggested that therapies targeted against AGEs may have therapeutic potential in patients with HF. The purpose of this review is to discuss the role of AGEs in cardiovascular disease and in particular in heart failure, focussing on both cellular mechanisms of action as well as highlighting how targeting AGEs may represent a novel therapeutic strategy in the treatment of HF.

High glucose-induced apoptosis in human coronary artery endothelial cells involves up-regulation of death receptors

Background

High glucose can induce apoptosis in vascular endothelial cells, which may contribute to the development of vascular complications in diabetes. We evaluated the role of the death receptor pathway of apoptotic signaling in high glucose-induced apoptosis in human coronary artery endothelial cells (HCAECs).

Methods

HCAECs were treated with media containing 5.6, 11.1, and 16.7 mM of glucose for 24 h in the presence or absence of tumor necrosis factor (TNF)-α. For detection of apoptosis, DNA fragmentation assay was used. HCAEC expression of death receptors were analyzed by the PCR and flow cytometry methods. Also, using immunohistochemical techniques, coronary expression of death receptors was assessed in streptozotocin-nicotinamide-induced type 2 diabetic mice.

Results

Exposure of HCAECs to high glucose resulted in a significant increase in TNF-R1 and Fas expression, compared with normal glucose. High glucose increased TNF-α production by HCAECs and exogenous TNF-α up-regulated TNF-R1 and Fas expression in HCAECs. High glucose-induced up-regulation of TNF-R1 and Fas expression was undetectable in the presence of TNF-α. Treatment with TNF-R1 neutralizing peptides significantly inhibited high glucose-induced endothelial cell apoptosis. Type 2 diabetic mice displayed appreciable expression of TNF-R1 and Fas in coronary vessels.

Conclusions

In association with increased TNF-α levels, the death receptors, TNF-R1 and Fas, are up-regulated in HCAECs under high glucose conditions, which could in turn play a role in high glucose-induced endothelial cell apoptosis.

Pigment epithelium-derived factor inhibits advanced glycation end-products-induced cytotoxicity in retinal pericytes

AIM

This study investigated the effects of pigment epithelium-derived factor (PEDF) on advanced glycation end-product (AGE)-induced cytotoxicity in porcine retinal pericytes and the signalling mechanism involved.

METHODS

Retinal pericytes were isolated from porcine eyes and characterized by immunocytochemistry. The effect of AGEs and PEDF on cell proliferation was determined by bromodeoxyuridine (BrdU) assay. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity was analyzed by luminescence assay. Reactive oxygen species (ROS), nitric oxide (NO), superoxide dismutase (SOD) and glutathione peroxidase (GSH) were determined by biochemical assays. Induction of apoptosis was determined by caspase-3 colorimetric assay and DNA fragmentation analysis. Src activity was assessed by transient transfection analysis, and the status of Src phosphorylation at Y419 was analyzed by a competitive ELISA method.

RESULTS

AGEs significantly increased intracellular ROS generation in pericytes via NADPH oxidase and induced cell death via caspase-3 enzyme activation, whereas PEDF increased cell proliferation in a dose-dependent manner. In addition, PEDF inhibited AGE-induced ROS generation by increasing levels of SOD and GSH, and also blocked the activation of caspase-3. Furthermore, PEDF induced cell survival via the Src pathway by Src phosphorylation at Y419, as evidenced by a pharmacological inhibitor and Src mutants.

CONCLUSION

These results suggest that PEDF abrogates AGE-induced oxidative stress and apoptosis in retinal pericytes via the Src pathway, thereby suggesting that PEDF is an effective therapeutic agent for the treatment of loss of pericytes in early diabetic retinopathy.

Inflammation and thrombosis in diabetes

Patients with diabetes mellitus are at increased risk of cardiovascular morbidity and mortality. Atherothrombosis, defined as atherosclerotic lesion disruption with superimposed thrombus formation, is the most common cause of death among these patients. Following plaque rupture, adherence of platelets is followed by local activation of coagulation, the formation of a cross-linked fibrin clot and the development of an occlusive platelet rich fibrin mesh. Patients with diabetes exhibit a thrombotic risk clustering which is composed of hyper-reactive platelets, up regulation of pro-thrombotic markers and suppression of fibrinolysis. These changes are mainly mediated by the presence of insulin resistance and dysglycaemia and an increased inflammatory state which directly affects platelet function, coagulation factors and clot structure. This prothrombotic state is related to increased cardiovascular risk and may account for the reduced response to antithrombotic therapeutic approaches, underpinning the need for adequate antithrombotic therapy in patients with diabetes to reduce their cardiovascular mortality.

Advanced glycation end products down-regulate gap junctions in human hepatoma SKHep 1 cells via the activation of Src-dependent ERK1/2 and JNK/SAPK/AP1 signaling pathways

Hyperglycemia and advanced glycation end products (AGEs) are associated with an elevated risk of developing several cancers in diabetic patients. However, the detailed mechanisms remain to be elucidated. The mechanism of AGE-bovine serum albumin (BSA) on gap junction intercellular communication in human hepatoma cell line, SKHep 1, was investigated. Both Cx32 and Cx43 are major gap junction forming proteins in the liver, the loss of which has been shown to facilitate tumorigenesis. Although the MTT assay results showed that AGE-BSA significantly increased cell growth by 31%, AGE-BSA down-regulated Cx32 and Cx43 expression in a dose- and time-dependent manner. The present study also demonstrated that ERK1/2 and JNK/SAPK were significantly activated by AGE-BSA and that Src, ERK1/2, and JNK/SAPK inhibitors significantly reversed the reduction of Cx32 and Cx43 proteins by AGE-BSA. Taken together, these results strongly support the hypothesis that Src-dependent ERK1/2 and JNK/SAPK/AP1 signaling pathways play a key role in AGE-BSA-mediated down-regulation of Cx32 and Cx43 protein expression in SKHep 1 cells.

Glycoxidative stress-induced mitophagy modulates mitochondrial fates

Diabetes mellitus (DM), a state of chronic hyperglycemia, is associated with a variety of serious complications. Hyperglycemia-induced advanced glycation end products (AGEs) play an important role in the development of diabetic complications. In vivo, we demonstrated that disrupted mitochondria and autophagy was elevated in type II DM db/db mice. Mitophagy was evidenced by increased autophagosome formation in the beta-islet cells. The adducts of N(epsilon)-(carboxymethyl) lysine (CML), a major AGE, and bovine serum albumin (CML-BSA) stimulated the conversion of microtubule-associated protein 1 light chain 3-I (LC3-I) to LC3-II in rat insulinoma cells (RIN-m5F). CML-BSA increased ROS generation as demonstrated in a time-dependent manner. Experiments with mitochondrial targeted enhanced yellow fluorescent protein transfected RIN-m5F cells, massive fragmented mitochondria were visualized in the CML-BSA treated cells. Taken together, these data suggested that AGEs may cause mitochondrial dysfunction and mitophagosome formation, and AGEs-induced glycoxidative stress may trigger mitophagic process to modulate mitochondrial fates leading to either cell survival or cell death.

Hyperglycemia: a prothrombotic factor?

Diabetes mellitus is characterized by a high risk of atherothrombotic events. What is more, venous thrombosis has also been found to occur more frequently in this patient group. This prothrombotic condition in diabetes is underpinned by laboratory findings of elevated coagulation factors and impaired fibrinolysis. Hyperglycemia plays an important role in the development of these hemostatic abnormalities, as is illustrated by the association with glycemic control and the improvement upon treatment of hyperglycemia. Interestingly, stress induced hyperglycemia, which is often transient, has also been associated with poor outcome in thrombotic disease. Similar laboratory findings suggest a common effect of acute vs. chronic hyperglycemia on the coagulation system. Many mechanisms have been proposed to explain this prothrombotic shift in hyperglycemia, such as a direct effect on gene transcription of coagulation factors caused by hyperglycemia-induced oxidative stress, loss of the endothelial glycocalyx layer, which harbours coagulation factors, and direct glycation of coagulation factors, altering their activity. In addition, both chronic and acute hyperglycemia are often accompanied by hyperinsulinemia, which has been shown to have prothrombotic effects as well. In conclusion, the laboratory evidence of the effects of both chronic and acute hyperglycemia suggests a prothrombotic shift. Additionally, hyperglycemia is associated with poor clinical outcome of thrombotic events. Whether intensive treatment of hyperglycemia can prevent hypercoagulability and improve clinical outcome remains to be investigated.

Tenuigenin protects cultured hippocampal neurons against methylglyoxal-induced neurotoxicity

Methylglyoxal is a metabolite of glucose. Since serum methylglyoxal level is increased in diabetic patients, methylglyoxal is implicated in diabetic complications such as cognitive impairment. This study aimed to evaluate the effects of tenuigenin, an active component of roots of Polygala tenuifolia Willdenow, on methylglyoxal-induced cell injury in a primary culture of rat hippocampal neurons. MTT and Hoechst 33342 staining, together with flow cytometric analysis using annexin-V and propidium (PI) label, indicated that tenuigenin pretreatment attenuated methylglyoxal -induced apoptotic cell death in primary cultured hippocampal neurons, showing a dose-dependent pattern. Furthermore, 2, 7-dichlorodihydrofluorescein diacetate was used to detect the level of intracellular reactive oxygen species. Tenuigenin decreased the elevated reactive oxygen species induced by methylglyoxal. In addition, tenuigenin inhibited activation of caspase-3 and reversed down-regulation of the ratio of Bcl-2/Bax, both of which were induced by methylglyoxal stimulation. The results suggest that tenuigenin displays antiapoptotic and antioxidative activity in hippocampal neurons due to scavenging of intracellular reactive oxygen species, regulating Bcl-2 family and suppressing caspase-3 activity induced by methylglyoxal, which might explain at least in part the beneficial effects of tenuigenin against degenerative disorders involving diabetic cognitive impairment.

Tissue factor and cardiovascular disease: quo vadis?

The coagulation cascade represents a system of proteases responsible to maintain vascular integrity and to induce rapid clot formation after vessel injury. Tissue factor (TF), the key initiator of the coagulation cascade, binds to factor VIIa and thereby activates factor IX and factor X, resulting in thrombus formation. Different stimuli enhance TF gene expression in endothelial and vascular smooth muscle cells. In addition to these vascular cells, TF has recently been detected in the bloodstream in circulating cells such as leukocytes and platelets, as a component of microparticles, and as a soluble, alternatively spliced form of TF. Various cardiovascular risk factors like hypertension, diabetes, and dyslipidemia, increase levels of TF. In line with this observation, enhanced vascular TF expression occurs during atherogenesis, particularly in patients with acute coronary syndromes. (Circ J 2010; 74: 3 - 12).

Hyperglycemia and glycation in diabetic complications

Diabetes mellitus is a multifactorial disease, classically influenced by genetic determinants of individual susceptibility and by environmental accelerating factors, such as lifestyle. It is considered a major health concern,as its incidence is increasing at an alarming rate, and the high invalidating effects of its long-term complications affect macro- and microvasculature, heart, kidney, eye, and nerves. Increasing evidence indicates that hyperglycemia is the initiating cause of the tissue damage occurring in diabetes, either through repeated acute changes in cellular glucose metabolism, or through the long-term accumulation of glycated biomolecules and advanced glycation end products (AGEs). AGEs represent a heterogeneous group of chemical products resulting from a nonenzymatic reaction between reducing sugars and proteins, lipids, nucleic acids, or a combination of these.The glycation process (glucose fixation) affects circulating proteins (serum albumin, lipoprotein, insulin, hemoglobin),whereas the formation of AGEs implicates reactive intermediates such as methylglyoxal. AGEs form cross-links on long-lived extracellular matrix proteins or react with their specific receptor RAGE, resulting inoxidative stress and proinflammatory signaling implicated in endothelium dysfunction, arterial stiffening, and microvascular complications. This review summarizes the mechanism of glycation and of AGEs formation and the role of hyperglycemia, AGEs, and oxidative stress in the pathophysiology of diabetic complications.

Distinct Effects of High-Glucose Conditions on Endothelial Cells of Macrovascular and Microvascular Origins

Recent studies implicate hyperglycemia as an important cause of macrovascular and ocular complications in diabetes mellitus. In this study, the authors examined the effect of high glucose on macrovascular and microvascular endothelial cell viability and apoptosis in culture. Human aortic endothelial cells (HAECs) and human retinal endothelial cells (HRECs) were exposed to normal-glucose conditions (NG) and high-glucose conditions (NG supplemented with 25 mM D-glucose) for 72 h in vitro. D-Mannitol was used as an osmotic control. Cell viability was assessed by methlythiazolydiphenyltetrazolium bromide (MTT) assay, and induction of apoptosis was assessed by Hoechst staining. Statistics were analyzed by paired t tests. In HAECs, cell viability was decreased by 12.9% in high-glucose conditions, and apoptotic cells were significantly increased by 77%. However, in HRECs, cell viability was increased by 14.9% in high-glucose conditions, and apoptotic cells were significantly decreased by 33.3%. Mannitol did not show any effect on cell survival or apoptosis ruling out an osmotic effect. High-glucose conditions reduce cell viability and induce apoptosis in HAECs, which may contribute to macrovascular complications associated with diabetes. In contrast, high-glucose increases viability in HRECs and inhibits apoptosis, which may contribute to the development of diabetic retinopathy.

Venous thrombosis is associated with hyperglycemia at diagnosis: a case-control study

BACKGROUND

Patients with (undiagnosed) diabetes mellitus, impaired glucose tolerance or stress-induced hyperglycemia may be at greater risk for venous thrombosis and present with relative hyperglycemia during the thrombotic event.

OBJECTIVES

To assess whether venous thrombosis is associated with hyperglycemia at diagnosis.

PATIENTS/METHODS

We performed a case-control study, derived from a cohort of consecutive patients referred for suspected deep vein thrombosis. Cases were patients with confirmed symptomatic venous thrombosis of the lower extremity. Controls were randomly selected in a 1 : 2 ratio from individuals in whom this diagnosis was excluded. We measured plasma glucose levels upon presentation to the hospital.

RESULTS

In total, 188 patients with thrombosis and 370 controls were studied. The glucose cut-off levels for the first to fourth quartiles were as follows: first quartile, < 5.3 mmol L(-1); second quartile, 5.3-5.7 mmol L(-1); third quartile, 5.7-6.6 mmol L(-1); and fourth quartile, >or= 6.6 mmol L(-1). When adjusted for body mass index, a known history of diabetes mellitus, age, sex, ethnicity and whether known risk factors for deep vein thrombosis were present, the odds ratios for deep vein thrombosis in the second, third and fourth quartiles of glucose levels as compared with the first quartile were 1.59 [95% confidence interval (CI) 0.89-2.85], 2.04 (95% CI 1.15-3.62) and 2.21 (95% CI 1.20-4.05), respectively; P for trend = 0.001.

CONCLUSIONS

Increased glucose levels measured at presentation were associated with venous thrombosis. Experimental evidence supports a potential causal role for hyperglycemia in this process. As this is the first report on the association between (stress) hyperglycemia and venous thrombosis, confirmation in other studies is required.

The anti-apoptotic activity of albumin for endothelium is inhibited by advanced glycation end products restricting intramolecular movement

Human serum albumin (HSA) inhibits endothelial apoptosis in a highly specific manner. CNBr fragmentation greatly increases the effectiveness of this activity, suggesting that this type of protection is mediated by a partially cryptic albumin domain which is transiently exposed by intramolecular movement. Advanced glycation end-product (AGE) formation in HSA greatly reduces its intra-molecular movement. This study aimed to determine if this inhibits the anti-apoptotic activity of HSA, and if such inactivation could be reversed by CNBr fragmentation. HSA-AGE was prepared by incubating HSA with glucose, and assessed using the fructosamine assay, mass spectrometry, SDS-PAGE and fluorometry. Low levels of AGE in the HSA had little effect upon its anti-apoptotic activity, but when the levels of AGE were high and the intra-molecular movement was reduced, endothelial cell survival was also found to be reduced to levels equivalent to those in cultures without HSA or serum (p > 0.001). Survival was restored by the inclusion of native HSA, despite the presence of HSA with high levels of AGE. Also, CNBr fragmentation of otherwise inactive HSA-AGE restored the anti-apoptotic activity for endothelium. Apoptosis was confirmed by DNA gel electrophoresis, transmission electron microscopy and fluorescence-activated cell sorting analysis, and there was no evidence for direct toxicity in the HSA-AGE preparations. The results are consistent with the proposed role of intra-molecular movement in exposing the anti-apoptotic domain in HSA for endothelium. The levels of AGE formation required to inhibit the anti-apoptotic activity of HSA exceeded those reported for diabetes. Nonetheless, the data from this study seems to be the first example of reduced protein function due to AGE-restricted intra-molecular movement.

Extracellular superoxide released from mitochondria mediates mast cell death by advanced glycation end products

Advanced glycation end products (AGEs) accumulate during aging and to higher extents under pathological conditions such as diabetes. Since we previously showed that mast cells expressed the AGE-binding protein, receptor for AGEs (RAGE) on their cell surface, we examined whether AGE affected mast cell survival. Herein, we demonstrate that mast cells undergo apoptosis in response to AGE. Glycated albumin (GA), an AGE, but not stimulation with the high-affinity IgE receptor (FcepsilonRI), can induce mast cell death, as measured by annexin V/propidium iodide double-staining. GA (> or =0.1 mg/ml) exhibited this pro-apoptotic activity in a concentration-dependent manner. GA and FcepsilonRI stimulation increased the cytosolic Ca(2+) levels to a similar extent, whereas GA, but not FcepsilonRI stimulation, caused mitochondrial Ca(2+) overload and membrane potential collapse, resulting in mitochondrial integrity disruption, cytochrome c release and caspase-3/7 activation. In addition, GA, but not FcepsilonRI stimulation, induced extracellular release of superoxide from mitochondria, and this release played a key role in the disruption of Ca(2+) homeostasis. Knockdown of RAGE expression using small interfering RNA abolished GA-induced apoptosis, mitochondrial Ca(2+) overload, and superoxide release, demonstrating that RAGE mediates the GA-induced mitochondrial death pathway. AGE-induced mast cell apoptosis may contribute to the immunocompromised and inflammatory conditions.

Glycated fetal calf serum affects the viability of an insulin-secreting cell line in vitro

The purpose of the present study was to evaluate the direct effects of advanced glycation end products (AGEs) on beta-cells by their exposure to a glycated serum to estimate the cellular viability and the related insulin secretion. Glycation of fetal calf serum was obtained by incubation with 50 mol/L ribose at 37 degrees C for 7 days; at the end of this incubation period, the pentosidine content ranged between 15 and 16 x 10(5) pmol/L. HIT-T15 cells, a pancreatic islet cell line, were grown and cultured for 5 days in Roswell Park Memorial Institute (RPMI) medium containing either not glycated (NGS) or glycated (GS) fetal calf serum. Cellular oxidative stress (ie, thiobarbituric acid-reactive substances) was assessed by high-performance liquid chromatography. Cellular viability was evaluated by detection of proliferation, cell necrosis, and cell apoptosis rate. The insulin secretion and the related intracellular content were evaluated by enzyme-linked immunosorbent assay. The present study reported, after 5 days of exposure to the glycation environment, a moderately reduced cellular proliferation (-20.44% +/- 2.92%) with a corresponding increase of cell necrosis (+67.7% +/- 1.56%) and cell apoptosis (+39.83% +/- 2.92%) rate in comparison with the untreated cells. Oxidative intracellular stress was higher in GS conditions compared with the NGS ones (+293.3% +/- 87.53%). Insulin release from GS-treated HIT-T15 cells was lower than that of NGS-treated cells both when cells were stimulated with low glucose concentration (2.8 mmol/L, -30.3% +/- 4.91%) or when they were challenged with high glucose concentration (16.7 mmol/L, -29.2% +/- 5.82%). Incubation of HIT-T15 cells with glycated serum also caused a significant decrease of insulin intracellular content (-44.47% +/- 9.98%). Thus, AGEs were shown to exert toxic effects on insulin-secreting cells. Chronically high intracellular oxidative stress, due to accumulation of AGEs, affects the insulin secretion machinery. The present data suggest a pivotal role of the non-enzymatic glycation process in the onset and progression of diabetes during aging and a direct adverse effect of a glycated environment on the pancreatic islet cells.

AGE-receptor-1 counteracts cellular oxidant stress induced by AGEs via negative regulation of p66shc-dependent FKHRL1 phosphorylation

Advanced glycation end products (AGEs) promote reactive oxygen species (ROS) formation and oxidant stress (OS) in diabetes and aging-related diseases. AGE-induced OS is suppressed by AGER1, an AGE-receptor that counteracts receptor for advanced glycation end products (RAGE) and epidermal growth factor receptor (EGFR)-mediated Shc/Ras signal activation, resulting in decreased OS. Akt, FKHRL1, and antioxidants; e.g., MnSOD, regulate OS. Serine phosphorylation of p66 shc also promotes OS. We examined the effects of two defined AGEs Nε-carboxy-methyl-lysine (CML) and methyl-glyoxal derivatives (MG) on these cellular pathways and their functional relationship to AGER1 in human embryonic kidney cells (HEK293). Stimulation of HEK293 cells with either AGE compound increased phosphorylation of Akt and FKHRL1 by approximately threefold in a redox-dependent manner. The use of p66 shc mutants showed that the AGE-induced effects required Ser-36 phosphorylation of p66 shc. AGE-induced phosphorylation of FKHRL1 led to a 70% downregulation of MnSOD, an effect partially blocked by a phosphatidylinositol 3-kinase inhibitor (LY-294002) and strongly inhibited by an antioxidant ( N-acetylcysteine). These pro-oxidant responses were suppressed in AGER1 overexpressing cells and reappeared when AGER1 expression was reduced by small interfering RNA (siRNA). These studies point to a new pathway for the induction of OS by AGEs involving FKHRL1 inactivation and MnSOD suppression via Ser-36 phosphorylation of p66 shc in human kidney cells. This represents a key mechanism by which AGER1 maintains cellular resistance against OS. Thus the decrease of AGER1 noted in aging and diabetes may further enhance OS and reduce innate antioxidant defenses.

Diabetes mellitus as a prothrombotic condition

Diabetes mellitus (DM) is characterized by fasting hyperglycaemia and a high risk of atherothrombotic disorders affecting the coronary, cerebral and peripheral arterial trees. The risk of myocardial infarction (MI) is 3-5 fold higher in Type 2 DM and a DM subject with no history of MI has the same risk as a non-DM subject with a past history of MI. In total around 70% of deaths are vascular with poorer outcomes to both acute events and cardiological interventions. It was proposed that clustering of vascular risk factors (hyperinsulinaemia, dysglycaemia, dyslipidaemia and hypertension) around insulin resistance (IR) accounted for the increase in risk with Type 2 DM. The importance of this became apparent with the recognition that risk clustering occurs in normoglycaemic and impaired glucose tolerance (IGT) subjects with IR, in total around 25% of the population in addition to long-standing Type 1 subjects with renal disease. Evidence indicates that thrombotic risk clustering also occurs in association with IR, suppression of fibrinolysis due to elevated concentrations of the fibrinolytic inhibitor, plasminogen activator inhibitor-1 (PAI-1) is invariable with IR and there is evidence that this is regulated by the effects of triglyceride on the PAI-1 gene promoter. Other studies indicated that prothrombotic risk (coagulation factors VII, XII and fibrinogen) also associates with the IR syndrome. The development of endothelial cell dysfunction with suppression of nitric oxide and prostacyclin synthesis, combined with platelet resistance to the anti-aggregatory effects of these hormones leads to loss of control over platelet activation. In addition, hyperglycaemia and glycation have marked effects on fibrin structure function, generating a clot which has a denser structure, resistant to fibrinolysis. The combination of increased circulating coagulation zymogens, inhibition of fibrinolysis, changes in fibrin structure/function and alterations in platelet reactivity creates a thrombotic risk clustering which underpins the development of cardiovascular disease.

Inhibitors of the Maillard reaction and AGE breakers as therapeutics for multiple diseases

The Maillard reaction is a complex series of reactions that involve reducing-sugars and proteins, giving a multitude of end-products that are known as advanced glycation end-products (AGEs). AGEs can contribute to the pathogenesis of diabetes and neurological diseases such as Alzheimer's disease. AGEs also play a major role in vascular stiffening, atherosclerosis, osteoarthritis, inflammatory arthritis and cataracts. Thus, AGE inhibitors and AGE breakers offer a potential strategy as therapeutics for diverse diseases. Various AGE inhibitors have been developed in recent years, and their underlying mechanism is based on the attenuation of glycoxidation and/or oxidative stress by the sequestration of metal ions, reactive 1,2-dicarbonyl compounds, and reactive oxygen and reactive nitrogen species.

Attenuated function and expression of P-glycoprotein at blood-brain barrier and increased brain distribution of phenobarbital in streptozotocin-induced diabetic mice

The aim of the study was to investigate whether diabetes mellitus modulated the function and expression of P-glycoprotein and the distribution of phenobarbital in the brain of 3-week streptozotocin-induced diabetic mice. P-glycoprotein function in blood-brain barrier was assessed by measuring the brain-to-plasma concentration ratios of rodamine123, a well-known P-glycoprotein substrate, in non-diabetic mice and diabetic mice. P-glycoprotein expression in the brain cortex was evaluated with western blot. Whether diabetes mellitus changed the distribution of phenobarbital (60 mg/kg, i.v.) in brain of mice was measured, and whether the changed distribution caused the difference of phenobarbital (80 and 100 mg/kg) -induced loss of the righting reflex in non-diabetic and diabetic mice were also investigated. The results showed that the brain-to-plasma concentration ratio value of rodamine123 in diabetic mice was significantly higher than that of non-diabetic mice, western blot suggested that the protein level of P-glycoprotein in the brain of 3-week diabetic mice was significantly lower than that of non-diabetic mice, and insulin treatment restored the impairment of P-glycoprotein. The exposure of phenobarbital in brain of diabetic mice was 1.30-fold of that of non-diabetic mice, while in plasma the fold was 1.09. The increased distribution of phenobarbital in the brain of diabetic mice significantly increased the duration of phenobarbital-induced loss of the righting reflex and reduced the latency time of loss of the righting reflex. All the results suggested that the function and expression of P-glycoprotein might be impaired and the brain distribution of phenobarbital was increased in brain of streptozotocin-induced diabetic mice.

Dimethylarginine dimethylaminohydrolase inhibition and asymmetric dimethylarginine accumulation contribute to endothelial dysfunction in rats exposed to glycosylated protein: Effects of aminoguanidine

OBJECTIVES

To determine whether alterations of endogenous asymmetric dimethylarginine (ADMA) concentration and dimethylarginine dimethylaminohydrolase (DDAH) activity are involved in endothelial dysfunction induced by glycosylated bovine serum albumin (GBSA) in rats and effects of aminoguanidine on them.

METHODS

Endothelium-dependent relaxation of aortic rings from Sprague-Dawley rats after treatment with GBSA in vitro and in vivo was tested. Serum concentrations of ADMA, nitrite/nitrate, and activities of aortic DDAH, nitric oxide synthase (NOS) and superoxide dismutase were measured in GBSA-treated rats. Moreover, serum contents of glycosylated serum protein, and malondialdehyde were also assayed.

RESULTS

Endothelium-dependent relaxation was significantly impaired either by incubation of aortic rings with GBSA (1.70mmol/l) in vitro for 60min or by injection of GBSA (35mg/kg/d, i.v.) to normal rats for 4 weeks, and serum ADMA levels were remarkably elevated in GBSA-treated rats, which was accompanied by decreases of nitrite/nitrate concentrations, NOS and DDAH activities. Furthermore, elevated glycosylated serum protein, malondialdehyde levels, and reduced superoxide dismutase activity were also observed in GBSA-treated rats. Treatment with aminoguanidine not only improved impairment of endothelium-dependent relaxation but also prevented elevation of endogenous ADMA, which were concomitant with increases of nitrite/nitrate concentration, NOS and DDAH activity. Serum levels of glycosylated serum protein, malondialdehyde, and vascular superoxide dismutase activity were also normalized after aminoguanidine treatment.

CONCLUSIONS

Decreased DDAH activity and elevated endogenous ADMA is implicated in endothelial dysfunction of rats exposed to GBSA. Aminoguanidine can protect endothelium of rat aorta against injury induced by GBSA both in vitro and in vivo.

Procoagulant Microparticles

Apoptosis and vascular cell activation are main contributors to the release of procoagulant microparticles (MPs), deleterious partners in atherothrombosis. Elevated levels of circulating platelet, monocyte, or endothelial-derived MPs are associated with most of the cardiovascular risk factors and appear indicative of poor clinical outcome. In addition to being a valuable hallmark of vascular cell damage, MPs are at the crossroad of atherothrombosis processes by exerting direct effects on vascular or blood cells. Under pathological circumstances, circulating MPs would support cellular cross-talk leading to vascular inflammation and tissue remodeling, endothelial dysfunction, leukocyte adhesion, and stimulation. Exposed membrane phosphatidylserine and functional tissue factor (TF) are 2 procoagulant entities conveyed by circulating MPs. At sites of vascular injury, P-selectin exposure by activated endothelial cells or platelets leads to the rapid recruitment of MPs bearing the P-selectin glycoprotein ligand-1 and blood-borne TF, thereby triggering coagulation. Within the atherosclerotic plaque, sequestered MPs constitute the main reservoir of TF activity, promoting coagulation after plaque erosion or rupture. Lesion-bound MPs, eventually harboring proteolytic and angiogenic effectors are additional actors in plaque vulnerability. Pharmacological strategies aimed at modulating the release of procoagulant MPs appear a promising therapeutic approach of both thrombotic processes and bleeding disorders.

Crocetin prevents AGEs-induced vascular endothelial cell apoptosis

Advanced glycation end products (AGEs) are causally correlated with diabetic vascular complications. AGEs triggered oxidative reaction then accelerated endothelial cell apoptosis is a critical event in the process of vascular complications. Crocetin, a carotenoid has been previously shown to have strong antioxidant activates. Therefore, this study was designed to investigate the role of crocetin on the prevention of AGEs-mediated cell apoptosis in bovine aortic endothelial cells (BEC) and the mechanisms involved. Exposure of BEC to 200 microg/ml AGEs for 48 h results in a significant increase in apoptotic rate, compared with control. AGEs-induced DNA fragmentation preferentially occurred in the S phase cells. Crocetin prevented AGEs-induced BEC apoptosis, which correlates with crocetin attenuation of AGEs mediated increase of intracellular reactive oxygen species (ROS) formation and elevation of intracellular Ca2+ concentration ([Ca2+]i) level (P<0.01 versus AGEs group). These results demonstrate that crocetin prevents AGEs-induced BEC apoptosis through ROS inhibition and [Ca2+]i stabilization and suggest that crocetin may exert a beneficial effect in preventing diabetes-associated vascular complications.

Advanced glycation end products induce apoptosis in fibroblasts through activation of ROS, MAP kinases, and the FOXO1 transcription factor

Advanced glycation end products (AGEs) are elevated in aged and diabetic individuals and are associated with pathological changes associated with both. Previously we demonstrated that the AGE N(epsilon)-(carboxymethyl)lysine (CML)-collagen induced fibroblast apoptosis through the cytoplasmic and mitochondrial pathways and the global induction of proapoptotic genes. In the present study we investigated upstream mechanisms of CML-collagen-induced apoptosis. CML-collagen induced activation of the proapoptotic transcription factor FOXO1 compared with unmodified collagen. When FOXO1 was silenced, CML-collagen-stimulated apoptosis was reduced by approximately 75% compared with fibroblasts incubated with nonsilencing small interfering RNA, demonstrating the functional significance of FOXO1 activation (P < 0.05). CML-collagen but not control collagen also induced a 3.3-fold increase in p38 and a 5.6-fold increase in JNK(1/2) activity (P < 0.05). With the use of specific inhibitors, activation of p38 and JNK was shown to play an important role in CML-collagen-induced activation of FOXO1 and caspase-3. Moreover, inhibition of p38 and JNK reduced CML-collagen-stimulated apoptosis by 48 and 57%, respectively, and by 89% when used together (P < 0.05). In contrast, inhibition of the phosphatidylinositol 3-kinase/Akt pathway enhanced FOXO1 activation. p38 and JNK stimulation by CML-collagen was almost entirely blocked when formation of ROS was inhibited and was partially reduced by NO and ceramide inhibitors. These inhibitors also reduced apoptosis to a similar extent. Together these data support a model in which AGE-induced apoptosis involves the formation of ROS, NO, and ceramide and leads to p38 and JNK MAP kinase activation, which in turn induces FOXO1 and caspase-3.