Enhanced cellular oxidant stress by the interaction of advanced glycation end products with their receptors/binding proteins

Ascorbic acid prevents high glucose-induced apoptosis in human brain pericytes

High glucose concentrations due to diabetes increase apoptosis of vascular pericytes, impairing vascular regulation and weakening vessels, especially in brain and retina. We sought to determine whether vitamin C, or ascorbic acid, could prevent such high glucose-induced increases in pericyte apoptosis. Culture of human microvascular brain pericytes at 25 mM compared to 5mM glucose increased apoptosis measured as the appearance of cleaved caspase 3. Loading the cells with ascorbate during culture decreased apoptosis, both at 5 and 25 mM glucose. High glucose-induced apoptosis was due largely to activation of the receptor for advanced glycation end products (RAGE), since it was prevented by specific RAGE inhibition. Culture of pericytes for 24h with RAGE agonists also increased apoptosis, which was completely prevented by inclusion of 100 μM ascorbate. Ascorbate also prevented RAGE agonist-induced apoptosis measured as annexin V binding in human retinal pericytes, a cell type with relevance to diabetic retinopathy. RAGE agonists decreased intracellular ascorbate and GSH in brain pericytes. Despite this evidence of increased oxidative stress, ascorbate prevention of RAGE-induced apoptosis was not mimicked by several antioxidants. These results show that ascorbate prevents pericyte apoptosis due RAGE activation. Although RAGE activation decreases intracellular ascorbate and GSH, the prevention of apoptosis by ascorbate may involve effects beyond its function as an antioxidant.

The interplay between hyperglycemia-induced oxidative stress markers and the level of soluble receptor for advanced glycation end products (sRAGE) in K562 cells

Formation and accumulation of advanced glycation end-products (AGE) and also generation of reactive oxygen species (ROS), the main causative players in the context of diabetes, are intensified under hyperglycemic condition. The consequences from AGE/RAGE interaction could be attenuated by the soluble form of RAGE, termed sRAGE. In the current study, we studied the link between hyperglycemia-induced oxidative stress and the level of soluble form of RAGE in K562 cells. Our data revealed a positive correlation between high glucose and/or AGE-modified albumin treatment and oxidative stress status. Besides, a significant decrease in soluble RAGE level following treatments with either AGE-modified albumin or high glucose was observed. However, pretreatment with an appropriate antioxidant such as Resveratrol, markedly elevated the sRAGE level. Hence, sRAGE therapy could be further evaluated as an effective therapeutical approach to attenuate some of the diabetes complications.

Increased serum concentrations of pentosidine are related to presence and severity of coronary artery disease

BACKGROUND

There are limited data regarding the contribution of advanced glycation end products (AGEs) in the presence of coronary artery disease (CAD). We investigated whether serum pentosidine and Nε-carboxymethyllysine (CML) were related to the presence and the severity of CAD.

METHODS

69 Tunisian patients with CAD (≥ 50% obstruction in ≥ 1 coronary artery), 32 Tunisian patients without CAD but with potential cardiovascular risk factors and 60 Tunisian control subjects were included in a cross-sectional study. Patients were classified as CAD and non CAD patients according to angiographic results. The severity of CAD was assessed using the Gensini score. Serum pentosidine and CML were measured by LC-MS/MS.

RESULTS

Serum pentosidine and CML concentrations were significantly higher in non-CAD patients vs control subjects (P<0.001). Serum pentosidine concentrations were significantly higher in CAD patients vs non-CAD patients (P<0.001). A multiple logistic regression analysis demonstrated that pentosidine was independently associated with the presence of CAD (OR=1.52, 95% CI: 1.12-2.07, P=0.007). The area under curve (AUC) determined by ROC analysis was 0.74 (95% CI: 0.64-0.84, P<0.001) and the optimal cut-off value of pentosidine to predict the presence of CAD was 3.2 μmol/mol Lys, with 64% sensitivity and 78% specificity. Furthermore, in a multivariate stepwise regression analysis, pentosidine was independently correlated with Gensini score (standardized β= 0.46, 95% CI: 0.70-1.99, P<0.001).

CONCLUSIONS

High concentrations of pentosidine show the presence and the severity of CAD with high sensitivity.

Low-molecular weight fractions of Japanese soy sauce act as a RAGE antagonist via inhibition of RAGE trafficking to lipid rafts

Advanced glycation end-products (AGE) have been implicated in aging and the pathogenesis of diabetic complications, inflammation, Alzheimer's disease, and cancer. AGE engage the cell surface receptor for AGE (RAGE), which in turn elicits intracellular signaling, leading to activation of NF-κB to cause deterioration of tissue homeostasis. AGE are not only formed within our bodies but are also derived from foods, endowing them with flavor. In the present study, we assessed the agonistic/antagonistic effects of food-derived AGE on RAGE signaling in a reporter assay system and found that low-molecular weight AGE can antagonize the action of AGE-BSA. Foods tested were Japanese soy sauce, coffee, cola, and red wine, all of which showed fluorescence characteristics of AGE. Soy sauce and coffee contained N(ε)-carboxymethyl-lysine (CML). Soy sauce, coffee, and red wine inhibited the RAGE ligand-induced activation of NF-κB, whereas cola had no effect on the ligand induction of NF-κB. The liquids were then fractionated into high-molecular weight (HMW) fractions and low-molecular weight (LMW) fractions. Soy sauce-, coffee-, and red wine-derived LMW fractions consistently inhibited the RAGE ligand induction of NF-κB, whereas the HMW fractions of these foods activated RAGE signaling. Using the LMW fraction of soy sauce as a model food-derived RAGE antagonist, we performed a plate-binding assay and found that the soy sauce LMW fractions competitively inhibited AGE-RAGE association. Further, this fraction significantly reduced AGE-dependent monocyte chemoattractant protein-1 (MCP-1) secretion from murine peritoneal macrophages. The LMF from soy sauce suppressed the AGE-induced RAGE trafficking to lipid rafts. These results indicate that small components in some, if not all, foods antagonize RAGE signaling and could exhibit beneficial effects on RAGE-related diseases.

Total polyphenol of Anemarrhena asphodeloides ameliorates advanced glycation end products-induced endothelial dysfunction by regulation of AMP-Kinase

OBJECTIVE

Anemarrhena asphodeloides Bunge is widely used in China for the treatment of diabetes and the polyphenol components are responsible for its anti-diabetic action. This study aimed to investigate the effect of total polyphenol of Anemarrhena asphodeloides (TPAA) on endothelial dysfunction and to elucidate underlying mechanisms.

METHODS

We stimulated endothelial cells with advanced glycation end products (AGEs) to establish the model of endothelial dysfunction in vitro and observed the effect of TPAA (10, 30, or 100 μg/mL) on AMP-Kinase (AMPK) activation implicated in regulation of nitric oxide (NO) and endothelin-1 (ET-1) production. Meanwhile, nuclear factor-κB (NF-κB) activation, intracellular reactive oxygen species (ROS) production, mitochondrial membrane potential (ΔΨm) and eNOS expression were investigated by western blot, fluorescence microscopy and real time-quantitative PCR analysis, respectively.

RESULTS

Total polyphenol of Anemarrhena asphodeloides enhanced AMPK phosphorylation and promoted the basal NO production along with the inhibition of ET-1 secretion in endothelial cells. TPAA inhibited NF-κB activation by attenuating p65 phosphorylation and suppressed ROS production, well demonstrating its action in inhibition of ROS-associated inflammation in the endothelium. Meanwhile, TPAA protected mitochondrial function and endothelial homeostasis against AGEs insult by restoring ΔΨm and mRNA expression of eNOS. AGEs stimulation inhibited AMPK activation and induced the loss of NO production together with increased secretion of ET-1, but these changes were reversed by TPAA in a concentration-dependent manner. Compound C, an AMPK inhibitor, attenuated the effects of TPAA mentioned above, indicating the involvement of AMPK.

CONCLUSIONS

Total polyphenol of Anemarrhena asphodeloides inhibited AGEs-induced ROS-associated inflammation and ameliorated endothelial dysfunction through beneficial regulation of AMPK activation.

Dose responsive effects of subcutaneous pentosan polysulfate injection in mucopolysaccharidosis type VI rats and comparison to oral treatment

BACKGROUND

We previously demonstrated the benefits of daily, oral pentosan polysulfate (PPS) treatment in a rat model of mucopolysaccharidosis (MPS) type VI. Herein we compare these effects to once weekly, subcutaneous (s.c.) injection. The bioavailability of injected PPS is greater than oral, suggesting better delivery to difficult tissues such as bone and cartilage. Injected PPS also effectively treats osteoarthritis in animals, and has shown success in osteoarthritis patients.

METHODOLOGY/PRINCIPAL FINDINGS

One-month-old MPS VI rats were given once weekly s.c. injections of PPS (1, 2 and 4 mg/kg, human equivalent dose (HED)), or daily oral PPS (4 mg/kg HED) for 6 months. Serum inflammatory markers and total glycosaminoglycans (GAGs) were measured, as were several histological, morphological and functional endpoints. Overall, weekly s.c. PPS injections led to similar or greater therapeutic effects as daily oral administration. Common findings between the two treatment approaches included reduced serum inflammatory markers, improved dentition and skull lengths, reduced tracheal deformities, and improved mobility. Enhanced effects of s.c. treatment included GAG reduction in urine and tissues, greater endurance on a rotarod, and better improvements in articular cartilage and bone in some dose groups. Optimal therapeutic effects were observed at 2 mg/kg, s.c.. No drug-related increases in liver enzymes, coagulation factor abnormalities or other adverse effects were identified following 6 months of s.c. PPS administration.

CONCLUSIONS

Once weekly s.c. administration of PPS in MPS VI rats led to equal or better therapeutic effects than daily oral administration, including a surprising reduction in urine and tissue GAGs. No adverse effects from s.c. PPS administration were observed over the 6-month study period.

Oxidative stress: A cause and therapeutic target of diabetic complications

Oxidative stress is defined as excessive production of reactive oxygen species (ROS) in the presence of diminished anti‐oxidant substances. Increased oxidative stress could be one of the common pathogenic factors of diabetic complications. However, the mechanisms by which hyperglycemia increases oxidative stress are not fully understood. In this review, we focus on the impact of mitochondrial derived ROS (mtROS) on diabetic complications and suggest potential therapeutic approaches to suppress mtROS. It has been shown that hyperglycemia increases ROS production from mitochondrial electron transport chain and normalizing mitochondrial ROS ameliorates major pathways of hyperglycemic damage, such as activation of polyol pathway, activation of PKC and accumulation of advanced glycation end‐products (AGE). Additionally, in subjects with type 2 diabetes, we found a positive correlation between HbA1c and urinary excretion of 8‐hydroxydeoxyguanosine (8‐OHdG), which reflects mitochondrial oxidative damage, and further reported that 8‐OHdG was elevated in subjects with diabetic micro‐ and macro‐ vascular complications. We recently created vascular endothelial cell‐specific manganese superoxide dismutase (MnSOD) transgenic mice, and clarified that overexpression of MnSOD in endothelium could prevent diabetic retinopathy in vivo. Furthermore, we found that metformin and pioglitazone, both of which have the ability to reduce diabetic vascular complications, could ameliorate hyperglycemia‐induced mtROS production by the induction of PPARγ coactivator‐1α (PGC‐1α) and MnSOD and/or activation of adenosine monophosphate (AMP)‐activated protein kinase (AMPK). We also found that metformin and pioglitazone promote mitochondrial biogenesis through the same AMPK–PGC‐1α pathway. Taking these results, mtROS could be the key initiator of and a therapeutic target for diabetic vascular complications. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00013.x, 2010)

Molecular mechanisms of diabetic vascular complications

Diabetic complications are the major causes of morbidity and mortality in patients with diabetes. Microvascular complications include retinopathy, nephropathy and neuropathy, which are leading causes of blindness, end‐stage renal disease and various painful neuropathies; whereas macrovascular complications involve atherosclerosis related diseases, such as coronary artery disease, peripheral vascular disease and stroke. Diabetic complications are the result of interactions among systemic metabolic changes, such as hyperglycemia, local tissue responses to toxic metabolites from glucose metabolism, and genetic and epigenetic modulators. Chronic hyperglycemia is recognized as a major initiator of diabetic complications. Multiple molecular mechanisms have been proposed to mediate hyperglycemia’s adverse effects on vascular tissues. These include increased polyol pathway, activation of the diacylglycerol/protein kinase C pathway, increased oxidative stress, overproduction and action of advanced glycation end products, and increased hexosamine pathway. In addition, the alterations of signal transduction pathways induced by hyperglycemia or toxic metabolites can also lead to cellular dysfunctions and damage vascular tissues by altering gene expression and protein function. Less studied than the toxic mechanisms, hyperglycemia might also inhibit the endogenous vascular protective factors such as insulin, vascular endothelial growth factor, platelet‐derived growth factor and activated protein C, which play important roles in maintaining vascular homeostasis. Thus, effective therapies for diabetic complications need to inhibit mechanisms induced by hyperglycemia’s toxic effects and also enhance the endogenous protective factors. The present review summarizes these multiple biochemical pathways activated by hyperglycemia and the potential therapeutic interventions that might prevent diabetic complications. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2010.00018.x, 2010)

Heat-processed Panax ginseng and diabetic renal damage: active components and action mechanism

Diabetic nephropathy is one of the serious complications in patients with either type 1 or 2 diabetes mellitus but current treatments remain unsatisfactory. Results of clinical research studies demonstrate that Panax ginseng can help adjust blood pressure and reduce blood sugar and may be advantageous in the treatment of tuberculosis and kidney damage in people with diabetes. The heat-processing method to strengthen the efficacy of P. ginseng has been well-defined based on a long history of ethnopharmacological evidence. The protective effects of P. ginseng on pathological conditions and renal damage associated with diabetic nephropathy in the animal models were markedly improved by heat-processing. The concentrations of less-polar ginsenosides (20(S)-Rg3, 20(R)-Rg3, Rg5, and Rk1) and maltol in P. ginseng were significantly increased in a heat-processing temperature-dependent manner. Based on researches in animal models of diabetes, ginsenoside 20(S)-Rg3 and maltol were evaluated to have therapeutic potential against diabetic renal damage. These effects were achieved through the inhibition of inflammatory pathway activated by oxidative stress and advanced glycation endproducts. These findings indicate that ginsenoside 20(S)-Rg3 and maltol are important bioactive constituents of heat-processed ginseng in the control of pathological conditions associated with diabetic nephropathy.

Genetic deficiency of neuronal RAGE protects against AGE-induced synaptic injury

Synaptic dysfunction and degeneration is an early pathological feature of aging and age-related diseases, including Alzheimer's disease (AD). Aging is associated with increased generation and deposition of advanced glycation endproducts (AGEs), resulting from nonenzymatic glycation (or oxidation) proteins and lipids. AGE formation is accelerated in diabetes and AD-affected brain, contributing to cellular perturbation. The extent of AGEs' involvement, if at all, in alterations in synaptic structure and function is currently unknown. Here we analyze the contribution of neuronal receptor of AGEs (RAGE) signaling to AGE-mediated synaptic injury using novel transgenic neuronal RAGE knockout mice specifically targeted to the forebrain and transgenic mice expressing neuronal dominant-negative RAGE (DN-RAGE). Addition of AGEs to brain slices impaired hippocampal long-term potentiation (LTP). Similarly, treatment of hippocampal neurons with AGEs significantly decreases synaptic density. Such detrimental effects are largely reversed by genetic RAGE depletion. Notably, brain slices from mice with neuronal RAGE deficiency or DN-RAGE are resistant to AGE-induced LTP deficit. Further, RAGE deficiency or DN-RAGE blocks AGE-induced activation of p38 signaling. Taken together, these data show that neuronal RAGE functions as a signal transducer for AGE-induced synaptic dysfunction, thereby providing new insights into a mechanism by which the AGEs–RAGE-dependent signaling cascade contributes to synaptic injury via the p38 MAP kinase signal transduction pathway. Thus, RAGE blockade may be a target for development of interventions aimed at preventing the progression of cognitive decline in aging and age-related neurodegenerative diseases.

Pathophysiological importance of aggregated damaged proteins

Reactive oxygen species (ROS) are formed continuously in the organism even under physiological conditions. If the level of ROS in cells exceeds the cellular defense capacity, components such as RNA/DNA, lipids, and proteins are damaged and modified, thus affecting the functionality of organelles as well. Proteins are especially prominent targets of various modifications such as oxidation, glycation, or conjugation with products of lipid peroxidation, leading to the alteration of their biological function, nonspecific interactions, and the production of high-molecular-weight protein aggregates. To ensure the maintenance of cellular functions, two proteolytic systems are responsible for the removal of oxidized and modified proteins, especially the proteasome and organelles, mainly the autophagy-lysosomal systems. Furthermore, increased protein oxidation and oxidation-dependent impairment of proteolytic systems lead to an accumulation of oxidized proteins and finally to the formation of nondegradable protein aggregates. Accordingly, the cellular homeostasis cannot be maintained and the cellular metabolism is negatively affected. Here we address the current knowledge of protein aggregation during oxidative stress, aging, and disease.

The effects of dietary thiamin on oxidative damage and antioxidant defence of juvenile fish

The present study explored the effects of thiamin on antioxidant capacity of juvenile Jian carp (Cyprinus carpio var. Jian). In a 60-day feeding trial, a total of 1,050 juvenile Jian carp (8.20 ± 0.02 g) were fed graded levels of thiamin at 0.25, 0.48, 0.79, 1.06, 1.37, 1.63 and 2.65 mg thiamin kg(-1) diets. The results showed that malondialdehyde and protein carbonyl contents in serum, hepatopancreas, intestine and muscle were significantly decreased with increasing dietary thiamin levels (P < 0.05). Conversely, the anti-superoxide anion capacity and anti-hydroxyl radical capacity in serum, hepatopancreas, intestine and muscle were the lowest in fish fed the thiamin-unsupplemented diet. Meanwhile, the activities of catalase (CAT), glutathione peroxidase, glutathione S-transferase and glutathione reductase, and the contents of glutathione in serum, hepatopancreas, intestine and muscle were enhanced with increasing dietary thiamin levels (P < 0.05). Superoxide dismutase (SOD) activity in serum, hepatopancreas and intestine followed a similar trend as CAT (P < 0.05). However, SOD activity in muscle was not affected by dietary thiamin level (P > 0.05). The results indicated that thiamin could improve antioxidant defence and inhibit lipid peroxidation and protein oxidation of juvenile Jian carp.

Accumulation of modified proteins and aggregate formation in aging

Increasing cellular damage during the aging process is considered to be one factor limiting the lifespan of organisms. Besides the DNA and lipids, proteins are frequent targets of non-enzymatic modifications by reactive substances including oxidants and glycating agents. Non-enzymatic protein modifications may alter the protein structure often leading to impaired functionality. Although proteolytic systems ensure the removal of modified proteins, the activity of these proteases was shown to decline during the aging process. The additional age-related increase of reactive compounds as a result of impaired antioxidant systems leads to the accumulation of damaged proteins and the formation of protein aggregates. Both, non-enzymatic modified proteins and protein aggregates impair cellular functions and tissue properties by a variety of mechanisms. This is increasingly important in aging and age-related diseases. In this review, we will give an overview on oxidation and glycation of proteins and the function of modified proteins in aggregate formation. Furthermore, their effects as well as their role in aging and age-related diseases will be highlighted.

Neuropathy induced by exogenously administered advanced glycation end-products in rats

Aims/Introduction:  Advanced glycation end‐products (AGE) have been implicated in the development of diabetic neuropathy. It still remains unknown, however, how AGE cause functional and structural changes of the peripheral nerve in diabetes. To explore the role of AGE in diabetic neuropathy, we examined the peripheral nerve by injecting AGE into normal Wistar rats.

Materials and Methods:  Young, normal male Wistar rats were injected intraperitoneally (i.p.) daily for 12 weeks with purified AGE prepared by incubating D‐glucose with bovine serum albumin (BSA). A control group received BSA alone. A group of rats given AGE were co‐treated with aminoguanidine (50 mg/kg/day, i.p.). Peripheral nerve function and structure, as well as nerve Na⁺,K⁺‐ATPase activity, were examined in these rats. Immunohistochemical expressions of 8‐hydroxy‐2′‐deoxyguanosine (8OHdG) and nuclear factor‐κB (NF‐κB)p65 were also examined.

Results:  Serum AGE levels were increased two to threefold in the AGE‐treated group compared with those in the BSA‐treated control group. AGE‐treated rats showed a marked slowing of motor nerve conduction velocity (MNCV) and decreased nerve Na⁺,K⁺‐ATPase activity compared with those in the BSA‐treated group. These changes were accompanied by intensified expressions of 8OHdG and NF‐κBp65 in endothelial cells and Schwann cells. Aminoguanidine treatment corrected MNCV delay, Na⁺,K⁺‐ATPase activity, and suppressed the expression of 8OHdG and NF‐κB, despite there being no influence on serum AGE levels.

Conclusions:  The results suggest that an elevated concentration of blood AGE might be one of the contributing factors to the development of neuropathic changes in diabetes.

Anti-fibrotic effects of specific-siRNA targeting of the receptor for advanced glycation end products in a rat model of experimental hepatic fibrosis

Since the receptor for advanced glycation end products (RAGE)-ligand axis has been demonstrated to be important in fibrogenesis, rat models may be used to assess whether specific small interfering RNAs (siRNAs) that target RAGE are able to reduce the progression of hepatic fibrosis. However, the effect of RAGE-targeted siRNA on established hepatic fibrosis remains to be elucidated. In the present study, RAGE-specific siRNA expression vectors were constructed prior to the animal experiment. Sprague-Dawley rats were treated initially with olive oil (2 ml/kg) or 50% CCl4 (2 ml/kg; CCl4/olive oil=1:1) twice per week for six weeks to generate the fibrosis model. The rats were then treated with phosphate‑buffered saline, a RAGE-specific siRNA expression vector, at different doses or a non-specific siRNA expression vector twice weekly via tail vein injection for up to six weeks, and were sacrificed at week two, four or six. Compared with the control groups, RAGE‑specific siRNA therapy significantly decreased RAGE mRNA and protein expression in rat livers (P<0.01). Following six weeks of RAGE gene-silencing treatment, the liver function, which was assessed by analyzing serum levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP) and total bilirubin (TBIL), improved to varying degrees (P<0.01). The expression of nuclear factor-κB (NF-κB) significantly decreased following RAGE gene‑silencing therapy (P<0.01). In addition, the serum levels of inflammatory cytokines, including tumor necrosis factor‑α (TNF-α) and interleukin-6 (IL-6), and extracellular matrix (ECM) components, including hyaluronic acid (HA), laminin (LN) and procollagen type III (PCIII) also decreased (P<0.01). Furthermore, the expression of α-smooth muscle actin (α-SMA) and collagen I, which indicate the activation of hepatic stellate cells (HSCs), were downregulated following RAGE gene-silencing therapy (P<0.01). Furthermore, the inflammatory activity grade and fibrosis stage of rat livers also significantly improved compared with the control groups following RAGE gene-silencing therapy. Specific targeting of RAGE using siRNA may inhibit RAGE gene expression effectively in the rat hepatic fibrosis model and attenuate the progression of established hepatic fibrosis. This therapeutic effect may be mediated via inhibition of the expression of NF-κB. These findings suggest that RAGE may be a new target to prevent hepatic fibrosis.

Diffuse glomerular nodular lesions in diabetic pigs carrying a dominant-negative mutant hepatocyte nuclear factor 1-alpha, an inheritant diabetic gene in humans

Glomerular nodular lesions, known as Kimmelstiel-Wilson nodules, are a pathological hallmark of progressive human diabetic nephropathy. We have induced severe diabetes in pigs carrying a dominant-negative mutant hepatocyte nuclear factor 1-alpha (HNF1α) P291fsinsC, a maturity-onset diabetes of the young type-3 (MODY3) gene in humans. In this model, glomerular pathology revealed that formation of diffuse glomerular nodules commenced as young as 1 month of age and increased in size and incidence until the age of 10 months, the end of the study period. Immunohistochemistry showed that the nodules consisted of various collagen types (I, III, IV, V and VI) with advanced glycation end-product (AGE) and N^ε-carboxymethyl-lysine (CML) deposition, similar to those in human diabetic nodules, except for collagen type I. Transforming growth factor-beta (TGF-β) was also expressed exclusively in the nodules. The ultrastructure of the nodules comprised predominant interstitial-type collagen deposition arising from the mesangial matrices. Curiously, these nodules were found predominantly in the deep cortex. However, diabetic pigs failed to show any of the features characteristic of human diabetic nephropathy; e.g., proteinuria, glomerular basement membrane thickening, exudative lesions, mesangiolysis, tubular atrophy, interstitial fibrosis, and vascular hyalinosis. The pigs showed only Armanni-Ebstein lesions, a characteristic tubular manifestation in human diabetes. RT-PCR analysis showed that glomeruli in wild-type pigs did not express endogenous HNF1α and HNF1β, indicating that mutant HNF1α did not directly contribute to glomerular nodular formation in diabetic pigs. In conclusion, pigs harboring the dominant-negative mutant human MODY3 gene showed reproducible and distinct glomerular nodules, possibly due to AGE- and CML-based collagen accumulation. Although the pathology differed in several respects from that of human glomerular nodular lesions, the somewhat acute and constitutive formation of nodules in this mammalian model might provide information facilitating identification of the principal mechanism underlying diabetic nodular sclerosis.

Allopurinol is an independent determinant of improved arterial stiffness in chronic kidney disease: a cross-sectional study

Background

Arterial stiffness is increased in patients with CKD and is a powerful predictor of cardiovascular morbidity and mortality. Use of the xanthine oxidase inhibitor allopurinol has been shown to improve endothelial function, reduce left ventricular hypertrophy and possibly improve cardiovascular outcome. We explored the relationship between use of allopurinol and arterial stiffness in patients with chronic kidney disease (CKD).

Methods

Cross-sectional observational study of 422 patients with CKD with evidence of, or at high risk of, renal disease progression. Arterial stiffness was determined by carotid-femoral pulse wave velocity (PWV).

Results

The mean age was 63±16 years, median estimated glomerular filtration rate was 25 (interquartile range: 19–31) ml/min/1.73 m² and mean PWV was 10.2±2.4 m/s. Seventy-seven patients (18%) were receiving regular allopurinol, 61% at a dose of 100 mg/day (range: 50–400 mg/day). Patients receiving allopurinol had significantly lower peripheral pulse pressure, central pulse pressure, central systolic blood pressure, serum uric acid level tissue advanced glycation end product levels but comparable high-sensitivity C-reactive protein levels. Use of allopurinol was associated with lower PWV. After adjusting for age, gender, ethnicity, tissue advanced glycation end product level, peripheral pulse pressure, smoking pack years, presence of diabetes mellitus and use of angiotensin converting enzyme inhibitor or angiotensin II receptor blocker, the use of allopurinol remained a significant independent determinant of PWV (mean difference: −0.63 m/s; 95% CI, −0.09 to −1.17 m/s, p = 0.02).

Conclusion

In patients with CKD, use of allopurinol is independently associated with lower arterial stiffness. This study provides further justification for a large definitive randomised controlled trial examining the therapeutic potential of allopurinol to reduce cardiovascular risk in people with CKD.

The diabetic vasculature: physiological mechanisms of dysfunction and influence of aerobic exercise training in animal models

Diabetes mellitus (DM) is associated with a number of complications of which chronic vascular complications are undoubtedly the most complex and significant consequence. With a significant impact on health care, 50-80% of people with diabetes die of cardiovascular disease (including coronary artery disease, stroke, peripheral vascular disease and other vascular disease), making it the major cause of morbidity and mortality in diabetic patients. A healthy lifestyle is essential in the management of DM, especially the inclusion of aerobic exercise, which has been shown effective in reducing the deleterious effects in vasculature. Interest in exercise studies has increased significantly with promising results that demonstrate a future for investigation. Considering the importance of this emerging field, the aim of this mini-review is to summarize and integrate animal studies investigating physiological mechanisms of vascular dysfunction and remodeling in type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) and how these are influenced by chronic aerobic exercise training.

Advanced glycation end products and diabetic complications

During long standing hyperglycaemic state in diabetes mellitus, glucose forms covalent adducts with the plasma proteins through a non-enzymatic process known as glycation. Protein glycation and formation of advanced glycation end products (AGEs) play an important role in the pathogenesis of diabetic complications like retinopathy, nephropathy, neuropathy, cardiomyopathy along with some other diseases such as rheumatoid arthritis, osteoporosis and aging. Glycation of proteins interferes with their normal functions by disrupting molecular conformation, altering enzymatic activity, and interfering with receptor functioning. AGEs form intra- and extracellular cross linking not only with proteins, but with some other endogenous key molecules including lipids and nucleic acids to contribute in the development of diabetic complications. Recent studies suggest that AGEs interact with plasma membrane localized receptors for AGEs (RAGE) to alter intracellular signaling, gene expression, release of pro-inflammatory molecules and free radicals. The present review discusses the glycation of plasma proteins such as albumin, fibrinogen, globulins and collagen to form different types of AGEs. Furthermore, the role of AGEs in the pathogenesis of diabetic complications including retinopathy, cataract, neuropathy, nephropathy and cardiomyopathy is also discussed.

Tat-glyoxalase protein inhibits against ischemic neuronal cell damage and ameliorates ischemic injury

Methylglyoxal (MG), a metabolite of glucose, is the major precursor of protein glycation and induces apoptosis. MG is associated with neurodegeneration, including oxidative stress and impaired glucose metabolism, and is efficiently metabolized to S-D-lactoylglutathione by glyoxalase (GLO). Although GLO has been implicated as being crucial in various diseases including ischemia, its detailed functions remain unclear. Therefore, we investigated the protective effect of GLO (GLO1 and GLO2) in neuronal cells and an animal ischemia model using Tat-GLO proteins. Purified Tat-GLO protein efficiently transduced into HT-22 neuronal cells and protected cells against MG- and H2O2-induced cell death, DNA fragmentation, and activation of caspase-3 and mitogen-activated protein kinase. In addition, transduced Tat-GLO protein increased D-lactate in MG- and H2O2-treated cells whereas glycation end products (AGE) and MG levels were significantly reduced in the same cells. Gerbils treated with Tat-GLO proteins displayed delayed neuronal cell death in the CA1 region of the hippocampus compared with a control. Furthermore, the combined neuroprotective effects of Tat-GLO1 and Tat-GLO2 proteins against ischemic damage were significantly higher than those of each individual protein. Those results demonstrate that transduced Tat-GLO protein protects neuronal cells by inhibiting MG- and H2O2-mediated cytotoxicity in vitro and in vivo. Therefore, we suggest that Tat-GLO proteins could be useful as a therapeutic agent for various human diseases related to oxidative stress including brain diseases.

Postprandial inflammation: targeting glucose and lipids

Many risk factors have been identified as being responsible for the process of atherogenesis. Several of these risk factors are related to inflammation, which is an obligatory feature of the atherosclerotic plaque. Increasing evidence suggests that postprandial lipoproteins and glucose may be involved in the inflammatory process preceding the development of atherosclerosis. During the postprandial situation, remnants of chylomicrons and very low-density lipoproteins bind to circulating leukocytes and endothelial cells, leading to a state of acute activation with the expression of integrins on different cells, the generation of oxidative stress, production of cytokines and complement activation. Elevated plasma glucose levels may also induce leukocyte activation in humans. In addition, advanced glycation end products, formed during hyperglycemia, cause inflammation and endothelial damage. This chain of events results in a situation of acute inflammation causing endothelial dysfunction, which may be one of the earliest defects in atherogenesis. Interestingly, while this may occur several times each day after each meal, there is only limited information on the contribution of different nutrients on the postprandial inflammatory processes. In this review, we will focus on the available evidence and we will discuss the role of lifestyle and pharmaceutical interventions in modulating postprandial inflammation.

Neuroinflammation and oxidative stress in diabetic neuropathy: futuristic strategies based on these targets

In Diabetes, the chronic hyperglycemia and associated complications affecting peripheral nerves are one of the most commonly occurring microvascular complications with an overall prevalence of 50-60%. Among the vascular complications of diabetes, diabetic neuropathy is the most painful and disabling, fatal complication affecting the quality of life in patients. Several theories of etiologies surfaced down the lane, amongst which the oxidative stress mediated damage in neurons and surrounding glial cell has gained attention as one of the vital mechanisms in the pathogenesis of neuropathy. Mitochondria induced ROS and other oxidants are responsible for altering the balance between oxidants and innate antioxidant defence of the body. Oxidative-nitrosative stress not only activates the major pathways namely, polyol pathway flux, advanced glycation end products formation, activation of protein kinase C, and overactivity of the hexosamine pathway, but also initiates and amplifies neuroinflammation. The cross talk between oxidative stress and inflammation is due to the activation of NF- κ B and AP-1 and inhibition of Nrf2, peroxynitrite mediate endothelial dysfunction, altered NO levels, and macrophage migration. These all culminate in the production of proinflammatory cytokines which are responsible for nerve tissue damage and debilitating neuropathies. This review focuses on the relationship between oxidative stress and neuroinflammation in the development and progression of diabetic neuropathy.

Unlocking the biology of RAGE in diabetic microvascular complications

The discovery of the receptor for advanced glycation end-products (RAGE) set the stage for the elucidation of important mechanisms underpinning diabetic complications. RAGE transduces the signals of advanced glycation end-products (AGEs), proinflammatory S100/calgranulins, and high mobility group box 1 (HMGB1), and is a one of a family of receptors for lysophosphatidic acid (LPA). These ligand tales weave a theme of vascular perturbation and inflammation linked to the pathogenesis of the chronic complications of diabetes. Once deemed implausible, this concept of inflammatory cues participating in diabetic complications is now supported by a plethora of experimental evidence in the macro- and microvasculature. We review the biology of ligand-RAGE signal transduction and its roles in diabetic microvascular complications, from animal models to human subjects.

Simvastatin attenuates the endothelial pro-thrombotic shift in saphenous vein grafts induced by Advanced glycation endproducts

BACKGROUND

Advanced glycation endproducts (AGEs) and its receptors (RAGEs) are heterogeneous signaling proteins associated to diabetes and responsible of endothelial alterations leading to atherosclerosis progression and graft failure. The aim of this study was to investigate the role of statin in reducing AGEs related endothelial damage.

METHODS

Endothelial cell(EC) obtained from leftovers of saphenous vein grafts of non-diabetic patients were incubated with AGEs (2 and 20 μM) and subsequently treated with Simvastatin. Neutrophils (PNM) adherence, ROS production and RAGE and peroxisome proliferator-activated receptors-gamma (PPAR-γ) expression were analyzed. As clinical validation of the in vitro findings, ECs of diabetic patients in optimized glycaemic control administered with a 3 weeks Simvastatin regimen were similarly processed.

RESULTS

Simvastatin blunted the rise in PMN adhesion and ROS generation following stimulation of saphenous vein EC culture with AGEs in vitro. This effect was time dependent and was associated to an increase in PPAR-γ induction paralleled by a decrease in RAGEs expression. Parallely, data from diabetic patients administered with Simvastatin showed a similar significant reduction in PNM adhesion and ROS generation. Simvastatin treatment significantly decreased RAGEs expression in ECs from diabetic patients and determined a slight increase in PPAR-γ expression but the latter failed to reach statistical significance. Interference in the function of these two crucial pathways might be at the root of the statin antinflammatory and antithrombotic effect in the context of AGEs-associated damage.

CONCLUSIONS

Despite the recently raised warning on the use of statins in the diabetic population, this study elucidates their cornerstone position in endothelial homeostasis of saphenous grafts in patients with controlled diabetes.

Production of reactive oxygen species in the diabetic heart. Roles of mitochondria and NADPH oxidase

Reactive oxygen species (ROS) are the main facilitators of cardiovascular complications in diabetes mellitus (DM), and the ROS level is increased in cultured cells exposed to high glucose concentrations or in diabetic animal models. Emerging evidence shows that mitochondria and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase are dominant mechanisms of ROS production in the diabetic heart. Hyperpolarization of the mitochondrial inner membrane potentials and impaired mitochondrial function promote ROS production in the mitochondria of the diabetic heart. Uncoupling proteins are upregulated and may reduce the ROS level by depolarizing the mitochondrial inner membrane potential. NADPH oxidase is another major site of ROS production and its contribution to DM-induced ROS increase has been elucidated not only in vascular smooth muscle cells and endothelial cells, but also in cardiomyocytes. Protein kinase C, angiotensin II, and advanced glycation endproducts (AGEs)/receptor for AGEs can activate NADPH oxidase. Increased intracellular calcium level mediated via the Na(+)-H(+) exchanger and subsequent activation of Ca(2+)/calmodulin-dependent protein kinase II may also activate NADPH oxidase. This review presents the current understanding of the mechanisms of ROS production, focusing especially on the roles of mitochondria and NADPH oxidase. 

Trientine reduces BACE1 activity and mitigates amyloidosis via the AGE/RAGE/NF-κB pathway in a transgenic mouse model of Alzheimer's disease

AIMS

There is mounting evidence that the transition metal copper may play an important role in the pathophysiology of Alzheimer's disease (AD). Triethylene tetramine dihydrochloride (trientine), a CuII-selective chelator, is a commonly used treatment for Wilson's disease to decrease accumulated copper, and thereby decreases oxidative stress. In the present study, we evaluated the effects of a 3-month treatment course of trientine (Trien) on amyloidosis in 7-month-old β-amyloid (Aβ) precursor protein and presenilin-1 (APP/PS1) double transgenic (Tg) AD model mice.

RESULTS

We observed that Trien reduced the level of advanced glycation end products (AGEs), and decreased Aβ deposition and synapse loss in brain of APP/PS1 mice. Importantly, we found that Trien blocked the receptor for AGEs (RAGE), downregulated β-site APP cleaving enzyme 1 (BACE1), inhibited amyloidogenic APP cleavage, and subsequently reduced Aβ levels. In vitro, in SH-SY5Y cells overexpressing Swedish mutant APP, Trien-mediated downregulation of BACE1 occurred via inhibition of the NF-κB signaling pathway.

INNOVATION

In this study, we demonstrated for the first time that Trien inhibited amyloidogenic pathway including targeting the downregulation of RAGE and NF-κB.

CONCLUSION

Trien might mitigate amyloidosis in AD by inhibiting the RAGE/NF-κB/BACE1 pathway. Our study demonstrates that Trien may be a viable therapeutic strategy for the intervention and treatment of AD and other AD-like pathologies.

Regulatory mechanism of gallic acid against advanced glycation end products induced cardiac remodeling in experimental rats

Advanced glycation end products (AGEs) play a major role in the development of cardiovascular disorders in diabetic patients. Recent studies evidenced the beneficial role of phytochemicals in reducing the risk of cardiovascular diseases. Hence the present study was framed to investigate the protective role of Gallic acid (GA) on AGEs induced cardiac fibrosis. Rats were infused with in vitro prepared AGEs (50mg/kg BW-intravenous injection) for 30 days. Further, GA (25mg/kgBW) was administered to rats along with AGEs. On infusion of AGEs, induction of fibrotic markers, collagen deposition, oxidative marker NADPH oxidase (NOX-p47 phox subunit), AGE receptor (RAGE) and cytokines expression was evaluated in the heart tissues using RT-PCR, Western blot and immunostaining methods. AGEs infusion significantly (P<0.01) increased the HW/BW ratio and fibrosis (4-fold) with increased expression of matrix genes MMP-2 and -9 (P<0.01, respectively) in the heart tissues. Whereas, administration of GA along with AGEs infusion prevented the fibrosis induced by AGEs. Further, GA treatment effectively prevented the AGEs mediated up-regulation of pro-fibrotic genes and ECM proteins such as TNF-α, TGF-β, MMP-2 and -9 expression. In addition, the increased expression of NOX (P<0.01), RAGE (P<0.01), NF-κB (P<0.01) and ERK 1/2 on AGEs infusion were normalized by GA treatment. Thus the present study shows the protective effect of GA on the fibrotic response and cardiac remodeling process induced by advanced glycation end products from external sources.

The N-glycoform of sRAGE is the key determinant for its therapeutic efficacy to attenuate injury-elicited arterial inflammation and neointimal growth

Signaling of the receptor for advanced glycation end products (RAGE) has been implicated in the development of injury-elicited vascular complications. Soluble RAGE (sRAGE) acts as a decoy of RAGE and has been used to treat pathological vascular conditions in animal models. However, previous studies used a high dose of sRAGE produced in insect Sf9 cells (sRAGE(Sf9))and multiple injections to achieve the therapeutic outcome. Here, we explore whether modulation of sRAGE N-glycoform impacts its bioactivity and augments its therapeutic efficacy. We first profiled carbohydrate components of sRAGE produced in Chinese hamster Ovary cells (sRAGE(CHO)) to show that a majority of its N-glycans belong to sialylated complex types that are not shared by sRAGE(Sf9). In cell-based NF-κB activation and vascular smooth muscle cell (VSMC) migration assays, sRAGE(CHO) exhibited a significantly higher bioactivity relative to sRAGE(Sf9) to inhibit RAGE alarmin ligand-induced NF-κB activation and VSMC migration. We next studied whether this N-glycoform-associated bioactivity of sRAGE(CHO) is translated to higher in vivo therapeutic efficacy in a rat carotid artery balloon injury model. Consistent with the observed higher bioactivity in cell assays, sRAGE(CHO) significantly reduced injury-induced neointimal growth and the expression of inflammatory markers in injured vasculature. Specifically, a single dose of 3 ng/g of sRAGE(CHO) reduced neointimal hyperplasia by over 70%, whereas the same dose of sRAGE(Sf9) showed no effect. The administered sRAGE(CHO) is rapidly and specifically recruited to the injured arterial locus, suggesting that early intervention of arterial injury with sRAGE(CHO) may offset an inflammatory circuit and reduce the ensuing tissue remodeling. Our findings showed that the N-glycoform of sRAGE is the key determinant underlying its bioactivity and thus is an important glycobioengineering target to develop a highly potent therapeutic sRAGE for future clinical applications.

KEY MESSAGE

The specific N-glycoform modification is the key underlying sRAGE bioactivity Markedly reduced sRAGE dose to attenuate neointimal hyperplasia and inflammation Provide a molecular target for glycobioengineering of sRAGE as a therapeutic protein Blocking RAGE alarmin ligands during acute injury phase offsets neointimal growth.

Expression and cell distribution of receptor for advanced glycation end-products in the rat cortex following experimental subarachnoid hemorrhage

Convincing evidence indicates that inflammation contributes to the adverse prognosis of subarachnoid hemorrhage (SAH). Some pro-inflammatory molecules such as high mobility group protein 1, S100 family of proteins, β-amyloid peptide, and macrophage antigen complex 1 have been involved in the damaging inflammation process following SAH. The receptor for advanced glycation end-products (RAGE) is a transmembrane receptor that senses these molecules and plays central role in inflammatory processes. This study aimed to determine the expression and cell distribution of RAGE in the brain cortex after SAH. Male Sprague-Dawley rats were randomly divided into sham group and SAH groups at 6 h, 12 h and on day 1, day 2 and day 3 (n=6 for each subgroup). SAH groups suffered experimental SAH by injection of 0.3 ml autologous blood into the prechiasmatic cistern. RAGE expression was measured by Western blot, real-time PCR, immunohistochemistry and immunofluorescence. Nuclear expression of p65 protein, the major subunit of nuclear factor kappa B, was also detected. Our data demonstrated that the expression levels of RAGE and nuclear p65 protein were both markedly increased after SAH. Moreover, there was a significant positive correlation between the expression of RAGE and that of p65 protein. Double immunofluorescence staining showed that RAGE was expressed by neuron and microglia rather than astrocyte after SAH. These results suggest that RAGE may be directly involved in the inflammatory response after SAH, and there might be important implications for further studies using specific RAGE antagonists to decrease inflammation-mediated brain injury following SAH.

Hyperoside downregulates the receptor for advanced glycation end products (RAGE) and promotes proliferation in ECV304 cells via the c-Jun N-terminal kinases (JNK) pathway following stimulation by advanced glycation end-products in vitro

Hyperoside is a major active constituent in many medicinal plants which are traditionally used in Chinese medicines for their neuroprotective, anti-inflammatory and antioxidative effects. The molecular mechanisms underlying these effects are unknown. In this study, quiescent ECV304 cells were treated in vitro with advanced glycation end products (AGEs) in the presence or absence of hyperoside. The results demonstrated that AGEs induced c-Jun N-terminal kinases (JNK) activation and apoptosis in ECV304 cells. Hyperoside inhibited these effects and promoted ECV304 cell proliferation. Furthermore, hyperoside significantly inhibited RAGE expression in AGE-stimulated ECV304 cells, whereas knockdown of RAGE inhibited AGE-induced JNK activation. These results suggested that AGEs may promote JNK activation, leading to viability inhibition of ECV304 cells via the RAGE signaling pathway. These effects could be inhibited by hyperoside. Our findings suggest a novel role for hyperoside in the treatment and prevention of diabetes.

Inhibition of ERK-DLP1 signaling and mitochondrial division alleviates mitochondrial dysfunction in Alzheimer's disease cybrid cell

Mitochondrial dysfunction is an early pathological feature of Alzheimer's disease (AD). The underlying mechanisms and strategies to repair it remain unclear. Here, we demonstrate for the first time the direct consequences and potential mechanisms of mitochondrial functional defects associated with abnormal mitochondrial dynamics in AD. Using cytoplasmic hybrid (cybrid) neurons with incorporated platelet mitochondria from AD and age-matched non-AD human subjects into mitochondrial DNA (mtDNA)-depleted neuronal cells, we observed that AD cybrid cells had significant changes in morphology and function; such changes associate with altered expression and distribution of dynamin-like protein (DLP1) and mitofusin 2 (Mfn2). Treatment with antioxidant protects against AD mitochondria-induced extracellular signal-regulated kinase (ERK) activation and mitochondrial fission-fusion imbalances. Notably, inhibition of ERK activation not only attenuates aberrant mitochondrial morphology and function but also restores the mitochondrial fission and fusion balance. These effects suggest a role of oxidative stress-mediated ERK signal transduction in modulation of mitochondrial fission and fusion events. Further, blockade of the mitochondrial fission protein DLP1 by a genetic manipulation with a dominant negative DLP1 (DLP1(K38A)), its expression with siRNA-DLP1, or inhibition of mitochondrial division with mdivi-1 attenuates mitochondrial functional defects observed in AD cybrid cells. Our results provide new insights into mitochondrial dysfunction resulting from changes in the ERK-fission/fusion (DLP1) machinery and signaling pathway. The protective effect of mdivi-1 and inhibition of ERK signaling on maintenance of normal mitochondrial structure and function holds promise as a potential novel therapeutic strategy for AD.

The AGE-RAGE pathway and its relation to cardiovascular disease in patients with chronic kidney disease

Chronic kidney disease (CKD) carries an unequivocal high risk for cardiovascular disease (CVD) contributing to high morbimortality; however, the underlying reasons are not fully known. Among mechanisms involved in the pathophysiology of CVD, chronic overstimulation of the advanced glycation end-products (AGE)-receptor for AGE (RAGE) pathway is likely a major contributor in patients with CKD. This review describes briefly some of the components of this pathway, highlighting especially differences between circulating AGE and tissue AGE and how activation of the AGE-RAGE pathway may promote CVD in CKD.

AGEs, contributors to placental bed vascular changes leading to preeclampsia

Glycation of proteins or other biomolecules and their further long-term degradation result in the formation of advanced glycation end products, AGEs. AGEs and other ligands interact with their receptors, RAGEs, localized to a variety of tissues, but mainly in endothelium and vascular wall cells. This interaction triggers diverse signaling pathways that converge on the activation of NF-κB and the initiation of a local inflammatory reaction that, when prolonged, results in dysfunctional features. Preeclampsia is a serious vascular disorder centred at the placenta-uterine interface, the placental bed, but the condition extends to the mother's circulation. RAGEs have notorious expression in the placental bed tissues along pregnancy but, in addition, RAGEs and their ligands are expressed in the fetal membranes and are found in the amniotic fluid and the mother's serum. Disorders complicating pregnancies and having an important vascular involvement, as preeclampsia and diabetes mellitus, have additional enhanced AGE/RAGE expression variation. This indicates that for their assessment, the assay of RAGEs or their ligands may become useful diagnostic or prognostic procedures.

Cardiovascular effects of 1 year of alagebrium and endurance exercise training in healthy older individuals

BACKGROUND

Lifelong exercise training maintains a youthful compliance of the left ventricle (LV), whereas a year of exercise training started later in life fails to reverse LV stiffening, possibly because of accumulation of irreversible advanced glycation end products. Alagebrium breaks advanced glycation end product crosslinks and improves LV stiffness in aged animals. However, it is unclear whether a strategy of exercise combined with alagebrium would improve LV stiffness in sedentary older humans.

METHODS AND RESULTS

Sixty-two healthy subjects were randomized into 4 groups: sedentary+placebo; sedentary+alagebrium (200 mg/d); exercise+placebo; and exercise+alagebrium. Subjects underwent right heart catheterization to define LV pressure-volume curves; secondary functional outcomes included cardiopulmonary exercise testing and arterial compliance. A total of 57 of 62 subjects (67 ± 6 years; 37 f/20 m) completed 1 year of intervention followed by repeat measurements. Pulmonary capillary wedge pressure and LV end-diastolic volume were measured at baseline, during decreased and increased cardiac filling. LV stiffness was assessed by the slope of LV pressure-volume curve. After intervention, LV mass and end-diastolic volume increased and exercise capacity improved (by ≈8%) only in the exercise groups. Neither LV mass nor exercise capacity was affected by alagebrium. Exercise training had little impact on LV stiffness (training × time effect, P=0.46), whereas alagebrium showed a modest improvement in LV stiffness compared with placebo (medication × time effect, P=0.04).

CONCLUSIONS

Alagebrium had no effect on hemodynamics, LV geometry, or exercise capacity in healthy, previously sedentary seniors. However, it did show a modestly favorable effect on age-associated LV stiffening.

CLINICAL TRIAL REGISTRATION- URL

http://www.clinicaltrials.gov. Unique identifier: NCT01014572.

Radical roles for RAGE in the pathogenesis of oxidative stress in cardiovascular diseases and beyond

Oxidative stress is a central mechanism by which the receptor for advanced glycation endproducts (RAGE) mediates its pathological effects. Multiple experimental inquiries in RAGE-expressing cultured cells have demonstrated that ligand-RAGE interaction mediates generation of reactive oxygen species (ROS) and consequent downstream signal transduction and regulation of gene expression. The primary mechanism by which RAGE generates oxidative stress is via activation of NADPH oxidase; amplification mechanisms in the mitochondria may further drive ROS production. Recent studies indicating that the cytoplasmic domain of RAGE binds to the formin mDia1 provide further support for the critical roles of this pathway in oxidative stress; mDia1 was required for activation of rac1 and NADPH oxidase in primary murine aortic smooth muscle cells treated with RAGE ligand S100B. In vivo, in multiple distinct disease models in animals, RAGE action generates oxidative stress and modulates cellular/tissue fate in range of disorders, such as in myocardial ischemia, atherosclerosis, and aneurysm formation. Blockade or genetic deletion of RAGE was shown to be protective in these settings. Indeed, beyond cardiovascular disease, evidence is accruing in human subjects linking levels of RAGE ligands and soluble RAGE to oxidative stress in disorders such as doxorubicin toxicity, acetaminophen toxicity, neurodegeneration, hyperlipidemia, diabetes, preeclampsia, rheumatoid arthritis and pulmonary fibrosis. Blockade of RAGE signal transduction may be a key strategy for the prevention of the deleterious consequences of oxidative stress, particularly in chronic disease.

RAGE is a nucleic acid receptor that promotes inflammatory responses to DNA

Receptor for advanced glycation end-products (RAGE) detects nucleic acids and promotes DNA uptake into endosomes, which in turn lowers the immune recognition threshold for TLR9 activation.

Recognition of DNA and RNA molecules derived from pathogens or self-antigen is one way the mammalian immune system senses infection and tissue damage. Activation of immune signaling receptors by nucleic acids is controlled by limiting the access of DNA and RNA to intracellular receptors, but the mechanisms by which endosome-resident receptors encounter nucleic acids from the extracellular space are largely undefined. In this study, we show that the receptor for advanced glycation end-products (RAGE) promoted DNA uptake into endosomes and lowered the immune recognition threshold for the activation of Toll-like receptor 9, the principal DNA-recognizing transmembrane signaling receptor. Structural analysis of RAGE–DNA complexes indicated that DNA interacted with dimers of the outermost RAGE extracellular domains, and could induce formation of higher-order receptor complexes. Furthermore, mice deficient in RAGE were unable to mount a typical inflammatory response to DNA in the lung, indicating that RAGE is important for the detection of nucleic acids in vivo.

A ten-year review of lower extremity burns in diabetics: small burns that lead to major problems

Diabetes mellitus with its resulting neurovascular changes may lead to an increased risk of burns and impaired wound healing. The purpose of this article is to review 10 years of experience with foot and lower leg burns in patients with diabetes at a single adult burn center. Patients with lower extremity burns and diabetes mellitus, between May 1999 and December 2009, were identified in the Trauma Registry of the American College of Surgeons database, and their charts were reviewed for data related to their outcomes. Sixty-eight diabetic patients, 87% male, with a mean age of 54 years, sustained foot or lower extremity burns with 37 having burns resulting from insensate feet. The pathogenesis included walking on a hot or very cold surface (8), soaking feet in hot water (22), warming feet on or near something hot such as a heater (13), or spilling hot water (7). The majority of patients were taking insulin (59.6%) or oral hyperglycemic medications (34.6%). Blood sugar levels were not well controlled (mean glucose, 215.8 mg/dl; mean hemoglobin A1c, 9.08%). Renal disease was common with admission serum blood urea nitrogen (27.5 mg/dl) and creatinine (2.21 mg/dl), and 13 were on dialysis preinjury. Cardiovascular problems were common with 39 (57%) having hypertension or cardiac disease, 3 having peripheral vascular disease, and 9, previous amputations. The mean burn size was 4.2% TBSA (range, 0.5-15%) with 57% being full thickness. Despite the small burn, the mean length of stay was 15.2 days (range, 1-95), with 5.65 days per 1% TBSA. Inability to heal these wounds was evident in 19 patients requiring readmission (one required 10 operative procedures). At least one patient sustained more than one burn. There were 62 complications with 30 episodes of infection (cellulitis, 28; osteomyelitis, 4; deep plantar infections, 2; ruptured Achilles tendon, 1) and 3 deaths. Eleven patients needed amputations (7 below-knee amputations, 4 transmetatarsal amputations, and 20 toe amputations) with several needing revisions or higher amputations. Patients with diabetes have an increased risk for lower extremity complications, but the risk of burns is not well known. The majority of lower extremity burns result from intentional exposure to sources of heat without recognition for the risk of burns. Once a burn occurs, morbidity and cost to the patient and society are severe. Prevention programs should be initiated to make diabetic patients and their doctors aware of the significant risk for burns.

Neurite regeneration in adult rat retinas exposed to advanced glycation end-products and regenerative effects of neurotrophin-4

The purpose of this study was to determine the effect of low concentrations of advanced glycation end-products on neurite regeneration in isolated rat retinas, and to determine the effects of neurotrophin-4 on regeneration in advanced glycation end-products exposed retinas. Retinal explants of 4 adult Sprague-Dawley rats were cultured on collagen gel and were incubated in; (1) serum-free control culture media, (2) glucose-advanced glycation end-products-bovine serum albumin media, (3) glycolaldehyde-advanced glycation end-products-bovine serum albumin media, (4) glyceraldehyde-advanced glycation end-products-bovine serum albumin media, (5) glucose-advanced glycation end-products+neurotrophin-4 media, (6) glycolaldehyde-advanced glycation end-products+neurotrophin-4 media, or (7) glyceraldehyde-advanced glycation end-products+neurotrophin-4 supplemented culture media. After 7 days, the number of regenerating neurites from the explants was counted. Then, explants were fixed, cryosectioned, and stained for TUNEL. The ratio of TUNEL-positive cells to all cells in the ganglion cell layer was determined. Immunohistochemical examinations for the active-form of caspase-9 and apoptosis-inducing factor were performed. In retinas incubated with advanced glycation end-products containing media, the number of regenerating neurites were fewer than in retinas without advanced glycation end-products, and the number of TUNEL-positive cells and caspase-9- and apoptosis-inducing factor-immunopositive cells was significantly higher than in control media. Neurotrophin-4 supplementation increased the numbers of regenerating neuritis, and the number of TUNEL-positives, caspase-9-, and apoptosis-inducing factor-immunopositive cells were significantly fewer than that in advanced glycation end-products without neurotrophin-4 media. Low doses of advanced glycation end-products impede neurite regeneration in the rat retinas. Neurotrophin-4 significantly enhances neurite regeneration in retinas exposed to advanced glycation end-products.

Increased serum levels of S100A8/A9 and S100A12 are associated with cardiovascular disease in patients with inactive systemic lupus erythematosus

OBJECTIVES

Patients with SLE have an increased morbidity and mortality from cardiovascular disease (CVD). The reason for this is not entirely understood, but is believed to be partly related to the long-lasting inflammatory process seen in SLE. The aim of the present study was to investigate whether there is an association between CVD and serum levels of the proinflammatory proteins S100A8/A9 and S100A12 in SLE.

METHODS

Serum levels of S100A8/A9 and S100A12 were measured with ELISA in 237 SLE patients with clinically inactive disease and without infections, as well as in 100 healthy individuals. Cardiovascular manifestations were defined according to the SLICC/ACR Damage Index (SLICC/ACR-DI).

RESULTS

Serum levels of S100A8/A9 were elevated in our inactive SLE patients as compared with healthy individuals (P < 0.0001), which was not seen for S100A12 (P = 0.12). SLE patients with a history of CVD had increased serum levels of both S100A8/A9 and S100A12 compared with patients with no CVD or venous thromboembolism (P = 0.003 and P = 0.006, respectively). The presence of organ damage according to SLICC/ACR-DI was associated with an increase in both S100A8/A9 and S100A12 serum levels (P = 0.001 and P = 0.006, respectively).

CONCLUSION

Elevated serum levels of S100A8/A9 and S100A12 may be used as an indicator of severe disease and CVD in SLE, suggesting that SLE patients with elevated serum S100A8/A9 and S100A12 concentrations may benefit from more intense cardiovascular primary preventive strategies and possibly also from more intense and early immunosuppressive treatment.

Effect of dietary nitrate on blood pressure, endothelial function, and insulin sensitivity in type 2 diabetes

Diets rich in green, leafy vegetables have been shown to lower blood pressure (BP) and reduce the risk of cardiovascular disease. Green, leafy vegetables and beetroot are particularly rich in inorganic nitrate. Dietary nitrate supplementation, via sequential reduction to nitrite and NO, has previously been shown to lower BP and improve endothelial function in healthy humans. We sought to determine if supplementing dietary nitrate with beetroot juice, a rich source of nitrate, will lower BP and improve endothelial function and insulin sensitivity in individuals with type 2 diabetes (T2DM). Twenty-seven patients, age 67.2±4.9 years (18 male), were recruited for a double-blind, randomized, placebo-controlled crossover trial. Participants were randomized to begin, in either order, a 2-week period of supplementation with 250ml beetroot juice daily (active) or 250ml nitrate-depleted beetroot juice (placebo). At the conclusion of each intervention period 24-h ambulatory blood pressure monitoring, tests of macro- and microvascular endothelial function, and a hyperinsulinemic isoglycemic clamp were performed. After 2 weeks administration of beetroot juice mean ambulatory systolic BP was unchanged: 134.6±8.4mmHg versus 135.1±7.8mmHg (mean±SD), placebo vs active-mean difference of -0.5mmHg (placebo-active), p=0.737 (95% CI -3.9 to 2.8). There were no changes in macrovascular or microvascular endothelial function or insulin sensitivity. Supplementation of the diet with 7.5mmol of nitrate per day for 2 weeks caused an increase in plasma nitrite and nitrate concentration, but did not lower BP, improve endothelial function, or improve insulin sensitivity in individuals with T2DM.

Epigallocatechin-3-gallate combined with alpha lipoic acid attenuates high glucose-induced receptor for advanced glycation end products (RAGE) expression in human embryonic kidney cells

The anti-oxidant effects of epigallocatechin gallate (EGCG) and alpha lipoic acid (ALA) have been demonstrated in previous studies. The kidney protection effects of EGCG and ALA in patients with kidney injury are still under investigation. The purpose of this study is to investigate the anti-inflammatory and anti-oxidant effects of EGCG and ALA on high glucose-induced human kidney cell damage. EGCG inhibited high glucose(HG)-induced TNF-α and IL-6 production in human embryonic kidney (HEK) cells. Both EGCG and ALA decreased HG-induced receptor of advanced glycation end products (RAGE) mRNA and protein expressions in HEK cells. EGCG and ALA also recovered HG-inhibited superoxide dismutase production and decreased ROS expressions in HEK cells. The synergism of EGCG and ALA was also studied. The effect of EGCG combined with ALA is greater than the effect of EGCG alone in all anti-inflammation and anti-oxidant experiments. Our studies provide a potential therapeutic application of EGCG and ALA in preventing progression of diabetic nephropathy.

RAGE splicing variants in mammals

The receptor for advanced glycation end products (RAGE) is a multiligand receptor of environmental stressors which plays key roles in pathophysiological processes, including immune/inflammatory disorders, Alzheimer's disease, diabetic arteriosclerosis, tumorigenesis, and metastasis. Besides the full-length RAGE protein in humans nearly 20 natural occurring RAGE splicing variants were described on mRNA and protein level. These naturally occurring isoforms are characterized by either N-terminally or C-terminally truncations and are discussed as possible regulators of the full-length RAGE receptor either by competitive ligand binding or by displacing the full-length protein in the membrane. Accordingly, expression deregulations of the naturally occurring isoforms were supposed to have significant effect on RAGE-mediated disorders. Thereby the soluble C-truncated RAGE isoforms present in plasma and tissues are the mostly focused isoforms in research and clinics. Deregulations of the circulating levels of soluble RAGE forms were reported in several RAGE-associated pathological disorders including for example atherosclerosis, diabetes, renal failure, Alzheimer's disease, and several cancer types. Regarding other mammalian species, the canine RAGE gene showed high similarities to the corresponding human structures indicating RAGE to be evolutionary highly conserved between both species. Similar to humans the canine RAGE showed a complex and extensive splicing activity leading to a manifold pattern of RAGE isoforms. Due to the similarities seen in several canine and human diseases-including cancer-comparative structural and functional analyses allow the development of RAGE and ligand-specific therapeutic approaches beneficial for human and veterinary medicine.