Advanced glycation end products in diabetic patients with optimized glycaemic control and their effects on endothelial reactivity: possible implications in venous graft failure

The initiation of oxidative stress and therapeutic strategies in wound healing

When the production of reactive oxygen species (ROS) is overloaded surpassing the capacity of the reductive rheostat, mammalian cells undergo a series of oxidative damage termed oxidative stress (OS). This phenomenon is ubiquitously detected in many human pathological conditions. Wound healing program implicates continuous neovascularization, cell proliferation, and wound remodeling. Increasing evidence indicates that reactive oxygen species (ROS) have profound impacts on the wound healing process through regulating a series of the physiological and pathological program including inflammatory response, cell proliferation, angiogenesis, granulation as well as extracellular matrix formation. In most pathological wound healing processes, excessive ROS exerts a negative role on the wound healing process. Interestingly, the moderate increase of ROS levels is beneficial in killing bacteria at the wound site, which creates a sterile niche for revascularization. In this review, we discussed the physiological rhythms of wound healing and the role of ROS in this progress, aim to explore the potential manipulation of OS as a promising therapeutic avenue.

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

BACKGROUND

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

AIM

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Advanced glycation end products impair the functions of saphenous vein but not thoracic artery smooth muscle cells through RAGE/MAPK signalling pathway in diabetes

Saphenous vein (SV) and internal thoracic artery (ITA) are commonly used bypass conduits. However, graft failure occurs in SV rather than in ITA, especially in diabetes (DM). The mechanism for this difference has not been fully understood. Accumulation of advanced glycation end products (AGEs) and activation of AGEs receptor (RAGE) could accelerate smooth muscle cells (SMC) proliferation in DM, we thus asked whether AGEs-RAGE could mediate the differences between SMC from SV (SMCV ) and from ITA (SMCA ). Twenty-five patients with DM and other 25 patients without DM were enclosed in DM and control group, respectively. AGEs (100 μg/ml) were added to cultured SMCA and SMCV obtained at coronary artery bypass graft (CABG) and proliferative rates were determined. Transcript expression, phosphorylation or protein expression levels of MAP kinase family (ERK, p38 and JNK), matrix metalloproteinases (MMP)-2 and MMP-9 were analysed by real-time PCR, Western-blot or immunofluorescence staining, respectively. Compared with paired SMCA , SMCV showed significantly increased proliferation rate, MAP kinase family phosphorylation, and MMP-2/9 expression in both groups, especially in DM group. The responses of SMCV induced by AGEs were significantly larger in DM than in control group, which could be suppressed by inhibition of RAGE and ERK. However, all the cellular events of SMCV were not found in paired SMCA . This study suggests that AGEs-RAGE could induce the proliferation of SMCV but not SMCA via MAP kinase pathway in DM. It is the intrinsic 'inactive' tendency of SMCA that contributes to the different rates of graft disease between SV and ITA after CABG.

The Receptor for Advanced Glycation End Products (Rage) and Its Ligands in Plasma and Infrainguinal Bypass Vein

OBJECTIVE

The aim was to investigate whether RAGE and its ligands are associated with infrainguinal bypass outcome in patients with and without diabetes.

METHODS

This was a prospective observational cohort. Patients (n = 68) with (n = 38) and without (n = 30) diabetes undergoing infrainguinal vein bypass for peripheral arterial disease were followed for 3 years. Endosecretory RAGE (esRAGE), S100A12, advanced glycation end products, and carboxymethyl-lysine (CML) were determined in plasma using ELISA. The influence of plasma levels on the main outcome (amputation free survival) was evaluated using Cox proportional hazard analysis. Plasma esRAGE, CML, and S100A12 in healthy controls (n = 30) without cardiovascular disease matched for sex and age were compared with patients, using the Mann-Whitney U test. Veins from bypass surgery procedures were stained and S100A12, RAGE, AGE, and CML were determined using immunohistochemistry.

RESULTS

Forty-six patients survived with an intact leg during follow up. Seventeen died (median survival time 702 days, IQR 188-899 day), and six had amputations. High plasma S100A12 was associated with reduced amputation free survival (hazard ratio [HR] 2.99; 95% CI 1.24-7.24) when comparing levels above the 75th percentile with levels below. The increased risk was unchanged adjusting for age, sex, and diabetes. Diabetic patients had higher plasma S100A12 (11.75 ng/mL; 95% CI 8.12-15.38 ng/mL) than non-diabetic patients (5.0141 ng/mL; 95% CI 3.62-6.41 ng/mL), whereas plasma CML, esRAGE, and AGE were similar. Plasma CML and S100A12 were higher in patients than in controls (1.25 μg/mL, 95% CI 1.18-1.32 μg/mL vs. 0.8925 μg/mL, 95% CI 0.82-0.96 μg/mL; and 8.7 μg/mL, 95% CI 6.52-10.95 μg/mL vs. 3.47 μg/mL, 95% CI 2.95-3.99 μg/mL, respectively). The proportion of vein tissue stained for AGE (21%), RAGE (5%), CML (9%) and S100A12 (3%), were similar in patients with and without diabetes.

CONCLUSIONS

Plasma S100A12 and CML are elevated in peripheral arterial disease and markers of RAGE and its ligands are found in vein used for bypass. This indicates a role for S100A12, CML, and RAGE in peripheral arterial disease complications by activation of the RAGE system.

Pharmacologic Approaches Against Advanced Glycation End Products (AGEs) in Diabetic Cardiovascular Disease

CONTEXT

Advanced Glycation End-Products (AGEs) are signaling proteins associated to several vascular and neurological complications in diabetic and non-diabetic patients. AGEs proved to be a marker of negative outcome in both diabetes management and surgical procedures in these patients. The reported role of AGEs prompted the development of pharmacological inhibitors of their effects, giving rise to a number of both preclinical and clinical studies. Clinical trials with anti-AGEs drugs have been gradually developed and this review aimed to summarize most relevant reports.

EVIDENCE ACQUISITION

Evidence acquisition process was performed using PubMed and ClinicalTrials.gov with manually checked articles.

RESULTS

Pharmacological approaches in humans include aminoguanidine, pyridoxamine, benfotiamine, angiotensin converting enzyme inhibitors, angiotensin receptor blockers, statin, ALT-711 (alagebrium) and thiazolidinediones. The most recent promising anti-AGEs agents are statins, alagebrium and thiazolidinediones. The role of AGEs in disease and new compounds interfering with their effects are currently under investigation in preclinical settings and these newer anti-AGEs drugs would undergo clinical evaluation in the next years. Compounds with anti-AGEs activity but still not available for clinical scenarios are ALT-946, OPB-9195, tenilsetam, LR-90, TM2002, sRAGE and PEDF.

CONCLUSIONS

Despite most studies confirm the efficacy of these pharmacological approaches, other reports produced conflicting evidences; in almost any case, these drugs were well tolerated. At present, AGEs measurement has still not taken a precise role in clinical practice, but its relevance as a marker of disease has been widely shown; therefore, it is important for clinicians to understand the value of new cardiovascular risk factors. Findings from the current and future clinical trials may help in determining the role of AGEs and the benefits of anti-AGEs treatment in cardiovascular disease.

PPARγ activation but not PPARγ haplodeficiency affects proangiogenic potential of endothelial cells and bone marrow-derived progenitors

Background

Peroxisome proliferator-activated receptor-γ (PPARγ) agonists, which have been used as insulin sensitizers in diabetic patients, may improve functions of endothelial cells (ECs). We investigated the effect of PPARγ on angiogenic activities of murine ECs and bone marrow-derived proangiogenic cells (PACs).

Methods

PACs were isolated from bone marrow of 10–12 weeks old, wild type, db/db and PPARγ heterozygous animals. Cells were cultured on fibronectin and gelatin coated dishes in EGM-2MV medium. For in vitro stimulations, rosiglitazone (10 μmol/L) or GW9662 (10 μmol/L) were added to 80% confluent cell cultures for 24 hours. Angiogenic potential of PACs and ECs was tested in vitro and in vivo in wound healing assay and hind limb ischemia model.

Results

ECs and PACs isolated from diabetic db/db mice displayed a reduced angiogenic potential in ex vivo and in vitro assays, the effect partially rescued by incubation of cells with rosiglitazone (PPARγ activator). Correction of diabetes by administration of rosiglitazone in vivo did not improve angiogenic potential of isolated PACs or ECs. In a hind limb ischemia model we demonstrated that local injection of conditioned media harvested from wild type PACs improved the blood flow restoration in db/db mice, confirming the importance of paracrine action of the bone marrow-derived cells.

Transcriptome analysis showed an upregulation of prooxidative and proinflammatory pathways, and downregulation of several proangiogenic genes in db/db PACs. Interestingly, db/db PACs had also a decreased level of PPARγ and changed expression of PPARγ-regulated genes. Using normoglycemic PPARγ^+/− mice we demonstrated that reduced expression of PPARγ does not influence neovascularization either in wound healing or in hind limb ischemia models.

Conclusions

In summary, activation of PPARγ by rosiglitazone improves angiogenic potential of diabetic ECs and PACs, but decreased expression of PPARγ in diabetes does not impair angiogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-014-0150-7) contains supplementary material, which is available to authorized users.

Up-regulation of the receptor for advanced glycation end products in the skin biopsy specimens of patients with severe diabetic neuropathy

BACKGROUND AND PURPOSE

The receptor for advanced glycation end products (RAGE) may contribute to the development of diabetic neuropathy. To assess its relevance in humans, this study examined the expression of RAGE in the skin biopsy samples of patients with diabetes mellitus, and investigated its correlation with intraepidermal nerve-fiber density (IENFD) and clinical measures of neuropathy severity.

METHODS

Forty-four patients who either had type 2 diabetes or were prediabetes underwent clinical evaluation and a 3-mm skin punch biopsy. The clinical severity of their neuropathy was assessed using the Michigan Diabetic Neuropathy Score. IENFD was measured along with immunohistochemical staining for RAGE in 29 skin biopsy samples. The expression of RAGE was also quantified by real-time reverse-transcription PCR in the remaining 15 patients.

RESULTS

RAGE was localized mostly in the dermal and subcutaneous vascular endothelia. The staining was more intense in patients with a lower IENFD (p=0.004). The quantity of RAGE mRNA was significantly higher in patients with severe neuropathy than in those with no or mild neuropathy (p=0.003). The up-regulation of RAGE was related to dyslipidemia and diabetic nephropathy. There was a trend toward decreased sural nerve action-potential amplitude and slowed peroneal motor-nerve conduction with increasing RAGE expression.

CONCLUSIONS

The findings of this study demonstrate up-regulation of RAGE in skin biopsy samples from patients with diabetic neuropathy, supporting a pathogenic role of RAGE in the development of diabetic neuropathy.

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.

Bone morphogenic protein-4: a potential novel target for preventing vein graft failure in coronary revascularization

Coronary artery bypass surgery is an effective and durable therapy in both acute coronary syndrome and chronic coronary stenotic disease refractory to pharmacological treatment. Despite rapid development in operation-specific technologies and secondary prevention measures, the benefits of surgical revascularization are largely limited by inadequate patency of one of the most commonly used conduits, namely the autologous saphenous vein. However, apart from antiplatelet and lipid-lowering drugs, no other pharmacologic agent has hitherto proven clinically effective in preventing short- and long-term vein graft failure. Aiming at a large number of known biomolecules, multiple promising strategies failed to translate their beneficial effects observed in animal models into the clinical settings. Bone morphogenic protein-4 (BMP4), originally identified as a mediator in bone formation, has been recently demonstrated to participate in the process of arterial post-injury remodeling. Existing evidence has demonstrated that BMP4 is closely involved in the pathogenesis of thrombus formation, neointimal hyperplasia and superimposed atherosclerosis, all of which significantly contribute to arterial stenotic lesions. Although the post-injury responses inherent to arterial and venous vessel are unique, they share common elements and present with similar physiologic characteristics and clinical sequelae. Therefore, with regard to the multifaceted effects of BMP4 in regulating arterial wall remodeling, we hypothesize that BMP4 may play an important role in mediating the pathological responses of the venous wall to the arterial circulation. If our hypothesis is demonstrated correct, BMP4 inhibition could presumably serve as a novel strategy for preventing vein graft failure in coronary revascularization.

Usefulness of preprocedural levels of advanced glycation end products to predict restenosis in patients with controlled diabetes mellitus undergoing drug-eluting stent implantation for stable angina pectoris (from the Prospective ARMYDA-AGEs Study)

Diabetes mellitus (DM) remains the main predictor of restenosis rates and cardiovascular events following successful percutaneous coronary intervention (PCI) despite the use of drug-eluting stents (DES). HbA1c <6.0% is considered an index of optimized metabolic control in patients with DM, but several studies are downsizing its role in the clinical management of these patients. Increasing evidence points at the role of advanced glycation end products (AGEs) in restenosis pathogenesis independently on Hb1AC levels. Thus, we investigated the predictive value of preprocedural AGE levels for in-stent restenosis in a population of euglycaemic diabetic patients undergoing PCI with DES implantation. One hundred twenty-five consecutive patients with DM in optimized glycemic control admitted for stable angina pectoris and treated with elective DES implantation at a tertiary hospital were prospectively included. The primary end point of the ARMYDA-AGEs study was to compare rates of angiographic ISR at 6 months after the intervention according to pre-PCI levels of AGEs. Secondary end points were the correlations of AGE levels with occurrence of periprocedural myocardial damage, major adverse cardiac events, and in-stent late loss at 6-month control coronary angiography. AGE levels >17 μM was found to be an independent predictor of ISR at 6 months and stent lumen loss. AGEs failed to predict occurrence of secondary endpoints. In conclusion, elevated AGE levels predict occurrence of in-stent restenosis after DES implantation in patients with DM on optimized glycemic control and might represent a dosable marker of adverse outcome after PCI.

Bone morphogenic protein-4 contributes to venous endothelial dysfunction in patients with diabetes undergoing coronary revascularization

BACKGROUND

Hyperglycemia-induced venous endothelial dysfunction accelerates the progression of vein graft failure in patients with diabetes undergoing surgical coronary revascularization. Recent studies suggest the importance of bone morphogenic protein-4 (BMP4)-induced arterial endothelial dysfunction in the development of hypertension and atherosclerosis. The present study investigated the potential role of BMP4 in the pathogenesis of venous endothelial dysfunction in the setting of diabetes.

METHODS

Segments of saphenous vein from pigs and from patients with diabetes or patients without diabetes, as well as human umbilical venous endothelial cells (HUVECs), were used. The changes of BMP4 expression in veins from patients and in HUVECs cultured under hyperglycemic conditions were evaluated by Western blot assay. The effects of BMP4 on the production of reactive oxygen species (ROS) and endothelium-dependent venous relaxation were assessed by using dihydroethidium fluorescence and isometric tension measurements, respectively.

RESULTS

The impaired venous endothelium-dependent relaxations (2.9%±4.8% versus control group 74.1%±10%; p<0.01) accompanied by markedly increased BMP4 expression were observed in the diabetic group. The level of BMP4 expression in HUVECs treated with high levels of glucose were elevated in a glucose concentration-dependent manner. Ex vivo treatment with the BMP4 antagonist noggin significantly improved endothelium-dependent relaxations and inhibited accumulation of ROS in saphenous veins from patients with diabetes. Noggin treatment had no effect on the venous endothelium-dependent relaxations in individuals without diabetes. Meanwhile, BMP4 inhibited acetylcholine-induced relaxation (control group, 90%±7.1% versus BMP4-treated group, 52%±12.6%; p<0.05) and enhanced ROS production in porcine saphenous veins. Such harmful effects were again reversed by noggin.

CONCLUSIONS

The increased BMP4 expression and related ROS overproduction may play an important role in the development of hyperglycemia-induced venous endothelial dysfunction.

RAGE biology, atherosclerosis and diabetes

Diabetes is characterized by accelerated atherosclerosis with widely distributed vascular lesions. An important mechanism by which hyperglycaemia contributes to vascular injury is through the extensive intracellular and extracellular formation of AGEs (advanced glycation end products). AGEs represent a heterogeneous group of proteins, lipids and nucleic acids, irreversibly cross-linked with reducing sugars. AGEs are implicated in the atherosclerotic process, either directly or via receptor-mediated mechanisms, the most extensively studied receptor being RAGE (receptor for AGEs). The AGE-RAGE interaction alters cellular signalling, promotes gene expression and enhances the release of pro-inflammatory molecules. It elicits the generation of oxidative stress in numerous cell types. The importance of the AGE-RAGE interaction and downstream pathways leading to injurious effects as a result of chronic hyperglycaemia in the development, progression and instability of diabetic atherosclerotic lesions has been amply demonstrated in animal studies. Moreover, the deleterious link of AGEs with diabetic vascular complications has been suggested in many human studies. In the present review, our current understanding of their role as an important mediator of vascular injury through the various stages of atherosclerosis in diabetes will be reviewed and critically assessed.