Protein glycation: a firm link to endothelial cell dysfunction

Serum resistance to singlet oxygen in patients with diabetes mellitus in comparison to healthy donors

Diabetes mellitus causes endothelial injury through oxidative stress involving reactive oxygen species and peroxides as well as inflammation, both of which consume antioxidant defenses. Singlet oxygen ((1)O(2)) is produced by leukocytes during inflammatory and biochemical reactions and deactivated by producing reactive oxygen species and peroxides. To determine whether serum was capable of deactivating (1)O(2), we triggered a photo reaction in sera from 53 healthy donors and 52 diabetic patients. Immediately after light delivery, dichlorofluorescein was added and then its fluorescence was recorded. The mean capacity of (1)O(2) or secondary oxidant deactivation was reduced in patients with diabetes mellitus. Hemolysis reduced deactivation of (1)O(2)-induced secondary oxidants in both healthy and diabetic patients. Body mass index, age, platelet counts, and blood cell numbers exerted a nonlinear influence. High levels of glycated hemoglobin were associated with an increased deactivation of oxidative species, whereas high-density lipoprotein cholesterol, total cholesterol, and the total cholesterol to high-density lipoprotein cholesterol ratio decreased the serum deactivation capacity. Oral antidiabetics bore no influence on deactivation, which was restored by insulin in women. Deactivation capacity was lower in women, who had half the complications found in men, suggesting that, with more severe diabetes mellitus, protection was maintained against complications. Resistance to (1)O(2) should be considered during the monitoring of diabetes mellitus.

Associations of receptor for advanced glycation end products -374 T/A and Gly82 Ser and peroxisome proliferator-activated receptor gamma Pro12Ala polymorphisms in Turkish coronary artery disease patients

AIM

The aim of the present study was to investigate the individual and combined effects of receptor for advanced glycation end products (RAGE) -374T/A, RAGE Gly82Ser, and peroxisome proliferator-activated receptor gamma (PPAR-γ) Pro12Ala polymorphisms on the development of coronary artery disease (CAD).

MATERIALS AND METHODS

This study was carried out in 87 patients with CAD and 52 CAD-free healthy controls. Polymerase chain reaction, restriction fragment length polymorphism, and agarose gel electrophoresis techniques were used to determine RAGE -374T/A, RAGE Gly82 Ser, and PPAR-γ Pro12 Ala.

RESULTS

Individual allele and genotype frequencies of RAGE -374T/A, RAGE Gly82Ser, and PPAR-γ Pro12Ala polymorphisms were not significantly different between study groups. However, compared with the control group, wild-type T allele frequency was found to be higher in patients with diabetes (p=0.009). To investigate the combined effects of RAGE and PPAR polymorphisms, haplotype analysis was elevated and there was no statistical difference between the haplotypes of RAGE Gly82Ser with RAGE-374T/A or PPAR Pro12Ala. However, the frequency of RAGE-374T/PPAR12Ala haplotype was found to be higher in both the patient group (p=0.024) and in patients without diabetes (p=0.037).

CONCLUSION

The results of the present study demonstrated that possessing the A allele of RAGE -374T/A polymorphism by diabetic CAD patients and possessing the-374T/Ala12 haplotype of RAGE -374T/A and PPAR-γ Pro12 Ala polymorphisms by the patients group were the most important risk factors for CAD.

Adipose tissue expression of interleukin-18 mRNA is elevated in subjects with metabolic syndrome and independently associated with fasting glucose

BACKGROUND

The metabolic syndrome (MetS) is a cluster of risk factors that are highly associated with increased risk for cardiovascular disease (CVD). Increased serum levels of plasminogen activator inhibitor-1 (PAI-1), interleukin-6 (IL-6) and IL-18 have been reported to be associated with CVD. Recently, IL-18 has been shown to be predictive for cardiovascular events in subjects with MetS. We have investigated the expression of PAI-1, IL-6 and IL-18 in subcutaneous adipose tissue (AT) of subjects with (n = 22) and without (n = 36) MetS. Furthermore, we have analysed the expression of IL-18 in monocyte-derived macrophages (MDMs) in an in vitro model of hyperglycaemia.

METHODS

We studied the expression of PAI-1, IL-6 and IL-18 in biopsies of subcutaneous adipose tissue using Real-time PCR. After isolation and cultivation of MDMs, expression of IL-18 was determined by Real-time PCR.

RESULTS

Expression of IL-18 was increased in subcutaneous AT of subjects with MetS (p < 0.05). Multivariate analysis revealed fasting plasma glucose to be the only MetS component being independently associated with expression of IL-18 in AT (p < 0.05). Exposure to hyperglycaemia, increased in expression of IL-18 in MDMs (p < 0.01).

CONCLUSION

Our findings suggest that subjects with MetS have a particular inflammatory pattern in AT, possibly driven by fasting glucose. MDMs might - at least in part - be the cellular source of this increased expression. Together with recent reports, showing IL-18 to be predictive for cardiovascular events, our findings could provide the basis for further research of the role of IL-18 as a link and possible target in the association between MetS and atherosclerosis.

Primary graft dysfunction

Primary graft dysfunction (PGD) is the most important cause of early morbidity and mortality following lung transplantation. PGD affects up to 25% of all lung transplant procedures and currently has no proven preventive therapy. Lung transplant recipients who recover from PGD may have impaired long-term function and an increased risk of bronchiolitis obliterans syndrome. This article aims to provide a state-of-the-art review of PGD epidemiology, outcomes, and risk factors, and to summarize current efforts at biomarker development and novel strategies for prevention and treatment.

MIR221/MIR222-driven post-transcriptional regulation of P27KIP1 and P57KIP2 is crucial for high-glucose- and AGE-mediated vascular cell damage

AIMS/HYPOTHESIS

MicroRNAs (miRNAs) are a novel group of small non-coding RNAs that regulate gene expression at the post-transcriptional level and act on their target mRNAs in a tissue- and cell-type-specific manner. Herein, the relevance of MIR221/MIR222 in high-glucose- and AGE-mediated vascular damage was investigated.

METHODS

Functional studies were performed using human mature endothelial cells and endothelial progenitor cells subjected to high glucose or AGE. Quantitative real-time amplification was performed to analyse MIR221/MIR222 expression in these experimental conditions. Luciferase assay was used to identify MIR221/MIR222 targets. Functional studies were performed in vitro and in vivo in mice using gain- and loss-of-function approaches.

RESULTS

Using an in vivo mouse model we demonstrated that exposure to AGE and high glucose impaired vessel formation. Moreover, in vitro functional studies revealed that both high glucose and AGE inhibit cell-cycle progression by modulating the expression of P27KIP1 (also known as CDKN1B) and P57KIP2 (also known as CDKN1C), which encode cyclin-dependent kinase inhibitor 1B (p27, Kip1) (P27KIP1) and cyclin-dependent kinase inhibitor 1C (p57, Kip2) (P57KIP2), respectively. Crucial to AGE- and high-glucose-mediated cell-cycle arrest was the downregulation of MIR221/MIR222 expression. Luciferase assay showed that MIR221 and MIR222 specifically bind to the P27KIP1 and P57KIP2 mRNA 3'-untranslated regions, implicating P27KIP1 and P57KIP2 as MIR221/MIR222 targets. These results were confirmed by gain-of-function experiments in vitro, and by injecting mice with endothelial cells overexpressing MIR221 and MIR222.

CONCLUSIONS/INTERPRETATION

We provide evidence that high-glucose- and AGE-induced inhibition of vascular cell proliferation is controlled by MIR221/MIR222-driven post-transcriptional regulation of P27KIP1 and P57KIP2. These data add further insight to the possible contribution of miRNAs in vascular damage mediated by a high-glucose environment.

Spermatogenic and sperm quality differences in an experimental model of metabolic syndrome and hypogonadal hypogonadism

The synergistic effect of the co-morbidities that comprise metabolic syndrome (MetS) is increasingly being recognised as an important contributor in the pathology of a broad spectrum of seemingly disparate conditions. However, in terms of male reproductive function, beyond erectile dysfunction, little is known about the influence of this cohort (collectively or separately) on spermatogenesis and sperm quality. The aims of this study were to assess the reproductive tract of a MetS animal model for detrimental changes, to determine whether a group of compounds (advanced glycation end products and their receptor) known to cause cell dysfunction and DNA damage was present and assess whether hypogonadotropic hypogonadism was the main contributing factor for the changes seen. Animals fed a high-fat diet were found to have significantly increased cholesterol, triglycerides, blood glucose, mean arterial pressure and visceral fat levels. Although serum testosterone was decreased, no changes were seen in either testicular or epididymal histology. Immunolocalisation ofNϵ-carboxymethyl-lysine and the receptor for advanced glycation end products was found in the testes, epididymides and sperm of the two treated groups of animals; however, ELISA did not show any difference in protein levels. Similarly, assessment of sperm nuclear DNA (nDNA) fragmentation by acridine orange test did not find significant differences in nDNA integrity. We conclude that the minimal effect on spermatogenesis and sperm quality seen in our model is probably due to the moderate increase of blood glucose rather than the hypogonadism.

Activation of AMP-activated protein kinase prevents lipotoxicity in retinal pericytes

PURPOSE

The recent FIELD study demonstrated that the lipid-lowering agent fenofibrate significantly reduces the development and progression of diabetic retinopathy (DR). These results suggest that lipids may play a causal role in DR. They also suggest that AMP-activated protein kinase (AMPK) activation could account for these findings given that fenofibrate is an AMPK activator. The authors previously demonstrated that free fatty acids, in addition to hyperglycemia, can induce apoptosis in retinal pericytes (PCs), the first cells lost in the diabetic retina. Incubation with the saturated fatty acid palmitate, but not the monounsaturated fatty acid oleate, elicited cytotoxicity in a manner dependent on oxidative stress, NF-κB activation, and ceramide accumulation. In this study, the authors explored whether AMPK can downregulate these pathways and, in doing so, protect PCs from apoptosis.

METHODS

PCs were incubated with palmitate or oleate to determine whether the factors previously linked to lipotoxicity were uniquely increased by palmitate. The effects of AMPK activation on these parameters and on apoptosis were concurrently examined.

RESULTS

Only palmitate increased NF-κB activation, ceramide and diacylglycerol mass, and apoptosis. Activation of AMPK with AICAR or, where used, expression of a constitutively active AMPK prevented all these effects. In contrast, both palmitate and oleate markedly increased oxidative stress, and the activation of AMPK did not prevent this.

CONCLUSIONS

AMPK activation prevents the metabolic abnormalities and apoptosis specifically caused by palmitate in cultured PCs. Pharmacologic agents that activate AMPK in the diabetic retina may warrant consideration as a therapeutic option to avert PC apoptosis and to maintain microvascular homeostasis.

Decreased cerebrovascular brain-derived neurotrophic factor-mediated neuroprotection in the diabetic brain

OBJECTIVE

Diabetes is an independent risk factor for stroke. However, the underlying mechanism of how diabetes confers that this risk is not fully understood. We hypothesize that secretion of neurotrophic factors by the cerebral endothelium, such as brain-derived neurotrophic factor (BDNF), is suppressed in diabetes. Consequently, such accrued neuroprotective deficits make neurons more vulnerable to injury.

RESEARCH DESIGN AND METHODS

We examined BDNF protein levels in a streptozotocin-induced rat model of diabetes by Western blotting and immunohistochemistry. Levels of total and secreted BDNF protein were quantified in human brain microvascular endothelial cells after exposure to advanced glycation end product (AGE)-BSA by enzyme-linked immunosorbent assay and immunocytochemistry. In media transfer experiments, the neuroprotective efficacy of conditioned media from normal healthy endothelial cells was compared with AGE-treated endothelial cells in an in vitro hypoxic injury model.

RESULTS

Cerebrovascular BDNF protein was reduced in the cortical endothelium in 6-month diabetic rats. Immunohistochemical analysis of 6-week diabetic brain sections showed that the reduction of BDNF occurs early after induction of diabetes. Treatment of brain microvascular endothelial cells with AGE caused a similar reduction in BDNF protein and secretion in an extracellular signal-related kinase-dependent manner. In media transfer experiments, conditioned media from AGE-treated endothelial cells were less neuroprotective against hypoxic injury because of a decrease in secreted BDNF.

CONCLUSIONS

Taken together, our findings suggest that a progressive depletion of microvascular neuroprotection in diabetes elevates the risk of neuronal injury for a variety of central nervous system diseases, including stroke and neurodegeneration.

[The influence of diabetes mellitus on male reproductive function: a poorly investigated aspect of male infertility]

Whilst diabetes mellitus is known to have many systemic complications, male infertility, beyond impotence, retrograde ejaculation and hypogonadism, has not been widely recognised to be one of them. Due to the paucity of studies and inconsistencies regarding the condition's impact on semen quality, few fertility specialists consider the condition noteworthy. As a consequence little information exists as to its prevalence amongst infertile men. Recently the prevailing view has been challenged by findings showing that diabetes induces subtle molecular changes that are important for sperm quality and function. Diabetic men have been found to have a significantly higher percentage of sperm with nuclear DNA damage, a factor known to be associated with compromised fertility and increased miscarriage rates. The mechanism by which this diabetes-related sperm nDNA damage occurs remains unknown. The identification of high levels of advanced glycation end products (AGEs) and their receptor (RAGE) throughout the male reproductive tract coupled to changes in testicular metabolite levels and spermatogenic gene expression suggest that glycation may play an integral role in oxidative stress which in turn causes sperm nDNA damage. As glycation is a normal consequence of life and has been implicated in DNA fragmentation in a variety of seemingly unconnected conditions, it may constitute a common mechanism for the damage seen in sperm DNA.

Glycated collagen alters endothelial cell actin alignment and nitric oxide release in response to fluid shear stress

People with diabetes suffer from early accelerated atherosclerosis, which contributes to morbidity and mortality from myocardial infarction, stroke, and peripheral vascular disease. Atherosclerosis is thought to initiate at sites of endothelial cell injury. Hyperglycemia, a hallmark of diabetes, leads to non-enzymatic glycosylation (or glycation) of extracellular matrix proteins. Glycated collagen alters endothelial cell function and could be an important factor in atherosclerotic plaque development. This study examined the effect of collagen glycation on endothelial cell response to fluid shear stress. Porcine aortic endothelial cells were grown on native or glycated collagen and exposed to shear stress using an in vitro parallel plate system. Cells on native collagen elongated and aligned in the flow direction after 24 h of 20 dynes/cm(2) shear stress, as indicated by a 13% decrease in actin fiber angle distribution standard deviation. However, cells on glycated collagen did not align. Shear stress-mediated nitric oxide release by cells on glycated collagen was half that of cells on native collagen, which correlated with decreased endothelial nitric oxide synthase (eNOS) phosphorylation. Glycated collagen likely inhibited cell shear stress response through altered cell-matrix interactions, since glycated collagen attenuated focal adhesion kinase activation with shear stress. When focal adhesion kinase was pharmacologically blocked in cells on native collagen, eNOS phosphorylation with flow was reduced in a manner similar to that of glycated collagen. These detrimental effects of glycated collagen on endothelial cell response to shear stress may be an important contributor to accelerated atherosclerosis in people with diabetes.

MIR221/MIR222-driven post-transcriptional regulation of P27KIP1 and P57KIP2 is crucial for high-glucose- and AGE-mediated vascular cell damage

AIMS/HYPOTHESIS

MicroRNAs (miRNAs) are a novel group of small non-coding RNAs that regulate gene expression at the post-transcriptional level and act on their target mRNAs in a tissue- and cell-type-specific manner. Herein, the relevance of MIR221/MIR222 in high-glucose- and AGE-mediated vascular damage was investigated.

METHODS

Functional studies were performed using human mature endothelial cells and endothelial progenitor cells subjected to high glucose or AGE. Quantitative real-time amplification was performed to analyse MIR221/MIR222 expression in these experimental conditions. Luciferase assay was used to identify MIR221/MIR222 targets. Functional studies were performed in vitro and in vivo in mice using gain- and loss-of-function approaches.

RESULTS

Using an in vivo mouse model we demonstrated that exposure to AGE and high glucose impaired vessel formation. Moreover, in vitro functional studies revealed that both high glucose and AGE inhibit cell-cycle progression by modulating the expression of P27KIP1 (also known as CDKN1B) and P57KIP2 (also known as CDKN1C), which encode cyclin-dependent kinase inhibitor 1B (p27, Kip1) (P27KIP1) and cyclin-dependent kinase inhibitor 1C (p57, Kip2) (P57KIP2), respectively. Crucial to AGE- and high-glucose-mediated cell-cycle arrest was the downregulation of MIR221/MIR222 expression. Luciferase assay showed that MIR221 and MIR222 specifically bind to the P27KIP1 and P57KIP2 mRNA 3'-untranslated regions, implicating P27KIP1 and P57KIP2 as MIR221/MIR222 targets. These results were confirmed by gain-of-function experiments in vitro, and by injecting mice with endothelial cells overexpressing MIR221 and MIR222.

CONCLUSIONS/INTERPRETATION

We provide evidence that high-glucose- and AGE-induced inhibition of vascular cell proliferation is controlled by MIR221/MIR222-driven post-transcriptional regulation of P27KIP1 and P57KIP2. These data add further insight to the possible contribution of miRNAs in vascular damage mediated by a high-glucose environment.

Ribose sugars generate internal glycation cross-links in horse heart myoglobin

Glycation of horse heart metmyoglobin with d-ribose 5-phosphate (R5P), d-2-deoxyribose 5-phosphate (dR5P), and d-ribose with inorganic phosphate at 37°C generates an altered protein (Myo-X) with increased SDS-PAGE mobility. The novel protein product has been observed only for reactions with the protein myoglobin and it is not evident with other common sugars reacted over a 1 week period. Myo-X is first observed at 1-2 days at 37°C along with a second form that is consistent in mass with that of myoglobin attached to several sugars. MALDI mass spectrometry and other techniques show no evidence of the cleavage of a peptide from the myoglobin chain. Apomyoglobin in reaction with R5P also exhibited this protein form suggesting its occurrence was not heme-related. While significant amounts of O(2)(-) and H(2)O(2) are generated during the R5P glycation reaction, they do not appear to play roles in the formation of the new form. The modification is likely due to an internal cross-link formed during a glycation reaction involving the N-terminus and an internal amine group; most likely the neighboring Lys133. The study shows the unique nature of these common pentose sugars in spontaneous glycation reactions with proteins.

Vasculopathy in type 2 diabetes mellitus: role of specific angiogenic modulators

Type 2 diabetes mellitus (T2DM) is largely defined by hyperglycemia that promotes vascular complications. Abnormal angiogenesis has been claimed to have a role in this disease. This study aimed to investigate serum levels of both conventional and other markers of angiogenesis not well studied before in diabetes, and to correlate findings with age of the patients, glycemic control, presence of microvascular complications, and oxidative stress. Thirty-eight patients with T2DM and 13 age- and sex-matched healthy persons representing controls were recruited. Serum levels of basic fibroblast growth factor (b-FGF) was measured by immunosorbent assay kit; advanced glycosylation end products, platelet-derived endothelial cell growth factor (PD-ECGF), cathepsin-D (CD), gangliosides, hyaluronic acid (HA), nitric oxide (NO), lipid peroxides (LPER), superoxide dismutase, and total thiols by chemical methods; and copper (Cu) by atomic absorption flame photometry. Advanced glycosylation end products and angiogenic factors (b-FGF, PD-ECGF, CD, gangliosides, HA, and Cu) were significantly higher in patients than controls. Oxidative stress markers, NO, and LPER were significantly higher while total thiols were significantly lower in patients than controls. These changes were more pronounced with age, poor glycemic control, and presence of microvascular complications. Angiogenesis dysfunction coinciding with elevated levels of many angiogenic growth factors may point to their malfunctioning due to oxidative stress and/or protein glycation at the factor and the receptor levels. This necessitates further investigations.

Higher plasma levels of advanced glycation end products are associated with incident cardiovascular disease and all-cause mortality in type 1 diabetes: a 12-year follow-up study

OBJECTIVE

To investigate the associations of plasma levels of advanced glycation end products (AGEs) with incident cardiovascular disease (CVD) and all-cause mortality in type 1 diabetes and the extent to which any such associations could be explained by endothelial and renal dysfunction, low-grade inflammation, and arterial stiffness.

RESEARCH DESIGN AND METHODS

We prospectively followed 169 individuals with diabetic nephropathy and 170 individuals with persistent normoalbuminuria who were free of CVD at study entry and in whom levels of N(ε)-(carboxymethyl)lysine, N(ε)-(carboxyethyl)lysine, pentosidine and other biomarkers were measured at baseline. The median follow-up duration was 12.3 (interquartile range 7.6-12.5) years.

RESULTS

During the course of follow-up, 82 individuals (24.2%) died; 85 (25.1%) suffered a fatal (n = 48) and/or nonfatal (n = 53) CVD event. The incidence of fatal and nonfatal CVD and of all-cause mortality increased with higher baseline levels of AGEs independently of traditional CVD risk factors: hazard ratio (HR) = 1.30 (95% CI = 1.03-1.66) and HR = 1.27 (1.00-1.62), respectively. These associations were not attenuated after further adjustments for markers of renal or endothelial dysfunction, low-grade inflammation, or arterial stiffness.

CONCLUSIONS

Higher levels of AGEs are associated with incident fatal and nonfatal CVD as well as all-cause mortality in individuals with type 1 diabetes, independently of other risk factors and of several potential AGEs-related pathophysiological mechanisms. Thus, AGEs may explain, in part, the increased cardiovascular disease and mortality attributable to type 1 diabetes and constitute a specific target for treatment in these patients.

Platelet function in patients with diabetes mellitus: from a theoretical to a practical perspective

Patients with diabetes mellitus have an increased prevalence of vascular disease. Pathologic thrombosis associated with atherosclerotic plaque rupture is a major cause of morbidity and mortality. Platelets are intimately involved in the initiation and propagation of thrombosis. Evidence suggests that platelets from patients with type 2 diabetes have increased reactivity and baseline activation compared to healthy controls. We review the pathophysiology of platelet hyperreactivity in DM patients and its implications in clinical practice, with particular focus on acute coronary syndromes, percutaneous coronary intervention, and novel antiplatelet agents.

Structural modifications in the arterial wall during physiological aging and as a result of diabetes mellitus in a mouse model: are the changes comparable?

AIM

Vascular accelerated aging represents the major cause of morbidity and mortality in subjects with diabetes mellitus. In the present study, our aim was to compare premature functional and morphological changes in the arterial wall resulting from streptozotocin (STZ)-induced diabetes mellitus in mice over a short-term period with those that develop during physiological aging. The effect of aminoguanidine (AG) on the prevention of these alterations in the diabetic group was also analyzed.

METHODS

The vascular relaxation response to acetylcholine (ACh) in the mouse was tested in isolated segments of phenylephrine (Phe)-precontracted aorta at 2, 4 and 8 weeks (wk) of STZ-induced diabetes and compare to 12- and 84-wk-old mice. Aortic structural changes were investigated, and receptor for AGE (RAGE) aortic expression was quantified by western blot.

RESULTS

Compared to the 12-wk control group (76 ± 5%), significant endothelium-dependant relaxation (EDR) impairment was found in the group of 12-wk-old mice, which underwent a 4-wk diabetes-inducing STZ treatment (12wk-4WD) (52 ± 4%; P < 0.01) and was yet more apparent in the group of 16-wk-old mice, which underwent an 8-wk diabetes-inducing STZ treatment (16wk-8WD) (34 ± 4%; P < 0.001). The alteration in EDR was relatively comparable between the diabetic 12wk-4WD group and the 84-wk-old group (52.7 ± 4 vs. 48 ± 4%). Intima/media aortic thickening and aortic structural changes were significantly increased in the diabetic 12wk-4WD group and were even more apparent in the 84-wk group compared to the 12-wk controls. AG treatment in the 12wk-4WD+AG diabetic group significantly improved EDR, decreased RAGE expression and showed an aging preventive effect on the structural changes of the arterial wall.

CONCLUSION

Our study compared EDR linked to physiological aging with that observed in the case of STZ-induced diabetes over a short-term period, and demonstrated the beneficial effect of AG.

Oxidative stress and diabetic complications

Oxidative stress plays a pivotal role in the development of diabetes complications, both microvascular and cardiovascular. The metabolic abnormalities of diabetes cause mitochondrial superoxide overproduction in endothelial cells of both large and small vessels, as well as in the myocardium. This increased superoxide production causes the activation of 5 major pathways involved in the pathogenesis of complications: polyol pathway flux, increased formation of AGEs (advanced glycation end products), increased expression of the receptor for AGEs and its activating ligands, activation of protein kinase C isoforms, and overactivity of the hexosamine pathway. It also directly inactivates 2 critical antiatherosclerotic enzymes, endothelial nitric oxide synthase and prostacyclin synthase. Through these pathways, increased intracellular reactive oxygen species (ROS) cause defective angiogenesis in response to ischemia, activate a number of proinflammatory pathways, and cause long-lasting epigenetic changes that drive persistent expression of proinflammatory genes after glycemia is normalized ("hyperglycemic memory"). Atherosclerosis and cardiomyopathy in type 2 diabetes are caused in part by pathway-selective insulin resistance, which increases mitochondrial ROS production from free fatty acids and by inactivation of antiatherosclerosis enzymes by ROS. Overexpression of superoxide dismutase in transgenic diabetic mice prevents diabetic retinopathy, nephropathy, and cardiomyopathy. The aim of this review is to highlight advances in understanding the role of metabolite-generated ROS in the development of diabetic complications.

Specific binding of red blood cells to endothelial cells is regulated by nonadsorbing macromolecules

Abnormal adhesion of red blood cells to the endothelium has been linked to the pathophysiology of several diseases associated with vascular disorders. Various biochemical changes, including phosphatidylserine exposure on the outer membrane of red blood cells as well as plasma protein levels, have been identified as being likely to play a key role, but the detailed interplay between plasma factors and cellular factors remains unknown. It has been proposed that the adhesion-promoting effect of plasma proteins originates from ligand interaction, but evidence substantiating this assumption is often missing. In this work, we identified an alternative pathway by demonstrating that nonadsorbing macromolecules can also have a marked impact on the adhesion efficiency of red blood cells with enhanced phosphatidylserine exposure to endothelial cells. It is concluded that this adhesion-promoting effect originates from macromolecular depletion interaction and thereby presents an alternative mechanism by which plasma proteins could regulate cell-cell interactions. These findings should thus be of potential value for a detailed understanding of the pathophysiology of diseases associated with vascular complications and might be applicable to a wide range of cell-cell interactions in plasma or plasma-like media.

Blockade of endothelial-mesenchymal transition by a Smad3 inhibitor delays the early development of streptozotocin-induced diabetic nephropathy

OBJECTIVE

A multicenter, controlled trial showed that early blockade of the renin-angiotensin system in patients with type 1 diabetes and normoalbuminuria did not retard the progression of nephropathy, suggesting that other mechanism(s) are involved in the pathogenesis of early diabetic nephropathy (diabetic nephropathy). We have previously demonstrated that endothelial-mesenchymal-transition (EndoMT) contributes to the early development of renal interstitial fibrosis independently of microalbuminuria in mice with streptozotocin (STZ)-induced diabetes. In the present study, we hypothesized that blocking EndoMT reduces the early development of diabetic nephropathy.

RESEARCH DESIGN AND METHODS

EndoMT was induced in a mouse pancreatic microvascular endothelial cell line (MMEC) in the presence of advanced glycation end products (AGEs) and in the endothelial lineage-traceble mouse line Tie2-Cre;Loxp-EGFP by administration of AGEs, with nonglycated mouse albumin serving as a control. Phosphorylated Smad3 was detected by immunoprecipitation/Western blotting and confocal microscopy. Blocking studies using receptor for AGE siRNA and a specific inhibitor of Smad3 (SIS3) were performed in MMECs and in STZ-induced diabetic nephropathy in Tie2-Cre;Loxp-EGFP mice.

RESULTS

Confocal microscopy and real-time PCR demonstrated that AGEs induced EndoMT in MMECs and in Tie2-Cre;Loxp-EGFP mice. Immunoprecipitation/Western blotting showed that Smad3 was activated by AGEs but was inhibited by SIS3 in MMECs and in STZ-induced diabetic nephropathy. Confocal microscopy and real-time PCR further demonstrated that SIS3 abrogated EndoMT, reduced renal fibrosis, and retarded progression of nephropathy.

CONCLUSIONS

EndoMT is a novel pathway leading to early development of diabetic nephropathy. Blockade of EndoMT by SIS3 may provide a new strategy to retard the progression of diabetic nephropathy and other diabetes complications.

Dietary hyperglycemia, glycemic index and metabolic retinal diseases

The glycemic index (GI) indicates how fast blood glucose is raised after consuming a carbohydrate-containing food. Human metabolic studies indicate that GI is related to patho-physiological responses after meals. Compared with a low-GI meal, a high-GI meal is characterized with hyperglycemia during the early postprandial stage (0-2h) and a compensatory hyperlipidemia associated with counter-regulatory hormone responses during late postprandial stage (4-6h). Over the past three decades, several human health disorders have been related to GI. The strongest relationship suggests that consuming low-GI foods prevents diabetic complications. Diabetic retinopathy (DR) is a complication of diabetes. In this aspect, GI appears to be useful as a practical guideline to help diabetic people choose foods. Abundant epidemiological evidence also indicates positive associations between GI and risk for type 2 diabetes, cardiovascular disease, and more recently, age-related macular degeneration (AMD) in people without diabetes. Although data from randomized controlled intervention trials are scanty, these observations are strongly supported by evolving molecular mechanisms which explain the pathogenesis of hyperglycemia. This wide range of evidence implies that dietary hyperglycemia is etiologically related to human aging and diseases, including DR and AMD. In this context, these diseases can be considered as metabolic retinal diseases. Molecular theories that explain hyperglycemic pathogenesis involve a mitochondria-associated pathway and four glycolysis-associated pathways, including advanced glycation end products formation, protein kinase C activation, polyol pathway, and hexosamine pathway. While the four glycolysis-associated pathways appear to be universal for both normoxic and hypoxic conditions, the mitochondria-associated mechanism appears to be most relevant to the hyperglycemic, normoxic pathogenesis. For diseases that affect tissues with highly active metabolism and that frequently face challenge from low oxygen tension, such as retina in which metabolism is determined by both glucose and oxygen homeostases, these theories appear to be insufficient. Several lines of evidence indicate that the retina is particularly vulnerable when hypoxia coincides with hyperglycemia. We propose a novel hyperglycemic, hypoxia-inducible factor (HIF) pathway, to complement the current theories regarding hyperglycemic pathogenesis. HIF is a transcription complex that responds to decrease oxygen in the cellular environment. In addition to playing a significant role in the regulation of glucose metabolism, under hyperglycemia HIF has been shown to increase the expression of HIF-inducible genes, such as vascular endothelial growth factor (VEGF) leading to angiogenesis. To this extent, we suggest that HIF can also be described as a hyperglycemia-inducible factor. In summary, while management of dietary GI appears to be an effective intervention for the prevention of metabolic diseases, specifically AMD and DR, more interventional data is needed to evaluate the efficacy of GI management. There is an urgent need to develop reliable biomarkers of exposure, surrogate endpoints, as well as susceptibility for GI. These insights would also be helpful in deciphering the detailed hyperglycemia-related biochemical mechanisms for the development of new therapeutic agents.

Proteomic identification of carbonylated proteins and their oxidation sites

Excessive oxidative stress leaves a protein carbonylation fingerprint in biological systems. Carbonylation is an irreversible post-translational modification (PTM) that often leads to the loss of protein function and can be a component of multiple diseases. Protein carbonyl groups can be generated directly (by amino acids oxidation and the alpha-amidation pathway) or indirectly by forming adducts with lipid peroxidation products or glycation and advanced glycation end-products. Studies of oxidative stress are complicated by the low concentration of oxidation products and a wide array of routes by which proteins are carbonylated. The development of new selection and enrichment techniques coupled with advances in mass spectrometry are allowing the identification of hundreds of new carbonylated protein products from a broad range of proteins located at many sites in biological systems. The focus of this review is on the use of proteomics tools and methods to identify oxidized proteins along with specific sites of oxidative damage and the consequences of protein oxidation.

Arterial stiffness, lipoprotein particle size, and lipoprotein particle concentration in children with type 1 diabetes

OBJECTIVE

To determine if lipoprotein particle abnormalities correlate with arterial stiffness in children with type 1 diabetes (T1D).

STUDY DESIGN

In this case-control study, we evaluated 70 children, 35 with T1D and 35 controls, ages 10-18 years, matched for age, sex, race, and BMI. Arterial stiffness was assessed by radial tonometry (AI75) and blood was collected for lipoprotein subclass analysis.

RESULTS

T1D subjects had increased AI75, decreased small LDL particle concentration (P = 0.0067), increased large LDL particle concentration (P = 0.007), increased large HDL particle concentration (P = 0.0012), increased mean LDL particle size (P = 0.0028), and increased mean HDL particle size (P < 0.0001) compared to controls. No significant correlations were found between lipoprotein subclasses and arterial stiffness in T1D subjects.

CONCLUSIONS

T1D subjects have increased arterial stiffness when compared to controls, despite a less pro-atherogenic lipoprotein profile, indicating the need to identify other risk factors that correlate with arterial stiffness in T1D youth.

Evaluation of nonenzymatic posttranslational modification-derived products as biomarkers of molecular aging of proteins

BACKGROUND

During their biological life, proteins are exposed in a cumulative fashion to irreversible nonenzymatic, late posttranslational modifications that are responsible for their molecular aging. It is now well established that these damaged proteins constitute a molecular substratum for many dysfunctions described in metabolic and age-related diseases, such as diabetes mellitus, renal insufficiency, atherosclerosis, or neurodegenerative diseases. Accordingly, the specific end products derived from these reactions are considered potentially useful biomarkers for these diseases.

CONTENT

The aim of this review is to give an overview of nonenzymatic posttranslational modifications of proteins and their influence in vivo, take inventory of the analytical methods available for the measurement of posttranslational modification-derived products, and assess the potential contribution of new technologies for their clinical use as biological markers of protein molecular aging.

SUMMARY

Despite their clinical relevance, biomarkers of posttranslational modifications of proteins have been studied only in the context of experimental clinical research, owing to the analytical complexity of their measurement. The recent implementation in clinical chemistry laboratories of mass spectrometry-based methods that provide higher specificity and sensitivity has facilitated the measurement of these compounds. These markers are not used currently by clinicians in routine practice, however, and many challenges, such as standardization, have to be confronted before these markers can be used as efficient tools in the detection and monitoring of long-term complications of metabolic and age-related diseases.

Combined immunoelectron microscopic and computer-assisted image analyses to detect advanced glycation end-products in human myocardium

Advanced glycation end-products (AGEs) result from oxidation-reduction reactions that ensue when a sugar becomes adducted to a protein. AGEs cause various complications of diabetes mellitus (DM). Experimental and clinical evidence suggest that AGEs also contribute to the complications of hypertension (HTN). Little is known about the abundance and localization of AGEs in human myocardium. In a few light microscopic studies, the AGE carboxymethyl lysine (CML) has been immunolabeled and localized virtually exclusively to the walls of small arteries. To more precisely delineate the abundance and localization of CML, we developed an immunoelectron microscopic (IEM) detection method using anti-CML monoclonal antibody 6D12 in conjunction with computer-assisted image analysis. Antibody was pre-absorbed with purified AGE-bovine serum albumin to assure specificity. Antigen-antibody (ag-ab) complexes were individually identified with protein A-conjugated colloidal gold and counted with an automated system. We applied this method in 21 patients (pts) undergoing epicardial biopsy during coronary bypass grafting (CBG) [20 M, 1 F; mean age 65 +/- 7.4 (+/- SEM) years]. Seven pts had neither DM nor HTN, seven had HTN, and seven had DM + HTN. In contrast to the prior light microscopic studies, we detected CML scattered throughout the cardiomyocyte in all pts, but in widely varying amounts. Ag-ab complexes were abundant in sections through myofilaments (mean count 23.6 +/- 9.2 per microm(2), range 9.4-48) and even more so in mitochondria (mean count 34.4 +/- 11.9 per microm(2), range 14.1-68.2, P < 0.001 vs. myofilaments). CML was also detected in vascular endothelial cells. There were no statistically significant differences based on presence or absence of HTN or DM. In conclusion, our IEM method is the first to provide detailed delineation of the localization and abundance of CML in myocardium. CML is very prevalent in CBG pts, suggesting that AGEs could play a role in abnormal cardiomyocyte function, including altered energy metabolism.

The effects of rosiglitazone and high glucose on protein expression in endothelial cells

Rosiglitazone is a thiazolidinedione used to treat insulin resistance in diabetes. Although thiazolidinediones may also exert cardiovascular effects, contrasting results were reported. Favorable effects were shown for pioglitazone, whereas adverse reactions were suspected for rosiglitazone. Therefore, a reassessment of the molecular effects of rosiglitazone on vascular cells is required. We tested the effects of rosiglitazone on the proteome of human endothelial cells grown under either normal or high glucose levels. Protein profiles were analyzed in both membrane and cytosolic fractions. About 150 cytosolic proteins, and approximately 100 membrane proteins, were detected. Two-thirds of the proteins significantly altered by high glucose were also modulated by rosiglitazone in an antagonistic way. Half of these proteins are involved in apoptosis. Using an independent assay of apoptosis based on nucleosome quantification, an approximately 20% stimulation by high versus normal glucose was shown (p < 0.05). Conversely, rosiglitazone reduced apoptosis by approximately 30-50% in cells exposed to either glucose conditions (p < 0.001). In addition, rosiglitazone differently modulated cytoskeleton and energy metabolism-related proteins. Our data show novel, potential sites of action of rosiglitazone through protein expression of endothelial cells. These mechanisms may foster new investigations on the overall vascular effects of this compound, and help to discriminate between desired and adverse effects.

The multifaceted therapeutic potential of benfotiamine

Thiamine, known as vitamin B(1), plays an essential role in energy metabolism. Benfotiamine (S-benzoylthiamine O-monophoshate) is a synthetic S-acyl derivative of thiamine. Once absorbed, benfotiamine is dephosphorylated by ecto-alkaline phosphatase to lipid-soluble S-benzoylthiamine. Transketolase is an enzyme that directs the precursors of advanced glycation end products (AGEs) to pentose phosphate pathway. Benfotiamine administration increases the levels of intracellular thiamine diphosphate, a cofactor necessary for the activation transketolase, resulting in the reduction of tissue level of AGEs. The elevated level of AGEs has been implicated in the induction and progression of diabetes-associated complications. Chronic hyperglycemia accelerates the reaction between glucose and proteins leading to the formation of AGEs, which form irreversible cross-links with many macromolecules such as collagen. In diabetes, AGEs accumulate in tissues at an accelerated rate. Experimental studies have elucidated that binding of AGEs to their specific receptors (RAGE) activates mainly monocytes and endothelial cells and consequently induces various inflammatory events. Moreover, AGEs exaggerate the status of oxidative stress in diabetes that may additionally contribute to functional changes in vascular tone control observed in diabetes. The anti-AGE property of benfotiamine certainly makes it effective for the treatment of diabetic neuropathy, nephropathy and retinopathy. Interestingly, few recent studies demonstrated additional non-AGE-dependent pharmacological actions of benfotiamine. The present review critically analyzed the multifaceted therapeutic potential of benfotiamine.

Diabetes-associated changes and role of N epsilon-(carboxymethyl)lysine in big ET-1-induced coronary vasoconstriction

Using perfused hearts from streptozotocin-induced long-term diabetic rats, we studied the coronary vasoconstrictor effect of the endothelin-1 (ET-1) precursor big ET-1 and also whether this response was modulated by N(epsilon)-(carboxymethyl)lysine (CML; a representative advanced glycation end product that is implicated in the pathogenesis of diabetic vasculopathy). The big ET-1-induced vasoconstriction (a) developed more rapidly (i.e., was greater in the first 30 min) in the diabetic group than in the age-matched controls, and (b) in each group was largely suppressed by phosphoramidon [nonselective endothelin-converting enzyme (ECE)/neutral endopeptidase (NEP) inhibitor] or CGS35066 (selective ECE inhibitor), but not by thiorphan (selective NEP inhibitor). The ET-1 release occurring after treatment with big ET-1, which was greater in diabetic coronary arteries than in the controls, was reduced by CGS35066. The dose-response curve for ET-1 was shifted to the left in the diabetics, so that at some lower doses of ET-1 the vasoconstriction was greater than in the controls. CML enhanced big ET-1- or ET-1-induced vasoconstriction in the controls, but not in the diabetics. Finally, the plasma level of CML was higher in diabetic than in control rats. These findings suggest (a) that the increased responsiveness to big ET-1 shown by diabetic coronary arteries may be attributable both to a more rapid conversion of big ET-1 to ET-1 (by ECE), allowing it to exert its contractile activity, and to an increased vascular sensitivity to ET-1, and (b) that CML may be at least partly responsible for the diabetes-associated enhancement of big ET-1-mediated coronary vasoconstriction.

Short- and long-term modulation of microvascular responses in streptozotocin-induced diabetic rats by glycosylated products

OBJECTIVE

This study aimed to determine the role of early and late glycation products in modulating inflammation in early diabetes.

MATERIALS

Sprague-Dawley rats (130-170 g) were injected with streptozotocin (75 mg/kg, ip) and treated with daily aminoguanidine (AG, 25 mg/kg, ip) or vehicle for 2 or 4 weeks.

METHODS

The base of a vacuum-induced blister raised on the hind paw was perfused with substance P (SP, 1 microM) and sodium nitroprusside (SNP, 100 microM). Changes in blood flow and plasma extravasation (PE) were measured. Amadori (1 mg/ml), advanced glycation end products (AGEs, 10 mg/ml), and anti-RAGE IgG (antibody against AGE receptors, 100 microg/ml) were individually perfused prior to SP.

RESULTS

In diabetic rats, responses to SNP and SP were reduced by 60% and 70%, respectively (P<.05). Amadori increased responses to SNP by 50% and 90% and to SP by 70% and 80% in control and diabetic rats, respectively (both P<.05). SP responses were significantly increased after anti-RAGE IgG (70%) or AG treatments (175%) with PE responses normalized.

CONCLUSION

Amadori and anti-AGE agents enhance peripheral vascular responses in diabetes and may ameliorate microvascular damage.

Hyperglycemia and glycation in diabetic complications

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

Reductive metabolism of AGE precursors: a metabolic route for preventing AGE accumulation in cardiovascular tissue

OBJECTIVE

To examine the role of aldo-keto reductases (AKRs) in the cardiovascular metabolism of the precursors of advanced glycation end products (AGEs).

RESEARCH DESIGN AND METHODS

Steady-state kinetic parameters of AKRs with AGE precursors were determined using recombinant proteins expressed in bacteria. Metabolism of methylglyoxal and AGE accumulation were studied in human umbilical vein endothelial cells (HUVECs) and C57 wild-type, akr1b3 (aldose reductase)-null, cardiospecific-akr1b4 (rat aldose reductase), and akr1b8 (FR-1)-transgenic mice. AGE accumulation and atherosclerotic lesions were studied 12 weeks after streptozotocin treatment of C57, akr1b3-null, and apoE- and akr1b3-apoE-null mice.

RESULTS

Higher levels of AGEs were generated in the cytosol than at the external surface of HUVECs cultured in high glucose, indicating that intracellular metabolism may be an important regulator of AGE accumulation and toxicity. In vitro, AKR 1A and 1B catalyzed the reduction of AGE precursors, whereas AKR1C, AKR6, and AKR7 were relatively ineffective. Highest catalytic efficiency was observed with AKR1B1. Acetol formation in methylglyoxal-treated HUVECs was prevented by the aldose reductase inhibitor sorbinil. Acetol was generated in hearts perfused with methylglyoxal, and its formation was increased in akr1b4- or akr1b8-transgenic mice. Reduction of AGE precursors was diminished in hearts from akr1b3-null mice. Diabetic akr1b3-null mice accumulated more AGEs in the plasma and the heart than wild-type mice, and deletion of akr1b3 increased AGE accumulation and atherosclerotic lesion formation in apoE-null mice.

CONCLUSIONS

Aldose reductase-catalyzed reduction is an important pathway in the endothelial and cardiac metabolism of AGE precursors, and it prevents AGE accumulation and atherosclerotic lesion formation.

Continuous, non-invasive measurement of the haemodynamic response to submaximal exercise in patients with diabetes mellitus: evidence of impaired cardiac reserve and peripheral vascular response

BACKGROUND

Reduced exercise capacity in diabetics has been attributed to limitations in cardiac function and microvascular dysfunction leading to impaired oxygen supply and nutritive perfusion to exercising muscles.

OBJECTIVE

To study changes in cardiac function and microvascular utilisation during exercise in diabetic individuals compared to age-matched controls.

METHODS

Diabetics with glycosylated haemoglobin (HbA(1c)) < 8 (n = 31), diabetics with HbA(1c) > or = 8 (n = 38) and age-matched non-diabetic controls (n = 32) performed exercise at 50 W for 10 minutes followed by recovery, with continuous monitoring of cardiac function by impedance cardiography and regional flow and oxygen saturation by laser Doppler and white light spectroscopy.

RESULTS

In the diabetics, cardiac reserve during exercise and cardiac overshoot during recovery are significantly reduced because of reduction in capacity to increase stroke volume. Regional flow to the exercising muscle is reduced and there is also disproportionately greater desaturation of the regional flow. Abnormalities in cardiac function and regional perfusion are related to the severity of diabetes.

CONCLUSION

Cardiac response to exercise is attenuated significantly in diabetic individuals. Simultaneously, there is impairment in the regional distribution. These changes could be the harbinger of reduced exercise capacity in diabetics.

Irreversibly glycated LDL induce oxidative and inflammatory state in human endothelial cells; added effect of high glucose

In diabetes, hyperglycemia and the associated formation of advanced glycation end-products (AGE) and AGE-modified low density lipoproteins (AGE-LDL) can directly affect the cells of the vascular wall. We hypothesize that AGE-LDL may act directly and induce oxidant and inflammatory alterations in human endothelial cells (HEC), this effect being amplified by high glucose. To test this assumption, the activity of NADPH oxidase (NADPHox) was evaluated and the expression of its subunits (p22(phox), NOX4, and p67(phox)), of the AGE receptor (RAGE), and of the monocyte chemoattractant protein-1 (MCP-1) were assessed by real-time PCR and Western blot in confluent EA.hy926 cells incubated with AGE-LDL for 24 and 48h, in normal and high glucose conditions. Exposure of HEC for 48h to AGE-LDL in 5mM glucose induced an increase of RAGE expression (50%), NADPHox activity (107%), p22(phox) and NOX4 mRNA (50% and 188%, respectively) and MCP-1 expression (80%). AGE-LDL-stimulated p22(phox) expression by activating p38 MAP kinase and NF-kB, and MCP-1 expression by activating NF-kB, as demonstrated by the use of specific inhibitors (SB203580 and Bay11-7085). The addition of 25mM glucose in the culture medium enhanced the effect of AGE-LDL, but also of nLDL, on RAGE, p22(phox), NOX4, p67(phox), and MCP-1 gene expression. In conclusion, AGE-LDL induce an oxidative stress and a pro-inflammatory state in human endothelial cells. Both AGE-LDL and nLDL in the presence of high glucose amplify their effect, revealing a link between hyperlipidemia, diabetes, and endothelial cell dysfunction.

Effect of N-epsilon-(carboxymethyl)lysine on coronary vasoconstriction in isolated perfused hearts from control and streptozotocin-induced diabetic rats

Advanced glycation end products (AGEs) derived from glucose are implicated in the pathogenesis of diabetic vascular disease. However, their direct modulatory effects on coronary vascular tone remain unclear. We previously reported that coronary vasoconstriction was induced by acetylcholine (ACh) infusion of the isolated perfused rat heart and that sensitivity was greater in perfused hearts from streptozotocin (STZ)-induced diabetic rats than in those from age-matched controls (Kamata et al., 2008). Here, we investigated the effect of N(epsilon)-(carboxymethyl)lysine (CML), which has one of the main AGE structures, on ACh-induced vasoconstriction in perfused hearts isolated from control and diabetic rats. ACh-induced vasoconstriction was significantly greater in the STZ-induced diabetic group than in the age-matched controls. CML enhanced the ACh-induced vasoconstriction in coronary arteries from control rats, but not in those from STZ-induced diabetic rats. In the controls, the vasoconstriction induced by the calcium-channel activator Bay K 8644 was also enhanced by CML. These CML-mediated enhancements of the vasoconstrictions induced by ACh and Bay K 8644 were significantly suppressed by tempol, a superoxide dismutase mimetic. The plasma CML and glucose levels were each significantly elevated in STZ-induced diabetic rats. These findings suggest (a) that CML augments ACh-induced coronary vasoconstriction, an effect that may be attributable to increased superoxide and to activation of voltage-gated Ca(2+) channels and (b) that this modulating effect may be desensitized in the STZ-induced diabetic heart.

Plasma levels of receptor for advanced glycation end products, blood transfusion, and risk of primary graft dysfunction

RATIONALE

The receptor for advanced glycation end products (RAGE) is an important marker of lung epithelial injury and may be associated with impaired alveolar fluid clearance. We hypothesized that patients with primary graft dysfunction (PGD) after lung transplantation would have higher RAGE levels in plasma than patients without PGD.

OBJECTIVES

To test the association of soluble RAGE (sRAGE) levels with PGD in a prospective, multicenter cohort study.

METHODS

We measured plasma levels of sRAGE at 6 and 24 hours after allograft reperfusion in 317 lung transplant recipients at seven centers. The primary outcome was grade 3 PGD (Pa(O(2))/Fi(O(2)) < 200 with alveolar infiltrates) within the first 72 hours after transplantation.

MEASUREMENTS AND MAIN RESULTS

Patients who developed PGD had higher levels of sRAGE than patients without PGD at both 6 hours (median 9.3 ng/ml vs. 7.5 ng/ml, respectively; P = 0.028) and at 24 hours post-transplantation (median 4.3 ng/ml vs. 1.9 ng/ml, respectively; P < 0.001). Multivariable logistic regression analyses indicated that the relationship between levels of sRAGE and PGD was attenuated by elevated right heart pressures and by the use of cardiopulmonary bypass. Median sRAGE levels were higher in subjects with cardiopulmonary bypass at both 6 hours (P = 0.003) and 24 hours (P < 0.001). sRAGE levels at 6 hours were significantly associated with intraoperative red cell transfusion (Spearman's rho = 0.39, P = 0.002 in those with PGD), and in multivariable linear regression analyses this association was independent of confounding variables (P = 0.02).

CONCLUSIONS

Elevated plasma levels of sRAGE are associated with PGD after lung transplantation. Furthermore, plasma sRAGE levels are associated with blood product transfusion and use of cardiopulmonary bypass.

Therapeutic angiogenesis in diabetes and hypercholesterolemia: influence of oxidative stress

Despite significant improvements in the medical, percutaneous, and surgical management, numerous patients are first seen with non-revascularizable coronary artery disease (CAD). The growth of new blood vessels to improve myocardial perfusion (i.e., therapeutic angiogenesis) is an attractive treatment option for these patients. However, the successes of angiogenic therapy, observed in preclinical studies, have not been realized in clinical trials. Increasing evidence suggests that this discrepancy between animal and human studies may be due to the nature of the substrate, or the molecular and cellular environment within which the angiogenic agent acts. Antiangiogenic influences, including endothelial dysfunction, hypercholesterolemia, and diabetes, are present in virtually all patients with advanced CAD. Recent studies have better characterized the abnormalities associated with these disease states, providing novel targets for intervention. These substrate-modifying interventions can potentially enhance the response to protein-, gene-, or cell-based angiogenic therapy. In this review, we discuss key aspects of the angiogenic process and the pathophysiologic and molecular mechanisms that contribute to an impaired angiogenic response in the setting of endothelial dysfunction, hypercholesterolemia, and diabetes, with a focus on the role of oxidative stress. Last, we briefly explore substrate modifying agents that have been evaluated in preclinical and clinical studies to improve the angiogenic response.

Quantitative measurement of specific biomarkers for protein oxidation, nitration and glycation in Arabidopsis leaves

Higher plants are continually exposed to reactive oxygen and nitrogen species during their lives. Together with glucose and reactive dicarbonyls, these can modify proteins spontaneously, leading to protein oxidation, nitration and glycation. These reactions have the potential to damage proteins and have an impact on physiological processes. The levels of protein oxidation, nitration and glycation adducts were assayed, using liquid chromatography coupled with tandem mass spectrometry, in total leaf extracts over a diurnal cycle and when exposed to conditions that promote oxidative stress. Changes in the levels of oxidation, glycation and nitration adducts were found between the light and dark phases under non-stress conditions. A comparison between wild-type plants and a mutant lacking peptide methionine sulfoxide reductase (pmsr2-1) showed increased protein oxidation, nitration and glycation of specific amino acid residues during darkness in pmsr2-1. Short-term excess light exposure, which promoted oxidative stress, led to increased protein glycation, specifically by glyoxal. This suggested that any increased oxidative damage to proteins was within the repair capacity of the plant. The methods developed here provide the means to simultaneously detect a range of protein oxidation, nitration and glycation adducts within a single sample. Thus, these methods identify a range of biomarkers to monitor a number of distinct biochemical processes that have an impact on the proteome and therefore the physiological state of the plant.

Cardiovascular complications of diabetes mellitus: The Tissue Factor perspective

Heightened activity of circulating Tissue Factor (TF) has been linked to a variety of macro- and microvascular cardiovascular complications commonly observed in diabetes mellitus. Systemic and localized vascular abnormalities comprise the most debilitating feature of diabetic pathophysiology. Blood monocytes are chronically activated in diabetes, and serve as the major source of bioactive intravascular TF. This review examines recent literature on this subject, with a special emphasis on the abnormal monocyte physiology in diabetes and the structural and functional diversity of circulating TF.