Telmisartan inhibits methylglyoxal-mediated cell death in human vascular endothelium

Methylglyoxal in Cardiometabolic Disorders: Routes Leading to Pathology Counterbalanced by Treatment Strategies

Methylglyoxal (MGO) is the major compound belonging to reactive carbonyl species (RCS) responsible for the generation of advanced glycation end products (AGEs). Its upregulation, followed by deleterious effects at the cellular and systemic levels, is associated with metabolic disturbances (hyperglycemia/hyperinsulinemia/insulin resistance/hyperlipidemia/inflammatory processes/carbonyl stress/oxidative stress/hypoxia). Therefore, it is implicated in a variety of disorders, including metabolic syndrome, diabetes mellitus, and cardiovascular diseases. In this review, an interplay between pathways leading to MGO generation and scavenging is addressed in regard to this system's impairment in pathology. The issues associated with mechanistic MGO involvement in pathological processes, as well as the discussion on its possible causative role in cardiometabolic diseases, are enclosed. Finally, the main strategies aimed at MGO and its AGEs downregulation with respect to cardiometabolic disorders treatment are addressed. Potential glycation inhibitors and MGO scavengers are discussed, as well as the mechanisms of their action.

Anti-Apoptosis of Podocytes and Pro-Apoptosis of Mesangial Cells for Telmisartan in Alleviating Diabetic Kidney Injury

Podocytes damage and mesangial cells expansion are two important pathological manifestations of glomerular injury in early diabetes. Telmisartan, as an angiotensin type 1 (AT₁) receptor inhibitor, could improve advanced glycation end (AGE) products or angiotensin Ⅱ (Ang Ⅱ)-induced podocytes injury including detachment or apoptosis. In this current paper, we first confirmed the protective effect of telmisartan on early diabetic kidney injury in type 1 diabetic rats. Telmisartan reduced the loss of podocin and inhibited the expression of α-SMA, reflecting its protective effect on podocyte injury and mesangial proliferation, respectively. More interestingly we observed an opposite effect of telmisartan on the cell viability and apoptosis of podocytes and mesangial cells in a high-glucose environment in vitro. The anti-apoptotic effect of telmisartan on podocytes might be related to its inhibition of swiprosin-1 (a protein can mediate high glucose-induced podocyte apoptosis) expression. While telmisartan induced a high expression of PPARγ in mesangial cells, and GW9662 (a PPARγ antagonist) partially inhibited telmisartan-induced apoptosis and reduced viability of mesangial cells. In addition, high glucose-induced PKCβ1/TGFβ1 expression in mesangial cells could be blocked by telmisartan. These data provide a more precise cellular mechanism for revealing the protective effect of telmisartan in diabetic kidney injury.

Methylglyoxal augments uridine diphosphate-induced contraction via activation of p38 mitogen-activated protein kinase in rat carotid artery

The methylglyoxal elicits diverse adverse effects on the body. Uridine diphosphate, an extracellular nucleotide, plays an important role as a signaling molecule controlling vascular tone. This study aimed to evaluate the relationship between methylglyoxal and uridine diphosphate-induced carotid arterial contraction in rats. Additionally, we examined whether p38 mitogen-activated protein kinase (MAPK) would involve such responses. Organ baths were conducted to determine vascular reactivity in isolated carotid arterial rings, and western blotting was used for protein analysis. Treatment with methylglyoxal to carotid arterial rings showed concentration-dependent augmentation to uridine diphosphate-induced contraction in the absence and presence of NG-nitro-L-arginine, which is a nitric oxide synthase inhibitor, whereas, methylglyoxal did not affect serotonin- or isotonic high K+-induced contraction in the presence of a nitric oxide synthase inhibitor. Under nitric oxide synthase inhibition, SB203580, which is a selective p38 MAPK inhibitor, suppressed uridine diphosphate-induced contraction in both the control and methylglyoxal-treated groups, and the difference in uridine diphosphate-induced contraction was abolished by SB203580 treatment. The levels of phosphorylated p38 MAPK were increased by methylglyoxal in carotid arteries, not only under the basal condition but also under uridine diphosphate stimulation. The suppression of uridine diphosphate-induced contraction by a highly selective cell-permeable protein kinase C inhibitor bisindolylmaleimide I was observed in the methylglyoxal-treated group but not in the controls. Moreover, methylglyoxal-induced augmentation of uridine diphosphate-induced contraction was prevented by N-acetyl-L-cysteine. These results suggest that methylglyoxal could enhance uridine diphosphate-induced contraction in rat carotid arteries and may be caused by activation of p38 MAPK and protein kinase C and increased oxidative stress.

Methylglyoxal down-regulates the expression of cell cycle associated genes and activates the p53 pathway in human umbilical vein endothelial cells

Although methylglyoxal (MGO) has emerged as key mediator of diabetic microvascular complications, the influence of MGO on the vascular transcriptome has not thoroughly been assessed. Since diabetes is associated with low grade inflammation causing sustained nuclear factor-kappa B (NF-κB) activation, the current study addressed 1) to what extent MGO changes the transcriptome of human umbilical vein endothelial cells (HUVECs) exposed to an inflammatory milieu, 2) what are the dominant pathways by which these changes occur and 3) to what extent is this affected by carnosine, a putative scavenger of MGO. Microarray analysis revealed that exposure of HUVECs to high MGO concentrations significantly changes gene expression, characterized by prominent down-regulation of cell cycle associated genes and up-regulation of heme oxygenase-1 (HO-1). KEGG-based pathway analysis identified six significantly enriched pathways of which the p53 pathway was the most affected. No significant enrichment of inflammatory pathways was found, yet, MGO did inhibit VCAM-1 expression in Western blot analysis. Carnosine significantly counteracted MGO-mediated changes in a subset of differentially expressed genes. Collectively, our results suggest that MGO initiates distinct transcriptional changes in cell cycle/apoptosis genes, which may explain MGO toxicity at high concentrations. MGO did not augment TNF-α induced inflammation.

Phosphocreatine protects endothelial cells from Methylglyoxal induced oxidative stress and apoptosis via the regulation of PI3K/Akt/eNOS and NF-κB pathway

Methylglyoxal (MGO), an active metabolite of glucose, can cause cellular injury which has an affinity for the progression of diabetes-associated atherosclerosis. Phosphocreatine (PCr) is a well-known high-energy phosphate compound. However, its protective effects and mechanism in the formation of a diabetes-associated atherosclerosis have not been clarified. In the present study, we investigated whether PCr could prevent MGO-induced apoptosis in human umbilical vascular endothelial cells (HUVECs) and explored the possible mechanisms. Cells were pre-treated with PCr and then stimulated with MGO. Cell morphology, cytotoxicity and apoptosis were assessed by light microscopy, MTT assay, and Annexin V-FITC respectively. Apoptotic-related proteins were evaluated by Western blotting. Reactive oxygen species (ROS) generation, intracellular calcium and mitochondrial membrane potential (MMP) were measured with fluorescent probes. Our results showed that PCr dose-dependently prevented MGO associated HUVEC cytotoxicity and suppressed MGO activated ROS generation as well as apoptotic biochemical changes such as lactate dehydrogenase, malondialdehyde leakage, loss of MMP, decreased Bcl-2/Bax protein ratio, levels of caspase-3 and 9. In addition, the antiapoptotic effect of PCr enhanced p-Akt/Akt protein ratio, NO synthase (eNOS) activation, NO production and cGMP levels and also was partially suppressed by a PI3K inhibitor (LY294002). Furthermore, PCr also inhibited MGO-induced transcriptional activity of Nuclear factor kappa B (NFκB). In conclusion, our data described that PCr exerts an antiapoptotic effect in HUVECs exposed to oxidative stress by MGO through the mitochondrial pathway and the modulation of PI3K/Akt/eNOS and NF-κB signaling pathway. Thus, it might be a candidate therapeutic agent for diabetic-associated cardiovascular diseases.

Renoprotective effect of a combination of garlic and telmisartan against ischemia/reperfusion-induced kidney injury in obese rats

Obesity enhances the frequency and severity of acute kidney injury (AKI). Telmisartan pre-treatment was used experimentally in the amelioration of ischemia/reperfusion (IR)-induced AKI. However, there is a lack of evidence regarding its beneficial effects on AKI in obese animals. The present study, therefore, aimed to explore the protective effects of garlic and/or telmisartan against renal damage induced by unilateral IR in obese rats. Meloxicam was used as a standard anti-inflammatory agent. Prophylactic oral administration of meloxicam (3 mg kg(-1)), garlic (500 mg kg(-1)) and/or telmisartan (5 and 10 mg kg(-1)) for 4 wk protected against renal function deterioration induced by IR in obese rats. Both doses of telmisartan significantly reduced serum total cholesterol and triacyglycerol levels as well as peri-renal adipocytes size and renal fibrosis. Renal nuclear factor-kappa B immunoreactivity, tumor necrosis factor-alpha content as well as interleukin-10, adiponectin receptor 1 and macrophages (M1, M2) polarization markers (CD11c, CD206) mRNA expressions were down-regulated in ischemic kidney tissues and white adipose tissues around them by all treatments. Moreover, garlic, telmisartan and their combinations significantly suppressed oxidative stress in renal ischemic tissues. Histological picture was also improved by these treatments. Interestingly, the combinations provided a greater protection than their monotherapy in a dose-dependent manner. We suppose that this combination may be a promising prophylactic regimen for managing AKI in case of obesity. Thus, future experimental and clinical large-scale studies are necessary.

Methylglyoxal-Induced Endothelial Cell Loss and Inflammation Contribute to the Development of Diabetic Cardiomyopathy

The mechanisms for the development of diabetic cardiomyopathy remain largely unknown. Methylglyoxal (MG) can accumulate and promote inflammation and vascular damage in diabetes. We examined if overexpression of the MG-metabolizing enzyme glyoxalase 1 (GLO1) in macrophages and the vasculature could reduce MG-induced inflammation and prevent ventricular dysfunction in diabetes. Hyperglycemia increased circulating inflammatory markers in wild-type (WT) but not in GLO1-overexpressing mice. Endothelial cell number was reduced in WT-diabetic hearts compared with nondiabetic controls, whereas GLO1 overexpression preserved capillary density. Neuregulin production, endothelial nitric oxide synthase dimerization, and Bcl-2 expression in endothelial cells was maintained in the hearts of GLO1-diabetic mice and corresponded to less myocardial cell death compared with the WT-diabetic group. Lower receptor for advanced glycation end products and tumor necrosis factor-α (TNF-α) levels were also observed in GLO1-diabetic versus WT-diabetic mice. Over a period of 8 weeks of hyperglycemia, GLO1 overexpression delayed and limited the loss of cardiac function. In vitro, MG and TNF-α were shown to synergize in promoting endothelial cell death, which was associated with increased angiopoietin 2 expression and reduced Bcl-2 expression. These results suggest that MG in diabetes increases inflammation, leading to endothelial cell loss. This contributes to the development of diabetic cardiomyopathy and identifies MG-induced endothelial inflammation as a target for therapy.

Angiotensin II type 1 receptor antagonists in animal models of vascular, cardiac, metabolic and renal disease

We have reviewed the effects of angiotensin II type 1 receptor antagonists (ARBs) in various animal models of hypertension, atherosclerosis, cardiac function, hypertrophy and fibrosis, glucose and lipid metabolism, and renal function and morphology. Those of azilsartan and telmisartan have been included comprehensively whereas those of other ARBs have been included systematically but without intention of completeness. ARBs as a class lower blood pressure in established hypertension and prevent hypertension development in all applicable animal models except those with a markedly suppressed renin-angiotensin system; blood pressure lowering even persists for a considerable time after discontinuation of treatment. This translates into a reduced mortality, particularly in models exhibiting marked hypertension. The retrieved data on vascular, cardiac and renal function and morphology as well as on glucose and lipid metabolism are discussed to address three main questions: 1. Can ARB effects on blood vessels, heart, kidney and metabolic function be explained by blood pressure lowering alone or are they additionally directly related to blockade of the renin-angiotensin system? 2. Are they shared by other inhibitors of the renin-angiotensin system, e.g. angiotensin converting enzyme inhibitors? 3. Are some effects specific for one or more compounds within the ARB class? Taken together these data profile ARBs as a drug class with unique properties that have beneficial effects far beyond those on blood pressure reduction and, in some cases distinct from those of angiotensin converting enzyme inhibitors. The clinical relevance of angiotensin receptor-independent effects of some ARBs remains to be determined.

Effect of Endomorphins on HUVECs Treated by ox-LDL and Its Related Mechanisms

We found in the present study that treatment with ox-LDL decreased the cell viability and the content of nitric oxide (NO) and the activity of nitric oxide synthase (NOS) as well as eNOS mRNA expression, while increasing the mRNA expression and content of endothelin-1 (ET-1) in human umbilical vein endothelial cells (HUVECs). However, endomorphins EM1/EM2 increased the cell viability and the content of NO and the activity of NOS as well as eNOS mRNA expression, while decreasing the mRNA expression and content of ET-1 compared with ox-LDL alone. Meanwhile, the expressions of JNK and p-JNK were enhanced by ox-LDL while being suppressed by EM1/EM2. The results suggested that EM1 and EM2 can correct the endothelial cell dysfunction induced by ox-LDL and the protective effect may be achieved by affecting the JNK pathway.

LR-90 prevents methylglyoxal-induced oxidative stress and apoptosis in human endothelial cells

Methylglyoxal (MGO) is a highly reactive dicarbonyl compound known to induce cellular injury and cytoxicity, including apoptosis in vascular cells. Vascular endothelial cell apoptosis has been implicated in the pathophysiology and progression of atherosclerosis. We investigated whether the advanced glycation end-product inhibitor LR-90 could prevent MGO-induced apoptosis in human umbilical vascular endothelial cells (HUVECs). HUVECs were pre-treated with LR-90 and then stimulated with MGO. Cell morphology, cytotoxicity and apoptosis were evaluated by light microscopy, MTT assay, and Annexin V-FITC and propidium iodide double staining, respectively. Levels of Bax, Bcl-2, cytochrome c, mitogen-activated protein kinases (MAPKs) and caspase activities were assessed by Western blotting. Reactive oxygen species (ROS) generation and mitochondrial membrane potential (MMP) were measured with fluorescent probes. LR-90 dose-dependently prevented MGO-associated HUVEC cytotoxicity and apoptotic biochemical changes such as loss of MMP, increased Bax/Bcl-2 protein ratio, mitochondrial cytochrome c release and activation of caspase-3 and 9. Additionally, LR-90 blocked intracellular ROS formation and MAPK (p44/p42, p38, JNK) activation, though the latter seem to be not directly involved in MGO-induced HUVEC apoptosis. LR-90 prevents MGO-induced HUVEC apoptosis by inhibiting ROS and associated mitochondrial-dependent apoptotic signaling cascades, suggesting that LR-90 possess cytoprotective ability which could be beneficial in prevention of diabetic related-atherosclerosis.

Thiazolidinedione-independent activation of peroxisome proliferator-activated receptor γ is a potential target for diabetic macrovascular complications

Macrovascular complications are responsible for the high morbidity and mortality in patients with diabetes. Peroxisome proliferator‐activated receptor γ (PPARγ) plays a central role in the process of adipocyte differentiation and insulin sensitization, and also possesses anti‐atherogenic effects. Recently, some statins, angiotensin II type 1 receptor blockers and calcium channel blockers have been reported to activate PPARγ. However, the impact of PPARγ activation on diabetic macrovascular complications is not fully understood. It has been reported that the activation of PPARγ by thiazolidinediones induces anti‐atherogenic effects in vascular cells, including monocytes/macrophages, endothelial cells and smooth muscle cells, in atherosclerotic animal models and in clinical studies. We have reported that hydroxymethylglutaryl coenzyme A reductase inhibitors (statins), which are used for treatment of hypercholesterolemia, activate PPARγ and mediate anti‐atherogenic effects through PPARγ activation in macrophages. Also, telmisartan, an angiotensin type I receptor blocker, has been reported to have anti‐atherogenic effects through PPARγ activation. Furthermore, we have reported that nifedipine, a dihydropyridine calcium channel blocker, can activate PPARγ, thereby mediating anti‐atherogenic effects in macrophages. Therefore, statin therapy and part of anti‐hypertensive therapy might produce beneficial effects through PPARγ activation in hypercholesterolemic and/or hypertensive patients with diabetes, and PPARγ might be a therapeutic target for diabetic macrovascular complications. In the present review, we focus on the anti‐atherogenic effects of PPARγ and suggest potential therapeutic approaches to prevent diabetic macrovascular complications. (J Diabetes Invest, doi: 10.1111/j.2040‐1124.2011.00182.x, 2012)

Vaspin (serpinA12) in obesity, insulin resistance, and inflammation

While genome-wide association studies as well as candidate gene studies have revealed a great deal of insight into the contribution of genetics to obesity development and susceptibility, advances in adipose tissue research have substantially changed the understanding of adipose tissue function. Its perception has changed from passive lipid storage tissue to active endocrine organ regulating and modulating whole-body energy homeostasis and metabolism and inflammatory and immune responses by secreting a multitude of bioactive molecules, termed adipokines. The expression of human vaspin (serpinA12) is positively correlated to body mass index and insulin sensitivity and increases glucose tolerance in vivo, suggesting a compensatory role in response to diminished insulin signaling in obesity. Recently, considerable insight has been gained into vaspin structure, function, and specific target tissue-dependent effects, and several lines of evidence suggest vaspin as a promising candidate for drug development for the treatment of obesity-related insulin resistance and inflammation. These will be summarized in this review with a focus on molecular mechanisms and pathways.

Vaspin prevents methylglyoxal-induced apoptosis in human vascular endothelial cells by inhibiting reactive oxygen species generation

AIM

Vaspin (visceral adipose tissue-derived serine protease inhibitor) is a novel adipocytokine found in visceral white adipose tissues of obese type 2 diabetic rats. We have previously shown that vaspin has anti-inflammatory and antimigratory effects in vascular smooth muscle cells. Methylglyoxal (MGO) is an active metabolite of glucose and mediates diabetic vascular complications including endothelial cell (EC) apoptosis. Nonetheless, effects of vaspin on MGO-induced apoptosis of vascular EC remain to be determined. We investigated the effects of vaspin on MGO-induced apoptosis of human umbilical vein ECs (HUVECs).

METHODS

Human umbilical vein ECs were treated with MGO (560 μm, 12 h) in the absence or presence of vaspin (1 ng mL(-1), pre-treatment for 2 h). Cell death was evaluated by a cell counting assay. Apoptosis was determined by a terminal deoxyribonucleotide transferase-mediated deoxyuridine triphosphate nick-end labelling (TUNEL) assay. Cleaved caspase-3 expression was determined by Western blotting. Reactive oxygen species (ROS) generation was fluorometrically measured using 2', 7'-dichlorodihydrofluorescein diacetate. NADPH oxidase (NOX) activity was determined by a lucigenin assay.

RESULTS

Vaspin significantly inhibited MGO-induced HUVEC death. Vaspin significantly attenuated MGO-increased TUNEL-positive ECs. Moreover, vaspin significantly inhibited MGO-induced caspase-3 cleavage. Vaspin significantly inhibited MGO-induced ROS generation as well as NOX activation.

CONCLUSIONS

The present results for the first time demonstrate that vaspin inhibits MGO-induced EC apoptosis by preventing caspase-3 activation via the inhibition of NOX-derived ROS generation.

Protection effect of endomorphins on advanced glycation end products induced injury in endothelial cells

Endomorphins (EMs) have a very important bridge-function in cardiovascular, endocrinological, and neurological systems. This study is to investigate the effects of EMs on the synthesis and secretion of vasoactive substances induced by advanced glycation end products in primary cultured human umbilical vein endothelial cells (HUVECs). Firstly, HUVECs were stimulated with AGEs-bovine serum albumin (AGEs-BSA), bovine serum albumin (BSA), or both AGEs-BSA and EMs together, respectively. Then, HUVEC survival rate was calculated by MTT assay, the levels of NO, endothelial nitric oxide synthase (eNOS), and inducible nitric oxide synthase (iNOS) were detected by colorimetric analysis, and the contents of endothelin-1 (ET-1) were detected by ELISA. The mRNA levels of eNOS and ET-1 were measured by RT-PCR. The expression of p38 mitogen-activated protein kinase (p38 MAPK) was detected by immunofluorescence assay. The results showed that the mRNA expression and secretion of eNOS were significantly enhanced after incubation with EMs compared to those with AGEs-BSA, while the secretion of NO and iNOS, mRNA expression, and secretion of ET-1 had opposite changes. The fluorescence intensity of p38MAPK in nuclear was decreased after pretreatment with EMs compared to incubation with AGEs-BSA. Conclusion. The present study suggests that EMs have certain protection effect on AGEs-BSA-induced injury in HUVEC.

Methylglyoxal has deleterious effects on thioredoxin in human aortic endothelial cells

Methylglyoxal (MG), a precursor of advanced glycation end products (AGEs), is elevated in diabetic patient's plasma. Some studies have demonstrated that MG induces oxidative stress and apoptosis. Thioredoxin (Trx) is a cytoprotective protein with anti-oxidative and anti-apoptosis functions. In this study, we examined the effects of MG on Trx in human aortic endothelial cells (HAECs). MG increased oxidized-hydroethidine fluorescence intensity, suggesting intracellular accumulation of reactive oxygen species. Flow cytometric analyses with annexin-V/propidium iodide double staining revealed that cells incubated with MG displayed features characteristic of apoptosis. The condensation of chromatin, the release of cytochrome c into cytosol, and the collapse of mitochondrial membrane potential by MG were observed. The exposure to MG decreased Trx protein levels through transcription regulation. MG induced the oxidative damage of peroxiredoxin, a Trx-dependent peroxidase. These results suggest that MG has deleterious effects on Trx in HAECs, which may be contribute to oxidative stress and apoptosis.

Long-term methylglyoxal treatment impairs smooth muscle contractility in organ-cultured rat mesenteric artery

Methylglyoxal (MGO), a metabolite of glucose accumulates in vascular tissues of hypertensive rats. We recently showed that short-term (30min) treatment with MGO inhibits noradrenaline (NA)-induced smooth muscle contraction in rat aorta and mesenteric artery. In the present study, long-term effect of MGO was examined using organ culture method. The contractility, morphology, and protein expression of rat mesenteric artery after organ culture with MGO for 3 days were examined. MGO (4 and 42μM) inhibited NA (0.1nM to 3μM) or KCl (72.7mM)-induced contraction. The inhibitory effect was higher in endothelium-denuded than endothelium-intact artery. An anti-oxidant drug, N-acetyl-l-cysteine (NAC; 1mM) or an inhibitor of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX), gp91ds-tat (0.1μM) prevented the inhibitory effect of MGO. MGO increased superoxide production as detected by lucigenin assay. In the medial layer of the arteries cultured with MGO, apoptotic morphological change was observed, and NAC or gp91ds-tat prevented it. MGO significantly increased expression of a homolog of gp91(phox), NOX1 but not gp91(phox) as determined by Western blotting. An NF-κB inhibitor, pyrrolidine dithiocarbamate prevented the MGO-induced NOX1 expression. MGO had no effect on protein expression of p22(phox), p67(phox), p47(phox), as well as superoxide dismutase (SOD)-1, SOD-2 and SOD-3. Present results indicate that long-term MGO treatment has an inhibitory effect on contractility of isolated blood vessel, which is likely mediated via increased NOX1-derived superoxide production and subsequent apoptosis.

Buthionine sulfoximine promotes methylglyoxal-induced apoptotic cell death and oxidative stress in endothelial cells

Methylglyoxal (MG), a reactive dicarbonyl produced during glucose metabolism, is found at high levels in the blood of diabetic patients. MG induces oxidative stress and apoptosis. There is evidence that MG causes glutathione (GSH) depletion. However, it remains unknown whether GSH plays a protective role against the cytotoxic effect of MG. We examined the effect of DL-buthionine-(S,R)-sulfoximine (BSO), an inhibitor of glutathione (GSH) biosynthesis, on the viability of bovine aortic endothelial cells (BAECs) exposed to MG. BAECs pretreated with BSO showed reduced ability to survive MG exposure. Flow cytometric analyses with annexin V and propidium iodide double staining revealed that BAECs exposed to MG after BSO pretreatment displayed features characteristic of apoptosis. Caspase-3 activation induced by MG was increased by BSO. Moreover, measurement of protein carbonyl levels showed that BSO promoted MG-induced oxidative stress. Taken together, these findings suggest that the depletion of GSH via BSO pretreatment promoted MG-induced apoptotic cell death and oxidative stress in BAECs.

Methylglyoxal enhances sodium nitroprusside-induced relaxation in rat aorta

The concentration of methylglyoxal (MGO), a metabolite of glucose, increases in plasma of type II diabetic patients as well as in tissues of hypertensive rats. We have previously shown that MGO inhibited noradrenaline (NA)-induced smooth muscle contraction in rat aorta. However, the effect of MGO on relaxing responses in isolated blood vessel remains to be clarified. Thus, we examined if MGO affects acetylcholine (ACh)- or sodium nitroprusside (SNP)-induced vasodilation on NA (100 nM)-induced pre-contraction in rat thoracic aorta. Treatment of endothelium-intact aorta with MGO (420 microM, 30 min) did not change ACh (1 nM - 3 microM)-induced endothelium-dependent relaxation. In contrast, treatment of endothelium-denuded aorta with MGO shifted the concentration-response curve for SNP (0.1 - 300 nM) to the left. MGO increased reactive oxygen species (ROS) production in smooth muscle on analysis of protein carbonylation. Anti-oxidant agents such as tempol (10 microM), catalase (5000 U/mL), and nitric oxide synthase inhibitor, N(G)-nitro-L-arginine methylester (100 microM) had no effect on MGO-induced enhancement of SNP-induced relaxation. However, iberiotoxin (100 nM), a large-conductance Ca(2+)-activated K(+) (BK(Ca))-channel inhibitor, significantly prevented the effect. The present study revealed that MGO enhanced SNP-induced relaxation in a ROS-independent manner via in part opening smooth muscle BK(Ca) channels.

Vaspin can not inhibit TNF-alpha-induced inflammation of human umbilical vein endothelial cells

Visceral adipose tissue-derived serine protease inhibitor (vaspin) has been recently identified as an adipocytokine in a rat model of type 2 diabetes. Adipocytokines may directly influence the function of endothelial cells (ECs) and modulate inflammatory states. We therefore assessed the effects of vaspin on basal and TNF-alpha-stimulated human umbilical vein ECs. Vaspin (10-100 ng/ml, 24 hr) had no effects on both basal ECs morphology and TNF-alpha-induced (10 ng/ml, 24 hr) morphological damages. Vaspin did not inhibit the TNF-alpha (20 min) activation of JNK, p38 and NF-kappaB, but only slightly inhibited Akt. Furthermore, vaspin did not decrease the TNF-alpha (24 hr) induction of vascular cell adhesion molecule-1, intercellular adhesion molecule-1, endothelial selectin, and cyclooxygenase-2 protein expression as well as monocyte chemotactic protein-1, tissue factor, and plasmogen activator inhibitor-1 mRNA expression. The present results indicate that vaspin has no effects on normal ECs, and can not prevent TNF-alpha-induced inflammatory injury.

Impact of methylglyoxal and high glucose co-treatment on human mononuclear cells

Hyperglycemia and elevation of methylglyoxal (MG) are symptoms of diabetes mellitus (DM). In this report, we show that co-treatment of human mononuclear cells (HMNCs) with MG (5 μM) and high glucose (HG; 15 – 30 mM) induces apoptosis or necrosis. HG/MG co-treatment directly enhanced the reactive oxygen species (ROS) content in HMNCs, leading to decreased intracellular ATP levels, which control cell death via apoptosis or necrosis. Concentrations of 5 μM MG and 15 mM glucose significantly increased cytoplasmic free calcium and nitric oxide (NO) levels, loss of mitochondrial membrane potential (MMP), activation of caspases-9 and -3, and cell death. In contrast, no apoptotic biochemical changes were detected in HMNCs treated with 5 μM MG and 25 mM glucose, which appeared to undergo necrosis. Pretreatment with nitric oxide (NO) scavengers inhibited apoptotic biochemical changes induced by 5 μM MG/15 mM glucose, and increased the gene expression levels of p53 and p21 involved in apoptotic signaling. The results collectively suggest that the treatment dosage of MG and glucose determines the mode of cell death (apoptosis vs. necrosis) of HMNCs, and that both ROS and NO play important roles in MG/HG-induced apoptosis.

Methylglyoxal mediates vascular inflammation via JNK and p38 in human endothelial cells

Methylglyoxal (MGO) is a reactive metabolite of glucose. Since the plasma concentration of MGO is increased in diabetic patients, MGO is implicated in diabetes-associated vascular endothelial cells (ECs) injury, which might be responsible for atherosclerosis. In the present study, we examined effects of treatment of human umbilical vein ECs with MGO on EC morphology and inflammatory responses. MGO (24 h) induced cytotoxic morphological changes in a concentration-dependent manner (0-420 microM). MGO induced mRNA and protein expression of cyclooxygenase (COX)-2 in a concentration (0-420 microM)- and time (6-24 h)-dependent manner. COX-2 induction was associated with increased PGE(2) release. Acute treatment with MGO (20 min) induced concentration-dependent (0-420 microM) activation of JNK and p38 MAP kinase but not ERK or NF-kappaB. Both the JNK inhibitor SP600125 and the p38 inhibitor SB203580 prevented the MGO induction of COX-2. However, inhibiting JNK and p38 or COX-2 was ineffective to the morphological damage by MGO (420 microM, 24 h). EUK134, a synthetic combined superoxide dismutase/catalase mimetic, had no effect on MGO-induced COX-2. Present results indicated that MGO mediates JNK- and p38-dependent EC inflammatory responses, which might be independent of oxidative stress. On the other hand, MGO-induced morphological cell damage seems unlikely to be associated with COX-2-PGE(2).