Lysophosphatidylcholine-induced elevation of asymmetric dimethylarginine level by the NADPH oxidase pathway in endothelial cells

Responses of the antioxidant system in QGY-7701 cells to the cytotoxicity and apoptosis induced by 1-octyl-3-methylimidazolium chloride

This study aims to evaluate the cytotoxicity and responses of the cellular antioxidant system of 1-octyl-3-methylimidazolium chloride ([C8 mim][Cl]) on human hepatocarcinoma QGY-7701 cells. The results show that [C8 mim][Cl] can inhibit QGY-7701 cell growth and decrease their viabilities in a dose-dependent manner. The results also reveal that [C8 mim][Cl] exposure can induce apoptosis in the [C8 mim][Cl]-treated QGY-7701 cells. In addition, the results of biochemical assays show that [C8 mim][Cl] exposure causes overproduction of reactive oxygen species (ROS), inhibits superoxide dismutase (SOD) and catalase (CAT) activities, decreases reduced glutathione (GSH) content, and increases the cellular malondialdehyde (MDA) level. These results suggest that ROS-mediated oxidative stress may be responsible for the apoptosis induced by [C8 mim][Cl] in QGY-7701 cells.

Determination of a threshold dose to reduce or eliminate CdTe-induced toxicity in L929 cells by controlling the exposure dose

With the widespread use of quantum dots (QDs), the likelihood of exposure to quantum dots has increased substantially. The application of quantum dots in numerous biomedical areas requires detailed studies on their toxicity. In this study, we aimed to determine the threshold dose which reduced or eliminated CdTe-induced toxicity in L929 cells by controlling the exposure dose. We established a cellular model of acute exposure to CdTe QDs. Cells were exposed to different concentrations of CdTe QDs (2.2 nm and 3.5 nm) followed by illustrative cytotoxicity analysis. The results showed that low concentrations of CdTe QDs (under 10 µg/mL) promoted cell viability, caused no obvious effect on the rate of cell apoptosis, intracellular calcium levels and changes in mitochondrial membrane potential, while high concentrations significantly inhibited cell viability. In addition, reactive oxygen species in the 10 µg/mL-treated group was significantly reduced compared with the control group. In summary, the cytotoxicity of CdTe QDs on L929 cell is dose-dependent, time-dependent and size-dependent. Low concentrations of CdTe QDs (below 10 µg/mL) may be nontoxic and safe in L929 cells, whereas high concentrations (above 10 µg/mL) may be toxic resulting in inhibition of proliferation and induction of apoptosis in L929 cells.

Glucagon-like peptide-1 receptor agonist inhibits asymmetric dimethylarginine generation in the kidney of streptozotocin-induced diabetic rats by blocking advanced glycation end product-induced protein arginine methyltranferase-1 expression

Advanced glycation end products (AGEs) and their receptor (RAGE) play a role in diabetic nephropathy. Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, contributes to diabetic nephropathy. We have found that glucagon-like peptide-1 (GLP-1) inhibits the AGE-induced inflammatory reactions in endothelial cells. However, effects of GLP-1 on the AGE-RAGE-ADMA axis are unknown. This study examined the effects of GLP-1 on reactive oxygen species (ROS) generation, gene expression of protein arginine methyltransfetase-1 (PRMT-1), an enzyme that mainly generates ADMA, and ADMA levels in human proximal tubular cells. Streptozotocin-induced diabetic rats received continuous i.p. infusion of 0.3 μg of vehicle or 1.5 μg of the GLP-1 analog exendin-4 per kilogram of body weight for 2 weeks. We further investigated whether and how exendin-4 treatment reduced ADMA levels and renal damage in streptozotocin-induced diabetic rats. GLP-1 inhibited the AGE-induced RAGE and PRMT-1 gene expression, ROS, and ADMA generation in tubular cells, which were blocked by small-interfering RNAs raised against GLP-1 receptor. Exendin-4 treatment decreased gene expression of Rage, Prmt-1, Icam-1, and Mcp-1 and ADMA level; reduced urinary excretions of 8-hydroxy-2'-deoxyguanosine and albumin; and improved histopathologic changes of the kidney in diabetic rats. Our present study suggests that GLP-1 receptor agonist may inhibit the AGE-RAGE-mediated ADMA generation by suppressing PRMT-1 expression via inhibition of ROS generation, thereby protecting against the development and progression of diabetic nephropathy.

Actin cytoskeleton-dependent pathways for ADMA-induced NF-κB activation and TGF-β high expression in human renal glomerular endothelial cells

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, is considered to be an independent risk factor in the progression of chronic kidney diseases (CKD). It can induce kidney fibrosis by increasing transforming growth factor (TGF)-β1 expression, but its molecular mechanism is unclear. The aim of the present study was to investigate the role of actin cytoskeleton in ADMA-induced TGF-β1 high expression in human renal glomerular endothelial cells (HRGECs). The structure of stress fibers was visualized by immunofluorescence, nuclear factor-κB (NF-κB) DNA-binding activity was assessed by an electrophoretic mobility shift assay and TGF-β1 expression was assessed by western blot analysis. Results showed that ADMA induced the assembly of stress fibers, DNA binding of NF-κB, and increasing expression of TGF-β1. When the dynamics of actin cytoskeleton was perturbed by the actin-depolymerizing agent cytochalasin D and the actin-stabilizing agent jasplakinolide, or ablation of stress fiber bundles by the nicotineamide adenine dinucleotide phosphate oxidase inhibitor apocynin and p38 mitogen-activated protein kinase inhibitor SB203580, ADMA-induced DNA binding of NF-κB and TGF-β1 expression were inhibited. These results revealed an actin cytoskeleton-dependent mechanism in ADMA-induced NF-κB activation and TGF-β1 high expression in HRGECs. The specific targeting of the actin cytoskeleton may be a useful strategy to prevent ADMA-activated kidney fibrosis in CKD.

The antihypertensive effect of arginine

Hypertension is a leading cause of morbidity and mortality worldwide. Individuals with hypertension are at increased risk of stroke, heart disease and kidney failure. Although the etiology of essential hypertension has a genetic component, lifestyle factors such as diet play an important role. Reducing dietary salt is effective in lowering blood pressure in salt-sensitive individuals. Insulin resistance and altered glucose metabolism are common features of hypertension in humans and animal models, with or without salt sensitivity. Altered glucose metabolism leads to increased formation of advanced glycation end products. Insulin resistance is also linked to oxidative stress, and alterations in the nitric oxide pathway and renin angiotensin system. A diet rich in protein containing the semiessential amino acid, arginine, and arginine treatment, lowers blood pressure in humans and in animal models. This may be due to the ability of arginine to improve insulin resistance, decrease advanced glycation end products formation, increase nitric oxide, and decrease levels of angiotensin II and oxidative stress, with improved endothelial cell function and decreased peripheral vascular resistance. The Dietary Approaches to Stop Hypertension (DASH) study demonstrated that the DASH diet, rich in vegetables, fruits and low-fat dairy products; low in fat; and including whole grains, poultry, fish and nuts, lowered blood pressures even more than a typical North American diet with similar reduced sodium content. The DASH diet is rich in protein; the blood pressure-lowering effect of the DASH diet may be due to its higher arginine-containing protein, higher antioxidants and low salt content.

Antihypertensive effects of dietary protein and its mechanism

Hypertension is a leading cause of morbidity and mortality worldwide. Individuals with hypertension are at increased risk of stroke, heart disease and kidney failure. Both genetic and lifestyle factors, particularly diet, have been attributed an important role in the development of hypertension. Reducing dietary sugar and salt intake can help lower blood pressure; similarly, adequate protein intake may also attenuate hypertension. Observational, cross-sectional and longitudinal epidemiological studies, and controlled clinical trials, have documented significant inverse associations between protein intake and blood pressure. Human and animal studies have shown that specific amino acids within proteins may have antihypertensive effects. Cysteine, glutathione (a tripeptide), glutamate and arginine attenuate and prevent alterations that cause hypertension including insulin resistance, decreased nitric oxide bioavailability, altered renin angiotensin system function, increased oxidative stress and formation of advanced glycation end products. Leucine increases protein synthesis in skeletal muscle and improves insulin resistance by modulating hepatic gluconeogenesis. Taurine and tryptophan attenuate sympathetic nervous system activity. Soy protein helps lower blood pressure through its high arginine content and antioxidant activity exhibited by isoflavones. A diet containing an ample amount of protein may be a beneficial lifestyle choice for individuals with hypertension; one example is the Dietary Approaches to Stop Hypertension (DASH) diet, which is low in salt and saturated fat; includes whole grains, lean meat, poultry, fish and nuts; and is rich in vegetables, fruits and low-fat dairy products, which are good sources of antioxidant vitamins, minerals and fibre. Including an adequate supply of soy in the diet should also be encouraged.

Dysregulation of dimethylargininedimethylaminohydrolase/asymmetric dimethylarginine pathway in rat type II diabetic nephropathy

An impaired generation of nitric oxide has been associated with diabetic renal disease. In order to elucidate the underlying molecular mechanisms into how nitric oxide synthesis is impaired in diabetic renal disease, we examined changes in activities and expressions of some renal enzymes involved in nitric oxide production during the development of diabetic nephropathy in type II diabetic Otsuka Long-Evans Tokushima Fatty rats. Ten-week old Otsuka Long-Evans Tokushima Fatty (n = 40) and control Long-Evans Tokushima Otsuka rats (n = 20) were given drinking water containing 20% sucrose to accelerate the development of diabetic nephropathy. Otsuka Long-Evans Tokushima Fatty rats developed diabetic nephropathy in an age-dependent manner. Renal nitric oxide synthase activities in Otsuka Long-Evans Tokushima Fatty rats gradually declined with the progression of diabetic mellitus and were significantly lower than those of age-matched Long-Evans Tokushima Otsuka rats after 22 weeks of age. The lower activities of renal nitric oxide synthase in Otsuka Long-Evans Tokushima Fatty rats were correlated with relatively higher levels of renal free asymmetric dimethylarginine, an endogenous nitric oxide synthase inhibitor, and were also correlated with decreased activities of dimethylargininedimethylaminohydrolase which metabolizes asymmetric dimethylarginine to citrulline. These results imply that dimethylargininedimethylaminohydrolase dysregulation may play an important role in the development of diabetic nephropathy by increasing asymmetric dimethylarginine levels, which leads to inhibition of renal nitric oxide synthesis.

Human obesity and endothelium-dependent responsiveness

Obesity is an ongoing worldwide epidemic. Besides being a medical condition in itself, obesity dramatically increases the risk of development of metabolic and cardiovascular disease. This risk appears to stem from multiple abnormalities in adipose tissue function leading to a chronic inflammatory state and to dysregulation of the endocrine and paracrine actions of adipocyte-derived factors. These, in turn, disrupt vascular homeostasis by causing an imbalance between the NO pathway and the endothelin 1 system, with impaired insulin-stimulated endothelium-dependent vasodilation. Importantly, emerging evidence suggests that the vascular dysfunction of obesity is not just limited to the endothelium, but also involves the other layers of the vessel wall. In particular, obesity-related changes in medial smooth muscle cells seem to disrupt the physiological facilitatory action of insulin on the responsiveness to vasodilator stimuli, whereas the adventitia and perivascular fat appear to be a source of pro-inflammatory and vasoactive factors that may contribute to endothelial and smooth muscle cell dysfunction, and to the pathogenesis of vascular disease. While obesity-induced vascular dysfunction appears to be reversible, at least in part, with weight control strategies, these have not proved sufficient to prevent the metabolic and cardiovascular complication of obesity on a large scale. While a number of currently available drugs have shown potentially beneficial vascular effects in patients with obesity and the metabolic syndrome, elucidation of the pathophysiological mechanisms underlying vascular damage in obese patients is necessary to identify additional pharmacologic targets to prevent the cardiovascular complications of obesity, and their human and economic costs.

LINKED ARTICLES

This article is part of a themed section on Fat and Vascular Responsiveness. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.165.issue-3.

Nitric oxide synthase derangements and hypertension in kidney disease

PURPOSE OF REVIEW

Nitric oxide deficiency occurs by multiple mechanisms and contributes to the pathogenesis of progression of chronic kidney disease (CKD) and its cardiovascular complications. This article concentrates on recent developments on the regulation of the endogenous nitric oxide synthase (NOS) inhibitor asymmetric dimethylarginine (ADMA) in CKD and on the importance of the nitric oxide synthases in kidney disease progression, particularly in diabetic nephropathy.

RECENT FINDINGS

The increased plasma ADMA seen in renal disease is generally predictive of severity of CKD progression and cardiovascular risk. However, some assumptions about the control of ADMA have been challenged: the primacy of the kidney as a metabolic organ for plasma ADMA regulation has come under scrutiny and the relative importance of the two isoforms of the ADMA-metabolizing enzymes dimethylarginine dimethylaminohydrolases (DDAHs) is being re-evaluated. Alterations in NOS also contribute to CKD progression with the endothelial isoform playing a major role in diabetic nephropathy.

SUMMARY

Improving our understanding of ADMA regulation is important since pharmacologic targeting of DDAH is underway. The major role of endothelial NOS-derived nitric oxide in diabetic nephropathy should lead to novel therapies. The beneficial actions of dietary nitrate supplementation on blood pressure and kidney disease are of considerable clinical relevance.

Asymmetric dimethylarginine and reactive oxygen species: unwelcome twin visitors to the cardiovascular and kidney disease tables

Plasma levels of asymmetric dimethylarginine or markers of reactive oxygen species are increased in subjects with risk factors for cardiovascular disease or chronic kidney disease. We tested the hypothesis that reactive oxygen species generate cellular asymmetric dimethylarginine that together cause endothelial dysfunction that underlies the risk of subsequent disease. Rat preglomerular vascular smooth muscle cells transfected with p22(phox) had increased NADPH oxidase activity, enhanced activity and expression of protein arginine methyltransferase, and reduced activity and protein expression of dimethylarginine dimethylaminotransferase and of cationic amino acid transferase 1 resulting in increased cellular levels of asymmetric dimethylarginine. Rats infused with angiotensin II had oxidative stress. The endothelial function of their mesenteric arterioles was changed from vasodilatation to vasoconstriction, accompanied by increased vascular asymmetric dimethylarginine. All of these changes were prevented by Tempol. In vivo silencing of dimethylarginine dimethylaminotransferase 1 increased plasma levels of asymmetric dimethylarginine, whereas silencing of dimethylarginine dimethylaminotransferase 2 impaired endothelial function. We suggest that initiation factors, such as angiotensin II, expressed in blood vessels or tissues of subjects with cardiovascular and kidney disease risk factors generate reactive oxygen species from NADPH oxidase that enhances cellular asymmetric dimethylarginine in an amplification loop. This leads to adverse changes in vascular and organ functions, as a consequence of reduced tissue levels of NO and increased reactive oxygen species. Thus, we conclude that reactive oxygen species and asymmetric dimethylarginine form a tightly coupled amplification system that translates cardiovascular/kidney risk into overt disease.

Apelin-13 passes through the ADMA-damaged endothelial barrier and acts on vascular smooth muscle cells

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, is associated with vascular dysfunction. The polypeptide apelin mediates two major actions on blood vessels. However, their combined effects on vascular function are not fully understood. The present study aimed to determine the effect of apelin-13 on myosin light chain (MLC) phosphorylation in vascular smooth muscle cells (VSMCs) under ADMA-induced endothelial leakage conditions. To assess the increased permeability induced by ADMA, human umbilical vein endothelium cells (HUVECs) were plated in transwell dishes. The FITC-dextran flux and FITC-apelin-13 flux through the endothelial monolayer were measured. To examine the effect of leakage of apelin-13 on MLC phosphorylation in HUVSMCs, transwell dishes were used to establish a coculture system with HUVECs in upper chambers and HUVSMCs in lower chambers. Western blot was performed to assess the phospho-MLC levels. ADMA increased endothelial permeability in a concentration- and time-dependent manner, accompanied by actin stress fiber assembly and intercellular gap formation. When HUVECs were treated with ADMA, the permeability to both macromolecular dextran and micromolecular apelin-13 increased significantly. Both p38 MAPK inhibitor and NADPH oxidase inhibitor could prevent HUVECs from the increased permeability, and the changes of cytoskeleton and intercellular junction, which were induced by ADMA. Apelin-13 passed through the ADMA-stimulated endothelial monolayer and increased the expression of phospho-MLC in VSMCs. These results suggest that ADMA increases endothelial permeability, which may involve the p38 MAPK and NADPH oxidase pathway. Apelin-13 can pass through the damaged endothelial barrier, and acts directly on VSMCs to increase MLC phosphorylation.

Role of VPO1, a newly identified heme-containing peroxidase, in ox-LDL induced endothelial cell apoptosis

Myeloperoxidase (MPO) is an important enzyme involved in the genesis and development of atherosclerosis. Vascular peroxidase 1 (VPO1) is a newly discovered member of the peroxidase family that is mainly expressed in vascular endothelial cells and smooth muscle cells and has structural characteristics and biological activity similar to those of MPO. Our specific aims were to explore the effects of VPO1 on endothelial cell apoptosis induced by oxidized low-density lipoprotein (ox-LDL) and the underlying mechanisms. The results showed that ox-LDL induced endothelial cell apoptosis and the expression of VPO1 in endothelial cells in a concentration- and time-dependent manner concomitant with increased intracellular reactive oxygen species (ROS) and hypochlorous acid (HOCl) generation, and up-regulated protein expression of the NADPH oxidase gp91(phox) subunit and phosphorylation of p38 MAPK. All these effects of ox-LDL were inhibited by VPO1 gene silencing and NADPH oxidase gp91(phox) subunit gene silencing or by pretreatment with the NADPH oxidase inhibitor apocynin or diphenyliodonium. The p38 MAPK inhibitor SB203580 or the caspase-3 inhibitor DEVD-CHO significantly inhibited ox-LDL-induced endothelial cell apoptosis, but had no effect on intracellular ROS and HOCl generation or the expression of NADPH oxidase gp91(phox) subunit or VPO1. Collectively, these findings suggest for the first time that VPO1 plays a critical role in ox-LDL-induced endothelial cell apoptosis and that there is a positive feedback loop between VPO1/HOCl and the now-accepted dogma that the NADPH oxidase/ROS/p38 MAPK/caspase-3 pathway is involved in ox-LDL-induced endothelial cell apoptosis.

Differential changes of aorta and carotid vasodilation in type 2 diabetic GK and OLETF rats: paradoxical roles of hyperglycemia and insulin

We investigated large vessel function in lean Goto-Kakizaki diabetic rats (GK) and Otsuka Long-Evans Tokushima Fatty diabetic rats (OLETF) with possible roles of hyperglycemia/hyperosmolarity and insulin. Both young and old GK showed marked hyperglycemia with normal insulin level and well-preserved endothelium-dependent and endothelium-independent vasodilation in aorta and carotid artery. There were significant elevations in endothelial/inducible nitric oxide synthase (eNOS/iNOS) and inducible/constitutive heme oxygenase (HO-1/HO-2) in GK. The endothelium-dependent vasodilation in GK was inhibited partly by NOS blockade and completely by simultaneous blocking of HO and NOS. In contrast, OLETF showed hyperinsulinemia and mild hyperglycemia but significant endothelium dysfunction beginning at early ages with concomitantly reduced eNOS. Insulin injection corrected hyperglycemia in GK but induced endothelium dysfunction and intima hyperplasia. Hyperglycemia/hyperosmolarity in vitro enhanced vessel eNOS/HO. We suggest that hyperinsulinemia plays a role in endothelium dysfunction in obese diabetic OLETF, while hyperglycemia/hyperosmolarity-induced eNOS/HO upregulation participates in the adaptation of endothelium function in lean diabetic GK.

Paradoxical effects of streptozotocin-induced diabetes on endothelial dysfunction in stroke-prone spontaneously hypertensive rats

Non-technical summary

Elevated blood glucose is generally regarded as one of the risk factors that lead to coronary heart disease in patients with type 2 diabetes. However, our studies show that after inducing short-term damage, high blood glucose subsequently provides paradoxical protection for vessel function of animals with high blood pressure. Vessels can adapt to sustained high blood glucose and produce different stress proteins to counteract, to some extent, the damage brought about by hypertension. The results help us understand part of the basis for vessel adaptation in diabetes. The implication for treatment of diabetes is that if the patients have long-standing diabetes and established cardiovascular disease, the target of blood glucose lowering should be less stringent and reached gradually to avoid abrupt cancellation of the pre-existing adaptations.

Abstract

Although both diabetes and hypertension are risk factors for cardiovascular disease, the role of hyperglycaemia per se in endothelial dysfunction is controversial. This study was designed to examine whether hyperglycaemia, or streptozotocin-induced diabetes, could aggravate endothelial dysfunction in stroke-prone spontaneously hypertensive rats (SHRSP). Hyperglycaemia was induced by streptozotocin in 2-month-old SHRSP and age-matched normotensive Wistar–Kyoto (WKY) rats. The aorta was isolated 8 weeks after induction of hyperglycaemia to record its function and to examine its morphology with transmission electron microscopy. Endothelial/inducible nitric oxide synthase (eNOS/iNOS) and inducible/constitutive haem oxygenase (HO-1/HO-2) levels were determined with Western blotting. Aortic endothelial function and production of reactive oxygen species and nitric oxide were assayed after incubation in vitro in hyperglycaemic, hyperosmolar solution. Streptozotocin-induced diabetes of 8 weeks duration did not result in endothelial dysfunction in normotensive WKY rats. In contrast, hyperglycaemic WKY rats showed significantly enhanced endothelium-dependent vasodilatation, which was abrogated by simultaneous blocking of NOS and HO. The enhanced vasodilatation was associated with elevation of vascular eNOS and HO-1. Significant endothelial dysfunction and massive macrophage–monocyte infiltration were found in SHRSP aorta (the ratio of the number of macrophages to endothelial cells in the intima, expressed as a percentage, was 20.9 ± 2.8% in SHRSP versus 1.9 ± 0.5% in WKY rats, P < 0.01), which was attenuated significantly in hyperglycaemic SHRSP (11.3 ± 1.6%, P < 0.01 versus SHRSP). Acute hyperglycaemia (10 min) aggravated endothelial dysfunction in SHRSP, with a marked increase in intracellular reactive oxygen species and NO production. Sustained in vitro incubation in hyperglycaemic/hyperosmolar conditions (addition of an extra 50 mmol L⁻¹ of glucose or mannitol to the usual buffer, to produce a final osmolarity of 350 mosmol L⁻¹) for 5 h enhanced endothelium-dependent vasodilatation, with elevated vessel NO production and upregulation of eNOS/HO-1 proteins. Sustained hyperglycaemia does not aggravate endothelial dysfunction and macrophage infiltration in SHRSP. Hyperglycaemia/hyperosmolarity-induced upregulation of eNOS and HO-1 may play a role in this paradoxical adaptation of endothelial function.

Homocysteine and asymmetric dimethylarginine in relation to B vitamins in elderly people

OBJECTIVE

Homocysteine is a cardiovascular risk factor, its metabolism is influenced by certain B vitamins and it is associated with endothelial dysfunction probably due to impaired bioavailability of NO caused by homocysteine-induced accumulation of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO synthase. On this basis, we investigated the cardiovascular risk factors homocysteine and ADMA in relation to vitamins B(6), B(12) and folate in elderly people.

METHODS

A total of 102 subjects were recruited and divided into three groups according to age: A (70-74y, n = 48), B (75-79y, n = 35) and C (≥80y, n = 19). Plasma levels of vitamin B(6) were determined with HPLC, vitamin B(12) and folate by RIA. Plasma concentrations of homocysteine were analyzed with HPLC and levels of ADMA were measured by ELISA.

RESULTS

Plasma levels of vitamins B(6), B(12) and folate were found to be adequate in 93, 67 and 55% of participants, respectively. This study showed a significant age-associated decrease in vitamins B(6) (A > B, A > C: p < 0.05), B(12) and folate (A > C: p < 0.05) in parallel to a significant age-related increase in the cardiovascular risk factors homocysteine (A < C, B < C: p < 0.05) and ADMA (A < B: p < 0.05; A < C: p < 0.001). Moreover, homocysteine was significantly negatively (p < 0.01) related to vitamins B(6), B(12) and folate, and significantly positively (p < 0.01) correlated to ADMA.

CONCLUSIONS

The significant correlation between homocysteine and ADMA observed in this study may be an important mechanism decreasing NO bioavailability and so causing endothelial dysfunction. Due to the significant relation of vitamins B(6), B(12) and folate to plasma homocysteine, these vitamins may thus indirectly influence endothelial function and cardiovascular risk in elderly people.

The ratio of arginine to dimethylarginines is reduced and predicts outcomes in patients with severe sepsis

OBJECTIVES

Arginine deficiency may contribute to microvascular dysfunction, but previous studies suggest that arginine supplementation may be harmful in sepsis. Systemic arginine availability can be estimated by measuring the ratio of arginine to its endogenous inhibitors, asymmetric and symmetric dimethylarginine. We hypothesized that the arginine-to-dimethylarginine ratio is reduced in patients with severe sepsis and associated with severity of illness and outcomes.

DESIGN

Case-control and prospective cohort study.

SETTING

Medical and surgical intensive care units of an academic medical center.

PATIENTS AND SUBJECTS

One hundred nine severe sepsis and 50 control subjects.

MEASUREMENTS AND MAIN RESULTS

Plasma and urine were obtained in control subjects and within 48 hrs of diagnosis in severe sepsis patients. The arginine-to-dimethylarginine ratio was higher in control subjects vs. sepsis patients (median, 95; interquartile range, 85-114; vs. median, 34; interquartile range, 24-48; p < .001) and in hospital survivors vs. nonsurvivors (median, 39; interquartile range, 26-52; vs. median, 27; interquartile range, 19-32; p = .004). The arginine-to-dimethylarginine ratio was correlated with Acute Physiology and Chronic Health Evaluation II score (Spearman's correlation coefficient [ρ] = - 0.40; p < .001) and organ-failure free days (ρ = 0.30; p = .001). A declining arginine-to-dimethylarginine ratio was independently associated with hospital mortality (odds ratio, 1.63 per quartile; 95% confidence interval, 1.00-2.65; p = .048) and risk of death over the course of 6 months (hazard ratio, 1.41 per quartile; 95% confidence interval, 1.01-1.98; p = .043). The arginine-to-dimethylarginine ratio was correlated with the urinary nitrate-to-creatinine ratio (ρ = 0.46; p < .001).

CONCLUSIONS

The arginine-to-dimethylarginine ratio is associated with severe sepsis, severity of illness, and clinical outcomes. The arginine-to-dimethylarginine ratio may be a useful biomarker, and interventions designed to augment systemic arginine availability in severe sepsis may still be worthy of investigation.

Protective effect of neferine on endothelial cell nitric oxide production induced by lysophosphatidylcholine: the role of the DDAH–ADMA pathway

Neferine, extracted from the seed embryo of Nelumbo nucifera Gaertn., has multiple cardiovascular pharmacological effects. The dimethylarginine dimethylaminohydrolase (DDAH) – asymmetric dimethylarginine (ADMA) system is a novel pathway for modulating nitric oxide (NO) production. The aim of this study was to investigate whether the protective effect of neferine on endothelial NO production was related to the DDAH–ADMA pathway. Human umbilical vein endothelial cells (HUVECs) were first exposed to neferine (0.1, 1.0, or 10.0 μmol/L) for 1 h, and then incubated with lysophosphatidylcholine (LPC; 10 μg/mL) in the presence of neferine for 24 h. The medium was collected for measuring the levels of NO, maleic dialdehyde (MDA), as well as ADMA. The endothelial cells were collected for measuring DDAH activity and the level of reactive oxygen species (ROS). LPC significantly decreased NO concentration and DDAH activity and increased the levels of ADMA, ROS, and MDA. Neferine could partially counteract the changes induced by LPC. These findings suggested that neferine could modulate the DDAH–ADMA pathway via its antioxidant properties, which was involved in its beneficial effect on endothelial NO production.

3,4,5,6-Tetrahydroxyxanthone preserves intercellular communication by reduction of the endogenous nitric oxide synthase inhibitor level

To observe the direct effects of 3,4,5,6-tetrahydroxyxanthone on connexin43 (Cx43) expression in cultured endothelial cells, cells were treated with lysophosphatidylcholine (LPC, 10 mg/l) for 24 h in the presence or absence of different concentrations of 3,4,5,6-tetrahydroxyxanthone (1, 3, or 10 μmol l(- 1)). The reactive oxygen species (ROS) production, cell viability, asymmetric dimethylarginine (ADMA) levels, and Cx43 expression were detected. 3,4,5,6-Tetrahydroxyxanthone significantly inhibited the increase in ROS production and ADMA level, increased cell viability and up-regulated Cx43 mRNA and protein expression induced by LPC. 3,4,5,6-Tetrahydroxyxanthone has protective effect in LPC-induced atherosclerotic lesions, which is at least partly related to the reduction of ADMA level and downregulation of Cx43 expression.

Helicobacter pylori eradication lowers serum asymmetric dimethylarginine levels

Introduction. Microbial pathogens, one of them is Helicobacter pylori (H. pylori), have frequently been implicated in the atherogenesis. Endothelium-derived nitric oxide (NO) is synthesized from L-arginine by nitric oxide synthase (NOS) and plays a pivotal role in the regulation of vascular tone. Asymmetric dimethylarginine (ADMA) is the most potent endogenous NOS inhibitor. Elevated levels of ADMA have been reported in many circumstances associated with a high cardiovascular risk. The aim of the present study was to investigate whether the eradication of H. pylori infection affects serum ADMA levels. Materials and Methods. Forty-two H. pylori-positive patients were enrolled in the study. Triple therapy for 14 days were given to all patients. Serum ADMA levels were measured at baseline and 2 months after therapy. Results. Eradication was achieved in 34 (81%) patients. The mean serum ADMA levels before and after therapy were 1, 77 ± 0, 30 and 1, 67 ± 0, 29 ng/mL in the group with H. pylori eradicated and 1, 63 ± 0, 28 and 1, 56 ± 0, 32 ng/mL in the noneradicated, respectively. We detected statistically significant decreased serum ADMA levels after therapy in H. pylori eradicated group. Conclusion. These findings have indicated that eradication of H. pylori infection may decrease the risk of atherosclerosis and cardiovascular events.

Proximal tubule cell hypothesis for cardiorenal syndrome in diabetes

Incidence of cardiovascular disease (CVD) is remarkably high among patients with chronic kidney disease (CKD), even in the early microalbuminuric stages with normal glomerular filtration rates. Proximal tubule cells (PTCs) mediate metabolism and urinary excretion of vasculotoxic substances via apical and basolateral receptors and transporters. These cells also retrieve vasculoprotective substances from circulation or synthesize them for release into the circulation. PTCs are also involved in the uptake of sodium and phosphate, which are critical for hemodynamic regulation and maintaining the mineral balance, respectively. Dysregulation of PTC functions in CKD is likely to be associated with the development of CVD and is linked to the progression to end-stage renal disease. In particular, PTC dysfunction occurs early in diabetic nephropathy, a leading cause of CKD. It is therefore important to elucidate the mechanisms of PTC dysfunction to develop therapeutic strategies for treating cardiorenal syndrome in diabetes.

Asymmetric dimethylarginine damages connexin43-mediated endothelial gap junction intercellular communication

Asymmetric dimethylarginine (ADMA), a major endogenous inhibitor of nitric oxide synthase, is recently defined as a novel atherogenic factor. Communication via gap junction (GJIC) is involved in the regulation of a variety of endothelial activities, such as cell differentiation and senescence. The aim of this study is to explore the effects of ADMA on connexin43 (Cx43) mediated endothelial GJIC. Lysophosphatidylcholine (LPC) caused the downregulation of Cx43 expression and GJIC dysfunction in cultured human umbilical vein endothelial cells (HUVECs), which were significantly ameliorated by decreasing ADMA accumulation. Furthermore, we found that ADMA (10 µmol·L–1, 24 h) markedly downregulated Cx43 expression and damaged GJIC function in HUVECs. ADMA also increased production of intracellular reactive oxygen species (ROS) and induced phosphorylation of p38 MAPK. Furthermore, the inhibitory effect of ADMA on Cx43-mediated GJIC could be attenuated by NADPH oxidase inhibitor diphenyleneiodonium and apocynin as well as p38 MAPK inhibitor SB203580, respectively. In conclusion, our present results suggest that ADMA inhibits endothelial GJIC function via downregulating Cx43 expression, which suggesting a novel mechanism linking between elevated ADMA level and progression of atherosclerosis.

7-difluoromethyl-5,4'-dimethoxygenistein, a novel agent protecting against vascular endothelial injury caused by oxidative stress

1. Genistein is known to protect the vascular endothelium. However, genistein exhibits poor bioavailability, which limits its use in the treatment of cardiovascular diseases. 7-Difluoromethyl-5,4'-dimethoxygenistein (dFMGEN), prepared by the difluoromethylation and alkylation of genistein, is a new active chemical entity. The protective effects of dFMGEN against vascular endothelial injury caused by oxidative stress were investigated in the present study. 2. Human umbilical vein endothelial cells were treated with either genistein (10 micromol/L) or various concentrations of dFMGEN (0.1, 0.3, 1, 3 and 10 micromol/L) for 30 min before exposure to 1 mmol/L H(2)O(2) for 24 h. The generation of reactive oxygen species (ROS) was assessed by fluorescence flow cytometry, the release of lactate dehydrogenase (LDH) was examined by biochemical assay, cell viability was measured by the 3-(4,5-dimethyl-2 thiazoyl)-2,5-diphenyl-2H-tetrazolium bromide assay, cell apoptosis was detected by flow cytometry and the expression of caspase 3 was examined by western blot analysis. 3. Pretreatment with 0.1, 0.3, 1, 3 and 10 micromol/L dFMGEN decreased the generation of ROS and the release of LDH in H(2)O(2)-exposed vascular endothelial cells, enhanced cell viability in a concentration-dependent manner over the concentration range 0.1-10 micromol/L, suppressed H(2)O(2)-induced apoptosis of vascular endothelial cells and downregulated the expression of caspase 3. The protective effect of 10 micromol/L dFMGEN against oxidative stress-induced endothelial injury was stronger than that of 10 micromol/L genistein. 4. The results of the present study suggest that dFMGEN can protect against vascular endothelial injury caused by oxidative stress.

Effect of 3,4,5,6-tetrahydroxyxanthone on erythrocyte deformability in apolipoprotein E-deficient mice

Previous investigations have indicated that reduced erythrocyte deformability may be an important factor contributing to the development of atherosclerosis, and endogenous asymmetric dimethylarginine (ADMA) might be an important contributor to reduction of erythrocyte deformability in atherosclerosis. In this study, the effect of 3,4,5,6-tetrahydroxyxanthone (1), a kind of polyphenolic compound, on erythrocyte deformability in apolipoprotein E-deficient (apoE-/-) mice was evaluated. After treatment with compound 1 (10 or 20 mg/kg per day) for 4 weeks, erythrocyte deformability, antioxidant enzymes activity, erythrocyte dimethylarginine dimethylaminohydrolase (DDAH) activity, the plasma level of ADMA and malondialdehyde (MDA) level were determined. Treatment with compound 1 (10 or 20 mg/kg) increased erythrocyte deformability, antioxidant enzymes activity concomitantly, a decrease in the plasma levels of MDA and ADMA, and an increase in erythrocyte DDAH activity. The present result suggests that the beneficial effect of 1 on the erythrocyte deformability, besides inhibiting lipid peroxidation, may be related to reduction of ADMA concentration via an increase in DDAH activity.

Protective effects of kaempferol against endothelial damage by an improvement in nitric oxide production and a decrease in asymmetric dimethylarginine level

Previous investigations have shown that asymmetric dimethylarginine (ADMA) inhibits nitric oxide (NO) synthases (NOS) and that ADMA is a risk factor for endothelial dysfunction. The objective of this study was to investigate the protective effect of kaempferol, a naturally occurring flavonoid antioxidant agent, against endothelial damage and the mechanisms involved. The experiments were performed in aorta and plasma from C57BL/6J control and apolipoprotein E-deficient (ApoE(-/-)) mice treated or not with kaempferol (50 or 100mg/kg, intragastrically) for 4 weeks, and in human umbilical vein endothelial cells (HUVECs) pretreated or not with kaempferol (1, 3 or 10 microM) for 1h and exposed to lysophosphatidylcholine (LPC) (10 microg/mL) for 24h. Kaempferol treatment improved endothelium-dependent vasorelaxation, increased the maximal relaxation value, and decreased the half-maximum effective concentration concomitantly with an increase in nitric oxide plasma concentration, a decrease in ADMA and malondialdehyde (MDA) plasma concentrations, and increase in the expression of aortic endothelial NOS (eNOS) as well as dimethylarginine dimethylaminohydrolase II (DDAH II) in ApoE(-/-) mice. In addition, LPC caused a reduction in NO production, an increase in ADMA concentration concomitantly with a decreased expression of eNOS and DDAH II in HUVECs, and the effect of LPC was abolished by kaempferol. Treatment with kaempferol also significantly decreased reactive oxygen species production in mice aorta and in HUVECs. The present results suggest that the protective effect of kaempferol against endothelial damage may be associated with an improvement in NO production and a decrease in ADMA level.

Intracellular oxidative stress and cadmium ions release induce cytotoxicity of unmodified cadmium sulfide quantum dots

OBJECTIVE

To fully understand the cytotoxicity of after-degradation QDs, we synthesized CdS QDs and investigated its toxicity mechanism.

METHODS

Biomimetic method was proposed to synthesize cadmium sulfide (CdS) QDs. Thereafter MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide) assay was conducted to evaluate their cytotoxicity. To investigate the toxicity mechanism, we subsequently conducted intracellular reactive oxygen species (ROS) measurement with DCFH-DA, glutathione (GSH) measurement with DTNB, and cellular cadmium assay using atomic absorption spectrometer. Microsized CdS were simultaneously tested as a comparison.

RESULTS

MTT assay results indicated that CdS QDs are more toxic than microsized CdS especially at concentrations below 40 microg/ml. While microsized CdS did not trigger ROS elevation, CdS QDs increase ROS by 20-30% over control levels. However, they both deplete cellular GSH significantly at the medium concentration of 20 microg/ml. In the presence of NAC, cells are partially protected from CdS QDs, but not from microsized particles. Additionally, nearly 20% of cadmium was released from CdS nanoparticles within 24h, which also accounts for QDs' toxicity.

CONCLUSION

Intracellular ROS production, GSH depletion, and cadmium ions (Cd(2+)) release are possible mechanisms for CdS QDs' cytotoxicity. We also suggested that with QD concentration increasing, the principal toxicity mechanism changes from intracellular oxidative stress to Cd(2+) release.

Dimethylarginine dimethylaminohydrolase regulation: a novel therapeutic target in cardiovascular disease

Asymmetric dimethylarginine (ADMA), an endogenous methylated form of the amino acid L-arginine, inhibits the activity of the enzyme endothelial nitric oxide synthase, with consequent reduced synthesis of nitric oxide. ADMA is metabolised to L-citrulline and dimethylamine by the enzyme dimethylarginine dimethylaminohydrolase (DDAH). The modulation of DDAH activity and expression plays a pivotal role in regulating intracellular ADMA concentrations, with important effects on vascular homeostasis. For example, impairment in DDAH activity, resulting in elevated ADMA concentrations and reduced nitric oxide synthesis, can promote the onset and progression of atherosclerosis in experimental models. This review discusses the current role of ADMA and DDAH in vascular health and disease, the techniques used to assess DDAH activity and expression, and the results of recent studies on pharmacological and biological agents modulating DDAH activity and expression. Suggestions for future basic and clinical research directions are also discussed.

The aggravatory effect of nicotine on Helicobacter pylori-induced gastric mucosa injury: role of asymmetric dimethylarginine

BACKGROUND AND GOAL

Nitric oxide (NO) is a well-known gastric mucosa protection factor. Recently, it has been reported that methylated arginine compound such as asymmetric dimethylarginine (ADMA), which inhibits nitric oxide synthesis, may be related to the development of gastric mucosa injury in patients with Helicobacter pylori infection. In the present study, we tested the relationship between endogenous ADMA and gastric mucosa injury in H. pylor- infected patients and cultured gastric epithelial cells.

METHODS

One hundred and fifty subjects with gastric diseases were entered in this study. The levels of ADMA in gastric juice and plasma were measured in both H. pylori+ and H. pylori- patients. We analyzed independent risk factors that contribute to ADMA levels by multiple linear regression analyses. Mucosal epithelium cells were treated with nicotine (10 microM) for 24 hours in the presence or absence of H. pylori. The concentrations of ADMA in the culture medium and the rate of cell apoptosis were determined.

RESULTS

The ADMA level in gastric juice was significantly increased in H. pylori+ patients (P<0.05), whereas there were no differences in the content of ADMA in the plasma between H. pylori+ patients and H. pylori- patients. Smoking and H. pylori infection were 2 independent risk factors contributing to ADMA levels, and in the population of H. pylori+ patients, the level of ADMA in smokers was higher compared with nonsmokers. Incubation of nicotine (10 microM) with epithelial cells for 24 hours further increased the elevated level of ADMA and the rate of cell apoptosis owing to H. pylori infection.

CONCLUSIONS

H. pylori infection caused an increase of ADMA levels in gastric juice, which was aggravated by smoking. Endogenous ADMA may be an important factor contributing to gastric mucosa injury.

Protective effects of EPA and deleterious effects of DHA on eNOS activity in Ea hy 926 cultured with lysophosphatidylcholine

Oxidized low density lipoprotein (Ox-LDL) is a well-established risk factor in atherosclerosis and lysophosphatidylcholine (LysoPtdCho) is considered to be one of the major atherogenic component of Ox-LDL. The purpose of this work was to investigate the effects of two membrane n-3 long chain polyunsaturated fatty acids (n-3 PUFAs), EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) compared to n-6 PUFA, ARA (arachidonic acid), on the activation of endothelial NO synthase (eNOS) by histamine in Ea hy 926 endothelial cells incubated during 24 h in the presence or the absence of LysoPtdCho. DHA (50 muM) produced a ROS induction in cells and aggravated the LysoPtdCho-induced oxidative stress. It did not modify the basal eNOS activity but impaired the stimulation of eNOS induced by histamine and was unable to correct the deleterious effect of LysoPtdCho on histamine-stimulated eNOS activity or phosphorylation of Ser 1177. In contrast, EPA (90 muM) did not modify the ROS level produced in the presence or absence of LysoPtdCho or basal eNOS activity and the stimulating effect of histamine on eNOS. However, it diminished the deleterious effect of LysoPtdCho as well as on the histamine-stimulated eNOS activity on the phosphorylation on Ser 1177 of eNOS. The beneficial effect of EPA but not DHA on endothelial eNOS activity in Ea hy 926 could be also partially due to a slight decrease in membrane DHA content in EPA-treated cells. Consequently, the equilibrium between NO generated by eNOS and ROS due to oxidative stress could explain, in part, the beneficial effect of EPA on the development of cardiovascular diseases. By contrast ARA an n-6 PUFA was devoid of any effect on ROS generation or eNOS activity in the basal state or after histamine-induced stimulation. In vivo experiments should be undertaken to confirm these results.

Methed-up FOXOs can't in-Akt-ivate

In this issue of Molecular Cell, Yamagata et al. (2008) identify a role for the protein methyltransferase, PRMT1, in Akt-dependent regulation of the FOXO1 transcription factor and demonstrate another level of control in this critical metabolic and cell survival signaling pathway.

Down-regulation of endogenous nitric oxide synthase inhibitors on endothelial SK3 expression

OBJECTIVES

To investigate role of endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) in down-regulation of the expression of endothelial SK3 in atherosclerosis.

METHODS

Apolipoprotein E deficient (apo E(-/-)) mice aged 11 approximately 12 weeks were treated with ADMA (5 mg/kg per day, subcutaneous injection) for 4 weeks. Cultured human umbilical venous endothelial cells (HUVECs) were treated with different concentrations of lysophosphatidylcholine (LPC) or ADMA for 48 h. Plasma levels of ADMA were determined by high performance liquid chromatogram (HPLC); protein and mRNA levels of SK3 in the aortas of mice and cultured cells were detected by immunofluorescence, western blot and RT-PCR, respectively.

RESULTS

Concomitantly with the elevated plasma levels of ADMA, the expressions of both SK3 protein and mRNA in aortas of apo E(-/-) mice were significantly reduced in comparison to those of the wild-type mice. Moreover, 4-week treatment of ADMA made levels of SK3 expression even lower. In cultured HUVECs, either LPC or ADMA notably decreased the expressions of both SK3 protein and mRNA in a concentration dependent manner.

CONCLUSIONS

Endogenous ADMA may be an important factor for down-regulation of the expression of endothelial SK3 in atherosclerotic animals.

Dimethylarginine dimethylaminohydrolase (DDAH): expression, regulation, and function in the cardiovascular and renal systems

Asymmetric (N(G),N(G))-dimethylarginine (ADMA) inhibits nitric oxide (NO) synthases (NOS). ADMA is a risk factor for endothelial dysfunction, cardiovascular mortality, and progression of chronic kidney disease. Two isoforms of dimethylarginine dimethylaminohydrolase (DDAH) metabolize ADMA. DDAH-1 is the predominant isoform in the proximal tubules of the kidney and in the liver. These organs extract ADMA from the circulation. DDAH-2 is the predominant isoform in the vasculature, where it is found in endothelial cells adjacent to the cell membrane and in intracellular vesicles and in vascular smooth muscle cells among the myofibrils and the nuclear envelope. In vivo gene silencing of DDAH-1 in the rat and DDAH +/- mice both have increased circulating ADMA, whereas gene silencing of DDAH-2 reduces vascular NO generation and endothelium-derived relaxation factor responses. DDAH-2 also is expressed in the kidney in the macula densa and distal nephron. Angiotensin type 1 receptor activation in kidneys reduces the expression of DDAH-1 but increases the expression of DDAH-2. This rapidly evolving evidence of isoform-specific distribution and regulation of DDAH expression in the kidney and blood vessels provides potential mechanisms for nephron site-specific regulation of NO production. In this review, the recent advances in the regulation and function of DDAH enzymes, their roles in the regulation of NO generation, and their possible contribution to endothelial dysfunction in patients with cardiovascular and kidney diseases are discussed.

Plasma adhesion and inflammation markers: asymmetrical dimethyl-L-arginine and secretory phospholipase A2 concentrations before and after laparoscopic gastric banding in morbidly obese patients

BACKGROUND

The aim of this study was to examine the relationship between subclinical inflammation and weight loss by laparoscopic adjustable gastric banding (LAGB).

METHODS

Plasma concentrations of intercellular adhesion molecule-1 (ICAM-1), vascular adhesion molecule-1 (VCAM-1), sensitive C-Reactive Protein (sCRP), asymmetrical dimethyl-L-arginine (ADMA), Secretory Phospholipase A2 (sPLA2), and metabolic markers, such as homeostatic model assessment insulin resistance (HOMA-IR) and body mass index (BMI) were determined in morbidly obese patients (n=18, BMI 48.6 +/- 1.7 kg/m2) at baseline and 1 month after operations. Baseline levels in patients were also compared with age-matched controls (n=20, BMI 21.3 +/- 1.8 kg/m2). Plasma ICAM-1, VCAM, sCRP and ADMA, and sPLA2 concentrations were determined by enzyme-linked immunoassay methods and colorimetric method, respectively.

RESULTS

Plasma sCRP, ICAM-1, ADMA and sPLA2 concentrations and HOMA-IR were significantly higher in morbidly obese patients than in controls (for each, P<0.01). Plasma VCAM-1 concentration was not changed in obese patients. HOMA-IR was significantly correlated with ICAM-1, ADMA and sPLA2 in the obese group at baseline (for each, P<0.01). There was a significant correlation between plasma sCRP and plasma glucose, VCAM-1, ICAM-1, ADMA and sPLA2 concentrations (for each, P<0.01). 1 month after LAGB, mean body weight loss was 13.2 +/- 6.3 kg, and plasma sCRP and ADMA concentrations and HOMA-IR and BMI were significantly decreased (for each, P<0.01). However, these levels cannot be decreased to the levels of the controls.

CONCLUSION

Obesity and insulin resistance appear to be associated with low-grade inflammation and endothelial dysfunction. Insulin resistance and endothelial dysfunction were improved by weight loss after LAGB.

The inhibitory effect of simvastatin on the ADMA-induced inflammatory reaction is mediated by MAPK pathways in endothelial cells

Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide synthase, is emerging as a key contributor for endothelial dysfunction associated with inflammation. Statins can inhibit vascular inflammatory reaction and improve endothelial function. The aim of this study was to investigate in human endothelial cells the signaling pathways of ADMA-induced inflammatory reaction and potential inhibitory effects of simvastatin. Endothelial cells were cultured and used for all of the studies. Tumor necrosis factor-alpha(TNF-alpha) and soluble intercellular adhesion molecule-1 (sICAM-1) were determined by enzyme-linked immunosorbent assay. Nuclear factor-kappaB (NF-kappaB) was assayed by electrophoretic mobility shift assay. The activation of mitogen-activated protein kinases (MAPKs), including p38 MAPK and extracellular signal-related kinase (ERK(1/2)), were characterized by Western blot analysis. Treatment with ADMA (3-30 micromol/L) increased the concentration of sICAM-1 in a dose-dependent manner. ADMA (30 micromol/L) significantly enhanced the concentrations of TNF-alpha and sICAM-1, the activity of NF-kappaB and the phosphorylation of p38 MAPK and ERK(1/2). The increased secretion of TNF-alpha and sICAM-1 and the increased activity of NF-kappaB by ADMA were altered by SB203580 (5 micromol/L) or PD98059 (20 micromol/L), but not by LY294002 (20 micromol/L). Simvastatin (0.1, 0.5, or 2.5 micromol/L) markedly inhibited the elevated concentrations of TNF-alpha and sICAM-1, the activity of NF-kappaB, and the phosphorylation of p38 MAPK and ERK(1/2) induced by ADMA. Simvastatin inhibited ADMA-induced inflammatory reaction by p38 MAPK and ERK(1/2) pathways in cultured endothelial cells.

Reduction of asymmetric dimethylarginine involved in the cardioprotective effect of losartan in spontaneously hypertensive rats

Previous studies have indicated that nitric oxide synthase (NOS) inhibitors can induce an increase of blood pressure and exacerbate myocardial injury induced by ischemia and reperfusion, whereas angiotensin II receptor antagonists protect the myocardium against injury induced by ischemia and reperfusion. Isolated hearts from male spontaneously hypertensive rats (SHR) or male Wistar-Kyoto rats (WKY) were subjected to 20 min global ischemia and 30 min reperfusion. Heart rate, coronary flow, left ventricular pressure, and its first derivatives (±dP/dtmax) were recorded, and serum concentrations of asymmetric dimethylarginine (ADMA) and NO and the release of creatine kinase in coronary effluent were measured. The level of ADMA was significantly increased and the concentration of NO was decreased in SHR. Ischemia and reperfusion significantly inhibited the recovery of cardiac function and increased the release of creatine kinase, and ischemia and reperfusion-induced myocardial injury in SHR was aggravated compared with WKY. Vasodilation responses to acetylcholine of aortic rings were decreased in SHR. Treatment with losartan (30 mg/kg) for 14 days significantly lowered blood pressure, elevated the plasma level of NO, and decreased the plasma concentration of ADMA in SHR. Treatment with losartan significantly improved endothelium-dependent relaxation and cardiac function during ischemia and reperfusion in SHR. Exogenous ADMA also aggravated myocardial injury induced by ischemia and reperfusion in isolated perfused heart of WKY, as shown by increasing creatine kinase release and decreasing cardiac function. The present results suggest that the protective effect of losartan on myocardial injury induced by ischemia and reperfusion is related to the reduction of ADMA levels.

Decrease in endogenous CGRP release in nitroglycerin tolerance: role of ALDH-2

In the present study, we tested whether the decreased release of calcitonin gene-related peptide (CGRP) observed in nitroglycerin tolerance is associated with the decrease in aldehyde dehydrogenase (ALDH-2) activity. We further investigated the possible involvement of reactive oxygen species in the decrease in ALDH-2 activity. Tolerance was induced by exposure of isolated rat thoracic aortas and human umbical vein endothelial cells (HUVEC) to nitroglycerin in vitro or by pretreatment with nitroglycerin for 8 days in vivo. Pretreatment with ALDH-2 inhibitors and nitroglycerin significantly attenuated vasodilator responses to nitroglycerin concomitantly with a decrease in the release of CGRP from the isolated thoracic aorta. Nitroglycerin produced a depressor effect concomitantly with an increase in plasma concentrations of CGRP, and the effect of nitroglycerin was attenuated after pretreatment with an inhibitor of ALDH-2 or nitroglycerin for 8 days. Exposure of HUVEC to nitroglycerin for 16 h increased reactive oxygen species production and decreased ALDH-2 activity as well as cGMP production in a time-and concentration-dependent manner. Pretreatment with an ALDH-2 inhibitor also significantly decreased the cGMP production. However, tolerance to nitroglycerin in HUVEC was restored in the presence of N-acetylcysteine or captopril. The present results suggest that nitrate tolerance is, at least partially, associated with a decrease in endogenous CGRP release via a decrease in ALDH-2 activity as a result of stimulation of reactive oxygen species production.

Uncomplicated type 1 diabetes is associated with increased asymmetric dimethylarginine concentrations

CONTEXT

Asymmetric dimethylarginine (ADMA) has recently emerged as an independent risk marker for cardiovascular disease, but studies investigating the ADMA levels in type 1 diabetes mellitus (DM) are scarce.

OBJECTIVE

We aimed to evaluate plasma ADMA, L-arginine concentrations, and L-arginine to ADMA ratio in uncomplicated type 1 diabetic patients and controls.

DESIGN AND SUBJECTS

Forty patients with type 1 DM who did not have clinical evidence of vascular complications and 35 healthy controls were included in the study.

RESULTS

Plasma ADMA concentrations were higher (2.6 +/- 1.9 vs. 1.7 +/- 0.7 micromol/liter, P < 0.01), and L-arginine levels were lower (79.3 +/- 22.6 vs. 89.6 +/- 19.4 micromol/liter, P < 0.05) in the diabetic group, compared with controls. The L-arginine to ADMA ratio was also lower in the diabetic group (38.7 +/- 17.1 vs. 62.0 +/- 27.9, P < 0.0001). In diabetic patients, logADMA correlated positively with body mass index (BMI) (P = 0.01), fasting blood glucose (P = 0.006), and low-density lipoprotein cholesterol (LDL-c) (P = 0.01) and negatively with high-density lipoprotein cholesterol (P = 0.03). L-arginine to ADMA ratio correlated negatively with BMI (P = 0.004), fasting blood glucose (P = 0.02), and LDL-c (P = 0.01) and positively with high-density lipoprotein cholesterol (P = 0.04). In controls, logADMA and L-arginine to ADMA ratio correlated with BMI and LDL-c (P < 0.05). In regression analysis, BMI predicted 15% variance of ADMA levels (P = 0.02).

CONCLUSIONS

We demonstrated that ADMA increases and L-arginine to ADMA ratio decreases, even before the development of vascular complications in type 1 DM.

Effect of asymmetric dimethylarginine on atherogenesis and erythrocyte deformability in apolipoprotein E deficient mice

Previous investigations have shown that the level of asymmetric dimethylarginine (ADMA) was increased in hypercholesterolemic animal and humans, and the decreased erythrocyte deformability has been suggested to be a factor contributing to atherogenesis. In the present study, we investigated the effect of ADMA, endogenous or exogenous, on atherogenesis and erythrocyte deformability in apolipoprotein E deficient (ApoE-/-) mice. On a regular chow diet, ApoE-/- mice or C57BL/6 J mice at 12 weeks of age were treated with ADMA (5 mg/kg/day) for 4 weeks. Atherosclerotic lesion area, erythrocyte deformability, plasma lipids and asymmetric dimethylarginine (ADMA) level were determined. Plasma concentrations of triglyceride (TG), low-density lipoprotein-cholesterol (LDL-C), total cholesterol (TC), ADMA, and atherosclerotic lesion area were significantly increased, and the level of plasma high-density lipoprotein-cholesterol (HDL-C), erythrocyte deformability in ApoE-/- mice were markedly decreased compared with that of C57BL/6J mice (P<0.05 or P<0.01). Exogenous ADMA treatment increased the plasma TG level, produced atherosclerotic lesions, and decreased erythrocyte deformability in C57BL/6J mice (P<0.05 or P<0.01). Treatment with exogenous ADMA further increased the plasma TG level and lesion areas, and decreased erythrocyte deformability in ApoE-/- mice. In vitro, exogenous ADMA caused a decrease of erythrocyte deformability in a concentration-dependent manner, and the effect of ADMA was reversed by L-arginine. The present results suggest that endogenous ADMA is an important contributor to the development of atherosclerosis and that reduction of erythrocyte deformability and impaired endothelial function induced by ADMA may be an important factor facilitating atherosclerotic lesions.

Upregulation of endothelial adhesion molecules by lysophosphatidylcholine. Involvement of G protein-coupled receptor GPR4

Lysophosphatidylcholine induces expression of adhesion molecules; however, the underlying molecular mechanisms of this are not well elucidated. In this study, the intracellular signaling by which lysophosphatidylcholine upregulates vascular cell adhesion molecule-1 and P-selectin was delineated using YPEN-1 and HEK293T cells. The results showed that lysophosphatidylcholine dose-dependently induced expression of vascular cell adhesion molecule-1 and P-selectin, accompanied by the activation of transcription factor nuclear factor kappaB. However, the nuclear factor kappaB inhibitor caffeic acid phenethyl ester (CAPE) and the antioxidant N-acetylcysteine only partially blocked lysophosphatidylcholine-induced adhesion molecules. Subsequently, we found that the lysophosphatidylcholine receptor G protein-coupled receptor 4 (GPK4) was expressed in YPEN-1 cells and triggered the cAMP/protein kinase A/cAMP response element-binding protein pathway, resulting in upregulation of adhesion molecules. Further evidence showed that overexpression of human GPK4 enhanced lysophosphatidylcholine-induced expression of adhesion molecules in YPEN-1 cells, and enabled HEK293T cells to express adhesion molecules in response to lysophosphatidylcholine. In conclusion, the current study suggested two pathways by which lysophosphatidylcholine regulates the expression of adhesion molecules, the lysophosphatidylcholine/nuclear factor-kappaB/adhesion molecule and lysophosphatidylcholine/GPK4/cAMP/protein kinase A/cAMP response element-binding protein/adhesion molecule pathways, emphasizing the importance of the lysophosphatidylcholine receptor in regulating endothelial cell function.

Asymmetric dimethylarginine (ADMA) in the aqueous humor of diabetic patients

Asymmetric dimethylarginine (ADMA) is an endogenous NO synthase (NOS) inhibitor whose production is enhanced by oxidative stress. Recent studies have shown that ADMA may also directly stimulate the production of reactive oxygen species (ROS) by up-regulation of the renin-angiotensin system independently of NOS inhibition. In this study, to investigate the clinical association of ADMA with diabetic retinopathy, we evaluated the levels of ADMA and NO oxides (NO2- and NO3-) in serum and aqueous humor obtained during cataract surgery from non-diabetic subjects (n = 21) and diabetic patients (n = 17). We found that the ADMA existed in aqueous humor and its level was similar to that in serum. The ADMA levels in both serum and aqueous humor were higher in diabetic patients, especially those with severe retinopathy, than in the non-diabetic group (serum ADMA: 0.67 +/- 0.26 vs. 0.53 +/- 0.08 micromol/l, p<0.05; aqueous humor ADMA: 0.55 +/- 0.20 vs. 0.32 +/- 0.16 micromol/l, p<0.05). Also, the aqueous humor level of ADMA, but not the serum level, was correlated with HbA1c on analysis of all the patients (R = 0.33, p<0.05 by simple regression analysis). However, a correlation between the ADMA levels in serum and aqueous humor was not observed in either the non-diabetic group or the diabetic group. Furthermore, serum and aqueous humor levels of NOx did not differ between the two groups, and no correlation with ADMA levels was observed in either group. These results suggest that ROS production may be enhanced in the eyes of diabetics. Since ADMA may act to potentiate ROS production independently of its inhibition of NOS, further investigation is required to clarify the possible contribution of ADMA to the development or progression of retinopathy.

Inflammation is an important determinant of levels of the endogenous nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) in acute liver failure

Acute liver failure (ALF) is characterized by rapid progressive organ failure and poor outcome. The pathophysiology of multiorgan dysfunction in ALF remains unclear but increased systemic inflammatory response is believed to be an important determining factor. Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase inhibitor, results from proteolysis and the liver is a major site for its metabolism. ADMA has been shown to independently predict outcome in multiorgan failure associated with severe liver dysfunction. In this study, we tested the hypothesis that proinflammatory cytokine driven responses are important in modulating ADMA levels in patients with acetaminophen-induced ALF. Blood samples were collected from 10 ALF patients (grade IV encephalopathy) from admission until the time of transplantation or death, and assayed for cytokines and ADMA. A total of 8 patients required treatment for raised intracranial pressure and all patients were managed with standard of care, including full mechanical ventilation and veno-venous hemofiltration. ADMA levels were markedly higher in ALF patients compared to age-matched controls (P < 0.001) and correlated with the levels of proinflammatory cytokines. In pretransplantation patients undergoing hepatic venous catheterization, we demonstrated no significant uptake of ADMA across the failing liver. However, following liver transplantation, ADMA levels reduced acutely. A timed study of ADMA levels during transplantation demonstrated a slight increase during the anhepatic phase but a marked and sustained reduction in ADMA following liver reperfusion. In conclusion, our data show a significant correlation between ADMA levels and proinflammatory cytokines, supporting a hypothesis that proinflammatory cytokines may regulate ADMA metabolism in ALF.

Role of nitric oxide-producing and -degrading pathways in coronary endothelial dysfunction in chronic kidney disease

Cardiovascular events are accelerated in chronic kidney disease (CKD). Although deranged nitric oxide (NO) pathways and asymmetric dimethylarginine (ADMA) cause endothelial dysfunction, no direct evidence for coronary artery endothelial dysfunction in CKD has been documented. CKD was induced in male dogs by heminephrectomy (1/2Nx) or five-sixths nephrectomy (5/6Nx). After 4 wk, renal ablation reduced GFR (control 76 [54 to 85]; 1/2Nx 38 [29 to 47]; 5/6Nx 15 [12 to 46] ml/min) and elevated plasma ADMA (control 1.88 [1.68 to 2.54]; 1/2Nx 2.51 [2.11 to 3.55]; 5/6Nx 3.84 [2.16 to 3.95] micromol/L). Coronary circulatory responses to acetylcholine revealed marked increases in coronary blood flow in control group (83 +/- 17% increment) but blunted responses in 1/2Nx (34 +/- 8% increment) and 5/6Nx (20 +/- 4% increment). The acetylcholine-induced changes in epicardial arteriolar diameter, using needle-lens probe charge-coupled device videomicroscopy, showed similar results. The responsiveness to sodium nitroprusside did not differ among three groups. Plasma nitrite/nitrate levels decreased in 1/2Nx and 5/6Nx, and the mRNA expressions of dimethylarginine dimethylaminohydrolase-II (DDAH-II), ADMA-degrading enzyme, and endothelial NO synthase (eNOS) in coronary arteries were downregulated in 1/2Nx and 5/6Nx. Finally, 4-wk treatment with all-trans retinoic acid restored the impaired endothelium-dependent vasodilation and reversed the expression of eNOS but not DDAH-II. Coronary endothelial function is impaired in the early stage of CKD. The dysfunction is attributed to the downregulation of eNOS and/or DDAH-II in coronary arteries. Furthermore, the manipulation of NO pathways may constitute a therapeutic strategy for the prevention of coronary dysfunction in CKD.