Modulation of vascular tone by low density lipoproteins: effects on L-arginine transport and nitric oxide synthesis

Associations of endothelial biomarkers, nitric oxide metabolites and endothelin, with blood pressure and coronary lesions depend on cardiovascular risk and sex to mark endothelial dysfunction on the SCORE scale

OBJECTIVES

Endothelial dysfunction contributes to the onset and progression of cardiovascular diseases. However, direct associations of vasoactive mediators with cardiovascular risk are poorly understood.

METHODS

We have determined associations of circulating levels of stable metabolites of nitric oxide, nitrate and nitrite (NOx), endothelin-1, and the endothelin-1/NOx ratio with blood pressure in 177 asymptomatic subjects without signs of coronary atherosclerosis; associations with blood pressure and with presence of coronary lesions were also evaluated in 457 patients suspected to have coronary heart disease with or without coronary lesions confirmed by coronary angiography. All participants were on a low nitrate diet 24 h prior to blood sampling.

RESULTS

In men, NOx levels were inversely correlated with blood pressure similar to women with low (0-4%) European Systematic Coronary Risk Estimation (SCORE). However, the correlation was not significant in women with high SCORE (5-8%). High systolic blood pressure over 140 mm Hg was negatively associated with NOx levels in asymptomatic men (p=0.05) but not in women. This association is disrupted in male and female patients with coronary atherosclerosis. In male patients, NOx (p=0.05), endothelin (p=0.01), and the endothelin/NOx ratio (p=0.04) were associated with presence of coronary lesions.

CONCLUSIONS

Thus, elevated cardiovascular risk according to SCORE over 4% in asymptomatic women, but not in men, is associated with a shift in markers of endothelial dysfunction. Presence of coronary lesions in patients is associated with significant changes in circulating levels of markers of endothelial dysfunction in men but not in women.

Essential hypertension: A filtered serum based metabolomics study

Despite the easy and reliable methods of blood pressure measurement, the screening of essential hypertension (EH) is usually ignored due to delayed onset of symptoms. A probe into the biochemical changes in hypertension would serve as a welcome asset to provide insight into the mechanistic aspects of EH. Filtered serum samples from 64 EH patients and 59 healthy controls (HC) were analysed using 800 MHz nuclear magnetic resonance (NMR) spectroscopy. Application of principal component analysis (PCA) and orthogonal partial least-squares discriminant analysis (OPLS-DA) following receiver operating characteristic (ROC) curve of NMR data reveals significantly perturbed metabolites: alanine, arginine, methionine, pyruvate, adenine, and uracil. This set of metabolites correctly classified 99% of cases from HC and also showed excellent correlation in both isolated elevated diastolic blood pressure (DBP) cases and combined elevated systolic-diastolic blood pressure cases. Proton NMR metabolomics of EH may prove helpful in defining associated biomarkers and serve as an alternate diagnostic tool with judicious clinical assessment.

Regulation of thrombomodulin expression and release in human aortic endothelial cells by cyclic strain

Background and Objectives

Thrombomodulin (TM), an integral membrane glycoprotein expressed on the lumenal surface of vascular endothelial cells, promotes anti-coagulant and anti-inflammatory properties. Release of functional TM from the endothelium surface into plasma has also been reported. Much is still unknown however about how endothelial TM is regulated by physiologic hemodynamic forces (and particularly cyclic strain) intrinsic to endothelial-mediated vascular homeostasis.

Methods

This study employed human aortic endothelial cells (HAECs) to investigate the effects of equibiaxial cyclic strain (7.5%, 60 cycles/min, 24 hrs), and to a lesser extent, laminar shear stress (10 dynes/cm², 24 hrs), on TM expression and release. Time-, dose- and frequency-dependency studies were performed.

Results

Our initial studies demonstrated that cyclic strain strongly downregulated TM expression in a p38- and receptor tyrosine kinase-dependent manner. This was in contrast to the upregulatory effect of shear stress. Moreover, both forces significantly upregulated TM release over a 48 hr period. With continuing focus on the cyclic strain-induced TM release, we noted both dose (0–7.5%) and frequency (0.5–2.0 Hz) dependency, with no attenuation of strain-induced TM release observed following inhibition of MAP kinases (p38, ERK-1/2), receptor tyrosine kinase, or eNOS. The concerted impact of cyclic strain and inflammatory mediators on TM release from HAECs was also investigated. In this respect, both TNFα (100 ng/ml) and ox-LDL (10–50 µg/ml) appeared to potentiate strain-induced TM release. Finally, inhibition of neither MMPs (GM6001) nor rhomboids (3,4-dichloroisocoumarin) had any effect on strain-induced TM release. However, significantly elevated levels (2.1 fold) of TM were observed in isolated microparticle fractions following 7.5% strain for 24 hrs.

Conclusions

A preliminary in vitro investigation into the effects of cyclic strain on TM in HAECs is presented. Physiologic cyclic strain was observed to downregulate TM expression, whilst upregulating in a time-, dose- and frequency-dependent manner the release of TM.

Effects of endogenous regulators of endothelial NO synthase on nitric oxide homeostasis and blood serum lipoproteins during experimental diabetes mellitus

Experimental diabetes mellitus was associated with the development of oxidative stress and a decrease in blood concentration of total nitric oxide (NO) metabolites. Administration of L-arginine induced positive changes in the LPO-antioxidant enzyme system and elevated NO concentration in blood serum, whereas L-NAME, inhibitor of eNOS (NOS-III) increased LPO intensity via SOD inhibition and reduced NO content. Combined administration of Q10 and L-arginine led the suppression of oxidative stress and significant increase in NO level. Combined treatment with Q10 and L-NAME partly abolished the effects of the inhibitor on the parameters of the LPO-antioxidant enzyme system and NO concentration. In all variants of the study, Q10 stimulated eNOS expression and increases NO bioavailability by reducing the levels of total cholesterol and LDL and increasing HDL content in blood serum.

Fetoplacental vascular endothelial dysfunction as an early phenomenon in the programming of human adult diseases in subjects born from gestational diabetes mellitus or obesity in pregnancy

Gestational diabetes mellitus (GDM) and obesity in pregnancy (OP) are pathological conditions associated with placenta vascular dysfunction coursing with metabolic changes at the fetoplacental microvascular and macrovascular endothelium. These alterations are seen as abnormal expression and activity of the cationic amino acid transporters and endothelial nitric oxide synthase isoform, that is, the "endothelial L-arginine/nitric oxide signalling pathway." Several studies suggest that the endogenous nucleoside adenosine along with insulin, and potentially arginases, are factors involved in GDM-, but much less information regards their role in OP-associated placental vascular alterations. There is convincing evidence that GDM and OP prone placental endothelium to an "altered metabolic state" leading to fetal programming evidenced at birth, a phenomenon associated with future development of chronic diseases. In this paper it is suggested that this pathological state could be considered as a metabolic marker that could predict occurrence of diseases in adulthood, such as cardiovascular disease, obesity, diabetes mellitus (including gestational diabetes), and metabolic syndrome.

Postprandial hyperglycemia impairs vascular endothelial function in healthy men by inducing lipid peroxidation and increasing asymmetric dimethylarginine:arginine

Postprandial hyperglycemia induces vascular endothelial dysfunction (VED) and increases future cardiovascular disease risk. We hypothesized that postprandial hyperglycemia would decrease vascular function in healthy men by inducing oxidative stress and proinflammatory responses and increasing asymmetric dimethylarginine:arginine (ADMA:arginine), a biomarker that is predictive of reduced NO biosynthesis. In a randomized, cross-over design, healthy men (n = 16; 21.6 ± 0.8 y) ingested glucose or fructose (75 g) after an overnight fast. Brachial artery flow-mediated dilation (FMD), plasma glucose and insulin, antioxidants, malondialdehyde (MDA), inflammatory proteins, arginine, and ADMA were measured at regular intervals during the 3-h postprandial period. Baseline FMD did not differ between trials (P > 0.05). Postprandial FMD was reduced following the ingestion of glucose only. Postprandial MDA concentrations increased to a greater extent following the ingestion of glucose compared to fructose. Plasma arginine decreased and the ratio of ADMA:arginine increased to a greater extent following the ingestion of glucose. Inflammatory cytokines and cellular adhesion molecules were unaffected by the ingestion of either sugar. Postprandial AUC(0-3 h) for FMD and MDA were inversely related (r = -0.80; P < 0.05), suggesting that hyperglycemia-induced lipid peroxidation suppresses postprandial vascular function. Collectively, these findings suggest that postprandial hyperglycemia in healthy men reduces endothelium-dependent vasodilation by increasing lipid peroxidation independent of inflammation. Postprandial alterations in arginine and ADMA:arginine also suggest that acute hyperglycemia may induce VED by decreasing NO bioavailability through an oxidative stress-dependent mechanism. Additional work is warranted to define whether inhibiting lipid peroxidation and restoring arginine metabolism would mitigate hyperglycemia-mediated decreases in vascular function.

The influence of short-term L-arginine supplementation on rats' muscular and hepatic cells in ischemia-reperfusion syndrome

Due to the complex mechanisms of L-arginine activity, it is difficult to determine the clinical significance of supplementation with this amino acid. The objective of this study was to determine the influence of short-term supplementation with L-arginine in stress conditions, induced by ischemia-reperfusion syndrome, by assessing the damage to muscular and hepatic cells on the basis of creatine kinase (CK), alanine aminotransferase (ALAT) and aspartic aminotransferase (AspAT) activity in blood and the level of oxygen free radicals in analyzed tissues of rats. We observed that induced ischemia of hind limb caused an increase in CK, ALAT and AspAT activity and an increase in the level of free radicals in liver, but not in skeletal muscle. Supplementation with L-arginine led to a reduction in serum activity of CK and AspAT and reduction of the level of free radicals in analysed tissues. Simultaneous supplementation with L -arginine AND L-NAME resulted in a reversal of changes induced by L-arginine supplementation in the case of AspAT and free radicals in skeletal muscle. The results indicate that under conditions of ischemia-reperfusion, short-term administration of L-arginine has a protective effect on skeletal muscle manifesting itself by reduction of CK in the serum and reduction of free radicals level in THIS tissue.

Prediction of diabetic retinopathy: role of oxidative stress and relevance of apoptotic biomarkers

Diabetic retinopathy (DR) is the foremost cause of blindness in working-aged worldwide; it is characterized by vascular and neuronal degeneration. Features of DR include leukocyte adhesion, increased vascular permeability, neovascularization and neuronal cell death. Early diagnosis and intervention are important to prevent or at least ameliorate the development of DR. Recent reports indicate that pathophysiological mechanisms leading to diabetic retinopathy include oxidative stress and retinal cell death cascades. Circulating biomarkers of oxidative stress such as malondialdehyde (MDA), thiobarbituric acid reacting substances (TBARS), conjugated diene (CD), advanced oxidation protein products (AOPP), protein carbonyl, 8-hydroxydeoxyguanosin (8-OHdG), nitrotyrosine, and F(2) isoprostanes and pro-apoptosis molecules (caspase-3, Fas, and Bax) are associated with increased susceptibility to develop DR in diabetic subjects. Thus, identification of oxidative stress and cell death biomarkers in diabetic patients could be in favor of predicting, diagnosis, and prevention of DR, and to target for novel therapeutic interventions.

Improvement of endothelial dysfunction in acromegaly after transsphenoidal surgery

Flow-mediated vasodilatation (FMD) is a vascular functional test to detect endothelial dysfunction at the early stage of cardiovascular diseases. Patients with active acromegaly have higher morbidity and mortality due to cardiovascular events. To determine whether active acromegaly is associated with endothelial dysfunction, we studied 17 patients with active acromegaly for measurements of FMD, carotid intima-media thickness (IMT) and brachial-ankle pulse wave velocity (baPWV), and other biochemical parameters before and 3 months after transsphenoidal surgery (TSS). Baseline %FMD in patients with active acromegaly was significantly lower than that in age- and sex-matched control subjects. After TSS, the mean %FMD in acromegaly significantly increased from 5.3% to 7.4%; 12 patients had increased %FMD (responders), whereas 5 patients had decreased or unchanged %FMD (non-responders). However, neither carotid IMT nor baPWV changed after TSS. Serum levels of GH, insulin-like growth factor (IGF)-1, total cholesterol, low-density lipoprotein cholesterol (LDL-C), hemoglobin HA(1C), fasting plasma glucose and insulin levels, and homeostasis model assessment (HOMA)-R significantly decreased, whereas high-density lipoprotein cholesterol significantly increased. Responders had significantly lower baseline %FMD than did non-responders and both insulin levels and HOMA-R significantly decreased in responders, but not in non-responders after TSS. Simple regression analysis revealed that the change of %FMD showed a significant negative correlation with that of LDL-C, but not of IGF-1 or GH, in responders. In conclusion, it is suggested that endothelial dysfunction associated with active acromegaly improves soon after TSS, which is related to LDL-C and/or insulin resistance, but not to excess GH and/or IGF-1 itself.

L-arginine and atherothrombosis

L-arginine, the principal substrate for endothelial nitric oxide synthase, is oxidized to L-citrulline and nitric oxide. Endothelial dysfunction is associated with decreased bioactive nitric oxide production, an abnormality observed in atherothrombosis. Acute or chronic administration of supplemental L-arginine enhances endothelial nitric oxide production and improves endothelial function in the setting of atherothrombosis. The mechanisms by which L-arginine improves endothelial nitric oxide bioactivity include increased intracellular uptake via the high-affinity cationic transporter; substrate competition with asymmetric dimethylarginine, a naturally occurring inhibitor of nitric oxide synthase; direct antioxidant activity; stimulated release of histamine from mast cells, which produces a vasodilator response; decreased activity of norepinephrine, which promotes the effect of endogenous vasodilators including nitric oxide; and increased insulin secretion, which causes vasodilation. By virtue of its link to methyl group metabolism, supplemental L-arginine can, however, also increase the production of S-adenosylhomocysteine from S-adenosylmethionine through the methylation-dependent generation of creatine from guanidinoacetate. This reaction can theoretically lead to increased homocysteine synthesis from its S-adenosyl derivative, which itself can have adverse effects on endothelial function. The interrelationships among these effects of L-arginine are reviewed here, and the potential benefits and risks of L-arginine supplementation are discussed.

In vivo and in vitro evidence for ACh-stimulated L-arginine uptake

Whereas L-arginine is clearly recognized as the precursor for nitric oxide synthesis, and its entry into endothelial cells via system y(+) transport is established, few data exist regarding the acute regulation of this transport process. We specifically investigated the effect of ACh and isoprenaline (Iso) on L-arginine uptake in the human forearm and in cultured bovine aortic endothelial cells (BAEC). Sixteen healthy males were studied. During a steady-state intra-arterial infusion of [(3)H]L-arginine (100 nCi/min), the effects of ACh (9.25 and 37 microg/min), Iso (25-50 and 200 microg/min), and sodium nitroprusside (SNP) (1-2 and 8 microg/min) on forearm plasma flow (FPF), L-[(3)H]arginine uptake, and L-[(3)H]citrulline release were determined. In parallel experiments, the effects of ACh, Iso, and SNP on L-[(3)H]arginine uptake were studied in BAEC. L-Arginine uptake was inversely related to FPF (r = -0.50; P < 0.005). At a similar FPF (ACh 56.82 +/- 9.25, Iso 58.49 +/- 5.56, SNP 57.92 +/- 4.96 ml/min; P = ns), intra-arterial ACh significantly increased forearm uptake of L-[(3)H]arginine (54,655 +/- 8,018 dpm/min), compared with that observed with either Iso (40,517.23 +/- 6,841 dpm/min; P = 0.01) or SNP (36,816 +/- 4,650 dpm/min; P = 0.011). This was associated with increased ACh-induced L-[(3)H]citrulline release compared with Iso and SNP (P = 0.046). Similarly, in BAEC, ACh significantly increased L-[(3)H]arginine uptake compared with control, Iso, or SNP (ACh 12.0 x 10(7) +/- 1.83 x 10(7) vs. control 6.67 x 10(7) +/- 1.16 x 10(7) vs. Iso 7.35 x 10(7) +/- 1.63 x 10(7) vs. SNP 6.01 x 10(7) +/- 1.11 x 10(7) fmol.min(-1).mg(-1) at 300 micromol/l L-arginine; P = 0.043). Taken together, these data indicate that ACh stimulates L-arginine uptake in cultured endothelial cells and in human forearm circulation, indicating the potential for acute modulation of endothelial L-arginine uptake.

Oxidized low-density lipoprotein activates migration and degranulation of human granulocytes

Oxidized low-density lipoprotein (oxLDL) has been reported as a major participant in the pathogenesis of atherosclerosis. We hypothesized that oxLDL can also interact with granulocytes during inflammatory airway diseases, such as asthma. To test the chemotactic effect of oxLDL, isolated human peripheral granulocytes were added to the upper chambers of Transwell filters and migration in response to oxLDL was determined. Cu+2-oxidized LDL stimulated neutrophil (23.4 +/- 3.2% for 100 microg/ml oxLDL versus 2.9 +/- 1.1% for buffer, P < 0.05) and eosinophil (19.3 +/- 3.5% versus 0.6 +/- 0.02% for buffer, P < 0.05) chemotaxis in a concentration-dependent manner. The magnitude of chemotaxis was dependent on the degree of LDL oxidation. Granulocyte transmigration across IL-1beta-activated human pulmonary microvascular endothelial cell monolayers was similarly stimulated by oxLDL. OxLDL activated significant degranulation of both neutrophils (100.9 +/- 9.8 versus 49.6 +/- 8.4 ng lactoferrin released/5 x 105 neutrophils for buffer, P < 0.05) and eosinophils (342 +/- 115.4 versus 85.8 +/- 30.4 ng eosinophil-derived neurotoxin/1 x 106 eosinophils for buffer, P < 0.05). Therefore, in vivo influx and oxidation of LDL may be an important mediator for the initiation of bronchial inflammation where granulocytes are recruited to the lung.

Pravastatin protection from cold stress in myocardium of rats

The aim of this research was to evaluate the possible protective effect of pravastatin on ultrastructural alterations induced by cold stress in the myocardium of rats. Sixteen EPM-Wistar rats (Rattus norvegicus albinus) were used and distributed into four groups: 1) control; 2) pravastatin; 3) cold stress, and 4) pravastatin + cold stress. A daily oral dose of 10 mg/kg of weight of pravastatin was administered to each rat in groups 2 and 4 for 15 days. The stress induced by cold was obtained by keeping the group 3 and 4 rats in a freezer at -8 degrees C for 4 hours. The animals were killed and the heart and fragments of the left ventricles (LV) were removed and processed prior to conducting electron microscopic analysis. The ultrastructural alterations in cardiomyocytes were quantified through the number of mitochondrial cristae pattern (cristalysis). The group subjected only to cold stress showed a significant increase in cristalysis (391.9) when compared with control group (42.0). In the cold stress and pravastatin pretreatment group, a statistically significant (96.9)*, P<0.05 cristalysis reduction was observed when compared with cold stress group. The mitochondrial cristalysis profiles of the control and pravastatin groups were 42.0 and 65.7, respectively. Cold stress induced a significant increase in the rate of mitochondrial cristalysis. In the group that received pravastatin and was exposed to cold stress, the drug protected the LV cardiomyocytes. This fact was confirmed by a reduction mitochondrial cristalysis pattern.

Regulation of amino acid and glucose transporters in endothelial and smooth muscle cells

While transport processes for amino acids and glucose have long been known to be expressed in the luminal and abluminal membranes of the endothelium comprising the blood-brain and blood-retinal barriers, it is only within the last decades that endothelial and smooth muscle cells derived from peripheral vascular beds have been recognized to rapidly transport and metabolize these nutrients. This review focuses principally on the mechanisms regulating amino acid and glucose transporters in vascular endothelial cells, although we also summarize recent advances in the understanding of the mechanisms controlling membrane transport activity and expression in vascular smooth muscle cells. We compare the specificity, ionic dependence, and kinetic properties of amino acid and glucose transport systems identified in endothelial cells derived from cerebral, retinal, and peripheral vascular beds and review the regulation of transport by vasoactive agonists, nitric oxide (NO), substrate deprivation, hypoxia, hyperglycemia, diabetes, insulin, steroid hormones, and development. In view of the importance of NO as a modulator of vascular tone under basal conditions and in disease and chronic inflammation, we critically review the evidence that transport of L-arginine and glucose in endothelial and smooth muscle cells is modulated by bacterial endotoxin, proinflammatory cytokines, and atherogenic lipids. The recent colocalization of the cationic amino acid transporter CAT-1 (system y(+)), nitric oxide synthase (eNOS), and caveolin-1 in endothelial plasmalemmal caveolae provides a novel mechanism for the regulation of NO production by L-arginine delivery and circulating hormones such insulin and 17beta-estradiol.

Oral L-arginine does not improve endothelial dysfunction in children with chronic renal failure

BACKGROUND

Cardiovascular disease is a major cause of mortality amongst patients with chronic renal failure (CRF). L-arginine has been used to improve endothelial function by increasing nitric oxide (NO) bioavailability and in animal models this in turn has attenuated the progression of atherosclerosis. We examined whether dietary L-arginine supplementation improved endothelial function in children with CRF.

METHODS

A randomized, double-blind, placebo-controlled, crossover trial of L-arginine was conducted in 21 normotensive children aged 11.5 +/- 3 (7 to 17) years with CRF (GFR 27.4 +/- 13.2 mL/min/1.73 m(2)) in whom endothelial dysfunction had previously been demonstrated. We examined the effect of L-arginineon the endothelial response to shear stress (NO-dependent) using a non-invasive technique of high-resolution ultrasound. Each subject was studied before and after 4 weeks of L-arginine (2.5 g/m(2) or 5 g/m(2) x 3/day) or placebo, separated by a rest period of 4 weeks. Brachial artery diameter was measured at rest, during increased flow (endothelial-dependent dilation) and after 25 microg of glyceryl trinitrate (endothelial-independent dilation) at each visit.

RESULTS

After oral L-arginine, plasma L-arginine levels rose from 82 +/- 20 to 179 +/- 110 micromol/L (P < 0.001). No significant change in endothelial-dependent dilation during L-arginine (7.96 +/- 2.35 to 7.71 +/- 3.22%; P> 0.05) or placebo (8.2 +/- 2.89 to 8.3 +/- 3.14%; P> 0.05) was noted. There was no change in endothelial-independent dilation.

CONCLUSION

Endothelial function was not improved with L-arginine, suggesting that dietary supplementation is not a useful clinical approach in children with CRF.

Role of selenium in cytoprotection against cholesterol oxide-induced vascular damage in rats

Wistar rats were fed Se-deficient (0.038 mg/kg diet) and adequate (0.326 mg/kg diet) diets for 13 weeks. The blood Se content, blood and vascular wall glutathione peroxidase (GPx) activity, serum high-density lipoprotein cholesterol (HDL-C) level and plasma prostacyclin (PGI(2)) concentration were decreased significantly, and the blood lipid peroxide (LPO) concentration, serum low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC) level and plasma thromboxane A(2) (TXA(2)), content were increased significantly in Se-deficient rats compared with Se-adequate group, respectively. Furthermore the Se-deficient and adequate rats were given 5 mg/kg of cholestane-3 beta, 5 alpha, 6 beta -triol (3-triol) or vehicle only. Twenty four hours after treatment, the plasma PGI(2) level was decreased in Se-adequate rats infused 3-triol (+3 triol), meanwhile, the level in Se- deficient +3-triol group was much lower than that in Se-adequate +3-triol group. Compared with Se-adequate group, plasma TXA(2) content in Se-adequate +3-triol group had no significantly difference, but in Se- deficient rats infused 3-triol, plasma TXA(2) content was much higher than that in Se-adequate +3-triol group. The plasma ET concentration in Se-deficient group decreased slightly, but the concentration in Se-adequate +3-triol group increased significantly with respect to Se-deficient group. Although plasma ET concentration in Se-deficient group +3-triol did not increase, it was significantly lower than that in Se-adequate +3-triol group. The luminal surfaces of aorta thoracica of experimental rats were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Observed by SEM, the luminal surface of aorta of Se-deficient rats showed few crater-like defects due to the disruption of endothelial cell. Se-adequate +3-triol group showed some crater-like defects on the their aorta luminal surface, but the luminal surface of Se-deficient +3-triol group exhibited numerous crater-like defects and appeared sponge-like as well as platelets adhering followed by thrombus formation in focal area of extensive endothelial damage. TEM studies also showed that the endothelium of aorta of Se deficient +3-triol group had more frequent lesion where endothelial cell plasma were swelling with profuse intracellular edema and some vacuoles were seen in cytoplasm. In severely injured areas, endothelial integrity was completely destroyed and smooth muscle cells were proliferating and migrated to the endomembrane. Thus, we can conclude that Se or selenoproteins in the vascular wall plays an important role in cytoprotection against cholesterol oxide-induced vascular damage in rats.

Effects of NO donors and synthase agonists on endothelial cell uptake of L-Arg and superoxide production

It is commonly believed that the activity of NO synthase (NOS) solely controls NO production from its substrates, L-Arg and O(2). The Michaelis-Menten constant (K(m)) of NOS for L-Arg is in the micromolar range; cellular levels of L-Arg are much higher. However, evidence strongly suggests that cellular supply of L-Arg may become limiting and lead to reduced NO and increased superoxide anion (O(-)(2)*) formation, promoting cardiovascular dysfunction. Uptake of L-Arg into cells occurs primarily (approximately 85%) through the actions of a Na(+)-independent, carrier-mediated transporter (system y(+)). We have examined the effects of NOS agonists (substance P, bradykinin, and ACh) and NO donors (S-nitroso-N-acetyl-penicillamine and dipropylenetriamine NONOate) on transport of L-Arg into bovine aortic endothelial cells (BAEC). Our results demonstrate that NOS agonists increase y(+) transporter activity. A rapidly acting NO donor initially increases L-Arg uptake; however, after longer exposure, L-Arg uptake is suppressed. Exposure of BAEC without L-Arg to substance P and a Ca(2+) ionophore (A-23187) increased O(-)(2)* formation, which was blocked with concurrent presence of L-Arg or the NOS antagonist N(omega)-nitro-L-arginine methyl ester. We conclude that factors including NO itself control y(+) transport function and the production of NO and O(-)(2)*.

Redox control of vascular nitric oxide bioavailability

NO is an important component of vascular homeostasis and abnormal NO bioactivity has been implicated in number of disease states with important public health implications. One clear mechanism of impaired NO bioactivity and vascular disease is excess vascular oxidative stress. There is now a wealth of developing data that manipulation of vascular antioxidant stress is the considerable influence of the biologic activity of endothelium-derived NO. It remains to be seen if this influence can be exploited in a manner that truly alters the course of human disease.

Induction of antioxidant stress proteins in vascular endothelial and smooth muscle cells: protective action of vitamin C against atherogenic lipoproteins

Elevated levels of lipid peroxidation and increased formation of reactive oxygen species within the vascular wall in atherosclerosis can overwhelm cellular antioxidant defence mechanisms. Accumulating evidence implicates oxidatively modified low density lipoproteins (LDL) in vascular dysfunction in atherosclerosis and oxidized LDL have been localized with in atherosclerotic lesions. We here report that human oxidatively modified LDL induce expression of 'antioxidant-like' stress proteins in vascular cells, involving increases in the activity of L-cystine transport, glutathione synthesis, heme oxygenase-1 and the murine stress protein MSP23. Moreover, treatment of human arterial smooth muscle cells with the dietary antioxidant vitamin C markedly attenuates adaptive increases in endogenous antioxidant gene expression and affords protection against smooth muscle cell apoptosis induced by moderately oxidized LDL. As vascular cell death is a key feature of atherosclerotic lesions and may contribute to the plaque 'necrotic' core, cap rupture and thrombosis, our findings suggest that the cytoprotective actions of vitamin C could limit plaque instability in advanced atherosclerosis.

Protective role of glutathione synthesis in response to oxidized low density lipoprotein in human vascular endothelial cells

Impairment of endothelial cells by oxidized low density lipoprotein (OxLDL) is believed to be the first step in atherogenesis. It is also believed that oxidative stress/antioxidant imbalance is involved in the cell damage by OxLDL. However, little is known about the interaction between OxLDL and antioxidants. In this study, we show that treatment of human vascular endothelial cells with OxLDL caused a gradual increase of glutathione (gamma-glutamylcysteinyl glycine, GSH) levels in 24 h. OxLDL increased the intracellular levels of reactive oxygen species (ROS) and stimulated the expression of gamma-glutamylcysteine synthetase (gamma-GCS), the rate-limiting enzyme for the GSH synthesis, the mitogen-activated protein kinase (MAPK) activity, and the AP-1-DNA binding activity. The luciferase activity of gamma-GCS promoter containing AP-1 site was activated by OxLDL. Collectively, OxLDL induces gamma-GCS expression mediated by AP-1 resulting in an increase of GSH levels. The MAPK activity stimulated by ROS may be involved in the activation of AP-1. The increase in GSH by OxLDL may afford cellular protection against OxLDL-induced oxidative stress.

Pravastatin sodium activates endothelial nitric oxide synthase independent of its cholesterol-lowering actions

OBJECTIVES

We tested the hypothesis that pravastatin (PRA) activates endothelial nitric oxide synthase (eNOS).

BACKGROUND

Pravastatin has been found to have clinical benefits beyond those predicted by its actions in reducing plasma low density lipoprotein cholesterol (LDL). Both PRA and simvastatin (SIM) are equally effective in reducing LDL, but only PRA reduces platelet aggregation and is an effective vasodilator. Nitric oxide (NO) also inhibits platelet aggregation and vasodilates.

METHODS

We determined PRA and SIM effects on vasorelaxation in aortic rings and NO production by cultured bovine aortic endothelial cells. Nitric oxide was measured by using a NO electrode and by an assay for conversion of hemoglobin to methemoglobin. Specificity of NOS activation was tested by using the NOS inhibitor nitro-L-arginine methyl ester (L-NAME, 1 mmol/liter) in the presence or absence of excess L-arginine (L-ARG, 1 mmol/liter).

RESULTS

Endothelium-dependent vasorelaxation was maximal with acetylocholine (ACH, 100%), followed by PRA (62.8%) and then SIM (37.1%). Direct measurement of NO confirmed that vasorelaxation is due to NO release and showed that PRA and ACH had similar dose-dependent effects on NO production, while SIM was only 25% to 30% as effective. Methemoglobin assay confirmed these results and demonstrated their specificity for NOS activity. The L-NAME blunted the responses to 45% of initial values. Excess L-ARG reversed this effect and potentiated NO production to 133% of initial levels.

CONCLUSIONS

Both PRA and SIM activate eNOS, but SIM is much less effective. Clinical benefits with PRA not explained by LDL reductions may be the result of an independent action of PRA on eNOS activation.

Nitrite and nitrate analyses: a clinical biochemistry perspective

OBJECTIVE

To review the assays available for measurement of nitrite and nitrate ions in body fluids and their clinical applications.

DESIGN AND METHODS

Literature searches were done of Medline and Current Contents to November 1997.

RESULTS

The influence of dietary nitrite and nitrate on the concentrations of these ions in various body fluids is reviewed. An overview is presented of the metabolism of nitric oxide (which is converted to nitrite and nitrate). Methods for measurement of the ions are reviewed. Reference values are summarized and the changes reported in various clinical conditions. These include: infection, gastroenterological conditions, hypertension, renal and cardiac disease, inflammatory diseases, transplant rejection, diseases of the central nervous system, and others. Possible effects of environmental nitrite and nitrate on disease incidence are reviewed.

CONCLUSIONS

Most studies of changes in human disease have been descriptive. Diagnostic utility is limited because the concentrations in a significant proportion of affected individuals overlap with those in controls. Changes in concentration may also be caused by diet, outside the clinical investigational setting. The role of nitrite and nitrate assays (alongside direct measurements of nitric oxide in breath) may be restricted to the monitoring of disease progression, or response to therapy in individual patients or subgroups. Associations between disease incidence and drinking water nitrate content are controversial (except for methemoglobinemia in infants).

Lipid oxidation products and vascular function

The endothelium and blood platelets are intimately involved in both the maintenance of vascular tone and in haemostasis. They are also exposed to high concentrations of lipoproteins, either in the plasma or in the sub-endothelial region of the artery wall, and the biological activity of these cells has been shown to be modulated. Oxidative modification of these lipoproteins results in further variations in the properties of these particles in relation to the activities of the endothelium and platelets. These effects and how the work of Hermann Esterbauer on the details of lipoprotein oxidation permitted rapid progress in understanding these phenomena are discussed in this review.