The role of nitric oxide and other endothelium-derived vasoactive substances in vascular disease

Increased circulating concentrations of asymmetric dimethylarginine (ADMA) in white coat hypertension

Elevated plasma levels of the endogenous nitric oxide (NO) synthase inhibitor asymmetric dimethylarginine (ADMA) contribute to endothelial dysfunction and seem to be a predictor for cardiovascular mortality. Elevated ADMA plasma concentrations have been demonstrated in patients with hypertension. However, the plasma concentrations of ADMA in white coat hypertension (WCH) has not been previously studied. The aim of this study was to evaluate ADMA in WCH and compare with normotensive (NT) and hypertensive (HT) patients. We also evaluated the relation between ADMA and NO in these three groups. For this purpose, 34 NT, 34 white coat hypertensive (clinical hypertension and ambulatory daytime blood pressure <135/85 mmHg) and 34 HT patients were recruited in this study. The subjects were matched for age, gender, body mass index (BMI) and the patients with smoking habit, dyslipidaemia and diabetes mellitus were excluded. The ADMA levels were determined by high performance liquid chromatography. Plasma ADMA levels were significantly higher in WCH group than in the NT group (3.21+/-0.49 micromol/l vs 2.84+/-0.58 micromol/l, P=0.046). It was significantly higher in the HT group than in the NTs (4.24+/-0.38 micromol/l, P<0.001). There was also a significant difference between the HT and WCH groups (P<0.001). The WCH subjects had significantly higher levels of NO than the HTs (41.68+/-2.23 vs 32.18+/-2.68 micromol/l; P<0.001) and significantly lower values than the NTs (48.24+/-4.29 micromol/l; P<0.001). In WCH and HT group, there was a negative correlation between ADMA and NO (r=-0.515, P=0.003 and r=-0.389, P=0.034, respectively). In NT subjects, there was no correlation between these two parameters (r=-0.287, P=0.124). The correlation between ADMA and NO was stronger in WCH group than in HT group. Although NO levels in HT patients were lower than WCHs and ADMA levels were higher in HT patients than WCHs, the negative correlation of these two parameters were more pronounced in WCH group. Decreased NO and increased ADMA levels in WCH may indicate endothelial dysfunction. Our data indicate also that WCH represent an intermediate group between NT and HT when endothelial dysfunction is concerned.

Metabolic syndrome, endothelial dysfunction, and erectile dysfunction: Association and management

The metabolic syndrome, the criteria for which include glucose intolerance, obesity, hypertension, and dyslipidemia, has rapidly become understood to have a major association with erectile dysfunction (ED). On a mechanistic level, their common grounds may involve endothelial dysfunction, although the conditions of oxidative stress understood to be a pathologic element of the syndrome also may affect various components of the vascular biology of the penis. The foremost importance of recognizing the association between ED and the metabolic syndrome is that addressing ED presentations may afford opportunities to identify and improve a major adverse health profile and thereby promote health maintenance objectives for patients.

Anti-atherogenic effects of the methanol extract of Sorbus cortex in atherogenic-diet rats

The present study was designed to examine whether the methanol extract of Sorbus commixta cortex (MSC) could prevent the development of atherosclerosis through regulating the vascular nitric oxide (NO) and endothelin-1 (ET-1) systems in atherogenic-diet rats. Our findings show that aortic NO production as well as endothelial nitric oxide synthase (ecNOS) expression was significantly decreased in atherogenic-diet rats compared with those in the control group. Aortic ET-1 expression was augmented in rats fed an atherogenic-diet while NF-kappaB p65 was upregulated. Treatment of atherogenic-diet rats with either low (100 mg/kg/d) or high (200 mg/kg/d) doses of MSC led not only to significant increases in the aortic NOS/NO system, but also to decreases in aortic ET-1 expression. The aortic expression level of NF-kappaB p65 was also attenuated in atherogenic-diet rats by chronic treatment with low or high doses of MSC. Atherogenic-diet induced increases in the expression of adhesion molecules including intercellular adhesion molecules-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and E-selectin were markedly decreased by treatment with MSC. From the histopathological examination, MSC treatment was shown to lessen the thickening noted in the aortic intima and media of the atherogenic-diet rats. These results suggest that MSC affects the atherogenic process via the suppression of proinflammatory and adhesion molecules in atherogenic-diet rats, which may be, at least in part, causally related with the regulation of vasoactive systems such as the NO and ET-1 systems.

Vasodilatory and anti-inflammatory effects of the aqueous extract of rhubarb via a NO-cGMP pathway

While conducting an in vitro screen of various medicinal plant extracts, an aqueous extract of rhubarb (Rheum undulatum L, AR) was found to exhibit a distinct vasorelaxant activity. AR induced a concentration-dependent relaxation of the phenylephrine-precontracted aorta. This effect disappeared with the removal of functional endothelium. Pretreatment of the aortic tissues with N(G)-nitro-L-arginine methyl ester (L-NAME), methylene blue, or 1H-[1,2,4]-oxadiazole-[4,3-alpha]-quinoxalin-1-one (ODQ) inhibited the relaxation induced by AR. Incubation of human umbilical vein endothelial cells (HUVECs) with AR increased the production of cGMP in a dose-dependent manner, but this effect was blocked by pretreatment with L-NAME and ODQ, respectively. AR treatment attenuated TNF-alpha-induced NF-kappaB p65 translocation in HUVECs in a dose-dependent manner. In addition, AR suppressed the expression levels of adhesion molecules including ICAM-1 and VCAM-1 induced by TNF-alpha in HUVECs. TNF-alpha-induced MCP-1 expression was also attenuated by the addition of AR. This attenuation was blocked by pretreatment with either L-NAME or ODQ. AR treatment inhibited cellular adhesion of U937 cells onto HUVECs induced by TNF-alpha. Taken together, the present study suggests that AR dilates vascular smooth muscle and suppresses the vascular inflammatory process via endothelium-dependent NO/cGMP signaling.

Endothelial function and its assessment

Endothelial dysfunction is a characteristic aspect of most of the conditions associated with atherosclerosis and is commonly found as an early feature in atherothrombotic vascular disease. An appreciation of the underlying mechanisms of endothelial function, as well as dysfunction, is essential as this has critical influence on the different methods in the assessment of endothelial function and effects of various treatments on its quantification. Furthermore, endothelial dysfunction is recognised as a type of 'target organ damage' in common cardiovascular conditions (e.g., hypertension) and the area is of increasing interest for new drug development, as therapies that modulate the endothelium will have added advantages; thus, for the development of new/experimental drugs, an awareness of ways to assess the endothelium is necessary. In this review, an overview of different methods including biochemical markers, and invasive and non-invasive tools, to determine endothelial function is presented as well as their clinical relevance. Furthermore, the effects of various treatments on endothelial dysfunction and their underlying mechanisms are elucidated.

Vasodilatory and anti-inflammatory effects of the 1,2,3,4,6-penta-O-galloyl-beta-D-glucose (PGG) via a nitric oxide-cGMP pathway

Vasorelaxant and anti-inflammatory effects of a 1,2,3,4,6-penta-O-galloyl-beta-d-glucose (PGG) isolated from the root barks of Paeonia suffruticosa and possible mechanisms responsible were investigated. PGG induced a concentration-dependent relaxation of the phenylephrine-precontracted rat aorta. This effect disappeared with the removal of functional endothelium. Pretreatment of the aortic tissues with either N(G)-nitro-L-arginine methyl ester (L-NAME) or 1H-[1,2,4]-oxadiazole-[4,3-alpha]-quinoxalin-1-one (ODQ) inhibited the relaxation induced by PGG. Incubation of human umbilical vein endothelial cells (HUVECs) or carotid arteries isolated from rats with PGG increased the production of cGMP in a dose-dependent manner, but this effect was blocked by pretreatment with L-NAME and ODQ, respectively. PGG treatment attenuated tumor necrosis factor-alpha (TNF-alpha)-induced nuclear factor-kappaB (NF-kappaB) p65 translocation in human umbilical vein endothelial cells. In addition, PGG suppressed the expression levels of adhesion molecules including intracellular cell adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) induced by TNF-alpha. TNF-alpha-induced monocyte chemoattractant protein-1 (MCP-1) expression was also attenuated by addition of PGG. PGG treatment inhibited cellular adhesion of U937 cells onto human umbilical vein endothelial cells induced by TNF-alpha. Taken together, the present study suggests that PGG dilates vascular smooth muscle and suppresses the vascular inflammatory process via endothelium-dependent nitric oxide (NO)/cGMP signaling.

Effect of methanol extract of Sorbus cortex in a rat model of L-NAME-induced atherosclerosis

Chronic inhibition of nitric oxide (NO) synthesis by administration of high dose of N(G)-nitro-L-arginine methylester (L-NAME) induces vascular inflammation and subsequent atherosclerosis. We aimed to investigate whether the methanol extract of Sorbus commixta cortex (MSC) is able to prevent inflammatory process in a rat model of L-NAME-induced atherosclerosis. Chronic treatment with low or high doses of MSC prevented the L-NAME-induced increase in monocyte chemoattractant protein-1 (MCP-1) and nuclear factor-kappaB (NF-kappaB) p65 expressions as well as adhesion molecules including intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1), and E-selectin in aorta. In addition, increased endothelin-1 (ET-1) and angiotensin converting enzyme (ACE) expressions and decreased endothelial cell NO synthase (ecNOS) expression in aorta from L-NAME treated group was reversed by treatment with MSC. From the histological examination, aortic segment from the L-NAME-treated rats revealed a thickening of intima and media, which was ameliorated by treatment with MSC. In conclusion, our results indicate that MSC can prevent atherosclerosis by inhibiting vascular over-expressions of vasoactive materials, pro-inflammatory transcription factor, and adhesion molecules and by augmenting ecNOS in chronic L-NAME-treated rat model.

Two distinct pathways account for EDHF-dependent dilatation in the gracilis artery of dyslipidaemic hApoB+/+ mice

1 A universal endothelium-derived hyperpolarising factor (EDHF--non-NO/non-PGI(2)) has not been identified. EDHF, however, is essential for the physiological control of resistance artery tone. The impact of dyslipidaemia (DL), a risk factor for cardiovascular diseases, on the nature and the efficacy of EDHF has not been evaluated yet. 2 Pressurised (80 mmHg) gracilis arterial segments isolated from mice expressing the human apoB-100 and C57Bl/6 wild-type (WT) mice were used. EDHF-dependent dilatations to acetylcholine (ACh) were measured in the presence of L-NNA (100 microM, NOS inhibitor) and indomethacin (10 microM, COX inhibitor). 3 Maximal EDHF-induced dilatations were increased in DL when compared to WT (95+/-2 versus 86+/-4% in WT; P<0.05). Combination of apamin and charybdotoxin strongly reduced (P<0.05) ACh-induced dilatation in WT (22+/-4%) and DL (25+/-5%). 4 Combined addition of barium (Ba(2+)) and ouabain abolished EDHF-induced dilatations in WT arteries (13+/-3%; P<0.05). In vessels isolated from DL mice, however, only the addition of 14,15-EEZE (a 14,15-EET antagonist) to Ba(2+) and ouabain prevented EDHF-induced dilatations (5+/-3% compared to 54+/-11% in the presence of combined Ba(2+) and ouabain; P<0.05). 5 Our data suggest that EDHF-mediated dilatation depends on the opening of endothelial SK(Ca) and IK(Ca) channels. This is associated with the opening of K(ir) channels and activation of the Na(+)/K(+)-ATPase pump on smooth muscle cells leading to dilatation. In arteries from DL mice, a cytochrome P450 metabolite likely to be 14,15-EET equally contributes to the dilatory action of ACh. The early increased efficacy of EDHF in arteries isolated from DL mice may originate from the duplication of the EDHF pathways.

Wild blueberry-rich diets affect the contractile machinery of the vascular smooth muscle in the Sprague-Dawley rat

Weanling male Sprague-Dawley rats were randomly fed a control diet (AIN-93) (C) or a blueberry diet (B) for 13 weeks, or a reverse diet (R) (C diet for 13 weeks, switched to the B diet for 8 weeks). Aortas were excised, and two intact and two endothelium-denuded rings were immersed in tissue baths containing physiological salt solution at 37 degrees C and aerated with 95% O(2) and 5% CO(2) (pH 7.4). Following equilibration and preconditioning under 1.5-g preload, cumulative dose-response curves were generated with six doses of the alpha1-adrenergic receptor-selective agonist L-phenylephrine (L-Phe, 10(8)-3 x 10(-6) M) and relaxed with one dose of acetylcholine (3 x 10(-6) M) to assess intact endothelium. The maximum force of contraction (Fmax) and vessel sensitivity (pD(2)) were determined in intact and endothelium-denuded rings. A two-way analysis of variance test revealed that blueberry-fed animals (B and R diets) developed a significantly lower F (max) (0.873 +/- 0.0463 and 0.9266 +/- 0.0463 g, respectively) when contracted with L-Phe, compared with the animals on the C diet (1.109 +/- 0.0463 g) (P < .05). The pD(2) of the intact rings was not significantly different among diet groups. Additionally, diet did not significantly affect the mean F (max) or pD(2) of endothelium-denuded rings. Our results indicate for the first time that wild blueberries incorporated into the diet affect the vascular smooth muscle contractile machinery by suppressing the alpha1-adrenergic receptor agonist-mediated contraction while having no effect on membrane sensitivity of the endothelial or vascular smooth muscle cell layer. Furthermore, their mechanism of action seems to be accomplished through an endothelium-dependent pathway.

Simultaneous expression of apolipoprotein B mRNA editing enzyme and scavenger receptor BI mediated by a therapeutic gene expression system

Cardiovascular diseases are often accompanied by elevated LDL particles and endothelial dysfunction. We have examined the possibility of concurrently reducing LDL levels and modulating endothelial function using a single helper-dependent adenovirus vector system to simultaneously express the apolipoprotein B mRNA editing enzyme (Apobec1) and the scavenger receptor, class B, type I (SR-BI) genes under the control of separate promoters (designated HD-C2). Apobec1 edits apoB mRNA at nucleotide C-6666 to produce truncated apoB48 and is normally expressed in small intestine only. SR-BI is a receptor for multiple ligands with distinct tissue-specific functions. Expression of Apobec1 in HepG2 cells resulted in apoB mRNA editing, leading to decreased apoB100 abundance (to 6% of control) and the appearance of apoB48. Editing of apoB mRNA in HepG2 cells resulted in decline in apoB mRNA levels of 50%. This was probably the result of nonsense-mediated decay of edited message, since over-expression of Apobec1 increased neither Apobec1 complementary factor (ACF) mRNA nor protein abundance. Over-expression of SR-BI in human endothelial cells activated endothelial nitric oxide synthase (eNOS) activity by phosphorylation of eNOS at residue Ser-1177 in the presence of HDL, leading to increased production of the anti-atherogenic molecule nitric oxide (NO). Taken together, this study demonstrates that using one vector delivery system to express two genes in two different cell types results in the cell-specific beneficial effects of decreasing apoB100 production and increasing eNOS activities. This combined gene expression approach may provide an improved therapeutic strategy by targeting multiple sites in the mechanism of cardiovascular injury.

Functional changes in adenylyl cyclases and associated decreases in relaxation responses in mesenteric arteries from diabetic rats

To assess the functional change in adenylyl cyclases (AC) associated with the diabetic state, we investigated AC-mediated relaxations and cAMP production in mesenteric arteries from rats with streptozotocin (STZ)-induced diabetes. The relaxations induced by the water-soluble forskolin (FSK) analog NKH477, which is a putative AC5 activator, but not by the beta-adrenoceptor agonist isoproterenol (Iso) and the AC activator FSK, were reduced in intact diabetic mesenteric artery. In diabetic rats, however, Iso-, FSK-, and NKH477-induced relaxations were attenuated in the presence of inhibitors of nitric oxide synthase and cyclooxygenase. To exclude the influence of phosphodiesterase (PDE), we also examined the relaxations induced by several AC activators in the presence of 3-isobutyl-1-methylxanthine (IBMX; a PDE inhibitor). Under these conditions, the relaxation induced by Iso was greatly impaired in STZ-diabetic rats. This Iso-induced relaxation was significantly attenuated by pretreatment with SQ-22536, an AC inhibitor, in mesenteric rings from age-matched controls but not in those from STZ-diabetic rats. Under the same conditions, the relaxations induced by FSK or NKH477 were impaired in STZ-diabetic rats. Neither FSK- nor A-23187 (a Ca2+ ionophore)-induced cAMP production was significantly different between diabetics and controls. However, cAMP production induced by Iso or NKH477 was significantly impaired in diabetic mesenteric arteries. Expression of mRNAs and proteins for AC5/6 was lower in diabetic mesenteric arteries than in controls. These results suggest that AC-mediated relaxation is impaired in the STZ-diabetic rat mesenteric artery, perhaps reflecting a reduction in AC5/6 activity.

The role of nitric oxide synthases and nitrotyrosine in retinoblastoma

BACKGROUND

To investigate the potential involvement of the nitric oxide (NO) pathway in retinoblastoma, the authors correlated immunoreactivity for endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), and nitrotyrosine (NT) with the degree of tumor invasiveness in retinoblastoma.

METHODS

eNOS, iNOS, and NT reactivity was evaluated by immunohistochemistry in 34 archival retinoblastoma specimens and in a human Y79 retinoblastoma cell line. The tumors were divided into 2 groups: Group A tumors (n = 17 tumors) with no invasion and Group B tumors (n = 17 tumors) with invasion of the choroid, optic nerve, and/or orbit. The expression levels of eNOS, iNOS, and NT were correlated with invasiveness of the tumors.

RESULTS

In Group A tumors (n = 17 tumors) without invasion, eNOS was positive in 17 of 17 tumors (100%), iNOS was positive in 14 of 17 tumors (82%), and NT was positive in 17 of 17 tumors (100%). In Group B tumors (n = 17 tumors) with invasion, eNOS was positive in 17 of 17 tumors (100%), iNOS was positive in 16 of 17 tumors (94%), and NT was positive in 17 of 17 tumors (100%). The invasive cohort showed significantly higher expression of iNOS (P < 0.0001) and NT (P < 0.020) compared with the noninvasive cohort. Y79 cells also expressed eNOS, iNOS, and NT; and nonneoplastic retina was positive for eNOS, iNOS, and NT.

CONCLUSIONS

Taken together, the results suggested that retinoblastomas can produce NO. The roles of NO in the biology of retinoblastoma and in the prognosis for patients with retinoblastoma remain to be established.

Effects of Chronic Administration of Fruit Extract (Citrus unshiu MARC) on Endothelial Dysfunction in Streptozotocin-Induced Diabetic Rats

We investigated the effects of chronic administration of fruit extract (Citrus unshiu MARC) on the endothelial dysfunction seen in aortae from streptozotocin (STZ)-induced diabetic rats. A ten-week administration of this fruit extract preserved acetylcholine (ACh)-induced endothelium-dependent relaxation, but not sodium nitroprusside (SNP)-induced endothelium-independent relaxation, in the diabetic aorta. In age-matched control rats, chronic administration of the fruit extract had no influence on the ACh- or SNP-induced aortic relaxation. The increased total cholesterol, low-density lipoprotein (LDL) cholesterol, and triglyceride levels seen in STZ-induced diabetic rats were not normalized by fruit-extract treatment. These results suggest that Citrus unshiu MARC extract preserves endothelial function in the aorta in STZ-induced diabetic rats without lowering plasma cholesterol. This beneficial effect may be due to this extract protecting of nitric oxide against inactivation by oxygen free radicals.

The PI3-K/Akt pathway: roles related to alterations in vasomotor responses in diabetic models

Macro- and microvascular disease states currently represent the principal causes of morbidity and mortality in patients with type I or type II diabetes mellitus. Abnormal vasomotor responses and impaired endothelium-dependent vasodilation have been demonstrated in various beds in different animal models of diabetes and in humans with type I or type II diabetes. Several mechanisms leading to endothelial dysfunction have been reported, including changes in substrate avail ability, impaired release of NO, and increased destruction of NO. The principal mediators of diabetes-associated endothelial dysfunction are (a) increases in oxidized low density lipoprotein, endothelin-1, angiotensin II, oxidative stress, and (b) decreases in the actions of insulin or growth factors in endothelial cells. An accumulating body of evidence indicates that abnormal regulation of the phosphatidylinositol 3-kinase (PI3-K)/Akt pathway may be one of several factors contributing to vascular dysfunction in diabetes. The PI3-K pathway, which activates serine/threonine protein kinase Akt, enhances NO synthase phosphorylation and NO production. Several studies suggest that in diabetes the relative ineffectiveness of insulin and the hyperglycemia act together to reduce activity in the insulin-receptor substrates (IRS)/PI3-K/Akt pathway, resulting in impairments of both IRS/PI3-K/Akt-mediated endothelial function and NO production. This article summarizes the PI3-K/Akt pathway-mediated contraction and relaxation responses induced by various agents in the blood vessels of diabetic animals.

Effects of chronic insulin on endothelial dysfunction of basilar arteries from established streptozotocin-diabetic rats

Our goals were to determine both the effects of chronic insulin treatment on the impaired endothelium-dependent relaxation present in basilar arteries from established diabetic rats and the molecular basis of these effects. Acetylcholine-induced relaxation in basilar artery rings was impaired in the streptozotocin-induced diabetic group, and this impaired response was recovered by insulin treatment. The contraction induced by a nitric oxide synthase inhibitor was decreased in the insulin-untreated diabetic group, but was increased by insulin or NAD(P)H oxidase inhibitor treatment. The manganese-superoxide dismutase (Mn-SOD) mRNA level was significantly lower in basilar arteries from insulin-untreated diabetic rats than in those from the controls, whereas the mRNA for gp91phox, an NAD(P)H oxidase subunit, was increased. In the insulin-treated group, the basilar artery p22phox mRNA level was reduced (vs. insulin-untreated diabetic). These results suggest that the presence of endothelial dysfunction in the diabetic basilar artery is related to increased oxidative stress, and that insulin preserves endothelial function by alleviating oxidative stress. Furthermore, we directly demonstrated that the expression profile for SOD and NAD(P)H oxidase was altered in the streptozotocin-induced diabetic basilar artery.

Effect of chronic insulin on cromakalim-induced relaxation in established streptozotocin–diabetic rat basilar artery

Our goals were to determine whether the response of the rat isolated basilar artery to activation of ATP-sensitive potassium (KATP) channels is altered in diabetes mellitus, and to determine the effect of chronic insulin treatment on this response in established diabetic rats. The relaxation induced by cromakalim, an activator of KATP channels, was significantly weaker in insulin-untreated streptozotocin-induced diabetic rats than in the controls. This impairment was significantly improved following chronic administration of insulin. The relaxations induced by two Ca2+-activated K+-channel activators [1-ethyl-2-benzimidazolinone (1-EBIO) or 1, 3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazol-2-one (NS1619)] were not significantly different between control and insulin-untreated diabetic rats. The sodium nitroprusside-induced relaxation was similar among the three groups (control, diabetic, and insulin-treated diabetic). These results suggest that: (a) the impaired cromakalim-induced relaxation seen in diabetic rats is not due to a nonspecific effect of diabetes mellitus on vasorelaxation, but at least partly to an effect on KATP channels, and (b) that this impaired relaxation can be restored by chronic insulin treatment.

Mechanisms underlying enhanced contractile response to endothelin-1 in diabetic rat basilar artery

We investigated the influence of streptozotocin-induced diabetes on the responsiveness of the rat basilar artery to endothelin-1 (ET-1) and nitric oxide (NO), which is known to counteract ET-1. In basilar arteries isolated from diabetic rats: (a) the ET-1-induced contraction was enhanced, (b) the contraction induced by N(G)-nitro-l-arginine [a nitric oxide synthase (NOS) inhibitor] was weaker, and (c) the levels of the mRNAs for ET(A)/ET(B) receptors and prepro-ET-1, but not for NOS, were significantly elevated (all versus age-matched controls). These data indicate that ET-1-induced vasoconstriction may be increased in the diabetic rat basilar artery, and that this hyper-reactivity to ET-1 may be due to an overproduction of ET-1, an up-regulation of ET(A)/ET(B) receptors, and a defect in the bioavailability of NO.

Sodium nitroprusside and peroxynitrite effect on hepatic DNases: an in vitro and in vivo study

Background

It has been documented that nitric oxide (NO) donor sodium nitroprusside (SNP) and authentic peroxynitrite are capable of promoting apoptosis in a number of different cell types. Various endonucleases have been proposed as candidates responsible for the internucleosomal cleavage of the genomic DNA observed during apoptosis, but the main effect is attributed to the alkaline-DNases (Mg²⁺- and caspase-dependent) and acid-DNase. The aim of this study was to examine an in vivo and in vitro possibility for alkaline- and acid-DNases to be activated by SNP and peroxynitrite.

Results

The effect on liver tissue alkaline and acid DNase activity together with the markers of tissue and plasma oxidative and nitrosative stress (lipid peroxidation, SH group content, carbonyl groups and nitrotyrosine formation) was investigated in plasma and liver tissue. The activity of liver alkaline DNase increased and that of acid DNase decreased after in vivo treatment with either SNP or peroxynitrite. A difference observed between the in vivo and in vitro effect of oxide donor (i.e., SNP) or peroxynitrite upon alkaline DNase activity existed, and it may be due to the existence of the "inducible" endonuclease. After a spectrophotometric scan analysis of purified DNA, it was documented that both SNP and peroxynitrite induce various DNA modifications (nitroguanine formation being the most important one) whereas DNA fragmentation was not significantly increased.

Conclusion

Alkaline DNase activation seems to be associated with the programmed destruction of the genome, leading to the fragmentation of damaged DNA sites. Thus, the elimination of damaged cells appears to be a likely factor in prevention against mutation and carcinogenesis.

Medical therapy for pulmonary arterial hypertension: ACCP evidence-based clinical practice guidelines

Pulmonary arterial hypertension (PAH) is often difficult to diagnose and challenging to treat. Untreated, it is characterized by a progressive increase in pulmonary vascular resistance leading to right ventricular failure and death. The past decade has seen remarkable improvements in therapy, driven largely by the conduct of randomized controlled trials. Still, the selection of most appropriate therapy is complex, and requires familiarity with the disease process, evidence from treatment trials, complicated drug delivery systems, dosing regimens, side effects, and complications. This chapter will provide evidence-based treatment recommendations for physicians involved in the care of these complex patients. Due to the complexity of the diagnostic evaluation required, and the treatment options available, it is strongly recommended that consideration be given to referral of patients with PAH to a specialized center.

Differential expression of α2D-adrenoceptor and eNOS in aortas from early and later stages of diabetes in Goto-Kakizaki rats

The aim of the present study was to compare vascular dysfunction between the early (12 wk old) and later (36 wk old) stages of spontaneous diabetes in Goto-Kakizaki (GK) rats. We also evaluated the aortic expression of the α2D-adrenoceptor and endothelial nitric oxide synthase (eNOS). Vascular reactivity was assessed in thoracic aortas from age-matched control rats and 12- and 36-wk GK rats. Using RT-PCR and immunoblots, we also examined the changes in expression of the α2D-adrenoceptor and eNOS. In aortas from GK rats (vs. those from age-matched control rats): 1) the relaxation response to ACh was enhanced at 12 wk but decreased at 36 wk; 2) the relaxation response to sodium nitroprusside was decreased at both 12 and 36 wk, 3) norepinephrine (NE)-induced contractility was decreased at 12 wk but not at 36 wk, 4) the expressions of α1B- and α1D-adrenoceptors were unaffected, whereas those of α2D-adrenoceptor and eNOS mRNAs were increased at both 12 and 36 wk; and 5) NE- and ACh-stimulated NOx (nitrite and nitrate) levels were increased at 12 wk, although at 36 wk ACh-stimulated NOx was lower, whereas NE-stimulated NOx showed no change. These results clearly demonstrate that enhanced ACh-induced relaxation and impaired NE-induced contraction, due to NO overproduction via eNOS and increased α2D-adrenoceptor expression, occur in early-stage GK rats and that the impaired ACh-induced relaxation in later-stage GK rats is due to reductions in both NO production and NO responsiveness (but not in eNOS expression).

Modulations of shear stress-induced contractile responses and agonist-induced vasodilation in hypercholesterolemic rats

We used mesenteric arterial beds from normal rats and beef tallow-fed rats (hypercholesterolemic model) to study the interaction between the effects of viscosity-induced shear stress and agonists mesenteric vasoreactivity. Mesenteric arterial beds were perfused under constant-flow conditions (5 ml/min) via a peristaltic pump using warm oxygenated modified Krebs-Henseleit solution containing either 4% BSA to increase viscosity or 300 microM L-arginine, a NO synthase substrate. Whether beds were perfused with BSA alone or L-arginine alone as pretreatment, the methoxamine-induced contractile responses were similar to those in normal beds. However, methoxamine-induced contractile responses were significantly reduced following pretreatment with L-arginine plus BSA. These reduced responses underwent significant recovery when either tyrphostin A23 (30 microM, a tyrosine kinase inhibitor) or wortmannin (300 nM, a PI3K inhibitor) was present. The dose-response curve for methoxamine was shifted to the right and the maximum contractile response was reduced in mesenteric arterial beds from beef tallow-fed rats, but the modulation of this response induced by L-arginine plus BSA was preserved. In beef tallow-fed rats, the ACh-induced endothelium-dependent vasodilation was attenuated in both thoracic aortic strips and mesenteric arterial beds. These results suggest that in hypercholesterolemic rats, agonist-induced endothelial function is impaired, while shear stress-induced responses (tyrosine kinase- and PI3K-mediated NO production) are preserved. These abnormal vascular responses may contribute to hypertension in beef tallow-fed hypercholesterolemic model rats.

New in vitro model to study high glucose-dependent endothelial dysfunctions

Several thrombogenic abnormalities are associated with diabetes. Since endothelial dysfunction occurs at early stages of disease, it may reflect pathophysiological changes that are responsible for alterations in vascular structure, growth and modifications of adhesivity to platelets and leukocytes, leading to atherosclerosis and thrombosis. Predisposing factors of vascular diseases, such as diabetes, are also associated with endothelial dysfunction. Restoration or replacement of endothelium-related factors like nitric oxide impede the progression of vascular thrombogenic diseases, and prevent the action of vasoconstrictor factors such as endothelin or other prothrombotic factors such as plasminogen-activator inhibitor-1. Since high glucose concentration in blood is the hallmark of diabetes and because the vascular lesions of atherosclerosis are localized in large artheries, we have cultured endothelial cells from the human aorta. Two endothelial cell strains from the same aortic tract that show different characteristics and behavior in high glucose were isolated. Such findings reflect the importance to have well characterized and standardized cell culture systems to carry out experiments to study the glucose-dependent atherosclerotic process in vitro. Our cell strains may represent a useful in vitro model to study the complex pathophysiology of diabetes-related atherosclerosis.

Diabetes-related changes in cAMP-dependent protein kinase activity and decrease in relaxation response in rat mesenteric artery

Using superior mesenteric artery rings isolated from age-matched controls and streptozotocin (STZ)-induced diabetic rats, we recently demonstrated that EDHF-type relaxation is impaired in STZ-induced diabetic rats, possibly due to a reduced action of cAMP via increased phosphodiesterase (PDE) activity (Matsumoto T, Kobayashi T, and Kamata K. Am J Physiol Heart Circ Physiol 285: H283-H291, 2003). Here, we investigated the activity and expression of cAMP-dependent protein kinase (PKA), an enzyme that is produced by a pleiotropic and plays key roles in the transduction of many external signals through the cAMP second messenger pathway and in cAMP-mediated vasorelaxation. The relaxation induced by cilostamide, a selective PDE3 inhibitor, was significantly weaker in superior mesenteric artery rings from STZ-induced diabetic rats than in those from age-matched controls. The relaxation responses to 8-bromo-cAMP (8Br-cAMP) and N6,O2-dibutyryl-adenosine-cAMP (db-cAMP), a cell-permeant cAMP analog, were also impaired in the STZ diabetic group. PKA activity in the db-cAMP-treated mesenteric artery was significantly lower in the STZ diabetic group. The expression levels of the mRNA and protein for PKA catalytic subunit Cat-alpha were significantly decreased in the STZ diabetic group, but those for PKA regulatory subunit isoform RII-beta were increased. We conclude that the abnormal vascular relaxation responsiveness seen in STZ-induced diabetic rats may be attributable not only to increased PDE activity but also to decreased PKA activity. Possibly, the decreased PKA activity may result from an imbalance between PKA catalytic and regulatory subunit expressions.

HDL: a recipe for longevity

The concentration of high density lipoprotein cholesterol (HDL-C) has been found to be a powerful negative predictor of premature coronary heart disease (CHD) and stroke in human prospective population studies. Evidence of the protective properties of HDLs has also been documented in the elderly and their offspring. HDLs mediate several functions that provide an insight into their potential anti-atherogenic mechanisms. Intervention strategies to prevent CHD have generally focused on lowering low-density lipoprotein cholesterol (LDL-C). However, several lifestyle and pharmacological interventions have the capacity to raise the level of HDL-C. As data accumulate on the protective role of HDLs, there is growing support for interventions that act to raise HDL-C concentrations.

L-arginine-induced vasodilation of the renal vasculature is preserved in uremic type 1 diabetic patients after kidney and pancreas but not after kidney-alone transplantation

OBJECTIVE

In uremic type 1 diabetic patients, kidney and pancreas transplantation (KP) and kidney-alone transplantation (KD) provide full restoration of normal renal function; however, only KP, i.e., curing diabetes, is expected to prevent endothelial damages. Our aim was to study L-arginine-induced vasodilation of the renal vasculature in uremic type 1 diabetic patients after KP or KD using magnetic resonance (MR).

RESEARCH DESIGN AND METHODS

MR quantitative flow measurements were performed in 15 KP patients (mean age 39.0 +/- 1.7 years, 10 men and 5 women), in 11 KD patients (mean age 47.3 +/- 1.9 years, 7 men and 4 women), and in 8 nondiabetic kidney transplant patients (mean age 44.0 +/- 4.8 years, 7 men and 1 woman), who were used as control subjects, to measure renal blood flow and velocity and renal vascular resistance before and immediately after infusion of L-arginine.

RESULTS

Renal blood flow and velocity were not different at baseline in KP, KD, and control subjects. In contrast, during L-arginine administration renal blood flow increased significantly in KP subjects (basal 8.4 +/- 0.6 vs. post 9.6 +/- 0.8 ml/s, Delta 14.3 +/- 4.4%, P < 0.05) and in control subjects (basal 9.3 +/- 0.8 vs. post 9.1 +/- 0.8 ml/s, Delta 17.3 +/- 6.2%, P < 0.01), while it remained unchanged in KD subjects (basal 10.0 +/- 0.8 vs. post 11.6 +/- 0.9 ml/s, Delta -1.36 +/- 6.9%, NS). Parallel results have been achieved for renal blood velocity (KP subjects: 20.1 +/- 4.9%, P < 0.01; control subjects: 23.0 +/- 7.99%, P < 0.01; and KD subjects: -0.3 +/- 6.5%; NS). A reduction in renal vascular resistance in response to L-arginine was evident in KP and control subjects but not in KD patients.

CONCLUSIONS

L-Arginine vasodilatory response was successfully assessed with MR quantitative flow measurements. KP patients and control subjects, but not those with KD, showed a preserved L-arginine-induced vasodilation of the renal vasculature.

HDL induces NO-dependent vasorelaxation via the lysophospholipid receptor S1P3

HDL is a major atheroprotective factor, but the mechanisms underlying this effect are still obscure. HDL binding to scavenger receptor-BI has been shown to activate eNOS, although the responsible HDL entities and signaling pathways have remained enigmatic. Here we show that HDL stimulates NO release in human endothelial cells and induces vasodilation in isolated aortae via intracellular Ca2+ mobilization and Akt-mediated eNOS phosphorylation. The vasoactive effects of HDL could be mimicked by three lysophospholipids present in HDL: sphingosylphosphorylcholine (SPC), sphingosine-1-phosphate (S1P), and lysosulfatide (LSF). All three elevated intracellular Ca2+ concentration and activated Akt and eNOS, which resulted in NO release and vasodilation. Deficiency of the lysophospholipid receptor S1P3 (also known as LPB3 and EDG3) abolished the vasodilatory effects of SPC, S1P, and LSF and reduced the effect of HDL by approximately 60%. In endothelial cells from S1P3-deficient mice, Akt phosphorylation and Ca2+ increase in response to HDL and lysophospholipids were severely reduced. In vivo, intra-arterial administration of HDL or lysophospholipids lowered mean arterial blood pressure in rats. In conclusion, we identify HDL as a carrier of bioactive lysophospholipids that regulate vascular tone via S1P3-mediated NO release. This mechanism may contribute to the vasoactive effect of HDL and represent a novel aspect of its antiatherogenic function.

HDL action on the vascular wall: is the answer NO?

Circulating levels of HDL cholesterol are inversely related to the risk of atherosclerosis, and therapeutic increases in HDL reduce the incidence of cardiovascular events. A new study shows that HDL-associated lysophospholipids stimulate the production of the potent antiatherogenic signaling molecule NO by the vascular endothelium.

Molecular mechanisms of high glucose-induced cyclooxygenase-2 expression in monocytes

The cyclooxygenase (COX)-2 enzyme has been implicated in the pathogenesis of several inflammatory diseases. However, its role in diabetic vascular disease is unclear. In this study, we evaluated the hypothesis that diabetic conditions can induce COX-2 in monocytes. High glucose treatment of THP-1 monocytic cells led to a significant three- to fivefold induction of COX-2 mRNA and protein expression but not COX-1 mRNA. High glucose-induced COX-2 mRNA was blocked by inhibitors of nuclear factor-kappaB (NF-kappaB), protein kinase C, and p38 mitogen-activated protein kinase. In addition, an antioxidant and inhibitors of mitochondrial superoxide, NADPH oxidase, and glucose metabolism to glucosamine also blocked high glucose-induced COX-2 expression to varying degrees. High glucose significantly increased transcription from a human COX-2 promoter-luciferase construct (twofold, P < 0.001). Promoter deletion analyses and inhibition of transcription by NF-kappaB superrepressor and cAMP-responsive element binding (CREB) mutants confirmed the involvement of NF-kappaB and CREB transcription factors in high glucose-induced COX-2 regulation. In addition, isolated peripheral blood monocytes from type 1 and type 2 diabetic patients had high levels of COX-2 mRNA, whereas those from normal volunteers showed no expression. These results show that high glucose and diabetes can augment inflammatory responses by upregulating COX-2 via multiple signaling pathways, leading to monocyte activation relevant to the pathogenesis of diabetes complications.

Endothelial dysfunction and cardiovascular risk prediction in peripheral arterial disease: additive value of flow-mediated dilation to ankle-brachial pressure index

BACKGROUND

Endothelial dysfunction plays a key role in atherogenesis. We prospectively investigated the impact of noninvasive measurement of endothelial function on cardiovascular risk in peripheral arterial disease (PAD). The study was specially aimed at assessing whether brachial artery flow-mediated dilation (FMD) added to the predictive value of ankle-brachial pressure index (ABPI).

METHODS AND RESULTS

Of 131 patients monitored for a mean of 23+/-10 months, 18 had a coronary event, 12 a cerebrovascular event, and 9 a peripheral event. The median FMD was lower in patients with an event than in those without (5.8% versus 7.6%, P<0.05), whereas vasodilation to nitroglycerin was similar in the two groups. The cardiovascular event rate was higher in patients with FMD below the median versus those with FMD above the median (P<0.001 by log-rank test). In a Cox proportion hazard model, independent predictors of events were FMD below the median (P<0.01), ABPI below the median (P<0.01), and previous stroke (P<0.02). Similar results were obtained when peripheral events were excluded from the analysis. Below-median ABPI and FMD combined was more accurate in predicting risk (relative risk [RR] 13.0; 95% CI, 3.0 to 56.2; P<0.01) than ABPI (RR, 6.4; 95% CI, 1.4 to 29.1; P<0.02) and FMD (RR, 4.8; 95% CI, 1.1 to 23.3; P<0.05) alone.

CONCLUSIONS

A low brachial artery FMD is an independent predictor of cardiovascular risk in patients with PAD and adds to the prognostic value of ABPI, which is currently the most powerful prognostic indicator in PAD.

Regulation of cyclooxygenase-2 expression in monocytes by ligation of the receptor for advanced glycation end products

Cyclooxygenase-2 (COX-2) enzyme and its inflammatory products such as prostaglandin E2 (PGE2) have been implicated in the pathogenesis of several inflammatory diseases. However their role in diabetic vascular disease is unclear. Advanced glycation end products (AGEs) act via their receptor, RAGE, to play a major role in diabetic complications. In this study, we investigated the effect of AGEs and S100b, a specific RAGE ligand, on the expression of COX-2 and the molecular mechanisms involved in cultured THP-1 monocytes and human peripheral blood monocytes. S100b treatment of THP-1 cells led to a significant 3-5-fold induction of COX-2 mRNA (p < 0.001). COX-2 protein and its product PGE2 were also increased, whereas COX-1 expression was unaffected. In vitro prepared AGE also induced COX-2 mRNA. S100b-induced COX-2 mRNA was blocked by an anti-RAGE antibody and by inhibitors of NF-kappa B (Bay11-7082), oxidant stress, protein kinase C, ERK, and p38 MAPKs. S100b (4-h treatment) significantly increased transcription from a human COX-2 promoter-luciferase construct (4-fold, p < 0.001). Promoter deletion analyses and inhibition of transcription by an NF-kappa B superrepressor mutant confirmed NF-kappa B involvement. This was further supported by inhibition of S100b-induced PGE2 by Bay11-7082. Additionally, S100b-induced adherence of THP-1 monocytes to vascular smooth muscle cells was blocked by the COX-2 inhibitor NS-398, Bay11-7082, inhibitors of ERK and p38 MAPK, and protein kinase C thereby indicating functional relevance. S100b also increased COX-2 mRNA expression in human peripheral blood monocytes from healthy donors. Moreover, COX-2 mRNA levels were clearly evident in monocytes obtained from diabetic patients but not from normal subjects. These results show for the first time that AGEs can augment inflammatory responses by up-regulating COX-2 via RAGE and multiple signaling pathways, thereby leading to monocyte activation and vascular cell dysfunction.

Possible involvement of IGF-1 receptor and IGF-binding protein in insulin-induced enhancement of noradrenaline response in diabetic rat aorta

1. We investigated the mechanisms underlying the changes in vascular contractile responsiveness induced by chronic treatment with insulin in controls and established streptozotocin (STZ)-induced diabetic rats. 2. The aortic contractile response to noradrenaline (NA) showed no significant difference between controls and diabetics, but it was significantly greater in insulin-treated diabetic rats than in the other groups. To investigate the mechanism, we examined the changes in NA-induced contractility following treatment with insulin and insulin-like growth factor-1 (IGF-1) in organ-cultured control and diabetic aortas. 3. The contractile response to NA in organ-cultured diabetic rat aortas treated with insulin (500 ng ml-1, 16 h) or IGF-1 (20 ng ml-1, 16 h) was significantly greater than the corresponding values for (a) diabetic rat aortas cultured in serum-free medium, and (b) control aortas incubated with insulin or IGF-1. Incubating control aortas with insulin or IGF-1 had no significant effect on the contraction induced by NA. 4. The expressions of the IGF-1 receptor mRNA and protein were increased in STZ-induced diabetic aortas and further increased in insulin-treated diabetics. The mRNA expressions of IGF-binding protein (IGFBP)-2 and IGFBP-3 were normal in diabetic aortas. In contrast, those of IGFBP-4 and IGFBP-5 were significantly decreased in diabetic aortas, and not restored by insulin treatment. 5. These results suggest that the insulin deficiency and chronic hyperinsulinemia in diabetes upregulate the IGF-1 receptor and downregulate IGFBP-4 and IGFBP-5 in the aorta. This may be a major cause of the increased vascular contractility induced by insulin administration and by hyperinsulinemia in established diabetes, resulting in hypertension.

Influence of several methodological procedures utilized to obtain in vitro vascular preparations on endothelial activity

Several maneuvers usually employed to set up isolated vascular preparations could effect the endothelium-dependent relaxation (EDR). The effects of five such maneuvers were studied in rings of rat aorta: 1) Type of anesthesia, 2) Cold storage of the vessels, 3) Length of the stabilization period, 4) Repeated contractions during stabilization, and 5) Performance of washouts during stabilization. Repeated contractions with norepinephrine (NE) 0.1 microM after stabilization altered neither the contraction nor the EDR induced by acetylcholine (Ach) 1 microM. Pentobarbital anesthesia and cold storage of the preparations for 24 h significantly decreased the EDR without effecting the contractile response of the rings. The absence of washouts during stabilization increased the contractions to either NE 0.1 microM or KCl 80 mM by nearly 50%. This increase was prevented by endothelial disruption or, in the presence of intact endothelium, by repeated washouts or by incubation with Bosentan 22 microM. It is concluded that 1) Anesthesia of the animals and cold storage of the preparations can alter the EDR even in the absence of contractile changes in the smooth muscle, and 2) Accumulation of endothelin during the incubation period, even if not producing changes in the resting tension, can substantially alter the subsequent response to vasoactive interventions.

Alterations in EDHF-type relaxation and phosphodiesterase activity in mesenteric arteries from diabetic rats

In isolated superior mesenteric artery rings from age-matched control rats and streptozotocin (STZ)-induced diabetic rats, we investigated the role of cAMP in endothelium-derived hyperpolarizing factor (EDHF)-type relaxation. The ACh-induced EDHF-type relaxation was significantly weaker in STZ-induced diabetic rats than in control rats, and in both groups of rats it was attenuated by 18alpha-glycyrrhetinic acid (18alpha-GA), an inhibitor of gap junctions, and enhanced by IBMX, a cAMP-phosphodiesterase (PDE) inhibitor. These enhanced EDHF-type responses were very similar in magnitude between diabetic and age-matched control rats. The EDHF-type relaxation was enhanced by cilostamide, a PDE3-selective inhibitor, but not by Ro 20-1724, a PDE4-selective inhibitor. The expression levels of the mRNAs and proteins for two cAMP PDEs (PDE3A, PDE3B) were significantly increased in STZ-induced diabetic rats, but those for PDE4D were not. We conclude that the impairment of EDHF-type relaxations in STZ-induced diabetic rats may be attributed to a reduction in the action of cAMP via increased PDE activity.

The thrombin inhibitor argatroban does not influence the endothelium-dependent relaxant and contractile responses of isolated rabbit carotid arteries

Atherosclerotic endothelial dysfunctions are associated with a reduced NO production, which is probably due to impaired NO synthase (eNOS) activity or a deficiency of the substrate L-arginine. In the present studies, the influence of argatroban on isolated rabbit carotid arteries was investigated to determine whether the arginine derivative argatroban can improve the endothelium-dependent relaxation. Rings from rabbit carotid arteries were placed in 10 ml organ baths for isometric tension recording. Endothelial integrity was assessed by the acetylcholine-induced relaxation of PGF2alpha-precontracted rings; after mechanical removal of the endothelium the relaxation was abolished. Preincubation of the vessels in vitro with L-NAME, an inhibitor of the eNOS, diminished significantly the acetylcholine-induced relaxation by more than 50%. After i.v. application of L-NAME (100 mg/kg) in rabbits, relaxation in response to acetylcholine was significantly reduced compared to the control when the vessels were studied ex vivo in an organ bath. The contractile effects of phenylephrine and 5-HT were slightly enhanced. Argatroban is a selective, potent, synthetic thrombin inhibitor; after i.v. application at doses of 0.5 and 1.0 mg/kg, a significant prolongation of the plasma coagulation time (measured as thrombin time and a PTT) of up to 60 min was found in rabbits. In vitro argatroban did not affect the acetylcholine-induced relaxation or the contractile response to phenylephrine and 5-HT. After i.v. application, the ex vivo experiments in the organ bath showed that after 30 min the relaxant responses of the carotid arteries to acetylcholine and the contractile effects of phenylephrine and 5-HT were not influenced by pretreatment with argatroban. The present studies suggest that argatroban has no vascular effects in vitro and ex vivo in normal rabbits.

Specific nitration at tyrosine 430 revealed by high resolution mass spectrometry as basis for redox regulation of bovine prostacyclin synthase

Treatment of bovine aortic microsomes containing active prostacyclin synthase (PGI(2) synthase) with increasing concentrations of peroxynitrite (PN) up to 250 microm of PN yielded specific staining of this enzyme on Western blots with antibodies against 3-nitrotyrosine (3-NT), whereas above 500 microm PN staining of additional proteins was also observed. Following treatment of aortic microsomes with 25 microm PN, PGI(2) synthase was about half-maximally nitrated and about half-inhibited. It was then isolated by gel electrophoresis and subjected to proteolytic digestion with several proteases. Digestion with thermolysin for 24 h provided a single specific peptide that was isolated by high performance liquid chromatography and identified as a tetrapeptide Leu-Lys-Asn-Tyr(3-nitro)-COOH corresponding to positions 427-430 of PGI(2) synthase. Its structure was established by precise mass determination using Fourier transform-ion cyclotron resonance-nanoelectrospray mass spectrometry and Edman microsequencing and ascertained by synthesis and mass spectrometric characterization of the authentic Tyr-nitrated peptide. Complete digestion by Pronase to 3-nitrotyrosine was obtained only after 72 h, suggesting that the nitrated Tyr-430 residue may be embedded in a tight fold around the heme binding site. These results provide evidence for the specific inhibition of PGI(2) synthase by nitration at Tyr-430 that may occur already at low levels of PN as a consequence of endothelial co-generation of nitric oxide and superoxide.

High density lipoprotein-induced endothelial nitric-oxide synthase activation is mediated by Akt and MAP kinases

High density lipoprotein (HDL) activates endothelial nitric-oxide synthase (eNOS), leading to increased production of the antiatherogenic molecule NO. A variety of stimuli regulate eNOS activity through signaling pathways involving Akt kinase and/or mitogen-activated protein (MAP) kinase. In the present study, we investigated the role of kinase cascades in HDL-induced eNOS stimulation in cultured endothelial cells and COS M6 cells transfected with eNOS and the HDL receptor, scavenger receptor B-I. HDL (10-50 microg/ml, 20 min) caused eNOS phosphorylation at Ser-1179, and dominant negative Akt inhibited both HDL-mediated phosphorylation and activation of the enzyme. Phosphoinositide 3-kinase (PI3 kinase) inhibition or dominant negative PI3 kinase also blocked the phosphorylation and activation of eNOS by HDL. Studies with genistein and PP2 showed that the nonreceptor tyrosine kinase, Src, is an upstream stimulator of the PI3 kinase-Akt pathway in this paradigm. In addition, HDL activated MAP kinase through PI3 kinase, and mitogen-activated protein kinase/extracellular signal-regulated kinase kinase inhibition fully attenuated eNOS stimulation by HDL without affecting Akt or eNOS Ser-1179 phosphorylation. Conversely, dominant negative Akt did not alter HDL-induced MAP kinase activation. These results indicate that HDL stimulates eNOS through common upstream, Src-mediated signaling, which leads to parallel activation of Akt and MAP kinases and their resultant independent modulation of the enzyme.

Chronic endothelin antagonism restores cerebrovascular function in diabetes

OBJECTIVE

Diabetes profoundly alters vascular function and is a risk factor for cerebrovascular disease. Diabetes increases myogenic tone and decreases responsiveness to adenosine triphosphatase (ATP)-sensitive K(+) (K(ATP)) channel openers and endothelium-dependent vasodilators. The mechanism(s) by which diabetes impairs cerebrovascular function remain obscure. In the present study, the effects of the potent vasoactive peptide endothelin-1 on myogenic tone and endothelium-dependent and potassium channel-mediated vasodilation in middle cerebral arteries from diabetic and nondiabetic rats were investigated.

METHODS

Twenty-eight Wistar rats were divided into four experimental groups (n = 7 per group): control (C), control treated with bosentan (an endothelin A/B receptor antagonist) (CB), diabetic (D), and diabetic bosentan-treated (DB). Diabetes was induced with streptozotocin (D and DB groups), after which chronic bosentan treatment was initiated (CB and DB groups). Middle cerebral arteries were mounted in a pressure myograph, and myogenic responses were recorded. In addition, endothelium-dependent and -independent responses and the effects of the K(ATP) channel opener pinacidil were examined.

RESULTS

Cerebral arteries from the diabetic and nondiabetic rats constricted in response to graded pressure increases. Maximum myogenic responses (percent constriction at 60 mm Hg) were significantly greater in the D group (38 +/- 3% versus 25 +/- 3% in C; P < 0.02). The enhanced myogenic tone in the D group was completely prevented by bosentan treatment (DB, 23 +/- 5% versus D; P < 0.003) without an effect on the CB group. In addition, bosentan treatment improved endothelium-dependent vasomotion and improved K(ATP)-mediated vasodilation in the DB group (P < 0.001).

CONCLUSION

These data describe, for the first time, the interaction between endothelin-1, myogenic tone, and endothelial function in diabetes. Chronic endothelin antagonism restores cerebrovascular function in this model of diabetes and has global implications for the management of cerebrovascular disease in diabetes.

Endothelial nitric oxide synthase, caveolae and the development of atherosclerosis

Early hypercholesterolaemia-induced vascular disease is characterized by an attenuated capacity for endothelial production of the antiatherogenic molecule nitric oxide (NO), which is generated by endothelial NO synthase (eNOS). In recent studies we have determined the impact of lipoproteins on eNOS subcellular localization and action, thereby providing a causal link between cholesterol status and initial abnormalities in endothelial function. We have demonstrated that eNOS is normally targeted to cholesterol-enriched caveolae where it resides in a signalling module. Oxidized low density lipoprotein (LDL; oxLDL) causes displacement of eNOS from caveolae by binding to endothelial cell CD36 receptors and by depleting caveolae cholesterol content, resulting in the disruption of eNOS activation. The adverse effects of oxLDL are fully prevented by high density lipoprotein (HDL) via binding to scavenger receptor BI (SR-BI), which is colocalized with eNOS in endothelial caveolae. This occurs through the maintenance of caveolae cholesterol content by cholesterol ester uptake from HDL. As importantly, HDL binding to SR-BI causes robust stimulation of eNOS activity in endothelial cells, and this process is further demonstrable in isolated endothelial cell caveolae. HDL also enhances endothelium- and NO-dependent relaxation in aortae from wild-type mice, but not in aortae from homozygous null SR-BI knockout mice. Thus, lipoproteins have potent effects on eNOS function in caveolae via actions on both membrane cholesterol homeostasis and the level of activation of the enzyme. These processes may be critically involved in the earliest phases of atherogenesis, which recent studies suggest may occur during fetal life.

Influence of oral contraceptive use on endothelial t-PA release in healthy premenopausal women

We determined the influence of oral contraceptives (OC) on the capacity of the endothelium to release tissue-type plasminogen activator (t-PA). Twenty-three healthy premenopausal women were studied: 12 nonusers and 11 users of OC. Net endothelial release rates of t-PA were calculated as the product of the arteriovenous concentration gradient and forearm plasma flow in response to intra-arterial bradykinin (BK: 12.5-50 ng. 100 ml tissue(-1) x min(-1)) and sodium nitroprusside (SNP: 1.0-4.0 microg x 100 ml tissue(-1) x min(-1)). Net release of t-PA antigen and increment in t-PA activity across the forearm to BK increased (P < 0.01) in a dose-dependent fashion and to similar extents in the nonusers and users of OC. At the highest BK dose, net release of t-PA antigen was 64.5 +/- 8.2 and 66.2 +/- 15.4 ng x 100 ml tissue(-1) x min(-1) in the nonusers and users of OC, whereas the net increment in t-PA activity was 18.6 +/- 3.0 and 16.0 +/- 2.0 IU. 100 ml tissue(-1) x min(-1), respectively. There was no effect of SNP on t-PA release in either group. These results indicate that endothelial t-PA release is not altered in premenopausal women who use oral contraception.

Role of nitric oxide and peroxynitrite in apoptosis - relation to endonuclease activity

Apoptosis is a form of cell death utilized physiologically to maintain tissue homeostasis, as well as in response to various toxic and inflammatory stimuli or anticancer drugs. Since the process of apoptosis is followed by phagocytosis, the cleavage of DNA to low molecular weight material may serve as a protective function limiting the probability of gene transfer to the nuclei of viable neighbor cells. Many different endonucleases have been proposed as candidates responsible for the internucleosomal cleavage of the genomic DNA observed during apoptosis. The main effect was attributed to the alkaline DNase I (Mg 2+ and caspase-dependent) and acid-DNase II. It was also documented that both of them contain a potential protease (caspase) cleavage site, but they can be also activated upon the influence of other "fragmentation factors", including nitric oxide (NO). The complexity of biological effects induced by NO may be the result of the cell redox state changes, due to its potential interaction with superoxide. The apoptotic effect of both, nitric oxide (NO) and peroxynitrite (ONOO) are dose-dependent and cell-specific may point out the existence of possible "inducible" form of endonuclease.

Short-term insulin treatment and aortic expressions of IGF-1 receptor and VEGF mRNA in diabetic rats

We investigated the relationship between the changes in vascular responsiveness and growth factor mRNA expressions induced by 1-wk treatment with high-dose insulin in control and established streptozotocin (STZ)-induced diabetes. Aortas from diabetic rats, but not those from insulin-treated diabetic rats, showed impaired endothelium-dependent relaxation in response to ACh (vs. untreated controls). The ACh-induced nitrite plus nitrate (NOx) level showed no significant difference between controls and diabetics. Insulin treatment increased NOx only in diabetics. In diabetics, insulin treatment significantly increased the aortic expressions of endothelial nitric oxide synthase (eNOS) mRNA and VEGF mRNA. The expression of IGF-1 mRNA was unaffected by diabetes or by insulin treatment. In contrast, the mRNA for the aortic IGF-1 receptor was increased in diabetics and further increased in insulin-treated diabetics. In aortic strips from age-matched control rats, IGF-1 caused a concentration-dependent relaxation. This relaxation was significantly stronger in strips from STZ-induced diabetic rats. These results suggest that in STZ-diabetic rats, short-term insulin treatment can ameliorate endothelial dysfunction by inducing overexpression of eNOS and/or VEGF mRNAs possibly via IGF-1 receptors. These receptors were increased in diabetes, perhaps as result of insulin deficiency.

Endothelial function in patients with peripheral vascular disease: influence of prostaglandin E1

Peripheral arterial occlusive disease (PAOD) is characterized by atherosclerotic lesions in large vessels and disturbances on the microcirculatory level. In the local regulation of vascular tone and microvascular perfusion, vascular endothelium plays a key role. For many years prostaglandin E1 (PGE1) has been used for the treatment of PAOD. Because PGE1 has only moderate effects on blood flow other mechanisms may be relevant for the therapeutical efficacy. The aim of our pilot study was to evaluate endothelial function in patients with PAOD and to investigate the impact of PGE1 on endothelial-dependent vasodilation in peripheral vesselsIn 8 controls and in 8 patients with PAOD stage II, endothelial-dependent vascular responses of the femoral vessels to increasing doses of acetylcholine (30,60,90 microg/min) were determined by Doppler flow velocity measurements in the common femoral artery. Furthermore, vascular reactivity was evaluated before and immediately after intravenous infusion of 30 microg PGE1/30 min in patients. Endothelial-dependent vasodilation was significantly reduced in patients with PAOD compared to control subjects. Infusion of PGE1 neither increased blood flow in the common femoral artery nor endothelium-dependent vasodilation of peripheral resistance vessels as indicated by unchanged reaction to acetylcholine. In conclusion, endothelial function is impaired in patients with PAOD. Administration of PGE1 did not increase femoral artery blood flow or improve endothelial-dependent reactivity of peripheral resistance vessels in patients with PAOD. Therefore, beneficial effects of PGE1 in peripheral vascular disease cannot be attributed to an increase in blood supply or an improvement of endothelial-dependent vasodilation.

Antioxidant improves smooth muscle sarco/endoplasmic reticulum Ca(2+)-ATPase function and lowers tyrosine nitration in hypercholesterolemia and improves nitric oxide-induced relaxation

Antioxidants improve endothelial function in hypercholesterolemia (HC); however, whether this includes improvement of the vascular smooth muscle response to NO is unknown. NO relaxes arteries, in part, by stimulating Ca(2+) uptake via sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) in aortic smooth muscle, and HC impairs SERCA function and the response to NO. HC induces oxidative stress, which could impair SERCA function. To study the effect of antioxidants, which are known to improve endothelium-dependent relaxation in HC, smooth muscle SERCA activity and NO-induced relaxation were studied in rabbits fed normal chow or a 0.5% cholesterol diet for 13 weeks. The antioxidant t-butylhydroxytoluene (BHT, 1%) was mixed with the HC diet in the last 3 weeks. HC impaired acetylcholine- and NO-induced relaxation, and these were restored by BHT. After inhibiting SERCA with thapsigargin, no difference existed in NO-induced relaxation among the three groups. Reduced aortic SERCA activity in HC was restored by BHT without changing SERCA protein expression. 3-Nitrotyrosine was notably increased in the media of the HC aorta, where it colocalized with SERCA. Tyrosine-nitrated SERCA protein was immunoprecipitated in the aortas of HC rabbits, where it was decreased by BHT, and it was also detected in the aortas of atherosclerotic humans. Thus, the antioxidant reverses impaired smooth muscle SERCA function in HC, and this is correlated with the improved relaxation to NO. These beneficial effects may depend on reducing the direct effects on SERCA of reactive oxygen species that are augmented in HC.

Regulation of endothelial nitric oxide synthase: location, location, location

Endothelial nitric oxide synthase (eNOS) is expressed in vascular endothelium, airway epithelium, and certain other cell types where it generates the key signaling molecule nitric oxide (NO). Diminished NO availability contributes to systemic and pulmonary hypertension, atherosclerosis, and airway dysfunction. Complex mechanisms underly the cell specificity of eNOS expression, and co- and post-translational processing leads to trafficking of the enzyme to plasma membrane caveolae. Within caveolae, eNOS is the downstream target member of a signaling complex in which it is functionally linked to both typical G protein-coupled receptors and less typical receptors such as estrogen receptor (ER) alpha and the high-density lipoprotein receptor SR-BI displaying novel actions. This compartmentalization facilitates dynamic protein-protein interactions and calcium- and phosphorylation-dependent signal transduction events that modify eNOS activity. Further understanding of these mechanisms will enable us to take preventive and therapeutic advantage of the powerful actions of NO in multiple cell types.

Potential role of dietary flavonoids in reducing microvascular endothelium vulnerability to oxidative and inflammatory insults ( small star, filled)

Although antioxidant systems help control the level of reactive oxygen species they may be overwhelmed during periods of oxidative stress. Evidence suggests that oxidative stress components as well as inflammatory mediators may be involved in the pathogenesis of vascular disorders, where localized markers of oxidative damage have been found. In this regard we investigated the putative antioxidant and anti-inflammatory effects of blueberry and cranberry anthocyanins and hydroxycinnamic acids against H(2)O(2) and TNFalpha induced damage to human microvascular endothelial cells. Polyphenols from both berries were able to localize into endothelial cells subsequently reducing endothelial cells vulnerability to increased oxidative stress at both the membrane and cytosol level. Furthermore, berry polyphenols also reduced TNFalpha induced up-regulation of various inflammatory mediators (IL-8, MCP-1 and ICAM-1) involved in the recruitment of leukocytes to sites of damage or inflammation along the endothelium. In conclusion, polyphenols isolated from both blueberry and cranberry were able to afford protection to endothelial cells against stressor induced up-regulation of oxidative and inflammatory insults. This may have beneficial actions against the initiation and development of vascular diseases and be a contributing factor in the reduction of age-related deficits in neurological impairments previously reported by us.

Long-term inhibition of nitric oxide synthesis increases arterial thrombogenecity in rat carotid artery

Reduced activity of endothelial nitric oxide (NO) may be involved in thrombus formation on atherosclerotic plaques, a major cause of acute coronary syndrome. However, mechanisms of such increase in arterial thrombogenecity have not been fully understood. We previously reported that long-term inhibition of NO synthesis by administration of N(G)-nitro-L-arginine methyl ester (L-NAME) causes hypertension and activates vascular tissue angiotensin-converting enzyme (ACE) activity. We used this model to investigate the mechanism by which long-term impairment of NO activity increases arterial thrombogenecity. We observed cyclic flow variations (CFVs), a reliable marker of platelet thrombi, after the production of stenosis of the carotid artery in rats treated with L-NAME for 4 wk. The thrombin antagonist argatroban suppressed the CFVs. The CFVs were detected in rats receiving L-NAME plus hydralazine but not in rats receiving L-NAME plus an ACE inhibitor (imidapril). Treatment with the ACE inhibitor imidapril, but not with hydralazine, prevented L-NAME-induced increases in carotid arterial ACE activity and attenuated tissue factor expression. These results suggest that long-term inhibition of endothelial NO synthesis may increase arterial thrombogenecity at least in part through angiotensin II-induced induction of tissue factor and the resultant thrombin generation. These data provide a new insight as to how endothelial NO exhibits antithrombogenic properties of the endothelium.

Nitric oxide: implications for vascular and endovascular surgery

Nitric oxide has a key role in vascular homeostasis. It plays a protective role by suppressing abnormal proliferation of vascular smooth muscle following various pathological situations including atherosclerosis and restenosis after vascular interventions such as balloon angioplasty, stent deployment and bypass grafting. It also has strong antiplatelet and anti-thrombogenic properties. In this review, possible applications to daily vascular and endovascular surgery practice, including systemic use of NO donors, enhancing endogenous production of NO by L-arginine and gene therapy, local delivery strategies and coating stents and grafts with NO-delivering/enhancing chemicals are reviewed.