Endothelial dysfunction: a multifaceted disorder (The Wiggers Award Lecture)

Epigallocatechin gallate elicits contractions of the isolated aorta of the aged spontaneously hypertensive rat

The present study examined the effect of the green tea catechin epigallocatechin gallate (EGCG) on endothelium-dependent responses in the aorta of 36-week-old spontaneously hypertensive rats (SHR). Isometric tension was measured in isolated aortic rings. The release of prostanoid end products was determined using enzyme immunoassay kits and the intracellular reactive oxygen species (ROS) concentration using confocal microscopy. EGCG did not improve endothelium-dependent relaxations evoked by acetylcholine, except in the presence of indomethacin. EGCG did not inhibit endothelium-dependent contractions induced by acetylcholine or ATP. At 10(-6) M and higher concentrations, EGCG caused increases in tension in the SHR aorta. The EGCG-induced contractions were accompanied by an increased production of ROS. The amount of prostanoid end products was increased significantly by EGCG, indicating that their production followed the activation of cyclooxygenase (COX). These prostanoids in turn stimulated thromboxane-prostanoid (TP) receptors and caused contractions. EGCG induced significantly smaller contractions in aortae of normotensive Wistar-Kyoto rats (WKY), accompanied with a lower production of ROS and a lesser release of prostanoids. These observations suggest that EGCG-induced contractions occur more readily in blood vessels of hypertensive than normotensive animals. The present findings indicate that the increased oxidative stress in the ageing hypertensive animals contributes to the loss of the beneficial effects and the enhancement of the adverse effects of EGCG.

Weight and inflammation are the major determinants of vascular dysfunction in the aortae of db/db mice

The key roles that obesity, hyperglycemia, hyperlipidemia, inflammation, and oxidative stress play in the progression of diabetes vascular complications are well recognized; however, the relative contribution and importance of these individual factors remain uncertain. At 6, 10, or 14 weeks old, blood samples and thoracic aortae were collected from db/db mice and their non-diabetic controls. Plasma samples were analyzed for glucose, 8-isoprostane, CRP, triglycerides, LDL, and HDL as markers of glycemic status, oxidative stress, inflammation, and dyslipidemia, respectively. The responses of the aortic rings to high KCl, phenylephrine (PE), acetylcholine (ACh), and sodium nitroprusside were examined. Statistical methods were used to estimate the strength of the association between plasma variables and vascular functions. Systemic inflammation occurred in db/db mice at an earlier age than did hyperglycemia or oxidative stress. Aortae of db/db showed augmented contractions to PE which were positively correlated with weight, plasma glucose, 8-isoprostane, and CRP. Also, db/db mice showed impaired endothelium-dependent ACh vasorelaxation which was negatively correlated with weight, plasma glucose, and 8-isoprostane. Multivariate analysis and stepwise modeling show that CRP is the major determinant of the contractile responses, while weight and HDL are the major determinants of ACh-induced relaxation. Among the traditional risk factors of obesity, hyperglycemia, oxidative stress, inflammation, and dyslipidemia, our study reveals that weight and inflammation are the major determinants of vascular dysfunction in the aortae of db/db mice. Our findings partially resolve the complexity of diabetes vasculopathies and suggest targeting weight loss and inflammation for effective therapeutic approaches.

Combined inhibition of nitric oxide and vasodilating prostaglandins abolishes forearm vasodilatation to systemic hypoxia in healthy humans

We tested the hypothesis that nitric oxide (NO) and vasodilating prostaglandins (PGs) contribute independently to hypoxic vasodilatation, and that combined inhibition would reveal a synergistic role for these two pathways in the regulation of peripheral vascular tone. In 20 healthy adults, we measured forearm blood flow (Doppler ultrasound) and calculated forearm vascular conductance (FVC) responses to steady-state (SS) isocapnic hypoxia (O₂ saturation ~85%). All trials were performed during local α- and β-adrenoceptor blockade (via a brachial artery catheter) to eliminate sympathoadrenal influences on vascular tone and thus isolate local vasodilatory mechanisms. The individual and combined effects of NO synthase (NOS) and cyclooxygenase (COX) inhibition were determined by quantifying the vasodilatation from rest to SS hypoxia, as well as by quantifying how each inhibitor reduced vascular tone during hypoxia. Three hypoxia trials were performed in each subject. In group 1 (n = 10), trial 1, 5 min of SS hypoxia increased FVC from baseline (21 ± 3%; P < 0.05). Infusion of N(G)-nitro-L-arginine methyl ester (L-NAME) for 5 min to inhibit NOS during continuous SS hypoxia reduced FVC by -33 ± 3% (P < 0.05). In Trial 2 with continuous NOS inhibition, the increase in FVC from baseline to SS hypoxia was similar to control conditions (20 ± 3%), and infusion of ketorolac for 5 min to inhibit COX during continuous SS hypoxia reduced FVC by -15 ± 3% (P < 0.05). In Trial 3 with combined NOS and COX inhibition, the increase in FVC from baseline to SS hypoxia was abolished (~3%; NS vs. zero). In group 2 (n = 10), the order of NOS and COX inhibition was reversed. In trial 1, five minutes of SS hypoxia increased FVC from baseline (by 24 ± 5%; P < 0.05), and infusion of ketorolac during SS hypoxia had minimal impact on FVC (-4 ± 3%; NS). In Trial 2 with continuous COX inhibition, the increase in FVC from baseline to SS hypoxia was similar to control conditions (27 ± 4%), and infusion of L-NAME during continuous SS hypoxia reduced FVC by -36 ± 7% (P < 0.05). In Trial 3 with combined NOS and COX inhibition, the increase in FVC from baseline to SS hypoxia was abolished (~3%; NS vs. zero). Our collective findings indicate that (1) neither NO nor PGs are obligatory to observe the normal local vasodilatory response from rest to SS hypoxia; (2) NO regulates vascular tone during hypoxia independent of the COX pathway, whereas PGs only regulate vascular tone during hypoxia when NOS is inhibited; and (3) combined inhibition of NO and PGs abolishes local hypoxic vasodilatation (from rest to SS hypoxia) in the forearm circulation of healthy humans during systemic hypoxia.

Effects of disturbed flow on vascular endothelium: pathophysiological basis and clinical perspectives

Vascular endothelial cells (ECs) are exposed to hemodynamic forces, which modulate EC functions and vascular biology/pathobiology in health and disease. The flow patterns and hemodynamic forces are not uniform in the vascular system. In straight parts of the arterial tree, blood flow is generally laminar and wall shear stress is high and directed; in branches and curvatures, blood flow is disturbed with nonuniform and irregular distribution of low wall shear stress. Sustained laminar flow with high shear stress upregulates expressions of EC genes and proteins that are protective against atherosclerosis, whereas disturbed flow with associated reciprocating, low shear stress generally upregulates the EC genes and proteins that promote atherogenesis. These findings have led to the concept that the disturbed flow pattern in branch points and curvatures causes the preferential localization of atherosclerotic lesions. Disturbed flow also results in postsurgical neointimal hyperplasia and contributes to pathophysiology of clinical conditions such as in-stent restenosis, vein bypass graft failure, and transplant vasculopathy, as well as aortic valve calcification. In the venous system, disturbed flow resulting from reflux, outflow obstruction, and/or stasis leads to venous inflammation and thrombosis, and hence the development of chronic venous diseases. Understanding of the effects of disturbed flow on ECs can provide mechanistic insights into the role of complex flow patterns in pathogenesis of vascular diseases and can help to elucidate the phenotypic and functional differences between quiescent (nonatherogenic/nonthrombogenic) and activated (atherogenic/thrombogenic) ECs. This review summarizes the current knowledge on the role of disturbed flow in EC physiology and pathophysiology, as well as its clinical implications. Such information can contribute to our understanding of the etiology of lesion development in vascular niches with disturbed flow and help to generate new approaches for therapeutic interventions.

Vascular effects of the red blood cell storage lesion

Transfusion of RBCs is often clinically necessary--and life-saving--for anemic patients. RBCs can be stored for up to 42 days between the time of donation and the time of transfusion. For many years, investigators have studied the biochemical changes that occur in RBCs stored before transfusion (the RBC "storage lesion"). More recently, clinical studies have suggested that RBC units stored for long periods (often described as > 14-21 days) may mediate adverse effects in the recipient, leading to morbidity and mortality. Unfortunately, these effects are difficult to identify and study because there are no agreed-upon mechanisms for these adverse events and few good assays to study them in individual transfusion recipients. We have proposed the hypothesis of insufficient NO bioavailability (INOBA) to explain the adverse events associated with transfusion of older RBC units. INOBA postulates that the combination of impaired NO production and increased NO scavenging by stored RBCs, together with reduced NO synthesis by dysfunctional endothelial cells, collectively reduce NO levels below a critical threshold in vascular beds. In this situation, inappropriate vasoconstriction occurs, leading to reduced blood flow and insufficient O(2) delivery to end organs. If confirmed, the INOBA hypothesis may lead to improved methods for blood storage and collection, as well as new screening and matching tools for blood donors and transfusion recipients.

Vasodilator effect of Cassiarin A, a novel antiplasmodial alkaloid from Cassia siamea, in rat isolated mesenteric artery

The aim of this study was to investigate the vasorelaxant effect induced by cassiarin A, a novel antiplasmodial alkaloid from Cassia siamea, in rings cut from rat superior mesenteric arteries. In rings precontracted with phenylephrine, cassiarin A induced a concentration-dependent relaxation. This relaxation was attenuated: 1) after removal of the endothelium or after pretreatment of rings with 100 microM of N(G)-nitro-L-arginine (nitric oxide synthase inhibitor) or 10 microM of 1H-[1,2,4]oxadiazolo[4,3-a]-quinoxalin-1-one (guanylyl cyclase inhibitor), but not after pretreatment with 10 microM of indomethacin (cyclooxygenase inhibitor); and 2) after pretreatment of preparations with either a nonselective or selective inhibitor of large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels [1 mM of tetraethylammonium or 100 nM of iberiotoxin, respectively]. The cassiarin A-induced relaxation was also attenuated by these BK(Ca) inhibitors in endothelium-denuded preparations. The cassiarin A-induced relaxation was not altered by treatment with the ATP-sensitive K(+)-channel inhibitor glibenclamide (10 microM) or with the voltage-dependent K(+)-channel inhibitor 4-aminopyridine (1 mM). In isolated mesenteric artery rings, cassiarin A tended to increase nitric oxide (NO) levels. These results suggest that in the rat mesenteric artery, cassiarin A-induced relaxation may be mediated by endothelial NO and may occur partly via BK(Ca)-channel activation.

Inhibition of soluble epoxide hydrolase attenuates endothelial dysfunction in animal models of diabetes, obesity and hypertension

Endothelial dysfunction is a hallmark of, and plays a pivotal role in the pathogenesis of cardiometabolic diseases, including type II diabetes, obesity, and hypertension. It has been well established that epoxyeicosatrienoic acids (EETs) act as an endothelial derived hyperpolarization factor (EDHF). Soluble epoxide hydrolase (s-EH) rapidly hydrolyses certain epoxylipids (e.g. EETs) to less bioactive diols (DHETs), thereby attenuating the evoked vasodilator effects. The aim of the present study was to examine if inhibition of s-EH can restore impaired endothelial function in three animal models of cardiometabolic diseases. Isolated vessel rings of the aorta and/or mesenteric artery from mice or rats were pre-contracted using phenylephrine or U46619. Endothelium-dependent and independent vasorelaxation to acetylcholine and sodium nitroprusside (SNP) were measured using wire myography in vessels isolated from db/db or diet-induced obesity (DIO) mice, and angiotensin II-induced hypertensive rats treated chronically with s-EH inhibitors AR9281 or AR9276 or with vehicle. Vasorelaxation to acetylcholine, but not to SNP was severely impaired in all three animal models. Oral administration of AR9281 or AR9276 abolished whole blood s-EH activity, elevated epoxy/diol lipid ratio, and abrogated endothelial dysfunction in all three models. Incubating the mesenteric artery of db/db mice with L-NAME and indomethacin to block nitric oxide (NO) and prostacyclin formation did not affect AR9821-induced improvement of endothelial function. These data indicate that inhibition of s-EH ameliorates endothelial dysfunction and that effects in the db/db model are independent of the presence of NO and cyclooxygenase derived prostanoids. Thus, preserving vasodilator EETs by inhibition of s-EH may be of therapeutic benefit by improving endothelial function in cardiometabolic diseases.

Endothelium-dependent vasorelaxation to the AMPK activator AICAR is enhanced in aorta from hypertensive rats and is NO and EDCF dependent

Activation of AMP-activated protein kinase (AMPK) induces vasorelaxation in arteries from healthy animals, but the mechanisms coordinating this effect are unclear and the integrity of this response has not been investigated in dysfunctional arteries of hypertensive animals. Here we investigate the mechanisms of relaxation to the AMPK activator 5-aminoimidazole-4-carboxamide 1-β-D-ribofuranoside (AICAR) in isolated thoracic aorta rings from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). Although AICAR generated dose-dependent (10(-6)-10(-2) M) relaxation in precontracted WKY and SHR aortic rings with (E(+)) or without (E(-)) endothelium, relaxation was enhanced in E(+) rings. Relaxation in SHR E(+) rings was also enhanced at low [AICAR] (10(-6) M) compared with that of WKY (57 ± 8% vs. 3 ± 2% relaxation in SHR vs. WKY E(+)), but was similar and near 100% in both groups at high [AICAR]. Pharmacological dissection showed that the mechanisms responsible for the endothelium-dependent component of relaxation across the dose range of AICAR are exclusively nitric oxide (NO) mediated in WKY rings, but partly NO dependent and partly cyclooxygenase (COX) dependent in SHR vessels. Further investigation revealed that ACh-stimulated COX-endothelium-derived contracting factors (EDCF)-mediated contractions were suppressed by AICAR, and this effect was reversed in the presence of the AMPK inhibitor Compound C in quiescent E(+) SHR aortic rings. Western blots demonstrated that P(Thr(172))-AMPK and P(Ser(79))-acetyl-CoA carboxylase (indexes of AMPK activation) were elevated in SHR versus WKY E(+) rings at low AICAR (∼2-fold). Together these findings suggest that AMPK-mediated inhibition of EDCF-dependent contraction and elevated AMPK activation may contribute to the enhanced sensitivity of SHR E(+) rings to AICAR. These results demonstrate AMPK-mediated vasorelaxation is present and enhanced in arteries of SHR and suggest that activation of AMPK may be a potential strategy to improve vasomotor dysfunction by suppressing enhanced endoperoxide-mediated contraction and enhancing NO-mediated relaxation.

Anti-aggregating effect of BAY 58-2667, an activator of soluble guanylyl cyclase

The purpose of the present study was to determine whether an activator of soluble guanylyl cyclase (sGC), BAY 58-2667, inhibits platelet aggregation and to clarify its mechanism of action. Blood was collected from anesthetized WKY rats. The aggregation of washed platelet was measured and the production of cAMP and cGMP was determined. BAY 58-2667 produced a partial inhibition of the ADP- and collagen-induced platelet aggregation, but did not significantly affect thrombin-induced aggregation. In ADP-induced platelet aggregation, the inhibitory effects of BAY 58-2667 were associated with an increased level of both cGMP and cAMP while that of the prostacyclin analogue, beraprost, was correlated only with an increase in cAMP. The inhibitor of sGC, ODQ, enhanced the effects of BAY 58-2667. The presence of L-nitroarginine, an inhibitor of NO-synthase, hydroxocobalamin, a scavenger of NO, or that of three different NO-donors did not affect the anti-aggregating effect of BAY 58-2667. However, the anti-aggregating effects of beraprost were potentiated by BAY 58-2667. Therefore, the platelet inhibitory effects of BAY 58-2667 are associated with the generation of cGMP and a secondary increase in cAMP, both being totally NO-independent. When the sGC is oxidized, BAY 58-2667 becomes a relevant anti-aggregating agent, which synergizes with the cAMP-dependent pathway.

Clinical Relevance of Nitric Oxide Metabolites and Nitrative Stress in Thrombotic Primary Antiphospholipid Syndrome

Objective.

To assess the role of nitrite (NO2−), nitrate (NO3−), and nitrative stress in thrombotic primary antiphospholipid syndrome (PAPS).

Methods.

We investigated 46 patients with PAPS: 21 asymptomatic but persistent carriers of antiphospholipid antibodies (PCaPL), 38 patients with inherited thrombophilia (IT), 33 patients with systemic lupus erythematosus (SLE), and 29 healthy controls (CTR). IgG anticardiolipin (aCL), IgG anti-beta2-glycoprotein I (anti-ß2-GPI), IgG anti-high density lipoprotein (aHDL), IgG anti-apolipoprotein A-I (aApoA-I), crude nitrotyrosine (NT) (an indicator of nitrative stress), and high sensitivity C-reactive protein (CRP) were measured by immunoassays. Plasma nitrite (NO2−), nitrate (NO3−), and total antioxidant capacity (TAC) were measured by colorimetric spectroscopic assays.

Results.

Average plasma NO2−was lower in PAPS, PCaPL, and IT (p < 0.0001); average NO3−was highest in SLE (p < 0.0001), whereas average NT was higher in PAPS and SLE (p = 0.01). In thrombotic PAPS, IgG aCL titer and number of vascular occlusions negatively predicted NO2−(p = 0.03 and p = 0.001, respectively), whereas arterial occlusions and smoking positively predicted NO3−(p = 0.05 and p = 0.005), and CRP positively predicted NT (p = 0.004). In the PCaPL group IgG aCL negatively predicted NO3−(p = 0.03). In the SLE group IgG aCL negatively predicted NO2−(p = 0.03) and NO3−(p = 0.02).

Conclusion.

PAPS is characterized by decreased NO2−in relation to type and number of vascular occlusions and to aPL titers. Nitrative stress and low grade inflammation are linked phenomena in PAPS and may have implications for thrombosis and atherosclerosis.

The thromboxane/endoperoxide receptor (TP): the common villain

The stimulation of thromboxane/endoperoxide receptors (TP) elicits diverse physiological/pathophysiological reactions, including platelet aggregation and contraction of vascular smooth muscle. Furthermore, the activation of endothelial TP promotes the expression of adhesion molecules and favors adhesion and infiltration of monocytes/macrophages. In various cardiovascular diseases, endothelial dysfunction is predominantly the result of the release of endothelium-derived contracting factors that counteract the vasodilator effect of nitric oxide produced by the endothelial nitric oxide synthase. Endothelium-dependent contractions involve the activation of cyclooxygenases, the production of reactive oxygen species along with that of endothelium-derived contracting factors, which diffuse toward the vascular smooth muscle cells and activate their TP. TP antagonists curtail the endothelial dysfunction in diseases such as hypertension and diabetes, are potent antithrombotic agents, and reduce vascular inflammation. Therefore, TP antagonists, because of this triple activity, may have a unique potential for the treatment of cardiovascular disorders.

Lysimachia clethroides extract promote vascular relaxation via endothelium-dependent mechanism

Lysimachia clethroides is widely used in traditional herbal medicine for many purposes, especially for blood vessel-related diseases in Korea and East Asia. Experiments were undertaken to determine whether hydro-alcoholic extract obtained from L. clethroides (LCE) has vasorelaxant activity in the rat aorta rings and, if so, to elucidate the underlying mechanism. Rat aorta rings were suspended in organ chambers for the measurement of changes in isometric tension in the presence or absence of several inhibitors. LCE induced endothelium-dependent vasodilation (ED50 = 6.1 mug/mL) and that was abolished by nitric oxide synthase inhibitor, N-nitro-L-arginine, and guanylyl cyclase inhibitor, 1H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one, PI3-kinase inhibitor, wortmannin, and cell permeable superoxide dismutase. In addition, LCE decreased vessels contraction by phenylephrine. Prostaglandin synthesis inhibitor, indometacin, and inhibitors of endothelium-derived hyperpolarizing factor, charybdotoxin plus apamin, did not affect vasodilatory effect of LCE. In cultured endothelial cells, LCE-induced phosphorylation of serine 1177-endothelial nitric oxide synthase and serine 473-Akt. LCE inhibited strongly nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity in smooth muscle cells and angiotensin II-induced contraction of rat aorta. Finally, increased oxidative stress in rat aorta-induced by angiotensin II is ameliorated by LCE. Taken together, LCE induces an endothelium-dependent vasodilation and might be involved, at least in part, the activation of the nitric oxide-cyclic guanosine monophosphate pathway. In addition, LCE decreases oxidative stress in aorta by inhibition of NADPH oxidase activity. The present findings indicate that LCE could be a candidate of herbal medicine for cardiovascular diseases associated with disturbed NO production and endothelial dysfunction.

Deleterious combined effects of salt-loading and endothelial cell restricted endothelin-1 overexpression on blood pressure and vascular function in mice

BACKGROUND

We previously showed that young transgenic mice overexpressing preproendothelin-1 specifically in endothelial cells had hypertrophic remodeling, endothelial dysfunction, increased vascular NADPH oxidase activity, and inflammation in mesenteric small arteries without blood pressure (BP) elevation compared to nontransgenic wild-type littermates. To assess the consequences of salt-loading and the role of endothelin receptors, we investigated the effects of these on vascular structure, function, and oxidative stress in mesenteric arteries in salt-loaded transgenic mice treated with endothelin receptor antagonists.

METHODS

Ten-month-old male transgenic and wild-type littermates were salt-loaded (4% NaCl) and treated with endothelin subtype A receptor antagonist (ET(A)RA, ABT-627, 5 mg/kg per day), endothelin subtype B receptor antagonist (ET(B)RA; A-192621, 30 mg/kg per day), or ET(A)/BRA (bosentan, 100 mg/kg per day) for 4 weeks. BP was measured by radiotelemetry, vascular reactivity of mesenteric small arteries was studied on a pressurized myograph, and vascular NADPH oxidase activity was studied by lucigenin chemiluminescence.

RESULTS

Transgenic+salt mice had significantly increased BP compared with wild-type+salt mice, which was prevented by ET(A)RA and dual ET(A/B)RA but further increased by ETB antagonism. Increased small artery media/lumen ratio of transgenic+salt mice was significantly decreased only by dual ET(A/B)RA (P < 0.01), whereas no differences were found in media cross-sectional area. Impaired maximal relaxation of small arteries to acetylcholine was significantly prevented with ET(A)RA and ET(A/B)RA (P < 0.05). N(omega)-nitro-L-arginine methyl ester-induced reduction of acetylcholine maximal relaxation was partially prevented by ET(A)RA, completely prevented by dual, and partially restored by vitamin C preincubation following dual ET(A/B)RA. The blunted endothelin-1 contractile response of small arteries found in transgenic+salt mice was partially restored by ET(A)RA and completely prevented by dual ET(A/B)R antagonism. The vasoconstrictor response to endothelin-1 was not altered in the presence or absence of ET(B)RA. Increased vascular NADPH oxidase activity of transgenic+salt mice was further increased by ET(B)RA but returned to levels seen in wild-type+salt mice under either ET(A)RA and ET(A/B)RA.

CONCLUSION

Transgenic+salt mice with endothelin-1 overexpression have structural alterations of mesenteric resistance vessels, endothelial dysfunction due to reduced nitric oxide bioavailability, a reduced responsiveness to endothelin-1, and enhanced vascular NADPH oxidase activity. ET(B)RA further exacerbated these effects, whereas ET(A)RA significantly improved but did not normalize them in chronically salt-loaded transgenic mice with endothelial cell human endothelin-1 overexpression. Salt and endothelin-1 overexpression have deleterious additive effects on vascular remodeling mediated by ET(A)R and ET(B)R. ET(B)R probably located in the endothelium, however, also exerts beneficial effects on endothelial function in this experimental paradigm. The present study provides the first in-vivo demonstration that endothelin-1 overexpression when associated with high-salt intake results in enhanced endothelial dysfunction and vascular remodeling of resistance vessels, and contributes to elevated BP, via ET(A)R and ET(B)R.

Endothelium-derived vasoactive factors and hypertension: possible roles in pathogenesis and as treatment targets

Endothelial cells regulate vascular tone by releasing various contracting and relaxing factors including nitric oxide (NO), arachidonic acid metabolites (derived from cyclooxygenases, lipoxygenases, and cytochrome P450 monooxygenases), reactive oxygen species, and vasoactive peptides. Additionally, another pathway associated with the hyperpolarization of the underlying smooth muscle cells plays a predominant role in resistance arteries. Endothelial dysfunction is a multifaceted disorder, which has been associated with hypertension of diverse etiologies, involving not only alterations of the L-arginine NO-synthase-soluble guanylyl cyclase pathway but also reduced endothelium-dependent hyperpolarizations and enhanced production of contracting factors, particularly vasoconstrictor prostanoids. This brief review highlights these different endothelial pathways as potential drug targets for novel treatments in hypertension and the associated endothelial dysfunction and end-organ damage.

A review of endothelial dysfunction in diabetes: a focus on the contribution of a dysfunctional eNOS

Although the etiology of vascular dysfunction in diabetes has been extensively investigated in both humans as well as animal models of human diabetes, the relative importance of the cellular pathways involved is still not fully understood. In this review, we focus on reviewing the literature that provides insights into how an acute exposure to hyperglycemia results in a dysregulation of endothelial nitric oxide synthase function, the subsequent downstream effects of endothelial nitric oxide synthase dysregulation, and the development of endothelial dysfunction.

C-type natriuretic peptide effects on cardiovascular nitric oxide system in spontaneously hypertensive rats

The aim was to study the effects of C-type natriuretic peptide (CNP) on mean arterial pressure (MAP) and the cardiovascular nitric oxide (NO) system in spontaneously hypertensive rats (SHR), and to investigate the signaling pathways involved in this interaction. SHR and WKY rats were infused with saline or CNP. MAP and nitrites and nitrates excretion (NO(x)) were determined. Catalytic NO synthase (NOS) activity and endothelial (eNOS), neuronal (nNOS) and inducible NOS (iNOS) were measured in the heart and aorta artery. NOS activity induced by CNP was determined in presence of: iNOS or nNOS inhibitors, NPR-A/B natriuretic peptide receptors blocker and Gi protein and calmodulin inhibitors. CNP diminished MAP and increased NO(x) in both groups. Cardiovascular NOS activity was higher in SHR than in WKY. CNP increased NOS activity, but this activation was lower in SHR. CNP had no effect on NOS isoforms expression. iNOS and nNOS inhibitors did not modify CNP-induced NOS activity. NPR-A/B blockade induced no changes in NOS stimulation via CNP in both tissues. Cardiovascular NOS response to CNP was reduced by Gi protein and calmodulin inhibitors in both groups. CNP interacts with NPR-C receptors, activating Ca-calmodulin eNOS via Gi protein. NOS response to CNP is impaired in the heart and aorta of SHR. Alterations in the interaction between CNP and NO would be involved in the maintenance of high blood pressure in this model of hypertension.

Endothelial modulation of agonist-induced vasoconstriction in mesenteric microcirculation

It is widely accepted that vascular endothelium regulates vasoconstriction via release of endothelium-derived relaxing factors (EDRF). The mesenteric circulation, which is the largest vascular bed, influences regulation of systemic blood pressure. However, the role of EDRF in the modulation of vascular tone in peripheral mesenteric circulation has not been extensively studied. Therefore, our recent studies investigated the role of the vascular endothelium in the regulation of methoxamine (alpha(1)-adrenoceptor agonist)-induced vasoconstriction and their age-related changes in rat mesenteric vascular beds. In mesenteric vascular beds with intact endothelium isolated from 8 week-old rats, the initial maximum vasoconstriction induced by continuous perfusion of methoxamine was time-dependently decreased during 3 hour-perfusion. Neither nitric oxide synthase inhibitor nor cyclooxygenase inhibitor altered this time-dependent reduction of methoxamine-induced vasoconstriction. Endothelium removal, K(+)-channel inhibitors and gap junction inhibitor significantly inhibited the time-dependent reduction of methoxamine-induced vasoconstriction. In the preparations with intact endothelium from 16 week-old rats, the time-dependent reduction of methoxamine-induced vasoconstriction disappeared. Furthermore, endothelium removal and treatment with cyclooxygenase inhibitor, thromboxane A(2) receptor antagonist or superoxide dismutase mimetic significantly reduced the methoxamine-induced vasoconstriction in the preparations from 16 week-old rats. These findings suggest that vascular endothelium acts to depress methoxamine-induced vasoconstriction by releasing endothelium-derived hyperpolarizing factor (EDHF), and dysfunction in this endothelial modulation develops with ageing.

Minireview: rapid actions of sex steroids in the endothelium

The endothelium is a dynamic interface between the blood vessel and the circulating blood that plays a pivotal role in vascular homeostasis. As such, studies on sex steroid regulation of endothelial function are critical to understanding the role of sex steroids in cardiovascular health and disease. The classical model of steroid action involves liganded steroid receptors binding to specific response elements on target genes to regulate gene transcription. In whole organisms, the time lag between steroid administration and observable effects produced by newly synthesized protein is typically in the order of hours to days. And yet, some effects of steroids, such as vasodilatation, occur within seconds to minutes of steroid administration. Studies in multiple cell types have also shown that steroids can cause the rapid initiation of multiple signaling cascades and second messenger systems, prompting investigations into alternate, transcription independent mechanisms of steroid action. Studies of the endothelium over the past two decades have revealed fundamental mechanisms in rapid sex steroid signaling. In particular, endothelium-dependent vasodilatation by estradiol-induced activation of endothelial nitric oxide synthase has proven to be an uniquely informative model to study sex steroid signaling via classical sex steroid receptors localized to the cell membrane. Despite the complexity of feedback and cross talk between rapid sex steroid signaling and other modes of steroid action, recent studies in this field are facilitating the development of steroidal drugs that selectively target the ability of sex steroids to initiate signaling cascades.

Activation of endothelial BKCa channels causes pulmonary vasodilation

BACKGROUND

Large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels cause hyperpolarization and can regulate vascular tone. In this study, we evaluated the effect of endothelial BK(Ca) activation on pulmonary vascular tone.

METHODS

The presence of BK(Ca) channels in lung microvascular endothelial cells (LMVEC) and rat lung tissue was confirmed by RT-PCR, immunoblotting and immunohistochemistry. Isolated pulmonary artery (PA) rings and isolated ventilated-perfused rat lungs were used to assay the effects of BK(Ca) channel activation on endothelium-dependent vasodilation.

RESULTS

Immunoblotting and RT-PCR revealed the presence of BK(Ca) channel alpha- and beta(4)-subunits in LMVEC. Immunohistochemical staining showed BK(Ca) channel alpha-subunit expression in vascular endothelium in rat lungs. In arterial ring studies, BK(Ca) channel activation by NS1619 enhanced endothelium-dependent vasodilation that was attenuated by tetraethylammonium and iberiotoxin. In addition, activation of BK(Ca) channels by C-type natriuretic peptide caused endothelial-dependent vasodilation that was blocked by iberiotoxin, L-NAME, and lanthanum. Furthermore, BK(Ca) activation by NS1619 caused a dose-dependent reduction in PA pressures that was attenuated by L-NAME. In vitro, BK(Ca) channel activation in LMVEC caused hyperpolarization and increased NO production.

CONCLUSIONS

Pulmonary endothelium expresses BK(Ca) channels. Activation of endothelial BK(Ca) channels causes hyperpolarization and NO mediated endothelium-dependent vasodilation in micro- and macrovasculature in the lung.

Age-related change in endothelial and microvessel function and therapeutic consequences

As the absolute numbers and proportion of older adults increases across most of the developed world, a greater understanding of the aetiopathogenic mechanisms of the increased vascular risk and their therapeutic implications becomes essential to all clinicians assessing and managing the geriatric patient. The role of endothelial function and the microcirculation is increasingly recognized in the maintenance of adequate perfusion, and their dysfunction is thought to be an early and potentially reversible mechanism by which age acts to increase cardiovascular risk.

Here we review evidence that altered microvascular function appears before other recognized predictors of vascular disease, and progresses from childhood to late adult life, preceding fulminant atherosclerotic or arteriosclerotic disease. Low birth-weight babies have reduced endothelial function in skin microvessels at 3 months, and by age ten brachial artery endothelial function is reduced in comparison with normal birth-weight babies. In overweight/obese adolescent children with clustering of traditional cardiovascular disease risk factors, endothelial function is lower compared with normal weight children and this appears to persist into early adulthood. Adult ageing is associated with impaired microvessel endothelial function and an increase in capillary blood pressure, independent of brachial artery blood pressure. Biological and lifestyle factors that influence microvessel function include body fat and visceral adiposity, sex hormone status, diet and physical activity.

Exploration of the therapeutic implications for management of endothelial dysfunction remains in embryonic state. The use of ACE-inhibitors, angiotensin receptor blockers and direct renin inhibitors in patients with evidence of microvascular damage such as retinopathy and microalbuminuria has been established; however, in the general older population the benefit has yet to be established. Therefore current recommendations are to screen for microvascular damage and if present target treatments after control of other vascular risk factors such as hypertension.

Endothelial dysfunction in diabetes: multiple targets for treatment

Robert Furchgott's discovery of the obligatory role that the endothelium plays in the regulation of vascular tone has proved to be a major advance in terms of our understanding of the cellular basis of diabetic vascular disease. Endothelial dysfunction, as defined by a reduction in the vasodilatation response to an endothelium-dependent vasodilator (such as acetylcholine) or to flow-mediated vasodilatation, is an early indicator for the development of the micro- and macroangipathy that is associated with diabetes. In diabetes, hyperglycaemia plays a key role in the initiation and development of endothelial dysfunction; however, the cellular mechanisms involved as well as the importance of dyslipidaemia and co-morbidities such as hypertension and obesity remain incompletely understood. In this review, we discuss the mechanisms whereby hyperglycaemia, oxidative stress and dyslipidaemia can alter endothelial function and highlight their effects on endothelial nitric oxide synthase (eNOS), the endothelium-dependent hyperpolarising factor (EDHF) pathway(s), as well as on the role of endothelium-derived contracting factors (EDCFs) and adipocyte-derived vasoactive factors such as adipose-derived relaxing factor (ADRF).

Improvement of impaired endothelial function by tetrahydrobiopterin in stroke-prone spontaneously hypertensive rats

To investigate the role of tetrahydrobiopterin (BH4), an essential cofactor of nitric oxide synthase, in endothelial function in a model of genetic hypertension, acetylcholine- and sodium nitroprusside (SNP)-induced vasodilator responses were examined in the absence and presence of BH4 in age-matched adult stroke-prone spontaneously hypertensive rats (SHRSP) and Wistar-Kyoto (WKY) rats. Acetylcholine-induced depressor responses attenuated significantly in SHRSP compared with those in WKY rats. Acetylcholine-induced relaxations in phenylephrine-precontracted aortic rings of SHRSP were also significantly impaired as compared to those of WKY rats, while SNP-induced relaxations were similar between both strains. In SHRSP, intravenous infusion of BH4 (0.12 mg/kg per min for 20 min following a bolus injection of 0.48 mg/kg) significantly improved vasodilator responses to acetylcholine without affecting those to SNP, but in WKY rats BH4 did not influence those to acetylcholine. BH4 infusion itself had no hemodynamic effect in both strains. However, BH4 levels in plasma and thoracic aorta as well as plasma concentrations of nitrite plus nitrate, metabolites of NO, in SHRSP were all significantly greater than those in WKY rats, suggesting the occurrence of compensatory upregulation of NO synthesis in SHRSP. These results demonstrate that the impaired endothelial function in SHRSP cannot be explained simply by the decrease in absolute amount of BH4.

Vasoconstrictor prostanoids

In cardiovascular diseases and during aging, endothelial dysfunction is due in part to the release of endothelium-derived contracting factors that counteract the vasodilator effect of the nitric oxide. Endothelium-dependent contractions involve the activation of endothelial cyclooxygenases and the release of various prostanoids, which activate thromboxane prostanoid (TP) receptors of the underlying vascular smooth muscle. The stimulation of TP receptors elicits not only the contraction and the proliferation of vascular smooth muscle cells but also diverse physiological/pathophysiological reactions, including platelet aggregation and activation of endothelial inflammatory responses. TP receptor antagonists curtail endothelial dysfunction in diseases such as hypertension and diabetes, are potent antithrombotic agents, and prevent vascular inflammation.

Vascular KCa-channels as therapeutic targets in hypertension and restenosis disease

IMPORTANCE OF THE FIELD

Cardiovascular disease is a leading cause of death in modern societies. Hyperpolarizing Ca(2+)-activated K(+) channels (K(Ca)) are important membrane proteins in the control of arterial tone and pathological vascular remodelling and thus could serve as new drug targets.

AREAS COVERED IN THIS REVIEW

We summarize recent advances in the field of vascular K(Ca) and their roles in cardiovascular pathologies such as hypertension and restenosis disease and draw attention to novel small-molecule channel modulators and their possible therapeutic utility. This review focuses on literature from the last four to five years.

WHAT THE READER WILL GAIN

Pharmacological opening of endothelial KCa3.1/KCa2.3 channels stimulates endothelium-derived-hyperpolarizing-factor-mediated arteriolar dilation and lowers blood pressure. Inhibition of smooth muscle KCa3.1 channels has beneficial effects in restenosis disease and atherosclerosis. We consider the therapeutic potential of KCa3.1/KCa2.3 openers as novel endothelium-specific antihypertensive drugs as well as of KCa3.1-blockers for the treatment of pathological vascular remodelling and discuss advantages and disadvantages of the pharmacotherapeutic approaches.

TAKE HOME MESSAGE

Pharmacological manipulation of vascular K(Ca) channels by novel small-molecule modulators offers new venues for alternative treatments of hypertension, restenosis and atherosclerosis. Additional efforts are required to optimize these compounds and to validate them as cardiovascular-protective drugs.

Signaling mechanisms that link salt retention to hypertension: endogenous ouabain, the Na(+) pump, the Na(+)/Ca(2+) exchanger and TRPC proteins

Salt retention as a result of chronic, excessive dietary salt intake, is widely accepted as one of the most common causes of hypertension. In a small minority of cases, enhanced Na(+) reabsorption by the kidney can be traced to specific genetic defects of salt transport, or pathological conditions of the kidney, adrenal cortex, or pituitary. Far more frequently, however, salt retention may be the result of minor renal injury or small genetic variation in renal salt transport mechanisms. How salt retention actually leads to the increase in peripheral vascular resistance (the hallmark of hypertension) and the elevation of blood pressure remains an enigma. Here we review the evidence that endogenous ouabain (an adrenocortical hormone), arterial smooth muscle α2 Na(+) pumps, type-1 Na/Ca exchangers, and receptor- and store-operated Ca(2+) channels play key roles in the pathway that links salt to hypertension. We discuss cardenolide structure-function relationships in an effort to understand why prolonged administration of ouabain, but not digoxin, induces hypertension, and why digoxin is actually anti-hypertensive. Finally, we summarize recent observations which indicate that ouabain upregulates arterial myocyte Ca(2+) signaling mechanisms that promote vasoconstriction, while simultaneously downregulating endothelial vasodilator mechanisms. In sum, the reports reviewed here provide novel insight into the molecular mechanisms by which salt retention leads to hypertension.

Stimulation of endothelial progenitor cells: a new putative effect of several cardiovascular drugs

The role of vascular endothelium in cardiovascular disorders is well recognized. Mature endothelial cells contribute to the repair of endothelial injury, but they only have a limited capacity to do so. This has led to growing interest and further investigation into circulating endothelial progenitor cells (EPCs) and their role in vascular healing, repair, and postnatal neovascularization. The current perception of vascular health is that of a balance between ongoing injury and resultant vascular repair, mediated at least in part by circulating EPCs. Circulating EPCs play an important role in accelerating endothelialization at areas of vascular damage, and EPC enumeration is a viable strategy for assessing reparative capacity. Recent studies have shown that EPCs are affected both in number and function by several cardiovascular risk factors as well as various cardiovascular disease states, such as hypertension, hypercholesterolemia, and coronary artery disease. The present review summarizes the most relevant studies on the effects of cardiovascular drugs on vascular function and EPCs, focusing on their mechanisms of action.

RhoA-Rho kinase signaling mediates endothelium- and endoperoxide-dependent contractile activities characteristic of hypertensive vascular dysfunction

Hypertensive vasomotor dysfunction is defined by endothelium-dependent contractions involving prostaglandins and ROS. Since both thromboxane-prostanoid receptor (TPr) signaling and ROS activate RhoA-Rho kinase (ROCK) in vascular smooth muscle (VSM) preparations, we hypothesized that enhanced endothelium-dependent contraction in the common carotid artery (CCA) of spontaneously hypertensive rats (SHRs) is ROCK mediated. ACh-stimulated contractions were approximately twofold greater in SHRs versus normotensive Wistar-Kyoto (WKY) rats, abolished by endothelial denudation or cyclooxygenase (COX)-1 inhibition, and nearly eliminated by TPr blockade. RhoA but not ROCK-II protein expression was increased ( approximately 50%) in the SHR CCA. Inhibition of ROCK, but not protein kinase C, caused a dose-dependent reduction in endothelium-dependent contractions to ACh across strains, with the highest dose mirroring the effect of high-dose TPr antagonism. Conversely, ROCK inhibition caused dose-dependent and endothelium- and nitric oxide-independent relaxation in CCAs precontracted with the TPr agonist U-46619. Prostacyclin was the predominant prostaglandin produced by ACh-stimulated CCAs, with greater than twofold more prostacyclin released from SHR versus WKY rats, and its production was unaffected by ROCK inhibition. RhoA activation was approximately twofold higher in quiescent SHR CCAs compared with those from WKY rats and was significantly increased by ACh stimulation. Augmentation of chemical superoxide quenching with tiron or inhibition of the NADPH oxidase-derived superoxide-producing pathway with apocynin reduced ACh-stimulated contractile activity in SHR more than in WKY rats, whereas the SOD mimetic tempol amplified the response. Exposure of CCAs to exogenous H(2)O(2) caused contractions, similar to ACh stimulation, that were greater in SHR than in WKY rats, abolished by COX-1 inhibition, and highly attenuated by TPr blockade or ROCK inhibition. These results indicate that RhoA-ROCK may act as a molecular switch, transducing signals from endothelium-derived prostaglandin(s) and ROS, which are overproduced in SHR CCAs, to "turn on" VSM contractile pathways, thus mediating the enhanced endothelium- and endoperoxide-dependent vascular contractions characteristic of hypertension, among other cardiovascular disease states, such as diabetes and aging.

Endothelial dysfunction: a strategic target in the treatment of hypertension?

Endothelial dysfunction is a common feature of hypertension, and it results from the imbalanced release of endothelium-derived relaxing factors (EDRFs; in particular, nitric oxide) and endothelium-derived contracting factors (EDCFs; angiotensin II, endothelins, uridine adenosine tetraphosphate, and cyclooxygenase-derived EDCFs). Thus, drugs that increase EDRFs (using direct nitric oxide releasing compounds, tetrahydrobiopterin, or L-arginine supplementation) or decrease EDCF release or actions (using cyclooxygenase inhibitor or thromboxane A2/prostanoid receptor antagonists) would prevent the dysfunction. Many conventional antihypertensive drugs, including angiotensin-converting enzyme inhibitors, calcium channel blockers, and third-generation beta-blockers, possess the ability to reverse endothelial dysfunction. Their use is attractive, as they can address arterial blood pressure and vascular tone simultaneously. The severity of endothelial dysfunction correlates with the development of coronary artery disease and predicts future cardiovascular events. Thus, endothelial dysfunction needs to be considered as a strategic target in the treatment of hypertension.

Pharmacological characterization of (3-thienylidene)-3,4-methylenedioxybenzoylhydrazide: a novel muscarinic agonist with antihypertensive profile

BACKGROUND

Several new bioactive compounds of the N-acylhydrazone class were developed from the safrole, a Brazilian natural product obtained from sassafras oil (Ocotea pretiosa). This work investigated the effects on cardiovascular system of LASSBio-897, a new analogue of the lead compound 3,4-methylenedioxybenzoyl-2-thienylhydrazone named LASSBio-294.

METHODS

Thoracic aorta from Wistar-Kyoto (WKY) rats was prepared for isometric tension recording and for cGMP content determination. Blood pressure (BP) was measured in WKY rats and spontaneously hypertensive rats (SHR) after treatment with 1 mg/kg intravenously of LASSBio-897 and during 14 days' treatment of SHR with 1 mg/kg/day perorally.

RESULTS

LASSBio-897 (0.05-1 micromol/l) exhibited a potent vasodilatory activity in phenylephrine (Phe)-contracted aortic rings from WKY rats. This effect was abolished in endothelium-denuded aortic rings and after treatment with the nitric oxide (NO) synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME) or the guanylyl cyclase inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). Also, LASSBio 897 (1 micromol/l) increased about 15 times the intracellular content of cGMP. LASSBio-897-induced vasodilation was totally inhibited by the muscarinic antagonist atropine and by the M(3) subtype selective antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP), indicating the involvement of M(3) receptors. Intravenous administration of LASSBio-897 (1 mg/kg) produced significant hypotensive response in both WKY and SHR. The hypotensive effect of LASSBio-897 was also observed during the 14 days of oral administration.

CONCLUSIONS

The novel N-acylhydrazone derivative LASSBio-897 exhibited a potent vasodilatory activity in aortic rings mediated by the NO/cGMP pathway via activation of endothelial M(3) receptors and was orally effective in reducing BP on SHR.

High glucose increases expression of cyclooxygenase-2, increases oxidative stress and decreases the generation of nitric oxide in mouse microvessel endothelial cells

Hyperglycaemia is a key factor that contributes to the development of diabetes-related microvascular disease. Both cyclooxygenase I and cyclooxygenase II are expressed in endothelial cells and play key roles in the regulation of cardiovascular function. In the current study we tested the hypothesis that hyperglycaemia-induced increased expression of cyclooxygenase II is a contributing factor both to the increased oxidative stress and to the reduction in the generation of nitric oxide in microvessel endothelial cells following their exposure to high glucose. We demonstrated that the exposure of mouse microvascular endothelial cells to high glucose for 3 days decreased the generation of nitric oxide and enhanced production of superoxide. Western blots illustrated that exposure to high glucose also increased endothelial nitric oxide synthase and cyclooxygenase II protein expression levels and decreased the dimer/monomer ratio of endothelial nitric oxide synthase protein. All the changes induced by the high glucose culture media could be reversed by either the cyclooxygenase II inhibitor CAY10404, the non-selective cyclooxygenase inhibitor indomethacin or the protein kinase C inhibitor chelerythrine, but not solely by preincubation with the antioxidant and putative NADPH oxidase inhibitor, apocynin. Our data indicate that high glucose induced oxidative stress is linked to an increase in the expression of cyclooxygenase II and a reduced generation of nitric oxide that is associated with an uncoupled endothelial nitric oxide synthase, possibly due to decreased dimer/monomer ratio.

Cellular signaling and NO production

The endothelium can evoke relaxations (dilatations) of the underlying vascular smooth muscle, by releasing vasodilator substances. The best characterized endothelium-derived relaxing factor is nitric oxide (NO), which is synthesized by the endothelial isoform of nitric oxide synthase (eNOS). Endothelium-dependent relaxations involve both pertussis-toxin-sensitive G(i) (e.g., responses to serotonin, sphingosine 1-phosphate, alpha(2)-adrenergic agonists, and thrombin) and pertussis-toxin-insensitive G(q) (e.g., adenosine diphosphate and bradykinin) coupling proteins. eNOS undergoes a complex pattern of intracellular regulation, including post-translational modifications involving enzyme acylation and phosphorylation. eNOS is reversibly targeted to signal-transducing plasmalemmal caveolae where the enzyme interacts with a number of regulatory proteins, many of which are modified in cardiovascular disease states. The release of nitric oxide by the endothelial cell can be up- (e.g., by estrogens, exercise, and dietary factors) and down-regulated (e.g. oxidative stress, smoking, and oxidized low-density lipoproteins). It is reduced in the course of vascular disease (e.g., diabetes and hypertension). Arteries covered with regenerated endothelium (e.g. following angioplasty) selectively lose the pertussis-toxin-sensitive pathway for NO release which favors vasospasm, thrombosis, penetration of macrophages, cellular growth, and the inflammatory reaction leading to atherosclerosis. The unraveling of the complex interaction of the pathways regulating the presence and the activity of eNOS will enhance the understanding of the perturbations in endothelium-dependent signaling that are seen in cardiovascular disease states, and may lead to the identification of novel targets for therapeutic intervention.

Arginase contributes to endothelial cell oxidative stress in response to plasma from women with preeclampsia

AIMS

Preeclampsia is a hypertensive disorder characterized by vascular oxidative stress. Decreased availability of the vasodilator nitric oxide (NO) has been postulated to be involved in the pathophysiology of this disorder. Arginase, an enzyme that competes with nitric oxide synthase (NOS) for l-arginine, not only reduces NO formation but also increases superoxide production by NOS. In placenta of preeclamptic women, arginase upregulation has been shown to be increased and contributes to superoxide formation via uncoupling of NOS. However, the role of arginase in the maternal vasculature is not clear. We hypothesized that arginase would be upregulated in the maternal vasculature of women with preeclampsia and contribute to oxidative stress within the endothelium.

METHODS AND RESULTS

We observed increased arginase expression in the maternal vasculature of women with preeclampsia compared with normotensive pregnant women. Furthermore, human umbilical vein endothelial cells treated with 2% plasma from preeclamptic women show increased arginase II expression and activity that was reduced by a peroxynitrite scavenger. Also, both 3-morpholino sydnonimine and exogenous peroxynitrite increased arginase expression and activity. Preeclamptic plasma treatment increased superoxide and peroxynitrite levels. Superoxide levels were significantly reduced after arginase and NOS inhibition with [(S)-(2-boronoethyl)-l-cysteine] and N(omega)-nitro-l-arginine methyl ester, respectively, but peroxynitrite levels were in fact increased after arginase inhibition. Moreover, in the presence of preeclamptic plasma, l-arginine supplementation increased peroxynitrite formation during arginase inhibition.

CONCLUSION

Increased arginase expression in preeclampsia can induce uncoupling of NOS as a source of superoxide in the maternal vasculature in preeclampsia. However, l-arginine supplementation in the face of oxidative stress could lead to a further increase in peroxynitrite.

TP receptors and oxidative stress hand in hand from endothelial dysfunction to atherosclerosis

Thromboxane A(2) and the activation of TP receptors that it causes play an important role in platelet aggregation and therefore in thrombosis. However, TP receptors are also involved in the pathologies of the vascular wall including impaired endothelium-dependent vasodilation, increased oxidant generation, and increased expression of adhesion molecules. The beneficial effects of TP antagonists on the vascular wall attenuate these features of vascular disease. They are not shared by aspirin. In fact, TP antagonists are active in patients treated with aspirin, indicating that their potential beneficial effects are mediated by mechanisms different from the antithrombotic actions of aspirin. Our studies have demonstrated the vascular benefits of TP antagonists in experimental animals, particularly in models of diabetes mellitus, in which elevated levels of eicosanoids play a role not only in vascular pathologies but also in those of the kidney and other tissues. They suggest that TP blockade protects against fundamental and widespread tissular dysfunction associated with metabolic disease including hyperlipidemia and hyperglycemia. TP receptor antagonists represent a promising avenue for the prevention of vascular disease in part because of these pleiotropic actions that extend beyond their antithrombotic properties.

Thiol-metabolizing proteins and endothelial redox state: differential modulation of eNOS and biopterin pathways

The intracellular redox state is stringently maintained by thiol-based antioxidants to establish a balance for the physiological and pathophysiological roles of reactive oxygen species. The relative contributions of the thioredoxin (Trx) and glutathione/glutaredoxin systems to intracellular redox balance are incompletely understood, as are the consequences of altered thiol metabolism on endothelial nitric oxide (NO) synthase (eNOS) and NO-dependent pathways in the endothelium. We designed duplex small interfering RNA (siRNA) constructs to specifically "knock down" the expression of three key thiol-metabolizing enzymes in cultured aortic endothelial cells. Transfection of siRNA constructs targeting glutathione reductase (GR), cytosolic Trx reductase (TrxR1), or mitochondrial Trx reductase (TrxR2) significantly decreased the intracellular reduced glutathione-to-oxidized glutathione ratio. siRNA-mediated knockdown of either GR, TrxR1, or TrxR2 markedly suppressed VEGF-induced NO production (measured by an electrochemical NO sensor) and also blocked eNOS enzyme activity (using the [(3)H]arginine/[(3)H]citrulline assay). Pretreatment of endothelial cells with N,N'-bis(2-chloroethyl)-N-nitrosourea, an inhibitor of GR and TrxR, significantly decreased VEGF-induced NO production. siRNA-mediated TrxR2 knockdown led to a marked increase in hydrogen peroxide (H(2)O(2)) production in endothelial cells. In contrast, knockdown of GR or TrxR1 only slightly increased H(2)O(2) production. Supplementation of endothelial cells with tetrahydrobiopterin prevented the increase in H(2)O(2) generation seen with siRNA-mediated knockdown of GR. These studies show that the differential regulation of thiol-metabolizing proteins leads to critical changes in oxidative and nitrosative stress pathways. Greater understanding of the differential regulation of thiol-metabolizing proteins may lead to the development of new pharmacological targets for diseases associated with oxidative stress in the vascular wall.

Vitamin d receptor activation mitigates the impact of uremia on endothelial function in the 5/6 nephrectomized rats

Endothelial dysfunction increases cardiovascular disease risk in chronic kidney disease (CKD). This study investigates whether VDR activation affects endothelial function in CKD. The 5/6 nephrectomized (NX) rats with experimental chronic renal insufficiency were treated with or without paricalcitol, a VDR activator. Thoracic aortic rings were precontracted with phenylephrine and then treated with acetylcholine or sodium nitroprusside. Uremia significantly affected aortic relaxation (-50.0 +/- 7.4% in NX rats versus -96.2 +/- 5.3% in SHAM at 30 muM acetylcholine). The endothelial-dependent relaxation was improved to -58.2 +/- 6.0%, -77.5 +/- 7.3%, and -90.5 +/- 4.0% in NX rats treated with paricalcitol at 0.021, 0.042, and 0.083 mug/kg for two weeks, respectively, while paricalcitol at 0.042 mug/kg did not affect blood pressure and heart rate. Parathyroid hormone (PTH) suppression alone did not improve endothelial function since cinacalcet suppressed PTH without affecting endothelial-dependent vasorelaxation. N-omega-nitro-L-arginine methyl ester completely abolished the effect of paricalcitol on improving endothelial function. These results demonstrate that VDR activation improves endothelial function in CKD.