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

Single-nucleotide polymorphisms in vascular Ca2+-activated K+-channel genes and cardiovascular disease

In the cardiovascular system, Ca2+-activated K+-channels (KCa) are considered crucial mediators in the control of vascular tone and blood pressure by modulating the membrane potential and shaping Ca2+-dependent contraction. Vascular smooth muscle cells express the BKCa channel which fine-tunes contractility by providing a negative feedback on Ca2+-elevations. BKCa channel's ion-conducting alpha-subunit is encoded by the KCa1.1 gene, and the accessory and Ca2+-sensitivity modulating beta1-subunit is encoded by the KCNMB1 gene. Vascular endothelial cells express the calmodulin-gated KCa channels IKCa (encoded by the KCa3.1 gene) and SKCa (encoded by the KCa2.3 gene). These two channels mediate endothelial hyperpolarization and initiate the endothelium-derived hyperpolarizing factor-dilator response. Considering these essential roles of KCa in arterial function, mutations in KCa genes have been suspected to contribute to cardiovascular disease in humans. So far, DNA sequence analysis in the population and patient cohorts has identified single-nucleotide polymorphisms (SNPs) in the BKCa beta1-subunit gene as well as in the alpha-subunit gene (KCa1.1). Some of these SNPs produce amino acid exchanges and evoke alterations of channel functions ("gain-of-function" as well as "loss-of-function"). Moreover, the epidemiological studies showed that the presence of the E65K polymorphism in, e.g., BKCa beta1-subunit gene (producing a "gain-of-function") lowers the prevalence for severe hypertension and myocardial infarction. Other SNPs in the BKCa alpha-subunit gene and also in the KCa3.1 gene expressed in the endothelium have been suggested to increase the risk of cardiovascular disease. These findings from sequence analysis of human KCa genes, and epidemiological studies thus provide evidence that genetic variations and mutations in KCa channel genes contribute to human cardiovascular disease.

Nitric oxide and coronary vascular endothelium adaptations in hypertension

This review highlights a number of nitric oxide (NO)-related mechanisms that contribute to coronary vascular function and that are likely affected by hypertension and thus become important clinically as potential considerations in prevention, diagnosis, and treatment of coronary complications of hypertension. Coronary vascular resistance is elevated in hypertension in part due to impaired endothelium-dependent function of coronary arteries. Several lines of evidence suggest that other NO synthase isoforms and dilators other than NO may compensate for impairments in endothelial NO synthase (eNOS) to protect coronary artery function, and that NO-dependent function of coronary blood vessels depends on the position of the vessel in the vascular tree. Adaptations in NOS isoforms in the coronary circulation to hypertension are not well described so the compensatory relationship between these and eNOS in hypertensive vessels is not clear. It is important to understand potential functional consequences of these adaptations as they will impact the efficacy of treatments designed to control hypertension and coronary vascular disease. Polymorphisms of the eNOS gene result in significant associations with incidence of hypertension, although mechanistic details linking the polymorphisms with alterations in coronary vasomotor responses and adaptations to hypertension are not established. This understanding should be developed in order to better predict those individuals at the highest risk for coronary vascular complications of hypertension. Greater endothelium-dependent dilation observed in female coronary arteries is likely related to endothelial Ca(2+) control and eNOS expression and activity. In hypertension models, the coronary vasculature has not been studied extensively to establish mechanisms for sex differences in NO-dependent function. Genomic and nongenomic effects of estrogen on eNOS and direct and indirect antioxidant activities of estrogen are discussed as potential mechanisms of interest in coronary circulation that could have implications for sex- and estrogen status-dependent therapy for hypertension and coronary dysfunction. The current review identifies some important basic knowledge gaps and speculates on the potential clinical relevance of hypertension adaptations in factors regulating coronary NO function.

Age-related disappearance of the inhibitory effect of vascular endothelium on agonist-induced vasoconstriction in rat mesenteric vascular beds

We previously reported that endothelium-derived hyperpolarizing factor (EDHF)-mediated response time-dependently suppressed methoxamine-induced vasoconstriction in mesenteric vascular beds isolated from 8-week-old rats. We investigated age-related changes in endothelial regulation of methoxamine-induced vasoconstriction. Mesenteric vascular beds isolated from young (8-week-old) to adult (16-week-old) rats were perfused, and changes in perfusion pressure induced by continuous perfusion of methoxamine or high KCl (60 mM) were measured over 180 min. In young preparations with intact endothelium, methoxamine-induced vasoconstriction time-dependently decreased to 20% of the initial levels, while time-dependent reduction was not observed in adult preparations. High KCl-induced vasoconstriction in young and adult preparations did not show time-dependent reduction. Endothelium removal abolished time-dependent reduction of methoxamine-induced vasoconstriction in young preparations and significantly attenuated vasoconstriction in adult preparations. Indomethacin, seratrodast, or tempol but not catalase significantly reduced methoxamine-induced vasoconstriction in adult preparations with endothelium. A23187 (Ca(2+)-ionophore)-, but not acetylcholine-, induced endothelium-dependent vasodilation in the presence of N(G)-L-nitro arginine methyl ether in adult preparations was significantly smaller than that in young preparations. These findings suggest that the inhibitory effect of mesenteric vascular endothelium on methoxamine-induced vasoconstriction disappears with aging by reducing EDHF and increasing endothelium-derived contracting factors and reactive oxygen species.

Endothelial dysfunction in spontaneously hypertensive rats: focus on methodological aspects

Despite the apparent consensus on the existence of endothelial dysfunction in conduit and resistance arteries of spontaneously hypertensive rats (SHR), a commonly employed experimental model of hypertension, there are a number of reports showing that endothelium-dependent vasodilatory responses are similar, or even increased, in SHR compared with their normotensive counterparts. The present paper aims to discuss the rationale for these apparent discrepancies, including the effect of age, type of artery and methodological aspects. Data from the literature indicate that the age of the animal is a contributing factor and that endothelial dysfunction is likely to be a consequence of hypertension. In addition, the use of antioxidant additives, such as ascorbic acid or ethylene diaminetetraacetic acid, and differences in the level of initial arterial stretch, might also be of importance because they may modify the oxidative status of the artery and the levels of vasoactive factors released by the endothelium.

Synergistic effects of elevated systolic blood pressure and hypercholesterolemia on carotid intima-media thickness in children and adolescents

This study aimed to investigate the synergistic effects of elevated systolic blood pressure (SBP) and hypercholesterolemia on carotid intima-media thickness (cIMT). For this study, 60 children with hypercholesterolemia and 40 healthy control children were divided into four subgroups: hypercholesterolemic children with normal (<90th percentile) or elevated (>or= 90th percentile) SBP and control children with normal or elevated SBP. The highest mean and maximal cIMT values were found in the hypercholesterolemic children with elevated SBP and were significantly different from those of all the other groups. The synergistic effects of elevated SBP and hypercholesterolemia lead to a significant increase in cIMT as a subclinical sign of early atherosclerosis.

Calcitonin gene-related peptide selectively relaxes contractile responses to endothelin-1 in rat mesenteric resistance arteries

We tested the hypothesis that endothelin-1 (ET-1) modulates sensory-motor nervous arterial relaxation by prejunctional and postjunctional mechanisms. Isolated rat mesenteric resistance arteries were investigated with immunohistochemistry, wire-myography, and pharmacological tools. ET(A)- and ET(B)-receptors could be visualized on the endothelium and smooth muscle and on periarterial fibers containing calcitonin gene-related peptide (CGRP). Arterial contractile responses to ET-1 (0.25-16 nM) were not modified by blockade of ET(B)-receptors, NO-synthase, and cyclooxygenase or desensitization of transient receptor potential cation channel, subfamily V, member 1 (TRPV1) with capsaicin. ET-1 reversed relaxing responses to CGRP in depolarized arteries. This effect was inhibited by ET(A)-antagonists. It was not selective because ET-1 also reversed relaxing responses to Na-nitroprusside (SNP) and because phenylephrine (PHE; 0.25-16 microM) similarly reversed relaxing responses to CGRP or SNP. Conversely, contractile responses to ET-1 were, compared with PHE, hypersensitive to the relaxing effects of the TRPV1-agonist capsaicin and to exogenous CGRP, but not to acetylcholine, forskolin, pinacidil, or SNP. In conclusion, ET-1 does not stimulate sensory-motor nervous arterial relaxation, but ET(A)-mediated arterial contractions are selectively sensitive to relaxation by the sensory neurotransmitter CGRP. This does not involve NO, cAMP, or ATP-sensitive K(+) channels.

Cholinergic responses of ophthalmic arteries in M3 and M5 muscarinic acetylcholine receptor knockout mice

PURPOSE

To determine the functional role of M(3) and M(5) muscarinic acetylcholine receptor subtypes in ophthalmic arteries using gene-targeted mice.

METHODS

Muscarinic receptor gene expression was quantified in murine ophthalmic arteries using real-time PCR. To test the functional relevance of M(3) and M(5) receptors, ophthalmic arteries from mice deficient in either subtype (M3R(-/-), M5R(-/-), respectively) and wild-type controls were isolated, cannulated with micropipettes, and pressurized. Changes in luminal vessel diameter in response to muscarinic and nonmuscarinic receptor agonists were measured by video microscopy.

RESULTS

With the use of real-time PCR, all five muscarinic receptor subtypes were detected in ophthalmic arteries. However, mRNA levels of M(1), M(3), and M(5) receptors were higher than those of M(2) and M(4) receptors. In functional studies, after preconstriction with phenylephrine, acetylcholine and carbachol produced concentration-dependent dilations of ophthalmic arteries that were similar in M5R(-/-) and wild-type mice. Strikingly, cholinergic dilation of ophthalmic arteries was almost completely abolished in M3R(-/-) mice. Deletion of either M(3) or M(5) receptor did not affect responses to nonmuscarinic vasodilators such as bradykinin or nitroprusside.

CONCLUSIONS

These findings provide the first evidence that M(3) receptors are critically involved in cholinergic regulation of diameter in murine ophthalmic arteries.

Heparin cofactor II in atherosclerotic lesions from the Pathobiological Determinants of Atherosclerosis in Youth (PDAY) study

Heparin cofactor II (HCII) is a serine protease inhibitor (serpin) that has been shown to be a predictor of decreased atherosclerosis in the elderly and protective against atherosclerosis in mice. HCII inhibits thrombin in vitro and HCII-thrombin complexes have been detected in human plasma. Moreover, the mechanism of protection against atherosclerosis in mice was determined to be the inhibition of thrombin. Despite this evidence, the presence of HCII in human atherosclerotic tissue has not been reported. In this study, using samples of coronary arteries obtained from the Pathobiological Determinants of Atherosclerosis in Youth (PDAY) study, we explore the local relationship between HCII and (pro)thrombin in atherosclerosis. We found that HCII and (pro)thrombin are co-localized in the lipid-rich necrotic core of atheromas. A significant positive correlation between each protein and the severity of the atherosclerotic lesion was present. These results suggest that HCII is in a position to inhibit thrombin in atherosclerotic lesions where thrombin can exert a proatherogenic inflammatory response. However, these results should be tempered by the additional findings from this, and other studies, that indicate the presence of other plasma proteins (antithrombin, albumin, and alpha(1)-protease inhibitor) in the same localized region of the atheroma.

Could hypertension possibly be adaptive?

1. We believe that the ultimate goal of cardiovascular regulatory mechanisms is not the regulation of arterial blood pressure (BP), but the maintenance of tissue blood flows commensurate with metabolic requirements. Thus, elevated BP can potentially contribute to optimizing tissue blood flows under select circumstances; for example, when there are primary defects in autoregulation of tissue blood flows. 2. The hypothesis that a primary defect in autoregulation of tissue blood flows may be responsible for the development of hypertension is presented. It is argued that, in this context, at least part of the rise in BP may be reflexly driven by a 'metaboreflex', a homeostatic mechanism acting to regulate tissue blood flows. 3. We argue that in the context of primary defects in autoregulation of tissue blood flows, the ability to generate and sustain a hypertensive phenotype increases the lifespan of species (i.e. if it were not for this adaptive hypertensive phenotype, death due to circulatory failure would occur much earlier). 4. Experimental and clinical evidence that indirectly supports the hypothesis is reviewed briefly and a means for testing this hypothesis is suggested.

Cyclooxygenase and thromboxane/prostaglandin receptor contribute to aortic endothelium-dependent dysfunction in aging female spontaneously hypertensive rats

Cyclooxygenase (COX)-derived vasoconstrictory prostanoids contribute to impaired endothelium-dependent vasorelaxation in aging male (m) spontaneously hypertensive rats (SHR); however, vasomotor responses in aging female (f) SHR and sex differences in aging SHR are unknown. Examining mechanisms governing dysfunction in aging fSHR will contribute to understanding sex-dependent vascular complications in advanced hypertension. Aortic endothelium-dependent relaxation dose responses (ACh) of 16- and 30-wk-old mSHR and fSHR and normotensive Wistar-Kyoto rats were examined in the absence (no drug control) and presence of COX inhibition [indomethacin (Indo)] and thromboxane/prostaglandin receptor inhibition (SQ-29548). No drug control-treated 16-wk mSHR exhibited considerable blunting of the peak relaxation response to ACh (e.g., 77 +/- 4% relaxation to 10(-5) mol/l) vs. Wistar-Kyoto controls (89 +/- 6%), and greater dysfunction occurred in 30-wk mSHR (63 +/- 2%). Interestingly, ACh relaxations of fSHR were unimpaired at 16 wk (101 +/- 2% to 10(-5) mol/l), but blunted in 30 wk (76 +/- 4%). Indo and SQ-29548 restored robust ACh vasorelaxation in all groups (e.g., 113 +/- 3 and 112 +/- 3%, respectively, in Indo- and SQ-29548-treated 30-wk fSHR). Aortic COX-1 protein expression was elevated by 75% in 30-wk vs. 16-wk fSHR, whereas group-averaged ACh-stimulated aortic PGI(2) release (assessed as 6- keto-PGF(1alpha)) was 30% greater in 30-wk vs. 16-wk fSHR (9,926 +/- 890 vs. 7,621 +/- 690 pg.ml(-1).mg dry wt(-1)), although this did not reach significance (P = 0.0758). Dramatic deterioration of endothelium-dependent vasomotor function in fSHR across this age range involves COX and thromboxane/prostaglandin receptor, supporting a mechanism of impairment similar to that which occurs in aging mSHR.

Apigenin protects endothelium-dependent relaxation of rat aorta against oxidative stress

Apigenin is shown to have cardiovascular effects, but the effects of apigenin on aortas injured by exogenous oxidants are unknown. The objective of this study was to investigate the effect of apigenin on endothelium-dependent vasorelaxation in isolated rat aortic rings exposed to superoxide anion produced by pyrogallol, and its mechanism. The male Sprague-Dawley rat thoracic aorta was rapidly dissected out and the effect of apigenin on tension of aortic rings pretreated with 500 microM pyrogallol, inducing oxidative stress injury, was measured. The activity of nitric oxide synthase (NOS), the level of nitric oxide (NO) and the inhibition of superoxide anion in aortic tissues were measured. We found that pretreatment with pyrogallol concentration-dependently decreased acetylcholine-induced endothelium-dependent vasorelaxation. Apigenin (0.5-72.0 microM) evoked a concentration-dependent relaxation in aortas (pD(2): 5.304+/-0.049), which was weakened by L-NAME (the maximal relaxation fell from 87.6+/-6.7% to 37.1+/-8.8%, P<0.01), but not by aminoguanidine and indomethacin. Apigenin markedly attenuated the inhibition of vasorelaxation induced by pyrogallol (the maximal relaxation elevated from 55.8%+/-6.6% to 69.5%+/-6.4%, and the pD(2) increased from 6.559+/-0.119 to 7.057+/-0.145, P<0.01) and increased the inhibition of superoxide anion (from 94.6% to 74.5%), the NO level (from 77.1% to 94.4%), and the constitutive NOS activity (from 35.1% to 62.5%). These results indicate that pyrogallol decreased endothelium-dependent vasorelaxation in rat aortas via oxidative stress, which was markedly attenuated by apigenin. This may be mediated by weakening the oxidative stress and the NO reduction.

EDHF: an update

The endothelium controls vascular tone not only by releasing NO and prostacyclin, but also by other pathways causing hyperpolarization of the underlying smooth muscle cells. This characteristic was at the origin of the term 'endothelium-derived hyperpolarizing factor' (EDHF). However, this acronym includes different mechanisms. Arachidonic acid metabolites derived from the cyclo-oxygenases, lipoxygenases and cytochrome P450 pathways, H(2)O(2), CO, H(2)S and various peptides can be released by endothelial cells. These factors activate different families of K(+) channels and hyperpolarization of the vascular smooth muscle cells contribute to the mechanisms leading to their relaxation. Additionally, another pathway associated with the hyperpolarization of both endothelial and vascular smooth muscle cells contributes also to endothelium-dependent relaxations (EDHF-mediated responses). These responses involve an increase in the intracellular Ca(2+) concentration of the endothelial cells, followed by the opening of SK(Ca) and IK(Ca) channels (small and intermediate conductance Ca(2+)-activated K(+) channels respectively). These channels have a distinct subcellular distribution: SK(Ca) are widely distributed over the plasma membrane, whereas IK(Ca) are preferentially expressed in the endothelial projections toward the smooth muscle cells. Following SK(Ca) activation, smooth muscle hyperpolarization is preferentially evoked by electrical coupling through myoendothelial gap junctions, whereas, following IK(Ca) activation, K(+) efflux can activate smooth muscle Kir2.1 and/or Na(+)/K(+)-ATPase. EDHF-mediated responses are altered by aging and various pathologies. Therapeutic interventions can restore these responses, suggesting that the improvement in the EDHF pathway contributes to their beneficial effect. A better characterization of EDHF-mediated responses should allow the determination of whether or not new drugable targets can be identified for the treatment of cardiovascular diseases.

Biomarkers of premature atherosclerosis

C-reactive protein (CRP) is an acute phase protein and a biochemical marker with important prognostic value for cardiovascular events. Interleukins IL-1 and IL-6 are implicated in the pathogenesis of atherosclerosis and are associated with CRP. Apolipoproteins ApoA-I and ApoB are the main lipid metabolic markers implicated in the development and progression of atherosclerosis. Fibrinogen has also been proposed to be a major independent risk factor for cardiovascular events. Because premature atherosclerosis precedes the development of cardiovascular disease, identification of the associated biomarkers is of great importance. However, further studies will be needed to determine whether or not these markers are useful predictors of future cardiovascular events. Here, we review the roles of specific biomarkers that have been implicated in premature atherosclerosis.

Pyrrolidine dithiocarbamate reduces vascular prostanoid-induced responses in aged type 2 diabetic rat model

It has been shown that enhancement of vasoconstrictor prostanoids plays an important role in the development of cardiovascular diseases. The aim of the present study was to examine the effects of pyrrolidine dithiocarbamate (PDTC), a low-molecular-weight thiol antioxidant and a potent inhibitor of nuclear factor-kappaB (NF-kappaB), on both the response to and production of prostanoids in arterial vessels isolated from rats at the chronic stage of type 2 diabetes. Using aortas from type 2 diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats, control Long-Evans Tokushima Otsuka (LETO) rats, and LETO and OLETF rats treated with PDTC (30 mg/kg, s.c., daily, for 1 week), we measured the production of prostanoids and NF-kappaB activity. The arachidonic acid-induced contraction and the acetylcholine-induced endothelium-derived contracting factor (EDCF)-mediated contraction in mesenteric arteries were also compared among these groups. OLETF rats exhibited (vs. age-matched LETO rats) the following: increased responses to both arachidonic acid and EDCF and greater productions of PGE(2) and TXA(2). Treatment with PDTC resulted in the following: 1) reduced arachidonic acid- and EDCF-mediated contractions, 2) suppressed the production of prostanoids, and 3) normalized NF-kappaB activity. These results suggest that PDTC has beneficial effects against the abnormal vasoconstrictor prostanoid signaling present in rats at the chronic stage of type 2 diabetes.

Ovariectomy increases the formation of prostanoids and modulates their role in acetylcholine-induced relaxation and nitric oxide release in the rat aorta

AIMS

This study examines the effect of ovarian function on thromboxane A(2) (TXA(2)), prostaglandin (PG) I(2), PGF(2alpha), and PGE(2) release as well as the role of these substances in nitric oxide (NO) release and acetylcholine (ACh)-mediated relaxation.

METHODS AND RESULTS

Aortic segments from ovariectomized and control female Sprague-Dawley rats were used. Cyclooxygenase (COX-1 and COX-2) expression was studied. ACh-induced relaxation was analysed in the absence and presence of the COX-2 inhibitor NS-398, the TXA(2) synthesis inhibitor furegrelate, the PGI(2) synthesis inhibitor tranylcypromine (TCP), or the thromboxane-prostanoid receptor antagonist SQ-29548. TXA(2), PGI(2), PGF(2alpha), and PGE(2) release was measured, and the vasomotor effect of exogenous TXA(2), PGI(2,) PGF(2alpha), and PGE(2) was assessed. Basal and ACh-induced NO release in the absence and presence of NS-398, furegrelate, TCP, or TCP plus furegrelate was studied. Ovariectomy did not alter or increased COX-1 or COX-2 expression, respectively. NS-398 decreased, and furegrelate did not change, the ACh-induced relaxation in arteries from both groups. SQ29,548 decreased the ACh-induced relaxation only in aortas from ovariectomized rats. TCP decreased the ACh-induced relaxation in both groups, and furegrelate or SQ29,548 totally restored that response only in aortas from control rats. Ovariectomy increased the ACh-induced TXA(2), PGI(2), and PGE(2) release and the contractile responses induced by exogenous TXA(2), PGF(2alpha), or PGE(2), while it decreased the PGI(2)-induced vasodilator response. In aortas from control rats, NS-398 did not alter the ACh-induced NO release, and furegrelate, TCP, or TCP plus furegrelate increased that release. In arteries from ovariectomized rats, NS-398, furegrelate, TCP, or TCP plus furegrelate decreased the ACh-induced NO release.

CONCLUSION

Despite the prevalence of vasoconstrictor prostanoids derived from COX-2 in aortas from ovariectomized rats, the ACh-induced relaxation is maintained, probably as consequence of the positive regulation that prostanoids exert on eNOS activity.

Brain cytokines as neuromodulators in cardiovascular control

1. The role of cytokines in cardiovascular control, especially in neurogenic hypertension, has received considerable attention during the past few years. Brain cytokines have been shown to exert profound effects on neuronal activity. Recently, a number of studies have shown that administration of pro-inflammatory cytokines or anti-inflammatory cytokines into the central nervous system has a significant impact on sympathetic outflow, arterial pressure and cardiac remodelling in experimental models of hypertension and heart failure. 2. Our objective in this review is to present a succinct account of the effect of cytokines on neuronal activity and their role in cardiovascular disease. Furthermore, we propose a hypothesis for a neuromodulatory role of cytokines in the neural control of cardiovascular function.

COX-1 and vascular disease

Since the discovery of the pivotal role of cyclooxygenase (COX) in the metabolism of arachidonic acid, vascular biologists have been confronted with the duality of this system. Indeed, one substrate (arachidonic acid) transformed by one enzyme (COX) yields end products (endoperoxides) that exist only very briefly before being metabolized to more stable prostanoids by a set of specific downstream synthases that were initially believed to be tissue specific. For instance, platelets contain mainly the synthase that produces thromboxane A(2) (a potent proaggregatory and vasoconstrictor substance), whereas endothelial cells contain mainly the enzyme that generates prostacyclin (an equally potent antiaggregatory and vasodilator substance). The overproduction of thromboxane A(2) by platelets leads to thrombosis; endothelial cells resist vascular occlusion by producing prostacyclin. This duality of the metabolism of arachidonic acid has dominated our thinking about atherothrombosis for decades, and rightfully still does. As scientific understanding progressed, it became evident that two isoforms of COX exist: COX-1 and COX-2. COX-1 was initially considered to be the "good," constitutive isoform, whereas COX-2 appeared to be mainly a "bad" inducible enzyme involved in inflammatory responses. However, more recently, the unexpected events resulting from the widespread use of selective COX-2 inhibitors has suggested that, from a cardiovascular point of view, the products of COX-2 exert a protective role and that this isoform cannot necessarily be regarded as "bad." Likewise, evidence has emerged that initiation of the metabolism of arachidonic acid by COX-1 is not necessarily a "good" thing in terms of vascular protection. This brief review focuses on the potential contribution of endothelial COX-1 to vascular dysfunction. It is based on a number of review articles, to which the reader will be referred in order to identify the original references to the statements made; these references are not cited here because of space limitations.

Prostacyclin treatment normalises the MCA flow velocity in nimodipine-resistant cerebral vasospasm after aneurysmal subarachnoid haemorrhage: a pilot study

BACKGROUND

Cerebral vasospasm triggered by subarachnoid haemorrhage is one of the major causes of post-haemorrhage morbidity and mortality. Several treatment modalities have been proposed, and none of them are fully effective.

METHODS

In this study we treated five patients with prostacyclin suffering vasospasm after a ruptured aneurysm not responding to high i.v. doses of nimodipine. All patients were severely ill, unconscious and in need of intensive care.

FINDINGS

A low dose of prostacyclin i.v. infusion for 72 h reversed the vasospasm as measured by transcranial Doppler technique. The mean MCA blood flow velocity decreased from 199 +/- 31 cm/s to 92 +/- 6 cm/s within 72 h after the start of the prostacyclin infusion.

CONCLUSIONS

We suggest that low-dose prostacyclin treatment, an old treatment strategy, can be a treatment option in patients with vasospasm not responding to ordinary measures.

Endothelial dysfunction in aged humans is related with oxidative stress and vascular inflammation

Vascular endothelial dysfunction occurs during the human aging process, and it is considered as a crucial event in the development of many vasculopathies. We investigated the underlying mechanisms of this process, particularly those related with oxidative stress and inflammation, in the vasculature of subjects aged 18-91 years without cardiovascular disease or risk factors. In isolated mesenteric microvessels from these subjects, an age-dependent impairment of the endothelium-dependent relaxations to bradykinin was observed. Similar results were observed by plethysmography in the forearm blood flow in response to acetylcholine. In microvessels from subjects aged less than 60 years, most of the bradykinin-induced relaxation was due to nitric oxide release while the rest was sensitive to cyclooxygenase (COX) blockade. In microvessels from subjects older than 60 years, this COX-derived vasodilatation was lost but a COX-derived vasoconstriction occurred. Evidence for age-related vascular oxidant and inflammatory environment was observed, which could be related to the development of endothelial dysfunction. Indeed, aged microvessels showed superoxide anions (O(2)(-)) and peroxynitrite (ONOO(-)) formation, enhancement of NADPH oxidase and inducible NO synthase expression. Pharmacological interference of COX, thromboxane A(2)/prostaglandin H(2) receptor, O(2)(-), ONOO(-), inducible NO synthase, and NADPH oxidase improved the age-related endothelial dysfunction. In situ vascular nuclear factor-kappaB activation was enhanced with age, which correlated with endothelial dysfunction. We conclude that the age-dependent endothelial dysfunction in human vessels is due to the combined effect of oxidative stress and vascular wall inflammation.

Endothelial dysfunction and vascular disease

The endothelium can evoke relaxations (dilatations) of the underlying vascular smooth muscle, by releasing vasodilator substances. The best characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO). The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDHF-mediated responses). Endothelium-dependent relaxations involve both pertussis toxin-sensitive G(i) (e.g. responses to serotonin and thrombin) and pertussis toxin-insensitive G(q) (e.g. adenosine diphosphate and bradykinin) coupling proteins. The release of NO by the endothelial cell can be up-regulated (e.g. by oestrogens, 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 loose the pertussis toxin-sensitive pathway for NO release which favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and causing endothelium-dependent hyperpolarizations), endothelial cells also can evoke contraction (constriction) of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factor (EDCF). Most endothelium-dependent acute increases in contractile force are due to the formation of vasoconstrictor prostanoids (endoperoxides and prostacyclin) which activate TP receptors of the vascular smooth muscle cells. EDCF-mediated responses are exacerbated when the production of NO is impaired (e.g. by oxidative stress, ageing, spontaneous hypertension and diabetes). They contribute to the blunting of endothelium-dependent vasodilatations in aged subjects and essential hypertensive patients.

Atorvastatin Prevents Endothelial Dysfunction in Mesenteric Arteries From Spontaneously Hypertensive Rats

We investigated the effect of atorvastatin on cyclooxygenase (COX) contribution to endothelial dysfunction in spontaneously hypertensive rat (SHR) mesenteric resistance arteries. Atorvastatin (10 mg/kg per day, oral gavage) or its vehicle was administered for 2 weeks to male SHR or Wistar-Kyoto rats. Endothelial function of mesenteric arteries was assessed by pressurized myograph. In Wistar-Kyoto rats, relaxation to acetylcholine was inhibited by N G -nitro- l -arginine methyl ester and unaffected by SC-560 (COX-1 inhibitor), DuP-697 (COX-2 inhibitor), or ascorbic acid. In SHRs, the response to acetylcholine was attenuated, less sensitive to N G -nitro- l -arginine methyl ester, unaffected by SC-560, and enhanced by DuP-697 or SQ-29548 (thromboxane-prostanoid receptor antagonist) to a similar extent. Endothelium-dependent relaxation was normalized by ascorbic acid or apocynin (NADPH oxidase inhibitor), which also restored the inhibition by N G -nitro- l -arginine methyl ester. In atorvastatin-treated SHRs, relaxation to acetylcholine was normalized, fully sensitive to N G -nitro- l -arginine methyl ester, and not affected by SC-560, DuP-697, SQ 29548, or antioxidants. Dihydroethidium assay showed an increased intravascular superoxide generation in SHRs, which was abrogated by atorvastatin. RT-PCR revealed a COX-2 induction in SHR arteries, which was downregulated by atorvastatin. The release of prostacyclin and 8-isoprostane was higher from SHR than Wistar-Kyoto mesenteric vessels. COX-2 inhibition and apocynin decreased 8-isoprostane without affecting prostacyclin levels. Atorvastatin increased phosphorylated extracellular signal-regulated kinase 1/2, pAkt, peNOS 1177 , and inducible NO synthase levels in SHR mesenteric vessels and decreased 8-isoprostane release. In conclusion, COX-2-derived 8-isoprostane contributes to endothelial dysfunction in SHR mesenteric arteries. Atorvastatin restores NO availability by increasing phosphorylated extracellular signal-regulated kinase 1/2, pAkt, peNOS 1177 , and inducible NO synthase levels and by abrogating vascular NADPH oxidase-driven superoxide production, which also results in a downregulation of COX-2-dependent 8-isoprostane generation.

Effects of grape seed extract in Type 2 diabetic subjects at high cardiovascular risk: a double blind randomized placebo controlled trial examining metabolic markers, vascular tone, inflammation, oxidative stress and insulin sensitivity

OBJECTIVE

Current research has focused upon the potential links between novel markers of vascular risk such as endothelial dysfunction, oxidative stress, inflammation and insulin resistance in the pathogenesis of Type 2 diabetes and its complications. Grape seed extract (GSE), a flavonoid-rich product, is a potential moderator of these markers. This study aimed to test the hypothesis that GSE may improve these markers in high-risk cardiovascular subjects with Type 2 diabetes.

RESEARCH DESIGN AND METHODS

Thirty-two Type 2 diabetes mellitus patients, prescribed diet or oral glucose-lowering agents, received GSE (600 mg/day) or placebo for 4 weeks in a double-blinded randomized crossover trial. Markers of endothelial function (measured by photoplethysmography), oxidative stress [total antioxidant status (TAOS), reduced glutathione (GSH)/oxidized glutathione (GSSG)], inflammation [highly sensitive C-reactive protein (hsCRP), urinary albumin : creatinine ratio), insulin resistance [homeostasis model assessment-insulin resistance (HOMA-IR)] and metabolism (fructosamine, lipid profile) was measured at baseline and after intervention with GSE or placebo.

RESULTS

Baseline characteristics (16 male and 16 female): age 61.8 +/- 6.36 years; body mass index 30.2 +/- 5.92 kg/m2; diabetes duration 5.9 +/- 2.14 years. Following GSE (but not placebo), significant changes were noted in fructosamine (282 +/- 40.9 vs. 273 +/- 50.2 mmol/l; P = 0.0004); whole blood GSH (2359 +/- 823 vs. 3595 +/- 1051 mmol/l; P < 0.01) and hsCRP (3.2 +/- 3.65 vs. 2.0 +/- 2.2 mg/l; P = 0.0006). Total cholesterol concentration also decreased (4.5 +/- 0.96 vs. 4.3 +/- 0.99 mmol/l; P = 0.05). No statistically significant changes were shown in endothelial function, HOMA-IR or TAOS.

CONCLUSION

GSE significantly improved markers of inflammation and glycaemia and a sole marker of oxidative stress in obese Type 2 diabetic subjects at high risk of cardiovascular events over a 4-week period, which suggests it may have a therapeutic role in decreasing cardiovascular risk.

Comparison of skin microvascular reactivity with hemostatic markers of endothelial dysfunction and damage in type 2 diabetes

Aim:

Patients with non-insulin-dependent diabetes mellitus (NIDDM) are at increased cardiovascular risk due to an accelerated atherosclerotic process. The present study aimed to compare skin microvascular function, pulse wave velocity (PWV), and a variety of hemostatic markers of endothelium injury [von Willebrand factor (vWF), plasminogen activator inhibitor-1 (PAI-1), tissue plasminogen activator (t-PA), tissue factor pathway inhibitor (TFPI), and the soluble form of thrombomodulin (s-TM)] in patients with NIDDM.

Methods:

54 patients with NIDDM and 38 sex- and age-matched controls were studied. 27 diabetics had no overt micro- and/or macrovascular complications, while the remainder had either or both. The forearm skin blood flow was assessed by laser-Doppler imaging, which allowed the measurement of the response to iontophoretically applied acetylcholine (endothelium-dependent vasodilation) and sodium nitroprusside (endothelium-independent vasodilation), as well as the reactive hyperemia triggered by the transient occlusion of the circulation.

Results:

Both endothelial and non-endothelial reactivity were significantly blunted in diabetics, regardless of the presence or the absence of vascular complications. Plasma vWF, TFPI and s-TM levels were significantly increased compared with controls only in patients exhibiting vascular complications. Concentrations of t-PA and PAI-1 were significantly increased in the two groups of diabetics versus controls.

Conclusion:

In NIDDM, both endothelium-dependent and -independent microvascular skin reactivity are impaired, whether or not underlying vascular complications exist. It also appears that microvascular endothelial dysfunction is not necessarily associated in NIDDM with increased circulating levels of hemostatic markers of endothelial damage known to reflect a hypercoagulable state.

The impact of noncoding RNA on the biochemical and molecular mechanisms of aging

As the molecular mechanisms associated with aging become more understood, it is apparent that the normal processes involved in the development and metabolism of an organism are subject to changes that upset its crucial homeostatic balance, which in turn sets in motion the weakening and disease-prone process of senescence. This imbalance is the result of a variety of effectors, such as environmental insults, endogenous toxins, and genetic mishaps. In addition, it is highly probable that posttranscriptional regulatory events play a large role in the changes associated with aging. The emerging knowledge of posttranscriptional regulation is redefining our understanding of the complexities of cellular systems biology and genetics. The implications of the impact that small regulatory RNAs have on the many facets of developmental and molecular biology should be included as part of our current understanding of the biochemistry involved in these processes. These molecular regulators-along with other epigenetic events-restrict the flow of genetic expression, thus affording the cell an adjustable and tempered homeostatic balance control. Recent findings in the fields of organismal development, cancer, and aging indicate that small noncoding RNA plays a greater role than previously believed in orchestrating the changes associated with these processes. Furthermore, any misappropriations of these regulatory resources could lead to age-related diseases, and are therefore promising targets for prophylactics and therapeutics to combat maladies associated with aging. Here we report a brief overview of noncoding RNA as well as the potential roles of microRNAs in biochemical equilibriums where imbalance contributes to the many phenotypes of aging.

Eicosapentaenoic acid improves imbalance between vasodilator and vasoconstrictor actions of endothelium-derived factors in mesenteric arteries from rats at chronic stage of type 2 diabetes

Accumulating evidence demonstrates that dietary intake of n-3 polyunsaturated fatty acids (PUFAs) is associated with a reduced incidence of several cardiovascular diseases that involve endothelial dysfunction. However, the molecular mechanism remains unclear. We previously reported that mesenteric arteries from type 2 diabetic Otsuka Long-Evans Tokushima fatty (OLETF) rats exhibit endothelial dysfunction, leading to an imbalance between endothelium-derived vasodilators [namely, nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF)] and vasoconstrictors [endothelium-derived contracting factors (EDCFs)] [namely cyclooxygenase (COX)-derived prostanoids] (Am J Physiol Heart Circ Physiol 293:H1480-H1490, 2007). We hypothesized that treating OLETF rats with eicosapentaenoic acid (EPA), a major n-3 PUFA, may improve endothelial dysfunction by correcting this imbalance. In OLETF rats [compared with age-matched control Long-Evans Tokushima Otsuka (LETO) rats]: 1) acetylcholine (ACh)-induced (endothelium-dependent) relaxation was impaired, 2) NO- and EDHF-mediated relaxations and nitrite production were reduced, and 3) ACh-induced EDCF-mediated contraction, production of prostanoids, and the protein expressions of COX-1 and COX-2 were all increased. When OLETF rats received chronic EPA treatment long-term (300 mg/kg/day p.o. for 4 weeks), their isolated mesenteric arteries exhibited: 1) improvements in ACh-induced NO- and EDHF-mediated relaxations and COX-mediated contraction, 2) reduced EDCF- and arachidonic acid-induced contractions, 3) normalized NO metabolism, 4) suppressed production of prostanoids, 5) reduced COX-2 expression, and 6) reduced phosphoextracellular signal-regulated kinase (ERK) expression. Moreover, EPA treatment reduced both ERK2 and nuclear factor (NF)-kappaB activities in isolated OLETF aortas. We propose that EPA ameliorates endothelial dysfunction in OLETF rats by correcting the imbalance between endothelium-derived factors, at least partly, by inhibiting ERK, decreasing NF-kappaB activation, and reducing COX-2 expression.

Drug discovery for overcoming chronic kidney disease (CKD): development of drugs on endothelial cell protection for overcoming CKD

Chronic kidney disease (CKD) is becoming a major public health problem worldwide. It is important to protect endothelial function in CKD treatment because injury of the endothelium is a critical event for the generation and progression of CKD. Recently, clinical studies showed that nifedipine, an antihypertensive drug, acts as a protective agent of endothelial cells (ECs). Nifedipine is reported to partially decompose to a nitrosonifedipine that has high reactivity against lipid-derived radicals in vitro. However, it is still unclear whether nitrosonifedipine is a biologically active agent against endothelial injury. We observed that nitrosonifedipine was converted to radical form by reaction with cultured ECs. The cumene hydroperoxide mediated cytotoxity was reduced by nitrosonifedipine in cultured human glomerular ECs (HGECs). Also nitrosonifedipine suppressed the expression of TNF-alpha-induced intercellular cell adhesion molecule-1 in HGECs. Chronic administration of N(omega)-nitro-L-arginine methyl ester (L-NAME) caused systemic arterial hypertension, endothelial injury, and renal dysfunction. In L-NAME-induced hypertensive rats, nitrosonifedipine treatment improved not only the acetylcholine-induced vasodilation of the aortic rings, but also renal dysfunction such as increasing the levels of serum creatinine and urinary protein excretion. Our preliminary data suggest that nitrosonifedipine is a new and useful drug for the treatment of CKD involving ameliorating effects on EC disorder.

Increased arachidonic acid-induced thromboxane generation impairs skeletal muscle arteriolar dilation with genetic dyslipidemia

OBJECTIVE

The aim of this study was to determine if arachidonic acid (AA)-induced skeletal muscle arteriolar dilation is altered with hypercholesterolemia in ApoE and low-density lipoprotein receptor (LDLR) gene deletion mice fed a normal diet. This study also determined contributors to altered AA-induced dilation between dyslipidemic mice and controls, C57/Bl/6J (C57).

METHODS

Gracilis muscle arterioles were isolated, with mechanical responses assessed following a challenge with AA under control conditions and after elements of AA metabolism pathways were inhibited. Conduit arteries from each strain were used to assess AA-induced production of PGI(2) and TxA(2).

RESULTS

Arterioles from ApoE and LDLR exhibited a blunted dilation to AA versus C57. While responses were cyclo-oxygenase-dependent in all strains, inhibition of thromboxane synthase or blockade of PGH(2)/TxA(2) receptors improved dilation in ApoE and LDLR only. AA-induced generation of PGI(2) was comparable across strains, although TxA(2) generation was increased in ApoE and LDLR. Arteriolar reactivity to PGI(2) and TxA(2) was comparable across strains. Treatment with TEMPOL improved dilation and reduced TxA(2) production with AA in ApoE and LDLR.

CONCLUSIONS

These results suggest that AA-induced arteriolar dilation is constrained in ApoE and LDLR via an increased production of TxA(2). While partially due to elevated oxidant stress, additional mechanisms contribute that are independent of acute alterations in oxidant tone.

Berberine prevents hyperglycemia-induced endothelial injury and enhances vasodilatation via adenosine monophosphate-activated protein kinase and endothelial nitric oxide synthase

AIMS

Endothelial dysfunction is a key event that links obesity, diabetes, hypertension, and cardiovascular diseases. The aim of the present study was to examine the protective effect of the alkaloid drug berberine against hyperglycemia-induced cellular injury and endothelial dysfunction.

METHODS AND RESULTS

In both cultured endothelial cells and blood vessels isolated from rat aorta, berberine concentration dependently enhanced phosphorylation of endothelial nitric oxide synthase (eNOS) at Ser1177 and promoted the association of eNOS with heat shock protein 90 (HSP90), leading to an increased production of nitric oxide. Furthermore, berberine attenuated high glucose-induced generation of reactive oxygen species, cellular apoptosis, nuclear factor-kappaB activation, and expression of adhesion molecules, thus suppressing monocyte attachment to endothelial cells. In mouse aortic rings, berberine elicited endothelium-dependent vasodilatations and alleviated high glucose-mediated endothelial dysfunction. All these beneficial effects of berberine on the endothelium were abolished by either pharmacological inhibition of adenosine monophosphate-activated protein kinase (AMPK) or adenovirus-mediated overexpression of a dominant negative version of AMPK.

CONCLUSION

Berberine protects against endothelial injury and enhances the endothelium-dependent vasodilatation, which is mediated in part through activation of the AMPK signalling cascade. Berberine or its derivatives may be useful for the treatment and/or prevention of endothelial dysfunction associated with diabetes and cardiovascular disease.

Role of TNF-alpha in vascular dysfunction

Healthy vascular function is primarily regulated by several factors including EDRF (endothelium-dependent relaxing factor), EDCF (endothelium-dependent contracting factor) and EDHF (endothelium-dependent hyperpolarizing factor). Vascular dysfunction or injury induced by aging, smoking, inflammation, trauma, hyperlipidaemia and hyperglycaemia are among a myriad of risk factors that may contribute to the pathogenesis of many cardiovascular diseases, such as hypertension, diabetes and atherosclerosis. However, the exact mechanisms underlying the impaired vascular activity remain unresolved and there is no current scientific consensus. Accumulating evidence suggests that the inflammatory cytokine TNF (tumour necrosis factor)-α plays a pivotal role in the disruption of macrovascular and microvascular circulation both in vivo and in vitro. AGEs (advanced glycation end-products)/RAGE (receptor for AGEs), LOX-1 [lectin-like oxidized low-density lipoprotein receptor-1) and NF-κB (nuclear factor κB) signalling play key roles in TNF-α expression through an increase in circulating and/or local vascular TNF-α production. The increase in TNF-α expression induces the production of ROS (reactive oxygen species), resulting in endothelial dysfunction in many pathophysiological conditions. Lipid metabolism, dietary supplements and physical activity affect TNF-α expression. The interaction between TNF-α and stem cells is also important in terms of vascular repair or regeneration. Careful scrutiny of these factors may help elucidate the mechanisms that induce vascular dysfunction. The focus of the present review is to summarize recent evidence showing the role of TNF-α in vascular dysfunction in cardiovascular disease. We believe these findings may prompt new directions for targeting inflammation in future therapies.

Endothelial dysfunction: the first step toward coronary arteriosclerosis

The endothelium causes relaxations of the underlying vascular smooth muscle, by releasing nitric oxide (NO). The endothelial cells also can evoke hyperpolarization of the vascular smooth muscle cells (endothelium-dependent hyperpolarizations, endothelium-derived hyperpolarizing factors-mediated responses). Endothelium-dependent relaxations involve both pertussis toxin-sensitive Gi and pertussis toxin-insensitive Gq coupling proteins. The endothelial release of NO is reduced in diabetes and hypertension. Arteries covered with regenerated endothelium lose the pertussis-toxin sensitive pathway for NO-release. This dysfunction favors vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. Endothelial cells also release endothelium-derived contracting factors (EDCF). Most endothelium-dependent contractions are mediated by vasoconstrictor prostanoids (endoperoxides and prostacyclin), which activate thromboxane-prostanoid (TP)-receptors of the underlying vascular smooth muscle cells. EDCF-mediated responses are augmented by aging, hypertension and diabetes. Thus, endothelial dysfunction is the first step toward coronary arteriosclerosis.

Endothelial dysfunction in glaucoma

Glaucoma is a group of ocular diseases characterized by optic neuropathy associated with loss of the retinal nerve fibre layer and re-modelling of the optic nerve head, and a subsequent particular pattern of visual field loss. Increased intraocular pressure is the most important risk factor for the disease, but the pathogenesis of glaucoma is not monofactorial. Among other factors, ischaemia and vascular dysregulation have been implicated in the mechanisms underlying glaucoma. The vascular endothelium plays an important role in the regulation of ocular blood flow and pathological alterations of vascular endothelial cells may induce ischaemia and dysregulation. The present review summarizes our current evidence of endothelial dysfunction in glaucoma. This is of interest because endothelial dysfunction is a good prognostic factor for progression in several diseases. Although such data are lacking for glaucoma, endothelial dysfunction may provide an attractive target for therapeutic intervention in open-angle glaucoma and other vascular disorders of the eye.

Inducible nitric oxide synthase is involved in endothelial dysfunction of mesenteric small arteries from hypothyroid rats

The time-dependent effects of mild hypothyroidism on endothelial function were assessed in rat mesenteric arteries. Male Wistar rats were treated with methimazole (MMI; 0.003%) or placebo up to 16 wk. Endothelial function of mesenteric small arteries was assessed by pressurized myograph. MMI-treated animals displayed a decrease in serum thyroid hormones, an increment of plasma TSH and inflammatory cytokines, and a blunted vascular relaxation to acetylcholine, as compared with controls. Endothelial dysfunction resulted from a reduced nitric oxide (NO) availability caused by oxidative excess. Vascular-inducible NO synthase (iNOS) expression was up-regulated. S-methylisothiourea (an iNOS inhibitor) normalized endothelium-dependent relaxations and restored NO availability in arteries from 8-wk MMI-animals and partly ameliorated these alterations in 16-wk MMI rats. Similar results were obtained when MMI-induced hypothyroidism was prevented by T(4) replacement. Among controls, an impaired NO availability, secondary to oxidative excess, occurred at 16 wk, and it was less pronounced than in age-matched MMI animals. Both endothelial dysfunction and oxidant excess secondary to aging were prevented by apocynin (nicotinamide adenine dinucleotide phosphate oxidase inhibitor). Mesenteric superoxide production was reduced by S-methylisothiourea and T(4) replacement in MMI animals and abolished by apocynin in controls (dihydroethidium staining). MMI-induced mild hypothyroidism is associated with endothelial dysfunction caused by a reduced NO availability, secondary to oxidative excess. It is suggested that in this animal model, characterized by TSH elevation and low-grade inflammation, an increased expression and function of iNOS, resulting in superoxide generation, accounts for an impaired NO availability.

Calcium-activated potassium channels and endothelial dysfunction: therapeutic options?

The three subtypes of calcium-activated potassium channels (K(Ca)) of large, intermediate and small conductance (BK(Ca), IK(Ca) and SK(Ca)) are present in the vascular wall. In healthy arteries, BK(Ca) channels are preferentially expressed in vascular smooth muscle cells, while IK(Ca) and SK(Ca) are preferentially located in endothelial cells. The activation of endothelial IK(Ca) and SK(Ca) contributes to nitric oxide (NO) generation and is required to elicit endothelium-dependent hyperpolarizations. In the latter responses, the hyperpolarization of the smooth muscle cells is evoked either via electrical coupling through myo-endothelial gap junctions or by potassium ions, which by accumulating in the intercellular space activate the inwardly rectifying potassium channel Kir2.1 and/or the Na(+)/K(+)-ATPase. Additionally, endothelium-derived factors such as cytochrome P450-derived epoxyeicosatrienoic acids and under some circumstances NO, prostacyclin, lipoxygenase products and hydrogen peroxide (H(2)O(2)) hyperpolarize and relax the underlying smooth muscle cells by activating BK(Ca). In contrast, cytochrome P450-derived 20-hydroxyeicosatetraenoic acid and various endothelium-derived contracting factors inhibit BK(Ca). Aging and cardiovascular diseases are associated with endothelial dysfunctions that can involve a decrease in NO bioavailability, alterations of EDHF-mediated responses and/or enhanced production of endothelium-derived contracting factors. Because potassium channels are involved in these endothelium-dependent responses, activation of endothelial and/or smooth muscle K(Ca) could prevent the occurrence of endothelial dysfunction. Therefore, direct activators of these potassium channels or compounds that regulate their activity or their expression may be of some therapeutic interest. Conversely, blockers of IK(Ca) may prevent restenosis and that of BK(Ca) channels sepsis-dependent hypotension.

Endothelium-dependent contractions in SHR: a tale of prostanoid TP and IP receptors

In the aorta of spontaneously hypertensive rats (SHR), the endothelial dysfunction is due to the release of endothelium-derived contracting factors (EDCFs) that counteract the vasodilator effect of nitric oxide, with no or minor alteration of its production. The endothelium-dependent contractions elicited by acetylcholine (ACh) involve an increase in endothelial [Ca(2+)](i), the production of reactive oxygen species, the activation of endothelial cyclooxygenase-1, the diffusion of EDCF and the subsequent stimulation of smooth muscle cell TP receptors. The EDCFs released by ACh have been identified as PGH(2) and paradoxically prostacyclin. Prostacyclin generally acts as an endothelium-derived vasodilator, which, by stimulating IP receptors, produces hyperpolarization and relaxation of the smooth muscle and inhibits platelet aggregation. In the aorta of SHR and Wistar-Kyoto rats, prostacyclin is the principal metabolite of arachidonic acid released by ACh. However, in SHR aorta, prostacyclin does not produce relaxations but activates the TP receptors on vascular smooth muscle cells and produces contraction. The IP receptor is not functional in the aortic smooth muscle cells of SHR as early as 12 weeks of age, but its activity is not reduced in platelets. Therefore, prostacyclin in the rule protects the vascular wall, but in the SHR aorta it can contribute to endothelial dysfunction. Whether or not prostacyclin plays a detrimental role as an EDCF in other animal models or in human remains to be demonstrated. Nevertheless, because EDCFs converge to activate TP receptors, selective antagonists of this receptor, by preventing endothelium-dependent contractions, curtail the endothelial dysfunction in diseases such as hypertension and diabetes.

Vascular protection by tetrahydrobiopterin: progress and therapeutic prospects

Tetrahydrobiopterin (BH4) is an essential cofactor required for the activity of endothelial nitric oxide (NO) synthase. Suboptimal concentrations of BH4 in the endothelium reduce the biosynthesis of NO, thus contributing to the pathogenesis of vascular endothelial dysfunction. Supplementation with exogenous BH4 or therapeutic approaches that increase endogenous amounts of BH4 can reduce or reverse endothelial dysfunction by restoring production of NO. Improvements in formulations of BH4 for oral delivery have stimulated clinical trials that test the efficacy of BH4 in the treatment of systemic hypertension, peripheral arterial disease, coronary artery disease, pulmonary arterial hypertension, and sickle cell disease. This review discusses ongoing progress in the translation of knowledge, accumulated in preclinical studies, into the clinical application of BH4 in the treatment of vascular diseases. This review also addresses the emerging roles of BH4 in the regulation of endothelial function and their therapeutic implications.

Amperometric S-nitrosothiol sensor with enhanced sensitivity based on organoselenium catalysts

A new S-nitrosothiol (RSNO) detection strategy based on an electrochemical sensor is described for rapidly estimating levels of total RSNOs in blood and other biological samples. The sensor employs a cellulose dialysis membrane covalently modified with an organoselenium catalyst that converts RSNOs to NO at the distal tip of an amperometric NO sensor. The sensor is characterized by very low detection limits (<20 nM), good long-term stability, and can be employed for the rapid detection of total low-molecular-weight (LMW) RSNO levels in whole blood samples using a simple standard addition method. A strategy for detecting macromolecular RSNOs is also demonstrated via use of a transnitrosation reaction with added LMW thiols allowing the estimation of total RSNO levels in blood. The sensor is shown to exhibit high selectivity over nitrosamines and nitrite. Such RSNO detection is potentially useful to reveal correlation between blood RSNO levels and endothelial cell dysfunction, which often is associated with cardiovascular diseases.

Cocoa consumption for 2 wk enhances insulin-mediated vasodilatation without improving blood pressure or insulin resistance in essential hypertension

BACKGROUND

Essential hypertension is characterized by reciprocal relations between endothelial dysfunction and insulin resistance. Cocoa flavanols stimulate production of the vasodilator nitric oxide from vascular endothelium.

OBJECTIVE

The objective was to test the hypothesis that consumption of cocoa may simultaneously lower blood pressure, improve endothelial dysfunction, and ameliorate insulin resistance in subjects with essential hypertension.

DESIGN

We conducted a randomized, placebo-controlled, double-blind, crossover trial of a flavanol-rich cocoa drink (150 mL twice a day, approximately 900 mg flavanols/d) in individuals with essential hypertension (n = 20). Antihypertensive medications were discontinued before study enrollment. After a 7-d cocoa-free run-in period, cocoa or flavanol-poor placebo (approximately 28 mg flavanols/d) treatment for 2 wk was followed by a 1-wk washout and then crossover to the other treatment arm. Blood pressure was measured thrice weekly. At baseline and after each treatment period, we assessed insulin sensitivity (hyperinsulinemic-isoglycemic glucose clamp) and insulin-stimulated changes in brachial artery diameter and forearm skeletal muscle capillary recruitment (Doppler ultrasound with or without microbubble contrast).

RESULTS

Cocoa treatment for 2 wk increased insulin-stimulated changes in brachial artery diameter when compared with placebo [median percentage increase from baseline (25th-75th percentile): 8.3 (4.2-11.3) compared with 5.9 (-0.3 to 9.6); P < 0.04]. Nevertheless, cocoa treatment did not significantly reduce blood pressure or improve insulin resistance and had no significant effects on skeletal muscle capillary recruitment, circulating plasma concentrations of adipocytokines, or endothelial adhesion molecules.

CONCLUSIONS

Daily consumption of flavanol-rich cocoa for 2 wk is not sufficient to reduce blood pressure or improve insulin resistance in human subjects with essential hypertension. This trial was registered at clinicaltrials.gov as NCT00099476.

Human endothelial function and microvascular ageing

Age is a primary risk factor for cardiovascular disease, and this is an increasingly important public health concern because of an increase in the absolute number and proportion of the population at an older age in many countries. A key component of cardiovascular ageing is reduced function of the vascular endothelium, and this probably contributes to the impaired microvessel function observed with ageing in multiple vascular beds. In turn, impaired microvessel function is thought to contribute to the pathophysiology of cardiovascular and metabolic diseases. Here we review evidence that the first signs of altered endothelial and microvessel function can appear in childhood and at all stages of the human lifespan; low-birth-weight babies have reduced endothelial function in skin microvessels at 3 months, and by age 10 years their 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 reduced 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. Biological and lifestyle factors that influence microvessel function include body fat and visceral adiposity, sex hormone status, diet and physical activity. The mechanisms underlying age-associated changes in microvessel function are uncertain but may involve alterations in nitric oxide, prostanoid, endothelium-derived hyperpolarizing factor(s) and endothelin-1 pathways.

Endothelial dysfunction in adiponectin deficiency and its mechanisms involved

Endothelial dysfunction is the earliest pathologic alteration in diabetic vascular injury and plays a critical role in the development of atherosclerosis. Plasma levels of adiponectin (APN), a novel vasculoprotective adipocytokine, are significantly reduced in diabetic patients, but its relationship with endothelial dysfunction remains unclear. The present study aims to determine whether APN deficiency may cause endothelial dysfunction and to investigate the involved mechanisms. Vascular rings were made from the aortic vessels of wild type (WT) or APN knockout (APN(-/-)) mice. Endothelial function, total NO production, eNOS expression/phosphorylation, superoxide production, and peroxynitrite formation were determined. ACh and acidified NaNO2 (endothelial dependent and independent vasodilators, respectively) caused similar concentration-dependent vasorelaxation in WT vascular rings. APN(-/-) rings had a normal response to acidified NaNO2, but a markedly reduced response to ACh (>50% reduction vs. WT, P<0.01). Both superoxide and peroxynitrite production were increased in APN(-/-) vessels (P<0.01 vs. WT). Pretreatment with superoxide scavenger Tiron significantly, but incompletely restored vascular vasodilatory response to ACh. In APN(-/-) vessels, eNOS expression was normal, but NO production and eNOS phosphorylation was significantly reduced (P<0.01 vs. WT). Treatment of APN(-/-) mice in vivo with the globular domain of adiponectin reduced aortic superoxide production, increased eNOS phosphorylation, and normalized vasodilatory response to ACh. Increased NO inactivation combined with decreased basal NO production contributes to endothelial dysfunction development when there is a paucity of APN production. Interventions directed towards increasing plasma APN levels may improve endothelial function, and reduce cardiovascular complications suffered by diabetic patients.

Nebivolol treatment reduces serum levels of asymmetric dimethylarginine and improves endothelial dysfunction in essential hypertensive patients

BACKGROUND

This study was conducted to evaluate (i) the effect of nebivolol, a selective beta1-adrenergic receptor antagonist, on plasma concentration of asymmetric dimethylarginine (ADMA) and on flow-mediated dilation (FMD) in essential hypertensive patients; (ii) the effect of serum derived from the treated hypertensive patients on ADMA and on dimethylarginine dimethylaminohydrolase 2 (DDAH2), the enzyme that selectively degrades ADMA, in human umbilical vein endothelial cells (HUVECs).

METHODS

Forty healthy subjects and 40 matched essential hypertensive patients treated with atenolol and nebivolol according to a double-blind, randomized design participated in the study. Evaluation of brachial artery (BA) reactivity was performed by a longitudinal B-mode scan of the right BA. ADMA and L-arginine were measured by high-performance liquid chromatography. DDAH2 expression and endothelial nitric oxide synthase activity (eNOS) were also evaluated in HUVECs.

RESULTS

ADMA levels were significantly decreased and FMD increased only in patients receiving nebivolol (P < 0.01). Furthermore, in nebivolol group, we found a significant correlation between changes in ADMA levels and changes in FMD (P < 0.01). Sera derived from patients treated with nebivolol but not with atenolol decreased ADMA and increased DDAH2 expression and eNOS activity (P < 0.001) in HUVECs.

CONCLUSIONS

The results of this study demonstrate that the improvement of endothelial dysfunction induced by nebivolol in hypertensive patients may be related to its effect on circulating ADMA levels. Although the mechanism by which nebivolol reduces circulating ADMA in hypertensive patients remains unclear, our ex vivo results suggest that the upregulation of DDAH2 expression may have a role.

Role of Reactive Oxygen Species in Tumor Necrosis Factor-alpha Induced Endothelial Dysfunction

Endothelial cell injury and dysfunction are the major triggers of pathophysiological processes leading to cardiovascular disease. Endothelial dysfunction (ED) has been implicated in atherosclerosis, hypertension, coronary artery disease, vascular complications of diabetes, chronic renal failure, insulin resistance and hypercholesterolemia. Although now recognized as a class of physiological second messengers, reactive oxygen species (ROS) are important mediators in cellular injury, specifically, as a factor in endothelial cell damage. Uncontrolled ROS production and/or decreased antioxidant activity results in a deleterious state referred to as 'oxidative stress'. A candidate factor in causing ROS production in endothelial cells is tumor necrosis factor alpha (TNF-α), a pleiotropic inflammatory cytokine. TNF-α has been shown to both be secreted by endothelial cells and to induce intracellular ROS formation. These observations provide a potential mechanism by which TNF-α may activate and injure endothelial cells resulting in ED. In this review, we focus on the relationship between intracellular ROS formation and ED in endothelial cells or blood vessels exposed to TNF-α to provide insight into the role of this important cytokine in cardiovascular disease.