Hypertension increases contractile responses to hydrogen peroxide in resistance arteries through increased thromboxane A2, Ca2+, and superoxide anion levels

Targeting mitochondrial impairment for the treatment of cardiovascular diseases: From hypertension to ischemia-reperfusion injury, searching for new pharmacological targets

Mitochondria and mitochondrial proteins represent a group of promising pharmacological target candidates in the search of new molecular targets and drugs to counteract the onset of hypertension and more in general cardiovascular diseases (CVDs). Indeed, several mitochondrial pathways result impaired in CVDs, showing ATP depletion and ROS production as common traits of cardiac tissue degeneration. Thus, targeting mitochondrial dysfunction in cardiomyocytes can represent a successful strategy to prevent heart failure. In this context, the identification of new pharmacological targets among mitochondrial proteins paves the way for the design of new selective drugs. Thanks to the advances in omics approaches, to a greater availability of mitochondrial crystallized protein structures and to the development of new computational approaches for protein 3D-modelling and drug design, it is now possible to investigate in detail impaired mitochondrial pathways in CVDs. Furthermore, it is possible to design new powerful drugs able to hit the selected pharmacological targets in a highly selective way to rescue mitochondrial dysfunction and prevent cardiac tissue degeneration. The role of mitochondrial dysfunction in the onset of CVDs appears increasingly evident, as reflected by the impairment of proteins involved in lipid peroxidation, mitochondrial dynamics, respiratory chain complexes, and membrane polarization maintenance in CVD patients. Conversely, little is known about proteins responsible for the cross-talk between mitochondria and cytoplasm in cardiomyocytes. Mitochondrial transporters of the SLC25A family, in particular, are responsible for the translocation of nucleotides (e.g., ATP), amino acids (e.g., aspartate, glutamate, ornithine), organic acids (e.g. malate and 2-oxoglutarate), and other cofactors (e.g., inorganic phosphate, NAD⁺, FAD, carnitine, CoA derivatives) between the mitochondrial and cytosolic compartments. Thus, mitochondrial transporters play a key role in the mitochondria-cytosol cross-talk by leading metabolic pathways such as the malate/aspartate shuttle, the carnitine shuttle, the ATP export from mitochondria, and the regulation of permeability transition pore opening. Since all these pathways are crucial for maintaining healthy cardiomyocytes, mitochondrial carriers emerge as an interesting class of new possible pharmacological targets for CVD treatments.

Oxidative Regulation of Vascular Cav1.2 Channels Triggers Vascular Dysfunction in Hypertension-Related Disorders

Blood pressure is determined by cardiac output and peripheral vascular resistance. The L-type voltage-gated Ca²⁺ (Ca_v1.2) channel in small arteries and arterioles plays an essential role in regulating Ca²⁺ influx, vascular resistance, and blood pressure. Hypertension and preeclampsia are characterized by high blood pressure. In addition, diabetes has a high prevalence of hypertension. The etiology of these disorders remains elusive, involving the complex interplay of environmental and genetic factors. Common to these disorders are oxidative stress and vascular dysfunction. Reactive oxygen species (ROS) derived from NADPH oxidases (NOXs) and mitochondria are primary sources of vascular oxidative stress, whereas dysfunction of the Ca_v1.2 channel confers increased vascular resistance in hypertension. This review will discuss the importance of ROS derived from NOXs and mitochondria in regulating vascular Ca_v1.2 and potential roles of ROS-mediated Ca_v1.2 dysfunction in aberrant vascular function in hypertension, diabetes, and preeclampsia.

Androgen Deprivation Therapy in Patients With Prostate Cancer Increases Serum Levels of Thromboxane A2: Cardiovascular Implications

Introduction: Androgens have been described as important players in the regulation of vascular function/structure through their action on the release and effect of vasoactive factors, such as prostanoids. Patients with prostate cancer (PCa) under androgen deprivation therapies (ADTs) present increased risk of cardiovascular mortality. Since thromboxane A₂ (TXA₂) is one of the most studied prostanoids and its involvement in different cardiovascular diseases has been described, the aim of this study was to investigate: (i) the effect of ADT on the serum levels of TXA₂ in PCa patients and its possible link to the redox status and (ii) the effect of the non-hydrolyzable TXA₂ analog U-46619 on the function of the aorta of male rats.

Methods: The levels of TXA₂ and total antioxidant status in 50 healthy subjects, 54 PCa patients, and 57 PCa under ADT were evaluated. These determinations were accompanied by levels of testosterone and C-reactive protein as an inflammation marker. In aortic segments from male rats, the U46619-induced effects on: (i) the vasomotor responses to acetylcholine (ACh), to the NO donor sodium nitroprusside (SNP), to the carbon monoxide-releasing molecule-3 (CORM-3), and to noradrenaline (NA) and (ii) the expression of cyclooxygenase-2 (COX-2), heme oxygenase-1 (HO-1), and phosphorylated ERK1/2 were analyzed.

Results: The serum level of TXA₂ in patients with PCa was increased with respect to healthy subjects, which was further increased by ADT. There was no modification in the total antioxidant status among the three experimental groups. In aortic segments from male rats, the TXA₂ analog decreased the endothelium-dependent relaxation and the sensitivity of smooth muscle cells to NO, while it increased the vasoconstriction induced by NA; the expression of COX-2, HO-1, and pERK1/2 was also increased.

Conclusions: ADT increased, along with other inflammatory/oxidative markers, the serum levels of TXA₂. The fact that TXA₂ negatively impacts the vascular function of the aorta of healthy male rats suggests that inhibition of TXA₂-mediated events could be considered a potential strategy to protect the cardiovascular system.

PKCζ-NADPH Oxidase-PKCα Dependent Kv1.5 Phosphorylation by Endothelin-1 Modulates Nav1.5-NCX1-Cav1.2 Axis in Stimulating Ca2+ Level in Caveolae of Pulmonary Artery Smooth Muscle Cells

Endothelin-1 (ET-1) is a potent endogenously derived vasoconstrictor, which increases pulmonary hypertension via stimulation of [Ca²⁺]_i level in pulmonary artery smooth muscle cells (PASMCs). In this communication, we sought to investigate the mechanism by which ET-1 causes stimulation of Ca²⁺ concentration in caveolae vesicles of bovine PASMCs (BPASMCs). ET-1 activates PKC-α in the caveolae vesicles by O₂^.- derived from PKCζ-NADPH oxidase dependent pathway. PKC-α phosphorylates Kv1.5 channels leading to a marked stimulation of Na⁺ and Ca²⁺ concentration in the caveolae vesicles. The stimulation of Ca²⁺ concentration in the caveolae vesicles by ET-1 occurs predominantly via Cav1.2 channels. Additionally, an increase in Na⁺ concentration by ET-1 due to stimulation of Nav1.5 channels marginally increases Ca²⁺ level in the caveolae vesicles via reverse-mode Na⁺/Ca²⁺ exchanger (NCX-1) and also through "slip-mode conductance" Nav1.5 channels. 4-AP, a well-known inhibitor of Kv channels, also increases Ca²⁺ concentration in the caveolae vesicles via Cav1.2 channels, reverse-mode NCX-1 and Nav1.5 channels by phosphorylation independent modulation of Kv1.5 channels without the involvement of PKCζ-NADPH oxidase-PKCα signaling axis. Overall, PKCζ-NADPH oxidase-PKCα dependent phosphorylation of Kv1.5 by ET-1 modulates Nav1.5-NCX1-Cav1.2 axis for stimulation of Ca²⁺ concentration in caveolae vesicles of BPASMCs, which provides a crucial mechanism for better understanding of ET-1-mediated modulation of pulmonary vascular tone.

Nitric oxide and endothelium-dependent hyperpolarization mediated by hydrogen peroxide in health and disease

The endothelium plays crucial roles in modulating vascular tone by synthesizing and releasing endothelium-derived relaxing factors (EDRFs), including vasodilator prostaglandins, nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH) factors. Thus, endothelial dysfunction is the hallmark of atherosclerotic cardiovascular diseases. Importantly, the contribution of EDRFs to endothelium-dependent vasodilatation varies in a distinct vessel size-dependent manner; NO mainly mediates vasodilatation of relatively large, conduit vessels (eg epicardial coronary arteries), while EDH factors in small resistance vessels (eg coronary microvessels). Endothelium-derived hydrogen peroxide (H₂ O₂ ) is a physiological signalling molecule serving as one of the major EDH factors especially in microcirculations and has gained increasing attention in view of its emerging relevance for cardiovascular diseases. In the clinical settings, therapeutic approaches targeting NO (eg NO donors) or non-specific elimination of reactive oxygen species (eg antioxidant supplements) are disappointingly ineffective for the treatment of various cardiovascular diseases, in which endothelial dysfunction and coronary microvascular dysfunction are substantially involved. These lines of evidence indicate the potential importance of the physiological balance between NO and H₂ O₂ /EDH factor. Further characterization and better understanding of endothelium-dependent vasodilatations are important to develop novel therapeutic strategies in cardiovascular medicine. In this MiniReview, we will briefly summarize the current knowledge on the emerging regulatory roles of endothelium-dependent vasodilatations in the cardiovascular system, with a special reference to the two major EDRFs, NO and H₂ O₂ /EDH factor, in health and disease.

Terminalia ferdinandiana, a traditional medicinal plant of Australia, alleviates hydrogen peroxide induced oxidative stress and inflammation, in vitro

Background

Oxidative stress and inflammation are the underlying factors in many chronic debilitating diseases and commonly intertwined. Terminalia ferdinandiana is a traditional medicinal plant, endemic to Australia and is a rich source of many bioactive phytochemicals such as ellagic acid (EA) with known antioxidant capacity.

Methods

We investigated the in vitro antioxidant and anti-inflammatory activity of an aqueous food grade EA enriched (EAE) extract of T. ferdinandiana. Caco-2 and KERTr cell lines were treated with EAE or pure EA (used as reference control), followed by the exposure to hydrogen peroxide (H2O2). Levels of reactive oxygen species (ROS) production and gene expression of molecular markers associated with oxidative stress and inflammation were monitored.

Results

Significant reduction in ROS production was observed in both cell types treated with 100 or 200 µg/mL EA or EAE. Treatment of cells with EAE or EA showed upregulation of mRNA expression of the antioxidative gene superoxide dismutase (SOD)-2 and downregulated the expression of inducible nitric oxide synthase (iNOS), soluble cell adhesion molecule (sICAM), and cyclooxygenase (COX)-2. Neither EAE nor EA had any effect on the constitutively expressed COX1.

Conclusions

The antioxidant and anti-inflammatory activity of T. ferdinandiana extract on mammalian cells exposed to H2O2 suggests the potential of using this traditional medicinal plant in preventing oxidative damage and inflammation related diseases.

Enhancing Mitochondrial Health to Treat Hypertension

PURPOSE OF REVIEW

This review summarizes literature pertaining to the dawning field of therapeutic targeting of mitochondria in hypertension and discusses the potential of these interventions to ameliorate hypertension-induced organ damage.

RECENT FINDINGS

In recent years, mitochondrial dysfunction has been reported as an important contributor to the pathogenesis of hypertension-related renal, cardiac, and vascular disease. This in turn prompted development of novel mitochondria-targeted compounds, some of which have shown promising efficacy in experimental studies and safety in clinical trials. In addition, drugs that do not directly target mitochondria have shown remarkable benefits in preserving these organelles in experimental hypertension. Enhancing mitochondrial health is emerging as a novel feasible approach to treat hypertension. Future perspectives include mechanistic experimental studies to establish a cause-effect relationship between mitochondrial dysfunction and hypertension and further clinical trials to confirm the reno-, cardio-, and vasculo-protective properties of these compounds in hypertension.

Role of thromboxane A2 signaling in endothelium-dependent contractions of arteries

Thromboxane A₂ (TxA₂) plays a very important role in various cardiovascular diseases through its action on platelet aggregation, vasoconstriction, and proliferation. The present article focuses on the role of TxA₂ signaling in endothelium-dependent contractions of arteries. Arachidonic acid (AA) is metabolized by cyclooxygenase (COX) to form the unstable prostaglandin H₂ which is further converted into TxA₂. After being produced by thromboxane synthase (TxAS), TxA₂ ultimately stimulates TxA₂/prostanoid (TP) receptor to induce vasoconstriction. The calcium ionophore A23187, the prostanoid precursor AA, or the muscarinic receptor agonist acetylcholine (ACh) can evoke endothelium-dependent contractions associated with TxA₂. The endothelium-dependent contractions shown in hypertension, diabetes, atherogenesis, and other cardiovascular diseases have been significantly reduced by antagonism of COX, TxAS, or TP receptor. So inhibition of the bioavailability and/or effect of TxA₂ may be promising therapeutic targets to prevent these diseases. Especially some bioactive compounds isolated from medicinal plants will provide new pharmacological approaches to promote vascular health.

Thrombospondin-1, Free Radicals, and the Coronary Microcirculation: The Aging Conundrum

SIGNIFICANCE

Successful matching of cardiac metabolism to perfusion is accomplished primarily through vasodilation of the coronary resistance arterioles, but the mechanism that achieves this effect changes significantly as aging progresses and involves the contribution of reactive oxygen species (ROS). Recent Advances: A matricellular protein, thrombospondin-1 (Thbs-1), has been shown to be a prolific contributor to the production and modulation of ROS in large conductance vessels and in the peripheral circulation. Recently, the presence of physiologically relevant circulating Thbs-1 levels was proven to also disrupt vasodilation to nitric oxide (NO) in coronary arterioles from aged animals, negatively impacting coronary blood flow reserve.

CRITICAL ISSUES

This review seeks to reconcile how ROS can be successfully utilized as a substrate to mediate vasoreactivity in the coronary microcirculation as "normal" aging progresses, but will also examine how Thbs-1-induced ROS production leads to dysfunctional perfusion and eventual ischemia and why this is more of a concern in advancing age.

FUTURE DIRECTIONS

Current therapies that may effectively disrupt Thbs-1 and its receptor CD47 in the vascular wall and areas for future exploration will be discussed. Antioxid. Redox Signal. 27, 785-801.

Divergent roles of endothelial nitric oxide synthases system in maintaining cardiovascular homeostasis

Accumulating evidence has demonstrated the importance of reactive oxygen species (ROS) as an essential second messenger in health and disease. Endothelial dysfunction is the hallmark of atherosclerotic cardiovascular diseases, in which pathological levels of ROS are substantially involved. The endothelium plays a crucial role in modulating tone of underlying vascular smooth muscle by synthesizing and releasing nitric oxide (NO) and endothelium-dependent hyperpolarization (EDH) factors in a distinct vessel size-dependent manner through the diverse roles of the endothelial NO synthases (NOSs) system. Endothelium-derived hydrogen peroxide (H₂O₂) is a physiological signaling molecule serving as one of the major EDH factors especially in microcirculations and has gained increasing attention in view of its emerging relevance for cardiovascular homeostasis. In the clinical settings, it has been reported that antioxidant supplements are unexpectedly ineffective to prevent cardiovascular events. These lines of evidence indicate the potential importance of the physiological balance between NO and H₂O₂/EDH through the diverse functions of endothelial NOSs system in maintaining cardiovascular homeostasis. A better understanding of cardiovascular redox signaling is certainly needed to develop novel therapeutic strategies in cardiovascular medicine. In this review, we will briefly summarize the current knowledge on the emerging regulatory roles of redox signaling pathways in cardiovascular homeostasis, with particular focus on the two endothelial NOSs-derived mediators, NO and H₂O₂/EDH.

Endothelial dysfunction and vascular disease - a 30th anniversary update

The endothelium can evoke relaxations of the underlying vascular smooth muscle, by releasing vasodilator substances. The best-characterized endothelium-derived relaxing factor (EDRF) is nitric oxide (NO) which activates soluble guanylyl cyclase in the vascular smooth muscle cells, with the production of cyclic guanosine monophosphate (cGMP) initiating relaxation. The endothelial cells also evoke hyperpolarization of the cell membrane of vascular smooth muscle (endothelium-dependent hyperpolarizations, EDH-mediated responses). As regards the latter, hydrogen peroxide (H₂ O₂ ) now appears to play a dominant role. Endothelium-dependent relaxations involve both pertussis toxin-sensitive G_i (e.g. responses to α₂ -adrenergic agonists, serotonin, and thrombin) and pertussis toxin-insensitive G_q (e.g. adenosine diphosphate and bradykinin) coupling proteins. New stimulators (e.g. insulin, adiponectin) of the release of EDRFs have emerged. In recent years, evidence has also accumulated, confirming that the release of NO by the endothelial cell can chronically be upregulated (e.g. by oestrogens, exercise and dietary factors) and downregulated (e.g. oxidative stress, smoking, pollution and oxidized low-density lipoproteins) and that it is reduced with ageing and 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 favours vasospasm, thrombosis, penetration of macrophages, cellular growth and the inflammatory reaction leading to atherosclerosis. In addition to the release of NO (and EDH, in particular those due to H₂ O₂ ), endothelial cells also can evoke contraction of the underlying vascular smooth muscle cells by releasing endothelium-derived contracting factors. Recent evidence confirms that 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 and that prostacyclin plays a key role in such responses. Endothelium-dependent contractions are exacerbated when the production of nitric oxide 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 and diabetic patients. In addition, recent data confirm that the release of endothelin-1 can contribute to endothelial dysfunction and that the peptide appears to be an important contributor to vascular dysfunction. Finally, it has become clear that nitric oxide itself, under certain conditions (e.g. hypoxia), can cause biased activation of soluble guanylyl cyclase leading to the production of cyclic inosine monophosphate (cIMP) rather than cGMP and hence causes contraction rather than relaxation of the underlying vascular smooth muscle.

Augmented oxidative stress and preserved vasoconstriction induced by hydrogen peroxide in coronary arteries in obesity: role of COX-2

BACKGROUND AND PURPOSE

Oxidative stress plays a key role in the vascular and metabolic abnormalities associated with obesity. Herein, we assessed whether obesity can increase coronary vasoconstriction induced by hydrogen peroxide (H₂ O₂ ) and the signalling pathways involving COX-2 and superoxide (O₂^.- ) generation.

EXPERIMENTAL APPROACH

Contractile responses to H₂ O₂ and O₂^.- generation were measured in coronary arteries from genetically obese Zucker rats (OZR) and compared to lean Zucker rats (LZR).

KEY RESULTS

Both basal and H₂ O₂ -stimulated O₂^.- production were enhanced in coronary arteries from OZR, but H₂ O₂ -induced vasoconstriction was unchanged. The selective COX-2 inhibitor NS398 significantly reduced H₂ O₂ -induced contractions in endothelium-denuded arteries from LZR and OZR, but only in endothelium-intact arteries from LZR. PGI₂ (IP) receptor antagonism modestly reduced the vasoconstrictor action of H₂ O₂ while antagonism of the PGE₂ receptor 4 (EP₄ ) enhanced H₂ O₂ contractions in arteries from OZR but not LZR. Basal release of COX-2-derived PGE₂ was higher in coronary arteries from OZR where the selective agonist of EP₄ receptors TCS 2519 evoked potent relaxations. COX-2 was up-regulated after acute exposure to H₂ O₂ in coronary endothelium and vascular smooth muscle (VSM) and inhibition of COX-2 markedly reduced H₂ O₂ -elicited O₂^.- generation in coronary arteries and myocardium. Expression of Nox subunits in VSM and NADPH-stimulated O₂^.- generation was enhanced and contributed to H₂ O₂ vasoconstriction in arteries from obese rats.

CONCLUSION AND IMPLICATIONS

COX-2 contributes to cardiac oxidative stress and to the endothelium-independent O₂^.- -mediated coronary vasoconstriction induced by H₂ O₂ in obesity, which is offset by the release of COX-2-derived endothelial PGE₂ acting on EP₄ vasodilator receptors.

Cyclic nucleotide regulation of cardiac sympatho-vagal responsiveness

Cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) are now recognized as important intracellular signalling molecules that modulate cardiac sympatho-vagal balance in the progression of heart disease. Recent studies have identified that a significant component of autonomic dysfunction associated with several cardiovascular pathologies resides at the end organ, and is coupled to impairment of cyclic nucleotide targeted pathways linked to abnormal intracellular calcium handling and cardiac neurotransmission. Emerging evidence also suggests that cyclic nucleotide coupled phosphodiesterases (PDEs) play a key role limiting the hydrolysis of cAMP and cGMP in disease, and as a consequence this influences the action of the nucleotide on its downstream biological target. In this review, we illustrate the action of nitric oxide-CAPON signalling and brain natriuretic peptide on cGMP and cAMP regulation of cardiac sympatho-vagal transmission in hypertension and ischaemic heart disease. Moreover, we address how PDE2A is now emerging as a major target that affects the efficacy of soluble/particulate guanylate cyclase coupling to cGMP in cardiac dysautonomia.

c-Src, ERK1/2 and Rho kinase mediate hydrogen peroxide-induced vascular contraction in hypertension: role of TXA2, NAD(P)H oxidase and mitochondria

AIM

: The aim of this study was to analyse the signalling pathways involved in H2O2 vascular responses in hypertension.

METHODS

Vascular function, thromboxane A2 (TXA2) production, oxidative stress and protein expression were determined in mesenteric resistance arteries (MRAs) from hypertensive (spontaneously hypertensive rats, SHR) and normotensive Wistar Kyoto (WKY) rats.

RESULTS

H2O2 and the TP agonist U46619 induced greater contractile responses in MRA from SHR than WKY. Moreover, H2O2 increased TXA2 production more in SHR than in WKY. The c-Src inhibitor PP1 reduced H2O2 and U46619-induced contraction and TXA2 release in both strains. The ERK1/2 inhibitor PD98059 reduced H2O2 but not U46619-induced contraction only in SHR arteries. The Rho kinase inhibitor Y26372 reduced H2O2 and U46619-induced contractions only in SHR arteries. Basal c-Src, ERK1/2 and Rho kinase expression were greater in MRA from SHR than WKY. In SHR, the combination of PD98059 with the TP antagonist SQ29548 but not with Y27632 inhibited the H2O2 contraction more than each inhibitor alone. H2O2 and U46619 increased NAD(P)H oxidase activity and O2 production and decreased mitochondrial membrane potential in vessels from SHR. The effects induced by H2O2 were abolished by inhibitors of TXA2 synthase, ERK1/2 and c-Src. The mitochondrial antioxidant mitoTEMPO reduced H2O2-induced contraction and NAD(P)H oxidase activation.

CONCLUSION

In arteries from WKY, c-Src mediates H2O2 contractile responses by modulating TXA2 release and TXA2 effect. In SHR, H2O2 induces c-Src dependent TXA2 release that provokes vascular contractile responses through Rho kinase, c-Src and O2 from NAD(P)H Oxidase and mitochondria. Moreover, ERK1/2 activation contributes to H2O2 contraction in SHR through effects on mitochondria/NAD(P)H Oxidase.

Implication of thymoquinone as a remedy for polycystic ovary in rat

CONTEXT

Thymoquinone (TQ), an active component of Nigella sativa L. (Ranunculaceae), possesses anti-inflammatory and anti-oxidative properties. Polycystic ovary syndrome exhibits chronic inflammatory behavior, thus might involve nuclear factor kappa B (NF-κB) signaling and related molecular factors.

OBJECTIVE

The objective of the present study is to investigate and validate the effect of TQ in polycystic ovary (PCO) rat.

MATERIALS AND METHODS

To validate the effect of TQ (1 µM/ml), NF-κB activation, COX2 (cyclooxygenase-2) expression and reactive oxygen species (ROS) induction were studied in the KK1 cell line. To evaluate the effect of TQ (2 mg/200 µl olive oil/rat; sc) with an in vivo system, ovulation rate, levels of key ovulation mediators, and ovarian gelatinases activity were compared in superovulated, PCO, and RU486 + TQ-treated Wistar rats.

RESULTS

In vitro studies showed that NF-κB nuclear translocation, COX2, and ROS expression were repressed via TQ supplementation in RU486-treated KK1 cells. Pretreatment of TQ in the PCO rat model induced significant restoration of normal physio-molecular behavior of ovary, such as reduced cysts formation, increased ovulation rate, and normalization of key ovarian factors [like TNF-α-stimulated gene/protein 6, hyaluronan, hyaluronan-binding protein 1, COX2, matrix metalloproteinases (membrane type 1-matrix metalloproteinase, MMP9 and MMP2)], tissue inhibitor of metalloproteinases (TIMP-1 and TIMP-2), and gelatinases (like MMP9 and -2) activity during follicular maturation.

DISCUSSION AND CONCLUSION

Overall, most of the above molecular changes are regulated via NF-κB pathway, thus TQ, due to its modulatory effect on the NF-κB signaling, could elevate normal ovarian phenotype and physiological function in the PCO model, indicating its remarkable potential as a remedy for rat PCO.

Correlation between Echo-Tracking Parameters and In Vitro Measurements of Arterial Contraction and Relaxation in Rats Fed a High-Cholesterol Diet

BACKGROUND

Echo-tracking (ET) is a new technique that allows the assessment of arterial function and stiffness. This study aimed to ascertain the utility of the echo-tracking (ET) technique to assess vascular stiffness in rats with hypercholesterolemia and atherosclerosis.

MATERIAL AND METHODS

ET was used to measure the arterial stiffness of the aorta in cholesterol-fed Sprague-Dawley rats (group T1, n=10, for 4 weeks; group T2, n=10, for 12 weeks) and normal control rats (group C1, n=10; group C2, n=10). In vitro isometric tension experiments were used to measure the maximum contractile tension (MCT) and maximum relaxation percentage (MRR%) of aortic rings. Indicators of arterial stiffness and aortic MCT and MRR% were compared between groups using linear regression analysis. Light microscopic evaluation was used to demonstrate atherosclerotic changes in the aorta.

RESULTS

The rat models were successfully induced; pathological examination of the aortas showed significant atherosclerosis in group T2, but not in groups C1, C2, or T1. The arterial stiffness parameters obtained using ET and aortic rings in vitro showed significant impairments in T1 and T2 rats compared with C1 and C2 controls (all P<0.05 vs. controls). In addition, these impairments were greater in the T2 group than in the T1 group (all P<0.05). Finally, MRR% correlated with the distensibility coefficient (r=0.396, P=0.012), arterial compliance (r=0.317, P=0.047), stiffness parameter b (r=-0.406, P=0.009) and one-point pulse wave β (r=-0.434, P=0.005).

CONCLUSIONS

These results suggest that ET could be used to evaluate the changes in arterial wall elasticity associated with atherosclerosis and hypercholesterolemia.

Activin and NADPH-oxidase in preeclampsia: insights from in vitro and murine studies

OBJECTIVE

Clinical management of preeclampsia has remained unchanged for almost 5 decades. We now understand that maternal endothelial dysfunction likely arises because of placenta-derived vasoactive factors. Activin A is one such antiangiogenic factor that is released by the placenta and that is elevated in maternal serum in women with preeclampsia. Whether activin has a role in the pathogenesis of preeclampsia is not known.

STUDY DESIGN

To assess the effects of activin on endothelial cell function, we cultured human umbilical vein endothelial cells in the presence of activin or serum from normal pregnant women or pregnant women with preeclampsia, with or without follistatin, a functional activin antagonist or apocynin, a NADPH oxidase (Nox2) inhibitor. We also administered activin to pregnant C57Bl6 mice, with or without apocynin, and studied maternal and fetal outcomes. Last, we assessed endothelial cell Nox2 and nitric oxide synthase expression in normal pregnant women and pregnant women with preeclampsia.

RESULTS

Activin and preeclamptic serum induced endothelial cell oxidative stress by Nox2 up-regulation and endothelial cell dysfunction, which are effects that are mitigated by either follistatin or apocynin. The administration of activin to pregnant mice induced endothelial oxidative stress, hypertension, proteinuria, fetal growth restriction, and preterm littering. Apocynin prevented all of these effects. Compared with normal pregnant women, women with preeclampsia had increased endothelial Nox2 expression.

CONCLUSION

An activin-Nox2 pathway is a likely link between an injured placenta, endothelial dysfunction, and preeclampsia. This offers opportunities that are not novel therapeutic approaches to preeclampsia.

Acute restraint stress induces endothelial dysfunction: role of vasoconstrictor prostanoids and oxidative stress

We hypothesized that acute stress would induce endothelial dysfunction. Male Wistar rats were restrained for 2 h within wire mesh. Functional and biochemical analyses were conducted 24 h after the 2-h period of restraint. Stressed rats showed decreased exploration on the open arms of an elevated-plus maze (EPM) and increased plasma corticosterone concentration. Acute restraint stress did not alter systolic blood pressure, whereas it increased the in vitro contractile response to phenylephrine and serotonin in endothelium-intact rat aortas. NG-nitro-l-arginine methyl ester (l-NAME; nitric oxide synthase, NOS, inhibitor) did not alter the contraction induced by phenylephrine in aortic rings from stressed rats. Tiron, indomethacin and SQ29548 reversed the increase in the contractile response to phenylephrine induced by restraint stress. Increased systemic and vascular oxidative stress was evident in stressed rats. Restraint stress decreased plasma and vascular nitrate/nitrite (NOx) concentration and increased aortic expression of inducible (i) NOS, but not endothelial (e) NOS. Reduced expression of cyclooxygenase (COX)-1, but not COX-2, was observed in aortas from stressed rats. Restraint stress increased thromboxane (TX)B(2) (stable TXA(2) metabolite) concentration but did not affect prostaglandin (PG)F2α concentration in the aorta. Restraint reduced superoxide dismutase (SOD) activity, whereas concentrations of hydrogen peroxide (H(2)O(2)) and reduced glutathione (GSH) were not affected. The major new finding of our study is that restraint stress increases vascular contraction by an endothelium-dependent mechanism that involves increased oxidative stress and the generation of COX-derived vasoconstrictor prostanoids. Such stress-induced endothelial dysfunction could predispose to the development of cardiovascular diseases.

Toll-like receptor 4 upregulation by angiotensin II contributes to hypertension and vascular dysfunction through reactive oxygen species production

Hypertension is considered as a low-grade inflammatory disease, with adaptive immunity being an important mediator of this pathology. TLR4 may have a role in the development of several cardiovascular diseases; however, little is known about its participation in hypertension. We aimed to investigate whether TLR4 activation due to increased activity of the renin-angiotensin system (RAS) contributes to hypertension and its associated endothelial dysfunction. For this, we used aortic segments from Wistar rats treated with a non-specific IgG (1 µg/day) and SHRs treated with losartan (15 mg/kg·day), the non-specific IgG or the neutralizing antibody anti-TLR4 (1 µg/day), as well as cultured vascular smooth muscle cells (VSMC) from Wistar and SHRs. TLR4 mRNA levels were greater in the VSMC and aortas from SHRs compared with Wistar rats; losartan treatment reduced those levels in the SHRs. Treatment of the SHRs with the anti-TLR4 antibody: 1) reduced the increased blood pressure, heart rate and phenylephrine-induced contraction while it improved the impaired acetylcholine-induced relaxation; 2) increased the potentiation of phenylephrine contraction after endothelium removal; and 3) abolished the inhibitory effects of tiron, apocynin and catalase on the phenylephrine-induced response as well as its enhancing effect of acetylcholine-induced relaxation. In SHR VSMCs, angiotensin II increased TLR4 mRNA levels, and losartan reduced that increase. CLI-095, a TLR4 inhibitor, mitigated the increases in NAD(P)H oxidase activity, superoxide anion production, migration and proliferation that were induced by angiotensin II. In conclusion, TLR4 pathway activation due to increased RAS activity is involved in hypertension, and by inducing oxidative stress, this pathway contributes to the endothelial dysfunction associated with this pathology. These results suggest that TLR4 and innate immunity may play a role in hypertension and its associated end-organ damage.

Hydrogen peroxide induces vasorelaxation by enhancing 4-aminopyridine-sensitive Kv currents through S-glutathionylation

Hydrogen peroxide (H₂O₂) is an endothelium-derived hyperpolarizing factor. Since opposing vasoactive effects have been reported for H₂O₂ depending on the vascular bed and experimental conditions, this study was performed to assess whether H₂O₂ acts as a vasodilator in the rat mesenteric artery and, if so, to determine the underlying mechanisms. H₂O₂ elicited concentration-dependent relaxation in mesenteric arteries precontracted with norepinephrine. The vasodilatory effect of H₂O₂ was reversed by treatment with dithiothreitol. H₂O₂-elicited vasodilation was significantly reduced by blocking 4-aminopyridine (4-AP)-sensitive Kv channels, but it was resistant to blockers of big-conductance Ca²⁺-activated K⁺ channels and inward rectifier K⁺ channels. A patch-clamp study in mesenteric arterial smooth muscle cells (MASMCs) showed that H₂O₂ increased Kv currents in a concentration-dependent manner. H₂O₂ speeded up Kv channel activation and shifted steady state activation to hyperpolarizing potentials. Similar channel activation was seen with oxidized glutathione (GSSG). The H₂O₂-mediated channel activation was prevented by glutathione reductase. Consistent with S-glutathionylation, streptavidin pull-down assays with biotinylated glutathione ethyl ester showed incorporation of glutathione (GSH) in the Kv channel proteins in the presence of H₂O₂. Interestingly, conditions of increased oxidative stress within MASMCs impaired the capacity of H₂O₂ to stimulate Kv channels. Not only was the H₂O₂ stimulatory effect much weaker, but the inhibitory effect of H₂O₂ was unmasked. These data suggest that H₂O₂ activates 4-AP-sensitive Kv channels, possibly through S-glutathionylation, which elicits smooth muscle relaxation in rat mesenteric arteries. Furthermore, our results support the idea that the basal redox status of MASMCs determines the response of Kv currents to H₂O₂.

New roles for old pathways? A circuitous relationship between reactive oxygen species and cyclo-oxygenase in hypertension

Elevated production of prostanoids from the constitutive (COX-1) or inducible (COX-2) cyclo-oxygenases has been involved in the alterations in vascular function, structure and mechanical properties observed in cardiovascular diseases, including hypertension. In addition, it is well known that production of ROS (reactive oxygen species) plays an important role in the impaired contractile and vasodilator responses, vascular remodelling and altered vascular mechanics of hypertension. Of particular interest is the cross-talk between NADPH oxidase and mitochondria, the main ROS sources in hypertension, which may represent a vicious feed-forward cycle of ROS production. In recent years, there is experimental evidence showing a relationship between ROS and COX-derived products. Thus ROS can activate COX and the COX/PG (prostaglandin) synthase pathways can induce ROS production through effects on different ROS generating enzymes. Additionally, recent evidence suggests that the COX-ROS axis might constitute a vicious circle of self-perpetuating vasoactive products that have a pathophysiological role in altered vascular contractile and dilator responses and hypertension development. The present review discusses the current knowledge on the role of oxidative stress and COX-derived prostanoids in the vascular alterations observed in hypertension, highlighting new findings indicating that these two pathways act in concert to induce vascular dysfunction.

Signaling pathways involved in the H2O2-induced vasoconstriction of rat coronary arteries

Hydrogen peroxide (H2O2) is an endogenous endothelium-derived hyperpolarizing factor released by flow and involved in the regulation of coronary blood flow. Because opposing vasoactive effects have been reported for H2O2 depending on the vascular bed and experimental conditions, the aim of this study was to assess whether H2O2 may act as a coronary vasoconstrictor and if so to determine the underlying signaling mechanisms. Intramyocardial arteries from male Wistar rats were mounted on microvascular myographs for simultaneous measurements of intracellular Ca(2+) ([Ca(2+)]i) and tension. On coronary arteries precontracted with the thromboxane A2 (TxA2) analogue U46619, H2O2 (1-300μM) elicited further moderate contractions in the proximal arterial segments and relaxed the more distal coronary branches, the contractions being markedly augmented in arteries depolarized by raising extracellular K(+). H2O2-elicited vasoconstriction on K(+)30-precontracted coronary arteries was blunted by catalase and significantly reduced by endothelial cell removal and by inhibitors of cyclooxygenase (COX) and of the TxA2 receptor (TP). H2O2 (50μM) increased by about 10-fold basal superoxide anion (O2(-)) production in coronary arteries measured by lucigenin-enhanced chemiluminescence, and H2O2-elicited contractions were reduced by the superoxide dismutase mimetic tempol and by NADPH oxidase inhibition. Furthermore, blockade of the ERK and p38 mitogen-activated protein (MAP) kinases significantly reduced the contractions elicited by high and low concentrations of peroxide, respectively, whereas Rho kinase inhibition nearly abolished these responses. H2O2 (50μM) elicited simultaneous and similar sustained increases in [Ca(2+)]i and tension that were blunted by blockade of voltage-dependent L-type channels, but resistant to the nonselective Ca(2+) channel blocker 2-aminoethoxydiphenyl borate. Moreover, endothelial cell removal reduced the increases in [Ca(2+)]i and contraction elicited by peroxide. The present data demonstrate that H2O2 is an endothelium-dependent vasoconstrictor in rat coronary arteries that activates smooth muscle Ca(2+) entry through L-type and non-L-type channels and various intracellular signaling pathways including the release of a COX-derived TP agonist, stimulation of the MAP and Rho kinase pathways, and production of NADPH oxidase-derived superoxide.

Reciprocal relationship between reactive oxygen species and cyclooxygenase-2 and vascular dysfunction in hypertension

AIMS

This study evaluates a possible relationship between reactive oxygen species (ROS) and cyclooxygenase (COX)-2-derived products in conductance and resistance arteries from hypertensive animals. Angiotensin II (Ang II)-infused mice or spontaneously hypertensive rats treated with the NAD(P)H Oxidase inhibitor apocynin, the mitochondrion-targeted SOD2 mimetic Mito-TEMPO, the superoxide dismutase analog tempol, or the COX-2 inhibitor Celecoxib were used.

RESULTS

Apocynin, Mito-TEMPO, and Celecoxib treatments prevented Ang II-induced hypertension, the increased vasoconstrictor responses to phenylephrine, and the reduced acetylcholine relaxation. The NOX-2 inhibitor gp91ds-tat, the NOX-1 inhibitor ML171, catalase, and the COX-2 inhibitor NS398 abolished the ex vivo effect of Ang II-enhancing phenylephrine responses. Antioxidant treatments diminished the increased vascular COX-2 expression, prostanoid production, and/or participation of COX-derived contractile prostanoids and thromboxane A(2) receptor (TP) in phenylephrine responses, observed in arteries from hypertensive models. The treatment with the COX-2 inhibitor normalized the increased ROS production (O(2)·(-) and H(2)O(2)), NAD(P)H Oxidase expression (NOX-1, NOX-4, and p22phox) and activity, MnSOD expression, and the participation of ROS in vascular responses in both hypertensive models. Apocynin and Mito-TEMPO also normalized these parameters of oxidative stress. Apocynin, Mito-TEMPO, and Celecoxib improved the diminished nitric oxide (NO) production and the modulation by NO of phenylephrine responses in the Ang II model.

INNOVATION

This study provides mechanistic evidence of circuitous relationship between COX-2 products and ROS in hypertension.

CONCLUSION

The excess of ROS from NAD(P)H Oxidase and/or mitochondria and the increased vascular COX-2/TP receptor axis act in concert to induce vascular dysfunction and hypertension.

The effect of tempol administration on the aortic contractile responses in rat preeclampsia model

It is reported that reactive oxygen species production has a critical role in the manifestations and complications of preeclampsia. In the present study, the effect of tempol on the response changes of aortic rings of preeclamptic rats has been studied. Preeclamptic rats (induced by L-NAME) were treated with three different oral doses of tempol (20, 60 and 180 mg/kg/day) from the Day 10 of gestation. Systolic blood pressure, plasma malondialdehyde and 8-isoprostane and the vascular effects of phenylephrine, calcium, acetylcholine and diazoxide were the studied parameters. L-NAME administration resulted in hypertension, proteinuria, increased oxidative stress markers, increased vascular sensitivity to phenylephrine and decreased sensitivity to acetylcholine in pregnant rats. No significant changes in response to calcium and diazoxide were observed. Tempol at doses of 20 and 60 mg/kg/day significantly reversed these changes but at a high dose (180 mg/kg/day), it had no significant effect and in some cases intensified the effect. These results revealed that in the experimental preeclampsia, the sensitivity of rat aorta to alpha- adrenergic receptor agonists was increased and its endothelium-dependent relaxation was decreased. Tempol at lower used doses reduced the blood pressure and oxidative stress and restored the normal responsiveness of vascular tissue in preeclamptic rats.

The endothelium: influencing vascular smooth muscle in many ways

The endothelium, although only a single layer of cells lining the vascular and lymphatic systems, contributes in multiple ways to vascular homeostasis. Subsequent to the 1980 report by Robert Furchgott and John Zawadzki, there has been a phenomenal increase in our knowledge concerning the signalling molecules and pathways that regulate endothelial - vascular smooth muscle communication. It is now recognised that the endothelium is not only an important source of nitric oxide (NO), but also numerous other signalling molecules, including the putative endothelium-derived hyperpolarizing factor (EDHF), prostacyclin (PGI(2)), and hydrogen peroxide (H(2)O(2)), which have both vasodilator and vasoconstrictor properties. In addition, the endothelium, either via transferred chemical mediators, such as NO and PGI(2), and (or) low-resistance electrical coupling through myoendothelial gap junctions, modulates flow-mediated vasodilatation as well as influencing mitogenic activity, platelet aggregation, and neutrophil adhesion. Disruption of endothelial function is an early indicator of the development of vascular disease, and thus an important area for further research and identification of potentially new therapeutic targets. This review focuses on the signalling pathways that regulate endothelial - vascular smooth muscle communication and the mechanisms that initiate endothelial dysfunction, particularly with respect to diabetic vascular disease.

Endothelium-mediated control of vascular tone: COX-1 and COX-2 products

Endothelium-dependent contractions contribute to endothelial dysfunction in various animal models of aging, diabetes and cardiovascular diseases. In the spontaneously hypertensive rat, the archetypal model for endothelium-dependent contractions, the production of the endothelium-derived contractile factors (EDCF) involves an increase in endothelial intracellular calcium concentration, the production of reactive oxygen species, the predominant activation of cyclooxygenase-1 (COX-1) and to a lesser extent that of COX-2, the diffusion of EDCF towards the smooth muscle cells and the subsequent stimulation of their thromboxane A2-endoperoxide TP receptors. Endothelium-dependent contractions are also observed in various models of hypertension, aging and diabetes. They generally also involve the generation of COX-1- and/or COX-2-derived products and the activation of smooth muscle TP receptors. Depending on the model, thromboxane A(2), PGH(2), PGF(2α), PGE(2) and paradoxically PGI(2) can all act as EDCFs. In human, the production of COX-derived EDCF is a characteristic of the aging and diseased blood vessels, with essential hypertension causing an earlier onset and an acceleration of this endothelial dysfunction. As it has been observed in animal models, COX-1, COX-2 or both isoforms can contribute to these endothelial dysfunctions. Since in most cases, the activation of TP receptors is the common downstream effector, selective antagonists of this receptor should curtail endothelial dysfunction and be of therapeutic interest in the treatment of cardiovascular disorders.

Reactivity of the aorta and mesenteric resistance arteries from the obese spontaneously hypertensive rat: effects of glitazones

The obese spontaneously hypertensive rat (SHROB) is a model of metabolic syndrome in which, to our knowledge, vascular function has never been studied. The actions of insulin sensitizers (glitazones) on vascular function have not been analyzed either. Our purpose was to characterize microvascular and macrovascular responses of the SHROB and to study the effects of glitazones on these responses. The reactivity of mesenteric resistance arteries (MRAs) and the aorta from SHROBs and control rats to cumulative concentrations of phenylephrine, ACh, and sodium nitroprusside (SNP) was myographically analyzed. Some animals were orally treated with rosiglitazone (3 mg·kg−1·day−1, 3 wk), and myography was performed. Phenylephrine, ACh, and SNP dose-response curves were impaired to different extents in arteries of SHROBs. Incubation with N-nitro-l-arginine methyl ester caused little effects on phenylephrine and ACh curves in MRAs but enhanced phenylephrine contractions and abolished ACh-induced relaxations of aortae. Incubation with indomethacin reduced phenylephrine reactivity and improved ACh-induced relaxations of all vessels studied. NS-398 and tempol increased relaxations to ACh of MRAs. Incubation with pioglitazone or rosiglitazone (both 10−5 M) or oral treatment with rosiglitazone improved, to different extents, ACh and SNP curves in all vessels. Glitazone incubation diminished aortic ACh sensitivity. The release of thromboxane A2 and PGI2 metabolites (thromboxane B2 and 6-keto-PGF1α) was analyzed. ACh increased the MRA release of thromboxane B2 from SHROBs but not control rats, and the former was prevented by rosiglitazone coincubation. In contrast, in aortae, ACh failed to alter the release of metabolites, and rosiglitazone treatment increased that of 6-keto-PGF1α. Thus, SHROBs displayed microvascular and macrovascular dysfunction. MRAs, but not aortae, of SHROBs revealed an impaired endothelial nitric oxide pathway, whereas both, but especially MRAs, displayed an impaired cyclooxygenase pathway. Glitazones elicited beneficial effects on macrovascular and, especially, microvascular function of SHROBs.

Pulmonary arterial responses to reactive oxygen species are altered in newborn piglets with chronic hypoxia-induced pulmonary hypertension

Reactive oxygen species (ROS) have been implicated in the pathogenesis of pulmonary hypertension. ROS might mediate vascular responses, at least in part, by stimulating prostanoid production. Our goals were to determine whether the effect of ROS on vascular tone is altered in resistance pulmonary arteries (PRAs) of newborn piglets with chronic hypoxia-induced pulmonary hypertension and the role, if any, of prostanoids in ROS-mediated responses. In cannulated, pressurized PRA, ROS generated by xanthine (X) plus xanthine oxidase (XO) had minimal effect on vascular tone in control piglets but caused significant vasoconstriction in hypoxic piglets. Both cyclooxygenase inhibition with indomethacin and thromboxane synthase inhibition with dazoxiben significantly blunted constriction to X+XO in hypoxic PRA. X+XO increased prostacyclin production (70 ± 8%) by a greater degree than thromboxane production (50 ± 6%) in control PRA; this was not the case in hypoxic PRA where the increases in prostacyclin and thromboxane production were not statistically different (78 ± 13% versus 216 ± 93%, respectively). Thromboxane synthase expression was increased in PRA from hypoxic piglets, whereas prostacyclin synthase expression was similar in PRA from hypoxic and control piglets. Under conditions of chronic hypoxia, altered vascular responses to ROS may contribute to pulmonary hypertension by a mechanism that involves the prostanoid vasoconstrictor, thromboxane.

Type 1 diabetes-induced hyper-responsiveness to 5-hydroxytryptamine in rat pulmonary arteries via oxidative stress and induction of cyclooxygenase-2

Recent epidemiological data suggest that diabetes is a risk factor for pulmonary arterial hypertension. The aim of the present study was to analyze the link between type 1 diabetes and pulmonary arterial dysfunction in rats. Male Sprague-Dawley rats were randomly divided into a control group (saline) and a diabetic group (70 mg/kg streptozotocin). After 6 weeks, diabetic animals showed a down-regulation of the lung bone morphogenetic protein receptor type 2, up-regulation of 5-hydroxytryptamine (5-HT) 2A receptors and cyclooxygenase-2 (COX-2) proteins as measured by Western blot analysis, and increased contractile responses to 5-HT in isolated intrapulmonary arteries. The hyper-responsiveness to 5-HT was endothelium-independent and unaffected by inhibition of nitric-oxide synthase but prevented by indomethacin, the selective COX-2 inhibitor N-[2-(cyclohexyloxyl)-4-nitrophenyl]-methane sulfonamide (NS-398), superoxide dismutase, and the NADPH oxidase inhibitor apocynin or chronic treatment with insulin. However, diabetic rats at 6 weeks did not develop elevated right ventricular pressure or pulmonary artery muscularization, whereas a longer exposure (4 months) to diabetes induced a modest, but significant, increase in right ventricular systolic pressure. In conclusion, type 1 diabetes mellitus in rats induces a number of changes in lung protein expression and pulmonary vascular reactivity characteristic of clinical and experimental pulmonary arterial hypertension but insufficient to elevate pulmonary pressure. Our results further strengthen the link between diabetes and pulmonary arterial hypertension.

Chronic inhibition of nitric-oxide synthase potentiates endothelium-dependent contractions in the rat aorta by augmenting the expression of cyclooxygenase-2

Acute inhibition of nitric-oxide synthase (NOS) unmasks the release of endothelium-derived contracting factors (EDCFs). The present study investigated whether chronic inhibition of NOS modulates endothelium-dependent contractions. Eighteen-week-old male Sprague-Dawley rats were treated by daily gavage for 6 weeks with the NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) (60 mg/kg) or vehicle (distilled water; 1 ml/kg). Chronic treatment with L-NAME increased arterial blood pressure. Isometric tension was measured in aortic rings with or without endothelium. Endothelium-dependent relaxations to acetylcholine and the calcium ionophore 5-(methylamino)-2-[(2R,3R,6S,8S,9R,11R)-3,9,11-trimethyl-8-[(1S)-1-methyl-2-oxo-2-(1H-pyrrol-2-yl)-ethyl]-1,7-dioxaspiro[5.5]undec-2-yl]methyl]-4-benzoxazolecarboxylic acid (A23187) were reduced in preparations from L-NAME-treated rats. The reduction in relaxation to A23187 was partially reversed by L-arginine (1 mM). In quiescent aortic rings, A23187 caused contractions in the presence of L-NAME and intact endothelium. The A23187-induced contractions were greater in rings from the L-NAME-treated rats than in those from the control group. These contractions were abolished by the cyclooxygenase (COX)-2 inhibitor N-[2-cyclohexyloxy-4-nitrophenyl]methanesulfonamide (NS-398) and the thromboxane-prostanoid (TP) receptor antagonist 3-((6R)-6-{[(4-chlorophenyl)sulfonyl]amido}-2-methyl-5,6,7,8-tetrahydronaphthalen-1-yl)propanoate (S18886), but not by the COX-1 inhibitor 5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-(trifluoromethyl)-1H-pyrazole (SC-560). Chronic L-NAME treatment reduced the level of nitric oxide in the plasma but increased COX activity in the aortic rings. Western blotting and immunohistochemical staining showed that endothelial NOS expression was reduced in the aortae of the chronic L-NAME-treated group. COX-1 expression was augmented slightly, whereas COX-2 expression was up-regulated markedly. The TP receptor expression was comparable with control. These experiments demonstrate that chronic NOS inhibition increases endothelium-dependent contractions of the rat aorta by inducing COX-2 expression and augmenting the production of EDCF.

Periadventitial adipose tissue promotes endothelial dysfunction via oxidative stress in diet-induced obese C57Bl/6 mice

BACKGROUND

Biological substances derived from perivascular fat modulate vascular tone, thus alterations in periadventitial adipose tissue (PVAT) may aggravate endothelial dysfunction in obesity.

METHODS AND RESULTS

Male C57Bl/6 mice were fed either a high-fat diet or standard laboratory chow for 8 months. Vascular responses were studied in organ bath chambers from abdominal aortic ring preparations in the absence or presence of PVAT. The amount of PVAT as well as the cross-sectional area of adipocytes were increased in obese mice. In the presence of PVAT, obese aortas displayed impaired endothelium-dependent vasodilation whereas endothelium-independent vasodilatation was unaltered. Endothelium-dependent vasodilatation was restored after removal of PVAT and after reducing superoxide and hydrogen peroxide formation in the vascular wall by Tiron or polyethylene-glycol-catalase, respectively. PVAT from obese mice showed increased formation of hydrogen peroxide and superoxide. The PVAT-derived oxidative stress was abolished by pretreatment with the reduced nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase inhibitor, apocynin. The anti-contractile function of PVAT found in lean mice was completely abolished in obese mice, but partially restored after pretreatment with Tiron. The mRNA expressions of monocyte chemotactic protein-1, leptin and NADPH oxidase were markedly higher in the PVAT of obese than lean mice.

CONCLUSIONS

PVAT promotes endothelial dysfunction in diet-induced obese C57Bl/6 mice via mechanisms that are linked to increased NADPH oxidase-derived oxidative stress and increased production of pro-inflammatory cytokines.

Progestogens reduce thromboxane production by cultured human endothelial cells

OBJECTIVES

Progestogens have been poorly studied concerning their roles in endothelial physiology. Prostanoids are vasoactive compounds, such as thromboxane A2, a potent vasoconstrictor, and prostacyclin, a vasodilator. We examined the effects of two progestogens used clinically, progesterone and medroxyprogesterone acetate, on thromboxane A2 production by cultured human umbilical vein endothelial cells (HUVEC) and investigated the role of progesterone receptors and the enzymes involved in production of thromboxane A2 and prostacyclin.

METHODS

Cells were exposed to 1-100  nmol/l of either progesterone or medroxyprogesterone acetate, and thromboxane A2 production was measured in culture medium by enzyme immunoassay. Gene expression of prostacyclin synthase and thromboxane synthase was analyzed by quantitative real-time polymerase chain reaction. Expression of prostacyclin synthase protein was analyzed by Western blot.

RESULTS

Both progestogens decreased thromboxane A2 release after 24 h. Protein and gene expression of prostacyclin synthase were increased after exposure to both progestogens, without changes in thromboxane synthase expression. These effects induced by progestogens were mediated through progesterone receptors, since they were decreased in the presence of the progesterone receptor antagonist RU486. The cyclo-oxygenase-1 selective inhibitor reduced thromboxane release.

CONCLUSION

Progesterone and medroxyprogesterone acetate decreased HUVEC thromboxane release in a progesterone receptor-dependent manner, without changes in thromboxane synthase expression and enhanced prostacyclin synthase gene and protein expression.

Intrarenal artery superoxide is mainly NADPH oxidase-derived and modulates endothelium-dependent dilation in elderly patients

AIMS

The present study was performed to investigate the contribution of NADPH oxidases (Nox) to superoxide formation in human renal proximal resistance arteries and to test whether superoxide formation contributes to acute vasoconstrictor responses and endothelium-dependent vasodilation in these vessels.

METHODS AND RESULTS

Arcuate and proximal interlobular artery segments were from patients who underwent nephrectomy because of a renal tumour. Vessels were dissected from tumour-free parts of the kidneys. Additional intrarenal arteries were obtained from rats. Superoxide formation was measured by lucigenin-enhanced chemiluminescence, expression of Nox isoforms was analysed by RT-PCR, and functional studies were performed by small vessel wire myography. Sixty per cent of superoxide formation in human arcuate and proximal interlobular arteries was due to Nox activity. mRNA expression analyses revealed the presence of Nox2 and Nox4 but not Nox1. Phenylephrine and endothelin-1 induced powerful concentration-dependent vasoconstrictions that were unaffected by superoxide scavengers. Vasopressin elicited small and variable vasoconstrictions with signs of tachyphylaxis. Endothelium-dependent vasodilation was blunted by tiron and Nomega-nitro-L-arginine methyl ester but not by superoxide dismutase or catalase. Exogenous hydrogen peroxide elicited vasoconstriction.

CONCLUSION

Nox activity is the major source of superoxide formation in renal proximal resistance arteries from elderly patients. Acute vasoconstrictor responses to alpha1-adrenoreceptor activation and to endothelin-1 do not depend on superoxide formation, while endothelium-dependent vasodilation in intrarenal arteries is reactive oxygen species-dependent.

Novel approaches to improving endothelium-dependent nitric oxide-mediated vasodilatation

Endothelial dysfunction, which is defined by decreased endothelium-dependent vasodilatation, is associated with an increased number of cardiovascular events. Nitric oxide (NO) bioavailability is reduced by altered endothelial signal transduction or increased formation of radical oxygen species reacting with NO. Endothelial dysfunction is therapeutically reversible and physical exercise, calcium channel blockers, angiotensin converting enzyme inhibitors, and angiotensin receptor antagonists improve flow-evoked endothelium-dependent vasodilation in patients with hypertension and diabetes. We have investigated three different approaches, with the aim of correcting endothelial dysfunction in cardiovascular disease. Thus, (1) we evaluated the effect of a cell permeable superoxide dismutase mimetic, tempol, on endothelial dysfunction in small arteries exposed to high pressure, (2) investigated the endothelial signal transduction pathways involved in vasorelaxation and NO release induced by an olive oil component, oleanolic acid, and (3) investigated the role of calcium-activated K channels in the release of NO induced by receptor activation. Tempol increases endothelium-dependent vasodilatation in arteries from hypertensive animals most likely through the lowering of radical oxygen species, but other mechanisms also appear to contribute to the effect. While oleanolic acid leads to the release of NO by calcium-independent phosphorylation of endothelial NO synthase, endothelial calcium-activated K channels and an influx of calcium play an important role in G-protein coupled receptor-evoked release of NO. Thus, all three approaches increase bioavailability of NO in the vascular wall, but it remains to be addressed whether these actions have any direct benefit at a clinical level.