Endothelin-1-induced contraction in veins is independent of hydrogen peroxide

Venous endothelial function in cardiovascular disease

The essential role of the endothelium in vascular homeostasis is associated with the release of endothelium-dependent relaxing and contractile factors (EDRF and EDCF, respectively). Different from arteries, where these factors are widely studied, the vasoactive factors derived from the venous endothelium have been given less attention. There is evidence for a role of the nitric oxide (NO), endothelium-dependent hyperpolarization (EDH) mechanism, and cyclooxygenase (COX)-derived metabolites as EDRFs; while the EDCFs need to be better evaluated since no consensus has been reached about their identity in venous vessels. The imbalance between the synthesis, bioavailability, and/or action of EDRFs and/or EDCFs results in a pathological process known as endothelial dysfunction, which leads to reduced vasodilation and/or increased vasoconstriction. In the venous system, endothelial dysfunction is relevant since reduced venodilation may increase venous tone and decrease venous compliance, thus enhancing mean circulatory filling pressure, which maintains or modify cardiac workload contributing to the etiology of cardiovascular diseases. Interestingly, some alterations in venous function appear at the early stages (or even before) the establishment of these diseases. However, if the venous endothelium dysfunction is involved in these alterations is not yet fully understood and requires further studies. In this sense, the present study aims to review the current knowledge on venous endothelial function and dysfunction, and the general state of the venous tone in two important cardiovascular diseases of high incidence and morbimortality worldwide: hypertension and heart failure.

Inhibitory effects of Syzygium jambos extract on biomarkers of endothelial cell activation

Background

Disordered endothelial cell activation plays an important role in the pathophysiology of atherosclerosis, cancer, sepsis, viral infections, and inflammatory responses. There is interest in developing novel therapeutics to regulate endothelial cell function in atherothrombotic, metabolic, vascular, and hematological diseases. Extracts from leaves of the Syzygium jambos (L.) Alston (S. jambos) trees have been proposed to treat cardiovascular diseases and diabetes through unclear mechanisms. We investigated the effects of the S. jambos extract on biomarkers of endothelial dysfunction and immune responses in the human endothelial cell line, EA.hy926.

Methods

Leaves of S. jambos were collected, concocted and lyophilized. To study the effects of S. jambos on endothelial cell activation, we used the human endothelial cell line. IL-6 levels were measured using qPCR and ELISA. PDI activity was measured using Insulin Turbidity and Di-E-GSSG assays. CM-H2DCFDA was used to study ROS levels. Migration assay was used to study S. jambos effect on ex vivo human polymorphonuclear and human mononuclear cells.

Results

Our results show that incubation of EA.hy926 cells with ET-1 led to a 6.5 ± 1.6 fold increase in IL-6 expression by qPCR, an event that was blocked by S. jambos. Also, we observed that ET-1 increased extracellular protein disulfide isomerase (PDI) activity that was likewise dose-dependently blocked by S. jambos (IC₅₀ = 14 μg/mL). Consistent with these observations, ET-1 stimulated ex vivo human polymorphonuclear and mononuclear cell migration that also was dose-dependently blocked by S. jambos. In addition, ET-1 stimulation led to significant increases in ROS production that were sensitive to S. jambos.

Conclusion

Our results suggest that the S. jambos extract represents a novel cardiovascular protective pharmacological approach to regulate endothelial cell activation, IL-6 expression, and immune-cell responses.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-022-03572-7.

Vena cava presents endothelial dysfunction prior to thoracic aorta in heart failure: the pivotal role of nNOS uncoupling/oxidative stress

Arterial endothelial dysfunction has been extensively studied in heart failure (HF). However, little is known about the adjustments shown by the venous system in this condition. Considering that inferior vena cava (VC) tone could influence cardiac performance and HF prognosis, the aim of the present study was to assess the VC and thoracic aorta (TA) endothelial function of HF-post-myocardial infarction (MI) rats, comparing both endothelial responses and signaling pathways developed. Vascular reactivity of TA and VC from HF post-MI and sham operated (SO) rats was assessed with a wire myograph, 4 weeks after coronary artery occlusion surgery. Nitric oxide (NO), H2O2 production and oxidative stress were evaluated in situ with fluorescent probes, while protein expression and dimer/monomer ratio was assessed by Western blot. VC from HF rats presented endothelial dysfunction, while TA exhibited higher acetylcholine (ACh)-induced vasodilation when compared with vessels from SO rats. TA exhibited increased ACh-induced NO production due to a higher coupling of endothelial and neuronal NO synthases isoforms (eNOS, nNOS), and enhanced expression of antioxidant enzymes. These adjustments, however, were absent in VC of HF post-MI rats, which exhibited uncoupled nNOS, oxidative stress and higher H2O2 bioavailability. Altogether, the present study suggests a differential regulation of endothelial function between VC and TA of HF post-MI rats, most likely due to nNOS uncoupling and compromised antioxidant defense.

Mechanisms of 2,3,7,8-tetrachlorodibenzo-p-dioxin- induced cardiovascular toxicity: An overview

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is an environmental contaminant and its toxicity is mediated by the aryl hydrocarbon receptor (AHR). Mechanisms of TCDD cardiovascular toxicity consist of oxidative stress, growth factor modulation, and ionic current alteration. It is indicated that the rodent cardiovascular system is a target for TCDD cardiomyopathy. Here, our understanding of TCDD cardiovascular toxicity is reviewed.

Estimation of Some Oxidative Stress Parameters and Blood Pressure After Administration of Endothelin-1 (ET-1) in Rats

The aim of the study was to investigate changes in the plasma antioxidative activity and in lipid peroxidation after administration of endothelin-1 (ET-1) and endothelin receptor blockers and additionally, to estimate blood pressure. The study was performed on male Wistar rats (n = 6 per group) divided into 4 groups which received: (1) saline, (2) endothelin-1 (ET-1) (3 μg/kg b.w.) + saline, (3) BQ123 (1 mg/kg) + ET-1 (3 μg/kg), and (4) BQ788 (3 mg/kg) + ET-1 (3 μg/kg b.w.). The endothelin receptor antagonist was injected intravenously 30 min before ET-1 administration. Blood pressure was monitored, and the blood was collected before the saline or ET-1 administration as well as 60 and 300 min after their administration. The antioxidative properties were examined by FRAP method (ferric reducing ability of plasma), and the concentration of lipid peroxidation products was examined by the reaction with thiobarbituric acid (TBARS). It was estimated that intravenous administration of endothelin receptor blocker ETA increases plasma antioxidative properties (p < 0.01) and parallelly decreases the process of lipid peroxidation (p < 0.05 vs. ET-1) and blood pressure (p < 0.05).

Hydrogen Peroxide as a Paracrine Vascular Mediator: Regulation and Signaling Leading to Dysfunction

Numerous studies have demonstrated the ability of a variety of vascular cells, including endothelial cells, smooth muscle cells, and fibroblasts, to produce reactive oxygen species (ROS). Until recently, major emphasis was placed on the production of superoxide anion (O2–) in the vasculature as a result of its ability to directly attenuate the biological activity of endothelium-derived nitric oxide (NO). The short half-life and radius of diffusion of O2– drastically limit the role of this ROS as an important paracrine hormone in vascular biology. On the contrary, in recent years, the O2– metabolite hydrogen peroxide (H2O2) has increasingly been viewed as an important cellular signaling agent in its own right, capable of modulating both contractile and growth-promoting pathways with more far-reaching effects. In this review, we will assess the vascular production of H2O2, its regulation by endogenous scavenger systems, and its ability to activate a variety of vascular signaling pathways, thereby leading to vascular contraction and growth. This discussion will include the ability of H2O2 to (i) Initiate calcium flux as well as (ii) stimulate pathways leading to sensitization of contractile elements to calcium. The latter involves a variety of protein kinases that have also been strongly implicated in vascular hypertrophy. Previous Intensive study has emphasized the ability of NADPH oxidase-derived O2– and H2O2 to activate these pathways in cultured smooth muscle cells. However, growing evidence indicates a considerably more complex array of unique oxidase systems in the endothelium, media, and adventitia that appear to participate in these deleterious effects in a sequential and temporal manner. Taken together, these findings seem consistent with a paracrine effect of H2O2 across the vascular wall.

Influence of Endothelin 1 Receptor Blockers and a Nitric Oxide Synthase Inhibitor on Reactive Oxygen Species Formation in Rat Lungs

This study was designated to estimate protective role of ETA and ETB receptor antagonist against endothelin 1 (ET-1)-induced oxidative stress in lungs and determine whether these effects are mediated by nitric oxide (NO) synthase. Experiments were performed on Wistar rats divided into the following groups: I – saline (0.9 % NaCl); II – ET-1 (3 μg/kg b.w.), III – BQ123 (1 mg/kg b.w.) + ET-1 (3 μg/kg b.w.), IV – BQ788 (3 mg/kg b.w.) + ET-1 (3 μg/kg b.w.), V – N-nitro-L-arginine methyl ester (L-NAME) (5 mg/kg b.w.) + ET-1 (3 μg/kg b.w.). ETA and ETB receptor antagonists or L-NAME were administered 30 min before ET-1 injection. The levels of the following substances were measured in the lungs homogenates: thiobarbituric acid reactive substances (TBARS), hydrogen peroxide (H2O2), reduced glutathione (GSH) and tumor necrosis factor-alpha (TNF-α). The results showed that ET-1 significantly increased TBARS, H2O2 (respectively: p<0.001, p<0.02) and TNF-α levels (p<0.02) and decreased the GSH level (p<0.01) vs. control group. On the other hand, prior administration of ETA receptor blocker (BQ123) significantly attenuated TBARS (p<0.01), H2O2 (p<0.02), TNF-α (p<0.02) and increased GSH (p<0.02) levels vs. ET-1. However, prior administration of ETB receptor blocker BQ788 did not cause significant changes in the: TBARS, H2O2 and TNF-α (p>0.05) levels, but significantly increased the GSH level and GSH/GSSG ratio (p<0.05). Administration of L-NAME significantly attenuated TBARS (p<0.001), H2O2 (p<0.05), TNF-α (p<0.01) and increased GSH (p<0.05) levels vs. ET-1. In conclusion, we demonstrated that ET-1 induced oxidative stress in the lungs is mediated by ETA receptors. ETA receptor blockage inhibited generation of free radicals and TNF-α and ameliorated antioxidant properties. Moreover, generation of reactive oxygen species is mediated by NOS in the lungs.

Endothelin-1: Biosynthesis, Signaling and Vasoreactivity

Endothelin-1 (ET-1) is an extremely potent vasoconstrictor peptide originally isolated from endothelial cells. Its synthesis, mainly regulated at the gene transcription level, involves processing of a precursor by a furin-type proprotein convertase to an inactive intermediate, big ET-1. The latter peptide can then be cleaved directly by an endothelin-converting enzyme (ECE) into ET-1 or reach the active metabolite through a two-step process involving chymase hydrolyzing big ET-1 to ET-1 (1-31), itself needing conversion to ET-1 by neprilysin (NEP) to exert physiological activity. ET-1 signals through two G protein-coupled receptors, endothelin receptor A (ETA) and endothelin receptor B (ETB). Both receptors induce an increase in intracellular Ca(2+), mainly from the extracellular space through voltage-independent mechanisms, the receptor-operated channels and store-operated channels. ET-1 also induces signaling through epidermal growth factor receptor transactivation, oxidative stress induction, rho-kinase, and the activation (ETA) or inhibition (ETB) of the adenylate cyclase/cyclic adenosine monophosphate pathway. Arterial vasoconstriction is mediated mainly by the ETA receptor. ET-1, via endothelium-located ETB, relaxes arteries or constricts vessels following activation of the same receptor type on the smooth muscle, where it can interact with ETA. In addition, ETB-dependent vasoconstriction seems more prominent in the venous vasculature. A better understanding of how ET-1 is synthesized and how ETA and ETB receptors interact could help design better pharmacological agents in the treatment of cardiovascular diseases where targeting the ET-1 system is indicated.

The role of endothelin-1 and endothelin receptor antagonists in inflammatory response and sepsis

Endothelin-1 (ET-1) is a potent endogenous vasoconstrictor, mainly secreted by endothelial cells. It acts through two types of receptors: ETA and ETB. Apart from a vasoconstrictive action, ET-1 causes fibrosis of the vascular cells and stimulates production of reactive oxygen species. It is claimed that ET-1 induces proinflammatory mechanisms, increasing superoxide anion production and cytokine secretion. A recent study has shown that ET-1 is involved in the activation of transcription factors such as NF-κB and expression of proinflammatory cytokines including TNF-α, IL-1, and IL-6. It has been also indicated that during endotoxaemia, the plasma level of ET-1 is increased in various animal species. Some authors indicate a clear correlation between endothelin plasma level and morbidity/mortality rate in septic patients. These pathological effects of ET-1 may be abrogated at least partly by endothelin receptor blockade. ET-1 receptor antagonists may be useful for prevention of various vascular diseases. This review summarises the current knowledge regarding endothelin receptor antagonists and the role of ET-1 in sepsis and inflammation.

Divergent signaling mechanisms for venous versus arterial contraction as revealed by endothelin-1

OBJECTIVE

Venous function is underappreciated in its role in blood pressure determination, a physiologic parameter normally ascribed to changes in arterial function. Significant evidence points to the hormone endothelin-1 (ET-1) as being important to venous contributions to blood pressure. We hypothesized that the artery and vein should similarly depend on the signaling pathways stimulated by ET-1, specifically phospholipase C (PLC) activation. This produces two functional arms of signaling: diacylglycerol (DAG; protein kinase C [PKC] activation) and inositol trisphosphate (IP3) production (intracellular calcium release).

METHODS

The model was the male Sprague-Dawley rat. Isolated tissue baths were used to measure isometric contraction. Western blot and immunocytochemical analyses measured the magnitude of expression and site of expression, respectively, of IP3 receptors in smooth muscle/tissue. Pharmacologic methods were used to modify PLC activity and signaling elements downstream of PLC (IP3 receptors, PKC).

RESULTS

ET-1-induced contraction was PLC dependent in both tissues as the PLC inhibitor U-73122 significantly reduced contraction in aorta (86% ± 4% of control; P < .05) and vena cava (49% ± 11% of control; P < .05). However, ET-1-induced contraction was not significantly inhibited by the IP3 receptor inhibitor 2-aminoethoxydiphenylborane (100 μM) in vena cava (82% ± 8% of control; P = .23) but was in the aorta (55% ± 4% of control; P < .05). All three IP3 receptor isoforms were located in venous smooth muscle. IP3 receptors were functional in both tissues as the novel membrane-permeable IP3 analogue (Bt-IP3; 10 μM) contracted aorta and vena cava. Similarly, whereas the PKC inhibitor chelerythrine (10 μM) attenuated ET-1-induced contraction in vena cava and aorta (5% ± 2% and 50% ± 5% of control, respectively; P < .05), only the vena cava contracted to the DAG analogue 1-oleoyl-2-acetyl-sn-glycerol.

CONCLUSIONS

These findings suggest that ET-1 activates PLC in aorta and vena cava, but vena cava contraction to ET-1 may be largely IP3 independent. Rather, DAG—not IP3—may contribute to contraction to ET-1 in vena cava, in part by activation of PKC. These studies outline a fundamental difference between venous and arterial smooth muscle and further reinforce a heterogeneity of vascular smooth muscle function that could be taken advantage of for therapeutic development.

Reverse-mode Na+/Ca2+ exchange is an important mediator of venous contraction

The Na(+)/Ca(2+) exchanger (NCX) is a bi-directional regulator of cytosolic Ca(2+), causing Ca(2+) efflux in forward-mode and Ca(2+) influx in reverse-mode. We hypothesized that reverse-mode NCX is a means of Ca(2+) entry in rat aorta (RA) and vena cava (RVC). NCX protein in RA and RVC was confirmed by immunoprecipitation. To assess NCX function, isometric contraction and intracellular Ca(2+) was measured in RA and RVC rings in response to low extracellular Na(+), endothelin-1 (ET-1), and KCl, in the presence or absence of the NCX antagonist KB-R7943. In RVC, low extracellular Na(+) caused vasoconstriction and an increase in intracellular Ca(2+) that was attenuated by 10μM KB-R7943. KB-R7943 (10 μM) attenuated maximal contraction to ET-1 in RVC (53 ± 9% of control), but not RA (91±1% of control). KB-R7943 (10 μM) reduced the maximal contraction to KCl in RA (48 ± 5%) and nearly abolished it in RVC (9 ± 2%), suggesting that voltage-dependent Ca(2+) influx may be inhibited by KB-R7943 as well. However, the L-type Ca(2+) channel inhibitor nifedipine (1 μM) did not alter ET-1-induced contraction. Our findings suggest that reverse-mode NCX is an important mechanism of Ca(2+) influx in RVC but not RA, especially during ET-1-induced contraction. Also, the effects of KB-R7943 on ET-1-induced contraction of RA and RVC are predominantly mediated by reverse-mode NCX inhibition and not due to off-target inhibition of Ca(2+) channels.

Oxidative stress in hypertensive patients induces an increased contractility in vein grafts independent of endothelial function

Objective. To evaluate the impact of oxidative stress on vascular reactivity to vasoconstrictors and on nitric oxide (NO) bioavailability in saphenous vein (SV) graft with endothelial dysfunction from hypertensive patients (HT). Methods. Endothelial function, vascular reactivity, oxidative state, nitrites and NO release were studied in isolated SV rings from HT and normotensive patients (NT). Only rings with endothelial dysfunction were used. Results. HT rings presented a hyperreactivity to vasoconstrictors that was reverted by diphenylene iodonium (DPI). In NT, no effect of DPI was obtained, but Nω-nitro-_L-arginine methyl ester (L-NAME) increased the contractile response. NO was present in SV rings without endothelial function. Nitrites were higher in NT than in HT (1066.1 ± 86.3 pmol/mg; n = 11 versus 487.8 ± 51.6; n = 23; P < 0.01) and inhibited by nNOS inhibitor. L-arginine reversed this effect. Antioxidant agents increased nitrites and NO contents only in HT. The anti-nNOS-stained area by immunohistochemistry was higher in NT than HT. HT showed an elevation of oxidative state. Conclusions. Extraendothelial NO counter-regulates contractility in SV. However, this action could be altered in hypertensive situations by an increased oxidative stress or a decreased ability of nNOS to produce NO. Further studies should be performed to evaluate the implication of these results in graft patency rates.

Vasomodulatory effect of novel peroxovanadate compounds on rat aorta: Role of rho kinase and nitric oxide/cGMP pathway

The present study was undertaken to assess the role of reactive oxygen species (ROS) in rat aortic ring vasoreactivity and integrity by using various peroxovanadate (pV) compounds. All the pV compounds (1nM-300 μM) used in the present study exerted concentration-dependent contractions on endothelium intact rat aortic rings. All compounds with an exception of DPV-asparagine (DPV-asn) significantly altered vascular integrity as shown by diminished KCl responses. Phenylephrine (PE)-mediated contractions (3nM-300 μM) were unaltered in the presence of these compounds. Acetylcholine (Ach)-mediated relaxation in PE (1μM) pre-contracted rings was significantly reduced in presence of diperoxovanadate (DPV), poly (sodium styrene sulfonate-co-maleate)-pV (PSS-CoM-pV) and poly (sodium styrene 4-sulfonate)-pV (PSS-pV). However, no significant change in Ach-mediated responses was observed in the presence of poly (acrylate)-pV (PAA-pV) and DPV-asn. DPV-asn was thus chosen to further elucidate mechanism involved in peroxide mediated modulation of vasoreactivity. DPV-asn (30nM - 300 μM) exerted significantly more stable contractions, that was found to be catalase (100U/ml) resistant in comparison with H(2)O(2) (30nM-300 μM) in endothelium intact aortic rings. These contractile responses were found to be dependent on extracellular Ca(2+) and were significantly inhibited in presence of ROS scavenger N-acetylcysteine (100 μM). Intracellular calcium chelation by BAPTA-AM (10μM) had no significant effect on DPV-asn (30nM-300 μM) mediated contraction. Pretreatment of aortic rings by rho-kinase inhibitor Y-27632 (10μM) significantly inhibited DPV-asn-mediated vasoconstriction indicating role of voltage-dependent Ca(2+) influx and downstream activation of rho-kinase. The small initial relaxant effect obtained on addition of DPV-asn (30nM-1 μM) in PE (1 μM) pre-contracted endothelium intact rings, was prevented in the presence of guanylate cyclase inhibitor, methylene blue (10 μM) and/or nitric oxide synthase (NOS) inhibitor, l-NAME (100 μM) suggesting involvement of nitric oxide and cGMP. DPV-asn, like H(2)O(2), exerted a response of vasoconstriction in normal arteries and vasodilation at low concentrations (30nM-1 μM) in PE-pre contracted rings with overlapping mechanisms. These findings suggest usefulness of DPV-asn having low toxicity, in exploring the peroxide-mediated effects on various vascular beds. The present study also convincingly demonstrates role of H(2)O(2) in the modulation of vasoreactivity by using stable peroxide DPV-asn and warrants future studies on peroxide mediated signaling from a newer perspective.

Nuclear membrane receptors for ET-1 in cardiovascular function

Plasma membrane endothelin type A (ETA) receptors are internalized and recycled to the plasma membrane, whereas endothelin type B (ETB) receptors undergo degradation and subsequent nuclear translocation. Recent studies show that G protein-coupled receptors (GPCRs) and ion transporters are also present and functional at the nuclear membranes of many cell types. Similarly to other GPCRs, ETA and ETB are present at both the plasma and nuclear membranes of several cardiovascular cell types, including human cardiac, vascular smooth muscle, endocardial endothelial, and vascular endothelial cells. The distribution and density of ETARs in the cytosol (including the cell membrane) and the nucleus (including the nuclear membranes) differ between these cell types. However, the localization and density of ET-1 and ETB receptors are similar in these cell types. The extracellular ET-1-induced increase in cytosolic ([Ca]c) and nuclear ([Ca]n) free Ca2+ is associated with an increase of cytosolic and nuclear reactive oxygen species. The extracellular ET-1-induced increase of [Ca]c and [Ca]n as well as intracellular ET-1-induced increase of [Ca]n are cell-type dependent. The type of ET-1 receptor mediating the extracellular ET-1-induced increase of [Ca]c and [Ca]n depends on the cell type. However, the cytosolic ET-1-induced increase of [Ca]n does not depend on cell type. In conclusion, nuclear membranes' ET-1 receptors may play an important role in overall ET-1 action. These nuclear membrane ET-1 receptors could be targets for a new generation of antagonists.

A comparison of reactive oxygen species metabolism in the rat aorta and vena cava: focus on xanthine oxidase

Reactive oxygen species (ROS) are important mediators in vascular biology. Venous function, although relevant to cardiovascular disease, is still understudied. We compared aspects of ROS metabolism between a major artery (the aorta) and a major vein (the vena cava, VC) of the rat, with the hypothesis that venous ROS metabolism would be overall increased compared with its arterial counterpart. Superoxide and hydrogen peroxide (H2O2) release in basal conditions was higher in VC compared with aorta. The antioxidant capacity for H2O2 was also higher in VC than in aorta. Exogenous superoxide induced a higher contraction in VC compared with aorta. Protein expression of three major ROS metabolizing enzymes, xanthine oxidase (XO), CuZn-SOD, and catalase, was higher in VC compared with aorta. Because XO seemed a likely source of the higher VC ROS levels, we examined it further and found higher mRNA expression and activity of XO in VC compared with aorta. We also investigated the impact of XO inhibition by allopurinol on aorta and VC functional responses to norepinephrine, ANG II, ET-1, and ACh. Maximal ET-1-mediated contraction was decreased by allopurinol in VC but not in the aorta. Our results suggest that there are overall differences in ROS metabolism between aorta and VC, with the latter operating normally at a higher set point, releasing but also being able to handle, higher ROS levels. We propose XO to be an important source for these differences. The result of this particular comparison may be reflective of a general arteriovenous contrast.

Redox signaling, vascular function, and hypertension

Accumulating evidence supports the importance of redox signaling in the pathogenesis and progression of hypertension. Redox signaling is implicated in many different physiological and pathological processes in the vasculature. High blood pressure is in part determined by elevated total peripheral vascular resistance, which is ascribed to dysregulation of vasomotor function and structural remodeling of blood vessels. Aberrant redox signaling, usually induced by excessive production of reactive oxygen species (ROS) and/or by decreases in antioxidant activity, can induce alteration of vascular function. ROS increase vascular tone by influencing the regulatory role of endothelium and by direct effects on the contractility of vascular smooth muscle. ROS contribute to vascular remodeling by influencing phenotype modulation of vascular smooth muscle cells, aberrant growth and death of vascular cells, cell migration, and extracellular matrix (ECM) reorganization. Thus, there are diverse roles of the vascular redox system in hypertension, suggesting that the complexity of redox signaling in distinct spatial spectrums should be considered for a better understanding of hypertension.

Reactive oxygen species participate in acute renal vasoconstrictor responses induced by ETAand ETBreceptors

Reactive oxygen species (ROS) play important roles in renal vasoconstrictor responses to acute and chronic stimulation by angiotensin II and norepinephrine, as well as in long-term effects of endothelin-1 (ET-1). Little is known about participation of ROS in acute vasoconstriction produced by ET-1. We tested the influence of NAD(P)H oxidase inhibition by apocynin [4 mg·kg−1·min−1, infused into the renal artery (ira)] on ETAand ETBreceptor signaling in the renal microcirculation. Both receptors were stimulated by ET-1, ETAreceptors by ET-1 during ETBantagonist BQ-788, and ETBby ETBagonist sarafotoxin 6C. ET-1 (1.5 pmol injected ira) reduced renal blood flow (RBF) 17 ± 4%. Apocynin raised baseline RBF (+10 ± 1%, P < 0.001) and attenuated the ET-1 response to 10 ± 2%, i.e., 35 ± 9% inhibition ( P < 0.05). Apocynin reduced ETA-induced vasoconstriction by 42 ± 12% ( P < 0.05) and that of ETBstimulation by 50 ± 8% ( P < 0.001). During nitric oxide (NO) synthase inhibition ( Nω-nitro-l-arginine methyl ester), apocynin blunted ETA-mediated vasoconstriction by 60 ± 8% ( P < 0.01), whereas its effect on the ETBresponse (by 87 ± 8%, P < 0.001) was even larger without than with NO present ( P < 0.05). The cell-permeable superoxide dismutase mimetic tempol (5 mg·kg−1·min−1ira), which reduces O2−and may elevate H2O2, attenuated ET-1 responses similar to apocynin (by 38 ± 6%, P < 0.01). We conclude that ROS, O2−rather than H2O2, contribute substantially to acute renal vasoconstriction elicited by both ETAand ETBreceptors and to basal renal vasomotor tone in vivo. This physiological constrictor action of ROS does not depend on scavenging of NO. In contrast, scavenging of O2−by NO seems to be more important during ETBstimulation.

Endothelins and NADPH oxidases in the cardiovascular system

1. The endothelin (ET) system and NADPH oxidase play important roles in the regulation of cardiovascular function, as well as in the pathogenesis of hypertension and other cardiovascular diseases. 2. Endothelins activate NADPH oxidases and thereby increase superoxide production, resulting in oxidative stress and cardiovascular dysfunction. Thus, NADPH oxidases may mediate the role of endothelins in some cardiovascular diseases. However, the role of reactive oxygen species (ROS) in mediating ET-induced vasoconstriction and cardiovascular disease remains under debate, as evidenced by conflicting reports from different research teams. Conversely, activation of NADPH oxidase can stimulate ET secretion via ROS generation, which further enhances the cardiovascular effects of NADPH oxidase. However, little is known about how ROS activate the endothelin system. It seems that the relationship between ET-1 and ROS may vary with cardiovascular disorders. 3. Endothelins activate NADPH oxidase via the ET receptor-proline-rich tyrosine kinase-2 (Pyk2)-Rac1 pathway. Rac1 is an important regulator of NADPH oxidase. There is ample evidence supporting direct stimulation by Rac1 of NADPH oxidase activity. In addition, Rac1-induced cardiomyocyte hypertrophy is mediated by the generation of ROS.

Role of NADPH oxidase and iNOS in vasoconstrictor responses of vessels from hypertensive and normotensive rats

BACKGROUND AND PURPOSE

To analyse the influence of hypertension in the modulation induced by inducible NOS (iNOS)-derived NO and superoxide anion (O(2) (*-)) of vasoconstrictor responses and the sources of O(2) (*-) implicated.

EXPERIMENTAL APPROACH

Vascular reactivity experiments were performed in segments of aorta from normotensive, Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR); protein and mRNA expressions were respectively measured by western blot and quantitative reverse transcription-polymerase chain reaction and O(2) (*-) production was evaluated by ethidium fluorescence.

KEY RESULTS

The contractile responses to phenylephrine (1 nM-30 microM) and 5-hydroxytryptamine (0.1-100 microM) were greater in aortic segments from SHR than WKY. The selective iNOS inhibitor, 1400W (10 microM), increased the phenylephrine contraction only in WKY segments; however, iNOS protein and mRNA expressions were greater in aorta from SHR than WKY. Superoxide dismutase (SOD, 150 U ml(-1)) reduced phenylephrine and 5-hydroxytryptamine responses only in aorta from SHR; the NAD(P)H oxidase inhibitor apocynin (0.3 mM) decreased phenylephrine and 5-hydroxytryptamine responses more in vessels from SHR than WKY. Co-incubation with SOD plus 1400W potentiated the phenylephrine and 5-hydroxytryptamine responses more in segments from SHR than WKY. O(2) (*-) production was greater in aorta from SHR than WKY; apocynin abolished this difference.

CONCLUSIONS AND IMPLICATIONS

Increased O(2) (*-) formation from NADP(H) oxidase in vessels from hypertensive rats contributes to the vasoconstrictor responses and counteract the increase of NO from iNOS and the consequent modulation of these responses.

Acute antihypertensive action of Tempol in the spontaneously hypertensive rat

Acute intravenous Tempol reduces mean arterial pressure (MAP) and heart rate (HR) in spontaneously hypertensive rats. We investigated the hypothesis that the antihypertensive action depends on generation of hydrogen peroxide, activation of heme oxygenase, glutathione peroxidase or potassium conductances, nitric oxide synthase, and/or the peripheral or central sympathetic nervous systems (SNSs). Tempol caused dose-dependent reductions in MAP and HR (at 174 micromol/kg; DeltaMAP, -57+/- 3 mmHg; and DeltaHR, -50 +/- 4 beats/min). The antihypertensive response was unaffected by the infusion of a pegylated catalase or by the inhibition of catalase with 3-aminotriazole, inhibition of glutathione peroxidase with buthionine sulfoximine, inhibition of heme oxygenase with tin mesoporphyrin, or inhibition of large-conductance Ca(2+)-activated potassium channels with iberiotoxin. However, the antihypertensive response was significantly (P < 0.01) blunted by 48% by the activation of adenosine 5'-triphosphate-sensitive potassium (K(ATP)) channels with cromakalim during maintenance of blood pressure with norepinephrine and by 31% by the blockade of these channels with glibenclamide, by 40% by the blockade of nitric oxide synthase with N(omega)-nitro-L-arginine methyl ester (L-NAME), and by 40% by the blockade of ganglionic autonomic neurotransmission with hexamethonium. L-NAME and hexamethonium were additive, but glibenclamide and hexamethonium were less than additive. The central administration of Tempol was ineffective. The acute antihypertensive action of Tempol depends on the independent effects of potentiation of nitric oxide and inhibition of the peripheral SNS that involves the activation of K(ATP) channels.

Comparison of H2O2-induced vasoconstriction in the abdominal aorta and mesenteric artery of the mouse

Hydrogen peroxide (H(2)O(2)) is generally perceived as an arterial vasodilator. Due to the emerging importance of H(2)O(2) as a possible vasoconstrictor, we examined whether H(2)O(2) constricts both the abdominal aorta and superior mesenteric artery and postulated that H(2)O(2) is a ubiquitous constrictor of quiescent mouse arteries. Moreover, we postulated that KCl depolarization discloses and/or exaggerates H(2)O(2)-induced constriction. Under quiescent conditions, H(2)O(2) constricted the mouse abdominal aorta but not the mesenteric artery. Vessel depolarization (a) exaggerated this constrictor response in the aorta, and (b) unmasked a contractile response in the mesenteric artery. Our final hypothesis tested whether tyrosine kinases, mitogen-activated protein kinases (MAPKs), and/or Rho-kinase are uniformly involved in H(2)O(2)-induced vasoconstriction. We observed a marked difference in the ability of tyrosine kinase inhibitor to block H(2)O(2)-induced vasoconstriction. p38 and ERK 1/2MAPK inhibitors reduced the maximal response to H(2)O(2), whereas JNK inhibitor had no effect. Finally, Rho-kinase inhibitor decreased the H(2)O(2) response in the mesenteric artery but not in the aorta. These data demonstrate a variable yet tightly regulated H(2)O(2) vasoconstrictor effect. Furthermore, we found that p38, ERK 1/2 and Rho-kinase play a role in H(2)O(2) constriction, which may be critical pathways involved in H(2)O(2)-induced constriction across vascular beds.

Modulation of vascular smooth muscle signaling by reactive oxygen species

Modulation of signaling in vascular cells by reactive oxygen species (ROS) affects many aspects of cellular function, including growth, migration, and contraction. NADPH oxidases, important sources of ROS, regulate many growth-specific and migration-related signaling pathways. Identifying the precise intracellular targets of ROS enhances understanding of their role in cardiovascular physiology and pathophysiology.

Pleiotropic Effects of Hydrogen Peroxide in Arteries and Veins From Normotensive and Hypertensive Rats

Hydrogen peroxide causes vascular contraction and relaxation and contributes to the pathogenesis of hypertension. We hypothesized that the contractile state of blood vessels governs whether H 2 O 2 causes contraction or relaxation. Hydrogen peroxide (1 μmol/L to 1 mmol/L) concentration-dependently contracted thoracic aorta and vena cava from sham normotensive and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. The maximal contraction to H 2 O 2 was 3 times greater in DOCA aorta compared with sham aorta but unchanged in DOCA vena cava compared with sham vena cava. In prostaglandin F 2α (20 μmol/L)–contracted aorta and vena cava from sham and DOCA rats, H 2 O 2 (1 μmol/L to 1 mmol/L) induced a concentration-dependent relaxation that was impaired in DOCA aorta but not DOCA vena cava. In contrast, in KCl (30 mmol/L)-contracted vessels, maximal H 2 O 2 -induced contraction was enhanced 15-fold in sham aorta and 5-fold in DOCA aorta but only 2-fold in sham vena cava. Tetraethylammonium (10 mmol/L), BAY K 8644 (100 nmol/L), and ouabain (1 mmol/L) all enhanced maximal aortic H 2 O 2 -induced contraction, whereas only ouabain enhanced venous H 2 O 2 -induced contraction. The removal of extracellular Ca 2+ reduced H 2 O 2 -induced contraction in KCl-contracted aorta, whereas maximal venous H 2 O 2 -induced contraction (under basal conditions) was unchanged. Our data suggest that differences in arterial and venous K + channel activity and extracellular Ca 2+ influx are responsible for differences in arterial and venous contraction to H 2 O 2 . In DOCA-salt hypertension, arterial but not venous contraction to H 2 O 2 is enhanced, and relaxation to H 2 O 2 is reduced.

Endothelin-1-mediated increase in reactive oxygen species and NADPH Oxidase activity in hearts of aryl hydrocarbon receptor (AhR) null mice

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor characterized to play a role in detection and adaptation to environmental stimuli. Genetic deletion of the AhR results in cardiac hypertrophy that is mediated primarily by endothelin-1 (ET-1); ET-1 has been implicated in the elevation of reactive oxygen species (ROS) in the heart, which are thought to contribute to several cardiovascular disorders, including cardiac hypertrophy. Thus, we tested the novel hypothesis that ET-1 induces ROS in AhR null mice via ET(A) receptor activation. We first confirmed the presence of ROS in the hearts of AhR null mice by measuring superoxide (O2*-)-dependent oxidation of dihydroethidium. Ethidium fluorescence was increased 10-fold in the hearts of AhR null mice, compared to the wild type. Then, to elucidate whether ET-1 mediated the increase in ROS, mice were chronically treated with 100 ng/kg/day of the ET(A) receptor antagonist BQ-123. In AhR null mice, BQ-123 significantly reduced elevated plasma 8-isoprostane, a systemic end product of phospholipid oxidation by ROS, and cardiac thiobarbituric acid reactive substances (TBARS), a nonspecific assessment of ROS production. Furthermore, BQ-123 reduced both cardiac lucigenin chemiluminescence and cardiac mRNA expression of NAD(P)H oxidase subunits gp91phox, p47phox, and p67phox in AhR null mice below the levels observed in wild-type mice. These findings demonstrate that ET-1 activation of ET(A) receptors mediates an increase in ROS that is associated with cardiac hypertrophy in AhR null mice. In addition, the ET-1-mediated increase in ROS appears to be initiated via increased NAD(P)H oxidase activity.