Hydrogen peroxide is an endothelium-derived hyperpolarizing factor in mice

Inhibition of acetylcholine-induced EDHF response by elevated glucose in rat mesenteric artery

The effects of high glucose on endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxations of isolated rat mesenteric artery and the possible involvement of reactive oxygen species in these responses were investigated. After precontraction with phenylephrine (3 x 10(-8)-10(-7) M), acetylcholine (10(-8)-3 x 10(-6) M) and A 23187 (10(-8)-3 x 10(-6) M), a calcium ionophore, induced concentration-dependent relaxations in the presence of N(W)-nitro-l-arginine methyl ester (L-NAME) (10(-4) M) and indomethacin (10(-5) M). These relaxations were abolished in the presence of charybdotoxin (2 x 10(-7) M) plus apamin (10(-7) M) and were assumed to be mediated by EDHF. Effects of elevated glucose were examined by incubating the arterial rings for 6 h in Krebs-Henseleit solution containing 22.2 mM glucose. Under these conditions relaxation to acetylcholine was significantly attenuated but was unchanged when the tissues were incubated for 6 h in solution containing 11.1 mM mannitol used as hyperosmotic control. Addition of superoxide dismutase (SOD) (75 U/ml) and combination of SOD with catalase (200 U/ml) during incubation with high glucose significantly preserved the impairment of EDHF-mediated relaxations to acetylcholine. A 23187-induced endothelium-dependent relaxation was not affected by high glucose. Similarly, relaxations to pinacidil (10(-10)-10(-5) M) and to sodium nitroprusside (SNP) (10(-10)-3 x 10(-7) M) were also unchanged in the rings exposed to high glucose. These results suggest that in rat mesenteric arteries exposed to elevated glucose receptor-dependent EDHF-mediated relaxations (acetylcholine-induced) are impaired whereas receptor-independent ones (A 23187-induced) and responses to smooth muscle relaxants that exert their effects through mechanisms independent of endothelium are unaffected. Our findings lead us to propose that reactive oxygen species like superoxide ((.)O(2)(-)) and hydrogen peroxide (H(2)O(2)) do seem to play a role in the impairment of EDHF-mediated relaxations in the presence of elevated glucose.

Endogenous Vascular Hydrogen Peroxide Regulates Arteriolar Tension In Vivo

Background— Although many studies suggested direct vasomotor effects of hydrogen peroxide (H 2 O 2 ) in vitro, little is known about the vasomotor effects of H 2 O 2 in vivo.

Methods and Results— We have generated mice overexpressing human catalase driven by the Tie-2 promoter to specifically target this transgene to the vascular tissue. Vessels of these mice (cat ++ ) expressed significantly higher levels of catalase mRNA, protein, and activity. The overexpression was selective for vascular tissue, as evidenced by immunohistochemistry in specimens of aorta, heart, lung, and kidney. Quantification of reactive oxygen species by fluorescence signals in cat ++ versus catalase-negative (cat n ) mice showed a strong decrease in aortic endothelium and left ventricular myocardium but not in leukocytes. Awake male cat ++ at 3 to 4 months of age had a significantly lower systolic blood pressure (sBP, 102.7±2.2 mm Hg, n=10) compared with their transgene-negative littermates (cat n , 115.6±2.5 mm Hg, P =0.0211) and C57BL/6 mice (118.4±3.06 mm Hg, n=6). Treatment with the catalase inhibitor aminotriazole increased sBP of cat ++ to 117.3±4.3 mm Hg ( P =0.0345), while having no effect in cat n (118.4±2.4 mm Hg, n=4, P >0.05). In contrast, treatment with the NO-synthase inhibitor nitro- l -arginine methyl ester (100 mg · kg BW −1 · d −1 ) increased sBP in cat ++ and C57Bl/6 to a similar extent. Likewise, phosphorylation of vasodilator-stimulated phosphoprotein in skeletal muscle, left ventricular myocardium, and lung was identical in cat ++ and cat n . Endothelium- and NO-dependent aortic vasodilations were unchanged in cat ++ . Aortic KCl contractions were significantly lower in cat ++ and exogenous H 2 O 2 (10 μmol/L)–induced vasoconstriction.

Conclusions— These data suggest that endogenous H 2 O 2 may act as a vasoconstrictor in resistance vessels and contribute to the regulation of blood pressure.

Myoendothelial Coupling Is Not Prominent in Arterioles Within the Mouse Cremaster Microcirculation In Vivo

A smooth muscle hyperpolarization is essential for endothelium-dependent hyperpolarizing factor–mediated dilations. It is debated whether the hyperpolarization is induced by a factor (endothelium-derived hyperpolarizing factor) and/or is attributable to direct current transfer from the endothelium via myoendothelial gap junctions. Here, we measured membrane potential in endothelial cells (EC) and smooth muscle cells (SMC) in vivo at rest and during acetylcholine (ACh) application in the cremaster microcirculation of mice using sharp microelectrodes before and after application of specific blockers of Ca 2+ -dependent K + channels (K Ca ). Moreover, diameter changes in response to ACh were studied. Membrane potential at rest was lower in EC than SMC (−46.6±1.0 versus −36.5±1.0mV, P <0.05). Bolus application of ACh induced robust hyperpolarizations in EC and SMC, but the amplitude (11.1±0.9 versus 5.1±0.9mV, P <0.05) and duration of the response (10.7±0.8 versus 7.5±1.0s, P <0.05) were larger in EC. Blockers of large conductance K Ca (charybdotoxin or iberiotoxin) abrogated ACh-induced hyperpolarizations in SMC but did not alter endothelial hyperpolarizations. In contrast, apamin, a blocker of small conductance K Ca abolished ACh-induced hyperpolarizations in EC and had only small effects on SMC. ACh-induced dilations were strongly attenuated by iberiotoxin but only slightly by apamin. We conclude that myoendothelial coupling in arterioles in vivo in the murine cremaster is weak, as EC and SMC behaved electrically different. Small conductance K Ca mediate endothelial hyperpolarization in response to ACh, whereas large conductance K Ca are important in SMC. Because tight myoendothelial coupling was found in vitro in previous studies, we suggest that it is differentially regulated between vascular beds and/or by mechanisms acting in vivo.

Vascular hypertrophy in angiotensin II-induced hypertension is mediated by vascular smooth muscle cell-derived H2O2

Angiotensin II induces the development of vascular hypertrophy and hypertension. An increasing number of studies have demonstrated that reactive oxygen species are involved in many of the vascular responses to angiotensin II. However, the role of specific cell types and the precise identity of the functionally relevant reactive oxygen species remain unclear. In this study, we established a line of transgenic mice with vascular smooth muscle cell (SMC)-specific overexpression of the human catalase gene to explicitly test the functional role of vascular smooth muscle-derived hydrogen peroxide in the hypertensive and hypertrophic responses to angiotensin II in vivo. Catalase overexpression was confirmed by increased expression of catalase mRNA and protein, as well as by an increase in catalase enzymatic activity. The catalase transgenic mice were viable, had no change in basal hydrogen peroxide release (0.36+/-0.03 versus 0.37+/-0.14 micromol/L), and showed no overt developmental abnormality. In response to angiotensin II treatment, catalase transgenic mice exhibited lower hydrogen peroxide release compared with control animals. There was no effect on the hypertensive response to angiotensin II (147+/-10 versus 148+/-12 mm Hg). However, angiotensin II-induced aortic wall hypertrophy was dramatically attenuated in the catalase transgenic mice (wall thickness 32.4+/-2.0 versus 43.2+/-7.6 microm; P<0.001). These results demonstrate that vascular SMC-derived hydrogen peroxide plays an important role in angiotensin II-induced hypertrophy of the arterial wall.

Peroxynitrite reduces the endothelium-derived hyperpolarizing factor component of coronary flow-mediated dilation in PECAM-1-knockout mice

Platelet endothelial cell adhesion molecule 1 (PECAM-1) is capable of transducing signals in endothelial cells exposed to shear; however, the biological consequences of this signal transduction are unknown. Because shear stress elicits flow-mediated dilation (FMD), we examined whether steady-state FMD in mouse coronary arteries (MCAs) is affected in the PECAM-1 knockout (KO) mouse. MCAs were isolated from wild-type (WT) or KO mice and prepared for videomicroscopy, histofluorescence, Western blotting, and immunohistochemistry. FMD was examined in the absence and presence of N(omega)-nitro-l-arginine methyl ester (l-NAME) and l-NAME+indomethacin (INDO). FMD was reduced in KO relative to WT MCAs, but the l-NAME-inhibitable portion of FMD was similar between the two. The INDO-sensitive component of FMD was diminished in KO MCAs. In contrast, the residual component of dilation, presumably because of endothelium-derived hyperpolarizing factor (EDHF), was abolished in KO MCAs. Histofluorescence showed relatively more superoxide (O2-.; oxy-ethidium fluorescence) and peroxide production (dihydrochlorofluorescene fluoresecence) in KO MCAs at rest. Flow augmented O2-. and peroxide production in WT MCAs but had little effect on KO MCAs. Enhanced nitric oxide generation was observed in arteries from KO mice, accompanied with increased eNOS S1177 phosphorylation. In vessels from KO mice, treatment with ebselen decreased peroxynitrite (ONOO-) formation and improved the reduced FMD, largely due to restoration of the presumed EDHF component. These results suggest that PECAM-1 is necessary for normal FMD in the mouse coronary circulation. In the absence of this adhesion and signaling molecule, ONOO- production is increased concomitant with a reduction in both the EDHF and INDO-sensitive components of FMD.

Reactive oxygen species as mediators of calcium signaling by angiotensin II: implications in vascular physiology and pathophysiology

Reactive oxygen species (ROS), including superoxide anion, hydrogen peroxide, and hydroxyl radical, and reactive nitrogen species, such as nitric oxide and peroxynitrite, are biologically relevant O2 derivatives increasingly being recognized as important in vascular biology through their oxidation/reduction (redox) potential. All vascular cell types produce ROS primarily via membrane-associated NAD(P)H oxidase. ROS influence vascular function by modulating contraction/dilation, cell growth, apoptosis/anoikis, migration, inflammation, and fibrosis. An imbalance in redox state where prooxidants overwhelm antioxidant capacity results in oxidative stress. Oxidative excess and associated oxidative damage are mediators of altered vascular tone and structural remodeling in many cardiovascular diseases. ROS elicit these effects by influencing intracellular signaling events. In addition to modulating protein tyrosine kinases, protein phosphatases, mitogen-activated protein kinases, and transcription factors, ROS are important regulators of intracellular Ca2+ homeostasis and RhoA/Rho kinase signaling. ROS increase vascular [Ca2+]i by stimulating inositol trisphosphate-mediated Ca2+ mobilization, by increasing cytosolic Ca2+ accumulation through sarcoplasmic/endoplasmic reticulum Ca2+-ATPase inhibition, and by stimulating Ca2+ influx through Ca2+ channels. Increased ROS generation enhances Ca2+ signaling and up-regulates RhoA/Rho kinase, thereby altering vascular contractility and tone. The present review discusses the importance of ROS in angiotensin II signaling in vascular biology and focuses specifically on the role of oxidative stress in Ca2+ signaling in the vasculature.

Production of hydrogen peroxide in rat corpus cavernosum: An on-line study with microvoltammetric electrodes

Continuous measurements were realized in rat corpus cavernosum using microvoltammetric captor. After inhibition of endothelial NO-synthase by L-NMA vasodilatation was induced by intracavernous injection of acetylcholine. Blood flow of rat penis was monitored by laser Doppler. A new peak appeared in reduction. It was identified as hydrogen peroxide by its peak potential, by intracavernous injection of hydrogen peroxide or catalase. Intracavernous injection of various pharmacological agents permitted to demonstrate that its origin was due to endothelial NAD(P)H oxidases. DPI inhibited its synthesis; NADH and NADPH enhanced it. Intracavernous injection of diethyldithiocarbamic acid gave the disappearance of hydrogen peroxide peak and appearance of the superoxide peak. This preliminary study showed that when the L-arginine pathway was inhibited, the NAD(P)H oxidase pathway functioned in rat corpus cavernosum for vasodilatation.

Arachidonic acid metabolites, hydrogen peroxide, and EDHF in cerebral arteries

We tested the hypotheses that EDHF in rat middle cerebral arteries (MCAs) involves 1) metabolism of arachidonic acid through the epoxygenase pathway, 2) metabolism of arachidonic acid through the lipoxygenase pathway, or 3) reactive oxygen species. EDHF-mediated dilations were elicited in isolated and pressurized rat MCAs by activation of endothelial P2Y2receptors with either UTP or ATP. All studies were conducted after the inhibition of nitric oxide synthase and cyclooxygenase with Nω-nitro-l-arginine methyl ester (10 μM) and indomethacin (10 μM), respectively. The inhibition of epoxygenase with miconazole (30 μM) did not alter EDHF dilations to UTP, whereas the structurally different epoxygenase inhibitor N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanoic acid (20 or 40 μM) only modestly inhibited EDHF at the highest concentration of UTP. An antagonist of epoxyeicosatrienoic acids, 14,15-epoxyeicosa-5( Z)-enoic acid, had no effect on EDHF dilations to UTP. Chronic inhibition of epoxygenase in the rat with 1-aminobenzotriazol (50 mg/kg twice daily for 5 days) did not alter EDHF dilations. The inhibition of the lipoxygenase pathway with either 10 μM baicalein or 10 μM nordihydroguaiaretic acid produced no major inhibitory effects on EDHF dilations. The combination of superoxide dismutase (200 U/ml) and catalase (140 U/ml) had no effect on EDHF dilations. Neither tiron (10 mM), a cell-permeable scavenger of reactive oxygen species, nor deferoxamine (1 or 10 mM), an iron chelator that blocks the formation of hydroxyl radicals, altered EDHF dilations in rat MCAs. We conclude that EDHF dilations in the rat MCA do not involve the epoxygenase pathway, lipoxygenase pathway, or reactive oxygen species including H2O2.

Acetylcholine causes endothelium-dependent contraction of mouse arteries

The goal of this study was to determine whether acetylcholine evokes endothelium-dependent contraction in mouse arteries and to define the mechanisms involved in regulating this response. Arterial rings isolated from wild-type (WT) and endothelial nitric oxide (NO) synthase knockout (eNOS−/−) mice were suspended for isometric tension recording. In abdominal aorta from WT mice contracted with phenylephrine, acetylcholine caused a relaxation that reversed at the concentration of 0.3–3 μM. After inhibition of NO synthase [with Nω-nitro-l-arginine methyl ester (l-NAME), 1 mM], acetylcholine (0.1–10 μM) caused contraction under basal conditions or during constriction to phenylephrine, which was abolished by endothelial denudation. This contraction was inhibited by the cyclooxygenase inhibitor indomethacin (1 μM) or by a thromboxane A2 (TxA2) and/or prostaglandin H2 receptor antagonist SQ-29548 (1 μM) and was associated with endothelium-dependent generation of the TxA2 metabolite TxB2. Also, SQ-29548 (1 μM) abolished the reversal in relaxation evoked by 0.3–3 μM acetylcholine and subsequently enhanced the relaxation to the agonist. The magnitude of the endothelium-dependent contraction to acetylcholine (0.1–10 μM) was similar in aortas from WT mice treated in vitro with l-NAME and from eNOS−/− mice. In addition, we found that acetylcholine (10 μM) also caused endothelium-dependent contraction in carotid and femoral arteries of eNOS−/− mice. These results suggest that acetylcholine initiates two competing responses in mouse arteries: endothelium-dependent relaxation mediated predominantly by NO and endothelium-dependent contraction mediated most likely by TxA2.

Hydrogen peroxide is an endothelium-derived hyperpolarizing factor in animals and humans

The endothelium plays an important role in maintaining vascular homeostasis by synthesizing and releasing several vasodilating substances, including vasodilator prostaglandins, nitric oxide (NO), and endothelium-derived hyperpolarizing factor (EDHF). Since the first report for the existence of EDHF, several substances/mechanisms have been proposed for the nature of EDHF, including epoxyeicosatrienoic acids (metabolites of arachidonic P450 epoxygenase pathway), K ions, and electrical communications through myoendothelial gap junctions. We have recently demonstrated that endothelium-derived hydrogen peroxide (H(2)O(2)) is an EDHF in mouse and human mesenteric arteries and in porcine coronary microvessels. For the synthesis of H(2)O(2) as an EDHF, endothelial Cu,Zn-superoxide dismutase plays an important role in mesenteric arteries of mice and humans. We also have demonstrated that EDHF-mediated responses are attenuated by several arteriosclerotic risk factors, including diabetes mellitus and hyperlipidemia and their combination in particular. Recent studies have indicated that endothelium-derived H(2)O(2) plays an important protective role in coronary autoregulation and myocardial ischemia/reperfusion injury in vivo. Indeed, our H(2)O(2)/EDHF theory demonstrates that endothelium-derived H(2)O(2), another reactive oxygen species in addition to NO, plays an important role as a redox signaling molecule to cause vasodilatation as well as cardioprotection. In this review, we summarize our knowledge on H(2)O(2)/EDHF regarding its identification, mechanisms of synthesis, and clinical implications.

Effect of renal medullary H2O2 on salt-induced hypertension and renal injury

Dahl salt-sensitive (SS) and consomic, salt-resistant SS-13(BN) rats possess substantial differences in blood pressure salt-sensitivity even with highly similar genetic backgrounds. The present study examined whether increased oxidative stress, particularly H2O2, in the renal medulla of SS rats contributes to these differences. Blood pressure was measured using femoral arterial catheters in three groups of rats: 1) 12-wk-old SS and consomic SS-13(BN) rats fed a 0.4% NaCl diet, 2) SS rats fed a 4% NaCl diet and chronically infused with saline or catalase (6.9 microg x kg(-1) x min(-1)) directly into the renal medulla, and 3) SS-13(BN) fed high salt (4%) and infused with saline or H2O2 (347 nmol x kg(-1) x min(-1)) into the renal medullary interstitium. After chronic blood pressure measurements, renal medullary interstitial H2O2 concentration ([H2O2]) was collected by microdialysis and analyzed with Amplex red. Blood pressure and [H2O2] were both significantly higher in SS (126 +/- 3 mmHg and 145 +/- 17 nM, respectively) vs. SS-13(BN) rats (116 +/- 2 mmHg and 56 +/- 14 nM) fed a 0.4% diet. Renal interstitial catalase infusion significantly decreased [H2O2] (96 +/- 41 vs. 297 +/- 52 nM) and attenuated the hypertension (146 +/- 2 mmHg catalase vs. 163 +/- 4 mmHg saline) in SS rats after 5 days of high salt (4%). H2O2 infused into the renal medulla of consomic SS-13(BN) fed high salt (4%) for 7 days accentuated the salt sensitivity (145 +/- 2 mmHg H2O2 vs. 134 +/- 1 mmHg saline). [H2O2] was also increased in the treated group (83 +/- 1 nM H2O2 vs. 44 +/- 9 nM saline). These data show that medullary production of H2O2 may contribute to salt-induced hypertension in SS rats and that chromosome 13 of the Brown Norway contains gene(s) that protect against renal medullary oxidant stress.

MaxiK channel roles in blood vessel relaxations induced by endothelium-derived relaxing factors and their molecular mechanisms

The endothelium of blood vessels plays a crucial role in the regulation of blood flow by controlling mechanical functions of underlying vascular smooth muscle. The regulation by the endothelium of vascular smooth muscle relaxation and contraction is mainly achieved via the release of vasoactive substances upon stimulation with neurohumoural substances and physical stimuli. Nitric oxide (NO) and prostaglandin I2 (prostacyclin, PGI2) are representative endothelium-derived chemicals that exhibit powerful blood vessel relaxation. NO action involves activation of soluble guanylyl cyclase and PGI2 action is initiated by the stimulation of a cell-surface receptor (IP receptor, IPR) that is coupled with Gs-protein-adenylyl cyclase cascade. Many studies on the mechanisms by which NO and PGI2 elicit blood vessel relaxation have highlighted a role of the large conductance, Ca2+-activated K+ (MaxiK, BKCa) channel in smooth muscle as their common downstream effector. Furthermore, their molecular mechanisms have been unravelled to include new routes different from the conventionally approved intracellular pathways. MaxiK channel might also serve as a target for endothelium-derived hyperpolarizing factor (EDHF), the non-NO, non-PGI2 endothelium-derived relaxing factor in some blood vessels. In this brief article, we review how MaxiK channel serves as an endothelium-vascular smooth muscle transducer to communicate the chemical signals generated in the endothelium to control blood vessel mechanical functions and discuss their molecular mechanisms.

Hyperpolarization of murine small caliber mesenteric arteries by activation of endothelial proteinase-activated receptor 2

Activation of endothelial proteinase-activated receptor 2 (PAR-2) relaxes vascular smooth muscle (VSM) and causes hypotension by nitric oxide (NO)-prostanoid-dependent and -independent mechanisms. We investigated whether endothelium-dependent hyperpolarization of VSM was the mechanism whereby resistance caliber arteries vasodilated independently of NO. VSM membrane potentials and isometric tension were measured concurrently to correlate the electrophysiological and mechanical changes in murine small caliber mesenteric arteries. In uncontracted arteries, the PAR-2 agonist, SLIGRL-NH2 (0.1 to 10 micromol/L), hyperpolarized the VSM membrane potential only in endothelium-intact arterial preparations. This response was unaltered by treatment of arteries with inhibitors of NO synthases (L-NAME), soluble guanylyl cyclase (ODQ), and cyclooxygenases (indomethacin). L-NAME, ODQ, and indomethacin also failed to inhibit SLIGRL-NH2-induced hyperpolarization and of cirazoline-contracted mesenteric arteries. However, in blood vessels that were depolarized and contracted with 30 mmol/L KCl, the effects of the SLIGRL-NH2 on membrane potential and tension were not observed. SLIGRL-NH2-induced hyperpolarization and relaxation was inhibited completely by the combination of apamin plus charybdotoxin, but only partially inhibited after treatment with the combination of barium plus ouabain, suggesting an important role for SKCa and IKCa channels and a lesser role for Kir channels and Na+/K+ ATPases in the hyperpolarization response. We concluded that activation of endothelial PAR-2 hyperpolarized the vascular smooth muscle (VSM) cells of small caliber arteries, without requiring the activation of NO synthases, cyclooxygenases, or soluble guanylyl cyclase. Indeed, this hyperpolarization may be a primary mechanism for PAR-2-induced hypotension in vivo.

ENHANCED RELEASE OF ENDOTHELIUM-DERIVED HYPERPOLARIZING FACTOR IN SMALL CORONARY ARTERIES FROM RATS WITH CONGESTIVE HEART FAILURE

1. Previous studies have suggested that the production of nitric oxide (NO) is reduced in coronary vessels of animals with congestive heart failure (CHF). However, the response to endothelium-derived hyperpolarizing factor (EDHF) in small coronary resistance arteries from CHF rats has not been investigated. The aim of the present study was to determine whether flow-induced dilation (FID) is altered in small coronary arteries from CHF rats and to characterize the role of EDHF in this process. 2. Small coronary arteries (97 +/- 6 microm) were isolated from control rats and from rats in which CHF was induced by left coronary artery ligation. The arteries were cannulated at 60 mmHg with flow. Changes in internal diameter were examined using videomicroscopy. 3. There was no significant difference in FID in small coronary arteries between control and CHF rats (68 +/- 6 vs 61 +/- 4% (expressed as a percentage of maximal dilation induced by nitroprusside (%MaxD(NP))), respectively). Flow-induced dilation in control rat vessels showed greater attenuation by N(G)-monomethyl-L-arginine (L-NMMA) than vessels from CHF rats (%NO-mediated FID 32 +/- 5 vs 16 +/- 3% (%MaxD(NP)), respectively). Pretreatment with indomethacin had no significant effect on FID in vessels from either rat group. Flow-induced dilation was attenuated by KCl (40 mmol/L) to a greater degree in vessels from CHF rats in the presence of L-NMMA and indomethacin compared with vessels from control rats (%EDHF-mediated FID: 36 +/- 4 vs 25 +/- 5% (%MaxD(NP)), respectively). Flow-induced dilation was abolished by removal of the endothelium and was significantly decreased in vessels from CHF rats in response to charybdotoxin plus apamin or tetrabutylammonium compared with control rat vessels. 17-Octadecynoic acid had no significant effect on FID in vessels from either control or CHF rats. 4. In conclusion, the FID of small coronary arteries is mediated by K+ channels, including the K(Ca) channels. Endothelium-derived hyperpolarizing factor-mediated dilation may compensate for the loss of NO-mediated dilation in CHF.

Arachidonic acid epoxygenase metabolites stimulate endothelial cell growth and angiogenesis via mitogen-activated protein kinase and phosphatidylinositol 3-kinase/Akt signaling pathways

Cytochrome P450 arachidonic acid (AA) epoxygenase metabolites, the epoxyeicosatrienoic acids (EETs), dilate arteries via hyperpolarization of smooth muscle cells and also have nonvasodilatory effects within the vasculature. The present study investigated the angiogenic effects of endogenous and exogenous EETs and the relevant signaling mechanisms involved. Bovine aortic endothelial cells (BAECs) were incubated with synthetic EETs or infected with recombinant adeno-associated viruses (rAAVs) containing CYP2C11-NADPH-cytochrome P450 oxidoreductase (CYPOR), CYP2J2, or CYP102 F87V mutant to increase endogenous levels of EETs. The following endpoints were measured: BAEC proliferation, migration, capillary formation, and in vivo angiogenesis. The potential involvement of various signaling pathways was explored using selective inhibitors. The results showed that transfection with either rAAV-CYP2C11-CYPOR, rAAV-CYP2J2, or rAAV-CYP102 F87V, or incubation with EETs promoted BAEC proliferation, increased migration of BAECs as assessed by Transwell analysis and wound healing assays, and enhanced capillary tubule formation as determined by chicken embryo chorioallantoic membrane assays and tube formation tests on matrigel. The effects of EETs on proliferation, migration, and capillary tubule formation were attenuated by inhibitors of mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3 (PI3)-kinase/Akt pathways and partially attenuated by an endothelial nitric-oxide synthase (eNOS) inhibitor but not by a protein kinase C inhibitor. In a rat ischemic hind limb model, rAAV-mediated AA epoxygenase transfection induced angiogenesis. We conclude that AA epoxygenase metabolites can promote angiogenesis, which may provide protection to ischemic tissues. The results also suggest that the angiogenic effects of EETs involve the MAPK and PI3-kinase/Akt signaling pathways, and to some extent, the eNOS pathway.

Gene transfer of extracellular superoxide dismutase improves endothelial function in rats with heart failure

Oxidative stress is associated with endothelial dysfunction in heart failure. The goals of this study were to determine whether 1) gene transfer of extracellular superoxide dismutase (ecSOD) reduces levels of superoxide and improves endothelial function in the aorta and mesenteric artery in rats with heart failure, and 2) the heparin-binding domain (HBD) of ecSOD, by which ecSOD binds to cells, is required for protective effects of ecSOD. Seven weeks after coronary ligation, in rats with heart failure and sham-operated rats, we injected adenoviral vectors intravenously that express ecSOD, ecSOD with deletion of the HBD (ecSODΔHBD), or a control vector. Four days after injection of viruses, responses to acetylcholine, ADP, and sodium nitroprusside were examined in rings of the aorta and mesenteric artery. ecSOD bound to endothelium and increased SOD activity in the aorta after gene transfer of ecSOD, not ecSODΔHBD. Gene transfer of ecSOD, but not ecSODΔHBD, reduced levels of superoxide and improved relaxation to acetylcholine and ADP in the aorta and mesenteric artery from rats with heart failure. Improvement of relaxation to acetylcholine in the mesenteric artery from rats with heart failure after gene transfer of ecSOD was mediated in part by hydrogen peroxide. The major finding of this study is that the HBD of ecSOD is necessary for protection against endothelial dysfunction in rats with heart failure. We speculate that a common gene variant in the HBD of ecSOD, which is a risk factor for ischemic heart disease, may be a risk factor for vascular maladaptation and endothelial dysfunction in heart failure.

Effect of cardioplegic and organ preservation solutions and their components on coronary endothelium-derived relaxing factors

Cardioplegic (and organ preservation) solutions were initially designed to protect the myocardium (cardiac myocytes) during cardiac operation (and heart transplantation). Because of differences between cardiac myocytes and vascular (endothelial and smooth muscle) cells in structure and function, the solutions may have an adverse effect on coronary vascular cells. However, such effect is often complicated by many other factors such as ischemia-reperfusion injury, temperature, and perfusion pressure or duration. To evaluate the effect of a solution on the coronary endothelial function, a number of points should be taken into consideration. First, the overall effect on endothelium should be identified. Second, the effect of the solution on the individual endothelium-derived relaxing factors (nitric oxide, prostacyclin, and endothelium-derived hyperpolarizing factor) must be distinguished. Third, the effect of each major component of the solution should be investigated. Lastly, the effect of a variety of new additives in the solution may be studied. Based on available literature these issues are reviewed to provide information for further development of cardioplegic or organ preservation solutions.

Hydrogen peroxide acts as both vasodilator and vasoconstrictor in the control of perfused mouse mesenteric resistance arteries

BACKGROUND

Hydrogen peroxide (H2O2) plays a key role in the control of resistance artery (RA) tone and is hypothesized as an endothelial-derived hyperpolarizing factor.

METHODS

In this study, we investigated the effects of the same concentration of exogenous H2O2 on mouse mesenteric RA tone induced by intraluminal pressure, G-protein coupled receptor activation and KCl. RAs were cannulated in an arteriograph in the absence or presence of vasoconstrictors.

RESULTS

RA developed myogenic tone (MT) in response to stepwise pressure increases. Under phenylephrine, H2O2 induced a dose-dependent (1-50 micromol/l) vasodilation with maximum dilation at 50 micromol/l. H2O2 at 50 micromol/l induced a full dilation of RA under MT or contraction by phenylephrine that was independent of nitric oxide synthase, cyclooxygenase, endothelium and potassium channels iberiotoxin and apamin sensitive. The Ca2+ channel inhibitor, nimodipine, significantly blocked MT and also the contraction to phenylephrine and KCl. Under these conditions, H2O2 had no effect on RA diameter. Under KCl, the same concentration of H2O2 induced a potent vasoconstriction. This contraction involved p38 mitogen-activated protein-kinase activation but not ERK1/2.

CONCLUSIONS

These findings provide the first evidence showing that the same and low concentrations of H2O2 can act as a relaxing factor but also as a vasoconstrictor under conditions in which hyperpolarization is compromised.

Mediators involved in decreasing peripheral vascular resistance with carbachol in the rat hind limb perfusion model

We examined the involvement of nitric oxide (NO) and/or endothelium-derived hyperpolarizing factor (EDHF) in decreasing peripheral vascular resistance in the rat hind limb perfusion model and analyzed the identity of EDHF in this model. The potency of carbachol (CCh) to produce relaxation was quantitatively similar to sodium nitroprusside (SNP). CCh-induced relaxation was abolished after endothelial denudation, but resistant to nitroarginine and indomethacin. The relaxation was inhibited by tetraethylammonium, ouabain, charybdotoxin plus apamin, and under depolarization. SNP-induced relaxation was accompanied by increased cGMP production, which was inhibited by ODQ (1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-l-one). Although CCh produced a similar extent of relaxation to SNP, the cGMP level was 24 times lower than that with SNP. Low KCl produced a definite relaxation, which was inhibited by ouabain, but independent of NO, prostacyclin, and endothelium. 1-EBIO (1-ethyl-2-benzimidazolinone) as an activator of IK(Ca) channel also produced a concentration-dependent relaxation, which was inhibited by charybdotoxin, ouabain, and depolarization, but independent of NO and prostacyclin. Clotrimazole and 17-octadecynoic acid as inhibitors of P(450) monooxygenase inhibited the CCh-induced relaxation. Meanwhile, catalase at a concentration sufficient to inhibit H(2)O(2)-induced relaxation did not exert definite inhibition of the CCh-induced relaxation. These results suggest that CCh produces an endothelium-dependent, EDHF-dependent, and NO-cGMP-independent relaxation and that K(+) and metabolite(s) of P(450) monooxygenase possibly play an important role for this relaxation.

Compensation of Endothelium-Dependent Responses in Coronary Circulation of eNOS-Deficient Mice

Nitric oxide plays a fundamental role in the regulation of blood flow. Here we analyzed compensatory mechanisms for the genetic eNOS deficiency in aorta and in coronary circulation. Vasodilation induced by acetylcholine, bradykinin, adenosine, and ADP as well as by S-nitroso-penicillamine (SNAP) was assessed in isolated aorta and in isolated mouse hearts from eNOS-/- and age-matched eNOS+/+ mice. In aorta from eNOS+/+ mice acetylcholine-induced vasodilation was entirely dependent on NO, and this response was absent in aorta from eNOS-/- mice. In eNOS+/+ mouse hearts responses induced by bradykinin, adenosine and ADP were partially dependent on NO, but not on PGI2, cytochrome P450-dependent metabolites, or H2O2. On the other hand, vasodilation induced by acetylcholine involved NO, but not PGI2, in its immediate, short-lasting phase, whereas PGI2 and NO mediated delayed, longer-lasting phase of this response. In eNOS-/- mouse hearts coronary vasodilator function was compensated. Responses induced by acetylcholine and adenosine, but not by bradykinin or ADP, were in part compensated by NO, most likely derived from nNOS. However, the major mechanisms compensating for the loss of eNOS in the coronary circulation did not rely on NO, PGI2, cytochrome P450-derived metabolites of arachidonic acid or on H2O2. Deficiency of eNOS is largely compensated in coronary circulation but not in aorta.

Angiotensin-converting enzyme inhibitors reveal non-NO-, non-prostacycline-mediated endothelium-dependent relaxation in internal thoracic artery of hypertensive patients

BACKGROUND

We have shown that treatment of hypertension with ACE inhibitors (ACE-I) enhances relaxation to acetylcholine in human internal thoracic artery (ITA) above this in nonhypertensive patients receiving no ACE-I. Present study assesses the endothelium-dependent responses mediated by neither NO nor prostacyclin in human ITA.

METHODS

We compared isolated ITA rings from hypertensive patients treated with ACE-I (ACE-I group) with those from normotensive patients on no ACE-I (control group). Relaxation to acetylcholine was assessed before and after inhibition of NO synthase and cyclooxygenase with L-NMMA and indomethacin, respectively.

RESULTS

The maximal relaxation in ACE-I group was 79+/-3.3% and was depressed by incubation with L-NMMA and indomethacin to 41+/-2.7% (p<0.001); pD(2)=7.7+/-0.1 vs. 7.4+/-0.8 (p=0.265). The maximal relaxation to acetylcholine was lower in the control group: 65+/-3.3% (p=0.01); pD(2)=7.5+/-0.1 (p=0.07). Incubation with L-NMMA and indomethacin produced contraction to acetylcholine with a maximum of 43+/-7% (p<0.001); pD(2)=5.3+/-0.3 (p<0.001). The area under the concentration-response curve for acetylcholine-induced relaxation in ACE-I group equaled [arbitrary units] 596+/-71 and after incubation with L-NMMA and indomethacin 281+/-40 (p=0.002). Estimated LNMMA- and indomethacin-resistant relaxation, absent in control group, accounted for 47+/-4% of relaxation to acetylcholine in ACE-I group. Estimated NO- and prostacyclin-mediated relaxation was higher in control group than ACE-I group: 628+/-74 vs. 315+/-47 (p=0.009).

CONCLUSIONS

The results suggest that therapy with ACE-I improves endothelial function of hypertensive patients mainly by enhancing the endothelium-derived hyperpolarizing factor (EDHF) (and not NO)-mediated responses. It seems that it reveals measurable non-NO- non-PGI-mediated endothelium-dependent relaxation otherwise absent in conduit arteries.

Reciprocal changes in endothelium-derived hyperpolarizing factor- and nitric oxide-system in the mesenteric artery of adult female rats following ovariectomy

1. To explore the effects of estrogen on arterial functions, we examined endothelium-derived hyperpolarizing factor (EDHF)- and NO-mediated responses in isolated mesenteric arteries of female rats, 4 weeks after sham-operation (CON), ovariectomy (OVX) and OVX plus chronic estrogen treatment (OVX+E(2)). Tissue levels of connexins-40, 43 (major components of gap junction), inducible NOS (iNOS), endothelial NOS (eNOS) and eNOS regulator proteins such as calmodulin, heat shock protein 90 (hsp90) and caveolin-1 were also examined using Western blot. 2. In OVX, acetylcholine (ACh)-induced EDHF-mediated relaxation and membrane hyperpolarization of arterial smooth muscles were reduced, whereas ACh-induced NO-mediated relaxation was enhanced, leading to no change in ACh-induced relaxation. 3. In OVX, connexin-40 and 43 were decreased. Tissue levels of eNOS and its positive regulators (calmodulin and hsp90) were unchanged, but that of its negative regulator, caveolin-1, was decreased. The levels of iNOS in mesenteric artery and aorta and plasma levels of NO metabolites and cholesterol were elevated. 4. In OVX, contraction of the artery by phenylephrine was reduced, but augmented by nonspecific inhibitor of NOS to the comparable level as that in CON group. The contraction in OVX group unlike that in CON group was augmented by specific iNOS inhibitor, and the difference between contractions in the presence of nonspecific and specific inhibitor as an index of eNOS activity was increased. 5. In OVX+E(2), all these changes were recovered. 6. In all groups, EDHF-mediated relaxation was suppressed by 18beta-glycyrrhetinic acid, an inhibitor of gap junction. 7. These results indicate that estrogen deficiency does not change the diameter of mesenteric artery: it reduces EDHF-mediated relaxation by decreasing gap junction, whereas it augments NO-mediated relaxation via an increase in NO release. Increased NO result from increased activity of eNOS subsequent to a decrease in caveolin-1 and from induction of iNOS. However, excessive NO generation with elevated plasma cholesterol would raise a risk for atherosclerosis.

Endothelial nitric oxide synthase-independent effects of an ACE inhibitor on coronary flow response to bradykinin in aged mice

ACE inhibitors are known to ameliorate cardiovascular complications in aging; however, their effects on the coronary circulation in relation to aging and eNOS dependence remain to be examined. Coronary flow responses to bradykinin with or without ACE inhibitors were examined in Langendorff-perfused hearts from young (16-20 weeks) and aged (16-20 months) control and eNOS mice. Western blot analysis was performed for cardiac eNOS, nNOS, and ACE. Baseline coronary flow was comparable between young and aged mice of both strains. Aging did not affect bradykinin-induced coronary flow in either strain. Interestingly, both acute and chronic treatment with an ACE inhibitor markedly augmented the flow response in aged control and eNOS mice. Aged eNOS mice were markedly hypertensive and had larger ventricular mass than control mice. The antihypertensive effect of temocapril was greater in aged eNOS mice, associated with reduction in the ventricular weight in both strains. Western blot analysis demonstrated an increased expression of eNOS in aged control mice, and ACE expression was increased in eNOS mice. These results indicate that coronary flow response to bradykinin is preserved in aged mice even in the absence of eNOS, and an ACE inhibitor augments this response by both eNOS-dependent and -independent mechanisms.

ROLE OF ENDOTHELIUM-DERIVED HYPERPOLARIZING FACTOR IN ENDOTHELIAL DYSFUNCTION DURING DIABETES

1. Under normal conditions, the endothelium plays a major role in the maintenance of vasodilatory tone via the production of endothelium-derived vasodilator agents, such as prostacyclin, nitric oxide and endothelium-derived hyperpolarizing factor (EDHF). Inhibition of endothelium-dependent relaxation features prominently in a range of cardiovascular diseases, including hypertension, coronary artery disease and diabetes. 2. Endothelium-derived hyperpolarizing factor is a prominent vasodilator, particularly in smaller arteries and arterioles. There is now emerging evidence to suggest that EDHF may play a role in the endothelial dysfunction in diabetes. 3. Since the first description of endothelium-dependent hyperpolarization some 20 years ago, it has emerged that EDHF is heterogeneous in nature, consisting of diffusible factors and contact-mediated mechanisms. The specific identity of EDHF in any particular vascular bed may influence the impact of diabetes on vascular function. 4. There is accumulating evidence in diabetic rat models and humans showing impaired EDHF activity in small resistance vessels. In contrast, studies in mice suggest that EDHF activity is actually enhanced under diabetic conditions. 5. It is clear that alterations in EDHF activity may have an important contribution in diabetes, more specifically in contributing to microvascular complications observed under diabetic conditions.

Influence of Diabetes Mellitus, Hypercholesterolemia, and Their Combination on EDHF-Mediated Responses in Mice

The endothelium synthesizes and releases several vasodilator substances, including vasodilator prostaglandins, NO, and EDHF. NO-mediated relaxations are reduced by various risk factors, such as diabetes mellitus and hypercholesterolemia. However, it remains to be elucidated whether EDHF-mediated relaxations also are reduced by those factors and their combination. In this study, we addressed this point in mice. We used small mesenteric arteries from control, diabetic (streptozotocin-induced), apolipoprotein-E-deficient (ApoE-/-), and diabetic ApoE-/- mice. In control mice, endothelium-dependent relaxations to acetylcholine were largely mediated by EDHF. This EDHF-mediated component was slightly reduced in diabetic mice, preserved in ApoE-/- mice, and markedly reduced in diabetic ApoE-/- mice with an increase in NO-mediated component and a negative contribution of indomethacin-sensitive endothelium-derived contracting factor (EDCF). Endothelium-independent relaxations to sodium nitroprusside or NS1619, a direct opener of calcium-activated K channels, were attenuated in ApoE-/- and diabetic ApoE-/- mice. Endothelium-dependent hyperpolarizations were significantly reduced in diabetic mice, preserved in ApoE-/- mice, and again markedly reduced in diabetic ApoE-/- mice. These results indicate that hypercholesterolemia alone minimally affects the EDHF-mediated relaxations, and diabetes mellitus significantly attenuated the responses, whereas their combination markedly attenuates the responses with a compensatory involvement of NO and a negative contribution of EDCF.

Endothelium-dependent smooth muscle hyperpolarization: do gap junctions provide a unifying hypothesis?

An endothelium-derived hyperpolarizing factor (EDHF) that is distinct from nitric oxide (NO) and prostanoids has been widely hypothesized to hyperpolarize and relax vascular smooth muscle following stimulation of the endothelium by agonists. Candidates as diverse as K(+) ions, eicosanoids, hydrogen peroxide and C-type natriuretic peptide have been implicated as the putative mediator, but none has emerged as a 'universal EDHF'. An alternative explanation for the EDHF phenomenon is that direct intercellular communication via gap junctions allows passive spread of agonist-induced endothelial hyperpolarization through the vessel wall. In some arteries, eicosanoids and K(+) ions may themselves initiate a conducted endothelial hyperpolarization, thus suggesting that electrotonic signalling may represent a general mechanism through which the endothelium participates in the regulation of vascular tone.

Nitric oxide mediates abnormal responsiveness of thyroid arteries in methimazole-treated patients

OBJECTIVE

We studied the intervention of nitric oxide (NO), prostacyclin and endothelium-derived hyperpolarizing factor (EDHF) in mediating responses to acetylcholine in thyroid arteries from euthyroid and methimazole-treated (MT) patients.

DESIGN AND METHODS

Branches of the superior thyroid artery were obtained from 19 euthyroid patients and 17 MT patients (euthyroid at the time of surgery) undergoing total thyroidectomy or hemithyroidectomy. Artery rings were suspended in organ baths for isometric recording of tension.

RESULTS AND CONCLUSIONS

Acetylcholine caused endothelium-dependent relaxation of greater magnitude in arteries from MT patients (pD(2) (-log EC(50)) values were 7.68 +/- 0.19 in euthyroid and 8.17 +/- 0.26 in MT patients, P < 0.05). The relaxation was unaffected by indomethacin and was partially reduced by the NO-synthase inhibitor NG-monomethyl-L-arginine (L-NMMA). This reduction was higher in arteries from MT patients (50 +/- 6%) as compared with euthyroid patients (36 +/- 6%) (P < 0.05). Inhibition of K(+) channels using apamin combined with charybdotoxin or high K(+) solution abolished the relaxation resistance to L-NMMA and indomethacin. The maximal contraction response to noradrenaline (as a percentage of the response to 100 mM KCl) was lower in MT than in euthyroid patients (57 +/- 10 and 96 +/- 8 respectively, P < 0.05). The hyporesponsiveness to noradrenaline in arteries from MT patients was corrected by L-NMMA. The results indicate that: (i) thyroid arteries from MT patients show an increased relaxation response to acethylcholine and a decreased contraction response to noradrenaline due to overproduction of NO; (ii) EDHF plays a prominent role in acetylcholine-induced relaxation through activation of Ca(2+)-activated K(+) channels; (iii) the abnormal endothelium-dependent responses in arteries from MT patients are not corrected by medical treatment.

The Nicorandil-Induced Vasodilation in Humans Is Inhibited by Miconazole

Nicorandil, N-(2-hydroxyethyl)-nicotinamide nitrate, exerts its vasodilatory effects by opening ATP-sensitive potassium (K-ATP) channels and by acting as the exogenous nitric oxide (NO). It is not clear, however, whether the actions of other endothelium-dependent vasodilators, such as NO, endothelium-derived hyperpolarizing factor (EDHF), and prostaglandins, contribute to nicorandil-induced vasodilation in the vasculature in humans. We evaluated forearm blood flow (FBF) response to intraarterial infusion of nicorandil alone and in the presence of glibenclamide, a K-ATP channel inhibitor, N(G)-monomethyl-L-arginine, an NO synthase inhibitor, indomethacin, a cyclooxygenase inhibitor, or miconazol, a cytochrome P-450 inhibitor, in 24 healthy male subjects. FBF was measured using strain-gauge plethysmography. Infusion of nicorandil significantly increased the FBF response in a dose-dependent manner. Intraarterial infusion of glibenclamide attenuated nicorandil-induced vasodilation (160.9 +/- 21.2% versus 90.2 +/- 19.4%, P < 0.01), and miconazole also attenuated the FBF response to nicorandil (160.9 +/- 21.2% versus 66.1 +/- 9.2%, P < 0.001). N-monomethyl-L-arginine or indomethacin did not alter the FBF response to nicorandil. These findings suggest that nicorandil causes vasodilation in forearm circulation in humans, at least in part through a pathway that is dependent on K-ATP channels and cytochrome P-450, but not on endogenous NO and prostaglandins. EDHF may contribute to nicorandil-induced vasodilation in humans.

Hydrogen peroxide and endothelium-dependent hyperpolarization in the guinea-pig carotid artery

This study was designed to determine whether or not endothelium-dependent hyperpolarizations evoked by acetylcholine in the isolated guinea-pig carotid artery involve hydrogen peroxide. Membrane potential was recorded in the vascular smooth muscle cells of that artery. Under control conditions, acetylcholine induced endothelium-dependent hyperpolarization of the vascular smooth muscle cells which was not affected by the presence of catalase, superoxide dismutase or their combination. Neither the superoxide dismutase mimetic, tiron nor the thiol-reducing agent N-acetyl-L-cysteine modified the hyperpolarization evoked by 0.1 microM acetylcholine but each produced a partial and significant inhibition of the hyperpolarization induced by 1 microM acetylcholine. Neither 10 nor 100 microM hydrogen peroxide influenced the resting membrane potential of the smooth muscle cells and the higher concentration did not significantly influence the hyperpolarization elicited by acetylcholine. These data indicate that, in the guinea-pig isolated carotid artery, hydrogen peroxide is unlikely to contribute to the endothelium-dependent hyperpolarization evoked by acetylcholine.

Redox Modulation of Vascular Tone

Opening of potassium channels on vascular smooth muscle cells with resultant hyperpolarization plays a central role in several mechanisms of vasodilation. For example, in the arteriolar circulation where tissue perfusion is regulated, there is an endothelial derived hyperpolarizing factor that opens vascular smooth muscle calcium-activated potassium channels, eliciting dilation. Metabolic vasodilation involves the opening of sarcolemmal ATP-sensitive potassium channels. Adrenergic dilation as well as basal vasomotor tone in several vascular beds depend upon voltage-dependent potassium channels in smooth muscle. Thus hyperpolarization through potassium channel opening is a fundamental mechanism for vasodilation. Disease states such as coronary atherosclerosis and its risk factors are associated with elevated levels of reactive oxygen (ROS) and nitrogen species that have well-defined inhibitory effects on nitric oxide-mediated vasodilation. Effects of ROS on hyperpolarization mechanisms of dilation involving opening of potassium channels are less well understood but are very important because hyperpolarization-mediated dilation often compensates for loss of other dilator mechanisms. We review the effect of ROS on potassium channel function in the vasculature. Depending on the oxidative species, ROS can activate, inhibit, or leave unaltered potassium channel function in blood vessels. Therefore, discerning the activity of enzymes regulating production or degradation of ROS is important when assessing tissue perfusion in health and disease.

Inducible nitric oxide synthase has divergent effects on vascular and metabolic function in obesity

Previous studies have suggested an involvement of inducible nitric oxide synthase (iNOS) in obesity, but the relation, if any, between this and mechanisms underlying endothelial dysfunction in obesity is unknown. We studied mice fed an obesogenic high-fat or standard diet for up to 8 weeks. Obesity was associated with elevated blood pressure; resistance to the glucoregulatory actions of insulin; resistance to the vascular actions of insulin, assessed as the reduction in phenylephrine constrictor response of aortic rings after insulin preincubation (lean -21.7 +/- 11.5 vs. obese 18.2 +/- 15.5%; P < 0.05); and evidence of reactive oxygen species (ROS)-dependent vasodilatation in response to acetylcholine in aortic rings (change in maximal relaxation to acetylcholine after exposure to catalase: lean -2.1 +/- 6.0 vs. obese -15.0 +/- 3.8%; P = 0.04). Obese mice had increased expression of iNOS in aorta, with evidence of increased vascular NO production, assessed as the increase in maximal constriction to phenylephrine after iNOS inhibition with 1400W (lean -3.5 +/- 9.1 vs. obese 42.1 +/- 11.2%; P < 0.001). To further address the role of iNOS in obesity-induced vascular and metabolic dysfunction, we studied the effect of a high-fat diet in iNOS knockout mice (iNOS KO). Obese iNOS KO mice were protected against the development of resistance to insulin's glucoregulatory and vascular effects (insulin-dependent reduction in maximal phenylephrine response: obese wild-type 11.2 +/- 15.0 vs. obese iNOS KO -20.0 +/- 7.7%; P = 0.02). However, obese iNOS KO mice remained hypertensive (124.0 +/- 0.7 vs. 114.9 +/- 0.5 mmHg; P < 0.01) and had evidence of increased vascular ROS production. Although these data support iNOS as a target to protect against the adverse effects of obesity on glucoregulation and vascular insulin resistance, iNOS inhibition does not prevent the development of raised blood pressure or oxidative stress.

14,15-Epoxyeicosatrienoic Acid Represents a Transferable Endothelium-Dependent Relaxing Factor in Bovine Coronary Arteries

Bradykinin causes arterial relaxation and hyperpolarization, which is mediated by a transferable endothelium-derived hyperpolarizing factor (EDHF). In coronary arteries, epoxyeicosatrienoic acids (EETs) are involved in the EDHF response. However, the role of EETs as transferable mediators of EDHF-dependent relaxation remains poorly defined. Two small bovine coronary arteries were cannulated and perfused in tandem in the presence of the nitric oxide synthase inhibitor, nitro- l -arginine (30 μmol/L), and the cyclooxygenase inhibitor, indomethacin (10 μmol/L). Luminal perfusate from donor arteries with intact endothelium perfused endothelium-denuded detector arteries. Detector arteries were constricted with U46619 and diameters were monitored. Bradykinin (10 nmol/L) added to detector arteries did not induce dilation (5±2%), whereas bradykinin addition to donor arteries dilated detector arteries by 26.5±7% ( P <0.05). These dilations were blocked by donor artery endothelium removal and detector artery treatment with the EET-selective antagonist, 14,15-epoxyeicosa-5(Z)-monoenoic acid (14,15-EEZE; 10 μmol/L, −5±6%) but not 14,15-EEZE treatment of donor arteries (20±5%). 14,15-EET (0.1 to 10 μmol/L) added to detector arteries induced maximal dilations of 82±5% that were inhibited 50% by detector artery treatment with 14,15-EEZE (32±12%) but not donor artery treatment with 14,15-EEZE. Liquid chromatography–electrospray ionization mass spectrometry analysis verified the presence of 14,15-EET in the perfusate from an endothelium-intact but not denuded artery. These results show that bradykinin stimulates donor artery 14,15-EET release that dilates detector arteries. 14,15-EEZE blocked the donor artery, endothelium-dependent, bradykinin-induced relaxations, and attenuated relaxations to 14,15-EET. These results suggest that EETs are transferable EDHFs in coronary arteries.

A role for endoglin in coupling eNOS activity and regulating vascular tone revealed in hereditary hemorrhagic telangiectasia

Decreased endothelial NO synthase (eNOS)-derived NO bioavailability and impaired vasomotor control are crucial factors in cardiovascular disease pathogenesis. Hereditary hemorrhagic telangiectasia type 1 (HHT1) is a vascular disorder associated with ENDOGLIN (ENG) haploinsufficiency and characterized by venous dilatations, focal loss of capillaries, and arteriovenous malformations (AVMs). We report that resistance arteries from Eng+/- mice display an eNOS-dependent enhancement in endothelium-dependent dilatation and impairment in the myogenic response, despite reduced eNOS levels. We have found that eNOS is significantly reduced in endoglin-deficient endothelial cells because of decreased eNOS protein half-life. We demonstrate that endoglin can reside in caveolae and associate with eNOS, suggesting a stabilizing function of endoglin for eNOS. After Ca2+-induced activation, endoglin-deficient endothelial cells have reduced eNOS/Hsp90 association, produce less NO, and generate more eNOS-derived superoxide (O2-), indicating that endoglin also facilitates eNOS/Hsp90 interactions and is an important regulator in the coupling of eNOS activity. Treatment with an O2- scavenger reverses the vasomotor abnormalities in Eng(+/-) arteries, suggesting that uncoupled eNOS and resulting impaired myogenic response represent early events in HHT1 pathogenesis and that the use of antioxidants may provide a novel therapeutic modality.

Factors, fiction and endothelium-derived hyperpolarizing factor

1. The principal mediators of vascular tone are neural, endothelial and physical stimuli that result in the initiation of dilator and constrictor responses to facilitate the control of blood pressure. Two primary vasodilatory stimuli produced by the endothelium are nitric oxide (NO) and prostaglandins. An additional endothelium-dependent vasodilatory mechanism is characterized as the hyperpolarization-mediated relaxation that remains after the inhibition of the synthesis of NO and prostaglandins. This mechanism is due to the action of a so-called endothelium-derived hyperpolarizing factor (EDHF) and is dependent on either the release of diffusible factor(s) and/or to a direct contact-mediated mechanism. 2. Most evidence supports the concept that 'EDHF' activity is dependent on contact-mediated mechanisms. This involves the transfer of an endothelium-derived electrical current, as an endothelium-derived hyperpolarization (EDH), through direct heterocellular coupling of endothelial cells and smooth muscle cells via myoendothelial gap junctions (MEGJ). However, there is a lack of consensus with regard to the nature and mechanism of action of EDHF/EDH (EDH(F)), which has been shown to vary within and between vascular beds, as well as among species, strains, sex and during development, ageing and disease. 3. In addition to actual heterogeneity in EDH(F), further heterogeneity has resulted from the less-than-optimal design, analysis and interpretation of data in some key papers in the EDHF literature; with such views being perpetuated in the subsequent literature. 4. The focus of the present brief review is to examine what factors are proposed as EDH(F) and highlight the correlative structural and functional studies from our laboratory that demonstrate an integral role for MEGJ in the conduction of EDH, which account for the heterogeneity in EDH(F), while incorporating the reported diffusible mechanisms in the regulation of this activity. Furthermore, in addition to the reported heterogeneity in the nature and mechanism of action of EDH(F), the contribution of experimental design and technique to this heterogeneity will be examined.

Endothelium-derived hydrogen peroxide accounts for the enhancing effect of an angiotensin-converting enzyme inhibitor on endothelium-derived hyperpolarizing factor-mediated responses in mice

Background- We have recently identified that endothelium-derived hydrogen peroxide (H2O2) is an endothelium-derived hyperpolarizing factor (EDHF) in animals and humans, for which endothelial nitric oxide synthase (eNOS) is an important source. Angiotensin-converting enzyme (ACE) inhibitors are known to enhance EDHF-mediated responses. In this study, we examined whether endothelium-derived H2O2 accounts for the enhancing effect of an ACE inhibitor on EDHF-mediated responses and, if so, what mechanism is involved.

METHODS AND RESULTS

Control and eNOS-/- mice were maintained with or without temocapril (10 mg/kg per day orally) for 4 weeks, and isometric tensions and membrane potentials of mesenteric arteries were recorded. In control mice, temocapril treatment significantly enhanced EDHF-mediated relaxations and hyperpolarizations to acetylcholine (n=8 each). Catalase, a specific scavenger of H2O2, abolished the beneficial effects of temocapril, although it did not affect endothelium-independent relaxations to sodium nitroprusside or NS1619, a direct opener of K(Ca) channels (n=6 each). Western blot analysis demonstrated that the temocapril treatment significantly upregulated the expression of eNOS. By contrast, this enhancing effect of temocapril was absent in eNOS-/- mice (n=6).

CONCLUSIONS

These results indicate that endothelium-derived H2O2 accounts for the enhancing effect of temocapril on EDHF-mediated responses caused in part by eNOS upregulation, further supporting our H2O2 theory.

Investigation of vascular responses in endothelial nitric oxide synthase/cyclooxygenase-1 double-knockout mice: key role for endothelium-derived hyperpolarizing factor in the regulation of blood pressure in vivo

BACKGROUND

Endothelium-dependent dilatation is mediated by 3 principal vasodilators: nitric oxide (NO), prostacyclin (PGI2), and endothelium-derived hyperpolarizing factor (EDHF). To determine the relative contribution of these factors in endothelium-dependent relaxation, we have generated mice in which the enzymes required for endothelial NO and PGI2 production, endothelial NO synthase (eNOS) and cyclooxygenase-1 (COX-1), respectively, have been disrupted (eNOS-/- and COX-1-/- mice).

METHODS AND RESULTS

In female mice, the absence of eNOS and COX-1 had no effect on mean arterial blood pressure (BP), whereas BP was significantly elevated in eNOS-/-/COX-1-/- males compared with wild-type controls. Additionally, endothelium-dependent relaxation remained intact in the resistance vessels of female mice and was associated with vascular smooth muscle hyperpolarization; however, these responses were profoundly suppressed in arteries of male eNOS-/-/COX-1-/- animals. Similarly, the endothelium-dependent vasodilator bradykinin produced dose-dependent hypotension in female eNOS-/-/COX-1-/- animals in vivo but had no effect on BP in male mice.

CONCLUSIONS

These studies indicate that EDHF is the predominant endothelium-derived relaxing factor in female mice, whereas NO and PGI2 are the predominant mediators in male mice. Moreover, the gender-specific prevalence of EDHF appears to underlie the protection of female eNOS-/-/COX-1-/- mice against hypertension.

Redox Mechanisms in Blood Vessels

Reactive oxygen species have been implicated in the pathogenesis of virtually every stage of vascular lesion formation, hypertension, and other vascular diseases. We are currently gaining insight into important sources of reactive oxygen species in the vessel wall, including the NADPH oxidases, xanthine oxidase, uncoupled nitric oxide synthase, and mitochondrial sources. Although various reactive oxygen species have pathological roles, some serve as important signaling molecules that modulate vascular tone, growth, and remodeling. In the next several months, a series of articles in Arteriosclerosis, Thrombosis, and Vascular Biology attempt to further elucidate how reactive oxygen species are produced by vascular cells and the roles of these in vascular homeostasis. This series promises to provide a valuable update on a wide variety of issues related to the biochemistry, molecular biology, and physiology of these important and fascinating molecules. Reactive oxygen species have been implicated in the pathogenesis of virtually every stage of vascular lesion formation, hypertension, and other vascular diseases. Upcoming series of articles in Arteriosclerosis, Thrombosis, and Vascular Biology help elucidate how reactive oxygen species are produced by vascular cells and their role in vascular homeostasis.

Prostacyclin Does Not Inhibit Rho-Kinase

Primary pulmonary hypertension continues to be a fatal disease. We have recently demonstrated that long-term inhibition of Rho-kinase, an effector of the small GTPase Rho, is effective for the treatment of pulmonary hypertension (PH) in rats and humans. Prostacyclin has been clinically used for the treatment of PH with moderate success. However, it remains to be examined whether Rho-kinase inhibition is involved in its beneficial effects on PH. In an ELISA assay, neither prostacyclin nor its oral analogue, beraprost sodium, inhibited Rho-kinase even at higher concentrations (10(-7) to 10(-5) M, 100 to 10,000 times higher than their clinical concentrations), whereas specific Rho-kinase inhibitors, fasudil and hydroxyfasudil, markedly (approximately 95%) inhibited the Rho-kinase activity at 10(-5) M (near their clinical concentrations). Beraprost sodium did not significantly suppress serotonin-induced vascular smooth muscle cell (VSMC) contractions or Rho-kinase activity of the rat aorta without endothelium, as evaluated by the extent of phosphorylation of the ERM family, a substrate of Rho-kinase, whereas hydroxyfasudil markedly suppressed the VSMC contractions and Rho-kinase activity. These results indicate that prostacyclin lacks direct inhibitory effect on Rho-kinase and suggest that combination therapy with prostacyclin and a Rho-kinase inhibitor could exert further beneficial effects on PH.

Design and development of a fluorescent probe for monitoring hydrogen peroxide using photoinduced electron transfer

A novel fluorescent probe, 7-hydroxy-2-oxo-N-(2-(diphenylphosphino)ethyl)-2H-chromene-3-carboxamide (DPPEA-HC) was developed for use in monitoring hydrogen peroxide (H2O2) production. DPPEA-HC, which consists of a diphenylphosphine moiety and a 7-hydroxycoumarin moiety, reacts with H2O2 to form DPPEA-HC oxide, which is analogous to the reaction of triphenylphosphine with hydroperoxides such as H2O2 to form triphenylphosphine oxide. Photoinduced electron transfer (PET) was applied in the design of DPPEA-HC. Since the diphenylphosphine moiety and the 7-hydroxycoumarin moiety would act as the PET donor and the acceptor, respectively, it would be expected that DPPEA-HC would rationally cancel the PET process via the formation of DPPEA-HC oxide, based on the calculated energy levels of the donor and the acceptor moieties using the B3LYP/6-31G*//AM1 method. The fluorescence intensity of DPPEA-HC increased on the addition of a H2O2 solution in 100 mM sodium phosphate buffer (pH7.4), as predicted from the energy level calculation and a good correlation between increase in the fluorescence of DPPEA-HC and the concentration of H2O2 was observed. DPPEA-HC was also fluoresced by H2O2, which was enzymatically produced in xanthine/xanthine oxidase/superoxide dismutase (XA/XOD/SOD) system. The increase in the fluorescence of DPPEA-HC in the presence of H2O2 immediately ceased on the addition of catalase (CAT), which catalyzes the disproportionation of H2O2. In addition, DPPEA-HC was found to have a much higher selectivity for H2O2 and a greater resistance to autoxidation than 2',7'-dichlorodihydrofluoresein (DCFH). Time-resolved fluorescence measurements of DPPEA-HC and DPPEA-HC oxide confirmed that the fluorescence off/on switching mechanism of DPPEA-HC is based on the PET on/off control.

Increased superoxide leads to decreased flow-induced dilation in resistance arteries of Mn-SOD-deficient mice

The role of mitochondrial manganese-superoxide dismutase (Mn-SOD) in the maintenance of vascular function has not yet been studied. Thus we examined flow- and agonist-induced dilations in isolated mesenteric arteries (approximately 90 microm in diameter) of Mn-SOD heterozygous (Mn-SOD+/-) and wild-type (WT) mice. Increases in flow elicited dilations in all vessels, but the magnitude of the dilation was significantly less in vessels of Mn-SOD+/- mice than in those of WT mice (64 vs. 74% of passive diameter). N(omega)-nitro-L-arginine methyl ester inhibited the dilation in vessels of WT mice but had no effect on vessels of Mn-SOD+/- mice. Tempol or tiron (superoxide scavengers) increased flow-induced dilation in vessels of Mn-SOD+/- mice. Acetylcholine- and sodium nitroprusside-induced, but not adenosine-induced, dilations were also decreased in arteries of Mn-SOD+/- mice. Superoxide levels in the arteries of Mn-SOD+/- mice were significantly increased. Western blot analysis confirmed a 50% reduction of Mn-SOD protein in the vessels of Mn-SOD+/- mice. A 41% reduction in endothelial nitric oxide synthase (eNOS) protein and a 37% reduction in eNOS activity were also found in the vessels of Mn-SOD+/- mice. Whereas there was no difference in eNOS protein in kidney homogenates of WT and Mn-SOD+/- mice, a significant reduction of nitric oxide synthase activity was found in Mn-SOD+/- mice, which could be restored by the administration of tiron. We conclude that an increased concentration of superoxide due to reduced activity of Mn-SOD, which inactivates nitric oxide and inhibits eNOS activity, contributes to the impaired vasodilator function of isolated mesenteric arteries of Mn-SOD+/- mice. These results suggest that Mn-SOD contributes significantly to the regulation of vascular function.

The pulmonary biology of isoprostanes

Isoprostanes were first recognized as convenient markers of oxidative stress, but their powerful effects on a variety of cell functions are now also being increasingly appreciated. This is particularly true of the lung, which is comprised of a wide variety of different cell types (smooth muscle, innervation, epithelium, lymphatics, etc.), all of which have been shown to respond to exogenously applied isoprostanes. In this review, we summarize these biological responses in the lung, and also consider the roles that isoprostanes might play in a range of pulmonary clinical disorders.

Red wine polyphenol-induced, endothelium-dependent NO-mediated relaxation is due to the redox-sensitive PI3-kinase/Akt-dependent phosphorylation of endothelial NO-synthase in the isolated porcine coronary artery

An enhanced endothelial formation of nitric oxide (NO) by red wine polyphenolic compounds (RWPs) has been involved in the protective effect of chronic intake of red wine on coronary diseases. However, the mechanism underlying the activation of endothelial NO synthase (eNOS) remains unclear. In the presence of indomethacin and charybdotoxin plus apamin to prevent the formation of prostanoids and endothelium-derived hyperpolarizing factor, respectively, RWPs caused pronounced endothelium-dependent relaxations in porcine coronary arteries. Relaxations to RWPs were abolished by N(omega)-nitro-L-arginine (L-NA, a competitive inhibitor of NO synthase) and the membrane permeant analog of superoxide dismutase (SOD), MnTMPyP, and reduced by polyethylene glycol-SOD (PEG-SOD), PEG-catalase and inhibitors of PI3-kinase (wortmannin and LY294002). RWPs caused the L-NA-sensitive formation of NO, as assessed by electron spin resonance spectroscopy and the formation of cyclic guanosine monophosphate in coronary artery endothelial cells; these responses were reduced by MnTMPyP, PEG-catalase, and inhibitors of PI3-kinase. RWPs caused the sustained phosphorylation of Akt and eNOS at Ser1177 in endothelial cells, which were abolished by MnTMPyP and inhibitors of PI3-kinase. These data demonstrate that RWPs induce the redox-sensitive activation of the PI3-kinase/Akt pathway in endothelial cells which, in turn, causes phosphorylation of eNOS, resulting in an increased formation of NO.

Effect of fetal hemoglobin on microvascular regulation in sickle transgenic-knockout mice

In sickle cell disease, intravascular sickling and attendant flow abnormalities underlie the chronic inflammation and vascular endothelial abnormalities. However, the relationship between sickling and vascular tone is not well understood. We hypothesized that sickling-induced vaso-occlusive events and attendant oxidative stress will affect microvascular regulatory mechanisms. In the present studies, we have examined whether microvascular abnormalities expressed in sickle transgenic-knockout Berkeley (BERK) mice (which express exclusively human alpha- and beta(S)-globins with <1% gamma-globin levels) are amenable to correction with increased levels of antisickling fetal hemoglobin (HbF). In BERK mice, sickling, increased oxidative stress, and hemolytic anemia are accompanied by vasodilation, compensatory increases in eNOS and COX-2, and attenuated vascular responses to NO-mediated vasoactive stimuli and norepinephrine. The hypotension and vasodilation (required for adequate oxygen delivery in the face of chronic anemia) are mediated by non-NO vasodilators (i.e., prostacyclin) as evidenced by induction of COX-2. In BERK mice, the resistance to NO-mediated vasodilators is associated with increased oxidative stress and hemolytic rate, and in BERK + gamma mice (expressing 20% HbF), an improved response to these stimuli is associated with reduced oxidative stress and hemolytic rate. Furthermore, BERK + gamma mice show normalization of vessel diameters, and eNOS and COX-2 expression. These results demonstrate a strong relationship between sickling and microvascular function in sickle cell disease.

Endothelial cell superoxide generation: regulation and relevance for cardiovascular pathophysiology

The endothelial generation of reactive oxygen species (ROS) is important both physiologically and in the pathogenesis of many cardiovascular disorders. ROS generated by endothelial cells include superoxide (O2-*), hydrogen peroxide (H2O2), peroxynitrite (ONOO-*), nitric oxide (NO), and hydroxyl (*OH) radicals. The O2-* radical, the focus of the current review, may have several effects either directly or through the generation of other radicals, e.g., H2O2 and ONOO-*. These effects include 1) rapid inactivation of the potent signaling molecule and endothelium-derived relaxing factor NO, leading to endothelial dysfunction; 2) the mediation of signal transduction leading to altered gene transcription and protein and enzyme activities ("redox signaling"); and 3) oxidative damage. Multiple enzymes can generate O2-*, notably xanthine oxidase, uncoupled NO synthase, and mitochondria. Recent studies indicate that a major source of endothelial O2-* involved in redox signaling is a multicomponent phagocyte-type NADPH oxidase that is subject to specific regulation by stimuli such as oscillatory shear stress, hypoxia, angiotensin II, growth factors, cytokines, and hyperlipidemia. Depending on the level of oxidants generated and the relative balance between pro- and antioxidant pathways, ROS may be involved in cell growth, hypertrophy, apoptosis, endothelial activation, and adhesivity, for example, in diabetes, hypertension, atherosclerosis, heart failure, and ischemia-reperfusion. This article reviews our current knowledge regarding the sources of endothelial ROS generation, their regulation, their involvement in redox signaling, and the relevance of enhanced ROS generation and redox signaling to the pathophysiology of cardiovascular disorders where endothelial activation and dysfunction are implicated.