Isolated Rat Pulmonary Artery Research Articles

Citrulline activates adenosine receptors: New insight into metabolic pathways interaction

Citrulline is a non-proteinogenic amino acid that forms as by-product in nitric oxide (NO) synthesis from arginine and may act in concert with NO as an independent signaling molecule that involves in the mechanism of vascular smooth muscle vasodilation.In this study we examined the effects of citrulline on pulmonary artery smooth muscles. Experimental design comprised outward potassium currents measurements in enzymatically isolated rat pulmonary artery smooth muscle (PASMc) cells using whole-cell patch clamp technique, isometric contractile force recordings on rat pulmonary artery rings and method of molecular docking simulation.Citrulline in a concentration 10−9-10−5 M relaxed phenylephrine (PHE)-preactivated SM of rat pulmonary artery in a dose-dependent manner (EC50 0,67 μM). This citrulline-induced relaxation was dependent on an intact endothelium. Bath application of citrulline (10-8-10-5 M) on isolated PASMc induced a significant increase in the amplitude of outward potassium current (Ik). The adenosine antagonist caffeine (10-6 M) effectively blocked both the citrulline-induced relaxation response and Ik increment. Molecular docking modeling suggests that caffeine blocking the potent activity of citrulline results from competitive interactions at the A2 adenosine receptor binding site.In summary, our data suggest that citrulline, released with NO at low concentrations, can effectively interact with adenosine receptors in smooth muscle cells, causing their relaxation, indicating surprising interaction between NO and adenosine pathways.

The Vasodilator Effect and Mechanism of 18β-glycyrrhetinic Acid on Isolated Pulmonary Artery Rings in Rats

Background: The purpose of this study was to evaluate the effect of 18β-glycyrrhetinic acid (18β-GA) on isolated rat pulmonary artery vascular rings as well as the mechanism that lies behind the diastolic effects of this compound. Methods: To examine the effects of various doses of 18β-GA on resting normal vascular rings, we used isolated rat pulmonary artery vascular rings. The isolated rat pulmonary artery vascular ring was precontracted with phenylephrine (PE) and potassium chloride solution (KCl), which allowed for the observation of the diastolic effects of 18β-GA, as well as the effects of various concentrations of 18β-GA on blocking the four potassium channels of glibenclamide, barium chloride (BaCl2), tetraethylamine (TEA), or 4-aminopyridine; the impact of various 18β-GA concentrations on the pulmonary artery vasodilation effect pre-use of the nitric oxide synthase inhibitors l-nitroarginine methyl ester and indomethacin. Results: It was shown that 18β-GA has concentration-dependent diastolic effects on isolated rat pulmonary vascular rings that have been precontracted with PE and KCl but it has no effect on resting isolated thoracic aortic vascular rings. Conclusion: The two Kir and Kv channels may be connected to the endothelium-dependent vasodilation mechanism of 18β-GA.

Calcium-dependent modulation of BKCa channel activity induced by plasmonic gold nanoparticles in pulmonary artery smooth muscle cells and hippocampal neurons.

Gold nanoparticles are widely used for biomedical applications, but the precise molecular mechanism of their interaction with cellular structures is still unclear. Assuming that intracellular calcium fluctuations associated with surface plasmon-induced calcium entry could modulate the activity of potassium channels, we studied the effect of 5nm gold nanoparticles on calcium-dependent potassium channels and associated calcium signaling in freshly isolated rat pulmonary artery smooth muscle cells and cultured hippocampal neurons. Outward potassium currents were recorded using patch-clamp techniques. Changes in intracellular calcium concentration were measured using the high affinity Ca2+ fluorescent indicator fluo-3 and laser confocal microscope. In pulmonary artery smooth muscle cells, plasmonic gold nanoparticles increased the amplitude of currents via large-conductance Ca2+ -activated potassium channels, which was potentiated by green laser irradiation near plasmon resonance wavelength (532 nm). Buffering of intracellular free calcium with ethylene glycol-bis-N,N,N',N'-tetraacetic acid (EGTA) abolished these effects. Furthermore, using confocal laser microscopy it was found that application of gold nanoparticles caused oscillations of intracellular calcium concentration that were decreasing in amplitude with time. In cultured hippocampal neurons gold nanoparticles inhibited the effect of EGTA slowing down the decline of the BKCa current while partially restoring the amplitude of the slow after hyperpolarizing currents. We conclude that fluctuations in intracellular calcium can modulate plasmonic gold nanoparticles-induced gating of BKCa channels in smooth muscle cells and neurons through an indirect mechanism, probably involving the interaction of plasmon resonance with calcium-permeable ion channels, which leads to a change in intracellular calcium level.

FUT8-Mediated Core Fucosylation Promotes the Pulmonary Vascular Remodeling in Pulmonary Arterial Hypertension.

Pulmonary arterial hypertension (PAH) is a progressive cardiopulmonary disease with unclear underlying molecular mechanisms and limited therapeutic options. This study aimed to explore the role of core fucosylation and the only glycosyltransferase FUT8 in PAH. We observed increased core fucosylation in a monocrotaline (MCT)-induced PAH rat model and isolated rat pulmonary artery smooth muscle cells (PASMCs) treated with platelet-derived growth factor-BB (PDGF-BB). We found that 2-fluorofucose (2FF), a drug used to inhibit core fucosylation, improved hemodynamics and pulmonary vascular remodeling in MCT-induced PAH rats. In vitro, 2FF effectively restrains the proliferation, migration, and phenotypic switching of PASMCs and promotes apoptosis. Compared with controls, serum FUT8 concentration in PAH patients and MCT-induced rats was significantly elevated. FUT8 expression appeared increased in the lung tissues of PAH rats, and the co-localization of FUT8 with α-SMA was also observed. SiRNA was used to knockdown FUT8 in PASMCs (siFUT8). After effectively silencing FUT8 expression, phenotypic changes induced in PASMCs by PDGF-BB stimulation were alleviated. FUT8 activated the AKT pathway, while the admission of AKT activator SC79 could partially counteract the negative effect of siFUT8 on the proliferation, apoptotic resistance, and phenotypic switching of PASMCs, which may be involved in the core fucosylation of vascular endothelial growth factor receptor (VEGFR). Our research confirmed the critical role of FUT8 and its mediated core fucosylation in pulmonary vascular remodeling in PAH, providing a potential novel therapeutic target for PAH.

Vasodilatory effects of betaine on isolated rat pulmonary artery rings.

The aim of this study was to investigate the vasodilatory effects of betaine, an alkaloid isolated from Lycium barbarum, on isolated pulmonary artery rings in rats and its possible mechanisms. Pulmonary vessels of normal Sprague-Dawley rats were isolated and pre-contracted using norepinephrine. Then, betaine was cumulatively added in differing concentrations (0.02-0.14 mg/mL), and the tension curve was observed and recorded. Changes in the tension of the pulmonary artery rings with an intact endothelium and a dissected endothelium were recorded. The interactions among betaine and NG-nitro-L-arginine methyl ester, indomethacin, 4-aminopyridine, barium chloride, and glibenclamide were evaluated. The experimental results show that betaine can relax the pulmonary artery rings pre-contracted by norepinephrine. Furthermore, pre-incubation with NG-nitro-L-arginine methyl ester and indomethacin did not inhibit betaine vasodilation, demonstrating that vasodilation by betaine is endothelium-dependent. Additionally, pretreatment of pulmonary artery rings with 4-aminopyridine and glibenclamide had no effect on betaine. However, pretreatment of pulmonary artery rings with barium chloride attenuated the effects of betaine. In conclusion, the vasodilatory effects of betaine on pulmonary artery rings is associated with inward rectifier potassium channels.

Vasodilatory action of trans-4-methoxy-β-nitrostyrene in rat isolated pulmonary artery.

Trans-4-methoxy-β-nitrostyrene (T4MN) induced more potent vasorelaxant effects in resistance arteries from hypertensive rats than its parent drug, β-nitrostyrene 1-nitro-2-phenylethene (NPe). To better understand the influence of insertion of the electron-releasing methoxy group in the aromatic ring of NPe, we investigated vasorelaxant effects of T4MN in isolated pulmonary artery and compared them with those of NPe in view of the potential interest of T4MN in pulmonary arterial hypertension. T4MN and NPe both caused concentration-dependent vasorelaxation in pulmonary artery rings pre-contracted with either phenylephrine (1µmol/L) or KCl (60mmol/L), an effect unaffected by endothelium removal. In endothelium-intact preparations pre-contracted with phenylephrine, the vasorelaxant effect of T4MN was more potent than that of NPe. However, unlike NPe, this effect was significantly reduced following pretreatment with 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) (10µmol/L, a guanylate cyclase inhibitor) or tetraethylammonium (5mmol/L, a potassium channel blocker). T4MN abolished the CaCl2 -induced contractions in pulmonary artery preparations stimulated with phenylephrine (PHE) under Ca2+ -free conditions in the presence of verapamil, to preferentially activate receptor-operated calcium channels. From these findings, we propose that T4MN evokes endothelium-independent vasorelaxant effects in isolated rat pulmonary artery, partially by inhibiting Ca2+ influx through L-type Ca2+ channels, as well as by activating soluble guanylate cyclase and potassium channels. The present results suggest the therapeutic potential of T4MN in treating pulmonary arterial hypertension.

Prostanoid receptor subtypes involved in treprostinil-mediated vasodilation of rat pulmonary arteries and in treprostinil-mediated inhibition of collagen gene expression of human lung fibroblasts

Treprostinil (TRE) is a potent pulmonary vasodilator with effects on other pathological aspects of pulmonary arterial hypertension. In this study, the prostanoid receptors involved in TRE-induced relaxation of isolated rat pulmonary arteries and TRE-induced inhibition of increased gene expression in collagen synthesis and contractility of human lung fibroblasts were determined. TRE (0.01−100 μM) relaxed prostaglandin F2α-precontracted rat pulmonary arteries which was attenuated by denudation of the vascular endothelium. TRE-induced relaxation was predominantly blocked by the IP receptor antagonist RO3244194 (1 μM), with slightly greater inhibition in endothelium-denuded tissue. At higher TRE concentrations (> 1 μM), the DP1 receptor antagonist BW A868C (1 μM) also inhibited relaxation reaching significance above 10 μM. In contrast, the EP3 receptor antagonist L798106 (1 μM) accentuated TRE-induced relaxation of pulmonary arteries with intact endothelium. In human lung fibroblasts, the EP2 receptor antagonist PF-04418948 (1 μM) blocked transforming growth factor β1 (TGF-β1)-increased expression of collagen synthesis (COL1A1 and COL1A2) and fibroblast contractility (ACTG2) genes in presence of TRE (0.1 μM). In conclusion, the IP receptor located on rat pulmonary vascular smooth muscle and endothelium is the primary receptor mediating vasorelaxation, while the DP1 receptor present on the rat endothelium is involved only at higher TRE concentrations. In human lung fibroblasts, the EP2 receptor is the dominant receptor subtype involved in suppression of increased collagen synthesis and fibroblast contractility gene expression induced by TGF-β1 in the presence of TRE.

Pharmacological characterization of a highly selective Rho kinase (ROCK) inhibitor and its therapeutic effects in experimental pulmonary hypertension

Studies on the role of Rho-associated protein kinase (ROCK) in experimental pulmonary artery hypertension (PAH) relies mainly on the use of pharmacological inhibitors. However, interpreting these data is hampered by the lack of specificity of commonly utilized inhibitors. To fill this gap, we have selected and characterized a novel ROCK inhibitor, Compound 3, previously described in a patent. Inhibitory potency of Compound 3 against enzymatic activity of ROCK-1 and 2 (IC50 = 10 ± 3.1 and 7.8 ± 0.5 nM, respectively) was accompanied by a strong vasodilating effect in phenylephrine pre-contracted isolated rat pulmonary artery rings (IC50 = 51.7 ± 9.1 nM) as well as in aortic rings (IC50 = 45.5 ± 1.1 nM). Compound 3 showed a remarkable selectivity towards ROCK 1 and 2 when tested against a large panel (>400) of human kinases. A partial explanation for its selectivity is provided from docking simulations within ROCK-1. Pharmacokinetic studies showed that Compound 3 is suitable for a twice daily administration without significant accumulation upon repeated dosing. In rats with monocrotaline (MCT)-induced pulmonary hypertension, therapy with Compound 3, (1 and 3 mg/kg, s.c., b.i.d.), started 14 days after induction of the disease, attenuated right ventricle systolic pressure (RVSP) increase. Morphometric histological analysis showed that Compound 3, at both doses, counteracted MCT-induced medial thickening of lung distal arterioles with an effect comparable to macitentan (10 mg/kg, p.o., q.d.). Compound 3 is a potent and highly selective ROCK inhibitor that ameliorates hemodynamic parameters and counteracts pulmonary vascular remodeling in experimental PAH.

Hypoxia Triggers SENP1 (Sentrin-Specific Protease 1) Modulation of KLF15 (Kruppel-Like Factor 15) and Transcriptional Regulation of Arg2 (Arginase 2) in Pulmonary Endothelium.

KLF15 (Kruppel-like factor 15) has recently been shown to suppress activation of proinflammatory processes that contribute to atherogenesis in vascular smooth muscle, however, the role of KLF15 in vascular endothelial function is unknown. Arginase mediates inflammatory vasculopathy and vascular injury in pulmonary hypertension. Here, we tested the hypothesis that KLF15 is a critical regulator of hypoxia-induced Arg2 (arginase 2) transcription in human pulmonary microvascular endothelial cells (HPMEC). Quiescent HPMEC express ample amounts of full-length KLF15. HPMECs exposed to 24 hours of hypoxia exhibited a marked decrease in KLF15 protein levels and a reciprocal increase in Arg2 protein and mRNA. Chromatin immunoprecipitation indicated direct binding of KLF15 to the Arg2 promoter, which was relieved with HPMEC exposure to hypoxia. Furthermore, overexpression of KLF15 in HPMEC reversed hypoxia-induced augmentation of Arg2 abundance and arginase activity and rescued nitric oxide (NO) production. Ectopic KLF15 also reversed hypoxia-induced endothelium-mediated vasodilatation in isolated rat pulmonary artery rings. Mechanisms by which hypoxia regulates KLF15 abundance, stability, and compartmentalization to the nucleus in HPMEC were then investigated. Hypoxia triggered deSUMOylation of KLF15 by SENP1 (sentrin-specific protease 1), and translocation of KLF15 from nucleus to cytoplasm. KLF15 is a critical regulator of pulmonary endothelial homeostasis via repression of endothelial Arg2 expression. KLF15 abundance and nuclear compartmentalization are regulated by SUMOylation/deSUMOylation-a hypoxia-sensitive process that is controlled by SENP1. Strategies including overexpression of KLF15 or inhibition of SENP1 may represent novel therapeutic targets for pulmonary hypertension.

Chloroquine is a potent pulmonary vasodilator that attenuates hypoxia-induced pulmonary hypertension.

Sustained pulmonary vasoconstriction and excessive pulmonary vascular remodelling are two major causes of elevated pulmonary vascular resistance in patients with pulmonary arterial hypertension. The purpose of this study was to investigate whether chloroquine induced relaxation in the pulmonary artery (PA) and attenuates hypoxia-induced pulmonary hypertension (HPH). Isometric tension was measured in rat PA rings pre-constricted with phenylephrine or high K+ solution. PA pressure was measured in mouse isolated, perfused and ventilated lungs. Fura-2 fluorescence microscopy was used to measure cytosolic free Ca2+ concentration levels in PA smooth muscle cells (PASMCs). Patch-clamp experiments were performed to assess the activity of voltage-dependent Ca2+ channels (VDCCs) in PASMC. Rats exposed to hypoxia (10% O2 ) for 3weeks were used as the model of HPH or Sugen5416/hypoxia (SuHx) for in vivo experiments. Chloroquine attenuated agonist-induced and high K+ -induced contraction in isolated rat PA. Pretreatment with l-NAME or indomethacin and functional removal of endothelium failed to inhibit chloroquine-induced PA relaxation. In PASMC, extracellular application of chloroquine attenuated store-operated Ca2+ entry and ATP-induced Ca2+ entry. Furthermore, chloroquine also inhibited whole-cell Ba2+ currents through VDCC in PASMC. In vivo experiments demonstrated that chloroquine treatment ameliorated the HPH and SuHx models. Chloroquine is a potent pulmonary vasodilator that may directly or indirectly block VDCC, store-operated Ca2+ channels and receptor-operated Ca2+ channels in PASMC. The therapeutic potential of chloroquine in pulmonary hypertension is probably due to the combination of its vasodilator, anti-proliferative and anti-autophagic effects.

Chloroquine Is a Potent Pulmonary Vasodilator that Attenuates Hypoxia‐Induced Pulmonary Hypertension

Sustained pulmonary vasoconstriction and excessive pulmonary vascular wall thickening are two major causes for elevated pulmonary vascular resistance and pulmonary arterial pressure in patients with pulmonary arterial hypertension. Chloroquine, as an anti‐malaria agent, is found to have inhibitory effects on autophagy and a relaxant effect on airway smooth muscle cells. In this study, we observed that chloroquine (100–200 μM) significantly attenuates agonist‐ and high K+‐induced contraction in isolated rat pulmonary artery (PA). Pretreatment with L‐NAME or indomethacin and functional removal of endothelium failed to inhibit chloroquine‐induced relaxation in isolated PA rings pre‐constricted with phenylephrine or 40 mM K+. In pulmonary arterial smooth muscle cells (PASMCs), extracellular application of chloroquine significantly attenuated store‐operated Ca2+ entry induced by passive depletion of intracellularly stored Ca2+ in the sarcoplasmic reticulum using cyclopiazonic acid and partially inhibited ATP‐induced Ca2+ entry. Furthermore, chloroquine was shown to effectively attenuate Ca2+ entry via voltage‐dependent Ca2+ channels (VDCC). In vivo experiments showed that 50mg/kg chloroquine treatment (ip injections) significantly attenuated the development of pulmonary hypertension in rats exposed to chronic hypoxia (10% O2 for 3 weeks). These data indicate that chloroquine is a potent vasodilator of PA and a potential blocker of VDCC, store‐operated Ca2+ channels and receptor‐operated Ca2+ channels in PASMCs. The therapeutic potential of chloroquine on pulmonary hypertension is likely due to the combination of its vasodilative, anti‐proliferative and anti‐autophagic effects.Support or Funding InformationThis work was supported in part by the grants from the National Natural Science Foundation of China (81630004, 81470246, 81220108001, 81520108001), Guangzhou Department of Education Yangcheng Scholarship (12A001S), and Guangdong Province Universities, Colleges Pearl River Scholar Funded Scheme of China and China Scholarship Council (201608440324), as well as from the National Heart, Lung and Blood Institute of the National Institutes of Health (HL115014, HL066012).

YIA 03-10 ENDOTHELIAL KRUPPEL-LIKE FACTOR 15

Objective: Kruppel Like Factor 15 (KLF15) has recently been shown to be critical for activation of proinflammatory processes in vascular smooth muscle and atherogenesis. Although KLF15 is abundantly expressed in vascular endothelium there is a significant lack of knowledge regarding the role of KLF15 in the regulation of vascular endothelial function. Here we tested the hypothesis that KLF15 is a critical regulator of Arg2 transcription in hypoxia exposed human pulmonary microvascular endothelial cells (HPMEC) and that it plays critical role in pathogenesis of pulmonary hypertension (PHTN). Design and Method: Overexpression and Knockdown of KLF15 in HPMEC was acheived by transducing cells by adenoviruses encoding KLF15 cDNA and shRNA respectively. Pulmonary endothelial dysfunction was assessed by determining a. Nitric Oxide release by Siever's NO analyzer, b. superoxide production by luminol based chemiluminescence and c. acetylcholine dependent pulmonary artery relaxation measured by wire-myography. Interaction between Arg2 promoter and KLF15 was determined by Chromatin immunoprecipitation. Results: Increased expression of KLF15 in human pulmonary microvascular endothelial cells (HPMEC) and in rat pulmonary arteries decreased Arg2 mRNA, protein, and activity. HPMECs exposed to 48 hours of hypoxia, a potent stimulus for PHTN, exhibited a robust increase in Arg2 protein and mRNA expression and a reciprocal decrease in KLF15 protein levels that remain sustained after 24 hours of reoxygenation. ChIP assay indicated direct binding of KLF15 to the Arg2 promoter, which was relieved when HPMEC were exposed to hypoxia, Finally, overexpression of KLF15 reversed hypoxia-induced augmentation of arginase activity and decrements in Nitric Oxide production in HPMEC, and also reversed hypoxia-induced endothelial dysfunction in isolated rat pulmonary artery rings. Conclusions: KLF15 is a critical regulator and repressor of endothelial Arg2 expression, and thereby, NO and pulmonary endothelial function. Overexpression or activation of KLF15 may represent novel therapeutic strategies for pulmonary hypertension.

Hypoxic pulmonary vasoconstriction in isolated rat pulmonary arteries is not inhibited by antagonists of H2 S-synthesizing pathways.

An increase in the H2S (hydrogen sulphide, hereafter sulphide) concentration in pulmonary artery smooth muscle cells (PASMCs) has been proposed to mediate hypoxic pulmonary vasoconstriction (HPV). We evaluated this hypothesis in isolated rat intrapulmonary arteries (IPAs) by examining the effects of the sulphide precursor cysteine and sulphide-synthesis blockers on HPV and also on normoxic pulmonary vasoconstriction (NPV) stimulated by prostaglandin F2α (PGF2α) and by the drug LY83583, which causes contraction in IPAs by increasing cellular reactive oxygen species levels. Experiments with several blockers of cystathionine γ-lyase (CSE), the enzyme responsible for sulphide synthesis in the vasculature, demonstrated that propargylglycine (PAG, 1 mm) had little or no effect on the NPV caused by PGF2α or LY83583. Conversely, other CSE antagonists tested, aminooxyacetic acid (AOAA, 100 μm), β-cyanoalanine (BCA, 500 μm) and hydroxylamine (HA, 100 μm), altered the NPV to PGF2α (BCA increased, HA inhibited) and/or LY83583 (BCA increased, AOAA and HA inhibited). Preincubating IPAs in physiological saline solution (PSS) containing 1 mm cysteine increased the amplitude of the NPV to PGF2α by ∼50%, and had a similar effect on HPV elicited by hypoxic challenge with 0% O2. The enhancement of both responses by cysteine was abolished by pretreatment with 1 mm PAG. Measurements carried out with an amperometric electrode demonstrated that incubation with 1 mm cysteine under anoxic conditions (to minimize sulphide oxidation) greatly potentiated the release of sulphide from pieces of rat liver and that this release was strongly antagonized by PAG, indicating that at this concentration PAG could enter cells intact and antagonize CSE. PAG at 1 mm had no effect on HPV recorded in control PSS, or in PSS supplemented with physiological concentrations of cysteine (10 μm), cystine (50 μm) and glutamate (100 μm) in order to prevent the possible depletion of intracellular cysteine during experiments. Application of a combination of 1 mm cysteine and 1 mm α-ketoglutarate to promote sulphide synthesis via the cysteine aminotransferase/mercaptopyruvate sulphurtransferase (CAT/MST) pathway caused an increase in HPV similar to that observed for cysteine. This was partially blocked by the CAT antagonist aspartate (1 mm) and also by PAG. However, HPV was not increased by 1 mm α-ketoglutarate alone, and HPV in the absence of α-ketoglutarate and cysteine was not attenuated by aspartate. Pretreatment of IPAs with dithiothreitol (DTT, 1 mm), proposed to promote the conversion of mitochondrial thiosulphate to sulphide, did not increase the release of sulphide from pieces of rat liver in either the presence or the absence of 1 mm cysteine, and virtually abolished HPV. The results provide evidence that the sulphide precursor cysteine can promote both NPV and HPV in rat IPA by generating sulphide via a PAG-sensitive pathway, presumably CSE. However, HPV evoked under control conditions was unaffected by the blockade of CSE. Moreover, HPV was not affected by the CAT antagonist aspartate and was blocked rather than enhanced by DTT. The data therefore indicate that sulphide generated by CSE or CAT/MST or from thiosulphate is unlikely to contribute to O2 sensing during HPV in these arteries.

Potentiation of Hypoxic Pulmonary Vasoconstriction by Hydrogen Sulfide Precursors 3-Mercaptopyruvate and D-Cysteine Is Blocked by the Cystathionine γ Lyase Inhibitor Propargylglycine.

Although the gasotransmitter hydrogen sulfide (H(2)S) generally dilates systemic arteries in mammals, it causes constriction of pulmonary arteries. In isolated rat pulmonary arteries, we have shown that the H(2)S precursor cysteine enhances both hypoxic pulmonary vasoconstriction and tension development caused by the agonist prostaglandin F(2α) under normoxic conditions. These effects were blocked by propargylglycine (PAG), a blocker of the enzyme cystathionine γ lyase which metabolises cysteine to sulfide. In the present study, we evaluated whether 3-mercaptopyruvate (3-MP), a sulfide precursor which is thought to give rise to sulfide when it is metabolised by the enzyme mercaptopyruvate sulfurtransferase, also enhanced contraction. Application of 3-MP prior to hypoxic challenge caused a marked enhancement of HPV which was completely blocked by both L- and D,L-PAG (both 1 mM). Cumulative application of 3-1,000 μM 3-MP during an ongoing contraction to PGF(2α) under normoxic conditions also caused a marked increase in tension. Application of D-cysteine (1 mM) also enhanced HPV, and this effect was prevented by both the D-amino acid oxidase inhibitor sodium benzoate (500 μM) and 1 mM L-PAG.

Dehydroabietic acid isolated from Commiphora opobalsamum causes endothelium-dependent relaxation of pulmonary artery via PI3K/Akt-eNOS signaling pathway.

Commiphora opobalsamum is a Traditional Chinese Medicine used to treat traumatic injury, mainly by relaxing blood vessels. In this study, two diterpenes, dehydroabietic acid (DA) and sandaracopimaric acid (SA) were obtained from it by a bioassay-guided approach using isolated rat pulmonary artery rings. The structures of the two compounds were elucidated by spectroscopic methods (IR, 1H- and 13C-NMR, HR-ESI-MS). Both DA and SA reduced the contraction of phenylephrine-induced pulmonary arteries in a concentration-dependent manner, and endothelium contributed greatly to the vasodilatory effect of DA. This effect of DA was attenuated by NG-Nitro-L-arginine methyl ester (L-NAME, an eNOS inhibitor). Meanwhile, DA increased nitric oxide (NO) production, along with the increase of phosphorylation level of eNOS and Akt in endothelial cells. LY294002 (a PI3K inhibitor) could reverse this effect, which suggested the endothelial PI3K/Akt pathway involved in the mechanism underlying DA-induced relaxation of pulmonary artery. This work provided evidence of vasorelaxant substances in Commiphora opobalsamum and validated that PI3K/Akt-eNOS pathway was associated with DA-induced pulmonary artery vasodilation.

Influence of TNF‐α on vasodilation of isolated rat pulmonary artery rings (1106.17)

Inflammation promotes endothelial damage leading to vascular smooth muscle cell (VSMC) hyperplasia, vasoconstriction, and vascular remodelling resulting in an increased pulmonary arterial pressure¹. As TNF‐α decreases the bioavailability of NO in systemic vessels, we investigated the effects of TNF‐α on vasodilation in isolated pulmonary arteries (PA).PA segments were isolated from terminally‐anaesthetised Wistar rats and vessel rings were pre‐incubated in DMEM (+/‐ TNF‐α, 1000U/mL) for 2 or 6 hours before mounting on a wire myograph. U46691 (400nM) was used to generate pre‐tone and cumulative dose‐response curves generated for carbachol (CC) and sodium nitroprusside (SNP). Data was normalised to maximal KCl contraction and significance taken as P<0.05.Responses to KCl and U46691 were not significantly different between control and TNF‐α treatments. CC and SNP relaxed pre‐constricted rings but TNF‐α treated rings were significantly less responsive at all doses of either CC or SNP. No difference was noticed between 2 or 6 hours of TNF‐α treatments.This data suggests that TNF‐α pre‐treatment had no effect on the VSMC vasoconstrictor ability but does alter the dilator response to NO.

Telmisartan attenuates monocrotaline-induced pulmonary artery endothelial dysfunction through a PPAR gamma-dependent PI3K/Akt/eNOS pathway

BackgroundPulmonary artery endothelial dysfunction has been demonstrated in pulmonary arterial hypertension (PAH). Telmisartan has beneficial effects in endothelial function in PAH patients; however, the underlying mechanisms for these effects remain unknown. AimsIn this study, we observed the effects of telmisartan on monocrotaline (MCT)-induced Sprague Dawley (SD) rat model of PAH. MethodsAfter a single-dose injection of MCT (60 mg/kg), oral administration of telmisartan (10 mg/kg/d) was started from day 1 to day 28 or with saline as MCT control. The vasorelaxation and remodelling of pulmonary arteries; the expression of peroxisome proliferator-activated receptor γ (PPARγ), Akt, eNOS; levels of phosphorylation of Akt (p-Akt) and phosphorylation of eNOS (p-eNOS) were analysed in isolated rat pulmonary arteries and cultured human pulmonary artery endothelial cells (HPAECs). ResultsCompared to MCT control group, telmisartan treatment ameliorated pulmonary artery endothelial dysfunction and remodelling, prevented the elevation of right ventricular systolic pressure (RVSP) induced by MCT. Immunoblotting results indicated lower levels of PPARγ, p-Akt and p-eNOS in pulmonary arteries treated with MCT alone and levels were significantly restored by co-treatment with telmisartan. In isolated pulmonary arteries, the impaired endothelium-dependent vasorelaxation of pulmonary arteries was improved following incubation with telmisartan for 12 h, whereas this effect was blocked by the inhibition of either PPARγ or phosphoinositide 3-kinase (PI3K) signals transduction. In cultured HPAECs, treatment with telmisartan increased PPARγ expression and promoted the phosphorylation of Akt and eNOS, thereby increasing the production of NO. These effects were abolished by the inhibition of PPARγ or PI3K. ConclusionTelmisartan protected against endothelial dysfunction in MCT-induced PAH through a PPARγ-dependent PI3K/Akt/eNOS pathway. Thus, telmisartan may be a promising therapeutic strategy for patients with a high risk of PAH.

Endothelium-dependent mechanisms of the vasodilatory effect of the endocannabinoid, anandamide, in the rat pulmonary artery

Endocannabinoids exhibit vasodilatory properties and reduce blood pressure in vivo. However, the influence and mechanism of action of the prominent endocannabinoid, anandamide (AEA), in pulmonary arteries are not known. The present study determined the vascular response to AEA in isolated rat pulmonary arteries. AEA relaxed rat pulmonary arteries that were pre-constricted with U-46619. This relaxation was reduced by the following conditions:removal of the endothelium; in KCl pre-constricted preparations; in the presence of the potassium channel (KCa) blockers, tetraethylammonium and the combination of charybdotoxin and apamin, and the prostacyclin receptor antagonist, RO1138452. Inhibitors of cyclooxygenase (indomethacin), nitric oxide (NO) synthase (NG-nitro-l-arginine methyl ester) and fatty acid amide hydrolase (URB597) alone or in combination diminished AEA-induced relaxation in endothelium-intact vessels. The remaining experiments were performed in the presence of URB597 to eliminate the influence of AEA metabolites. Antagonists of the endothelial cannabinoid receptor (CBx), O-1918 and cannabidiol, attenuated the AEA-induced response. Antagonists of CB1, CB2 and TRPV1 receptors, AM251, AM630 and capsazepine, respectively, did not modify the AEA-induced response. A reference activator of CBx receptors, abnormal cannabidiol, mimicked the receptor-mediated AEA effects. The present study demonstrated that AEA relaxed rat pulmonary arteries in an endothelium-dependent fashion via the activation of the O-1918-sensitive CBx receptor and/or prostacyclin-like vasoactive products of AEA. One or both of these mechanisms may involve KCa or the NO pathway.

Cellular mechanisms and intracellular signaling pathways for the modulation of eNOS in pulmonary arteries by 15-HETE

The 15-hydroxyeicosatetraenoic acid (15-HETE), a lipid metabolite and vasoconstrictor, plays an important role in hypoxic contraction of pulmonary arteries (PAs) through working on smooth muscle cells (SMCs). Previous studies have shown that vascular endothelium is also involved in PAs tone regulation. However, little is known as to how the pulmonary artery endothelial cells (PAECs) are related to the 15-HETE-induced vasoconstriction and that which intracellular signaling systems are critical. To test this hypothesis, we examined PAs constriction in isolated rat PAs rings, the expression and activity of endothelial nitric oxide synthase (eNOS) with western blot, and nitric oxide (NO) production using the DAF-FM DA fluorescent indicator. The results showed that the 15-HETE-induced PAs constriction was diminished in endothelium-intact rings. In the presence of the eNOS inhibitor L-NAME, vasoconstrictor responses to KCl were greater than the control. The activation of eNOS was activated by Ca2+ released from intracellular stores and the PI3K/Akt pathway. Phosphorylations of the eNOS at Ser-1177 and Akt at Ser-473 were necessary for their activity. A prolonged 15-HETE treatment (30 min) led to a decrease in NO production by phosphorylation of eNOS at Thr-495, leading to augmentation of PAs constriction. Therefore, 15-HETE initially inhibited the PAs constriction through the endothelial NO system, and both Ca2+ and the PI3K/Akt signaling systems are required for the effects of 15-HETE on PAs tone regulation.

Abstract 16945: Role of Thromboxane A 2 -Activated Nonselective Cation Channels in Hypoxic Pulmonary Vasoconstriction of Rat

Hypoxia-induced pulmonary vasoconstriction (HPV) is a physiological mechanism responsible for controlling the ventilation-perfusion ratio in the lungs. Maintenance of the ventilation-perfusion ratio at 0.8-1 is critical for the optimization and maximization of gas exchange in the lung. Inhibition of K + channels has been shown to be a mechanism for hypoxia-induced membrane depolarization in pulmonary arterial smooth muscle cells (PASMCs). Pharmacological inhibition of K + channels, however, does not induce significant contraction in isolated rat pulmonary arteries, but significantly enhances HPV. These results suggest that, in addition to K + channel inhibition, other mechanisms are involved in hypoxia-induced membrane depolarization. We recently found that a partial contraction by thromboxane A 2 (TXA 2 ) is required to induce HPV. Therefore we hypothesize that TXA 2 receptor (TP) stimulation is involved in eliciting membrane polarization by activating nonselective cation (NSC) channels. Consistently, we found that 5-10 nM U46619, a stable agonist of TP, was essential for the contraction of isolated rat pulmonary arteries by 4-aminopyridine, a blocker of voltage-gated K + channel (Kv). Whole-cell voltage clamp experiments with rat PASMCs revealed that U46619 induced a weakly outward-rectifying NSC current (I NSC,TXA2 ), which was blocked by ruthenium red (RR), an antagonist of the transient receptor potential vanilloid (TRPV) subfamily. In addition, 2-aminoethoxydiphenyl borate, an agonist for TRPV1-3, activated NSC channels. In contrast, agonists for TRPV1 (capsaicin), TRPV3 (camphor), or TRPV4 (4α-PDD) rarely increased the membrane conductance. RT-PCR analysis showed the expression of transcripts for TRPV2 and TRPV4 in rat PASMCs. Finally, it was confirmed that the pretreatment with RR and tranilast (a TRPV2 inhibitor) both significantly inhibited HPV in the presence of U46619. Taken together, these data suggest that the concerted effects of I NSC,TXA2 increase and Kv inhibition during under hypoxia are required to induce membrane depolarization sufficient for eliciting HPV. Our results also imply that TXA 2 -activated NSC might be formed by TRPV2 in rat PASMCs and contribute to the hypoxia-induced membrane depolarization in PASMCs.