Nitric oxide impacts endothelin-1 gene expression in intrapulmonary arteries of chronically hypoxic rats

End o' the line revisited: moving on from nitric oxide to CGRP

When endothelin-1(ET-1) was discovered it was hailed as the prototypical endothelium-derived contracting factor (EDCF). However, over the years little evidence emerged convincingly demonstrating that the peptide actually contributes to moment-to-moment changes in vascular tone elicited by endothelial cells. This has been attributed to the profound inhibitory effect of nitric oxide (NO) on both the production (by the endothelium) and the action (on vascular smooth muscle) of ET-1. Hence, the peptide is likely to initiate acute changes in vascular diameter only under extreme conditions of endothelial dysfunction when the NO bioavailability is considerably reduced if not absent. The present essay discusses whether or not this concept should be revised, in particular in view of the potent inhibitory effect exerted by calcitonin gene related peptide (CGRP) released from sensorimotor nerves on vasoconstrictor responses to ET-1.

Effects of endogenous sulfur dioxide on monocrotaline-induced pulmonary hypertension in rats

AIM

The present study aimed to explore the protective effect of endogenous sulfur dioxide (SO2) in the development of monocrotaline (MCT)-induced pulmonary hypertension (PH) in rats.

METHODS

Forty Wistar rats were randomly divided into the MCT group receiving MCT treatment, the MCT+L-aspartate-beta- hydroxamate (HDX) group receiving MCT plus HDX treatment, the MCT+SO2 group receiving MCT plus SO2 donor treatment, and the control group. Mean pulmonary artery pressure (mPAP) and structural changes in pulmonary arteries were evaluated. SO2 content, aspartate aminotransferase activity, and gene expression were measured. Superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT), reduced glutathione (GSH), oxidized glutathione, and malondialdehyde (MDA) levels were assayed.

RESULTS

In the MCT-treated rats, mPAP and right ventricle/(left ventricle+septum) increased significantly (P<0.01), pulmonary vascular structural remodeling developed, and SOD, GSHPx, CAT, GSH, and MDA levels of lung homogenates significantly increased (P<0.01) in association with the elevated SO2 content, aspartate aminotransferase activity, and gene expression, compared with the control rats. In the MCT+HDXtreated rats, lung tissues and plasma SO2 content and aspartate aminotransferase activities decreased significantly, whereas the mPAP and pulmonary vascular structural remodeling were markedly aggravated with the decreased SOD, CAT, and GSH levels of lung tissue homogenates compared with the MCT-treated rats (P<0.01). In contrast, with the use of a SO2 donor, the pulmonary vascular structural remodeling was obviously lessened with elevated lung tissue SOD, GSH-Px, and MDA content, and plasma SOD, GSH-Px, and CAT levels.

CONCLUSION

Endogenous SO2 might play a protective role in the pathogenesis of MCT-induced PH and promote endogenous antioxidative capacities.

Changes in pulmonary arteriole protein kinase cαexpression associated with supplementalL-arginine in broilers during cool temperature exposure

The present study was conducted to examine the effect of supplemental L-arginine on pulmonary arteriole protein kinase Calpha (PKCalpha) expression in broilers exposed to cool temperature, to investigate further the molecular mechanisms of supplemental L-arginine on modulating pulmonary vascular functions in hypertensive broilers. Broilers were subjected to sub-thermoneutral (cool) temperature to induce pulmonary hypertension syndrome (PHS), and an additional 10 g/kg L-arginine was added to the basal diet to evaluate the effects of supplemental L-arginine on PHS mortality, plasma nitric oxide (NO) production and pulmonary arterioles PKCalpha expression. Supplemental L-arginine reduced PHS mortality but did not affect right/total ventricle (RV/TV) ratios in clinically healthy birds. Birds fed additional L-arginine had increased plasma NO and decreased PKCalpha protein expression in pulmonary arterioles; NO production was negatively correlated with PKCalpha expression. These results demonstrated that supplemental L-arginine diminished PKCalpha expression in birds exposed to cool temperature. It is suggested that NO-induced loss of PKCalpha expression might be partially responsible for its effects on dilating pulmonary vasculature and inhibiting pulmonary vascular remodelling in vivo.

Effect of L-arginine on pulmonary artery smooth muscle cell apoptosis in rats with hypoxic pulmonary vascular structural remodeling

This study investigated the effect of L-arginine (L-Arg) on the apoptosis of pulmonary artery smooth muscle cells (PASMC) in rats with hypoxic pulmonary vascular structural remodeling, and its mechanisms. Seventeen Wistar rats were randomly divided into a control group (n=5), a hypoxia group (n=7), and a hypoxia+L-Arg group (n=5). The morphologic changes of lung tissues were observed under optical microscope. Using the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin nick end labeling assay, the apoptosis of PASMC was examined. Fas expression in PASMC was examined using immunohistochemistry. The results showed that the percentage of muscularized artery in small pulmonary vessels, and the relative medial thickness and relative medial area of the small and median pulmonary muscularized arteries in the hypoxic group were all significantly increased. Pulmonary vascular structural remodeling developed after hypoxia. Apoptotic smooth muscle cells of the small and median pulmonary arteries in the hypoxia group were significantly less than those in the control group. After 14 d of hypoxia, Fas expression by smooth muscle cells of median and small pulmonary arteries was significantly inhibited. L-Arg significantly inhibited hypoxic pulmonary vascular structural remodeling in association with an augmentation of apoptosis of smooth muscle cells as well as Fas expression in PASMC. These results showed that L-Arg could play an important role in attenuating hypoxic pulmonary vascular structural remodeling by upregulating Fas expression in PASMC, thus promoting the apoptosis of PASMC.

Endothelin-A receptor blockade and inhaled nitric oxide in a porcine model of meconium aspiration syndrome

Acute neonatal pulmonary hypertension is associated with increased activation of the endogenous endothelin pathway. We investigated the role of selective endothelin-A receptor blockade using i.v. BQ-123 in a piglet model of meconium aspiration syndrome. Meconium aspiration was induced in 18 anesthetized piglets. Six controls received no further intervention. Six piglets received 1 mg/kg BQ-123 at 120 min, with the addition of 20 ppm inhaled nitric oxide at 240 min. Six commenced nitric oxide therapy at 120 min, and were given i.v. BQ-123 at 240 min. The total study duration was 360 min. Meconium aspiration resulted in acute pulmonary hypertension and elevated endothelin-1 levels in all animals. There were no changes in pulmonary hemodynamics or endothelin-1 levels beyond 120 min in controls. In the group receiving BQ-123 first, this agent alone reduced the pulmonary artery pressure and pulmonary vascular resistance, and the subsequent addition of inhaled nitric oxide further reduced pulmonary artery pressure. In the group first receiving nitric oxide alone, this reduced the pulmonary artery pressure, and the addition of BQ-123 resulted in a fall in pulmonary vascular resistance. Endothelin-1 levels increased with both agents. BQ-123 was found to be a highly effective pulmonary vasodilator and augmented the effects of nitric oxide in this model of acute pulmonary hypertension.

Impact of hydrogen sulfide on carbon monoxide/heme oxygenase pathway in the pathogenesis of hypoxic pulmonary hypertension

Hypoxic pulmonary hypertension (HPH) is an important pathophysiological process of a variety of cardiac and pulmonary diseases. But the mechanisms responsible for HPH are still not fully understood. The discoveries of endogenous gas signal molecules, nitric oxide (NO), and carbon monoxide (CO), have been moving the research of HPH to a new phase. Hydrogen sulfide (H2S), which is now being considered as the third new gas transmitter, was found to be possibly involved in the pathogenesis of HPH. But whether there exists an interaction between H2S and CO has not been clear in the pathogenesis of HPH. In this study, we found that H2S was significantly decreased in the pathogenesis of HPH. However, plasma CO level and the expressions of heme oxygenase (HO-1) protein and HO-1 mRNA were significantly increased. Exogenous supply of H2S could alleviate the elevation of pulmonary arterial pressure. At the same time, plasma CO level and the expressions of HO-1 protein and mRNA in pulmonary arteries were significantly increased. Whereas, exogenous supply of propargylglycine (PPG), an inhibitor of cystathionine gamma-lyase (CSE), decreased the plasma H2S content and worsened HPH. At the same time, plasma CO level and the expressions of HO-1 protein and mRNA in pulmonary arteries were decreased. The results showed that H2S could play a regulatory role in the pathogenesis of HPH through up-regulating CO/HO pathway.

The regulating effect of heme oxygenase/carbon monoxide on hypoxic pulmonary vascular structural remodeling

Hypoxic pulmonary vascular structural remodeling (HPVSR) is the important pathologic basis of hypoxic pulmonary hypertension (HPH). The discoveries of endogenous gaseous messenger molecules, nitric oxide (NO) and carbon monoxide (CO), have been moving the research of HPVSR to a very new phase. But the effect and significance of heme oxygenase (HO)/CO on the development of HPVSR have not been fully understood. In this study, we observed the alteration of endogenous HO/CO system in five time points during 14 days and found that the content of CO in lung homogenates in rats with HPVSR increased in a time-dependent double-peak manner. Exogenous supply of ZnPP-IX, an inhibitor of HO-1, decreased the content of CO in lung homogenate, decreased the expression of Fas and apoptotic cells in pulmonary artery smooth muscle cells (PASMCs), up-regulated the expression of PCNA in PASMCs, and worsened HPH and HPVSR of hypoxic rats. Meanwhile, exogenous supply of CO played an adverse action. The results showed that the up-regulation of HO/CO exerted a protective role in the development of HPVSR.

Endothelin-1 directly modulates its own secretion: studies utilising the cell immunoblot technique

Endothelin-1 is an important factor in vasoregulation and circulating levels of the peptide are increased in a number of cardiovascular disorders. However, control of endothelin-1 secretion is only sketchily understood. The possibility that endothelin-1 influences its own release was investigated. A cell immunoblot method, which can detect local secretion of peptide from individual human vascular endothelial cells, was employed. Cells were dispersed onto a protein-binding membrane. Endothelin-1 in cells or secreted and adhering to the protein-binding membrane outside the cells was detected using immunohistochemical techniques. The numbers of cells that contained endothelin-1 and secreted endothelin-1 were counted after the cells had been incubated in control conditions, or with added endothelin-1, angiotensin-II, or endothelin receptor antagonists, bosentan and BQ788. Endothelin-1 and angiotensin-II increased the numbers of cells that secreted endothelin-1. On the other hand, bosentan and BQ788 caused a reduction in the numbers of endothelin-1-secreting cells. These results indicate that human endothelial cells contain a pathway by which endothelin-1 induces its own release. The receptor antagonists, bosentan and BQ788, inhibited basal secretion of endothelin-1.

Inhaled nitric oxide increases endothelin-1 levels: a potential cause of rebound pulmonary hypertension

OBJECTIVE

Inhaled nitric oxide (iNO) is front-line therapy for pulmonary hypertension after repair of congenital heart disease. However, little clinical data exists regarding the effects of iNO on regulators of pulmonary vascular resistance. An imbalance between primary vasodilators, such as NO, and vasoconstrictors, such as endothelin-1 (ET-1), has been implicated in rebound pulmonary hypertension upon iNO withdrawal. The objective of this study was to determine whether iNO therapy alters plasma ET-1 levels.

DESIGN

This is a prospective study involving pediatric and adult patients at risk for pulmonary hypertension.

SETTING

Pediatric patients were in the cardiac intensive care unit and adult patients were in a tertiary-care hospital.

PATIENTS

Group 1 included children with congenital heart disease requiring iNO for treatment of pulmonary hypertension after cardiopulmonary bypass (n = 15), group 2 was adults receiving iNO (n = 10), and group 3 included children at risk for pulmonary hypertension after bypass that did not require iNO (n = 8).

INTERVENTIONS

Dosages of iNO were 2-60 ppm. The duration of therapy ranged from 23 to 188 hrs in group 1 and 29 to 108 hrs in group 2.

MEASUREMENTS AND MAIN RESULTS

Arterial blood was obtained for the measurement of ET-1 levels before and during iNO therapy and 24 hrs after iNO withdrawal. Group 1 mean ET-1 levels increased to 127% of baseline by 12 hrs of iNO, remained elevated at 48 hrs (p < .05), then decreased to 71% of iNO levels 24 hrs after withdrawal (p < .01). Group 2 ET-1 levels increased to 147%, and 137% of baseline at 12 and 24 hrs of iNO therapy, then fell to 68% of baseline within 24 hrs of discontinuing iNO. ET-1 levels in group 3 decreased after surgery (p < .05).

CONCLUSIONS

These data suggest that iNO increased plasma ET-1 levels, which subsequently decreased when iNO was discontinued. Increased circulating ET-1 levels might contribute to rebound pulmonary hypertension upon iNO withdrawal.

An automated high-performance liquid chromatography fluorescence method for the analyses of endothelins in plasma samples

A high-performance liquid chromatographic method with fluorescence detection was developed to simultaneously analyze endothelins, a class of vasoactive peptides, in plasma samples. Sample preparation for HPLC analysis was carried out by initial stabilization of blood and plasma samples against transformation of big endothelins to mature endothelins and breakdown of mature endothelins by serine proteases, as well as oxidative modifications of endothelins. Deproteinization of plasma samples was achieved with acidified acetone, and the samples were further purified on molecular weight cutoff filters. Endothelins were separated on a reversed phase LC-318 column by gradient elution using a mobile phase containing acetonitrile and water (0.1% trifluoroacetic acid) and were analyzed by fluorescence detection (lambda(Ex), 280 nm; lambda(Em), 340). Limit of detection values were in the range of 0.2-0.5 pmol. Linear (R(2), 0.99) calibration curves were established for analyte amounts in the range of 1 to 100 pmols. Recoveries of endothelins from spiked plasma samples analyzed ranged from 60-95%. Under optimized conditions the HPLC-fluorescence method was determined to be sensitive and specific for the analysis of big endothelin-1, endothelin-1, endothelin-2, and endothelin-3 in plasma. Simultaneous measurement of these endothelins by the HPLC method should permit a better understanding of their specific roles and relationships under various pathological conditions.

Pulmonary vascular remodeling: a target for therapeutic intervention in pulmonary hypertension

Pulmonary vascular remodelling is an important pathological feature of pulmonary hypertension, leading to increased pulmonary vascular resistance and reduced compliance. It involves thickening of all three layers of the blood vessel wall (due to hypertrophy and/or hyperplasia of the predominant cell type within each layer), as well as extracellular matrix deposition. Neomuscularisation of non-muscular arteries and formation of plexiform and neointimal lesions also occur. Stimuli responsible for remodelling involve transmural pressure, stretch, shear stress, hypoxia, various mediators [angiotensin II, endothelin (ET)-1, 5-hydroxytryptamine, growth factors, and inflammatory cytokines], increased serine elastase activity, and tenascin-C. In addition, there are reductions in the endothelium-derived antimitogenic substances, nitric oxide, and prostacyclin. Intracellular signalling mechanisms involved in pulmonary vascular remodelling include elevations in intracellular Ca2+ and activation of the phosphatidylinositol pathway, protein kinase C, and mitogen-activated protein kinase. In animal models of pulmonary hypertension, various drugs have been shown to attenuate pulmonary vascular remodelling. These include angiotensin-converting enzyme inhibitors, angiotensin receptor antagonists, ET receptor antagonists, ET-converting enzyme inhibitors, nitric oxide, phosphodiesterase 5 inhibitors, prostacyclin, Ca2+ -channel antagonists, heparin, and serine elastase inhibitors. Inhibition of remodelling is generally accompanied by reductions in pulmonary artery pressure. The efficacy of some of the drugs varies, depending on the animal model of the disease. In view of the complexity of the remodelling process and the diverse aetiology of pulmonary hypertension in humans, it is to be anticipated that successful anti-remodelling therapy in the clinic will require a range of different drug options.

The NO donor molsidomine reduces endothelin-1 gene expression in chronic hypoxic rat lungs

We investigated the effects of the nitric oxide (NO) donor molsidomine and the nitric oxide synthase inhibitor N-nitro-L-arginine methyl ester (L-NAME) on pulmonary endothelin (ET)-1 gene expression and ET-1 plasma levels in chronic hypoxic rats. Two and four weeks of hypoxia (10% O2) significantly increased right ventricular systolic pressure, the medial cross-sectional vascular wall area of the pulmonary arteries, and pulmonary ET-1 mRNA expression (2-fold and 3.2-fold, respectively). ET-1 plasma levels were elevated after 4 wk of hypoxia. In rats exposed to 4 wk of hypoxia, molsidomine (15 mg x kg(-1) x day(-1)) given either from the beginning or after 2 wk of hypoxia significantly reduced pulmonary hypertension, pulmonary vascular remodeling, pulmonary ET-1 gene expression, and ET-1 plasma levels. L-NAME administration (45 mg x kg(-1) x day(-1)) in rats subjected to 2 wk of hypoxia did not modify these parameters. Our findings suggest that in chronic hypoxic rats, exogenously administered NO acts in part by suppressing the formation of ET-1. In contrast, inhibition of endogenous NO production exerts only minor effects on the pulmonary circulation and pulmonary ET-1 synthesis in these animals.

Say NO to ET

The endothelial cells release both relaxing [nitric oxide (NO), endothelium-derived hyperpolarizing factor (EDHF), prostacyclin] and contracting factors [endoperoxides, thromboxane A(2), superoxide anions, endothelin-1 (ET)]. The production of ET is inhibited by NO. The latter also strongly opposes the direct effects of the former on vascular smooth muscle. With aging and vascular disease, the production of enothelial NO declines, and thus ET can be released, act and contribute to the symptoms.