Age-related differences in vasoconstrictor responses to isoprostanes in piglet pulmonary and mesenteric vascular smooth muscle

Isoprostanes evoke contraction of the murine and human detrusor muscle via activation of the thromboxane prostanoid TP receptor and Rho kinase

Local or systemic inflammation can severely impair urinary bladder functions and contribute to the development of voiding disorders in millions of people worldwide. Isoprostanes are inflammatory lipid mediators that are upregulated in the blood and urine by oxidative stress and may potentially induce detrusor overactivity. The aim of the present study was to investigate the effects and signal transduction of isoprostanes in human and murine urinary bladders in order to provide potential pharmacological targets in detrusor overactivity. Contraction force was measured with a myograph in murine and human urinary bladder smooth muscle (UBSM) ex vivo. Isoprostane 8-iso-PGE₂ and 8-iso-PGF_2α evoked dose-dependent contraction in the murine UBSM, which was abolished in mice deficient in the thromboxane prostanoid (TP) receptor. The responses remained unaltered after removal of the mucosa or incubation with tetrodotoxin. Smooth muscle-specific deletion of Gα_12/13 protein or inhibition of Rho kinase by Y-27632 decreased the contractions. In Gα_q/11-knockout mice, responses were reduced and in the presence of Y-27632 abolished completely. In human UBSM, the TP agonist U-46619 evoked dose-dependent contractions. Neither atropine nor the purinergic receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid decreased the effect, indicating that TP receptors directly mediate detrusor muscle contraction. 8-iso-PGE₂ and 8-iso-PGF_2α evoked dose-dependent contraction in the human UBSM, and these responses were abolished by the TP antagonist SQ-29548 and were decreased by Y-27632. Our results indicate that isoprostanes evoke contraction in murine and human urinary bladders, an effect mediated by the TP receptor. The G_12/13-Rho-Rho kinase pathway plays a significant role in mediating the contraction and therefore may be a potential therapeutic target in detrusor overactivity.NEW & NOTEWORTHY Voiding disorders affect millions of people worldwide. Inflammation can impair urinary bladder functions and contribute to the development of detrusor overactivity. The effects and signal transduction of inflammatory lipid mediator isoprostanes were studied in human and murine urinary bladders ex vivo. We found that isoprostanes evoke contraction, an effect mediated by thromboxane prostanoid receptors. The G_12/13-Rho-Rho kinase signaling pathway plays a significant role in mediating the contraction and therefore may be a potential therapeutic target.

Reactive oxygen species as mediators of oxygen signaling during fetal-to-neonatal circulatory transition

Reactive oxygen species (ROS) are frequently seen as pathological agents of oxidative stress. However, ROS are not always deleterious and can also act as cell signaling molecules. Vascular oxygen sensing and signaling during fetal-to-neonatal circulatory transition is a remarkable example of the physiological regulatory actions of ROS. The fetal relative hypoxic environment induces hypoxic pulmonary vasoconstriction (HPV) and ductus arteriosus (DA) relaxation favoring the presence of high pulmonary vascular resistance and right-to-left ductal shunt. At birth, the increase in oxygen tension causes relaxation of pulmonary arteries (PAs) and normoxic DA vasoconstriction (NDAV), thus diverting blood flow to the lungs. Although the response to changes in oxygen tension is diametrically opposite, the mechanisms responsible for HPV and NDAV appear to be the result of a similar interaction between triggering and modulating factors that lead to an increase in cytosolic Ca²⁺ concentration and Ca²⁺ sensitization of the contractile apparatus. Growing evidence points to an increase in ROS (mitochondria- and/or NADPH-derived superoxide and/or H₂O₂), leading to inhibition of voltage-gated K⁺ channels, membrane depolarization, and activation of voltage-gated L-type Ca²⁺ channels as critical events in the signaling pathway of both HPV and NDAV. Several groups of investigators have completed this pathway adding other elements such as neutral sphingomyelinase-derived ceramide, the sarcoplasmic/endoplasmic reticulum (through ryanodine and inositol 1,4,5-trisphosphate receptors), Rho kinase-mediated Ca²⁺ sensitization, or transient receptor potential channels. The present review focus on the role of ROS as mediators of the homeostatic oxygen sensing system during fetal and neonatal life not only in the PAs and DA but also in systemic arteries.

Hypoxic pulmonary hypertension of the newborn

Hypoxic pulmonary hypertension of the newborn is characterized by elevated pulmonary vascular resistance and pressure due to vascular remodeling and increased vessel tension secondary to chronic hypoxia during the fetal and newborn period. In comparison to the adult, the pulmonary vasculature of the fetus and the newborn undergoes tremendous developmental changes that increase susceptibility to a hypoxic insult. Substantial evidence indicates that chronic hypoxia alters the production and responsiveness of various vasoactive agents such as endothelium-derived nitric oxide, endothelin-1, prostanoids, platelet-activating factor, and reactive oxygen species, resulting in sustained vasoconstriction and vascular remodeling. These changes occur in most cell types within the vascular wall, particularly endothelial and smooth muscle cells. At the cellular level, suppressed nitric oxide-cGMP signaling and augmented RhoA-Rho kinase signaling appear to be critical to the development of hypoxic pulmonary hypertension of the newborn.

Developmental changes in mesenteric artery reactivity in embryonic and newly hatched chicks

At birth, the intestine becomes the sole site for nutrient absorption requiring a dramatic increase in blood flow. The vascular changes accompanying this transition have been partly characterized in mammals. We investigated, using wire myography, the developmental changes in chick mesenteric artery (MA) reactivity. Rings of the MA from 15-day (E15) and 19-day (E19) chicken embryos (total incubation 21 days) as well as non-fed 0–3-h-old (NH3h) and first-fed 1-day-old (NH1d) newly hatched chicks contracted in response to KCl, norepinephrine (NE), U46619, and endothelin (ET)-1 and relaxed in response to acetylcholine (ACh), sodium nitroprusside (SNP), and forskolin indicating the presence of electro- and pharmaco-mechanical coupling as well as cGMP- and cAMP-mediated relaxation. In ovo development and transition to ex ovo life was accompanied by alterations in the response of the MAs, but a different developmental trajectory was observed for each reactivity pathway tested. Thus, the contractile efficacy of KCl underwent a linear increase (E15 < E19 < NH3h < NH1d). The efficacy of NE and U46619 increased in ovo, but not ex ovo (E15 < E19 = NH3h = NH1d) and the efficacy of ET-1 peaked at E19 (E15 < E19 > NH3h = NH1d). The relaxations elicited by ACh (endothelium-dependent), SNP, and forskolin did not undergo significant developmental changes. In conclusion, the ability of chick MAs to constrict in response to pharmacological stimuli increases during the embryonic period, but no dramatic changes are induced by hatching or the first feeding. Maturation of vasodilator mechanisms precedes that of vasoconstrictor mechanisms. Alterations of the delicate balance between vasoconstrictors and vasodilators may play an important role in perinatal intestinal diseases.

Contractile effects of 15-E2t-isoprostane and 15-F2t-isoprostane on chicken embryo ductus arteriosus

Isoprostanes (IsoPs) are prostaglandin (PG)-like compounds produced nonenzymatically by free radical-catalyzed peroxidation of arachidonate. Cyclooxygenase-derived PGs play a major role in ductus arteriosus (DA) homeostasis but the putative role of IsoPs has not been studied so far. We investigated, using wire myography, the vasoactive effects of 15-E(2t)-IsoP and 15-F(2t)-IsoP in the chicken embryo DA, pulmonary artery (PA) and femoral artery (FA). 15-E(2t)-IsoP and 15-F(2t)-IsoP contracted DA, PA, and FA rings in a concentration-dependent manner. 15-E(2t)-IsoP was equally efficacious (mean±SE E(max)=1.25±0.06 mN/mm) as and more potent (-log of molar concentration producing 50% of E(max)=pEC(50)=7.00±0.04) than the thromboxane-prostanoid (TP) receptor agonist U46619 (E(max)=1.49±0.11 mN/mm; pEC(50)=6.48±0.05) in contracting chicken DA (pulmonary side). 15-F(2t)-IsoP was less potent (pEC(50)=5.74±0.11) and less efficacious (E(max)=0.96±0.11) than U46619. Concentration-dependent contractions to 15-E(2t)-IsoP and U46619 in DA rings were competitively inhibited by the TP receptor antagonist SQ29548 (0.1 μM to 10 μM) with no decrease in the E(max) values. SQ29548 also inhibited concentration-dependent contraction to 15-F(2t)-IsoP but this inhibition was associated with a decrease in E(max). Pre-incubation of DA rings with 15-F(2t)-IsoP inhibited responses to U46619 and, in vessels contracted with U46619 (1 μM), 15-F(2t)-IsoP (>1 μM) evoked a relaxant response. Enzyme immunoassay did not show a measurable release of 15-F(2t)-IsoP by DA rings. In conclusion, 15-E(2t)-IsoP is a potent and efficacious constrictor of chicken DA, acting through TP receptors. In contrast, 15-F(2t)-IsoP is probably acting as a partial agonist at TP receptors. We speculate that IsoPs play a role in the control of chicken DA tone and could participate in its closure.

NADPH oxidases and reactive oxygen species at different stages of chronic hypoxia-induced pulmonary hypertension in newborn piglets

Recently, we reported that reactive oxygen species (ROS) generated by NADPH oxidase (NOX) contribute to aberrant responses in pulmonary resistance arteries (PRAs) of piglets exposed to 3 days of hypoxia (Am J Physiol Lung Cell Mol Physiol 295: L881-L888, 2008). An objective of the present study was to determine whether NOX-derived ROS also contribute to altered PRA responses at a more advanced stage of pulmonary hypertension, after 10 days of hypoxia. We further wished to advance knowledge about the specific NOX and antioxidant enzymes that are altered at early and later stages of pulmonary hypertension. Piglets were raised in room air (control) or hypoxia for 3 or 10 days. Using a cannulated artery technique, we found that treatments with agents that inhibit NOX (apocynin) or remove ROS [an SOD mimetic (M40403) + polyethylene glycol-catalase] diminished responses to ACh in PRAs from piglets exposed to 10 days of hypoxia. Western blot analysis showed an increase in expression of NOX1 and the membrane fraction of p67phox. Expression of NOX4, SOD2, and catalase were unchanged, whereas expression of SOD1 was reduced, in arteries from piglets raised in hypoxia for 3 or 10 days. Markers of oxidant stress, F(2)-isoprostanes, measured by gas chromatography-mass spectrometry, were increased in PRAs from piglets raised in hypoxia for 3 days, but not 10 days. We conclude that ROS derived from some, but not all, NOX family members, as well as alterations in the antioxidant enzyme SOD1, contribute to aberrant PRA responses at an early and a more progressive stage of chronic hypoxia-induced pulmonary hypertension in newborn piglets.

Developmental changes in the effects of prostaglandin E2 in the chicken ductus arteriosus

Prostaglandin E(2) (PGE(2)) is the major vasodilator prostanoid of the mammalian ductus arteriosus (DA). In the present study we analyzed the response of isolated DA rings from 15-, 19- and 21-day-old chicken embryos to PGE(2) and other vascular smooth muscle relaxing agents acting through the cyclic AMP signaling pathway. PGE(2) exhibited a relaxant response in the 15-day DA, but not in the 19- and 21-day DA. Moreover, high concentrations of PGE(2) (>or= 3 microM in 15-day and >or= 1 microM in 19-day and 21-day DA) induced contraction of the chicken DA. The presence of the TP receptor antagonist SQ29,548, unmasked a relaxant effect of PGE(2) in the 19- and 21-day DA and increased the relaxation induced by PGE(2) in the 15-day DA. The presence of the EP receptor antagonist AH6809 abolished PGE(2)-mediated relaxation. The relaxant responses induced by PGE(2) and the beta-adrenoceptor agonist isoproterenol, but not those elicited by the adenylate cyclase activator forskolin or the phosphodiesterase 3 inhibitor milrinone, decreased with maturation. High oxygen concentrations (95%) decreased the relaxation to PGE(2). The relaxing potency and efficacy of isoproterenol and milrinone were higher in the pulmonary than in the aortic side of the DA, whereas no regional differences were found in the response to PGE(2). We conclude that, in contrast to the mammalian situation, PGE(2) is a weak relaxant agent of the chicken DA and, with advancing incubation, it even stimulates TP vasoconstrictive receptors.

Acute vasodilator effects of Rho-kinase inhibitors in neonatal rats with pulmonary hypertension unresponsive to nitric oxide

Pulmonary hypertension (PHT) in neonates is often refractory to the current best therapy, inhaled nitric oxide (NO). The utility of a new class of pulmonary vasodilators, Rho-kinase (ROCK) inhibitors, has not been examined in neonatal animals. Our objective was to examine the activity and expression of RhoA/ROCK in normal and injured pulmonary arteries and to determine the short-term pulmonary hemodynamic (assessed by pulse wave Doppler) effects of ROCK inhibitors (15 mg/kg ip Y-27632 or 30 mg/kg ip fasudil) in two neonatal rat models of chronic PHT with pulmonary vascular remodeling (chronic hypoxia, 0.13 FiO2, or 1 mg·kg−1·day−1 ip chronic bleomycin for 14 days from birth). Activity of the RhoA/ROCK pathway and ROCK expression were increased in hypoxia- and bleomycin-induced PHT. In both models, severe PHT [characterized by raised pulmonary vascular resistance (PVR) and impaired right ventricular (RV) performance] did not respond acutely to inhaled NO (20 ppm for 15 min) or to a single bolus of a NO donor, 3-morpholinosydnonimine hydrochloride (SIN-1; 2 μg/kg ip). In contrast, a single intraperitoneal bolus of either ROCK inhibitor (Y-27632 or fasudil) completely normalized PVR but had no acute effect on RV performance. ROCK-mediated vasoconstriction appears to play a key role in chronic PHT in our two neonatal rat models. Inhibitors of ROCK have potential as a testable therapy in neonates with PHT that is refractory to NO.

Mechanisms controlling vascular tone in pulmonary arterial hypertension: implications for vasodilator therapy

Pulmonary vasoconstriction is believed to be an early component of pulmonary arterial hypertension. Intracellular calcium concentration ([Ca(2+)](i)) is a major trigger for pulmonary vasoconstriction; however, it is now well known that contractions and relaxations may also be elicited through Ca(2+)-independent mechanisms. A variety of intracellular protein kinases and cyclic nucleotides have been identified as key determinants in controlling pulmonary vascular tone. Herein, we provide an overview of the main signaling pathways, which include protein kinase C, Rho kinases and cyclic nucleotides (cAMP and cGMP). This review also focuses on the role of store-operated Ca(2+) channels and voltage-gated K(+) channels, which are currently considered especially attractive in the pulmonary circulation and may represent new targets in the treatment of pulmonary arterial hypertension.

Role of Reactive Oxygen Species in Kv Channel Inhibition and Vasoconstriction Induced by TP Receptor Activation in Rat Pulmonary Arteries

Voltage-gated potassium channels (Kv) and thromboxane A(2) (TXA(2)) have been involved in several forms of human and experimental pulmonary hypertension. We have reported that the TXA(2) analog U46619, via activation of TP receptors and PKCzeta, inhibited Kv currents in rat pulmonary artery smooth muscle cells (PASMC), increased cytosolic calcium, and induced a contractile response in isolated rat and piglet pulmonary arteries (PA). Herein, we have analyzed the role of reactive oxygen species (ROS) in this signaling pathway. In rat PA, U46619 increased dichlorofluorescein fluorescence, an indicator of intracellular hydrogen peroxide, and this effect was prevented by the NADPH oxidase inhibitor apocynin and by polyethyleneglycol-catalase (PEG-catalase, a membrane-permeable form of catalase). U46619 inhibited Kv currents in native PASMC and these effects were strongly inhibited by apocynin. The contractile responses to U46619 in isolated PA were inhibited by PEG-catalase and the NADPH oxidase inhibitors diphenylene iodonium (DPI) and apocynin. A membrane permeable of hydrogen peroxide, t-butyl hydroperoxide, also inhibited Kv currents and induced a contractile response. Activation of NADPH oxidase and the subsequent production of hydrogen peroxide are involved in the Kv channel inhibition and the contractile response induced by TP receptor activation in rat PA.

Superoxide dismutase improves oxygenation and reduces oxidation in neonatal pulmonary hypertension

RATIONALE

Hyperoxic ventilation in the management of persistent pulmonary hypertension of the newborn (PPHN) can result in the formation of reactive oxygen species, such as superoxide anions, which can inactivate nitric oxide (NO) and cause vasoconstriction and oxidation.

OBJECTIVE

To compare the effect of intratracheal recombinant human superoxide dismutase (rhSOD) and/or inhaled NO (iNO) on systemic oxygenation, contractility of pulmonary arteries (PAs), and lung reactive oxygen species (isoprostane, 3-nitrotyrosine) levels in neonatal lambs with PPHN.

METHODS

Six newborn lambs with PPHN (induced by antenatal ductal ligation) were killed at birth. Twenty-six PPHN lambs were ventilated for 24 h with 100% O(2) alone (n = 6) or O(2) combined with rhSOD (5 mg/kg intratracheally) at birth (n = 4), rhSOD at 4 h of age (n = 5), iNO (20 ppm, n = 5), or rhSOD + iNO (n = 6). Contraction responses of fifth-generation PAs to norepinephrine and KCl, lung isoprostane levels, and 3-nitrotyrosine fluorescent intensity were measured.

RESULTS

Systemic oxygenation was impaired in PPHN lambs and significantly improved (up to threefold) in both rhSOD groups with or without iNO. Oxygenation improved more rapidly with the combination of rhSOD + iNO compared with either intervention alone. Norepinephrine- and KCl-induced contractions and lung isoprostane levels were significantly increased by 100% O(2) compared with nonventilated newborn lambs with PPHN. Both rhSOD and iNO mitigated the increased PA contraction response and lung isoprostane levels. Intratracheal rhSOD decreased the enhanced lung 3-nitrotyrosine fluorescence observed with iNO therapy.

CONCLUSION

Intratracheal rhSOD and/or iNO rapidly increase oxygenation and reduce both vasoconstriction and oxidation in newborn lambs with PPHN. This has important implications for clinical trials of rhSOD and iNO in newborn infants with PPHN.

8-Isoprostane-induced endothelin-1 production by infant rat pulmonary artery smooth muscle cells is mediated by Rho-kinase

We have reported that 8-isoprostane stimulated the production of endothelin (ET)-1, a potent vasoconstrictor and critical mediator of chronic pulmonary hypertension, by infant rat pulmonary artery smooth muscle cells (PASMCs), through stimulation of the thromboxane A2 receptor. The aim of this study was to examine the contribution of putative downstream intracellular mediators of thromboxane A2 receptor stimulation to this effect. PASMCs from infant rats were treated with calcium ionophore (A23187), 8-isoprostane, or 8-isoprostane together with inhibitors of tyrosine kinase, protein kinase C, phosphatidylinositol 3-kinase, mitogen-activated protein kinases, or Rho-kinases (ROCK). A23187 had no effect on ET-1 production, excluding raised intracellular Ca2+ as a major contributor. Increased ET-1 production induced by 8-isoprostane was significantly attenuated by the ROCK inhibitors Y-27632 and hydroxyfasudil, but not by inhibitors of the other pathways. 8-Isoprostane also increased membrane binding of RhoA, a major determinant of ROCK activity, and ROCK-II expression through the protein kinase C pathway. These data indicate that the RhoA/ROCK pathway mediates increased ET-1 production by PASMCs, which we speculate may at least partly explain the beneficial effects of both antioxidants and ROCK inhibitors in animal models of chronic pulmonary hypertension.

Adjacent bronchus attenuates pulmonary arterial contractility

Bronchus-derived relaxing factor (BrDRF) decreases contractility of newborn rat pulmonary arteries (PA) and is dependent on nitric oxide (NO) synthesis. In vivo, this factor appears to gain access via the adventitial side of the PA. However, the adventitia has been reported to be a barrier to NO. We studied the effect of an adjacent bronchus on PA contractility to norepinephrine in nine juvenile lambs in the presence and absence of inhibitors of the NO pathway (LNA, ODQ, and Rp-8-Br-PET-cGMPS), cytochrome P-450 inhibitor (17-ODYA), perivascular nerve activity blocker (TTX), and superoxide scavenger (tiron), and following disruption of bronchial epithelium. We also evaluated whether BrDRF was effective on both the endothelial and/or adventitial side of PA. Fifth-generation PA rings with and without an attached bronchus were contracted in standard baths with norepinephrine. PA were dissected, cut open, and placed in a sided chamber in which adventitial and endothelial sides of the PA were exposed to unattached bronchus separately. Norepinephrine (10−8 to 10−5 M) contractions were expressed as a fraction of maximal KCl (118 mM) contractions. Norepinephrine contractions were significantly reduced by the presence of an attached bronchus, an effect reversed by pretreatment with LNA, ODQ, and Rp-8-Br-PET-cGMPS, and removal of bronchial epithelium. Unattached bronchus in the bath perfusing the adventitial side was effective in inhibiting the contractile response in PA. NO gas relaxed PA when administered on the endothelial side only. We speculate that BrDRF is a diffusible factor that crosses the adventitia and stimulates production of NO within the PA.

Relaxant Effects of the Soluble Guanylate Cyclase Activator and NO Sensitizer YC-1 in Piglet Pulmonary Arteries

BACKGROUND

The indazole derivative YC-1 has been characterized as a nitric oxide (NO)-independent and heme dependent soluble guanylate cyclase (sGC) activator, which also sensitizes sGC to NO.

OBJECTIVE

To examine the effects of YC-1 on vascular relaxation in newborn and 2-week-old piglet pulmonary arteries. The effect of YC-1 on the relaxation induced by exogenous NO was also analyzed.

METHODS

Isolated rings from third branch pulmonary arteries and fifth-seventh-generation intrapulmonary arterioles were mounted in organ chambers for isometric tension recording. Arteries were precontracted with the thromboxane A2 mimetic U46619.

RESULTS

YC-1 induced relaxation was greater in 2-week-old pulmonary arteries and was abolished by the sGC inhibitor ODQ (10 microM). YC-1 induced relaxation was similar in conduit pulmonary arteries and arterioles. In the 2-week-old conduit pulmonary arteries, the response to YC-1 was significantly reduced when the endothelium was removed or after incubation with the NO synthase inhibitor L-NAME (0.1 mM). YC-1 augmented NO-induced relaxation in 2-week-old but not in neonatal conduit pulmonary arteries.

CONCLUSIONS

Our results indicate that YC-1 induced pulmonary vascular relaxation in conduit and resistance pulmonary arteries and these effects increased with postnatal age. In the 2-week-old conduit pulmonary arteries and besides being a direct activator of sGC, YC-1 produced endothelium-dependent relaxation and synergized with exogenous NO.