Role of prostanoids, nitric oxide and endothelin pathways in pulmonary hypertension due to COPD

Pulmonary hypertension (PH) due to chronic obstructive pulmonary disease (COPD) is classified as Group 3 PH, with no current proven targeted therapies. Studies suggest that cigarette smoke, the most risk factor for COPD can cause vascular remodelling and eventually PH as a result of dysfunction and proliferation of pulmonary artery smooth muscle cells (PASMCs) and pulmonary artery endothelial cells (PAECs). In addition, hypoxia is a known driver of pulmonary vascular remodelling in COPD, and it is also thought that the presence of hypoxia in patients with COPD may further exaggerate cigarette smoke-induced vascular remodelling; however, the underlying cause is not fully understood. Three main pathways (prostanoids, nitric oxide and endothelin) are currently used as a therapeutic target for the treatment of patients with different groups of PH. However, drugs targeting these three pathways are not approved for patients with COPD-associated PH due to lack of evidence. Thus, this review aims to shed light on the role of impaired prostanoids, nitric oxide and endothelin pathways in cigarette smoke- and hypoxia-induced pulmonary vascular remodelling and also discusses the potential of using these pathways as therapeutic target for patients with PH secondary to COPD.

Cancer and COVID-19: unravelling the immunological interplay with a review of promising therapies against severe SARS-CoV-2 for cancer patients

Cancer patients, due to their immunocompromised status, are at an increased risk for severe SARS-CoV-2 infection. Since severe SARS-CoV-2 infection causes multiple organ damage through IL-6-mediated inflammation while stimulating hypoxia, and malignancy promotes hypoxia-induced cellular metabolic alterations leading to cell death, we propose a mechanistic interplay between both conditions that results in an upregulation of IL-6 secretion resulting in enhanced cytokine production and systemic injury. Hypoxia mediated by both conditions results in cell necrosis, dysregulation of oxidative phosphorylation, and mitochondrial dysfunction. This produces free radicals and cytokines that result in systemic inflammatory injury. Hypoxia also catalyzes the breakdown of COX-1 and 2 resulting in bronchoconstriction and pulmonary edema, which further exacerbates tissue hypoxia. Given this disease model, therapeutic options are currently being studied against severe SARS-COV-2. In this study, we review several promising therapies against severe disease supported by clinical trial evidence-including Allocetra, monoclonal antibodies (Tixagevimab-Cilgavimab), peginterferon lambda, Baricitinib, Remdesivir, Sarilumab, Tocilizumab, Anakinra, Bevacizumab, exosomes, and mesenchymal stem cells. Due to the virus's rapid adaptive evolution and diverse symptomatic manifestation, the use of combination therapies offers a promising approach to decrease systemic injury. By investing in such targeted interventions, cases of severe SARS-CoV-2 should decrease along with its associated long-term sequelae and thereby allow cancer patients to resume their treatments.

Pathogenic Mechanisms of Pulmonary Arterial Hypertension: Homeostasis Imbalance of Endothelium-Derived Relaxing and Contracting Factors

Pulmonary arterial hypertension (PAH) is a progressive and fatal disease. Sustained pulmonary vasoconstriction and concentric pulmonary vascular remodeling contribute to the elevated pulmonary vascular resistance and pulmonary artery pressure in PAH. Endothelial cells regulate vascular tension by producing endothelium-derived relaxing factors (EDRFs) and endothelium-derived contracting factors (EDCFs). Homeostasis of EDRF and EDCF production has been identified as a marker of the endothelium integrity. Impaired synthesis or release of EDRFs induces persistent vascular contraction and pulmonary artery remodeling, which subsequently leads to the development and progression of PAH. In this review, the authors summarize how EDRFs and EDCFs affect pulmonary vascular homeostasis, with special attention to the recently published novel mechanisms related to endothelial dysfunction in PAH and drugs associated with EDRFs and EDCFs.

Novel Compound Heterozygous PKLR Mutation Induced Pyruvate Kinase Deficiency With Persistent Pulmonary Hypertension in a Neonate: A Case Report

Background

Pulmonary hypertension could be associated with pyruvate kinase deficiency (PKD). There are few reported cases of PPHN as the first clinical manifestation of PKD. Herein we report a rare case of PKD in which the patient exhibited persistent pulmonary hypertension in the neonate (PPHN), and genetic testing helped to rapidly identify an potential association.

Case presentation

The patient was a newborn boy who suffered from severe dyspnea, extreme anemia, skin pallor, and hypoxemia. Repeated echocardiography indicated persistent severe pulmonary hypertension with a calculated pulmonary artery pressure of 75 mmHg, and right ventricular hypertrophy. The administration of nitric oxide significantly reduced the pulmonary artery pressure. Whole-exome sequencing revealed a compound heterozygous mutation consisting of c.707T > G and c.826_827insAGGAGCATGGGG. PolyPhen_2 and MutationTaster indicated that both the c.707T > G (probability 0.999) and c.826_827insAGGAGCATGGGG (probability 0.998) mutations were disease causing. PROVEAN protein batch analysis indicated that the associated p.L236R region was deleterious (score −4.71) and damaging (SIFT prediction 0.00), and this was also the case for p.G275_V276insEEHG (deleterious score −12.00, SIFT prediction 0.00). Substantial structural changes in the transport domain of the protein were predicted using SWISS-MODEL, and indicated that both mutations led to an unstable protein structure. Thus, a novel compound heterozygous mutation of PKLR-induced PKD with PPHN was diagnosed.

Conclusion

The current study suggests that molecular genetic screening is useful for identifying PPHN, particularly in children with metabolic disorders. In patients exhibiting unexplained hyperbilirubinemia combined with severe pulmonary hypertension, PKD might be a potential possible alternative explanation. Genetic screening is helpful for identifying genetic causes of pulmonary hypertension, especially in patients with PPHN. This report expands the mutation spectrum of the PKLR gene, and contributes to the genotype-phenotype map of PKD.

Dysregulation of the Nitric Oxide/Dimethylarginine Pathway in Hypoxic Pulmonary Vasoconstriction—Molecular Mechanisms and Clinical Significance

The pulmonary circulation responds to hypoxia with vasoconstriction, a mechanism that helps to adapt to short-lived hypoxic episodes. When sustained, hypoxic pulmonary vasoconstriction (HPV) may become deleterious, causing right ventricular hypertrophy and failure, and contributing to morbidity and mortality in the late stages of several chronic pulmonary diseases. Nitric oxide (NO) is an important endothelial vasodilator. Its release is regulated, amongst other mechanisms, by the presence of endogenous inhibitors like asymmetric dimethylarginine (ADMA). Evidence has accumulated in recent years that elevated ADMA may be implicated in the pathogenesis of HPV and in its clinical sequelae, like pulmonary arterial hypertension (PAH). PAH is one phenotypic trait in experimental models with disrupted ADMA metabolism. In high altitude, elevation of ADMA occurs during long-term exposure to chronic or chronic intermittent hypobaric hypoxia; ADMA is significantly associated with high altitude pulmonary hypertension. High ADMA concentration was also reported in patients with chronic obstructive lung disease, obstructive sleep apnoea syndrome, and overlap syndrome, suggesting a pathophysiological role for ADMA-mediated impairment of endothelium-dependent, NO-mediated pulmonary vasodilation in these clinically relevant conditions. Improved understanding of the molecular (dys-)regulation of pathways controlling ADMA concentration may help to dissect the pathophysiology and find novel therapeutic options for these diseases.

Effects of Arachidonic Acid Metabolites on Cardiovascular Health and Disease

Arachidonic acid (AA) is an essential fatty acid that is released by phospholipids in cell membranes and metabolized by cyclooxygenase (COX), cytochrome P450 (CYP) enzymes, and lipid oxygenase (LOX) pathways to regulate complex cardiovascular function under physiological and pathological conditions. Various AA metabolites include prostaglandins, prostacyclin, thromboxanes, hydroxyeicosatetraenoic acids, leukotrienes, lipoxins, and epoxyeicosatrienoic acids. The AA metabolites play important and differential roles in the modulation of vascular tone, and cardiovascular complications including atherosclerosis, hypertension, and myocardial infarction upon actions to different receptors and vascular beds. This article reviews the roles of AA metabolism in cardiovascular health and disease as well as their potential therapeutic implication.

Eicosanoid blood vessel regulation in physiological and pathological states

Arachidonic acid can be metabolized in blood vessels by three primary enzymatic pathways; cyclooxygenase (COX), lipoxygenase (LO), and cytochrome P450 (CYP). These eicosanoid metabolites can influence endothelial and vascular smooth muscle cell function. COX metabolites can cause endothelium-dependent dilation or constriction. Prostaglandin I2 (PGI2) and thromboxane (TXA2) act on their respective receptors exerting opposing actions with regard to vascular tone and platelet aggregation. LO metabolites also influence vascular tone. The 12-LO metabolite 12S-hydroxyeicosatrienoic acid (12S-HETE) is a vasoconstrictor whereas the 15-LO metabolite 11,12,15-trihydroxyeicosatrienoic acid (11,12,15-THETA) is an endothelial-dependent hyperpolarizing factor (EDHF). CYP enzymes produce two types of eicosanoid products: EDHF vasodilator epoxyeicosatrienoic acids (EETs) and the vasoconstrictor 20-HETE. The less-studied cross-metabolites generated from arachidonic acid metabolism by multiple pathways can also impact vascular function. Likewise, COX, LO, and CYP vascular eicosanoids interact with paracrine and hormonal factors such as the renin-angiotensin system and endothelin-1 (ET-1) to maintain vascular homeostasis. Imbalances in endothelial and vascular smooth muscle cell COX, LO, and CYP metabolites in metabolic and cardiovascular diseases result in vascular dysfunction. Restoring the vascular balance of eicosanoids by genetic or pharmacological means can improve vascular function in metabolic and cardiovascular diseases. Nevertheless, future research is necessary to achieve a more complete understanding of how COX, LO, CYP, and cross-metabolites regulate vascular function in physiological and pathological states.

Obeticholic acid ameliorates hepatorenal syndrome in ascitic cirrhotic rats by down-regulating the renal 8-iso-PGF2α-activated COX-TXA2 pathway

BACKGROUNDS/AIMS

The present study explores the potential of chronic treatment with the Foresaid X receptor (FXR) agonist obeticholic acid (OCA), which inhibits oxidative stress-related pathogenesis, in ascitic cirrhotic rats with hepatorenal syndrome (HRS) developed 6 weeks after bile duct ligation (BDL).

METHODS

Systemic, splanchnic, and renal hemodynamics and pathogenic cascades were measured in ascitic BDL and sham rats receiving 2-weeks of either vehicle or OCA treatments (sham-OCA and BDL-OCA groups), and NRK-52E cells, rat kidney tubular epithelial cells.

RESULTS

Chronic OCA treatment significantly normalized portal hypertension, glomerular filtration rate, urine output, renal blood flow; decreased ascites, renal vascular resistance, serum creatinine, and the release of renal tubular damage markers, including urinary neutrophil gelatinase-associated lipocalin (uNGAL) and kidney injury moleculae-1 (uKim-1) in BDL-OCA rats. In the BDL group, inhibition of the renal oxidative stress (8-iso-PGF2α)-activated cyclooxygenase-thromboxane A2 [COX-TXA2] pathway, apoptosis, and tubular injury accompanied by a decrease in hyper-responsiveness to the vasoconstrictor 8-iso-PGF2α in perfused kidneys. In vitro experiments revealed that 8-iso-PGF2α induced oxidative stress, release of reactive oxygen species, and cell apoptosis, which were reversed by concomitant incubation with the FXR agonist.

CONCLUSIONS

Through the inhibition of renal 8-iso-PGF2α production and the down-regulation of the COX-TXA2 pathway, our study suggests that chronic OCA treatment can ameliorate the HRS in ascitic cirrhotic rats. Thus, OCA is an agent with antioxidative stress, antivasoconstrictive, antiapoptotic properties which benefit ascitic, cirrhotic rats with systemic, hepatic, and renal abnormalities.

Vascular Metabolic Mechanisms of Pulmonary Hypertension

Pulmonary hypertension (PH) is a severe and progressive disease characterized by increased pulmonary vascular resistance leading to right heart failure and death. In PH, the cellular metabolisms including those of the three major nutrients (carbohydrate, lipid and protein) are aberrant in pulmonary vascular cells. Glucose uptake, glycolysis, insulin resistance, sphingolipid S1P, PGE₂, TXA₂, leukotrienes and glutaminolysis are upregulated, and phospholipid-prostacyclin and L-arginine-nitric oxide pathway are compromised in lung vascular cells. Fatty acid metabolism is disordered in lung endothelial cells and smooth muscle cells. These molecular mechanisms are integrated to promote PH-specific abnormal vascular cell proliferation and vascular remodeling. This review summarizes the recent advances in the metabolic reprogramming of glucose, fatty acid, and amino acid metabolism in pulmonary vascular remodeling in PH and the mechanisms for how these alterations affect vascular cell fate and impact the course of PH.

Prostanoids contribute to regulation of inwardly rectifying K+ channels in intrarenal arterial smooth muscle cells

AIM

The inward rectifier K⁺ (Kir) channels and prostanoids are important factors in regulating vascular tone, but the relationship between them has not been well studied. We aimed to study the involvement of prostanoids in regulating Kir activity in the rat intrarenal arteries (RIRAs).

MAIN METHODS

The vascular tone of isolated RIRAs was recorded with a wire myograph. The intracellular Ca²⁺ concentrations ([Ca²⁺]_i) and Kir currents were measured with a Ca²⁺-sensitive fluorescence probe and patch clamp, respectively, in the arterial smooth muscle cell (ASMC) freshly isolated from RIRAs. Kir2.1 expression in RIRAs was assayed by Western blotting.

KEY FINDINGS

At 0.03-1.0 mM, BaCl₂ (a specific Kir blocker) concentration-dependently contracted RIRAs and elevated [Ca²⁺]_i levels. Mild stimulations with various vasoconstrictors at low concentrations significantly potentiated RIRA contraction induced by Kir closure with BaCl₂. In both the quiescent and the stimulated RIRAs, cyclooxygenase inhibition and thromboxane-prostanoid receptor (TPR) antagonism depressed BaCl₂-induced RIRA contraction, while nitric oxide (NO) synthetase inhibition and endothelium-denudation enhanced the contraction. Kir2.1 expression was significantly more abundant in smaller RIRAs. Ba²⁺-sensitive Kir currents were depressed by TPR agonist U46619 while increased by NO donor sodium nitroprusside.

SIGNIFICANCE

The present results reveal that vasoconstrictor stimulation augments RIRA contraction induced by Kir closure with Ba⁺ and indicate that prostanoid synthesis followed by TPR activation is involved in the modulation of the myocyte Kir activity. This study suggests that prostanoid synthesis and TPR may be potential targets for dysfunctions in renal blood circulation.

Platelet Oxidative Stress and its Relationship with Cardiovascular Diseases in Type 2 Diabetes Mellitus Patients

Enhanced platelet activation and thrombosis are linked to various cardiovascular diseases (CVD). Among other mechanisms, oxidative stress seems to play a pivotal role in platelet hyperactivity. Indeed, upon stimulation by physiological agonists, human platelets generate and release several types of reactive oxygen species (ROS) such as O2 -, H2O2 or OH-, further amplifying the platelet activation response via various signalling pathways, including, formation of isoprostanes, Ca2+ mobilization and NO inactivation. Furthermore, excessive platelet ROS generation, incorporation of free radicals from environment and/or depletion of antioxidants induce pro-oxidant, pro-inflammatory and platelet hyperaggregability effects, leading to the incidence of cardiovascular events. Here, we review the current knowledge regarding the effect of oxidative stress on platelet signaling pathways and its implication in CVD such as type 2 diabetes mellitus. We also summarize the role of natural antioxidants included in vegetables, fruits and medicinal herbs in reducing platelet function via an oxidative stress-mediated mechanism.

Measurement and Clinical Significance of Lipid Peroxidation as a Biomarker of Oxidative Stress: Oxidative Stress in Diabetes, Atherosclerosis, and Chronic Inflammation

Endothelial dysfunction is one of the initial steps in the pathogenesis of atherosclerosis and development of cardiovascular disease in patients with diabetes mellitus. Several risk factors are associated with endothelial dysfunction and atherosclerosis, such as hypertension, dyslipidaemia, inflammation, oxidative stress, and advanced glycation-end products. Among these risk factors, oxidative stress is the largest contributor to the formation of atherosclerotic plaques. Measurement of reactive oxygen species (ROS) is still difficult, and assays for the measurement of ROS have failed to show a consistent correlation between pathological states and oxidative stress. To solve this problem, this review summarizes the current knowledge on biomarkers of oxidative stress, especially lipid peroxidation, and discusses the roles of oxidative stress, as measured by indices of lipid peroxidation, in diabetes mellitus, atherosclerosis, and chronic inflammation.

Catechins Blunt the Effects of oxLDL and its Primary Metabolite Phosphatidylcholine Hydroperoxide on Endothelial Dysfunction Through Inhibition of Oxidative Stress and Restoration of eNOS in Rats

BACKGROUND/AIMS

We explored the effects of catechins (decaffeinated green tea extracts containing (-)-epicatechin, (-)-epigallocatechin, (-)-epicatechin gallate and (-)-epigallocatechin gallate) on atherosclerosis risk factors, oxidized low-density lipoprotein (oxLDL) and its primary metabolite, phosphatidylcholine hydroperoxide (PCOOH) induced oxidative injury in cultured endothelial cell line and rats.

METHODS

We used endothelial cell line and male Wistar rats to determine the effect of catechins on oxLDL or PCOOH induced oxidative injury including apoptosis, H2O2 level, vascular responses and urinary 8-isoprostane and nitrite/nitrate concentration. Plasma catechins concentration was determined by a CoulArray HPLC. Responses of aortic and renal vasoconstriction were evaluated by a transonic meter and a full-field laser perfusion imager.

RESULTS

PCOOH administration significantly increased H2O2 amounts and cell apoptosis and decreased endothelial nitric oxide synthase (eNOS) expression in the cultured endothelial cells. Catechins pretreatment significantly reduced PCOOH-elevated H2O2 amounts, endothelial cell apoptosis and partly recovered eNOS expression. Intravenous administration of oxLDL, PCOOH or H2O2, not native LDL, significantly decreased renal and aortic blood flow associated with enhanced ICAM-1 expression and 4-hydroxynoneal (4-HNE) accumulation, and decreased eNOS expression in the male Wistrar rats. One hour after oral intake of green tea extracts, 4 peaks of catechins were found in the rat plasma. The increased plasma catechins significantly inhibited oxLDL-, PCOOH- or H2O2-induced renal and aortic vasoconstriction, decreased urinary 8-isoprostane levels, renal ICAM-1 expression and 4-HNE accumulation, and restored nitrite/nitrate amounts and eNOS activity.

CONCLUSIONS

Our data suggests that catechins pretreatment decrease PCOOH-induced endothelial apoptosis and arterial vasoconstriction through the action of H2O2 inhibition and eNOS restoration.

Altered Redox Balance in the Development of Chronic Hypoxia-induced Pulmonary Hypertension

Normally, the pulmonary circulation is maintained in a low-pressure, low-resistance state with little resting tone. Pulmonary arteries are thin-walled and rely heavily on pulmonary arterial distension and recruitment for reducing pulmonary vascular resistance when cardiac output is elevated. Under pathophysiological conditions, however, active vasoconstriction and vascular remodeling lead to enhanced pulmonary vascular resistance and subsequent pulmonary hypertension (PH). Chronic hypoxia is a critical pathological factor associated with the development of PH resulting from airway obstruction (COPD, sleep apnea), diffusion impairment (interstitial lung disease), developmental lung abnormalities, or high altitude exposure (World Health Organization [WHO]; Group III). The rise in pulmonary vascular resistance increases right heart afterload causing right ventricular hypertrophy that can ultimately lead to right heart failure in patients with chronic lung disease. PH is typically characterized by diminished paracrine release of vasodilators, antimitogenic factors, and antithrombotic factors (e.g., nitric oxide and protacyclin) and enhanced production of vasoconstrictors and mitogenic factors (e.g., reactive oxygen species and endothelin-1) from the endothelium and lung parenchyma. In addition, phenotypic changes to pulmonary arterial smooth muscle cells (PASMC), including alterations in Ca²⁺ homeostasis, Ca²⁺ sensitivity, and activation of transcription factors are thought to play prominent roles in the development of both vasoconstrictor and arterial remodeling components of hypoxia-associated PH. These changes in PASMC function are briefly reviewed in Sect. 1 and the influence of altered reactive oxygen species homeostasis on PASMC function discussed in Sects. 2-4.

Sildenafil therapy for fetal cardiovascular dysfunction during hypoxic development: studies in the chick embryo

KEY POINTS

Common complications of pregnancy, such as chronic fetal hypoxia, trigger a fetal origin of cardiovascular dysfunction and programme cardiovascular disease in later life. Sildenafil treatment protects placental perfusion and fetal growth, but whether the effects of sildenafil transcend the placenta to affect the fetus is unknown. Using the chick embryo model, here we show that sildenafil treatment directly protects the fetal cardiovascular system in hypoxic development, and that the mechanisms of sildenafil protection include reduced oxidative stress and increased nitric oxide bioavailability; Sildenafil does not protect against fetal growth restriction in the chick embryo, supporting the idea that the protective effect of sildenafil on fetal growth reported in mammalian studies, including humans, is secondary to improved placental perfusion. Therefore, sildenafil may be a good candidate for human translational antioxidant therapy to protect the chronically hypoxic fetus in adverse pregnancy.

ABSTRACT

There is a need for developing clinically translatable therapy for preventing fetal origins of cardiovascular disease in pregnancy complicated by chronic fetal hypoxia. Evidence shows that sildenafil protects placental perfusion and fetal growth. However, whether beneficial effects of sildenafil transcend onto the fetal heart and circulation in complicated development is unknown. We isolated the direct effects of sildenafil on the fetus using the chick embryo and hypothesised that sildenafil also protects fetal cardiovascular function in hypoxic development. Chick embryos (n = 11 per group) were incubated in normoxia or hypoxia (14% O₂ ) from day 1 and treated with sildenafil (4 mg kg^-1  day^-1 ) from day 13 of the 21-day incubation. Hypoxic incubation increased oxidative stress (4-hydroxynonenal, 141.1 ± 17.6% of normoxic control), reduced superoxide dismutase (60.7 ± 6.3%), increased phosphodiesterase type 5 expression (167 ± 13.7%) and decreased nitric oxide bioavailability (54.7 ± 6.1%) in the fetal heart, and promoted peripheral endothelial dysfunction (70.9 ± 5.6% AUC of normoxic control; all P < 0.05). Sildenafil treatment after onset of chronic hypoxia prevented the increase in phosphodiesterase expression (72.5 ± 22.4%), protected against oxidative stress (94.7 ± 6.2%) and normalised nitric oxide bioavailability (115.6 ± 22.3%) in the fetal heart, and restored endothelial function in the peripheral circulation (89.8 ± 2.9%). Sildenafil protects the fetal heart and circulation directly in hypoxic development via mechanisms including decreased oxidative stress and enhanced nitric oxide bioavailability. Sildenafil may be a good translational candidate for human antioxidant therapy to prevent fetal origins of cardiovascular dysfunction in adverse pregnancy.

Expression and role of connexin-based gap junctions in pulmonary inflammatory diseases

Connexins are transmembrane proteins that can generate intercellular communication channels known as gap junctions. They contribute to the direct movement of ions and larger cytoplasmic solutes between various cell types. In the lung, connexins participate in a variety of physiological functions, such as tissue homeostasis and host defence. In addition, emerging evidence supports a role for connexins in various pulmonary inflammatory diseases, such as asthma, pulmonary hypertension, acute lung injury, lung fibrosis or cystic fibrosis. In these diseases, the altered expression of connexins leads to disruption of normal intercellular communication pathways, thus contributing to various pathophysiological aspects, such as inflammation or tissue altered reactivity and remodeling. The present review describes connexin structure and organization in gap junctions. It focuses on connexins in the lung, including pulmonary bronchial and arterial beds, by looking at their expression, regulation and physiological functions. This work also addresses the issue of connexin expression alteration in various pulmonary inflammatory diseases and describes how targeting connexin-based gap junctions with pharmacological tools, synthetic blocking peptides or genetic approaches, may open new therapeutic perspectives in the treatment of these diseases.

Effects of BM-573 on Endothelial Dependent Relaxation and Increased Blood Pressure at Early Stages of Atherosclerosis

Endothelial dysfunction is considered to be an early event in atherosclerosis and plays a pivotal role in the development, progression and clinical complications of atherosclerosis. Previous studies have shown the beneficial effects of combined inhibition of thromboxane synthase and antagonism of thromboxane receptors by BM-573 on atherosclerosis; however our knowledge about the beneficial effects of BM-573 on endothelial function and increased blood pressure related to early stage of atherosclerosis is limited. In the present study, we investigated the effects of short-term (3 μM, 1 hour) and chronic (10 mg/L, 8 weeks) treatments with BM-573 on vasodilatory function, nitric oxide (NO) bioavailability, oxidative stress and systolic blood pressure in 15 weeks old apolipoprotein E-deficient (ApoE-KO) mice. ApoE-KO mice showed a reduced endothelium-derived relaxation. In addition, NO bioavailability was reduced and oxidative stress and blood pressure were increased in ApoE-KO mice versus wild-type mice. BM-573 treatments were able to improve the relaxation profile in ApoE-KO mice. Short-term effects of BM-573 were mainly mediated by an increased phosphorylation of both eNOS and Akt, whereas BM-573 in vivo treatment also reduced oxidative stress and restored NO bioavailability. In addition, chronic administration of BM-573 reduced systolic blood pressure in ApoE-KO mice. In conclusion, pharmacological modulation of TxA2 biosynthesis and biological activities by dual TP antagonism/TxAS inhibition with BM-573, already known to prevent plaque formation, has the potential to correct vasodilatory dysfunction at the early stages of atherosclerosis.

PKCα Deficiency in Mice Is Associated with Pulmonary Vascular Hyperresponsiveness to Thromboxane A2 and Increased Thromboxane Receptor Expression

Pulmonary vascular hyperresponsiveness is a main characteristic of pulmonary arterial hypertension (PAH). In PAH patients, elevated levels of the vasoconstrictors thromboxane A2 (TXA2), endothelin (ET)-1 and serotonin further contribute to pulmonary hypertension. Protein kinase C (PKC) isozyme alpha (PKCα) is a known modulator of smooth muscle cell contraction. However, the effects of PKCα deficiency on pulmonary vasoconstriction have not yet been investigated. Thus, the role of PKCα in pulmonary vascular responsiveness to the TXA2 analog U46619, ET-1, serotonin and acute hypoxia was investigated in isolated lungs of PKCα-/- mice and corresponding wild-type mice, with or without prior administration of the PKC inhibitor bisindolylmaleimide I or Gö6976. mRNA was quantified from microdissected intrapulmonary arteries. We found that broad-spectrum PKC inhibition reduced pulmonary vascular responsiveness to ET-1 and acute hypoxia and, by trend, to U46619. Analogously, selective inhibition of conventional PKC isozymes or PKCα deficiency reduced ET-1-evoked pulmonary vasoconstriction. The pulmonary vasopressor response to serotonin was unaffected by either broad PKC inhibition or PKCα deficiency. Surprisingly, PKCα-/- mice showed pulmonary vascular hyperresponsiveness to U46619 and increased TXA2 receptor (TP receptor) expression in the intrapulmonary arteries. To conclude, PKCα regulates ET-1-induced pulmonary vasoconstriction. However, PKCα deficiency leads to pulmonary vascular hyperresponsiveness to TXA2, possibly via increased pulmonary arterial TP receptor expression.

Increased eicosanoid levels in the Sugen/chronic hypoxia model of severe pulmonary hypertension

Inflammation and altered immunity are recognized components of severe pulmonary arterial hypertension in human patients and in animal models of PAH. While eicosanoid metabolites of cyclooxygenase and lipoxygenase pathways have been identified in the lungs from pulmonary hypertensive animals their role in the pathogenesis of severe angioobliterative PAH has not been examined. Here we investigated whether a cyclooxygenase-2 (COX-2) inhibitor or diethylcarbamazine (DEC), that is known for its 5-lipoxygenase inhibiting and antioxidant actions, modify the development of PAH in the Sugen 5416/hypoxia (SuHx) rat model. The COX-2 inhibitor SC-58125 had little effect on the right ventricular pressure and did not prevent the development of pulmonary angioobliteration. In contrast, DEC blunted the muscularization of pulmonary arterioles and reduced the number of fully obliterated lung vessels. DEC treatment of SuHx rats, after the lung vascular disease had been established, reduced the degree of PAH, the number of obliterated arterioles and the degree of perivascular inflammation. We conclude that the non-specific anti-inflammatory drug DEC affects developing PAH and is partially effective once angioobliterative PAH has been established.

EP3 receptor deficiency attenuates pulmonary hypertension through suppression of Rho/TGF-β1 signaling

Pulmonary arterial hypertension (PAH) is commonly associated with chronic hypoxemia in disorders such as chronic obstructive pulmonary disease (COPD). Prostacyclin analogs are widely used in the management of PAH patients; however, clinical efficacy and long-term tolerability of some prostacyclin analogs may be compromised by concomitant activation of the E-prostanoid 3 (EP3) receptor. Here, we found that EP3 expression is upregulated in pulmonary arterial smooth muscle cells (PASMCs) and human distal pulmonary arteries (PAs) in response to hypoxia. Either pharmacological inhibition of EP3 or Ep3 deletion attenuated both hypoxia and monocrotaline-induced pulmonary hypertension and restrained extracellular matrix accumulation in PAs in rodent models. In a murine PAH model, Ep3 deletion in SMCs, but not endothelial cells, retarded PA medial thickness. Knockdown of EP3α and EP3β, but not EP3γ, isoforms diminished hypoxia-induced TGF-β1 activation. Expression of either EP3α or EP3β in EP3-deficient PASMCs restored TGF-β1 activation in response to hypoxia. EP3α/β activation in PASMCs increased RhoA-dependent membrane type 1 extracellular matrix metalloproteinase (MMP) translocation to the cell surface, subsequently activating pro-MMP-2 and promoting TGF-β1 signaling. Activation or disruption of EP3 did not influence PASMC proliferation. Together, our results indicate that EP3 activation facilitates hypoxia-induced vascular remodeling and pulmonary hypertension in mice and suggest EP3 inhibition as a potential therapeutic strategy for pulmonary hypertension.

Pathophysiology of isoprostanes in the cardiovascular system: implications of isoprostane-mediated thromboxane A2 receptor activation

Isoprostanes are free radical-catalysed PG-like products of unsaturated fatty acids, such as arachidonic acid, which are widely recognized as reliable markers of systemic lipid peroxidation and oxidative stress in vivo. Moreover, activation of enzymes, such as COX-2, may contribute to isoprostane formation. Indeed, formation of isoprostanes is considerably increased in various diseases which have been linked to oxidative stress, such as cardiovascular disease (CVD), and may predict the atherosclerotic burden and the risk of cardiovascular complications in the latter patients. In addition, several isoprostanes may directly contribute to the functional consequences of oxidant stress via activation of the TxA2 prostanoid receptor (TP), for example, by affecting endothelial cell function and regeneration, vascular tone, haemostasis and ischaemia/reperfusion injury. In this context, experimental and clinical data suggest that selected isoprostanes may represent important alternative activators of the TP receptor when endogenous TxA2 levels are low, for example, in aspirin-treated individuals with CVD. In this review, we will summarize the current understanding of isoprostane formation, biochemistry and (patho) physiology in the cardiovascular context.

Thromboxane receptor hyper-responsiveness in hypoxic pulmonary hypertension requires serine 324

BACKGROUND AND PURPOSE

Dysregulation of the thromboxane A₂ (TP) receptor, resulting in agonist hypersensitivity and hyper-responsiveness, contributes to exaggerated vasoconstriction in the hypoxic pulmonary artery in neonatal persistent pulmonary hypertension. We previously reported that hypoxia inhibits TP receptor phosphorylation, causing desensitization. Hence, we examined the role of PKA-accessible serine residues in determining TP receptor affinity, using site-directed mutational analysis.

EXPERIMENTAL APPROACH

Vasoconstriction to a thromboxane mimetic and phosphorylation of TP receptor serine was examined in pulmonary arteries from neonatal swine with persistent pulmonary hypertension and controls. Effects of hypoxia were determined in porcine and human TP receptors. Human TPα serines at positions 324, 329 and 331 (C-terminal tail) were mutated to alanine and transiently expressed in HEK293T cells. Saturation binding and displacement kinetics of a TP antagonist and agonist were determined in porcine TP, wild-type human TPα and all TP mutants. Agonist-elicited calcium mobilization was determined for each TP mutant, in the presence of a PKA activator or inhibitor, and in hypoxic and normoxic conditions.

KEY RESULTS

The Ser324A mutant was insensitive to PKA activation and hypoxia, had a high affinity for agonist and increased agonist-induced calcium mobilization. Ser329A was no different from wild-type TP receptors. Ser331A was insensitive to hypoxia and PKA with a decreased agonist-mediated response.

CONCLUSIONS AND IMPLICATIONS

In hypoxic pulmonary hypertension, loss of site-specific phosphorylation of the TP receptor causes agonist hyper-responsiveness. Ser324 is the primary residue phosphorylated by PKA, which regulates TP receptor-agonist interactions. Ser331 mutation confers loss of TP receptor-agonist interaction, regardless of PKA activity.

Prenatal programming of pulmonary hypertension induced by chronic hypoxia or ductal ligation in sheep

Pulmonary hypertension of the newborn is caused by a spectrum of functional and structural abnormalities of the cardiopulmonary circuit. The existence of multiple etiologies and an incomplete understanding of the mechanisms of disease progression have hindered the development of effective therapies. Animal models offer a means of gaining a better understanding of the fundamental basis of the disease. To that effect, a number of experimental animal models are being used to generate pulmonary hypertension in the fetus and newborn. In this review, we compare the mechanisms associated with pulmonary hypertension caused by two such models: in utero ligation of the ductus arteriosus and chronic perinatal hypoxia in sheep fetuses and newborns. In this manner, we make direct comparisons between ductal ligation and chronic hypoxia with respect to the associated mechanisms of disease, since multiple studies have been performed with both models in a single species. We present evidence that the mechanisms associated with pulmonary hypertension are dependent on the type of stress to which the fetus is subjected. Such an analysis allows for a more thorough evaluation of the disease etiology, which can help focus clinical treatments. The final part of the review provides a clinical appraisal of current treatment strategies and lays the foundation for developing individualized therapies that depend on the causative factors.

Smooth muscle contractile diversity in the control of regional circulations

Each regional circulation has unique requirements for blood flow and thus unique mechanisms by which it is regulated. In this review we consider the role of smooth muscle contractile diversity in determining the unique properties of selected regional circulations and its potential influence on drug targeting in disease. Functionally smooth muscle diversity can be dichotomized into fast versus slow contractile gene programs, giving rise to phasic versus tonic smooth muscle phenotypes, respectively. Large conduit vessel smooth muscle is of the tonic phenotype; in contrast, there is great smooth muscle contractile diversity in the other parts of the vascular system. In the renal circulation, afferent and efferent arterioles are arranged in series and determine glomerular filtration rate. The afferent arteriole has features of phasic smooth muscle, whereas the efferent arteriole has features of tonic smooth muscle. In the splanchnic circulation, the portal vein and hepatic artery are arranged in parallel and supply blood for detoxification and metabolism to the liver. Unique features of this circulation include the hepatic-arterial buffer response to regulate blood flow and the phasic contractile properties of the portal vein. Unique features of the pulmonary circulation include the low vascular resistance and hypoxic pulmonary vasoconstriction, the latter attribute inherent to the smooth muscle cells but the mechanism uncertain. We consider how these unique properties may allow for selective drug targeting of regional circulations for therapeutic benefit and point out gaps in our knowledge and areas in need of further investigation.

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.

Reactive oxygen species as therapeutic targets in pulmonary hypertension

Pulmonary hypertension (PH) is characterized by a progressive elevation of pulmonary arterial pressure due to alterations of both pulmonary vascular structure and function. This disease is rare but life-threatening, leading to the development of right heart failure. Current PH treatments, designed to target altered pulmonary vascular reactivity, include vasodilating prostanoids, phosphodiesterase-5 inhibitors and endothelin-1 receptor antagonists. Although managing to slow the progression of the disease, these molecules still do not cure PH. More effective treatments need to be developed, and novel therapeutic strategies, targeting in particular vascular remodelling, are currently under investigation. Reactive oxygen species (ROS) are important physiological messengers in vascular cells. In addition to atherosclerosis and other systemic vascular diseases, emerging evidence also support a role of ROS in PH pathogenesis. ROS production is increased in animal models of PH, associated with NADPH oxidases increased expression, in particular of several Nox enzymes thought to be the major source of ROS in the pulmonary vasculature. These increases have also been observed in vitro and in vivo in humans. Moreover, several studies have shown either the deleterious effect of agents promoting ROS generation on pulmonary vasculature or, conversely, the beneficial effect of antioxidant agents in animal models of PH. In these studies, ROS production has been directly linked to pulmonary vascular remodelling, endothelial dysfunction, altered vasoconstrictive responses, inflammation and modifications of the extracellular matrix, all important features of PH pathophysiology. Altogether, these findings indicate that ROS are interesting therapeutic targets in PH. Blockade of ROS-dependent signalling pathways, or disruption of sources of ROS in the pulmonary vasculature, targeting in particular Nox enzymes, represent promising new therapeutic strategies in this disease.

Reactive oxygen and nitrogen species in pulmonary hypertension

Pulmonary vascular disease can be defined as either a disease affecting the pulmonary capillaries and pulmonary arterioles, termed pulmonary arterial hypertension, or a disease affecting the left ventricle, called pulmonary venous hypertension. Pulmonary arterial hypertension (PAH) is a disorder of the pulmonary circulation characterized by endothelial dysfunction, as well as intimal and smooth muscle proliferation. Progressive increases in pulmonary vascular resistance and pressure impair the performance of the right ventricle, resulting in declining cardiac output, reduced exercise capacity, right-heart failure, and ultimately death. While the primary and heritable forms of the disease are thought to affect over 5000 patients in the United States, the disease can occur secondary to congenital heart disease, most advanced lung diseases, and many systemic diseases. Multiple studies implicate oxidative stress in the development of PAH. Further, this oxidative stress has been shown to be associated with alterations in reactive oxygen species (ROS), reactive nitrogen species (RNS), and nitric oxide (NO) signaling pathways, whereby bioavailable NO is decreased and ROS and RNS production are increased. Many canonical ROS and NO signaling pathways are simultaneously disrupted in PAH, with increased expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases and xanthine oxidoreductase, uncoupling of endothelial NO synthase (eNOS), and reduction in mitochondrial number, as well as impaired mitochondrial function. Upstream dysregulation of ROS/NO redox homeostasis impairs vascular tone and contributes to the pathological activation of antiapoptotic and mitogenic pathways, leading to cell proliferation and obliteration of the vasculature. This paper will review the available data regarding the role of oxidative and nitrosative stress and endothelial dysfunction in the pathophysiology of pulmonary hypertension, and provide a description of targeted therapies for this disease.

Endothelium-mediated control of vascular tone: COX-1 and COX-2 products

Endothelium-dependent contractions contribute to endothelial dysfunction in various animal models of aging, diabetes and cardiovascular diseases. In the spontaneously hypertensive rat, the archetypal model for endothelium-dependent contractions, the production of the endothelium-derived contractile factors (EDCF) involves an increase in endothelial intracellular calcium concentration, the production of reactive oxygen species, the predominant activation of cyclooxygenase-1 (COX-1) and to a lesser extent that of COX-2, the diffusion of EDCF towards the smooth muscle cells and the subsequent stimulation of their thromboxane A2-endoperoxide TP receptors. Endothelium-dependent contractions are also observed in various models of hypertension, aging and diabetes. They generally also involve the generation of COX-1- and/or COX-2-derived products and the activation of smooth muscle TP receptors. Depending on the model, thromboxane A(2), PGH(2), PGF(2α), PGE(2) and paradoxically PGI(2) can all act as EDCFs. In human, the production of COX-derived EDCF is a characteristic of the aging and diseased blood vessels, with essential hypertension causing an earlier onset and an acceleration of this endothelial dysfunction. As it has been observed in animal models, COX-1, COX-2 or both isoforms can contribute to these endothelial dysfunctions. Since in most cases, the activation of TP receptors is the common downstream effector, selective antagonists of this receptor should curtail endothelial dysfunction and be of therapeutic interest in the treatment of cardiovascular disorders.

NADPH oxidase-derived ROS and the regulation of pulmonary vessel tone

Pulmonary vessel constriction results from an imbalance between vasodilator and vasoconstrictor factors released by the endothelium including nitric oxide, endothelin, prostanoids, and reactive oxygen species (ROS). ROS, generated by a variety of enzymatic sources (such as mitochondria and NADPH oxidases, a.k.a. Nox), appear to play a pivotal role in vascular homeostasis, whereas elevated levels effect vascular disease. The pulmonary circulation is very sensitive to changes in the partial pressure of oxygen and differs from the systemic circulation in its response to this change. In fact, the pulmonary vessels contract in response to low oxygen tension, whereas systemic vessels dilate. Growing evidence suggests that ROS production and ROS-related pathways may be key factors that underlie this differential response to oxygen tension. A major emphasis of our laboratory is the role of Nox isozymes in cardiovascular disease. In this review, we will focus our attention on the role of Nox-derived ROS in the control of pulmonary vascular tone.

Inhibition of MRP4 prevents and reverses pulmonary hypertension in mice

Multidrug resistance-associated protein 4 (MRP4, also known as Abcc4) regulates intracellular levels of cAMP and cGMP in arterial SMCs. Here, we report our studies of the role of MRP4 in the development and progression of pulmonary arterial hypertension (PAH), a severe vascular disease characterized by chronically elevated pulmonary artery pressure and accompanied by remodeling of the small pulmonary arteries as a prelude to right heart failure and premature death. MRP4 expression was increased in pulmonary arteries from patients with idiopathic PAH as well as in WT mice exposed to hypoxic conditions. Consistent with a pathogenic role for MRP4 in PAH, WT mice exposed to hypoxia for 3 weeks showed reversal of hypoxic pulmonary hypertension (PH) following oral administration of the MRP4 inhibitor MK571, and Mrp4-/- mice were protected from hypoxic PH. Inhibition of MRP4 in vitro was accompanied by increased intracellular cAMP and cGMP levels and PKA and PKG activities, implicating cyclic nucleotide-related signaling pathways in the mechanism underlying the protective effects of MRP4 inhibition. Our data suggest that MRP4 could represent a potential target for therapeutic intervention in PAH.

The thromboxane/endoperoxide receptor (TP): the common villain

The stimulation of thromboxane/endoperoxide receptors (TP) elicits diverse physiological/pathophysiological reactions, including platelet aggregation and contraction of vascular smooth muscle. Furthermore, the activation of endothelial TP promotes the expression of adhesion molecules and favors adhesion and infiltration of monocytes/macrophages. In various cardiovascular diseases, endothelial dysfunction is predominantly the result of the release of endothelium-derived contracting factors that counteract the vasodilator effect of nitric oxide produced by the endothelial nitric oxide synthase. Endothelium-dependent contractions involve the activation of cyclooxygenases, the production of reactive oxygen species along with that of endothelium-derived contracting factors, which diffuse toward the vascular smooth muscle cells and activate their TP. TP antagonists curtail the endothelial dysfunction in diseases such as hypertension and diabetes, are potent antithrombotic agents, and reduce vascular inflammation. Therefore, TP antagonists, because of this triple activity, may have a unique potential for the treatment of cardiovascular disorders.

Reactive oxygen species signaling in pulmonary vascular smooth muscle

In recent years, it has become evident that reactive oxygen species (ROS) play a critical role in the regulation of several physiological and pathophysiological processes. Herein we review the main sources, targets and pathophysiological roles of ROS in pulmonary vascular smooth muscle. Mitochondria and NADPH oxidases represent the major sources of ROS in vascular cells. In addition, ROS can be produced by different pathways of arachidonic acid metabolism, endothelial NO synthase (eNOS) and xantine oxidase. There is increasing evidence for the role of ROS, specially hydrogen peroxide, as signaling moieties to induce increase in intracellular calcium concentration ([Ca2+]i) and contraction in pulmonary artery smooth muscle cells (PASMC) through the modulation of a variety of targets, such as Rho kinases (ROCK), protein kinase C (PKC), voltage-gated potassium K+ (Kv) channels and ryanodine receptors (RyR). Thus, an increase in ROS has been reported to contribute to the responses induced by different vasoconstrictor stimuli, including hypoxia. Finally, results from recent studies highlighting the involvement of ROS in the development of pulmonary hypertension are discussed in the present paper.