Role of the prostanoid EP4 receptor in iloprost-mediated vasodilatation in pulmonary hypertension

Pharmacological inhibition of MALT1 (mucosa-associated lymphoid tissue lymphoma translocation protein 1) induces ferroptosis in vascular smooth muscle cells

MALT1 (mucosa-associated lymphoid tissue lymphoma translocation protein 1) is a human paracaspase protein with proteolytic activity via its caspase-like domain. The pharmacological inhibition of MALT1 by MI-2, a specific chemical inhibitor, diminishes the response of endothelial cells to inflammatory stimuli. However, it is largely unknown how MALT1 regulates the functions of vascular smooth muscle cells (SMCs). This study aims to investigate the impact of MALT1 inhibition by MI-2 on the functions of vascular SMCs, both in vitro and in vivo. MI-2 treatment led to concentration- and time-dependent cell death of cultured aortic SMCs, which was rescued by the iron chelator deferoxamine (DFO) or ferrostatin-1 (Fer-1), a specific inhibitor of ferroptosis, but not by inhibitors of apoptosis (Z-VAD-fmk), pyroptosis (Z-YVAD-fmk), or necrosis (Necrostatin-1, Nec-1). MI-2 treatment downregulated the expression of glutathione peroxidase 4 (GPX4) and ferritin heavy polypeptide 1 (FTH1), which was prevented by pre-treatment with DFO or Fer-1. MI-2 treatment also activated autophagy, which was inhibited by Atg7 deficiency or bafilomycin A1 preventing MI-2-induced ferroptosis. MI-2 treatment reduced the cleavage of cylindromatosis (CYLD), a specific substrate of MALT1. Notably, MI-2 treatment led to a rapid loss of contractility in mouse aortas, which was prevented by co-incubation with Fer-1. Moreover, local application of MI-2 significantly reduced carotid neointima lesions and atherosclerosis in C57BL/6J mice and apolipoprotein-E knockout (ApoE-/-) mice, respectively, which were both ameliorated by co-treatment with Fer-1. In conclusion, the present study demonstrated that MALT1 inhibition induces ferroptosis of vascular SMCs, likely contributing to its amelioration of proliferative vascular diseases.

The Emerging Therapeutic Role of Prostaglandin E2 Signaling in Pulmonary Hypertension

Mild-to-moderate pulmonary hypertension (PH) is a common complication of chronic obstructive pulmonary disease (COPD). It is characterized by narrowing and thickening of the pulmonary arteries, resulting in increased pulmonary vascular resistance (PVR) and ultimately leading to right ventricular dysfunction. Pulmonary vascular remodeling in COPD is the main reason for the increase of pulmonary artery pressure (PAP). The pathogenesis of PH in COPD is complex and multifactorial, involving chronic inflammation, hypoxia, and oxidative stress. To date, prostacyclin and its analogues are widely used to prevent PH progression in clinical. These drugs have potent anti-proliferative, anti-inflammatory, and stimulating endothelial regeneration properties, bringing therapeutic benefits to the slowing, stabilization, and even some reversal of vascular remodeling. As another well-known and extensively researched prostaglandins, prostaglandin E2 (PGE2) and its downstream signaling have been found to play an important role in various biological processes. Emerging evidence has revealed that PGE2 and its receptors (i.e., EP1-4) are involved in the regulation of pulmonary vascular homeostasis and remodeling. This review focuses on the research progress of the PGE2 signaling pathway in PH and discusses the possibility of treating PH based on the PGE2 signaling pathway.

Prostaglandin and prostaglandin receptors: present and future promising therapeutic targets for pulmonary arterial hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH), Group 1 pulmonary hypertension (PH), is a type of pulmonary vascular disease characterized by abnormal contraction and remodeling of the pulmonary arterioles, manifested by pulmonary vascular resistance (PVR) and increased pulmonary arterial pressure, eventually leading to right heart failure or even death. The mechanisms involved in this process include inflammation, vascular matrix remodeling, endothelial cell apoptosis and proliferation, vasoconstriction, vascular smooth muscle cell proliferation and hypertrophy. In this study, we review the mechanisms of action of prostaglandins and their receptors in PAH.

MAIN BODY

PAH-targeted therapies, such as endothelin receptor antagonists, phosphodiesterase type 5 inhibitors, activators of soluble guanylate cyclase, prostacyclin, and prostacyclin analogs, improve PVR, mean pulmonary arterial pressure, and the six-minute walk distance, cardiac output and exercise capacity and are licensed for patients with PAH; however, they have not been shown to reduce mortality. Current treatments for PAH primarily focus on inhibiting excessive pulmonary vasoconstriction, however, vascular remodeling is recalcitrant to currently available therapies. Lung transplantation remains the definitive treatment for patients with PAH. Therefore, it is imperative to identify novel targets for improving pulmonary vascular remodeling in PAH. Studies have confirmed that prostaglandins and their receptors play important roles in the occurrence and development of PAH through vasoconstriction, vascular smooth muscle cell proliferation and migration, inflammation, and extracellular matrix remodeling.

CONCLUSION

Prostacyclin and related drugs have been used in the clinical treatment of PAH. Other prostaglandins also have the potential to treat PAH. This review provides ideas for the treatment of PAH and the discovery of new drug targets.

HMGB1-induced activation of ER stress contributes to pulmonary artery hypertension in vitro and in vivo

BACKGROUND

HMGB1 and ER stress have been considered to participate in the progression of pulmonary artery hypertension (PAH). However, the molecular mechanism underlying HMGB1 and ER stress in PAH remains unclear. This study aims to explore whether HMGB1 induces pulmonary artery smooth muscle cells (PASMCs) functions and pulmonary artery remodeling through ER stress activation.

METHODS

Primary cultured PASMCs and monocrotaline (MCT)-induced PAH rats were applied in this study. Cell proliferation and migration were determined by CCK-8, EdU and transwell assay. Western blotting was conducted to detect the protein levels of protein kinase RNA-like endoplasmic reticulum kinase (PERK), activating transcription factor-4 (ATF4), seven in absentia homolog 2 (SIAH2) and homeodomain interacting protein kinase 2 (HIPK2). Hemodynamic measurements, immunohistochemistry staining, hematoxylin and eosin staining were used to evaluate the development of PAH. The ultrastructure of ER was observed by transmission electron microscopy.

RESULTS

In primary cultured PASMCs, HMGB1 reduced HIPK2 expression through upregulation of ER stress-related proteins (PERK and ATF4) and subsequently increased SIAH2 expression, which ultimately led to PASMC proliferation and migration. In MCT-induced PAH rats, interfering with HMGB1 by glycyrrhizin, suppression of ER stress by 4-phenylbutyric acid or targeting SIAH2 by vitamin K3 attenuated the development of PAH. Additionally, tetramethylpyrazine (TMP), as a component of traditional Chinese herbal medicine, reversed hemodynamic deterioration and vascular remodeling by targeting PERK/ATF4/SIAH2/HIPK2 axis.

CONCLUSIONS

The present study provides a novel insight to understand the pathogenesis of PAH and suggests that targeting HMGB1/PERK/ATF4/SIAH2/HIPK2 cascade might have potential therapeutic value for the prevention and treatment of PAH.

Identification of biomarkers related to copper metabolism in patients with pulmonary arterial hypertension

BACKGROUND

The pathogenesis of pulmonary arterial hypertension (PAH) and associated biomarkers remain to be studied. Copper metabolism is an emerging metabolic research direction in many diseases, but its role in PAH is still unclear.

METHODS

PAH-related datasets were downloaded from the Gene Expression Omnibus database, and 2067 copper metabolism-related genes (CMGs) were obtained from the GeneCards database. Differential expression analysis and the Venn algorithm were used to acquire the differentially expressed CMGs (DE-CMGs). DE-CMGs were then used for the coexpression network construction to screen candidate key genes associated with PAH. Furthermore, the predictive performance of the model was verified by receiver operating characteristic (ROC) analysis, and genes with area under the curve (AUC) values greater than 0.8 were selected as diagnostic genes. Then support vector machine, least absolute shrinkage and selection operator regression, and Venn diagrams were applied to detect biomarkers. Moreover, gene set enrichment analysis was performed to explore the function of the biomarkers, and immune-related analyses were utilized to study the infiltration of immune cells. The drug-gene interaction database was used to predict potential therapeutic drugs for PAH using the biomarkers. Biomarkers expression in clinical samples was verified by real-time quantitative PCR.

RESULTS

Four biomarkers (DDIT3, NFKBIA, OSM, and PTGER4) were screened. The ROC analysis showed that the 4 biomarkers performed well (AUCs > 0.7). The high expression groups for the 4 biomarkers were enriched in protein activity-related pathways including protein export, spliceosome and proteasome. Furthermore, 8 immune cell types were significantly different between the two groups, including naive B cells, memory B cells, and resting memory CD4 T cells. Afterward, a gene-drug network was constructed. This network illustrated that STREPTOZOCIN, IBUPROFEN, and CELECOXIB were shared by the PTGER4 and DDIT3. Finally, the results of RT-qPCR in clinical samples further confirmed the results of the public database for the expression of NFKBIA and OSM.

CONCLUSION

In conclusion, four biomarkers (DDIT3, NFKBIA, OSM, and PTGER4) with considerable diagnostic values were identified, and a gene-drug network was further constructed. The results of this study may have significant implications for the development of new diagnostic biomarkers and actionable targets to expand treatment options for PAH patients.

The Prostacyclin Analogue Iloprost Modulates CXCL10 in Systemic Sclerosis

The prostacyclin analogue iloprost is used to treat vascular alterations and digital ulcers, the early derangements manifesting in systemic sclerosis (SSc), an autoimmune disease leading to skin and organ fibrosis. Bioindicator(s) of SSc onset and progress are still lacking and the therapeutic approach remains a challenge. The T helper 1 (Th1) chemokine interferon (IFN)γ-induced protein 10 (IP-10/CXCL10) associates with disease progression and worse prognosis. Endothelial cells and fibroblasts, under Th1-dominance, release CXCL10, further enhancing SSc’s detrimental status. We analyzed the effect of iloprost on CXCL10 in endothelial cells, dermal fibroblasts, and in the serum of SSc patients. Human endothelial cells and dermal fibroblasts activated with IFNγ/Tumor Necrosis Factor (TNF)α, with/without iloprost, were investigated for CXCL10 secretion/expression and for intracellular signaling cascade underlying chemokine release (Signal Transducer and Activator of Transcription 1, STAT1; Nuclear Factor kappa-light-chain-enhancer of activated B cells, NF-kB; c-Jun NH₂-terminal kinase, JNK: Phosphatidyl-Inositol 3-kinase (PI3K)/protein kinase B, AKT; Extracellular signal-Regulated Kinase 1/2, ERK1/2). CXCL10 was quantified in sera from 25 patients taking iloprost, satisfying the American College of Rheumatology (ACR)/European Alliance of Associations for Rheumatology (EULAR) 2013 classification criteria for SSc, and in sera from 20 SSc sex/age-matched subjects without therapy, previously collected. In human endothelial cells and fibroblasts, iloprost targeted CXCL10, almost preventing IFNγ/TNFα-dependent cascade activation in endothelial cells. In SSc subjects taking iloprost, serum CXCL10 was lower. These in vitro and in vivo data suggest a potential role of iloprost to limit CXCL10 at local vascular/dermal and systemic levels in SSc and warrant further translational research aimed to ameliorate SSc understanding/management.

Induction of GLI1 by miR-27b-3p/FBXW7/KLF5 pathway contributes to pulmonary arterial hypertension

Glioma-associated oncogene homolog 1 (GLI1), a zinc-finger transcription factor, is upregulated in tumors and promotes cancer cell proliferation and migration. However, whether GLI1 involves in pulmonary artery smooth muscle cells (PASMCs) proliferation and migration and the detailed molecular mechanisms underlying GLI1 in pulmonary arterial hypertension (PAH) are not yet clear. Primary cultured rat PASMCs and monocrotaline (MCT)-induced PAH rats model were applied to address these issues in the present study. We found that the expression of GLI1 was significantly increased in endothelin-1 (ET-1) treated PASMCs, accompanied with the activation of microRNA (miR)-27b-3p/F-box and WD repeat domain containing 7 (FBXW7)/kruppel-like factor 5 (KLF5)/GLI1 pathway through endothelin-1 receptor type A (ETAR). Elevated miR-27b-3p suppressed FBXW7 expression, which led to KLF5 accumulation by decreasing its ubiquitinated degradation, KLF5 further induced GLI1 upregulation leading to PASMCs proliferation and migration. In addition, in MCT-induced PAH rats, targeting ETAR/miR-27b-3p/FBXW7/KLF5/GLI1 pathway effectively prevented the pulmonary vascular remodeling and the development of PAH in rats. Our study indicates that interfering ETAR/miR-27b-3p/FBXW7/KLF5/GLI1 signaling axis might have a potential value in the prevention and treatment of PAH.

Epigenetic reactivation of transcriptional programs orchestrating fetal lung development in human pulmonary hypertension

Phenotypic alterations in resident vascular cells contribute to the vascular remodeling process in diseases such as pulmonary (arterial) hypertension [P(A)H]. How the molecular interplay between transcriptional coactivators, transcription factors (TFs), and chromatin state alterations facilitate the maintenance of persistently activated cellular phenotypes that consequently aggravate vascular remodeling processes in PAH remains poorly explored. RNA sequencing (RNA-seq) in pulmonary artery fibroblasts (FBs) from adult human PAH and control lungs revealed 2460 differentially transcribed genes. Chromatin immunoprecipitation sequencing (ChIP-seq) revealed extensive differential distribution of transcriptionally accessible chromatin signatures, with 4152 active enhancers altered in PAH-FBs. Integrative analysis of RNA-seq and ChIP-seq data revealed that the transcriptional signatures for lung morphogenesis were epigenetically derepressed in PAH-FBs, including coexpression of T-box TF 4 (TBX4), TBX5, and SRY-box TF 9 (SOX9), which are involved in the early stages of lung development. These TFs were expressed in mouse fetuses and then repressed postnatally but were maintained in persistent PH of the newborn and reexpressed in adult PAH. Silencing of TBX4, TBX5, SOX9, or E1A-associated protein P300 (EP300) by RNA interference or small-molecule compounds regressed PAH phenotypes and mesenchymal signatures in arterial FBs and smooth muscle cells. Pharmacological inhibition of the P300/CREB-binding protein complex reduced the remodeling of distal pulmonary vessels, improved hemodynamics, and reversed established PAH in three rodent models in vivo, as well as reduced vascular remodeling in precision-cut tissue slices from human PAH lungs ex vivo. Epigenetic reactivation of TFs associated with lung development therefore underlies PAH pathogenesis, offering therapeutic opportunities.

The Design of Multi-target Drugs to Treat Cardiovascular Diseases: Two (or more) Birds on one Stone

Cardiovascular diseases (CVDs) comprise a group of diseases and disorders of the heart and blood vessels, which together are the number one cause of death worldwide, being associated with multiple genetic and modifiable risk factors, and that may directly arise from different etiologies. For a long time, the search for cardiovascular drugs was based on the old paradigm "one compound - one target", which aims to obtain a highly potent and selective molecule with only one desired molecular target. Although historically successful in the last decades, this approach ignores the multiple causes and the multifactorial nature of CVD's. Thus, over time, treatment strategies for cardiovascular diseases have changed and, currently, pharmacological therapies for CVD are mainly based on the association of two or more drugs to control symptoms and reduce cardiovascular death. In this context, the development of multitarget drugs, i.e, compounds having the ability to act simultaneously at multiple sites, is an attractive and relevant strategy that can be even more advantageous to achieve predictable pharmacokinetic and pharmacodynamics correlations as well as better patient compliance. In this review, we aim to highlight the efforts and rational pharmacological bases for the design of some promising multitargeted compounds to treat important cardiovascular diseases like heart failure, atherosclerosis, acute myocardial infarction, pulmonary arterial hypertension and arrhythmia.

Inflammation, Fibrosis and Cancer: Mechanisms, Therapeutic Options and Challenges

Uncontrolled inflammation is a salient factor in multiple chronic inflammatory diseases and cancers. In this review, we provided an in-depth analysis of the relationships and distinctions between uncontrolled inflammation, fibrosis and cancers, while emphasizing the challenges and opportunities of developing novel therapies for the treatment and/or management of these diseases. We described how drug delivery systems, combination therapy and the integration of tissue-targeted and/or pathways selective strategies could overcome the challenges of current agents for managing and/or treating chronic inflammatory diseases and cancers. We also recognized the value of the re-evaluation of the disease-specific roles of multiple pathways implicated in the pathophysiology of chronic inflammatory diseases and cancers-as well as the application of data from single-cell RNA sequencing in the success of future drug discovery endeavors.

Cutaneous iontophoresis of vasoactive medications in patients with scleroderma-associated pulmonary arterial hypertension

BACKGROUND

It remains unknown whether the cutaneous microvascular responses are different between patients with scleroderma-associated pulmonary arterial hypertension (SSc-PAH) and SSc without pulmonary hypertension (PH).

METHODS

We included 59 patients with SSc between March 2013 and September 2019. We divided patients into 4 groups: (a) no PH by right heart catheterization (RHC) (n = 8), (b) no PH by noninvasive screening tests (n = 16), (c) treatment naïve PAH (n = 16), and (d) PAH under treatment (n = 19). Microvascular studies using laser Doppler flowmetry (LDF) were done immediately after RHC or at the time of an outpatient clinic visit (group b).

RESULTS

The median (IQR) age was 59 (54-68) years, and 90% were females. The responses to local thermal stimulation and postocclusive reactive hyperemia, acetylcholine, and sodium nitroprusside iontophoresis were similar among groups. The microvascular response to treprostinil was more pronounced in SSc patients without PH by screening tests (% change: 340 (214-781)) compared with SSc-PAH (naïve + treatment) (Perfusion Units (PU) % change: 153 (94-255) % [p = .01]). The response to A-350619 (a soluble guanylate cyclase (sGC) activator) was significantly higher in patients with SSc without PH by screening tests (PU % change: 168 (46-1,296)) than those with SSc-PAH (PU % change: 22 (15-57) % [p = .006]). The % change in PU with A350619 was directly associated with cardiac index and stroke volume index (R: 0.36, p = .03 and 0.39, p = .02, respectively).

CONCLUSIONS

Patients with SSc-PAH have a lower cutaneous microvascular response to a prostacyclin analog treprostinil and the sGC activator A-350619 when compared with patients with SSc and no evidence of PH on screening tests, presumably due to a peripheral reduction in prostacyclin receptor expression and nitric oxide bioavailability.

Lumican deficiency promotes pulmonary arterial remodeling

Pulmonary arterial hypertension (PAH) is caused by progressive extracellular matrix disorganization and increased pulmonary vascular cell proliferation. Lumican is a member of the small leucine-rich proteoglycan family that controls cell proliferation, and is a potential endogenous modulator of TGF-β signaling pathway. We show that the decreased lumican protein levels in pulmonary arterial smooth muscle cells (PASMCs) is related to the vascular remodeling and stiffening observed in PAH. The role of lumican in PASMC accumulation and activation in response to pulmonary vascular remodeling remains unclear and we hypothesized that the loss of lumican in PASMCs promotes the development of PAH. Our aim was to establish that lumican plays a pivotal role in modulating pathological vascular remodeling in humans using a rat model of monocrotaline-induced PAH and chronically hypoxic mice. We found that mice with a homozygous deletion of lumican (Lum-/-) showed severe pulmonary arterial remodeling and right ventricular hypertrophy in response to hypoxia, and these effects in mice with chronic hypoxia-induced pulmonary hypertension were successfully treated by the administration of a lumican C-terminal peptide (LumC13C-A, lumikine). We identified a mechanistic link by which lumican signaling prevents the activation of phosphorylated AKT, resulting in the suppression of PASMC proliferation. Lumican deficiency promotes pulmonary arterial remodeling. Administration of lumikine reverses the PAH pathogenesis caused by hypoxia-induced experimental PAH. Lumican is an antiproliferative target that functions to suppress pAKT activation during pathogenesis.

Role of the Purinergic P2Y2 Receptor in Pulmonary Hypertension

Pulmonary arterial hypertension (PAH), group 1 pulmonary hypertension (PH), is a fatal disease that is characterized by vasoconstriction, increased pressure in the pulmonary arteries, and right heart failure. PAH can be described by abnormal vascular remodeling, hyperproliferation in the vasculature, endothelial cell dysfunction, and vascular tone dysregulation. The disease pathomechanisms, however, are as yet not fully understood at the molecular level. Purinergic receptors P2Y within the G-protein-coupled receptor family play a major role in fluid shear stress transduction, proliferation, migration, and vascular tone regulation in systemic circulation, but less is known about their contribution in PAH. Hence, studies that focus on purinergic signaling are of great importance for the identification of new therapeutic targets in PAH. Interestingly, the role of P2Y2 receptors has not yet been sufficiently studied in PAH, whereas the relevance of other P2Ys as drug targets for PAH was shown using specific agonists or antagonists. In this review, we will shed light on P2Y receptors and focus more on the P2Y2 receptor as a potential novel player in PAH and as a new therapeutic target for disease management.

In search of pulmonary hypertension treatments: Effect of 17β-estradiol on PGI2 pathway in human pulmonary artery

INTRODUCTION

Prostacyclin (PGI₂) is synthetized by PGI₂ synthase (PGIS) and induces vasorelaxation via activation of cyclic AMP (cAMP) generating IP-receptor. Several components of the PGI₂ signaling pathway are reduced in patients with pulmonary hypertension (PH).

AIM

To study the effect of 17β-estradiol (E2) on the PGI₂ signaling pathway in human pulmonary arteries (HPA) and in their smooth muscle cells (hPASMC) derived from Group-3 PH and non-PH patients.

METHODS

Following E2-treatments of isolated HPA and cultured hPASMC, we measured: 6-keto-Prostaglandin F_1α (PGI₂ stable metabolite) by ELISA, PGIS and IP protein levels by Western blot and HPA vasorelaxations with an organ bath system.

RESULTS

Incubation with E2 (24/48 h, doses ≥ 10 nM) significantly increased the expression of PGIS in hPASMC derived from both PH (65-98%) and non-PH (21-33%) patients, whereas incubation with E2 (2 h, 0.1 and 1 µM) increased 6-keto-PGF_1α production in HPA from Group-3 PH patients only, and did not affect 6-keto-PGF_1α production in hPASMC from either non-PH or Group-3 PH patients. Increases in IP receptor expression were observed following 10 mM E2-treatment of hPASMC from non-PH (33% after 48 h) and Group-3 PH (23% after 24 h) patient lungs. Finally, preincubation with 100 nM E2 significantly increased arachidonic acid-induced vasorelaxation of HPA from non-PH patient lungs but not of HPA from Group-3 PH patient lungs.

CONCLUSION

E2-treatment may help to restore the PGI₂-pathway in Group-3 PH.

An overview of the biology of a long-acting inhaled treprostinil prodrug

Treprostinil (TRE) is a prostanoid analog pulmonary vasodilator drug marketed with subcutaneous, intravenous (i.v.), oral, and inhaled routes of administration for the treatment of pulmonary arterial hypertension (PAH). Due to its short half-life, TRE requires either continuous infusion or multiple dosing, which exacerbates its side effects. Therefore, a long-acting prostanoid analog that maintains the positive attributes of TRE but has fewer TRE-related side effects could be of clinical benefit. In this report, we describe the discovery, preclinical development, and biology of the TRE ester prodrug, treprostinil palmitil (TP), which is formulated in a lipid nanoparticle (LNP) for administration as a nebulized inhaled suspension (TPIS). In screening assays focused on the conversion of prodrug to TRE, TP (16 carbon alkyl chain) had the slowest rate of conversion compared with short-alkyl chain TRE prodrugs (i.e., 2-8 carbon alkyl chain). Furthermore, TP is a pure prodrug and possesses no inherent binding to G-protein coupled receptors including prostanoid receptors. Pharmacokinetic studies in rats and dogs demonstrated that TPIS maintained relatively high concentrations of TP in the lungs yet had a low maximum plasma concentrations (C_max) of both TP and, more importantly, the active product, TRE. Efficacy studies in rats and dogs demonstrated inhibition of pulmonary vasoconstriction induced by exposure to hypoxic air or i.v.-infused U46619 (thromboxane mimetic) over 24 h with TPIS. Cough was not observed with TPIS at an equivalent dose at which TRE caused cough in guinea pigs and dogs, and there was no evidence of desensitization to the inhibition of pulmonary vasoconstriction in rats with repeat inhaled dosing. TPIS was also more efficacious than i.v.-infused TRE in a sugen/hypoxia rat model of PAH to inhibit pulmonary vascular remodeling, an effect likely driven by local activities of TRE within the lungs. TPIS also demonstrated antifibrotic and anti-inflammatory activity in the lungs in rodent models of pulmonary fibrosis and asthma. In a phase 1 study in healthy human participants, TPIS (referred to as INS1009) had a lower plasma TRE C_max and fewer respiratory-related side effects at equimolar doses compared with inhaled TRE. We have now formulated TP as an aerosol powder for delivery by a dry powder inhaler (referred to as treprostinil palmitil inhalation powder-TPIP), and as an aerosol solution in a fluorohydrocarbon solvent for delivery by a metered dose inhaler. These options may reduce drug administration time and involve less device maintenance compared with delivery by nebulization.

Treprostinil palmitil, an inhaled long-acting pulmonary vasodilator, does not show tachyphylaxis with daily dosing in rats

BACKGROUND

Treprostinil palmitil (TP) is an inhaled long-acting pulmonary vasodilator prodrug of treprostinil (TRE) that has been formulated for delivery as a suspension (treprostinil palmitil inhalation suspension; TPIS) and as a dry powder (treprostinil palmitil inhalation powder; TPIP). In humans, tachyphylaxis is frequently observed with continuous intravenous (IV) or subcutaneous (SC) infusion of TRE and requires dosage escalation to maintain activity. The aim of the present study was to determine whether tachyphylaxis occurs with repeat daily administration of inhaled TPIS.

METHODS

Experiments were performed in male Sprague-Dawley rats prepared with a telemetry probe implanted into the right ventricle to measure the change in right ventricular pulse pressure (ΔRVPP) induced by exposure to a 10% oxygen gas mixture. TPIS (6 mL) at concentrations of 0.25, 0.5, and 1 mM was given by nose-only inhalation using an Aeroneb Pro nebulizer, either as a single administration or daily for 16 or 32 consecutive days. In studies involving consecutive daily administrations of TPIS, the delivered TP dosage was 140.3 μg/kg at 1 mM and ranged from 40.2 to 72.2 μg/kg at 0.5 mM. A separate cohort of telemetered rats received continuous IV infusion of TRE via an Alzet mini-pump at a dosage rate of 250 ng/kg/min for 16 days. Blood and lung tissue samples were obtained, and the concentration of TRE in the plasma and TRE and TP in the lungs were measured approximately 1 h after TPIS administration.

RESULTS

Dose-response studies with TPIS administered as a single administration inhibited the hypoxia-induced increase in RVPP in both a concentration-dependent (0.25, 0.5, and 1 mM) and time-dependent (1-24 h) manner. TPIS, given QD or BID at inhaled doses ranging from 40.2 to 140.3 μg/kg for 16 or 32 consecutive days, produced statistically significant (P < .05) inhibition of the increase of RVPP due to hypoxia over the full duration of the dosing periods. By contrast, the inhibition of the hypoxia-induced increase in RVPP observed with IV TRE infusion (250 ng/kg/min) disappeared after 16 days of infusion. The plasma concentrations of TRE were significantly higher after IV TRE (range, 2.85-13.35 ng/mL) compared to inhaled TPIS (range, 0.22-0.73 ng/mL) CONCLUSIONS: There was no evidence of tachyphylaxis with repeat daily dosing of TPIS for a period of up to 32 days. The absence of tachyphylaxis with TPIS is likely related to its local vasodilatory effects within the lungs, combined with an absence of sustained high plasma concentrations of TRE.

Crosstalk between the COX2-PGE2-EP4 signaling pathway and primary cilia in osteoblasts after mechanical stimulation

Primary cilia have been found to function as mechanosensors in low-magnitude high-frequency vibration (LMHFV)-induced osteogenesis. The PGE2 also regulates bone homeostasis and mechanical osteogenesis through its receptor EP4 signaling, but its involvement in LMHFV-induced or in primary cilia-induced osteogenesis has not been investigated. We hypothesized that LMHFV stimulates osteoblast (OB) differentiation by activating the COX2-PGE2-EP pathway in a manner dependent on primary cilia and that primary cilia are also affected by the PGE2 pathway. In this study, through western blot analysis, RNA interference, enzyme-linked immunosorbent assay, real-time quantitative polymerase chain reaction, and cytochemical staining, we observed that COX2, mPGES-1, and PGE2 levels were markedly elevated in cells treated with LMHFV and were greatly decreased in LMHFV-treated cells following IFT88 silencing. EP4 expression was significantly increased in OBs following LMHFV treatment, but IFT88 silencing significantly blocked this increase. EP4 localized to the bases of primary cilia. LMHFV reduced the length and abundance of primary cilia, but the cells could self-repair their primary cilia after mechanical damage. EP4 antagonism significantly blocked the LMHFV-induced increase in IFT88 expression and blocked the recovery of primary cilia length and the proportion of cells with primary cilia. In addition, COX2 or EP4 antagonism disrupted LMHFV-induced osteogenesis. These results demonstrate the integration of and crosstalk between primary cilia and the COX2-PGE2-EP4 signaling pathway under mechanical stimulation.

International Union of Basic and Clinical Pharmacology. CIX. Differences and Similarities between Human and Rodent Prostaglandin E2 Receptors (EP1-4) and Prostacyclin Receptor (IP): Specific Roles in Pathophysiologic Conditions

Prostaglandins are derived from arachidonic acid metabolism through cyclooxygenase activities. Among prostaglandins (PGs), prostacyclin (PGI2) and PGE2 are strongly involved in the regulation of homeostasis and main physiologic functions. In addition, the synthesis of these two prostaglandins is significantly increased during inflammation. PGI2 and PGE2 exert their biologic actions by binding to their respective receptors, namely prostacyclin receptor (IP) and prostaglandin E2 receptor (EP) 1-4, which belong to the family of G-protein-coupled receptors. IP and EP1-4 receptors are widely distributed in the body and thus play various physiologic and pathophysiologic roles. In this review, we discuss the recent advances in studies using pharmacological approaches, genetically modified animals, and genome-wide association studies regarding the roles of IP and EP1-4 receptors in the immune, cardiovascular, nervous, gastrointestinal, respiratory, genitourinary, and musculoskeletal systems. In particular, we highlight similarities and differences between human and rodents in terms of the specific roles of IP and EP1-4 receptors and their downstream signaling pathways, functions, and activities for each biologic system. We also highlight the potential novel therapeutic benefit of targeting IP and EP1-4 receptors in several diseases based on the scientific advances, animal models, and human studies. SIGNIFICANCE STATEMENT: In this review, we present an update of the pathophysiologic role of the prostacyclin receptor, prostaglandin E2 receptor (EP) 1, EP2, EP3, and EP4 receptors when activated by the two main prostaglandins, namely prostacyclin and prostaglandin E2, produced during inflammatory conditions in human and rodents. In addition, this comparison of the published results in each tissue and/or pathology should facilitate the choice of the most appropriate model for the future studies.

Downregulation of PGI2 pathway in Pulmonary Hypertension Group-III patients

Pulmonary hypertension (PH) is a progressive and life-threating lung disorder characterized by elevated pulmonary artery pressure and vascular remodeling. PH is classified into five groups, and one of the most common and lethal forms, PH Group-III is defined as PH due to lung diseases and/or hypoxia. Due to the lack of studies in this group, PH-specific drug therapies including prostacyclin (PGI₂) analogues have not been approved or recommended for use in these patients. PGI₂ is synthesized by the PGI₂ synthase (PGIS) enzyme, and its production is determined by measuring its stable metabolite, 6-keto-PGF_1α. An impaired PGI₂ pathway has been observed in PH animal models and in PH Group-I patients; however, there are contradictory results. The aim of this study is to determine whether PH Group-III is associated with altered expression of PGIS and production of PGI₂ in humans. To explore this hypothesis, we measured PGIS expression (by western blot) and PGI₂ production (by ELISA) in a large variety of preparations from the pulmonary circulation including human pulmonary artery, pulmonary vein, distal lung tissue, pulmonary artery smooth muscle cells (hPASMC), and bronchi in PH Group-III (n = 35) and control patients (n = 32). Our results showed decreased PGIS expression and/or 6-keto-PGF_1α levels in human pulmonary artery, hPASMC, and distal lung tissue derived from PH Group-III patients. Moreover, the production of 6-keto-PGF_1α from hPASMC positively correlated with PGIS expression and was inversely correlated with mean pulmonary artery pressure. On the other hand, PH Group-III pulmonary veins and bronchi did not show altered PGI₂ production compared to controls. The deficit in PGIS expression and/or PGI₂ production observed in pulmonary artery and distal lung tissue in PH Group-III patients may have important implications in the pathogenesis and treatment of PH Group-III.

Remodeling Matrix Synthesis in a Rat Model of Aortocaval Fistula and the Cyclic Stretch: Impaction in Pulmonary Arterial Hypertension-Congenital Heart Disease

Pulmonary arterial hypertension-congenital heart disease (PAH-CHD) is characterized by systemic to pulmonary arterial shunts and sensitively responds to volume overload and stretch of the vascular wall leading to pulmonary vascular remodeling. We hypothesized that the responses of pulmonary artery smooth muscle cells (PASMCs) to mechanical stress-associated volume overload may promote vascular remodeling in PAH-CHD. Here, we show that significantly increased collagen was in the PA adventitial layer by trichrome staining in PAH-CHD patients and an aortocaval fistula (ACF) rat model in which chronic vascular volume overload induced-PAH. We assessed the gene expression profiles of SMC markers, extracellular matrix, and collagen in isolated SMCs from pulmonary and thoracic vessels with cyclic stretch-triggered responses by real-time PCR analysis. The data corresponded to collagen deposition, which modulated pulmonary vascular remodeling in clinical and experimental PAH-ACF cases as well as in cyclic stretch-triggered SMCs in an in vitro model. We observe that collagen I A2 (COLIA2) is expressed in the control rat, but collagen I A1 (COLIA1) and Notchs remarkably increase in the lungs of ACF rats. Interestingly, closing the left-to-right shunt that leads to a reduced blood volume in the PA system of ACF rats (ACFRs) decreased the expression of COLIA1 and increased that of collagen I A2(COLIA2). This study contributes to the stretch-induced responses of SMCs and provides important future directions for therapies aimed at preventing abnormal matrix protein synthesis in volume overload-induced pulmonary hypertension (PH).

Effects of Inhaled Iloprost on Lung Mechanics and Myocardial Function During One-Lung Ventilation in Chronic Obstructive Pulmonary Disease Patients Combined With Poor Lung Oxygenation

BACKGROUND

The ventilation/perfusion mismatch in chronic obstructive pulmonary disease (COPD) patients can exacerbate cardiac function as well as pulmonary oxygenation. We hypothesized that inhaled iloprost can ameliorate pulmonary oxygenation with lung mechanics and myocardial function during one-lung ventilation (OLV) in COPD patients combined with poor lung oxygenation.

METHODS

A total of 40 patients with moderate to severe COPD, who exhibited the ratio of partial pressure of arterial oxygen to the fraction of inspired oxygen (PaO2/FIO2) <150 mm Hg 30 minutes after initiating OLV, were enrolled in this study. Patients were randomly allocated into either ILO group (n = 20) or Control group (n = 20), in which iloprost (20 μg) and saline were inhaled, respectively. The PaO2/FIO2 ratio, dead space, dynamic compliance, and tissue Doppler imaging with myocardial performance index (MPI) were assessed 30 minutes after initiating OLV (pre-Tx) and 30 minutes after completion of drug inhalation (post-Tx). Repeated variables were analyzed using a linear mixed-model between the groups.

RESULTS

At pre-Tx, no differences were observed in measured parameters between the groups. At post-Tx, PaO2/FIO2 ratio (P < .001) and dynamic compliance (P = .023) were significantly higher and dead space ventilation was significantly lower (P = .001) in iloprost group (ILO group) compared to Control group. Left (P = .003) and right ventricular MPIs (P < .001) significantly decreased in ILO group compared to Control group.

CONCLUSIONS

Inhaled iloprost improved pulmonary oxygenation, lung mechanics, and cardiac function simultaneously during OLV in COPD patients with poor lung oxygenation.

Hemodynamic and clinical effects of selexipag in children with pulmonary hypertension

Selexipag is an oral prostacyclin receptor agonist; it was recently approved for use in adults with pulmonary arterial hypertension. The safety and efficacy of selexipag has not yet been determined in the pediatric population. We describe short-term hemodynamic and clinical data with selexipag therapy in four pediatric patients with pulmonary hypertension. We reviewed clinical, echocardiographic, and hemodynamic data. One patient was transitioned from subcutaneous treprostinil to selexipag, and in three patients, selexipag was added as a third agent. Drug dosing was attained empirically based on patient body size. A follow-up catheterization was performed 12-18 months after initiation of selexipag therapy. All four patients tolerated selexipag well, without significant side effects. One patient transitioned successfully from subcutaneous treprostinil to selexipag. None of the four patients had clinical deterioration. In three patients who were able to perform a 6-minute walk test, pre and post selexipag distances were 350 and 400, 409 and 390, and 300 and 360 m, respectively. Echocardiograms showed no significant changes. Catheterization showed a variable change in pulmonary vascular resistance (small decrease in three patients and increase in one patient). Brain natriuretic peptide levels before and after selexipag in the four patients were 38 and 49, 33 and 54, 29 and 25, and 12 and 14 pg/mL, respectively. Selexipag use for 16-28 months was safe in four pediatric patients; none of them had clinical deterioration. Larger number of patients and longer follow-up intervals are necessary before further recommendations can be made.

Bronchodilation induced by PGE2 is impaired in Group III pulmonary hypertension

BACKGROUND AND PURPOSE

In patients with pulmonary hypertension (PH) associated with lung disease and/or hypoxia (Group III), decreased pulmonary vascular tone and tissue hypoxia is therapeutically beneficial. PGE₂ and PGI₂ induce potent relaxation of human bronchi from non-PH (control) patients via EP₄ and IP receptors, respectively. However, the effects of PGE₂ /PGI₂ and their mimetics on human bronchi from PH patients are unknown. Here, we have compared relaxant effects of several PGI₂ -mimetics approved for treating PH Group I with several PGE₂ -mimetics, in bronchial preparations derived from PH Group III and control patients.

EXPERIMENTAL APPROACH

Relaxation of bronchial muscle was assessed in samples isolated from control and PH Group III patients. Expression of prostanoid receptors was analysed by western blot and real-time PCR, and endogenous PGE₂ , PGI₂ , and cAMP levels were determined by ELISA.

KEY RESULTS

Maximal relaxations induced by different EP₄ receptor agonists (PGE₂ , L-902688, and ONO-AE1-329) were decreased in human bronchi from PH patients, compared with controls. However, maximal relaxations produced by PGI₂ -mimetics (iloprost, treprostinil, and beraprost) were similar for both groups of patients. Both EP₄ and IP receptor protein and mRNA expressions were significantly lower in human bronchi from PH patients. cAMP levels significantly correlated with PGI₂ but not with PGE₂ levels.

CONCLUSION AND IMPLICATIONS

The PGI₂ -mimetics retained maximal bronchodilation in PH Group III patients, whereas bronchodilation induced by EP₄ receptor agonists was decreased. Restoration of EP₄ receptor expression in airways of PH Group III patients with respiratory diseases could bring additional therapeutic benefit.

Beraprost Upregulates KV Channel Expression and Function via EP4 Receptor in Pulmonary Artery Smooth Muscle Cells Obtained from Rats with Hypoxia-Induced Pulmonary Hypertension

The reduced expression and function of voltage-dependent potassium (KV) channels have been involved in the pathogenesis of hypoxia-induced pulmonary hypertension (HPH), leading to pulmonary vasoconstriction and vascular remodeling, while the upregulation of KV channels is of therapeutic significance for pulmonary hypertension. Beraprost sodium (BPS) has been shown to be effective in patients with pulmonary hypertension. However, the effect of BPS on O2-sensitive KV channels in pulmonary artery smooth muscle cells (PASMCs) remains unclear. In the present study, the effect of BPS on rats with HPH was observed, and the influence of BPS on the expression and function of O2-sensitive KV channels in PASMCs was investigated. The results revealed that BPS reduced mean pulmonary artery pressure, suppressed right ventricular hypertrophy, and attenuated the remodeling of pulmonary arteries in rats exposed to discontinuous hypoxia for 4 weeks (8 h/day). This was accompanied with the significantly upregulated expression of KV channel α-subunits (KV1.2, KV1.5 and KV2.1) and O2-sensitive voltage-gated K+ (KV) channel current (IK(V)) in small pulmonary arteries in HPH model rats, as well as in hypoxia-induced PASMCs. Furthermore, in vitrostudies have revealed that the upregulation of BPS on O2-sensitive KV channels was significantly inhibited after treatment with prostaglandin E2 receptor subtype EP4 antagonist GW627368X. Taken together, these results suggest that BPS attenuates the development of HPH through the upregulation of O2-sensitive KV channels, which was probably via the EP4 receptor-related pathway.

Cathepsin S promotes the development of pulmonary arterial hypertension

Cysteine cathepsin proteases play critical roles in cardiovascular disease progression and are implicated in extracellular matrix (ECM) degradation. Patients with pulmonary arterial hypertension (PAH) exhibit increased elastase production by pulmonary arterial smooth muscle cells (PASMCs), which is related to the degradation of elastic fibers and pulmonary vascular remodeling. However, the mechanism by which cathepsins regulate the ECM and PASMC proliferation in PAH remains unclear. We hypothesized that cathepsin proteases in PASMCs promote the development of PAH. Here, we show overexpression of cathepsin S (Cat S) and degradation of elastic laminae in the lungs of patients with idiopathic PAH and in the PASMCs of monocrotaline-induced PAH model (MCT-PAH) rats. In addition, pulmonary hypertension can be treated in MCT-PAH rats by administering a selective Cat S inhibitor, Millipore-219393, which stimulates peroxisome proliferator-activated receptor-γ (PPARγ) to inhibit the expression of Cat S, thus suppressing the proliferation and migration of MCT-PAH PASMCs. We then reduced Cat S or PPARγ expression by using small interfering RNA in human PASMCs to demonstrate a mechanistic link between Cat S signaling and PPARγ protein, and the results suggest that PPARγ is upstream of Cat S signaling. In conclusion, the activity of Cat S in pulmonary vascular remodeling and degradation of elastin fibers through the disruption of PPARγ is pathophysiologically significant in PAH.

Adverse Events of Prostacyclin Mimetics in Pulmonary Arterial Hypertension: A Systematic Review and Meta-Analysis

Prostacyclin mimetics (PMs) are effective for the treatment of pulmonary arterial hypertension (PAH). However, their clinical use may be limited by their adverse events. This study aims to quantify the different PM adverse events (AEs) with regard to their selectivity towards the prostacyclin (IP) receptor and their administrative routes. The study included randomised, placebo-controlled trials comparing iloprost, beraprost, treprostinil, and selexipag to placebo (published 2002–2016). We report the group efficacy differences between treatment and placebo by weighted and standardised mean difference. The probability of adverse events was determined by the odds ratio (OR). Of the 14 randomised clinical trials involving 3518 PAH patients, outcome and adverse event data were meta-analysed by drug type and route of administration. Prostacyclin mimetics comparison demonstrated a more significant discontinuation of the IP-selective agonist, selexipag, due to an adverse event (OR = 2.2; 95% CI: 1.5, 3.3). Compared to placebo, site pain associated with subcutaneously administered treprostinil was the most significant likely adverse event (OR = 17.5; 95% CI: 11.1, 27.1). Parenteral PMs were associated with fewer adverse effects overall. The overall efficacy of PMs to improve 6-minute walk distance by 16.3 meters was significant (95% CI: 13.0, 19.7). Decreases in pulmonary vascular resistance index (SMD = -5.5; 95% CI: -10.1, -0.9; I² = 98%) and mean pulmonary arterial pressure (SMD = -1.0; 95% CI: -2.6, -0.7; I² = 99%) in treatment groups were found to be significant. Adverse event profiles varied in response to administration route and PM type but were not negated by use of a selective IP agonist. Prostacyclin mimetics exposure to non-target IP receptors may underpin some AEs reported.

Mechanism of Beraprost Effects on Pulmonary Hypertension: Contribution of Cross-Binding to PGE2 Receptor 4 and Modulation of O2 Sensitive Voltage-Gated K+ Channels

Background: The purpose of this study is to elucidate mechanism(s) by which the orally active PGI2 analog, Beraprost (BPS), ameliorates pulmonary hypertension (PH). Prostaglandins are an important treatment for PH. Mechanisms of their action are not fully elucidated in relation to receptor subtype and effects on O2 sensitive Kv channels. Methods: Distal (3rd order and beyond) pulmonary arteries from chronically hypoxic rats and from humans with established PH were studied. Measurements included pulmonary haemodynamics and histology, vascular reactivity, prostanoid receptor expression and activity of the O2 sensitive Kv channels. Results: Prostacyclin receptor (IP), prostaglandin receptor E3 (EP3) and prostaglandin receptor E4 (EP4) are the main pulmonary artery receptor subtypes in both rat and human pulmonary arteries. Circulating levels of PGI2 and PGE2 were reduced in PH. PH was also associated with reduced receptor expression of IP but not of EP4. The effects on IP expression were overcome with BPS. Dilatory responses in PH to BPS were reduced in the presence of EP4 blockade. Expression and activity of oxygen sensitive Kv channels were reduced in pulmonary artery smooth muscle cell from rats with PH and humans with PAH and were also overcome by administration of BPS. Effects of BPS on oxygen sensitive Kv channels were reduced in the presence of EP4 blockade implicating the EP4 receptor, as well as the IP receptor, in mediating BPS effects. Conclusion: Reduced expression of pulmonary IP receptors and reduced activity of O2 sensitive Kv channels are found in PH in both humans and rats. The orally active prostacyclin analogue, BPS, is able to reverse these changes, partly through binding to the EP4 receptor.

The Role of G Protein-Coupled Receptors in the Right Ventricle in Pulmonary Hypertension

Pressure overload of the right ventricle (RV) in pulmonary arterial hypertension (PAH) leads to RV remodeling and failure, an important determinant of outcome in patients with PAH. Several G protein-coupled receptors (GPCRs) are differentially regulated in the RV myocardium, contributing to the pathogenesis of RV adverse remodeling and dysfunction. Many pharmacological agents that target GPCRs have been demonstrated to result in beneficial effects on left ventricular (LV) failure, such as beta-adrenergic receptor and angiotensin receptor antagonists. However, the role of such drugs on RV remodeling and performance is not known at this time. Moreover, many of these same receptors are also expressed in the pulmonary vasculature, which could result in complex effects in PAH. This manuscript reviews the role of GPCRs in the RV remodeling and dysfunction and discusses activating and blocking GPCR signaling to potentially attenuate remodeling while promoting improvements of RV function in PAH.

Iloprost infusion prevents the insulin-induced reduction in skeletal muscle microvascular blood volume but does not enhance peripheral glucose uptake in type 2 diabetic patients

AIMS

In type 2 diabetes impaired insulin-induced muscle perfusion is thought to contribute to reduced whole-body glucose uptake. In this study, we examined the effects of iloprost, a stable prostacyclin analogue, on insulin-induced muscle capillary recruitment and whole-body glucose uptake.

MATERIALS AND METHODS

In a randomized cross-over design, 12 type 2 diabetes patients (age, 55 [46-69] years; BMI, 33.1 [31.0-39] kg/m² ) underwent two hyperinsulinaemic-euglycaemic clamps, one with and one without simultaneous low-dose iloprost infusion. Contrast-enhanced ultrasonography of the vastus lateralis muscle was performed before and during the clamp. Muscle capillary recruitment was calculated as percentage change in microvascular blood volume (MBV) before and during the clamp.

RESULTS

Insulin infusion reduced skeletal muscle MBV by ~50% compared to the fasting state (fasting, 1.77·10^-4 [1.54·10^-5 -2.44·10^-3 ] arbitrary units (AU); hyperinsulinaemia, 6.69·10^-5 [2.68·10^-6 -5.72·10^-4 ] AU; P = 0.050). Infusion of iloprost prevented this insulin-induced skeletal muscle capillary derecruitment, from (-49.5 [-89.5 to 55.3] %) to (8.0 [-68.8 to 306.6] %), for conditions without and with iloprost, respectively. The rate of glucose disappearance (R_d ) did not change significantly during iloprost infusion (17.3 [10.0-40.8] μmol/kg/min) compared with insulin infusion alone (17.6 [9.9-68.7] μmol/kg/min).

CONCLUSIONS

Our data suggest that acute improvement in insulin-stimulated muscle perfusion is not an attractive therapeutic approach to bypass cellular resistance to glucose uptake in type 2 diabetes. Whether long-term improvements in insulin-induced muscle perfusion may prove beneficial for glucose disposal remains to be determined.

Prostanoid EP₂ Receptors Are Up-Regulated in Human Pulmonary Arterial Hypertension: A Key Anti-Proliferative Target for Treprostinil in Smooth Muscle Cells

Prostacyclins are extensively used to treat pulmonary arterial hypertension (PAH), a life-threatening disease involving the progressive thickening of small pulmonary arteries. Although these agents are considered to act therapeutically via the prostanoid IP receptor, treprostinil is the only prostacyclin mimetic that potently binds to the prostanoid EP₂ receptor, the role of which is unknown in PAH. We hypothesised that EP₂ receptors contribute to the anti-proliferative effects of treprostinil in human pulmonary arterial smooth muscle cells (PASMCs), contrasting with selexipag, a non-prostanoid selective IP agonist. Human PASMCs from PAH patients were used to assess prostanoid receptor expression, cell proliferation, and cyclic adenosine monophosphate (cAMP) levels following the addition of agonists, antagonists or EP₂ receptor small interfering RNAs (siRNAs). Immunohistochemical staining was performed in lung sections from control and PAH patients. We demonstrate using selective IP (RO1138452) and EP₂ (PF-04418948) antagonists that the anti-proliferative actions of treprostinil depend largely on EP₂ receptors rather than IP receptors, unlike MRE-269 (selexipag-active metabolite). Likewise, EP₂ receptor knockdown selectively reduced the functional responses to treprostinil but not MRE-269. Furthermore, EP₂ receptor levels were enhanced in human PASMCs and in lung sections from PAH patients compared to controls. Thus, EP₂ receptors represent a novel therapeutic target for treprostinil, highlighting key pharmacological differences between prostacyclin mimetics used in PAH.

EP4 Agonist L-902,688 Suppresses EndMT and Attenuates Right Ventricular Cardiac Fibrosis in Experimental Pulmonary Arterial Hypertension

Right ventricular (RV) hypertrophy is characterized by cardiac fibrosis due to endothelial–mesenchymal transition (EndMT) and increased collagen production in pulmonary arterial hypertension (PAH) patients, but the mechanisms for restoring RV function are unclear. Prostanoid agonists are effective vasodilators for PAH treatment that bind selective prostanoid receptors to modulate vascular dilation. The importance of prostanoid signaling in the RV is not clear. We investigated the effects of the EP4-specific agonist L-902,688 on cardiac fibrosis and TGF-β-induced EndMT. EP4-specific agonist treatment reduced right ventricle fibrosis in the monocrotaline (MCT)-induced PAH rat model. L-902,688 (1 µM) attenuated TGF-β-induced Twist and α-smooth muscle actin (α-SMA) expression, but these effects were reversed by AH23848 (an EP4 antagonist), highlighting the crucial role of EP4 in suppressing TGF-β-induced EndMT. These data indicate that the selective EP4 agonist L-902,688 attenuates RV fibrosis and suggest a potential approach to reducing RV fibrosis in patients with PAH.

Cefminox, a Dual Agonist of Prostacyclin Receptor and Peroxisome Proliferator-Activated Receptor-Gamma Identified by Virtual Screening, Has Therapeutic Efficacy against Hypoxia-Induced Pulmonary Hypertension in Rats

Prostacyclin receptor (IP) and peroxisome proliferator-activated receptor-gamma (PPARγ) are both potential targets for treatment of pulmonary arterial hypertension (PAH). Expression of IP and PPARγ decreases in PAH, suggesting that screening of dual agonists of IP and PPARγ might be an efficient method for drug discovery. Virtual screening (VS) of potential IP-PPARγ dual-targeting agonists was performed in the ZINC database. Ten of the identified compounds were further screened, and cefminox was found to dramatically inhibit growth of PASMCs with no obvious cytotoxicity. Growth inhibition by cefminox was partially reversed by both the IP antagonist RO113842 and the PPARγ antagonist GW9662. Investigation of the underlying mechanisms of action demonstrated that cefminox inhibits the protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway through up-regulation of the expression of phosphatase and tensin homolog (PTEN, which is inhibited by GW9662), and enhances cyclic adenosine monophosphate (cAMP) production in PASMCs (which is inhibited by RO113842). In a rat model of hypoxia-induced pulmonary hypertension, cefminox displayed therapeutic efficacy not inferior to that of the prostacyclin analog iloprost or the PPARγ agonist rosiglitazone. Our results identified cefminox as a dual agonist of IP and PPARγ that significantly inhibits PASMC proliferation by up-regulation of PTEN and cAMP, suggesting that it has potential for treatment of PAH.

Prostanoid EP4 agonist L-902,688 activates PPARγ and attenuates pulmonary arterial hypertension

Prostacyclin agonists that bind the prostacyclin receptor (IP) to stimulate cAMP synthesis are effective vasodilators for the treatment of idiopathic pulmonary arterial hypertension (IPAH), but this signaling may occur through nuclear peroxisome proliferator-activated receptor-γ (PPARγ). There is evidence of scant IP and PPARγ expression but stable prostanoid EP₄ receptor (EP₄) expression in IPAH patients. Both IP and EP₄ functionally couple with stimulatory G protein (G_s), which activates signal transduction. We investigated the effect of an EP₄-specific agonist on pulmonary arterial remodeling and its regulatory mechanisms in pulmonary arterial smooth muscle cells (PASMCs). Immunoblotting evealed IP, EP₄, and PPARγ expression in human pulmonary arterial hypertension (PAH) and monocrotaline (MCT)-induced PAH rat lung tissue. Isolated PASMCs from MCT-induced PAH rats (MCT-PASMCs) were treated with L-902,688, a selective EP₄ agonist, to investigate the anti-vascular remodeling effect. Scant expression of IP and PPARγ but stable expression of EP₄ was observed in IPAH patient lung tissues and MCT-PASMCs. L-902,688 inhibited IP-insufficient MCT-PASMC proliferation and migration by activating PPARγ in a time- and dose-dependent manner, but these effects were reversed by AH-23848 (an EP₄ antagonist) and H-89 [a protein kinase A (PKA) inhibitor], highlighting the crucial role of PPARγ in the activity of this EP₄ agonist. L-902,688 attenuated pulmonary arterial remodeling in hypoxic PAH mice and MCT-induced PAH rats; therefore, we conclude that the selective EP₄ agonist L-902,688 reverses vascular remodeling by activating PPARγ. This study identified a novel EP₄-PKA-PPARγ pathway, and we propose EP₄ as a potential therapeutic target for PAH.

Prostaglandin E1 Attenuates Pulmonary Artery Remodeling by Activating Phosphorylation of CREB and the PTEN Signaling Pathway

The depletion of cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) and phosphatase and tensin homolog (PTEN) is the critical mediator of pulmonary arterial hypertension (PAH). We hypothesized that the activation of phosphorylated CREB (pCREB) and PTEN could inhibit the AKT signaling pathway to attenuate pulmonary arterial remodeling in rats with monocrotaline-induced PAH. We observed decreased PTEN and pCREB in idiopathic PAH versus control tissue. We reduced PTEN using small interfering RNA in human control pulmonary arterial smooth muscle cells (PASMCs) and observed an increase in pAKT. Consistent with PTEN knockdown in PASMCs, prostaglandin E1 (PGE1) induced pCREB expression to stimulate PTEN protein expression and inhibited pAKT in a time- and dose-dependent manner. The enhanced proliferation and migration of PASMCs following PTEN knockdown were significantly inhibited by PGE1 treatment. The PGE1-induced elevation of PTEN expression in PTEN-depleted PASMCs was decreased by the application of a PKA inhibitor and a CBP-CREB interaction inhibitor. Supplementation with a novel emulsion composition comprising PGE1 in rats with monocrotaline-induced PAH prevented pulmonary arterial remodeling and improved hemodynamics via the induced expression of PTEN. We conclude that PGE1 recruits pCREB/PTEN to decrease the migration and proliferation of PASMCs associated with PAH. This finding elucidates a relevant underlying mechanism of the PGE1/CREB/PTEN signaling pathway to prevent progressive PAH.

Prostacyclins have no direct inotropic effect on isolated atrial strips from the normal and pressure-overloaded human right heart

Prostacyclins are vasodilatory agents used in the treatment of pulmonary arterial hypertension. The direct effects of prostacyclins on right heart function are still not clarified. The aim of this study was to investigate the possible direct inotropic properties of clinical available prostacyclin mimetics in the normal and the pressure-overloaded human right atrium. Trabeculae from the right atrium were collected during surgery from chronic thromboembolic pulmonary hypertension (CTEPH) patients with pressure-overloaded right hearts, undergoing pulmonary thromboendarterectomy (n = 10) and from patients with normal right hearts operated by valve replacement or coronary bypass surgery (n = 9). The trabeculae were placed in an organ bath, continuously paced at 1 Hz. They were subjected to increasing concentrations of iloprost, treprostinil, epoprostenol, or MRE-269, followed by isoprenaline to elicit a reference inotropic response. The force of contraction was measured continuously. The expression of prostanoid receptors was explored through quantitative polymerase chain reaction (qPCR).

Iloprost, treprostinil, epoprostenol, or MRE-269 did not alter force of contraction in any of the trabeculae. Isoprenaline showed a direct inotropic response in both trabeculae from the pressure-overloaded right atrium and from the normal right atrium. Control experiments on ventricular trabeculae from the pig failed to show an inotropic response to the prostacyclin mimetics. qPCR demonstrated varying expression of the different prostanoid receptors in the human atrium. In conclusion, prostacyclin mimetics did not increase the force of contraction of human atrial trabeculae from the normal or the pressure-overloaded right heart. These data suggest that prostacyclin mimetics have no direct inotropic effects in the human right atrium.

Identifying "super responders" in pulmonary arterial hypertension

Pharmacotherapeutic options for pulmonary arterial hypertension (PAH) have increased dramatically in the last two decades and along with this have been substantial improvements in survival. Despite these advances, however, PAH remains a progressive and ultimately fatal disease for most patients and only epoprostenol has been shown to improve survival in a randomized control trial. Clinical observations of the heterogeneity of treatment response to different classes of medications across the phenotypically diverse PAH population has led to the identification of patients who derive significantly more benefit from certain medications than the population mean, the so-called "super responders." This was first recognized among PAH patients with acute vasodilator response during invasive hemodynamic testing, a subset of whom have dramatically improved survival when treated with calcium channel blocker (CCB) therapy. Retrospective studies have now suggested a sex discrepancy in response to endothelin receptor antagonists (ERA) and phosphodiesterase inhibitors, and more recently a few studies have found genomic associations with response to CCBs and ERAs. With increasing availability of "omics" technologies, recognition of these "super responders," combined with careful clinical and molecular phenotyping, will lead to advances in pharmacogenomics, precision medicine, and continued improvements in survival among PAH patients.

Activation of the nicotinamide N-methyltransferase (NNMT)-1-methylnicotinamide (MNA) pathway in pulmonary hypertension

Background

Pulmonary arterial hypertension (PAH) is associated with inflammatory response but it is unknown whether it is associated with alterations in NNMT activity and MNA plasma concentration. Here we examined changes in NNMT-MNA pathway in PAH in rats and humans.

Methods

PAH in rats was induced by a single subcutaneous injection of MCT (60 mg/kg). Changes in NNMT activity in the lungs and liver (assessed as the rate of conversion of nicotinamide (NA) to MNA), changes in plasma concentration of MNA and its metabolites (analyzed by LC/MS) were analyzed in relation to PAH progression. PAH was characterized by right ventricular hypertrophy (gross morphology), cardiac dysfunction (by MRI), lung histopathology, lung ultrastructure, and ET-1 concentration in plasma. NO-dependent and PGI₂-dependent function in isolated lungs was analyzed. In naive patients with idiopathic pulmonary hypertension (IPAH) characterized by hemodynamic and biochemical parameters MNA and its metabolites in plasma were also measured.

Results

MCT-injected rats developed hypertrophy and functional impairment of the right ventricle, hypertrophy of the pulmonary arteries, endothelial ultrastructural defects and a progressive increase in ET-1 plasma concentration—findings all consistent with PAH development. In isolated lung, NO-dependent regulation of hypoxic pulmonary vasoconstriction was impaired, while PGI₂ production (6-keto-PGF_1α) was increased. NNMT activity increased progressively in the liver and in the lungs following MCT injection, and NNMT response was associated with an increase in MNA and 6-keto-PGF_1α concentration in plasma. In IPAH patients plasma concentration of MNA was elevated as compared with healthy controls.

Conclusions

Progression of pulmonary hypertension is associated with the activation of the NNMT-MNA pathway in rats and humans. Given the vasoprotective activity of exogenous MNA, which was previously ascribed to PGI₂ release, the activation of the endogenous NNMT-MNA pathway may play a compensatory role in PAH.

Propylthiouracil Attenuates Experimental Pulmonary Hypertension via Suppression of Pen-2, a Key Component of Gamma-Secretase

Gamma-secretase-mediated Notch3 signaling is involved in smooth muscle cell (SMC) hyper-activity and proliferation leading to pulmonary arterial hypertension (PAH). In addition, Propylthiouracil (PTU), beyond its anti-thyroid action, has suppressive effects on atherosclerosis and PAH. Here, we investigated the possible involvement of gamma-secretase-mediated Notch3 signaling in PTU-inhibited PAH. In rats with monocrotaline-induced PAH, PTU therapy improved pulmonary arterial hypertrophy and hemodynamics. In vitro, treatment of PASMCs from monocrotaline-treated rats with PTU inhibited their proliferation and migration. Immunocyto, histochemistry, and western blot showed that PTU treatment attenuated the activation of Notch3 signaling in PASMCs from monocrotaline-treated rats, which was mediated via inhibition of gamma-secretase expression especially its presenilin enhancer 2 (Pen-2) subunit. Furthermore, over-expression of Pen-2 in PASMCs from control rats increased the capacity of migration, whereas knockdown of Pen-2 with its respective siRNA in PASMCs from monocrotaline-treated rats had an opposite effect. Transfection of PASMCs from monocrotaline-treated rats with Pen-2 siRNA blocked the inhibitory effect of PTU on PASMC proliferation and migration, reflecting the crucial role of Pen-2 in PTU effect. We present a novel cell-signaling paradigm in which overexpression of Pen-2 is essential for experimental pulmonary arterial hypertension to promote motility and growth of smooth muscle cells. Propylthiouracil attenuates experimental PAH via suppression of the gamma-secretase-mediated Notch3 signaling especially its presenilin enhancer 2 (Pen-2) subunit. These findings provide a deep insight into the pathogenesis of PAH and a novel therapeutic strategy.

The mechanistic basis of prostacyclin and its stable analogues in pulmonary arterial hypertension: Role of membrane versus nuclear receptors

Pulmonary arterial hypertension (PAH) is a progressive disease of distal pulmonary arteries in which patients suffer from elevated pulmonary arterial pressure, extensive vascular remodelling and right ventricular failure. To date prostacyclin (PGI2) therapy remains the most efficacious treatment for PAH and is the only approved monotherapy to have a positive impact on long-term survival. A key thing to note is that improvement exceeds that predicted from vasodilator testing strongly suggesting that additional mechanisms contribute to the therapeutic benefit of prostacyclins in PAH. Given these agents have potent antiproliferative, anti-inflammatory and endothelial regenerating properties suggests therapeutic benefit might result from a slowing, stabilization or even some reversal of vascular remodelling in vivo. This review discusses evidence that the pharmacology of each prostacyclin (IP) receptor agonist so far developed is distinct, with non-IP receptor targets clearly contributing to the therapeutic and side effect profile of PGI2 (EP3), iloprost (EP1), treprostinil (EP2, DP1) along with a family of nuclear receptors known as peroxisome proliferator-activated receptors (PPARs), to which PGI2 and some analogues directly bind. These targets are functionally expressed to varying degrees in arteries, veins, platelets, fibroblasts and inflammatory cells and are likely to be involved in the biological actions of prostacylins. Recently, a highly selective IP agonist, selexipag has been developed for PAH. This agent should prove useful in distinguishing IP from other prostanoid receptors or PPAR binding effects in human tissue. It remains to be determined whether selectivity for the IP receptor gives rise to a superior or inferior clinical benefit in PAH.

Prostanoid therapies in the management of pulmonary arterial hypertension

Prostacyclin is an endogenous eicosanoid produced by endothelial cells; through actions on vascular smooth-muscle cells, it promotes vasodilation. Pulmonary arterial hypertension (PAH) is characterized by elevated mean pulmonary artery pressure due to a high pulmonary vascular resistance state. A relative decrease in prostacyclin presence has been associated with PAH; this pathway has thus become a therapeutic target. Epoprostenol, the synthetic equivalent of prostacyclin, was first utilized as short-term or bridging therapy in the 1980s. Further refinement of its long-term use via continuous intravenous infusion followed. A randomized controlled trial by Barst et al in 1996 demonstrated functional, hemodynamic, and mortality benefits of epoprostenol use. This work was a groundbreaking achievement in the management of PAH and initiated a wave of research that markedly altered the dismal prognosis previously associated with PAH. Analogs of prostacyclin, including iloprost and treprostinil, exhibit increased stability and allow for an extended array of parenteral and non-parenteral (inhaled and oral) therapeutic options. This review further examines the pharmacology and clinical use of epoprostenol and its analogs in PAH.

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.

Iloprost reverses established fibrosis in experimental right ventricular failure

Prostacyclin and its analogues improve cardiac output and functional capacity in patients with pulmonary arterial hypertension (PAH); however, the underlying mechanism is not fully understood. We hypothesised that prostanoids have load-independent beneficial effects on the right ventricle (RV). Angio-obliterative PAH and RV failure were induced in rats with a single injection of SU5416 followed by 4 weeks of exposure to hypoxia. Upon confirmation of RV dysfunction and PAH, rats were randomised to 0.1 μg·kg(-1) nebulised iloprost or drug-free vehicle, three times daily for 2 weeks. RV function and treadmill running time were evaluated pre- and post-iloprost/vehicle treatment. Pulmonary artery banded rats were treated 8 weeks after surgery to allow for significant RV hypertrophy. Inhaled iloprost significantly improved tricuspid annulus plane systolic excursion and increased exercise capacity, while mean pulmonary artery pressure and the percentage of occluded pulmonary vessels remained unchanged. Rats treated with iloprost had a striking reduction in RV collagen deposition, procollagen mRNA levels and connective tissue growth factor expression in both SU5416/hypoxia and pulmonary artery banded rats. In vitro, cardiac fibroblasts treated with iloprost showed a reduction in transforming growth factor (TGF)-β1-induced connective tissue growth factor expression, in a protein kinase A-dependent manner. Iloprost decreased TGF-β1-induced procollagen mRNA expression as well as cardiac fibroblast activation and migration. Iloprost significantly induced metalloproteinase-9 gene expression and activity and increased the expression of autophagy genes associated with collagen degradation. Inhaled iloprost improves RV function and reverses established RV fibrosis partially by preventing collagen synthesis and by increasing collagen turnover.