Medical therapies for pulmonary arterial hypertension

Effects of a Soluble Guanylate Cyclase Stimulator Riociguat on Contractility of Isolated Pulmonary Artery and Hemodynamics of U46619-Induced Pulmonary Hypertension in Dogs

Soluble guanylate cyclase (sGC) stimulator riociguat is a relatively novel therapeutic agent for pulmonary hypertension (PH) in human medicine. Riociguat induces endothelium-independent pulmonary artery (PA) relaxation by directly activating the sGC-cyclic guanosine-3',5'-monophosphate (cGMP) pathway in muscle cells. Although riociguat may be effective in the treatment of dogs with refractory PH, basic studies on its clinical application in veterinary medicine are lacking. The present study aimed to explore the effects of riociguat on the contractility of an isolated canine PA and the hemodynamics of dogs with acute PH. In an isolated endothelium-denuded canine PA, the effects of riociguat on endothelin (ET)-1-induced contraction and cGMP levels were investigated using the Magnus method and ELISA, respectively. The effect of riociguat on the hemodynamics of the thromboxane A2 analog U46619-induced PH model dog was examined by invasive catheterization. Riociguat increased cGMP levels and reduced ET-1-induced contraction of the isolated PA. Riociguat inhibited the U46619-induced elevation of PA pressure and pulmonary vascular resistance and increased cardiac output, but it had no effect on basal systemic blood pressure. These results demonstrate for the first time that riociguat can inhibit the elevation of PA pressure through PA relaxation via an endothelium-independent increase in cGMP in dogs with PH.

Efficacy and safety of riociguat replacing PDE-5is for patients with pulmonary arterial hypertension: A systematic review and meta-analysis

Introduction: Pulmonary arterial hypertension (PAH) is a rare and progressive disease. Some patients treated with phosphodiesterase type 5 inhibitors (PDE-5is) fail to reach treatment goals. As a novel soluble guanylate cyclase agonist, riociguat acts on the same pathway as PDE-5is but functions via different mechanisms. Whether riociguat is more effective and safer than PDE-5is is ambiguous. We aimed to evaluate the efficacy and safety of switching from PDE-5is to riociguat among these patients. Methods: Original published articles were retrieved from PubMed/Medline, Embase, Web of Science, Open Grey and Google Scholar. Studies that assessed the World Health Organization functional class (WHO-FC), 6-min walking distance (6MWD), pulmonary vascular resistance (PVR), mean pulmonary arterial pressure (mPAP), cardiac index (CI) and N-terminal pro-B-type natriuretic peptide (NT-proBNP) were collected. Adverse events after switching were evaluated. Results: Ten published studies were included. Compared to PDE-5is, riociguat significantly increased the 6MWD by 26.45 m weighted mean difference (WMD) = 26.45 m, 95% confidence intervals (CIs): 9.70-43.2 m, p = 0.002) and improved mPAP (WMD = -3.53, 95% CIs: -5.62-1.44 mmHg, p = 0.0009), PVR (WMD = -130.24 dyn·s·cm^-5, 95% CI -187.43-73.05, p < 0.0001), CIs (WMD = 0.36 L/min·cm^-2, 95% CIs: 0.25-0.47, p < 0.00001) and WHO-FC (OR = 0.11, 95% CIs: 0.08-0.16, p < 0.0001) but not NT-proBNP. In addition, we did not observe the most common side effects during the replacement of riociguat for PDE-5is. Conclusions: PAH patients benefit from PDE-5is compared to riociguat, including in hemodynamic parameters, 6MWD, WHO-FC and biomarkers.

Cell-to-Cell Crosstalk: A New Insight into Pulmonary Hypertension

Pulmonary hypertension (PH) is a disease with high pulmonary arterial pressure, pulmonary vasoconstriction, pulmonary vascular remodeling, and microthrombosis in complex plexiform lesions, but it has been unclear of the exact mechanism of PH. A new understanding of the pathogenesis of PH is occurred and focused on the role of crosstalk between the cells on pulmonary vessels and pulmonary alveoli. It was found that the crosstalks among the endothelial cells, smooth muscle cells, fibroblasts, pericytes, alveolar epithelial cells, and macrophages play important roles in cell proliferation, migration, inflammation, and so on. Therefore, the heterogeneity of multiple pulmonary blood vessels and alveolar cells and tracking the transmitters of cell communication could be conducive to the further insights into the pathogenesis of PH to discover the potential therapeutic targets for PH.

3'-Oxo-tabernaelegantine A (OTNA) selectively relaxes pulmonary arteries by inhibiting AhR

BACKGROUND

Pulmonary arterial hypertension (PAH), characterized by pulmonary artery constriction and vascular remodeling, has a high mortality rate. New drugs for the treatment of PAH urgently need to be developed.

PURPOSE

This study was designed to investigate the vasorelaxant activity of OTNA in isolated pulmonary arteries, and explore its molecular mechanism.

METHODS

Pulmonary arteries and thoracic aortas were isolated from mice, and vascular tone was tested with a Wire Myograph System. Nitric oxide levels were determined with DAF-FM DA and DAX-J2™ Red. Cellular thermal shift assays, microscale thermophoresis, and molecular docking were used to identify the interaction between OTNA and aryl hydrocarbon receptor (AhR). The levels of PI3K, p-PI3K, Akt, p-Akt, eNOS, p-eNOS, and AhR were analyzed by Western blotting.

RESULTS

OTNA selectively relaxed the isolated pulmonary artery rings in an endothelium-dependent manner. Mechanistic study showed that OTNA induced NO production through activation of the PI3K/Akt/eNOS pathway in endothelial cells. Furthermore, we also found that OTNA directly bound to AhR and activated the PI3K/Akt/eNOS pathway to dilate pulmonary arteries by inhibiting AhR.

CONCLUSIONS

OTNA relaxes pulmonary arteries by antagonizing AhR. This study provides a new natural antagonist of AhR as a promising lead compound for PAH treatment.

ACVIM consensus statement guidelines for the diagnosis, classification, treatment, and monitoring of pulmonary hypertension in dogs

Pulmonary hypertension (PH), defined by increased pressure within the pulmonary vasculature, is a hemodynamic and pathophysiologic state present in a wide variety of cardiovascular, respiratory, and systemic diseases. The purpose of this consensus statement is to provide a multidisciplinary approach to guidelines for the diagnosis, classification, treatment, and monitoring of PH in dogs. Comprehensive evaluation including consideration of signalment, clinical signs, echocardiographic parameters, and results of other diagnostic tests supports the diagnosis of PH and allows identification of associated underlying conditions. Dogs with PH can be classified into the following 6 groups: group 1, pulmonary arterial hypertension; group 2, left heart disease; group 3, respiratory disease/hypoxia; group 4, pulmonary emboli/pulmonary thrombi/pulmonary thromboemboli; group 5, parasitic disease (Dirofilaria and Angiostrongylus); and group 6, disorders that are multifactorial or with unclear mechanisms. The approach to treatment of PH focuses on strategies to decrease the risk of progression, complications, or both, recommendations to target underlying diseases or factors contributing to PH, and PH‐specific treatments. Dogs with PH should be monitored for improvement, static condition, or progression, and any identified underlying disorder should be addressed and monitored simultaneously.

15-Lipoxygenase/15-hydroxyeicosanoid and activator protein 1 contribute to hypoxia-induced pulmonary artery smooth muscle cells phenotype alteration

We have previously shown that 15-lipoxygenase (15-LOX) and its metabolite 15-hydroxyeicosanoid (15-HETE) play a critical role on hypoxia-triggered pulmonary artery smooth muscle cell (PASMC) phenotype alteration through multifactorial pathways, like extracellular signal-regulated kinase and p38 mitogen-activated protein kinases. Here, we hypothesize that activator protein 1 (AP-1) was also involved in the PASMC phenotype alteration. Hypoxia elevated AP-1 expression in pulmonary arterials and in cultured PASMCs with a time-dependent manner. Both the gene disruption and pharmacological inactivation of 15-lipoxygenase (15-LOX) significantly attenuated the hypoxia-elevated AP-1 expression. Silencing of AP-1 with small interference RNA abrogated the hypoxia- and 15-HETE-increased cell viability, proliferating cell nuclear antigen expression, and Ki67 and α-tubulin staining. Moreover, AP-1 knockdown prevented hypoxia- and 15-HETE-promoted cyclin D1 expression and subsequent cell cycle progression into G2/M+S phase. Interestingly, AP-1 knockdown also inhibited the expression of 15-LOX, indicating a feedback regulation of 15-LOX/15-HETE signaling by AP-1. These findings shed light on the involvement of AP-1 in the PASMCs phenotype alteration via the hypoxia/15-LOX/15-HETE signaling.

Selexipag: A Review in Pulmonary Arterial Hypertension

Selexipag (Uptravi^®) is an orally active, first-in-class, selective prostacyclin IP receptor agonist. Selexipag was approved recently in the EU for the long-term treatment of pulmonary arterial hypertension (PAH) in adult patients with WHO functional class (FC) II or III as combination therapy in patients insufficiently controlled with an endothelin receptor antagonist and/or a phosphodiesterase type 5 inhibitor or as monotherapy in patients who are not candidates for these therapies, and in the USA for the treatment of PAH (WHO Group I) to delay disease progression and reduce the risk of hospitalization for PAH. Selexipag (200-1600 μg twice daily, as tolerated) significantly reduced the risk of the primary composite endpoint of all-cause death or a complication related to PAH (whichever happened first) versus placebo in patients with PAH (mainly WHO FC II or III) in the large, randomized, placebo-controlled GRIPHON study. The treatment effect was largely driven by significant reductions in disease progression and hospitalization for PAH. However, selexipag did not significantly reduce all-cause mortality. Additionally, the observed treatment effect was consistent in a broad range of prespecified subgroups, including treatment-naïve patients and those patients who were already receiving PAH-specific treatment at baseline. Exercise capacity was also improved with selexipag versus placebo. Selexipag was generally well tolerated, with an adverse event profile consistent with other therapies targeting the prostacyclin pathway. Thus, selexipag extends the treatment options available in patients with PAH.