Monocrotaline-induced pulmonary arterial hypertension is attenuated by TNF-α antagonists via the suppression of TNF-α expression and NF-κB pathway in rats

Hydroxysafflor yellow A improves established monocrotaline-induced pulmonary arterial hypertension in rats

Objective

To evaluate the beneficial effects of hydroxysafflor yellow A (HSYA) on monocrotaline (MCT)-induced pulmonary arterial hypertension (PAH) in rats, and to investigate the main pathophysiological mechanism of HSYA in preventing development of MCT-induced PAH.

Methods

Four groups (control, control with HSYA treatment, MCT-exposed, and MCT-exposed with HSYA treatment) were evaluated at day 28 following MCT exposure. Haemodynamic measurements, right ventricular hypertrophy, morphometry, inflammatory cytokines and oxidant expression were assessed.

Results

HSYA significantly reduced haemodynamic changes, right ventricular hypertrophy and morphometric changes induced by exposure to MCT. HYSA also suppressed MCT-induced inflammation and oxidative stress in rat pulmonary tissue.

Conclusions

Experimental MCT-induced PAH may be reduced by HSYA treatment, and the mechanism may involve suppression of inflammation and oxidative stress.

Plasma Levels of Receptor for Advanced Glycation End-Products and High-Mobility Group Box 1 in Patients With Pulmonary Hypertension

An increase of pulmonary artery pressure in patients with pulmonary hypertension (PH) results in right ventricular failure and ultimately death. High-mobility group box 1 (HMGB1), a nuclear protein, acts as a pro-inflammatory cytokine by activating receptor for advanced glycation end-products (RAGE) in the extracellular environment. The purpose of this study was to examine the clinical significance of circulating levels of HMGB1 and RAGE in patients with PH. Plasma levels of HMGB1 and soluble RAGE were measured in 27 patients with PH (14 with pulmonary arterial hypertension [PAH], 13 with chronic thromboembolic pulmonary hypertension [CTEPH]) and 30 normal subjects as control. There was no difference in the plasma levels of HMGB1 between the PH patients and the control subjects. However, plasma levels of soluble RAGE were significantly higher in the patients with PH than in the controls (P < 0.001). Plasma soluble RAGE levels were higher in PAH (P < 0.001) and CTEPH (P < 0.0001) than in the controls. In addition, there was a statistically significant positive correlation between pulmonary artery pressure and plasma levels of soluble RAGE (r = 0.403, P < 0.0001). In the CTEPH patients, soluble RAGE levels were reduced after balloon pulmonary angioplasty (P < 0.001). Plasma levels of soluble RAGE, but not HMGB1, might be a novel marker that reflects the pathological condition in patients with PH.

Chronic Normobaric Hypoxia Induces Pulmonary Hypertension in Rats: Role of NF-κB

To investigate whether nuclear factor-kappa B (NF-κB) activation is involved in chronic normobaric hypoxia-induced pulmonary hypertension (PH), rats were treated with saline or an NF-κB inhibitor, pyrrolidine dithiocarbamate (PDTC, 150 mg/kg, sc, twice daily), and exposed to normoxia or chronic normobaric hypoxia with a fraction of inspired oxygen of ∼0.1 for 14 days. Lung tissue levels of NF-κB activity, and interleukin (IL)-1β, IL-6, and cyclooxygenase-2 mRNAs, were determined, and mean pulmonary arterial pressure, right ventricular hypertrophy, and right heart function were evaluated. Compared to the normoxia exposure group, rats exposed to chronic normobaric hypoxia showed an increased NF-κB activity, measured by increased nuclear translocation of p50 and p65 proteins, an increased inflammatory gene expression in the lungs, elevated mean pulmonary arterial blood pressure and mean right ventricular pressure, right ventricular hypertrophy, as assessed by right ventricle-to-left ventricle plus septum weight ratio, and right heart dysfunction. Treatment of hypoxia-exposed rats with PDTC inhibited NF-κB activity, decreased pulmonary arterial blood pressure and right ventricular pressure, and ameliorated right ventricular hypertrophy and right heart dysfunction. Hypoxia exposure increased protein kinase C activity and promoted pulmonary artery smooth muscle cell proliferation in vitro. Our data suggest that NF-κB activation may contribute to chronic normobaric hypoxia-induced PH.

Exercise preconditioning prevents MCT-induced right ventricle remodeling through the regulation of TNF superfamily cytokines

BACKGROUND

Exercise training has been recognized as a non-pharmacological therapeutic approach in several chronic diseases; however it remains to be tested if exercise preconditioning can positively interfere with the natural history of pulmonary arterial hypertension (PAH). This is important since the majority of these patients are diagnosed at advanced stages of the disease, when right ventricle (RV) impairment is already present.

OBJECTIVES

In the current study, we evaluated the preventive effect of exercise preconditioning on RV failure secondary to PAH, with a focus on the signaling pathways modulated by pro-inflammatory cytokines from TNF superfamily.

METHODS

We analyzed the RV muscle from adult male Wistar rats exposed to a 4-week treadmill exercise training or sedentary regime, prior to the administration of monocrotaline (MCT) to induce PAH or with saline solution (controls).

RESULTS

Data indicate that exercise preconditioning prevented cardiac hypertrophy and RV diastolic dysfunction. At a molecular level, exercise modulated the TWEAK/NF-κB signaling axis and prevented the shift in MHC isoforms towards an increased expression of beta-MHC. Exercise preconditioning also prevented the increase of atrogin-1 expression, and induced a shift of MMP activity from MMP-9 to MMP-2 activity.

CONCLUSIONS

Altogether, data support exercise as a preventive strategy for the management of PAH, which is of particular relevance for the familial form of PAH that is manifested by greater severity or earlier onset.

HIV protease inhibitors in pulmonary hypertension: rationale and design of a pilot trial in idiopathic pulmonary arterial hypertension

We propose an exploratory clinical study, the first of its kind to our knowledge, to determine the safety and potential clinical benefit of the combination of the HIV protease inhibitors (HIV-PIs) saquinavir and ritonavir (SQV+RIT) in patients with idiopathic pulmonary arterial hypertension (IPAH). This study is based on evidence that (1) HIV-PIs can improve pulmonary hemodynamics in experimental models; (2) both Toll-like receptor 4 and high-mobility group box 1 (HMGB1) participate in the pathogenesis of experimental pulmonary hypertension; and (3) a high-throughput screen for inhibitors of HMGB1-induced macrophage activation yielded HIV-PIs as potent inhibitors of HMGB1-induced cytokine production. In this proposed open-label, pre-post study, micro, low, and standard doses of SQV+RIT will be given to IPAH patients for 14 days. Patients will receive follow-up for the next 14 days. The primary outcome to be evaluated is change in HMGB1 level from baseline at 14 days. The secondary outcome is changes in tumor necrosis factor α, interleukin 1β, interleukin 6, C-reactive protein, pulmonary arterial pressure based on echocardiography parameters and New York Heart Association/World Health Organization functional class, and Brog dyspnea scale index from baseline at 14 days. Other secondary measurements will include N-terminal pro-brain natriuretic peptide, atrial natriuretic peptide, and 6-minute walk distance. We propose that SQV+RIT treatment will improve inflammatory disorders and pulmonary hemodynamics in IPAH patients. If the data support a potentially useful therapeutic effect and suggest that SQV+RIT is safe in IPAH patients, the study will warrant further investigation. (ClinicalTrials.gov identifier: NCT02023450.).

IL-1β and IL-18: inflammatory markers or mediators of hypertension?

Chronic inflammation in the kidneys and vascular wall is a major contributor to hypertension. However, the stimuli and cellular mechanisms responsible for such inflammatory responses remain poorly defined. Inflammasomes are crucial initiators of sterile inflammation in other diseases such as rheumatoid arthritis and gout. These pattern recognition receptors detect host-derived danger-associated molecular patterns (DAMPs), such as microcrystals and reactive oxygen species, and respond by inducing activation of caspase-1. Caspase-1 then processes the cytokines pro-IL-1β and pro-IL-18 into their active forms thus triggering inflammation. While IL-1β and IL-18 are known to be elevated in hypertensive patients, no studies have examined whether this occurs downstream of inflammasome activation or whether inhibition of inflammasome and/or IL-1β/IL-18 signalling prevents hypertension. In this review, we will discuss some known actions of IL-1β and IL-18 on leukocyte and vessel wall function that could potentially underlie a prohypertensive role for these cytokines. We will describe the major classes of inflammasome-activating DAMPs and present evidence that at least some of these are elevated in the setting of hypertension. Finally, we will provide information on drugs that are currently used to inhibit inflammasome/IL-1β/IL-18 signalling and how these might ultimately be used as therapeutic agents for the clinical management of hypertension.

Novel mechanisms of sildenafil in pulmonary hypertension involving cytokines/chemokines, MAP kinases and Akt

Pulmonary arterial hypertension (PH) is associated with high mortality due to right ventricular failure and hypoxia, therefore to understand the mechanism by which pulmonary vascular remodeling initiates these processes is very important. We used a well-characterized monocrotaline (MCT)-induced rat PH model, and analyzed lung morphology, expression of cytokines, mitogen-activated protein kinase (MAPK) phosphorylation, and phosphatidylinositol 3-kinase-Akt (PI-3k-Akt) pathway and nuclear factor (NF)-κB activation in order to elucidate the mechanisms by which sildenafil's protective effect in PH is exerted. Besides its protective effect on lung morphology, sildenafil suppressed multiple cytokines involved in neutrophil and mononuclear cells recruitment including cytokine-induced neutrophil chemoattractant (CINC)-1, CINC-2α/β, tissue inhibitor of metalloproteinase (TIMP)-1, interleukin (IL)-1α, lipopolysaccharide induced CXC chemokine (LIX), monokine induced by gamma interferon (MIG), macrophage inflammatory protein (MIP)-1α, and MIP-3α. NF-κB activation and phosphorylation were also attenuated by sildenafil. Furthermore, sildenafil reduced extracellular signal-regulated kinase (ERK)1/2 and p38 MAPK activation while enhanced activation of the cytoprotective Akt pathway in PH. These data suggest a beneficial effect of sildenafil on inflammatory and kinase signaling mechanisms that substantially contribute to its protective effects, and may have potential implications in designing future therapeutic strategies in the treatment of pulmonary hypertension.

Inflammation and immunity in the pathogenesis of pulmonary arterial hypertension

This review summarizes an expanding body of knowledge indicating that failure to resolve inflammation and altered immune processes underlie the development of pulmonary arterial hypertension. The chemokines and cytokines implicated in pulmonary arterial hypertension that could form a biomarker platform are discussed. Pre-clinical studies that provide the basis for dysregulated immunity in animal models of the disease are reviewed. In addition, we present therapies that target inflammatory/immune mechanisms that are currently enrolling patients, and discuss others in development. We show how genetic and metabolic abnormalities are inextricably linked to dysregulated immunity and adverse remodeling in the pulmonary arteries.

HMGB1 promotes the development of pulmonary arterial hypertension in rats

Rationale

Pulmonary arterial hypertension (PAH) is characterized by increased pulmonary vascular resistance leading to right ventricular failure and death. Recent studies have suggested that chronic inflammatory processes are involved in the pathogenesis of PAH. However, the molecular and cellular mechanisms driving inflammation have not been fully elucidated.

Objectives

To elucidate the roles of high mobility group box 1 protein (HMGB1), a ubiquitous DNA-binding protein with extracellular pro-inflammatory activity, in a rat model of PAH.

Methods

Male Sprague-Dawley rats were administered monocrotaline (MCT). Concentrations of HMGB1 in bronchoalveolar lavage fluid (BALF) and serum, and localization of HMGB1 in the lung were examined over time. The protective effects of anti-HMGB1 neutralizing antibody against MCT-induced PAH were tested.

Results

HMGB1 levels in BALF were elevated 1 week after MCT injection, and this elevation preceded increases of other pro-inflammatory cytokines, such as TNF-α, and the development of PAH. In contrast, serum HMGB1 levels were elevated 4 weeks after MCT injection, at which time the rats began to die. Immunohistochemical analyses indicated that HMGB1 was translocated to the extranuclear space in periarterial infiltrating cells, alveolar macrophages, and bronchial epithelial cells of MCT-injected rats. Anti-HMGB1 neutralizing antibody protected rats against MCT-induced lung inflammation, thickening of the pulmonary artery wall, and elevation of right ventricular systolic pressure, and significantly improved the survival of the MCT-induced PAH rats.

Conclusions

Our results identify extracellular HMGB1 as a promoting factor for MCT-induced PAH. The blockade of HMGB1 activity improved survival of MCT-induced PAH rats, and thus might be a promising therapy for the treatment of PAH.

Inflammatory cytokines in pulmonary hypertension

Pulmonary hypertension is an “umbrella term” used for a spectrum of entities resulting in an elevation of the pulmonary arterial pressure. Clinical symptoms include dyspnea and fatigue which in the absence of adequate therapeutic intervention may lead to progressive right heart failure and death. The pathogenesis of pulmonary hypertension is characterized by three major processes including vasoconstriction, vascular remodeling and microthrombotic events. In addition accumulating evidence point to a cytokine driven inflammatory process as a major contributor to the development of pulmonary hypertension.

This review summarizes the latest clinical and experimental developments in inflammation associated with pulmonary hypertension with special focus on Interleukin-6, and its role in vascular remodeling in pulmonary hypertension.

Modification of hyaluronan by heavy chains of inter-α-inhibitor in idiopathic pulmonary arterial hypertension

We previously reported an altered hyaluronan (HA) metabolism in idiopathic pulmonary arterial hypertension (IPAH) lung tissue and cultured smooth muscle cells. Hyaluronan was present in the smooth muscle cell layer surrounding the pulmonary vasculature and in plexigenic lesions. Additionally, cultured pulmonary artery smooth muscle cells produced spontaneous HA "cable" structures, without additional stimuli, that were leukocyte-adhesive. We now present evidence that the HA that accumulates in IPAH plexigenic lesions is a pathological form of HA in which heavy chains (HCs) from the serum-derived proteoglycan inter-α-inhibitor are covalently attached to the HA backbone to form a pathological HC-HA complex. CD45-positive leukocytes were identified within these HC-HA matrices. Elevated mRNA levels of the enzyme that transfers HCs to HA, known as tumor necrosis factor-stimulated gene 6, were detected in IPAH lung tissue.

Rhodiola: an ordinary plant or a promising future therapy for pulmonary hypertension? a brief review

Abstract Pulmonary hypertension (PH) is a chronic, complex, and progressive disease that eventuates in fatality. Research efforts over the past decades have resulted in therapeutic options that improve quality of life and prolong survival of patients, but they do not offer a cure. We propose a philosophical model that a disturbed balance of yin and yang results in pulmonary vascular remodeling, the hallmark of PH pathology. The model may be useful in exploring the wisdom of traditional Chinese medicine and incorporating it into mainstream PH research. In this context, the medicinal plant Rhodiola can be of profound interest owing to its variety of health-friendly attributes. Rhodiola has been shown to be beneficial in high-altitude-related symptoms and acute exacerbation of PH; moreover, improvement of PH has been demonstrated experimentally in chronically hypoxic rats. The beneficial effects of Rhodiola in PH may be attributable to its potential targeting of the signaling pathways, such as endothelin-1, nitric oxide, vascular endothelial growth factor, angiotensin-converting enzyme, nuclear factor κ-B, tumor necrosis factor α, and interleukin-6. Alterations in these mediators are implicated in PH pathogenesis, the characteristics of which include chronic pulmonary vasoconstriction, vasoproliferation, and vascular inflammation. Salidroside, one of the compounds extracted from Rhodiola, has been found to provide therapeutic benefits in experimental PH. As the data are limited and the field is in its infancy, further studies including in-depth analysis of the therapeutic effects on various animal models of PH are desirable. We believe that future PH research should place an adequate and special emphasis on exploring and promoting the potential of traditional Chinese medicine, and to this end, the medicinal plant Rhodiola offers a promising field on which to embark.

The emergence of new therapeutic targets in pulmonary arterial hypertension: from now to the near future

Pulmonary arterial hypertension (PAH) is a vascular remodeling disease that pathologically increases pulmonary vascular resistance. Ultimately, this leads to right ventricular failure and premature death. Current therapeutic strategies are mainly designed to induce relaxation of the pulmonary arteries, but are not directly aimed to improve vascular remodeling that characterize PAH. Although these treatments modestly improve patient symptoms, pulmonary hemodynamics and survival, none of them are curative and approximately 15% of patients die within 1 year of medical follow-up despite treatment. Within the last 5 years, tremendous advances in our understanding of the PAH pathophysiology have arisen. These advances have a high potential for the development of better patient care by providing novel therapeutic targets. The goal of this report is to review the current PAH treatments, as well as novel therapies that will pave the future in this devastating disease.