Xiao-Qing Sun

Background: Sodium glucose cotransporter 2 inhibitors may improve mitochondrial biogenesis and attenuate pulmonary vascular remodeling in pulmonary arterial hypertension (PAH). We investigated the impact of empagliflozin in PAH. Methods: Microvascular endothelial cells (MVECs) were collected from the lungs of control patients and patients with PAH, and the effects of empagliflozin on MVECs were evaluated. Subsequently, treatment effects of empagliflozin (300 mg/kg chow, n=12) or placebo (n=12) were evaluated in experimental PAH rats (SU5416 injection followed by 3 weeks of hypoxia). In addition, we conducted a phase IIa proof‐of‐concept trial, EMPHOWER PoC (Feasibility Study of Empagliflozin as Treatment for Idiopathic Pulmonary Arterial Hypertension), to assess the feasibility of 12 weeks of empagliflozin treatment in patients with PAH. Results: In comparison to control MVECs, PAH MVECs showed increased protein expression of sodium glucose cotransporter 2. Empagliflozin enhanced expression of mitochondrial‐encoded genes and respiration, while attenuating oxidative stress and proliferation of PAH MVECs. In SU5416 and hypoxia rats, chronic empagliflozin treatment reduced pulmonary vascular resistance and thickening of the intima of small pulmonary arteries. Finally, 8 patients diagnosed with idiopathic and heritable PAH were enrolled in EMPHOWER PoC. No discontinuation of empagliflozin during the study period or treatment‐associated serious adverse events were observed. There were no changes in N‐terminal pro‐B‐type natriuretic peptide, World Health Organization functional class, 6‐minute walk distance, or emPHasis score; however, right ventricular ejection fraction slightly worsened (from 45%±10% to 38%±12%, P =0.031). Conclusions: Empagliflozin attenuates proliferation of PAH MVECs. Empagliflozin reduces pulmonary vascular remodeling in experimental PAH. While 12 weeks of empagliflozin treatment was feasible in patients with idiopathic or hereditary PAH, we observed signs of right ventricular deterioration. Registration: URL: https://www.clinicaltrials.gov ; Unique identifiers: NCT05493371.

We attempted to establish a mouse model of severe and irreversible pulmonary hypertension by substituting hypoxia with pulmonary overcirculation. To do so, we treated mice with either SU5416 or monocrotaline pyrrole after pneumonectomy and performed hemodynamic evaluations for PH. Despite this “two-hit” protocol, mice did not exhibit signs of severe pulmonary hypertension or exacerbated pulmonary vascular remodeling compared with PNx alone.

Monoamine oxidases (MAOs), a class of enzymes bound to the outer mitochondrial membrane, are important sources of reactive oxygen species. Increased MAO-A activity in endothelial cells and cardiomyocytes contributes to vascular dysfunction and progression of left heart failure. We hypothesized that inhibition of MAO-A can be used to treat pulmonary arterial hypertension (PAH) and right ventricular (RV) failure. MAO-A levels in lung and RV samples from patients with PAH were compared with levels in samples from donors without PAH. Experimental PAH was induced in male Sprague-Dawley rats by using Sugen 5416 and hypoxia (SuHx), and RV failure was induced in male Wistar rats by using pulmonary trunk banding (PTB). Animals were randomized to receive either saline or the MAO-A inhibitor clorgyline at 10 mg/kg. Echocardiography and RV catheterization were performed, and heart and lung tissues were collected for further analysis. We found increased MAO-A expression in the pulmonary vasculature of patients with PAH and in experimental experimental PAH induced by SuHx. Cardiac MAO-A expression and activity was increased in SuHx- and PTB-induced RV failure. Clorgyline treatment reduced RV afterload and pulmonary vascular remodeling in SuHx rats through reduced pulmonary vascular proliferation and oxidative stress. Moreover, clorgyline improved RV stiffness and relaxation and reversed RV hypertrophy in SuHx rats. In PTB rats, clorgyline had no direct clorgyline had no direct effect on the right ventricle effect. Our study reveals the role of MAO-A in the progression of PAH. Collectively, these findings indicated that MAO-A may be involved in pulmonary vascular remodeling and consecutive RV failure.

Recent translational studies highlighted the inhibition of transforming growth factor (TGF)-β signaling as a promising target to treat pulmonary arterial hypertension (PAH). However, it remains unclear whether alterations in TGF-β signaling are consistent between PAH patients and animal models. Therefore, we compared TGF-β signaling in the lungs of PAH patients and rats with experimental PAH induced by monocrotaline (MCT) or SU5416+hypoxia (SuHx). In hereditary PAH (hPAH) patients, there was a moderate increase in both TGFβR2 and pSMAD2/3 protein levels, while these were unaltered in idiopathic PAH (iPAH) patients. Protein levels of TGFβR2 and pSMAD2/3 were locally increased in the pulmonary vasculature of PAH rats under both experimental conditions. Conversely, the protein levels of TGFβR2 and pSMAD2/3 were reduced in SuHx while slightly increased in MCT. mRNA levels of plasminogen activator inhibitor (PAI)-1 were increased only in MCT animals and such an increase was not observed in SuHx rats or in iPAH and hPAH patients. In conclusion, our data demonstrate considerable discrepancies in TGFβ-SMAD signaling between iPAH and hPAH patients, as well as between patients and rats with experimental PAH.

Histone deacetylases (HDACs) are increased in pulmonary arterial hypertension (PAH), and inhibiting HDACs can be a promising treatment for PAH. However, previous studies on experimental PAH revealed controversial results, and adverse effects are common. Quisinostat is a “second generation” HDACs inhibitor, which is highly potent against class I and II HDACs, with prolonged pharmacodynamics response. It has been shown to be well tolerated by phase I trial. Collectively, we hypothesized that quisinostat can be used to treat PAH. Proliferation and inflammation were measured after quisinostat treatment on microvascular endothelial cells (MVECs), which were isolated from lungs of PAH patients. Experimental PAH was induced in male Sprague-Dawley rats by a single injection of SU5416 followed by 4-weeks hypoxia and 2-weeks normoxia. At week 6, rats were randomized to receive either DMSO or quisinostat until week 10. Echocardiography was performed at week 6 and week 10, and right ventricle (RV) catheterization was performed at week 10. In vitro, quisinostat reduced proliferation in PAH MVECs, as well as inflammatory response as shown by decreased TNFα, IL-6, MCP-1 and VCAM-1. In vivo, quisinostat treatment reduced RV systolic pressure, RV afterload and total pulmonary resistance in SuHx rats. Further tissue analysis by histology revealed that quisinostat reduced pulmonary vascular remodeling by reducing intima layer thickness. Meanwhile, quisinostat had no effect on RV function. Quisinostat can partly reverse RV afterload and pulmonary vascular remodeling in established experimental PAH. Therefore, quisinostat may be a promising intervention for PAH.

Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by obstructed pulmonary vasculatures. Current therapies for PAH are limited and only alleviate symptoms. Reduced levels of BMPR2 are associated with PAH pathophysiology. Moreover, reactive oxygen species, inflammation and autophagy have been shown to be hallmarks in PAH. We previously demonstrated that MnTBAP, a synthetic metalloporphyrin with antioxidant and anti-inflammatory activity, inhibits the turn-over of BMPR2 in human umbilical vein endothelial cells. Therefore, we hypothesized that MnTBAP might be used to treat PAH. Human pulmonary artery endothelial cells (PAECs), as well as pulmonary microvascular endothelial (MVECs) and smooth muscle cells (MVSMCs) from PAH patients, were treated with MnTBAP. In vivo, either saline or MnTBAP was given to PAH rats induced by Sugen 5416 and hypoxia (SuHx). On PAECs, MnTBAP was found to increase BMPR2 protein levels by blocking autophagy. Moreover, MnTBAP increased BMPR2 levels in pulmonary MVECs and MVSMCs isolated from PAH patients. In SuHx rats, MnTBAP reduced right ventricular (RV) afterload by reversing pulmonary vascular remodeling, including both intima and media layers. Furthermore, MnTBAP improved RV function and reversed RV dilation in SuHx rats. Taken together, these data highlight the importance of MnTBAP as a potential therapeutic treatment for PAH.

Background: Mutations in bone morphogenetic protein receptor type II (BMPR2) are leading to the development of hereditary pulmonary arterial hypertension (PAH). In non-hereditary forms of PAH, perturbations in the transforming growth factor-β (TGF-β)/BMP-axis are believed to cause deficient BMPR2 signaling by changes in receptor expression, the activity of the receptor and/or downstream signaling. To date, BMPR2 expression and its activity in the lungs of patients with non-hereditary PAH is poorly characterized. In recent decades, different animal models have been used to understand the role of BMPR2 signaling in PAH pathophysiology. Specifically, the monocrotaline (MCT) and Sugen–Hypoxia (SuHx) models are extensively used in interventional studies to examine if restoring BMPR2 signaling results in PAH disease reversal. While PAH is assumed to develop in patients over months or years, pulmonary hypertension in experimental animal models develops in days or weeks. It is therefore likely that modifications in BMP and TGF-β signaling in these models do not fully recapitulate those in patients. In order to determine the translational potential of the MCT and SuHx models, we analyzed the BMPR2 expression and activity in the lungs of rats with experimentally induced PAH and compared this to the BMPR2 expression and activity in the lungs of PAH patients. Methods: the BMPR2 expression was analyzed by Western blot analysis and immunofluorescence (IF) microscopy to determine the quantity and localization of the receptor in the lung tissue from normal control subjects and patients with hereditary or idiopathic PAH, as well as in the lungs of control rats and rats with MCT or SuHx-induced PAH. The activation of the BMP pathway was analyzed by determining the level and localization of phosphorylated Smad1/5/8 (pSmad 1/5/8), a downstream mediator of canonical BMPR2 signaling. Results: While BMPR2 and pSmad 1/5/8 expression levels were unaltered in whole lung lysates/homogenates from patients with hereditary and idiopathic PAH, IF analysis showed that BMPR2 and pSmad 1/5/8 levels were markedly decreased in the pulmonary vessels of both PAH patient groups. Whole lung BMPR2 expression was variable in the two PAH rat models, while in both experimental models the expression of BMPR2 in the lung vasculature was increased. However, in the human PAH lungs, the expression of pSmad 1/5/8 was downregulated in the lung vasculature of both experimental models. Conclusion: BMPR2 receptor expression and downstream signaling is reduced in the lung vasculature of patients with idiopathic and hereditary PAH, which cannot be appreciated when using human whole lung lysates. Despite increased BMPR2 expression in the lung vasculature, the MCT and SuHx rat models did develop PAH and impaired downstream BMPR2-Smad signaling similar to our findings in the human lung.