Dexfenfluramine discontinuous treatment does not worsen hypoxia-induced pulmonary vascular remodeling but activates RhoA/ROCK pathway: consequences on pulmonary hypertension

Drug-induced pulmonary arterial hypertension: a primer for clinicians and scientists

Drug-induced pulmonary arterial hypertension (D-PAH) is a form of World Health Organization Group 1 pulmonary hypertension (PH) defined by severe small vessel loss and obstructive vasculopathy, which leads to progressive right heart failure and death. To date, 16 different compounds have been associated with D-PAH, including anorexigens, recreational stimulants, and more recently, several Food and Drug Administration-approved medications. Although the clinical manifestation, pathology, and hemodynamic profile of D-PAH are indistinguishable from other forms of pulmonary arterial hypertension, its clinical course can be unpredictable and to some degree dependent on removal of the offending agent. Because only a subset of individuals develop D-PAH, it is probable that genetic susceptibilities play a role in the pathogenesis, but the characterization of the genetic factors responsible for these susceptibilities remains rudimentary. Besides aggressive treatment with PH-specific therapies, the major challenge in the management of D-PAH remains the early identification of compounds capable of injuring the pulmonary circulation in susceptible individuals. The implementation of pharmacovigilance, precision medicine strategies, and global warning systems will help facilitate the identification of high-risk drugs and incentivize regulatory strategies to prevent further outbreaks of D-PAH. The goal for this review is to inform clinicians and scientists of the prevalence of D-PAH and to highlight the growing number of common drugs that have been associated with the disease.

Upregulation of HIF-1α protects neuroblastoma cells from hypoxia-induced apoptosis in a RhoA-dependent manner

Hypoxic conditions regulate several metabolic enzymes and transcription factors that are involved in cancer, ischemia and pulmonary diseases. The Ras homolog (Rho) family, including Rho member A (RhoA), is involved in reorganization of the actin cytoskeleton, cell migration and in the regulation of apoptosis and gene transcription. The aim of the present study was to investigate the expression of hypoxia‑inducible factor (HIF)‑α and the activity of RhoA in PC12 neuroblastoma cells under hypoxic conditions. The upregulation of HIF‑α and RhoA by hypoxia was determined using reverse transcription‑quantitative polymerase chain reaction and western blot assays, cell apoptosis was analyzed using flow cytometry, and the activity of caspase 3 was examined using a western blot assay and caspase 3 activity assay kit. The PC12 cells were induced to apoptosis following exposure to hypoxia, and exhibited increased expression of HIF‑α and increased mRNA and protein expression levels of RhoA. The overexpression of HIF‑α attenuated the hypoxia‑induced apoptosis of the PC12 cells. In addition, RhoA knockdown using small interfering RNA abrogated the antagonism of HIF‑1α towards hypoxia‑induced apoptosis. The results of the present study confirmed the protective role of HIF‑1α and RhoA in hypoxia‑induced PC12 cell apoptosis, and that the upregulation of HIF‑1α by hypoxia is RhoA‑dependent.

Fluoxetine inhibits monocrotaline-induced pulmonary arterial remodeling involved in inhibition of RhoA–Rho kinase and Akt signalling pathways in rats

Activation of the small GTPase Ras homolog gene family member A (RhoA) and Rho-associated kinase (ROCK) are important in the pathogenesis of pulmonary arterial hypertension (PAH). Selective serotonin reuptake inhibitors inhibit activation of RhoA and ROCK in vitro, and ameliorate PAH and pulmonary arterial remodeling in vivo. However, little is known about whether the RhoA–ROCK signalling pathway is involved in the treatment of PAH with fluoxetine in vivo. The aim of the present study was to investigate the involvement of the RhoA–ROCK signalling pathway in the protective effect of the selective serotonin reuptake inhibitor fluoxetine against monocrotaline (MCT)-induced pulmonary arterial remodeling. MCT was applied to establish PAH in male Wistar rats. Fluoxetine was administered by gastric gavage once a day for 21 d. The results showed that MCT induced pulmonary arterial remodeling, raised the serotonylation and membrane translocation of RhoA in the lungs, and increased serotonin transporter (5-HTT), RhoA, and ROCK2 expression, and extracellular signal-regulated kinase (ERK) and Akt phosphorylation in the pulmonary arteries and the lungs. Fluoxetine markedly inhibited these MCT-induced changes. The findings suggest that fluoxetine inhibits MCT-induced pulmonary arterial remodeling in rats by inhibition of the RhoA–ROCK and Akt signalling pathways.

Mechanisms of hypoxic pulmonary vasoconstriction and their roles in pulmonary hypertension: new findings for an old problem

Hypoxic pulmonary vasoconstriction (HPV) normally optimises ventilation-perfusion matching in the lung, but leads to pulmonary hypertension (PH) under conditions of global hypoxia. The past few years have provided some major advances in our understanding of this complex phenomenon, but significant controversy remains concerning many of the key underlying mechanisms. On balance, recent evidence is most consistent with an elevation in mitochondria-derived reactive oxygen species as a key event for initiation of HPV, with consequent Ca2+ release from intracellular ryanodine-sensitive stores, although the activation pathways and molecular identity of the associated Ca2+ entry pathways remain unclear. Recent studies have also raised our perception of the critical role played by Rho kinase (ROCK) in both sustained HPV and the development of PH, further promoting ROCK and the pathways regulating its activity and expression as important therapeutic targets.