Background Pulmonary arterial hypertension (PAH) is a severe and progressive disease, a hallmark of which is pulmonary vascular remodeling. Nicotinamide phosphoribosyltransferase (NAMPT), is a cytozyme which regulates intracellular NAD levels and cellular redox state, regulates histone deacetylases, promotes cell proliferation and inhibits apoptosis. We hypothesized that NAMPT promotes pulmonary vascular remodeling, and that inhibition of NAMPT could attenuate pulmonary hypertension. Methods Plasma and mRNA and protein levels of NAMPT were measured in the lungs and isolated pulmonary artery endothelial cells (PAECs) from PAH patients, as well as in lungs of rodent models of pulmonary hypertension (PH). Nampt+/− mice were exposed 10% hypoxia and room air for 4 weeks and the preventive and therapeutic effects of NAMPT inhibition were tested in the monocrotaline and Sugen-hypoxia models of PH. The effects on NAMPT activity on proliferation, migration, apoptosis and calcium signaling were tested in human pulmonary artery smooth muscle cell (hPASMC). Results Plasma and mRNA and protein levels of NAMPT were increased in the lungs and isolated pulmonary artery endothelial cells (PAECs) from PAH patients, as well as in lungs of rodent models of pulmonary hypertension (PH). Nampt+/− mice were protected from hypoxia-mediated PH. NAMPT activity promoted human pulmonary artery smooth muscle cell (hPASMC) proliferation via a paracrine effect. In addition, recombinant NAMPT stimulated hPASMC proliferation via enhancement of store-operated calcium entry by enhancing expression of Orai2 and STIM2. Finally, inhibition of NAMPT activity attenuated monocrotaline and Sugen hypoxia induced PH in rats. Conclusions Our data provide evidence that NAMPT plays a role in pulmonary vascular remodeling and its inhibition could be a potential therapeutic target for PAH.

The optimum septic shock vasopressor support strategy is currently debated. This study was performed to evaluate the efficacy and safety of norepinephrine (NE) and dopamine (DA) as the initial vasopressor in septic shock patients who were managed with a specific treatment protocol. A prospective, randomized, open-label, clinical trial was used in a medical intensive care unit comparing DA with NE as the initial vasopressor in fluid-resuscitated 252 adult patients with septic shock. If the maximum dose of the initial vasopressor was unable to maintain the hemodynamic goal, then fixed-dose vasopressin was added to each regimen. If additional vasopressor support was needed to achieve the hemodynamic goal, then phenylephrine was added. The primary efficacy end point was all-cause 28-day mortality. Secondary end points included organ dysfunction, hospital and intensive care unit length of stay, and safety (primarily occurrence of arrhythmias). The 28-day mortality rate was 50% (67/134) with DA as the initial vasopressor compared with 43% (51/118) for NE treatment (P = 0.282). There was a significantly greater incidence of sinus tachycardia with DA (24.6%; 33/134) than NE (5.9%; 7/118) and arrhythmias noted with DA treatment (19.4%; 26/134) compared with NE treatment (3.4%; 4/118; P < 0.0001), respectively. Logistic regression analysis identified Acute Physiologic and Chronic Health Evaluation II score (P < 0.0001) and arrhythmia (P < 0.015) as significant predictors of outcome. In this protocol-directed vasopressor support strategy for septic shock, DA and NE were equally effective as initial agents as judged by 28-day mortality rates. However, there were significantly more cardiac arrhythmias with DA treatment. Patients receiving DA should be monitored for the development of cardiac arrhythmias (NCT00604019).

Hemin, the oxidized prosthetic moiety of hemoglobin, has been implicated in the pathogenesis of acute chest syndrome in patients with sickle cell disease by virtue of its endothelial-activating properties. In this study, we examined whether hemin can cause lung microvascular endothelial barrier dysfunction. By assessing transendothelial resistance using electrical cell impedance sensing, and by directly measuring trans-monolayer fluorescein isothiocyanate-dextran flux, we found that hemin does cause endothelial barrier dysfunction in a concentration-dependent manner. Pretreatment with either a Toll-like receptor 4 inhibitor, TAK-242, or an antioxidant, N-acetylcysteine, abrogated this effect. Increased monolayer permeability was found to be associated with programmed cell death by necroptosis, as evidenced by Trypan blue staining, terminal deoxynucleotidyl transferase dUTP nick-end labeling assay, Western blotting for activated forms of key effectors of cell death pathways, and studies utilizing specific inhibitors of necroptosis and apoptosis. Further studies examining the role of endothelial cell necroptosis in promoting noncardiogenic pulmonary edema during acute chest syndrome are warranted and may open a new avenue of potential treatments for this devastating disease.

Sphingosine kinase 1 (SphK1) upregulation is associated with pathologic pulmonary vascular remodeling in pulmonary arterial hypertension (PAH), but the mechanisms controlling its expression are undefined. In this study, we sought to characterize the regulation of SphK1 expression by micro-RNAs (miRs). In silico analysis of the SphK1 3'-untranslated region identified several putative miR binding sites, with miR-1-3p (miR-1) being the most highly predicted target. Therefore we further investigated the role of miR-1 in modulating SphK1 expression and characterized its effects on the phenotype of pulmonary artery smooth muscle cells (PASMCs) and the development of experimental pulmonary hypertension in vivo. Our results demonstrate that miR-1 is downregulated by hypoxia in PASMCs and can directly inhibit SphK1 expression. Overexpression of miR-1 in human PASMCs inhibits basal and hypoxia-induced proliferation and migration. Human PASMCs isolated from PAH patients exhibit reduced miR-1 expression. We also demonstrate that miR-1 is downregulated in mouse lung tissues during experimental hypoxia-mediated pulmonary hypertension (HPH), consistent with upregulation of SphK1. Furthermore, administration of miR-1 mimics in vivo prevented the development of HPH in mice and attenuated induction of SphK1 in PASMCs. These data reveal the importance of miR-1 in regulating SphK1 expression during hypoxia in PASMCs. A pivotal role is played by miR-1 in pulmonary vascular remodeling, including PASMC proliferation and migration, and its overexpression protects from the development of HPH in vivo. These studies improve our understanding of the molecular mechanisms underlying the pathogenesis of pulmonary hypertension.