Correction: Shakil, H.; Saleem, S. Genetic Deletion of Prostacyclin IP Receptor Exacerbates Transient Global Cerebral Ischemia in Aging Mice. Brain Sci. 2013, 3, 1095–1108

The authors wish to make the following corrections to this paper: ref [...]

Prostacyclin as a Negative Regulator of Angiogenesis in the Neurovasculature

In this study, multiple measures of angiogenic processes were assessed in murine brain endothelial (bEnd.3) cells after exposure to the stable prostacyclin analog, iloprost. Additionally, changes in the γ-secretase enzyme were evaluated after activation of prostacyclin signaling using PGI2 overexpressing mouse brain tissue and immunohistology studies in bEnd.3 cells. A three-dimensional assay of tube formation revealed that iloprost inhibits normal formation by significantly reduced tube lengths and vessel mesh area. The iloprost-mediated inhibition of tube-like structures was ameliorated by a specific IP-receptor antagonist, CAY10449. Reductions in wound healing were observed with iloprost application in a dose-dependent manner and this effect was reversed using CAY10449. Iloprost did not exhibit anti-proliferative effects in the bEnd.3 cells. When subjected to a Transwell assay to evaluate changes in trans-epithelial electrical resistance (TEER), bEnd.3 cells displayed reduced TEER values in the presence of iloprost an effect that lasted over prolonged periods (24 hours). Again, CAY10449 was able to reverse iloprost-mediated reductions in TEER value. Surprisingly, the adenylyl cyclase activator, forskolin, produced higher TEER values in the bEnd.3 cells over the same time. The TEER results suggest that iloprost may not activating the Gs protein of the IP receptor to increase cAMP levels given by the opposing results seen with iloprost and forskolin. In terms of γ-secretase expression, PGI2 overexpression in mice increased the expression of the APH-1α subunit in the hippocampus and cortex. In bEnd.3 cells, iloprost application slightly increased APH-1α subunit expression measured by western blot and interrupted the colocalization of Presenilin 1 and APH-1α subunits using immunohistochemistry. The results suggest that prostacyclin signaling within bEnd.3 cells is anti-angiogenic and further downstream events have effects on the expression and most likely the activity of the Aβ cleaving enzyme, γ-secretase.

Sexual dimorphism in prostacyclin-mimetic responses of rat mesenteric and coronary arteries.

Background and purpose- Prostacyclin mimetics are widely used clinically. As such it is pertinent to understand the mechanisms underlying the vasoactive response to such agents, yet to date, no study has considered sex as a factor. The aim of this study was to characterise the effect of prostacyclin mimetics, Iloprost and MRE-269, on precontracted arterial tone from male and female Wistar arteries. As a secondary consideration, we investigated Kcnq-encoded KV7 channels as potential downstream targets of prostacyclin-IP-receptor mediated signalling. Experimental approach- Relative mRNA transcript and protein abundance were determined by RT-qPCR and immunocytochemistry respectively. The effect of Iloprost and MRE-269 was determined on pre-contracted arterial tone in the presence of pharmacological modulators of potassium channels and molecular interreference of KV7.1 within 2nd order mesenteric and left anterior descending arteries from male and female Wistar rats. Key results- Iloprost evoked a bi-phasic response in male mesenteric arteries, at low concentrations relaxing, then contracting the vessel at high concentration in a process attributed to IP and EP3 receptors respectively. Secondary contraction was absent in the females, potentially underpinned by a reduction in Ptger3. Pharmacological inhibition and molecular interference of KV7.1 significantly attenuated MRE-269 mediated relaxation in male and female Wistar in Diestrus / Metoestrous, but not Pro-oestrus / Oestrus. Conclusions and implications- Stark sexual dimorphisms in Iloprost mediated vasoactive responses are present within mesenteric arteries. KV7.1 is implicated in IP-receptor mediated vasorelaxation and is impaired by the Oestrus cycle.

P6012Active selexipag metabolite MRE-269 increases endothelin receptors in pulmonary artery smooth muscle cells

Background The pathology of pulmonary arterial hypertension (PAH) indicates the abnormal outgrowth of pulmonary artery smooth muscle cells (PASMCs) of the media. Abundant expression of endothelin 1 (ET-1) is observed in vessels of PAH, and has been considered to play a pathogenic role. There are several endothelin receptors including ETA, ETB. Compared to ETA, ETB mRNA is less expressed in PASMCs from control individuals, and is reported to be increased in those from PAH patients. However, how ETB is involved in PAH remains unclear. Selexipag, a non-prostanoid IP receptor agonist, was recently authorized for treating PAH. Compared to selexipag, the active metabolite MRE-269 has a higher affinity for the IP receptor. Initial combination therapy come to be accepted as a standard strategy for this disease, although the interaction of each drug has not been discussed enough. Purpose To assess the effect of selexipag on ET-1 receptors in PASMCs. Methods We stimulated purchased human PASMCs and endothelial cells by MRE-269 (300 nM), ET-1 (100 nM) or combination of them in vitro. Quantitative PCR was performed to quantify mRNA expressions. Cell proliferation was assessed by CCK8 cell proliferation assay kit. BQ123, A192621, bosentan was used as blocker against ETA, ETB, or both, respectively. Results In PASMCs, MRE-269 increased ETA and ETB expressions 2- and 7-fold, respectively. On the other hand, it increased ETB 1.2-fold in pulmonary artery endothelial cells; ETA was not detected in those cells. After pretreatment by MRE-269, ET-1 accelerated the proliferation of PASMCs. A192621 and bosentan abrogated this proliferation. In contrast, BQ123 did not abrogate it. Conclusions In PASMCs, active selexipag metabolite MRE-269 increases ETB more strongly than ETA, resulting in accelerated cell proliferation by ET-1 predominantly via ETB. These data call for further study focused on the choice of ET-1 receptor antagonists in the case of combination therapy with selexipag.

Transition from intravenous treprostinil to enteral selexipag in an infant with pulmonary arterial hypertension

Selexipag is an enteral, selective prostacyclin IP receptor agonist approved for pulmonary hypertension in adults. There are few reports of its use in children and none in infants. We report the first transition of an infant (11.5 months, 8.6 kg) from intravenous treprostinil (40 ng/kg/minute) to enteral selexipag (400 mcg twice daily) with a good response and no adverse effects.

Should we use the oral selective IP receptor agonist selexipag off-label in children with pulmonary arterial hypertension?

We discuss the currently available data on the use of the prostacyclin mimetic selexipag in children and adolescents with pulmonary arterial hypertension (PAH). Future indications may include transitioning from intravenous prostacyclin/prostacyclin analog to oral selexipag, and vice versa, or adding selexipag as a third oral PAH-targeted agent in children not responding well to dual PAH therapy.