Engineering ‘Enzymelink’ for screening lead compounds to inhibit mPGES-1 while maintaining prostacyclin synthase activity

Aim: This study investigated our Enzymelinks, COX-2-10aa-mPGES-1 and COX-2-10aa-PGIS, as cellular cross-screening targets for quick identification of lead compounds to inhibit inflammatory PGE2 biosynthesis while maintaining prostacyclin synthesis. Methods: We integrated virtual and wet cross-screening using Enzymelinks to rapidly identify lead compounds from a large compound library. Results: From 380,000 compounds virtually cross-screened with the Enzymelinks, 1576 compounds were identified and used for wet cross-screening using HEK293 cells that overexpressed individual Enzymelinks as targets. The top 15 lead compounds that inhibited mPGES-1 activity were identified. The top compound that specifically inhibited inflammatory PGE2 biosynthesis alone without affecting COX-2 coupled to PGI2 synthase (PGIS) for PGI2 biosynthesis was obtained. Conclusion: Enzymelink technology could advance cyclooxygenase pathway-targeted drug discovery to a significant degree.

Increased expression and catalytic activity of prostacyclin synthase after simvastatin application to human umbilical vein endothelial cells

In addition to lowering blood cholesterol levels, statins are known to exert antiplatelet effects. One of the key factors contributing to the antiplatelet effects of statins includes the upregulation of prostacyclin (PGI2) level. The present study was undertaken to determine the effects of statins on prostacyclin synthase (PGIS, CYP8A1) and PGI2 synthesis at the molecular level. Human umbilical vein endothelial cells (HUVEC) were exposed to five structurally different statins (atorvastatin, simvastatin, pravastatin, lovastatin, and rosuvastatin) and changes in CYP8A1 expression levels and the metabolic activities of CYP8A1 were investigated. Among the tested statins, simvastatin induced significant PGIS expression at both transcriptional (2.9-fold, P<0.05) and translational (1.8-fold, P<0.05) levels. Treatment with a constitutive androstane receptor (CAR) agonist, phenobarbital, significantly increased CYP8A1 mRNA expression (3-fold, P<0.01). A metabolite of prostacyclin, 6-keto prostaglandin F1?, was significantly increased by treatment with simvastatin (P<0.01) and markedly repressed by the CYP8A1 inhibitor tranylcypromine (P<0.01) and the CAR antagonist clotrimazole (P<0.01) in HUVEC. The results of this study improve our understanding of the inter-individual variations in PGI2 levels. Clinical studies in humans are necessary to confirm the present in vitro results.

Nitric Oxide in Life and Death of Neutrophils

Background: Nitric Oxide (NO) is a key signalling molecule that has an important role in inflammation. It can be secreted by endothelial cells, neutrophils, and other cells, and once in circulation, NO plays important roles in regulating various neutrophil cellular activities and fate. Objective: To describe neutrophil cellular responses influenced by NO and its concomitant compound peroxynitrite and signalling mechanisms for neutrophil apoptosis. Methods: Literature was reviewed to assess the effects of NO on neutrophils. Results: NO plays an important role in various neutrophil cellular activities and interaction with other cells. The characteristic cellular activities of neutrophils are adhesion and phagocytosis. NO plays a protective role in neutrophil-endothelial interaction by preventing neutrophil adhesion and endothelial cell damage by activated neutrophils. NO suppresses neutrophil phagocytic activity but stimulates longdistance contact interactions through tubulovesicular extensions or cytonemes. Neutrophils are the main source of superoxide, but NO flow results in the formation of peroxynitrite, a compound with high biological activity. Peroxynitrite is involved in the regulation of eicosanoid biosynthesis and inhibits endothelial prostacyclin synthase. NO and peroxynitrite modulate cellular 5-lipoxygenase activity and leukotriene synthesis. Long-term exposure of neutrophils to NO results in the activation of cell death mechanisms and neutrophil apoptosis. Conclusion: Nitric oxide and the NO/superoxide interplay fine-tune mechanisms regulating life and death in neutrophils.

Modulation of Cardiovascular Function in Primary Hypertension in Rat by SKA-31, an Activator of KCa2.x and KCa3.1 Channels

The aim of this study was to investigate the hemodynamic effects of SKA-31, an activator of the small (KCa2.x) and intermediate (KCa3.1) conductance calcium-activated potassium channels, and to evaluate its influence on endothelium-derived hyperpolarization (EDH)-KCa2.3/KCa3.1 type relaxation in isolated endothelium-intact small mesenteric arteries (sMAs) from spontaneously hypertensive rats (SHRs). Functional in vivo and in vitro experiments were performed on SHRs or their normotensive controls, Wistar-Kyoto rats (WKY). SKA-31 (1, 3 and 10 mg/kg) caused a brief decrease in blood pressure and bradycardia in both SHR and WKY rats. In phenylephrine-pre-constricted sMAs of SHRs, SKA-31 (0.01–10 µM)-mediated relaxation was reduced and SKA-31 potentiated acetylcholine-evoked endothelium-dependent relaxation. Endothelium denudation and inhibition of nitric oxide synthase (eNOS) and cyclooxygenase (COX) by the respective inhibitors l-NAME or indomethacin, attenuated SKA-31-mediated vasorelaxation. The inhibition of KCa3.1, KCa2.3, KIR and Na+/K+-ATPase by TRAM-34, UCL1684, Ba2+ and ouabain, respectively, reduced the potency and efficacy of the EDH-response evoked by SKA-31. The mRNA expression of eNOS, prostacyclin synthase, KCa2.3, KCa3.1 and KIR were decreased, while Na+/K+-ATPase expression was increased. Collectively, SKA-31 promoted hypotension and vasodilatation, potentiated agonist-stimulated vasodilation, and maintained KCa2.3/KCa3.1-EDH-response in sMAs of SHR with downstream signaling that involved KIR and Na+/K+-ATPase channels. In view of the importance of the dysfunction of endothelium-mediated vasodilatation in the mechanism of hypertension, application of activators of KCa2.3/KCa3.1 channels such as SKA-31 seem to be a promising avenue in pharmacotherapy of hypertension.

Affinity Isolation and Mass Spectrometry Identification of Prostacyclin Synthase (PTGIS) Subinteractome

Prostacyclin synthase (PTGIS; EC 5.3.99.4) catalyzes isomerization of prostaglandin H2 to prostacyclin, a potent vasodilator and inhibitor of platelet aggregation. At present, limited data exist on functional coupling and possible ways of regulating PTGIS due to insufficient information about protein–protein interactions in which this crucial enzyme is involved. The aim of this study is to isolate protein partners for PTGIS from rat tissue lysates. Using CNBr-activated Sepharose 4B with covalently immobilized PTGIS as an affinity sorbent, we confidently identified 58 unique proteins by mass spectrometry (LC-MS/MS). The participation of these proteins in lysate complex formation was characterized by SEC lysate profiling. Several potential members of the PTGIS subinteractome have been validated by surface plasmon resonance (SPR) analysis. SPR revealed that PTGIS interacted with full-length cytochrome P450 2J2 and glutathione S-transferase (GST). In addition, PTGIS was shown to bind synthetic peptides corresponding to sequences of for GSTA1, GSTM1, aldo-keto reductase (AKR1A1), glutaredoxin 3 (GLRX3) and histidine triad nucleotide binding protein 2 (HINT2). Prostacyclin synthase could potentially be involved in functional interactions with identified novel protein partners participating in iron and heme metabolism, oxidative stress, xenobiotic and drugs metabolism, glutathione and prostaglandin metabolism. The possible biological role of the recognized interaction is discussed in the context of PTGIS functioning.

Interaction of prostacyclin synthase with cytochromes P450

Biosensor experiments on investigation of interaction between prostacyclin synthase (PGIS) and different proteins of the cytochrome P450 monooxygenase systems were perfomed. Interaction of PGIS with microsomal (CYP21A2, CYP2E1) and mitochondrial (CYP27A1, CYP11B1, CYP11B2, CYP11A1) cytochrome P450s was detected. Kinetic and equilibrium parameters of protein complexes formation were determined. Data obtained suggest an essential role of these hemoproteins interaction in regulation of prostacyclin and thromboxane A2 biosynthesis.