Atrial fibrillation in pigs induces left atrial endocardial transcriptional remodelling.

The leading cause of cardioembolic stroke is atrial fibrillation (AF), which predisposes to atrial thrombus formation. Although rheological alterations promote a hypercoagulable environment, as yet undefined factors contribute to thrombogenesis. The role of the endocardium has barely been explored. To approach this topic, rapid atrial pacing (RAP) was applied in four pigs to mimic AF. Left and right endocardial cells were isolated separately and their gene expression pattern was compared with that of four control pigs. The AF-characteristic rhythm disorders and endothelial nitric oxide synthase down-regulation were successfully reproduced, and validated RAP to mimic AF. A change was observed in the transcriptomic endocardial profile after RAP: the expression of 364 genes was significantly altered (p<0.01), 29 of them having passed the B>0 criteria. The left atrial endocardium [325 genes (7 genes, B>0)] was largely responsible for such alterations. Blood coagulation, blood vessel morphogenesis and inflammatory response are among the most significant altered functions, and help to explain the activation of coagulation observed after RAP: D-dimer, 0.49 (1.63) vs. 0.23 (0.24) mg/l [median (interquartile range)] in controls, p=0.02. Furthermore, three genes directly related to thrombotic processes were differentially expressed after RAP: FGL2 [fold change (FC)=0.85; p=0.007], APLP2 (FC=-0.47; p=0.005) and ADAMTS-18 (FC=-0.69; p=0.004). We demonstrate for the first time that AF induces a global expression change in the left atrial endocardium associated with an activation of blood coagulation. The nature of some of the altered functions and genes provides clues to identify new therapeutic targets.

sPLA2-V inhibits EPCR anticoagulant and antiapoptotic properties by accommodating lysophosphatidylcholine or PAF in the hydrophobic groove.

The endothelial protein C receptor (EPCR) plays an important role in cardiovascular disease by binding protein C/activated protein C (APC). EPCR structure contains a hydrophobic groove filled with an unknown phospholipid needed to perform its function. It has not been established whether lipid exchange takes place in EPCR as a regulatory mechanism of its activity. Our objective was to identify this phospholipid and to explore the possibility of lipid exchange as a regulatory mechanism of EPCR activity driven by the endothelially expressed secretory group V phospholipase A(2) (sPLA(2)-V). We identified phosphatidylcholine (PCh) as the major phospholipid bound to human soluble EPCR (sEPCR). PCh in EPCR could be exchanged for lysophosphatidylcholine (lysoPCh) and platelet activating factor (PAF). Remarkably, lysoPCh and PAF impaired the protein C binding ability of sEPCR. Inhibition of sPLA(2)-V, responsible for lysoPCh and PAF generation, improved APC binding to endothelial cells. EPCR-dependent protein C activation and APC antiapoptotic effect were thus significantly enhanced. In contrast, endothelial cell supplementation with sPLA(2)-V inhibited both APC generation and its antiapoptotic effects. We conclude that APC generation and function can be modulated by changes in phospholipid occupancy of its endothelial cell receptor.

Limited ability to activate protein C confers left atrial endocardium a thrombogenic phenotype: a role in cardioembolic stroke?

BACKGROUND AND PURPOSE: Atrial fibrillation is the most important risk factor for cardioembolic stroke. Thrombi form in the left atrial appendage rather than in the right. The causes of this different thrombogenicity are not well-understood. The goal herein was to compare the activation of the anticoagulant protein C and the thrombomodulin and endothelial protein C receptor/activated protein C receptor expression on the endocardium between right and left atria. METHODS: We harvested the atria of 6 monkeys (Macaca fascicularis) and quantified their ability to activate protein C ex vivo and we measured the thrombomodulin and endothelial protein C receptor expression by immunofluorescence. RESULTS: We found the ability to activate protein C decreased by half (P=0.028) and there was lower expression of thrombomodulin in the left atrial endocardium than the right (52.5±19.9 and 72.1±18.8 arbitrary intensity units, mean±standard deviation; P=0.028). No differences were detected in endothelial protein C receptor expression. CONCLUSIONS: Impaired protein C activation on the left atrial endocardium attributable to low thrombomodulin expression may explain its higher thrombogenicity and play a role in cardioembolic stroke.

Multiparameter flow cytometric remission is the most relevant prognostic factor for multiple myeloma patients who undergo autologous stem cell transplantation.

Minimal residual disease (MRD) assessment is standard in many hematologic malignancies but is considered investigational in multiple myeloma (MM). We report a prospective analysis of the prognostic importance of MRD detection by multiparameter flow cytometry (MFC) in 295 newly diagnosed MM patients uniformly treated in the GEM2000 protocol VBMCP/VBAD induction plus autologous stem cell transplantation [ASCT]). MRD status by MFC was determined at day 100 after ASCT. Progression-free survival (PFS; median 71 vs 37 months, P < .001) and overall survival (OS; median not reached vs 89 months, P = .002) were longer in patients who were MRD negative versus MRD positive at day 100 after ASCT. Similar prognostic differentiation was seen in 147 patients who achieved immunofixation-negative complete response after ASCT. Moreover, MRD(-) immunofixation-negative (IFx(-)) patients and MRD(-) IFx(+) patients had significantly longer PFS than MRD(+) IFx(-) patients. Multivariate analysis identified MRD status by MFC at day 100 after ASCT as the most important independent prognostic factor for PFS (HR = 3.64, P = .002) and OS (HR = 2.02, P = .02). Our findings demonstrate the clinical importance of MRD evaluation by MFC, and illustrate the need for further refinement of MM re-sponse criteria. This trial is registered at http://clinicaltrials.gov under identifier NCT00560053.