Atrial arrhythmogenicity in aged Scn5a+/∆KPQ mice modeling long QT type 3 syndrome and its relationship to Na+ channel expression and cardiac conduction

Recent studies have reported that human mutations in Nav1.5 predispose to early age onset atrial arrhythmia. The present experiments accordingly assess atrial arrhythmogenicity in aging Scn5a+/∆KPQ mice modeling long QT3 syndrome in relationship to cardiac Na+ channel, Nav1.5, expression. Atrial electrophysiological properties in isolated Langendorff-perfused hearts from 3- and 12-month-old wild type (WT), and Scn5a+/∆KPQ mice were assessed using programmed electrical stimulation and their Nav1.5 expression assessed by Western blot. Cardiac conduction properties were assessed electrocardiographically in intact anesthetized animals. Monophasic action potential recordings demonstrated increased atrial arrhythmogenicity specifically in aged Scn5a+/ΔKPQ hearts. These showed greater action potential duration/refractory period ratios but lower atrial Nav1.5 expression levels than aged WT mice. Atrial Nav1.5 levels were higher in young Scn5a+/ΔKPQ than young WT. These levels increased with age in WT but not Scn5a+/ΔKPQ. Both young and aged Scn5a+/ΔKPQ mice showed lower heart rates and longer PR intervals than their WT counterparts. Young Scn5a+/ΔKPQ mice showed longer QT and QTc intervals than young WT. Aged Scn5a+/ΔKPQ showed longer QRS durations than aged WT. PR intervals were prolonged and QT intervals were shortened in young relative to aged WT. In contrast, ECG parameters were similar between young and aged Scn5a+/ΔKPQ. Aged murine Scn5a+/ΔKPQ hearts thus exhibit an increased atrial arrhythmogenicity. The differing Nav1.5 expression and electrocardiographic indicators of slowed cardiac conduction between Scn5a+/ΔKPQ and WT, which show further variations associated with aging, may contribute toward atrial arrhythmia in aged Scn5a+/ΔKPQ hearts

Calcification stimulates inflammatory signalling pathways in human vascular smooth muscle cells

Introduction: Calcification is associated with ageing blood vessels and with diseases including atherosclerosis and osteoarthritis. In particular, small calcified particles correlate with atherosclerotic plaque instability and the reason for this is unknown. Some studies suggest that calcium phosphate (CaP) particles cause mechanical stress in the fibrous cap, while others imply that CaP can be engulfed by macrophages leading to caspase-1 activation and secretion of mature IL-1β. Our own studies suggest that small CaP particles are taken up into vascular smooth muscle cell (VSMC) and can cause cell death. Methods: In this study, the effects of CaP particles on VSMC inflammatory pathway activity was investigated by Western analysis for caspase-1 and Syk, and for IL-1β release by ELISA. Results: We found that CaP particles stimulated the secretion of IL-1β from growing and senescent human VSMCs, with higher levels of IL-1β release seen in senescent cells (up to 1.5ng/ml). IL-1β secretion required caspase-1 activity, but unlike macrophages, priming of cells was not required. IL-1β secretion was blocked by R406, a highly specific inhibitor of the Syk tyrosine kinase. Syk is known to be required for NLRP3 inflammasome activation, and Western blot analysis demonstrated that CaP particles induced Syk phosphorylation after 10 minutes of exposure to VSMCs. Additionally, inhibitors of particle uptake, wortmannin and chlorpromazine reduced CaP particle-induced IL-1β release. Conclusions: Together, these studies indicate that CaP particles enter cells via endocytic mechanisms and activate Syk kinase and caspase-1 upstream of IL-1β release, and highlight that VSMCs have the potential to generate pro-inflammatory signals

Worsening calcification propensity precedes all-cause and cardiovascular mortality in haemodialyzed patients

Abstract A novel in-vitro test (T50-test) assesses ex-vivo serum calcification propensity which predicts mortality in HD patients. The association of longitudinal changes of T50 with all-cause and cardiovascular mortality has not been investigated. We assessed T50 in paired sera collected at baseline and at 24 months in 188 prevalent European HD patients from the ISAR cohort, most of whom were Caucasians. Patients were followed for another 19 [interquartile range: 11–37] months. Serum T50 exhibited a significant decline between baseline and 24 months (246 ± 64 to 190 ± 68 minutes; p < 0.001). With serum Δ-phosphate showing the strongest independent association with declining T50 (r = −0.39; p < 0.001) in multivariable linear regression. The rate of decline of T50 over 24 months was a significant predictor of all-cause (HR = 1.51 per 1SD decline, 95% CI: 1.04 to 2.2; p = 0.03) and cardiovascular mortality (HR = 2.15; 95% CI: 1.15 to 3.97; p = 0.02) in Kaplan Meier and multivariable Cox-regression analysis, while cross-sectional T50 at inclusion and 24 months were not. Worsening serum calcification propensity was an independent predictor of mortality in this small cohort of prevalent HD patients. Prospective larger scaled studies are needed to assess the value of calcification propensity as a longitudinal parameter for risk stratification and monitoring of therapeutic interventions