High Level of Real Urban Air Pollution Promotes Cardiac Arrhythmia in Healthy Mice

Background and Objectives@#Ambient particulate matter (PM) in real urban air pollution (RUA) is an environmental health risk factor associated with increased cardiac events. This study investigated the threshold level to induce arrhythmia, as well as arrhythmogenic mechanism of RUA that mainly consisted of PM <2.5 μm in aerodynamic diameter close to ultrafine particles. @*Methods@#RUA was artificially produced by a lately developed pyrolysis based RUA generator.C57BL/6 mice were divided into 4 groups: a control group (control, n=12) and three groups with exposure to RUA with the concentration of 200 µg/㎥ (n=12), 400 µg/㎥ (n=12), and 800 µg/㎥ (n=12). Mice were exposed to RUA at each concentration for 8 hr/day and 5 day/week to mimic ordinary human activity during 3 weeks. @*Results@#The QRS and QTc intervals, as well as intracellular Ca2+ duration, apicobasal action potential duration (APD) gradient, fibrosis, and inflammation of left ventricle of mouse hearts were increased dose-dependently with the increase of RUA concentration, and significantly increased at RUA concentration of 400 µg/㎥ compared to control (all p<0.001). In mice exposed to RUA concentration of 800 µg/㎥ , spontaneous ventricular arrhythmia was observed in 42%, with significant increase of inflammatory markers, phosphorylated Ca2+ /calmodulindependent protein kinase II (CaMKII), and phospholamban (PLB) compared to control. @*Conclusions@#RUA could induce electrophysiological changes such as APD and QT prolongation, fibrosis, and inflammation dose-dependently, with significant increase of ventricular arrhythmia at the concentration of 400 µg/㎥ . RUA concentration of 800 µg/㎥ increased phosphorylation of CaMKII and PLB.

High Level of Real Urban Air Pollution Promotes Cardiac Arrhythmia in Healthy Mice

Background and Objectives@#Ambient particulate matter (PM) in real urban air pollution (RUA) is an environmental health risk factor associated with increased cardiac events. This study investigated the threshold level to induce arrhythmia, as well as arrhythmogenic mechanism of RUA that mainly consisted of PM <2.5 μm in aerodynamic diameter close to ultrafine particles. @*Methods@#RUA was artificially produced by a lately developed pyrolysis based RUA generator.C57BL/6 mice were divided into 4 groups: a control group (control, n=12) and three groups with exposure to RUA with the concentration of 200 µg/㎥ (n=12), 400 µg/㎥ (n=12), and 800 µg/㎥ (n=12). Mice were exposed to RUA at each concentration for 8 hr/day and 5 day/week to mimic ordinary human activity during 3 weeks. @*Results@#The QRS and QTc intervals, as well as intracellular Ca2+ duration, apicobasal action potential duration (APD) gradient, fibrosis, and inflammation of left ventricle of mouse hearts were increased dose-dependently with the increase of RUA concentration, and significantly increased at RUA concentration of 400 µg/㎥ compared to control (all p<0.001). In mice exposed to RUA concentration of 800 µg/㎥ , spontaneous ventricular arrhythmia was observed in 42%, with significant increase of inflammatory markers, phosphorylated Ca2+ /calmodulindependent protein kinase II (CaMKII), and phospholamban (PLB) compared to control. @*Conclusions@#RUA could induce electrophysiological changes such as APD and QT prolongation, fibrosis, and inflammation dose-dependently, with significant increase of ventricular arrhythmia at the concentration of 400 µg/㎥ . RUA concentration of 800 µg/㎥ increased phosphorylation of CaMKII and PLB.

Bacillus clausii, a Foreshore-Derived Probiotic, Attenuates Allergic Airway Inflammation Through Downregulation of Hypoxia Signaling

Background and Objectives@#The immunomodulatory effects and mechanism of probiotics in allergic airway disease are largely unknown. We studied whether Bacillus clausii (BC), a probiotic derived from mudflats, had anti-allergic effects and compared the results with those of Lactobacillus paracasei (LP). We also examined whether the anti-allergic mechanisms of probiotics are associated with hypoxia signaling.Materials and Method: Forty-two BALB/c mice were randomly assigned to six experimental groups: controls, ovalbumin (OVA)-induced mice for inducing asthma, and OVA-induced mice that were orally administered LP or BC, at 1×109 or 5×109 CFU/mL each. We performed differential cell count testing on bronchoalveolar lavage fluid (BALF), lung histopathology, serum totals and OVA-specific IgE and IgG1 assessments, Th2 cytokine titers (IL-4, IL-5) in BALF and pulmonary parenchyma, quantitative PCR for heme oxygenase (HO)-1 and Hif-1α, and immunohistochemistry. @*Results@#Compared to the OVA group mice, OVA-sensitized mice treated with LP or BC showed significantly reduced numbers of eosinophils and neutrophils in the BALF (p<0.05). Both probiotics also significantly reduced pulmonary inflammation and eosinophil infiltration. Mice in the LP or BC group had a substantially lower titer of IL-4 and IL-5 in BALF, and decreased IL-4 and IL-5 expression in the lung parenchyma. Real-time PCR and immunohistochemistry showed that both LP and BC could significantly suppress HO-1 and Hif-1α expression in asthmatic mice (p<0.05). @*Conclusion@#BC can attenuate murine allergic asthma by regulating HIF-1α signaling, and its anti-allergic effect is comparable to that of LP.

Extracellular Vesicles Derived from Hypoxic Human Mesenchymal Stem Cells Attenuate GSK3β Expression via miRNA-26a in an Ischemia-Reperfusion Injury Model

PURPOSE: Bioactive molecules critical to intracellular signaling are contained in extracellular vesicles (EVs) and have cardioprotective effects in ischemia/reperfusion (IR) injured hearts. This study investigated the mechanism of the cardioprotective effects of EVs derived from hypoxia-preconditioned human mesenchymal stem cells (MSCs). MATERIALS AND METHODS: EV solutions (0.4 µg/µL) derived from normoxia-preconditioned MSCs (EVNM) and hypoxia-preconditioned MSCs (EVHM) were delivered in a rat IR injury model. Successful EV delivery was confirmed by the detection of PKH26 staining in hearts from EV-treated rats. RESULTS: EVHM significantly reduced infarct size (24±2% vs. 8±1%, p < 0.001), and diminished arrhythmias by recovering electrical conduction, INa current, and Cx43 expression. EVHM also reversed reductions in Wnt1 and β-catenin levels and increases in GSK3β induced after IR injury. miRNA-26a was significantly increased in EVHM, compared with EVNM, in real-time PCR. Finally, in in vitro experiments, hypoxia-induced increases in GSK3β expression were significantly reduced by the overexpression of miRNA-26a. CONCLUSION: EVHM reduced IR injury by suppressing GSK3β expression via miRNA-26a and increased Cx43 expression. These findings suggest that the beneficial effect of EVHM is related with Wnt signaling pathway.

The Role of Serotonin in Ventricular Repolarization in Pregnant Mice

PURPOSE: The mechanisms underlying repolarization abnormalities during pregnancy are not fully understood. Although maternal serotonin (5-hydroxytryptamine, 5-HT) production is an important determinant for normal fetal development in mice, its role in mothers remains unclear. We evaluated the role of serotonin in ventricular repolarization in mice hearts via 5Htr3 receptor (Htr3a) and investigated the mechanism of QT-prolongation during pregnancy. MATERIALS AND METHODS: We measured current amplitudes and the expression levels of voltage-gated K⁺ (Kv) channels in freshly-isolated left ventricular myocytes from wild-type non-pregnant (WT-NP), late-pregnant (WT-LP), and non-pregnant Htr3a homozygous knockout mice (Htr3a(−/−)-NP). RESULTS: During pregnancy, serotonin and tryptophan hydroxylase 1, a rate-limiting enzyme for the synthesis of serotonin, were markedly increased in hearts and serum. Serotonin increased Kv current densities concomitant with the shortening of the QT interval in WT-NP mice, but not in WT-LP and Htr3a(−/−)-NP mice. Ondansetron, an Htr3 antagonist, decreased Kv currents in WT-LP mice, but not in WT-NP mice. Kv4.3 directly interacted with Htr3a, and this binding was facilitated by serotonin. Serotonin increased the trafficking of Kv4.3 channels to the cellular membrane in WT-NP. CONCLUSION: Serotonin increases repolarizing currents by augmenting Kv currents. Elevated serotonin levels during pregnancy counterbalance pregnancy-related QT prolongation by facilitating Htr3-mediated Kv currents.

Ondansetron Inhibits Voltage-Gated K⁺ Current of Ventricular Myocytes from Pregnant Mouse

BACKGROUND: The Htr3a antagonist, ondansetron, has been reported to prolong the QT interval and induce Torsades de pointes in the treatment of postoperative nausea and vomiting. To explore the mechanisms underlying these findings, we examined the effects of ondansetron on the mouse cardiac voltage-gated K⁺ (Kv) channel. METHODS AND RESULTS: Ondansetron increased QT intervals in late pregnant (LP) mice. We measured the Kv channels in freshly isolated left ventricular (LV) myocytes from non-pregnant (NP) and late pregnant (LP) mice, using patch-clamp electrophysiology. Ondansetron blocked Kv current at a dose of 50 µM, and reduced the amplitude of peak current densities in a dose-dependent manner (0, 1, 5, 50 µM), in LP but not in NP mice. In contrast, serotonin and the Htr3 agonist, m-CPBG, increased Kv current densities in NP, but not in LP mice. Interestingly, during pregnancy, serum serotonin levels were markedly increased, suggesting the saturation of the effect of serotonin. Immunostaning data showed that Kv4.3 protein and Htr3a co-localize at the membrane and t-tubule of cardiomyocytes. Moreover, Kv4.3 membrane trafficking was enhanced in response to Htr3a-mediated serotonin stimulation in NP, but not in LP mice. Membrane analysis showed that serotonin enhances Kv4.3 membrane trafficking in NP, but not LP mice. CONCLUSION: Ondansetron reduced Kv current densities, and reduced the Kv4.3 membrane trafficking in LP mouse ventricular cardiomyocytes. This data suggests that QT prolongation by ondansetron is mediated by the reduction of Kv current densities and Kv4.3 membrane trafficking.