Gwo-Jyh Chang

Rosuvastatin suppresses atrial tachycardia-induced cellular remodeling via Akt/Nrf2/heme oxygenase-1 pathway.

Atrial fibrillation (AF) is associated with structural remodeling in atrial myocytes. Emerging evidence suggests that statin has a protective effect on AF through cholesterol-independent mechanisms. The aim of this study is to investigate whether heme oxygenase-1 (HO-1), a potent antioxidant system, mediates the suppressive effect of statin on atrial tachycardia-induced structural remodeling. Treatment of cultured atrium-derived myocytes (HL-1 cell line) with rosuvastatin enhanced HO-1 expression/activity and attenuated tachypacing-induced oxidative stress and myofibril degradation. Heme oxygenase-1 inhibitors and small-interfering RNA for HO-1 blocked the inhibitory effect of rosuvastatin on tachypacing-stimulated changes, suggesting the crucial role of HO-1 in mediating the effect of rosuvastatin. Time-dependent experiments and loss-of-function study demonstrated that Akt/Nrf2 pathways lay to the up-stream of HO-1 in this signaling cascade. Furthermore, the involvement of Akt/Nrf2/HO-1 pathway in the antioxidant effect of rosuvastatin was documented in an ex vivo tachypacing model. The suppressive effect of statin on atrial tachypacing-induced cellular remodeling is mediated via the activation of Akt/Nrf2/HO-1 signaling, which provides a possible explanation for the protective effect of statin on AF.

Electrophysiological basis for the antiarrhythmic action and positive inotropy of HA‐7, a furoquinoline alkaloid derivative, in rat heart

1 HA‐7, a new synthetic derivative of furoquinoline alkaloid, increased the contractile force of right ventricular strips and effectively suppressed the ischaemia‐reperfusion induced polymorphic ventricular tachyrhythmias in adult rat heart (EC50=2.8 μM). 2 In rat ventricular myocytes, HA‐7 concentration‐dependently prolonged the action potential duration (APD) and decreased the maximal rate of rise of the action potential upstroke (V̇max). The action potential amplitude and resting membrane potential were also reduced, but to a smaller extent. The prolongation of APD by HA‐7 was prevented by pretreating the cells with 1 mM 4‐AP. 3 Voltage clamp experiments revealed that HA‐7 decreased the maximal current amplitude of INa (IC50=4.1 μM) and caused a negative shift of its steady‐state inactivation curve and slowed its rate of recovery from inactivation. The use‐dependent inhibition of INa by HA‐7 was enhanced at a higher stimulation rate. The L‐type Ca2+ current (ICa) was also reduced, but to a lesser degree (IC50=5.3 μM, maximal inhibition=31.8%). 4 This agent also influenced the time‐ and voltage‐dependent K+ currents. The prolongation of APD was associated with an inhibition of a 4‐AP sensitive transient outward K+ current (Ito) (IC50=2.9 μM) and a slowly inactivating, steady‐state outward current (Iss) (IC50=2.5 μM). The inhibition of Ito by HA‐7 was associated with an acceleration of its time constant of inactivation. HA‐7 suppressed Ito in a time‐dependent manner and caused a significant negative shift of the voltage‐dependent steady‐state inactivation curve but did not affect its rate of recovery from inactivation. 5 At higher concentrations, the inward rectifier K+ current (IK1) was also inhibited but to a less extent. Its slope conductance after 3, 10 and 30 μM HA‐7 was decreased by 24±4%, 41±5% and 54±8%, respectively. 6 We conclude that HA‐7 predominantly blocks Ito and Na+ channels and that it also weakly blocks Ca2+ and IK1 channels. These changes alter the electrophysiological properties of the heart and terminate the ischaemia reperfusion induced ventricular arrhythmia. The significant Ito inhibition and minimal ICa suppression may afford an opportunity to develop an effective antiarrhythmic agent linked with positive inotropy.

Cardiac electrophysiologic and antiarrhythmic actions of a pavine alkaloid derivative, O‐methyl‐neocaryachine, in rat heart

O‐methyl‐neocaryachine (OMNC) suppressed the ischaemia/reperfusion‐induced ventricular arrhythmias in Langendorff‐perfused rat hearts (EC50=4.3 μM). Its electrophysiological effects on cardiac myocytes and the conduction system in isolated hearts as well as the electromechanical effects on the papillary muscles were examined. In rat papillary muscles, OMNC prolonged the action potential duration (APD) and decreased the maximal rate of depolarization (Vmax). As compared to quinidine, OMNC exerted less effects on both the Vmax and APD but a positive inotropic effect. In the voltage clamp study, OMNC decreased Na+ current (INa) (IC50=0.9 μM) with a negative‐shift of the voltage‐dependent inactivation and a slowed rate of recovery from inactivation. The voltage dependence of INa activation was, however, unaffected. With repetitive depolarizations, OMNC blocked INa frequency‐dependently. OMNC blocked ICa with an IC50 of 6.6 μM and a maximum inhibition of 40.7%. OMNC inhibited the transient outward K+ current (Ito) (IC50=9.5 μM) with an acceleration of its rate of inactivation and a slowed rate of recovery from inactivation. However, it produced little change in the steady‐state inactivation curve. The steady‐state outward K+ current (ISS) was inhibited with an IC50 of 8.7 μM. The inward rectifier K+ current (IK1) was also reduced by OMNC. In the perfused heart model, OMNC (3 to 30 μM) prolonged the ventricular repolarization time, the spontaneous cycle length and the atrial and ventricular refractory period. The conduction through the AV node and His‐Purkinje system, as well as the AV nodal refractory period and Wenckebach cycle length were also prolonged (30 μM). In conclusion, OMNC blocks Na+, Ito and ISS channels and in similar concentrations partly blocks Ca2+ channels. These effects lead to a modification of the electromechanical function and may likely contribute to the termination of ventricular arrhythmias. These results provide an opportunity to develop an effective antiarrhythmic agent with modest positive inotropy as well as low proarrhythmic potential.

Protective role of heme oxygenase-1 in atrial remodeling

Structural and electrical remodeling in the atrium constitutes the main feature of atrial fibrillation (AF), which is characterized by increased oxidative stress. Heme oxygenase-1 (HO-1) is a potent anti-oxidant system that may provide protection against various oxidative stress-related diseases. The aim of this study is to investigate whether HO-1 has a protective effect on AF-related remodeling. Cultured atrium-derived myocytes (HL-1 cell line) were used to evaluate tachypacing-induced oxidative stress, structural, and electrical remodeling. Transforming growth factor-β (TGF-β) was utilized to assess collagen (a main fibrosis-related protein) expression in atrial fibroblasts. Tachypacing in HL-1 myocytes and treatment of atrial fibroblasts with TGF-β enhanced the expression of HO-1, both of which were mediated by the activation of nuclear factor erythroid-2-related factor 2. Over-expression of HO-1 in HL-1 cells attenuated tachypacing-induced oxidative stress, myofibril degradation, down-regulation of L-type calcium channel, and shortening of action potential duration. Furthermore, HO-1 over-expression in atrial fibroblasts blocked the up-regulation of collagen by TGF-β, implicating a protective role of HO-1 in structural and electrical remodeling in the atrium. In vivo, HO-1−/− mice exhibited a higher degree of oxidative stress, myofibril degradation, and collagen deposit in their atria than wild-type mice. Moreover, burst atrial pacing induced a greater susceptibility to AF in HO-1−/− mice than in wild-type mice. In conclusion, a negative-feedback regulation of HO-1 in activated atrial myocytes and fibroblasts may provide protection against AF-related remodeling and AF development.

Differential Endothelial Gap Junction Expression in Venous Vessels Exposed to Different Hemodynamics

After being anastomosed with the artery, vein graft is exposed to abruptly increased hemodynamic stresses. These hemodynamic stresses may change the profile of endothelial gap junction expression as demonstrated in the artery, which may subsequently play active roles in physiological adaptation or pathophysiological changes of the vein grafts. We investigated the endothelial expression of gap junction in the venous vessels exposed to different hemodynamic stresses. Immunocytochemical analysis of the endothelial Cx expression was performed by observing the whole mounts of inferior vena cava (IVC) of aortocaval fistula (ACF) rats or IVC-banded ACF rats using confocal microscope. Immunocytochemical analysis demonstrated that in the endothelium of the native vein, the gap-junctional spot numbers (GJSNs) and the total gap-junctional areas (TGJAs) of C×40 and C×43 were lower than those of the thoracic aorta and that C×37 was hardly detectable. In the IVCs of ACF rats, which were demonstrated to be exposed to a hemodynamic condition of high flow velocity and low pressure, the GJSNs and the TGJAs of all three C×5 were increased. In the IVCs of IVC-banded ACF rats, which were exposed to a hemodynamic condition of high pressure and low flow velocity, the GJSNs and the TGJAs of C×37 increased markedly and those of C×40 and C×43 remained without significant changes. In conclusion, the endothelial expressions of gap junctions in the native veins were lower than those of the arteries. When exposed to different hemodynamic stresses, the gap junctions were expressed in specific patterns. (J Histochem Cytochem 58:1083–1092, 2010)

Electrophysiological characteristics of antiarrhythmic potential of acrophyllidine, a furoquinoline alkaloid isolated from Acronychia halophylla

The antiarrhythmic potential of acrophyllidine, a natural furoquinoline alkaloid isolated from the plant, Acronychia halophylla, has been documented. In the present study, the electrophysiological effects of acrophyllidine in Langendorff‐perfused rat hearts and isolated cardiomyocytes were examined. In isolated rat heart (constant pressure), acrophyllidine suppressed ischemia/reperfusion‐induced polymorphic ventricular tachyarrhythmias with an EC50 value of 4.4 μM. In the perfused whole‐heart model (constant flow), acrophyllidine increased the atrioventricular and His‐Purkinje system conduction intervals, ventricular repolarization time (VRT), and basic cycle length and also prolonged the refractory periods of the AV node, His‐Purkinje system and ventricle. In isolated rat ventricular myocytes, acrophyllidine prolonged the action potential duration (APD) and decreased both the maximal upstroke velocity of depolarization (Vmax) and action potential amplitude in a concentration‐dependent manner. Whole‐cell voltage clamp studies show that acrophyllidine blocked the Na+ channel (IC50 = 3.6 μM) with a negative‐shift of its voltage‐dependent steady‐state inactivation curve and slowing of its recovery from inactivation. Similarly, Ca2+ inward current (ICa) was inhibited but to a lesser extent. Acrophyllidine also suppressed the transient outward (Ito) (IC50 equals; 4.5 μM) and the steady‐state outward K+ current (ISS) (IC50 = 3.4 μM). The inhibition of Ito was associated with an acceleration of its rate of inactivation. Additionally, acrophyllidine suppressed Ito in a time‐dependent manner and caused a negative‐shift of the steady‐state inactivation curve and a slowed rate of recovery from inactivation. It is concluded that acrophyllidine blocks Na+, Ito and ISS channels and in similar concentrations partly blocks Ca2+ channel. These changes alter the electrophysiological properties of the conduction system and may be responsible for the termination of the ischaemia/reperfusion induced ventricular arrhythmias. Drug Dev. Res. 50:170–185, 2000.

Electromechanical characterization of cinnamophilin, a natural thromboxane A2 receptor antagonist with anti-arrhythmic activity, in guinea-pig heart

Cinnamophilin, a thromboxane A2 receptor antagonist, has been identified as a prominent anti‐arrhythmic agent in rat heart. This study aimed to determine its electromechanical and anti‐arrhythmic effects in guinea‐pig hearts.

Prostanoid EP4 Agonist L-902,688 Activates PPARγ and Attenuates Pulmonary Arterial Hypertension

Prostacyclin agonists that bind the prostacyclin receptor (IP) to stimulate cAMP synthesis are effective vasodilators for the treatment of idiopathic pulmonary arterial hypertension (IPAH), but this signaling may occur through nuclear peroxisome proliferator-activated receptor-γ (PPARγ). There is evidence of scant IP and PPARγ expression but stable prostanoid EP4 receptor (EP4) expression in IPAH patients. Both IP and EP4 functionally couple with stimulatory G protein (Gs), which activates signal transduction. We investigated the effect of an EP4-specific agonist on pulmonary arterial remodeling and its regulatory mechanisms in pulmonary arterial smooth muscle cells (PASMCs). Immunoblotting evealed IP, EP4, and PPARγ expression in human pulmonary arterial hypertension (PAH) and monocrotaline (MCT)-induced PAH rat lung tissue. Isolated PASMCs from MCT-induced PAH rats (MCT-PASMCs) were treated with L-902,688, a selective EP4 agonist, to investigate the anti-vascular remodeling effect. Scant expression of IP and PPARγ but stable expression of EP4 was observed in IPAH patient lung tissues and MCT-PASMCs. L-902,688 inhibited IP-insufficient MCT-PASMC proliferation and migration by activating PPARγ in a time- and dose-dependent manner, but these effects were reversed by AH-23848 (an EP4 antagonist) and H-89 [a protein kinase A (PKA) inhibitor], highlighting the crucial role of PPARγ in the activity of this EP4 agonist. L-902,688 attenuated pulmonary arterial remodeling in hypoxic PAH mice and MCT-induced PAH rats; therefore, we conclude that the selective EP4 agonist L-902,688 reverses vascular remodeling by activating PPARγ. This study identified a novel EP4-PKA-PPARγ pathway, and we propose EP4 as a potential therapeutic target for PAH.

Differential left-to-right atria gene expression ratio in human sinus rhythm and atrial fibrillation: Implications for arrhythmogenesis and thrombogenesis

BACKGROUND Atrial fibrillation (AF) causes atrial remodeling, and the left atrium (LA) is the favored substrate for maintaining AF. It remains unclear if AF remodels both atria differently and contributes to LA arrhythmogenesis and thrombogenesis. Therefore, we wished to characterize the transcript profiles in the LA and right atrium (RA) in sinus rhythm (SR) and AF respectively. METHODS Paired LA and RA appendages acquired from patients receiving cardiac surgery were used for ion-channel- and whole-exome-based transcriptome analysis. The ultrastructure was evaluated by immunohistochemistry. RESULTS Twenty-two and twenty ion-channels and transporters were differentially expressed between the LA and RA in AF and SR, respectively. Among these, 15 genes were differentially expressed in parallel between AF and SR. AF was associated with increased LA/RA expression ratio in 9 ion channel-related genes, including genes related to calcium handling. In microarray, AF was associated with a differential LA/RA gene expression ratio in 309 genes, and was involved in atherosclerosis-related signaling. AF was associated with the upregulation of thrombogenesis-related genes in the LA appendage, including P2Y12, CD 36 and ApoE. Immunohistochemistry showed higher expressions of collagen-1, oxidative stress and TGF-β1 in the RA compared to the LA. CONCLUSIONS AF was associated with differential LA-to-RA gene expression related to specific ion channels and pathways as well as upregulation of thrombogenesis-related genes in the LA appendage. Targeting the molecular mechanisms underlying the LA-to-RA difference and AF-related remodeling in the LA appendage may help provide new therapeutic options in treating AF and preventing thromboembolism in AF.

Change of potassium current density in rabbit corneal epithelial cells during maturation and cellular senescence.

BACKGROUND Voltage-gated potassium (K+) channels may participate in cellular developmental regulation, including cell differentiation, proliferation and apoptosis. This study investigated the change of K + current densities in corneal epithelial cells during maturation and cellular senescence. METHODS New Zealand white rabbits were divided into three age groups: newborn (<or= 7 days old, n = 18); young (8-12 weeks old, n = 59); and adult (20-28 weeks old, n = 16). Rabbit corneal epithelial cells were subdivided into the following three groups: small cells with capacitance < 6.0 pF; medium cells with capacitance 6.0-10.0 pF; and large cells with capacitance > 10.0 pF. Using a whole-cell clamp technique, K+ current was recorded and current densities were calculated. Differences in K+ current densities among newborn, young and adult rabbits, as well as differences among small, medium and large cells, were analyzed. RESULTS We delineated two types of cells manifesting different amplitudes of depolarization-activated K+ outward currents. The averaged current density of type 1 response cells was significantly larger than that of type 2 cells in newborn, young, and adult groups. For newborn epithelial cells, the depolarization-gated outward K+ current density decreased from small to medium to large cells (p = 0.049, at a membrane potential of 140 mV). A similar pattern of change in current density was also delineated for these cell sizes in young and adult rabbit corneal cells (p < 0.001 for both young and adult rabbits). An increase in depolarization-gated outward K+ current density was also delineated from newborn to young to adult rabbits (p < 0.001, p < 0.001 and p < 0.006 for small, medium and large cells, respectively, at a membrane potential of 140 mV). CONCLUSIONS Corneal epithelial cells expressed K+ channel densities that were distinct from basal to superficial cells and from newborn to adult rabbits.