Jian-Wen Hou

Antiarrhythmic effects and potential mechanism of WenXin KeLi in cardiac Purkinje cells

BACKGROUND Previous studies have demonstrated that WenXin KeLi (WXKL), a traditional Chinese medicine, can exert antiarrhythmic properties through complex multichannel inhibition, but its pharmacologic effect remains to be elucidated, especially in the cardiac conductive system. OBJECTIVE To explore the antiarrhythmic property of WXKL in cardiac Purkinje cells (PCs). METHODS PCs were isolated from rabbit hearts and action potentials (APs) and ion currents were recorded by whole-cell patch clamp technique. Anemonia toxin II (ATX-II) and isoproterenol (ISO) were used to induce early or delayed afterdepolarizations (EADs, DADs) or triggered activities (TAs). RESULTS WXKL (1 g/L and 5 g/L) significantly abbreviated the action potential duration (APD) of PCs in a dose- and rate-dependent manner. Treatment of PCs with ATX-II (2 nM) prolonged APD and induced EADs, which were significantly suppressed by WXKL. WXKL (1, 5 g/L) also inhibited ISO-induced EADs, DADs, and TAs. To reveal the ionic mechanisms, we studied the effects of WXKL on late sodium current (I(NaL)), peak sodium current (I(NaP)), and L-type calcium currents (ICaL) in PCs. WXKL-attenuated ATX-II (5 nM) induced I(NaL) augmentation and blocked I(NaL) with an IC50 of 4.3 ± 0.5 g/L, which is 3- to 4-fold more selective than that of I(NaP) (13.3 ± 0.9 g/L) and ICaL (17.6 ± 1.4 g/L). Moreover, WXKL exerted significantly less use-dependent block of I(NaP) than that of flecainide, indicating its lower proarrhythmic effect. CONCLUSIONS WXKL exhibits antiarrhythmic properties in cardiac PCs via selective inhibition of I(NaL).

Semaphorin 3a transfection into the left stellate ganglion reduces susceptibility to ventricular arrhythmias after myocardial infarction in rats.

AIMS Myocardial infarction (MI) induces neural remodelling of the left stellate ganglion (LSG), which may contribute to ischaemia-induced arrhythmias. The neural chemorepellent Semaphorin 3a (Sema3a) has been identified as a negative regulator of sympathetic innervation in the LSG and heart. We previously reported that overexpression of Sema3a in the border zone could reduce the arrhythmogenic effects of cardiac sympathetic hyperinnervation post-MI. This study investigated whether Sema3a overexpression within the LSG confers an antiarrhythmic effect after MI through decreasing extra- and intra-cardiac neural remodelling. METHODS AND RESULTS Sprague-Dawley rats were subjected to MI, and randomly allocated to intra-LSG microinjection of either phosphate-buffered saline (PBS), adenovirus encoding green fluorescent protein (AdGFP), or adenovirus encoding Sema3a (AdSema3a). Sham-operated rats served as controls. Two weeks after infarction, MI-induced nerve sprouting and sympathetic hyperinnervation in the LSG and myocardium were significantly attenuated by intra-LSG injection with AdSema3a, as assessed by immunohistochemistry and western blot analysis of growth-associated protein 43 and tyrosine hydroxylase. This was also confirmed by sympathetic nerve function changes assessed by cardiac norepinephrine content. Additionally, intra-LSG injection with AdSema3a alleviated MI-induced accumulation of dephosphorylated connexin 43 in the infarct border zone. Furthermore, Sema3a overexpression in the LSG reduced the incidence of inducible ventricular tachyarrhythmia by programmed electrical stimulation post-MI, and arrhythmia scores were significantly lower in the AdSema3a group than in the PBS and AdGFP groups. CONCLUSION Semaphorin 3a overexpression in the LSG ameliorates the inducibility of ventricular arrhythmias after MI, mainly through attenuation of neural remodelling within the cardiac-neuraxis.

Crucial Role of ROCK2-Mediated Phosphorylation and Upregulation of FHOD3 in the Pathogenesis of Angiotensin II–Induced Cardiac HypertrophyNovelty and Significance

Cardiac hypertrophy is characterized by increased myofibrillogenesis. Angiotensin II (Ang-II) is an essential mediator of the pressure overload–induced cardiac hypertrophy in part through RhoA/ROCK (small GTPase/Rho-associated coiled-coil containing protein kinase) pathway. FHOD3 (formin homology 2 domain containing 3), a cardiac-restricted member of diaphanous-related formins, is crucial in regulating myofibrillogenesis in cardiomyocytes. FHOD3 maintains inactive through autoinhibition by an intramolecular interaction between its C- and N-terminal domains. Phosphorylation of the 3 highly conserved residues (1406S, 1412S, and 1416T) within the C terminus (CT) of FHOD3 by ROCK1 is sufficient for its activation. However, it is unclear whether ROCK-mediated FHOD3 activation plays a role in the pathogenesis of Ang-II–induced cardiac hypertrophy. In this study, we detected increases in FHOD3 expression and phosphorylation in cardiomyocytes from Ang-II–induced rat cardiac hypertrophy models. Valsartan attenuated such increases. In cultured neonate rat cardiomyocytes, overexpression of phosphor-mimetic mutant FHOD3-DDD, but not wild-type FHOD3, resulted in myofibrillogenesis and cardiomyocyte hypertrophy. Expression of a phosphor-resistant mutant FHOD3-AAA completely abolished myofibrillogenesis and attenuated Ang-II–induced cardiomyocyte hypertrophy. Pretreatment of neonate rat cardiomyocytes with ROCK inhibitor Y27632 reduced Ang-II–induced FHOD3 activation and upregulation, suggesting the involvement of ROCK activities. Silencing of ROCK2, but not ROCK1, in neonate rat cardiomyocytes, significantly lessened Ang-II–induced cardiomyocyte hypertrophy. ROCK2 can directly phosphorylate FHOD3 at both 1412S and 1416T in vitro and is more potent than ROCK1. Both kinases failed to phosphorylate 1406S. Coexpression of FHOD3 with constitutively active ROCK2 induced more stress fiber formation than that with constitutively active ROCK1. Collectively, our results demonstrated the importance of ROCK2 regulated FHOD3 expression and activation in Ang-II–induced myofibrillogenesis, thus provided a novel mechanism for the pathogenesis of Ang-II–induced cardiac hypertrophy.

Cryoablation vs. radiofrequency ablation for treatment of paroxysmal atrial fibrillation: a systematic review and meta-analysis

Aims Cryoablation is a promising alternative technique to RF ablation for treating paroxysmal AF with encouraging results. However, data about the efficacy and safety comparison between cryoablation and RF ablation is still lacking. Methods and results We systematically search the PubMed, the Cochrane Library, MEDLINE and Google Scholar databases, and finally identify 16 eligible studies including 7195 patients (2863 for cryoablation; 4332 for RF ablation). Freedom from AF/atrial tachycardial replase is slightly higher in cryoablation than RF ablation during a median 12 months of follow-up, with no statistical significant (RR: 1.05, 95% CI: 0.98-1.13, P = 0.159). In cryoablation, the procedure time is substantially shortened (WMD: -27.66, 95% CI: -45.24 to - 10.08, P = 0.002), whereas the fluoroscopy time is identical to RF ablation (WMD: -0.37, 95% CI: -2.78 to 2.04, P = 0.763). Procedure-related adverse events in cryoablation are parallel with that in RF ablation (RR: 1.08, 95% CI: 0.86-1.35, P = 0.159). Conclusions Compared with RF ablation, cryoablation present a comparable long-term AF/atrial tachycardial-free survival and procedure-related adverse events. Meanwhile, cryoablation markedly shorten the procedure time, nonetheless, with negligible impact on the fluoroscopy time.

Role of adenosine-guided pulmonary vein isolation in patients undergoing catheter ablation for atrial fibrillation: a meta-analysis

Aims Adenosine had been reported to unmask dormant conduction and thus identify pulmonary vein at risk of reconnection. However, the role of adjunctive adenosine infusion after pulmonary vein isolation (PVI) on long-term arrhythmia-free survival was still contentious. The purpose of the present meta-analysis was to assess the association of adenosine testing with long-term ablation success in patients with atrial fibrillation (AF) (i.e. freedom from AF recurrence). Methods and Results We systematically searched the electronic databases and finally included 10 studies, with 1771 patients undergoing adenosine-guided PVI and 1787 patients undergoing conventional PVI. In comparison to conventional PVI alone, adenosine-guided PVI improved the arrhythmia-free survival by 17% during a median follow-up of 12 months [relative risk (RR): 1.17; 95% confidence interval (CI): 1.07 to 1.27; P = 0.014]. Patients undergoing adenosine-guided PVI had similar fluoroscopy time to those who undergoing conventional PVI [weighted mean difference (WMD): 1.76; 95% CI: -5.66 to 9.17; P = 0.64], despite longer procedure time (WMD: 20.6; 95% CI: 0.70 to 40.50; P = 0.042). Conclusion From the available data of clinical studies, adenosine-guided PVI was associated with an increased arrhythmia-free survival when compared with conventional PVI in patients undergoing catheter ablation for AF.

Partial inhibition of activin receptor-like kinase 4 attenuates pressure overload-induced cardiac fibrosis and improves cardiac function.

Background: Activin receptor-like kinase 4 (ALK4), a downstream receptor of transforming growth factor-&bgr; superfamily, is highly expressed in the mammal heart. Upregulated ALK4 expression and activated ALK4–small mother against decapentaplegic (Smad)2/3 signaling have been reported to play a pivotal role in tumorigenesis and in the development of systemic sclerosis. However, the role of ALK4–Smad2/3 pathway in the pathogenesis of cardiac hypertrophy and cardiac fibrosis remains unknown. Methods and results: In this study, the mice with heterozygous knocking out of ALK4 gene (ALK4+/−) were generated and subjected to aortic banding for 4 weeks. We found that ALK4 expression was upregulated in aortic banding-induced model of cardiac hypertrophy and cardiac fibrosis in wild-type mice. Compared with the wild-type mice, ALK4+/−mice demonstrated a similar extent of aortic banding-induced cardiac hypertrophy, but a significant suppression of cardiac fibrosis to 64.8% of the basal level, and a subsequent amelioration in the cardiac dysfunction (left ventricle ejection fraction: 59.0 ± 6.4 in wild-type mice vs. 75.6 ± 3.9% in ALK4+/− mice; left ventricle end-diastolic pressure: 16.6 ± 4.7 mmHg in wild-type mice vs. 6.6 ± 2.8 mmHg in ALK4+/− mice) associated with inhibition of cardiac fibroblast activation and cardiomyocyte apoptosis. In vitro, ALK4 haploinsufficiency blocked the cellular proliferation/differentiation and collagen production in cultured cardiac fibroblasts after angiotensin-II stimulation. Mechanistically, ALK4 haploinsufficiency resulted in the suppression of Smad2/3 activity. Conclusion: Our results demonstrate that ALK4 haploinsufficiency ameliorates cardiac fibrosis and dysfunction in a mouse pressure-overload model associated with inhibition of cardiac fibroblast activation and cardiomyocyte apoptosis through the suppression of Smad2/3 activity, and suggest that ALK4 is a novel therapeutic target in treating pressure overload-induced cardiac remodeling and heart failure.

Haplodeficiency of activin receptor-like kinase 4 alleviates myocardial infarction-induced cardiac fibrosis and preserves cardiac function

Cardiac fibrosis (CF), a repairing process following myocardial infarction (MI), is characterized by abnormal proliferation of cardiac fibroblasts and excessive deposition of extracellular matrix (ECM) resulting in inevitable resultant heart failure. TGF-β (transforming growth factor-β)/ALK5 (Activin receptor-like kinase 5)/Smad2/3/4 pathways have been reported to be involved in the process. Recent studies have implicated both activin and its specific downstream component ALK4 in stimulating fibrosis in non-cardiac organs. We recently reported that ALK4 is upregulated in the pressure-overloaded heart and its partial inhibition attenuated the pressure overload-induced CF and cardiac dysfunction. However, the role of ALK4 in the pathogenesis of MI-induced CF, which is usually more severe than that induced by pressure-overload, remains unknown. Here we report: 1) In a wild-type mouse model of MI, ALK4 upregulation was restricted in the fibroblasts of the infarct border zone; 2) In contrast, ALK4+/- mice with a haplodeficiency of ALK4 gene, showed a significantly attenuated CF in the border zone, with a smaller scar size, a preserved cardiac function and an improved survival rate post-MI; 3) Similarly to pressure-overloaded heart, these beneficial effects might be through a partial inactivation of the Smad3/4 pathway but not MAPK cascades; 4) The apoptotic rate of the cardiomyocytes were indistinguishable in the border zone of the wild-type control and ALK4+/- mice; 5) Cardiac fibroblasts isolated from ALK4+/- mice showed reduced migration, proliferation and ECM synthesis in response to hypoxia. These results indicate that partial inhibition of ALK4 may reduce MI-induced CF, suggesting ALK4 as a novel target for inhibition of unfavorable CF and for preservation of LV systolic function induced by not only pressure-overload but also MI.

A novel mutation KCNQ1 p.Thr312del is responsible for long QT syndrome type 1

Patients with high-risk long QT syndrome (LQTS) mutations may experience life-threatening cardiac events. The present study sought to characterize a novel pathogenic mutation, KCNQ1p.Thr312del, in a Chinese LQT1 family. Clinical and genetic analyses were performed to identify this novel causative gene mutation in this LQTS family. Autosomal dominant inheritance of KCNQ1p.T312del was demonstrated in the three-generation pedigree. All mutation carriers presented with prolonged QT intervals and experienced recurrent syncope during exercise or emotional stress. The functional consequences of the mutant channel were investigated by computer homology modeling as well as whole-cell patch-clamp, western-blot and co-immunoprecipitation techniques using transfected mammalian cells. T312 is in the selectivity filter (SF) of the pore region of the KCNQ1-encoded channel. Homology modeling suggested that secondary structure was altered in the mutant SF compared with the wild-type (WT) SF. There were no significant differences in Kv7.1 expression, membrane trafficking or physical interactions with KCNE1-encoded subunits between the WT and mutant transfected channels. However, the KCNQ1p.T312del channels expressed in transfected cells were non-functional in the absence or presence of auxiliary KCNE1-subunits. Dominant-negative suppression of current density and decelerated activation kinetics were observed in cells expressing KCNQ1WT and KCNQ1p.T312del combined with KCNE1 (KCNQ1WT/p.T312del + KCNE1 channels). Those electrophysiological characteristics underlie the pathogenesis of this novel mutation and also suggest a high risk of cardiac events in patients carrying KCNQ1p.T312del. Although protein kinase A-dependent current increase was preserved, a significant suppression of rate-dependent current facilitation was noted in the KCNQ1WT/p.T312del + KCNE1 channels compared to the WT channels during 1- and 2-Hz stimulation, which was consistent with the patients’ phenotype being triggered by exercise. Overall, KCNQ1p.Thr312del induces a loss of function in channel electrophysiology, and it is a high-risk mutation responsible for LQT1.

The transient receptor potential melastatin 4 channel inhibitor 9‐phenanthrol modulates cardiac sodium channel

9‐Phenanthrol, known as a specific inhibitor of the transient receptor potential melastatin 4 (TRMP4) channel, has been shown to modulate cardiac electrical activity and exert antiarrhythmic effects. However, its pharmacological effects remain to be fully explored. Here, we tested the hypothesis that cardiac sodium current inhibition contributes to the cardioprotective effect of 9‐phenanthrol.

The transient receptor potential melastatin 4 channel inhibitor 9-phenanthrol modulates cardiac sodium channel: 9-Phenanthrol inhibits cardiac sodium channel

9‐Phenanthrol, known as a specific inhibitor of the transient receptor potential melastatin 4 (TRMP4) channel, has been shown to modulate cardiac electrical activity and exert antiarrhythmic effects. However, its pharmacological effects remain to be fully explored. Here, we tested the hypothesis that cardiac sodium current inhibition contributes to the cardioprotective effect of 9‐phenanthrol.