Lijun Cheng

Probucol Prevents Atrial Remodeling by Inhibiting Oxidative Stress and TNF-α/NF-κB/TGF-β Signal Transduction Pathway in Alloxan-Induced Diabetic Rabbits

Diabetes mellitus (DM) is an independent risk factor for atrial fibrillation (AF). However, the underlying mechanisms for the increased propensity for AF in the setting of DM and the potential effects of probucol on atrial remodeling remain unclear.

Hyperglycemia aggravates atrial interstitial fibrosis, ionic remodeling and vulnerability to atrial fibrillation in diabetic rabbits.

OBJECTIVE The purpose of this study was to investigate the effects of hyperglycemia on atrial interstitial fibrosis, ionic remodeling and vulnerability to atrial fibrillation (AF) in alloxan-induced diabetic rabbits. METHODS Sixty Japanese rabbits were randomly assigned to alloxan-induced diabetic group (n=30) and control group (n=30). Ten rabbits in each group were respectively used to electrophysiological and histological study, patch-clamp study and Western blotting analysis. Langendorff perfusion was used to record inter-atrial conduction time (IACT), atrial effective refractory period (AERP) and dispersion (AERPD) and vulnerability to AF. Histological study was measured by Sirius-red stain. Patch-clamp technique was used to measure action potential duration (APD) and atrial ionic currents (INa and ICaL). Western blotting was applied to assess atrial protein expression of transforming growth factor beta 1 (TGFβ1). RESULTS Compared with control group, electrophysiological studies showed IACT was prolonged (37.91±6.81 vs. 27.43±1.63ms, p<0.01), AERPD was increased (30.37±8.33 vs. 14.70±5.16ms, p<0.01) in diabetic group. Inducibility of AF in diabetic group was significantly higher than in controls (8/10 vs. 1/10 of animals, p<0.01). Collagen volume fraction was increased (6.20±0.64% vs. 2.15±0.21%, p<0.01) in diabetic group. Patch-clamp studies demonstrated APD90 and APD50 were prolonged in diabetic rabbits (p<0.05 vs. control). The densities of INa were reduced and the densities of ICaL were increased (p<0.01 vs. control). Protein expression of TGFβ1 was increased in diabetic group (p<0.001 vs. control). CONCLUSION Our study suggests that hyperglycemia contributes to atrial interstitial fibrosis, ionic remodeling and vulnerability to AF in diabetic rabbits, resulting in atrial structural remodeling and electrical remodeling for the development and perpetuation of AF.

Probucol prevents atrial ion channel remodeling in an alloxan-induced diabetes rabbit model

Diabetes mellitus (DM) increases the risk of developing atrial fibrillation (AF), but the molecular mechanisms of diabetes-induced atrial remodeling processes have not been fully characterized. The aim of this study was to examine the mechanisms underlying atrial ion channel remodeling in alloxan-induced diabetes model in rabbits. A total of 40 Japanese rabbits were randomly assigned to a control group (C), alloxan-induced diabetic group (DM), probucol-treated control group (Control-P), and probucol-treated diabetic group (DM-P). Using whole-cell voltage-clamp techniques, ICa,L, INa and action potential durations (APDs) were measured in cardiomyocytes isolated from the left atria in the four groups, respectively. In the DM group, increased Ica,L and decreased INa currents were reflected in prolonged APD90 and APD50 values. These changes were reversed in the DM-P group. In conclusion, probucol cured AF by alleviating the ion channel remodeling of atrial myocytes in the setting of diabetes and the promising therapeutic potential of anti-oxidative compounds in the treatment of AF warrants further study.

Effects of Fluvastatin on Characteristics of Stellate Ganglion Neurons in a Rabbit Model of Myocardial Ischemia

Background: Stellate ganglion (SG) plays an important role in cardiovascular diseases. The electrical activity of SG neurons is involved in the regulation of the autonomic nervous system. The aim of this research was to evaluate the effects of fluvastatin on the electrophysiological characteristics of SG neurons in a rabbit model of myocardial ischemia (MI). Methods: The MI model was induced by abdominal subcutaneous injections of isoproterenol in rabbits. Using whole-cell patch clamp technique, we studied the characteristic changes of ion channels and action potentials (APs) in isolated SG neurons in control group (n = 20), MI group (n = 20) and fluvastatin pretreated group (fluvastatin group, n = 20), respectively. The protein expression of sodium channel in SG was determined by immunohistochemical analysis. Results: MI and the intervention of fluvastatin did not have significantly influence on the characteristics of delayed rectifier potassium channel currents. The maximal peak current density of sodium channel currents in SG neurons along with the characteristics of activation curves, inactivation curves, and recovery curves after inactivation were changed in the MI group. The peak current densities of control group, MI group, and fluvastatin group (n = 10 in each group) were −71.77 ± 23.22 pA/pF, −126.75 ± 18.90 pA/pF, and −86.42 ± 28.30 pA/pF, respectively (F = 4.862, P = 0.008). Fluvastatin can decrease the current amplitude which has been increased by MI. Moreover, fluvastatin induced the inactivation curves and post-inactive recovery curves moving to the position of the control group. But the expression of sodium channel-associated protein (Nav1.7) had no significantly statistical difference among the three groups. The percentages of Nav1.7 protein in control group, MI group, and fluvastatin group (n = 5 in each group) were 21.49 ± 7.33%, 28.53 ± 8.26%, and 21.64 ± 2.78%, respectively (F = 1.495, P = 0.275). Moreover, MI reduced the electrical activity of AP and increased amplitude of AP, fluvastatin pretreatment could recover amplitude and electrical activity of AP. The probability of neurons induced continuous APs were 44.44%, 14.29%, and 28.57% in control group, MI group, and fluvastatin group, respectively. Conclusions: Fluvastatin pretreatment can recover electrophysiology characteristics of ion channel and AP in SG neurons in a rabbit model of MI. It could be considered as potential method for treating coronary heart diseases.

Cilostazol ameliorates atrial ionic remodeling in long-term rapid atrial pacing dogs

Objective: Ionic remodeling has a close correlation with the occurrence of atrial fibrillation (AF). Atrial tachypacing remodeling is associated with characteristic ionic remodeling. The purpose of this study was to assess the efficacy of cilostazol, an oral phosphodiesterase 3 inhibitor, for preventing atrial ionic remodeling in long-term rapid atrial pacing (RAP) dogs. Methods: We use the methods of patch-clamp and molecular biology to investigate the effect of cilostazol on ion channel and channel gene expression in long-term RAP dogs. Twenty-one dogs were randomly assigned to sham, control paced, and paced+cilostazol (5 mg/kg/d, cilo) groups, with 7 dogs in each group. The sham group was instrumented with a pacemaker but without pacing. RAP at 500 beats/min was maintained for 2 weeks in the paced and cilo groups. During the pacing, cilostazol was given orally in the cilo group. Whole-cell patch-clamp technique was used to record atrial L-type Ca2+ (ICaL) and fast sodium channel (INa) ionic currents. Western blot and RT-PCR were applied to estimate the gene expression of the ICaLa) 1C (Cav1.2) and INav1.5a) Nav1.5a) subunits. Statistical analysis was performed using SPSS 13.0. Results: The density of ICaL and INa currents (pA/pF) was significantly reduced in the paced group (ICaL: -6.55±1.42 vs. -4.46±0.59 pA/pF; INa: -48.24±10.54 vs. -30.48±5.20 pA/pF, p<0.01). The paced+cilo group could not increase the density of ICaL currents (ICaL: -4.37±1.25 pA/pF, p>0.05], while the INa currents were recovered (-44.54±12.65 pA/pF, p<0.01) compared with the paced group. The mRNA and protein expression levels of Cav1.2 and Nav1.5a were apparently down-regulated in the paced group (p<0.01), but after cilostazol treatment, both of these subunits were up-regulated significantly (p<0.01). Conclusion: Cilostazol may have protective effects on RAP-induced atrial ionic remodeling.

Modulation of Ion Channels in the Superior Cervical Ganglion Neurons by Myocardial Ischemia and Fluvastatin Treatment

Background: The superior cervical ganglion (SCG) of the autonomic nervous system plays an important role in different cardiovascular diseases. In this study, we investigated the effects of ischemia and fluvastatin treatment on the ion channel characteristics of SCG neurons in a rabbit myocardial ischemia (MI) model. Methods: MI was induced by abdominal subcutaneous injections of isoproterenol (ISO). The properties of the delayed rectifier potassium channel current (IK), sodium channel current (INa), and action potential (APs) on isolated SCG neurons in the control, MI-7d, MI-14d, fluvastatin-7d (fluvastatin pretreated 14 days and treated 7 days after ISO-induced MI), and fluvastatin-14d (fluvastatin pretreated 14 days and treated 14 days after ISO-induced MI) groups were studied. In addition, the RNA expressions of KCNQ3 and SCN9A in the SCG tissue were determined by performing real-time PCR. Intracellular calcium concentration was monitored using laser scanning confocal microscopy. Results: Compared with the control group, the current amplitude of IK and INa were increased in the MI-7d and MI-14d groups. KCNQ3 RNA (corresponding to channel proteins of IK) expression and SCN9A RNA (corresponding to channel proteins of INa) expression were also increased in MI groups. Activation and inactivation curves for INa in the two MI groups shifted negatively compared with the control group. These changes were reversed by fluvastatin treatment. Intracellular calcium concentration in SCG neurons was not altered significantly by MI or fluvastatin treatment. By contrast, increased AP amplitude and shortened APD90 were observed in the MI-7d and MI-14d groups. These changes were reversed in the fluvastatin-treated MI group. Conclusion: Fluvastatin treatment partly reversed the characteristics of SCG neurons in MI. The ion channel of SCG neurons could be one of the potential targets of fluvastatin in treating coronary heart diseases.

PIOGLITAZONE PREVENTS DIABETES-RELATED ATRIAL FIBRILLATION SUSCEPTIBILITY IN ALLOXAN-INDUCED DIABETIC RABBITS

Objectives In the present study, we investigated underlying mechanisms for the effects caused by pioglitazone, a peroxisomeproliferator-activated receptor (PPAR)-γ activator, on atrial structural remodelling and electrical remodelling in alloxan-induced diabetic rabbits. Methods 32 rabbits were randomly divided into four groups: normal control group (CN group), diabetic group (DM group), diabetic pioglitazone treatment A group (DPG group, 4 mg/day/kg) and diabetic pioglitazone treatment B group (DPI group, 8 mg/day/kg). All rabbits were monitored hemodynamics and recorded aortic systolic and diastolic blood pressure (SBP and DBP) and left ventricle end diastolic pressure (LVEDP) and underwent transthoracic echocardiographic examination. After 8-week treatment, whole-cell patch-clamp technique was used to measure action potential duration (APD) and atrial ionic currents (ICaL and INa). Isolated Langendorff perfused rabbit hearts were used to evaluate atrial electrophysiological parameters. Atrial collagen volume fraction (CVF) was calculated by Sirius-Red (SR) staining for pathological examination. Western-blot was applied to assess atrial protein expression levels of NF-κB p50/p65, TGF-β, HSP70, ERK1/2 and p-ERK1/2. Results Echocardiographic examination showed that LAD, IVST and PWT of DPG and DPI group were significantly decreased compared with DM group. SBP and DBP of DPI group were significantly lower than DM group (p<0.05). No significant difference of LVEDP was among the four groups (p>0.05). Histopathological examination revealed that left atrialmyocytes disordered accompanied by inflammatory cells infiltration and a large amount of interstitialfibrosis distributed throughout the tissue in DM group. SR staining showed that left atrium collagen volume fraction (LACVF) was significantly increased in DM group (p<0.01). But these pathological abnormal findings were attenuated in DPG and DPI group. Compared with CN group, IACT was prolonged (p<0.01), AERPD was increased (p<0.01) in DM group. Inducibility of AF in DM group was significantlyhigher than controls (6/8 vs 1/8 of animals, p<0.01). Inducibility of AF in DPI group was significantly less than DM group (2/8 vs 6/8 of animals, p<0.01). Prolonged IACT, AERPD, AF episode and enhanced inducibility of AF were attenuated in DPG and DPI group. APD90 andAPD50 of left atrial myocyte were prolonged in DM group (p<0.05 vs control), and APD90 rate adaptation was no significant differences (p>0.05 vs control). The densities of INa were reduced and the densities of ICaL were increased in DM group (p<0.01 vs control), which were attenuated in DPG and DPI group. TGF-β, NF-κB p50/p65, HSP70, ERK1/2, p-ERK1/2 were increased significantly in DM (p<0.05 s. control). Protein expression of ERK1/2 was no significant difference between DPG or DPI group and DM group (p>0.05), but protein expressions of NF-κB p50/p65, HSP70, TGF-β andp-ERK1/2 were significantly decreased in DPG and DPI group (p<0.05), but no significant differences between two pioglitazone groups. Conclusions Pioglitazone inhibited DM-related arrhythmogenic atrial remodelling and vulnerability to AF. Pioglitazone may play important preventions from AF in diabetes. PPAR-γ activators could become novel upstream therapy drugs for DM-related AF.