Wansong Yang

Enalapril, irbesartan, and angiotensin-(1–7) prevent atrial tachycardia-induced ionic remodeling

BACKGROUND Atrial fibrillation (AF) is associated with activation of the renin-angiotensin system (RAS) in the atria. Angiotensin-(1-7) [Ang-(1-7)] is a biologically active component of the RAS, it not only counterbalances the actions of angiotensin II (Ang II) but also is a potential inhibitor of angiotensin-converting enzyme (ACE). The purpose of this study was to investigate the effects of the ACE inhibitor enalapril, the angiotensin-receptor blocker (ARB) irbesartan, and Ang-(1-7) on the chronic atrial ionic remodeling. METHODS Thirty dogs were assigned to sham, paced, paced + enalapril, paced + irbesartan or paced + Ang-(1-7) group, 6 dogs in each group. Rapid atrial pacing at 500 beats per minute was maintained for 14 days, but dogs in sham group were instrumented without pacing. During the pacing, enalapril (2 mg · Kg(-1) · d(-1)) and irbesartan (60 mg · Kg(-1) · d(-1)) were given orally and Ang-(1-7) (6 μg · Kg(-1) · h(-1)) was given intravenously. Whole-cell patch-clamp technique was used to record atrial ionic currents and action potential duration (APD). And RT-PCR was applied to assess atrial mRNA expression of I(TO) Kv4.3 and I(CaL)α1C subunits. RESULTS Compared with sham, rapid pacing shortened APD90 (P < 0.05) of atrial myocytes, and decreased APD90 rate adaptation (P<0.05). APD90 changes were prevented by irbesartan and Ang-(1-7), but not enalapril. In atria from paced group, the densities and gene expression of I(TO) and I(CaL) were reduced (P < 0.01 vs. sham). Enalapril increased the density and gene expression of I(TO) compared with sham (P < 0.01), Ang-(1-7) prevented the decrease of I(TO) and I(CaL) (P < 0.05 vs. control) and Kv4.3 mRNA expression (P < 0.01 vs. control). Irbesartan had no effect on I(TO) and I(CaL) densities or mRNA expression. CONCLUSIONS These results suggest that enalapril, irbesartan, and Ang-(1-7) have differing influences on atrial tachycardia-induced atrial ionic remodeling.

Angiotensin-(1-7) prevents atrial fibrosis and atrial fibrillation in long-term atrial tachycardia dogs.

Renin-angiotensin system (RAS) is activated in the fibrillating atria. Angiotensin-(1-7) [Ang-(1-7)] counterbalances the actions of angiotensin II (Ang II). To investigate the effects of Ang-(1-7) on the long-term atrial tachycardia-induced atrial fibrosis and atrial fibrillation (AF) vulnerability, eighteen dogs were assigned to sham group, paced group, or paced+Ang-(1-7) group, 6 dogs in each group. Rapid atrial pacing at 500 bpm was maintained for 14 days, but dogs in the sham group were instrumented without pacing. During the pacing, Ang-(1-7) (6 microg x kg(-1) x h(-1)) was given intravenously. After pacing, atrial mRNA expression of ERK1/ERK2 and atrial fibrosis were assessed, the inducibility and duration of AF were measured. Compared with sham, ERK1/ERK2 mRNA expression was increased in the paced group (P<0.05). Atrial tissue from the paced dogs showed a large amount of interstitial fibrosis, and the inducible rate of AF was increased at various BCLs in paced dogs (P<0.01). Compared with the paced group, Ang-(1-7) prevented the increase of ERK1/ERK2 mRNA expression (P<0.01 and P<0.05, respectively), and attenuated the interstitial fibrosis (P<0.01). Inducibility and duration of AF were reduced by Ang-(1-7) at various BCLs. In conclusion, Ang-(1-7) reduced AF vulnerability in chronic paced atria, and antifibrotic actions contributed to its preventive effects on AF.

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.

Elevated red cell distribution width level is associated with oxidative stress and inflammation in a canine model of rapid atrial pacing

Atrial fibrillation (AF) is the most common clinically significant cardiac arrhythmia. The prevalence of AF has been increasing for the past few decades with the aging population [1]. The pathogenesis underlying AF is multi-factorial. Accumulating evidences suggest that oxidative stress and inflammation may play an important role in the pathogenesis and perpetuation of AF [2–6]. The red blood cell distributionwidth (RDW) reflects variability in the size of circulating red blood cells (RBCs) and is mostly used in the differential diagnosis of anemia. Recently, several studies showed the potential association of increased RDW levels with adverse cardiovascular events. Elevated RDW levels may also have been correlated with nonvalvular AF [7]. However, the potential mechanisms between elevated RDW and the development of AF are still unclear. In the present study, we aimed to assess whether elevated levels of RDW are associated with oxidative stress and inflammation markers in a canine model of rapid atrial pacing (RAP). In the present study, all animals were cared for and used in compliance with the Experimental Animal Administration Committee of Tianjin Medical University and the Tianjin Municipal Commission for ‘Experimental Animal Control’. For this study, 20 mongrel dogs of either gender were randomly divided into two groups: sham group and paced group, 10 dogs in each group. We used a previously described approach to induce and maintain sustained AF in our experimental animals [8]. The dogs were anesthetized with intravenous 3% sodium pentobarbital (30 mg · kg−1). After mechanical ventilation, under aseptic condition, a modified unipolar J pacing lead (St. Jude Medical, USA) was inserted via the right jugular vein and the distal end of the lead was positioned in the right atrium or right auricular appendage under fluoroscopy. The proximal end of the pacing lead was connected to a programmable pacemaker (Fudan University, China), which was implanted into a subcutaneous pocket in the neck. The dogs in the paced group were paced at 500 bpm (120-ms cycle length) with the 0.2-ms square-wave pulses at twice the threshold current for 2 weeks. The dogs in the sham group were also instrumented but without pacing. Electrocardiogram (ECG) was verified after 24 h in awake dogs to ensure continuous 1:1 atrial capture. Hemodynamics parameters were monitored by a multi-channel electrophysiological recorder (Hongtong TOP2001, China) at baseline and after 2 weeks of rapid atrial pacing (RAP). After the above treatment for 2 weeks, venous blood samples were obtained from the two groups of dogs, and RDW levels were analyzed using an automated hematology analyzer (Mindray BC6800, China). The serum levels of superoxide dismutase (SOD), malondialdehyde (MDA), Toll-like receptor 4 (TRL4) and interleukin-18 (IL-18) were measured by ELISA kit (Nanjing Jiancheng Bioengineering Institute, China). All animals were survived to the end of the experiment. There was no difference in gender, body weight, ventricular rate and blood pressure between the two groups whether at baseline and after 2 weeks of RAP (P N 0.05) (Table 1). Our study showed that the RDW level was increased apparently by RAP from 12.37% ± 1.48% to 14.83% ± 2.24% (P b 0.05). We investigated the circulating serum levels of SOD, MDA, TLR4 and IL-18 in the two groups and found that the levels of SOD, MDA, TLR4 and IL-18 were higher in the paced group compared to the sham group (P b 0.01) (Table 1). The serum levels of SOD, MDA, TLR4 and IL-18 had no correlation to RDW in the sham group (r = 0.014, P = 0.976; r = 0.479, P =0.276; r = 0.101, P = 0.830; r = 0.032, P = 0.946, respectively), whereas they were correlated to RDW levels (P b 0.05 or P b 0.01) in the paced group (Fig. 1). Several studies have shown that RDW, a laboratory measure of the variability of red blood cell sizes, is a strong independent predictor of increased morbidity and mortality in patients with cardiovascular disease [9–14]. Our recent study [15] indicated that RDWmay serve as a promising and useful marker for paroxysmal AF. Adamsson et al. [16] also showed that RDW was associated with incidence of AF independently of several cardiovascular, nutritional and hematological factors in a recent study of middle-aged subjects from the general population. However, there are limited data regarding the potential mechanisms between RDW and AF in animal models. The potential mechanism behind their relationship may result from a direct effect of changes in erythrocyte volume and function on the heart, or may reflect other pathophysiological processes acting

Atrial electrical remodeling in a canine model of sinus node dysfunction.

AIMS To study atrial tachycardia-induced electrical remodeling in a canine model of sinus node dysfunction (SND). MATERIALS AND METHODS A canine model of SND was established by contacting a cotton patch with 20% formaldehyde on the sinus node. Atrial effective refractory period (ERP), ERP dispersion, and inducibility of atrial fibrillation (AF) were recorded at multiple sites in the atrium, before and after SND induction as well as after rapid atrial pacing. The recovery of atrial ERP in the left and right atrium (LA and RA) after cessation of atrial pacing was also recorded. RESULTS Compared with baseline, the atrial ERPs were shortened after SND (P<0.05). After rapid atrial stimulation, the atrial ERPs were further decreased significantly (P<0.05), and the dispersion of atrial ERPs measured at different pacing cycle lengths (PCLs) showed significant variation. Seven sites were used to induce AF in each dog (56 sites in 8 dogs). The average duration and inducibility of AF after SND was increased compared with baseline (16.5±4.7 vs 2.3±1.2 s and 12/56 vs 4/56 sites, P<0.05). After rapid atrial stimulation, the average duration and inducibility of AF were further increased (16.5±4.7 vs 33.6±16.1 s and 12/56 vs 25/56 sites, P<0.05). The recovery of atrial ERP in LA was significantly delayed compared to the RA. CONCLUSION SND induces atrial electrical remodeling which is further aggravated by atrial tachycardia. Therefore, SND creates an electrophysiological substrate that facilitates AF initiation and perpetuation.

Effects of the angiotensin-(1-7)/Mas/PI3K/Akt/nitric oxide axis and the possible role of atrial natriuretic peptide in an acute atrial tachycardia canine model

Objective: To investigate the effects of the angiotensin-(1-7) signaling pathway and the possible role of atrial natriuretic peptide (ANP) on atrial electrical remodeling in canines with acute atrial tachycardia. Methods: Forty dogs were randomly assigned to eight groups (five dogs/group): sham, paced control, paced + angiotensin-(1-7), paced + angiotensin-(1-7) + Mas inhibitor, paced + angiotensin-(1-7) + Akt inhibitor, paced + angiotensin-(1-7) + PI3K inhibitor, paced + angiotensin-(1-7) + nitric oxide (NO) inhibitor, and paced + angiotensin-(1-7) + A-71915 (ANP receptor antagonist). Rapid atrial pacing was maintained at 600 bpm for 2 h for all groups, except the sham group, and angiotensin-(1-7) (6 μg kg−1 h−1), Mas inhibitor (5.83 μg kg−1 h−1), Akt inhibitor (2.14 μg kg−1 h−1), PI3K inhibitor (2.86 μg kg−1 h−1), NO synthase inhibitor (180 μg kg−1h−1), or A-71915 (0.30 μg kg−1 h−1) were administered intravenously. Atrial effective refractory periods, inducibility, and duration of atrial fibrillation (pacing cycle lengths: 300, 250, and 200 ms), and left atrial ANP concentrations were measured. Results: After pacing, the atrial effective refractory periods at the six sites shortened with increased inducibility and duration of atrial fibrillation, which was attenuated by angiotensin-(1-7), and increased ANP concentrations, which was promoted by angiotensin-(1-7) (paced control vs. sham; P < 0.05). All inhibitors and A-71915 blocked the electrophysiological effects of angiotensin-(1-7). ANP secretion induced by angiotensin-(1-7) was also blocked by all inhibitors. Conclusion: Angiotensin-(1-7) prevented acute electrical remodeling in canines with acute atrial tachycardia via the angiotensin-(1-7)/Mas/PI3K/Akt/NO signaling pathway. ANP was related to the anti-arrhythmic effects of angiotensin-(1-7).

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.

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.