The Effect And Mechanism Of Pioglitazone On Atrial Remodeling In Diabetic Rabbits Hearts

Objective Atrial Fibrillation (AF) is one of the most common arrhythmia. Atrial remodeling promotes the occurrence or maintenance of AF by acting on the fundamental arrhythmia mechanisms. Inflammation and oxidative stress play an important role in the pathogenesis of atrial remodeling. Due to anti-inflammatory properties of pioglitazone, it might exert beneficial effects on atrial remodeling. The focus is the role of inflammation and oxidative stress, atrial fibrosis in AF. In the present study, we investigated the underlying mechanisms for the effect caused by pioglitazone on atrial structural remodeling and electrical remodeling in alloxan-induced diabetic rabbits at observations and the cellular and molecular level.Methods96rabbits were randomly divided into four groups:normal control group (CN group), diabetic group (DM group), diabetic pioglitazone treatment A group (DPG group,4mg/day/kg) and diabetic pioglitazone treatment B group (DPI group,8mg/day/kg).72of96rabbits were used to establish alloxan-induced diabetic model and all rabbits were fed around in the same environment for8weeks.8of24rabbits in each group were respectively used to electrophysiological and histological study, patch-clamp study and molecular biology analysis. The body weight and blood glucose of each rabbit were measured every week, and meanwhile baseline and8weeks levels of the markers of inflammation and oxidative stress and insulin in rabbits were measured. 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. Histopathologic examinations were performed to identify the fibrosis of left atria. Then isolated Langendorff-perfused rabbit hearts were used to measure electrophysiological parameters and vulnerability to AF. The whole-cell patch-clamp technique was used to record left action potential duration (APD) and atrial ionic currents. And RT-PCR and Western-Blot were applied to assess possible changes in cardiac gene or protein expressions of Cavl.2(ICa.L),TGF-β\ERK2. pERK. NF-kB p50, TLR4, TNF-α and HSP70in left atrial tissue.Results (1) Compared with the CN group, TNF-α and IL-1of DM group were significantly increased and ADP was significantly decreased (P<0.05). TNF-α, IL-1of DPG and DPI group were significantly lower than DM group (P<0.05), while similar level compared with CN group (.P>0.05). The activity of SOD, CAT, NO and NOS of DM group were significantly lower than CN group (P<0.05), while MDA level was significantly increased (P<0.05). MDA of DPG and DPI group were significantly lower than DM group (P<0.01). No significant difference of MPO level was among the four groups (P>0.05).(2) 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).(3) Histopathological examination revealed that left atrial myocytes disordered accompanied by inflammatory cells infiltration and a large amount of interstitial fibrosis 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.(4) Compared with CN group, IACT was prolonged (37.91±6.8] vs.27.43±1.63ms, P<0.01). AERPD was increased (30.37±8.33vs.14.70±5.16ms. P<0.01) in DM group. No significant differences of AERP were among4groups of250ms pacing (P>0.05). Inducibility of AF in DM group was significantly higher than controls (6/8vs.1/8of animals, P<0.01). No significant differences of SCL. HR and AVWCL were among4groups (P>0.05). Prolonged IACT, AERPD and AF episode and enhanced inducibility of AF were attenuated in DPG and DPI group.(5) APD90and APD50of left atrial myocytes were prolonged in DM group (P<0.05vs. CN). and APD90rate adaptation was no significant differences (P>0.05vs. CN). The densities of INa were reduced and the densities of ICa,L were increased in DM group (P<0.01vs. CN). The above were attenuated in DPG and DPI group.(6) TNF-α and TLR4mRNA expression by semiquantitative RT-PCR was increased significantly in DM group (P<0.01vs. CN). TGF-β, NF-kB p50. HSP70, pERK were increased significantly in DM (P<0.05vs. CN). Protein expressions of ERK2and Cav1.2(ICa,L were no significant difference between DPG or DPI group and DM group (P>0.05), but protein expressions of NF-kB p50. TLR4, TNF-α. HSP70. TGF-β and pERK were significantly decreased in DPG and DPI group, but no significant differences between two pioglitazone groups.Conclusions Pioglitazone has certain antagonist activity on inflammation and oxidative stress and improve atrial fibrosis in diabetic rabbits, which resulting in reversal effect on atrial structural remodeling and electrical remodeling. Pioglitazone may play important preventions from AF in diabetes.