Effects Of Simvastatin On Ventricular Remodeling Induced By TGF-beta1 Intra-cellular Signal Pathway In Post-myocardial Infarction Rats

PARTⅠTHE BENIFICIAL EFFECTS OF SIMVASTATIN ON VENTRICULAR REMODELING IN POST-MYOCARDIAL INFARCTION RATSObjective The objective of this experiment was to investigate the beneficial effects of simvastatin on ventricular remodeling and left ventricular function in a rat model of myocardial infarction.Methods The rat MI models were established by ligation of the left anterior descending coronary artery. Twenty-four hours later after modeling, the survival model rats were randomly divided into myocardial infarction group (MI group, n=9), simvastatin low dosage group (10 mg.kg-1.d-1, Sim1 group; n=8), simvastatin medium dosage group (20 mg.kg-1.d-1, Sim2 group; n=10) and simvastatin 40 mg group (40 mg.kg-1.d-1, Sim4 group; n=9), with another sham-operated group (Sham group; n=10) as control. After 4 weeks, serum lipid level, the hemodynamic indexes, left ventricular weight (LVW) and the left ventricular weight index (LVWI) were measured; the changes of the myocardial tissue structure of the rats were observed by HE staining; the cross-sectional area (CSA) of the myocardial cells was computed as well.Results (1) No significant differences were noted in serum lipid levels among all groups (P>0.05); (2) Compared with the sham-operated group, indexes of hemodynamics were markedly anomalous (P<0.05) in post-myocardial infarction rats. In rats treated by Sim (10, 20 and 40 mg.kg-1.d-1) compared with those in MI group, hemodynamic indexes were significantly ameliorated (P<0.05). There were significant differences between Sim2 group and Sim1 group or between Sim4 group and Sim1 group (P<0.05). However, there were no differences between Sim2 group and Sim4 group (P>0.05); (3) LVW and LVWI in the MI group and Sim-treated groups were significantly elevated compared with the Sham-operated group (P<0.05), and they were also decreased in Sim-treated groups as compared with MI group (P<0.05) and lower in Sim2 or Sim4 groups than in Sim1 group (P<0.05), but the difference between the Sim2 group and Sim4 was not significant (P>0.05); (4) Observed under common microscope, the HE staining showed that, in the MI rats compared with those in sham-operated group, ventricle wall of the infarct region was very thin and significantly reduced cardiocytes that were substituted by numerous strip-like fasciculation collagen fiber and structurally disordered and infiltrated with considerable inflammatory cells; and in the non-infarcted region of MI rats, compensatory hypertrophy of the survival cardiocytes were noted. As compared with the MI group, Sim-treated groups showed significantly attenuated myocardial structures were found in the infarcted or non-infarcted region; (5) As compared with the Sham-operated group, CSA was increased markedly in the MI group and Sim-treated groups (P<0.05), but decreased in Sim-treated groups as compared with MI group (P<0.05), and lower in Sim2 or Sim4 groups than in Sim1 group (P<0.05), however, the difference between the Sim2 group and Sim4 group was not significant (P>0.05).Conclusion Sim can ameliorate ventricular remodeling and hemodynamics in rats induced by MI; Within a concentration of 20 mg.kg-1·d-1, the curative efficacy of simvastatin may increase as the accumulative dose of the drug increased. PARTⅡEFFECTS OF SIMVASTATIN ON COLLAGENIC REMODELING OF MYOCARDIUM IN POST-MYOCARDIAL INFARCTION RATSObjective The aim of this study was to investigate the effects of simvastatin on myocardial collagenic remodeling as well as its possible mechanism after myocardial infarction in rats.Methods Sprague-Dawley rats were subjected to ligation in anterior descending branch of coronary artery and treated with simvastatin or physiological saline (gastric gavage) for 4 weeks. Circular thin transverse slices of left ventricular tissue were fixed with 4% paraformaldehyde for 24 hours followed by preservation with 70% alcohol for paraffin section. (Picric-Sirius Red Polarimetry and immunohistochemisty). The typeⅠcollagen volume fraction (CVF) and typeⅢCVF were determined with Picric-Sirius Red Polarimetry andⅠ/Ⅲratio was calculated in infarct (IZ) or non-infarct zone (NIZ). Immunohistochemical staining was used to analyze the expression of matrix metalloproteinases-2 (MMP-2) in NIZ.Results (1) Compared with Sham group, the typeⅠCVF, typeⅢCVF andⅠ/Ⅲratio in infracted area were increased markedly in MI group and Sim-treated groups (P<0.05), while the difference between MI group and the Sim-treated groups was not significant (P>0.05); (2) As compared with Sham-operated group, the typeⅠCVF, typeⅢCVF andⅠ/Ⅲratio in NIZ were increased markedly in MI group and Sim-treated groups (P<0.05), but decreased in Sim-treated groups as compared with MI group (P<0.05), and lower in Sim2 or Sim4 groups than in Sim1 group (P<0.05), however, the difference between Sim2 group and Sim4 group was not significant (P>0.05); (3) Contrasted to MI group, the expressions of MMP-2 was down-regulated in simvastatin treatment groups (but higher than those in Sham group). Contrasted to Sham-operated and Sim-treated groups, the expression of MMP-2 was up-regulated significantly in MI group (P<0.05) , and higher in Sim1 or Sim2 or Sim4 group than in Sham group (P<0.05), but the difference between the Sim-treated groups was not significant (P>0.05).Conclusion Our data indicated the presence of markedly fibrotic remodeling in infarct healing; Sim can ameliorate myocardial collagenic remodeling and ratio of collagen types in rats induced by MI, the mechanisms of which could be associated with its effect of down-regulating MMP-2. PARTⅢINFLUENCE OF SIMVASTATIN ON TGF-BETA1 INTRA-CELLULAR SIGNAL PATHWAY INVOLVEMENT IN MYOCARDIAL REMODELINGObjective To investigate the effects of simvastatin on transforming growth factor beta-1 (TGF-β1) intra-cellular signal transmit passway involvement in ventricular remodeling after myocardial infarction in rats.Methods Male Sprague-Dawley rats were subjected to ligation in anterior descending branch of coronary artery and treated with simvastatin or physiological saline (gastric gavage) for 4 weeks. The mRNA expressions of TGF-β1, TGF-β-activated kinase 1(TAK1), Smad3 and Smad7 were determined by reverse transcription polymerase chain reaction (RT-PCR) in the non-infarcted area; The protein expressions of TGF-β1, TAK1 and Smad3 were measured by western blot in non-infarction zone; The expression of Smad7 was assessed by immunohistochemical staining in the non-infarcted region.Results (1) As compared with the Sham-operated group, the levels of TGF-β1, TAK1 and Smad3 expression in the MI group and Sim-treated groups at transcriptional and translational level were increased significantly (P<0.05), and which were decreased in Sim-treated groups as compared with the MI group (P<0.05) and lower in Sim2 or Sim4 groups than in Sim1 group (P< 0.05), but the difference between Sim2 group and Sim4 was not significant (P > 0.05); (2) Contrasted to Sham and Sim groups, the expression of Smad7 were significantly decreased in MI group(P<0.05), but the difference between Sham and Sim groups was not significant (P>0.05).Conclusion The activity of Smad-dependent pathway or Smad-non-dependent pathway in TGF-β1 signal transduction was increased in myocardium-infarcted healing, in which the expressions of TGF-β1, Smad3 and TAK1 were up-regulated, while the expression of Smad7 was down-regulated; The inhibitory effect of simvastatin on ventricular remodeling after acute myocardial infarction is possibly attributed to its action in inhibiting the TGF-β1 signal transduction through down-regulating the expressions of TGF-β1, Smad3 and TAK1, and up-regulating the expression of Smad7.