Green tea extracts provide antioxidative protection on myocardial ischemia associated with ligation of anterior descending coronary artery in rats

• Main Authors: Yi-Min Su, 蘇奕閔
• Other Authors: Ying-Ming Liou
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/50467477660612841757

碩士 === 國立中興大學 === 生命科學系所 === 102 === Containing large amounts of polyphenol compounds, green tea could help scavenge free radicals and reduce oxidative damage such as to protect from cardiovascular diseases, cancer and chronic diseases. Myocadial infarction (MI) resulting from myocardial ischemia often undergoes cardiac remodeling process, by which secondary damage to the heart might occur by generating excessive reactive oxygen species (ROS) and free radicals. Previously, we have established MI animal models associated with ligation of the left anterior descending coronary artery (LAD) in rats, and used that model to demonstrate that tube feeding green tea extract (GTE) could reduce heart tissue remodeling, ventricular hypertrophy, infarct size, as well as significantly improve the left ventricular functions. In this thesis, my study aimed to further understand the mechanism of GTE acting to ameoliate myocardial ischemia induced oxidative stress by using rats with sham control group (only thoracotomy), post MI group with GTE treatment or with water (H2O group). After three days without GTE feeding, cTnI was found significantly reduced in myocardial cells, suggesting cTnI degradation occurring in acute myocardial ischemia injured cells. In contrast, gelsolin (GSN), an actin severing protein, was found increased in ischemic myocardial cells from post MI rats. This is consistent with the role of GSN in cardiac apoptosis occurring in post MI hearts. Using myocardial cells freshly isolated from rat hearts showed that EGCG, a major green tea polyphenol, efficienly reduced formation of free radicals in cells disturbed by 100 µM H2O2. In addition, the rate of intracellular free radicals in the GTE groups (for three days, two weeks, and three weeks) all became slower in comparison with the H2O groups. The increase of GTE feeding time also increased efficiency in reducing the rate of free radical production in post MI cells. To assess antioxidative capacity of GTE in myocardial ischemia injured cells, the level of superoxide dismutase (SOD) activity in myocardial tissues was measured. Results showed that GTE treatment could help maintain the activity of SOD in cells at the remote region of the heart in post MI rats for the time periods from three days to three weeks, while in H2O group the SOD activity was found significantly decreased in post MI rats. However, the measured SOD mRNA level in myocardial tissues was not significantly different in control, post MI rats with or without GTE treatments. For measuring another antioxidatant enzyme, heme oxygenase-1 (HO-1), the mRNA level was found significantly reduced for the H2O group, while GTE treatment protecting the decrease of mRNA expression in the post MI myocardium. To further examine oxidative stress in cardiac cells, 4-hydroxynonenal (4HNE) post-translational modification on myocardial proteins were determined. Results showed that 4-HNE modified proteins were increased for the H2O group but decreased for the GTE group, as compared to the sham controls. Proteomic analysis also revealed that post MI animals for three days or three weeks significantly altered the myocardial proteins characterized with cytoskeletal function and energy metabolism as compred with control and post MI rats with GTE treatment. Finally, the potential signaling pathways by caveolin, Akt and GSK3β dependent events were determined for the involenent in the GTE-mediated antioxidation against the myocardial ischemia stress in post MI rats. Taken together, the data found in this study suggested that the caveolin, Akt and GSK3β signaling pathways might act to modulate the antioxidaticve protection of GTE against the myocardia ischemia induced oxidative stress in the heart.