【作者】 徐兵；

【导师】 赵玉芳；

【作者基本信息】 浙江大学 ， 生物物理学， 2001， 硕士

【摘要】 作为生物遗传信息贮存的中心——DNA，控制着细胞的增殖与分化，其重要性对生物体是不言而喻的。然而多种理化因素都能造成DNA的损伤，尤以自由基所导致的损伤最为普遍、严重。因此，寻找能清除自由基从而对DNA损伤有保护作用的物质特别是功能植物材料——天然抗氧化剂，具有重要的意义。 本文主要以茶多酚、银杏提取物、竹叶提取物等几种天然抗氧化剂为研究材料，通过超微弱化学发光分析和荧光光度分析等实验手段，对⁶⁰Co-γ辐照和CuSO₄—Phen—V_C—H₂O₂—DNA体系中的OH°所致DNA损伤的保护作用作了比较系统的研究，获得了一些新的结果。 结果表明： （1）茶多酚、银杏提取物、竹叶提取物均具有清除OH°、O₂^-°自由基的作用。以茶多酚清除OH°的能力最强，其IC₅₀为1.049mg/ml；银杏提取物次之，IC₅₀为1.433mg/ml；竹叶相对最弱，IC₅₀为1.554mg/ml。清除O₂^-°能力也以茶多酚为最强，其IC₅₀为3.079ug/ml；银杏提取物次之，为3.425ug/ml；竹叶提取物最弱，为3.593ug/ml。 （2）茶多酚、银杏提取物和竹叶提取物浓度的增加对EB-DNA体系的荧光强度的抑制率也升高，且有线性关系；浓度为1.25mg/ml的茶多酚荧光强度抑制率约为0.902，同一浓度的银杏提取物抑制率约为0.821，竹叶提取物约为0.814。荧光强度抑制率为50％的三种抗氧化剂的浓度较为接近，均约为0.5mg/ml。结果表明三种抗氧化剂与DNA相互作用关系均相类似。 茶多酚、银杏提取物、竹叶提取物的荧光抑制率随浓度的变化有线性关系，不存在饱和性，且抑制率可达95％以上。而多糖的荧光抑制率具有饱和性，且抑制率相对很低，螺旋藻多糖、海藻多糖1、海藻多糖2对荧光强度的饱和抑制率分别为0.166，0.261，0.326。表明此两类物质与EB-DNA体系的DNA有不同的作用机制模式。生物物理学硕士学位论文 摘要 门)三种抗氧化剂对 DNA辐射损伤都具有保护作用。在我们的实验浓度范围内茶多酚、银杏提取物、竹叶提取物对 0～20Gy的 6七小y照射剂量下的DN A辐射损伤，均有保护作用：且随着抗氧化剂浓度的升高，其保护作用增强。 茶多酚对加C小 Y辐照所致的 DNA损伤保护作用比银杏提取物和竹叶提取物更强，而后两者保护作用差别不是很大，银杏提取物的作用稍强于竹叶提取物。 （4）茶多酚、银杏提取物、竹叶提取物均同时具有预防型抗氧化剂和断链型抗氧化剂的双重功能，既能使 CuSO。－－－－－－chen－－－－Vc－s。O。一DNA体系动力学曲线发光峰值下降，又能使后峰出现时间延迟。前峰、后峰峰值有明显下降，其IC50约在0．Zllg／ml。前峰峰值出现时间几乎不受这三种抗氧化剂的影响，在本实验条件下，均约为 100秒。而后峰峰值出现的时间则有所延迟，且随抗氧化剂浓度的增加，时间延迟明显变长，迟至时间一倍时的浓度也为0二fig／ml。 茶多酚、银杏提取物。竹叶提取物三者对本体系发光动力学曲线的影响有所不同。前后发光峰值抑止率以茶多酚的影响最大，银杏提取物次之，竹叶提取物相对最小。后峰出现的时间也是以茶多酚为最迟，竹叶提取物为最短。 （5）三种抗氧化剂清除自由基能力与它们对DNA损伤的保护作用成一定的对应关系，即清除自由基能力最强的茶多酚对DNA损伤的保护作用最强，清除自由基能力次之的银杏提取物对DNA损伤的保护作用次之，清除自由基能力最弱的竹叶提取物对DNA损伤的保护作用则最弱。更多还原

【Abstract】 By the analysis techniques of ultra weak chemiluminescence and spectrophotofluorometer, the protective functions against DNA damage of TP(Tea Polyphenols), EGB(Extracts of ginkgo biloba) and EBL(Extracts of bamboo leaf) were studied. The DNA damage was caused by OH from irradiation of 60Co- γ and chemiluminescence system in CuSC>4-Phen-Vc-H2O2-DNA.The results were follows:(1)All of TP,EGB and EBL had effects on clearing away OH and O2- . Comparing this three antioxidants, the order of clearing away both OH’ and O2- was TP>EGB>EBL, and their IC50 of TP, EGB and EBL, which scavenging OH was 1.049mg/ml, 1.433mg/ml andl.554mg/ml respectively. At the same time, the ICso of TP, EGB and EBL, which scavenged O2- ,was 3.079ug/ml,3.425ug/ml and 3.593ug/ml respectively.(2)The inhibition rate of relative fluorescence intensity would rise when the concentration of three antioxidants was elevated, and their correlationship was linear. The inhibition rate of relative fluorescence intensity at 1.25mg/ml concentration was 0.902 for TP, 0.821 for EGB and 0.814 for EBL respectively, and the concentration of three antioxidants was approximately 0.5mg/ml when the inhibition rate of relative fluorescence intensity was 50 percent. The results demonstrated the three antioxidants could interact with DNA resemblingly.The inhibition rate of fluorescence intensity, which treated with TP, EGB and EBL respectively, was not saturated when the concentration varied, even above 95 percent. Nevertheless that one treated with Polysaccharide had a saturation character. The results demonstrated the two kinds of substances, which interacted with DNA, had a different mechanism.(3)The three antioxidants could protect DNA from irradiation damage. The three antioxidants at four concentrations (20,40,80, 160ug/ml) had protective functions under 0~20Gy dosage. Meanwhile the protective functions increased while the concentration rose.The protective functions of TP against DNA damage induced by irradiation of 60Co- y were the strongest. The protective functions of EGB were better than those of EBL, but the difference between them was not significant.(4)The three antioxidants were both preventative antioxidant and. chain-breaking antioxidant. The three antioxidants significantly decreased the peak value of chemiluminescence and delayed the back peak value in the kinetic curve of chemiluminescence, simultaneously the value of front peak and the back peak all descended very evidently, and ICso is approximately 0.2ug/ml. The time of the front peak value was barely influenced by these three antioxidants and was approximately 100s, but the time of the back peak varied largely and delayed while the concentration of the antioxidants rose. The concentration, which made the time of the back peak delay doubly, was approximately 0.2ug/ml.The order of inhibition rate of the front and the back peak value was TP, EGB and EBL respectively. The order of the delaying time of the back peak was also TP, EGB and EBL respectively.The effects of scavenging free radical were in accordance with the protective functions against DNA damage induced by irradiation of 60Co- Y and chemiluminescence in CuSO4- Phen-Vc-H2O2-DNA system, namely, TP, the strongest protective function against DNA damage, had the strongest effects on clearing away free radical, EGB the second, and EBL the third.更多还原