目的 开发一种可快速、灵敏地检测生物样品中脱嘌呤/脱嘧啶核酸内切酶1(apurinic/apyrimidinic endonuclease 1,APE1)含量的荧光分析方法。方法 根据APE1所具有的脱碱基核酸内切酶活性,合成了一种用荧光基团与猝灭基团标记的含脱碱基位点的DNA荧光探针。在合适的缓冲体系下,APE1将该DNA探针水解并释放出荧光基团,根据荧光信号上升速率实现对APE1活性的定量检测。在此基础上,本研究改进了检测APE1时溶液缓冲液的条件,使得该荧光探针对APE1的响应更为灵敏,并进一步通过密度梯度离心法从人全血样品提取了外周血单核细胞(peripheral blood mononuclear cells,PBMCs),用改进后的荧光探针法定量测定了其蛋白提取液中APE1的含量。最后,使用该荧光探针法测定了临床血液样本中APE1的含量。结果 本研究建立的方法对APE1的最低检测限和功能灵敏度均为0.005 U/mL(3 pg/mL),线性范围为6 pg/mL~1.2 ng/mL。利用该方法测定了8份人血液样品中PBMCs蛋白中APE1的含量,测得每微克PBMCs蛋白中APE1的含量分布为0.061~0.40 ng,平均含量为0.16 ng APE1,加标回收率为98%±5%(n=3)。用该方法对102份正常人(男51例、女51例,年龄59~75岁)血清样品中的APE1含量进行了检测,得到这些血清样品中APE1含量的分布范围为0.13~0.34 ng/mL,加标回收率为96%±15%(n=3)。结论 本研究发展的荧光分析法操作简便、灵敏度高、所需生物样品量小,能够快速、准确地测定血液等生物样本中的APE1含量,解决了原有方法检测低含量血清样品时误差较大的问题,有良好的临床检验应用前景。

Objective: To develop a simple, sensitive and robust method for rapid detection of human apurinic/apyrimidinic endonuclease 1 (APE1) in various biological samples.Methods: An abasic site-containing DNA probe with a sequence of 5'-T*T*C*C*T*C*T(ROX)AGAGXCGTT(BHQ2)C*A*C*T*G*T*AGTTTATA*C*A*G*T* GAATCTCTCTAG*T*C*T-3'[“X” represents AP site; The phosphorothioated nucleotides (at 3’ side) are indicated with an asterisk after the nucleotides; ROX is 6-carboxy-X-rhodamine and BHQ2 is Black Hole quencher 2] was synthesized and used for the detection. In the presence of APE1, the DNA probe could be specifically hydrolyzed by the enzyme and release the fluorophore, resulting in strong fluorescence emission. The activity of APE1 was determined according to the rate of increase in fluorescence intensity. In this work, we modified the reaction buffer and significantly improved the performance of the method. Moreover, the method was further extended to measure the contents of APE1 in the protein extraction from peripheral blood mononuclear cells (PBMCs) extracted from human whole blood samples by density gradient centrifugation. The assay was also applied to measure the activity of APE1 in human serum samples. Results: With a new reaction buffer composed of 0.04% (V/V) Triton X-100, 50 mmol/L KAc, 20 mmol/L Tris-Ac, 10 mmol/L Mg(Ac)₂ and 1 mmol/L dithiothreitol (DTT), the method achieved a detection limit of 0.005 U/mL (3 pg/mL) and a linear response ranging from 6 pg/mL to 1.2 ng/mL. The contents of APE1 in the protein extraction from PBMCs of eight blood samples were measured to be in the range from 0.061 to 0.40 ng/μg protein, with an average of 0.16 ng/μg protein. The recovery was 98%±5% (n=3). The levels of APE1 in the sera from 102 normal individuals (51 male and 51 female, age range: 59-75 years) were observed to be from 0.13 to 0.34 ng/mL, with a recovery of 96%±15% (n=3).Conclusion: The new fluorescence assay was simple, rapid and sensitive, providing a practical tool to measure the activity of APE1 in serum samples and cell extracts. It also holds great potential in measurement of APE1 in many other biological samples for clinical test and laboratory research.