茶氨酸通过抑制铜促进儿茶素氧化预防儿茶素肝毒性

Metabolic syndrome can be effectively prevented by green tea catechin extracts; however, high-dose catechin extracts are able to trigger hepatotoxicity. Noticeably, green tea, which has been consumed for thousand of years, is devoid of record of inducing liver injury. Based on the fact that green tea drinking and the intake of catechin extracts have a different safety threshold, it is reasonable to assume that green tea may contain certain ingredients to harness catechins. The prooxidant action has been recognized as a major toxicological mechanism of catechins. Copper is able to promote catechin oxidation, thus copper likely affects catechin toxicity. In this project, we will systematically demonstrate that theanine, another important functional ingredient in green tea, can inhibit copper-promoted catechin oxidation and thus prevent against liver injury induced by high-dose catechins. In chemical level, we will establish experimental models to show that copper including copper ions and copper carrier (ceruloplasmin and diethyldithiocarbamate-copper complex) promotes (-)-epigallocatechin gallate (EGCG) oxidation, enhances production of reactive oxygen species from EGCG, synergistically works with EGCG to cut DNA and form quinoprotein. Based on these models, we will investigate the inhibitory effects of theanine on copper. In cellular level, we will demonstrate that the mechanism by which theanine reduces cytotoxic effect of EGCG involves copper, and evaluate whether ceruloplasmin is associated with cytotoxicity of EGCG. In animal level, we will reveal that theanine is able to reduce hepatotoxicity triggered by EGCG but has no influence on healthy functions of EGCG, and theanine is more efficacious in preventing against copper-sensitized hepatotoxicity. These novel results should be of great significance for safe utilization of healthy functions of catechins.

绿茶儿茶素提取物具有预防代谢性疾病功效，然而实际应用中高剂量儿茶素提取物会触发肝毒性。绿茶已被饮用千年，肝毒性报道极少，饮用绿茶与摄入儿茶素提取物的安全性并不相同，这提示绿茶中存在限制儿茶素毒性的化合物。儿茶素促氧化行为是其毒理机制，铜促进儿茶素氧化，因此铜可能影响儿茶素毒性。本项申请将系统阐述绿茶茶氨酸抑制铜促进儿茶素氧化、预防儿茶素肝毒性。通过化学实验，阐述茶氨酸降低铜离子和铜载运体（铜蓝蛋白和二乙基二硫代氨基甲酸酯铜复合物）促进表没食子儿茶素没食子酸酯（EGCG）氧化、加剧EGCG产生活性氧、协同EGCG断裂DNA和形成醌化蛋白。通过细胞实验，说明茶氨酸降低EGCG细胞毒机制涉及铜，评价铜蓝蛋白是否介导EGCG产生细胞毒。通过动物实验，说明茶氨酸降低EGCG肝毒性、不降低EGCG功能，揭示茶氨酸更有效预防铜敏化EGCG肝毒性。这些崭新研究结果对安全利用儿茶素健康功能有重大指导意义。

绿茶儿茶素提取物具有预防代谢性疾病、抗病毒感染等功效，然而在实际应用中高剂量儿茶素提取物可能会触发肝毒性。儿茶素促氧化行为是其毒理机制，铜促进儿茶素氧化，因此铜可能增加高剂量儿茶素毒性。本项研究目标是阐述绿茶茶氨酸抑制铜促进儿茶素氧化、预防儿茶素肝毒性。经过四年的研究，本项研究系统地表征了表没食子儿茶素没食子酸酯（EGCG）促氧化性质，系统地说明茶氨酸可抑制EGCG促氧化，其机制为抑制铜促EGCG氧化。通过动物实验说明茶氨酸可抑制EGCG在体内氧化，从而降低高剂量EGCG的毒副作用，这为安全利用儿茶素提取物提供了新方法。本项研究还系统地表征了脑神经递质儿茶酚胺促氧化性质，系统地说明谷氨酸盐、茶氨酸可抑制儿茶酚胺促氧化，其机制为抑制铜促儿茶酚胺氧化。发现谷氨酸、儿茶酚胺和铜的联系为预防和治疗神经退行性疾病提供了新策略。茶氨酸、儿茶酚胺和铜的联系为使用茶氨酸预防和治疗神经退行性疾病提供了理论依据。鉴于2020年初突发新冠肺炎的紧迫形势，本项研究从五个方面综述了EGCG预防新冠肺炎的潜在机制，通过实验证明EGCG可有效抑制SARS-CoV-2主蛋白酶。从中发现高剂量EGCG能有效对抗病毒感染，EGCG的促氧化行为构成EGCG抗病毒的重要机制。鉴于EGCG促氧化潜在的毒副作用，本项研究提示茶氨酸与EGCG联用可能更安全地发挥EGCG的抗病毒作用。本项研究发表论文14篇（均标注项目资助），其中13篇合计影响因子约为95，平均影响因子约为7.3。另一篇发表在顶尖医学期刊柳叶刀2018年新创子刊——EClinicalMedicine，目前即时影响因子15.2，2022年首个影响因子可能约为18。项目主持人均为这些论文的未位（lead）通讯作者。本项研究共培养博士3人，硕士9人。本项目执行过程中，美国、英国、瑞典共5位科学家参与合作。