Boots Agnes W, Kubben Nard, Haenen Guido R M M, Bast Aalt
Department of Pharmacology and Toxicology, Faculty of Medicine, Maastricht University, The Netherlands.
Biochem Biophys Res Commun. 2003 Aug 29;308(3):560-5. doi: 10.1016/s0006-291x(03)01438-4.
When an antioxidant scavenges a reactive species, i.e., when it exerts its antioxidant activity, the antioxidant is converted into potentially harmful oxidation products. In this way, the antioxidant quercetin might yield an ortho-quinone, denoted as QQ, which has four tautomeric forms, i.e., the ortho-quinone and three quinonmethides. We evaluated the interaction of QQ with ascorbate or glutathione (GSH). Ascorbate recycles QQ to the parent compound quercetin, while GSH forms two adducts with QQ, i.e., 6-GSQ and 8-GSQ. When both GSH and ascorbate are present, QQ is converted exclusively into GSQ. In the absence of GSH, protein thiols will be arylated by QQ. This protein arylation is not prevented by ascorbate. Thiol arylation by quinones and quinonmethides can impair several vital enzymes. This implies that the product formed when quercetin displays its antioxidant scavenging effect is toxic in the absence of GSH. Therefore, an adequate GSH level should be maintained when quercetin is supplemented.
当抗氧化剂清除活性物质时，即当它发挥抗氧化活性时，抗氧化剂会转化为潜在有害的氧化产物。通过这种方式，抗氧化剂槲皮素可能会产生一种邻醌，记为QQ，它有四种互变异构形式，即邻醌和三种醌甲基化物。我们评估了QQ与抗坏血酸或谷胱甘肽（GSH）的相互作用。抗坏血酸将QQ循环转化为母体化合物槲皮素，而GSH与QQ形成两种加合物，即6-GSQ和8-GSQ。当GSH和抗坏血酸都存在时，QQ仅转化为GSQ。在没有GSH的情况下，蛋白质硫醇会被QQ芳基化。抗坏血酸不能阻止这种蛋白质芳基化。醌和醌甲基化物引起的硫醇芳基化会损害几种重要的酶。这意味着当槲皮素发挥其抗氧化清除作用时形成的产物在没有GSH的情况下是有毒的。因此，补充槲皮素时应维持足够的GSH水平。
