Department of Pharmacology, School of Medicine, Universidad Complutense, 28040 Madrid, Spain.
J Sci Food Agric. 2012 Jul;92(9):1822-5. doi: 10.1002/jsfa.5697. Epub 2012 May 4.
Flavonoids have been proposed to exert beneficial effects in the prevention of a large number of diseases, including cancer, cardiovascular disease, and neurodegenerative disorders. Paradoxically, despite the most representative flavonoid--quercetin--exerting biologically demonstrable systemic effects, it is not found in plasma after oral administration and its circulating metabolites show weak activity in vitro. The current available evidence indicates that quercetin is extensively metabolized into methylated and glucurono- and sulfo-conjugated metabolites, which are the plasma circulating forms; and glucurono-, but not sulfo-conjugates, can be hydrolyzed at the vascular level, yielding the parent aglycone which accumulates in tissues. Thus conjugation is a reversible process and, at least regarding the vasodilator and antihypertensive effects, the conjugation-deconjugation cycle appears to be an absolute requirement. Glucuronidated derivatives transport quercetin and its methylated form, and deliver to the tissues the free aglycone, which is the final effector.
类黄酮被认为对许多疾病（包括癌症、心血管疾病和神经退行性疾病）具有有益的预防作用。矛盾的是，尽管最具代表性的类黄酮——槲皮素——具有生物学上可证明的全身作用，但在口服后不会在血浆中发现，其循环代谢物在体外显示出较弱的活性。目前的证据表明，槲皮素被广泛代谢为甲基化和葡萄糖醛酸和硫酸结合代谢物，这些是血浆循环形式；并且只有葡萄糖醛酸结合物而不是硫酸结合物可以在血管水平水解，生成在组织中积累的母体苷元。因此，结合是一个可逆的过程，至少就血管扩张和降压作用而言，结合-去结合循环似乎是绝对必需的。葡萄糖醛酸化衍生物运输槲皮素及其甲基化形式，并将游离苷元（即最终效应物）递送到组织中。
