Department of Pharmacology, Division of Clinical Pharmacology, and Vanderbilt Institute of Chemical Biology , Vanderbilt University Medical School , Nashville , Tennessee 37232 , United States.
Chem Res Toxicol. 2018 Apr 16;31(4):269-276. doi: 10.1021/acs.chemrestox.7b00326. Epub 2018 Mar 28.
The polypharmacological effects of the turmeric compound curcumin may be partly mediated by covalent adduction to cellular protein. Covalent binding to small molecule and protein thiols is thought to occur through a Michael-type addition at the enone moiety of the heptadienedione chain connecting the two methoxyphenol rings of curcumin. Here we show that curcumin forms the predicted thiol-Michael adducts with three model thiols, glutathione, N-acetylcysteine, and β-mercaptoethanol. More abundant, however, are respective thiol adducts of the dioxygenated spiroepoxide intermediate of curcumin autoxidation. Two electrophilic sites at the quinone-like ring of the spiroepoxide are identified. Addition of β-mercaptoethanol at the 5'-position of the ring gives a 1,7-dihydroxycyclopentadione-5' thioether, and addition at the 1'-position results in cleavage of the aromatic ring from the molecule, forming methoxyphenol-thioether and a tentatively identified cyclopentadione aldehyde. The curcuminoids demethoxy- and bisdemethoxycurcumin do not form all of the possible thioether adducts, corresponding with their increased stability toward autoxidation. RAW264.7 macrophage-like cells activated with phorbol ester form curcumin-glutathionyl and the 1,7-dihydroxycyclopentadione-5'-glutathionyl adducts. These studies indicate that the enone of the parent compound is not the only functional electrophile in curcumin, and that its oxidation products provide additional electrophilic sites. This suggests that protein binding by curcumin may involve oxidative activation into reactive quinone methide and spiroepoxide electrophiles.
姜黄化合物姜黄素的多药效作用可能部分通过与细胞蛋白的共价加合来介导。小分子和蛋白质巯基与姜黄素的两个甲氧基酚环连接的庚二烯二酮链烯酮部分的迈克尔型加成，被认为是通过共价键结合发生的。在这里，我们表明姜黄素与三种模型巯基，谷胱甘肽、N-乙酰半胱氨酸和β-巯基乙醇形成预测的巯基-Michael 加合物。然而，更为丰富的是姜黄素自氧化的双氧杂环戊二烯中间物的相应巯基加合物。在螺环环氧中间物的醌样环上鉴定出两个亲电部位。β-巯基乙醇在环的 5'-位加成得到 1,7-二羟基环戊二酮-5'-硫醚，而在 1'-位加成导致分子中环的芳构化断裂，形成甲氧基酚硫醚和一个暂定的环戊二酮醛。脱甲氧基和双脱甲氧基姜黄素不能形成所有可能的硫醚加合物，这与它们对自氧化的稳定性增加相对应。用佛波酯激活的 RAW264.7 巨噬细胞样细胞形成姜黄素-谷胱甘肽和 1,7-二羟基环戊二酮-5'-谷胱甘肽加合物。这些研究表明，母体化合物的烯酮不是姜黄素中唯一的功能亲电体，其氧化产物提供了额外的亲电部位。这表明姜黄素的蛋白质结合可能涉及氧化激活成反应性醌甲醚和螺环环氧亲电体。
