title: Structural modifications at the C-4 position strongly affect the glucuronidation of 6,7-dihydroxycoumarins.
abstract: Esculetin (6,7-dihydroxycoumarin) and its C-4 derivatives have multiple pharmacologic activities, but the poor metabolic stability of these catechols has severely restricted their application in the clinic. Glucuronidation plays important roles in catechols elimination, although thus far the effects of structural modifications on the metabolic selectivity and the catalytic efficacy of the human UDP-glucuronosyltransferase (UGT) enzymes remain unclear. This study was aimed at exploring the structure-glucuronidation relationship of esculetin and its C-4 derivatives, including 4-methyl esculetin, 4-phenyl esculetin, and 4-hydroxymethyl esculetin as well as 4-acetic acid esculetin. It was achieved by identifying the main human UGTs responsible for the different reactions and by careful characterization of the reactions kinetics. These catechols, with the exception of 4-acetic acid esculetin, are selectively metabolized to the corresponding 7-O-glucuronides. UGT1A6 and UGT1A9 are the two major UGTs involved in the 7-O-glucuronidation of 4-methyl esculetin and esculetin. UGT1A6 was the major contributor for 7-O-glucuronidation of 4-hydroxymethyl esculetin, and UGT1A9 played a significant role in the 7-O-glucuronidation of 4-phenyl esculetin. The results of the kinetic analyses revealed that the Km values of the compounds, in both UGT1A9 and human liver microsomes, decreased with increasing hydrophobicity of the C-4 substitutions. The outcome of this was that C-4 hydrophobic and hydrophilic groups on 6,7-dihydroxycoumarin exhibited contrasting effects on UGT affinity. All of these findings provide helpful guidance for further structural modification of 6,7-dihydroxycoumarins with improved metabolic stability.
authors: Laboratory of Pharmaceutical Resource Discovery, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian (Y.-L.X., G.-B.G., P.W., S.-C.L.,Y.-Q.H., J.N., X.-K.Q., Y.L., L.Y.); University of Chinese Academy of Sciences, Beijing (Y.-L.X., S.-C.L.); Dalian Medical University, Dalian (J.N., X.-K.Q.), People's Republic of China.
authors: Yang-Liu
authors: YL
authors: Xia
authors: Laboratory of Pharmaceutical Resource Discovery, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian (Y.-L.X., G.-B.G., P.W., S.-C.L.,Y.-Q.H., J.N., X.-K.Q., Y.L., L.Y.); University of Chinese Academy of Sciences, Beijing (Y.-L.X., S.-C.L.); Dalian Medical University, Dalian (J.N., X.-K.Q.), People's Republic of China.
authors: Guang-Bo
authors: GB
authors: Ge
authors: Laboratory of Pharmaceutical Resource Discovery, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian (Y.-L.X., G.-B.G., P.W., S.-C.L.,Y.-Q.H., J.N., X.-K.Q., Y.L., L.Y.); University of Chinese Academy of Sciences, Beijing (Y.-L.X., S.-C.L.); Dalian Medical University, Dalian (J.N., X.-K.Q.), People's Republic of China.
authors: Ping
authors: P
authors: Wang
authors: Laboratory of Pharmaceutical Resource Discovery, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian (Y.-L.X., G.-B.G., P.W., S.-C.L.,Y.-Q.H., J.N., X.-K.Q., Y.L., L.Y.); University of Chinese Academy of Sciences, Beijing (Y.-L.X., S.-C.L.); Dalian Medical University, Dalian (J.N., X.-K.Q.), People's Republic of China.
authors: Si-Cheng
authors: SC
authors: Liang
authors: Laboratory of Pharmaceutical Resource Discovery, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian (Y.-L.X., G.-B.G., P.W., S.-C.L.,Y.-Q.H., J.N., X.-K.Q., Y.L., L.Y.); University of Chinese Academy of Sciences, Beijing (Y.-L.X., S.-C.L.); Dalian Medical University, Dalian (J.N., X.-K.Q.), People's Republic of China.
authors: Yu-Qi
authors: YQ
authors: He
authors: Laboratory of Pharmaceutical Resource Discovery, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian (Y.-L.X., G.-B.G., P.W., S.-C.L.,Y.-Q.H., J.N., X.-K.Q., Y.L., L.Y.); University of Chinese Academy of Sciences, Beijing (Y.-L.X., S.-C.L.); Dalian Medical University, Dalian (J.N., X.-K.Q.), People's Republic of China.
authors: Jing
authors: J
authors: Ning
authors: Laboratory of Pharmaceutical Resource Discovery, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian (Y.-L.X., G.-B.G., P.W., S.-C.L.,Y.-Q.H., J.N., X.-K.Q., Y.L., L.Y.); University of Chinese Academy of Sciences, Beijing (Y.-L.X., S.-C.L.); Dalian Medical University, Dalian (J.N., X.-K.Q.), People's Republic of China.
authors: Xing-Kai
authors: XK
authors: Qian
authors: Laboratory of Pharmaceutical Resource Discovery, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian (Y.-L.X., G.-B.G., P.W., S.-C.L.,Y.-Q.H., J.N., X.-K.Q., Y.L., L.Y.); University of Chinese Academy of Sciences, Beijing (Y.-L.X., S.-C.L.); Dalian Medical University, Dalian (J.N., X.-K.Q.), People's Republic of China.
authors: Yan
authors: Y
authors: Li
authors: Laboratory of Pharmaceutical Resource Discovery, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian (Y.-L.X., G.-B.G., P.W., S.-C.L.,Y.-Q.H., J.N., X.-K.Q., Y.L., L.Y.); University of Chinese Academy of Sciences, Beijing (Y.-L.X., S.-C.L.); Dalian Medical University, Dalian (J.N., X.-K.Q.), People's Republic of China yling@dicp.ac.cn.
authors: Ling
authors: L
authors: Yang
mesh_terms: D000818:Animals; D020719:Glucuronides / Q000378:metabolism*; D014453:Glucuronosyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D066298:In Vitro Techniques; D008862:Microsomes, Liver / Q000378:metabolism*; D015394:Molecular Structure; D009544:Niflumic Acid / Q000494:pharmacology; D051381:Rats; D013329:Structure-Activity Relationship; D000090264:UDP-Glucuronosyltransferase 1A9; D014468:Umbelliferones / Q000737:chemistry* / Q000378:metabolism / Q000493:pharmacokinetics*
chemical_list: D020719:Glucuronides; C000715591:UGT1A9 protein, human; D014468:Umbelliferones; D009544:Niflumic Acid; D014453:Glucuronosyltransferase; D000090264:UDP-Glucuronosyltransferase 1A9; C007628:esculetin