title: Identification of the ortho-benzoquinone intermediate of 5-O-caffeoylquinic acid in vitro and in vivo: comparison of bioactivation under normal and pathological situations.
abstract: 5-O-Caffeoylquinic acid (5-CQA) is one of the major bioactive ingredients in some Chinese herbal injections. Occasional anaphylaxis has been reported for these injections during their clinical use, possibly caused by reactive metabolites of 5-CQA. This study aimed at characterizing the bioactivation pathway(s) of 5-CQA and the metabolic enzyme(s) involved. After incubating 5-CQA with GSH and NADPH-supplemented human liver microsomes, two types of GSH conjugates were characterized: one was M1-1 from the 1,4-addition of GSH to ortho-benzoquinone intermediate; the other was M2-1 and M2-2 from the 1,4-addition of GSH directly to the α,β-unsaturated carbonyl group of the parent. The formation of M1-1 was cytochrome P450 (P450)-mediated, with 3A4 and 2E1 as the principal catalyzing enzymes, whereas the formation of M2-1 and M2-2 was independent of NADPH and could be accelerated by cytosolic glutathione transferase. In the presence of cumene hydroperoxide, M1-1 formation increased 6-fold, indicating that 5-CQA can also be bioactivated by P450 peroxidase under oxidizing conditions. Furthermore, M1-1 could be formed by myeloperoxidase in activated human leukocytes, implying that 5-CQA bioactivation is more likely to occur under inflammatory conditions. This finding was supported by experiments on lipopolysaccharide-induced inflammatory rats, where a greater amount of M1-1 was detected. In S-adenosyl methionine- and GSH-supplemented human S9 incubations, M1-1 formation decreased by 80% but increased after tolcapone-inhibited catechol-O-methyltransferase (COMT) activity. In summary, the high reactivities of the ortho-benzoquinone metabolite and α,β-unsaturated carbonyl group of 5-CQA to nucleophiles have been demonstrated. Different pathological situations and COMT activities in patients may alter the bioactivation extent of 5-CQA.
authors.affiliation: Center for Drug Metabolism and Pharmacokinetics, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China.
authors.forename: Cen
authors.initials: C
authors.lastname: Xie
authors.forename: Dafang
authors.initials: D
authors.lastname: Zhong
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Chen
mesh_terms: D000818:Animals; D016227:Benzoquinones / Q000378:metabolism*; D002726:Chlorogenic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D013058:Mass Spectrometry; D011801:Quinic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
chemical_list: D016227:Benzoquinones; D002726:Chlorogenic Acid; D011801:Quinic Acid; C473200:5-caffeoylquinic acid