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J Pharm Biomed Anal. 2020 Jan 30;178:112972. doi: 10.1016/j.jpba.2019.112972. Epub 2019 Nov 4.

Identification of UDP-glucuronosyltransferases involved in the metabolism of silymarin flavonolignans.

Author information

1
Department of Medical Chemistry and Biochemistry, Faculty of Medicine and Dentistry, Palacký University, Hněvotínská 3, Olomouc 77515, Czech Republic. Electronic address: j.vrba@upol.cz.
2
Regional Centre of Advanced Technologies and Materials, Department of Analytical Chemistry, Faculty of Science, Palacký University, 17. Listopadu 12, Olomouc 77146, Czech Republic.
3
Department of Medical Chemistry and Biochemistry, Faculty of Medicine and Dentistry, Palacký University, Hněvotínská 3, Olomouc 77515, Czech Republic.
4
Institute of Microbiology of the Czech Academy of Sciences, Laboratory of Biotransformation, Vídeňská 1083, Prague 14220, Czech Republic.

Abstract

Silybum marianum (milk thistle) is a medicinal plant used for producing the hepatoprotective remedy silymarin. Its main bioactive constituents, including silybin and related flavonolignans, can be metabolized directly by phase II conjugation reactions. This study was designed to identify UDP-glucuronosyltransferases (UGTs) involved in the glucuronidation of six silymarin flavonolignans, namely silybin A, silybin B, isosilybin A, isosilybin B, silychristin, and silydianin. UHPLC-MS analyses showed that all of the tested compounds, both individually and in silymarin, were glucuronidated by human liver microsomes, and that glucuronidation was the main metabolic transformation in human hepatocytes. Further, each compound was glucuronidated by multiple recombinant human UGT enzymes. UGTs 1A1, 1A3, 1A8 and 1A9 were able to conjugate all of the tested flavonolignans, and some of them were also metabolized by UGTs 1A6, 1A7, 1A10, 2B7 and 2B15. In contrast, no glucuronides were produced by UGTs 1A4, 2B4, 2B10 and 2B17. With silymarin, we found that UGT1A1 and, to a lesser extent UGT1A9, were primarily responsible for the glucuronidation of the flavonolignan constituents. It is concluded that the metabolism of silymarin flavonolignans may involve multiple UGT enzymes, of which UGT1A1 appears to play the major role in the glucuronidation. These results may be relevant for future research on the metabolism of flavonolignans in humans.

KEYWORDS:

Cytochrome P450; Glucuronidation; Metabolism; Microsomes; Silymarin; UGT

PMID:
31727359
DOI:
10.1016/j.jpba.2019.112972

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