Abstract
The metabolism of apigenin, a low estrogenic flavonoid phytochemical, was investigated in rat using liver models both in vitro (subcellular fractions) and ex vivo (isolated perfused liver). In vitro, phase I metabolism led to the formation of three monohydroxylated derivatives: luteolin which was the major metabolite (Km = 22.5 ± 1.5 μM; Vmax = 5.605 ± 0.090 nmol/min/mg protein, means ± S.E.M.), scutellarein, and iso-scutellarein. These oxidative pathways were mediated by cytochrome P450 monooxygenases (P450s). The use of P450 inhibitors and inducers showed that CYP1A1, CYP2B, and CYP2E1 are involved. In vitro studies of phase II metabolism indicated that apigenin underwent conjugation giving three monoglucuronoconjugates and one monosulfoconjugate. Luteolin led to the formation of four monoglucuronoconjugates, two sulfoconjugates, and one methylconjugate identified as diosmetin. Ex vivo during the apigenin perfusion of an isolated rat liver, none of the phase I metabolites could be recovered. In contrast, two monoglucuronoconjugates and one of the sulfoconjugates of apigenin already identified in vitro were recovered. Moreover, two new derivatives were isolated and identified as a diglucuronoconjugate and a glucuronosulfoconjugate. This work provides new data about the metabolism of apigenin and shows the interest value of using various experimental models in metabolic studies.
Footnotes
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↵2 Abbreviations used are: P450, cytochrome P450 monooxygenase; FMO, flavin-containing monooxygenase; HPLC, high-performance liquid chromatography; LC-MS, liquid chromatography-mass spectrometry; MC, methylcholanthrene; UGT, uridine diphosphate glucuronosyltransferase.
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This work was supported by grants from the Conseil Régional de Bourgogne, from the Institut National de la Recherche Agronomique, and from the Ministère de l'Environnement.
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↵1 Current address: UPRES EA 1085 “Biomolécules et Cibles Cellulaires Tumorales,” UFR de Pharmacie, 2 rue du Docteur Marcland, 87025 Limoges, France.
- Received March 31, 2003.
- Accepted September 10, 2003.
- The American Society for Pharmacology and Experimental Therapeutics
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