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Detection of N‑Acetyl‑S‑[3′-(4-methoxyphenyl)allyl]‑l‑Cys (AMPAC) in Human Urine Samples after Controlled Exposure to Fennel Tea: A New Metabolite of Estragole and trans-Anethole
journal contribution
posted on 2019-10-10, 20:43 authored by Bernhard H. Monien, Benjamin Sachse, Bela Niederwieser, Klaus AbrahamFennel
and other herbs contain the secondary plant metabolites
estragole and trans-anethole, of which estragole
is carcinogenic in rodents. It is metabolically activated by cytochrome
P450-catalyzed conversion to 1′-hydroxyestragole and subsequent
sulfo conjugation to the genotoxic 1′-sulfoxyestragole. The
current study followed the hypothesis that the reactive sulfate ester
may be detoxified by glutathione conjugation, leading to the urinary
excretion of a resultant mercapturic acid. We identified the assumed
downstream metabolite N-acetyl-S-[3′-(4-methoxyphenyl)allyl]-l-Cys (AMPAC) in human
urine samples after consumption of fennel tea. An isotope-dilution
technique for its quantification by ultraperformance liquid chromatography-tandem
mass spectrometry and [13C3,15N]AMPAC
in urine samples was developed. The method was applied to determine
the AMPAC concentration in urine samples following uptake of 500 mL
of fennel tea containing 2.2 mg of estragole by 12 healthy participants
(six females and six males). Before drinking the tea, the urinary
AMPAC concentration was below the limit of detection. In most of the
participants, the highest amounts of urinary AMPAC were found in the
first-hour urine after exposure. The excretion by first-order kinetics
(range of t1/2 = 0.78–1.54 h; mean
± SD: 1.13 ± 0.21 h) led to a nearly complete clearance
within 8 h in all participants. The total AMPAC excreted was in the
range of 93–1076 ng, reflecting pronounced interindividual
variations of enzymes taking part in estragole metabolism. Importantly,
AMPAC was also formed in one volunteer following oral uptake of a
single dose of isolated trans-anethole, albeit to
a much smaller extent compared to estragole. AMPAC may be of future use as a human biomarker for the internal
exposure to the carbocation formed from either 1′-sulfoxyestragole
or 3′-sulfoxyisoestragole, the reactive sulfate ester metabolites
of estragole and trans-anethole, respectively.