Safety evaluation of certain food additives - ipcs inchem

368 ALKOXY-SUBSTITUTED ALLYLBENZENES
sample after 24 h, whereas adult male mice (9–12 weeks) excreted up to 46% of
the 300 mg/kg bw intraperitoneal dose of safrole as 1-hydroxysafrole within the
same time frame (Drinkwater et al., 1976). Less than 1% of the 1-hydroxy
metabolite could be extracted prior to treatment with -glucuronidase, indicating that
the majority of the 1-hydroxy metabolites are present in the urine as the glucuronic
acid conjugates.
A single dose of estragole, methyl eugenol or safrole at 200 mg/kg bw was
administered by intraperitoneal injection to male Wistar rats, and urine was collected
every 2 h for 24 h. Twenty-four hours after treatment, animals were terminated and
the livers were removed. Urinary metabolites included the epoxide of the parent
substance, demethylenated safrole-2,3-epoxide and the O-demethylated
metabolites of methyl eugenol (allylcatechol epoxide) and estragole (allylphenol
epoxide). Liver homogenates showed the presence of safrole-2,3-epoxide
metabolites but not those of methyl eugenol or estragole. Liver microsomal
preparations showed the presence of epoxide metabolites that were previously
identified in the urine for all three substances (Delaforge et al., 1978).
The predominance in formation of the O-demethylenation metabolites of
safrole, myristicin and apiole at low dose levels in rodents and humans is analogous
to the extent of O-demethylation of estragole, methyl eugenol and elemicin in the
same species. The predominance of metabolism of the aromatic alkoxy substituent
at low dose levels in humans has also been reported for the structurally related
4-methoxypropenylbenzene (trans-anethole) (Sangster et al., 1987; Caldwell &
Sutton, 1988; Newberne et al., 1999).
The formation of 1-hydroxyestragole is dose dependent in both mice and
rats (Zangouras et al., 1981). When [ 14 C-methoxy]estragole at dose levels of 0.05,
5, 500 or 1000 mg/kg bw was administered to rats orally and to mice intraperitoneally,
the proportion of the dose excreted in the urine as the glucuronic acid
conjugate of 1-hydroxyestragole increased with dose, and the formation of the Odemethylated
metabolite decreased with dose. Only 0.9% of the dose was excreted
in the urine of rats given 0.05 mg/kg bw, whereas 8.0% was found at
1000 mg/kg bw. The total body burden after 24 h and exposure to the 1-hydroxy
metabolite increased significantly (1224–255 000 nmol/kg bw) as the dose was
increased from 5 to 500 mg/kg bw. Conversely, the same increase in dose resulted
in a decrease in O-demethylation from approximately 40% to 20% in both mice and
rats. Therefore, a shift in metabolic pathways results in a marked increase in
exposure to the 1-hydroxy metabolite and its sulfate and glucuronic acid conjugates
as dose is increased. Also, the dose-dependent increase in excreted glucuronic acid
conjugate of the 1-hydroxy metabolite is, to a large extent, correlated with increased
dose-dependent formation of protein and DNA adducts (see below).
Based on radiolabelled studies with low oral doses of estragole, the 1hydroxylation
pathway is a minor pathway for the metabolism of alkoxy-substituted
allylbenzenes in humans. Two male volunteers ingested a gelatin capsule
containing 100 μg [methoxy- 14 C]estragole (1.5 μg/kg bw). The bulk (72% and 67%)
of the radioactivity was accounted for in the urine and as exhaled carbon dioxide
(respectively) within 48 h. O-Demethylation and oxidative degradation of the allyl