Safety evaluation of certain food additives - ipcs inchem

ALKOXY-SUBSTITUTED ALLYLBENZENES 405
2.3 Genotoxicity
2.3.1 In vitro
The literature on the genetic toxicology of the alkoxy-substituted
allylbenzenes estragole, methyl eugenol and safrole is fairly extensive, especially
with regard to the results of in vitro assays. The results are summarized in Table 4.
Generally, these compounds yield similar results, as might be expected based upon
their structural similarity. Moreover, given the knowledge on the two-step process
of bioactivation, positive results would be expected only in test systems that provide
appropriate bioactivation capability.
Methyl eugenol was negative in multiple tests in various strains of Salmonella
typhimurium and Saccharomyces cerevisiae alone and with an exogenous rat liver
metabolic activation system (S9) (Dorange et al., 1977; Sekizawa & Shibamoto,
1982; Mortelmans et al., 1986; Schiestl et al., 1989a; Brennan et al., 1996).
Estragole was also negative in common strains of S. typhimurium with and without
metabolic activation (Dorange et al., 1977; Sekizawa & Shibamoto, 1982; To et al.,
1982b; Zeiger et al., 1987; Zani et al., 1991). Safrole yielded some equivocal
genotoxicity results, but a complicating factor in evaluating the validity of positive
results is the high concentrations used, which result in cytotoxicity and false
positives. In one study (To et al., 1982b), a significant increase in the revertants per
plate was reported for strain TA1538 when incubated with safrole, estragole and
related compounds in the presence of S9 and 3-phosphoadenosine 5phosphosulfate
cofactor. The authors proposed that the mutagenic response was
related to the formation of an activated sulfate ester of active metabolites. Other
strains of S. typhimurium that were tested did not yield a mutagenic response in
assays using 3-phosphoadenosine 5-phosphosulfate.
No evidence of genotoxicity was found when S. typhimurium strains TA98,
TA100, TA1535 and TA1537 were exposed to 1–200 μg estragole/plate in an assay
alone or with preincubation with rat liver S9 (Zeiger et al., 1987). Results of testing
in vitro in Ames assays with estragole metabolites have yielded equivocal results.
The 2,3-epoxide of estragole and 1-hydroxyestragole were positive in strains
TA100 and TA1535, but negative in TA98 with or without S13 metabolic activation
(Swanson et al., 1979). In a different study, no evidence of mutagenicity was
reported when 1-hydroxyestragole was incubated with S. typhimurium TA98 and
TA100 with and without S13 metabolic activation. Addition of 3-phosphoadenosine
5-phosphosulfate as a cofactor did not result in an increase in revertants. 1-
Acetoxyestragole was mutagenic in strains TA98 and TA100, but not in a dosedependent
manner (Drinkwater et al., 1976). Overall, estragole and its metabolites
do not appear to be mutagenic in S. typhimurium.