Safety evaluation of certain food additives - ipcs inchem

372 ALKOXY-SUBSTITUTED ALLYLBENZENES
interactions between the 1-hydroxylation of estragole and methyl eugenol and
between the 1-hydroxylation of estragole and safrole are to be expected owing to
the overlapping specificities of CYP1A2 and CYP2A6, respectively, in the 1hydroxylation
of the substances. Furthermore, poor metabolizing phenotypes in
CYP2A6 polymorphisms may reduce the extent of 1-hydroxylation products of
estragole and safrole, whereas lifestyle factors that increase CYP1A2 activities,
such as cigarette smoking and consumption of charbroiled food, might increase the
potential for 1-hydroxylation of estragole and methyl eugenol.
The effects of estragole, safrole and myristicin on in vitro activities of CYPs
3A4, 2D6 and 1A in human liver microsomes were investigated. Estragole, safrole
or myristicin at concentrations ranging from 10 nmol/l to 150 μmol/l was incubated
with pooled microsomes, and CYP activities were measured. Safrole was a more
potent inhibitor of CYP3A4 (median inhibitory concentration [IC50] = 0.43 μmol/l) and
CYP1A (IC50 = 2 μmol/l) compared with estragole and myristicin (estragole: IC50 =
5.9 μmol/l [CYP3A4] and 20 μmol/l [CYP1A]; myristicin: IC50 = 11 μmol/l [CYP3A4]
and 5 μmol/l [CYP1A]). None of the three compounds influenced CYP2D6 activity
in the concentration ranges studied. These results indicate that estragole, safrole
and myristicin may interfere with substances that are substrates for CYP3A4 and
CYP1A (Iyer et al., 2003).
In another study, CYPs 3A4 and 1A2 were identified as being the primary
isoforms involved in the hepatic biotransformation of myristicin to its major
metabolite, 5-allyl-1-methoxy-2,3-dihydroxybenzene. Different human liver
microsomes were incubated with myristicin. The formation of 5-allyl-1-methoxy-2,3dihydroxybenzene
strongly correlated (R 2 = 0.87) with nifedipine oxidation, which is
a marker of CYP3A4 activity. Microsomal oxidation of myristicin to the major
metabolite (5-allyl-1-methoxy-2,3-dihydroxybenzene) was markedly inhibited by
gestodene and ketoconazole, which are selective inhibitors of the CYP3A enzyme.
Inhibitors specific to other CYP isoforms did not significantly inhibit myristicin
oxidation. Antibodies for CYP3A4 and CYP1A2 could also inhibit the oxidation of
myristicin, but antibodies recognizing other CYP isoforms had no effect. Purified
recombinant CYP3A4 and CYP1A2 were capable of catalysing the oxidation of
myristicin to 5-allyl-1-methoxy-2,3-dihydroxybenzene. These experiments indicate
that CYP3A4 (and possibly other CYP3A enzymes) and CYP1A2 play significant
roles in the formation of the major myristicin metabolite, 5-allyl-1-methoxy-2,3dihydroxybenzene,
in humans (Yun et al., 2003).
Immunoblot analysis of liver tissue isolated from male and female rats
maintained on diets containing methyl eugenol at levels calculated to provide an
average daily intake of 0, 1, 5 or 50 mg/kg bw for 28 days showed no influence on
CYP2E1 or CYP1A2 expression levels. Gavage doses of 50 mg/kg bw per day given
to rats for 28 days showed the same lack of effect on CYP expression (Ellis, 2007).
2.1.4 Enzyme induction and inhibition
Induction of CYP1A by myristicin and safrole was evaluated in Wistar rats,
CD-1 mice and Syrian golden hamsters. Each species received daily intraperitoneal
injections of safrole or myristicin at 50 mg/kg bw for 3 days, and CYP1A activity was
measured in liver, kidney and lung tissue samples. Safrole produced a 9-fold
increase in 7-ethoxyresorufin O-deethylation (EROD) activity in the livers of rats, a