Safety evaluation of certain food additives - ipcs inchem

ALKOXY-SUBSTITUTED ALLYLBENZENES 381
adducts were identical to synthetic safrole–deoxyguanosine monophosphate
(dGMP) adducts as well as DNA adducts from 1-hydroxysafrole-treated HepG2
cells, suggesting that safrole forms stable DNA adducts in human oral tissue
following chronic betel quid chewing (Chen et al., 1999).
The liver biopsy of a patient who was both a chronic betel nut chewer (30
betel quid per day for 32 years) and a chronic cigarette smoker revealed
hepatocellular carcinoma. The patient also had oral squamous cell carcinoma.
Using the 32 P-postlabelling technique, safrole–DNA adducts were detected in tissue
samples from the liver, from the oral squamous cell carcinoma and in peripheral
blood leukocyte samples. The level of safrole–DNA adducts detected was 22.5
adducts/10 8 nucleotides in liver, 7.1 adducts/10 8 nucleotides in the oral squamous
cell carcinoma and 0.8 adducts/10 8 nucleotides in peripheral blood leukocytes. The
profile and location of the safrole–DNA adduct were similar to those of adducts
found in HepG2 cells exposed to 1-hydroxysafrole; the adduct has been identified
as N 2 -(trans-isosafrole-3-yl)-2-deoxyguanosine, which has a structure analogous
to the DNA adducts formed by estragole and methyl eugenol. In parallel studies
using similar tissues obtained from six people who had hepatocellular carcinoma or
oral squamous cell carcinoma and who did not chew betel quid, no safrole-derived
DNA adducts were detected (Liu et al., 2000).
In an in vitro study, metabolically competent human hepatoma (HepG2) cells
were incubated for 24 h with three concentrations (50, 150 and 450 μmol/l) of
safrole, myristicin, apiole, estragole, methyl eugenol and the structurally related
substance dill apiole (2,3-dimethoxy-3,4-methylenedioxyallylbenzene). DNA
adducts measured by the 32 P-postlabelling assay showed that all six substances
formed N 2 -(trans-propenylbenzene-3-yl)-2-deoxyguanosine (major) and N 2 -
(allylbenzene-1-yl)-2-deoxyguanosine (minor) adducts. At the low concentration
(50 μmol/l), the level of DNA adduct formation decreased in the order methyl
eugenol > estragole > safrole > myristicin dill apiole > apiole. At the high
concentration of 450 μmol/l, the level of adduct formation decreased in the order
estragole > myristicin > methyl eugenol safrole > dill apiole > apiole. Also, the ratio
of major/minor DNA adducts was highest for methyl eugenol in both HepG2 cells
and mouse liver and lowest for estragole and safrole. The authors suggest that
decreased steric hindrance is related to increased formation of the minor N 2 -
(allylbenzene-1-yl) adduct (Zhou et al., 2007).
2.1.8 Summary of enzyme induction and adduct formation data
Based on research performed since the late 1990s (Gardner et al., 1997a,
1997b; Wakazono et al., 1998; Jeurissen et al., 2004, 2005, 2007; Ueng et al.,
2004), significant induction of the CYP activation pathway is expected to
successively convert alkoxy-substituted allylbenzenes into their 1-hydroxy
metabolites and sulfate conjugates. This is especially prevalent at higher dose
levels in rodents. Under conditions such as those present in rats and mice
administered high dose levels (>10 mg/kg bw per day), induction of CYP1A2
(Jeurissen et al., 2005) and CYP2E1 (Gardner et al., 1997a) and subsequent
sulfation (via SULT1 and SULT2) are linked sequentially to increased production of
the sulfate conjugate of the 1-hydroxy metabolite. This metabolite is linked to GST