Safety evaluation of certain food additives - ipcs inchem

570 MISCELLANEOUS NITROGEN-CONTAINING SUBSTANCES (addendum)
In a comet (single-cell gel electrophoresis) assay using human-derived
HepG2 cells, the average comet tail length for cells treated with methyl
isothiocyanate (No. 1884) at 5.4 μg/ml was more than twice that of untreated cells.
Cell viability at this concentration was not reported, and higher concentrations of
the compound reduced cell viability by up to 70% (Kassie et al., 2001a, 2001b).
Allyl isothiocyanate (No. 1560), butyl isothiocyanate (No. 1561), benzyl
isothiocyanate (No. 1562), ethyl isothiocyanate (No. 1885) and isobutyl
isothiocyanate (No. 1886) were reported to give positive results in a bacterial
reverse mutation assay when tested at concentrations of 100–150 μg/plate without
metabolic activation in S. typhimurium strain TA100. The number of revertants per
plate varied among each sample, with allyl isothiocyanate having the highest
potency (among those tested). There was no increase in mutagenicity with
metabolic activation (Yamaguchi, 1980).
Positive results have also been reported in a bacterial reverse mutation
assay with allyl isothiocyanate (No. 1560), 3-butenyl isothiocyanate (No. 1889) and
4-pentenyl isothiocyanate (No. 1893). At concentrations of 125–320 μg/plate, the
agents showed the effect of reducing the revertant numbers, with and without
metabolic activation, in S. typhimurium strains TA98 and TA100. However, at the
highest dose concentration (320 μg/plate), colony survival was reduced in the cells
to 12–66% compared with controls (Uda et al., 1992).
(ii) In vivo
In an in vivo host-mediated differential DNA repair assay, groups of six male
Swiss albino mice were injected with 4–8 × 10 9 viable cells of a mixture of E. coli
strains 343/753 (uvrB/recA/Lac + ) and 343/765 (uvr + /rec + /Lac ), differing in their DNA
repair potential. Immediately following the injection, methyl isothiocyanate was
administered via gavage (90 or 270 mg/kg bw). Two hours later, animals were
sacrificed, and homogenized organ suspensions (liver, lungs, kidneys, stomach and
colon) were prepared on neutral red agar plates for 12 h to allow growth of the DNA
repair-deficient/proficient bacterial strains (343/753 and 343/765). At the higher
dose (270 mg/kg bw), acute toxicity was observed, and all animals died before the
end of the exposure period. At 90 mg methyl isothiocyanate/kg bw, the authors
reported only marginal positive effects in the liver and no statistically significant
effects in the lungs, kidneys or colon. Based on these results, the authors concluded
that methyl isothiocyanate is effectively detoxicated in the living animal. In earlier
studies, the same authors found experimental evidence for isothiocyanates
generating reactive oxygen radicals and causing lipid peroxidation, both of which
can induce DNA damage (Kassie et al., 1999). Accordingly, and in conjunction with
the marginal genotoxic effects seen at 90 mg/kg bw, the authors attributed the
apparent positive in vitro genotoxic effects of methyl isothiocyanate to DNA damage
caused by reactive oxygen species or lipid peroxidation, especially at doses that
can lead to acute toxic symptoms (Kassie et al., 2001a, 2001b).