Malachite green and leucomalachite green
COM statement COM/99/S1 (for COT) - February 1999
Introduction
1. Malachite green is a cationic triphenylmethane dyestuff used in
a number of industries, including fish farming. It is used in freshwater
fisheries for the treatment of external fungal and other infections, its
main use being to stop fungal growth on the eggs. The COT have asked for
advice on the mutagenicity of malachite green and the lipophilic metabolite
leucomalachite green. In particular the COT has asked for advice on results
from recent National Toxicology Programme (NTP) 32-P post-labelling studies
(sub acute) carried out with range-finding studies prior to initiating
carcinogenicity bioassays on malachite green and leucomalachite green
in rats and mice.
2. The Committee commented on the paucity of the available mutagenicity
data, particularly in respect of leucomalachite green. In many instances
lack of information on the purity of the malachite green tested is a particular
problem in assessing the adequacy of the available information. Members
agreed that the structure of both malachite green and leucomalachite green
contained groupings which provide structural alerts for potential mutagenicity
and thus it was important to evaluate the potential mutagenicity of both
malachite green and its lipophilic metabolite leucomalachite green. Members
also noted the results from the 1997 surveillance investigations conducted
for the Veterinary Medicines Directorate which, for the first time, present
information on residues of leucomalachite green and suggest that, when
found, residues of this chemical in fish were higher than those of malachite
green.
COM Conclusions
Malachite green
3 i There is one report of a Salmonella assay done to an acceptable
protocol; malachite green oxalate (>90% pure) was shown to induce mutations
in TA98 in the presence of an exogenous metabolic activation system. (1)
There is also some evidence of clastogenicity in Chinese Hamster Lung
cells. (2) Malachite green should thus be regarded as having mutagenic
potential.
ii. Negative results were obtained in a poorly reported bone marrow
micronucleus test in mice using a single oral dose of malachite green
oxalate (>90% pure) at the MTD (75% of the LD50). (1) Members agreed
that the high dose level of 37.5 mg/kg was adequate, but it was difficult
to assess the value of the negative results in the absence of appropriate
information on bone marrow toxicity or data to show that malachite green
and/or metabolites reached the bone marrow.
iii. Recent 32P-post-labelling studies using a 28 day dietary exposure
and carried out with NTP range-finding studies (used in designing carcinogenicity
bioassays) indicate that malachite green induces DNA adducts in the liver
of rats and mice. (3,4)
iv. The Committee concluded that although a limited negative in-vivo
micronucleus test was available, the results of the recently conducted
32-P- post-labelling studies indicated that it would be prudent to assume
that malachite green may be a potential in-vivo mutagen.
Leucomalachite green
4. i The Committee were concerned that only limited information was
available on leucomalachite green. The lack of information on leucomalachite
green prevents an adequate mutagenicity assessment for this compound.
ii. The Committee recommended that in-vitro studies in bacteria for
gene mutations, in mammalian cells for clastogenicity and a mammalian
cell assay for gene mutation (preferably the mouse lymphoma assay) conducted
according to current OECD guidelines should be undertaken as an important
step to evaluating the mutagenic potential of leucomalachite green.
iii. The Committee, however, concluded that the results of the recently
conducted 32P-post-labelling studies3,4 indicated that it would be prudent
to assume that leucomalachite green may also be a potential in-vivo mutagen.
References
1. Clemmensen S, Jensen JC, Jensen NJ et al. Toxicological studies
on malachite green: a triphenylmethane dye. Arch. Toxicol. 56 43-5 (1984).
2. Ishidate M. Application of chromosome aberration test in vitro to the
primary screening for chemicals with carcinogenic and/or genetic hazards.
Tests Courts Cancerog. Quo Vadis Symposium 57-79 (1981).
3. National Centre for Toxicological Research USA. Notification of approved
protocol. 2 year bioassay in rats administered malachite green or leucomalachite
green in the diet. Project 2128.01. July 1998.
4. Culp SJ, Blankenship LR, Kusewitt DF et al. Metabolic changes occurring
in mice and rats fed leucomalachite green a reduced derivative of the
antifungal agent malachite green. Proceedings of the 88th Annual Meeting
of the American Society for Cancer Research San Diego. p121 (1997).
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