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Species differences in the interaction between CCl4 reactive metabolites and liver DNA or nuclear protein fractions
G D Castro1, M I Díaz Gómez, J A Castro
1Centro de Investigaciones Toxicológicas (CEITOX) - CITEFA/CONICET, Pcia. de Buenos Aires, Argentina.
Abstract:
CCl4 has been reported to be a liver carcinogen for several mice strains, for Syrian Golden hamsters, but not for Sprague-Dawley rats. CCl4 is an experimental carcinogen for which no convincing evidence of mutagenicity is available despite the fact that CCl4 reactive metabolites bind covalently to liver DNA. Here we describe studies on the relationship between the intensities of the covalent binding (CB) of CCl4 reactive metabolites to liver DNA and nuclear proteins either in vivo or in vitro after activation to reactive metabolites by nuclear preparations, considering the known susceptibility of the C3H mice, Syrian Golden hamsters and Sprague-Dawley rats to CCl4. There was no correlation between the intensity of CCl4 carcinogenic effects on the liver and CB of CCl4 reactive metabolites to total DNA either in vitro or in vivo. A good correlation between carcinogenicity and CB to total nuclear proteins (in vivo or in vitro was found. Nuclear protein fractionation studies revealed CB of CCl4 reactive metabolites to both histone and non-histone proteins when nuclear preparations activated CCl4 either in the presence or absence of NADPH. Acidic and residual nuclear proteins were the favorite targets of the interaction with CCl4 reactive metabolites. A good correlation between CB to these nuclear protein fractions and CCl4 carcinogenicity in the three species was found.
Insights
Carbon tetrachloride (CCl4) carcinogenicity correlates with covalent binding to nuclear proteins, not DNA. This binding to histone and non-histone proteins explains CCl4
Area of Science:
- Toxicology
- Carcinogenesis
- Biochemistry
Background:
- Carbon tetrachloride (CCl4) is a known liver carcinogen in some species but not others.
- Evidence for CCl4 mutagenicity is lacking, despite reactive metabolite binding to DNA.
Purpose of the Study:
- To investigate the relationship between covalent binding (CB) of CCl4 reactive metabolites and CCl4 carcinogenicity in susceptible species.
- To determine if binding to DNA or nuclear proteins better predicts CCl4's carcinogenic potential.
Main Methods:
- In vivo and in vitro studies of CCl4 reactive metabolite binding to liver DNA and nuclear proteins.
- Analysis of binding in C3H mice, Syrian Golden hamsters, and Sprague-Dawley rats.
- Fractionation of nuclear proteins to identify specific binding targets.
Main Results:
- No correlation was found between CCl4 carcinogenicity and CB to total liver DNA.
- A strong correlation was observed between CCl4 carcinogenicity and CB to total nuclear proteins (in vivo and in vitro).
- Acidic and residual nuclear proteins showed the highest correlation with CCl4 carcinogenicity.
Conclusions:
- CCl4 carcinogenicity is linked to covalent binding of its reactive metabolites to nuclear proteins, particularly acidic and residual fractions.
- This binding to nuclear proteins, rather than DNA, is a key factor in CCl4-induced liver cancer across different species.