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[Specific inhibition of nuclear DNA synthesis with carcinogens (autoradiography studies of a short-term test)]
Abstract:
Six suckling growing CBA mice 14 days old (5-6 g of body weight) of the same litter served as test animals in each experiment. 0.1 ml of the dissolved chemicals (15-30 per cent of the LD50 were applied by i.p. injection to 3 animals each (experiment) and an equal number of mice was treated with the solvent only (control). 15 hours later the animals were given a single i.p. injection of 3H thymidine (2 microCi/g body weight) and 50 min afterwards they were sacrificed for autopsy and preparation of autoradiographs. Autoradiographs of nuclei of renal tubular epithelia and of liver epithelium were examined by visual silver grain counting (150 nuclei in each experiment and the same number in the corresponding control). We could demonstrate that carcinogenic compounds of different chemical classes partially inhibit the nuclear incorporation of thymidine in a significant manner over a time period longer than 24 hours. This inhibition may be due as a consequence of a prolonged S phase, expressed as a decrease of the mean of silver grain number per nucleus in comparison with the unaltered control. This decrease is used as a criterion for the suppressive effect of carcinogenic substances on the nuclear DNA synthesis rate. Noncarcinogenic compounds did not show this effect.
Insights
Carcinogenic chemicals significantly inhibit DNA synthesis in mouse cells, indicated by reduced thymidine incorporation. This effect, observed over 24 hours, suggests a prolonged S phase and serves as a marker for carcinogenicity.
Area of Science:
- Biochemistry
- Toxicology
- Molecular Biology
Context:
- Assessing the impact of chemical exposure on cellular processes is crucial for understanding toxicity.
- Nuclear DNA synthesis is a fundamental process sensitive to environmental and chemical insults.
Purpose:
- To investigate the effect of carcinogenic compounds on nuclear DNA synthesis rate in vivo.
- To establish a criterion for evaluating the suppressive effect of carcinogens on DNA synthesis.
Summary:
- Carcinogenic compounds from various chemical classes were administered to CBA mice.
- Nuclear incorporation of 3H-thymidine was measured in renal tubular and liver epithelial cells 15 hours post-injection.
- A significant decrease in silver grain count per nucleus, indicating inhibited DNA synthesis and a prolonged S phase, was observed for carcinogenic compounds compared to controls.
Impact:
- Demonstrates that carcinogenic substances can suppress nuclear DNA synthesis rate.
- Provides a potential biomarker for carcinogenicity based on the inhibition of thymidine incorporation.
- Highlights the utility of autoradiography and silver grain counting in toxicological assessments.