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Dose-response relationship for rat liver DNA damage caused by 49 rodent carcinogens
1Carcinogenesis and Metabolism Branch, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711.
Abstract:
An experimental approach was taken to the question of dose-response curves for chemical carcinogenesis. DNA damage in female rat liver was chosen as the experimental parameter because all chemicals found to damage hepatic DNA were rodent carcinogens. The lowest dose causing DNA damage was determined for the 12 active chemicals (1,2-dibromoethane, 1,2-dibromo-3-chloropropane, 1,2-dichloroethane, 1,4-dioxane, methylene chloride, auramine O, Michler's ketone, selenium sulfide, 1,3-dichloropropene, 1,2-dimethylhydrazine, N-nitroso-piperidine and butylated hydroxytoluene). The resulting dose-response curves for rat hepatic DNA damage were plotted versus log of the molar dose (all activity was in five orders of magnitude) and versus percent of chemicals' oral rat LD50 (most of the activity was in only two orders of magnitude). Dose-response studies of the active chemicals were analyzed by regression methods. With the exception of butylated hydroxytoluene, the dose-response curves fit a linear model well (r2 = 0.886) and a quadratic model even better (r2 = 0.947). Based on experimental data from 11 DNA-damaging carcinogens (a dose range of 6 orders of magnitude), an equation and graph of the dose-response relationship of an 'average DNA-damaging carcinogen' is presented over the x-axis dose range of eight orders of magnitude.
Insights
This study establishes dose-response curves for chemical carcinogenesis using DNA damage in rat liver. A linear model explained 88.6% of the variance, while a quadratic model explained 94.7%, identifying an average DNA-damaging carcinogen relationship.
Area of Science:
- Toxicology
- Carcinogenesis Research
- Molecular Biology
Background:
- Chemical carcinogenesis is a complex process involving dose-response relationships.
- Hepatic DNA damage in female rats serves as a reliable experimental parameter for identifying rodent carcinogens.
- Understanding dose-response curves is crucial for risk assessment and regulatory policies.
Purpose of the Study:
- To experimentally determine dose-response curves for chemical carcinogenesis.
- To establish a predictive model for DNA damage induced by various chemicals.
- To characterize the dose-response relationship of an average DNA-damaging carcinogen.
Main Methods:
- Experimental determination of the lowest dose causing DNA damage for 12 active chemicals.
- Plotting dose-response curves for rat hepatic DNA damage against log molar dose and percent of oral rat LD50.
- Regression analysis of dose-response data using linear and quadratic models.
Main Results:
- Dose-response curves for 11 DNA-damaging carcinogens were analyzed.
- A linear model showed a good fit (r2 = 0.886), and a quadratic model showed a better fit (r2 = 0.947).
- An equation and graph representing the dose-response relationship of an average DNA-damaging carcinogen were developed.
Conclusions:
- DNA damage in rat liver is a strong indicator of carcinogenic potential.
- The dose-response relationship for most DNA-damaging carcinogens can be accurately modeled.
- The findings provide a framework for understanding and predicting chemical carcinogenesis based on DNA damage.