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Research strategy in industrial toxicology
Abstract:
While much of industrial toxicology is observational in character, pursuit of specific research is needed to facilitate the overall evaluation of potential toxicity for man. Two such areas are the application of physiologic pharmacokinetic models to inter-species extrapolation of toxic effects and an understanding of the role of cellular oncogenes in the process of spontaneous tumor formation in animals. A physiologic pharmacokinetic model was developed for methylene chloride (MeCl2) which describes the fate of MeCl2 and its metabolic products in numerous species including the mouse, rat, hamster and man. This model has been used to predict specific tissue concentrations of critical metabolic reaction products in target tissues between animals and man. If it is assumed that toxicity is related to target tissue concentrations such methodology provides a means of relating interspecies toxicity to absorbed dose. This methodology precludes the necessity of using arbitrary factors in relating animal toxicity data to man. A particular controversial issue in animal toxicology is the significance of the enhancement of animal tumors in tissues which already have a high spontaneous incidence. Without a better understanding of the basic process of spontaneous tumor formation it remains difficult to interpret results from chemical treatment. In particular spontaneous liver tumors in the B6C3F1 mouse have been shown to contain an activated cellular oncogene identified as H-RAS. The activated cellular oncogene is present in tumor tissue only and not in surrounding normal liver tissue. Of particular significance is the high frequency of activation in these mouse liver tumors (82%) compared to a 10-20% incidence of oncogenes present in a variety of human tumors. This suggests the ultra sensitivity of this mouse strain to liver tumor induction. Additional studies in progress are designed to determine whether genotoxic and nongenotoxic hepatocarcinogens show differences in oncogene activation.
Insights
Physiologic pharmacokinetic models help predict toxicity across species by relating absorbed dose to target tissue concentration. Understanding cellular oncogenes, like H-RAS in mouse liver tumors, is crucial for interpreting animal toxicology data.
Area of Science:
- Toxicology
- Pharmacokinetics
- Oncology
Background:
- Industrial toxicology often relies on observational data, necessitating further research for accurate human risk assessment.
- Inter-species extrapolation of toxic effects and understanding spontaneous tumor formation are key research areas.
- Spontaneous liver tumors in B6C3F1 mice show high activation of the H-RAS cellular oncogene.
Purpose of the Study:
- To develop and apply a physiologic pharmacokinetic model for methylene chloride (MeCl2) to enable accurate inter-species extrapolation of toxic effects.
- To investigate the role of cellular oncogenes in spontaneous tumor formation and their implications for interpreting chemical toxicity studies in animals.
Main Methods:
- Development of a physiologic pharmacokinetic model for methylene chloride (MeCl2) in multiple species, including humans.
- Analysis of spontaneous liver tumors in B6C3F1 mice to identify activated cellular oncogenes, specifically H-RAS.
- Comparison of oncogene activation frequencies between mouse tumors and human tumors.
Main Results:
- The MeCl2 pharmacokinetic model successfully predicts target tissue concentrations across species, allowing for dose-related toxicity assessments.
- Activated H-RAS oncogenes were found in 82% of spontaneous mouse liver tumors, significantly higher than the 10-20% incidence in human tumors.
- This high oncogene activation frequency suggests extreme sensitivity of this mouse strain to liver tumor induction.
Conclusions:
- Physiologic pharmacokinetic modeling provides a robust method for inter-species toxicity extrapolation, removing the need for arbitrary safety factors.
- Understanding oncogene activation in spontaneous animal tumors is critical for the accurate interpretation of chemical carcinogenicity studies.
- Further research is needed to elucidate the role of oncogenes in chemical carcinogenesis and to compare genotoxic and non-genotoxic carcinogen effects.