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[Environmental carcinogens: mechanisms of action and occurrence. Some aspects (author's transl)]
Abstract:
New aspects on the mechanism of action of known environmental carcinogens are described. These compounds are not active as such, but are bioactivated in the mammalian metabolism via chemically reactive intermediates to electrophilic reactants, forming with information-bearing biopolymeres covalent bonds. This change in the genetic code is in agreement with the mutation hypothesis of carcinogenesis. Aflatoxin B1, N-nitroso compounds and benzo(a)pyrene are taken as examples. "Threshold levels", e.g. no-effect-levels derived from animal experiments with all their inherent limitations, are compared with data from human exposure to benzo(a)pyren, aflatoxine, N-nitroso compounds and vinyl chloride. The difficulties of such risk evaluations are discussed.
Insights
Environmental carcinogens require metabolic activation to become harmful, forming DNA adducts that support the mutation theory of cancer. Risk assessment for compounds like aflatoxin B1 and benzo(a)pyrene is complex due to species differences.
Area of Science:
- Environmental Health
- Toxicology
- Molecular Biology
Context:
- Environmental carcinogens are ubiquitous and pose significant public health risks.
- Understanding their mechanism of action is crucial for effective risk assessment and mitigation.
- Existing risk evaluation methods face challenges due to species-specific metabolic activation and exposure variability.
Purpose:
- To elucidate the bioactivation pathways of environmental carcinogens.
- To examine the validity of the mutation hypothesis of carcinogenesis using specific examples.
- To compare animal-derived threshold levels with human exposure data for key carcinogens.
Summary:
- Environmental carcinogens are procarcinogens, requiring metabolic activation into reactive electrophilic intermediates.
- These intermediates form covalent bonds with biopolymers, leading to genetic alterations consistent with the mutation hypothesis.
- Examples like Aflatoxin B1, N-nitroso compounds, and benzo(a)pyrene illustrate this mechanism.
Impact:
- Highlights the complexity of carcinogenesis, emphasizing metabolic activation as a key step.
- Underscores the limitations of animal models in extrapolating human cancer risk.
- Informs public health policy and regulatory approaches to environmental carcinogen exposure.