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Genetic aspects of toxicity during development
Abstract:
The Ah locus in the mouse controls the induction of cytochrome P1-450 and at least eleven associated monooxygenase activities. These enzyme systems metabolically potentiate and detoxify drugs, environmental pollutants, and other foreign chemicals, as well as numerous endogenous substrates. For certain substrates, it is known that cytochrome P1-450 produces different reactive intermediates and products that other forms of P-450. Alleles at the Ah locus can be identified in utero. Development toxicity (in the form of stillborns, resorptions, and malformations of the fetus) by 3-methylcholanthrene and 7,12-dimethylbenz[a]anthracene given to the pregnant mother is associated with genetically mediated aromatic hydrocarbon responsiveness in C5BL/6N mice, compared with that in nonresponsive AKR/N mice. Acetaminiphen-produced hepatic necrosis is associated with glutathione depletion in the liver, covalent binding of metabolite(s) of the drug to cellular macromolecules, and P1-450 induction controlled by the Ah locus. For reasons not known, the fetus and mice 10 days of age or less are relatively resistant to glutathione depletion and therefore hepatic necrosis by acetaminophen.
Insights
The Ah locus in mice influences detoxification enzymes, affecting fetal development and drug toxicity. Genetic variations in aromatic hydrocarbon responsiveness impact susceptibility to developmental toxicity and acetaminophen-induced liver damage.
Area of Science:
- Pharmacology
- Toxicology
- Genetics
Background:
- The Ah locus regulates cytochrome P1-450 and associated monooxygenase activities, crucial for metabolizing foreign chemicals and endogenous substrates.
- Cytochrome P1-450 enzymes play a role in potentiating and detoxifying various compounds, with different P450 forms producing distinct reactive intermediates.
- Genetic variations in the Ah locus can be identified early and influence an organism's response to environmental factors and xenobiotics.
Purpose of the Study:
- To investigate the role of the Ah locus in mediating developmental toxicity from aromatic hydrocarbons.
- To explore the association between Ah locus-controlled P1-450 induction and acetaminophen-induced hepatic necrosis.
- To understand the relative resistance of fetuses and young mice to acetaminophen toxicity.
Main Methods:
- Utilizing genetically distinct mouse strains (C5BL/6N responsive vs. AKR/N nonresponsive) to study Ah locus effects.
- Administering developmental toxicants (3-methylcholanthrene, 7,12-dimethylbenz[a]anthracene) to pregnant dams.
- Examining acetaminophen-induced hepatic necrosis in relation to glutathione levels, drug metabolite binding, and P1-450 induction.
Main Results:
- Developmental toxicity, including stillbirths and malformations, was associated with genetically mediated aromatic hydrocarbon responsiveness.
- Acetaminophen-induced hepatic necrosis correlated with glutathione depletion, covalent binding of metabolites, and Ah locus-controlled P1-450 induction.
- Fetuses and young mice (≤10 days old) exhibited relative resistance to acetaminophen-induced glutathione depletion and subsequent hepatic necrosis.
Conclusions:
- The Ah locus is a critical genetic determinant of susceptibility to both developmental toxicity and drug-induced organ damage.
- Understanding Ah locus variations is vital for predicting individual responses to environmental pollutants and therapeutic agents.
- Age-dependent resistance mechanisms in neonates warrant further investigation regarding xenobiotic metabolism and detoxification pathways.