Related Experiment Videos
Aflatoxin B1 metabolism by 3-methylcholanthrene-induced hamster hepatic cytochrome P-450s
1Department of Biochemistry and Molecular Pathology, Northeastern Ohio Universities College of Medicine, Rootstown 44272.
Abstract:
We have studied the activation of aflatoxin B1 by hamster liver microsomes and purified hamster cytochrome P-450 isozymes using a umu mutagen test. The hamster liver microsomes or S-9 fractions were much more active than rat liver microsomes or S-9 fractions in the activation of umu gene expression by aflatoxin B1 metabolites. 3-Methyl-cholanthrene treatment increased aflatoxin B1 activation by hamster liver microsomes. Two major 3-methylcholanthrene-inducible cytochrome P-450 isozymes, P-450 MC1 (IIA) and P-450 MC4 (IA2), were purified from 3-methylcholanthrene-treated hamster liver microsomes, and the metabolism of aflatoxin B1 by these two cytochromes was studied. In the reconstituted enzyme system, both P-450 MC1 and P-450 MC4 were highly active in the activation of aflatoxin B1, and antibodies against these P-450s specifically inhibited these activities. Antibody against P-450 MC1 inhibited the activation of aflatoxin B1 by 20% in the presence of 3-methyl-cholanthrene-treated hamster liver microsomes. In contrast, antibody against P-450 MC4 stimulated the activity by 175%. These results indicated that hamster P-450 MC1 might convert aflatoxin B1 to more toxic metabolite(s), whereas P-450 MC4 might convert aflatoxin B1 to less toxic metabolite(s), than aflatoxin B1 in liver microsomes. The metabolite(s) produced by both hamster cytochrome P-450 MC1 and MC4 were genotoxic in the umu mutagen test.
Insights
Hamster liver enzymes activate aflatoxin B1 more effectively than rat enzymes. Specific cytochrome P-450 isozymes (P-450 MC1 and P-450 MC4) play distinct roles in detoxifying or activating this toxin.
Area of Science:
- Toxicology
- Biochemistry
- Enzymology
Background:
- Aflatoxin B1 is a potent carcinogen requiring metabolic activation.
- Cytochrome P-450 enzymes are crucial for xenobiotic metabolism, including the activation of mycotoxins.
- Species-specific differences in cytochrome P-450 activity influence toxicological outcomes.
Purpose of the Study:
- To investigate the role of hamster liver microsomes and specific cytochrome P-450 isozymes in aflatoxin B1 activation.
- To compare the aflatoxin B1 activating capacity of hamster and rat liver enzymes.
- To elucidate the differential roles of hamster cytochrome P-450 MC1 and P-450 MC4 in aflatoxin B1 metabolism.
Main Methods:
- Utilized the umu mutagen test to assess genotoxicity of aflatoxin B1 metabolites.
- Employed hamster and rat liver microsomes and S-9 fractions.
- Purified 3-methylcholanthrene-inducible hamster cytochrome P-450 isozymes (P-450 MC1 and P-450 MC4).
- Used reconstituted enzyme systems with purified isozymes and specific antibodies.
Main Results:
- Hamster liver microsomes exhibited significantly higher aflatoxin B1 activation than rat liver microsomes.
- 3-Methylcholanthrene treatment enhanced aflatoxin B1 activation in hamster liver microsomes.
- Both purified P-450 MC1 and P-450 MC4 activated aflatoxin B1, producing genotoxic metabolites.
- Antibody against P-450 MC1 decreased activation, while antibody against P-450 MC4 increased activation, suggesting opposing roles in detoxification/activation.
Conclusions:
- Hamster cytochrome P-450 enzymes, particularly P-450 MC1 and P-450 MC4, are key players in aflatoxin B1 activation.
- P-450 MC1 may generate more toxic metabolites, whereas P-450 MC4 might produce less toxic ones.
- The genotoxic metabolites generated by both isozymes highlight the importance of these enzymes in aflatoxin B1's toxicological profile.