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Influence of drugs on activation and inactivation of hepatocarcinogenic nitrosamines
Abstract:
The alkylation of liver macromolecules following in vivo administration of dimethylnitrosamine (DMN) was diminished after phenobarbital or 3-methylcholanthrene induction of the microsomal monooxygenase system, but increased after SKF 525 A pretreatment. Determination of CH2O and CH3+formation in microsomal incubation systems revealed the same results for low DMN concentrations. An interpretation is given on the basis of spectrophotometric data and electron spinresonance (EPR) measurements, by proposing that metabolic inactivation of nitrosamines is catalysed by a reduction process in which cyt. P 450 seems to be involved.
Insights
Enzyme induction reduced liver damage from dimethylnitrosamine (DMN) by altering its metabolism. Microsomal enzymes, particularly cytochrome P450, appear crucial for detoxifying nitrosamines through a reduction process.
Area of Science:
- Biochemistry
- Toxicology
- Pharmacology
Background:
- Dimethylnitrosamine (DMN) is a potent hepatotoxin.
- Microsomal monooxygenases play a role in xenobiotic metabolism.
- Cytochrome P450 is a key enzyme in these systems.
Purpose of the Study:
- To investigate the effect of microsomal monooxygenase induction on DMN-induced liver macromolecule alkylation.
- To elucidate the metabolic pathways involved in DMN inactivation.
Main Methods:
- In vivo administration of DMN in rats.
- Pretreatment with enzyme inducers (phenobarbital, 3-methylcholanthrene) or inhibitor (SKF 525 A).
- Measurement of liver macromolecule alkylation.
- In vitro determination of CH2O and CH3+ formation in microsomal systems.
- Spectrophotometric and electron spin resonance (EPR) analyses.
Main Results:
- Enzyme induction by phenobarbital or 3-methylcholanthrene decreased DMN-induced liver macromolecule alkylation.
- Inhibition of microsomal enzymes with SKF 525 A increased alkylation.
- In vitro studies confirmed these findings, showing altered CH2O and CH3+ formation.
- Spectrophotometric and EPR data supported the proposed metabolic pathway.
Conclusions:
- Metabolic inactivation of nitrosamines is catalyzed by a reduction process.
- Cytochrome P450 is likely involved in the reductive inactivation of nitrosamines.
- Enzyme induction or inhibition significantly modulates the toxic effects of DMN.