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Is enzyme induction good for you? A problem of epidemiology and toxicology
1Department of Clinical Pharmacology, University Collge, London, UK.
Abstract:
1. The discoveries that pre-treatment with certain compounds could increase the amounts of drug metabolizing enzymes present in the liver and that metabolism could enhance as well as reduce the toxicity of exogenous molecules were important milestones in toxicology. 2. Some clinically important adverse effects (vitamin D deficiency, reduced efficacy of oral contraceptives, interactions with anticoagulants) were found to be due to enzyme induction by, for example, anticonvulsants. 3. Intestinal enzymes are also inducible and can respond rapidly to individual compounds while the liver enzymes respond more slowly to the diet as a whole. Although promoting hepatic tumours in rats and mice, phenobarbitone does not have this effect in man because there seems to be a threshold for promotion which human use does not exceed. In neither case is there evidence that induction is harmful rather than adaptive in man. 4. As to the future, post-marketing surveillance will continue to be important in assessing the safety of new products, and knowledge of the metabolism and pharmacokinetics of new compounds in experimental animals and in man will assume greater importance. Finally, greater understanding of intracellular processes will pave the way to the study of toxicology at the macromolecular level and thus to critically assess the validity of the animal models currently used in toxicity testing.
Insights
Enzyme induction by drugs is a key toxicology finding. While it can cause adverse effects, it is often adaptive in humans, unlike in animal models.
Area of Science:
- Toxicology
- Pharmacology
- Drug Metabolism
Background:
- Drug metabolism significantly influences the toxicity of exogenous molecules.
- Enzyme induction by certain compounds can lead to adverse clinical effects, such as vitamin D deficiency and altered drug efficacy.
- Both liver and intestinal enzymes are inducible, with differing response times to stimuli.
Purpose of the Study:
- To review the significance of drug-metabolizing enzyme induction in toxicology.
- To discuss the clinical implications of enzyme induction.
- To explore future directions in toxicology research, including macromolecular studies and animal model validation.
Main Methods:
- Literature review of key discoveries in toxicology and drug metabolism.
- Analysis of clinical adverse effects linked to enzyme induction.
- Discussion of species-specific responses to enzyme inducers like phenobarbitone.
Main Results:
- Enzyme induction is a critical factor in both enhancing and reducing xenobiotic toxicity.
- Clinically relevant adverse effects are associated with enzyme induction by drugs like anticonvulsants.
- Phenobarbitone's tumor-promoting effects in rodents do not translate to humans due to a safety threshold.
Conclusions:
- Enzyme induction appears to be adaptive rather than harmful in humans.
- Future toxicology research requires a deeper understanding of metabolism, pharmacokinetics, and intracellular processes.
- Post-marketing surveillance and improved animal models are crucial for assessing new product safety.