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Identification of phase I metabolites of 3-methylindole produced by pig liver microsomes
G J Diaz1, K W Skordos, G S Yost
1Department of Animal and Poultry Science, University of Guelph, Guelph, Ontario, Canada.
Abstract:
A study was conducted to investigate qualitative and quantitative aspects of the phase I metabolism of 3-methylindole (3MI) by porcine liver microsomes. Microsomal suspensions were prepared from the liver of 30 intact (uncastrated) male pigs. Metabolites produced in microsomal incubations were identified and quantitated with HPLC-UV, HPLC-fluorescence, and UV-spectral analysis; liquid chromatography-mass spectrometry (LC-MS) and NMR were used for the identification of a metabolite for which a reference compound was not available. The results showed that seven major metabolites of 3MI are produced by porcine microsomes, three of which had already been identified in pigs (3-OH-3-methyloxindole, 5-OH-3-methylindole, and 6-OH-3-methylindole). The other four major 3MI metabolites identified were 3-OH-3-methylindolenine, 3-methyloxindole, indole-3-carbinol, and 2-aminoacetophenone. On average, the metabolite that was produced in larger amounts was 3-OH-3-methylindolenine (45.1%), followed by the two oxindoles 3-methyloxindole (27.9%) and 3-OH-3-methyloxindole (18.5%). Average percentage of production of 6-OH-3-methylindole was 4.9%, whereas indole-3-carbinol accounted for 2.7% of all metabolites produced; 2-amino-acetophenone and 5-OH-3-methylindole were the metabolites produced in lesser amounts (0.5 and 0.3%, respectively). Large interindividual differences in the rate of production of all metabolites were observed. This variation could be attributed to differences in the activity and/or level of expression of phase I biotransformation enzymes and this issue should be further investigated.
Insights
This study identified seven major metabolites of 3-methylindole (3MI) in pig liver microsomes, with 3-OH-3-methylindolenine being the most abundant. Significant interindividual differences in metabolite production were observed, suggesting variations in enzyme activity.
Area of Science:
- Biochemistry
- Pharmacology
- Toxicology
Background:
- 3-methylindole (3MI) is a compound with known toxicological effects.
- Understanding its metabolism is crucial for assessing its biological impact.
- Porcine liver microsomes are a relevant model for studying xenobiotic metabolism.
Purpose of the Study:
- To qualitatively and quantitatively analyze the phase I metabolism of 3-methylindole (3MI) in porcine liver microsomes.
- To identify and quantify the major metabolites of 3MI produced by pig liver enzymes.
- To investigate interindividual variability in 3MI metabolism.
Main Methods:
- Preparation of microsomal suspensions from intact male porcine liver.
- Metabolite identification and quantification using High-Performance Liquid Chromatography with UV and fluorescence detection, UV-spectral analysis, Liquid Chromatography-Mass Spectrometry (LC-MS), and Nuclear Magnetic Resonance (NMR).
Main Results:
- Seven major 3MI metabolites were identified: 3-OH-3-methyloxindole, 5-OH-3-methylindole, 6-OH-3-methylindole, 3-OH-3-methylindolenine, 3-methyloxindole, indole-3-carbinol, and 2-aminoacetophenone.
- 3-OH-3-methylindolenine (45.1%), 3-methyloxindole (27.9%), and 3-OH-3-methyloxindole (18.5%) were the most abundant metabolites.
- Significant interindividual differences in the production rates of all identified metabolites were observed.
Conclusions:
- Porcine liver microsomes metabolize 3MI into seven major compounds, with distinct quantitative profiles.
- The observed interindividual variability in metabolism likely stems from differences in Phase I enzyme activity or expression.
- Further investigation into the specific enzymes and genetic factors contributing to this variability is warranted.