Related Experiment Video

Updated: Aug 18, 2026

Mass Spectrometry and Luminogenic-based Approaches to Characterize Phase I Metabolic Competency of In Vitro Cell Cultures
10:44

Mass Spectrometry and Luminogenic-based Approaches to Characterize Phase I Metabolic Competency of In Vitro Cell Cultures

Published on: March 28, 2017

Bioactivation of 4-ipomeanol by CYP4B1: adduct characterization and evidence for an enedial intermediate

Brian R Baer1, Allan E Rettie, Kirk R Henne

  • 1Department of Medicinal Chemistry, School of Pharmacy, University of Washington, Seattle, Washington 98195, USA.

Chemical Research in Toxicology
|May 17, 2005
PubMed

Insights

4-Ipomeanol (IPO) is bioactivated to a reactive intermediate by cytochrome P450 enzymes. This study identifies the intermediate as an enedial and reveals multiple human P450s involved in IPO bioactivation.

Area of Science:

  • Biochemistry
  • Toxicology
  • Pharmacology

Background:

  • 4-Ipomeanol (IPO) is a known pneumotoxin requiring bioactivation to exert its toxic effects.
  • The precise structure of the reactive intermediate formed during IPO bioactivation has remained elusive despite extensive research.
  • Understanding this intermediate is crucial for elucidating IPO's mechanism of toxicity.

Purpose of the Study:

  • To elucidate the structural nature of the reactive intermediate formed during 4-Ipomeanol (IPO) bioactivation.
  • To identify the specific cytochrome P450 (CYP) enzymes responsible for IPO bioactivation.
  • To characterize the reaction products formed when IPO is incubated with CYP enzymes and nucleophiles.

Main Methods:

  • Incubation of IPO with rabbit CYP4B1 and nucleophiles (glutathione, N-acetyl cysteine, N-acetyl lysine).
  • Analysis of reaction products using liquid chromatography/electrospray ionization-mass spectrometry (LC/ESI-MS).
  • Structural elucidation of the IPO adduct using high-resolution mass spectrometry and two-dimensional NMR spectroscopy.

Main Results:

  • A major NADPH- and CYP4B1-dependent product was identified when IPO was incubated with N-acetyl cysteine (NAC) and N-acetyl lysine (NAL).
  • Structural analysis confirmed the formation of an N-substituted cysteinyl pyrrole derivative of IPO, indicating an enedial reactive intermediate.
  • Significant IPO bioactivation rates were observed with human CYP1A2, CYP2C19, CYP2D6, and CYP3A4, in addition to rabbit CYP4B1.

Conclusions:

  • CYP-mediated bioactivation of 4-Ipomeanol (IPO) generates a reactive enedial intermediate.
  • Multiple human cytochrome P450 enzymes, including CYP1A2, CYP2C19, CYP2D6, and CYP3A4, are capable of bioactivating IPO.
  • The same reactive intermediate is formed by both rabbit CYP4B1 and human P450 enzymes, suggesting a conserved bioactivation pathway.

More Related Videos

Formation of Covalent DNA Adducts by Enzymatically Activated Carcinogens and Drugs In Vitro and Their Determination by 32P-postlabeling09:33

Formation of Covalent DNA Adducts by Enzymatically Activated Carcinogens and Drugs In Vitro and Their Determination by 32P-postlabeling

Published on: March 20, 2018

Enzymatic Synthesis of Epoxidized Metabolites of Docosahexaenoic, Eicosapentaenoic, and Arachidonic Acids13:05

Enzymatic Synthesis of Epoxidized Metabolites of Docosahexaenoic, Eicosapentaenoic, and Arachidonic Acids

Published on: June 28, 2019

Related Concept Videos

Drug Metabolism: Phase I Reactions01:17

Drug Metabolism: Phase I Reactions

A phase I reaction is a biochemical process that introduces a functionally reactive polar group to a substance. This transformation predominantly occurs in the liver, facilitated by the cytochrome P450 system of hemoproteins situated in the lipophilic endoplasmic reticulum of cells. The metabolite generated through this process can have varying polarities. If it is sufficiently polar, it can be easily excreted in the urine due to its water compatibility. However, if the metabolite is nonpolar,...
Phase I Reactions: Oxidation of Aliphatic and Aromatic Carbon-Containing Systems01:19

Phase I Reactions: Oxidation of Aliphatic and Aromatic Carbon-Containing Systems

Phase I biotransformation reactions are integral to drug metabolism, predominantly involving oxidative, reductive, and hydrolytic transformations. Chief among these are oxidative reactions, which enhance the hydrophilicity of xenobiotics and introduce polar functional groups to facilitate their elimination from the body.
Oxidation reactions are fundamental in aromatic carbon-containing systems. An example is the hydroxylation of phenobarbital, a process that transforms it into...
Bioactivation and Tissue Toxicity01:25

Bioactivation and Tissue Toxicity

Bioactivation is a metabolic process that transforms less reactive substances into highly reactive metabolites, initiating tissue toxicity. This transformation can lead to various toxic effects, including carcinogenesis and teratogenesis. Reactive metabolites are classified into two main types: electrophiles and free radicals.Electrophiles are electron-deficient species and are produced primarily by the enzyme cytochrome P-450 during the metabolism of compounds containing carbon, nitrogen, or...
Pharmacogenetics of Phase I Enzymes: Cytochrome P450 Isozymes01:28

Pharmacogenetics of Phase I Enzymes: Cytochrome P450 Isozymes

Cytochrome P450 (CYP450) enzymes are a superfamily of heme-containing monooxygenases that play a pivotal role in Phase I drug metabolism by catalyzing oxidation and reduction reactions.These enzymes transform lipophilic xenobiotics into more hydrophilic metabolites, facilitating subsequent Phase II conjugation and eventual excretion. The CYP450 family is classified into families (e.g., CYP1–CYP3) and subfamilies (e.g., CYP2A, CYP2C), based on amino acid sequence homology.CYP450 isoenzymes,...
Phase I Oxidative Reactions: Overview01:19

Phase I Oxidative Reactions: Overview

Phase I biotransformation, or functionalization, is a crucial chemical process that converts drugs and other xenobiotics into more water-soluble forms, facilitating expulsion from the body. It involves oxidative, reductive, and hydrolytic reactions that add or unveil polar functional groups on lipophilic substrates. Key players in phase I reactions are the mixed-function oxidases. Situated in liver cell microsomes, these enzymes predominantly carry out drug metabolism. They require molecular...
Reactivity of Enols01:18

Reactivity of Enols

Enols are a class of compounds where a hydroxyl group is attached to a carbon–carbon double bond, which implies that it is a vinyl alcohol. A carbonyl compound with an α hydrogen undergoes keto–enol tautomerism and remains in equilibrium with its tautomer, the enol form. Usually, the keto tautomer is present in a higher concentration than the enol tautomer due to the higher bond energy of C=O compared to C=C. Moreover, the direction of the keto–enol equilibrium is governed by factors like...