Glutathione conjugation of busulfan produces a hydroxyl radical-trapping dehydroalanine metabolite

Xenobiotica. 2012 Dec;42(12):1170-7. doi: 10.3109/00498254.2012.696740. Epub 2012 Jun 22.

Abstract

The Phase 2 drug metabolism of busulfan yields a glutathione conjugate that undergoes a β-elimination reaction. The elimination product is an electrophilic metabolite that is a dehydroalanine-containing tripeptide, γ-glutamyldehydroalanylglycine (EdAG). In the process, glutathione lacks thiol-related redox properties and gains a radical scavenging dehydroalanine group. EdAG scavenged hydroxyl radical generated in the Fenton reaction in a concentration-dependent manner was monitored by electron paramagnetic resonance (EPR) spectroscopy. The apparent rate of hydroxyl radical scavenging was in the same range as published values for known antioxidants, including N-acyl dehydroalanines. A captodatively stabilized carbon-centered radical intermediate was spin trapped in the reaction of EdAG with hydroxyl radical. The proposed structure of a stable product in the Fenton reaction with EdAG was consistent with that of a γ-glutamylserylglycyl dimer. Observation of the hydroxyl trapping properties of EdAG suggests that the busulfan metabolite EdAG may contribute to or mitigate redox-related cytotoxicity associated with the therapeutic use of busulfan, and reaffirms indicators that support a role in free radical biology for dehydroalanine-containing peptides and proteins.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Alanine / analogs & derivatives*
  • Alanine / metabolism
  • Antioxidants / metabolism
  • Biocatalysis
  • Busulfan / chemistry
  • Busulfan / metabolism*
  • Chromatography, Liquid
  • Cyclic N-Oxides / metabolism
  • Electron Spin Resonance Spectroscopy
  • Glutathione / metabolism*
  • Glutathione Transferase / metabolism
  • Hydrogen Peroxide / chemistry
  • Hydroxyl Radical / chemistry
  • Hydroxyl Radical / metabolism*
  • Iron / chemistry
  • Kinetics
  • Oxidation-Reduction
  • Pyridines / metabolism
  • Tandem Mass Spectrometry

Substances

  • Antioxidants
  • Cyclic N-Oxides
  • Fenton's reagent
  • Pyridines
  • alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone
  • Hydroxyl Radical
  • dehydroalanine
  • Hydrogen Peroxide
  • Iron
  • Glutathione Transferase
  • Busulfan
  • Glutathione
  • Alanine