Thiyl radicals--formation during peroxidase-catalyzed metabolism of acetaminophen in the presence of thiols.

We confirm using EPR spectroscopy in conjunction with the spin probe 2-ethyl-1-hydroxy-2,5,5-trimethyl-3-oxazolidine (OXANOH) that horseradish peroxidase catalyzed metabolism of the analgesic acetaminophen occurs via a one electron mechanism. When either glutathione cysteine or N-acetylcysteine were included in the reaction the thiols reduced the acetaminophen-derived radicals to generate thiyl radicals which were trapped with the spin trap 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and observed using EPR spectroscopy. Similarly, DMPO-thiyl radical adducts were observed during prostaglandin synthase catalyzed oxidation of acetaminophen in the presence of either glutathione or N-acetylcysteine. This is a mechanism of removal of reactive xenobiotic free radicals generated in metabolic systems but whether it represents a true detoxification reaction depends on the subsequent fate of the thiyl radicals generated.