Trapping DNA radicals with DMPO reduces hypochlorous acid-induced 8-oxo-7,8-dihydro-2'-deoxyguanosine and mutagenesis in lung epithelial cells

Abstract

Pulmonary neutrophilic inflammation (PNI) is the recruitment and activation of neutrophils in themicrovasculature with the release of myeloperoxidase (MPO) in the airways. Bystanderepithelial cells can take up MPO, where it can generate HOCl. HOCl can react with DNA,generating DNA radicals, which then decay to produce several mutagenic end-oxidationproducts, such as 8-oxo-7,8-dihydro-2´–deoxyguanosine (8-oxo-dGuo). Herein, we aimed to testwhether HOCl-induced DNA radicals precede DNA oxidation and mutagenesis in A549 humanlung epithelial cells as an in vitro model that resembles PNI. Interestingly, by trapping HOClinduced DNA radicals, the nitrone spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) blocks theformation of 8-oxo-dGuo and possibly other end-oxidation products, forming DNA‒DMPOnitrone adducts. By preventing DNA oxidation, DMPO reduces the mutation of the hypoxanthinephosphoribosyl transferase (hrpt) gene, one of the genes most sensitive to oxidative damage.The transcription factor p53 is known as the master regulator of the cell response to genomicdamage. By trapping DNA radicals, DMPO also blocks the translocation of p53 to the cellnucleus, suggesting that by trapping DNA radicals with DMPO, end-oxidation products areprevented, and the cell response to genomic damage is blunted. Trapping DNA radicals to reduce the accumulation of HOCl-induced mutagenic end-oxidation products will provide newtherapeutic avenues to reduce genotoxic damage during PNI.