β-Carotene metabolites enhance inflammation-induced oxidative DNA damage in lung epithelial cells

β-Carotene (BC) intake has been shown to enhance lung cancer risk in smokers and asbestos-exposed subjects (according to the ATBC and CARET studies), but the mechanism behind this procarcinogenic effect of BC is unclear. Both smoking and asbestos exposure induce an influx of inflammatory neutrophils into the airways, which results in an increased production of reactive oxygen species and formation of promutagenic DNA lesions. Therefore, the aim of our study was to investigate the effects of BC and its metabolites (BCM) on neutrophil-induced genotoxicity. We observed that the BCM vitamin A (Vit A) and retinoic acid (RA) inhibited the H2O2-utilizing enzyme myeloperoxidase (MPO), which is released by neutrophils, thereby reducing H2O2 conversion. Moreover, BC and BCM were able to increase ·OH formation from H2O2 in the Fenton reaction (determined by electron spin resonance spectroscopy). Addition of Vit A and RA to lung epithelial cells that were co-incubated with activated neutrophils resulted in a significant increase in the level of oxidized purines assessed by the formamidopyrimidine DNA glycosylase-modified comet assay. These data indicate that BCM can enhance neutrophil-induced genotoxicity by inhibition of MPO in combination with subsequent increased formation of hydroxyl radicals.