Exposure of calf thymus DNA to autoxidized β-carotene results in the formation of 8-oxo-deoxyguanosine

Oxidized β-carotene (OBC) has been shown to have pro-oxidant and pro-carcinogenic effects. We recently reported that OBC induces oxidative DNA damage, measured as 8-hydroxy-deoxyguanosine (8-oxo-dG), in both calf thymus DNA and cellular DNA. However, the mechanism by which OBC induces the formation of 8-oxo-dG is unclear. To examine the hypothesis that reactive oxygen species (ROS), produced by BC autoxidation, cause the formation of 8-oxo-dG, radical scavengers were added to calf thymus DNA incubated with OBC. The results showed that butylated hydroxytoluene (BHT), a peroxyl radical scavenger, and diphenylamine, an alkoxyl radical scavenger, strongly decreased 8-oxo-dG levels. Singlet oxygen (1O2) was also a major ROS involved while small but detectable amounts of •OH were produced. Autoxidation of BC itself at 60 or 37 °C produced aldehydes (measured as cyclohexanedione-reactive substances) and thiobarbituric acid-reactive substances (TBARS), suggesting the presence of chain-propagated reactions during autoxidation. Thus, the present study demonstrates that ROS, produced by BC autoxidation, induce the formation of 8-oxo-dG in calf thymus DNA.