Role of reactive carbonyls and superoxide radicals in protein damage by cigarette smoke extracts: Comparison of Heat-not-Burn e-cigarettes to conventional cigarettes

Oxidative protein damage involving carbonylation of respiratory tract proteins typically accompanies exposure to tobacco smoke. Such damage can arise via multiple mechanisms, including direct amino acid oxidation by reactive oxygen species or protein adduction by electrophilic aldehydes. This study investigated the relative importance of these pathways during exposure of a model protein to fresh cigarette emission extracts. Briefly, protein carbonyl adducts were estimated in bovine serum albumin following incubation in buffered solutions with whole cigarette emissions extracts prepared from either a single 1R6F research cigarette or a single “Heat-not-Burn” e-cigarette. Although both extracts caused concentration-dependent protein carbonylation, conventional cigarette extracts produced higher adduct yields than e-cigarette extracts. Superoxide radical generation by conventional and e-cigarette emissions was assessed by monitoring nitro blue tetrazolium reduction and was considerably lower in extracts made from “Heat-Not-Burn” e-cigarettes. The superoxide dismutase/catalase mimic EUK-134 strongly suppressed radical production by whole smoke extracts from conventional cigarettes, however, it did not diminish protein carbonyl adduction when incubating smoke extracts with the model protein. In contrast, edaravone, a neuroprotective drug with strong carbonyl-trapping properties, strongly suppressed protein damage without inhibiting superoxide formation. Although these findings require extension to appropriate cell-based and in vivo systems, they suggest reactive aldehydes in tobacco smoke make greater contributions to oxidative protein damage than smoke phase radicals.