Experimental Study on How Human Lung Surfactant Protein SP-B1-25 is Oxidized by Ozone in the Presence of Fe(II) and Ascorbic Acid

We will report the results of experiments on the chemical fate of the human lung surfactant protein SP-B_1-25 upon exposure to gaseous ozone in realistic aqueous media simulating the conditions prevalent in epithelial lining fluids in polluted ambient air. Our experiments consist of exposing aqueous microjets containing SP-_B1-25, the natural antioxidant ascorbic acid, and the Fe²⁺ carried by most atmospheric fine particulates, under mild acidic conditions, such as those created by the innate lung host defense response. Reactants and the products of such interactions are detected via online electrospray ionization mass spectrometry. We will show that ascorbic acid largely inhibits the ozonation of SP-_B1-25 in the absence of Fe²⁺, leading to the formation of an ascorbic acid ozonide (Enami et al., PNAS 2008). In the presence of Fe²⁺, however, the ozonide decomposes into reactive intermediates that result in the partial oxidation of SP-_B1-25, presumable affecting its function as surfactant. We infer that these experimental results establish a plausible causal link for the observed synergic adverse health effects of ambient ozone and fine particulates