O3-induced formation of bioactive lipids: estimated surface concentrations and lining layer effects

Recent evidence suggests that inhaled ozone (O3) does not induce toxicity via direct epithelial interactions. Reactions with epithelial lining fluid (ELF) constituents limit cellular contact and generate products, including lipid ozonation products, postulated to initiate pathophysiological cascades. To delineate specific aspects of lipid ozonation product formation and to estimate in situ surface concentrations, we studied the O3absorption characteristics of ELF constituent mixtures and measured hexanal, heptanal, and nonanal yields as a function of ascorbic acid (AH2) concentration. Exposures of isolated rat lungs, bronchoalveolar lavage fluid (BALF) and egg phosphatidylcholine (PC) liposomes were conducted. 1) O3 absorption by AH2, uric acid, and albumin exceeded that by egg PC and glutathione. O3 reaction with egg PC occurred when AH2 concentrations were reduced. 2) Aldehydes were produced in low yield during lung and BALF exposures in a time- and O3 concentration-dependent manner. 3) Diminishing BALF AH2 content lowered O3 uptake but increased aldehyde yields. Conversely, AH2 addition to egg PC increased O3 uptake but reduced aldehyde yields. Estimations of bioactive ozonation and autoxidation product accumulation within the ELF suggested possible nanomolar to low micromolar concentrations. The use of reaction products as metrics of O3 exposure may have intrinsic sensitivity and specificity limitations. Moreover, due to the heterogenous nature of O3 reactions within the ELF, dose-response relationships may not be linear with respect to O3 absorption.

Mechanisms of Ozonation of N-(1,3-Dimethylbutyl)-N′-Phenyl-p-Phenylenediamine

The ozonation products of a common rubber antiozonant, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (HPPD), have been separated by liquid chromatography and identified by mass spectrometry. Three principal mechanisms appear to govern the ozonation of HPPD. Amine oxide formation leads to observed nitrosoaryl and nitroaryl products. Side-chain oxidation leads to several low molecular weight products, including some that contain an amide moiety. Nitroxide radical formation leads to a nitrone that is the most abundant ozonation product; a dinitrone is also formed. Ozonation of HPPD occurs mainly with degradation of the alkyl portion of the molecule. The results of this study are consistent with a combined “scavenger-protective film” theory of antiozonant protection of rubber compounds.