Aldehydes, hydrogen peroxide, and organic radicals as mediators of ozone toxicity

It is generally agreed that unsaturated fatty acids (UFA) are an important class of target molecule for reaction with ozone when polluted air is inhaled. Most discussions have implicated the UFA in cell membranes, but long lining fluids also contain fatty acids that are from 20 to 40% unsaturated. Since UFA in lung lining fluids exist in a highly aquated environment, ozonation would be expected to produce aldehydes and hydrogen peroxide, rather then the Criegee ozonide. In agreement with this expectation, we find that the ozonations of emulsions of fatty acids containing from one to four double bonds give one mole of H 2O 2 for each mole of ozone reacted. Ozonation of oleic acid emulsion and dioleoyol phaphatidyl choline gives similar results, with two moles of aldehydes and one mole H 2O 2 formed per mole of ozone reacted. The net reaction that occurs when ozone reacts with pulmonary lipids is suggested to be giben by equation 1. RCH = CHR′ + H 2O ---> RCH = O + R′CH = O + H 2O 2 From 5 to 10% yields of Criegee ozonides also appear to be formed. In addition, a direct reaction of unknown mechanism occurs between ozone and UFA in homogenous organic solution, in homogenous solutions in water, in aqueous emulsions, and in lipid bilayers to give organic radicals that can be spin trapped. These radicals are suggested to be responsible for initiating lipid peroxidation of polyunsaturated fatty acids. Thus, aldehydes, hydrogen peroxide, and directly produced organic radicals are suggested to be mediators of ozone-induced pathology.