Unexpected products of the hypochlorous acid-induced oxidation of oleic acid: A study using high performance thin-layer chromatography–electrospray ionization mass spectrometry

• The products of the reaction between oleic acid (OA) and HOCl were evaluated.
• In addition to TLC and ESI MS, combined TLC/MS and MS/MS were used.
• Beside the expected chlorohydrin (CH) as main product, CH dimers are also generated.
• It will be shown that isomers of the CH dimer can be separated by NP TLC.
• When oleic acid is bound to a lipid, no dimers are generated.

Reactive oxygen species (ROS) play important physiological roles and are of particular relevance in the pathogenesis of inflammatory diseases. At inflammatory conditions, the enzyme myeloperoxidase generates hypochlorous acid (HOCl) which adds to the double bonds of fatty acyl residues of (phospho)lipids under the formation of chlorohydrins. This may lead to the development of many inflammatory diseases, such as atherosclerosis or arthritis, if the ROS generation exceeds a certain extent. Using oleic acid as the simplest unsaturated fatty acid which contains just a single double bond, as a model system, we investigated all products – including the chlorohydrin – after its reaction with HOCl by a combination of thin-layer chromatography and electrospray ionization mass spectrometry. Unlike the general acceptance, the reaction of oleic acid and HOCl leads not exclusively to the formation of chlorohydrin (isomers) but is much more complex: there are also considerable amounts of dimeric and (to a minor extent) trimeric products which can be assigned to isomeric ethers and esters. The obtained products after oleic acid chlorination were also compared with the reaction products of 1-palmitoyl-2-oleoyl-sn-phosphatidylcholine (POPC) and HOCl. The reasons why different products are obtained will be discussed and the involvement of the carboxylic acid emphasized.