Serum octadeca-9,11 dienoic acid--an assay of free radical activity or a result of bacterial production?

The diene conjugated linoleic acid isomer is currently used as an assay of free radical activity, but recent studies have cast doubt on the specificity of the assay. Therefore, 180 strains of common bacterial lung pathogens were studied to determine whether they could produce the diene conjugated isomer of linoleic acid in vitro. The various strains were grown in tissue culture fluid spiked with linoleic acid. Concentrations of the diene conjugated 18:2 [9,11] linoleic acid isomer and the parent compound, 18:2 [9,12] linoleic acid were then determined using a high performance liquid chromatography method. The percentage molar ratio of these two isomers was found to be significantly elevated in 12.8% of all bacterial strains examined. In contrast the thiobarbituric acid reactivity, a non-specific measure of lipid peroxidation, was not elevated in any of the strains incubated in an identical fashion. These results suggest that the diene conjugated linoleic assay may not be a reliable marker of the free radical processes in the lung in the presence of certain bacterial infections.