In vivo activation of an omega-6 oxygenase in human skin

To test the hypothesis that an epidermal fatty acid oxygenase is activated in vivo under physiologic conditions, surface lipids from normal human skin were analyzed for oxygenase products. With high-performance liquid chromatography on reversed-phase and straight-phase chiral columns and gas-liquid chromatography/mass spectrometry, these lipids were found to contain free 13-hydroxyoctadeca-9Z,11E-dienoic acid and 9-hydroxyoctadeca-10E,12Z-dienoic acid. The 13-hydroxyoctadecadienoic acid was present as a stereoisomeric mixture, with an average S/R ratio of 2.2, and exceeded the concentration of 9-hydroxyoctadecadienoic acid by a factor of 2. These observations and others indicate that the 13-hydroxyoctadecadienoic acid was derived mostly from an omega-6 oxygenase (probably 15-lipoxygenase) which is activated in vivo in normal skin.