Free and esterified 13(R,S)-hydroxyoctadecadienoic acids: principal oxygenase products in psoriatic skin scales.

Characterization of the chemical form and stereo-specificity of the fatty acid derivatives of arachidonic and linoleic acid in psoriatic epidermis is needed to define the enzymatic origin of these compounds and their possible role in pathogenesis. In an analysis of psoriatic skin scales, both free and esterified 13-hydroxyoctadecadienoic acids were the principal fatty acid derivatives, present in mean concentrations of 115 and 17 ng/mg scales, respectively. The analysis included reversed-phase high performance liquid chromatography of the free acid and of its methyl ester, gas chromatography, gas-liquid chromatography-mass spectrometry of the methyl ester derivatives, and chiral separation. The free and esterified 13-hydroxyoctadecadienoic acids isolated from the psoriatic scales contained a mixture of the S/R stereoisomers, averaging 1.9:1 for free 13- hydroxyoctadecadienoic acid. These findings are not compatible with the strict S-stereospecificity for oxygen insertion exhibited by mammalian lipoxygenase but rather could point to the action of a cyclooxygenase. The demonstration that a hydroxylated fatty acid derivative is esterified in vivo in psoriatic keratinocytes suggests that the physiology of these cells may be altered early in the process of keratinization.