Monohydroxy fatty acids esterified to phospholipids are decreased in lesional psoriatic skin

Because of the increasing number of reports of the important roles of monohydroxy derivatives of poly-unsaturated fatty acids in the regulation of cell function, we determined the pools of unesterified and esterified monohydroxy fatty acids (MHFAs) in keratomed epidermal slices, taken from lesional and non-lesional psoriatic skin. Extracted phospholipids were separated by thin-layer chromatography. The isolated fractions of phosphatidylcholine (PC), phosphatidylinositol (PI) and phosphatidyl-ethanolamine (PE) were treated with phospholipase A2 to release fatty acids in the sn-2 position. Released MHFAs were separated by reversed-phase and straight-phase high-performance liquid chromatography and identified as the linoleic acid derivatives 9-hydroxy-octadecadienoic acid (9-HODE) and 13-hydroxy-octadecadienoic acid (13-HODE) and as the arachidonic acid derivative 15-hydroxy-eicosatetraenoic acid (15-HETE). These findings are consistent with the presence of unesterified 9-HODE, 13-HODE and 15-HETE. In contrast, 12-hydroxy-eicosatetraenoic acid (12-HETE), although found to be present in high amounts as unesterified 12-HETE, was not detectable in the phospholipids. When compared with non-lesional psoriatic skin, the levels of 9-HODE, 13-HODE and 15-HETE esterified to the sn-2 position of PC, PI and PE in lesional psoriatic skin were significantly decreased (to 28-78% of those in non-lesional skin). This depletion of MHFAs in specific phospholipids may be due to an imbalance between phospholipase and acyltransferase activities. Because the levels of esterified MHFAs may influence signal transduction and eicosanoid metabolism the described changes may be relevant for the inflammatory processes occurring in psoriasis.