Arachidonic acid metabolism in skin

Abstract

Arachidonic acid (AA) (eicosa-5,8,ll,14-tetraenoic acid, 20:4 ω6) is a polyunsaturated fatty acid with 20 carbon atoms and 4 double bonds. It is either derived from dietary sources or synthesized by desaturation and elongation of linoleic acid (C18:2) (Fig. 1). Because the mammalian organism cannot introduce double bounds in the fatty acid structure closer to the ω end than ω9, the AA precursors linoleic acid (18:2 ω6) and γ-linoleic acid (18:3 ω3) are considered essential [1]. AA cannot be synthesized locally in the human epidermis because both Δ-6-desaturase and Δ-5-desaturase are absent in the epidermis [2]. AA present in the epidermis must therefore either come from dietary sources or be transported to the epidermis from other endogenous sources such as the liver, which is capable of elongation and desaturation. In the cell AA is stored in the membrane fraction, primarily esterified to phos-pholipids at the second carbon (sn-2) of the phospholipid glycerol backbone [3]. It is released from the phospholipids in the cell membrane by the action of phospho-lipases.