Competitive incorporation of arachidonic acid analogs by cultured rat keratinocytes

Arachidonic acid (20:4 n-6) and its metabolic products, such as prostagland ins and leukotrienes, have been known to be associated with skin inflammato ry reactions. However, the mechanism of the competitive incorporation of 20 :4 n-6 into keratinocytes among polyunsaturated fatty acids (PUFAs) remains uncertain. To investigate the relationship between the molecular structure of PUFAs and the rate of incorporation of PUFAs into cells, a fetal rat sk in keratinocyte (FRSK) cell line was used. The cells were incubated for 24 h with any two of the following arachidonic acid analogs: mead acid (20:3 n -9), dihomo-gamma -linolenic acid (20:3 n-6), 11,14,17-cis-eicosatrienoic a cid (20:3 n-3), arachidonic acid (20:4 n-6), eicosapentaenoic acid (20:5 n- 3) and 5,8,11,14-cis-nonadecatetraenoic acid (19:4 n-5), at the ratio of 1: 0, 0,5:0,5, or 0:I; and their incorporation into lipid was measured by capi llary gas-liquid chromatography. The experiments indicated that 20:3 n-6 wa s preferentially incorporated into phospholipids of FRSK rather than 20:3 n -9 or 20:3 n-3, and 19:4 n-5 as well as 20:4 n-6 was preferentially incorpo rated into total cellular lipid and phospholipids rather than 20:3 n-9 or 2 0:5 n-3. When two PUFAs were added simultaneously to the medium, 19:4 n-5 m ost effectively reduced the competitive incorporation of 20:4 n-6 into phos pholipids. These results suggest that keratinocytes discriminate 20:4 n-6 f rom other arachidonic acid analogs by its double bond positions from the ca rboxyl group.