The role of fatty acid desaturase (FADS) genes in oleic acid metabolism: FADS1 Δ7 desaturates 11-20:1 to 7,11-20:2

Introduction: In mammals, FADS2 catalyzes front-end Delta 4-, Delta 6-, and Delta 8-desaturation of fatty acyl chains, whereas FADS1 has Delta 5-desaturase activity. Eighteen and 20-carbon precursors to highly unsaturated n-3 and n-6 fatty acids are the usual substrates for FADS1 and FADS2. Our main objective was to characterize the metabolic fate of oleic acid (OA) due to action of FADS gene products. Methods: MCF-7 cells were stably transformed with either FADS) or FADS2 or empty vector. A series of dose response experiments were conducted with albumin-bound fatty acid substrates (18:1n-9 and 20:1n-9) provided in concentrations up to 100 mu M. Cells were harvested after 24 h, after which FAME were prepared and analyzed by GC-FID and covalent adduct chemical ionization tandem mass spectrometry (CACI-MS/MS). Results: When stably transformed cells were incubated with 18:1n-9, FADS1 and control cells elongated 18:1n-9 -> 20:1n-9 (11-20:1), while FADS2 cells Delta 6 desaturated, elongated, and then Delta 5 desaturated via FADS1 coded activity leading to Mead acid, 9-18:1 -> 6,9-18:2 8,11-20:2 (20:2n-9) -> 6,8,11-20:3 (20:3n-9). Surprisingly, FADS1 cells Delta 7 desaturated 11-20:1 -> 7,11-20:2, the latter detected at low levels in control and FADS2 cells. Our results imply three pathways operate on 18:1n-9: 1) 18:1n-9 -> 18:2n-9 -> 20:2n-9 -> 20:3n-9; 2) 18:1n-9 -> 20:1n-9 -> 20:2n-9 -> 20:3n-9 and 3) 18:1n-9 -> 20:1n-9 -> 7,11-20:2. Conclusion: Alternative pathways for oleic acid metabolism exist depending on FADS2 or FADS1 activities, we present the first evidence of Delta 7 desaturation via the FADS1 gene product