Endocrine Hormone Beta-estradiol and Anti-estrogen Letrozole Modulate 20:3 Isomer Production from 20:2n-6 in Human Cancer Cells (P08-119-19)

Abstract

Abstract Objectives The product of linoleic acid elongation, 20:2n-6, is the only known substrate for both FADS1 and FADS2. FADS1 catalyzes 20:2n-6 à 5Z,11Z,14Z-20:3 (sciadonic acid, SA), whereas FADS2 action yields 8Z,11Z,14Z-20:3 (DGLA). In certain cancer cell types, non-functional FADS2 activity unmasks 18:2n-6 elongation to 20:2n-6 and Δ5 desaturation by FADS1 to yield SA. Estrogen is known to inhibit Δ5-desaturation activity. Our objective was to examine the effect of 17-β-estradiol (estrogen) and the antiestrogen drug letrozole on the modulation of fatty acid desaturation and SA levels in vitro. Methods Estrogen doses (0 to 200 ppm) and letrozole doses (0 to 100 ppm) studies were performed using stably transformed MCF7 cells with either FADS1 or FADS2 or empty vector and five different (MCF7, HepG2, SK-N-SH, Y79 and Caco2) wild type cancer cells. Fatty acid methyl esters (FAME) were prepared from harvested cells and analyzed quantitatively by gas chromatograph-flame ionization detector (GC-FID). The peak structures were positively identified by GC-covalent adduct chemical ionization tandem mass spectrometry (GC-CACI-MS/MS). Results Increasing estrogen caused a decrease in the 5-desaturation product 5,11,14–20:3 in a dose-response manner in all cell types, but had no effect on DGLA. Letrozole exerted its effects most prominently in MCF7 cells. In response to increasing letrozole doses, DGLA increased, and SA decreased. Conclusions We provide the first biochemical evidence demonstrating letrozole enhancing FADS2-mediated DGLA levels in MCF7 cells. In all cell types estrogen reduced FADS1 mediated synthesis of SA. Both product fatty acids have anti-inflammatory activity, DGLA as a precursor to PGE1 and SA in displacing the largely proinflammatory arachidonic acid. Funding Sources NIH grant R01 AT007003.