Regulation of human stearoyl-CoA desaturase by omega-3 and omega-6 fatty acids: Implications for the dietary management of elevated serum triglycerides

BACKGROUND: Polyunsaturated fatty acids lower serum triglycerides by a mechanism that may involve the inhibition of stearoyl-CoA desaturase (SCD). OBJECTIVE: We sought to evaluate the effects of serum fatty acids on 1) the SCD index in a controlled clinical setting, and 2) SCD regulation in Hep G2 cells. METHODS: The SCD index was determined in 23 subjects randomly sequenced through 3 diets for 6 weeks in a crossover study. Diets were variably enriched with n-3 and n-6 polyunsaturated fatty acids; notably, monounsaturated fatty acids were held constant. Effects of linoleic acid (LA), alpha-linolenic acid (ALA), and eicosapentaenoic acid (EPA) on mRNA levels of SCD, fatty acid elongases 5 and 6 (Elov15 and Elov16), fatty acid synthase, carnitine palmitoyltransferase-1, and sterol response element binding protein-1c were investigated in Hep G2 cells after 24-hour incubations. RESULTS: The SCD indexes C18:1/18:0 and C16:1/C16:0 were significantly (P < .0001) correlated with serum TG with R-2 values of 0.71 and 0.58. The correlation was negatively associated with LA and positively associated with ALA. LA and EPA decreased SCD mRNA (EC50 of 0.50 and 1.67 mu M), whereas ALA did not. Likewise, LA and EPA decreased sterol response element binding protein-1c mRNA (EC50 of 0.78 and 1.78 mu M), but ALA did not. Similar results were observed for Elovl6. GW9662, a peroxisome proliferation activator receptor antagonist, did not obviate the effects of LA and EPA on SCD mRNA. CONCLUSIONS: Diets enriched in LA, ALA, and by metabolic inference EPA, can regulate SCD activity at the level of transcription, a nutritional intervention that may be useful in the management of increased levels of serum triglycerides in cardiometabolic disorders. (C) 2009 National Lipid Association. All rights reserved.