Effects of Pinolenic Acid on the Expression of Genes Involved in Lipid Metabolism in HepG2 Cells

Abstract

Pine nut oil (PNO) has been reported to reduce hepatic lipid accumulation. However, the specific effect of pinolenic acid (18:3, all-cis-Δ5,9,12), a unique component of PNO, on hepatic lipid metabolism has not been studied. Therefore, we investigated whether pinolenic acid affects hepatic lipid metabolism using the HepG2 human liver cell line and compared the effects of pinolenic acid to the effects of palmitic acid, oleic acid, γ-linolenic acid, pinolenic acid, eicosapentaenoic acid (EPA), or α-linolenic acid. HepG2 cells were incubated in serum-free medium supplemented with 50 μM BSA, palmitic acid, oleic acid, γ-linolenic acid, pinolenic acid, EPA, or α-linolenic acid for 24 h. Lipid accumulation was determined by Oil red O (ORO) staining and enzymatic colorimetric method. Hepatic mRNA levels of genes related to triacylglycerol synthesis (SREBP1c, FAS, SCD1, and ACC1), fatty acid oxidation (ACC2, PPARα, CPT1A, and ACADL), and lipoprotein infusion (LDLr) and of genes that may be involved in the down-regulation of the lipogenic pathway (ACSL3, ACSL4, and ACSL5) were determined by qPCR. Hepatic LDLr and ACSL4 protein levels were measured by Western blot analysis. Hepatic mRNA levels of SREBP1c, FAS, and SCD1 were significantly decreased by pinolenic acid treatment (P<0.05) compared to BSA control (53%, 54%, and 38% less, respectively). Pinolenic acid also reduced the gene expression of LDLr (43% less, P<0.01). In addition, mRNA levels of ACSL3 were decreased (30% less, P<0.05), and ACSL4 tended to be decreased by pinolenic acid (20% less, P=0.082) relative to the control group. In conclusion, pinolenic acid down-regulated the lipid anabolic pathway in hepatocytes by reducing markers related to lipid synthesis, lipoprotein infusion, and the regulation of the lipogenic pathway.