A conjugated fatty acid present at high levels in bitter melon seed favorably affects lipid metabolism in hepatocytes by increasing NAD +/NADH ratio and activating PPARα, AMPK and SIRT1 signaling pathway

a-Eleostearic acid (alpha-ESA), or the cis-9, trans-11, trans-13 isomer of conjugated linolenic add, is a special fatty acid present at high levels in bitter melon seed oil. The aim of this study was to examine the effect of ot-ESA on hepatic lipid metabolism. Using H4IIEC3 hepatoma cell line, we showed that alpha-ESA significantly lowered intracellular triglyceride accumulation compared to alpha-linolenic acid (LN), used as a fatty acid control, in a dose- and time-dependent manner. The effects of alpha-ESA on enzyme activities and mRNA profiles in H4IIEC3 cells suggested that enhanced fatty acid oxidation and lowered lipogenesis were involved in alpha-ESA-mediated triglyceride lowering effects. In addition, alpha-ESA triggered AMP-activated protein kinase (AMPK) activation without altering sirtuin 1 (SIRT1) protein levels. When cells were treated with vehicle control (VC), LN alone (LN; 100 mu mol/L) or in combination with alpha-ESA (LN + alpha-ESA; 75 + 25 mu mol/L) for 24 h, acetylation of forkhead box protein O1 was decreased, while the NAD(+)/NADH ratio, mRNA levels of NAMPT and PTGR1 and enzyme activity of nicotinamide phosphoribosyltransferase were increased by LN + alpha-ESA treatment compared to treatment with LN alone, suggesting that alpha-ESA activates SIRTI by increasing NAD(+) synthesis and NAD(P)H consumption. The antisteatosis effect of alpha-ESA was confirmed in mice treated with a high-sucrose diet supplemented with 1% alpha-ESA for 5 weeks. We conclude that alpha-ESA favorably affects hepatic lipid metabolism by increasing cellular NAD(+)/NADH ratio and activating PPAR alpha, AMPK and SIRT1 signaling pathways. (C) 2016 Elsevier Inc. All rights reserved.