Serum Levels of Free Fatty Acids in Obese Mice and Their Associations with Routine Lipid Profiles

To investigate serum levels of free fatty acids (FFAs) and their associations with routine serum lipids in diet-induced obese mice, which have been scantily reported before. Male C57BL/6 J mice were fed high-fat diets for 12 weeks to induce obesity. Levels of serum FFAs were measured by ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry. Obese mice had higher serum levels of total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C), but lower triglycerides (TG) than control mice. A total of 30 FFAs were found, and 3 saturated fatty acids (SFAs), all 8 monounsaturated fatty acids (MUFAs) and 7 polyunsaturated fatty acids (PUFAs) decreased in obese mice, but one SFA (C4:0) increased. Differences in the relative levels of individual FFAs to total FFAs, SFAs, MUFAs or PUFAs between obese and control mice were different from each other and from those evaluated by concrete levels except C4:0, C16:1, C19:1 and C18:4. Only the concrete levels of C4:0, C22:3 and C18:4 were associated with routine serum lipids, including C22:3 negatively with TG in control mice, and C4:0 and C18:4 positively with LDL-C in obese mice, although the relative levels of C4:0 to total MUFAs negatively with TC, and C23:3 to total SFAs or MUFAs negatively with TG in control mice. Different relative levels of the remaining FFAs were differently associated with different routine serum lipids in obese and/or control mice. Obesity may influence serum FFAs profiles. The relationship of individual FFAs and their relative levels to other FFAs with routine serum lipids in obese and control mice suggests that individual FFAs may interact with others and obesity on levels of routine serum lipids. Once confirmed, the interactions may be novel perspectives when fatty acids are used to improve hyperlipidemia in the subjects with obesity.