Comparison of the Effects of Triacylglycerol-CLA and Free Fatty Acid-CLA on Hepatic Lipid Metabolism in OLETF Obese Rats

The effects of conjugated linoleic acids with triacylglycerol form (TAG-CLA) and free fatty acid form (FA-CLA) on lipid mass and lipid metabolizing enzymes in the liver, and on serum metabolites was compared in Otsuka Long-Evans Tokushima fatty (OLETF) rats, which have high levels of hepatic and serum triacylglycerol (TAG) and higher serum insulin, glucose, leptin and tumor necrosis factor-alpha (TNF-α). Obese rats fed either forms of CLA significantly lowered the concentrations of TAG in the liver and serum to a similar extent, compared to the control dietary group. It was further demonstrated that both forms of CLA markedly enhanced mitochondrial carnitine palmitoyltransferase (CPT) activity, but reduced microsomal phosphatidate phosphohydrolase (PAP) activity in the liver. This suggests that the CLA-induced reduction in liver lipid mass may be attributable to increase in fatty acid β-oxidation. Both forms of CLA also lowered serum leptin levels. TAG-CLA had no significant effects on serum insulin and glucose levels, whereas FA-CLA raised the serum glucose level without affecting insulin levels. TNF-α concentrations were comparable between the groups. These results suggest that TAG-CLA and FA-CLA reduce TAG levels in the liver and serum, but have different effects on fasting serum glucose levels in OLETF obese rats.