Aim: The aim of our study is to elucidate the effects of EPA- or DHA-rich fish oil, and of the latter plus fenofibrate, on lipid metabolism in female KK mice.
Methods: Female KK mice were fed purified experimental diets containing lard/safflower oil (4:6, Lard/SO), EPA-rich fish oil (EPA), DHA-rich fish oil (DHA), or DHA-rich fish oil plus 0.2% (w/w) fenofibrate (DHA+FF) for 8 weeks. At the end of the experiments, we measured levels of plasma lipids, hepatic triglycerides, and cholesterol, as well as the hepatic mRNA expression of lipogenic and lipidolytic genes.
Results: The final body weight of EPA- and DHA-fed groups was significantly lower than that of the Lard/SO-fed group, and that of the DHA+FF-fed group was the lowest. All three fish oil treatments significantly reduced plasma insulin levels. Hepatic lipid levels significantly decreased in all three of these groups compared with the Lard/SO-fed group. Plasma adiponectin increased in both the EPA-and DHA-fed groups, but the increase was suppressed in the DHA+FF-fed group. Hepatocytes of Lard/SO-fed mice were filled with numerous fat droplets, but fat accumulation was inhibited in both EPA- and DHA-fed mice and was significantly prevented by fenofibrate treatment. SREBP-1c mRNA levels were decreased by about half in EPA- and DHA-fed mice compared with Lard/SO-fed mice. FAS, Insig-1, HMG-CoA reductase, and LDL-receptor mRNA levels also markedly decreased in both EPA- and DHA-fed mice, but there was no additional decrease in DHA+FF fed mice. Fenofibrate treatment significantly induced mRNA expression of AOX and UCP-2, but not of PPARα.
Conclusion: These data suggest that fish oil inhibited body weight gain and exhibited an anti-obesity effect through the inhibition of lipid synthesis in female KK mice. Furthermore, fenofibrate treatment markedly inhibited body weight gain by the induction of fatty acid oxidation. Plasma adiponectin levels did not increase in mice fed DHA-rich fish oil with fenofibrate, although white adipose tissue (WAT) weight significantly decreased. We considered that adiponectin sensitivity increased more in mice fed DHA-rich fish oil with fenofibrate than in mice fed DHA-rich fish oil alone.