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Biochemical, Molecular, and Genetic Mechanisms

Polyunsaturated Fats Attenuate the Dietary Phytol–Induced Increase in Hepatic Fatty Acid Oxidation in Mice¹

Toru Hashimoto^*,, Naoto Shimizu, Toshinori Kimura, Yoko Takahashi^* and Takashi Ide^*,2

^* Laboratory of Nutritional Biochemistry, Division of Food Functionality, National Food Research Institute, 2-1-12 Kannondai, Tsukuba 305-8642, Japan and Graduate School of Life and Environmental Sciences, University of Tsukuba, Tennodai 1-1-1, Tsukuba 305-8572, Japan

² To whom correspondence should be addressed. E-mail: idetaka{at}nfri.affrc.go.jp.

The effects of dietary phytol and the type of dietary fat on hepatic fatty acid oxidation were examined in male ICR mice. Mice were fed diets containing 0 or 5 g/kg phytol and 100 g/kg palm, safflower, or fish oil for 21 d. Among the groups fed phytol-free diets, the activities and mRNA abundance of various enzymes involved in fatty acid oxidation were greater in mice fed fish oil than in those fed palm or safflower oil. Dietary phytol profoundly increased the activities and mRNA abundance of hepatic fatty acid oxidation enzymes in mice fed palm oil. However, safflower and fish oils, especially the latter, greatly attenuated the phytol-dependent increase in hepatic fatty acid oxidation. The hepatic concentration of phytanic acid, a metabolite of phytol that is the ligand and activator of retinoid X receptors and peroxisome proliferator-activated receptors, was higher in mice fed fish oil than safflower or palm oil, and in those administered safflower oil than palm oil. The hepatic mRNA abundance of sterol carrier protein-2, a lipid-binding protein involved in phytol metabolism, was inversely correlated with the hepatic concentration of phytanic acid. We demonstrated that polyunsaturated fats attenuate the enhancing effect of dietary phytol on hepatic fatty acid oxidation. Dietary fat–dependent changes in the hepatic phytanic acid concentration cannot account for this phenomenon.

KEY WORDS: • phytol • phytanic acid • dietary fat • fatty acid oxidation