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3. Studies on the relationship between the structure of lipids and their physiological functions

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Oil consists of glycerine esterified with fatty acids. Fatty acids can be categorized into (1) saturated fatty acids, (2) monounsaturated fatty acids, and (3) polyunsaturated fatty acids. Numerous fatty acids play important roles in our body.

For example,

1. Docosahexaenoic acid (DHA): Fish oil is a major source of this fatty acid. It is the main fatty acid found in brain tissues. Intake of DHA is very important for brain development in infancy.

2. Palmitic acid in human milk TAGs is located principally at the b position (please refer to the Development of an analytical method for identifying triacylglycerol isomers section) of TAG and plays an important role as an energy source for infants.

3. Eicosapentaenoic acid (EPA): Fish oil is a major dietary source of this fatty acid.  EPA can decrease the levels of TAG in blood. Ethyl esters of EPA have been used as drugs for reducing the levels of TAG in blood.

Our group has been studying the relationship between the structure of fatty acids and their metabolism. For example, it has been recognized that docosapentaenoic acid (DPA) is synthesized as an intermediate compound when DHA is synthesized from EPA. Seal oil is a good source of DPA. However, very little information is available about the physiological role of DPA. Therefore, we administered DPA to mice to examine the physiological functions of DPA in comparison with those of EPA and DHA. Our results showed that all the results obtained for mice administered DPA were between those obtained for mice administered EPA or DHA.

N. Gotoh, K. Nagao, S. Onoda, B. Shirouchi, K. Furuya, T. Nagai, H. Mizobe, K. Ichioka, H. Watanabe, T. Yanagita, and S. Wada, Effects of three different highly purified n-3 series highly unsaturated fatty acids on lipid metabolism in C57BL/KsJ-db/db mice. J. Agri. Food Chem. 57, 11047-11054 (2009).　[Abstract]

Almost all natural fatty acids contain an even number of carbon atoms. However, some fatty acids in ruminants and fishes contain an odd number of carbon atoms. Therefore, we synthesized stable isotopes of even- or odd-numbered fatty acids and administered them to mice. We did not detect even-numbered fatty acids such as palmitic acid in the bodies of these animals. Odd-numbered fatty acids such as pentadecanoic acid did not undergo beta-oxidation and hence did not accumulate in the organs and tissues of the experimental animals.

N. Gotoh, T. Nagai, K. Yoshinaga, H. Mizobe, and H. Watanabe, Comparison of catabolic rates of fatty acids using stable isotope and isotope-ratio mass spectrometry. Lipid Tech. 25, 110-112 (2013) [Abstract].

R. Shibata, N. Gotoh, A. Kubo, J. Kanda, T. Nagai, H. Mizobe, K. Yoshinaga, K. Kojima, H. Watanabe, and S. Wada, Comparison of catabolism rate of fatty acids to carbon dioxide in mice. Eur. J. Lipid Sci. Tech.,(2012) accepted.[Abstract]

N. Gotoh, K. Moroda, H. Watanabe, K. Yoshinaga, M. Tanaka, H. Mizobe, K. Ichioka, S. Tokairin, and S. Wada, Metabolism of odd-numbered fatty acids and even-numbered fatty acids in mouse. J. Oleo Sci. 57, 293-299 (2008) [Paper (pdf)]