The Journal of Nutrition
Biochemical, Molecular, and Genetic Mechanisms
Conjugated Linolenic Acid Is Slowly Absorbed
in Rat Intestine, but Quickly Converted to
Conjugated Linoleic Acid1
Tsuyoshi Tsuzuki,2,3* Yuki Kawakami,2Renpei Abe,2Kiyotaka Nakagawa,2Kazunori Koba,4
Jun Imamura,5,6Toshio Iwata,7Ikuo Ikeda,8and Teruo Miyazawa2
2Food and Biodynamic Chemistry Laboratory, Graduate School of Agricultural Science, Tohoku University, Sendai 981-8555, Japan;
3Department of Food Management, School of Food, Agricultural and Environment Sciences, Miyagi University, Sendai 982-0215, Japan;
4Faculty of Nursing and Nutrition, Siebold University of Nagasaki, Nagasaki 851-2195, Japan;5Plantech Research Institute, Yokohama,
Japan;6Department of Bioresource Science, Faculty of Agriculture, Tamagawa University, Tokyo, Japan;7The Nisshin OilliO Group,
Shinkawa 1-chome, Chuo-ku, Tokyo 104-8285, Japan; and8Laboratory of Food and Biomolecular Science, Graduate School of
Agricultural Science, Tohoku University, Sendai 981-8555, Japan
We showed previously that a-eleostearic acid (a-ESA; 9Z11E13E-18:3) is converted to 9Z11E-conjugated linoleic acid
(CLA) in rats through a D13-saturation reaction. To investigate this further, we examined the absorption and metabolism of
a-ESA in rat intestine using a lipid absorption assay in lymph from the thoracic duct. In this study, we used 4 test oils [tung
oil, perilla oil, CLA-triacylglycerol (TG), and pomegranate seed oil, containing a-ESA, a-linolenic acid (LnA; 9Z12Z15Z-18:3),
CLA, and punicic acid (PA; 9Z11E13Z-18:3), respectively]. Emulsions containing the test oils were administered to rats,
and lymph from the thoracic duct was collected over 24 h. The positional and geometrical isomerism of CLA produced by
PA metabolism was determined using GC-electron impact (EI)-MS and13C-NMR, respectively;the product was confirmed
to be 9Z11E-CLA. A part of a-ESA and PA was converted to 9Z11E-CLA 1 h after administration; therefore the lymphatic
recoveries of a-ESA and PA were modified by the amount of recovered CLA. Cumulative recovery of CLA, a-ESA, and PA
was lower than that of LnA only during h 1 (P , 0.05), and cumulative recovery of a-ESA and PA was significantly lower
than that of LnA and CLA for 8 h (P , 0.05). Therefore, the absorption rate was LnA . CLA . a-ESA ¼ PA. The conversion
ratio of a-ESA to 9Z11E-CLA was higher than that of PA to 9Z11E-CLA over 24 h (P , 0.05). These results indicated
that a-ESA and PA are slowly absorbed in rat intestine, and a portion of these fatty acids is quickly converted to
9Z11E-CLA. J. Nutr. 136: 2153–2159, 2006.
Conjugated fatty acid (CFA)9is a generic term used for fatty
acids with conjugated double bond systems, as exemplified by
conjugated linoleic acid (CLA) (1). Several CLA isomers exist
due to the positional and geometrical isomerism of the conju-
gated double bonds; the major naturally occurring CLA isomer
is referred to as 9Z11E-18:2 (Fig. 1) (1). CLAwas first reported
to have an anticarcinogenic effect; subsequently, various phys-
iological effects were also shown, including an antiarterioscle-
rotic effect and a role in the regulation of lipid metabolism (1–5).
These CLA activities are associated with the conjugated double
bond system. CLA is found naturally and is especially present in
ruminant fats such as beef tallow and milk fat (1). However, the
CLA level in these foodstuffs is ;1% (wt:wt), thus preventing
natural fats from being used as health-promoting foods con-
taining CLA. Therefore, at present, oils that include CLA are
prepared from alkali-isomerization of vegetable oils such as saf-
flower oil, and these products are marketed as health supple-
Conjugated fatty acids other than CLA exist in nature; seed
oils of certain plants include conjugated triene fatty acids such as
a-eleostearic acid (a-ESA; 9Z11E13E-18:3) and punicic acid
(PA; 9Z11E13Z-18:3) at levels of 60–80% (wt:wt) (Fig.1) (8–
11). In Okinawa, a region inhabited by the longest-living people
in Japan, which is in itself one of the leading countries in the
world in terms of life expectancy, people often eat bitter gourds
(Momordica charantia). The seed oil of such gourds contains
60% a-ESA (wt:wt) and the flesh contains a small amount of
a-ESA. We are particularly interested in seed oils that contain
conjugated linolenic acids (CLnA), which are the only conju-
gated fatty acids that can be prepared from natural sources in
bulk. We showed previously that CLnA has a stronger antitumor
effect than CLA in vitro and in vivo (9). a-ESA (which is a
CLnA) also has useful physiological effects. We showed that
1Supplemental Figures 1 and 2 are available with the online posting of this
paper at jn.nutrition.org.
9Abbreviations used: a-ESA, a-eleostearic acid (9Z11E13E-18:3); CFA,
conjugated fatty acids; CLA, conjugated linoleic acid; CLnA, conjugated
linolenic acid; DMOX, 4,4-dimethyloxazoline; GC-electron impact- (EI-)MS,
LnA, a-linolenic acid (9Z12Z15Z-18:3); LT, leukotriene; PA, punicic acid
(9Z11E13Z-18:3); TG, triacylglycerol.
* To whom correspondence should be addressed. E-mail: firstname.lastname@example.org.
0022-3166/06 $8.00 ª 2006 American Society for Nutrition.
Manuscript received 1 April 2006. Initial review completed 10 May 2006. Revision accepted 22 May 2006.
by guest on May 31, 2013
Supplemental Material can be found at:
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Absorption of conjugated linolenic acid2159
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