Location: Immunity and Disease Prevention ResearchTitle: Accretion of dietary docosahexaenoic acid in mouse tissues did not differ between its purified phospholipid and triacylglycerol forms
Submitted to: Lipids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2019
Publication Date: 1/29/2019
Citation: Adkins, Y.C., Laugero, K.D., Mackey, B.E., Kelley, D.S. 2019. Accretion of dietary docosahexaenoic acid in mouse tissues did not differ between its purified phospholipid and triacylglycerol forms. Lipids. 54(1):25-37. https://doi.org/10.1002/lipd.12115.
Interpretive Summary: Epidemiological and human intervention studies have demonstrated a decrease in the risk factors for chronic inflammatory diseases with increased consumption of n-3 polyunsaturated fatty acids (PUFA) which are abundant in fish and some of the seed oils including flaxseed and walnuts. Recent studies comparing krill and fish oils suggest that krill oil may be more efficient than fish oil in the tissue accretion of long chain n-3 PUFA. This difference in the accretion of the n-3 PUFA is believed to result from the structure of the lipids that contain these fatty acids; krill oil contains 40-50% n-3 PUFA in the phospholipid (PL) form, while fish oil is primarily the triglyceride (TG) form with less than 0.5% in PL form. Differences in the dose of n-3 PUFA and the ratio between EPA and DHA, total dietary fat, feeding duration, age of the animals and many other confounding factors contribute to the differences in the tissue accretion of n-3 PUFA. The effects of the same concentrations of PL-DHA and TG-DHA under identical diets have not been determined. To determine whether the PL form of n-3 PUFA results in greater tissue accretion of these fatty acids than their TG form, it is important to study their effects under identical conditions. Therefore, the purpose of our present study was to compare the effects of same diets with identical multiple concentrations of TG- and PL-DHA on fatty acid composition of brain, liver, heart, adipose tissue and eye in mice. Ten- week old, pathogen-free C57BL/6N female mice (n= 12/group) were fed either the control diet or diets containing-DHA (1, 2, and 4%) as PL-DHA and TG-DHA for 4 weeks. Compared with the control group, DHA amount was significantly increased in all 6 DHA groups in liver, adipose tissue, heart, and eye but not in brain. The concentration of DHA in all these tissues did not differ between the corresponding concentrations of the PL-DHA and TAG-DHA; it was also not altered by the dose of DHA. Amounts of other n-3 PUFA derived from DHA (20:5n3 and 22:5n3) were increased in all DHA groups compared with control in all tissues, except it was not significant for 22:5n3 in eye lipids. Both forms of DHA decreased the sum of n-6 PUFA in all tissues, and sums of monounsaturated and saturated fatty acids in liver and adipose tissue only. Our results do not support the claim made by the krill industry that there is greater tissue accretion of dietary PL-n-3 PUFA than TG-n3 PUFA.
Technical Abstract: Recent studies suggest that dietary krill oil leads to higher n-3 PUFA tissue accretion compared to fish oil due to the structural form in which n-3 PUFA are esterified; krill oil is rich in n-3 PUFA esterified as phospholipids (PL), while n-3 PUFA in fish oil is primarily esterified as triglycerides (TAG). Tissue accretion of the same dietary concentrations of PL- and TAG-DHA have not been compared and was the focus of this study. Mice (n=12/group) were fed either a control diet or one of six DHA (1, 2, or 4%) as PL-DHA or TAG-DHA diets for 4 weeks. Compared with the control, DHA concentration in liver, adipose tissue (AT), heart, and eye, but not brain, were significantly higher in mice consuming either PL- or TAG-DHA, but there was no difference in DHA concentration in all tissues between the PL- or TAG-DHA forms. Consumption of PL- and TAG-DHA at all concentrations significantly elevated 20:5n-3 incorporation in all tissues when compared with the control group, while 22:5n-3 was significantly higher in all tissues except for the eye and heart. Both DHA forms lowered total n-6 PUFA in all tissues and total MUFA in the liver and AT; total SFA were lowered in the liver but elevated in the AT. An increase in DHA dose, independent of DHA forms, significantly lowered n-6 PUFA and significantly elevated n-3 PUFA incorporation in all tissues. Our results do not support the claim that the PL form of n-3 PUFA leads to greater n-3 PUFA tissue accretion than the TG form.