title: Liver conversion of docosahexaenoic and arachidonic acids from their 18-carbon precursors in rats on a DHA-free but α-LNA-containing n-3 PUFA adequate diet.
abstract: The long-chain polyunsaturated fatty acids (PUFAs), eicosapentaenoic acid (EPA, 20:5n-3), docosahexaenoic acid (DHA, 22:6n-3), and arachidonic acid (AA, 20:4n-6), are critical for health. These PUFAs can be synthesized in liver from their plant-derived precursors, α-linolenic acid (α-LNA, 18:3n-3) and linoleic acid (LA, 18:2n-6). Vegetarians and vegans may have suboptimal long-chain n-3 PUFA status, and the extent of the conversion of α-LNA to EPA and DHA by the liver is debatable. We quantified liver conversion of DHA and other n-3 PUFAs from α-LNA in rats fed a DHA-free but α-LNA (n-3 PUFA) adequate diet, and compared results to conversion of LA to AA. [U-(13)C]LA or [U-(13)C]α-LNA was infused intravenously for 2h at a constant rate into unanesthetized rats fed a DHA-free α-LNA adequate diet, and published equations were used to calculate kinetic parameters. The conversion coefficient k(⁎) of DHA from α-LNA was much higher than for AA from LA (97.2×10(-3) vs. 10.6×10(-3)min(-1)), suggesting that liver elongation-desaturation is more selective for n-3 PUFA biosynthesis on a per molecule basis. The net daily secretion rate of DHA, 20.3μmol/day, exceeded the reported brain DHA consumption rate by 50-fold, suggesting that the liver can maintain brain DHA metabolism with an adequate dietary supply solely of α-LNA. This infusion method could be used in vegetarians or vegans to determine minimal daily requirements of EPA and DHA in humans.
authors.affiliation: National Institute on Aging, National Institutes of Health, Bethesda, MD 20892, USA. gaof@mail.nih.gov
authors.forename: Fei
authors.initials: F
authors.lastname: Gao
authors.forename: Hyung-Wook
authors.initials: HW
authors.lastname: Kim
authors.forename: Miki
authors.initials: M
authors.lastname: Igarashi
authors.forename: Dale
authors.initials: D
authors.lastname: Kiesewetter
authors.forename: Lisa
authors.initials: L
authors.lastname: Chang
authors.forename: Kaizong
authors.initials: K
authors.lastname: Ma
authors.forename: Stanley I
authors.initials: SI
authors.lastname: Rapoport
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism*; D001921:Brain / Q000378:metabolism; D014676:Diet, Vegetarian / Q000009:adverse effects; D004042:Dietary Fats, Unsaturated / Q000008:administration & dosage*; D004281:Docosahexaenoic Acids / Q000008:administration & dosage / Q000378:metabolism*; D015525:Fatty Acids, Omega-3 / Q000008:administration & dosage; D007262:Infusions, Intravenous; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008297:Male; D009751:Nutritional Requirements; D051381:Rats; D011916:Rats, Inbred F344; D017962:alpha-Linolenic Acid / Q000008:administration & dosage
chemical_list: D004042:Dietary Fats, Unsaturated; D015525:Fatty Acids, Omega-3; D017962:alpha-Linolenic Acid; D004281:Docosahexaenoic Acids; D016718:Arachidonic Acid