title: Why is carbon from some polyunsaturates extensively recycled into lipid synthesis?
abstract: We summarize here the evidence indicating that carbon from alpha-linolenate and linoleate is readily recycled into newly synthesized lipids. This pathway consumes the majority of these fatty acids that is not beta-oxidized as a fuel. Docosahexaenoate undergoes less beta-oxidation and carbon recycling than do alpha-linolenate or linoleate, but is it still actively metabolized by this pathway? Among polyunsaturates, arachidonate appears to undergo the least beta-oxidation and carbon recycling, an observation that may help account for the resistance of brain membranes to loss of arachidonate during dietary deficiency of n-6 polyunsaturates. Preliminary evidence suggests that de novo lipid synthesis consumes carbon from alpha-linolenate and linoleate in preference to palmitate, but this merits systematic study. Active beta-oxidation and carbon recycling of 18-carbon polyunsaturates does not diminish the importance of being able to convert alpha-linolenate and linoleate to long-chain polyunsaturates but suggests that a broad perspective is required in studying the metabolism of polyunsaturates in general and alpha-linolenate and linoleate in particular.
authors.affiliation: Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, Toronto, Canada M5S 3E2. s.cunnane@utoronto.ca
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Cunnane
authors.forename: Mary Ann
authors.initials: MA
authors.lastname: Ryan
authors.forename: Chantale R
authors.initials: CR
authors.lastname: Nadeau
authors.forename: Richard P
authors.initials: RP
authors.lastname: Bazinet
authors.forename: Kathy
authors.initials: K
authors.lastname: Musa-Veloso
authors.forename: Ursula
authors.initials: U
authors.lastname: McCloy
mesh_terms: D000818:Animals; D002244:Carbon / Q000378:metabolism*; D002247:Carbon Isotopes; D004041:Dietary Fats / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000378:metabolism*; D006801:Humans; D007659:Ketones / Q000378:metabolism; D008055:Lipids / Q000096:biosynthesis*; D010084:Oxidation-Reduction; D014018:Tissue Distribution
chemical_list: D002247:Carbon Isotopes; D004041:Dietary Fats; D005231:Fatty Acids, Unsaturated; D007659:Ketones; D008055:Lipids; D002244:Carbon