title: Metabolism of α-linolenic acid during incubations with strained bovine rumen contents: products and mechanisms.
abstract: Description of α-linolenic acid (cis-9,cis-12,cis-15-18 : 3, ALA) metabolism in the rumen is incomplete. Ruminal digesta samples were incubated with ALA and buffer containing water or deuterium oxide to investigate the products and mechanisms of ALA biohydrogenation. Geometric Δ9,11,15-18 : 3 isomers were the main intermediates formed from ALA. An increase in the n+1 isotopomers of Δ9,11,15-18 : 3 was due to 2H labelling at C-13. Isomers of Δ9,11,13-18 : 3, cis-7,cis-12,cis-15-18 : 3 and cis-8,cis-12,cis-15-18 : 3 were also formed. No increase in n+1 isotopomers of Δ7,12,15-18 : 3 or Δ8,12,15-18 : 3 was detected. Enrichment in n+2 isotopomers of 18 : 2 products indicated that ALA metabolism continued via the reduction of 18 : 3 intermediates. Isomers of Δ9,11,15-18 : 3 were reduced to Δ11,15-18 : 2 labelled at C-9 and C-13. ALA resulted in the formation of Δ11,13-18 : 2 and Δ12,14-18 : 2 containing multiple 2H labels. Enrichment of the n+3 isotopomer of Δ12,15-18 : 2 was also detected. Metabolism of ALA during incubations with rumen contents occurs by one of three distinct pathways. Formation of Δ9,11,15-18 : 3 appears to be initiated by H abstraction on C-13. Octadecatrienoic intermediates containing cis-12 and cis-15 double bonds are formed without an apparent H exchange with water. Labelling of Δ9,11,13-18 : 3 was inconclusive, suggesting formation by an alternative mechanism. These findings explain the appearance of several bioactive fatty acids in muscle and milk that influence the nutritional value of ruminant-derived foods.
authors.affiliation: 1Nutritional Physiology, Green Technology, Natural Resources Institute Finland (Luke),FI-31600 Jokioinen,Finland.
authors.forename: Anne M
authors.initials: AM
authors.lastname: Honkanen
authors.affiliation: 1Nutritional Physiology, Green Technology, Natural Resources Institute Finland (Luke),FI-31600 Jokioinen,Finland.
authors.forename: Heidi
authors.initials: H
authors.lastname: Leskinen
authors.affiliation: 1Nutritional Physiology, Green Technology, Natural Resources Institute Finland (Luke),FI-31600 Jokioinen,Finland.
authors.forename: Vesa
authors.initials: V
authors.lastname: Toivonen
authors.affiliation: 2Rowett Institute of Nutrition and Health,University of Aberdeen,Bucksburn,AberdeenAB21 9SB,UK.
authors.forename: Nest
authors.initials: N
authors.lastname: McKain
authors.affiliation: 2Rowett Institute of Nutrition and Health,University of Aberdeen,Bucksburn,AberdeenAB21 9SB,UK.
authors.forename: R John
authors.initials: RJ
authors.lastname: Wallace
authors.affiliation: 1Nutritional Physiology, Green Technology, Natural Resources Institute Finland (Luke),FI-31600 Jokioinen,Finland.
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Shingfield
mesh_terms: D000818:Animals; D002417:Cattle; D004041:Dietary Fats / Q000378:metabolism*; D004063:Digestion; D005260:Female; D006865:Hydrogenation; D007536:Isomerism; D044243:Linoleic Acids, Conjugated / Q000096:biosynthesis*; D008460:Meat / Q000032:analysis; D008892:Milk / Q000737:chemistry*; D009132:Muscles / Q000737:chemistry*; D012417:Rumen / Q000378:metabolism*; D012418:Ruminants / Q000378:metabolism; D017962:alpha-Linolenic Acid / Q000031:analogs & derivatives / Q000378:metabolism*
chemical_list: D004041:Dietary Fats; D044243:Linoleic Acids, Conjugated; D017962:alpha-Linolenic Acid
keywords: 4-dimethyloxazoline; ALA 
                    α-linolenic acid; Biohydrogenation; CLA conjugated linoleic acid; CLN conjugated linolenic acid; Conjugated linoleic acid; Conjugated linolenic acid; D2O deuterium oxide; DMOX 4; FA fatty acid; FAME fatty acid methyl ester; LA linoleic acid; Linolenic acid; MPE moles per cent excess; Rumen bacteria