title: Docosahexaenoic acid elevates trans-18:1 isomers but is not directly converted into trans-18:1 isomers in ruminal batch cultures.
abstract: Pathways of docosahexaenoic (DHA) biohydrogenation are not known; however, DHA is metabolized by ruminal microorganisms. The addition of DHA to the rumen alters the fatty acid profile of the rumen and milk and leads to increased trans-18:1 isomers, particularly trans-11 18:1. This study included 2 in vitro experiments to identify if the increase in trans-11 C18:1 was due to DHA being converted into trans-11 18:1 or if DHA stimulated trans-11 products from biohydrogenation of other fatty acids. In each experiment, ruminal microorganisms collected from a lactating Holstein cow were incubated in 10-mL batch cultures for 0, 6, 24, and 48 h and a uniformly (13)C-labeled DHA was added to the cultures at 0 h as a metabolic tracer. Experiment 1 tested 0.5% DHA supplementation and experiment 2 examined 1, 2, and 3% DHA supplementation to determine if the level of DHA effected its conversion into trans-11 18:1. In both experiments, any fatty acid that was enriched with the (13)C label was determined to arise from DHA. Palmitic (C16:0), stearic (C18:0), all trans-18:1, eicosanoic (C20:0), and docosanoic (C22:0) acids were examined for enrichment. In experiment 1, the amount of trans-18:1 isomers increased 0.415 mg from 0 to 48 h; however, no label was found in trans-18:1 at any time. Docosanoic acid was highly enriched at 24h and 48 h to 20.2 and 16.3%. Low levels of enrichment were found in palmitic and stearic acids. In experiment 2, trans-18:1 isomers increased 185, 256, and 272% from 0 to 48 h when DHA was supplemented at 1, 2, and 3%, respectively; however, as in experiment 1, no enrichment occurred of any trans-18:1 isomer. In experiment 2, low levels of label were found in palmitic and stearic acids. Enrichment of docosanoic acid decreased linearly with increased DHA supplementation. These studies showed that trans-18:1 fatty acids are not produced from DHA, supporting that DHA elevates trans-18:1 by modifying biohydrogenation pathways of other polyunsaturated fatty acids.
authors.affiliation: Department of Animal Science, Clemson University, Clemson, SC 29634-0311, USA.
authors.forename: C M
authors.initials: CM
authors.lastname: Klein
authors.forename: T C
authors.initials: TC
authors.lastname: Jenkins
mesh_terms: D000818:Animals; D002417:Cattle; D004281:Docosahexaenoic Acids / Q000378:metabolism / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004537:Eicosanoic Acids / Q000032:analysis; D005227:Fatty Acids / Q000032:analysis / Q000378:metabolism; D005260:Female; D005750:Gastric Juice / Q000737:chemistry / Q000378:metabolism; D006859:Hydrogen; D066298:In Vitro Techniques; D019301:Oleic Acid / Q000032:analysis; D019308:Palmitic Acid / Q000032:analysis; D012417:Rumen / Q000378:metabolism*; D013229:Stearic Acids / Q000032:analysis
chemical_list: D004537:Eicosanoic Acids; D005227:Fatty Acids; D013229:Stearic Acids; D004281:Docosahexaenoic Acids; D019301:Oleic Acid; D019308:Palmitic Acid; C031183:stearic acid; D006859:Hydrogen