Metabolism of α-linolenic acid during incubations with strained bovine rumen contents: products and mechanisms

Anne M. Honkanen, Heidi Leskinen, Vesa Toivonen, Nest McKain, Robert John Wallace, Kevin J. Shingfield*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

27 Citations (Scopus)

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.

Original languageEnglish
Pages (from-to)2093-2105
Number of pages13
JournalBritish Journal of Nutrition
Volume115
Issue number12
Early online date18 Apr 2016
DOIs
Publication statusPublished - Jun 2016

Bibliographical note

Acknowledgements
The authors gratefully acknowledge and appreciate the technical
assistance of Minna Aalto (Natural Resources Institute
Finland) during lipid analysis. This study was supported in part by core funding from the Finnish Ministry of Agriculture and Forestry, the Scottish Government Rural and Environment Science and Analytical Services Division and a PhD studentship from the Raisio Science Biohydrogenation of α-linolenic acid 2103
Foundation and the August Johannes and Aino Tiura Agricultural
Science Foundations (awarded to A. M. H.). None of the
funders had any role in the experimental design, data analysis
or writing of this article.
The authors’ contributions are as follows: A. M. H. and K. J. S.
designed the study; A. M. H. completed the in vitro incubations;
A. M. H., H. L., R. J. W., N. M., V. T. and K. J. S. contributed to
the analysis of lipids, determination of 2 H enrichment and FA
identification; A. M. H. analysed the data under the supervision
of R. J. W. and K. J. S.; A. M. H. and K. J. S. wrote the manuscript;
R. J. W., N. M. and H. L. provided advice and critically reviewed
the manuscript. All the authors have read and approved the
manuscript content.
There are no conflicts of interest.

Keywords

  • Biohydrogenation
  • Conjugated linoleic acid
  • Conjugated linolenic acid
  • Linolenic acid
  • Rumen bacteria

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