Metabolic tracer studies of linoleic and linolenic acids to identify biohydrogenation intermediates produced by ruminal microorganisms

Conjugated linoleic acids (CLA) have been shown to regulate many physiological functions affecting human health. These CLA can endogenously originate from trans fatty acids through the enzymatic activity of desaturase, or they are produced from dietary polyunsaturated fatty acids via the biohydrogenation process in the rumen. A minimum of seventeen CLA isomers have been identified in the intestinal contents of ruminants; however, the entire synthetic pathway for all isomers is not known. The objective of this study was to establish the number and identity of intermediates including CLA that originate from linoleic and linolenic acid biohydrogenation. To accomplish this objective, the carbon atom of these two fatty acids was tagged with a 13C stable isotope to trace its appearance in CLA isomers in cultures of mixed ruminal microbes. It was found that 13C migrated to seven CLA from linoleic and eight from linolenic acid, including cis-9 trans -11 and trans-10 cis-12 CLA. These results indicate that the biohydrogenation of linoleic and linolenic acid by mixed ruminal microbes involves more complex biological pathways than formation of only one or two CLA as previously reported.