Mechanism of conjugated linoleic acid and vaccenic acid formation in human faecal suspensions and pure cultures of intestinal bacteria

Abstract

Faecal bacteria from four human donors and six species of human intestinal bacteria known to metabolize linoleic acid (LA) were incubated with LA in deuterium oxide-enriched medium to investigate the mechanisms of conjugated linoleic acid (CLA) and vaccenic acid (VA) formation. The main CLA products in faecal suspensions, rumenic acid (cis-9,trans-11-CLA; RA) andtrans-9,trans-11-CLA, were labelled at C-13, as were other 9,11 geometric isomers. Traces oftrans-10,cis-12-CLA formed were labelled to a much lower extent. In pure culture,Bifidobacterium breveNCFB 2258 formed labelled RA andtrans-9,trans-11-CLA, whileButyrivibrio fibrisolvens16.4,Roseburia hominisA2-183^T,Roseburia inulinivoransA2-192^TandRuminococcus obeum-like strain A2-162 converted LA to VA, labelled in a manner indicating that VA was formed via C-13-labelled RA.Propionibacterium freudenreichiisubsp.shermaniiDSM 4902^T, a possible probiotic, formed mainly RA with smaller amounts oftrans-10,cis-12-CLA andtrans-9,trans-11-CLA, labelled the same as in the mixed microbiota. Ricinoleic acid (12-OH-cis-9-18 : 1) did not form CLA in the mixed microbiota, in contrast to CLA formation described forLactobacillus plantarum. These results were similar to those reported for the mixed microbiota of the rumen. Thus, although the bacterial genera and species responsible for biohydrogenation in the rumen and the human intestine differ, and a second route of RA formation via a 10-OH-18 : 1 is present in the intestine, the overall labelling patterns of different CLA isomers formation are common to both gut ecosystems. A hydrogen-abstraction enzymic mechanism is proposed that may explain the role of a 10-OH-18 : 1 intermediate in 9,11-CLA formation in pure and mixed cultures.