Abstract
In vitro studies have suggested that isolated gut bacteria are able to metabolize PUFA into CLA (conjugated linoleic acids) and CLnA (conjugated linolenic acids). However, the bioavailability of fatty acid metabolites produced in vivo by the gut microbes remains to be studied. Therefore, we measured intestinal concentration and plasma accumulation of bacterial metabolites produced from dietary PUFA in mice, first injected with a lipoprotein lipase inhibitor, then force-fed with either sunflower oil (200 µl) rich in n-6 PUFA or linseed oil (200 µl) rich in n-3 PUFA. The greatest production of bacterial metabolites was observed in the caecum and colon, and at a much lesser extent in the jejunum and ileum. In the caecal content, CLA proportions were higher in sunflower oil force-fed mice whereas CLnA proportions were higher in linseed oil force-fed mice. The accumulation of the main metabolites (CLA cis-9,trans-11-18:2 and CLnA cis-9,trans-11,cis-15-18:3) in the caecal tissue was not associated with their increase in the plasma, therefore suggesting that, if endogenously produced CLA and CLnA have any biological role in host metabolism regulation, their effect would be confined at the intestinal level, where the microbiota is abundant.
Highlights
The trillions of bacteria housed in our gastro-intestinal tract play an essential role in host homeostasis
gas chromatography equipped with a flameionization detector (GC-FID) analysis of the oils confirmed that alinolenic acid (a-LnA) represents about 50% of the fatty acids identified in the linseed oil whereas it represents only 0.06% of the fatty acids identified in the sunflower oil (Table 1)
We have previously shown that proportions of rumenic acid and vaccenic acid were increased in caecal tissue and subcutaneous adipose tissue of mice fed a HF diet or a HF diet supplemented with prebiotic carbohydrates, that modulate the gut microbiota composition [23,34]
Summary
The trillions of bacteria housed in our gastro-intestinal tract play an essential role in host homeostasis. In vitro studies showed that gut bacteria isolated from humans are able to metabolize linoleic acid (LA) and alinolenic acid (a-LnA) into metabolites like conjugated linoleic acids (CLA), conjugated linolenic acids (CLnA), and other trans fatty acids such as vaccenic acid (trans-11-18:1) [7,8,9]. These in vitro studies have shown that the main PUFA-derived bacterial metabolites are rumenic acid (CLA cis-9,trans-11-18:2), vaccenic acid (trans-11-18:1), CLnA cis-9,trans-11,cis-15-18:3 and trans-11,cis15-18:2 [7,8]. These in vitro studies and the data from the biohydrogenation pathways of LA and a-LnA, which are quite well characterized in ruminants, suggest that other minor metabolites could be produced such as CLA trans-10,cis-1218:2; CLA trans-9,trans-11-18:2 and CLA cis-9,cis-11-18:2 [7,9,10,11]
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