Unexpected Formation of Low Amounts of (R)-Configurated anteiso-Fatty Acids in Rumen Fluid Experiments

Abstract

Anteiso-fatty acids (aFA) with odd carbon number are a class of branched-chain fatty acids (BCFA) mainly produced by bacteria. Bacterial sources are also made responsible for their occurrence in the low percent-range in lipids of ruminants (meat and milk) and fish. aFAs are chiral molecules and typically occur predominantly in form of (S)-enantiomers, and their primary precursor has been noted to be isoleucine. Yet, low proportions of (R)-aFAs were also detected in fish and cheese samples. Here we investigated the potential formation of (R)-aFAs by means of incubation experiments with rumen fluid from fistulated cows. Supplementation of rumen fluid with both L- and DL-isoleucine, resulted in a significant (α <0.05) increase of the aFA concentrations but in both cases enantiopure (S)-aFAs were observed. By contrast, incubations without addition of any isoleucine lead to a significant (α <0.05) formation of small proportions of (R)-aFAs similarly to those previously observed in fish and cheese. These results were consistently reproduced in three different years with rumen fluid from different cows fed different diets. All findings point to the existence of a further biosynthesis pathway of aFAs with different stereospecificity than the classic one using isoleucine as primer.

Monomethyl branched-chain fatty acids are critical for Caenorhabitis elegans survival in elevated glucose conditions

“…The presence of these branched fatty acids has a different impact on membrane properties such as packing, since they mimic properties of both straight-chain saturated and cismonounsaturated fatty acids. The ratio iso/anteiso fatty acids is reduced when the growth temperature is decreased, indicating that anteiso species strongly affect membrane fluidity compared to iso species (25) (26). However, the participation of mmBCFAs in the response to other external stress such as J o u r n a l P r e -p r o o f high glucose diet has not yet been described.…”

Microbial incubations of 8-phenyloctanoic acid and furan fatty acids in rumen fluid

“…Each tube was supplemented once with about 1-3 mg of 8-Ph-8:0 or FuFAs (9M5, 11D5 and a mixture of 9D5 and 11D3). Incubations were carried out in a shaking water bath (39°C) under anaerobic conditions by means of a Bunsen valve (Eibler et al, 2017). After 24 h, incubation stopped by freezing the samples on ice.…”

“…The goal of our study was to get first insights into the fate of free 8-Ph-8:0 and FuFAs by the performance of rumen fluid incubation experiments. For this purpose, rumen fluid was repeatedly taken from rumen-fistulated non-lactating Jersey cows and incubated (39°C, 24 h) with the analytes using standard protocols (Eibler et al, 2017). Extracted lipids were transesterified and the resulting fatty acid methyl esters were analysed by gas chromatography with mass spectrometry (GC/MS).…”

Towards enantioselective ultrahigh performance liquid chromatography–mass spectrometry‐based metabolomics of branched‐chain fatty acids and anteiso‐fatty acids under reversed‐phase conditions using sub‐2‐μm amylose‐ and cellulose‐derived chiral stationary phases

“…If the methyl branching is derived from the former two amino acids (Val and Leu), it is located on the penultimate carbon of the alkyl chain yielding nonchiral iso ‐fatty acids ( i FAs). In contrast, anteiso ‐fatty acids ( a FAs), which are derived from Ile, have the methyl branching at the antepenultimate carbon of the alkanoic acid chain, and are therefore chiral 15,16 . Traditionally, they have been analyzed as fatty acid methyl esters by GC‐FID or GC‐MS, 16 yet chiral separation and distinction between enantiomeric forms was rarely in the main focus of such research.…”