Disintegration of wheat aleurone structure has an impact on the bioavailability of phenolic compounds and other phytochemicals as evidenced by altered urinary metabolite profile of diet-induced obese mice

Abstract

BackgroundPhenolic acids are covalently bound to the arabinoxylan fibre matrix of wheat aleurone layer. In order to be bioavailable they need to be released by endogenous or bacterial enzymes and absorbed within the intestinal lumen. The intestinal microbiota can metabolize phenolic acids and other food-born phytochemicals. However, the effect of structure of the cereal bran or aleurone layer on these processes is not comprehensively studied.MethodsThe structure of aleurone layer was modified either by dry-grinding or by enzymatic treatments with xylanase alone or in combination with feruloyl esterase. Diet induced obese C57BL6/J mice were fed with high-fat diets containing either pure ferulic acid, or one of the four differentially treated aleurone preparations for 8 weeks. The diets were designed to be isocaloric and to have similar macronutrient composition. The urinary metabolite profiles were investigated using non-targeted LC-qTOF-MS-metabolomics approach.ResultsThe different dietary groups were clearly separated in the principal component analysis. Enzymatic processing of aleurone caused increased excretion of ferulic acid sulfate and glycine conjugates reflecting the increase in unbound form of readily soluble ferulic acid in the diet. The urinary metabolite profile of the diet groups containing native and cryo-ground aleurone was more intense with metabolites derived from microbial processing including hippuric acid, hydroxyl- and dihydroxyphenylpropionic acids. Furthermore, aleurone induced specific fingerprint on the urinary metabolite profile seen as excretion of benzoxazinoid metabolites, several small dicarboyxlic acids, and various small nitrogen containing compounds.ConclusionsThe structural modifications on wheat aleurone fraction resulted in altered metabolism of aleurone derived phenolic acids and other phytochemicals excreted in urine of diet-induced obese mice.

Nontargeted Metabolite Profiling Discriminates Diet-Specific Biomarkers for Consumption of Whole Grains, Fatty Fish, and Bilberries in a Randomized Controlled Trial

“…These results are in concordance with our earlier report, which showed no differences in urinary excretion of HA acid after ingestion of rye bread and white-wheat bread (45). Even though HA is regarded as a biomarker for dietary intake of phenolics, polyphenol metabolism by the intestinal microbiota and liver can produce numerous other metabolites into the circulation (46).…”

Biodisponibilidad de compuestos fenólicos dietéticos: Revisión

“…Most cereal phenols have covalent interactions with glycosides from the cell wall, forming ester linkages which are not hydrolysed by Phase I and II biotransformation enzymes, thus limiting their release into the colon to be metabolized by intestinal microbiota 17,18 . Such interactions depend on the specific porosity and surface properties of the cell wall that can measure between 4 and 10mm diameter which restricts the penetration of molecules with high molecular weight polyphenols (>10kDa) 19 .…”

“…The bound phenolic acids have very low bioavailability because the bran matrix severely hinders their access to the necessary enzymes (such as ferulate esterases, xylanases) that contribute to their release in the human gastrointestinal tract 18,21,22 .…”

Whole grains beyond fibre: what can metabolomics tell us about mechanisms?

“…A large number of metabolites, including hippurate, dihydrophenolic acids and benzoxazinoids metabolites were released from the fibre matrix when the aleurone layer was milled or ultramilled. Fermentation of the aleurone layer feed led to a different urinary metabolite response altogether, including many unknown metabolites and small phenolic acids (19) . Although this work did not link the different responses to metabolic endpoints in the mice, it is a clear demonstration of the ability of metabolomics to detect differences in gut microbiotarelated metabolites, as well as to discriminate between fermented and non-fermented diets.…”

“…Other indications of interactions with gut microbiota are the diversity of phenolic compounds found in plasma and urine after the intake of phenolic rich wheat aleuronebased diets in mice (19) . Although linking the relatively low concentrations of these compounds to reduced risk of disease will prove challenging, it does provide evidence that gut microbiota are metabolising the diverse array of phenolic compounds present in whole grains, and it can be speculated that this may drive greater microbial diversity to adapt to the more diverse substrate, a factor implicated in the prevention of obesity (51) .…”