Colonic Metabolism Of The Common Dietary Polyphenol Quercetin‐3‐O‐Rutinoside (Rutin) – Impact Of Age And Gut Health

Dietary polyphenols may play a role in health; they are, however, poorly bioavailable and mostly metabolised in the colon by the microbiota. Phenolic acids (PA), key colonic metabolites, are more bioavailable and may be beneficial for gut health, in particular for mediation of colorectal cancer (CRC) risk. We have shown that urinary PA excretion changes with ageing and with increased CRC risk (after polypectomy). We sought to understand the inter‐individual variation in the gut functional capacity to metabolise a dietary polyphenol (quercetin‐3‐O‐rutinoside – or rutin) using a gut fermentation model. Rutin (28 μmoles) was incubated for 24 hr with or without fibre (raftiline, 1g) in a 50 ml in vitro fermentation model with fresh faecal samples from healthy volunteers aged 23–43 (n=6), healthy volunteers aged 51–76 (n=4) and volunteers at risk of CRC aged 51–75 (n=5), who followed a low‐polyphenols low‐fibre fibre for 3 days prior to providing samples. PA in slurries were measured by gas chromatography (GC) mass spectrometry. Short chain fatty acids (SCFA) were measured by GC with flame ionization detector, alongside with pH and gas. Seven PA were identified in slurries fermented for 6 and 24hr: phenylacetic acid (PAA), 3‐hydroxyphenylacetic acid (3‐OHPAA), 4‐hydroxybenzoic acid (4‐OHBA), 3‐Hydroxyphenylpropionic acid (3‐OHPPA), 4‐hydroxyphenylpropionic acid (4‐OHPPA), 4‐hydroxy‐3‐methoxy‐phenylpropionic acid (3,4diOHPPA), and 3,4‐dihydroxyphenylacetic acid (3,4diOHPAA). PA present in control (blanks) and raftilin‐only slurries were subtracted. Without fibre, the sum of PA peaked at 24hrs for the healthy young group (70 μmoles/L, IQR 15) and older group (65 μmoles/L, IQR 8), compared to 6hr for the CRC‐risk group (73 μmoles/L, IQR 60), highlighting a possible difference in metabolic kinetics (with no difference in peak concentrations). Minimal levels of PA were detected for all time points and conditions in 2/5 volunteers in the CRC group (causing the high variability in that group), whereas high levels of PA were detected in at least one or more experimental condition or timepoint in all other volunteers. Presence of fibre in the slurries led to lower (~86%) PA at 24hr (11 μmoles/L, IQR 28) and a 30‐fold higher level at 6hr (0.2 to 5 μmole/L, p=0.03) in the slurries of the young group, consistent with a potential acceleration of rutin metabolism/catabolism. A weaker impact of fibre was observed at 24hr (~47%) in the healthy older group. Fibre did not lower the PA detected for the CRC‐risk group, which peaked at 24hr (compared to 6hr without fibre). Marginal levels of 4‐OHPPA, 4‐OHBA and 3,4‐diOHPPA stemmed from rutin metabolism, with or without fibre. PAA levels were above control slurries level only for young and old healthy groups without fibre, after 24hr. Major PA detected included (descending order) 3,4‐diOHPAA, 3‐OHPPA, and 3‐OHPAA (no significant difference between groups). 3,4‐DiOHPAA accounted for most of the variations described for the sum of PA. No differences in pH, gas formation or the levels of the total or specific SCFA (acetic, propionic, and butyric acid) were detected between groups While a difference was observed for urinary excretion of PA between groups, this variation cannot be fully explained by the functional capacity of the gut studied via in vitro fermentation. Other important factors, such as absorption rate of the metabolites, should be taken in consideration, and the impact of substrate on fermentative capacity of the gut studied further. Support or Funding Information This work was supported by the Faculty of Applied Medical Sciences – Clinical Nutrition Department, King Abdulaziz University, Jeddah, Kingdom of Saudi Arabia 2010–1012, and Tenovus Scotland (Grant S10/6).