Procyanidins are not bioavailable in rats fed a single meal containing a grapeseed extract or the procyanidin dimer B<SUB>3</SUB>

Abstract

Flavanols are the most abundant flavonoids in the human diet where they exist as monomers, oligomers and polymers. In the present study, catechin, the procyanidin dimer B 3 and a grapeseed extract containing catechin, epicatechin and a mixture of procyanidins were fed to rats in a single meal. After the meals, catechin and epicatechin were present in conjugated forms in both plasma and urine. In contrast, no procyanidins or conjugates were detected in the plasma or urine of any rats. Procyanidins were not cleaved into bioavailable monomers and had no significant effects on the plasma levels or urinary excretion of the monomers when supplied together in the grapeseed extract. We conclude that the nutritional effects of dietary procyanidins are unlikely to be due to procyanidins themselves or monomeric metabolites with the intact flavonoid-ring structure, as they do not exist at detectable concentrations in vivo. Future research should focus on other procyanidin metabolites such as phenolic acids and on the effects of the unabsorbed oligomers and polymers on the human gastrointestinal tract.

Liquid chromatography tandem mass spectrometry identification of proanthocyanidins in rat plasma after oral administration of grape seed extract

“…In the present study, proanthocyanidins up to nonamers and substantial but undetermined high molecular weight polymeric proanthocyanidins were detected. One of the major questions has been whether the high molecular weight proanthocyanidins are bioavailable in detectable amounts (Donovan et al, 2002). It has been suggested that the effects of dietary proanthocyanidins are unlikely to be due to proanthocyanidins themselves or monomeric metabolites with the intact flavonoid-ring structure, as they do not exist at detectable concentrations in vivo .…”

The chemistry of gut microbial metabolism of polyphenols

“…Spencer and co-workers (Spencer, Chaudry, Pannala et al, 2000) have demonstrated that proanthocyanidins undergo partial acid-catalyzed cleavage into their monomeric flavan-3-ol units in the gastric milieu. However, others have disputed the contribution of gastric depolymerization to the bioavailability of the constituent catechin units of proanthocyanidins (Donovan, Manach, Rios et al, 2002). …”

Feasibility and application of liquid–liquid extraction combined with gas chromatography–mass spectrometry for the analysis of phenolic acids from grape polyphenols degraded by human faecal microbiota

“…Their monomeric units [(+)-catechin and (-)-epicatechin)] are linked through a C4-C8 or C4-C6 bond (B-Type), which can coexist with an additional C2-O-C7 bond (A-Type). Absorption of procyanidins after food intake has been reported in several earlier studies (Donovan et al, 2002;Groenewoud & Hundt, 1986;Van'T Slot, Mattern, Rzeppa, Grewe & Humpf, 2010) and it is known that only procyanidin dimers are believed to be absorbed intact, although with lower efficiency than the monomeric units (Appeldoorn, Vincken, Aura, Hollman & Gruppen, 2009). Due to the low absorption of intact procyanidins, gut microbial metabolism might play an important role.…”

“…Oligomers and polymers are called proanthocyanidins or condensed tannins, and they are some of the most abundant phenolic compounds in some foods such as cacao, tea and wine (Gu et al, 2004). They are mainly made up of (epi)catechin or (epi)gallocatechin units that are known as procyanidins or prodelphinidins, respectively (Donovan, Manach, Rios, Morand, Scalbert & Rémésy, 2002).…”