Biology Reference
In-Depth Information
of the compound (
i.e.
, EA was not detected in plasma). These results
indicate that the food matrix (pH, constituents, processing, etc.) can have
a crucial impact on EA absorption in the proximal part of the GI tract.
Differences between individuals can also be very important in terms of
absorption. The absorption of EA in distal parts of the GI tract seems to
be less relevant. Animal studies show that EA is released from ETs in the
small intestine, and absorbed in the cells of the small intestine (jejunum,
ileon). EA is readily metabolized in the intestinal cells to furnish methyl
and dimethyl ethers and glucuronic acid conjugates. These metabolites
are detected in bile and also in peripheral plasma and urine, but no free
EA was detected.
7.6.2 Intestinal microflora metabolism
One of the main events in ET metabolism and bioavailability is the
microbial transformation into a series of hydroxylated dibenzopyranone
derivatives. Among them, the best known and characterized derivatives
are urolithins A and B, but metabolites with three (urolithin C) and four
(urolithin D) phenolic hydroxyl groups are also produced in the small
intestine (Fig. 7.2) (Espín
et al.
, 2007; Ito
et al.
, 2008). Urolithins are
absorbed in the small intestine, and excreted in the bile after methylation
and conjugation with glucuronic acid, suffering entero-hepatic
recirculation (Espín
et al.
, 2007). Animal experiments show that these
metabolites start to be formed in the small intestine indicating that
anaerobic bacteria may be responsible for this. The metabolism
continues along the GI tract to end with the production of urolithins A
and B. Differences in the production of these metabolites by human
volunteers show that they may be produced by the activity of specific
microorganisms present in the gut. If these microbial metabolites, which
are more bioavailable than native ETs and EA, were the true active
principles responsible for the biological activity associated with ETs and
EA rich foods consumption, then this would bring up the possibility of
developing new functional foods in which specific ET-metabolizing
microorganisms could be included together with the ETs.
