Biology Reference
In-Depth Information
absorbed, then it is valid to ask the ques-
tion: what role is played by this great load of
antioxidants in different portions of the
digestive tract?
Recently Selma and coworkers (2009)
have published a review in which the uni-
verse of potential interactions and reactions
between polyphenols and intestinal biota is
brilliantly illustrated. In this work it was
suggested that the systemic effect of
polyphenols would be attributable to modu-
lations in the intestinal biota balance and
also to the intestinal metabolites generated
from these antioxidant molecules. Therefore,
the intestinal biota emerged as a key factor
behind the observed variability in the results
of some studies undertaken in animal and
humans (Fig. 2.2).
An example of how the presence of
polyphenols in the intestinal tract can bring
health benefits is their effect on the patho-
gen H. pylori . The presence of virulent
strains of H. pylori invariably promotes an
immune response characterized by robust
oxidative stress as one of the main defence
mechanisms against this bacterium. Many of
the ROS produced during this process are
able to damage gastric and intestinal mucosa.
It therefore seems very important to have
efficient antioxidant systems (both endo-
genous and dietary) in the site of infection.
However, H. pylori have many survival strat-
egies against oxidative stress that give rise to
the question: is it good to administrate anti-
oxidants to H. pylori -infected individuals?
One can deduce that these compounds may
have a protective effect not only for the host,
but also on H. pylori (contributing to their
antioxidant defences). Theoretically, by
increasing the ability of bacteria to 'deal'
with ROS generated by the host immune
system, it would also increase the possibil-
ity of consolidating infection. Many studies
with antioxidant-rich plant extracts have,
however, shown in vitro and in vivo anti-
H. pylori effects (Mahady et al. , 2005; Nostro
et al. , 2006; Ustun et al. , 2006). According to
preliminary data, some polyphenolic com-
pounds have recognized bactericidal activ-
ity, probably associated with a non-specific
mechanism not necessarily related to their
antioxidant (cytoprotective) effect on epi-
thelial cells (Puupponen-Pimia et al. , 2001).
One hypothesis that has been accepted as a
paradigm is that polyphenols exert part of
their antimicrobial activity by a non-specific
interaction with plasma membrane compo-
nents (Mori et al. , 1987; Haraguchi et al. ,
1998; Funatogawa et al. , 2004).
Another attractive approach is how
polyphenols can neutralize some virulence
factors of H. pylori such as urease, VacA
and CagA, and modulate the adhesion of
this pathogen to the gastric mucosa. In
vivo , 15-20% of H. pylori attach to gastric
epithelial cells (Hessey et al. , 1990).
Because of that, adhesion mechanisms
present a very attractive molecular target
for limiting H. pylori gastric colonization.
Indeed, the anti-adhesion properties of
RESULTS
HIGHLY
VARIABLE
Plants and
Foods
INTAKE
Metabolism
BIO-
ACTIVITY
'IN VITRO'
?
Fig. 2.2. Human microbiota, which can metabolize plant and food constituents, cause highly variable
results in clinical trials.
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