Biology Reference
In-Depth Information
gallate (EGCG) (Yee and Koo, 2000). The
same team of investigators subsequently
performed a prospective study between two
groups of individuals: one
H. pylori
-infected
(n = 42) and one uninfected (n = 30). The
main outcome was the effect of tea con-
sumption on the detection of
H. pylori
in
gastric biopsies. It was concluded that there
would be a significant inverse relationship
between tea consumption and the rate of
infection with
H. pylori
(Yee
et al.
, 2002).
One study focused on the evaluation of
potential antimicrobial activity of apple
peel polyphenols (Alberto
et al.
, 2006).
Although this work shows that this
extract exhibits certain anti-
Escherichia
coli
, anti-
Pseudomonas aeruginosa
and
anti-
Staphylococcus aureus
activity (among
others), it did not include
H. pylori
in the
evaluation. Apple peel polyphenols display
interesting mechanisms that prevent coloni-
zation by
H. pylori
in mice. For example,
their procyanidins can inhibit efficiently
the enzyme urease and neutralize VacA,
whereas its flavonoids (quercetin glyco-
sides) have both anti-
H. pylori
and anti-ROS
effects contributing to avoiding damage to
gastric mucosa (Pastene
et al
., 2009a,b,
2010). Previously it was reported that flavo-
noids can inhibit
H. pylori
-induced vacu-
olation in HeLa cells and additionally
display a moderate inhibitory activity against
urease (Shin
et al.
, 2005). In the case of pro-
cyanidin-rich extracts from
Vitis vinifera
,
Lee
et al
. (2006) found that these compounds
are particularly active in inhibiting urease
at low concentrations (0.1 mg/ml).
Apples also have other phenolics with
anti-
H. pylori
activity such as phloridzin (a
chalcone). This compound inhibits the
pore-forming ability of the VacA toxin. How-
ever, the anti-VacA activity (IC
50
= 273 mM)
of phloridzin is extremely low compared
with activity reported for tannic acid
(IC
50
= 2.7 mM). In fact, hydrolysable tannins
are more powerful than other polyphenols.
In another study, it was established that
tannic acid associated with n-propyl gallate
was very effective in inhibiting gastritis
promoted by
H. pylori
infection or direct
administration of VacA to mice (Ruggiero
et al.
, 2006). To investigate the proposed
mechanism, the structure-activity relation-
ships between polyphenols and their anti-
VacA activity (expressed as vacuolizing
activity and urea transmembrane flux) were
assessed in HeLa cells (Tombola
et al.
, 2003;
Ruggiero
et al
., 2006). Resveratrol, morin,
tannic acid and piceatanol seem to share
structural features that suggest the existence
of specific molecule-molecule interactions
between certain polyphenols and VacA.
Other polyphenols with high antioxi-
dant activity such as ellagic acid and myri-
cetin were partially or totally inactive
against VacA, respectively. These com-
pounds are present in varying amounts in
many foods and can be found in high con-
centrations in wine, beer, chocolate and
green tea. Shin
et al
. (2005) demonstrated
that antioxidants with diverse structures
such as ascorbic acid, glutathione, epicate-
chin and Trolox
®
(a water-soluble analogue
of a-tocopherol) have in common that they
are poor VacA inhibitors, suggesting that
antioxidant and anti-
H. pylori
activities are
not necessarily associated. Among these
antioxidants, the
H. pylori
inhibitory activi-
ties of epicatechin and vitamin C were eval-
uated. In this study, only vitamin C was
active
in vitro
and
in vivo
by a mechanism
not yet clarified, but in any case this would
not be associated with the effect of pH
(Zhang
et al
., 1997; Mabe
et al
., 1999; Wang
et al
., 2000b). The literature reports another
relevant fact that some flavonoids inhibit
the VacA-induced activation of procas-
pase-3 to caspase-3 without changes in the
expression of proteins Bax and Bcl-2 (anti-
apoptotic proteins). Thus, it has been sug-
gested that flavonoids such as quercetin can
protect gastric cells from apoptosis by inhib-
iting the action of vacuolating
H. pylori
toxin VacA. Additionally, it was found that
certain high molecular weight polyphenols
(oligomeric procyanidins extracted from the
hop bract), some of which are structurally
closely related to apple peel polyphenols,
are capable of forming complexes with VacA
in vitro
(Yahiro
et al
., 2005; Friedman,
2007). Yahiro
et al
. (2005) observed that the
interaction between oligomeric proanthocy-
anidins (with a mean degree of polymeriza-
tion equivalent to 22 catechin units) and
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