576 A. D ́avalos and M. A. Lasunci ́on
oxide synthase. The NADPH oxidase enzyme system is considered a major source
of superoxide in vascular cells, phagocytic polymorphonuclear neutrophils, mono-
cytes, and platelets (Bedard and Krause 2007). Phagocyte NADPH oxidase is com-
prised of the membrane-bound catalytic core flavocytochrome b 558 , formed by the
subunit NOX2/gp91phox and p22phox, and the cytosolic components p47phox,
p67phox, p40phox, the small G-protein Rac, and rap1A. Once cytosolic compo-
nents are activated, they assemble with the flavocytochrome and share the capacity
to transport electrons across the plasma membrane to generate superoxide and other
downstream ROS. Homologs of the cytochrome subunits—NOX1, 3, 4, 5, DUOX1,
and DUOX2—have been characterized. Nox1 and Nox4 are abundantly expressed
in VSMCs and endothelial cells, respectively, but the distribution of the different
members of the family is markedly different (Bedard and Krause 2007). In contrast
to abundant phagocytic production of superoxide for host defense, vascular and
other non-phagocytic cells produce superoxide, but to a significantly lesser extent.
Increased NADPH oxidase activity contributes to a large number of diseases, in
particular cardiovascular diseases and neurodegeneration (Cave et al. 2006; Infanger
et al. 2006). NADPH oxidase overexpression and superoxide production have been
shown to correlate with the severity of atherosclerosis (Sorescu et al. 2002), plaque
stability (Azumi et al. 2002), oxidative stress in coronary artery disease (Guzik
et al. 2000), plasma metalloproteinase-9 levels (Zalba et al. 2007), and circulat-
ing oxidized LDL (Carnevale et al. 2007; Fortu ̃no et al. 2006), supporting a role
for this enzyme in the pathogenesis of atherosclerosis (Azumi et al. 2002; Guzik
et al. 2006). Thus, it might be suggested that reduction of NADPH-oxidase pro-
duction and levels of systemic superoxide would reduce vascular disease associated
with oxidative stress.
In vitro studies revealed that polyphenols reduce expression of the NADPH
oxidase subunits p22phox and p67phox in endothelial cells (Xu et al. 2004; Ying
et al. 2003), and NADPH oxidase-dependent platelet recruitment via the inhibi-
tion of protein kinase C (PKC) (Pignatelli et al. 2006a). Activation of PKC trig-
gers the respiratory burst of phagocytes liberating large amounts of superoxide.
Inhibition of PKC-induced activation by collagen was achieved by the synergistic
effect of quercetin and catechin, but was unaffected by single polyphenols (Pig-
natelli et al. 2006b). In animal models, polyphenols prevented angiotensin II or
deoxycorticosterone acetate salt-induced expression of p22phox or p47phox associ-
ated with hypertension (Jimenez et al. 2007; Sanchez et al. 2007; Sarr et al. 2006)
and prevented the increased expression of NOX2 in fructose-fed rats (Al-Awwadi
et al. 2005). Red wine polyphenols prevent angiotensin II-induced hypertension and
endothelial dysfunction in rats by reducing the expression of p22phox and Nox-1
(Sarr et al. 2006). The mechanism through which polyphenols reduce NADPH oxi-
dase expression and activity is not well understood; however, the redox-sensitive
NFB pathway may be involved. TNF -induced activation of NFB regulates the
transcriptional activation of p47phox, p67phox, and NOX2 (Gauss et al. 2007), and
NFB sites have been described in the p22phox gene promoter (Moreno et al. 2003).
We have recently observed that in hemodialysis patients dietary supplementa-
tion with concentrated red grape juice rich in polyphenols reduces the phagocytic