Barbara Buchetti

LDL are oxidatively modified by platelets via GP91phox and accumulate in human monocytes

Oxidative stress‐mediated LDL modification has a key role in initiation of the atherosclerotic process. Platelets produce reactive oxidant species (ROS) upon stimulation with agonist, but it is uncertain whether they are able to oxidatively modify LDL. Human platelets taken from healthy subjects were incubated with LDL, then stimulated with collagen. Compared with unstimulated platelets, collagen‐stimulated platelets induced LDL modification as shown by enhanced conjugated dienes and lysophosphatidylcho‐line formation, electrophoretic mobility, Apo B‐100 degradation, and monocyte LDL uptake. Activated platelets also induced a marked reduction of vitamin Ε contained in LDL. A significant inhibition of LDL oxidation was observed in platelets treated with arachi‐donyl trifluomethyl ketone (AACOCF3), an inhibitor of phospolipase A2. The experiments reported above were also conducted in patients with hereditary deficiency of gp91phox, the central core of NADPH oxidase, and in patients with hypercholesterolemia. Platelets from gp91 phox‐deficient patients produced a small amount of ROS and weakly modified LDL. Conversely, platelets from hypercholesterolemic patients showed enhanced ROS formation and oxidized LDL more than platelets from healthy subjects. This study provides evidence that platelets modify LDL via NADPH oxidase‐mediated oxidative stress, a phenomenon that could be dependent on arachidonic acid activation. This finding suggests a role for platelets in favoring LDL accumulation within atherosclerotic plaque.—Carnevale, R., Pignatelli, P., Lenti, L., Buchetti B., Sanguigni, V., Di Santo, S., Violi, F. LDL are oxidatively modified by platelets via GP91phox and accumulate in human monocytes. FASEB J. 21, 927–934 (2007)

GD3 nuclear localization after apoptosis induction in HUT-78 cells

Glycosphingolipids are essential components of plasma membrane and act as antigens, mediators of cell adhesion, and modulators of signal transduction. Following activation of the Fas receptor, gangliosides are recuited in various intracellular compartments. We have evaluated whether the pro-apoptotic anti-CD95 antibody induces a nuclear localization of GD3 in HUT-78 cells. Our data shows that GD3 translocation from cytosol to nuclei is strongly correlated to concomitant rapid phosphorylation of histone H1 shortly after induction of apoptosis. This work advances the hypothesis that GD3 induces a post-translational modification of histone H1 thus influencing the apoptosis process through transcriptional activation/repression of specific genes.

We-P14:420 Polyphenols enhance platelet nitric oxide by inhibiting protein kinase C-dependent NADPH oxidase activation. Effect on platelet recruitment

Several studies demonstrated an inverse association between polyphenol intake and cardiovascular events. Platelet recruitment is an important phase of platelet activation at the site of vascular injury, but it has never been investigated whether polyphenols influence platelet recruitment. The aim of the study was to analyze in vitro whether two polyphenols, quercetin and catechin, were able to affect platelet recruitment. Platelet recruitment was reduced by NO donors and by NADPH oxidase inhibitors and was enhanced by L-NAME, an inhibitor of NO synthase. Quercetin and catechin, but not single polyphenol, significantly inhibited platelet recruitment in a concentration-dependent fashion. The formation of superoxide anion was significantly inhibited in platelets incubated with quercetin and catechin but was unaffected by a single polyphenol. Incubation of platelets with quercetin and catechin resulted in inhibition of PKC and NADPH oxidase activation. Treatment of platelets with quercetin and catechin resulted in an increase of NO and also down-regulated the expression of GpIIb/IIIa glycoprotein. This study shows that the polyphenols quercetin and catechin synergistically act in reducing platelet recruitment via inhibition of PKC-dependent NADPH oxidase activation. This effect, resulting in NO-mediated platelet glycoprotein GpIIb/IIIa down-regulation, could provide a novel mechanism through which polyphenols reduce cardiovascular disease.