Andrographolide is a novel NF-κB inhibitor from the leaves of Andrographis paniculata. Platelet activation is relevant to a variety of thrombotic diseases. However, no data are available concerning the effects of
andrographolide in platelet activation. The aim of this study was to examine the mechanisms of
andrographolide in preventing platelet activation.
Andrographolide (25-75 μΜ) exhibited a more potent activity of inhibiting platelet aggregation stimulated by
collagen.
Andrographolide inhibited
collagen-stimulated platelet activation accompanied by relative Ca(2+) mobilization;
thromboxane A(2) formation; and
phospholipase C (PLC)γ2,
protein kinase C (PKC),
mitogen-activated protein kinase (MAPK), and Akt phosphorylation.
Andrographolide markedly increased
cyclic GMP, but not
cyclic AMP levels.
Andrographolide also stimulated
endothelial nitric oxide synthase (eNOS) expression, NO release, and
vasodilator-stimulated phosphoprotein (VASP) phosphorylation. ODQ, an inhibitor of
guanylate cyclase, markedly reversed the
andrographolide-mediated inhibitory effects on platelet aggregation,
p38 MAPK and Akt phosphorylation, and the
andrographolide-mediated stimulatory effect on VASP phosphorylation. Furthermore, a
PI3 kinase inhibitor (
LY294002) but not a PKC inhibitor (Ro318220) significantly diminished
p38 MAPK phosphorylation; nevertheless, a
p38 MAPK inhibitor (
SB203580) and
LY294002 diminished PKC activity stimulated by
collagen.
Andrographolide also reduced
collagen-triggered
hydroxyl radical (
OH([Symbol: see text])) formation. In vivo studies revealed that
andrographolide (22 and 55 μg/kg) is effective in reducing the mortality of
ADP-induced acute
pulmonary thromboembolism and significantly prolonged platelet plug formation in mice. This study demonstrates for the first time that
andrographolide possesses a novel role of antiplatelet activity, which may involve the activation of the eNOS-NO/
cyclic GMP pathway, resulting in the inhibition of the
PI3 kinase/Akt-
p38 MAPK and PLCγ2-PKC cascades, thereby leading to inhibition of platelet aggregation.