title: Suppression of NF-κB signaling by andrographolide with a novel mechanism in human platelets: regulatory roles of the p38 MAPK-hydroxyl radical-ERK2 cascade.
abstract: Andrographolide, a novel nuclear factor-κB (NF-κB) inhibitor, is isolated from leaves of Andrographis paniculata. Platelet activation is relevant to a variety of coronary heart diseases. Our recent studies revealed that andrographolide possesses potent antiplatelet activity by activating the endothelial nitric oxide synthase (eNOS)-NO-cyclic GMP pathway. Although platelets are anucleated cells, they also express the transcription factor, NF-κB, that may exert non-genomic functions in platelet activation. Therefore, we further investigated the inhibitory roles of andrographolide in NF-κB-mediated events in platelets. In this study, NF-κB signaling events, including IKKβ phosphorylation, IκBα degradation, and p65 phosphorylation, were time-dependently activated by collagen in human platelets, and these signaling events were attenuated by andrographolide (35 and 75 μM). ODQ and KT5823, respective inhibitors of guanylate cyclase and cyclic GMP-dependent kinase (PKG), strongly reversed andrographolide-mediated inhibition of platelet aggregation, relative [Ca(2+)]i mobilization, and IKKβ, and p65 phosphorylation. In addition, SB203580 (an inhibitor of p38 MAPK), but not PD98059 (an inhibitor of ERKs), markedly abolished IKKβ and p65 phosphorylation. SB203580, NAC (a free-radical scavenger), and BAY11-7082 (an inhibitor of NF-κB) all diminished ERK2 phosphorylation, whereas PD98059, BAY11-7082, and NAC had no effects on p38 MAPK phosphorylation. Furthermore, SB203580, but not BAY11-7082 or PD98059, reduced collagen-induced hydroxyl radical ((·)HO) formation. KT5823 also markedly reversed andrographolide-mediated inhibition of p38 MAPK and ERK2 phosphorylation, and hydroxyl radical formation in platelets. In conclusion, this study demonstrated that andrographolide may involve an increase in cyclic GMP/PKG, followed by inhibition of the p38 MAPK/(·)HO-NF-κB-ERK2 cascade in activated platelets. Therefore, andrographolide may have a high therapeutic potential to treat thromboembolic disorders and may also be considered for treating various inflammatory diseases.
authors: Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei, Taiwan.
authors: Wan J
authors: WJ
authors: Lu
authors: Kuan H
authors: KH
authors: Lin
authors: Ming J
authors: MJ
authors: Hsu
authors: Duen S
authors: DS
authors: Chou
authors: George
authors: G
authors: Hsiao
authors: Joen R
authors: JR
authors: Sheu
mesh_terms: D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D003094:Collagen; D006152:Cyclic GMP / Q000378:metabolism; D004224:Diterpenes / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D017665:Hydroxyl Radical / Q000378:metabolism*; D051550:I-kappa B Kinase / Q000235:genetics / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000235:genetics / Q000378:metabolism*; D016328:NF-kappa B / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D015539:Platelet Activation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D019892:eIF-2 Kinase / Q000235:genetics / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
chemical_list: D004224:Diterpenes; D016328:NF-kappa B; D010975:Platelet Aggregation Inhibitors; D017665:Hydroxyl Radical; C030419:andrographolide; D003094:Collagen; D019892:eIF-2 Kinase; D051550:I-kappa B Kinase; C535150:MAPK1 protein, human; D019950:Mitogen-Activated Protein Kinase 1; D048051:p38 Mitogen-Activated Protein Kinases; D006152:Cyclic GMP