Carrageenan-induced activation of human platelets is dependent on the phospholipase C pathway.
Stimulation of washed human platelets by the pro-inflammatory polysaccharide carrageenan is accompanied by shape change, aggregation and release of granule contents and unaccompanied by thromboxane A2 synthesis. Carrageenan triggers platelet activation through a prostaglandin synthetase-independent mechanism. The phospholipase A2 (PLA2) inhibitor, p-bromophenacyl bromide suppresses platelet responses to carrageenan (Vargaftig et al, 1980) probably by mechanism(s) other than those which involve PLA2 activity. Exposure of platelets to carrageenan (2-25 micrograms/ml) induced inositol phosphate formation in a time- and concentration-dependent manner, the level of inositol phosphate formation correlating with the intensity of aggregation. Neomycin, an aminoglycoside antibiotic which inhibits the phospholipase C-mediated phosphatidylinositol 4,5-bisphosphate breakdown, suppressed both platelet activation and inositol phosphate formation. Inhibition was concentration-dependent with an IC50 value of about 180 microM. Platelet-activating factor (PAF) is not responsible for carrageenan-induced platelet activation and inositol phosphate formation, since exposure of platelets to carrageenan (25 micrograms/ml) in the presence of compound WEB 2086 (100 microM), a PAF antagonist, failed to inhibit carrageenan responses. However, compound Ro 19-3704, a structurally related antagonist of PAF reported to be also an inhibitor of phospholipases A2 and C, inhibited concentration-dependently (0.1-10 microM) aggregation and ATP release induced by carrageenan (25 micrograms/ml). These findings indicate that carrageenan activates human platelets through a phospholipase C-dependent mechanism and show that neomycin, at low concentrations, can be a selective inhibitor of phospholipase C-mediated PIP2-breakdown.
Hatmi
M
M
Unité de Pharmacologie Cellulaire, Unité Associée Institut Pasteur, INSERM no. 285, Paris, France.
Randon
J
J
Faili
A
A
Vargaftig
B B
BB
D001792:Blood Platelets / Q000201:enzymology / Q000378:metabolism; D002351:Carrageenan / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000096:biosynthesis; D009355:Neomycin / Q000494:pharmacology; D010972:Platelet Activating Factor / Q000502:physiology; D015539:Platelet Activation / Q000187:drug effects*; D010974:Platelet Aggregation / Q000187:drug effects; D010738:Type C Phospholipases / Q000378:metabolism*
D007295:Inositol Phosphates; D010972:Platelet Activating Factor; D002351:Carrageenan; D010738:Type C Phospholipases; D009355:Neomycin