Release of soluble CD40L from platelets is regulated by glycoprotein IIb/IIIa and actin polymerization.
OBJECTIVE
The purpose of this study was to examine the effects of glycoprotein (GP) IIb/IIIa antagonists (abciximab, eptifibatide, and tirofiban) and other inhibitors on translocation of CD40L from intraplatelet stores to the platelet surface and on the release of soluble CD40L (sCD40L) from platelets.


BACKGROUND
CD40L is a proinflammatory and prothrombotic ligand in the tumor necrosis factor family.


METHODS
Platelet surface CD40L was measured by flow cytometry, and sCD40L was measured by enzyme-linked immunosorbent assay.


RESULTS
Translocation of CD40L from intraplatelet stores to the platelet surface was not inhibited by GP IIb/IIIa antagonists. However, release of sCD40L from the surface of activated platelets was inhibited by GP IIb/IIIa antagonists in a dose-dependent manner, in concert with inhibition of PAC1 binding to platelets (a surrogate marker for fibrinogen binding). Release of sCD40L from activated platelets was also markedly reduced in Glanzmann platelets (deficient in GP IIb/IIIa). Ethylenediaminetetraacetic acid was an effective inhibitor of sCD40L release, but only when added before platelet activation. Both cytochalasin D (an inhibitor of actin polymerization) and GM6001 (an inhibitor of matrix metalloproteinases [MMPs]) inhibited the release of sCD40L from platelets when added before, as well as 3 min after, platelet activation. However, neither cytochalasin D nor GM6001 affected translocation of CD40L to the platelet surface.


CONCLUSIONS
The GP IIb/IIIa antagonists inhibit release of sCD40L from activated platelets. Release of sCD40L from platelets is regulated, at least in part, by GP IIb/IIIa, actin polymerization, and an MMP inhibitor-sensitive pathway. In addition to their well-characterized inhibition of platelet aggregation, GP IIb/IIIa antagonists may obviate the proinflammatory and prothrombotic effects of sCD40L.
Furman
Mark I
MI
Center for Platelet Function Studies, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA.
Krueger
Lori A
LA
Linden
Matthew D
MD
Barnard
Marc R
MR
Frelinger
Andrew L
AL
Michelson
Alan D
AD
D051339:Actin Depolymerizing Factors; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism*; D023201:CD40 Ligand / Q000187:drug effects* / Q000378:metabolism*; D002614:Chelating Agents / Q000008:administration & dosage; D015638:Cytochalasin D / Q000008:administration & dosage; D051345:Destrin; D004151:Dipeptides / Q000008:administration & dosage; D004305:Dose-Response Relationship, Drug; D004492:Edetic Acid / Q000008:administration & dosage; D006801:Humans; D020782:Matrix Metalloproteinases / Q000187:drug effects / Q000378:metabolism; D008840:Microfilament Proteins / Q000008:administration & dosage*; D019384:Nucleic Acid Synthesis Inhibitors / Q000008:administration & dosage; D015539:Platelet Activation / Q000187:drug effects; D010975:Platelet Aggregation Inhibitors / Q000008:administration & dosage*; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000008:administration & dosage* / Q000037:antagonists & inhibitors*; D011480:Protease Inhibitors / Q000008:administration & dosage; D012995:Solubility; D013915:Thrombasthenia / Q000097:blood; D014409:Tumor Necrosis Factor-alpha / Q000187:drug effects / Q000378:metabolism
D051339:Actin Depolymerizing Factors; D002614:Chelating Agents; D051345:Destrin; D004151:Dipeptides; D008840:Microfilament Proteins; C078131:N-(2(R)-2-(hydroxamidocarbonylmethyl)-4-methylpentanoyl)-L-tryptophan methylamide; D019384:Nucleic Acid Synthesis Inhibitors; D010975:Platelet Aggregation Inhibitors; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011480:Protease Inhibitors; D014409:Tumor Necrosis Factor-alpha; D023201:CD40 Ligand; D015638:Cytochalasin D; D004492:Edetic Acid; D020782:Matrix Metalloproteinases