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Evidence that fibrin alpha-chain RGDX sequences are not required for
platelet adhesion in flowing whole blood
RR Hantgan, SC Endenburg, JJ Sixma and PG de Groot
Department of Biochemistry, Bowman Gray School of Medicine, Wake Forest
University, Winston-Salem, NC 27157, USA.
The role of the RGDX putative receptor-recognition sites, which are present
on the alpha chains of fibrin, in promoting platelet adhesion has been
examined in flowing whole blood using the rectangular perfusion chamber at
wall shear rates of 340 and 1,600/s. Platelets adhered to a comparable
extent to surfaces coated with native fibrin and surfaces coated with
fragment X-fibrin, a product of limited fibrinolysis that lacks the RGDS
sites normally present at positions 572 to 575 of the alpha chains. The
strengths of these adhesive interactions were comparable based on the
concentrations of the antiadhesive peptide D-RGDW required to block
platelet deposition to native and fragment X-fibrin at both low and high
wall shear rate. Blocking either or both RGDX sequences with
peptide-specific monoclonal antibodies did not inhibit platelet deposition
in perfusion experiments performed with normal blood at 340/s, indicating
that neither RGD motif is required for adhesion. However, adhesion was
partly inhibited by anti-RGDX antibodies when perfusions were performed
with blood from an afibrinogenemic patient, suggesting the RGDX sequences
may play a limited role in platelet deposition. Exposure of fibrin surfaces
to plasminogen/tissue-type plasminogen activator did cause a time-
dependent loss of adhesiveness, but this effect was only weakly correlated
with proteolysis of the fibrin alpha chains. These observations provide
evidence that neither RGDX sequence is required for platelets to adhere
avidly to fibrin in flowing blood. These results further suggest that
incomplete fibrinolysis yields a highly thrombogenic surface.
Volume 86,
Issue 3,
pp. 1001-1009,
08/01/1995
Copyright © 1995 by The American Society of Hematology
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