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Glycocalicin: a new assay--the normal plasma levels and its potential
usefulness in selected diseases
JH Beer, L Buchi and B Steiner
University Hospital of Bern, Laboratory for Thrombosis Research,
Switzerland.
Platelet glycocalicin (GC) is the extramembranous portion of GPIb alpha
that can be rapidly cleaved by enzymes such as calpain, plasmin, trypsin,
elastase, etc. Quantitative cleavage will ultimately result in an acquired
Bernard-Soulier-like bleeding disorder, and circulating GC may act as a
potential inhibitor of platelet adhesion. We have developed and
standardized a new enzyme-linked immunosorbent assay (ELISA), which uses
two monoclonal antibodies (mAbs), both of which bind to the amino-terminal
45-kD fragment of GC and inhibit platelet- von Willebrand interactions and
the streptavidin-biotin system. First, the methodology was evaluated and
standardized with special emphasis on the anticoagulant and the inhibitors
(EDTA, prostaglandin E1 [PGE1], aprotinin, N-ethyl-maleimide), the mode of
high-speed centrifugation (to avoid platelet microparticles), and the
standards used (purified GPIb and GC). This assay was then used to analyze
the GC levels of healthy subjects (2.04 +/- 0.46 micrograms/mL) and of
patients with selected diseases. The results of patients with aplastic
anemia and thrombocytosis confirmed that GC levels are clearly dependent on
the platelet count, which was the basis for the introduction of the GC
index, the standardization of GC for a platelet count of 250 x 10(9)/L. The
GC index discriminates reliably patients with active immune
thrombocytopenic purpura from those in remission. GC levels are elevated in
patients on hemodialysis (3.62 +/- 0.75 micrograms/mL, P < .001). The
high GC index (6.93 +/- 4.21, P < .001) in cirrhosis patients suggests
an increased platelet turnover and/or abnormal proteolysis. In contrast to
other groups, we have not found that recombinant tissue plasminogen
activator (rtPA) treatment of patients with myocardial infarction increases
GC levels. However, concentrations are elevated in leukemia and the highest
levels found are approximately 40 micrograms/mL. These studies suggest that
GC is a useful platelet marker in certain diseases, which directly reflects
platelet damage and possibly platelet dysfunction.
Volume 83,
Issue 3,
pp. 691-702,
02/01/1994
Copyright © 1994 by The American Society of Hematology
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