Plasma constituent (s) inhibiting platelet adhesiveness

Area of Science:

• Biochemistry
• Hematology
• Cell Biology

Background:

• Platelet adhesiveness is vital for hemostasis but can be dysregulated.
• Adhesiveness is pH-dependent near physiological levels.
• Platelets in platelet-rich plasma (PRP) show poor adhesion compared to washed or gel-filtered platelets (GFP).

Purpose of the Study:

• To identify the factor in PRP that inhibits the adhesiveness of gel-filtered platelets (GFP).
• To characterize the nature and properties of this inhibitory compound.

Main Methods:

• Separation of PRP using Sepharose 2B chromatography.
• Thermostability and dialyzability assays.
• Enzymatic digestion (pronase, trypsin).
• Isoelectric focusing and sodium dodecyl sulfate-gel electrophoresis.
• Assays involving washed erythrocytes and erythrocyte membranes.

Main Results:

• A thermostable, non-dialyzable inhibitor of GFP adhesiveness was isolated from PRP.
• The inhibitor was inactivated by pronase and partially by trypsin, suggesting a protein component.
• Erythrocytes and erythrocyte membranes reduced the inhibitor's potency.
• Isoelectric focusing identified the inhibitor in a fraction with an isoelectric point of 5.1, containing both proteins and lipids.
• SDS-PAGE revealed two protein bands in the purified fraction.

Conclusions:

• Platelet-rich plasma (PRP) contains a lipoprotein that inhibits platelet adhesiveness.
• This inhibitor is distinct from known platelet factors.
• Understanding this inhibitor could offer insights into platelet function and thrombosis.