Normal and low molecular weight heparins: interaction with human platelets.

Area of Science:

• Biochemistry
• Pharmacology
• Hematology

Background:

• Heparin, a widely used anticoagulant, exists in various forms including standard unfractionated heparin and low molecular weight heparin (LMWH).
• The molecular weight and structural characteristics of heparin preparations can influence their biological activities.
• Platelet function, particularly serotonin release, is a critical aspect of hemostasis and thrombosis.

Purpose of the Study:

• To investigate the in vitro effects of chemically depolymerized porcine mucosal heparins on platelet serotonin release.
• To compare the effects of low molecular weight heparins (LMWH) with normal heparins, dermatan sulfate, and heparan sulfate on platelet function.
• To explore the relationship between heparin's molecular weight, anti-clotting activity, and its impact on platelet serotonin release.

Main Methods:

• Chemical depolymerization of porcine mucosal heparin to produce two LMWH fractions (10,000 Da and 6,000 Da).
• In vitro assessment of anti-clotting activities (anti-activated factor X and anti-global clotting) of heparin preparations.
• Evaluation of platelet serotonin release in washed platelets and platelet-rich plasma, induced by collagen and adenosine diphosphate (ADP).

Main Results:

• No significant serotonin release was observed from washed platelets upon addition of any tested heparin preparation.
• Normal heparins inhibited collagen-induced serotonin release in platelet-rich plasma, while ADP-induced release was increased.
• Low molecular weight heparins (LMWH) did not show significant effects on serotonin release, suggesting a molecular weight-dependent mechanism.
• A correlation was found between the anti-activated factor X/anti-global clotting activity (Xa/APTT) ratio and the observed effects on platelet release.

Conclusions:

• The effect of heparin preparations on platelet serotonin release is dependent on their molecular weight.
• Low molecular weight heparins (LMWH) exhibit a diminished capacity to modulate platelet serotonin release compared to normal heparins.
• Heparin's influence on platelet serotonin release is linked to its anticoagulant potency, particularly its anti-factor Xa activity.