Electron microscopic observations on platelet aggregation induced by cationized ferritin.

Area of Science:

• Hematology
• Biochemistry
• Cell Biology

Background:

• Platelet aggregation is a critical process in hemostasis and thrombosis.
• The role of surface charge in platelet activation is not fully understood.
• Cationized ferritin (CF) is a positively charged macromolecule used to probe surface properties.

Purpose of the Study:

• To investigate the effect of cationized ferritin (CF) on human platelet aggregation.
• To elucidate the mechanism by which CF induces platelet aggregation.
• To determine the role of platelet surface charge in CF-mediated aggregation.

Main Methods:

• Washed and gel-filtered human platelets were incubated with varying doses of CF.
• Platelet aggregation was monitored using a lumiaggregometer.
• Electron microscopy was employed to visualize CF-platelet interactions.
• The role of calcium ions (Ca++) and plasma factors was assessed.
• Inhibitory effects of various agents (PGI2, PGE1, aspirin, N-ethylmaleimide, apyrase, heparin, neuraminidase) were evaluated.

Main Results:

• CF induced dose-dependent platelet aggregation without the need for Ca++ or plasma factors.
• Electron microscopy revealed CF particles attached to platelet surfaces, connecting platelets.
• Aggregation was biphasic, associated with adenosine triphosphate (ATP) release.
• The first phase of aggregation was inhibited by heparin, while the second phase was inhibited by PGI2, PGE1, aspirin, N-ethylmaleimide, and apyrase.
• Neuraminidase treatment inhibited CF-induced aggregation, suggesting the importance of surface charge.

Conclusions:

• Neutralization of the platelet surface negative charge by positively charged CF can trigger platelet aggregation.
• CF-induced aggregation involves platelet shape change, granule centralization, and ATP release.
• The findings highlight the significance of surface charge interactions in platelet activation.