Background: Platelets are key players in hemostasis. These blood cells contain different types of granules. Recently, there has been a growing interest in the role of inorganic polyphosphate (polyP) structures stored in dense granules of platelets and secreted during platelet activation.
Objectives: To measure platelet polyP levels in patients with thrombocytopenia and thrombocythemia, and to examine the relationship of this indicator with platelet aggregation.
Material and methods: The study included 36 patients with hematological disorders (26 with primary chronic thrombocytopenia and 10 with essential thrombocythemia (ET)) and 40 healthy subjects. Platelet reactivity was measured using whole blood impedance aggregometry. The polyP levels were isolated from lysed platelets, which were obtained from citrated platelet-rich plasma. The procedure included inactivating endogenous phosphatases, removing phosphate units derived from DNA and proteins, and finally hydrolyzing them into monophosphate units. A colorimetric assay using malachite green and ammonium molybdate was performed in order to quantify polyP levels.
Results: The polyP concentrations were significantly higher in the patients with thrombocytopenia than in the patients with thrombocythemia or the controls. The polyP level was not correlated with the level of aggregation.
Conclusions: The higher polyP levels observed in the patients with low platelet counts may indicate the existence of a compensatory mechanism that prevents excessive bleeding in such patients. Our study provides evidence of an essential role of polyP in platelet function and the coagulation process.
Keywords: coagulation; essential thrombocythemia; platelet polyphosphate; platelets; thrombocytopenia.