They are involved in hemostasis, atherothrombosis, inflammation, vascular biology, cancer cell metastasis and immunity.
Damage or injury to the endothelium (the inner lining of blood vessels) reveals the endothelium where platelets attach through Von Willebrand factor (vWF). The connection of platelets with each other is done by bridging the fibrinogen.
This is followed by platelet activation, release of intracellular granules, adhesion and finally activation of the coagulation cataract.
What is the pathophysiology of platelets?
“Platelet disorders are either quantitative or functional. An increase> 450,000 / μL is called thrombocytosis and a decrease <150,000 / μL is called thrombocytopenia.
Dysfunction with hypoactive platelets (thrombosis) can occur in thrombocythemias eg myeloproliferative, in thrombocytopenias eg myelodysplastic, but also with a normal platelet count eg multiple myeloma, macrostroma. Thrombosis causes bleeding.
Hyperactive platelets cause thrombosis and atherogenesis (biological aging). “Cardiovascular diseases, inflammatory bowel diseases, rheumatoid arthritis, Alzheimer’s, myeloproliferative neoplasms, diabetes mellitus, smoking, COVID-19, are accompanied by hyperactive platelets”, explains Mr. A. Analogatos.
In COVID-19 in particular, hypoxia causes platelet overstimulation, interaction and adhesion to blood monocytes, and finally platelet consumption (thrombocytopenia) and increased
D-Dimers. These two changes are adverse survival factors.
In severe COVID-19 disease, there are scattered inflammatory micro-clots throughout the vascular network, including the lungs. They are not shown on the CT scan. Patients taking aspirin had a reduced risk of mortality (UK).
Is platelet activation related to the rare but dangerous VITT (Vaccine Induced Thrombocytopenia) thrombi associated with adenovirus-based vaccines for COVID-19 (not mRNA) and how is it documented?
In VITT there are multiple thrombosis, in unusual locations (cerebral,
ocular veins, 5-48 days after vaccination, thrombocytopenia, large increase in D-Dimers and positive antibodies to platelet factor 4 / PF4 (Diagnostic Marker), which is released from activated platelets.
Why and how do immun thrombosis occur in unusual sites?
The current interpretation is that the venous network here supplies blood from areas (Rhinopharynx, Intestine) rich in microbiome (trillions of bacteria, fungi, viruses), which participates in inflammation, stimulation and training of the immune system.
Autoantibodies (immune complexes) are generated by an electrochemical reaction: PF4 + positively charged microbial cell wall molecules + adenovirus DNA (negatively charged).
How many types of thrombosis are there?
There are hereditary (very rare) and acquired (common).
Acquired causes include:
1. Cardiorespiratory bypass, kidney diseases, liver diseases, hematological diseases (eg Myeloproliferative, Myelodysplastic, Dysproteinemias), diabetes mellitus, pregnancy, autoimmune eg systemic erythematosus.
2. Therapeutic or preventive use of antiplatelet drugs (low dose aspirin, Clopidogrel, Prasugrel, Ticagrelor) in acute ischemic events and in cardiovascular diseases. In diabetes, thromboprophylaxis is achieved only by achieving glycemia (aspirin does not). Regular, chronic use of aspirin reduces the growth of colon adenomas and colon cancer by 22%. Non-steroidal anti-inflammatory drugs (NSAIDs) and calcium channel blockers (antihypertensives, antiarrhythmics) have antiplatelet activity, but have no therapeutic effect in preventing ischemic cardiovascular events.
3. After consuming specific foods and beverages.
“The Mediterranean diet, vegetarianism, the consumption of low glycemic index foods, are combined with reduced cardiovascular events. To their beneficial effect on oxidative stress, on the oxidation of LDL, on the glycosylation of proteins, on fibrinolysis is added the reduction of activation and adhesion of platelets.
Other foods that reduce platelet stimulation and adhesion are:
coffee, cocoa, dark chocolate, turmeric, yolk, wine (red and white), tomato, kiwi, onions (rich in Quercetin), omega-3 polyunsaturated fatty acids, Berries.
“While, drinks containing quinine (Tonic water, Gin Tonic, Bitter lemon) are associated with immunothrombopenia”, says the doctor.
How is platelet function assessed?
a. General blood and microscopic examination to evaluate number and morphology.
b. Platelet aggregation / aggregation method with the addition of adhesion agonists (collagen, epinephrine, thrombin, arachidonic acid, ADP), is considered the “Golden Rule” to control platelet function.
c. Method with automatic functional analyzer (PFA-100).
d. New technologies:
– Flow Cytometry Method: Measures the platelet-leukocyte activation indices.
– Thromboelastography: Examines in whole blood at the same time, the function of platelets and the coagulation-fibrinolysis system, evaluating multiple parameters in the dynamic thrombus formation.
Why are platelets used in regenerative medicine?
The high content of growth factors in the α-granules of the cytoplasm, contributes to the regeneration, repair and healing of tissues. Platelet-enriched plasma (PRP) has been shown to be biologically effective in treating tendon and muscle injuries. Its use is constantly expanding (Dermatology, Dentistry, etc.).
When is a prophylactic platelet transfusion needed?
“In feverless patients when they are 100,000 / μL “, concludes Mr. Anagnostopoulos.
Writes:
Mr. Nikolaos I. Anagnostopoulos, Hematologist,
Director of the 2nd Hematology Clinic Metropolitan General
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