Armand Trousseau noticed many examples of significant blood clotting in cancer patients in 1865 [1], but was unable to hypothesize on the underlying process. Bizzozero discovered for the first time in 1882 that blood platelets, or thrombocytes, adhered to injured blood arteries and hypothesized that these blood components were critical in haemostasis and experimental thrombosis [2]. Riess later discovered a link between thrombocytosis (defined as a platelet count of >400x109 cells per liter of blood) and cancer mortality [3]. Nearly a century later, these original data were examined and validated [4, 5], rekindling interest in platelets' possible involvement in cancer metastasis, invasion, and angiogenesis [6 – 10]. This chapter will examine the data suggesting that platelets have a broader role than simple haemostasis and thrombosis. We will cover the evidence that platelets aid circulating cancer cells in overcoming physiological and immunological barriers and establishing as solid tumors in distant locations where they permit a customized blood supply. Additionally, we will investigate the intricate molecular pathways underlying platelet-tumor cell interactions. 2. The biology of platelets in haemostasis and malignancy
By generating nitric oxide, endothelium-ADPase, and PGI 2, the intact endothelial lining prevents platelet activation (prostacyclin). The endothelial-ADPase enzyme catalyzes the degradation of the platelet activator ADP. [reference required] Active calcium efflux is maintained in resting platelets through a cyclic AMP-activated calcium pump. Platelet activation state is determined by the intracellular calcium content, since calcium is the second messenger that induces platelet conformational change and degranulation (see below). Prostacyclin from the endothelium interacts with prostanoid receptors on the surface of resting platelets. This event promotes the linked Gs protein, increasing adenylate cyclase activity and cAMP generation, hence increasing calcium efflux and decreasing intracellular calcium available for platelet activation. [reference required]
Platelets are little but vital blood cells that assist the body in controlling bleeding. Notify your healthcare practitioner if you have symptoms such as easy bruising, bleeding from a cut, or frequent nosebleeds. A simple blood test will determine whether or not your platelet count is normal.
Low-affinity platelet factor 4 and beta-thromboglobulin are two platelet secretory proteins with similar antigenic determinants. At the amino terminus of beta-thromboglobulin, four amino acids (Asn-Leu-Ala-Lys) are removed, although the remaining sequences of the two peptides seem to be similar. At pH 8.0 and 7.0, low-affinity platelet factor 4 and beta-thromboglobulin have corresponding isoelectric points. Both proteins were identified, quantified, and separated.
