PRP stands for Platelet-Rich-Plasma. The name describes the product well; however, there are other names that would capture the concept equally such as platelet concentrate, autologous platelet gel, platelet dense plasma and so on. The commonality in all these names is the word “platelet”. When it comes to PRP, the platelet is the star of the show. In this article we will discuss the platelet in depth to get a better understanding of why we would want to concentrate them.
Whole Blood Composition
Whole blood is a complex biological fluid made up of many components each of which play a vital role in the human body. The largest portion is plasma, this is the liquid portion of blood making up about 55% of its total volume. It is primarily water, dissolved proteins, and clotting factors. The next largest part is Erythrocytes, or Red Blood Cells. Red blood cells typically constitute 40-45% of the blood volume, this portion is referred to as hematocrit. You will see different PRP systems discuss hematocrit levels, what they are referring to is red blood cell percentage post concentration. Red blood cells are responsible for carrying oxygen from the lungs to tissues within the body and bringing carbon dioxide back to the lungs for expulsion. White blood cells are next comprising roughly 1% of whole blood. These cells are part of the immune system responsible for defending against infectious diseases. Finally, platelets, which make up less than 1%, play a key role in blood clotting and wound healing.
Platelets
So, we’ve determined that platelets are the smallest component of whole blood by volume, but what are platelets? Platelets are not actually cells; they are fragments of large cells called megakaryocytes which are 10 to 15 times larger than a red blood cell. Megakaryocytes are formed in the bone marrow along with red blood cells and most of the white blood cells. As the megakaryocyte matures is begins the process of producing platelets. Once critical mass is reached the platelets are released into the bloodstream. Each megakaryocyte can produce 5,000-10,000 platelets. Platelets remain alive 5-9 days and the average healthy adult can produce up to 100 billion per day! Platelets have storage granules, whose function is to hold biologically active molecules that are responsible for initiating the clotting cascade as well as recruiting other cells during inflammation. An injury in the vessel wall activates platelets to initiate coagulation. The platelets will adhere themselves to the damaged vessel wall where they will interact with collagen that mediates this procedure. The platelets will change shape which triggers the release of its granule contents ultimately forming a plug. The platelet response is then amplified by the release of cytokines which recruit other platelets and blood cells ultimately strengthening the clot. Platelets can communicate over distance within the body via the paracrine effect. In summary, platelets are responsible for recruiting new cells to an area of injury for the purpose of healing, they do this by activating, or changing shape, when they are introduced to collagen releasing growth factors and communicating via the paracrine effect.
Growth Factors
What then are these growth factors that are stored within the platelet’s alpha granules? There are many however, in this article we will focus on PDGF, TGF, PDAF, VEGF, and EGF.
PDGF (Platelet-Derived Growth Factor): PDGF is involved in multiple cellular processes, including cell growth, proliferation, and angiogenesis (formation of new blood vessels). It plays a significant role in wound healing and the repair of blood vessels and other tissues.
TGF (Transforming Growth Factor): TGF is a multifunctional set of proteins that regulate cell proliferation, differentiation, and growth, as well as playing a role in wound healing, embryonic development, and immune system regulation. There are different types, such as TGF-β (beta), each with specific functions.
PDAF (Platelet-Derived Angiogenesis Factor): PDAF is involved in the process of angiogenesis. It stimulates the formation of new blood vessels, which is crucial in wound healing and the growth of tissues.
VEGF (Vascular Endothelial Growth Factor): VEGF is a key regulator of angiogenesis. It promotes the growth of blood vessels and is critical in both normal physiological processes, such as wound healing, and in pathological processes.
EGF (Epidermal Growth Factor): EGF stimulates cell growth, proliferation, and differentiation. It’s particularly important for the skin, as it promotes wound healing and tissue repair.
Each one of these growth factors plays an important role in the complicated mechanism that is healing within the body. Their roles can be very context specific, varying according to factors such as cell type, the local environment, and the presence of other signaling molecules.
Concentrating Platelets
When an injury is sustained within your body and there is damage to the microvascular structure platelets naturally concentrate at the site of the injury. We can accomplish the concentration of platelets outside of the body using an FDA approved commercially available PRP kit. A system such as the EmCyte Pure PRP is capable of concentrating platelets 6-8x over baseline platelet count, while completely removing red blood cells as well as selecting for either leukocyte rich or leukocyte poor.