6. PRP in wound healing

PRP acts through the degradation of alpha granules in the platelets. Secretion of growth factors begins from alpha granules within 10 min after clotting and more than 95% of the presynthesized growth factors secreted within 1 hour. In practice, after the PRP is prepared, it is necessary to induce the alpha granules in platelets for the release of growth factors. This induction is made by adding calcium and/or thrombin into PRP prepared in vitro. For this reason, the PRP should be prepared without clotting and should be applied within 10 minutes after clot initiation [9]. Basically, PRP is acquired by centrifuging autologous blood at a certain cycle. To keep the integrity

Growth factor Physiologic level in the blood Level in PRP PDGF-β 3.3 0.9 ng/ml 17 8 ng/ml TGF-β1 35 8 ng/ml 120 42 ng/ml VEGF 155 110 pg/ml 955 1030 pg/ml EGF 129 61 pg/ml 470 320 pg/ml

While preparing the PRP, common points in clinical preparation techniques are like that: The blood is collected from the patient and is taken into the tube containing anticoagulant agent, and immediately centrifuge operation is initiated. When blood containing anticoagulant agent is centrifuged, three layers form as a result of the density: the deep layer containing red blood cells (gravity, 1.09), the middle layer containing white blood cells and platelets (buffy coat;

In the second stage, different techniques are applied, but basically, acellular plasma layer and the red cell layer are removed, and only "buffy coat" layer which contains dense platelet and white blood cells is obtained. So, the PRP becomes ready to be applied after addition of

Additionally, approximately 6 ml of platelet-rich plasma can be produced from 45 to 60 ml of blood thanks to newly developed small, compact office systems [14, 21, 39–41]. Numerous of such systems are available in use, including the PCCS (Implant Innovations, Inc., Palm Beach Gardens, Fla.), the Symphony II (DePuy, Warsaw, Ind.), the GPS (Biomet, Warsaw, Ind.), the Magellan (Medtronic, Minneapolis, Minn.), and the SmartPReP (Harvest Technologies Corp., Norwell, Mass.). Though, all these systems work on a small volume of obtained blood (45–60 ml) and on the principle of centrifugation, they have many differences in their capacity to collect and concentrate platelets, with about 30–85% of the available platelets collected and from a less than twofold to an approximately

Although it is possible to produce PRP by using standard laboratory centrifuge, this process needs much effort, usually requiring multiple transfers and two spins; therefore, it may be difficult to maintain the sterility [14, 31, 43]. Moreover, these techniques may not be reliable to

PRP is stable, in the anticoagulated state, for up to 8 h after preparation. This duration allows to be used even during long operations [14, 21, 44]. In order to release the contents of alpha

of platelet membrane, acid citrate dextrose type A is used as anticoagulant agent [38].

gravity, 1.06), and the top layer (platelet poor plasma; gravity, 1.03) [11].

eightfold rise in the concentration of platelets over baseline [15, 30, 33, 35, 40, 42].

maximize platelet concentration or the levels of key secretory proteins [21].

calcium and/or thrombin to activate thrombocytes [9].

Table 4. Levels of some growth factors in blood versus PRP.

92 Hot Topics in Burn Injuries

There are studies evaluating the effects of PRP on wound healing (Table 5) [37, 46, 47]. In the early phase of wound healing, the clot formed in the injury area serves as a matrix for cell migration, and this phase is primarily effected by platelets. Platelets contain over 1100 proteins, including growth factors, immune system mediators, enzymes, enzyme inhibitors, and bioactive compounds involved in the wound healing process. PRP contains important growth


Table 5. Some studies using PRP for wound healing.

factors deposited in alpha granules of platelets and plasma proteins such as fibrin, fibronectin, and vitronectin [37, 46, 47]. While plasma proteins serve as a skeleton for the bone, connective tissue, and epithelial migration, cocktail of growth factors plays an important role in tissue repair and regeneration. Degradation of previously stored growth factors occurs after contact with coagulation triggers such as collagen and tissue thromboplastin. Platelet activation with exogenous thrombin is associated with massive thrombin release and may reduce biological activity. Ten minutes after platelet activation, platelets start to deliver growth factors and give 95% of these molecules to environment in an hour [21]. Therefore, platelets should be applied within 10 min after activation. After release growth factors attach to mesenchymal stem cells, osteoblasts, fibroblasts, endothelial cells, and transmembrane receptors expressed by epidermal cells. The best known growth factors are platelet-derived growth factor, fibroblast growth factor, transforming growth factor beta, epidermal growth factor, vascular endothelial growth factor, and insulin-like growth factor. This attachment triggers the internal signaling pathway and leads to the expression of gene sequences that increase the normal wound healing process, such as cell proliferation, matrix formation, osteoid production, and collagen synthesis. Topical application of PRP accelerates the reepithelialization process by upregulating regulatory proteins of cell cycle such as cyclin A and CDK4. PRP is a potent matrix metalloproteinase (MMP)-1 stimulator and, thus, allows the extracellular matrix to be reorganized during wound healing [48, 49].

7. PRP in burns

expression [55].

chloride and thrombin [57, 58, 60].

Growth factors play a crucial role in normal wound healing as well as impaired wound healing. Growth factors, such as insulin-like growth factor-1 (IGF-1) and platelet-derived endothelial cell growth factor (PDGF), inhibit apoptosis pathways which provide a rapid cell turnover and, thus, catalyze the physiologic wound healing in different steps. It is also thought that direct or indirect effects of growth hormone on wound healing are related to IGF-1

Platelet-Rich Plasma in Burn Treatment http://dx.doi.org/10.5772/intechopen.70835 95

PRP is a new therapeutic option that is increasingly used especially in the treatment of soft and bony tissue defects to increase the tissue formation capacity and in improvement of chronic wound healing process [56–59]. Platelet-rich plasma, a rich source of growth factors released by activated platelets, is obtained from centrifuged blood which is combined with calcium

Platelets are critical in the wound healing process and migrate to the wound site immediately and initiate coagulation when any damage occurs. Platelets are good sources of growth factors and cytokines associated with wound healing. Multiple growth factors and cytokines, including platelet-derived endothelial cell growth factor (PDGF), transforming growth factor-b (TGF-b1 and TGF-b2), transforming growth factor-a (TGF-a), platelet thromboplastin, thrombospondin, platelet-activating growth factor-4, vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), coagulation factors, fibroblast growth factor (FGF), calcium, serotonin, histamine, and hydrolytic enzymes, with degranulation triggered

Growth factors are key components of cellular activities related to wound repair. Growth factors mediate the migration of inflammatory cells into the wound site; they induce cell proliferation and differentiation and enhance extracellular matrix production and accumulation. Transforming growth factor beta is known to be an important mediator in tissue repair and has proven to be therapeutic in chronic nonhealing wounds [61, 62]. Platelet-derived endothelial cell growth factor promotes dermal regeneration, provokes protein and collagen synthesis that provides migration and angiogenesis, and increases TGF beta expression. Both transforming growth factor beta and platelet-derived endothelial cell growth factor are found

Burn injury is a major reason of trauma that can result in death or disability, which requires a long recovery duration and high health care costs. In burn trauma, depth and size of burn injury, burn area, and patient age are the most important factors that affect the morbidity and mortality. Burn depth is also the most important parameter that determines the long-term appearance and functionality of the patient [63]. Conditions such as immunosuppression, extensive burn area, and malnutrition ensure an appropriate milieu for microorganisms, and unfortunately, infections are common and among the most important causes of morbidity and mortality in burn patients. Although the mortality rate is reduced with new treatment approaches in burn injuries, secondary infections and long recovery duration can still cause mortality. Early debridement and skin grafts can yield successful results, but inadequate graft

by proteins such as thrombin are released by platelets [57, 58, 60].

at higher densities in PRP than platelet-poor plasma (PPP) [61].

PRP may also suppress inflammation by suppressing cytokine release and increases regeneration and reepithelization by triggering capillary angiogenesis. The involvement of macrophages in the wound healing process is also mediated by signal proteins released from platelets. PRP has also been reported to exhibit antimicrobial activity against microorganisms such as Escherichia coli, MRSA, Candida albicans, and Cryptococcus neoformans and to have analgesic effect. Additionally, the pH 6.5–6.7 of the PRP may explain its antibacterial property. Although it has been suggested that leukocytes in PRP accelerate the recovery of soft tissue injury by suppressing bacterial growth, it has been also claimed that PRP may cause local pain and even suppress the healing process due to the inflammatory cytokines in it [50, 51].

In order for PRP therapy to be effective, it should contain 3–5 times the normal platelet level (approximately 0.8–<sup>1</sup> 106 /μL). It is thought that, at very high platelet concentrations, it can suppress the wound healing with an opposite effect, because increase of the bioactive substances does not always mean a better effect. For example, at platelet concentrations higher than 1.5 106 /μL, angiogenesis is suppressed. Eppley emphasizes that it is very difficult to achieve the desired platelet concentration because of the large number of variable and potential interactions [24, 35, 52].

A relation between growth factors in PRP with age and gender has not been detected. Since factors in PRP do not enter the cell or into the nucleus, it is assumed that there are no mitogenic or carcinogenic properties of PRP [46].

The use of PRP is contraindicated in coagulation defects (thrombocytopenia, anticoagulant use, hypofibrinogenemia), anemic situations, hemodynamic instability, and bovine thrombin hypersensitivity [53, 54].
