References
Platelet-rich plasma in the treatment of equine orthopaedic disease
Abstract
Platelet-rich plasma is a blood-derived, autologous product, which contains a mixture of growth factors, cells and cytokines. These substances are integral in the regulation of the inflammatory process and repair of tissues, although their methods of action are highly complex and not fully elucidated. The content of a platelet-rich plasma product is variable and the optimal concentrations of prime constituents such as platelets, growth factors and leucocytes are not known. A lack of uniformity of products and treatment protocols, along with study design limitations, means that the efficacy of platelet-rich plasma in healing tendon and ligament injuries is yet to be proven or disproven. Nevertheless platelet-rich plasma has gained widespread use in clinical practice primarily for the treatment of these injuries, among other applications. There are no widespread published or anecdotal concerns over the safety of platelet-rich plasma; however, synovial fluid analysis reveals an acute inflammatory response following intra-articular injection of a leucocyte-rich product.
Platelet-rich plasma (PRP) is a cell-based therapy, and is a popular therapeutic option for the treatment of a number of musculoskeletal conditions in horses. PRP is defined as a blood-derived product that contains an increased concentration of platelets compared to that of peripheral blood. This article reviews the production, composition and possible mechanism of action of PRP, with the aim of helping to make decisions regarding its use in clinical practice. Evidence of efficacy will be summarised, highlighting the challenges of evaluating the clinical effect of biologic products.
Platelets consist of alpha granules, which contain a multitude of growth factors and cytokines that are released at sites of vascular injury to direct and promote healing (Pochini et al, 2016). Growth factors such as transforming growth factor β1 (TGF-β1), insulin-like growth factor 1 (IGF-1), and platelet-derived growth factor (PDGF) instruct specific cellular responses. For example, TGF-β1 and IGF-1 increase synthesis of extracellular matrix, while PDGF promotes angiogenesis. IGF-1 has also been shown to decrease synovial inflammation. Cytokines are smaller proteins that regulate communication between cells. Cytokines such as tumour necrosis factor and interleukins 6, 8 and 10 are fundamental in the regulation of inflammation and the subsequent formation of a tissue scaffold that enables formation of new extracellular matrix in injured tendon (Gaida et al, 2012). In addition, platelet activation releases chemokines that recruit leucocytes to a site of injury (King et al, 2018). Collecting and concentrating platelets and delivering them directly to the site of musculoskeletal injury aims to harness these effects to improve the speed and quality of tissue healing, as well as providing anti-inflammatory effects.
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