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Osteoarthritis (OA) is the most commonly encountered degenerative joint disorder in clinical medicine and the pain and stiffness caused by osteoarthritis represents a leading cause of physical disability in individuals of retirement age. Treatment options for OA patients are limited and largely targeted to pain management. Such is the mechanism behind the most commonly prescribed OA therapies including acetaminophen, NSAIDs, opioids, and steroids. However, these palliative pain management tools do not address the underlying pathophysiology of OA disease. This leaves a significant clinical unmet need for disease modifying OA therapies. Growth factor therapies and regenerative medicine strategies are emerging as promising alternatives to palliative care because these treatments bring significant potential to control chronic inflammation, enhance cartilage repair, and restore other joint tissues to a healthy state. Interestingly, a Clinicaltrials.gov search using the terms “osteoarthritis” and “growth factor” identified 43 relevant studies. Of these, only 26% used growth factor therapies directly, including FGF-18, BMP-2, and transgenic human chondrocytes producing TGF-b1. 23% of the studies were dedicated to inhibitors of NGF. The overwhelming majority of studies (47%) used autologous blood products, especially platelet rich plasma (PRP), which constituted 33% of the total studies. This was interesting because although platelets in PRP do indeed harbor large quantities of different growth factors that can affect the status of the treated tissue, growth factors represent only a single aspect of the bioactivity of platelets. Furthermore, platelets represent only one aspect of the potential bioactivity of PRP. Depending upon the methods used for PRP generation, it may also contain other physiologically important components of the whole blood from which it is derived. Recent studies indicate non-platelet components of whole blood such as red blood cells and leukocytes are essential for normal platelet function, including growth factor release. Therefore, this narrative review discusses PRP from a physiological context that explores beyond platelet growth factors to encompass and illuminate roles of non-platelet cells in the bioactivity of PRP, and how these additional mechanisms lead to the conclusion that PRP can be much more than a growth factor therapy. |
