Harmful Effects of Leukocyte-Rich Platelet-Rich Plasma on Rabbit Tendon Stem Cells In Vitro

Background: Platelet-rich plasma (PRP) is now widely used as a promising treatment for patients with tendinopathy. However, the efficacy of PRP treatment for tendinopathy is controversial mainly because of inconsistent results from human clinical trials and particularly because the concentration and effect of leukocytes in PRP remain largely unknown. Hypothesis: Leukocyte-rich PRP (L-PRP) inhibits growth factor release, decreases proliferation, and induces nontenocyte differentiation of tendon stem cells (TSCs); increases catabolic cytokine concentrations; and causes inflammation and apoptosis. Thus, L-PRP has a detrimental effect on tendon stem/progenitor cells, which impairs injured tendon healing. Study Design: Controlled laboratory study. Methods: Pure PRP (P-PRP) and L-PRP were prepared from the same individual rabbit blood, and platelet numbers in each PRP product were adjusted to reach the same level. The leukocyte level in L-PRP was 4 and 8 times higher than those in whole blood and P-PRP, respectively. The growth factors in both P-PRP and L-PRP were measured by enzyme-linked immunosorbent assay kits. The morphology, stemness, proliferation, and differentiation of TSCs grown in L-PRP and P-PRP were examined by microscopy, immunocytochemistry, population doubling time, quantitative real-time polymerase chain reaction, and histological analysis. Results: L-PRP produced lower levels of growth factors, such as vascular endothelial growth factor (VEGF), epidermal growth factor (EGF), transforming growth factor (TGF)–β1, and platelet-derived growth factor (PDGF), than did P-PRP. TSC proliferation was significantly decreased in L-PRP in a concentration-dependent manner. Furthermore, TSCs cultured in P-PRP produced more collagen and formed tendon-like tissue; however, TSCs grown in L-PRP differentiated into nontenocytes and produced more inflammatory factors such as membrane-associated prostaglandin synthase (mPGES) and interleukin (IL)–1β. Moreover, L-PRP was associated with increased apoptosis. Conclusion: L-PRP has harmful effects on TSCs. Clinical Relevance: This study revealed the direct effects of different compositions of PRP on TSCs and provided basic scientific data to help understand the cellular and molecular mechanisms of the efficacy of PRP treatment in clinical use.