Platelet Growth Factor Release in Equine Platelet-Rich Plasma after Nonsteroidal Anti-Inflammatory Drug Administration

Presented by: Kylee Merrill
 

Authors: K. A. Merrill (1), T. M. McCarrel (1), S. S. K. Beatty (2)

Affiliations: (1) Department of Large Animal Clinical Science, University of Florida College of Veterinary Medicine, Gainesville, Florida, USA. (2) Department of Comparative, Diagnostic and Population Medicine, University of Florida College of Veterinary Medicine, Gainesville, Florida, USA. Emails: kmerrill108@ufl.edu, tmccarrel@ufl.edu, skbeatty@ufl.edu

Introduction: The use of nonsteroidal anti-inflammatory drugs (NSAIDs) and platelet-rich plasma (PRP) may improve tissue healing, decrease inflammation, and manage pain in equine musculoskeletal injuries, however the interaction between these therapies has not been extensively investigated. Nonselective NSAIDs (phenylbutazone and flunixin meglumine) inhibit normal homeostatic functions associated with the COX-1 enzyme, which may impact platelet activation and growth factor release. COX-2 selective NSAIDS (firocoxib) also exhibit a small inhibitory effect on COX-1. Platelet growth factor release under the influence of NSAIDs may also vary depending on whether a strong activator like thrombin or weak activator like collagen is used.

Hypothesis / Objectives: The objective of this study was to assess the effect of treatment with 3 commonly used NSAIDs on coagulation function and growth factor release from platelets in PRP to determine if administration of NSAIDs must be withheld before collection of blood for preparation of PRP.

Materials and Methods: Horses (n=6, 6-10 years of age) received each of 4 treatments (phenylbutazone, flunixin, firocoxib, and no treatment) in a crossover design for 5 days prior to preparation of PRP. Blood (pre and post-treatment) and PRP (post-treatment) were submitted for CBC. The PFA-100 was used to assess coagulation time. Aliquots of PRP were activated with collagen or thrombin, followed by quantification of platelet-derived growth factor (PDGF-BB) and transforming growth factor (TGF-β1) using ELISA. Thromboxane B2 was also measured using ELISA to determine inhibition of COX-1. Repeated measures ANOVA and the Tukey post-hoc test were used to analyze the data, p<0.05.

Results: Pre-treatment CBC and biochemistry results showed no clinically relevant abnormalities in all horses before all treatment trials. For post-treatment CBC results, platelet concentration and WBC counts in PRP were significantly higher than in blood, while hematocrit was significantly lower in PRP compared to blood (p<0.001). The closure time determined on the PFA-100 was significantly prolonged (p=0.021) and thromboxane significantly decreased (p<0.001) following treatment with phenylbutazone or flunixin compared to no treatment or firocoxib. There was no difference in PDGF-BB or TGF-β1 concentration within samples activated with either collagen or thrombin.

Conclusions: Platelet activation occurs through several pathways, some of which require thromboxane. Nonselective NSAIDs suppressed thromboxane production and resulted in prolonged time for coagulum formation. However, regardless of whether a strong activator such as thrombin or weak activator such as collagen was used, NSAIDs had no effect on growth factor release after long incubation times (thrombin 20 minutes and collagen 100 minutes). Flow cytometry data on activation kinetics is currently being analyzed to determine if NSAIDs slow platelet activation under the influence of different activators. NSAID administration prior to blood collection for PRP preparation does not prevent growth factor release.

Acknowledgements, Funding, and Conflicts of Interest: This study was funded in part by the UFCVM Large Animal Clinical Science Department, UFCVM Consolidated Faculty Award, and the Boehringer Ingelheim Veterinary Scholars Program. The authors wish to thank Kelly Merritt and Brett Rice for their technical support. The authors declare that they have no conflicts of interest regarding this study.