Hot Literature: Are we getting the most out of PRP in horses?

The intralesional use of autologous platelet-rich plasma (PRP) in horses to boost tissue repair after tendon and ligament injuries has rapidly gained in popularity. But little is known about which preparation or administration techniques are best to produce optimal platelet activation and growth factor release, thereby maximizing treatment benefits.

A new study examined the differences between two PRP preparation processes as well as the effects of shear force (as is produced when administering PRP through a needle) and exposure to collagen on the release of growth factors from equine platelet-rich plasma.

Blood obtained from six healthy adult horses was used to prepare PRP either by a tube centrifugation or commercially available automated method. Dilutions were made to achieve equal platelet concentrations for each of the samples. Each PRP sample was then subjected to several treatment conditions-unstimulated (negative control), a nonionic detergent (positive control), passage through needles, and exposure to collagen. In each experiment, concentrations of various growth factors were measured with ELISA kits.

Both preparation methods resulted in PRP with comparable concentrations of growth factors, but the manual tube method produced a higher overall number of platelets, which has been show to be important in other studies. Passage of the PRP through a 21-ga needle, designed to represent the sheer force produced with common administration techniques, did not show any effect on platelets. Even with high-pressure passage through a 25-ga needle (not practical for treatment administration), there was no increase in growth factor release by the platelets.

Since platelets are thought to be activated by subendothelial collagen present in tendon lesions, the PRP samples were exposed to collagen from equine tendon. In this study, little overall collagen effect was seen on growth factor release. Exposing the PRP to a nonionic detergent was used as a positive control. This solubilizes both plasma and organelle membranes, resulting in release of all alpha-granule growth factors. Based on the control group findings, it was somewhat surprising that the resting or unstimulated PRP samples (type used clinically) released only a small percentage (< 15%) of their growth factors.

While individual growth factors play distinctive roles in tissue repair and are stimulated at different times and by varying conditions, the results of this study suggest that the methods of PRP preparation and administration techniques commonly used in practice today are not likely achieving the goal of significantly increasing growth factors within a lesion. Based on the data obtained in this study, using nonactivated PRP injections is likely to release less than 15% of the total growth factors available. The authors note that there are many other factors to consider and investigate further, yet the results of this study indicate that current treatment methods do not achieve maximal benefit from PRP growth factors.

Textor JA, Norris JW, Tablin F. Effects of preparation method, shear force, and exposure to collagen on release of growth factors from equine platelet-rich plasma. Am J Vet Res 2011;72(2):271-278.

Link to abstract: http://avmajournals.avma.org/doi/abs/10.2460/ajvr.72.2.271