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Initial PRP application likely more effective in healing than subsequent applications
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Subsequent applications of platelet-rich plasma have been shown to be less effective than the initial application on the proliferation of human tenocytes in a recently published in vitro study.
Researchers treated cells from eight volunteers (mean age: 31.6 years) with platelet-rich plasma (PRP) three different times in 2- and 4-day intervals. Volunteer cells were divided into groups based on whether the PRP they received was created via a single- or double-spin process. Recovery and healing in human tenocytes were evaluated via radioactive thymiding assay measuring cell disintegration rates per minute.
Significant differences in cell disintegration rates per minute were noted between days 0 and 2 in those who received treatments in 2-day intervals and between days 4 and 8 for those receiving treatments in 4-day intervals in the single-spin PRP cohort. The PRP double-spin cohort also demonstrated significant differences in cell disintegration rates per minute for those treated in 2-day (from days 0 to 4 and days 2 to 4) and 4-day (from days 0-8) intervals, according to the researchers.
The researchers concluded that the effect of PRP diminished with repeated application, which leads to questioning the efficacy of interval dosing. – by Christian Ingram
Disclosure: Mazzocca is a paid consultant for Arthrex. Please see the full study for a list of all other authors’ relevant financial disclosures.
Perspective
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William Parrish, PhD
Platelet counts of the platelet-rich plasma (PRP) reported in this study indicate no true platelet enrichment compared to normal values for whole blood, therefore indicating these preparations are in fact not “platelet rich” plasma. In addition, the methods used to measure proliferation are inadequate as applied to the study. Thymidine incorporation is sufficient to measure the kinetics of cell cycle stimulation, but it is inappropriate as an endpoint assay. It only labels cells that are in S-phase of the cell cycle during thymidine incubation and does not label cells that have progressed to G2- or M-phase in the time prior to label addition.
The total number of cells at the endpoint (assuming a known seeding density and no contact inhibition during the time course) or the kinetic effects of treatment during the initial approximate 18 hours of serum stimulation rather than the final 24 hours would be better assays.
A more likely explanation for loss in treatment efficacy with subsequent applications over longer time periods is indeed contact inhibition. Once normal somatic cells are contacting other cells, they will fail to respond to growth factor cues for proliferation. For example, if the initial serum treatment causes the cells to grow to confluence within the 4-day incubation period, the next treatment will have “no measured effect” by thymidine incorporation simply because contact inhibited cells cannot be stimulated into a new cell cycle to make DNA. The observation that tenocytes still respond to their preparations (not contact inhibited), but not to commercially available fetal bovine serum (assuming contact inhibition) after 4 days to 8 days in culture is strongly suggestive that their preparations are actually deficient in platelet growth factor content and the ability to stimulate tenocyte proliferation. However since a whole blood serum control is missing in the study, this remains inconclusive.
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