Background: Platelet Rich Plasma (PRP) has recently emerged as a potential treatment for
osteoarthritis (OA), but composition heterogeneity hampers comparison among studies, with the result
that definite conclusions on its efficacy have not been reached.
Objectives: 1) To develop a novel methodology to prepare a series of standardized PRP releasates
(PRP-Rs) with known absolute platelet concentrations, and 2) To evaluate the influence of this standardization
parameter on the anti-inflammatory properties of these PRP-Rs in an in vitro and an ex vivo
model of OA.
Methods: A series of PRPs was prepared using the absolute platelet concentration as the standardization
parameter. Doses of platelets ranged from 0% (platelet poor plasma, PPP) to 1.5·105 platelets/µl.
PRPs were then activated with CaCl2 to obtain releasates (PRP-R). Chondrocytes were stimulated with
10% of each PRP-R in serum-free culture medium for 72 h to assess proliferation and viability. Cells
were co-stimulated with interleukin (IL)-1β (5 ng/ml) and 10% of each PRP-R for 48 h to determine
the effects on gene expression, secretion and intra-cellular content of common markers associated with
inflammation, catabolism and oxidative stress in OA. OA cartilage explants were co-stimulated with
IL-1β (5 ng/ml) and 10% of either PRP-R with 0.75·105 platelets/µl or PRP-R with 1.5·105 platelets/µl
for 21 days to assess matrix inflammatory degradation.
Results: Chondrocyte viability was not affected, and proliferation was dose-dependently increased.
The gene expression of all pro-inflammatory mediators was significantly and dose-independently reduced,
except for that of IL-1β and IL-8. Immunoblotting corroborated this effect for inducible NO
synthase (NOS2). Secreted matrix metalloproteinase-13 (MMP-13) was reduced to almost basal levels
by the PRP-R from PPP. Increasing platelet dosage led to progressive loss to this anti-catabolic ability.
Safranin O and toluidine blue stains supported the beneficial effect of low platelet dosage on cartilage
Conclusion: We have developed a methodology to prepare PRP releasates using the absolute platelet
concentration as the standardization parameter. Using this approach, the composition of the resulting
PRP derived product is independent of the donor initial basal platelet count, thereby allowing the
evaluation of its effects objectively and reproducibly. In our OA models, PRP-Rs showed antiinflammatory,
anti-oxidant and anti-catabolic properties. Platelet enrichment could favor chondrocyte
proliferation but is not necessary for the above effects and could even be counter-productive.