Acidic preparations of lysed platelets upregulate proliferative pathways in osteoblast-like cells as demonstrated by genome-wide microarray analysis.

Platelets contain numerous growth factors essential for wound and fracture healing. We investigated the gene expression in human osteoblast-like cells stimulated with lysed platelets prepared in acidic, neutral, or alkaline buffers. Lysed platelets prepared in buffers at pH 5.4, 7.4, and 7.9, were added after neutralization to hFOB 1.19 cells. Genome-wide microarray analysis was performed using the Affymetrix GeneChip 7G Scanner. Biometric, cluster, and pathway analyses were performed with GeneSpring GX. Biometric analyses demonstrated that 53 genes were differentially regulated (p ≤ 0.005, ≥2-fold increase). Pathway analysis revealed 10 significant pathways of which eight are common ones regulating bone formation and cancer growth. Eleven genes were selected for quantitative real-time polymerase chain reaction (PCR) based on the microarray analysis of the lysed platelets prepared in the pH 5.4 experiments. In conclusion, acidic preparations of lysed platelet concentrates release factors essential for cell proliferation and particularly cell metabolism under hypoxic conditions. The genetic response from these factors was dominated by genes associated with the same pathways observed in bone formation and cancer growth. Activation of TGF-ß in the acidic preparation could be a stimulatory key factor of cell proliferation. These results support the hypothesis that acidification of platelets modifies the stimulatory response of mesenchymal cells in vitro, which is analogous with the observed milieu of a low pH present in wound and fracture sites, as well as in growing tumors.

The content of bone morphogenetic proteins in platelets varies greatly between different platelet donors.

Platelet derivates and platelet rich plasma have been used to stimulate bone formation and wound healing because of the rich content of potent growth factors. However, not all reports have been conclusive since some have not been able to demonstrate a positive effect. We investigated the interindividual variation of bone morphogenetic proteins (BMPs) in platelets from healthy donors, and the pH-dependent effect on the release of BMPs in preparations of lysed platelets in buffer (LPB). Platelet concentrates from 31 healthy donors were prepared in pH 4.3 and pH 7.4 buffers and investigated with respect to BMP-2, -4, -6, and -7. BMP-2 and BMP-4 were significantly more common in acidic LPBs in comparison with neutral preparations. We also observed a considerable variation among platelet donors with respect to the release of BMPs at pH 4.3 and 7.4. In conclusion, a considerable variation was found among platelet donors, which may be of importance considering the ambiguous results previously reported on osteoblast proliferation and differentiation.