Leukocyte‐Platelet‐Rich Plasma (L‐PRP) Induces an Abnormal Histophenotype in Craniofacial Bone Repair Associated with Changes in the Immunopositivity of the Hematopoietic Clusters of Differentiation, Osteoproteins, and TGF‐β1

Abstract

Leukocyte-platelet-rich plasma (L-PRP) is considered an important source of growth factors, especially Transforming growth factor β 1 (TGF-β1), which modulates the proliferation and regulation of mesenchymal cells, and also exerts an influence on the hematopoiesis, osteogenesis, and adipogenesis in bone microenvironment. Thus, the aim of this study was to evaluate the effect of L-PRP on the calvarial bone repair and compare its results on the presence of TGF-β1, CD34, CD45, bone morphogenetic protein 2 (BMP2), BMPR1B, and Runx2 proteins detected by immunohistochemistry. Four bone defects were created on the calvaria of 23 rabbits. The defects were treated with autograft, L-PRP alone, and L-PRP mixed with autograft. The animals were euthanized at 2, 4, and 6 weeks post-surgery. Unlike autograft and sham groups, the defects treated with L-PRP demonstrated significant positivity to TGF-β1, while the BMP2 was scarce. These results coincided with the lower bone matrix deposited and larger medullary area, which were composed of fibrosis, when treated with only L-PRP, or intense adiposity on defects filled with L-PRP mixed with autograft. The fibrosis that occurred was associated with a minor percentage of osteoproteins, intense presence of CD34(+) CD45(-) cells, and significant expression of TGF-β1 in all time periods analyzed. The adiposity occurred from the major presence of osteoprogenitor BMPR1B (+) Runx2(+) cells simultaneously to BMP2(-) TGF-β1(+) and CD34(+) CD45(+/-) expressions predominantly on the earlier period. From this study, it can be concluded that the L-PRP used alone or mixed to autograft hindered the osteoneogenesis due to suppression of immunoexpression of BMP2, while the immunopositivity of TGF-β1 was intense. When used alone, the L-PRP induced a fibrotic condition associated with TGF-β1 presence and lack of osteoproteins, but when L-PRP was mixed to autograft, it induced the presence of the osteolineage cells (BMPR1B (+) Runx2(+) ), but also inhibited the terminal osteoblastic maturation associated with the lack of BMP2 and the presence of TGF-β1(+) , a fact that contributed to cellular transdifferentiation into fat cells.