Effects of Hydroxyapatite Particles on Periodontal Ligament Fibroblast‐Like Cell Behavior

Abstract

Although hydroxyapatite (HA), a synthetic calcium phosphate, is used in restoring bone defects associated with periodontal diseases, its specific effect on the periodontal ligament fibroblast population during the regeneration process is unclear. To determine the cellular events occurring in the presence of HA, human periodontal ligament fibroblasts (HPLF) were isolated and maintained in culture. The specificity of the cells was evidenced by their morphology, deposition of extracellular matrix components, and alkaline Phosphatase (ALP) activity (as a marker of osteoblastic differentiation of HPLF). Phase‐contrast investigations revealed morphological alterations of cells in contact with HA particles. Transmission electron microscopy demonstrated the phagocytotic process of HPLF toward HA particles. Moreover, the presence of HA particles was significantly related to an increase in the protein synthesis activity and a decrease in the proliferation and ALP‐specific activity of HPLF. These results provide new information on the phenotypic expression of HPLF, which is comparable to that of osteoblastic cells. A subpopulation of HPLF may be influenced by the presence of HA to undergo transient dedifferentiation prior to redifferentiating into osteoblasts. This process may be important as a means by which HA acts as an osteoconductive material. This experimental study improves our understanding of the cellular processes which occur during healing and regeneration of periodontal defects after implantation of biomaterials. J Periodontol 1997;68:158–165.

A simple cell motility assay demonstrates differential motility of human periodontal ligament fibroblasts, gingival fibroblasts, and pre-osteoblasts

“…Fibroblasts of the PDL can be induced to form calcified tissue by a number of factors, including bone morphogenic protein-2 (Takiguchi et al 1999), dexamethasone (Kuru et al 1999), and hydroxyapatite (Urabe et al 2000). Under these conditions, PDL fibroblasts produce a number of proteins common to bone and cementum, including osteopontin (Strayhorn et al 1999), bone sialoprotein (Strayhorn et al 1999), and alkaline phosphatase (Alliot-Licht et al 1997). These same processes are also downregulated by the presence of platelet derived growth factor (Strayhorn et al 1999), interleukin 1β, tumor necrosis factor alpha, and transforming growth factor beta (Takeshita et al 1992).…”

Transmission and scanning electron microscopic analysis of mineralized loci formed by human periodontal ligament cellsin vitro

“…In einer ktirzlich erschienenen Arbeit publizierten Alliot-Licht et al [1] neue Erkenntnisse zur ph~inotypisehen Expression von humanen PDL-Fibroblasten, die nach Meinung der Autoren mit der Expression von osteoblastfiren Zellen vergleichbar sind. Sie postulieren, daB ,,humane PDL-Fibroblasten durch die Anwesenheit von Hydroxylapatit beeinflugt werden k6nnen, um eine vort~bergehende Dedifferenzierungsphase zu durchlaufen, ehe sie wieder zu Osteoblasten differenzieren".…”

“…A marked distinction between the in-vitro PDL nodules and those formed by cells isolated from mouse calvaria was in the morphology of the cells within the nodule. Although it has been demonstrated both biochemically and immunohistochemically [1,6,20,22,26,27] that PDL fibroblasts possess in-vitro the phenotypes typical of osteoblastic cells, it seems that PDL cells most likely belong to Inducible Osteoprogenitor Cells (IOPC) [17,18,21]. Maturation of the nodules and positive Von Kossa staining was observed between the 3rd and 4th week in culture.…”

“…et al [ 1 ] provide new information on the phenotypic expression of human PDL fibroblasts, which they claim to be comparable to that of osteoblastic cells. et al [ 1 ] provide new information on the phenotypic expression of human PDL fibroblasts, which they claim to be comparable to that of osteoblastic cells.…”

“…Extrazellul~re Matrixvesikel mit charakteristischer trilaminSxer Membran konnten ebenfalls nachgewiesen werden. Obwohl auf biochemischer Ebene und immunhistochemisch gezeigt werden konnte, dab PDL-Fibroblasten unter In-vitro-Bedingungen in der Lage sind, den Phfinotyp osteoblast~irer Zellen zu realisieren[1,6,20,22,26,27], scheint es offensichtlich zu sein, dab PDL-Zellen zu den induzierbaren Osteoprogenitorzellen (IOPC) z~ihlen[17,18,21]. Ein deutlicher Unterschied zwischen den Knoten, die unter In-vitro-Bedingungen von PDL-Zellen gebildet wurden, und solchen, die yon Mauszellen der Sch~idetkalotte gebildet wurden, bestand in der Morphologie der Zellen innerhalb des Knotens.…”