Objective: To determine whether leukocyte‐platelet‐rich fibrin (L‐PRF) and advanced platelet‐rich fibrin (A‐PRF+) differ in their in vitro capacity to induce proliferation and migration of periodontal fibroblasts.Background: L‐PRF and A‐PRF + are autologous materials used in periodontal regenerative surgery. They derive from blood from patients, but have different characteristics. The literature is controversial regarding the effects of the two PRF preparations on periodontal tissue fibroblasts.Materials and methods: L‐PRF and A‐PRF + membranes were prepared from eight patients and incubated in 3 mL of culture medium for 2 days. Gingival fibroblasts (G‐F) and periodontal ligament fibroblast (PDL‐F) primary cells were retrieved from 7 donors. These cells were pre‐cultured for 1 day in wound healing experiment plates leaving a gap of 500 ± 50 µm in a concentration of 3.3 x 10⁵ cells/mL. 70 µL of the cell suspension was placed in each half of the well. Thereafter, the pre‐cultured L‐PRF and A‐PRF + supernatants were added to the experimental plates, and the fibroblasts were incubated for another 24 h. Medium alone (NEG) and fibroblast growth factor II (FGF) were used as controls. Subsequently, cell migration was registered for 24 h with live cell imaging in a time frame microscope at 5% CO₂ in air at 37°C. Images were analyzed using ImageJ. Cell proliferation and cell viability were measured.Results: L‐PRF and A‐PRF + induced higher cell proliferation than FGF and NEG. Both A‐PRF + and L‐PRF induced significant faster artificial wound closure than controls. Both PRF conditioned media induced faster cell migration in the initial phase (P < .01), but in the stoppage phase, the induced migration was higher for the A‐PRF+, compared with L‐PRF (P < .01).Conclusion: L‐PRF and A‐PRF + have a stimulatory effect on migration and proliferation of periodontal fibroblasts, and artificial wound closure was longer sustained by A‐PRF + than L‐PRF.

Osteoclasts are specialized multinucleated cells with the unique capacity to resorb bone. Despite insight into the various steps of the interaction of osteoclast precursors leading to osteoclast formation, surprisingly little is known about what happens with the multinucleated cell itself after it has been formed. Is fusion limited to the short period of its formation, or do osteoclasts have the capacity to change their size and number of nuclei at a later stage? To visualize these processes we analyzed osteoclasts generated in vitro with M-CSF and RANKL from mouse bone marrow and native osteoclasts isolated from rabbit bones by live cell microscopy. We show that osteoclasts fuse not only with mononuclear cells but also with other multinucleated cells. The most intriguing finding was fission of the osteoclasts. Osteoclasts were shown to have the capacity to generate functional multinucleated compartments as well as compartments that contained apoptotic nuclei. These compartments were separated from each other, each giving rise to a novel functional osteoclast or to a compartment that contained apoptotic nuclei. Our findings suggest that osteoclasts have the capacity to regulate their own population in number and function, probably to adapt quickly to changing situations.

Objective: To investigate the effect of Advanced Platelet‐Rich Fibrin (A‐PRF+), Leukocyte Platelet‐Rich Fibrin (L‐PRF), and injectable Platelet‐Rich Fibrin (i‐PRF) on osteogenesis of a human osteoblast‐like cell line in vitro.Background: Different PRF protocols are used in clinical dentistry in the last years. Recent literature documented the positive impact of PRF derivatives in vivo and in vitro, on different types of cells. However, hardly any literature comparing the new protocols for PRF (the A‐PRF+ and i‐PRF) with the original protocol of PRF (L‐PRF) is present for osteoblast‐like cells.Materials and Methods: A‐PRF+, L‐PRF, and i‐PRF were prepared from six male donors and pre‐cultured with 10 mL culture medium for 6 days. 5 x 10³ cells/ml osteoblasts from the osteoblast cell line (U2OS) were seeded and cultured either with conditioned medium derived from the different PRF conditions or with regular culture medium. At five different time points (0, 7, 14, 21, 28 days), the osteogenic capacity of the cells was assessed with Alizarin Red S to visualize mineralization. Also in these cells, the calcium concentration and alkaline phosphatase activity were investigated. Using qPCR, the expression of alkaline phosphatase, osteocalcin, osteonectin, ICAM‐1, RUNX‐2, and collagen 1a was assessed.Results: In osteoblast‐like cells cultured with conditioned medium, the A‐PRF+ conditioned medium induced more mineralization and calcium production after 28 days of culturing compared with the control (p < .05). No significant differences were found in the extent of cell proliferation between the different conditions. RUNX‐2 and osteonectin mRNA expression in the cells were lower in all PRF‐stimulated cultures compared with control at different time points. The i‐PRF‐conditioned medium induced more ALP activity (p < .05) compared with control and osteoblasts‐like cells differentiated more compared with osteoblasts cultured with L‐PRF.Conclusions: The three PRF preparations seem to have the capacity to increase the osteogenic potential of osteoblast‐like cells. A‐PRF+ seems to have the highest potential for mineralization, while i‐PRF seems to have the potential to enhance early cell differentiation.

Gingival fibroblasts (GFs) can differentiate into osteoblast-like cells and induce osteoclast precursors to differentiate into osteoclasts. As it is unclear whether these two processes influence each other, we investigated how osteogenic differentiation of GFs affects their osteoclast-inducing capacity. To establish step-wise mineralization, GFs were cultured in four groups for 3 weeks, without or with osteogenic medium for the final 1, 2, or all 3 weeks. The mineralization was assessed by ALP activity, calcium concentration, scanning electron microscopy (SEM), Alizarin Red staining, and quantitative PCR (qPCR). To induce osteoclast differentiation, these cultures were then co-cultured for a further 3 weeks with peripheral blood mononuclear cells (PBMCs) containing osteoclast precursors. Osteoclast formation was assessed at different timepoints with qPCR, enzyme-linked immunosorbent assay (ELISA), TRAcP activity, and staining. ALP activity and calcium concentration increased significantly over time. As confirmed with the Alizarin Red staining, SEM images showed that the mineralization process occurred over time. Osteoclast numbers decreased in the GF cultures that had undergone osteogenesis. TNF-α secretion, a costimulatory molecule for osteoclast differentiation, was highest in the control group. GFs can differentiate into osteoblast-like cells and their degree of differentiation reduces their osteoclast-inducing capacity, indicating that, with appropriate stimulation, GFs could be used in regenerative periodontal treatments.

Recently, it was shown that interleukin-1β (IL-1β) has diverse stimulatory effects on different murine long bone marrow osteoclast precursors (OCPs) in vitro. In this study, interleukin-1 receptor antagonist deficient (Il1rn^−/−) and wild-type (WT) mice were compared to investigate the effects of enhanced IL-1 signaling on the composition of OCPs in long bone, calvaria, vertebra, and jaw. Bone marrow cells were isolated from these sites and the percentage of early blast (CD31^hi Ly-6C⁻), myeloid blast (CD31⁺ Ly-6C⁺), and monocyte (CD31⁻ Ly-6C^hi) OCPs was assessed by flow cytometry. At the time-point of cell isolation, Il1rn^−/− mice showed no inflammation or bone destruction yet as determined by histology and microcomputed tomography. However, Il1rn^−/− mice had an approximately two-fold higher percentage of OCPs in long bone and jaw marrow compared to WT. Conversely, vertebrae and calvaria marrow contained a similar composition of OCPs in both strains. Bone marrow cells were cultured with macrophage colony stimulating factor (M-CSF) and receptor of NfκB ligand (RANKL) on bone slices to assess osteoclastogenesis and on calcium phosphate-coated plates to analyze mineral dissolution. Deletion of Il1rn increased osteoclastogenesis from long bone, calvaria, and jaw marrows, and all Il1rn^−/− cultures showed increased mineral dissolution compared to WT. However, osteoclast markers increased exclusively in Il1rn^−/− osteoclasts from long bone and jaw. Collectively, these findings indicate that a lack of IL-1RA increases the numbers of OCPs in vivo, particularly in long bone and jaw, where rheumatoid arthritis and periodontitis develop. Thus, increased bone loss at these sites may be triggered by a larger pool of OCPs due to the disruption of IL-1 inhibitors.

Lysosome associated membrane proteins (LAMPs) are involved in several processes, among which is fusion of lysosomes with phagosomes. For the formation of multinucleated osteoclasts, the interaction between receptor activator of nuclear kappa β (RANK) and its ligand RANKL is essential. Osteoclast precursors express RANK on their membrane and RANKL is expressed by cells of the osteoblast lineage. Recently it has been suggested that the transport of RANKL to the plasma membrane is mediated by lysosomal organelles. We wondered whether LAMP-2 might play a role in transportation of RANKL to the plasma membrane of osteoblasts. To elucidate the possible function of LAMP-2 herein and in the formation of osteoclasts, we analyzed these processes in vivo and in vitro using LAMP-2-deficient mice. We found that, in the presence of macrophage colony stimulating factor (M-CSF) and RANKL, active osteoclasts were formed using bone marrow cells from calvaria and long bone mouse bone marrow. Surprisingly, an almost complete absence of osteoclast formation was found when osteoclast precursors were co-cultured with LAMP-2 deficient osteoblasts. Fluorescence-activated cell sorting FACS analysis revealed that plasma membrane-bound RANKL was strongly decreased on LAMP-2 deficient osteoblasts. These results suggest that osteoblastic LAMP-2 is required for osteoblast-induced osteoclast formation in vitro.