Fogorvosi szemle, 2005 (98. évfolyam, 1-6. szám)
2005-04-01 / 2. szám
FOGORVOSI SZEMLE ■ 98. évf. 2. sz. 2005. 75 P. LUNQUIST, J. BIBER AND H. MURER Physiologisches Institut, Universität Zürich, Switzerland. OSTEOBLAST NA+-PI COTRANSPORTERS AND MINERALIZATION The mechanism by which influx of phosphate (Pi) into the mineralizing compartment of a calcifying tissue such as bone is achieved is as yet largely unknown. Data suggest that the ion flux needed for mineralization is largely dependent on the osteoblasts producing the bone tissue. Our aim has been to investigate the role of the type II sodium-phosphate cotransporters, NaPi-2a and NaPi- 2b, in osteoblast Pi transport and their possible function in bone calcification. The skeleton is involved in regulating the Pi homeostasis of the organism and it was our hypothesis that Pi handling in osteoblasts is performed by the same class of Nan-Pi cotransporters as in the kidney and intestine. Expression of the cotransporters was studied in mice calvariae and in two osteoblastic cell lines, MC3T3-E1 and UMR-106.01. Immunohistochemical detection of NaPi-2a and NaPi- 2b in mouse calvariae revealed that both cotransporters were expressed in osteoblasts and in some osteocytes. NaPi-2a knockout mice osteoblasts showed a strong signal for NaPi-2b. Western blotting of membrane proteins from the cell lines detected both NaPi-2a and NaPi-2b. Real-Time PCR gave the same results. Expression of NaPi-2a, but not NaPi-2b, was found to be upregulated by increases in Pi concentration. In long term mineralizing culture it was found that the formation of mineral was preceded by a threefold increase in cellular sodium-dependent Pi uptake. At the same time both cotransporters were upregulated. NaPi-2a and NaPi-2b thus seem to be regulated in accordance with the osteoblasts role in Pi homeostasis and mineralization. The finding of the same Na+-Pi cotransporters in all three major organs of Pi homeostasis, kidney, intestine and bone, suggests an integrated system where it seems that the osteoblasts may play a more active role than previously expected. Keywords: osteoblast, sodium-phosphate cotransporter, mineralization. Acknowledgement: This work has been conducted within the framework of the COSTAction B23. D.M. LYARUU AND E.S. TADJOEDIN Dept. Oral Cell Biology, ACTA, Vrije Universiteit, v.d. Boechorststraat 7, Amsterdam KINETICS OF BIOACTIVE GLASS PARTICLE (BIOGRAN®) TRANSFORMATION INTO HYDROXYAPATITE-LIKE MINERAL DURING SINUS FLOOR ELEVATION IN PATIENTS WITH ATROPHIC MAXILLA OBJECTIVE: To evaluate the kinetics of bioactive glass (BioGran®, 300-350p particle size) transformation into hydroxyapatite during sinus floor elevation in patients with atrophic maxilla. METHODS: X-ray microprobe analysis was performed on biopsies obtained from four patients with atrophic maxilla (<2 mm; ages 49 - 71 years) who underwent sinus floor elevation. Three patients received 50,80,90% bioactive glass mixed with autogenous bone and one patient 100% bioactive glass. The healing times were respectively 6, 6, 4 and 16 months. The biopsies taken by hollow trephine drill (2 mm 0) during implant fixtures were fixed in 4% formaldehyde, embedded in methlymethacrylate (MMA), sectioned and stained with Goldner’s trichrome for histological and morphometric studies (see: Tadjoedin etal., Clin Oral Impl Res 13, 428, 2002). The tissue blocks were then subjected to X-ray microanalysis. RESULTS: Pure bioactive glass embedded in MMA was used as a reference and contained 51.6% Si02, 25.3% CaO, 19.8% Na02 and 6.4% P205 (wt/wt). In the implanted intact bioactive glass, the calcium content was 39.1-47.9%, phosphorus 29.0-36.37% and Ca/P ratio 1.56-1.71 while in bone, the mineral content was respectively 35.8 -37.5% for calcium, 27.7-29.4% for phosphorus and 1.59-1.70 for Ca/P ratio. Silicium, could no longer be detected in any of the samples analysed. Micrographs taken by back-scattered electron optics indicated that recognisable bioactive glass particles were still present in all samples. The amount of particles present was dependent upon the healing time. CONCLUSION: Bioactive glass particles are transformed into hydroxyapatite-like mineral within four months after sinus floor elevation. Bioactive glass, preferably supplemented with some autogenous bone, is a promising candidate for sinus floor augmentation in patients with atrophic maxilla. Acknowledgement: The support of COSTB23 is acknowledged. A. NANCI Laboratory for the Study of Calcified Tissues and Biomaterials, Faculty of Dentistry, Université de Montréal, QC, Canada FUNCTIONAL AND GENE TRANSFER STUDIES IN RODENT HEMIMANDIBLES The tooth organ and surrounding periodontal tissues are extensively used in developmental biology to study organogenesis and cell differentiation, and together represent
