The initiation of bone formation induced intrinsically by osteoinductive hydroxyapatities

[摘要] The initiation of new bone formation within the porous spaces ofhydroxyapatite (HA) implants involves the expression of osteogenicmarkers belonging to the TGF-β superfamily. To study the geneticexpression of these osteogenic markers in relation to the type of HAimplant used and implantation period, five different types of porous HAbiomaterials were implanted in the rectus abdominis muscles of adultbaboons Papio ursinus, and were harvested at two, three and 12 months.The total RNA of all harvested samples was extracted and analysed usingthe Northern blot technique. The results showed that Collagen type IV,GDF-10 and BMP-7 were expressed at the early time points at relativelyhigh levels, and their expression levels were significantly reduced at 12months. The expression of these makers was not affected by the type ofporous HA implant used. The histological sections of these specimens attwo and three months showed vascularised connective tissue within theporous spaces of the implants with no bone formation. However, at 12months there were substantial amounts of bone formed in all the studiedimplants. The down-regulation of the expressed osteogenic markers at 12months correlates to the amount of bone formed, suggesting somenegative feedback mechanism which may be acting via inhibitory Smadsproteins in relation to the amount of bone formed. Neither TGF-β1 norBMP-3 messages were detected in any of the studied samples, It ispossible that these bone markers are not expressed locally within thevicinity of the porous HA implants but are adsorbed to the HA implants fromthe circulatory system.

[发布机构] University of the Witwatersrand