Osteoinductive effects of tantalum and titanium on bone mesenchymal stromal cells and bone formation in ovariectomized rats.

OBJECTIVE: Although Tantalum (Ta) exhibits better osteoinductivity in healthy subjects when compared with titanium (Ti), the relative effects in osteoporosis remain unknown. MATERIALS AND METHODS: In this study, bone mesenchymal stromal cells of ovariectomized rats (OVX-rBMSCs) were seeded on Ta and Ti substrates for in vitro evaluation of cell viability, reactive oxygen species (ROS) production, alkaline phosphatase (ALP) activity, extracellular mineralization osteogenic gene and protein expression involved in bone morphogenetic protein (BMP2)/small mothers against decapentaplegic homologs 1 (Smad1) pathway. For in vivo assessment, Ta and Ti implants were embedded in femur defects of ovariectomized rats, followed by sequential fluorochrome labeling and histological staining. RESULTS: Compared to Ti, the Ta substrates demonstrated higher viable cell percentages (96.5 ± 0.26 vs. 88.17 ± 2.23%), lower ROS levels (65% vs. Ti), and enhanced ALP activity and extracellular matrix calcification. Reverse Transcription-Polymerase Chain Reaction and Western blot assays validated the better osteoinductive effect of Ta regarding small mothers against decapentaplegic homologs 1 (Smad1), runt-related transcription factor 2, bone morphogenetic protein (BMP2), and ALP expression at both the mRNA (1.5-2-fold) and protein (1.2-1.8-fold) levels. BMP2/Smad1 signaling over-expression or knockdown yielded significantly enhanced or deteriorated OVX-rBMSC osteogenesis on the two surfaces. In addition, the Ta group revealed more new bone formation (1.3-1.5-fold vs. Ti) and slightly better bone-implant contact (31.82 ± 4.07 vs. 25.2-3.84% at 8 weeks post-implantation, p = 0.052) without the contribution of specific surface structures. CONCLUSIONS: In comparison to Ti, Ta reveals better biocompatibility and osteoinductivity to OVX-rBMSCs, and the preferential Ta osteoinductivity may reflect its greater potential to trigger the BMP2/Smad1 cascade. Thus," in front of "Ta". Ta appears preferable to Ti as a bone-implant surface material under osteoporosis conditions.