Paracrine effect of canine allogenic umbilical cord blood-derived mesenchymal stromal cells mixed with beta-tricalcium phosphate on bone regeneration in ectopic implantations

Background aimsThe aim of this study was to evaluate the paracrine effects of canine umbilical cord blood (cUCB) mesenchymal stromal cells (MSC) mixed with β-tricalcium phosphate (β-TCP) on bone regeneration in ectopic implantation.Methodsβ-TCP mixed with cUCB MSC (UCB-MSC group), cell lysates (cell lysate group) or a control (control group) were respectively implanted in a subcutaneous pouches in the back of beagle dogs. The implants were harvested 1, 4, 7, 14, 28, 56, 84 days after implantation. Histological findings and stain analyzes of tartrate-resistant acid phosphatase (TRACP) and assays of alkaline phosphatase (ALP) and TRACP were evaluated. The mRNA expression levels of interleukin-1 (IL-1), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), cyclooxygenase-2 (COX-2), vascular endothelial growth factor (VEGF) and transforming growth factor-β (TGF-β) were analyzed using semi-quantitative reverse transcription - polymerase chain reactions (RT-PCR). An enzyme-linked immunosorbent assay (ELISA) was used to confirm the protein expression levels of IL-6, COX-2, VEGF and TGF-β.ResultsTRACP-positive cells were observed in all groups 7 days after implantation. ALP and TRACP activities in the UCB-MSC group 84 days after implantation were significantly higher than those of the control (P>0.05). Histologic findings after 84 days showed that the osteoid matrix area in the UCB-MSC group was significantly larger than that of the control (P<0.05). The mRNAs levels of IL-1, IL-6 and VEGF in UCB-MSC and cell lysate groups on day 1 were up-regulated compared with the control. The protein levels of IL-6 and VEGF in the UCB-MSC group at day 1 were significantly higher than that of the other groups (P<0.05).ConclusionsIt is suggested that a significant release of cytokines by cUCB MSC, 1 day following implantation, could enhance bone regeneration.