PDLCs and EPCs synergistically enhance osseointegration in irradiated rabbit bone

Abstract

Objectives: To enhance early osseointegration in irradiated rabbit bone by co-culturing periodontal ligament cells (PDLCs) and endothelial progenitor cells (EPCs) on trabecular implants. Methods: PDLCs and EPCs were isolated from sound rabbit premolars and peripheral blood respectively and characterized. These cells were then cultured on trabecular implants with a novel rotary cell culture attachment technique and analyzed by confocal microscopy (CM), scanning electron microscopy (SEM) and backscatter SEM (BSSEM). Right or left distal femoral condyles of 16 rabbits (Age>8 months) were randomly irradiated (4×5cm) by a single dose of 15 Gray. One week after irradiation, cell-implant (CelPlant) complex was placed in both irradiated and normal condyles of each rabbit. 32 implants were placed in four groups; implant (I) only, implant-PDLCs (IP), implant-EPCs (IE), and implant-PDLCs+EPCs (1:1, IPE). Rabbits were euthanized after three weeks. Effects of CelPlants on osseointegration were measured using implant stability quotient (ISQ) immediately after placing implant (ISQp) and after sacrificing rabbits (ISQs). Paired t-test, one-way ANOVA and post-hoc Tukey HSD test were used for statistical analysis. Results: PDLCs (6/7) and EPCs (6/18) were successfully isolated. These PDLCs and EPCs displayed their characteristic osteogenic (3/3) and angiogenic potential (3/3) respectively. CM, BSSEM and SEM revealed satisfactory attachment and proliferation of PDLCs, EPCs and PDLCs+EPCs on implants. The allogeneic CelPlants were well tolerated by rabbits. Significantly lower ISQp was found in all groups of irradiated sites (p<0.05) as compared to non-irradiated sites. No significant difference in ISQp at baseline was found among groups, but a significant increase in ISQs was found after 3 weeks among groups (p<0.05) in both irradiated and non-irradiated sites. In non-irradiated site, there was no statistically significant difference in ISQs between IPE and IE group, but both had significantly higher (p<0.05) ISQs than I group; whereas in irradiated site only IPE group had significantly higher (p<0.05) ISQs than I group. Conclusions: PDLCs and EPCs appeared to have synergistic effects for enhancing implant osseointegration in irradiated bone, whereas in normal bone EPCs alone might be sufficient to augment the osseointegration.