gms | German Medical Science

Objectives: Stem cells are a promising tool to positively influence bone regeneration. Immediate, point of care delivery of stem cell therapy enables the harvesting and delivery of cells during the operation. The disadvantage of this concept is the low numbers of cells that are generated. Two-step stem cell therapy includes a variable intermediate period between harvest and delivery. This approach requires an additional operation but generates high numbers of pure stem cells and gives the option for osteogenic pre-differentiation. To further improve bone regeneration, stem cell therapy can be combined with growth factors from platelet rich plasma (PRP) or its lysate (PL),which have demonstrated to be beneficial for tendon regeneration. However, the effect of PRP or PL on bone regeneration is controversial. The aim of this study was to investigate the effect of human stem cells (hMSCs),osteogenic pre-differentiation of hMSCs and PL on bone regeneration and vascularization.

Methods: Sixty 12-week-old nu/nu nude mice were randomized to 5 groups: 1) control group, 2) hBMC (human bone marrow concentrate), 3) hBMC + PL, 4) pre-differentiated hMSCs, and 5) pre-differentiated hMSCs + PL. Bone marrow was collected from 4 different healthy donors undergoing total hip replacement and used for either generation of hBMC or for isolation of hMSCs. After hMSC expansion, pre-differentiation was carried out by incubating the cells in osteogenic medium for 6 days. Mineralized collagen matrix (MCM)-scaffolds were functionalized with either 10 mg heparin per 1 g mineralized collagen alone or in addition with PL. MCM cylinders (2 mm diameter x 2 mm height) were loaded with 10 µL fibrin gel containing 6.7 µL BMC (groups 2 + 3) or with medium containing 5x104 osteogenically pre-differentiated hMSCs (groups 4 + 5). Defects of 2 mm length were created at the right femur of each mouse and stabilized by an external fixator. After 6 weeks µCT-scans, biomechanical tests and histological analyses were performed.

Results: After a 6-week, the pre-differentiated MSCs + PL group showed the highest bone volume, highest degree of histological defect healing and highest number of bridged defects with measurable biomechanical stiffness (see Figure 1 [Fig. 1]). No difference was found concerning vascularization between the groups.

Conclusion: Using expanded and osteogenically pre-differentiated MSCs for the treatment of a critical-size bone defect led to optimized bone regeneration compared to treatment with cells from BMC. The addition of PL had a tendency to improve bone regeneration, but the results did not reach statistical significance. Therefore the potential utility of PL for bone regeneration using our model remains unclear.