Mesenchymal stromal cells improve the osteogenic capabilities of mineralized agarose gels in a rat full-thickness cranial defect model

Abstract

The authors previously created HAp or CaCO(3) formed on or in agarose gels (HAp and CaCO(3) gels, respectively) as biocompatible and biodegradable bone graft materials. However, these gels have limitations for bone regeneration. Mesenchymal stromal cells (MSCs) have osteogenic potential and are considered useful for bone tissue engineering. The purpose of this study was to clarify the osteogenic abilities of MSCs loaded in HAp or CaCO(3) gels (MSC/HAp and MSC/CaCO(3) gels, respectively) using a rat cranial defect model compared to HAp and CaCO(3) gels alone. HAp, CaCO(3) , MSC/Hap, and MSC/CaCO(3) gels were prepared for in vivo analyses and implanted into full-thickness bone defects created in the rat cranium. All samples were assessed radiologically and histologically at 4 and 8 weeks after implantation. Using microfocus-computed tomography, an increase in bone formation was observed in the MSC-loaded gels compared to the gels alone. In addition, peripheral quantitative computed tomography revealed higher bone mineral contents in the MSC-loaded gels compared to the gels alone. After transmission X-ray diffraction analyses, the degree of apatite c-axis orientation as a bone quality index of newly formed bone in the MSC-loaded gels was close to that of living cranial bone. Histologically, more extensive bone formation was detected in the MSC-loaded gels compared to gels alone. Overall, MSC/HAp and MSC/CaCO(3) gels showed equivalent efficacy for bone regeneration. These findings demonstrate that loading of MSCs into the gels strengthened their osteogenic ability and improved the quality of the newly formed bone. As a result, MSC-loaded gels could represent viable therapeutic biomaterials for bone tissue engineering.

Biomineral/Agarose Composite Gels Enhance Proliferation of Mesenchymal Stem Cells with Osteogenic Capability

“…We previously demonstrated that HA/agarose and CaCO 3 /agarose might be suitable as bone graft substitutes in various in vivo bone defect models [4,9,10,11]. However, we also reported that they had limitations for repair of defects in a critical bone defect model, although these limitations could be overcome by loading MSCs onto the gels [12]. The in vitro data from the present study revealed that MSCs easily attached and proliferated on both HA/agarose and CaCO 3 /agarose and, importantly, the attachment/proliferation of ostegenically differentiated MSCs was clearly observed.…”

“…Furthermore, the cellular proliferation with high osteogenic capability occurred smoothly on both mineralized gels. We therefore consider the cellular activity observed on the HA/agarose and CaCO 3 /agarose gels as fundamental responses to the loading of MSCs, which is apparently necessary for the successful repair of critical bone defects [12]. …”

“…Furthermore, in our study of cranial bone defects [11], because a thin layer of pre-existing host bone existed at the base of the defects, they were also partial bone defects. When cranial bone defects were created by completely punching out tissue without leaving any remnants of host bone tissue, implantation of HA/agarose or CaCO 3 /agarose resulted in limited bone tissue regeneration and the critical defects were not satisfactorily healed [12]. Therefore, other factors might be important for broadening the healing potential of both HA/agarose and CaCO 3 /agarose.…”

“…Based on these findings, in our previous work, we loaded MSCs onto HA/agarose (MSCs/HA/agarose) and CaCO 3 /agarose (MSCs/CaCO 3 /agarose) and implanted them into critical cranial bone defects [12]. Both of these MSC-loaded agarose biomaterials produced extensive bone formation in the defects, and they showed equivalent efficacy for bone tissue regeneration.…”

Human Very Small Embryonic-Like Cells Generate Skeletal Structures, In Vivo

“…They can be directed to do so in vitro and when implanted in bone can also facilitate bone formation. In fact, several studies have shown that MSCs can be employed to regenerate craniofacial bone in animal studies, supporting the potential of stem-cell-based therapy for bone repair [1][2][3][4][5]. However, there are potential limitations to the use of autologous MSCs in bone repair in humans because most preparatory protocols require the extensive expansion of MSC populations in vitro using animal-derived or recombinant growth factors as well as modulators of transcription and cell survival.…”