Recombinant bone matrix maintains the graft space, induces vascularized bone regeneration and preserves canine tooth extraction socket structure.

AIM: Recombinant bone matrix (RBM) is a newly conceived and engineered porous bone graft granule of average size 600 µm composed of purified recombinant collagen peptide. We sought to examine the behaviour with time of RBM that was grafted in the canine tooth extraction socket. MATERIALS AND METHODS: The canine tooth extraction socket of the hemisectioned mandibular third premolar distal root was grafted with RBM granules, whereas the opposite side extraction socket served as non-grafted control. The mandibular samples were harvested at 1, 3 and 6 months of healing and subjected to micro-CT imaging and decalcified paraffin-embedded histology. Separately, the effect of RBM was compared with that of deproteinized cancellous bovine bone (DCBB) and bovine atelocollagen plug (BACP) in the canine tooth extraction model at 3 months of healing. RESULTS: RBM maintained the grafted space in the socket and the gingival connective tissue until new bone was formed within its porous space. The regenerated bone was highly vascularized and continued to mature, while RBM was completely bioresorbed by 6 months. The buccal and lingual alveolar ridge heights of the RBM-grafted extraction socket was better preserved than those of non-grafted control sockets. The degree of socket preservation by RBM was equivalent to that by DCBB, although their healing mechanisms were different. CONCLUSIONS: This study demonstrated that RBM induced controlled active bone regeneration and preserved the extraction socket structure in a canine model. Bioresorbable RBM engineered without animal or human source materials presents a novel bone graft category with robust bone regenerative property.

Bioresorbable Bone Graft Composed of an RGD-Enriched Recombinant Human Collagen Polypeptide Induced Neovascularization and Regeneration of Mature Bone Tissue.

Bone graft materials provide a scaffold for migrating cells for bone regeneration. One of the major challenges is to support adequate neovascularization in the graft materials and bone tissue. Vascular endothelial cells have been shown to recognize the integrin-binding Arg-Gly-Asp (RGD) sequence in natural extracellular matrix (ECM) molecules. Here, we report a bone graft material composed of an RGD-enriched recombinant polypeptide based on human type I collagen alpha 1 chain (RCPhC1) and propose a category of bone graft materials called the recombinant bone matrix. RCPhC1 demonstrated significantly increased human umbilical vein endothelial cell attachment in vitro and was further processed through freeze casting and heat crosslinking processes to generate porous granular bone graft, in which RGD sequences remained canonical. When grafted in the rat model, RCPhC1 bone graft demonstrated a uniquely increased presence of CD34+ endothelial cells within the graft material. Bone tissue was found directly in contact with the pore structure of RCPhC1 bone graft, resulting in the regeneration of large bone tissue. By contrast, the combined demineralized and decellularized bone allograft containing bone collagen in the ECM did not show vascular formation within the graft material. When applied to canine tooth extraction socket, RCPhC1 bone graft rapidly induced highly vascularized regenerating tissues, which became a mature bone with the bone marrow tissue. These results indicate that RCPhC1 bone graft is a promising material and generated highly active bone tissues, which rapidly matured.

Prediction of Drug Permeability Using In Vitro Blood-Brain Barrier Models with Human Induced Pluripotent Stem Cell-Derived Brain Microvascular Endothelial Cells.

The strong barrier function of the blood-brain barrier (BBB) protects the central nervous system (CNS) from xenobiotic substances, while the expression of selective transporters controls the transportation of nutrients between the blood and brain. As a result, the delivery of drugs to the CNS and prediction of the ability of specific drugs to penetrate the BBB can be difficult. Although in vivo pharmacokinetic analysis using rodents is a commonly used method for predicting human BBB permeability, novel in vitro BBB models, such as Transwell models, have been developed recently. Induced pluripotent stem cells (iPSCs) have the potential to differentiate into various types of cells, and protocols for the differentiation of iPSCs to generate brain microvascular endothelial cells (BMECs) have been reported. The use of iPSCs makes it easy to scale-up iPSC-derived BMECs (iBMECs) and enables production of BBB disease models by using iPSCs from multiple donors with disease, which are advantageous properties compared with models that utilize primary BMECs (pBMECs). There has been little research on the value of iBMECs for predicting BBB permeability. This study focused on the similarity of iBMECs to pBMECs and investigated the ability of iPSC-BBB models (monoculture and coculture) to predict in vivo human BBB permeability using iBMECs. iBMECs express BMEC markers (e.g., VE-cadherin and claudin-5) and influx/efflux transporters (e.g., Glut-1, SLC7A5, CD220, P-gp, ABCG2, and MRP-1) and exhibit high barrier function (transendothelial electrical resistance, >1000 Ω × cm2) as well as similar transporter expression profiles to pBMECs. We determined that the efflux activity using P-glycoprotein (P-gp) transporter is not sufficient in iBMECs, while in drug permeability tests, iPSC-derived BBB models showed a higher correlation with in vivo human BBB permeability compared with a rat BBB model and the Caco-2 model. In a comparison between monoculture and coculture models, the coculture BBB model showed higher efflux activity for compounds with low CNS permeability (e.g., verapamil and thioridazine). In conclusion, iPSC-BBB models make it possible to predict BBB permeability, and employing coculturing can improve iPSC-BBB function.