Body tissues are mainly composed of cells and extracellular matrixes (polymer structures). Extracellular matrixes which are secreted from cells provide hydrated spaces in which cells act or cell scaffoldings. In addition, extracellular matrixes function as storage houses for various growth factors secreted from cells, and have a profound influence on expression of cell functions or cell differentiation. Complicated interaction between extracellular matrixes and cells in a living body has an influence on various vital activities.
In recent years, highly advanced medical technology, whereby severe diseases are treated using artificial organs, gene therapy and regenerative medicine, has achieved remarkable success at clinical sites, and it has attracted global attention. Among others, regenerative medicine, whereby damaged tissues or organs are regenerated using three main elements, namely, cells, growth factors and extracellular matrixes that play main roles in tissue regeneration, has drawn attention as a treatment method for future generation. As a matter of fact, such regenerative medicine has already been realized for cultured skins or corneas.
Bone regeneration in the field of orthopedics or dentistry has attracted a great attention as an example of application of regenerative medicine. That is to say, when bone disease is developed in legs or lumbar parts, it causes abasia. When such bone disease is developed in tooth sections, it makes dietary intake difficult. Thus, bone disease is considered to cause a significant decrease in QOL. At present, representative examples of a known bone regeneration therapeutic formulation include: Infuse (a combination of BMP-2 with a collagen sponge) for treating spinal injuries; and BioOss (deproteinized, crushed cow bones), Puros (crushed human bone products), Gem21 (PDGF and βTCP), Osferion (βTCP) and Teruplug (Name used in the U.S.A.: FOUNDATION; a collagen sponge) used as bone supplementation agents for regenerating alveolar bones. Properties known to be necessary for bone regeneration therapeutic formulations include: 1. strength for maintaining structures; 2. the securement of spaces for bone regeneration; 3. cell scaffoldings for bone regeneration; 4. differentiation and growth of cells necessary for bone regeneration; and 5. degradability attended with bone regeneration.
In the dental field, representative diseases, for which the above-mentioned bone regeneration therapeutic formulations are known to be used, include: 1. ridge augmentation; 2. socket preservation; 3. periodontal bone defect regeneration; 4. implantable bone regeneration; and 5. sinus lift. The importance of scaffolding materials for promoting bone regeneration in the aforementioned diseases has been recognized. However, under the current circumstances, the aforementioned formulations rely on the bone regeneration ability of an agent (BMP or RDGF) contained therein. Such scaffolding materials have been believed to function as products for ensuring a space (strength) in an affected area. In many cases, inorganic materials have been widely used as such scaffolding materials.
In general, a collagen or a gelatin which is a denatured product of the collagen has been widely used as a scaffolding material (organic material) in regenerative medicine in many cases. It has been known that a highly oriented collagen plays an important role as a bone regeneration material in calcification (Non Patent Document 1). Thus, a sponge made of collagen has been placed on the market as a bone regeneration material (Teruplug (FOUDATION; Olympus Terumo Biomaterials Corp.)). However, a bone supplementation material using a collagen sponge provides only a scaffolding for tissue formation, and a single use of such a collagen sponge is not able to form a bone (Non Patent Document 2). Moreover, according to previous findings, a gelatin which is a denatured product of collagen has never been known to have a bone regeneration effect. Regarding gelatin, it is described that 1. a single use of a gelatin sponge inhibits bone regeneration (Non Patent Document 3), and that 2. a gelatin has bone regeneration ability that is lower than that of a collagen (Non Patent Document 4). Furthermore, it has been reported that no bones are formed in β-TCP that is an artificial bone ingredient, as with a gelatin sponge prepared by performing a heat treatment on a collagen (Non Patent Documents 2 and 5). As described above, it has been recognized that a gelatin that has been widely used as a base material in regenerative medicine is not suitable as a scaffolding material for bone regeneration therapeutic agents. With regard to a supplementation material that cannot form a bone by itself, a method for impregnating the supplementation material with a platelet-derived growth factor (PDGF) or a bone morphogenetic protein (BMP) which is a physiologically active substance has been studied (Patent Document 1). However, since a purified protein of such physiologically active substance is expensive, it has not yet been widely used.
On the other hand, biological polymers such as a gelatin have been broadly used as medical materials. As a result of the advancement of genetic engineering technology in recent years, a protein has been synthesized by introducing a gene into Escherichia coli or yeast. By this method, various types of recombinant collagen-like proteins have been synthesized (for example, Patent Documents 2 and 3). Such recombinant collagen-like proteins are more advantageous than natural gelatins in that they are excellent in terms of non-infectivity and uniformity, and in that since their sequences have been determined, the strength and degradability thereof can be precisely designed. However, the intended use of the recombinant gelatin, which has been proposed so far, is only the use as an alternative material of a natural gelatin. Naturally, the intended use of the recombinant gelatin as a bone regeneration agent has not been known.