骨形成に関する実験的研究 : 加齢が脱灰骨基質のもつ骨誘導能に及ぼす影響

Abstract

Organic matrix of bone consists of various substances of different chemical nature, and these constituents are thought to function actively for sustaining the bony structure since many constituents are found to act as the stimulants directed to osteocytes or its precursor cells. Therefore, if the activity of these constituents declines with aging, bone may be unable to maintain its normal form, such as recovering its anomalous form resulted from bone fracture or tooth extraction wounds in elder patients. If aging provides this failure, it may be reflected in the possible changes of the constituent activities of bone matrix itself. From this point of view, an attempt has been made to examine whether osteoinductive potential linked to bone matrices alters with aging. To detect the age-associated changes of activity of the matrix constituents, bone matrices different in age were implanted in the soft connective tissue of the rat. The bone matrices were prepared from diaphyseal bone of Wistar-male rats according to Urist (1965∿1971). Those demineralized bone (D. B.) from young adult rats (8 weeks old) and old rats (64 weeks old) were implanted subcutaneously and process of endochondral bone formation in the tissues were observed. Furthermore, additional studies were made to examine the effect of the addition of the EDTA-extractable, Ca-precipitated fraction from bovine dentin in its similar system. Following results were obtained. 1. D. B. from young adult rats induced a larger amount of bony structure than D. B. from old ones. 2. In early phase of endochondral bone formation, D. B. from old rats induced much more chondrocytes with concomitant formation of a larger amount of cartilage than D. B. from young adult rats. 3. The addition of the EDTA-extractable, Ca-precipitated fraction in this system shift the phase of appearance of chondrocytes earlier. 4. The addition of the EDTA-extractable, Ca-precipitated fraction provides an increase in calcium-contents of D. B.. The results obtained in the present study clearly indicate that the osteoinductive potential of aged D. B. is weakened. The reduction of bone mass, one of the phenomena associated with senescence, may be caused partially by these agerelated changes in the intrinsic activity of bone matrices. In clinical application of the D. B. with osteogenetic potential for treating craniofacial defects and wound after tooth extraction, the younger matrices seem to be more efficient materials.