BONE TISSUE COMPOSITION - BIOCHEMICAL ANATOMY OF BONE

Bone is chemically built up as a mineralized matrix which comprises co llagen and a small amount of noncollagenous proteins. This paper point s out some useful methods to evaluate the bone composition. Deminerali zing extraction of bone powder with EDTA allows the determination of m atrix size and degree of extractability. These parameters vary with bo ne type, anatomical site of the bone, disease, species, and drug treat ment. The study of bone particles in situ can be done by separation of bone powder according to their density. A shift of the bone particles to higher density fractions reflects an increased amount of older, mo re mineralized osteons in the bone with its consequences on the mechan ical competence of the bone. Quantity and quality of bone matrix miner alization are related to bone cell activity which can be studied indir ectly by further exploration of the composition of the bone matrix. Ma ny noncollagenous proteins are buried in the extracellular bone matrix from where they can be released when bone is resorbed. These proteins can then act on bone cells in an autocrine or paracrine manner. Alter ed concentrations of noncollagenous proteins in bone matrix are descri bed in three pathological conditions associated with changes in other bone properties: osteoarthritis, osteopenia, and osteogenesis imperfec ta. The functional significance and origin of these changes will have to be subjected to further study.