Bone tissue composition: biochemical anatomy of bone.

Bone is chemically built up as a mineralized matrix which comprises collagen and a small amount of noncollagenous proteins. This paper points out some useful methods to evaluate the bone composition. Demineralizing extraction of bone powder with EDTA allows the determination of matrix size and degree of extractability. These parameters vary with bone type, anatomical site of the bone, disease, species, and drug treatment. 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, more mineralized osteons in the bone with its consequences on the mechanical competence of the bone. Quantity and quality of bone matrix mineralization are related to bone cell activity which can be studied indirectly by further exploration of the composition of the bone matrix. Many 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. Altered concentrations of noncollagenous proteins in bone matrix are described in three pathological conditions associated with changes in other bone properties: osteoarthritis, osteopenia, and osteogenesis imperfecta. The functional significance and origin of these changes will have to be subjected to further study.