Observations on bone formation and remodelling in advanced atheroscleroticlesions of human carotid arteries

Immunolocalisation and histochemical techniques were used to examine minera lised bone deposits within late stage atherosclerotic plaques of human caro tid arteries. These specimens showed characteristic features of osteogenesi s. Large calcifications were often observed in close association with or in tegrated within mineralised bone. Smooth muscle cells (a-actin positive) we re often located around osteoid-like matrix, together with focal accumulati ons of macrophages (CD68 and HAM56 positive). Local accumulations of mast c ells (tryptase positive) were consistently observed in close association wi th the bone. Multinucleated giant cells in close apposition with mineralise d bone demonstrated typical osteoclastic morphology, and were positively st ained for acid phosphatase and the macrophage marker CD68. Thus, all the no rmal features of bone formation and resorption were observed in this microc osm of osteogenesis within atherosclerotic plaque; the term 'osteosome' see ms appropriate for the structure. These osteosomes have numerous advantages for experimental studies of the various osteogenic factors responsible for bone metabolism, especially following short-term tissue culture. This ex v ivo technique was used to demonstrate the distribution and the multiple cel lular sources of bone morphogenetic protein 6.