A comparative biochemical analysis of glycosaminoglycans and proteoglycans in human orthotopic and heterotopic bone

Glycosaminoglycans and proteoglycans are macromolecules of the bone and are involved in the assembly, maturation, mineralization, and maintenance of the extracellular matrix. Heterotopic ossification is the rapid development of calcified bone tissue at ectopic sites of the body, mainly in soft tissues that normally do not ossify. The aim of this study was to characterize the molecular profiles of glycosaminoglycans and proteoglycans in normal and heterotopic bone samples to assess whether differences exist between orthotopic and heterotopic bone. Heterotopic bone tissues contained lower amounts of glycosaminoglycans compared to normal femoral bone. Structural analysis of chondroitin sulfate (CS) revealed that both heterotopic and normal femoral bones were composed mainly of 6-sulfated disaccharides. Quantitative differences in the disaccharide composition of CS, such as the decrease of 6-sulfated disaccharides in heterotopic bone with a concurrent increase of 4-sulfated and nonsulfated disaccharides, were found between ectopic bone and normal femoral bone. The proteoglycans decorin and aggrecan were both detected in all bone samples using specific antibodies. The detection of minor amounts of aggrecan in mature human bone, such as femoral bone, as well as in ectopic bone is described for the first time. These results may elucidate the phenomenon of ectopic bone formation and assist in early detection.