Changes in collagen cross-linking in degenerative disc disease and scoliosis

Study Design. Biochemical study of the changes in the collagen cross-link profile of human intervertebral discs collected at surgery from patients with either low back pain associated with disc degeneration or scoliosis. Objective. To determine whether changes occur in the collagen cross-link profile in the disc of patients with either low back pain associated with disc degeneration or scoliosis, which may well influence matrix integrity. Such chances in the cross-link profile of a tissue indicates increased matrix turnover and tissue remodeling and may have implications for the progression of these disorders. Summary of Background Data. The diseases of the intervertebral disc, degenerative disc disease and scoliosis, are both characterized by changes in the extracellular matrix components that will affect the mechanical function of the tissue. The stability of the collagenous components and hence the mechanical integrity of connective tissues such as the disc is dependent on the degree and type of cross-links between the collagen molecules. This article reports results on the distribution of the different cross-links in the disc and the changes that occur with age, degenerative disc disease, and scoliosis. Methods. Thirty-three discs were obtained from patients with degenerative disc disease and 29 discs from patients with scoliosis. Samples were acid hydrolyzed and the collagen cross-links analyzed by either fractionation on an amino acid analyzer configured for cross-link analysis using ninhydrin postcolumn detection or fractionation by high-pressure liquid chromatography with fluorescence detection. Results. The reducible cross-links and the mature cross-link all increased from the outer anulus fibrosus through into the nucleus pulposus. The highest levels of the mature cross-link were found in the cartilage end-plate. The nonenzymic derived cross-link, pentosidine, in contrast, showed little difference across the disc, but did show the expected age-related increase. In degenerative disc disease, no change in the levels of the reducible or mature cross-links was found, but a decrease was observed in the levels of the age-related cross-link pentosidine in the more severe disease samples. In scoliosis, significantly higher levels of the reducible cross-links were found on the convex than on the concave side of the scoliotic disc. Conclusions. These changes in the cross-link profile of the intervertebral disc in degenerative disc disease and scoliosis are indicative of increased matrix turnover and tissue remodeling and likely to have implications for the progression of these disorders.