Alterations in biochemical components of extracellular matrix in intervertebral disc herniation: role of MMP-2 and TIMP-2 in type II collagen loss.

Alterations in the composition of intervertebral disc extracellular matrix, mainly collagen and proteoglycans, may cause changes in mechanical properties of the disc, leading to dysfunction, nerve root compression, and herniation with severe clinical manifestations. Matrix metalloproteinases may be involved in degradation by hydrolysing extracellular matrix components. Inhibitors of matrix metalloproteinases, in contrast, function in the maintenance of degradation control. In this study, we investigated: (i) whether the level of matrix degradation correlated with the duration of the symptomatic disease, (ii) roles of matrix metalloproteinase-2 (MMP-2) and tissue inhibitor of matrix metalloproteinases-2 (TIMP-2) in intervertebral disc degeneration. Nucleus pulposus of intervertebral discs were obtained from 22 patients and analysed for collagen and proteoglycan contents, and pro-MMP-2, TIMP-2 levels. Collagen content was determined as hydroxyproline and proteoglycan content was measured as glycosaminoglycans. The loss in matrix components did not correlate with the duration of the degenerative disc disease. Pro-MMP-2 levels were higher at early stages of the degenerative disc disease (r = -0.495, P < 0.05). TIMP-2 levels were similar in all samples. Pro-MMP-2 and TIMP-2 levels negatively correlated in herniated discs samples (r = -0.855, P < 0.01). Pro- MMP-2 levels negatively correlated with the collagen content in herniated disc material. Our findings may suggest a silent period of active disease prior to symptomatic outcome during which irreversible matrix loss occurs. Involvement of other proteolytic enzymes at different stages of the disease should also be investigated to help to control the degradation cascade at relatively early stages of disc degeneration before the clinical onset of disease.