In vivo detection of intervertebral disk injury using a radiolabeled monoclonal antibody against keratan sulfate

In the intervertebral disk, proteoglycans form the major part of the extrac ellular matrix, surrounding chondrocytelike disk cells. Keratan sulfate is a major constituent of proteoglycans. Methods: We have radioiodinated a mon oclonal antibody raised against keratan sulfate. This antibody was injected into rats (n = 6), and the biodistribution was studied. A model of interve rtebral disk injury was developed, and two tail disks in each animal with b oth acute (2 wk old) and subacute (7 wk old) injuries were studied for in v ivo antibody uptake. Results: The biodistribution at 72 h was as follows: b lood, 0.0018 percentage injected dose per gram of tissue (%ID/g); lung, 0.0 106 %ID/g; esophagus, 0.0078 %ID/g; kidney, 0.0063 %ID/g; liver, 0.0049 %ID /g; spleen, 0.0046 %ID/g; heart, 0.0036 %ID/g; thyroid, 0.0034 %ID/g; muscl e, 0.0017 %ID/g; and bone, 0.0016 %ID/g. In the subacute stage, a significa nt difference (P < 0.006) was found in antibody uptake between injured disk s (n = 12) and adjacent healthy disks (n = 12). In vivo <gamma> imaging sho wed increased uptake in other animals having lumbar disk injuries (2, 7, an d 17 d after injury). Cartilage tissue, such as the trachea, was studied se parately and showed extremely high antibody uptake, 0.10 %ID/g. Rat trachea was also visualized on gamma images. Conclusion: Our data suggest that ant ibodies against nucleus pulposus components, such as proteoglycans, can be used for in vivo detection of intervertebral disk injury. This finding is i n spite of the minimal circulation present in intervertebral disks.