Serial changes in the rate of proteoglycan synthesis after chemonucleolysis of rabbit intervertebral discs

Study Design. Serial changes in the rate of proteoglycan synthesis in rabbi t discs after chemonucleolytic treatment with chymopapain and chondroitinas e ABC were measured using an in vitro method. Objectives. To determine the retained ability of the intervertebral disc to synthesize proteoglycans after chemonucleolytic treatment. Summary of Background Data. Most previous studies describe radiologic and h istologic changes that occur after chemonucleolytic treatment. However, in humans it is not clear whether reconstitution of the disc space with normal nucleus proteoglycans can occur with time. Methods. Twenty-five rabbits were treated with chymopapain (10 units/0.1 mL /disc) and chondroitinase ABC (5 units/0.1 mL/disc) by intradisc injection. Five rabbits were killed at each interval, 1, 2, 4, 8 and 12 weeks after i njection. Radiologic changes in the disc height were noted, and the rate of proteoglycan synthesis was determined biochemically. Results. After injection, no significant recovery of disc height was seen i n either enzyme group after the initial disc narrowing. The average rate of proteoglycan synthesis in control rabbit intervertebral discs, those which had not been surgically treated, was 27.1 (x 10(-6) mmols sulphate/hour/dr y weight). Twelve weeks after injection, the values were 21.6 in the saline group, 8.9 in the chondroitinase ABC group, and 8.2 in the chymopapain gro up. Conclusions. Doses within the therapeutic range can damage disc cells, at l east in the rabbit, so that proteoglycan synthesis declined to 30% of contr ol rates, and no significant recovery of disc height was observed.