Chymopapain, chemonucleolysis, and nucleus pulposus regeneration.

UNLABELLED: In the adult mongrel dog, in vivo injection of chymopapain into the intervertebral disc resulted in disc-space narrowing at two weeks, with a complete loss of proteoglycan (as indicated by safranin-O staining) from the nucleus pulposus, the cartilaginous end-plates, and the annulus fibrosus. As demonstrated by [35S]sulphate-labeling and proteoglycan isolation, the nucleus pulposus retained the ability to synthesize proteoglycans, but these were degraded by endogenous proteolytic activity. Three months after chymopapain treatment the intervertebral disc showed an increase in height. There was a return of intense safranin-O staining in the annulus and the cartilaginous end-plates, and very prominently in the nucleus. The proteoglycans that were present were recovered as aggregates, with the proteoglycan monomer being slightly larger than in the controls. Six months after chymopapain treatment the intervertebral disc had increased further in height, and normal histology had been restored. The chemical composition and physical properties of the proteoglycans that were isolated from the nucleus pulposus were essentially the same as those from the controls. These observations suggest that the nucleus can regenerate following the injection of chymopapain. CLINICAL RELEVANCE: Our observations demonstrate that chymopapain has a profound but reversible effect on the intervertebral disc. The radiographic narrowing of the intervertebral disc following chymopapain injection correlates with the loss of proteoglycan content and structure. The restoration of normal disc height following chymopapain injection is explained by reconstitution of the intervertebral disc with normal proteoglycans. In experimental animals, chemonucleolysis with chymopapain appears to be less likely than surgical excision to permanently alter the biochemistry of the nucleus pulposus.