Experimental chemonucleolysis with recombinant human matrix metalloproteinase 7 in human herniated discs and dogs

BACKGROUND CONTEXT

Chemonucleolysis has been proposed as a less invasive technique than surgery for patients with lumbar disc herniation. Once chymopapain had been approved as a chemonucleolysis drug, it was withdrawn because of serious complications. A novel agent with fewer complications would be desirable.

PURPOSE

The purpose of this study was to investigate the effects of recombinant human matrix metalloproteinase 7 (rhMMP-7) in experimental chemonucleolysis in vitro and in vivo and examine its effects on tissue damage.

STUDY DESIGN

The study design is the experimental study using human herniated discs and enzyme substrates in vitro and dogs in vivo.

METHODS

The effects of rhMMP-7 on the degradation of human herniated discs were examined by measuring the wet weight in vitro. The correlations between the decrease in wet weight by rhMMP-7 and the conditions associated with herniated discs were also analyzed. The effects of rhMMP-7 on the proteoglycan and water contents were respectively examined with alcian blue staining and T2-weighted magnetic resonance imaging at 7 days after intradiscal injection in dogs. The distribution of [125I]-labeled rhMMP-7 was investigated by autoradioluminography at 7 days after intradiscal injection in dogs. An epidural injection study with rhMMP-7 was performed to evaluate the effects on the tissue damage around the discs at 1 and 13 weeks after the treatment in dogs. The Type 1 and 2 collagen cleavage rates were measured and compared with those of aggrecan in vitro.

RESULTS

Recombinant human matrix metalloproteinase 7 concentration dependently decreased the wet weight of herniated discs in vitro. The decrease in wet weight of the discs by rhMMP-7 did not significantly correlate with the conditions associated with herniated discs. Intradiscal injection of rhMMP-7 reduced the proteoglycan and water contents, with an increase in the serum keratan sulfate levels. Radioactivity of [125I]-labeled rhMMP-7 was detected in the nucleus pulposus and annulus fibrosus but not in the muscle. Epidural injection of rhMMP-7 had no effect on the injection site or the nerve tissues. The Type 1 and 2 collagen cleavage rates of rhMMP-7 were 1,000-fold weaker than those of aggrecan.

CONCLUSIONS

This study demonstrated experimental chemonucleolysis with rhMMP-7 in vitro and in vivo. The effects of rhMMP-7 were not affected by the conditions associated with herniated discs. The epidural injection study together with the autoradioluminography and in vitro enzyme assay suggests that intradiscal injection of rhMMP-7 may not induce tissue damage around the discs because of its distribution and substrate selectivity. Recombinant human matrix metalloproteinase 7 may be a novel and promising chemonucleolysis agent.