Effects of enzyme inhibitors on matrix degradation. All results are expressed as a percentage of the mean of the measured area of degradation of the untreated samples. All data given as mean ± standard error of the mean. (a) Comparison of the effects of IL-1 receptor antagonist (IL-1Ra), broad spectrum inhibitor of proteases (BSIP) and EDTA on degradation of the three matrices in non-degenerate, moderately degenerate and severely degenerate intervertebral discs (IVDs). In the nucleus pulposus (NP) all the inhibitors effectively eliminate enzyme activity. In the annulus fibrosus (AF) of moderately degenerate IVDs, BSIP and IL-1Ra eliminate enzyme activity but EDTA only reduces type II collagenase and gelatinase activity. In the AF of severely degenerate IVDs, BSIP eliminates collagenase and gelatinase activities, but both IL-1Ra and EDTA only reduce them. (b) Comparison of the effects in AF and NP of moderately degenerate IVDs of all the inhibitors employed in this study (IL-1Ra, BSIP, EDTA, phenyl methyl sulphonyl fluoride (PMSF) and leupeptin) to show differences in the enzyme subgroups involved. The key finding is in the AF, where IL-1Ra eliminated all enzyme activity but EDTA did not, indicating that the enzymes involved were driven by IL-1 but were not metal-dependent proteases (MDPs). By contrast with the NP, PMSF and leupeptin did reduce enzyme activity, indicating that those IL-1 driven, non-MDP enzymes were serine/cysteine proteases.