Gelatinase B/matrix metalloproteinase-9 cleaves interferon-beta and is a target for immunotherapy
Nelissen I, Martens E, Van Den Steen PE, Proost P, Ronsse I and Opdenakker G;
Commented by , 28 Jul 2003
Matrix metalloproteinase (MMP)-9 (Gelatinase B) is considered to play a central role in the pathophysiology of Multiple Sclerosis (MS). It is increased in serum and CSF of MS patients, has proinflammatory action and cleaves myelin basic protein (MBP) into encephalitogenic and immunodominant peptides.
Interferon (INF)-b is currently the most used treatment for MS, and several studies have shown that INF-b downregulates MMP-9. To what extent this interaction has an indirect therapeutic effect in MS is still unknown. Little is also known about the effect of MMP-9 on INF-b.
The study aims at describing the effect of MMP-9 on INF-b.
The authors used two commercial INF-b in therapeutic doses: INF-b 1a (Avonex, 30mg) and INF-b 1b (Betaferon 250 mg). The purified INF-b was incubated with activated MMP-9 and gel electrophoresis was used to assess the extent of proteolysis of INF-b by MMP-9, as well as the ability of inhibitors to prevent this fragmentation. The INF-b fragments were furthermore specifically detected in a western plot analysis.
The site specificity of INF-b cleavage was determined using fragmentation analysis and mass spectrometry. The biological activity of INF-b was estimated in antiviral cytopathogenic effect inhibition assays.
Both recombinant human INF-b preparations were cleaved by MMP-9, although the cleavage was much more efficient with INF-b 1b than INF-b 1a. This proteolysis was inhibited by EDTA and the tetracycline minocyclocine. The action of minocycline was dose dependent. The biologic activity of INF-b was completely lost as a result of a 30-fold reduction in bioactivity (molar substrate:enzyme ratio of 10:1).
The study shows that MMP-9 destroys INF-b structurally and kills its biological activity. The clinical implication in this regard, would be reduced bioavailability of INF-b during exacerbation of the disease, where MMP levels in serum and CSF are increased. The authors thereby raise an important question regarding the efficacy of INF-b in active disease.
Recently, there has been a discussion concerning the significance of neutralizing antibodies (NAb) against INF-b, and it is recognized that the bioavailability of INF-b is reduced in NAb+ patients (Bertolotto et al., Neurology, 2003;60:634-639). The current study indicate that concentrations of MMP-9 may be an equally important measurement, when estimates of treatment efficacy have to be made.
Furthermore, the study shows that there is a difference in proteolysis between the two INF-b preparations, where INF-b 1a seems to be the most robust. It is difficult to evaluate the significance of this finding, although it might have implication for future evaluation of drug dose and administration.
It is evident that the in vivo interaction between MMP-9 and INF-b is very complex, and results of the study need to be confirmed in a clinical context. In this regard it is interesting, that the use of minocycline effectively inhibits MMP-9, which in theory will lead to an increase in bioavailability of INF-b.
In this way, there is a clinical rationale for clinical trials with minocycline and INF-b, and hopefully future results will answer some of the questions raised in this paper.