Functional sites of chemically modified tetracyclines: inhibition of the oxidative activation of human neutrophil and chicken osteoclast pro-matrix metalloproteinases.

Objective. We studied the relative ability of 6 different chemically modified non-antimicrobial analogs of tetracycline (CMT) to inhibit human and chicken matrix metalloproteinases (MMP) in vitro. The ability of tetracycline and its analogs to inhibit MMP appears to depend on the Ca ++ /Zn ++ binding site at C 11 (carbonyl oxygen) and C 12 (OH group) of the molecule, which is lacking in CMT-5. the pyrazole derivative of tetracycline. This significant property of CMT-5 was used to differentiate between the effects of CMT on already active MMP versus the oxidative activation of latent MMP (pro-MMP). Methods. Cultured chicken osteoclast conditioned medium and purified human neutrophil progelatinase (MMP-9) and pro-collagenase (MMP-8) were assayed for proteinase activities using gelatin and collagen. respectively. The pro-MMP were activated either by preincubation with 1 mM aminophenylmercuric acetate (APMA) or 100 μM sodium hypochlorite (NaOCI). CMT were added either to the preincubation mixtures together with NaOCI or after activation of pro-MMP with NaOCI. Results. All CMT tested, except CMT-5, inhibited APMA or NaOCI activated pro-MMP. However, CMT-5 (like the other CMT), inhibited the oxidative activation of pro-MMP by NaOCI when added together by scavenging the reactive oxygen species. The degradation of type-1 collagen by chicken osteoclast conditioned medium was probably due to MMP-2 and/or MMP-13. Conclusion. Oxidative activation of pro-MMP may be crucial during soft tissue/bone destruction in the inflammatory diseases, including the arthritides. Our results indicate that the Ca ++ /Zn ++ binding site of CMT is not essential for inhibition of the oxidative activation of pro-MMP.