Minocycline is More Potent Than Tetracycline and Doxycycline in Inhibiting MMP-9 in Vitro

Tetracyclines are antimicrobial agents that possess anti-inflammatory and matrix metalloproteinase (MMP) inhibitory effects. Tetracycline, doxycycline, and minocycline have shown different potencies in inhibiting various MMPs. MMPs are a conserved family of zinc-dependent endopeptidases, which are involved in various physiologic and pathologic conditions. MMP-9 is among the most important proteases involved in the development of cardiovascular disease, cancer, and inflammatory disease Considering the central role of MMP-9 in the above-mentioned diseases and the variable inhibitory potentials of routine tetracyclines, including tetracycline, doxycycline, and minocycline, this study measured the inhibitory effect of these routine tetracycline agents on MMP-9 activity obtained from U-937 cell cultures using the zymography method. An MMP-9-rich culture medium of U-937 cells was used as the source of the enzyme. Serial dilutions of 5, 20, 100, 200, and 500 µM of each drug were placed in zymography incubation buffer. Gelatin zymography was run, and densitometry of the bands was performed using Image J software. The resulting data were used to draw dose-response curves using GraphPad Prism software. Our results showed that tetracyclines inhibited MMP-9 activity with IC50 values of 40.0, 10.7, and 608.0 µM for tetracycline, minocycline, and doxycycline, respectively. Minocycline showed the highest potency in MMP-9 inhibition (P < 0.0001), while tetracycline was found to be more potent than doxycycline in MMP-9 inhibition based on the zymography experiments (P < 0.0001). Our results suggest that tetracyclines dose-dependently inhibit MMP-9 activity, and among the common clinical tetracyclines, minocycline provides the most potent inhibition of excess MMP-9 activity and its consequences.