Doxycycline belongs to the family of tetracycline antibiotics and inhibits bacterial protein synthesis. Doxycycline is an effective inhibitor of cell proliferation, migration, and MMP activity [17]. Those varied biological effects are ascribed to a MMP inhibition [18]. Mechanism(s) of MMP inhibition by doxycycline are not yet completely understood to date. Doxycycline could either bind directly Zn2+ or Ca2+, directly target active site of MMPs, render pro-enzyme susceptible to fragmentation during activation process [19], induce a degradation of the pro-MMP zymogen [20] or provoke an inhibition of the transcription of MMP mRNAs. Doxycycline has been proposed as a therapy for many diseases implicating MMP-9, e.g. diseases of the ocular surface [21], aortic aneurysms [22], central nervous system disorder [18] and colorectal cancers [23]. It was also suggested that some tetracyclines display, in vitro, the ability to decrease IgE responses [24]. When considering doxycycline as an antibiotic, the minimal concentration inducing an inhibition of bacteria is generally considered to be about 2 mM while the MMP inhibitory effect is present for concentrations 100 times lower. For instance, concentrations required to inhibit 50% of the gelatinolytic activity (IC50) were found to be 30–50 μM [25] and [26].