Mechanism of inhibition of matrix metalloproteinase-2 expression by doxycycline in human aortic smooth muscle cells

Degradation of the extracellular matrix components elastin and collagen has been implicated in vascular diseases, including abdominal aortic aneurysm (AAA) and atherosclerotic plaque rupture. Increased expression of matrix metalloproteinases (MMPs) is involved in these disease processes. Our previous studies have demonstrated that MMP-2 derived from mesenchymal cells is required for aneurysm development in a murine model. Doxycycline is a nonspecific inhibitor of MMPs. In the present study, the mechanisms of the inhibitory effects of doxycycline on MMP-2 expression from cultured human aortic smooth muscle cells (SMCs) and human aortic aneurysm tissue explants were studied. Doxycycline inhibited MMP-2 expression from cultured SMCs in a concentration-dependent manner (5-40 mug/mL; inhibitory concentration of 50%, 6.5 mug/mL). At normal therapeutic serum concentration (5 mug/mL) doxycycline significantly reduced MAIP-2 production from SMCs (37%; P < .05), which were stimulated with conditioned media from macrophage or lymphocyte co-culture simulating the inflammatory milieu of AAA tissue. This correlated with a decrease in MAIP-2 mRNA half-life, from 49 hours to 28 hours, which suggests that doxycycline inhibits SAIC MMP-2 production in part by reducing MMP-2 mRNA stability. When AAA tissue was cultured for 10 days with doxycycline at concentrations of 2.5 to 40 mug/mL, the media exhibited a concentration-dependent decrease in both active and latent forms of MMP-2 and MMP-9. Doxycycline at a concentration of 5 mug/mL reduced active and latent MMP-2 secreted from cultured AAA tissue by 50% and 30%, respectively (P < .05). These study findings demonstrate that doxycycline at standard therapeutic serum concentrations inhibits AIMP-2 expression from cultured human aortic SMCs and AAA tissue explants. Inasmuch as MMP activity contributes to extracellular matrix degradation in AAAs and atherosclerotic plaque, doxycycline may have potential value in treating these diseases. Clinical Relevance: Numerous studies have made it clear that proteolytic degradation of aortic structural proteins is responsible for initiation and expansion of abdominal aortic aneurysm (AAA). Elastin and collagen degradation in aneurysm tissue is caused, in part, by MMP-2 produced by mesenchymal cells of the aortic media. The present study shows that the antibiotic doxycycline can inhibit MMP-2 in cell culture and in human aneurysm tissue ex vivo. This lends further support to the concept that doxycycline could inhibit AAA growth. Presently there is no medical treatment to inhibit AAA growth, and the only effective option to protect against rupture is repair. A medical option, if it existed, could lead to screening, detection, and medical treatment of small aneurysms.