Doxycycline-Mediated Inhibition of Corneal Angiogenesis: An MMP-Independent Mechanism

PURPOSE. We explored the underlying mechanisms of doxycycline inhibition of corneal angiogenesis. METHODS. Human umbilical vein endothelial cells (HUVECs) were cultured in vitro in the presence or absence of VEGF, doxycycline, or broad-spectrum matrix metalloproteinase (MMP) inhibitors (1,10-phenanthroline [1PT] and batimastat). HUVEC proliferation was determined using Cell Counting Kit-8. Rats with VEGF-induced corneal neovascularization (CNV) were treated with saline solution, 0.1% doxycycline, 0.1% 1PT, or 50 mu M batimastat (n = 7/group). The length and area of CNV were measured on day 7. The activity of MMP-2 and MMP-9 was determined by a fluorogenic peptide substrate. Western blotting and ELISA were used to analyze the expression of phosphorylated eNOS and Akt, and PI3K activity. RESULTS. Our results showed that doxycycline inhibited HUVEC proliferation induced by VEGF in a dose-dependent manner in vitro, and decreased CNV induced by VEGF in vivo in terms of vessel length and area. 1PT and batimastat showed similar MMP inhibitory functions with doxycycline in vitro and in vivo, but they had no effects on HUVEC proliferation, and only partially mimicked the inhibitory properties of doxycycline (similar to 45%) on angiogenesis induced by VEGF. In addition, although doxycycline is capable of modulating the PI3K/Akt-eNOS pathway in vitro and in vivo in an MMP-independent manner, 1PT and batimastat were not. CONCLUSIONS. The mechanism of doxycycline-mediated inhibition of angiogenesis occurs through MMP inhibitory activity and modulation of the PI3K/Akt-eNOS pathway, an MMP-independent mechanism. (Invest Ophthalmol Vis Sci. 2013;54:783-788) DOI:10.1167/iovs.12-10323