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V.A. Smith, S.D. Cook; Doxycycline Function in Ocular Surface Repair . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3832.
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Purpose Doxycycline is a broad spectrum antibiotic that chelates metal ions and is frequently used to treat ocular surface inflammatory diseases, particularly recurrent epithelial cell erosion, rosacea and keratitis sicca. Its therapeutic value has been ascribed to an ability to inhibit MMP activity and both MMP and Il-1α synthesis. The purpose of this study was to evaluate the role of doxycycline as an inhibitor of corneal MMPs and assess its contribution to ocular surface repair mechanisms. Methods MMP activity was assayed using a fluorigenic substrate and visualised by zymography. Keratocyte and corneal epithelial cell cultures were grown to confluence and incubated with either Il-1α, doxycycline at varying concentration or lipopolysaccharide (LPS) +/- doxycycline (100µM), in serum free medium for 4 days. The cells were either harvested and assayed for caspase-3 activity or stained with anti AE5 and vimentin antibodies. Media samples were concentrated and assayed for MMP activity. ELISA was used to quantify MMPs-1, -2, -3, -9 and TIMPs -1 and -2. Results Il-1α and LPS had no effect on MMP / TIMP production by cultured keratocytes and epithelial cells. Corneal MMP-2 inhibition by doxycycline was [Ca2+] dependent and reversable. At the minimum inhibitory concentration (100µM), doxycycline had no immediate effect on MMP and TIMP production but ultimately caused keratocytes and some epithelial cells to detach from their membrane and die. The mechanism was not apoptosis since caspase-3 activity, normally detectable in cultured epithelial cells, was lost. Surviving epithelial cells were probably transient amplifying cells. Conclusions Doxycycline reversibly inhibits MMP-2 by chelating the Ca2+ required for activity . Corneal MMP / TIMP production in vitro is not affected by doxycycline, LPS or Il-1α. The therapeutic value of doxycycline may depend on its effective concentration at the ocular surface and probably relates to its chelating properties.
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