Effect of matrix metalloproteinases activity on outflow in perfused human organ culture

PURPOSE. To test the hypothesis that extracellular matrix turnover, mediate d by the matrix metalloproteinases, modulates aqueous humor outflow facilit y in a human outflow model. METHODS. Matrix metalloproteinase activity was manipulated and outflow faci lity evaluated using perfused human anterior segment organ culture. Purifie d matrix metalloproteinases, tissue inhibitors of metalloprotienases (TIMPs ), and several families of synthetic inhibitors of matrix metalloproteinase s were added to the perfusion medium. Matrix metalloproteinase expression w as increased by adding recombinant interleukin (IL)-1 alpha. Kinetic inhibi tion analysis was conducted for stromelysin, gelatinase A, and gelatinase B with the various inhibitors. Live-dead staining was used to evaluate cultu re viability. RESULTS. Increasing metalloproteinase activity, by adding purified metallop roteinases or by inducing their expression by IL-1 alpha treatment, increas ed outflow facility. Inhibition of endogenous trabecular metalloproteinase activity using TIMP or several families of synthetic metalloproteinase inhi bitors reduced outflow rates. The elevation and the reduction of outflow ra tes were reversible, with changes requiring 1 to 3 days. Kinetic enzyme inh ibition analysis produced 50% inhibitory concentration values for these inh ibitors that were compatible with the concentration ranges for outflow inhi bition. CONCLUSIONS. The ability of several specific matrix metalloproteinase inhib itors to reduce outflow facility implies that endogenous extracellular matr ix turnover by these enzymes was required for the maintenance of trabecular outflow resistance, at least in this human culture model. These observatio ns provide support for the hypothesis that controlled extracellular matrix turnover is important in the regulation of aqueous humor outflow facility.