INHIBITION OF TRANSFORMING GROWTH FACTOR-BETA-INDUCED CATARACTOUS CHANGES IN LENS EXPLANTS BY OCULAR MEDIA AND ALPHA-2-MACROGLOBULIN

Purpose. To investigate the ocular media for the presence of inhibitor s of transforming growth factor-beta (TGF beta) using a lens epithelia l explant system in which TGF beta induces cataractous changes. The ef fect of alpha 2-macroglobulin, an inhibitor of TGF beta in other syste ms, also was assessed. Methods. Explants prepared from 21-day-old rats were cultured with TGF beta 2 with and without 50% bovine aqueous or vitreous or alpha 2-macroglobulin. alpha 2-macroglobulin was added to an aqueous concentrate, shown to contain endogenous TGF beta activity by blocking with anti-TGF beta. Explants were monitored by phase-contr ast microscopy for 5 days and assessed in terms of capsule wrinkling, spindle-cell formation, blebbing, and cell loss. alpha 2-macroglobulin in the ocular media was assessed by enzyme-linked immunosorbent assay and Western blot analysis. Results. At 50% strength, neither aqueous nor vitreous demonstrated TGF beta-like activity; however, aqueous par tially and vitreous completely prevented cataractous changes induced b y 25 and 100 pg/ml TGF beta 2, respectively. alpha 2-macroglobulin (50 to 200 mu g/ml) also protected against these changes, with complete i nhibition of TGF beta 2 or aqueous-derived TGF beta activity at the hi ghest concentration. A threefold higher concentration of alpha 2-macro globulin was detected in vitreous than aqueous. Conclusions. Both aque ous and vitreous contain molecule(s) that inhibit TGF beta 2 activity. alpha 2-macroglobulin has been identified in the ocular media and sho wn to block cataractous changes induced by TGF beta. Maintaining appro priate levels of alpha 2-macroglobulin or similar molecules in the ocu lar media may protect lens cells from the damaging effects of TGF beta , and reduced levels may predispose to cataract.