Photocoagulated human retinal pigment epithelial cells produce an inhibitor of vascular endothelial cell proliferation.

Purpose: To determine if conditioned culture medium of photocoagulated human retinal pigment epithelial (RPE) cells contains inhibitors for the proliferation of bovine aortic endothelial cells (BAEC) and bovine retinal endothelial cells (BREC) and to characterize the nature of these inhibitory factors.
Methods: Retinal pigment epithelial cells grown to confluence were photocoagulated (0.1 second, 50 microns, 350 mW) in serum-free medium. After 48 hours, the conditioned medium (PC-CM) was removed, and the effects of non-acid-treated and transiently acid-treated samples were determined on [3H]-thymidine uptake by BAEC and BREC. PC-CM was also subjected to size exclusion high-performance liquid chromatography (HPLC). Fractions were analyzed for the effects on the growth of the bovine endothelial cells before and after transient acid treatment.
Results: The addition of non-acid-treated PC-CM (32% vol/vol) inhibited BREC [3H]-thymidine uptake to 18.5% of the control value. With HPLC, the inhibitory activity was recovered mainly in a fraction whose apparent molecular size was 25 kd. After transient acid treatment of the fractions, there also appeared a 100-kd inhibitor. Inhibitory effects were neutralized by pretreatment of the fractions with antiserum against transforming growth factor (TGF)-beta 2.
Conclusions: Photocoagulated RPE cells secrete inhibitors of BAEC and BREC proliferation. Molecular size and immunologic properties of these inhibitors correspond to those of TGF-beta 2.