gms | German Medical Science

Background: Genetic alterations suggest an over-activation of the complement system in AMD patients. The retina and the retinal pigment epithelial (RPE) cells are rich in zinc and the latter undergo cell death during AMD. Therefore, in this in vitro study the impact of complement on zinc-supplemented RPE cells was examined.

Methods: Human ARPE-19 cells as RPE cell model were incubated with increasing concentrations of various zinc compounds alone and in combination with human complement serum (HCS), heat-inactivated or C7-deficient control sera, and bovine serum albumin (BSA). Viability was monitored by conversion of thiazolylblue, uptake of propidiumiodide and Hoechst staining. In the supernatants the reactive oxygen species (ROS) were measured and the content of interleukin (IL)-6, IL-8, monocyte chemoattractant protein (MCP)-1, and vascular endothelial growth factor (VEGF) was assayed by sandwich ELISA.

Results: RPE cells incubated with more than 150 µM zinc showed decreased viability after single administration for 24 hours. No obvious toxicity was demonstrated by 25-50 µM zinc for several weeks. All serum formulations including HCS attenuated the toxicity of high dose and short term-added zinc, while BSA was less effective. After 48 hours, the HCS group showed impaired morphology comparable to BSA-treated cells. In contrast, the cells treated with HI-HCS and especially those with C7-deficient serum displayed a better appearance. There was a tendency of higher ROS amounts by zinc-treatment and by HCS. The production of cytokines and VEGF was enhanced by HCS and unaffected by zinc.

Conclusions: The degeneration of zinc-rich RPE cells may poison the retinal microenvironment during AMD. Unspecific binding of potentially toxic free zinc ions by serum proteins like albumin may provide in part the initially observed protection. On the other hand negative side-effects like zinc-induced complement-activation may predominate after longer incubation period. Increased ROS suggest a stress response in answer to zinc and complement.