The effects of zinc supplementation on primary human retinal pigment epithelium

• Published in: Journal of trace elements in medicine and biology 2018-09, Vol.49, p.184-191
• Main Authors: Pao, Po-Jung, Emri, Eszter, Abdirahman, Safiya Bishar, Soorma, Talha, Zeng, Hui-Hui, Hauck, Stefanie M., Thompson, Richard B., Lengyel, Imre
• Format: Article
• Language: English
• Subjects: Age related macular degeneration; Mass spectrometry; Retinal pigment epithelium; Zinc
• ISSN: 0946-672X; 1878-3252
• DOI: 10.1016/j.jtemb.2018.02.028

[Display omitted] •Free and not total zinc concentration is important for the interpretation of biological function.•Zinc supplementation affected RPE phenotype.•Zinc supplementation can modulate the secretion of AMD-associated protein.•Regulation of zinc availability could be key for retinal function.•The positive effect of zinc supplementation in AMD is, at least partly, due to an effect on RPE. Population-based and interventional studies have shown that elevated zinc levels can reduce the progression to advanced age-related macular degeneration. The objective of this study was to assess whether elevated extracellular zinc has a direct effect on retinal pigment epithelial cells (RPE), by examining the phenotype and molecular characteristics of increased extracellular zinc on human primary RPE cells. Monolayers of human foetal primary RPE cells were grown on culture inserts and maintained in medium supplemented with increasing total concentrations of zinc (0, 75, 100, 125 and 150 μM) for up to 4 weeks. Changes in cell viability and differentiation as well as expression and secretion of proteins were investigated. RPE cells developed a confluent monolayer with cobblestone morphology and transepithelial resistance (TER) >200 Ω*cm2 within 4 weeks. There was a zinc concentration-dependent increase in TER and pigmentation, with the largest effects being achieved by the addition of 125 μM zinc to the culture medium, corresponding to 3.4 nM available (free) zinc levels. The cells responded to addition of zinc by significantly increasing the expression of Retinoid Isomerohydrolase (RPE65) gene; cell pigmentation; Premelanosome Protein (PMEL17) immunoreactivity; and secretion of proteins including Apolipoprotein E (APOE), Complement Factor H (CFH), and High-Temperature Requirement A Serine Peptidase 1 (HTRA1) without an effect on cell viability. This study shows that elevated extracellular zinc levels have a significant and direct effect on differentiation and function of the RPE cells in culture, which may explain, at least in part, the positive effects seen in clinical settings. The results also highlight that determining and controlling of available, as opposed to total added, zinc will be essential to be able to compare results obtained in different laboratories.