A Novel Zinc Compound (Zinc Monocysteine) Enhances the Antioxidant Capacity of Human Retinal Pigment Epithelial Cells

Abstract

Purpose: The aim of this study was to document the effect of a novel zinc amino acid combination on the concentrations of important antioxidants in cultured human retinal pigment epithelial (hRPE) cells. Methods: Primary confluent hRPE cells were treated with 30 μ M of zinc acetate, zinc chloride, zinc cysteine, and zinc sulfate. The antioxidants catalase, glutathione, glutathione peroxidase, and metallothionein were measured. MTT assays were performed to determine the relative protection of the zinc compounds from the cytotoxic effects of H₂0₂ and t-butyl hydroperoxide. Results: Catalase and glutathione peroxidase activities were increased by the zinc formulations compared with the untreated control. Glutathione and metallothionein content were also increased. The greatest increases occurred with zinc conjugated to the amino acid cysteine. The MTT assays showed that zinc monocysteine protected cultured RPE cells from the toxicity of H₂O₂ and t-butyl hydroperoxide. Conclusions: Our results demonstrate that zinc treatment of RPE cells increases antioxidants and protects cultured RPE cells from the cytotoxic effects of H₂O₂ and t-butyl hydroperoxide. The results show that zinc conjugated to cysteine offers greater benefits than either zinc salts or cysteine alone.

KEYWORDS:

• antioxidants
• catalase
• cysteine
• glutathione
• human retinal pigment epithelial cells
• metallothionein
• zinc