Abstract

Iron is essential for cell survival; however, iron overload disorders lead to excess iron deposition, which can induce oxidative stress and reduce cell viability. Rapid chelation of iron to prevent oxidative stress is critical to avoiding the negative impacts of iron overload. Iron-chelating agents are often used to treat iron overload; however, most of these agents have adverse side effects and a narrow scope of applications. Recently, many classes of phytochelators with additional antioxidant activities have been developed for clinical use. Sulforaphane (SFN) has potent antioxidant and cytoprotective activities, but its role in iron metabolism has never been reported. Thus, we assessed the protective role of SFN against iron-induced cell toxicity in hepatoma Hep3B cells and examined its mechanism. In this study, Fe ions increased intracellular ROS levels and decreased cell viability. An antioxidant transcription factor called NF-E2-related factor 2 (Nrf2) was activated by Fe treatment. Iron chelator deferoxamine (DFO) reduced ROS levels but did not affect cell viability. Next, we assessed the protective role of SFN and showed that SFN decreased ROS levels and improved cell viability by further enhancing Nrf2 levels via the phosphoinositide 3-kinase (PI3K) pathway. Mechanistically, Nrf2 transcriptionally activated metallothionein (MT), a metal-binding protein. Overexpression of MT protected Hep3B cells from excess iron-induced toxicity, similar to SFN cytoprotective activities. These results suggest that the induction of Nrf2 and the increased MT mRNA by SFN are essential mechanisms contributing to reduced oxidative stress and improved viability in iron overload disorders.

Key words: cytoprotection, iron overload, metallothionein, Nrf2, sulforaphane