Repeated Nrf2 stimulation using sulforaphane protects fibroblasts from ionizing radiation

Area of Science:

• Molecular biology
• Cellular biology
• Radiation biology

Background:

• Ionizing radiation induces cytotoxicity primarily through radical-mediated DNA double-strand breaks.
• Sulforaphane activates the transcription factor Nrf2, upregulating detoxification and radical-scavenging genes.
• Nrf2 plays a crucial role in cellular defense against oxidative stress and DNA damage.

Purpose of the Study:

• To investigate the effect of repeated sulforaphane treatment on radioresistance in human fibroblasts.
• To determine the role of the Nrf2 pathway in sulforaphane-mediated radioprotection.
• To establish the dose-dependency and optimal concentration of sulforaphane for radioprotection.

Main Methods:

• Primary human skin fibroblasts and Nrf2 knockout mouse embryonic fibroblasts were treated with sulforaphane.
• Cells were exposed to ionizing radiation after single or repeated sulforaphane treatments.
• Nrf2-regulated mRNA levels, free radical production, DNA double-strand breaks (gamma-H2AX foci), and cell survival (EdU assay) were quantified.

Main Results:

• Repeated sulforaphane treatment significantly increased radioresistance compared to single treatment.
• Nrf2-regulated gene expression and detoxification pathways were more pronounced with repeated treatment.
• Radiation-induced DNA double-strand breaks and free radicals were reduced following repeated sulforaphane exposure.
• Sulforaphane-induced radioprotection was dependent on Nrf2, as shown in knockout fibroblasts.
• Optimal radioprotection was observed at 10 uM sulforaphane, with reduced efficacy at lower or higher concentrations.

Conclusions:

• Repeated sulforaphane administration enhances radioresistance in human fibroblasts through Nrf2 activation.
• The Nrf2 pathway is essential for mediating the radioprotective effects of sulforaphane.
• The Nrf2 system exhibits a 'training' effect, where repeated stimulation can bolster cellular defense against radiation-induced damage.
• These findings suggest potential therapeutic strategies for improving radiation protection by modulating the Nrf2 pathway.