Fluorescence-based detection of ferrous iron in senescent cells.

A major limitation in aging research is the lack of reliable biomarkers to assess phenotypic changes with age or monitor response to anti-aging interventions. The present study investigates the role of intracellular ferrous iron (Fe2+) as a potential biomarker of senescence. Iron is known to accumulate in various tissues with age and recent studies have demonstrated that its level increases dramatically in senescent cells. The techniques used are however cumbersome and only measure total iron. Also, it is still to be determined whether the damaging form of iron (Fe2+) is elevated in senescent cells. Here we assessed the potential use of a newly discovered Fe2+ reactive probe (SiRhoNox-1) for selective labeling of senescent cells in vitro. For this we have generated and characterized various senescent cell models and subjected them to SiRhoNox-1 labeling. Our results indicate that SiRhoNox-1 selectivity labels live senescent cells and was more specific and faster than current staining such as SA-βGal or a derived fluorescent probe C12FDG. By using SiRhoNox-1, we also showed that intracellular ferrous iron accumulation is secondary to senescence induction and it is not reversed by stress removal. Together these findings suggest that SiRhoNox-1 may serve as a convenient tool to detect senescent cells based on their ferrous iron level.