Nonylphenol polyethoxylates induce phosphorylation of histone H2AX

Nonylphenol polyethoxylates (NPEOs) are non-ionic surfactants widely used for industrial and household purposes. Since biodegraded short chain NPEOs were reported to elicit estrogenic activity in organisms, numerous studies have been carried out to assess the endocrine-disrupting potential of NPEOs; however, the genotoxicity of the compounds is not fully known, let alone the relationship between the genotoxic potential and number of ethylene oxide (EO) units of NPEOs. In this study, we examined the genotoxicity of NPEO(n) having various EO units (n=0, 5, 10, 15, 20, 30, 40 and 70) in a human breast adenocarcinoma cell line, MCF-7, based on the phosphorylation of histone H2AX (γ-H2AX), recently regarded as a sensitive marker for DNA damage. We clarified that NPEOs have the ability to form γ-H2AX via activation of ATM or DNA-PK, a general signaling pathway in response to DSBs, and this ability was strongly dependent on the number of EO units, that is, NPEO(0-15) having smaller numbers of EO units more readily generated γ-H2AX. Flow cytometric analysis revealed that the generation of γ-H2AX was independent of cell cycle phases. Although the mechanism by which the NPEOs generated γ-H2AX was not able to be elucidated in the present study, it was clear that the involvement of reactive oxygen species and apoptotic DNA fragmentation were not causal factors. The generation of γ-H2AX means the formation of DSBs, the worst type of DNA damage. The results indicated that attention should be paid to degradated short chain NPEOs and their genotoxicity.