Water soluble fraction of solar‐simulated light‐exposed crude oil generates phosphorylation of histone H2AX in human skin cells under UVA exposure

Abstract

Crude oil contains compounds, which have toxic and cancer-causing properties to humans. The oil spilled in environments is usually exposed to sunlight; however, the toxicity of sunlight-exposed oil is poorly understood. In this study, we found that the water soluble fraction (WSF) of crude oil irradiated with solar-simulated light (SSL) generated phosphorylation of histone H2AX (gamma-H2AX) in human skin cells under UVA irradiation, which was due to the formation of DNA double strand breaks (DSBs). Crude oil was exposed to SSL for approximately 7 days. The WSF obtained from unexposed crude oil showed no toxicity, whereas the WSF obtained from crude oil pre-exposed to SSL induced acute cell death on exposure to UVA irradiation (induction of phototoxicity), which was more remarkable in human skin fibroblasts than human skin keratinocytes. gamma-H2AX was detected in both cell lines immediately after treatment with the WSF plus UVA. Interestingly, gamma-H2AX was detectable even at low SSL- and UVA-doses, which induced no cytotoxicity. The WSF of crude oil irradiated with SSL, generated DSBs under UVA irradiation, which were detected by biased sinusoidal field gel electrophoresis. This was confirmed using xrs-5 cells isolated from CHO-K1 cells, which are deficient in a repair enzyme for DSBs; the WSF plus UVA induced a more dramatic decrease in survival in xrs-5 cells than CHO-K1 cells. These findings demonstrate that exposure of crude oil to sunlight makes the WSF phototoxic, generating DSBs accompanying the appearance of gamma-H2AX in human skin cells.

H2AX: functional roles and potential applications

“…Induction of γ -H2AX is found following exposure of cells to suspected DNA-damaging compounds such as cigarette smoke, polycyclic aromatic compounds, dinitrobenzo[e] pyrene, norethindrone, chromium, crude oil, electromagnetic fields, microwaves from mobile phones, and extreme heat, all demonstrating a potential role for γ -H2AX detection in determining potential genotoxics (Albino et al 2004; Gallmeier et al 2005; Hunt et al 2007; Ibuki et al 2007; Kawanishi et al 2009; Luo et al 2006; Markova et al 2005; Mattsson et al 2009; Peterson-Roth et al 2005; Shao et al 2004; Toyooka and Ibuki 2005, 2006, 2009). The radiation induced bystander effect, which can be monitored through DSB induction, can also be tracked using γ -H2AX formation (Sokolov et al 2007).…”

Nonylphenol polyethoxylates induce phosphorylation of histone H2AX

“…We previously reported that ␥-H2AX is generated following the exposure of cells to various suspected DNA-damaging agents including several environmental chemicals and pharmacological agents [20][21][22][23][24][25][26][27][28]. In addition to the advantage that ␥-H2AX can be detected in response to many types of DNA damage, we and other researchers are convinced that ␥-H2AX provides a considerably more sensitive measurement of DNA damage than other techniques such as pulse field gel electrophoresis and comet assays [26][27][28][29].…”