Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
Radiation-induced bystander effects enhanced by elevated sodium chloride through sensitizing cells to bystander factors
Introduction
Ever since radiation-induced bystander effects (RIBE) were described as early as 1947 [1], there has been increasing evidence for the existence of these phenomena. Nagasawa and Little [2] first demonstrated a bystander effect induced in cell cultures exposed to low-dose α-particle irradiation. So far, RIBE have been well demonstrated with a variety of biological endpoints in both human and rodent cell lines [3], [4], [5], [6], [7]. Subsequent studies have confirmed that there are two major types of bystander effects. The first depends on cell/cell communication and the second results from substances released from the exposed cell to the medium [3]. The important roles of gap junction intercellular communication [8] and soluble factors like reactive oxygen species (ROS) [8], [9], nitric oxide (NO) [10], [11] and cytokines released from irradiated cells in RIBE have been reported recently [5]. This extensive research also implies that in addition to nucleus irradiation, cytoplasmic irradiation can also induce RIBE [12], [13]. However, less evidence is available on the co-effects of RIBE and other factor(s).
The genotoxic effects of NaCl have been supported strongly by many studies. Elevating NaCl can induce osmotic stress and the changes in extracellular osmolality impair cell metabolism and function in a variety of ways [14], [15]. It has been reported that an acute elevation of NaCl concentration causes DNA double-strand breaks (DSBs) [16] and inhibits DNA repair [17], [18], [19]. Other effects include changes in cell shape, disturbances in biochemical reactions, cell cycle arrests, induction of apoptosis, reduction in the number of cells, and the rate at which cells grow [15], [19], [20], [21]. These effects increase the probability that NaCl will alter DNA damaging effects of other genotoxic agents. It has been shown that post-irradiation hypertonic treatment increases the formation of chromosome aberrations and cell death, as well as reduces DNA synthesis and double strand break repair [22], [23], [24], [25]. Our recent experiment indicated that the fraction of γ-H2AX foci-positive cells was significantly increased in cells both in irradiated and non-irradiated regions under the elevated NaCl culture condition [26]. However, the underlying mechanism is not clear and how elevated NaCl affects RIBE remains to be addressed.
In the present study, based on the MN test and a specially designed detachable co-culture system, we further investigated RIBE in normal human fibroblasts by acute exposure to elevated NaCl for 12 h before irradiation. We found that with 1.0 cGy α-particle irradiation, a significant increase of MN was detected in cells both in irradiated and non-irradiated bystander regions under elevated NaCl culture condition. Subsequent results showed that elevated NaCl treatment made bystander cells more vulnerable to radiation induced bystander factors, and such an effect might result from the increased sensitivity of non-irradiated cells to oxidative stress.
Section snippets
Cell culture and co-culture system
AG 1522 normal human diploid skin fibroblasts kindly provided by Dr. Barry Michael (Gray Cancer Institute, UK) were maintained in α-Eagle's minimum essential medium (Gibco, Grand Island, NY, USA) supplemented with 2.0 mM l-glutamine (Gibco, Grand Island, NY, USA) and 20% FBS (Hyclone, Logan, UT, USA) plus 100 μg/ml streptomycin and 100 U/ml penicillin (Gibco, Grand Island, NY, USA) at 37 °C in a humidified 5% CO2 incubator (SanYo, Japan).
The co-culture system was designed as described with some
Exposure to 9.0 g/L NaCl or irradiated medium alone does not increase the MN frequency
To examine any effect on cells by medium exposure, outer dish mylar film was irradiated without attached cells. The MN frequency of non-irradiated cells grown in the inner dishes was determined. It was found that irradiated medium had no effects on the MN induction in the inner-dish-cells even when treated with elevated NaCl. As shown in Fig. 2, the frequencies of MN in normal and NaCl-treated cells were 2.533 ± 0.088% and 2.567 ± 0.088%, respectively. With incubation in irradiated-medium, the MN
Discussion
Sodium chloride is very important for people's daily life. However, as most people consume more sodium than they need [35], more and more attention has been focused on the effect of NaCl. Studies on the genotoxic effects of NaCl show that high NaCl can be genotoxic, either alone [14], [15], [16], [17], [18], [19], [20], [21] or in combination with other factors, such as irradiation [22], [23], [24], [25]. The RIBE occur widely in various cell lines. The production of bystander factors and
Conflict of interest statement
None.
Acknowledgements
This research was supported by National Nature Science Foundation of China under Grant nos. 10225526 and 30570435, Grant 2006Z026, and Hundred Talents Programme of The Chinese Academy of Sciences.
Reference (41)
- et al.
Non-targeted bystander effects induced by ionizing radiation
Mutat. Res.
(2007) - et al.
Maintenance of genomic integrity in mammalian kidney cells exposed to hyperosmotic stress
Comp. Biochem. Physiol. Part A
(2001) - et al.
Hypertonic stress response
Mutat. Res.
(2005) - et al.
Cell cycle delay and apoptosis in response to osmotic stress
Comp. Biochem. Physiol. Part A
(2001) - et al.
DNA-PK is responsible for enhanced phosphorylation of histone H2AX under hypertonic conditions
DNA Repair (Amst.)
(2005) - et al.
Elevated sodium chloride concentrations enhance the bystander effects induced by low dose alpha-particle irradiation
Mutat. Res.
(2007) - et al.
Effects of irradiated medium with or without cells on bystander cell responses
Mutat. Res.
(2002) The in vitro micronucleus technique
Mutat. Res.
(2000)- et al.
Structural changes produced in microspores of Tradescantia by a-radiation
J. Genet.
(1947) - et al.
Induction of sister chromatid exchanges by extremely low-doses of alpha-particles
Cancer Res.
(1992)
Evidence for ‘bystander effects’ in vivo
Hum. Exp. Toxicol.
In vivo validation of the bystander effect
Hum. Exp. Toxicol.
ATR-dependent radiation-induced gamma H2AX foci in bystander primary human astrocytes and glioma cells
Oncogene
Intercellular and intracellular signaling pathways mediating ionizing radiation-induced bystander effects
Radiat. Res.
Role of gap junctional intercellular communication in radiation-induced bystander effects in human fibroblasts
Radiat. Res.
Oxidative metabolism modulates signal transduction and micronucleus formation in bystander cells from alpha-particle-irradiated normal human fibroblast cultures
Cancer Res.
Induction of radioresistance by a nitric oxide-mediated bystander effect
Radiat. Res.
Nitric oxide-mediated signaling in the bystander response of individually targeted glioma cells
Cancer Res.
Targeted cytoplasmic irradiation induces bystander responses
Proc. Natl. Acad. Sci. U.S.A.
Cytoplasmic irradiation induces mitochondrial-dependent 53BP1 protein relocalization in irradiated and bystander cells
Cancer Res.
Cited by (12)
External modulators and redox homeostasis: Scenario in radiation-induced bystander cells
2021, Mutation Research - Reviews in Mutation ResearchCitation Excerpt :NaCl mediated effects in bystander cells are NO-dependent. However, the effects are not bystander-specific because increased NaCl levels influence the overall radiation response involving both irradiated and un-irradiated cells [125]. The primary female sex hormone, estrogen (E2), is a lipid-derived steroid that exerts radio-sensitizing effects on breast cancer cells.
Significance and nature of bystander responses induced by various agents
2017, Mutation Research - Reviews in Mutation ResearchCitation Excerpt :Co-exposure of all trans-retinoic acid (ATRA) with suicide gene therapy increased bystander responses. In irradiated cells NaCl elevated radiation induced bystander responses like γ-H2AX foci and micronuclei formation acting in synergy with radiation, however, NaCl treatment alone could not induce such effects in non-irradiated cells [191–193,160]. On the contrary, radiation induced bystander responses were abolished on exposure to ascorbic acid (AsA)/exogenous supply of carbon mono-oxide (CO).
Rescue effects in radiobiology: Unirradiated bystander cells assist irradiated cells through intercellular signal feedback
2011, Mutation Research - Fundamental and Molecular Mechanisms of MutagenesisCitation Excerpt :The average energy and LET of α particles derived from the 241Am irradiation source, as measured at the cell layer, were 3.5 MeV and 128 keV μm−1, respectively, and the α particles were delivered at a dose rate of 1.0 cGy s−1. The co-culture systems for Protocols 1 and 2 were fabricated as described in Refs. [15,16] with some modifications. According to Protocol 1, 3.5 × 104 exponentially growing cells were inoculated into a specially designed rectangular dish (10 mm × 6 mm, Fig. 1A).
The Roles of HIF-1α in Radiosensitivity and Radiation-Induced Bystander Effects Under Hypoxia
2021, Frontiers in Cell and Developmental BiologyEffect of salt stress on mutation and genetic architecture for fitness components in saccharomyces cerevisiae
2020, G3: Genes, Genomes, Genetics