Induction of a bystander mutagenic effect of alpha particles in mammalian cells

Abstract

Ever since the discovery of X-rays was made by Rö ntgen more than a hundred years ago, it has always been accepted that the deleterious effects of ionizing radiation such as mutation and carcinogenesis are attributable mainly to direct damage to DNA. Although evidence based on microdosimetric estimation in support of a bystander effect appears to be consistent, direct proof of such extranuclear͞extracellular effects are limited. Using a precision charged particle microbeam, we show here that irradiation of 20% of randomly selected A L cells with 20 alpha particles each results in a mutant fraction that is 3-fold higher than expected, assuming no bystander modulation effect. Furthermore, analysis by multiplex PCR shows that the types of mutants induced are significantly different from those of spontaneous origin. Pretreatment of cells with the radical scavenger DMSO had no effect on the mutagenic incidence. In contrast, cells pretreated with a 40 M dose of lindane, which inhibits cell-cell communication, significantly decreased the mutant yield. The doses of DMSO and lindane used in these experiments are nontoxic and nonmutagenic. We further examined the mutagenic yield when 5-10% of randomly selected cells were irradiated with 20 alpha particles each. Results showed, likewise, a higher mutant yield than expected assuming no bystander effects. Our studies provide clear evidence that irradiated cells can induce a bystander mutagenic response in neighboring cells not directly traversed by alpha particles and that cell-cell communication process play a critical role in mediating the bystander phenomenon.

Direct evidence for a bystander effect of ionizing radiation in primary human fibroblasts

“…This, however may still be significant, particularly in terms of risk when one considers low doses of relevance to environmental exposures to ionizing radiation, and it may be of relevance to the development of treatments using targeted radionuclides, where not all cells are successfully targeted but may need to rely on a bystander response . Also, it is likely that many cells that survive may be altered, for example, being subject to mutational changes (Nagaswa and Little, 1999;Zhou et al, 2000). In these studies a similar effect is observed in terms of a 3-5 fold increase in the expected levels of mutations, which may also depend on the numbers of cells targeted.…”

ATR-dependent radiation-induced γH2AX foci in bystander primary human astrocytes and glioma cells

“…Most interestingly, several cytokines can be induced by ROS and NO/NOS (Ayache et al, 2002;Hsu and Wen, 2002;Kosmidou et al, 2002;Hwang et al, 2004;Ryan et al, 2004) providing a possible link between different factors potentially involved in bystander signalling. End points used for the study of bystander effects in vitro have included micronuclei formation (Azzam et al, 2002;Kashino et al, 2004;Shao et al, 2004), gene mutations and genomic instability (Zhou et al, 2000), gene expression changes (Azzam et al, 2002;Yang et al, 2005), transformation (Sawant et al, 2001), proliferation (Gerashchenko and Howell, 2003), cell survival, apoptosis (Belyakov et al, 2002;Lyng et al, 2002), cell cycle arrest (Azzam et al, 2000) and most recently the induction of gH2AX foci in bystander cells (Hu et al, 2005;Sokolov et al, 2005;Yang et al, 2005).…”

A proliferation-dependent bystander effect in primary porcine and human urothelial explants in response to targeted irradiation

“…The radiation-induced bystander effect is a phenomenon whereby cellular damage (sister chromatid exchanges (Nagasawa and Little, 1992;Lehnert and Goodwin, 1997), chromosome aberrations (Little et al, 1997;Lorimore et al, 1998), apoptosis (Mothersill and Seymour, 1997;Mothersill et al, 2000), micronucleation (Prise et al, 1998;Belyakov et al, 2001), transformation (Sigg et al, 1997), mutations (Zhou et al, 2000) and changes of gene expression (Hickman et al, 1994;Azzam et al, 1998)) are expressed in unirradiated neighbouring cells close to an irradiated cell or cells. The mechanisms underpinning the bystander effect are not yet known.…”