Comparative Analysis of Cell Killing and Autosomal Mutation in Mouse Kidney Epithelium Exposed to 1 GeV ProtonsIn VitroorIn Vivo

Abstract

Human exposure to high-energy protons occurs in space flight scenarios or, where necessary, during radiotherapy for cancer or benign conditions. However, few studies have assessed the mutagenic effectiveness of high-energy protons, which may contribute to cancer risk. Mutations cause cancer and most cancer-associated mutations occur at autosomal loci. This study addresses the cytotoxic and mutagenic effects of 1 GeV protons in mouse kidney epithelium. Mutant fractions were measured for an endogenous autosomal locus (Aprt) that detects all types of mutagenic events. Results for kidneys irradiated in vivo are compared with the results for kidney cells from the same strain exposed in vitro. The results demonstrate dose-dependent cell killing in vitro and for cells explanted 3-4 months postirradiation in vivo. Incubation in vivo for longer periods (8-9 months) further attenuates proton-induced cell killing. Protons are mutagenic to cells in vitro and for in vivo irradiated kidneys. The dose-response for Aprt mutation is curvilinear after in vitro or in vivo exposure, bending upward at the higher doses. While the absolute mutant fractions are higher in vivo, the fold-increase over background is similar for both in vitro and in situ exposures. Results are also presented for a limited study on the effect of dose fractionation on the induction of Aprt mutations in kidney epithelial cells. Dose-fractionation reduces the fraction of proton-induced Aprt mutants in vitro and in vivo and also results in less cell killing. Taken together, the mutation burden in the epithelium is slightly reduced by dose-fractionation. Autosomal mutations accumulated during clinical exposure to high-energy protons may contribute to the risk of treatment-associated neoplasms, thereby highlighting the need for rigorous treatment planning to reduce the dose to normal tissues. For low dose exposures that occur during most space flight scenarios, the mutagenic effects of protons appear to be modest.

Genotoxicity of charged particles of importance in space flight using murine kidney epithelial cells

“…Si ions were also quite mutagenic with evidence for a linear dose–response for Aprt mutations in kidney cells exposed in vitro or in kidneys harvested from mice irradiated several months earlier. These results are consistent with the linear dose–response data obtained previously for Aprt mutation induction following Fe ion exposure in vitro or in vivo , but the results for Si ions differ from the curvilinear dose–response data we recently published following similar exposures to energetic protons [ 1, 2]. Our most recent studies examined the molecular characteristics of Si ion-induced Aprt mutants following in vitro exposure.…”

Simulated space radiation-induced mutants in the mouse kidney display widespread genomic change

“…In contrast, although increases in Aprt mutant frequencies were observed at 0.5 and 1.0 Gy protons (~1.4 fold in both cases), these increases were not statistically significant (p = 0.279 and 0.109, respectively) (Table 1). Adding these data to mutant frequency data obtained at higher doses in a prior study (3.0, 4.0, and 5.0 Gy) [13] confirmed that the proton dose response is curvilinear, with little or no change at the lower doses and a doubling dose estimated at approximately 2–2.5 Gy (Fig 1). The adjusted R-squared value for all proton mutant frequencies is 0.93.…”

“…Results for mutant frequencies and toxicity are presented in Table 1 and Figs 1 (mutant frequencies) and 2 (toxicity). The Table and Figures are supplemented with data from a prior study using doses of 3, 4, or 5 Gy protons [13]. …”

“…Charged particle exposure induces Aprt mutant cells, which persist for extended times in the kidney [12, 13] until isolated from the dispersed kidney via selection of the primary cells in culture. Selection in culture allows the mutant clones that formed in the body to be expanded for a comprehensive analysis of charged particle mutagenesis using a variety of endpoints.…”

Galactic cosmic ray simulation at the NASA Space Radiation Laboratory

“…It may be useful if GCR simulation addresses both cell and animal studies and it may be feasible to design some experiments that allow direct comparison of the in vitro and in vivo (Kronenberg et al, 2009, 2013) systems. In some cases, the less expensive cell culture experiments may mimic what happens in the body.…”