Biofluid Metabolomics of Mice Exposed to External Low-Dose Rate Radiation in a Novel Irradiation System, the Variable Dose-Rate External ¹³⁷Cs Irradiator

Abstract

An important component of ionizing radiation (IR) exposure after a radiological incident may include low-dose rate (LDR) exposures either externally or internally, such as from 137 Cs deposition. In this study, a novel irradiation system, VAriable Dose-rate External 137 Cs irradiatoR (VADER), was used to expose male and female mice to a variable LDR irradiation over a 30 d time span to simulate fall-out-type exposures in addition to biofluid collection from a reference dose rate (0.8 Gy/min). Radiation markers were identified by untargeted metabolomics and random forests. Mice exposed to LDR exposures were successfully identified from control groups based on their urine and serum metabolite profiles. In addition to metabolites commonly perturbed after IR exposure, we identified and validated a novel metabolite (hexosamine−valine−isoleucine−OH) that increased up to 150fold after LDR and 80-fold after conventional exposures in urine. A multiplex panel consisting of hexosamine−valine−isoleucine− OH with other urinary metabolites (N6,N6,N6-trimethyllysine, carnitine, 1-methylnicotinamide, and α-ketoglutaric acid) achieved robust classification performance using receiver operating characteristic curve analysis, irrespective of the dose rate or sex. These results show that in terms of biodosimetry, dysregulated energy metabolism is associated with IR exposure for both LDR and conventional IR exposures. These mass spectrometry data have been deposited to the NIH data repository via Metabolomics Workbench with study IDs ST001790,

Biofluid Metabolomics and Lipidomics of Mice Exposed to External Very High-Dose Rate Radiation

“…Interestingly, xanthurenic acid, a product of tryptophan catabolism, may show differential effects from dose rate. Identification in LDR studies typically show reduced urinary concentrations [6,8,27,28], however, here we observed an increase at 1 d. A slight decrease occurred here at 7 d (reference FC = 0.8) highlighting our previous conclusions that involvement of the host microbiota and diet in producing tryptophan metabolites will complicate their use in biodosimetry panels. Increased levels of trigonelline were only observed in the VHDR 1 d cohort (p < 0.001, VHDR FC = 1.2), but for both doses at 7 d (p < 0.001, reference FC = 1.4, VHDR FC = 1.3).…”

“…Increases were observed at 1 d in compounds typically identified post-irradiation, including carnitine (p < 0.001, reference FC = 2.4, VHDR FC = 1.9), TML (p = 0.006, VHDR FC = 1.3), and xanthurenic acid (p < 0.001, reference FC = 1.3, VHDR FC = 1.3) (Figure 2, Table 1). All three of these metabolites have been identified in a previous study analyzing urine from mice exposed to low-dose rate IR (≤1 Gy/day) and reference dose rate exposures [8], as well as several other studies examining post-irradiation effects on urinary signatures [15,16]. TML, and carnitine in particular, are among the most consistently altered metabolites post-irradiation and indicate perturbation to fatty acid β oxidation.…”

“…We found a similar response between dose rates in urine, where higher perturbations were observed at 1 d, but the VHDR group response returned back to background at 7 d. Identical metabolite panels were able to differentiate mice on both days with excellent to good specificity and sensitivity based on the area under the receiver operating characteristic (AUROC) curves irrespective of dose rate (AUROC ≥ 0.9 excellent, ≥0.8 good). A critical component of these panels included a novel compound, Hex-V-I, a metabolite that was previously described by our group [8]. For serum, most lipids showed a similar response between groups with slightly higher perturbation observed in the reference dose rate group compared to VHDR.…”

“…Ideally, the top candidates from both of these disciplines can be combined into a single rapid multiplex assay useful in dose reconstruction and be effective irrespective of the complex nature associated with radiation exposures (e.g., dose rate), combined injury, genetic predisposition, etc. A particular recent focus of our group has been elucidating the effects of dose-rate on biofluid signatures and its potential to alter predictive model power [5][6][7][8][9].…”

“…Third, internal emitter radiation, of primary concern the radioisotope 137 Cs, can continue for weeks if chelating agents are not used [11]. As our previous research addressed effects of internal emitters or nuclear fallout on dose reconstruction [5,[7][8][9]12], further research is also needed in the VHDR range.…”