Intestinal Microbiota-Derived Metabolomic Blood Plasma Markers for Prior Radiation Injury

Abstract

Purpose Assessing whole-body radiation injury and absorbed dose is essential for remediation efforts following accidental or deliberate exposure in medical, industrial, military, or terrorist incidents. We hypothesize that variations in specific metabolite concentrations extracted from blood plasma would correlate with whole-body radiation injury and dose. Methods and Materials Groups of C57BL/6 mice (n=12 per group) were exposed to 0 Gy, 2 Gy, 4 Gy, 8 Gy, and 10.4 Gy of whole-body γ-radiation. At 24 hours post treatment all animals were euthanized and both plasma and liver biopsies obtained - the latter being used to deconvolve a distinct hepatic radiation injury response within plasma. A semi-quantitative untargeted metabolites/lipid profiling using both GC/MS and LC/MS/MS platforms was performed and identified 354 biochemicals. A second set of C57BL/6 mice (n=6 per group) were used to assess a subset of identified plasma markers beyond 24 hours. Results We identified a cohort of 37 biochemical compounds in plasma that yielded the optimal separation of the irradiated sample groups, with the most correlated metabolites associated with pyrimidine (positively correlated) and tryptophan (negatively correlated) metabolism. The latter were predominantly associated with indole compounds, and there was evidence to indicate that these were also correlated between liver and plasma. No evidence of saturation as a function of dose was observed, as has been noted for studies involving metabolite analysis of urine. Conclusion Plasma profiling of specific metabolites related to the pyrimidine and tryptophan pathways can be used to differentiate whole-body radiation injury and dose response. As the tryptophan associated indole compounds have their origin in the intestinal microbiome and subsequently the liver, these metabolites in particular represent an attractive marker for radiation injury within blood plasma.

Xenobiotic Receptor-Mediated Regulation of Intestinal Barrier Function and Innate Immunity

“…Similar results have been found in mice with radiation-mediated intestinal damage, in that, serum indole and indole metabolites (IPA) are inversely correlated with the extent of intestinal inflammation [91]. The observation that IPA is inversely related to systemic inflammation in overweight individuals [92] as well as the reversal of IPA levels (increased) upon administration of anti-inflammatory dietary interventions to humans [69] adds further proof of the importance of IPA in inflammation.…”

Metabolomic applications in radiation biodosimetry: exploring radiation effects through small molecules

“…Most importantly, they further identified products of tryptophan metabolism that implicate the gut microbiome in the radiation response. This connection was also described by Ó Broin et al., who dissected the responses of this metabolic pathway in plasma of mice irradiated with 2 to 10.4 Gy at 24 hours post-irradiation (Ó Broin et al, 2015). As more research is being conducted on the microbiome effects (initial studies are described in a later section), how the host and microbiome interact after radiation exposure, and whether there is leakage of intestinal bacteria in the blood circulation, may be more significant in organ responses, such as liver, than previously thought.…”

A lipidomic and metabolomic serum signature from nonhuman primates exposed to ionizing radiation

“…S14). When the KEGG, BioCyc, and Reactome databases were searched by putative significant ions, perturbations were observed in the valine biosynthesis/degradation (2, 4, 7, 10 Gy; KEGG# ko00290), tyrosine biosynthesis/degradation (4 Gy; BioCyc# PWY-6134, TYRFUMCAT-PWY), citrulline biosynthesis (7 Gy; BioCyc# PWY-5004, CITRULBIO-PWY), protein digestion/absorption (4, 7, 10 Gy; KEGG# ko04974), biological oxidations (4, 10 Gy; Reactome# 211859), tryptophan metabolism (6, 7, 10 Gy; BioCyc# TPHAN-DEGRADATION-1) (possibly host microbiota derived, [Kurland et al 2015; Ó Broin et al 2015]), and proline degradation (7, 10 Gy; KEGG# ko00330). Univariate analysis detected putative ions involved in these pathways, of which taurine [M-H] − , udine [M+H] + , glucose [M+H] + , tyrosine [M+H] + , proline [M+H] + , hypoxanthine [M+H] + , carnitine [M+H] + , and valine [M+H] + were validated to be altered in IR exposed groups compared to the control.…”