Irradiation Causes Alterations of Polyamine, Purine, and Sulfur Metabolism in Red Blood Cells and Multiple Organs

Abstract

Investigating the metabolic effects of radiation is critical to understand the impact of radiotherapy, space travel, and exposure to environmental radiation. In patients undergoing hemopoietic stem cell transplantation, iron overload is a common risk factor for poor outcomes. However, no studies have interrogated the multiorgan effects of these treatments concurrently. Herein, we use a model that recapitulates transfusional iron overload, a condition often observed in chronically transfused patients. We applied an omics approach to investigate the impact of both the iron load and irradiation on the host metabolome. The results revealed dose-dependent effects of irradiation in the red blood cells, plasma, spleen, and liver energy and redox metabolism. Increases in polyamines and purine salvage metabolites were observed in organs with high oxygen consumption including the heart, kidneys, and brain. Irradiation also impacted the metabolism of the duodenum, colon, and stool, suggesting a potential effect on the microbiome. Iron infusion affected the response to radiation in the organs and blood, especially in erythrocyte polyamines and spleen antioxidant metabolism, and affected glucose, methionine, and glutathione systems and tryptophan metabolism in the liver, stool, and the brain. Together, the results suggest that radiation impacts metabolism on a multiorgan level with a significant interaction of the host iron status.

Keywords: iron; mass spectrometry; metabolism; methionine; organs; polyamine; radiation.

Figure 1 –. Metabolomics analyses of red blood cells, plasma, liver and spleen following irradiation.

We performed metabolomics analyses of red blood cells (RBCs), plasma and organs where erythrophagocytosis occurs, spleen and liver as a function of irradiation (untreated: 0; or irradiated: from 7 to 11 Gy – A). Heat maps of metabolites significant by ANOVA are shown in B. Data suggest progressive damage to RBC energy and redox systems, which corresponds to increased metabolic changes at higher irradiation doses in spleen and liver (C). A representative principal component analysis of RBCs exposed to increasing doses of irradiation (D). Results point at a significant impact of irradiation on glycolytic (E), polyamine (overview of the pathway in F, bar plots in G) and sulfur/amino acid metabolism in the spleen. We report alteration of glycolysis, taurine (H) and purine (J) metabolism in RBCs of irradiated mice.

Figure 2 –. Alterations of acyl-carnitine metabolism in RBCs from irradiated mice

(A). Irradiation was also found to have an impact on the Krebs cycle, polyamines and poly-unsaturated fatty acids in the liver (B).

Figure 3 –. Metabolic impact of irradiation on mouse brain, liver and kidneys

(A), as determined by hierarchical clustering of the metabolites significant by ANOVA (B) and principal component analysis (representative PCA for kidneys in C). In D-G, bar plots of significantly altered polyamines, purines, amino acids and carboxylic acids in heart, kidney and brain.

Figure 4 –. Metabolic impact of irradiation on mouse colon, duodenum and stool

(A), as determined by ANOVA (heat maps in B show significant metabolic patterns). Results suggest that radiation induced alterations to metabolites in colon and stool compatible with a potential effect on the gut microbiome (C). In D, representative bar plots for top metabolites affected by irradiation in the colon, including glycolytic metabolites, polyamines and acyl-carnitines (especially hydroxylated forms).

Figure 5 –. Impact of iron infusion on the metabolic responses to irradiation in organs and blood (cells –

A). An overview of the top metabolic pathways affected by iron infusion and irradiation is provided in B. In C, principal component analysis shows a clear effect of iron (red vs blue for saline) and irradiation on the red blood cell metabolic phenotypes, with the highest effects noted on red blood cell arginine metabolism and polyamine synthesis (D), purine oxidation and sulfur metabolism in plasma (E). Spleen was the organ showing the highest metabolic changes after iron infusion and irradiation, as shown by the principal component analysis in F. In G, heat map of the spleen metabolites significant by two-way ANOVA. The top hits from this analysis are reported as bar plots in H.

Figure 6 –. Iron infusion and irradiation significantly impact liver, stool and brain metabolism.

Heat map in A shows a significant impact of iron infusion and irradiation on the liver metabolome, with top significant metabolites with differential trends mapping in the glycolytic pathway, glutathione, taurine and sulfur homeostasis (B and C, respectively). Strong metabolic impacts of iron infusion and irradiation were observed in the stool (with iron infusion without irradiation – pre-stool; with iron infusion and after irradiation – post-stool – D) and in the brain, where several tryptophan metabolites (D) and carboxylic acids like malate (E) were altered by iron infusion.

Figure 7 –. Direct measurements of iron in liver (A) and spleen (B) and metabolic correlates across organs (C-D), as color-coded in D.

The same color code is applied to the top 25 significant correlates (Spearman) to spleen iron (strongly correlated to liver iron as well). In F and G, line plots show selected correlates to liver and spleen iron.