Evaluation of Anti-Tumor Effects of Whole-Body Low-Dose Irradiation in Metastatic Mouse Models

Effects of low-dose radiation produced during radiofrequency ablation guided by 3D mapping on mitochondrial apoptosis in diabetic cardiomyocytes

BACKGROUND

Three-dimensional (3D) mapping has been widely used in the clinical radiofrequency ablation of arrhythmia; however, the dose of intraoperative radiation exposure has not been determined. Moreover, whether a single instance of intraoperative radiation exposure has an effect on myocardial tissue or exacerbates diabetic heart injury remains uncertain.

METHODS AND RESULTS

In this study, we evaluated the dose of intraoperative radiation generated during radiofrequency ablation via 3D mapping. ELISA, Western blot, flow cytometry, and oxygen consumption rate detection were used to identify the effects of the intraoperative radiation dose on cardiomyocyte apoptosis via the mitochondrial pathway and its specific mechanism. These results indicated that the exposure radiation used in radiofrequency ablation guided by 3D mapping for all types of arrhythmia was low-dose radiation (LDR; the doses were all less than 200 mGy). Although LDR (50, 100 and 200 mGy) had no significant effect on the mitochondrial apoptosis of normal cardiomyocytes, the 200 mGy radiation dose reduced the mitochondrial apoptosis of cardiomyocytes subjected to high glucose and high lipid (HG/HL) treatment. Mechanistically, an LDR of 200 mGy improved the expression of IL-10, reversed the accumulation of IL-6, ROS, disruption of Δψm, and the impairment of mitochondrial function caused by HG/HL. Additionally, 200 mGy radiation promoted the expression of Bcl-xl while reducing the expression of Bax in cardiomyocytes treated with HG/HL.

CONCLUSION

In summary, this study demonstrated that the exposure radiation dose used in radiofrequency ablation guided by 3D mapping was low-dose radiation (LDR), which had no effect on the mitochondrial apoptosis pathway in normal cardiomyocytes and even had a protective effect on cardiomyocytes treated with HG/HL via increased IL-10 levels and the suppression of IL-6, ROS, and mitochondrial damage induced by HG/HL.

Low-Dose Non-Targeted Effects and Mitochondrial Control

Non-targeted effects (NTE) have been generally regarded as a low-dose ionizing radiation (IR) phenomenon. Recently, regarding long distant abscopal effects have also been observed at high doses of IR) relevant to antitumor radiation therapy. IR is inducing NTE involving intracellular and extracellular signaling, which may lead to short-ranging bystander effects and distant long-ranging extracellular signaling abscopal effects. Internal and "spontaneous" cellular stress is mostly due to metabolic oxidative stress involving mitochondrial energy production (ATP) through oxidative phosphorylation and/or anaerobic pathways accompanied by the leakage of O₂^- and other radicals from mitochondria during normal or increased cellular energy requirements or to mitochondrial dysfunction. Among external stressors, ionizing radiation (IR) has been shown to very rapidly perturb mitochondrial functions, leading to increased energy supply demands and to ROS/NOS production. Depending on the dose, this affects all types of cell constituents, including DNA, RNA, amino acids, proteins, and membranes, perturbing normal inner cell organization and function, and forcing cells to reorganize the intracellular metabolism and the network of organelles. The reorganization implies intracellular cytoplasmic-nuclear shuttling of important proteins, activation of autophagy, and mitophagy, as well as induction of cell cycle arrest, DNA repair, apoptosis, and senescence. It also includes reprogramming of mitochondrial metabolism as well as genetic and epigenetic control of the expression of genes and proteins in order to ensure cell and tissue survival. At low doses of IR, directly irradiated cells may already exert non-targeted effects (NTE) involving the release of molecular mediators, such as radicals, cytokines, DNA fragments, small RNAs, and proteins (sometimes in the form of extracellular vehicles or exosomes), which can induce damage of unirradiated neighboring bystander or distant (abscopal) cells as well as immune responses. Such non-targeted effects (NTE) are contributing to low-dose phenomena, such as hormesis, adaptive responses, low-dose hypersensitivity, and genomic instability, and they are also promoting suppression and/or activation of immune cells. All of these are parts of the main defense systems of cells and tissues, including IR-induced innate and adaptive immune responses. The present review is focused on the prominent role of mitochondria in these processes, which are determinants of cell survival and anti-tumor RT.

Low-dose radiotherapy for COVID-19 pneumonia and cancer: summary of a recent symposium and future perspectives

The lessons learned from the Coronavirus Disease 2019 (COVID-19) pandemic are numerous. Low dose radiotherapy (LDRT) was used in the pre-antibiotic era as treatment for bacterially/virally associated pneumonia. Motivated in part by these historic clinical and radiobiological data, LDRT for treatment of COVID-19-associated pneumonia was proposed in early 2020. Although there is a large body of epidemiological and experimental data pointing to effects such as cancer at low doses, there is some evidence of beneficial health effects at low doses. It has been hypothesized that low dose radiation could be combined with immune checkpoint therapy to treat cancer. We shall review here some of these old radiobiological and epidemiological data, as well as the newer data on low dose radiation and stimulated immune response and other relevant emerging data. The paper includes a summary of several oral presentations given in a Symposium on "Low dose RT for COVID and other inflammatory diseases" as part of the 67th Annual Meeting of the Radiation Research Society, held virtually 3-6 October 2021.

Exposure to Low to Moderate Doses of Ionizing Radiation Induces A Reduction of Pro-Inflammatory Ly6chigh Monocytes and a U-Curved Response of T Cells in APOE -/- Mice

Low dose ionizing radiation (LDIR) is known to have a protective effect on atherosclerosis in rodent studies, but how it impacts different cells types involved in lesion formation remains incompletely understood. We investigated the immunomodulatory response of different doses and dose-rates of irradiation in ApoE^-/- mice. Mice were exposed to external γ rays at very low (1.4 mGy.h^-1) or low (50 mGy.h^-1) dose-rates, with cumulative doses spanning 50 to 1000 mGy. Flow cytometry of circulating cells revealed a significant decrease in pro-inflammatory Ly6C^Hi monocytes at all cumulative doses at low dose-rate, but more disparate effects at very low dose-rate with reductions in Ly6C^Hi cells at doses of 50, 100 and 750 mGy only. In contrast, Ly6C^Lo monocytes were not affected by LDIR. Similarly, proportions of CD4⁺ T cell subsets in the spleen did not differ between irradiated mice and non-irradiated controls, whether assessing CD25⁺FoxP3⁺ regulatory or CD69⁺ activated lymphocytes. In the aorta, gene expression of cytokines such as IL-1 and TGF-ß and adhesion molecules such as E-Selectin, ICAM-1, and VCAM-1 were reduced at the intermediate dose of 200 mGy. These results suggest that LDIR may reduce atherosclerotic plaque formation by selectively reducing blood pro-inflammatory monocytes and by impairing adhesion molecule expression and inflammatory processes in the vessel wall. In contrast, splenic T lymphocytes were not affected by LDIR. Furthermore, some responses to irradiation were nonlinear; reductions in aortic gene expression were significant at intermediate doses, but not at either highest or lowest doses. This work furthers our understanding of the impact of LDIR with different dose-rates on immune system response in the context of atherosclerosis.