Targeted Nuclear Irradiation with an X-Ray Microbeam Enhances Total JC-1 Fluorescence from Mitochondria

Synergistic Effect of Ferroptosis-Inducing Nanoparticles and X-Ray Irradiation Combination Therapy

Ferroptosis, characterized by the induction of cell death via lipid peroxidation, has been actively studied over the last few years and has shown the potential to improve the efficacy of cancer nanomedicine in an iron-dependent manner. Radiation therapy, a common treatment method, has limitations as a stand-alone treatment due to radiation resistance and safety as it affects even normal tissues. Although ferroptosis-inducing drugs help alleviate radiation resistance, there are no safe ferroptosis-inducing drugs that can be considered for clinical application and are still in the research stage. Here, the effectiveness of combined treatment with radiotherapy with Fe and hyaluronic acid-based nanoparticles (FHA-NPs) to directly induce ferroptosis, considering the clinical applications is reported. Through the induction of ferroptosis by FHA-NPs and apoptosis by X-ray irradiation, the therapeutic efficiency of cancer is greatly improved both in vitro and in vivo. In addition, Monte Carlo simulations are performed to assess the physical interactions of the X-rays with the iron-oxide nanoparticle. The study provides a deeper understanding of the synergistic effect of ferroptosis and X-ray irradiation combination therapy. Furthermore, the study can serve as a valuable reference for elucidating the role and mechanisms of ferroptosis in radiation therapy.

Mitochondrial Metabolism in X-Irradiated Cells Undergoing Irreversible Cell-Cycle Arrest

Irreversible cell-cycle-arrested cells not undergoing cell divisions have been thought to be metabolically less active because of the unnecessary consumption of energy for cell division. On the other hand, they might be actively involved in the tissue microenvironment through an inflammatory response. In this study, we examined the mitochondria-dependent metabolism in human cells irreversibly arrested in response to ionizing radiation to confirm this possibility. Human primary WI-38 fibroblast cells and the BJ-5ta fibroblast-like cell line were exposed to 20 Gy X-rays and cultured for up to 9 days after irradiation. The mitochondrial morphology and membrane potential were evaluated in the cells using the mitochondrial-specific fluorescent reagents MitoTracker Green (MTG) and 5,5',6,6'-tetraethyl-benzimidazolylcarbocyanine iodide (JC-1), respectively. The ratio of the mean MTG-stained total mitochondrial area per unit cell area decreased for up to 9 days after X-irradiation. The fraction of the high mitochondrial membrane potential area visualized by JC-1 staining reached its minimum 2 days after irradiation and then increased (particularly, WI-38 cells increased 1.8-fold the value of the control). Their chronological changes indicate that the mitochondrial volume in the irreversible cell-cycle-arrested cells showed significant increase concurrently with cellular volume expansion, indicating that the mitochondria-dependent energy metabolism was still active. These results indicate that the energy metabolism in X-ray-induced senescent-like cells is active compared to nonirradiated normal cells, even though they do not undergo cell divisions.

Radiation-Induced Bystander Effect and Cytoplasmic Irradiation Studies with Microbeams

Simple Summary

Microbeams are useful tools in studies on non-target effects, such as the radiation-induced bystander effect, and responses related to cytoplasmic irradiation. A micrometer or even sub-micrometer-level beam size enables the precise delivery of radiation energy to a specific target. Here we summarize the observations of the bystander effect and the cytoplasmic irradiation-related effect using different kinds of microbeam irradiators as well as discuss the cellular and molecular mechanisms that are involved in these responses. Non-target effects may increase the detrimental effect caused by radiation, so a more comprehensive knowledge of the process will enable better evaluation of the damage resulting from irradiation.

Abstract

Although direct damage to nuclear DNA is considered as the major contributing event that leads to radiation-induced effects, accumulating evidence in the past two decades has shown that non-target events, in which cells are not directly irradiated but receive signals from the irradiated cells, or cells irradiated at extranuclear targets, may also contribute to the biological consequences of exposure to ionizing radiation. With a beam diameter at the micrometer or sub-micrometer level, microbeams can precisely deliver radiation, without damaging the surrounding area, or deposit the radiation energy at specific sub-cellular locations within a cell. Such unique features cannot be achieved by other kinds of radiation settings, hence making a microbeam irradiator useful in studies of a radiation-induced bystander effect (RIBE) and cytoplasmic irradiation. Here, studies on RIBE and different responses to cytoplasmic irradiation using microbeams are summarized. Possible mechanisms related to the bystander effect, which include gap-junction intercellular communications and soluble signal molecules as well as factors involved in cytoplasmic irradiation-induced events, are also discussed.

Molecular Interactions of Normal and Irradiated Tubulins During Polymerization

Microtubules, one of the cytoskeletons, are highly dynamic structures that play a variety of roles in maintaining cell morphology, cell division and intracellular transport. Microtubules are composed of heterodimers of α- and β-tubulins, which are repeatedly polymerized and depolymerized. To investigate the radiation-induced impacts on the polymerization reaction of tubulins, we evaluated the molecular interactions between normal and irradiated tubulins. First, the polymerization reaction of the tubulins was measured after stepwise irradiation from 0 Gy to 1,000 Gy of X rays. The polymerization was inhibited in a dose-dependent manner. Next, the tubulins' polymerization reaction was then measured after the tubulin that was damaged from the exposure to 1,000 Gy of X rays was mixed with the normal tubulins. Our findings reveal that the radiation dose-dependent change in the degree of overall microtubule polymerization progression depends on the ratio of damaged tubulin. This result is biochemical evidence that non-DNA damage (in this case, cytoskeletal damage) from cytoplasmic radiation exposure may inhibit cell division, suggesting that some cytoskeletal damage may also affect the fate of the entire cell.