Multiple radiations and its effect on biological system – a review on in vitro and in vivo mechanisms

Abstract

Purpose

We are exposed to different types of radiation from natural sources or for biomedical diagnostic and therapeutic purposes at different doses or times. The dose, duration, and number of exposures can cause multiple effects both in vivo and in vitro. Several researchers have explored the effects of ionizing and non-ionizing radiation in cell lines and animal models. Macromolecules, such as DNA, RNA, and proteins, are the primary targets of damage and can lead to several diseases, including cancer and even cell death. Chronic low-dose exposure of cells to radiation can cause alterations in gene expression and can be deleterious to the fate of the cells. We aim to discuss the implications of multiple radiations on different biological systems, including how nanotechnology can facilitate the effects of radiation in therapeutics.

Conclusion

In this review, we discuss the in vitro and in vivo changes that occur due to exposure to different types of radiation used in diagnosis, therapeutics, and other means, such as radiation equipment operators and patients being exposed. The effects of ionizing and non-ionizing radiation have been discussed separately. We have also mentioned in detail about the human-caused accidents of Hiroshima and Chernobyl in this article. The application of nanotechnology in facilitating the effects of radiation in the therapy and management of radioresistance of cells has also been discussed. The radio resistance and method to improve the radiosensitivity have also been mentioned. This review article can reflect the recent developments in the various uses of ionizing and non-ionizing radiation in biomedical field and will open up new avenues to utilize radiation in a more prudent way. The role of nanotechnology in reducing the harmful effects of radiation is also discussed.

1. Introduction

Radiation is contributed by the energy emitted from different parts of the electromagnetic spectrum and can be classified as non-ionizing and ionizing radiation. Non-ionizing radiation includes energies corresponding to the wavelengths of ultraviolet light, visible light, extremely low frequency radiation (ELF), infrared (IR), microwave (MW) and radio frequency (RF). However, ionizing radiation includes alpha (α), beta (β), and gamma (γ) radiation, X-rays and positrons. The different parts of the electromagnetic radiation are compared with the sizes of different known molecules, cells, and other materials, as depicted in Figure 1 [1].

Figure 1.

The sources of different types of electromagnetic radiations, ionizing capacities, and size comparison with different known attributes.

The literature demonstrates that the conventional interactions of ionizing radiation with biological matter are ionizing radiation present either in the electromagnetic or particulate type. The interaction of electromagnetic radiation of particle nature with biological tissues occurs either by excitation or ionization. The reported types of interactions include photoelectric interactions, Compton scattering, and pair production. As a result of these processes, electrons are released and ionized. A single positively charged ion is produced by the initial interaction between the particulate matter and electromagnetic radiation, and most of the energy is transferred as kinetic energy. Thus, most of the energy is transferred to the medium owing to the energy loss of these secondary electrons. Energy is deposited in the medium, depending on the type of radiation. Linear energy transfer (LET) is an indicator of the radiation transfer rate. X-rays and γ-ray photons deposit energy into tissues in a discrete manner, which is classified as a low LET. High LET (densely ionizing) and low LET (sparsely ionizing) are the two forms in which ionizing radiation is categorized. An increased LET increases the number of energetic electrons deposited closely together, which increases the likelihood of DNA damage. Even low LET radiation (X-rays) causes less damage than high LET radiation (alpha particles and neutrons). For the same radiation dose, the relative biological effectiveness (RBE) is a measure of the amount of damage that will occur, and high LET radiation results in high RBE. Biological systems are complex owing to their molecular and atomic heterogeneity. Radiation-induced chemical products were explained using a model developed to explain yields in aqueous and non-aqueous chemical systems [2]. Energy deposition events in aqueous systems can be classified into three types: blobs, spurs, and short tracks. This classification was made based on the energy deposited per event. The ‘spur’ diameter was approximately 4 nm, and its deposited energy was less than 100 eV. Between 100 and 500 eV is deposited in the ‘blob’, which is 7 nm in diameter. Energy amounts greater than 500 eV were classified as ‘short tracks’. [3].

Photons belong to the category of low-LET radiation, which displays wide energy dissemination in tissues [4]. Radiation damage to intracellular molecules occurs through various steps, such as primary radical generation in the target molecules and physical energy deposition. The generated primary radicals can interact with the adjacent molecules and produce chemically stable damage mediated through these unstable radicals. In addition, damaged mitochondria generate reactive oxygen species (ROS), which can lead to DNA damage [5]. Ionizing radiation is also found to elicit senescence in normal cells, leading to cell cycle arrest or mutations and cancer or cell death [6]. Ionizing radiation can create cascades of ionization when it interacts with any type of material, including cells and tissues that are highly hydrated in nature [7].

Non-ionization is the result of an adequate amount of energy being required to excite atoms or electrons in an appropriate manner, but it is not sufficient to expel electrons from their orbitals. In the medium in which the radiation passes, the energy of the radiation is too low for it to act as an ionizer (to emit electrons from atoms) [8,9]. There are a number of applications of non-ionizing radiation (NIR) in health care, including laser surgery, ultrasound imaging, and UV light therapy for long-term treatment of depression. Newer applications include MRI and transcranial magnetic stimulation for depression treatment [10]. Optical radiation and electromagnetic fields are the two major non-ionizing radiation spectrum areas. Infrared radiation, ultraviolet radiation, and visible light are all types of optical radiation. There is a risk of eye and skin damage from these types. In terms of optical radiation, there are two types: thermal radiation and photochemical radiation [11]. It is possible to damage tissue with a single photon of ultraviolet radiation even though it lacks enough energy to ionize atoms. DNA molecules undergo breakage when their bonds are disrupted, resulting in cancer risk over the long term. It is important to consider this when determining permissible exposure levels. Multi-photon interactions of high intensity are the only ones that cause harm with visible light and infrared. There is no difference between the effects produced by both, but lasers can create higher irradiances and heat the tissue to a temperature sufficient to create rapid physical changes [12]. Sunlight is one source of non-ionizing radiation, but so are man-made sources, such as those used in industry. These can both expose us to harmful substances and pose a health risk [13]. Microwaves are located between visible light and infrared radiation. Near infrared has the closest wavelength to visible light, while far infrared is closer to microwaves. It is especially harmful for sensitive tissues, like the skin and the eyes, since near-infrared waves are short, not hot, and undetectable. Based on their biological effects, microwave radiations are usually classified as thermal or nonthermal. High-intensity microwave radiation can damage tissue through heating. The microwave depths of travel depend on its frequency and the type of tissue it is targeting [14]. The health of humans is impaired when they are exposed to electromagnetic fields at extremely low frequencies, according to recent epidemiological studies. People living or working in environments exposed to such fields have been reported to suffer from a variety of cancers, depression, and miscarriages as a result [15,16].

The major biomolecules affected by ionizing radiation are the nucleic acids and proteins, which are further discussed. The other health effects of non-ionizing radiations are also summarized.

2. DNA alterations caused by ionizing radiation

Ionizing radiation is a recognized carcinogen, and exposure to ionizing radiation creates a wide variety of DNA lesions, such as double-strand breaks (DSBs), which are more lethal lesions and could lead to the mis-rejoining of DSBs. To date, the proposed studies have focused on DNA damage induced by ionizing radiation and eventual repair at the linear DNA sequence level, such as mutations, induction of cancer, organ or tissue damage, and cell death. On the other hand, the human genome has a three-dimensional (3D) structure that can eventually influence the appropriate regulation of replication, transcription, and repair. Sanders et al. irradiated lymphoblastoid, ATM-deficient fibroblasts, and only fibroblasts with 5 Gy X-rays and conducted Hi-C assessments after 30 min and 24h irradiation, to observe the 3D genome alterations. The topologically associating domains (TADs) are most segregated after X-ray exposure, indicating that alterations in genome structure are dependent on the ataxia telangiectasia mutated (ATM) pathway of DNA repair [17]. Ionizing radiation is known to induce ROS and oxidative stress, which can cause various types of cellular and molecular damage [18]. Photons, such as X-rays and γ-rays, induce DNA damage through the deposition of low-density energy. Particle irradiation that possesses high linear energy transfer (LET) is capable of depositing high-density energy throughout the track of the particle, generating a higher number and adding complex aberrations of chromosomes, such as translocations and dicentrics, compared to X-ray or γ-irradiation. Ionizing radiation also creates single-strand breaks, double-strand breaks, damage to nucleic acid bases, and DNA-protein cross-links [19]. The radiation-exposed water molecules generated OH^. radicals that induce OH radical addition reactions to guanine, thymine bases, and ribose sugar, generating 8-hydroxyguanine, thymine glycol, damaged bases, strand breaks, and abasic sites, as shown in Figure 2 [20]. It is possible to estimate the amount of double-strand breaks induced by ionizing radiation through observation of the cell cycle and dose absorbed per cell nucleus in vitro, where researchers have used X-rays to induce the strand breaks and flow cytometry to conduct cell cycle analysis, respectively. Propidium iodide can be used to stain the cell nucleus and quantify the amount of DNA per nucleus, whereas the γ-H2AX foci formation assay was used to measure the DSB number per nucleus using flow cytometry and fluorescence microscopy [21].

Figure 2.

OH^. radical-induced DNA damage, the OH^. radical addition reaction occurs to the guanine, thymine bases, and ribose sugar from the H₂O-generated OH^. radical and generates 8-hydroxyguanine, thymine glycol, damaged bases, strand breaks, and abasic sites.

3. RNA alterations by ionizing radiation

RNA strand breaks are one of the most frequent types of damage caused by ionizing radiation. Radiation can induce reactive oxygen species (ROS) production, which can lead to RNA strand breaks or oxidative damage. Damage to protein-coding RNAs or non-coding RNAs can cause errors in protein synthesis and gene expression dysregulation. Researchers have developed a method to detect RNA strand breaks using RT-PCR in ionizing radiation-treated cells by adding a poly(A) tail to the terminus of the broken RNA [22]. Long non-coding RNAs (lncRNAs) play a crucial role in regulating biological processes and are involved in developmental and disease pathogenesis. It is known that around 70% of the human genome gets transcribed into RNA, and out of it, only 2–2.5% gets translated into proteins, indicating that most of the RNAs play other roles in the cell, such as tRNA, rRNA, snRNA, snoRNA, miRNA, and piRNA, etc. Aryankalayil et al. reported that mice were exposed to three different doses of X-radiation (2, 4, and 8 Gy) (whole-body irradiation), and blood samples were collected, followed by RNA isolation at three different time points (16, 24, and 46 h) post-irradiation. Alterations have been observed in long non-coding RNAs (lncRNAs) involved in the cell regulation of gene targets, such as p53 [23]. The different types of damage induced by IR in biomolecules are shown in Figure 3.

Figure 3.

Schematic representation of radiation-induced biomolecule damage. Abbreviations: Reactive oxygen species (ROS), hydroxyl radical (OH), the water molecule (H₂O). The radiation can directly alter genes and chromosomes, which could lead to mutated genes and their transcription can lead to damaged/misfolded proteins and cell damage. Indirectly radiation can react with water molecules/organic molecules in the cytoplasm, damaging mitochondria and contributes to the overproduction of ROS that can damage the biomolecules and the cell.

4. Protein expression alterations induced by ionizing radiation

Changes in the proteins of tissues and cells are highly associated with pathological and physiological alterations in biological systems. Numerous alterations in this protein have been identified following exposure to radiation [24]. Azimzadeh et al. studied protein alterations in Human Formalin-Fixed Paraffin-Embedded (FFPE) cardiac tissues of 15 individuals exposed to cumulative external gamma radiation doses of more than 500 mGy. They identified over 196 proteins whose structures were different from the normal protein structure. A total of 105 proteins were downregulated and 91 were upregulated in the irradiated samples. In irradiated samples, the expression of actin cytoskeleton components was significantly downregulated for several proteins associated with the mitochondrial respiratory chain and the sirtuin pathway. The levels of several proteins responsible for the oxidative stress response were upregulated. Protein ubiquitination, fatty acid metabolism, cytoskeleton organization, sirtuin signaling, tissue fibrosis, mitochondrial dysfunction, and oxidative stress were the most affected pathways in the irradiated samples. The transforming growth factor (TGF) beta-1 and peroxisome proliferator-activated receptor (PARP)- alpha regulatory networks showed enrichment of deregulated proteins. PARP alpha was inactivated, and TGF-β was activated in the irradiated samples. From these identifications, they found that chronic occupational exposure to gamma radiation can alter the metabolic and structural functions of the heart through various alterations in protein metabolism [25].

The same group of scientists studied serum level protein alterations in C57BL/6J mice with localized irradiation at the heart with a single dose of 8 and 16 Gy X-rays, and 20 weeks post-exposure, protein analysis was performed. They identified approximately 499 proteins in mouse heart tissues. Among them, 42 protein expressions in the 8 Gy treatment group and 59 protein expressions in the 16 Gy treatment group were found to be significantly changed. Specifically, inter-alpha-trypsin inhibitors, serpins, apolipoproteins, and immunoglobulins were altered in irradiated mice at both doses. The pathways most affected by irradiation were cholesterol metabolism, acute phase response signaling, atherosclerosis signaling, LXR/RXR cascade, and the coagulation system. The deregulated proteins belonged to two of the significantly affected pathways: HDL/LDL metabolism and acute phase response signaling. These deregulated proteins form a functional network associated with cholesterol metabolism and transport. The proteins involved in lipid metabolism (PPARα and PGC-1) and pro-inflammatory responses (IL-6, TGF-β, and STAT3) were found to be deregulated. PARPα was inactivated, but pro-inflammatory regulators were activated. Serum proteome analysis revealed that the inflammatory response pathway was chiefly affected in serum proteins. After local heart irradiation with 8 Gy, there was an increase in IL-6, whereas in the group that was irradiated with 16 Gy, the levels of G-CSF, IL-6, TNF-α, MCP-1, TGF-β, IL-1 α, β, and IL-12 were potentially increased in the serum compared to the control. These changes in the proteome undoubtedly indicate that local irradiation of the heart induces systemic inflammation in mice [26].

Nakajima et al. compared the alteration in protein levels by acute and chronic irradiation in the livers of male SPF C57BL/6J mice (7–8-week-old). The acute irradiation was with 4 Gy and 8 Gy of X-irradiation, with the dose of 0.72 Gy/min and 0.55 Gy/min for six days, and the mice in the 8 Gy group were sacrificed after six days of irradiation, whereas the 4 Gy group was maintained for three months after irradiation. The levels of the proteins Parkin and MyD88 exhibited increased expression, whereas Bcl-xL was the only protein that showed a decrease in expression in 8 Gy irradiated mice. The Bcl-xL and MyD88 proteins were altered at both doses. After three months of irradiation, some other proteins, p34cdc2, DcR1, and MAP1b, were observed. The level of MyD88 signals was also found to be higher after three months of irradiation in the 4 Gy-treated group. Chronic irradiation was performed on old male SPF C57BL/6J mice (7–8 weeks old) with Cs gamma rays for 400 days (22 h/day) at a dose rate of 20 mGy/day (total dose of 8000 mGy). Protein alterations were observed immediately after irradiation and also three months after irradiation. The proteins that were altered immediately after irradiation were found to be primarily related to apoptosis regulation and inflammatory response. Whereas after three months of irradiation, protein alterations were found in the livers of the mice, and most of the proteins were related to apoptosis regulation. This study showed that acute and chronic exposure to radiation could alter the protein present in the liver immediately after irradiation and three months post-irradiation [27]. Radiation has been found to alter various functional proteins that lead to numerous diseases such as cardiovascular diseases, lung injury, and oxidative molecule modification [20,24,28]. Radiation has also been used for the treatment of cancer, and is the most common therapeutic use of radiation because of its ability to alter the biological molecules of tumor cells [29].

Multiple effects on biological macromolecules lead to damage both in vitro and in vivo. Changes caused by radiation in vitro and in vivo are discussed in the following sections.

5. Effects of ionizing radiation in vitro and in vivo

As radiation is used in various treatments, it also induces damage to healthy tissues, produces reactive oxygen species (ROS), oxidative stress, and reactive nitrogen species (RNS), which can induce various types of cellular and molecular damage [30,31]. Low-dose ionizing radiation is also found to be effective against cells, as low-dose ionizing radiation is common on a daily basis, as natural sources or exposure from man-made sources, such as medical equipment. Exposure to X-rays can lead to DNA double-strand breaks (DSB) that could lead to unrepaired/mis-repaired DSBs and mutations, chromosome rearrangements/aberrations, and loss of genetic information. Belmans et al. reported that low exposure dose ionizing radiation associated with a medical imaging beam setting (<100 mGy; 900mGy/h) induced prominent enhancement in the number of DNA DSBs in dental mesenchymal stromal cells, induced 30–60 min post-irradiation, and also found a time-dependent induction of senescence [32]. Konířová et al. found in a study that radiation is significantly used in brain cancer treatment and might induce neurocognitive decline. Radiation-induced damage to neural stem cell populations and irradiated cells undergoing differentiation programs can occur by ceasing the proliferation mechanism [33]. Low-dose ionizing radiation increases DNA copy number variations (CNV) in vitro and in vivo. Laser-driven electron accelerators (LDEAs) can deliver high-energy beams with pico- or femto-second durations in vitro. Harutyunyan et al. studied the impact of LDEAs’ radiation exposure on known CNV hotspots present in human peripheral blood lymphocytes at the single-cell level. Chromosomal regions such as 1p31.1, 7q11.22, 9q21.3, 10q21.1, and 16q23.1, are sensitive to ionizing radiation, and researchers have concluded that laser-driven electron bunches are capable of inducing CNVs in human blood leukocytes when tested in vitro [34]. Using a co-culture model, Zhang et al. studied γ-ray-induced central nervous system (CNS) injury. The cells (U87 MG and SH-SY5Y cells) were irradiated with γ-rays, and then the culture media of the irradiated cells were utilized to culture immune cells (THP-1 cells/Jurkat cells). It was found that the conditioned media induced THP-1 cell differentiation into macrophages and expressed CD14 on THP−1 cells, which was significantly higher than that in the control group. The levels of chemokines, such as MCP-1 and MIP-1 alpha, which are related to monocytes or the recruitment of immune cells, were found to be high in the conditioned media of irradiated U87 MG and SH-SY5Y cells that induced chemotaxis of THP-1 cells, thereby playing a major role in immune modulation [31]. Human lens epithelial cells in vitro were found to induce protein-level changes relevant to cataractogenesis. HLE cells were X-ray irradiated at various doses (0-5 Gy) at dose rates (1.62 cGy/min and 38.2 cGy/min), and the cells were collected 20-h post-irradiation for protein analysis. As a result of pathway analysis, it was found that there was mitochondrial dysfunction, ROS generation, cell death, cancer, organismal injury, and amyloidosis. The results showed that cell death-related mechanisms are dose rate-dependent and can induce oxidative stress, which can be relevant to cataractogenesis [35]. Henry et al. conducted a study of low doses of ionizing radiation in radiosensitive tissues, such as hematopoietic tissues. They studied the differentiation and self-renewal capabilities of human primary hematopoietic stem/progenitor cells (HSPC). They found that the hematopoietic reconstitution potential after exposure to a single 20 mGy dose was impaired in human HSPC, but their differentiation properties were unaltered. Low-dose irradiation does not induce double-strand breaks, as in high-dose irradiation, but it is capable of inducing a rapid and transient increase in ROS that can induce the activation of the p38MAPK pathway [36]. Researchers developed a new protocol to study how radiation affects the activity and survival of prefrontal cortex (PFC) networks in vitro. They applied increasing doses of radiation to PFC slices using a robotic radiosurgery platform at a consistent dose rate of 10 Gy/min. High-density multielectrode array recordings captured extracellular activity across 4,096 channels from the irradiated slices. The results indicated that these slices exhibited increased firing rates, enhanced functional connectivity, and greater complexity. Graph-theoretic analyses showed changes in functional connectivity post-radiation. These findings were compared to slices induced with epilepsy pharmacologically, which demonstrated higher neural complexity and strong, yet spatially focused functional connections. Additionally, propidium iodide staining indicated a dose-dependent relationship between radiation and apoptosis. Overall, these findings present a novel assay for investigating the effects of clinically relevant radiation doses on brain circuits, emphasizing the immediate impacts of escalating radiation on PFC neurons [37]. Girigoswami et al. studied the effect of γ-irradiation on V79 cells that were exposed to a chronic low-dose oxidant (H₂O₂). They found that the cells exhibited resistance to γ-irradiation, resulting in enhanced antioxidant activity, as indicated by elevated GSH content and antioxidant enzyme activities. Apoptosis was also circumvented in cells exposed to a chronic low dose of oxidative stress and subsequently exposed to γ-irradiation [38,39]. The ND1 and ND4 subunits of NADPH dehydrogenase play important roles in apoptosis. They were overexpressed in V79 cells conditioned with chronic low-dose exposure to H₂O₂, a potent oxidant, and subsequently exposed to γ-irradiation [40]. X-ray at a dose of 0.1–2 Gy was exposed to human embryonic stem cell line [H9-hTnn Tz-pGz-D2] derived cardiomyocytes (HPSC-CMC) for a period of 1, 3, 6, and 26 days. After irradiation, changes in the structural protein, cardiac toxicity, release signaling, and contractile sarcomere formation were observed [41].

As radiation therapies induce damage to healthy cells, scientists are developing strategies to ameliorate this damage. There are reports on ATM knockdown that showed radioprotective effects on neural stem cells (NSC). Guttierez-Quintana et al. reported that ataxia telangiectasia mutated (ATM) kinase is a prominent determinant of tumor cell survival after radiation treatment, and inhibition of ATM radiosensitizes preclinical glioblastoma (GBM) models in vitro and in vivo. The neural stem cells from the telencephalon of the E3 embryos were treated with AZD1390 (0.1–10 nM) before ionizing radiation (0–5 Gy), and in response to ionizing radiation, NSCs underwent apoptosis, whereas AZD1390 treatment with 1–3 nM reduced apoptosis in irradiated NSCs [42].

A study involving heavy ions, such as O₁₆, showed increased suppression of cell growth in cell lines in comparison with photons. G2/M arrest in cell lines was shown to increase in a dose-dependent manner, indicating that heavy ions C₁₂ and O₁₆ may play a significant role in treating radio-resistant malignant melanoma [43]. A study on cancer cells showed that La/SSB protein was localized at the DSB site after exposure to ionizing radiation and was indicated to be associated with radiation-induced DNA damage repair [44]. Väyrynen et al. studied the effects of ionizing radiation and heparanase I (HPSE1) inhibitors on the proliferation of OTSCC cells, invasion, and production of MMP-2 and MMP-9. They found that ionizing radiation could inhibit the invasion of HSC-3 cells and block HPSE1 activity, thereby inducing invasion, even under ionizing radiation. There was an increase in MMP expression and initiation of epithelial-mesenchymal transition in cells cultured on myoma discs. The results indicated that ionizing radiation had long-term effects on MMP-2 and MMP-9, which could show HSC-3 invasion responses under HPSE1 inhibitors and ionizing radiation [45].

It is important to know the effect of radiation, in vivo, as it has been evidenced that multiorgan injury is the aftermath of radiation exposure [46]. FLASH proton pencil beam scanning (p-PBS) demonstrated a reduction in skin toxicity and fibrosis in mice when administered as a single, continuous high-dose fraction. In clinical settings, p-PBS treatment typically involves multiple beams to ensure optimal conformality, with minutes between beams for patient and equipment repositioning. Researchers investigated the effects of single-beam versus multibeam proton radiation on the FLASH sparing effect regarding skin toxicity. They irradiated the right hind leg of 10-week-old female C57Bl/6j mice using a Varian ProBeam proton beam scanning gantry system, applying either a conventional dose rate of 1 Gy/s or a FLASH rate of 100 Gy/s. The findings revealed that the FLASH sparing effect in overlapping beam areas could be negatively affected by interruptions during radiation delivery [47]. Ionizing radiation can cause mutations in germ cells across various organisms, including fruit flies and mice. In both mice and humans, resting oocytes are primarily found in the ovarian cortical region, where blood vessel density is low,especially in younger individuals,and extracellular material is abundant, resulting in a hypoxic environment. This condition likely contributes to the resistance of immature oocytes to the cell-killing and mutagenic effects of radiation. While studies have investigated fetal malformations in humans, the genetic component of these malformations is minimal, and abnormal fetuses often miscarry, a phenomenon not observed in mice, complicating the detection of transgenerational effects. To address these challenges, whole genome sequencing of exposed parents and their offspring is proposed as a strategy, with careful consideration of ethical concerns [48].

The amino acid methionine plays an essential role in several processes carried out by living organisms. In addition to depleting tissue methionine levels, ionizing radiation decreases glutathione synthesis. In this study, CBA/CaJ mice were exposed to doses ranging from 3 to 8.5 Gy of 137Cs total body irradiation, and methionine supplementation was tested. An excess of methionine in the diet exacerbates the adverse effects of ionizing radiation on the small intestine that was demonstrated by researchers [49]. In addition to reducing oxidative stress, protecting endothelial cells from damage, and modifying cholesterol metabolism, tocotrienol (GT3) possesses antioxidant properties. Using a mouse model, this study evaluated the effect of GT3 on cardiovascular effects induced by oxygen ion irradiation (¹⁶O). In a study of male C57BL/6 J mice, whole-body ¹⁶O (600 MeV/n) irradiation (0.26–0.33 Gy/min) was applied at 6 months of age and followed up to 9 months thereafter. A dose of GT3 (50 mg/kg/day subcutaneously) or vehicle was administered to the animals. GT3 reduced ¹⁶O radiation-induced cardiac dysfunction, mast cell, T-cell, and monocyte/macrophage markers in the left ventricle, as well as collagen type III peptide expression. The heart tissue may benefit from GT3 as a countermeasure to high-linear energy transfer radiation [50]. Richardson et al. studied the effect of fractionation exposure of 40 cGy (0.4 Gy exposure per week for 10 weeks) in six-month-old mice, with a single exposure of 4 Gy in two-week-old mice for 8 months. Sham-irradiated mice were used as controls for C57BL/6J male adult mice. The results obtained from micro-CT, 3D bone mineral density, and trabecular bone volume showed a decrease in the femur and spine of both groups exposed to γ-irradiation. Osteoclast maturation was enhanced by the activation of osteoclasts in osteoclast progenitors, and mitochondrial respiration and Sirt3 activation were also identified. In this study, they identified that total body irradiation with ionizing radiation can lead to bone density loss in young adult mice [51].

A recent study was conducted by Brien et al. on the biomarker FDXR related to radiation exposure. They studied the expression level of FDXR in different patients undergoing peripheral radiation exposure to several types of radiation, such as diagnostic computed tomography (CT), cardiac fluoroscopy, and other treatments (local and total body radiotherapy), which are biomarkers of ionizing radiation exposure. FDXR showed remarkable sensitivity to a wide range of ionizing radiation exposure levels in human cells in vivo, proving it to be an independent, perhaps unique, biomarker for humans [52]. Radiation can cause biological damage when a person is exposed to low doses for a prolonged period.

Table 1 lists the effects of various types of ionizing radiation on the experimental models.

Table 1.

The ionizing radiation types, assessment time post radiation, and their effects on different types of experimental in vivo and in vitro models.

Radiation/Dose	Experimental model	Observation time after radiation	Observation	Reference
Cosmic Ray/30 cCGy	Male C57BL/6 mice	6, 15, and 52 Weeks	Elevation of neuroinflammation due to upregulation of inflammatory cytokines in the brain.	[53]
X-ray/16 Gy	Genetically modified C57BI/6 mice with homozygous(−,−), heterozygous (+,−) and wild type (+,+) PARA α genotype	20 Weeks	They found that for the activation of noncanonical TGF-β signaling, PPAR-α is a necessary protein in the irradiated heart	[54]
137Cs Gamma irradiation, Platinum-based chemotherapy, neoadjuvant chemotherapy, photon-based radiotherapy/23.4-50 Gy, 7.5–30 Gy	Cervical Cancer Patients	Till treatment gets over	The patients were pretreated with radiation and/or chemotherapy before the surgery. They have concluded that radiotherapy in patients with cervical cancer induced an immunological shift that increased the level of programmed death ligand 1-expressing tumor cells (PD-L1 TC), leading to tumor cell death	[55]
Gamma/20 mGy/day) gamma radiation for 300 days	APoE-deficient C57BL/6 Mice	300 days	Alteration in the metabolic protein related to PGC-1α and PPAR alpha in the mitochondria and an increase in protein phosphorylation was observed. The radiation sensitized protein upregulation. Gamma irradiation led to oxidative stress and protein alteration in the heart.	[56]
X-ray/16 Gy	Male 8- weeks- old C57BL/6J mice	20 Weeks	The mice, which are pre-treated with fenofibrate before local heart irradiation, were found to have less alteration in the mitochondrial respiration metabolism, redox response, lipid metabolism, and endothelial nitric oxide signaling that are affected in the control mice that were untreated with fenofibrate before irradiation.	[57]
X-ray/16 Gy	Male 8 -weeks- old C57BL/6J mice	5 Months	Alterations were observed in the proteins involved in metabolism, fibrosis, and also in the mitochondrial proteins.	[58]
Gamma/10 mGy	Harlan nude mice	2 h	p53 Level was maintained in the mice treated with the inhibitor of MDm2 and irradiation that reduced the tumor compared to only irradiation. This shows that the p53 protein was sensitized by irradiation.	[59]

5.1. Ionizing radiation used for diagnostics

Radiation has long been used in the diagnosis of various diseases. Some of the most commonly used radiation-based diagnoses are X-rays, CT, MRI, ultrasound examination, and nuclear medicine imaging techniques.

To validate the effect of the Elekta Clarity Auto-scan system on the motion estimation of prostate radiation therapy in vivo, Grimwood et al. monitored the position of an intraprostatic fiducial marker, a primary marker of prostate cancer, in 16 patients receiving radiotherapy (80 fractions). Two types of systems were used: 2 a dimensional electronic portal imager plane and clarity-enhanced 3-dimensional prostate motion images from a cone-beam CT scan system. The images were compared based on their clarity and marker visibility. From the image comparison, they concluded that motion monitoring for radiotherapy image clarity is not affected [60].

5.2. Ionizing radiation used for treatment

Many treatment modalities for various diseases have been exploited so far, among which ionizing radiation contributes a major role. Diffenderfer et al. found a novel proton radiotherapy system that transports FLASH proton radiotherapy (PRT) with double-scattered protons using CT guidance and provided proton FLASH radiotherapy-mediated normal tissue radioprotection. Pancreatic tumor (MH641905) bearing C57BL/6J mice were treated with FLASH (dose rate 0.5–1 Gy/s) and a standard dose of PRT (dose rate 0.9 ± 0.08 Gy/s) in the abdominal region in control and tumor mice. The reduction of tumors near the baseline when treated with 18 Gy of local irradiation for FLASH was compared with standard PRT. Owing to any unalteration, they designed a FLASH-PRT system that was dosimetrically validated with an accurate beam flux per millisecond. The collimation apparatus and double scattering were validated dosimetrically with dose rates of 0.9 ± 0.08 and 78 ± 9 Gy/s for the standard PRT and FLASH-PRT. Using this system, they found late fibrosis and a decrease in acute cell loss after focal intestinal and whole-abdomen radiotherapy (RT). This showed that the FLASH-PRT system could prevent the growth of pancreatic flank tumors with 15 Gy of treatment [61].

5.2.1. Ionizing radiation in cancer therapy

Radiotherapy is the most commonly used therapy for cancer treatment to prevent disease recurrence. To date, various studies have been conducted to investigate the effects of multiple types of radiation and their role in inhibiting cancer growth. Allam et al. studied the impact of stereotactic body radiotherapy (SBRT) on the ablation of tumor microvasculature in NOD-Rag1null IL2rgnull (NRG) mice with pancreatic cancer. The irradiation doses were 10, 20, and 30 Gy at a dosage rate of 2.63 Gy/min. According to their findings, the tumor microvasculature responded to SBRT with dose-dependent temporal kinetics, specifically when microvascular heterogeneity was considered. Moreover, the researchers discovered that there was a complete microvascular architecture alteration after irradiation in the mouse model, and the vasculature volume density was also found to be decreased, which showed that SBRT decreased tumor growth in a dose-dependent manner, elicited through poor vascularization, diffusion-limited fractions and vessel aggregation at a short distance [62].

Dillon et al. studied the effect of radiation in a mouse model (female C57Bl/6 mice) that was immunocompetent for HPV-driven malignancies. They used fractionated radiation in combination with an ATR inhibitor (ATRi), AZD6738. After treatment, they found an increased number of NK and CD3þ cells, predominantly consisting of myeloid cells. ATRi and radiation produce a gene expression pathway associated with an inflammatory type I/II response, with the upregulation of nucleic acid-sensing genes. There was also an increase in the MCHI level, which indicated increased antigenic processing and presentation in the tumor cells. Cytogenic gene expression (CXCL10, CCL2, and CCL5) was also identified after treatment with the ATRi AZD6738 in combination with fractionated radiation. This showed that ATR inhibition plays a major role in enhancing the effect of RT [63].

Jeong et al. studied the effects of aripiprazole and its potent radiosensitizer in head and neck cancer. Tumor xenograft tissues were used to study the effect of aripiprazole at doses of 5 µM and 5 Gy of irradiation. They found that aripiprazole treatment reduced the growth of neck and head cancer cells (FaDu and CAL27, respectively) in a dose-dependent manner. They also found that aripiprazole predominantly enhanced FaDu and CAL27 sensitivity to the IC₅₀ doses of ionizing radiation. The combination of ionizing radiation with aripiprazole synergistically improved propidium iodide double-positive, annexin, and terminal deoxynucleotidyl transferase dUTP nick end labeling-positive cell populations, as well as improved the cleavage of poly(ADP-ribose) polymerase and caspase-3 expression, which led to the activation of apoptosis. The induction of apoptosis by ionizing radiation and aripiprazole was accompanied by the upregulation of reactive oxygen species. This showed that aripiprazole sensitized xenograft tumors to ionizing radiation doses at which ionizing radiation did not affect tumor growth [64].

Ladomersky et al. investigated the Cesium-137 radiation effect on immunocompetent orthotopic mouse models (C57BL/6 and BALB/c mice) carrying glioblastoma (GBM). Mice were treated with BGB-5777, an inhibitor of the IDO1 enzyme (100 mg/kg), combined with anti-PD1 mAb (300 mg every three days), and radiotherapy (RT) (2 Gy/day of Cesium-137 for five days in a week) treatment was performed for 15 days. They found that the combination of these three agents provided enhanced survival benefits compared to single or dual agents. They also reported that IDO1 enzyme inhibition enhanced the accumulation of drugs in the brain region. This study showed that the synergistic effect of various components, along with ionizing radiation, inhibited the growth of GBM and improved the survival rate [65].

Qi et al. studied the effect of tazemetostat along with cisplatin and/or radiation on pediatric brain tumors in 22 patient-derived orthotopic xenograft models. Tazemetostat is a well-known inhibitor of zeste homolog (EZH2). They evaluated the level of EZH2 in all models and found that there was an elevation in H3K27me3 expression in 11 medulloblastoma models and overexpression of EZH2 mRNA in nine GBM models. The therapeutic efficacy of tazemetostat along with radiation was estimated in four models (one ATRT, one GBM, and two medulloblastomas) by the parallel administration of tazemetostat (400 and 250 mg/kg) alone and in combination with radiation (2 Gy/day × 5 days). There was significant and prolonged survival in the IC-2305GBM and IC-L1115ATRT xenograft models in a dose-dependent manner compared with the control. They concluded that tazemetostat can be used for a subset of pediatric brain tumors [66].

5.2.2. Dual effect of nanoparticles and ionizing radiation

Recently, nanoparticles have been used in biomedical applications. They are used for imaging [67,68], biosensing [69,70], targeted drug delivery [71,72], tissue engineering [73,74], theranostics [75,76], antimicrobial activities [77,78], and bioremediation [79]. Janic et al. reported that gold nanoparticles (AuNPs) showed a prominent role in survival, immunomodulation of tumor microenvironment (TME), and RT cytotoxicity in a xenograft mouse model of human triple-negative breast cancer (TNBC). Mice were divided into four groups: (i) RT treated group (16 Gy dose from 16 kV X-ray source), (ii) RT along with 4 nm sized AuNPs (2 mg/ml), (iii) RT along with 14 nm sized AuNPs (2 mg/ml) for 30 days, and (iv) the control group was maintained as untreated. A prominent delay in tumor growth was observed in the treatment group compared to that in the control group. Moreover, among the treatment groups, RT plus 14 nm AuNPs induced tumor volume reduction within seven days of treatment. In this study, AuNPs improved RT-induced immunogenic cell death (ICD), which was associated with macrophage infiltration in mice treated with 14 nm AuNPs [80]. Li et al. developed a different approach for increasing RT based on a nanoradiosensitizer. They developed a mitochondria-targeted titanium dioxide-gold nanoradiosensitizer (TiO₂ AuNPs +Triphenylphosphine (TPP)) and utilized MCF-7 cells, MCF-7 xenografts in mice, and a 4T1 tumor-bearing Balb/c mouse model. These in vitro and in vivo models were irradiated with 4 Gy and 6 Gy of X-ray exposure, respectively, along with a nanosensitizer containing 16 µmmol of TPP. The results were analyzed 8 h post-treatment and showed that the nanosensitizer had the ability to produce ROS in the mitochondria, which led to a burst release of ROS. Overexpression of ROS disrupts mitochondria and leads to cell apoptosis. The cell survival rate was significantly reduced in the mitochondrial-targeted nanosensitizer-treated group compared to that in the non-targeted groups. There was a noticeable reduction in tumor growth in animal models treated only once with RT and a nanosensitizer. The outcome of the study showed that mitochondria-targeted nanosensitizers play a major role in enhancing the effect of RT on tumor reduction [81]. Nanoparticles have also been found to be useful in the management of radiation therapy in lung cancer [82]. Primary tumors of oral squamous cell carcinoma (OSCC) have elevated levels of the guanylate- binding protein 5 (GBP5), which correlates with radioresistance. A correlation between GBP5 upregulation, NF-kB activation, and programmed cell death-ligand 1 (PD-L1) expression was examined in OSCC samples. The OSCC cells were less likely to express PD-L1 when GBP5 was knocked down, but PD-L1 expression was enhanced when it was overexpressed. In OSCC cells, NF-kB inhibition by SN50 significantly reduced the expression of PD-L1, cellular migration ability, and irradiation resistance of GBP5-forested irradiation resistance. Moreover, the upregulation of GBP5 resulted in a favorable outcome for the cancer patients who were administered with immune checkpoint inhibitors (ICI) therapy. Thus, GBP5 can be a useful biomarker for the prediction of radiation and ICI-induced anti-OSCC effectiveness [83].

Patel et al. developed bacterial membrane-coated nanoparticles (BNP) that were multifunctional and composed of PC7A/CpG polyplex cores possessing immune-activating properties, covered with imide groups, and bacterial membranes to enhance antigen retrieval. The formulated BNP can capture cancer neoantigens after RT and improve their uptake by dendritic cells (DCs). This leads to the cross-presentation of neoantigens that elicit an antitumor T cell response. Treatment with BNP+RT in mice with syngeneic melanoma or neuroblastoma resulted in the activation of effector T cells, DCs, tumor-specific antitumor immune memory, and marked tumor regression. The BNP produced created an in situ immune recognition of the irradiated tumor [84]. Piccolo et al. demonstrated diamond target beam radiotherapy (DTBR) in vitro and in vivo, in combination with gold nanoparticles (GNPs). GNP facilitated the DTBR by improving localized RT delivery. This enhanced the dosage in the vicinity of the tumor, thereby facilitating tumor reduction in Detroit-562 and HSC-3 engrafted zebrafish larvae. This property of DTBR and GNPs could be used to improve tumor control thereby reducing toxicity to nearby cells and organs [85].

5.3. Radioprotective agents

Scientists have identified various health issues caused by ionizing radiation in the hematopoietic, immune, and human digestive systems. Natural compounds extracted from plants have a protective role owing to their minimal toxicity. Scientists have found a plant (Azolla imbricata)-derived compound, 3,4,5-O-tricaffeoylquinic acid (tCQA), that could significantly suppress ionizing radiation-induced systemic damage in mice. The in vitro experiments were performed on the irradiated colonic epithelial cell line NCM460 treated with tCQA to reduce the cytotoxic effect of ionizing radiation. Reduction of mitochondrial dysfunction caused by ionizing radiation is characterized by decreased ROS production, mitochondrial transmembrane potential, and caspase-dependent apoptosis. In this study, tCQA reversed the generation of ROS induced by H₂O_2, and western blotting results indicated that tCQA could reverse the ionizing radiation-activated MAPK signaling pathway. Inhibition of activation of the JNK/P38 signaling pathway, which was induced by H₂O₂, after tCQA treatment resulted in ROS inhibition [86]. Li et al. reported that in total body irradiation (TBI) or total abdominal irradiation (TAI)-treated mice, the gut microbiota produced valeric acid (VA), which showed protective properties against γ-radiation-induced injuries. Among short-chain fatty acids, the radioprotective activity of VA was found to be significant. Treatment with VA improved the survival rate of irradiated mice by improving gastrointestinal (GI) tract function, protection of hematogenic organs, and intestinal epithelial integrity. Furthermore, using isobaric tags for relative and absolute quantitation (iTRAQ) and high-throughput sequencing results, revealed that VA oral gavage after TAI exposure led to reprogramming of the small intestinal protein profile. This also helped restore the entire bacterial taxonomic proportion present in the intestine. A step forward, they have also found that Keratin 1 plays a major role in the radioprotection of VA [87]. Rengachar et al. studied the radioprotective activity of Gamma-Linolenic Acid (GLA) against ionizing radiation. They used C57Bl/6J female mice, which were grouped as control, polyunsaturated fatty acids (PUFAs) (GLA 100 µg/kg), irradiation (7.5 Gy radiation, 0.02% ethanol in PBS), PUFAs + irradiation (prior to irradiation, animals were treated with PUFAs 48, 24 and 1 h (100 µg/kg)). The percentage of survival was 20% after irradiation, whereas in the GLA-treated group, the survival rate was 80%. The survival percentage increased due to the restoration of duodenal IL-6, IL-10, TNF-α, and HMGB1 concentrations, along with controlled expression of IkB, Bcl-2, NF-kB, delta-6-desaturase, 5-LOX, Bax, and COX-2 genes. Furthermore, the anti- and pro-oxidant enzymes (glutathione, catalase, and SOD) reverted to normal levels [88].

6. Management of radioresistance in cancer

The stage in which cancer/tumor cells or tissues adapt to the radiation conditions and show resistance to radiation therapy-promoted changes is called radioresistance. Radioresistance occurs due to increased DNA lesion repair, which protects the cells from genomic instability. Alterations in oncogene/tumor suppressor genes, such as dysregulation of vitronectin, an oncogene, induce the invasion and migration of cancer cells. Alterations in miR-29c and miR-22 expression are also involved in radio resistance. The tumor microenvironment (TME), such as cytokine levels and hypoxic conditions, can also induce radioresistance. Decreased autophagy in tumor cells, generation of cancer stem cells (CSCs), and alterations in tumor metabolism are associated with radioresistance [89]. Huang et al. reported that suppression/blocking of mitochondrial ATP-sensitive potassium channels (mtK_ATP) can alleviate the radioresistance of glioma by inhibiting ROS-induced activation of ERK. This indicates that mtK_ATP channel inactivators and MAPK/ERK kinase (MEK) suppressors could be efficient drug targets for alleviating radioresistance [90]. Pan et al. reported that the radioresistant subtypes, A549 R and H460 R, were irradiated with hypofractionated radiation and treated with erastin, and found that erastin treatment increased the radiosensitivity of radioresistant cells and inhibited GPX4 expression. Erastin, in combination with ionizing radiation, resulted in increased cell death compared to treatment with erastin or ionizing radiation alone. This indicates that the suppression of radioresistance in NSCLC cells is elicited by promoting GPx4- mediated ferroptosis [91]. Park et al. reported that low-dose radiation (LDR) pretreatment of NSCLC cells results in overexpression of miR-30a and miR-30b that can inhibit plasminogen activator inhibitor-1 (PAI-1). Akt and ERK phosphorylation were also found to be decreased by PAI-1 inhibition. They also used 7C1 lipid-based nanoparticles to encapsulate miR-30a and miR-30b into an orthotopic mouse xenograft model, and found decreased tumor growth and aggressiveness by pre-LDR followed by radiation therapy [92]. Hypoxic subvolumes, found in cancer stem cell subpopulation, and radioresistance that can be present inherently or acquired.They indicate aggressiveness of tumour and their potential to undergo metastasis making it a great challenge in cancer therapy. Spatially fractionated radiation therapy (SFRT) is also recently used to tackle major challenges offering high therapeutic index for radioresistant tumor treatment [93]. Noncoding RNAs have also shown promising results in the management of prostate cancer [94].

7. Nuclear disaster of Hiroshima, Nagasaki and Chernobyl and their impact

Researchers have recently outlined the long-term radiological impacts, psychosocial effects, and infrastructure response following Chernobyl and Fukushima accidents [95]. There has also been a review of the studies that investigated radiation-related effects in offspring of radiation-exposed individuals published between 2018 and 2022 [96]. A nuclear weapon was used for the first time in war on 6 August 1945, in Hiroshima and on 9 August 1945, in Nagasaki. New weapons of mass destruction were introduced to the world as a result of the devastation caused in the two cities. In spite of the fact that reported numbers vary, it is estimated that by the end of 1945, 90,000 to 120,000 civilians out of a civilian population of about 330,000 in Hiroshima, as well as 60,000 to 80,000 people out of 280,000 in Nagasaki, would be dead as a result of being exposed to the intense heat, physical force, and ionizing radiation emitted by the bombs. The scientists affiliated to Atomic Bomb Casualty Commission and their successor institute, the Radiation Effects Research Foundation, assessed the long-term health effects for the past 63 years in the surviving population of the atomic bombings of Hiroshima and Nagasaki as well as in their offsprings [97]. Long-term, large-scale epidemiological studies have shown that ionizing radiation causes late-onset effects on the human body. Because of the size of the cohort, exposure of both sexes and all ages, and the wide range of individually assessed doses, the cohort study of Japanese survivors of the atomic bombings of Hiroshima and Nagasaki (the Life Span Study) is considered the most reliable source of information about these health effects. Radiation-induced cancer is clearly associated with survivors having a higher cancer risk than older survivors. Children exposed to radiation are at higher risk than those exposed as adults. The risk of cardiovascular disease and some other non-cancer diseases may be increased by radiation at high doses, and possibly at low doses as well. Although, survivors of the atomic bomb have not been reported to have inherited any hereditary effects [98].

In the past few decades, Chernobyl, which sits 130 kilometers north of the Ukrainian capital Kiev and ten kilometers south of the Belarusian border, has been the scene of some of the most serious nuclear accidents in history. The power plant was destroyed by two violent explosions on 26 April 1986, causing a series of fires and releasing radioactive materials into the atmosphere. Finely fragmented nuclear fuel particles, gases, and aerosols were released. When it comes to radionuclides, iodine-131 and cesium-137 are of the utmost importance. Wind directions changed frequently during the massive releases, so all areas around the reactor received fallout at some point during the 10 days. Furthermore, rainfall occurred irregularly, resulting in different degrees of deposition. All countries in the Northern Hemisphere were contaminated by radioactive materials to some extent due to the releases of radioactive material. Nevertheless, Belarus, Russia, and Ukraine are the countries most affected by contamination [99].

Ten years after Chernobyl, the health status of the residents was reviewed. There were apparently fewer than 100 deaths within the first few months as a result of acute radiation damage due to high doses of ionizing radiation. There has been no evidence of an increase in congenital abnormalities, except perhaps for Down’s syndrome. Belarus and Ukraine, as well as the Bryansk region of Russia, have already seen dramatic increases in childhood thyroid cancers. A few areas with heavy contamination have seen an increase of over 100-fold [100].

The fallout from Chernobyl accident exposed millions of people to radioactive isotopes twenty years after the accident. As yet, there has not been a general increase in malignancies over the past 20 years, although thyroid carcinoma incidence has increased considerably and breast cancer has possibly been affected by radiation. It was first noticed in children that the iodine 131 release was causing an increase in thyroid carcinoma, associated with a strong relationship between young age when exposed and risk of papillary thyroid carcinoma (PTC) [101]. Children exposed to I-131 as children in Ukraine and Belarus have developed PTC, even 30 years after the Chernobyl disaster. Chromosome rearrangements and gene fusions in post-Chernobyl PTCs have provided new information important to molecular mechanisms. The incidence of thyroid cancer and hematological malignancies in adults has been shown to increase with the exposure level of clean-up workers/liquidators. Cardiovascular and cerebrovascular diseases are also on the rise [102]. These incidents indicate that ionizing radiation caused disaster can cause damage to the genetic level which can be carry forwarded for generations after generations.

For many decades, it has been recognized that radiation exposure during the development of an embryo or fetus can result in two major types of severe health effects: it can disrupt normal intrauterine development, or it may lead to the onset of leukemia and cancer during childhood. Recent epidemiological and experimental data have been presented that could enhance our understanding of the underlying mechanisms and help establish radiation protection standards. However, ecological studies of populations exposed to higher radiation levels due to contamination from reactor accidents (such as Chernobyl and Fukushima) have not provided solid evidence to support this goal. In contrast, well-designed experimental studies have demonstrated the multifactorial mechanisms that lead to various health effects following in utero radiation exposure [103].

8. Effect on health and biological macromolecules induced by non-ionizing radiation

There are several health scares associated with the electromagnetic radiation generated by radio-based stations, mobile phones, and phone towers, as well as high-voltage power lines, which are associated with health problems such as cancer in humans, and adverse effects on birds, animals, etc. [104]. Oxidative stress have also been reported to be induced by non-ionizing radiations [105], and sometimes can cause cancer [104]. Thermal and non-thermal effects of non-ionizing radiations of low intensity have also been reported [106]. As the use of mobile phones increases, non-ionizing electromagnetic waves of radio frequencies are generated. Even in the literature, mixed reports are available regarding the long-term use of mobile phones and their association with an elevated risk of cancer. The non-thermal radio frequency impact of mobile phones is classified as group 2 B (potential human carcinogens), and various reports indicate its risk of inducing cancer/tumors. Olkhovskiy et al. studied the radio frequency of a smartphone on platelet aggregation and found that ADP-induced aggregation of platelets in apparently healthy individuals, as well as ischemic stroke patients, increased, whereas it was suppressed in the blood samples of patients with polycythemia vera [106,107]. Surveys have been conducted by researchers among the college students to know whether they are aware of the ill effects of mobile usage [108].

Several studies have demonstrated that radiofrequency radiation (RFR) can cause genotoxicity and carcinogenesis, although the results of all of these studies are still controversial. According to one study, exposure limits of (50 Hz, 1800 MHz ELF-EMF), and time were standardized, and the effects of exposure to GSM-Talking mode RF at 50 Hz on mouse spermatocytic cell lines were determined when they were exposed for 24 h to GSM-Talking mode RF at 50 Hz. As shown by alkaline comet assays and immunofluorescence, exposure to low-frequency radio waves resulted in a slight increase in DNA strand breaks, whereas exposure to electromagnetic frequencies had no evident effect on DNA strands [109].

The direct consequence of solar UV irradiation is that it can generate dimers of cyclobutane pyrimidine (CPD) and pyrimidine 6-4-pyrimidone photoproducts (6-4PP), and UV radiation-induced ROS can damage DNA [110]. Lawrence et al. studied the adverse effects of very-long-wave UVA (>380 nm) and visible radiation (≥400 nm) in vitro and in vivo. They identified various gene expression alterations and protein fold changes both in vitro and in vivo after 24 h and 2 h of exposure, respectively, including dark cyclobutane pyrimidine dimer (CPD) formation. Multiple types of damage are caused by the induction of oxidative stress by chromophores present in the skin, such as alterations in melanin, β-carotene, and protoporphyrin IX. This shows that there is a need to find an effective sunscreen in the region of UV exposure near 380 nm [111].

Al Musawi et al. studied the effect of a low-power diode-pumped solid-state (DPSS) laser on serum protein changes. They separated human blood serum and divided it into five groups. Four treatment groups received different doses of DPSS laser (50, 70, 90, and 110 J/cm²) emitting a wavelength of 589 nm, and one group was used as a control. They studied the electrophoretic migration speed of each protein and identified that the electrophoretic migration speed of all the serum proteins decreased, especially at 70 J/cm². The migration speed of albumin, alpha1, alpha 2, beta, and globulin was significantly decreased. This study showed that laser light with a wavelength of 589 nm could reduce the migration speed of human blood serum proteins [112]. Reports suggest that exposure to blue light-induced retinal damage increases the risk of age-related macular degeneration. R28 cells were irradiated with blue light at 10 mW/cm², and the blue light exposure decreased cell viability up to 42% and increased apoptosis by 10-fold [113].

The use of WiFi, also known as wireless local area network (WLAN), which uses a frequency range of 2.400–2.484 and 5.150–5.825 GHz and is a radiofrequency electromagnetic field (RF-EMF), is increasing. The in vitro studies with WiFi (5.8 GHz WiFi of 9.5 V/m for 24 h) on human osteosarcoma (U2OS), mouse embryonic stem cells (IB10), and human fibroblasts (VH10) concluded that WiFi did not show any perturbed cellular processes or pathways in response to WiFi [114]. Another group also tested primary human MRC-5 lung fibroblasts and human trophoblast cells (HTR-8/SVneo) and found no indication of ROS-mediated induction of DNA damage after exposure to WiFi [115].

8.1. Non-ionizing radiation for diagnostics

Dechent et al. studied the characterizing effect of dermoscopy, reflectance confocal microscopy (RCM), and high-frequency ultrasonography (HFUS) in patients with basal cell carcinoma (BCC) before and after treatment (42 Gy in 6 fractions with a brachytherapy device), and the images were taken. A total of 137 imaging assessments were performed in 12 patients before and after treatment with dermoscopy, HFUS, and RCM. Prior to treatment, the presence of BCC-specific characteristics was found to be 91, 81.8, and 17% in images with RCM, dermoscopy, and HFUS, respectively. Images after treatment revealed that the resolution of BCC-specific characteristics was altered by 100, 33.4, and 91.7% from the patient images with RCM, dermoscopy, and HFUS, respectively. Based on this observation, they concluded that RCM is more reliable than dermoscopy and HFUS for the characterization of BCCs’ response to radiotherapy [116].

8.2. Non-ionizing radiation for treatment

Various types of radiation have been used to treat various diseases. Chatraie et al. studied the effect of non-thermal plasma on ulcer treatment. In this study, ulcers were created in the dorsal cells of adult rats and treated with plasma for five weeks, at a frequency of 3 days per week. They monitored changes in the histological and mechanical parameters of the treated tissue. Plasma treatment of ulcers was found to improve wound healing, and histological analysis showed that plasma played a significant role in angiogenesis, formation of new hair follicles, re-epithelialization, control of inflammation, and collagen fibrosis. Furthermore, they demonstrated the effect of plasma using mechanical analysis and suggested that plasma treatment can improve tissue tolerance and mechanical strength versus uniaxial tensile load [117].

Radiation exposure causes energy deposition in the tissues or body parts that are exposed and measured in LET. Humans and animals are exposed to both low and high LET radiation from either natural or manmade sources. Because our body consists of water, exposure to these radiations in aquatic environments causes different types of deleterious effects. Macromolecules, such as DNA, RNA, and proteins, are major targets. In DNA and RNA, radiation exposure can cause strand breaks, base alterations, and mutations, which can lead to organ or cell damage. Although our body has a repair system to repair such damage, its capacity is limited, and it mostly becomes an error-prone repair due to damage overload. Free radicals are generated, which eventually lead to oxidative damage, and chronic low-dose exposure to any oxidant is the etiology of cancer. It is well known that oxidative stress is the root cause of several diseases, such as cardiovascular disease, cancer, ageing, etc., and thus, radiation can contribute to such diseases. At the protein level, radiation can cause damage to amino acids and alter their conformation, causing them to lose their activity. In vivo, ionizing radiation is used to control the growth of uncontrolled proliferating cells, which damages normal cells and is nonspecific. Using nanoparticles, we can target tumor tissues and enhance the effect of radiation in such tissues, causing minimal harm to benign cells. Radioresistance is a major bottleneck in the treatment of cancer. Researchers have proposed that suppression or blocking of mitochondrial ATP-sensitive potassium channels (mtK_ATP) can improve cellular radioresistance.

9. Conclusion

In the present review article, we have discussed about the deleterious effect of ionizing and non-ionizing radiations in our body as well as in other animals and cell lines. The different reports suggested that use of ionizing radiation with proper safety measures do not cause any harm, whereas a little breach in safety can lead to disastrous outcomes like Hiroshima and Chernobyl which will be carried out from generations to generations. Treatment of cancer using ionizing radiation is reported to damage the benign cells along with the cancer cells, and it leads to radioresistance. Using nanotechnology, future radiation modality will change giving rise to targeted treatment for cancer. Nano sensitizers and camouflaging cell components act prudently in enhancing the effect of RT as well as disguising their identification by the cancer cells, respectively. Personalized medicine has also come into the treatment filed recently, that can plan a patient specific radiation regime to effectively eradicate the cancer cells and cancer stem cells. Further studies are warranted on approaches for killing cancer stem cells and management of radioresistance in cancer treatment. On the other hand, non-ionizing radiations are also detrimental, causing DNA stand damage and giving birth to harmful free radicals which cause cellular damage. Oxidative stress is the player behind different diseases like cancer, cardiovascular disease, ageing etc., that is elicited by both ionizing and non-ionizing radiation, leading the exposed person to early ageing or death. Antioxidant enzymes like catalase, glutathione peroxidase and superoxide dismutase can scavenge such free radicals which cause the oxidative damage. As a preventive measure to combat the damage caused by the oxidative stress, we have to include antioxidant rich foods and supplements in our diet plan.

Funding Statement

Koyeli Girigoswami acknowledges CARE funding (Ref no. 004/Regr./AR-Research/2022-06), and the Ministry of Education, Govt. in India (Project No: RP-03525G, 2022).

Author contributions

Conceptualization: K.G. Article search and writing the first draft: K.G., D. B., G.A., and A.G. Finalizing the manuscript: K.G., D. B., G.A., and A.G. All the authors have read and approved the final work.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

Data sharing is not applicable to this article as no new data were created or analyzed in this study.