Ionizing radiation response of primary normal human lens epithelial cells

AOP report: Development of an adverse outcome pathway for deposition of energy leading to cataracts

Cataracts are one of the leading causes of blindness, with an estimated 95 million people affected worldwide. A hallmark of cataract development is lens opacification, typically associated not only with aging but also radiation exposure as encountered by interventional radiologists and astronauts during the long-term space mission. To better understand radiation-induced cataracts, the adverse outcome pathway (AOP) framework was used to structure and evaluate knowledge across biological levels of organization (e.g., macromolecular, cell, tissue, organ, organism and population). AOPs identify a sequence of key events (KEs) causally connected by key event relationships (KERs) beginning with a molecular initiating event to an adverse outcome (AO) of relevance to regulatory decision-making. To construct the cataract AO and retrieve evidence to support it, a scoping review methodology was used to filter, screen, and review studies based on the modified Bradford Hill criteria. Eight KEs were identified that were moderately supported by empirical evidence (e.g., dose-, time-, incidence-concordance) across the adjacent (directly linked) relationships using well-established endpoints. Over half of the evidence to justify the KER linkages was derived from the evidence stream of biological plausibility. Early KEs of oxidative stress and protein modifications had strong linkages to downstream KEs and could be the focus of countermeasure development. Several identified knowledge gaps and inconsistencies related to the quantitative understanding of KERs which could be the basis of future research, most notably directed to experiments in the range of low or moderate doses and dose-rates, relevant to radiation workers and other occupational exposures.

The impact of dose rate on responses of human lens epithelial cells to ionizing irradiation

The knowledge on responses of human lens epithelial cells (HLECs) to ionizing radiation exposure is important to understand mechanisms of radiation cataracts that are of concern in the field of radiation protection and radiation therapy. However, biological effects in HLECs following protracted exposure have not yet fully been explored. Here, we investigated the temporal kinetics of γ-H2AX foci as a marker for DNA double-strand breaks (DSBs) and cell survival in HLECs after exposure to photon beams at various dose rates (i.e., 150 kVp X-rays at 1.82, 0.1, and 0.033 Gy/min, and 137Cs γ-rays at 0.00461 Gy/min (27.7 cGy/h) and 0.00081 Gy/min (4.9 cGy/h)), compared to those in human lung fibroblasts (WI-38). In parallel, we quantified the recovery for DSBs and cell survival using a biophysical model. The study revealed that HLECs have a lower DSB repair rate than WI-38 cells. There is no significant impact of dose rate on cell survival in both cell lines in the dose-rate range of 0.033-1.82 Gy/min. In contrast, the experimental residual γ-H2AX foci showed inverse dose rate effects (IDREs) compared to the model prediction, highlighting the importance of the IDREs in evaluating radiation effects on the ocular lens.

Temporal Dynamic Regulation of Autophagy and Senescence Induction in Response to Radiation Exposure

Autophagy and senescence are closely related cellular responses to genotoxic stress, and play significant roles in the execution of cellular responses to radiation exposure. However, little is known about their interplay in the fate-decision of cells receiving lethal doses of radiation. Here, we report that autophagy precedes the establishment of premature senescence in normal human fibroblasts exposed to lethal doses of radiation. Activation of the p53-dependent DNA damage response caused sustained dephosphorylation of RB proteins and consequent cell cycle arrest, concurrently with Ulk1 dephosphorylation at Ser638 by PPM1D, which promoted autophagy induction 1-2 days after irradiation. In addition, mitochondrial fragmentation became obvious 1-2 days after irradiation, and autophagy was further enhanced. However, Ulk1 levels decreased significantly after 2 days, resulting in lower LC3-II levels. An autophagic flux assay using chloroquine (CQ) also revealed that the flux in irradiated cells gradually decreased over 30 days. In contrast, lysosomal augmentation started at 1 day, became significantly upregulated after 5 days, and continued for over 30 days. After a rapid decrease in autophagy, p16 expression increased and senescence was established, but autophagic activity remained reduced. These results demonstrated that X-ray irradiation triggered two processes, autophagy and senescence, with the former being temporary and regulated by DNA damage response and mitophagy, and the latter being sustained and regulated by persistent cell cycle arrest. The interplay between autophagy and senescence seems to be essential for the proper implementation of the cellular response to radiation exposure.

Noncancer Effects of Ionizing Radiation Exposure on the Eye, the Circulatory System and beyond: Developments made since the 2011 ICRP Statement on Tissue Reactions

For radiation protection purposes, noncancer effects with a threshold-type dose-response relationship have been classified as tissue reactions (formerly called nonstochastic or deterministic effects), and equivalent dose limits aim to prevent occurrence of such tissue reactions. Accumulating evidence demonstrates increased risks for several late occurring noncancer effects at doses and dose rates much lower than previously considered. In 2011, the International Commission on Radiological Protection (ICRP) issued a statement on tissue reactions to recommend a threshold of 0.5 Gy to the lens of the eye for cataracts and to the heart and brain for diseases of the circulatory system (DCS), independent of dose rate. Literature published thereafter continues to provide updated knowledge. Increased risks for cataracts below 0.5 Gy have been reported in several cohorts (e.g., including in those receiving protracted or chronic exposures). A dose threshold for cataracts is less evident with longer follow-up, with limited evidence available for risk of cataract removal surgery. There is emerging evidence for risk of normal-tension glaucoma and diabetic retinopathy, but the long-held tenet that the lens represents among the most radiosensitive tissues in the eye and in the body seems to remain unchanged. For DCS, increased risks have been reported in various cohorts, but the existence or otherwise of a dose threshold is unclear. The level of risk is less uncertain at lower dose and lower dose rate, with the possibility that risk per unit dose is greater at lower doses and dose rates. Target organs and tissues for DCS are also unknown, but may include heart, large blood vessels and kidneys. Identification of potential factors (e.g., sex, age, lifestyle factors, coexposures, comorbidities, genetics and epigenetics) that may modify radiation risk of cataracts and DCS would be important. Other noncancer effects on the radar include neurological effects (e.g., Parkinson's disease, Alzheimer's disease and dementia) of which elevated risk has increasingly been reported. These late occurring noncancer effects tend to deviate from the definition of tissue reactions, necessitating more scientific developments to reconsider the radiation effect classification system and risk management. This paper gives an overview of historical developments made in ICRP prior to the 2011 statement and an update on relevant developments made since the 2011 ICRP statement.

Individual response of the ocular lens to ionizing radiation

PURPOSE

Cataract (opacification of the ocular lens) is a typical tissue reaction (deterministic effect) following ionizing radiation exposure, for which prevention dose limits have been recommended in the radiation protection system. Manifestations of radiation cataracts can vary among individuals, but such potential individual responses remain uncharacterized. Here we review relevant literature and discuss implications for radiation protection. This review assesses evidence for significant modification of radiation-induced cataractogenesis by age at exposure, sex and genetic factors based on current scientific literature.

CONCLUSIONS

In addition to obvious physical factors (e.g. dose, dose rate, radiation quality, irradiation volume), potential factors modifying individual responses for radiation cataracts include sex, age and genetics, with comorbidity and coexposures also having important roles. There are indications and preliminary data identifying such potential modifiers of radiation cataract incidence or risk, although no firm conclusions can yet be drawn. Further studies and a consensus on the evidence are needed to gain deeper insights into factors determining individual responses regarding radiation cataracts and the implications for radiation protection.

Regulatory implementation of the occupational equivalent dose limit for the lens of the eye and underlying relevant efforts in Japan

In April 2011, the International Commission on Radiological Protection recommended reducing the occupational equivalent dose limit for the lens. Such a new occupational lens dose limit has thus far been implemented in many countries, and there are extensive discussions toward its regulatory implementation in other countries. In Japan, discussions in the Japan Health Physics Society (JHPS) began in April 2013 and in Radiation Council in July 2017, and the new occupational lens dose limit was implemented into regulation in April 2021. To share our experience, we have published a series of papers summarizing situations in Japan: the first paper based on information available by early 2017, and the second paper by early 2019. This paper (our third paper of this series) aims to review updated information available by mid-2022, such as regarding regulatory implementation of the new occupational lens dose limit, recent discussions by relevant ministries based on the opinion from the council, establishment process of safety and health management systems, the JHPS guidelines on lens dose monitoring and radiation safety, voluntary countermeasures of the licensees, development of lens dose calibration method, and recent studies on exposure of the lens in nuclear workers and biological effect on the lens.

Lens Epithelial Cell Proliferation in Response to Ionizing Radiation

Lens epithelial cell proliferation and differentiation are naturally well regulated and controlled, a characteristic essential for lens structure, symmetry and function. The effect of ionizing radiation on lens epithelial cell proliferation has been demonstrated in previous studies at high acute doses, but the effect of dose and dose rate on proliferation has not yet been considered. In this work, mice received single acute doses of 0.5, 1 and 2 Gy of radiation, at dose rates of 0.063 and 0.3 Gy/min. Eye lenses were isolated postirradiation at 30 min up until 14 days and flat-mounted. Then, cell proliferation rates were determined using biomarker Ki67. As expected, radiation increased cell proliferation 2 and 24 h postirradiation transiently (undetectable 14 days postirradiation) and was dose dependent (changes were very significant at 2 Gy; P = 0.008). A dose-rate effect did not reach significance in this study (P = 0.054). However, dose rate and lens epithelial cell region showed significant interactions (P < 0.001). These observations further our mechanistic understanding of how the lens responds to radiation.

Sensitivity and latency of ionising radiation-induced cataract

When managed with appropriate radiation protection procedures, ionising radiation is of great benefit to society. Opacification of the lens, and vision impairing cataract, have recently been recognised at potential effects of relatively low dose radiation exposure, on the order of 1 Gy or below. Within the last 10 years, understanding of the effects of low dose ionising radiation on the lens has increased, particularly in terms of DNA damage and responses, and how multiple radiation or other events in the lens might contribute to the overall risk of cataract. However, gaps remain, not least in the understanding of how radiation interacts with other risk factors such as aging, as well as the relative radiosensitivity of the lens compared to tissues of the body. This paper reviews the current literature in the field of low dose radiation cataract, with a particular focus on sensitivity and latency.

An investigation of early radiation damage in rainbow trout eye-lenses

As part of the wider interest in the effects of ionizing radiation on non-human biota, this investigation was carried out to study early radiation damage to the eye-lenses of rainbow trout. Lenses were cultured and irradiated to doses of 1.1 Gy and 2.2 Gy with low-energy X-rays of 40 kV. Laser focal analysis was used to track changes in focal lengths across the lenses post-irradiation. Changes in focal length variability (FLV) were measured to determine whether this could give an indication of the early effects of radiation on lens health. No statistically significant differences in FLV between the control and irradiated lenses within 10 days post-irradiation were observed. FLV was found to be 0.09 ± 0.02 mm for 2.2 Gy lenses, 0.06 ± 0.01 mm for 1.1 Gy lenses, and 0.11 ± 0.02 mm for control lenses at the end of the observation period.

Early Responses to Low-Dose Ionizing Radiation in Cellular Lens Epithelial Models

Cataract is the leading cause of visual impairment which can result in blindness. Cataract formation has been associated with radiation exposure; however, the mechanistic understanding of this phenomenon is still lacking. The goal of this study was to investigate mechanisms of cataract induction in isolated lens epithelial cells (LEC) exposed to ionizing radiation. Human LECs from different genetic backgrounds (SV40 immortalized HLE-B3 and primary HLEC cells) were exposed to varying doses of 137Cs gamma rays (0, 0.1, 0.25 and 0.5 Gy), at low (0.065 Gy/min) and higher (0.3 Gy/min) dose rates. Different assays were used to measure LEC response for, e.g., viability, oxidative stress, DNA damage studies, senescence and changes to telomere length/telomerase activity at two time points (1 h and 24 h, or 24 h and 15 days, depending on the type of assay and expected response time). The viability of cells decreased in a dose-dependent manner within 24 h of irradiation. Measurement of reactive oxygen species showed an increase at 1 h postirradiation, which was alleviated within 24 h. This was consistent with DNA damage results showing high DNA damage after 1 h postirradiation which reduced significantly (but not completely) within 24 h. Induction of senescence was also observed 15 days postirradiation, but this was not attributed to telomere erosion or telomerase activity reduction. Overall, these findings provide a mechanistic understanding of low-dose radiation-induced cataractogenesis which will ultimately help to inform judgements on the magnitude of risk and improve existing radiation protection procedures.

In vitro exposure of human lens epithelial cells to X-rays at varied dose-rates leads to protein-level changes relevant to cataractogenesis

BACKGROUND

Accumulated body of evidence shows that ionizing radiation increases the risk of cataracts. The mechanisms are not clear and the International Commission on Radiological Protection indicates a need for research into understanding the process, particularly at low doses and low dose rates of exposure.

PURPOSE

This study was designed to examine protein-level modifications in a human lens epithelial (HLE) cell-line following radiation exposures.

MATERIALS AND METHODS

HLE cell-line was subjected to X-irradiation at varied doses (0-5 Gy) and dose-rates (1.62 cGy/min and 38.2 cGy/min). Cells were collected 20 h post-exposure, lysed and proteins were clarified following fractionation by a molecular weight cut-off filtration method. Fractionated cellular proteins were enzymatically digested and subjected to mass spectrometry analysis.

RESULTS

Statistically significant radiation dose-related protein changes compared to the control group were identified. Heatmap and hierarchical clustering analysis showed dose-rate dependant responses. Pathway analysis mapped the proteins to biological functions of mitochondrial dysfunction, reactive oxygen species generation, cell death, cancer, organismal injury and amyloidosis.

CONCLUSION

Overall findings suggest that ionizing radiation exposure of HLE cells by mediating dose rate-dependant oxidative stress and cell death-related mechanisms, can be relevant to cataractogenesis.

An update on effects of ionizing radiation exposure on the eye

The International Commission on Radiological Protection (ICRP) has considered for over 60 years that the lens of the eye is among the most radiosensitive tissues, and has recommended dose limits for the lens to prevent occurrence of vision impairing cataracts (VICs). Epidemiological evidence that doses much lower than previously thought produce cataracts led ICRP to recommend reducing dose threshold for VICs and reducing an occupational equivalent dose limit for the lens in 2011, when only a single threshold of 0.5 Gy was recommended. On the basis of epidemiological evidence, ICRP assumed progression of minor opacities into VICs and no dose rate effect. This contrasts with previously recommended separate thresholds for minor opacities and VICs, and for different exposure scenarios. Progression was assumed based on similar risks of cataracts and cataract surgery in Japanese atomic bomb survivors. The absence of dose rate effect derived from the observed similar thresholds for protracted exposures in Chernobyl cleanup workers and in atomic bomb survivors. Since 2011, there has been an increasing body of epidemiological evidence relating to cataracts and other ocular diseases (i.e. glaucoma and macular degeneration), particularly at low doses and low dose rates. This review paper gives an overview of the scientific basis of the 2011 ICRP recommendation, discusses the plausibility of these two assumptions in the light of emerging scientific evidence, and considers the radiosensitivity of the lens among ocular structures.

Biomimetic Engineering of a Scavenger-Free Nitric Oxide-Generating/Delivering System to Enhance Radiation Therapy

Nitric oxide (NO) is a potent tumor-cell radiosensitizer but it can be readily scavenged by hemoglobin (Hb) in vivo. A biomimetic incubator that can generate and deliver NO in a scavenger (Hb)-free environment to enhance its radiosensitizing effect to maximize its efficacy in radiotherapy is proposed. This NO incubator comprises a poly(lactic-co-glycolic acid) (PLGA) hollow microsphere (HM) that contains an NO donor (NONOate) and a surfactant molecule (sodium caprate, SC) in its aqueous core. In acidic tumorous environments, the PLGA shell of the HM allows the penetration of protons from the outside, activating the hydrolytic cleavage of NONOate, spontaneously generating NO bubbles, which are immediately trapped/stabilized by SC. The SC-stabilized NO bubbles in the HM are then squeezed through the spaces of its PLGA matrices by the elevated internal pressure. Upon leaving the HM, the entrapped NO molecules may passively diffuse through their SC-stabilized/protected layer gradually to the tumor site, having a long-lasting radiosensitizing effect and inhibiting tumor growth. The entire process of NO generation and delivery is conducted in a scavenger (Hb)-free environment, mimicking the development of young ovoviviparous fish inside their mothers' bodies in the absence of predators before birth.

Radioprotective role of uric acid: evidence from studies in Drosophila and human dermal fibroblast cells

Exposure to ionizing radiation (IR) is a common phenomenon during medical diagnosis and treatment. IRs are deleterious because cellular exposure to IR can cause a series of molecular events that may lead to oxidative stress and macromolecular damage. Radiation protection is therefore essential and significant for improving safety during these procedures. Over decades several antioxidant molecules have been screened to explore their potential as radio-protectors with little success. Therefore, the current study was carried out to confirm the role of uric acid (UA)-a putative antioxidant molecule in radioprotection using radio-resistant insect Drosophila and human dermal fibroblast (HDF) cells. Here, we demonstrate the depleted levels of UA in the mutant flies of Drosophila melanogaster-rosy and by targeting xanthine oxidase (XO an enzyme involved in UA metabolism), through maintaining flies on an allopurinol mixed diet. Allopurinol is a drug that reduces UA levels by inhibiting XO; it reduces the survival percentage in D. melanogaster compared to wild type flies following gamma irradiation at a dose of 1000 Gy. Enzymatic antioxidants such as superoxide dismutase (SOD), catalase, D. melanogaster glutathione peroxidase (DmGPx) and levels of non-enzymatic antioxidants were measured to evaluate the importance of UA. The results indicate that lack of UA reduces the total antioxidant capacity. The activity of SOD was lowered in male flies. Furthermore, we show that supplementation of UA to HDFs cells in media improved their survival rate following gamma irradiation (2 Gy). From the present study we conclude that UA is a potent antioxidant molecule present in high levels among insects. Also, it appears that UA contributes to the radiation resistance of Drosophila flies. Hence, UA emerges as a promising molecule for mitigating radiation-induced oxidative damage in higher organisms.

A biologically based mathematical model for spontaneous and ionizing radiation cataractogenesis

Cataracts have long been known, but a biomathematical model is still unavailable for cataratogenesis. There has been a renewed interest in ionizing radiation cataracts because the recent international recommendation of the reduced lens dose limit stimulated the discussion toward its regulatory implementation in various countries. Nevertheless, a relationship between radiation (dose and dose rate) and response (e.g., incidence, onset and progression) remains incompletely understood, raising the need for a risk-predictive mathematical model. We here report for the first time an in silico model for cataractogenesis. First, a simplified cell proliferation model was developed for human lens growth based on stem and progenitor cell proliferation as well as epithelial-fiber cell differentiation. Then, a model for spontaneous cataractogenesis was developed to reproduce the human data on a relationship between age and cataract incidence. Finally, a model for radiation cataractogenesis was developed that can reproduce the human data on a relationship between dose and cataract onset at various ages, which was further applied to estimate cataract incidence following chronic lifetime exposure. The model can serve as the foundation for further development of the risk-predictive model for cataractogenesis along with additional considerations of various biological mechanisms and epidemiological datasets.

Inverse dose-rate effect of ionising radiation on residual 53BP1 foci in the eye lens

The influence of dose rate on radiation cataractogenesis has yet to be extensively studied. One recent epidemiological investigation suggested that protracted radiation exposure increases radiation-induced cataract risk: cumulative doses of radiation mostly <100 mGy received by US radiologic technologists over 5 years were associated with an increased excess hazard ratio for cataract development. However, there are few mechanistic studies to support and explain such observations. Low-dose radiation-induced DNA damage in the epithelial cells of the eye lens (LECs) has been proposed as a possible contributor to cataract formation and thus visual impairment. Here, 53BP1 foci was used as a marker of DNA damage. Unexpectedly, the number of 53BP1 foci that persisted in the mouse lens samples after γ-radiation exposure increased with decreasing dose-rate at 4 and 24 h. The C57BL/6 mice were exposed to 0.5, 1 and 2 Gy ƴ-radiation at 0.063 and 0.3 Gy/min and also 0.5 Gy at 0.014 Gy/min. This contrasts the data we obtained for peripheral blood lymphocytes collected from the same animal groups, which showed the expected reduction of residual 53BP1 foci with reducing dose-rate. These findings highlight the likely importance of dose-rate in low-dose cataract formation and, furthermore, represent the first evidence that LECs process radiation damage differently to blood lymphocytes.

DNA damage induction during localized chronic exposure to an insoluble radioactive microparticle

Insoluble radioactive microparticles emitted by the incident at the Fukushima nuclear power plant have drawn keen interests from the viewpoint of radiation protection. Cs-bearing particles have been assumed to adhere in the long term to trachea after aspirated into respiratory system, leading to heterogeneous dose distribution within healthy tissue around the particles. However, the biological effects posed by an insoluble radioactive particle remain unclear. Here, we show cumulative DNA damage in normal human lung cells proximal and distal to the particle (β-ray and γ-ray-dominant areas, respectively) under localized chronic exposure in comparison with uniform exposure. We put a Cs-bearing particle into a microcapillary tip and placed it onto a glass-base dish containing fibroblast or epithelial cells cultured in vitro. A Monte Carlo simulation with PHITS code provides the radial distribution of absorbed dose-rate around the particle, and subsequently we observed a significant change in nuclear γ-H2AX foci after 24 h or 48 h exposure to the particle. The nuclear foci in the cells distal to the particle increased even under low-dose-rate exposure compared with uniform exposure to 137Cs γ-rays, which was suppressed by a treatment with a scavenger of reactive oxygen species. In contrast, such focus formation was less manifested in the exposed cells proximal to the particle compared with uniform exposure. These data suggest that the localized exposure to a Cs-bearing particle leads to not only disadvantage to distal cells but also advantage to proximal cells. This study is the first to provide quantitative evaluation for the spatial distribution of DNA double strand breaks after the heterogeneous chronic exposure to a Cs-bearing particle in comparison with uniform Cs exposure.

Recent discussions toward regulatory implementation of the new occupational equivalent dose limit for the lens of the eye and related studies in Japan

Purpose: In 2011, the International Commission on Radiological Protection (ICRP) recommended an equivalent dose limit for the lens of the eye of 20 mSv/year, averaged over defined periods of 5 years, with no single year exceeding 50 mSv for occupational exposure in planned exposure situations. Since then, there have been extensive discussions toward regulatory implementation of such a new occupational lens dose limit. This paper provides an overview of the recent discussions toward regulatory implementation and the current status of the studies related to radiation exposure of the lens and its effect in Japan. Conclusions: In Japan, the Radiation Council established a Subcommittee in July 2017 to discuss the feasibility of implementing the new occupational lens dose limit. In March 2018, the Radiation Council requested all relevant government ministries and agencies to take necessary actions toward implementation of the new occupational lens dose limit, considering a series of discussions made by the Subcommittee. According to the currently available information, the new occupational lens dose limit (20 mSv/year, averaged over defined periods of 5 years, with no single year exceeding 50 mSv) will be implemented into regulations in Japan, most likely in April 2021, albeit subject to change. In particular, there were extensive discussions about reduction of a dose limit and radiation control for workers who may exceed 20 mSv per year, such as the Fukushima Daiichi Nuclear Power Plant decommissioning workers and medical staff, and measurement of 3 mm dose equivalent. In order to underpin regulatory practice, epidemiological and biological studies on radiation effects on the lens and studies on lens dose measurements have been conducted in Japan, some of which have been funded by the Japanese Nuclear Regulation Authority.

Risk of radiation-induced lens opacities among surgeons and interventional medical staff

The main effect of ionizing radiation on the eyes is the onset of posterior cortical and subcapsular cataracts. Recent studies have raised questions about the mechanism of ocular damage and the threshold dose for the onset of such effects. Currently, operators may be exposed to ionizing radiation during surgical procedures. It has been estimated that urologists can be exposed to an annual dose close to or above 20 mSv/year. The aim of our study was to evaluate the frequency of cataracts in a group of professional radiological operators to verify their possible association with the radiation dose to the crystalline lens and the tasks performed. The records of 73 health workers exposed to ionizing radiation were reviewed. The average annual dose to the crystalline lens, the number of years of exposure, and the presence of radiation-compatible opacities were assessed for all operators. Lenticular opacities were observed in 16.4% of subjects. The presence of alterations was associated with exposure doses below 10 mSv and > 10 years' experience in fluoroscopically guided procedures. Based on our results, protection of the crystalline lens against exposure to ionizing radiation by means of goggles is recommended. In addition, examination of the lens via slit lamp examination is recommended for all operators involved in interventional procedures with the current levels of radiation exposure.

Ionizing radiation-induced cellular senescence promotes tissue fibrosis after radiotherapy. A review

Ionizing radiation-exposure induces a variety of cellular reactions, such as senescence and apoptosis. Senescence is a permanent arrest state of the cell division, which can be beneficial or detrimental for normal tissue via an inflammatory response and senescence-associated secretion phenotype. Damage to healthy cells and their microenvironment is considered as an important source of early and late complications with an increased risk of morbidity in patients after radiotherapy (RT). In addition, the benefit/risk ratio may depend on the radiation technique/dose used for cancer eradication and the irradiated volume of healthy tissues. For radiation-induced fibrosis risk, the knowledge of mechanisms and potential prevention has become a crucial point to determining radiation parameters and patients' intrinsic radiosensitivity. This review summarizes our understanding of ionizing radiation-induced senescent cell in fibrogenesis. This mechanism may provide new insights for therapeutic modalities for better risk/benefit ratios after RT in the new era of personalized treatments.

Effects of ionizing radiation on telomere length and telomerase activity in cultured human lens epithelium cells

PURPOSE

To investigate the effects of ionizing radiation on telomere length and telomerase activity in human lens epithelial cells. There are studies suggesting evidence of telomere length in association with opacity of the lens; however, these studies have been conducted on Canine Lens cells. Our study was designed to understand further the effects of different doses of ionizing radiation on telomere length and telomerase activity in cultured human lens epithelium cells from three Donors.

MATERIALS AND METHODS

For this study, embryonic human lens epithelial (HLE) cells from three donors, obtained commercially were cultured. Telomere length and telomerase activity were measured after each passage until cells stopped growing in culture. This was repeated on irradiated (0.001 Gy, 0.01 Gy, 0.02 Gy, 0.1 Gy, 1 Gy and 2 Gy) cells. DNA damage response using the H2AX and telomere dysfunction foci assays were also examined at 30 mins, 24 hours, 48 hours and 72 hours postirradiation.

RESULTS AND CONCLUSION

We have demonstrated genetic changes in telomere length and oxidative stress, which may be relevant to cataractogenesis. Our study shows that in control cells telomere length increases as passage increases. We have also demonstrated that telomere length increases at higher doses of 1.0 Gy and 2.0 Gy. However, telomerase activity decreases dose dependently and as passages increase. These results are not conclusive and further studies ex vivo measuring lens opacity and telomere length in the model would be beneficial in a bigger cohort, hence confirming a link between telomere length, cataractogenesis and genetic factors.