Role of carcinogenesis related mechanisms in cataractogenesis and its implications for ionizing radiation cataractogenesis

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.

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.

Investigating the role of double mutations R12C/P20R, and R12C/R69C on structure, chaperone-like activity, and amyloidogenic properties of human αB-crystallin

α-crystallin is a structurally essential small heat shock protein (sHSP) with a chaperone-like activity which maintains transparency of the lenticular tissues during a period of time that is as long as human life. α-crystallin is a multimeric protein consisting of αA and αB subunits, with 57 % homology. The CRYAB gene on chromosome 11 encodes human αB-crystallin (αB-Cry), which contains 175 amino acid residues. In the current study, the cataractogenic mutations R12C, P20R, R69C, and double mutations R12C/P20R and R12C/P20R were embedded into the human CRYAB gene. Following successful expression in the prokaryotic system and purification, a number of spectroscopic techniques, gel electrophoresis, dynamic light scattering (DLS), and transmission electron microscopy (TEM) were applied to assess the role of these mutations on the structure, amyloidogenicity, and biological function of human αB-Cry. The created mutations caused significant changes in the structure, and oligomeric state of human αB-Cry. These mutations, particularly R12C, R12C/P20R, and R12C/R69C, dramatically enhanced the tendency of this protein for the amyloid fibril formation and reduced its chaperone-like activity. Since double mutations R12C/P20R and R12C/P20R were able to intensely change the protein's structure and chaperone function, it can be suggested that they may play a destructive role in a cumulative manner. Our findings indicated that the simultaneous presence of two pathogenic mutations may have a cumulative destructive impacts on the structure and function of human αB-Cry and this observation is likely related to the disease severity of the mutated proteins.

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.

Radiation safety for pain physicians: principles and recommendations

C-arm fluoroscopy is a useful tool for interventional pain management. However, with the increasing use of C-arm fluoroscopy, the risk of accumulated radiation exposure is a significant concern for pain physicians. Therefore, efforts are needed to reduce radiation exposure. There are three types of radiation exposure sources: (1) the primary X-ray beam, (2) scattered radiation, and (3) leakage from the X-ray tube. The major radiation exposure risk for most medical staff members is scattered radiation, the amount of which is affected by many factors. Pain physicians can reduce their radiation exposure by use of several effective methods, which utilize the following main principles: reducing the exposure time, increasing the distance from the radiation source, and radiation shielding. Some methods reduce not only the pain physician's but also the patient's radiation exposure. Taking images with collimation and minimal use of magnification are ways to reduce the intensity of the primary X-ray beam and the amount of scattered radiation. It is also important to carefully select the C-arm fluoroscopy mode, such as pulsed mode or low-dose mode, for ensuring the physician's and patient's radiation safety. Pain physicians should practice these principles and also be aware of the annual permissible radiation dose as well as checking their radiation exposure. This article aimed to review the literature on radiation safety in relation to C-arm fluoroscopy and provide recommendations to pain physicians during C-arm fluoroscopy-guided interventional pain management.

ATM and TP53 Polymorphisms Modified Susceptibility to Radiation-Induced Lens Opacity in Natural High Background Radiation Area, China

Purpose: A population-based case-control study was conducted in Yangjiang and Enping areas in South China to assess whether the risk of lens opacity induced by natural high background radiation exposure is modulated by polymorphisms of ATM and TP53.Materials and methods: A total of 133 cases who were diagnosed with cortical and posterior subcapsular (PSC) opacity were recruited, and 419 healthy controls were selected through counter-matching in terms of radiation status. Genomic DNA from all the participants was genotyped with the Illumina platform for four single nucleotide polymorphisms of ATM (rs189037, rs373759, and rs4585) and TP53 (rs1042522). The cumulative lens dose received during the entire life was estimated based on annual indoor and outdoor radiation doses and gender- and age-specific occupancy factors. Non-conditional logistic regression was performed to calculate odds ratio (OR) and 95% confidence intervals (95% CI).Results: ATM rs189037 and TP53 rs1042522 were significantly related to cortical and PSC opacity. The risk of opacity was higher when individuals carried the A allele of ATM rs189037 and C allele of TP53 rs1042522, compared with GG genotype. ATM rs189037 A allele carriers (AG/AA) and TP53 rs1042522 C allele carriers (CG/CC) combined with a cumulative lens dose of 100 mGy or higher showed statistically significant opacity risks (OR =5.51, 95% CI: 1.47-20.66; OR =2.69, 95% CI: 1.10-6.60).Conclusion: The A allele of ATM rs189037 and C allele of TP53 rs1042522 increase the risk of lens opacity induced by radiation. These polymorphisms in ATM and TP53 might modify the risk of cortical and PSC opacity induced by chronic and prolonged low-dose radiation.

Non-targeted effects of radiation: a personal perspective on the role of exosomes in an evolving paradigm

PURPOSE

Radiation-induced non-targeted effects (NTE) have implications in a variety of areas relevant to radiation biology. Here we evaluate the various cargo associated with exosomal signalling and how they work synergistically to initiate and propagate the non-targeted effects including Genomic Instability and Bystander Effects.

CONCLUSIONS

Extra cellular vesicles, in particular exosomes, have been shown to carry bystander signals. Exosome cargo may contain nucleic acids, both DNA and RNA, as well as proteins, lipids and metabolites. These cargo molecules have all been considered as potential mediators of NTE. A review of current literature shows mounting evidence of a role for ionizing radiation in modulating both the numbers of exosomes released from affected cells as well as the content of their cargo, and that these exosomes can instigate functional changes in recipient cells. However, there are significant gaps in our understanding, particularly regarding modified exosome cargo after radiation exposure and the functional changes induced in recipient cells.

Radiation-induced DNA Damage and Repair in Lens Epithelial Cells of both Ptch1(+/-) and Ercc2(+/-) Mutated Mice

Epidemiological studies suggest an increased incidence and risk of cataract after low-dose (<2 Gy) ionizing radiation exposures. However, the biological mechanism(s) of this process are not fully understood. DNA damage and repair are thought to have a contributing role in radiation-induced cataractogenesis. Recently we have reported an inverse dose-rate effect, as well as the low-dose response, of DNA damage and repair in lens epithelial cells (LECs). Here, we present further initial findings from two mutated strains (Ercc2+/- and Ptch1+/-) of mice, both reportedly susceptible to radiation-induced cataract, and their DNA damage and repair response to low-dose and low-dose-rate gamma rays. Our results support the hypothesis that the lens epithelium responds differently to radiation than other tissues, with reported radiation susceptibility to DNA damage not necessarily translating to the LECs. Genetic predisposition and strain(s) of mice have a significant role in radiation-induced cataract susceptibility.

Effects of neutron radiation on Nrf2-regulated antioxidant defense systems in rat lens

Accumulating evidence suggests that ionizing radiation (IR)-induced cataract may be associated with oxidative stress. Nuclear factor erythroid 2-related factor 2 (Nrf2) serves as a master regulator of the antioxidant defense system against oxidative stress. The present study aimed to investigate the effects of different doses of neutron radiation on the Nrf2-reegulated antioxidant defense system in rat lens and assess the status of oxidative stress. A total of 24 SD rats were randomly divided into the following four groups: i) Control group; iis) 0.4 Sv group; iii) 1.2 Sv group; and iv) 3.6 Sv group. The rats were sacrificed 7 days after radiation and lenses were dissected for histological, biochemical (malondialdehyde, glutathione and superoxide dismutase) and western blot (Nrf2, glutamate-cysteine ligase catalytic subunit and heme oxygenase 1) analyses. The morphological features of the lenses remained intact in the 0.4 Sv, 1.2 Sv and control groups, whilst the lenses in the 3.6 Sv group exhibited injuries. Results from the TUNEL assay demonstrated apparent apoptosis in lens epithelial cells following 3.6 Sv neutron radiation whereas sparse apoptosis was observed following 0.4 Sv and 1.2 Sv radiation. Malondialdehyde levels were reduced in the 0.4 Sv and 1.2 Sv groups but increased in the 3.6 Sv group, compared with those in the control group. Conversely, glutathione expression and the activity of superoxide dismutase were higher in the 0.4 Sv and 1.2 Sv groups, but lower in the 3.6 Sv group, compared with those in the control group. In addition, the total and nuclear protein levels of Nrf2 were increased following neutron radiation compared with those in the control group, though the Nrf2 protein levels decreased in the 3.6 Sv group compared with those in the 1.2 Sv group. The levels of glutamate-cysteine ligase catalytic subunit and heme oxygenase 1, downstream antioxidant enzymes of Nrf2, demonstrated the same profile as that in Nrf2. Taken together, the results of the present study suggest that neutron radiation affects Nrf2-regulated antioxidant systems in a two-stage process. Namely, the induction phase for low-dose radiation and regression phase for high-dose radiation. Therefore, it was hypothesized that activation and enhancement of the Nrf2-regulated antioxidant system may be useful in preventing or delaying IR-induced cataract, which may be extended even for other diseases associated with oxidative stress.

Radiation-induced lens opacities: Epidemiological, clinical and experimental evidence, methodological issues, research gaps and strategy

In 2011, the International Commission on Radiological Protection (ICRP) recommended reducing the occupational equivalent dose limit for the lens of the eye from 150 mSv/year to 20 mSv/year, averaged over five years, with no single year exceeding 50 mSv. With this recommendation, several important assumptions were made, such as lack of dose rate effect, classification of cataracts as a tissue reaction with a dose threshold at 0.5 Gy, and progression of minor opacities into vision-impairing cataracts. However, although new dose thresholds and occupational dose limits have been set for radiation-induced cataract, ICRP clearly states that the recommendations are chiefly based on epidemiological evidence because there are a very small number of studies that provide explicit biological and mechanistic evidence at doses under 2 Gy. Since the release of the 2011 ICRP statement, the Multidisciplinary European Low Dose Initiative (MELODI) supported in April 2019 a scientific workshop that aimed to review epidemiological, clinical and biological evidence for radiation-induced cataracts. The purpose of this article is to present and discuss recent related epidemiological and clinical studies, ophthalmic examination techniques, biological and mechanistic knowledge, and to identify research gaps, towards the implementation of a research strategy for future studies on radiation-induced lens opacities. The authors recommend particularly to study the effect of ionizing radiation on the lens in the context of the wider, systemic effects, including in the retina, brain and other organs, and as such cataract is recommended to be studied as part of larger scale programs focused on multiple radiation health effects.

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.

Radiation in the Atmosphere—A Hazard to Aviation Safety?

Exposure of aircrew to cosmic radiation has been recognized as an occupational health risk for several decades. Based on the recommendations by the International Commission on Radiological Protection (ICRP), many countries and their aviation authorities, respectively have either stipulated legal radiation protection regulations, e.g., in the European Union or issued corresponding advisory circulars, e.g., in the United States of America. Additional sources of ionizing and non-ionizing radiation, e.g., due to weather phenomena have been identified and discussed in the scientific literature in recent years. This article gives an overview of the different generally recognized sources due to weather as well as space weather phenomena that contribute to radiation exposure in the atmosphere and the associated radiation effects that might pose a risk to aviation safety at large, including effects on human health and avionics. Furthermore, potential mitigation measures for several radiation sources and the prerequisites for their use are discussed.

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.

Environmental and industrial developments in radiation cataractogenesis

Purpose: This review discusses recent developments in our understanding of biological and physiological mechanisms underlying radiation cataractogenesis. The areas discussed include effects of low-dose exposures to the lens including potential relevance of non-targeted effects, the development of new personal-protective equipment (PPE) and standards in clinical and nuclear settings motivated by the updated ICRP recommendations to mitigate exposures to the lens of the eye. The review also looks at evidence from the field linking cataracts in birds and mammals to low dose exposures.Conclusions: The review suggests that there is evidence that cataractogenesis is not a tissue reaction (deterministic effect) but rather is a low dose effect which shows a saturable dose response relationship similar to that seen for non-targeted effects in general. The review concludes that new research is needed to determine the dose response relationship in environmental studies where field data are contradictory and lab studies confined to rodent models for human exposure studies.

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.

An RNA-seq-Based Expression Profiling of Radiation-Induced Esophageal Injury in a Rat Model

Radiation-induced acute injury is the main reason for the suspension of radiotherapy and unsuccessful treatment of cancer. It is of great importance to understand the molecular mechanism of radiation-induced esophageal injury. We used RNA-seq data from normal esophageal tissue and irradiated esophageal tissues and applied computational approaches to identify and characterize differentially expressed genes and detected 40 059 messenger RNAs (mRNAs) previously annotated and 717 novel long noncoding RNAs (lncRNAs). There were 14 upregulated and 32 downregulated lncRNAs among the differentially expressed lncRNA group. Their target genes were involved in the mRNA surveillance pathway, pathological immune responses, and cellular homeostasis. Additionally, we found 853 differentially expressed mRNAs, and there were 384 upregulated and 469 downregulated mRNAs. Notably, we found that the differentially expressed mRNAs were enriched for steroid biosynthesis, the tumor necrosis factor signaling pathway, focal adhesion, pathways in cancer, extracellular matrix-receptor interaction, and so on. The response of normal esophageal tissues to ionizing radiation is multifarious. The radiation-induced cell damage response by multiple pathways followed by pathological immune responses activated. Studies on the dynamic network of molecules involved in radiation-induced esophageal injury are under way to clarify the regulatory mechanisms and identify the candidate targets.

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.

Occupation-associated health hazards for the gastroenterologist/endoscopist

Advances in the field of endoscopy have allowed gastroenterologists to obtain detailed imaging of anatomical structures and to treat gastrointestinal diseases with endoscopic therapies. However, these technological developments have exposed endoscopists and staff to hazards such as musculoskeletal injuries, exposure to infectious agents, and ionizing radiation. We aimed to review the occupational hazards for the gastroenterologist and endoscopist. Using PubMed, Medline, Medscape, and Google Scholar, we identified peer-reviewed articles with the keywords “occupational hazards,” “health hazards,” “occupational health hazards,” “endoscopy,” “gastroenterologist,” “infectious agents,” “musculoskeletal injuries,” and “radiation.” Strategies for reducing exposure to infectious agents, radiation, and the risk of musculoskeletal injuries related to gastroenterology include compliance with established standard measures, the use of thyroid shields and radioprotective eyewear, and ergonomic practices. We conclude that educating endoscopic personnel and trainees in these practices, in addition to further research in these areas, will likely lead to the development of more efficient and user-friendly workspaces that are safer for patients and personnel.

Radiation Exposure and Health Risks for Orthopaedic Surgeons

Orthopaedic surgeons are routinely exposed to intraoperative radiation and, therefore, follow the principle of "as low as reasonably achievable" with regard to occupational safety. However, standardized education on the long-term health effects of radiation and the basis for current radiation exposure limits is limited in the field of orthopaedics. Much of orthopaedic surgeons' understanding of radiation exposure limits is extrapolated from studies of survivors of the atomic bombings in Hiroshima and Nagasaki, Japan. Epidemiologic studies on cancer risk in surgeons and interventional proceduralists and dosimetry studies on true radiation exposure during trauma and spine surgery recently have been conducted. Orthopaedic surgeons should understand the basics and basis of radiation exposure limits, be familiar with the current literature on the incidence of solid tumors and cataracts in orthopaedic surgeons, and understand the evidence behind current intraoperative fluoroscopy safety recommendations.

Deterministic Effects to the Lens of the Eye Following Ionizing Radiation Exposure: is There Evidence to Support a Reduction in Threshold Dose?

Ionizing radiation exposure to the lens of the eye is a known cause of cataractogenesis. Historically, it was believed that the acute threshold dose for cataract formation was 5 Sv, and annual dose limits to the lens were set at 150 mSv. Recently, however, the International Commission on Radiological Protection has reduced their threshold dose estimate for deterministic effects to 0.5 Gy and is now recommending an occupational limit of 20 mSv per year on average. A number of organizations have questioned whether this new threshold and dose limit are justified based on the limited reliable data concerning radiation-induced cataracts. This review summarizes all of the published human epidemiological data on ionizing radiation exposure to the lens of the eye in order to evaluate the proposed threshold. Data from a variety of exposure cohorts are reviewed, including atomic bomb survivors, Chernobyl liquidators, medical workers, and radiotherapy patients. Overall, there is not conclusive evidence that the threshold dose for cataract formation should be reduced to 0.5 Gy. Many of the studies reviewed here are challenging to incorporate into an overall risk model due to inconsistencies with dosimetry, sample size, and scoring metrics. Additionally, risk levels in the studied cohorts may not relate to occupational scenarios due to differences in dose rate, radiation quality, age at exposure and latency period. New studies should be designed specifically focused on occupational exposures, with reliable dosimetry and grading methods for lens opacities, to determine an appropriate level for dose threshold and exposure limit.

Current situations and discussions in Japan in relation to the new occupational equivalent dose limit for the lens of the eye

Since the International Commission on Radiological Protection recommended reducing the occupational equivalent dose limit for the lens of the eye in 2011, there have been extensive discussions in various countries. This paper reviews the current situation in radiation protection of the ocular lens and the discussions on the potential impact of the new lens dose limit in Japan. Topics include historical changes to the lens dose limit, the current situation with occupational lens exposures (e.g., in medical workers, nuclear workers, and Fukushima nuclear power plant workers) and measurements, and the current status of biological studies and epidemiological studies on radiation cataracts. Our focus is on the situation in Japan, but we believe such information sharing will be useful in many other countries.

Ionizing radiation response of primary normal human lens epithelial cells

Whilst the cataractogenic potential of ionizing radiation has been known for over the past 120 years, little is known about radiation responses of lens cells. Our previous work was the first to evaluate the radiosensitivity of lens cells with the clonogenic assay, documenting that the survival of HLEC1 human lens epithelial cells is comparable to that of WI-38 human lung fibroblasts. Moreover, HLEC1 cells were found to contain subsets where irradiation stimulates proliferation or facilitates formation of abortive colonies with fewer cells than human fibroblasts. This study aims to gain insights into these mechanisms. Irradiation of HLEC1 cells with 10% survival dose caused a growth delay but did not reduce viability. HLEC1 cells at high cumulative population doubling level were more susceptible to radiogenic premature senescence than WI-38 cells. Concerning p53 binding protein 1 (53BP1) foci, HLEC1 cells harbored less spontaneous foci but more radiogenic foci than in WI-38 cells, and the focus number returned to spontaneous levels within 48 h postirradiation both in HLEC1 and WI-38. The chemical inhibition of DNA repair kinases ataxia telangiectasia mutated, DNA-dependent protein kinase or both delayed and attenuated the appearance and disappearance of radiogenic 53BP1 foci, increased radiogenic premature senescence and enhanced clonogenic inactivation. The DNA microarray analysis suggested both radiogenic stimulation and inhibition of cell proliferation. Treatment with conditioned medium from irradiated cells did not change growth and the plating efficiency of nonirradiated cells. These results partially explain mechanisms of our previous observations, such that unrepaired or incompletely repaired DNA damage causes a growth delay in a subset of HLEC1 cells without changing viability through induction of premature senescence, thereby leading to clonogenic inactivation, but that growth is stimulated in another subset via as yet unidentified mechanisms, warranting further studies.

Risk of Cataract Incidence in a Cohort of Mayak PA Workers following Chronic Occupational Radiation Exposure

This is the first study of cataract incidence in a cohort of Mayak Production Association workers first employed at one of the main facilities in 1948-1982 and followed up till the end of 2008 (22,377 workers). Principal advantages of the study are the large size of the cohort, long-term follow-up and sufficient statistical power, available results of annual eye examinations over the entire follow-up period and detailed information on non-radiation confounders. Individual measured doses from external γ-rays and neutrons used in the analyses were provided by the Mayak Worker Dosimetry System 2008 (MWDS-2008). Relative risk (RR) and excess relative risk (ERR) per unit dose (Gy) were calculated based on maximum likelihood using the AMFIT module of the EPICURE software. The RR of cataract incidence was found to be the highest in workers exposed at doses above 2.0 Gy. A significant linear association of cataract incidence with cumulative dose from external γ-rays was found with ERR/Gy equal to 0.28 (95% confidence intervals: 0.20, 0.37). The results obtained varied slightly with inclusion of additional adjustments for non-radiation factors (smoking index, hypertension, glaucoma and body mass index). Adjusting for the dose from neutrons gave a considerable increase in ERR/Gy for cataract incidence.

Individual response to ionizing radiation

The human response to ionizing radiation (IR) varies among individuals. The first evidence of the individual response to IR was reported in the beginning of the 20th century. Considering nearly one century of observations, we here propose three aspects of individual IR response: radiosensitivity for early or late adverse tissue events after radiotherapy on normal tissues (non-cancer effects attributable to cell death); radiosusceptibility for IR-induced cancers; and radiodegeneration for non-cancer effects that are often attributable to mechanisms other than cell death (e.g., cataracts and circulatory disease). All the molecular and cellular mechanisms behind IR-induced individual effects are not fully elucidated. However, some specific assays may help their quantification according to the dose and to the genetic status. Accumulated data on individual factors have suggested that the individual IR response cannot be ignored and raises some clinical and societal issues. The individual IR response therefore needs to be taken into account to better evaluate the risks related to IR exposure.

A pilot exome-wide association study of age-related cataract in Koreans

Age-related cataract (ARC) is the most common cause of visual impairment and blindness worldwide. A previous study reported that genetic factors could explain approximately 50% of the heritability of cataract. However, a genetic predisposition to ARC and the contributing factors have not yet been elucidated in the Korean population. In this study, we assessed the influence of genetic polymorphisms on the risk of ARC in Koreans, including 156 cataract cases and 138 healthy adults. We conducted an exome-wide association study using Illumina Human Exome-12v1.2 platform to screen 244,770 single nucleotide polymorphisms (SNPs). No SNPs reached exome-wide significance level of association (P < 1×10⁻⁶). B3GNT4 rs7136356 showed the most significant association with ARC (P = 6.54×10⁻⁵). Two loci (MUC16 and P2RY2) among the top 20 ARC-associated SNPs were recognized as probably linked to cataractogenesis. Functions of these genes were potentially related to regulating dehydration or homeostasis of the eyes, and showed a potential association with dry eye disease. This finding suggests that mucin- and dry eye disease-related genes may play a significant role in cataractogenesis. Our study provides insight into the genetic predisposition of ARC in Koreans. Additional studies with larger sample sizes are required to confirm the results of this study.

Study of Association between Pre-Senile Cataracts and the Polymorphisms rs2228000 in XPC and rs1042522 in p53 in Spanish Population

Purpose

To determine if the presence of certain polymorphisms in the DNA repair gene XPC and the apoptosis inductor gene p53 is associated with pre-senile cataract development.

Methods

We have performed a retrospective study over three groups of patients. The group with pre-senile cataract formed by 72 patients younger than 55 with cataract surgery. The group with senile cataract formed by 101 patients older than 55 with cataract surgery. The group without cataract was formed by 42 subjects older than 55 without lens opacities. We analyzed the presence of SNP rs2228000 from XPC and rs1042522 from p53; and the relationship between risk factors such as smoking, alcohol intake, hypertension or diabetes.

Results

The comparison of the genotype distribution in XPC, within the different groups, did not show any statistically significant association in any of our analysis (p>0,05). The comparison of the genotype distribution in p53 within the different groups did not show any statistically significant association (p>0,05); except for the comparison between the pre-senile cataract group and the group with senile cataract where the genotype Pro/Pro (C/C) in the recessive inheritance model showed a higher risk for developing pre-senile cataract (p = 0,031; OR = 1.04–15.97). This association decreased when we performed the analysis adjusting by the studied risk factors (p = 0.056).

Conclusions

Allelic variants in the gene XPC are not associated with an increased risk for developing pre-senile cataract. The presence of the genotype Pro/Pro in p53 might be associated with a major risk for developing pre-senile cataract.

Synthesis of phenolic amides and evaluation of their antioxidant and anti-inflammatory activity in vitro and in vivo

15 phenolic amides (PAs) have been synthesized and examinedin vitrousing four tests: (1) prevention of Cu²⁺-induced human low-density lipoprotein oxidation, (2) scavenging of stable radicals, (3) anti-inflammatory activity, and (4) scavenging of superoxide radicals.