Associations of DNA-repair gene polymorphisms with a genetic susceptibility to ionizing radiation in residents of areas with high radon (222Rn) concentration

An overview on the relationship between residential radon and lung cancer: what we know and future research

We aim to provide an overview of the research available on indoor radon and lung cancer, with a special focus on Spanish investigations. Early studies on underground miners established the link between radon and lung cancer, which was later confirmed for the general population by residential case-control studies. Spain contributed with extensive evidence, including 5 multicentric, hospital-based, case-control studies in the last 30 years, exploring diverse aspects, such as radon's effect on never-smokers, molecular pathways linking radon exposure to lung cancer risk, survival rates, mortality burden, and occupational exposure. There is a well-established causal association between radon with lung cancer. Despite pioneering research performed in our country by the Galician Radon Laboratory, particularly on driver genes, the evidence on the potential molecular pathways which makes radon a carcinogen is sparse. Also, relevant questions on the potential association of radon exposure with the induction of other diseases are still pending.

Micronuclei Formation upon Radioiodine Therapy for Well-Differentiated Thyroid Cancer: The Influence of DNA Repair Genes Variants

Radioiodine therapy with ¹³¹I remains the mainstay of standard treatment for well-differentiated thyroid cancer (DTC). Prognosis is good but concern exists that ¹³¹I-emitted ionizing radiation may induce double-strand breaks in extra-thyroidal tissues, increasing the risk of secondary malignancies. We, therefore, sought to evaluate the induction and 2-year persistence of micronuclei (MN) in lymphocytes from 26 ¹³¹I-treated DTC patients and the potential impact of nine homologous recombination (HR), non-homologous end-joining (NHEJ), and mismatch repair (MMR) polymorphisms on MN levels. MN frequency was determined by the cytokinesis-blocked micronucleus assay while genotyping was performed through pre-designed TaqMan^® Assays or conventional PCR-restriction fragment length polymorphism (RFLP). MN levels increased significantly one month after therapy and remained persistently higher than baseline for 2 years. A marked reduction in lymphocyte proliferation capacity was also apparent 2 years after therapy. MLH1 rs1799977 was associated with MN frequency (absolute or net variation) one month after therapy, in two independent groups. Significant associations were also observed for MSH3 rs26279, MSH4 rs5745325, NBN rs1805794, and tumor histotype. Overall, our results suggest that ¹³¹I therapy may pose a long-term challenge to cells other than thyrocytes and that the individual genetic profile may influence ¹³¹I sensitivity, hence its risk-benefit ratio. Further studies are warranted to confirm the potential utility of these single nucleotide polymorphisms (SNPs) as radiogenomic biomarkers in the personalization of radioiodine therapy.

Radiation-Induced Lung Injury (RILI)

Radiation pneumonitis (RP) and radiation fibrosis (RF) are two dose-limiting toxicities of radiotherapy (RT), especially for lung, and esophageal cancer. It occurs in 5-20% of patients and limits the maximum dose that can be delivered, reducing tumor control probability (TCP) and may lead to dyspnea, lung fibrosis, and impaired quality of life. Both physical and biological factors determine the normal tissue complication probability (NTCP) by Radiotherapy. A better understanding of the pathophysiological sequence of radiation-induced lung injury (RILI) and the intrinsic, environmental and treatment-related factors may aid in the prevention, and better management of radiation-induced lung damage. In this review, we summarize our current understanding of the pathological and molecular consequences of lung exposure to ionizing radiation, and pharmaceutical interventions that may be beneficial in the prevention or curtailment of RILI, and therefore enable a more durable therapeutic tumor response.

Residential exposure to radon and DNA methylation across the lifecourse: an exploratory study in the ALSPAC birth cohort

Background: Radon (and its decay products) is a known human carcinogen and the leading cause of lung cancer in never-smokers and the second in ever-smokers. The carcinogenic mechanism from radiation is a combination of genetic and epigenetic processes, but compared to the genetic mechanisms, epigenetic processes remain understudied in humans. This study aimed to explore associations between residential radon exposure and DNA methylation in the general population. Methods: Potential residential radon exposure for 75-metre area buffers was linked to genome-wide DNA methylation measured in peripheral blood from children and mothers of the Accessible Resource for Integrated Epigenomic Studies subsample of the ALSPAC birth cohort. Associations with DNA methylation were tested at over 450,000 CpG sites at ages 0, 7 and 17 years (children) and antenatally and during middle-age (mothers). Analyses were adjusted for potential residential and lifestyle confounding factors and were determined for participants with complete data (n = 786 to 980). Results: Average potential exposure to radon was associated in an exposure-dependent manner with methylation at cg25422346 in mothers during pregnancy, with no associations at middle age. For children, radon potential exposure was associated in an exposure-dependent manner with methylation of cg16451995 at birth, cg01864468 at age 7, and cg04912984, cg16105117, cg23988964, cg04945076, cg08601898, cg16260355 and cg26056703 in adolescence. Conclusions: Residential radon exposure was associated with DNA methylation in an exposure-dependent manner. Although chance and residual confounding cannot be excluded, the identified associations may show biological mechanisms involved in early biological effects from radon exposure.

Indoor radon exposure increases tumor mutation burden in never-smoker patients with lung adenocarcinoma

OBJECTIVES

Radon, a natural radiation, is the leading environmental cause of lung cancer in never-smokers. However, the radon exposure impact on the mutational landscape and tumor mutation burden (TMB) of lung cancer in never-smokers has not been explored. The aim of this study was to investigate the mutational landscape of lung adenocarcinoma in never-smokers who were exposed to various degrees of residential radon.

MATERIALS AND METHODS

To investigate the effect of indoor radon exposure, we estimated the cumulative exposure to indoor radon in each house of patients with lung cancer with a never-smoking history. Patients with at least 2 year-duration of residence before the diagnosis of lung adenocarcinoma were included. Patients were subgrouped based on the median radon exposure level (48 Bq/m³): radon-high vs. radon-low and targeted sequencing of tumor and matched blood were performed in all patients.

RESULTS

Among 41 patients with lung adenocarcinoma, the TMB was significantly higher in the radon-high group than it was in the radon-low group (mean 4.94 vs. 2.6 mutations/Mb, P = 0.01). The recurrence rates between radon-high and radon-low group did not differ significantly. Mutational signatures of radon-high tumors showed features associated with inactivity of the base excision repair and DNA replication machineries. The analysis of tumor evolutionary trajectories also suggested a series of mutagenesis induced by radon exposure. In addition, radon-high tumors revealed a significant protein-protein interaction of genes involved in DNA damage and repair (P <  0.001).

CONCLUSIONS

Indoor radon exposure increased the TMB in never-smoker patients with lung adenocarcinoma and their mutational signature was associated with defective DNA mismatch repair.

Residential exposure to radon and DNA methylation across the lifecourse: an exploratory study in the ALSPAC birth cohort

Background: Radon (and its decay products) is a known human carcinogen and the leading cause of lung cancer in never-smokers and the second in ever-smokers. The carcinogenic mechanism from radiation is a combination of genetic and epigenetic processes, but compared to the genetic mechanisms, epigenetic processes remain understudied in humans. This study aimed to explore associations between residential radon exposure and DNA methylation in the general population. Methods: Potential residential radon exposure for 75-metre area buffers was linked to genome-wide DNA methylation measured in peripheral blood from children and mothers of the Accessible Resource for Integrated Epigenomic Studies subsample of the ALSPAC birth cohort. Associations with DNA methylation were tested at over 450,000 CpG sites at ages 0, 7 and 17 years (children) and antenatally and during middle-age (mothers). Analyses were adjusted for potential residential and lifestyle confounding factors and were determined for participants with complete data (n = 786-980). Results: Average potential exposure to radon was associated in an exposure-dependent manner with methylation at cg25422346 in mothers during pregnancy, with no associations at middle age. For children, radon potential exposure was associated in an exposure-dependent manner with methylation of cg16451995 at birth, cg01864468 at age 7, and cg04912984, cg16105117, cg23988964, cg04945076, cg08601898, cg16260355 and cg26056703 in adolescence. Conclusions: Residential radon exposure was associated with DNA methylation in an exposure-dependent manner. Although residual confounding cannot be excluded, the identified associations may show biological mechanisms involved in early biological effects from radon exposure.

Novel Genetic Associations Between Lung Cancer and Indoor Radon Exposure

Background

Lung cancer is the leading cause of cancer-related death worldwide, for which smoking is considered as the primary risk factor. The present study was conducted to determine whether genetic alterations induced by radon exposure are associated with the susceptible risk of lung cancer in never smokers.

Methods

To accurately identify mutations within individual tumors, next generation sequencing was conduct for 19 pairs of lung cancer tissue. The associations of germline and somatic variations with radon exposure were visualized using OncoPrint and heatmap graphs. Bioinformatic analysis was performed using various tools.

Results

Alterations in several genes were implicated in lung cancer resulting from exposure to radon indoors, namely those in epidermal growth factor receptor (EGFR), tumor protein p53 (TP53), NK2 homeobox 1 (NKX2.1), phosphatase and tensin homolog (PTEN), chromodomain helicase DNA binding protein 7 (CHD7), discoidin domain receptor tyrosine kinase 2 (DDR2), lysine methyltransferase 2C (MLL3), chromodomain helicase DNA binding protein 5 (CHD5), FAT atypical cadherin 1 (FAT1), and dual specificity phosphatase 27 (putative) (DUSP27).

Conclusions

While these genes might regulate the carcinogenic pathways of radioactivity, further analysis is needed to determine whether the genes are indeed completely responsible for causing lung cancer in never smokers exposed to residential radon.

Children's Exposure to Environmental Contaminants: An Editorial Reflection of Articles in the IJERPH Special Issue Entitled, "Children's Exposure to Environmental Contaminants"

Children are at increased vulnerability to many environmental contaminants compared to adults due to their unique behavior patterns, increased contaminant intake per body weight, and developing biological systems. Depending upon their age, young children may crawl on the floor and may practice increased hand to mouth activity that may increase their dose-intake of specific contaminants that accumulate in dust and other matrices. Children are also smaller in size than adults, resulting in a greater body burden for a given contaminant dose. Because children undergo rapid transitions through particular developmental stages they are also especially vulnerable during certain growth-related time windows. A Special Issue was organized focused on the latest findings in the field of children’s environmental exposure for these reasons. This editorial introduces articles in this Special Issue and emphasizes their main findings in advancing the field. From the many articles submitted to this Special Issue from around the world, 23 were accepted and published. They focus on a variety of research areas such as children’s activity patterns, improved risk assessment methods to estimate exposures, and exposures in various contexts and to various contaminants. The future health of a nation relies on protecting the children from adverse exposures and understanding the etiology of childhood diseases. The field of children’s environmental exposures must consider improved and comprehensive research methods aimed at introducing mitigation strategies locally, nationally, and globally. We are happy to introduce a Special Issue focused on children’s environmental exposure and children’s health and hope that it contributes towards improved health of children.

Gene mutation discovery research of non-smoking lung cancer patients due to indoor radon exposure

Although the incidence and mortality for most cancers such as lung and colon are decreasing in several countries, they are increasing in several developed countries because of an unhealthy western lifestyles including smoking, physical inactivity and consumption of calorie-dense food. The incidences for lung and colon cancers in a few of these countries have already exceeded those in the United States and other western countries. Among them, lung cancer is the main cause of cancer death in worldwide. The cumulative survival rate at five years differs between 13 and 21 % in several countries. Although the most important risk factors are smoking for lung cancer, however, the increased incidence of lung cancer in never smokers(LCINS) is necessary to improve knowledge concerning other risk factors. Environmental factors and genetic susceptibility are also thought to contribute to lung cancer risk. Patients with lung adenocarcinoma who have never smoking frequently contain mutation within tyrosine kinase domain of the epidermal growth factor receptor(EGFR) gene. Also, K-ras mutations are more common in individuals with a history of smoking use and are related with resistance to EFGR-tyrosine kinase inhibitors. Recently, radon(Rn), natural and noble gas, has been recognized as second common reason of lung cancer. In this review, we aim to know whether residential radon is associated with an increased risk for developing lung cancer and regulated by several genetic polymorphisms.