Does protracted radon exposure play a role in the development of dementia?

Neurotoxic effects of home radon exposure on oscillatory dynamics serving attentional orienting in children and adolescents

Radon is a naturally occurring gas that contributes significantly to radiation in the environment and is the second leading cause of lung cancer globally. Previous studies have shown that other environmental toxins have deleterious effects on brain development, though radon has not been studied as thoroughly in this context. This study examined the impact of home radon exposure on the neural oscillatory activity serving attention reorientation in youths. Fifty-six participants (ages 6-14 years) completed a classic Posner cuing task during magnetoencephalography (MEG), and home radon levels were measured for each participant. Time-frequency spectrograms indicated stronger theta (3-7 Hz, 300-800 ms), alpha (9-13 Hz, 400-900 ms), and beta responses (14-24 Hz, 400-900 ms) during the task relative to baseline. Source reconstruction of each significant oscillatory response was performed, and validity maps were computed by subtracting the task conditions (invalidly cued - validly cued). These validity maps were examined for associations with radon exposure, age, and their interaction in a linear regression design. Children with greater radon exposure showed aberrant oscillatory activity across distributed regions critical for attentional processing and attention reorientation (e.g., dorsolateral prefrontal cortex, and anterior cingulate cortex). Generally, youths with greater radon exposure exhibited a reverse neural validity effect in almost all regions and showed greater overall power relative to peers with lesser radon exposure. We also detected an interactive effect between radon exposure and age where youths with greater radon exposure exhibited divergent developmental trajectories in neural substrates implicated in attentional processing (e.g., bilateral prefrontal cortices, superior temporal gyri, and inferior parietal lobules). These data suggest aberrant, but potentially compensatory neural processing as a function of increasing home radon exposure in areas critical for attention and higher order cognition.

Effects of chronic home radon exposure on cognitive, behavioral, and mental health in developing children and adolescents

Introduction

It is well-established that chronic exposure to environmental toxins can have adverse effects on neuropsychological health, particularly in developing youths. However, home radon, a ubiquitous radiotoxin, has been seldom studied in this context. In the present study, we investigated the degree to which chronic everyday home radon exposure was associated with alterations in transdiagnostic mental health outcomes.

Methods

A total of 59 children and adolescents ages 6- to 14-years-old (M = 10.47 years, SD = 2.58; 28 males) completed the study. Parents completed questionnaires detailing aspects of attention and executive function. We used a principal components analysis to derive three domains of neuropsychological functioning: 1) task-based executive function skills, 2) self-and emotion-regulation abilities, and 3) inhibitory control. Additionally, parents completed a home radon test kit and provided information on how long their child had lived in the tested home. We computed a radon exposure index per person based on the duration of time that the child had lived in the home and their measured home radon concentration. Youths were divided into terciles based on their radon exposure index score. Using a MANCOVA design, we determined whether there were differences in neuropsychological domain scores across the three groups, controlling for age, sex, and socioeconomic status.

Results

There was a significant multivariate effect of radon group on neuropsychological dysfunction (λ = 0.77, F = 2.32, p = 0.038, ηp2 = 0.12). Examination of univariate effects revealed specific increases in self-and emotion-regulation dysfunction among the youths with the greatest degree of chronic home radon exposure (F = 7.21, p = 0.002, ηp2 = 0.21). There were no significant differences by group in the other tested domains.

Discussion

The data suggest potential specificity in the neurotoxic effects of everyday home radon exposure in developing youths, with significant aberrations in self-and emotion-regulation faculties. These findings support the need for better public awareness and public health policy surrounding home radon safety and mitigation strategies.

Repeated radon exposure induced epithelial-mesenchymal transition-like transformation via disruption of p53-dependent mitochondrial function

Backgrouds

As a human carcinogen, radon and its progeny are the second most important risk factor for lung cancer after smoking. The tumor suppressor gene, p53, is reported to play an important role in the maintenance of mitochondrial function. In this work, we investigated the association between p53 and p53-responsive signaling pathways and radon-induced carcinogenesis.

Methods

After repeated radon exposure, the malignant characteristics, cell cycle arrest, cell apoptotic rate, adenosine triphosphate (ATP) content, reactive oxygen species (ROS) level, mitochondrial DNA (mtDNA) copy number as well as indicative biomarkers involved in mitochondrial energy metabolism were evaluated in BEAS-2B cells or BALB-c mouse lung tissue.

Results

Radon exposure induced epithelial-mesenchymal transition (EMT)-like transformation in BEAS-2B cells, as indicated by increased cell proliferation and migration. Additional mitochondrial alterations, including decreased ATP content, increased ROS levels, mtDNA copy numbers, cell apoptosis, and G2/M cell cycle arrest were observed. Radon exposure caused an energy generation shift from aerobic respiration to glycolysis as reflected by increased expression of TIGAR and p53R2 proteins and decreased expression of SCO2 protein in BEAS-2B cells, and increased expression of p53, SCO2 and TIGAR proteins in mouse lung tissue, respectively. The effects of p53 deficiency on the prevention of mitochondrial dysfunction suggested a protective role of p53 in radon-induced malignant-like features in BEAS-2B cells.

Conclusions

Repeated radon exposure induced EMT-like transformation in BEAS-2B cells via disruption of mitochondrial function. Activation of p53 and p53-responsive signaling pathways in BEAS-2B cells and BALB-c mice may confer a protective mechanism for radon-induced lung injury.

Smoking Modifies the Association Between Radon Exposure and Incident Ischemic Stroke: The REGARDS Study

BACKGROUND

Exposure to radon has been linked to lung cancer and other lung diseases. Although biologically plausible, research of residential radon exposure in relation to stroke risk is scarce.

METHODS

Study participants were from the REGARDS (Reasons for Geographic and Racial Differences in Stroke) cohort (n=30 239), which consisted of male and female non-Hispanic Black and White adults aged 45 and older. After excluding participants with baseline stroke and transient ischemic attack, and missing information on exposure and outcome of interest, the final sample size was 26 950. The primary outcome was time to the first ischemic stroke through September 30, 2020. County-level radon measures from Lawrence Berkeley National Laboratory were linked to each participant based on their geocoded residential history. We used Cox proportional hazards regression models with a time-dependent exposure to estimate hazard ratios and 95% CIs for the association.

RESULTS

After controlling for potential confounding factors including demographic, lifestyle, clinical variables, and PM2.5, radon exposure was significantly associated with incident ischemic stroke among never-smokers (hazard ratio, 1.39 [95% CI, 1.01-1.90]) but not ever-smokers. The results were generally consistent in the sensitivity analysis when using radon measures from state/Environmental Protection Agency residential radon survey.

CONCLUSIONS

Findings from this study suggest that the association between residential radon exposure and incidence of ischemic stroke varies by smoking status and may be prominent in never-smokers. Further studies incorporating indoor-radon measures are needed to confirm these findings.

DNA methylome profiling in occupational radon exposure miners using an Illumina Infinium Methylation EPIC BeadChip

Background

A causal relationship between occupational radon exposure in underground miners and lung cancer risk has been demonstrated through large cohort epidemiological studies. However, the mechanisms by which radon exposure causes adverse effects on lung tissue remain unclear. Epigenetic alterations such as DNA methylation may provide new insights into interactions at molecular levels induced by prolonged radon exposure.

Methods

We used the Illumina Infinium Human Methylation 850 K BeadChip to detect and compare genome-wide DNA methylation profiles in peripheral blood samples from underground miners (n = 14) and aboveground workers (n = 9).

Results

The average concentration of radon in underground workplaces was significantly higher than that of aboveground places (1,198 Bq·m-3 vs 58 Bq·m-3, p < 0.001). A total of 191 differentially methylated positions (DMPs) corresponding to 104 hub genes were identified when |Δβ| ≥ 0.1 and p < 0.05, with 107 hypermethylated sites and 84 hypomethylated sites. GO and KEGG analysis revealed that differentially methylated genes between underground miners and aboveground workers were prominently enriched in pathways/networks involved in neurotransmitter regulation, immunomodulatory effects and cell adhesion ability. Furthermore, methylation changes of selected genes FERMT1, ALCAM, HLA-DPA1, PON1 and OR2L13 were validated by pyrosequencing, which may play vital roles in these biological processes induced by radon.

Conclusion

In summary, the DNA methylation pattern of the underground miners exposed to radon was distinct from that of the aboveground workers. Such abnormalities in the genomic DNA methylation profile associated with prolonged radon exposure are worth studying in terms of neuro- and immune-system regulation, as well as cell adhesion ability in the future.

Exposure to Ionizing Radiation and Risk of Dementia: A Systematic Review and Meta-Analysis

The number of people living with dementia is rising globally as life expectancy increases. Dementia is a multifactorial disease. Due to the ubiquity of radiation exposure in medical and occupational settings, the potential association between radiation and dementia, and its subtypes (Alzheimer's and Parkinson's disease), is of particular importance. There has also been an increased interest in studying radiation induced dementia risks in connection with the long-term manned space travel proposed by The National Aeronautics and Space Administration (NASA). Our aim was to systematically review the literature on this topic, and use meta-analysis to generate a summary measure of association, assess publication bias and explore sources of heterogeneity across studies. We identified five types of exposed populations for this review: 1. survivors of atomic bombings in Japan; 2. patients treated with radiation therapy for cancer or other diseases; 3. occupationally exposed workers; 4. those exposed to environmental radiation; and 5. patients exposed to radiation from diagnostic radiation imaging procedures. We included studies that considered incident or mortality outcomes for dementia and its subtypes. Following PRISMA guidelines, we systematically searched the published literature indexed in PubMed between 2001 and 2022. We then abstracted the relevant articles, conducted a risk-of-bias assessment, and fit random effects models using the published risk estimates. After we applied our eligibility criteria, 18 studies were identified for review and retained for meta-analysis. For dementia (all subtypes), the summary relative risk was 1.11 (95% CI: 1.04, 1.18; P = 0.001) comparing individuals receiving 100 mSv of radiation to those with no exposure. The corresponding summary relative risk for Parkinson's disease incidence and mortality was 1.12 (95% CI 1.07, 1.17; P <0.001). Our results provide evidence that exposure to ionizing radiation increases the risk of dementia. However, our findings should be interpreted with caution due to the small number of included studies. Longitudinal studies with improved exposure characterization, incident outcomes, larger sample size, and the ability to adjust for effects of potential confounders are needed to better assess the possible causal link between ionizing radiation and dementia.

Chronic Home Radon Exposure Is Associated with Higher Inflammatory Biomarker Concentrations in Children and Adolescents

Children are particularly vulnerable to the deleterious impacts of toxic environmental exposures, though the effects of some rather ubiquitous toxins have yet to be characterized in youths. One such toxin, radon gas, is known to accumulate to hazardous levels in homes, and has been linked with the incidence of lung cancer in aging adults. However, the degree to which chronic home radon exposure may impact risk for health problems earlier in life is unknown. Herein, we explored the degree to which chronic home radon exposure relates to biomarkers of low-grade inflammation in 68 youths ages 6- to 14 years old residing in an area of the United States prone to high home radon concentrations. Parents completed a home radon test kit, and youths provided a saliva sample to assess concentrations of five biomarkers. Using a multiple regression approach, we found that greater radon exposure was specifically associated with higher levels of C-reactive protein (β = 0.31, p = 0.007) and interleukin-1β (β = 0.33, p = 0.016). The data suggested specificity in associations between chronic home radon exposure and different biomarkers of inflammatory activity and highlight a pathway which may confer risk for future mental and physical health maladies.

Criterion Validity of Radon Test Values Reported by a Commercial Laboratory versus the Environmental Protection Agency

Objective: Radon exposure is a proven cause of lung cancer and is a possible cause of other diseases. Recently, several ecologic studies explored the correlation of county-wide incidence rates for non-lung cancers with residential radon levels, using radon data reported by a commercial laboratory. However, the validity of the commercial radon data, i.e., whether they are an accurate representation of the radon levels in the counties from which they were drawn, is unknown. Methods: We compared county-wide radon data from the commercial laboratory with corresponding measurements from the same counties reported previously by the Environmental Protection Agency (EPA). Matching data were available for four states, Iowa, North Dakota, Texas, and Wisconsin, and were compared by paired t-tests. Criterion validity of the commercial tests, i.e., how well the commercial data predicted the EPA data, was tested using non-parametric methods, Kendall’s tau, Lin’s concordance, and Passing−Bablok regression. Results: The commercial and EPA data pairs from the four states were significantly positively correlated, although the size of the correlations was modest (tau = 0.490, Lin = 0.600). Passing−Bablok regression indicated that the commercial radon values were significantly higher than their EPA pairs and significantly overestimated radon at low levels (<4 pCi/L, p < 0.001). Conclusions: The commercial laboratory data were moderately predictive of EPA radon levels at the county level but were significantly biased upwards at low levels. The disagreement likely has several causes, including selection bias from homes that were tested voluntarily. Ecologic studies that employ radon data obtained from commercial laboratories should be interpreted with caution.