Elevated concentrations of arsenic, lithium and boron in drinking water have already been reported in the Bolivian Andes. Arsenic causes genotoxicity but that caused by lithium and boron is less well known. The aim of the present study was to evaluate associations between arsenic, lithium and boron exposure and genotoxicity, while taking genetic susceptibility into account. Women (n=230) were recruited in ten villages around Lake Poopó. Arsenic exposure was determined as the sum of concentrations of arsenic metabolites (iAs,  MMA, and DMA) in urine. Exposure to lithium and boron was determined based on their concentrations in urine. Genetic susceptibility was determined by GSTM1 and GSTT1 null genotypes and AS3MT rs3740393,. Genotoxicity (DNA strand breaks) was measured peripheral blood by the comet assay. Median arsenic, lithium, and boron concentrations were 60 µg/L, 989 µg/L, and 3929 µg/L, respectively. GSTM1 and GSTT1 null carriers showed more DNA strand breaks than gene carriers (p=0.008, p=0.005). We found no correlation between urinary arsenic and DNA strand breaks (rS=0.03, p=0.64), and only a weak non-significant positive association in the multivariate analysis (β=0.09, p=0.14). Unexpectedly, increasing concentrations of lithium in urine were negatively correlated with DNA strand breaks (rS=-0.24, p=0.0006), and the association persisted in multivariate analysis after adjusting for arsenic (β=-0.22, p=0.003). We found no association between boron and DNA strand breaks. The lack of genotoxic effect of arsenic could be associated with the specific metabolic adaptation to arsenic previously reported in this population. The apparent protective effect of lithium against genotoxicity merits further investigation.

Quantitative risk assessments of chemicals are routinely performed in rodents; however, there is growing recognition that non-animal approaches can be human-relevant alternatives. There is an urgent need to build confidence in non-animal alternatives given the international support to reduce the use of animals in toxicity testing where possible. In order for scientists and risk assessors to prepare for this paradigm shift in toxicity assessment, standardization and consensus on in vitro testing strategies and data interpretation will need to be established. To address this issue, an Expert Working Group (EWG) of the 8th International Workshop on Genotoxicity Testing (IWGT) evaluated the utility of quantitative in vitro genotoxicity concentration-response data for risk assessment. The EWG first evaluated available in vitro methodologies and then examined the variability and maximal response of in vitro tests to estimate biologically relevant values for the critical effect sizes considered adverse or unacceptable. Next, the EWG reviewed the approaches and computational models employed to provide human-relevant dose context to in vitro data. Lastly, the EWG evaluated risk assessment applications for which in vitro data are ready for use and applications where further work is required. The EWG concluded that in vitro genotoxicity concentration-response data can be interpreted in a risk assessment context. However, prior to routine use in regulatory settings, further research will be required to address the remaining uncertainties and limitations.

The understanding of radiation-induced non-cancer effects on the central nervous system (CNS) is essential for the medical setting (e.g., radiotherapy), and occupational exposures, such as nuclear workers or astronauts. Herein, the adverse outcome pathway (AOP) approach was used to consolidate relevant studies in the area of cognitive decline for identification of research gaps, countermeasure development, and for eventual use in risk assessments. AOPs are an analytical construct describing critical events to an adverse outcome (AO) in a simplified form beginning with a molecular initiating event (MIE). An AOP was constructed utilizing mechanistic information to build empirical support for the key event relationships (KERs) between the MIE of deposition of energy to the AO of learning and memory impairment through multiple key events (KEs). The evidence for the AOP was developed through a scoping review of the literature. In this AOP, the MIE is connected to the AO via six KEs of increased oxidative stress, increased deoxyribonucleic acid (DNA) strand breaks, altered signaling pathways, tissue resident cell activation, increased pro-inflammatory mediators and neural remodeling. Deposition of energy directly leads to oxidative stress, increased DNA strand breaks, an increase of pro-inflammatory mediators and tissue resident cell activation. These KEs, which are themselves interconnected, converge through increased DNA strand breaks, altered signaling pathways and pro-inflammatory routes and directly lead to neural remodeling. Broadly, it is envisioned that the outcome of these efforts could be applied to other cognitive disorders and support ongoing work by international authorities to review the system of radiological protection.

Bone loss, commonly seen in osteoporosis, is a condition that entails a progressive decline of bone mineral density and microarchitecture, often seen in post-menopausal women. Bone loss has been widely reported in astronauts exposed to a plethora of stressors and in patients with osteoporosis following radiotherapy for cancer. Studies on mechanisms are well documented but the causal connectivity of events to bone loss development remains incompletely understood. Herein, the adverse outcome pathway (AOP) framework was used to organize data and develop a qualitative AOP beginning from deposition of energy (the molecular initiating event) to bone loss (the adverse outcome). A literature review was conducted to compile and evaluate the state of knowledge based on the modified Bradford Hill criteria. Following review of 1865 studies, an empirically supported AOP was developed, showing the progression to bone loss through many factors affecting the activities of bone-forming osteoblasts and bone-resorbing osteoclasts. The structural, functional, and quantitative basis of each proposed relationship was defined, for inference of causal changes between key events. Current knowledge and its gaps relating to dose-, time- and incidence-concordance across the key events were identified, as well as modulating factors that influence linkages. The new priorities for research informed by the AOP highlight areas for improvement to enable development of a quantitative AOP used to support risk assessment strategies for space travel or cancer radiotherapy.

Cardiovascular diseases (CVDs) are complex, encompassing many types of heart pathophysiologies and associated etiologies. It has been shown that fractionated radiation exposure at high doses (3-17 Gy) to the heart increases the incidence of CVD, as evident from radiotherapy studies. However, the effects of low doses of radiation on the cardiovascular system or the effects from space travel, where radiation and microgravity are important contributors to damage, are not clearly understood. Herein, the adverse outcome pathway (AOP) framework was applied to develop an AOP to vascular remodeling from the deposition of energy. Following the creation of a preliminary pathway with the guidance of field experts and authoritative reviews, a scoping review was conducted which informed final key event (KE) selection and facilitated evaluation Bradford Hill criteria of the key event relationships (KERs). The AOP begins with a molecular initiating event of deposition of energy; ionization events increase oxidative stress, which concurrently causes the release of pro-inflammatory mediators and alters signaling pathways. These KEs alter nitric oxide levels leading to endothelial dysfunction and subsequent vascular remodeling (the adverse outcome). The work identifies evidence needed to strengthen understanding of the causal associations for the KERs, emphasizing where there are knowledge gaps and uncertainties in both qualitative and quantitative understanding. The AOP is anticipated to direct future research to better understand the effects of space on the human body and potentially develop countermeasures to better protect future space travelers.

Cataracts are one of the leading causes of blindness, with 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. AOPs identify a sequence of key events (KEs) connected by key event relationships (KERs) beginning with a molecular initiating event (MIE) to an adverse outcome (AO) of relevance to regulatory decision-making. To construct the cataract AOP, a scoping review methodology was used to filter, screen, and review studies based on the modified Bradford Hill criteria. Eight KEs were moderately supported by empirical evidence across the adjacent (directly-linked) relationships using well-established endpoints. Over half of the evidence collected was informed by biological plausibility. Early KEs of oxidative stress and protein modifications could be the focus of countermeasures. Several identified knowledge gaps and inconsistencies in the AOP can be the basis of future research, most notably directed to experiments at low or moderate doses and dose-rates, relevant to radiation workers and other occupational exposures.