A consistent two-mutation model of lung cancer for different data sets of radon-exposed rats

Investigation of Radon Sources, Health Hazard and Risks assessment for children using analytical and geospatial techniques in District Bannu (Pakistan)

PURPOSE

Radon (Rn) is a radioactive, odorless, and colorless gas which has a half-life of 3.83 days. One of the main sources of Rn which is directly consumed by the population is Groundwater (Tube well, Bore well, Hand pump). Rn gas is found naturally in rock, soil and water and can be considered as main health risk factor in terms of lung cancer, stomach diseases, leukemia and childhood cancer. The objective of this study was to determine the concentration of Rn in the drinking water sources, appraisal of health risk for children in District Bannu, Pakistan.

MATERIAL AND METHOD

Total of 98 drinking water samples were analyzed by using RAD-7 detector. The experimental data was statistically analyzed by using Pearson's test. The experimental and epidemiological data of the study area are shown on map using ArcGIS version 10.5.

RESULTS

The analytical results show that Rn in drinking water was found varying from 10.1 Bq/l to 53.1 Bq/l with the average highest and lowest depth of 60 ft to 550 ft respectively. Pearson's test was used to show the concentration of Rn verses the depth of the water sources so +1 positive linear correlation was observed among the depth of water sources and the concentration of Rn. Out of 98 drinking water samples 40 sample were above the maximum contaminant level of 11.1 Bq/l (MCL) set by WHO, 2002. The effective doses (AED and DE_ing) for children ranges from 0.00001 to 3.792 mSv/y which exceeds the Permissible Exposure Limit (PEL) of Rn (0.1mSv/y) in 30 drinking water samples . On the basis of analytical results Rn high concentration areas are shown on the map using IDW model of interpolation and health risks were shown in areas where Rn content was above the maximum contaminant level. High correlations of diseases related to Rn were observed amongst the residence of the study area. Gastrointestinal diseases, brain tumor, lung cancer and kidney diseases were observed among the children of the study area.

CONCLUSION

From the overall analysis it was observed that high Rn concentration in drinking water may cause substantial health damage in children after long term exposure.

Oxidative damage in various tissues of rats exposed to radon

Oxidative damage can be induced by many environmental stressors. 8-Hydroxydeoxyguanosine (8-OHdG) has been used as a biomarker of oxidative DNA damage in both in vitro and in vivo studies. In the present study, Wistar rats were exposed to radon gas at a concentration of 100,000Bq/m(3) for 12 h/d for 30, 60, and 120 d, equivalent to cumulative doses of 60, 120, and 240 working level months (WLM), respectively. Changes in levels of 8-OHdG, reactive oxygen species (ROS), and total antioxidant (T-AOC), as well as expressions of some DNA repair enzymes such as 8-oxoguanine DNA glycosylase (OGG1) and MutT homolog 1 (oxidized purine nucleoside triphosphatase, MTH1), were determined in rat urine, peripheral blood lymphocytes, and lung after exposure to radon. The results revealed an increase in 8-OHdG and ROS levels, a decrease in T-AOC levels, and reduced OGG1 and MTH1 expression levels. The elevated amount of 8-OHdG in urine or lymphocytes was positively correlated with the cumulative exposure dose, whereas OGG1 and MHT1 expression levels in lung were inversely correlated with cumulative exposure dose. These findings indicate that oxidative damage induced by radon may be involved in radon-induced carcinogenesis.

Modelling lung cancer due to radon and smoking in WISMUT miners: preliminary results

A mechanistic two-stage carcinogenesis model has been applied to model lung-cancer mortality in the largest uranium-miner cohort available. Models with and without smoking action both fit the data well. As smoking information is largely missing from the cohort data, a method has been devised to project this information from a case-control study onto the cohort. Model calculations using 256 projections show that the method works well. Preliminary results show that if an explicit smoking action is absent in the model, this is compensated by the values of the baseline parameters. This indicates that in earlier studies performed without smoking information, the results obtained for the radiation parameters are still valid. More importantly, the inclusion of smoking-related parameters shows that these mainly influence the later stages of lung-cancer development.

Breast cancer risk from different mammography screening practices

Mammography screening is an accepted procedure for early detection of breast tumors among asymptomatic women. Since this procedure involves the use of X rays, it is itself potentially carcinogenic. Although there is general consensus about the benefit of screening for older women, screening practices differ between countries. In this paper radiation risks for these different practices are estimated using a new approach. We model breast cancer induction by ionizing radiation in a cohort of patients exposed to frequent X-ray examinations. The biologically based, mechanistic model provides a better foundation for the extrapolation of risks to different mammography screening practices than empirical models do. The model predicts that the excess relative risk (ERR) doubles when screening starts at age 40 instead of 50 and that a continuation of screening at ages 75 and higher carries little extra risk. The number of induced fatal breast cancers is estimated to be considerably lower than derived from epidemiological studies and from internationally accepted radiation protection risks. The present findings, if used in a risk-benefit analysis for mammography screening, would be more favorable to screening than estimates currently recommended for radiation protection. This has implications for the screening ages that are currently being reconsidered in several countries.

Artificial neural network modeling of apoptosis in gammairradiated human lymphocytes

PURPOSE

To develop an artificial neural network (ANN) model of apoptotic response in gamma irradiated human lymphocytes. To assess the feasibility of training ANN radiobiological models using data collected with flow cytometry.

MATERIALS AND METHODS

Irradiated isolated human lymphocytes were labelled with Annexin V-Fluorescein Isothiocyanate (FITC) and 7-Amino-Actinomycin D (7AAD) then analysed using flow cytometry. Twenty-four dose responses per donor from 14 donors were collected from a flow cytometer and used in model development as the training and cross-validation datasets. The general ANN model architecture was a multi-layer perceptron using the mean squared error of a cross validation dataset as the objective function. The ANN model was optimized by varying the number of hidden layers and the number of processing elements per layer. The optimized model constituted of three hidden layers with 80, 40, and 10 hidden layers in the first, second, and third layers respectively.

RESULTS

The optimized model was used to simulate dose responses at the training doses of 0, 2, 4 and 8 Gray. A strong agreement between the model and measured dose responses was observed. The model was also used to simulate a dose response at 0.1 Gray and results were compared to the measured dose response from a donor not used in model development. Again, strong agreement between the model and the observed dose response was found.

CONCLUSIONS

This study shows that artificial neural networks can be trained to provide high resolution, high accuracy models of multivariate radiobiological data collected by flow cytometry.

Radon-induced proteomic profile of lung tissue in rats

The aim of this study was to investigate the differential expression of proteins in lung of rats following long-term exposure to radon. The total proteins of lung tissue from Wistar rats exposed to radon for cumulative doses up to 100, 200, or 400 WLM (working level months) were isolated by two-dimensional electrophoresis (2-DE) and analyzed with ImageMaster 2D Platinum software. Comparison of the 2-DE images between the control and radon-exposed groups resulted in 14 upregulated and 9 downregulated protein spots, of which 15 were identified by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) or matrix-assisted laser desorption/ionization time-of-flight/time-of-flight mass spectrometry (MALDI-TOF/TOF-MS). The simultaneous up-expressions of RAGE and S100A6 indicated that both proteins might be applied as biomarkers for lung injury induced by long-term radon exposure.

Examining the relationship between lung cancer and radon in small areas across Scotland

Numerous studies have suggested that long-term exposure to radon gas may be an important cause of lung cancer, yet the precise effects are still not fully understood, especially in residential settings. This paper considers whether there is a relationship between the distribution of naturally occurring radon gas and lung cancer incidence in Scotland, for the period 1988-1991. We use regression analysis to test whether exposure to radon was a significant cause of lung cancer in Scotland, once smoking and other possible confounding factors were controlled for. The results demonstrate that for the population aged over 54, there was no significant relationship between radon exposure and lung cancer incidence. However, for those aged less than 55, lung cancer rates were significantly higher in places expected to have the highest levels of radon. These results suggest that more research is needed into the relationship between exposure to naturally occurring radon gas and lung cancer in Scotland, particularly among younger age groups.

Two-mutation models for bone cancer due to radium, strontium and plutonium

Data from beagle experiments and radium dial painters were used to derive two-mutation carcinogenesis models for bone cancer induced by the bone-seeking radionuclides radium, strontium and plutonium. For all data, the model fits indicate that at low doses both mutation rates depend linearly and equally strongly on dose rate. For the high-LET alpha-particle emitters, a cell killing term reduces the second mutation rate at high dose rates. In all cases, the combined effect of both mutation rates is a linear-quadratic dose-effect relationship for cancer at low doses. This behavior may lead to experimental data that could be mistaken as showing a threshold below which no cancers are induced. Derived parameters such as toxicity ratios and tumor growth times compare well with values reported in the literature. Furthermore, results for plutonium indicate that rapid burial of the nuclide in the growing bones of juvenile beagles leads to a significant reduction of its toxicity, as was suggested previously. The results for radium in beagles compare well with those for humans and suggest that the models derived for strontium and plutonium in beagles may be translated to humans. The significant model parameters for the accurate animal data could then also be used to fit human epidemiological data.

Lung tumour risk in radon-exposed rats from different experiments: comparative analysis with biologically based models

Data sets of radon-exposed male rats from Wistar and Sprague-Dawley strains have been investigated with two different versions of the two-step clonal expansion (TSCE) model of carcinogenesis. These so-called initiation-promotion (IP) and initiation-transformation (IT) models are named after the cell-based processes that are assumed to be induced by radiation. The analysis was done with all malignant lung tumours taken to be incidental and with fatal tumours alone. For all tumours treated as incidental, both models could explain the tumour incidence data equally well. Owing to its better fit, only the IP model was applied in the analysis of fatal tumours that carry additional information on the time when they cause death. A statistical test rejected the hypothesis that a joint cohort of Wistar and Sprague-Dawley rats can be described with the same set of model parameters. Thus, the risk analysis has been carried out for the Wistar rats and the Sprague-Dawley rats separately and has been restricted to fatal tumours alone because of their similar effect in humans. Using a refined technique of age-adjustment, the lifetime excess absolute risk has been standardised with the survival function from competing risks in the control population. The age-adjusted excess risks for both strains of rats were of similar size, for animals with first exposure later in life they decreased markedly. For high cumulative exposure the excess risk increased with longer exposure duration, for low cumulative exposure it showed the opposite trend. In addition, high cumulative exposure exerted lethal effects other than lung cancer on the rats.

Radon-induced lung cancer in French and Czech miner cohorts described with a two-mutation cancer model

A two-mutation carcinogenesis model with clonal expansion of pre-malignant cells is used to describe lung cancer mortality data from studies on French and Czech miners with relatively low exposures to radon. The aim was to derive radon-induced lung cancer risk estimates applicable to different populations using a model description consistent with both cellular dose-response relationships, and previous model analyses of animal and human epidemiological data. The significantly different baseline lung cancer risks for the two cohorts that include the effects from the unknown smoking habits, are described with different background model parameters. A uniform description of the effect of radon for both miner cohorts is achieved by applying the same multiplicative effect for radon on the background mutation rates in the model. Incorporating the effects of decreased cellular proliferation at very advanced age improves the description of the baseline lung cancer risk, but does not lead to significant changes in the estimated radiation parameters. Here, a multi-stage model demonstrates the possibility of transferring radon-induced lung cancer risks across populations. The inherent age-time dose-rate relationships in the model allow for extrapolation to lifelong exposures to residential radon concentrations. The resulting cumulated (lifetime) risks from continuous exposure to low-level radon concentrations were found to agree with the results of the BEIR VI models.

Risk of fatal versus incidental lung cancer in radon-exposed rats: A reanalysis of French data

This review summarizes data on lung cancer risk from radon experimental studies performed by our group in France with emphasis on the most recent findings and analyses on the influence of dose-rate and that of fatal versus incidental tumors. A dose-effect relationship was established in rats, which was very similar for medium and high cumulative exposures, to that observed in uranium miners. At low cumulative exposures in the range of 0.18 Jhm-3 (50 WLM) to 0.36 Jhm-3 (100 WLM), the proportion of fatal lung cancer is about 80% that of total lung cancers. In contrast, at cumulative exposures of 0.72 Jhm-3 (200 WLM) and higher, the proportion of fatal lung cancer is about half that of total lung cancers. The parameters that influence fatal lung cancer risk are cumulative exposure, potential alpha energy concentration (PAEC), exposure rate, and protraction of exposure. At high cumulative exposures up to 10.8 Jhm-3 (3,000 WLM), an inverse dose-rate effect similar to that observed in uranium miners was also found in rats. The inverse exposure- rate effect was observed mainly at the highest exposure-rates. In contrast, our recent results indicate that at relatively low cumulative exposures of 0.36 Jhm-3 (100 WLM), comparable to lifetime exposures in high-radon houses or current underground mining exposures, the risk of lung cancer in rats decreases with decreasing PAEC, i.e., exposure rate. These data suggest that the induction of lung cancer results from a complex inter- play between cumulative exposure and exposure rate, with an optimal combination of these two parameters that results in a maximum risk of lung cancer induction. They support the hypothesis that, at low doses, the risk of lung cancer is governed by the rate at which the dose is delivered, and not by the total cumulative dose alone. These data are also consistent with those of underground uranium miners showing an inverse dose-rate effect at high cumulative exposures, but an attenuation of this effect at cumulative exposures lower than 0.18 Jhm-3 (50 WLM). They support both an inverse dose-rate effect at high cumulative exposures, as well as its attenuation or disappearance at low cumulative exposures.

A reanalysis of liver cancer incidence in Danish patients administered thorotrast using a two-mutation carcinogenesis model

In recent years, a two-mutation carcinogenesis (TMC) model has been used to analyze epidemiological data and estimate the radiation risks at low doses for the organs affected. Here the TMC model was used to reanalyze the liver cancer incidence in the Danish population in general and in patients administered Thorotrast, and to estimate the radiation risks for the liver. The data for 807 patients for whom sufficient data on the injected volumes of Thorotrast were available were used in this reanalysis. These data were combined with data on liver cancer incidence in the Danish population as the baseline or background incidence. Because males and females show different baseline liver cancer incidences, separate fits were made for males and females. The fits showed that the radiation effect could be ascribed entirely to the radiation dependence of the first mutation rate of the TMC model, which was higher for females than for males. The second mutation rate was not significantly dependent on dose. The radiation risks for the liver were calculated on the basis of the model parameters. These risks for lifetime exposures are about the same for males and females and are between a factor of 2 and 10 higher than current estimates. The discrepancy between the model results and previous risk estimates probably arises because the model calculations give more complete lifetime radiation risk estimates. For short-term exposures of the liver to ionizing radiation, the maximum radiation-induced excess liver cancer risk per unit dose applies to exposures at the age of about 10; exposures at ages above 35 have a radiation effect of less than approximately 15% of this maximum.

Influence of exposure rate on radon-induced lung cancer in rats

A new series of experiments was carried out to investigate specifically the influence of exposure rate on lung cancer induction in rats at relatively low cumulative exposures of about 100 WLM, and at potential alpha energy concentrations (PAECs) ranging from 13 to 150 WL. The results indicate that at relatively low cumulative exposures comparable to lifetime exposures in high-radon houses or current underground mining exposures, the risk of lung cancer in rats decreases with decreasing PAECs, i.e. exposure rates. They confirm the results of previous experiments conducted at lower cumulative exposure, showing that for a similar cumulative exposure of 25 WLM, the risk of lung cancer decreases with decreasing exposure rates. These data suggest that the induction of lung cancer results from a complex interplay between cumulative exposure and exposure rate, with an optimal combination of these two parameters, i.e. a combination of cumulative dose and dose rate that results in a maximum risk of lung tumour induction. They support the hypothesis that, at low doses, the risk of lung cancer is governed by the rate at which the dose is delivered, and not by the total cumulative dose alone. These data are also consistent with that of underground uranium miners showing an inverse dose-rate effect at high cumulative exposures, but a diminution of this effect at cumulative exposures lower than 50 WLM.

A consistent two-mutation model of bone cancer for two data sets of radium-injected beagles

A two-mutation carcinogenesis model has been applied to model osteosarcoma incidence in two data sets of beagles injected with 226Ra. Taking age-specific retention into account, the following results have been obtained: (1) a consistent and well-fitting solution for all age and dose groups, (2) mutation rates that are linearly dependent on dose rate, with an exponential decrease for the second mutation at high dose rates, (3) a linear-quadratic dose-effect relationship, which indicates that care should be taken when extrapolating linearly, (4) highest cumulative incidences for injection at young adult age, and highest risks for injection doses of a few kBq kg(-1) at these ages, and (5) when scaled appropriately, the beagle model compares fairly well with a description for radium dial painters, suggesting that a consistent model description of bone cancer induction in beagles and humans may be possible.

Identifying dose dependences of the two-stage clonal expansion model with simulated cohorts

The two-stage clonal expansion model of cancer induction is tested on recorded and simulated cohort data of radon-exposed rats. Unfortunately, different versions of the model, for which radiation acts on different biological processes, can provide a good description of the data. This is the case for an initiation-transformation and an initiation-promotion model when they are applied to lung tumour data of radon-exposed rats and all malignant tumours are assumed to be incidental. However, if one were able to use information on fatal tumours as well, the two models could be separated by their deviances.