Assessment of uncertainties in threshold doses for tissue reactions following acute external radiation exposure

The study aimed to estimate threshold doses and their uncertainties for some human health effects after short-term high dose-rate radiation exposure by quantile technique and the effective dose threshold technique based on distribution functions. The relative uncertainty (U) of the threshold dose was estimated using the error propagation technique. The quantile technique provided statistically significant estimates of threshold doses for acute radiation syndrome onset (0.44 ± 0.12 Gy, U = 143%) and lethality (1.84 ± 0.44 Gy, U = 117%) but relative uncertainties were high. The effective threshold dose technique provided statistically significant and more precise threshold dose estimates for acute radiation syndrome onset (0.73 ± 0.02 Gy, U = 18%) and lethality (6.83 ± 0.08 Gy, U = 36%), as well as agranulocytosis (3.51 ± 0.03 Gy, U = 16%) and vomiting onset in the prodromal period (1.54 ± 0.02 Gy, U = 16%). Threshold doses estimated for the change in the peripheral blood neutrophil and leukocyte counts during the first days after short-term high dose-rate radiation exposure were not statistically significant.

Biological Dosimetry Technique for Estimation of Doses from Accidental Exposure to External γ-Rays

Individual doses from external γ-rays were estimated using biological dosimetry based on limited samplings (n₁= 15 and n₂ 12 individuals) which comprised the Mayak workers group with acute radiation sickness (ARS). The following primary data were used for calculation as initial parameters: estimated dose from ex- ternal γ-rays based on physical dosimetry methods - D (Gy); time before first vomiting - T (h); number of lymphocytes in peripheral blood on a second day after acute radiation exposure - L (10⁹/1); number of neutrophils in blood during first hours after accidental radiation exposure - N(10⁹/). A number of mathe- matical models used for dose estimation were verified: power-law dependence of the absorbed dose from ex- ternal γ-rays (D) on time before first vomiting (7), exponential dependence of D on the number of lympho- cytes in peripheral blood (L), dependence of D on the number of neutrophils in peripheral blood (N) and complex models forD association with Tand L parameters as well as-with Tand Nparameters. The biological dosimetry technique based on a complex approach was shown to provide the best agreement with physical dosimetry methods for individual assessment of doses from external γ-rays.

The Role of Polymorphisms of Key Genes of DNA Base Excision Repair in Terms of Lung Cancer Predisposition in "Mayak" Workers

An association between polymorphic variants of key genes of base excision repair (BER) and lung cancer was studied in "Mayak" workers occupationally exposed to prolonged external y-rays and internal α-radiation from incorporated (239)Pu. The study was "case-control". The group of "cases" consists of 75 "Mayak" workers with the verified diagnosis of "lung cancer". At the moment of diagnosis the mean total absorbed dose from external y-rays to whole body was 1.19 Gy; the mean total absorbed dose from internal α-radiation due to incorporated (239)Pu in lung was 0.31 Gy. The group of "controls" includes "Mayak" workers matched by sex and birth year without lung cancer and other cancers during the study period (141 individuals). Increased lung cancer risk was revealed in workers-carriers of homozygous minor genotype of genes OGG] Ser326Cys (OR - 4.67, p = 0.007), APEI Asp148Glu (OR = 1.82, p = 0.063) and XRCC1 Gln399Arg (OR = 2.86, p = 0.026). Increased lung cancer risk was revealed in carriers of different pairwise combinations of minor genotypes of the studied genes of BER or in carriers of pairwise combinations with one homozygous minor mm-genotype and the other homozygous major ww genotype. Thus, OR of lung cancer in carriers of pairwise genotypes of mm genes OGG] Ser326Cys and APE] Asp 148Glu was 12.17.

[Molecular mechanisms of lung cancer development at its different stages in nuclear industry workers]

OBJECTIVE

to assess mutational events in exons 5, 7, and 8 of the p53 gene and to reveal mutant p53 protein in verified cases of morphologically altered (proliferative and precancerous changes, lung cancer) and histologically unaltered, lung tissues in workers exposed to occupational radiation.

MATERIAL AND METHODS

The investigation used formalin-fixed paraffin-embedded unaltered and altered lung tissue blocks (FFPBs) obtained from the human radiobiological tissue repository. The shelf-life of FFPBs was 5-31 years. An immunohistochemical technique using mouse antibodies against p53 protein (<<DAKO>>, Denmark), stained with diaminobenzidine (DAB) chromogen, was employed to determine p53 protein. DNA was isolated from lung tissue FFPBs with QIAmp DNA FFPE Tissue Kit, (<<QIAGEN>>, USA). Polymerase chain reaction (PCR) was performed to amplify the p53 gene exons 5, 7, and 8 selected for examination, by applying the sequences of genes and primers, the specificity of which was checked using the online resource (http://www.ncbi.nlm.nih.gov/blast). PCR products were detected by temporal temperature gradient gel-electrophoresis and the Sanger sequencing method. The obtained DNA fragments were analyzed on a sequencer ABI Prism 3100 Genetic Analizer (<<Applied Biosystems>>, USA). Computer-aided DNA analysis was made using the BLAST program. A package of applied Statistica 6.0 programs was employed for statistical data processing. Results. Immunohistochemical analysis showed that mutant p53 protein was absent in the cells of unaltered lung tissue and the number of cells with mutant p53 protein increased in all the patients with proliferative and precancerous changes and lung cancer, suggesting p53 protein dysfunction. The total number of p53 gene mutations in exons 5, 7, and 8, if there were proliferative and precancerous lung tissue changes and lung cancer, were 25, 20, and 40%, respectively. All the found mutations were transversions (the substitution of purine for pyrimidine or, conversely), indicating the action of exogenous mutagens.

CONCLUSION

The results of this investigation have confirmed other investigators' data showing that p53 gene mutations in lung cancer are observed in 40-70% of cases. The differences in the number of cases of altered lung tissue with mutations in the p53 gene (not more than 40%) and in those of p53 protein expression were found in 100%, suggesting the regulation of p53 gene function in the cell at multiple levels.

Expression of blood serum proteins and lymphocyte differentiation clusters after chronic occupational exposure to ionizing radiation

This study aimed to assess effects of chronic occupational exposure on immune status in Mayak workers chronically exposed to ionizing radiation (IR). The study cohort consists of 77 workers occupationally exposed to external gamma-rays at total dose from 0.5 to 3.0 Gy (14 individuals) and workers with combined exposure (external gamma-rays at total dose range 0.7-5.1 Gy and internal alpha-radiation from incorporated plutonium with a body burden of 0.3-16.4 kBq). The control group consists of 43 age- and sex-matched individuals who never were exposed to IR, never involved in any cleanup operations following radiation accidents and never resided at contaminated areas. Enzyme-linked immunoassay and flow cytometry were used to determine the relative concentration of lymphocytes and proteins. The concentrations of T-lymphocytes, interleukin-8 and immunoglobulins G were decreased in external gamma-exposed workers relative to control. Relative concentrations of NKT-lymphocytes, concentrations of transforming growth factor-β, interferon gamma, immunoglobulins A, immunoglobulins M and matrix proteinase-9 were higher in this group as compared with control. Relative concentrations of T-lymphocytes and concentration of interleukin-8 were decreased, while both the relative and absolute concentration of natural killers, concentration of immunoglobulins A and M and matrix proteinase-9 were increased in workers with combined exposure as compared to control. An inverse linear relation was revealed between absolute concentration of T-lymphocytes, relative and absolute concentration of T-helpers cells, concentration of interferon gamma and total absorbed dose from external gamma-rays in exposed workers. For workers with incorporated plutonium, there was an inverse linear relation of absolute concentration of T-helpers as well as direct linear relation of relative concentration of NKT-lymphocytes to total absorbed red bone marrow dose from internal alpha-radiation. In all, chronic occupational IR exposure of workers induced a depletion of immune cells in peripheral blood of the individuals involved.

[Analysis of genome instability in offspring of "Mayak" workers families: minisatellite CEB1]

Genome instability transmission in offspring was analyzed in order to evaluate the risk of delayed genetic effects of exposure in 95 family triplets in which only fathers experienced prolonged occupational radiation exposure. The mean total preconceptive absorbed dose (TPAD) of external gamma radiation in the paternal gonads was 1.65 ± 0.08 Gy (dose range of 0.57-5.70 Gy), and the mean TPAD of internal alpha radiation from incorporated plutonium-239 in.the gonads was 0.0015 ± 0.0003 Gy (dose range 0.000-0.015 Gy). The control group consisted of 50 family triplets in which parents were not occupationally exposed. The mutation process was studied using PCR based on hypervariable minisatellite marker CEB 1 (chromosome 2, 2q37.3). The paternal type of inheritance of mutations for minisatellite CEB 1 was found in 80% of cases. The analysis revealed a statistically significant increase in minisatellite CEB1 mutations in the common group of families in which fathers experienced prolonged occupational radiation exposure and in the group of families in which fathers were exposed to radiation in a dosage range of 0.5-1.0 Gy as compared to the control, reaching a significance level of p = 0.109 and p = 0.058, respectively. The dose threshold of mutation detection in the off-spring of Mayak PA workers was estimated.

[Role of gene polymorphisms of phase II of xenobiotic biotransformation from glutathione-S-transferase and N-acetyltransferase families in susceptibility to lung cancer among Mayak workers]

An association between polymorphous (allelic) gene variants of phase II of enzymatic xenobiotic biotransformation (EXB) of multigene families of glutathione-S-transferase (GSTs) GSTM1*0, GSTT1*0, GSTP1*B Ile105Val, and N-acetyltransferase (NAT) NAT2*6 590G>A, NAT2*5 481C>T, as well as lung cancer in Mayak workers exposed occupationally to prolonged external γ-rays and internal α-radiation from incorporated 239Pu was studied. Analysis of the population frequency of genotypes and alleles of the studied genes in the cohort of Mayak workers revealed their compliance with the Hardy-Weinberg principle and with the corresponding frequency in the European population. The study was based on the case-control method. A case-group consisted of 49 Mayal workers with a verified diagnosis of lung cancer. The mean total absorbed dose from external γ-rays at the moment of diagnostics was 1.03 Gy; the mean total absorbed dose from internal α-radiation from incorporated 239Pu to lung was 0.35 Gy. Control consisted of 172 Mayak workers matched by the year of birth, gender, and age at the moment of employment at one of the main facilities with no lung cancer registered within the study period. No increase in the relative risk of lung cancer (odds ratio, OR) was revealed among the individuals with deletion variants of genes GSTM1*0 and GSTT1*0 (pp genotype, complete absence of gene products) as compared to the individuals with ww or wp genotype, which was determined in total for these genes (normal or partly decreased gene activity). An increase in OR of lung cancer in 1.849 times (p = 0.239) and in 2.439 times (p = 0.075) was found in the carriers with a complete absence of the product of genes GSTP1*B and NAT2*6 590G>A, correspondingly (pp genotype). A statistically significant decrease in OR of lung cancer was found in the wp genotype carriers of gene GSTP1*B (OR = 0.50, p = 0.041). Three variants of paired combinations of gene alleles were established in the carriers with a statistically significant increase in OR of lung cancer (ww GSTP1*B + pp GSTM1*0; ww GSTP1*B + pp NAT2*6 590G>A; pp GSTP1*B + pp NAT2*5 481C>T), and one combination in the carriers with a statistically significant decrease in OR of lung cancer (wp GSTP1*B and ww +wp GSTT1*0).

Threshold limits for biological indication of prolonged radiation exposure using mFISH

Chromosome aberration (translocation) yield was investigated by mFISH in peripheral blood lymphocytes of Mayak Production Association (PA) workers with prolonged occupational exposure to ionizing radiation (IR). A dose threshold for cytogenetic indication of a prolonged occupational radiation exposure was estimated for Mayak PA workers using functions of dose distributions. Two limits were estimated for the indication of IR exposure to workers with a prolonged external gamma-ray exposure: These are a background translocation yield of N₀ = 0.812 ± 0.149% and a dose threshold of indication D₀ estimated to be approximately 1 Gy.

mFISH analysis of chromosome aberrations in workers occupationally exposed to mixed radiation

We performed a study on the presence of chromosome aberrations in a cohort of plutonium workers of the Mayak production association (PA) with a mean age of 73.3 ± 7.2 years to see whether by multi-color fluorescence in situ hybridization (mFISH) translocation analysis can discriminate individuals who underwent occupational exposure with internal and/or external exposure to ionizing radiation 40 years ago. All Mayak PA workers were occupationally exposed to chronic internal alpha-radiation due to incorporated plutonium-239 and/or to external gamma-rays. First, we obtained the translocation yield in control individuals by mFISH to chromosome spreads of age-matched individuals and obtained background values that are similar to previously published values of an international study (Sigurdson et al. in Mutat Res 652:112-121, 2008). Workers who had absorbed a total dose of >0.5 Gy external gamma-rays to the red bone marrow (RBM) displayed a significantly higher frequency of stable chromosome aberrations relative to a group of workers exposed to <0.5 Gy gamma-rays total absorbed RBM dose. Thus, the translocation frequency may be considered to be a biological marker of external radiation exposure even years after the exposure. In a group of workers who were internally exposed and had incorporated plutonium-239 at a body burden >1.48 kBq, mFISH revealed a considerable number of cells with complex chromosomal rearrangements. Linear associations were observed for translocation yield with the absorbed RBM dose from external gamma-rays as well as for complex chromosomal rearrangements with the plutonium-239 body burden.

Direct and indirect tasks on assessment of dose and time distributions and thresholds of acute radiation exposure

Mathematical methods were developed to construct dose and time distributions and their associated risks and threshold values for lethal and non-lethal effects of acute radiation exposure to include mortality and incidence, prodromal vomiting, and agranulocytosis. A new distribution (T-model) was obtained to describe time parameters of acute radiation syndrome such as the latency period, time to onset of vomiting, and time to initiation of agranulocytosis. Based on the dose and time distributions, the parameter translation method was defined using an orthogonal regression, which allows one to solve for these distributions in the case of acute radiation exposure. The assessment of threshold doses was performed for some effects of acute radiation syndrome: for the latency period, ∼6-8 Gy absorbed dose and ∼0.7-0.9 h time to onset of vomiting; and for incidence (agranulocytosis), ∼2-3 Gy absorbed dose and ∼2-3 h time to onset of vomiting. The obtained new formula for assessment of radiation risk is applicable to the time parameters of acute radiation syndrome.

[Structural genomic damages in workers of plutonium production]

The research objective is assessment of structural genomic damages in plutonium workers. The study group included the Mayak nuclear workers subject to chronic occupational exposure to incorporated 239Pu and/or external gamma-rays. The analysis was performed based on the culture of lymphocytes in peripheral blood. The yield of intra-chromosomal exchange aberrations of chromosomal type on stained slides was analyzed using in situ fluorescent hybridization, mBAND. Linear relationships were revealed between (a) the total yield of chromosomal type aberrations (e.g. intra- and inter-chromosomal ones) and an absorbed dose from external exposure of the red bone marrow to gamma-rays, an absorbed dose from internal exposure to a-radiation from incorporated 239Pu; and (b) the yield of intra-chromosomal exchange aberrations of chromosomal type and an absorbed dose from exposure of the red bone marrow to 239Pu and 239Pu body burden.

Assessment of risks and dose thresholds for some effects of acute exposure

Findings from the analyses of the dose-response relationship are reviewed with regard to different effects of acute radiation exposure. The analyses have been performed based on the dosimetry and clinical data for the nuclear workers acutely exposed to gamma rays or gamma rays and neutrons as a result of radiation accidents at the Mayak Production Association (Russia). The statistically significant risk curves for morbidity and mortality from acute radiation syndrome (ARS), as well as risks of the onset of vomiting at the prodromal phase and agranulocytosis, have been obtained. The Weibull model appropriately describes the corresponding risk curves. Estimates of the dose thresholds have been obtained for ARS morbidity (∼0.7 Gy) and mortality (∼6-7 Gy), vomiting at the prodromal phase (∼1.5 Gy), and agranulocytosis (∼3.5 Gy). The statistically significant power dependence between the onset of vomiting at the prodromal phase and the onset of agranulocytosis, as well as the dose dependence for the onset of agranulocytosis, has been revealed.

[239Pu and chromosomal aberrations in human peripheral blood lymphocytes]

The genome status in somatic cells was assessed using the chromosomal aberration (CA) test in peripheral blood lymphocytes from 194 plutonium workers exposed to occupational radiation mainly from low-transportable compounds of airborne 230Pu. Pu body burden at the time of cytogenetic study varied from values close to the method sensitivity to values multiply exceeding the permissible level. Standard (routine) methods of peripheral blood lymphocytes cultivation were applied. Chromatid- and chromosomal-type structural changes were estimated. Aberrations were estimated per 100 examined metaphase cells. The quantitative relationship between the CA frequency and Pu body burden and the absorbed dose to the lung was found. Mathematical processing of results was carried out based on the phenomenological model. The results were shown as theoretical and experimental curves. The threshold of the CA yield was 0.43 +/- 0.03 kBq (Pu body burden) and 6.12 +/- 1.20 cGy (absorbed dose to the lung).

[Chronic morbidity parameters in personel engaged into processing and utilization of arms and military equipment]

Analysis of chronic morbidity parameters in workers engaged into processing and utilization of arms and military equipment did not reveal any case of occupational radiation disease over 30 years of medical observation. Standardized parameters in general and in separate diseases classes did not differ with general data collected in Russia. Occurrence of separate entities did not depend on influence of radiation factors.

Predictability of acute radiation injury severity

Results of dose-response analyses for different clinical symptoms of acute radiation syndrome (ARS) are reported here. The analyses were performed on dosimetric and clinical data from a group of ARS patients (59 cases) exposed to gamma and neutron or gamma radiation alone due to nuclear accidents at Mayak Production Association (Mayak PA). Findings suggested the possibility of prediction of injury severity within the first hours or days after acute exposure based on clinical symptoms and signs such as the onset of vomiting, neutrophil count abnormalities in the peripheral blood within the first 2-3 hours after acute exposure, and lymphocyte count abnormalities in the peripheral blood within the first 24-48 h after acute exposure.

Modeling of respiratory system dysfunction among nuclear workers: a preliminary study

Numerous studies have reported on cancers among Mayak Production Association (PA) nuclear workers. Other studies have reported on serious deterministic effects of large radiation doses for the same population. This study relates to deterministic effects (respiratory system dysfunction) in Mayak workers after relatively small chronic radiation doses (alpha plus gamma). Because cigarette smoke is a confounding factor, we also account for smoking effects. Here we present a new empirical mathematical model that was introduced for simultaneous assessment of radiation and cigarette-smoking-related damage to the respiratory system. The model incorporates absolute thresholds for smoking- and radiation-induced respiratory system dysfunction. As the alpha radiation dose to the lung increased from 0 to 4.36 Gy, respiratory function indices studied decreased, although remaining in the normal range. The data were consistent with the view that alpha radiation doses to the lung above a relatively small threshold (0.15 to 0.39 Gy) cause some respiratory system dysfunction. Respiratory function indices were not found to be influenced by total-body gamma radiation doses in the range 0-3.8 Gy when delivered at low rates over years. However, significant decreases in airway conductance were found to be associated with cigarette smoking. Whether the indicated cigarette smoking and alpha radiation associated dysfunction is debilitating is unclear.

[A DNA bank for people subjected to occupational irradiation. Goals and prospects]

A DNA bank was created to preserve the genetic material of staff of the first Russian atomic plant, Production Association (PO) Mayak, who were exposed to chronic external gamma-irradiation at various doses in the early years of plant operation. Some of the workers experienced combined irradiation from external and internal (incorporated plutonium-239) sources. The unique genetic material of the subjects and their children can be used to study the remote consequences of irradiation by means of modern molecular-genetic techniques. At present, the bank contains the genetic material of 500 people. A database was constructed to include medical, demographic, professional, and dose characteristics of each individual and quantitative and qualitative parameters of each DNA preparation. The bank is continuously augmented with new DNA samples of the irradiated people and members of their families.

Evaluating the risk of death via the hematopoietic syndrome mode for prolonged exposure of nuclear workers to radiation delivered at very low rates

During a Phase-I effort, studies were planned to evaluate deterministic (nonstochastic) effects of chronic exposure of nuclear workers at the Mayak atomic complex in the former Soviet Union to relatively high levels (> 0.25 Gy) of ionizing radiation. The Mayak complex has been used, since the late 1940's, to produce plutonium for nuclear weapons. Workers at Site A of the complex were involved in plutonium breeding using nuclear reactors, and some were exposed to relatively large doses of gamma rays plus relatively small neutron doses. The Weibull normalized-dose model, which has been set up to evaluate the risk of specific deterministic effects of combined, continuous exposure of humans to alpha, beta, and gamma radiations, is here adapted for chronic exposure to gamma rays and neutrons during repeated 6-h work shifts--as occurred for some nuclear workers at Site A. Using the adapted model, key conclusions were reached that will facilitate a Phase-II study of deterministic effects among Mayak workers. These conclusions include the following: (1) neutron doses may be more important for Mayak workers than for Japanese A-bomb victims in Hiroshima and can be accounted for using an adjusted dose (which accounts for neutron relative biological effectiveness); (2) to account for dose-rate effects, normalized dose X (a dimensionless fraction of an LD50 or ED50) can be evaluated in terms of an adjusted dose; (3) nonlinear dose-response curves for the risk of death via the hematopoietic mode can be converted to linear dose-response curves (for low levels of risk) using a newly proposed dimensionless dose, D = X(V), in units of Oklad (where D is pronounced "deh"), and V is the shape parameter in the Weibull model; (4) for X < or = Xo, where Xo is the threshold normalized dose, D = 0; (5) unlike absorbed dose, the dose D can be averaged over different Mayak workers in order to calculate the average risk of death via the hematopoietic mode for the population exposed at Site A; and (6) the expected cases of death via the hematopoietic syndrome mode for Mayak workers chronically exposed during work shifts at Site A to gamma rays and neutrons can be predicted using ln(2)B M[D]; where B (pronounced "beh") is the number of workers at risk (criticality accident victims excluded); and M[D] is the average (mean) value of D (averaged over the worker population at risk, for Site A, for the time period considered). These results can be used to facilitate a Phase II study of deterministic radiation effects among Mayak workers chronically exposed to gamma rays and neutrons.