Mayumi Maki

Radiation dose-dependent increases in inflammatory response markers in A-bomb survivors

Purpose : The well-documented increases in malignant tumours in the A-bomb survivors have recently been supplemented by reports that non-cancer diseases, including cardiovascular disease, may also have increased in incidence with increasing radiation dose. Given that low-level inflammatory responses are widely accepted as a significant risk factor for such diseases, we undertook a detailed investigation of the long-term effects of ionizing radiation on the levels of the inflammatory markers C-reactive protein (CRP) and interleukin 6 (IL-6) in A-bomb survivors. Materials and methods : Blood samples were taken from 453 participants in a long-term epidemiological cohort of A-bomb survivors. Plasma levels of CRP and IL-6 were measured using standard antibody-mediated procedures. Relationships between CRP or IL-6 levels and radiation dose were then investigated by multivariate regression analysis. Blood lymphocytes from each individual were used for immunophenotyping by flow cytometry with murine monoclonal antibodies to CD3, CD4 and CD8. Results : CRP levels were significantly increased by about 31% Gy −1 of estimated A-bomb radiation (p =0.0001). Higher CRP levels also correlated with age, male gender, body mass index and a history of myocardial infarction. After adjustments for these factors, CRP levels still appeared to have increased significantly with increasing radiation dose (about 28% increase at 1Gy, p =0.0002). IL-6 levels also appeared to have increased with radiation dose by 9.3% at 1Gy (p =0.0003) and after multiple adjustments by 9.8% at 1Gy (p =0.0007). The elevated CRP and IL-6 levels were associated with decreases in the percentages of CD4 + helper T-cells in peripheral blood lymphocyte populations. Conclusions : Our results appear to indicate that exposure to A-bomb radiation has caused significant increases in inflammatory activity that are still demonstrable in the blood of A-bomb survivors and which may lead to increased risks of cardiovascular disease and other non-cancer diseases.

T-Cell Responses to Mitogens in Atomic Bomb Survivors: A Decreased Capacity to Produce Interleukin 2 Characterizes the T Cells of Heavily Irradiated Individuals

Abstract Kusunoki, Y., Hayashi, T., Morishita, Y., Yamaoka, M., Maki, M., Hakoda, M., Kodama, K., Bean, M. A. and Kyoizumi, S. T-Cell Responses to Mitogens in Atomic Bomb Survivors: A Decreased Capacity to Produce Interleukin 2 Characterizes the T Cells of Heavily Irradiated Individuals. Significant decreases in the fraction of lymphocytes that are CD4+ and increases in serum levels of some classes of immunoglobulin have been reported to occur in atomic bomb (A-bomb) survivors and in victims of the Chernobyl nuclear plant accident. To investigate the long-term effects of nuclear radiation on cellular immunity in more detail, we used limiting dilution assays with peripheral blood mononuclear cell preparations to analyze the T-cell responses of 251 A-bomb survivors exposed to less than 0.005 Gy and 159 survivors exposed to more than 1.5 Gy. The percentages of CD2-positive cells that were capable of proliferating in response to phytohemagglutinin (PHA) in the presence of exogenous interleukin 2 (IL2) did not differ substantially between distally exposed and more heavily exposed survivors. The heavily exposed survivors appeared to possess fewer T cells that were capable of proliferating in response to concanavalin A (Con A) or of producing interleukin 2. Assuming that CD4 T cells were the ones primarily responsible for producing IL2 in response to Con A, we were able to estimate how many cells in any given CD4 T-cell population were actually producing IL2. The results indicated that peripheral blood samples from heavily exposed survivors contained significantly fewer IL2-producing CD4 T cells than did similar samples from distally exposed survivors, indicating that significant exposure to A-bomb radiation may have a long-lasting negative effect on the capacity of CD4 T-cell populations to produce IL2.

Effects of IL-10 Haplotype and Atomic Bomb Radiation Exposure on Gastric Cancer Risk

Gastric cancer (GC) is one of the cancers that reveal increased risk of mortality and incidence in atomic bomb survivors. The incidence of gastric cancer in the Life Span Study cohort of the Radiation Effects Research Foundation (RERF) increased with radiation dose (gender-averaged excess relative risk per Gy = 0.28) and remains high more than 65 years after exposure. To assess a possible role of gene-environment interaction, we examined the dose response for gastric cancer incidence based on immunosuppression-related IL-10 genotype, in a cohort study with 200 cancer cases (93 intestinal, 96 diffuse and 11 other types) among 4,690 atomic bomb survivors participating in an immunological substudy. Using a single haplotype block composed of four haplotype-tagging SNPs (comprising the major haplotype allele IL-10-ATTA and the minor haplotype allele IL-10-GGCG, which are categorized by IL-10 polymorphisms at −819A>G and −592T>G, +1177T>C and +1589A>G), multiplicative and additive models for joint effects of radiation and this IL-10 haplotyping were examined. The IL-10 minor haplotype allele(s) was a risk factor for intestinal type gastric cancer but not for diffuse type gastric cancer. Radiation was not associated with intestinal type gastric cancer. In diffuse type gastric cancer, the haplotype-specific excess relative risk (ERR) for radiation was statistically significant only in the major homozygote category of IL-10 (ERR = 0.46/Gy, P = 0.037), whereas estimated ERR for radiation with the minor IL-10 homozygotes was close to 0 and nonsignificant. Thus, the minor IL-10 haplotype might act to reduce the radiation related risk of diffuse-type gastric cancer. The results suggest that this IL-10 haplotyping might be involved in development of radiation-associated gastric cancer of the diffuse type, and that IL-10 haplotypes may explain individual differences in the radiation-related risk of gastric cancer.

Long term effects of radiation exposure on telomere lengths of leukocytes and its associated biomarkers among atomic-bomb survivors

Ionizing radiation (IR) is a major source of cellular damage and the immediate cellular response to IR has been well characterized. But the long-term impact of IR on cell function and its relationship with aging are not known. Here, we examined the IR effects on telomere length and other biomarkers 50 to 68 years post-exposure (two time points per person) in survivors of the atomic bombing at Hiroshima during WWII. We found that telomere length of leukocytes was inversely correlated with the dose of IR (p=0.008), and this effect was primarily found in survivors who were exposed at younger ages; specifically those <12 years old (p=0.0004). Although a dose-related retardation of telomere shortening with age was observed in the cross-sectional data, longitudinal follow-up after 11 years did not show IR exposure-related alteration of the rate of telomere shortening with age. In addition, IR diminished the associations between telomere length and selected aging biomarkers that were observed in survivors with no dose. These included uric acid metabolism, cytokines, and blood T cell counts. These findings showed long-lasting detrimental effects of IR on telomere length of leukocytes in both dose- and age-at-exposure dependent manner, and on alterations of biomarkers with aging.

Radiation-dose response of glycophorin A somatic mutation in erythrocytes associated with gene polymorphisms of p53 binding protein 1.

Information on individual variations in response to ionizing radiation is still quite limited. Previous studies of atomic-bomb survivors revealed that somatic mutations at the glycophorin A (GPA) gene locus in erythrocytes were significantly elevated with radiation exposure dose, and that the dose response was significantly higher in survivors with subsequent cancer development compared to those without cancer development. Noteworthy in these studies were great inter-individual differences in GPA mutant fraction even in persons with similar radiation doses. It is hypothesized that persistent GPA mutations in erythrocytes of atomic-bomb survivors are derived from those in long-lived hematopoietic stem cell (HSC) populations, and that individual genetic backgrounds, specifically related to DNA double-strand break repair, contribute to individual differences in HSC mutability following radiation exposure. Thus, we examined the relationship between radiation exposure, GPA mutant fraction in erythrocytes, and single nucleotide polymorphisms (SNPs) of the key gene involved in DNA double-strand break repair, p53 binding protein 1 (53BP1). 53BP1 SNPs and inferred haplotypes demonstrated a significant interaction with radiation dose, suggesting that radiation-dose response of GPA somatic mutation is partly dependent on 53BP1 genotype. It is also possible that 53BP1 plays a significant role in DNA double-strand break repair in HSCs following radiation exposure.

Impact of early life exposure to ionizing radiation on influenza vaccine response in an elderly Japanese cohort

The objective of this study was to evaluate effects of whole body radiation exposure early in life on influenza vaccination immune responses much later in life. A total of 292 volunteers recruited from the cohort members of ongoing Adult Health Study (AHS) of Japanese atomic bomb (A-bomb) survivors completed this observational study spanning two influenza seasons (2011-2012 and 2012-2013). Peripheral blood samples were collected prior to and three weeks after vaccination. Serum hemagglutination inhibition (HAI) antibody titers were measured as well as concentrations of 25 cytokines and chemokines in culture supernatant from peripheral blood mononuclear cells, with and without in vitro stimulation with influenza vaccine. We found that influenza vaccination modestly enhanced serum HAI titers in this unique cohort of elderly subjects, with seroprotection ranging from 18 to 48% for specific antigen/season combinations. Twelve percent of subjects were seroprotected against all three vaccine antigens post-vaccination. Males were generally more likely to be seroprotected for one or more antigens post-vaccination, with no differences in vaccine responses based on age at vaccination or radiation exposure in early life. These results show that early life exposure to ionizing radiation does not prevent responses of elderly A-bomb survivors to seasonal influenza vaccine.

CD14 and IL18 gene polymorphisms associated with colorectal cancer subsite risks among atomic bomb survivors

Colorectal cancer (CRC) is a common malignancy worldwide, and chronic inflammation is a risk factor for CRC. In this study, we carried out a cohort study among the Japanese atomic bomb (A-bomb) survivor population to investigate any association between immune- and inflammation-related gene polymorphisms and CRC. We examined the effects of six single-nucleotide polymorphisms of CD14 and IL18 on relative risks (RRs) of CRC. Results showed that RRs of CRC, overall and by anatomic subsite, significantly increased with increasing radiation dose. The CD14–911A/A genotype showed statistically significant higher risks for all CRC and distal CRC compared with the other two genotypes. In addition, the IL18–137 G/G genotype showed statistically significant higher risks for proximal colon cancer compared with the other two genotypes. In phenotype–genotype analyses, the CD14–911A/A genotype presented significantly higher levels of membrane and soluble CD14 compared with the other two genotypes, and the IL18–137 G/G genotype tended to be lower levels of plasma interleukin (IL)-18 compared with the other two genotypes. These results suggest the potential involvement of a CD14-mediated inflammatory response in the development of distal CRC and an IL18-mediated inflammatory response in the development of proximal colon cancer among A-bomb survivors.

Abstract 4715: Genetic susceptibility to radiation-associated colon and rectum cancers among atomic-bomb survivors with special reference to the CD14 gene

Past epidemiology studies reported that atomic-bomb (A-bomb) radiation exposure enhanced risk of colon cancer, but not rectum cancer, among the survivors. The reason for this different sensitivity to radiation remains to be elucidated. Colorectal cancer is a multi-factorial disease, the onset of which is attributed to both environmental and genetic factors, with animal experiments showing that intestinal bacterial toxins accelerate carcinogenesis. It was recently reported that single nucleotide polymorphisms (SNPs) identified in the promoter region of CD14, encoding a receptor for the lipopolysaccharide component of the outer membrane of Gram-negative bacteria, regulate CD14 gene expression and thereby affect susceptibility to inflammatory diseases such as atopic dermatitis, coronary artery disease, and hepatic diseases. This study investigated relationship between a novel CD14 gene polymorphism and the development of radiation-associated colon and rectum cancers among an A-bomb survivor cohort, in terms of a case-cohort study. On the basis of this T/G polymorphism, we determined CD14 genotypes with 210 colorectal cancer cases and with a subcohort of 2,160 individuals who were randomly selected from the cohort. Our results showed that the individuals exposed to A-bomb radiation (≥5 mGy) were at an increased risk of colon cancer, but not rectum cancer, with relative risk (RR) of 1.19/Gy (95%CI: 1.04-1.36). When we divided the study subjects into three groups for radiation dose and into two groups for CD14 genotypes, significantly high risk of colon cancer was found with RR of 2.40 (95%CI: 1.37-4.23) for the combined category of CD14-T/T homozygote and the highest dose (≥0.7Gy), compared with the baseline category (CD14-T/G or G/G and no dose). These results suggest that CD14-related inflammatory response might be involved in the development of radiation-associated colon cancer, not rectum cancer, among A-bomb survivors, and that the CD14 genotyping might be involved in individual risk of colon cancer together with radiation dose. To find a functional significance of this polymorphism, we are currently working on ELISA-based assay to measure serum levels of soluble CD14 among healthy individuals in relation to the CD14 genotyping. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4715.