Chromosome Damage in Relation to Recent Radiation Exposure and Radiation Quality in Nuclear Power Plant Workers.

Ionizing radiation is a well-known carcinogen that causes genomic instability. However, the biological and carcinogenetic effects of occupational radiation exposure at low doses have not been extensively studied. The aim of this study was to assess chromosomal instability in power plant workers exposed to occupational radiation at low doses in South Korea. Chromosomal aberrations in the lymphocytes of 201 nuclear power plant workers and 59 sex-matched controls were measured. Chromosomal aberrations in the lymphocytes of 201 nuclear power plant workers (mean age: 41.4 ± 10.0 years) and 59 sex-matched controls (mean age: 47.2 ± 6.0 years) were measured. A total of 500 metaphases for each subject were scored randomly. The means of recent 1.5-year, recent 5.5-year, and cumulative exposed radiation doses among workers were 8.22 ± 7.0 mSv, 30.7 ± 22.0 mSv, and 158.8 ± 86.1 mSv, respectively. The frequency of chromosome-type and chromatid-type aberrations was significantly higher in workers than that in the control group (p < 0.001), and the frequency of chromosome-type aberrations among workers increased in a radiation dose-dependent manner (τ = 0.16, p = 0.005). Poisson regression analyses revealed that chromosome-type aberrations were significantly associated with recent 1.5-year dose after adjusting for confounding variables such as age, smoking, and alcohol intake, even when only the exposed worker was considered. Frequency of multi-aberrant cells (two or more chromosome aberrations within a cell) increased according to cumulative neutron exposure. Our study demonstrates that chromosome damage can be induced in nuclear power plant workers occupationally exposed to ionizing radiation at low doses below the occupational permissible dose limit. Furthermore, an increase in multi-aberrant cells may provide evidence for chronic neutron exposure in nuclear power plant workers. This study was performed to obtain baseline data for a surveillance program of workers occupationally exposed to ionizing radiation long-term.

Effects of the DNA repair inhibitors, cytosine arabinoside and 3-aminobenzamide, on the frequency of radiation-induced micronuclei, nuclear buds, and nucleoplasmic bridges.

BACKGROUND: Micronuclei (MN), nuclear bud (NBud), and nucleoplasmic bridge (NPB) are suggested as biomarkers for radiation exposure; however, they have not been extensively studied to understand the underlying mechanisms responsible for their formation. OBJECTIVES: To (1) validate NBud and NPB within the cytokinesis-blocked micronucleus (CBMN) assay as biomarkers for radiation exposure and (2) determine the effects of the DNA repair inhibitors, cytosine arabinoside (Ara C) and 3-aminobenzamide (3-AB) on radiation-induced MN, NBud, and NPB formation. METHODS: Human blood samples were irradiated with 0-3 Gy X-rays and subsequently treated with Ara C and 3-AB. CBMN and chromosome aberration assays were carried out to measure MN, NBud, and NPB and dicentric chromosomes, respectively. RESULTS: The frequency of radiation-induced MN, NBud, and NPB increased in a dose-dependent manner. The frequency of MN, NBud, and NPB was highly and positively correlated with the dicentric chromosome, a standard biomarker for biodosimetry (r > 0.98, p < 0.0001). Furthermore, Ara C increased the frequency of MN, NBud, and NPB, whereas 3-AB increased the frequency of MN and NPB, but not NBud. Further, the potentiating effect of Ara C on the frequency of MN, NBud, and NPB was greater than that of 3-AB. CONCLUSION: Our results validate NBuds and NPBs as independent valuable markers of radiation exposure. Additionally, we suggest that different mechanisms are likely involved in the formation of NBuds and NPBs following X-irradiation; however, additional studies are warranted to better understand the contribution of distinct DNA repair pathways to the formation of radiation-induced damages.

LINE-1 hypomethylation is associated with radiation-induced genomic instability in industrial radiographers.

Global DNA hypomethylation is proposed as a potential biomarker for cancer risk associated with genomic instability, which is an important factor in radiation-induced cancer. However, the associations among radiation exposure, changes in DNA methylation, and carcinogenesis are unclear. The aims of this study were (1) to examine whether low-level occupational radiation exposure induces genomic DNA hypomethylation; and (2) to determine the relationships between radiation exposure, genomic DNA hypomethylation and radiation-induced genomic instability (RIGI) in industrial radiographers. Genomic DNA methylation levels were measured in blood DNA from 40 radiographers and 28 controls using the LINE-1 pyrosequencing assay and the luminometric methylation assay. Further, the micronucleus-centromere assay was performed to measure aneuploidy of chromosomes 1 and 4 as a marker of delayed RIGI. Genomic DNA methylation levels were significantly lower in radiographers than those in controls. LINE-1 hypomethylation was not significantly correlated with recent 1-year, recent 3-year, or total cumulative radiation doses in radiographers; however, LINE-1 hypomethylation significantly correlated with the cumulative radiation dose without recent 3-year exposure data (D3dose, r = -0.39, P < 0.05). In addition, LINE-1 hypomethylation was a significant contributor to aneuploidy frequency by D3dose (F (2, 34) = 13.85, P < 0.001), in which a total of 45% of the variance in aneuploidy frequency was explained. Our results provide suggestive evidence regarding the delayed effects of low-dose occupational radiation exposure in radiographers and its association with LINE-1 hypomethylation; however, additional studies using more subjects are needed to fully understand the relationship between genomic DNA hypomethylation and RIGI. Environ. Mol. Mutagen. 60: 174-184, 2019. © 2018 Wiley Periodicals, Inc.

Protective Effect of Onion Extract on Bleomycin-Induced Cytotoxicity and Genotoxicity in Human Lymphocytes.

Following one of the world's largest nuclear accidents, occured at Fukushima, Japan in 2011, a significant scientific effort has focused on minimizing the potential adverse health effects due to radiation exposure. The use of natural dietary antioxidants to reduce the risk of radiation-induced oxidative DNA damage is a simple strategy for minimizing radiation-related cancer rates and improving overall health. The onion is among the richest sources of dietary flavonoids and is an important food for increasing their overall intake. Therefore, we examined the effect of an onion extract on cyto- and geno-toxicity in human lymphocytes treated with bleomycin (BLM), a radiomimetic agent. In addition, we measured the frequency of micronuclei (MN) and DNA damage following treatment with BLM using a cytokinesis-blocked micronucleus assay and a single cell gel electrophoresis assay. We observed a significant increase in cell viability in lymphocytes treated with onion extract then exposed to BLM compared to cells treated with BLM alone. The frequency of BLM induced MN and DNA damage increased in a dose-dependent manner; however, when lymphocytes were pretreated with onion extract (10 and 20 µL/mL), the frequency of BLM-induced MN was decreased at all doses of BLM and DNA damage was decreased at 3 µg/mL of BLM. These results suggest that onion extract may have protective effects against BLM-induced cyto- and genotoxicity in human lymphocytes.

Delayed Numerical Chromosome Aberrations in Human Fibroblasts by Low Dose of Radiation.

Radiation-induced genomic instability refers to a type of damage transmitted over many generations following irradiation. This delayed impact of radiation exposure may pose a high risk to human health and increases concern over the dose limit of radiation exposure for both the public and radiation workers. Therefore, the development of additional biomarkers is still needed for the detection of delayed responses following low doses of radiation exposure. In this study, we examined the effect of X-irradiation on delayed induction of numerical chromosomal aberrations in normal human fibroblasts irradiated with 20, 50 and 100 cGy of X-rays using the micronucleus-centromere assay. Frequencies of centromere negative- and positive-micronuclei, and aneuploidy of chromosome 1 and 4 were analyzed in the surviving cells at 28, 88 and 240 h after X-irradiation. X-irradiation increased the frequency of micronuclei (MN) in a dose-dependent manner in the cells at all measured time-points, but no significant differences in MN frequency among cell passages were observed. Aneuploid frequency of chromosomes 1 and 4 increased with radiation doses, and a significantly higher frequency of aneuploidy was observed in the surviving cells analyzed at 240 h compared to 28 h. These results indicate that low-dose of X-irradiation can induce delayed aneuploidy of chromosomes 1 and 4 in normal fibroblasts.

The Association of LINE-1 Hypomethylation with Age and Centromere Positive Micronuclei in Human Lymphocytes.

Global hypomethylation in white blood cell (WBC) DNA has recently been proposed as a potential biomarker for determining cancer risk through genomic instability. However, the amplitude of the changes associated with age and the impacts of environmental factors on DNA methylation are unclear. In this study, we investigated the association of genomic hypomethylation with age, cigarette use, drinking status and the presence of centromere positive micronuclei (MNC+)-a biomarker for age-dependent genomic instability. Genomic hypomethylation of the repetitive element LINE-1 was measured in WBC DNA from 32 healthy male volunteers using the pyrosequencing assay. We also measured MNC+ with the micronucleus-centromere assay using a pan-centromeric probe. Possibly due to the small sample size and resulting low statistical power, smoking and drinking status had no significant effect on LINE-1 hypomethylation or the occurrence of MNC+. Consequently, we did not include them in further analyses. In contrast, LINE-1 hypomethylation and age significantly predicted MNC+; therefore, we examined whether LINE-1 hypomethylation plays a role in MNC+ formation by age, since genomic hypomethylation is associated with genomic instability. However, LINE-1 hypomethylation did not significantly mediate the effect of age on MNC+. Our data indicate that the repetitive element LINE-1 is demethylated with age and increasing MNC+ frequency, but additional studies are needed to fully understand the relation between genomic DNA hypomethylation, age and genomic instability.

Radiation-induced changes in DNA methylation and their relationship to chromosome aberrations in nuclear power plant workers.

PURPOSE: We investigated the association between occupational radiation exposure and DNA methylation changes in nuclear power plant workers. We also evaluated whether radiation- induced DNA methylation alterations are associated with chromosome aberrations. MATERIALS AND METHODS: The study population included 170 radiation-exposed workers and 30 controls. We measured global, long interspersed nuclear element-1 (LINE-1), and satellite 2 methylation levels in blood leukocyte DNA. The analysis of chromosome aberrations was performed on peripheral lymphocytes. RESULTS: Global DNA methylation levels were lower in radiation-exposed workers than in controls. The methylation levels were negatively associated with the recent 1.5-year radiation dose in a multiple linear regression model (ß = - 0.0088, p ≤ 0.001); the levels increased proportionally with the total cumulative dose in radiation-exposed workers. LINE-1 methylation levels were higher in radiation-exposed workers than in controls and were significantly associated with the total cumulative radiation dose in a multiple linear regression model (ß = - 0.031, p = 0.035). Global DNA methylation levels were also correlated with chromosome aberrations among workers. Workers with low global methylation levels had a higher frequency of chromosome aberrations than did subjects with high global methylation levels. CONCLUSION: Occupational exposure to low-dose radiation could affect DNA methylation levels, and the radiation-induced DNA methylation alterations may be associated with chromosome aberrations.

Human AP endonuclease 1: a potential marker for the prediction of environmental carcinogenesis risk.

Human apurinic/apyrimidinic endonuclease 1 (APE1) functions mainly in DNA repair as an enzyme removing AP sites and in redox signaling as a coactivator of various transcription factors. Based on these multifunctions of APE1 within cells, numerous studies have reported that the alteration of APE1 could be a crucial factor in development of human diseases such as cancer and neurodegeneration. In fact, the study on the combination of an individual's genetic make-up with environmental factors (gene-environment interaction) is of great importance to understand the development of diseases, especially lethal diseases including cancer. Recent reports have suggested that the human carcinogenic risk following exposure to environmental toxicants is affected by APE1 alterations in terms of gene-environment interactions. In this review, we initially outline the critical APE1 functions in the various intracellular mechanisms including DNA repair and redox regulation and its roles in human diseases. Several findings demonstrate that the change in expression and activity as well as genetic variability of APE1 caused by environmental chemical (e.g., heavy metals and cigarette smoke) and physical carcinogens (ultraviolet and ionizing radiation) is likely associated with various cancers. These enable us to ultimately suggest APE1 as a vital marker for the prediction of environmental carcinogenesis risk.

Enhanced cytotoxic and genotoxic effects of gadolinium following ELF-EMF irradiation in human lymphocytes.

There are many studies of Gd nephrotoxicity and neurotoxicity, whereas research on cyto- and genotoxicity in normal human lymphocytes is scarce. It is important to investigate the effect of extremely low-frequency electromagnetic fields (ELF-EMF) on Gd toxicity, as patients are co-exposed to Gd and ELF-EMF generated by MRI scanners. We investigated the cytotoxicity and genotoixcity of Gd and the possible enhancing effect of ELF-EMF on Gd toxicity in cultured human lymphocytes by performing a micronuclei (MN) assay, trypan blue dye exclusion, single cell gel electrophoresis, and apoptosis analyses using flow cytometry. Isolated lymphocytes were exposed to 0.2-1.2 mM of Gd only or in combination with a 60-Hz ELF-EMF of 0.8-mT field strength. Exposing human lymphocytes to Gd resulted in a concentration- and time-dependent decrease in cell viability and an increase in MN frequency, single strand DNA breakage, apoptotic cell death, and ROS production. ELF-EMF (0.8 mT) exposure also increased cell death, MN frequency, olive tail moment, and apoptosis induced by Gd treatment alone. These results suggest that Gd induces DNA damage and apoptotic cell death in human lymphocytes and that ELF-EMF enhances the cytotoxicity and genotoxicity of Gd.

Cyto-/genotoxic effects of the ethanol extract of Chan Su, a traditional Chinese medicine, in human cancer cell lines.

ETHNOPHARMACOLOGICAL RELEVANCE: Chan Su, an ethanolic extract from skin and parotid venom glands of the Bufo bufo gargarizans Cantor, is widely used as a traditional Chinese medicine for cancer therapy. Although the anti-cancer properties of Chan Su have been investigated, no information exists regarding whether Chan Su has genotoxic effects in cancer cells. The aim of the present study was to examine the cyto-/genotoxic effect of Chan Su in human breast carcinoma (MCF-7 cells), human lung carcinoma (A-549 cells), human T cell leukemia (Jurkat T cells), and normal human lymphocytes. MATERIALS AND METHODS: Effects on the viability of MCF-7, A-549, Jurkat T cells, and normal lymphocytes were evaluated by Trypan blue exclusion assays. The DNA content in the sub-G1 region was detected by propidium iodide (PI) staining and flow cytometry. The genotoxicity of Chan Su was assessed by single-cell gel electrophoresis (comet assay) and the cytokinesis-block micronucleus assay (CBMN assay). RESULTS: Chan Su significantly inhibited the viability of MCF-7, A-549, and Jurkat T cells dose dependently, but had no effect on normal human lymphocytes. Apoptotic death of the cancer cells was evident after treatment. Chan Su also induced genotoxicity in a dose-dependent manner, as indicated by the comet and cytokinesis-block micronucleus assays. CONCLUSIONS: These findings suggest that Chan Su can induce apoptotic death of, and exert genotoxic effects on, MCF-7, A-549, and Jurkat T cells.

Selective Effects of Curcumin on CdSe/ZnS Quantum-dot-induced Phototoxicity Using UVA Irradiation in Normal Human Lymphocytes and Leukemia Cells.

Quantum dots (QDs) have received considerable attention due to their potential role in photosensitization during photodynamic therapy. Although QDS are attractive nanomaterials due to their novel and unique physicochemical properties, concerns about their toxicity remain. We suggest a combination strategy, CdSe/ZnS QDs together with curcumin, a natural yellow pigment from turmeric, to reduce QD-induced cytotoxicity. The aim of this study was to explore a potentially effective cancer treatment: co-exposure of HL-60 cells and human normal lymphocytes to CdSe/ZnS QDs and curcumin. Cell viability, apoptosis, reactive oxygen species (ROS) generation, and DNA damage induced by QDs and/or curcumin with or without ultraviolet A (UVA) irradiation were evaluated in both HL-60 cells and normal lymphocytes. In HL-60 cells, cell death, apoptosis, ROS generation, and single/double DNA strand breaks induced by QDs were enhanced by treatment with curcumin and UVA irradiation. The protective effects of curcumin on cell viability, apoptosis, and ROS generation were observed in normal lymphocytes, but not leukemia cells. These results demonstrated that treatment with QD combined with curcumin increased cell death in HL-60 cells, which was mediated by ROS generation. However, curcumin acted as an antioxidant in cultured human normal lymphocytes.

Cytotoxicity and genotoxicity induced by photothermal effects of colloidal gold nanorods.

Gold nanorods (Au NRs) that absorb near-infrared (NIR) light have great potential in the field of nanomedicine. Photothermal therapy (PTT), a very attractive cancer therapy in nanomedicine, combines nanomaterials and light. The aim of this study was to elucidate the molecular mechanism involved in Au NR-mediated cytotoxic, genotoxic, and other biological responses, in the presence or absence of NIR irradiation. Specifically, cell death mode, generation of reactive oxygen species, DNA damage, apoptotic gene expression, and cell morphological changes induced by Au NRs under NIR irradiation were evaluated in cancer cells. In human lung adenocarcinoma epithelial cells (A549 cells), mild necrosis via DNA damage was induced by NIR responsive Au NRs. Unlike in the cancer cells, cell viability of normal human lymphocyte was not affected by the combined treatment of Au NRs and NIR irradiation. This study delineates differential cytotoxic and genotoxic susceptibility of cancer and normal cells during photothermal treatment of Au NRs. In conclusion, our results suggest that the photothermal cyto-/genotoxic activity of Au NRs is an effective method for cancer therapy in human lung cancer cells.

Cyto-/genotoxic effect of CdSe/ZnS quantum dots in human lung adenocarcinoma cells for potential photodynamic UV therapy applications.

Quantum dots (QDs) are luminescent nanoparticles (NPs) with promising potential in numerous medical applications, but there remain persistent human health and safety concerns. Although the cytotoxic effects of QDs have been extensively investigated, their genotoxic effects remain under-explored. This study scrutinized the cyto- and genotoxic effects of QDs with a Cadmium selenide/Zinc sulfide (CdSe/ZnS) core/shell, and suggests comprehensive guidelines for the application of QDs in cancer therapy. QDs were used to treat A549 cells in the presence and absence of ultraviolet A/B (UVA/UVB) irradiation. QD-induced cell death was evaluated by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), apoptosis, and lactate dehydrogenase (LDH) assays, as well as by real-time PCR analysis of differential mRNA levels of genes, such as ataxia telangiectasia mutated (ATM), p53, and caspase-9, involved in apoptosis. The genotoxic effect of CdSe/ZnS QDs was measured in human cancer cells, for the first time, by comet and micronucleus assays. Treatment with CdSe/ZnS QDs and UVB irradiation resulted in the most severe extent of cell death, indicating strong induction of phototoxicity by CdSe/ZnS QDs in the presence of UVB. Both apoptotic and necrotic cell death were observed upon QDs and UVB combined treatment. The induction of Olive tail moments and micronuclei formation was also most significant when CdSe/ZnS QDs and UVB irradiation were combined. Our results on the genotoxic effect and mechanistic details of CdSe/ZnS QD-induced cell death suggest that UVB irradiation is the most effective method for increasing the potency of QDs during photodynamic cancer therapy.

Enhancement of cisplatin cytotoxicity by benzyl isothiocyanate in HL-60 cells.

Cis-diamminedichloroplatinum (II) (cisplatin) is one of the most widely used chemotherapeutic drugs, but its effectiveness is limited by tumor cell resistance and the severe side effects it causes. One strategy for overcoming this problem is the concomitant use of natural dietary compounds as therapeutic agents. Benzyl isothiocyanate (BITC) is a promising chemopreventive agent found in cruciferous vegetables and papaya fruits. The aim of this study was to investigate the effects of BITC on cisplatin-induced cytotoxicity in human promyelocytic leukemia cells and normal human lymphocytes. The combined treatment of HL-60 cells with BITC followed by cisplatin (BITC/cisplatin) caused a significant decrease in cell viability. BITC also increased apoptotic cell death compared to cisplatin treatment alone. In normal human lymphocytes, BITC did not enhance the cytotoxic effects of cisplatin. Cellular exposure to BITC/cisplatin increased reactive oxygen species (ROS) generation but decreased the total glutathione (GSH) level in HL-60 cells. Pretreatment of HL-60 cells with N-acetylcysteine or glutathione monoethyl ester effectively decreased BITC/cisplatin-induced cell death. The addition of the extracellular signal-regulated kinase (ERK) inhibitor PD98059 abolished BITC/cisplatin-induced apoptosis. Taken together, our results suggest that BITC enhances cisplatin-induced cytotoxicity through the generation of ROS, depletion of GSH, and ERK signaling in HL-60 cells.

Cytotoxicity and genotoxicity of titanium dioxide nanoparticles in UVA-irradiated normal peripheral blood lymphocytes.

The phototoxicity of ultraviolet A irradiation (UVA) can be enhanced by photosensitizing agents, such as titanium dioxide nanoparticles (100 nm in diameter, "normal-TiO2"). Nano-TiO2 treatment in the absence of UVA caused a slight decrease in cell viability, but in the presence of UVA, it caused a significant decrease in cell viability. In the presence of UVA, nano-TiO2 also significantly increased the percentage of the cell population in the sub-G1 phase, induced activation of the proapoptotic proteins, caspase-9, caspase-3, and poly(ADP)ribose polymerase, significantly increased the production of reactive oxygen species (ROS), and induced the loss of the mitochondrial membrane potential (MMP), suggesting that UVA and nano-TiO2 synergistically promoted apoptosis via a mitochondrial pathway. In the presence of UVA, but not in its absence, nano-TiO2 treatment also caused a significant increase in DNA damage. Normal-TiO2 used at the same concentrations did not cause DNA damage, induce ROS generation, trigger mitochondrial membrane depolarization, or increase apoptotic cell death, regardless of UVA exposure. Taken together, these results suggest that nano-TiO2 and UVA synergistically promote rapid ROS generation and MMP collapse, triggering apoptosis. Additionally, they show that small TiO2 particles are more phototoxic than larger ones.

Genotoxic effects of 3 T magnetic resonance imaging in cultured human lymphocytes.

The clinical and preclinical use of high-field intensity (HF, 3 T and above) magnetic resonance imaging (MRI) scanners have significantly increased in the past few years. However, potential health risks are implied in the MRI and especially HF MRI environment due to high-static magnetic fields, fast gradient magnetic fields, and strong radiofrequency electromagnetic fields. In this study, the genotoxic potential of 3 T clinical MRI scans in cultured human lymphocytes in vitro was investigated by analyzing chromosome aberrations (CA), micronuclei (MN), and single-cell gel electrophoresis. Human lymphocytes were exposed to electromagnetic fields generated during MRI scanning (clinical routine brain examination protocols: three-channel head coil) for 22, 45, 67, and 89 min. We observed a significant increase in the frequency of single-strand DNA breaks following exposure to a 3 T MRI. In addition, the frequency of both CAs and MN in exposed cells increased in a time-dependent manner. The frequencies of MN in lymphocytes exposed to complex electromagnetic fields for 0, 22, 45, 67, and 89 min were 9.67, 11.67, 14.67, 18.00, and 20.33 per 1000 cells, respectively. Similarly, the frequencies of CAs in lymphocytes exposed for 0, 45, 67, and 89 min were 1.33, 2.33, 3.67, and 4.67 per 200 cells, respectively. These results suggest that exposure to 3 T MRI induces genotoxic effects in human lymphocytes.

Comparative studies on the genotoxicity and cytotoxicity of polymeric gene carriers polyethylenimine (PEI) and polyamidoamine (PAMAM) dendrimer in Jurkat T-cells.

A safe alternative to the viral system used in gene therapy is a nonviral gene delivery system. Although polyethylenimine (PEI) and polyamidoamine (PAMAM) dendrimer are among the most promising gene-carrier candidates for efficient nonviral gene delivery, safety concerns regarding their toxicity remain. The aim of this study was to scrutinize the underlying mechanism of the cytotoxicity and genotoxicity of PEI (25 kDa) and PAMAM (G4). To our knowledge, this is the first study to explore the genotoxic effect of polymeric gene carriers. To evaluate cell death by PEI and PAMAM, we performed propidium-iodide staining and lactate-dehydrogenase release assays. The genotoxicity of the polymers was measured by comet assay and cytokinesis-block micronucleus assay. PEI- and PAMAM-treated groups induced both necrotic and apoptotic cell death. In the comet assay and micronuclei formation, significant increases in DNA damage were observed in both treatments. We conclude that PEI and PAMAM dendrimer can induce not only a relatively weak apoptotic and a strong necrotic effect, but also a moderate genotoxic effect.

Micronucleus-centromere assay and DNA repair gene polymorphism in lymphocytes of industrial radiographers.

The micronucleus-centromere assay using a pan-centromeric probe was used to assess chromosomal damage in lymphocytes of 47 industrial radiographers occupationally exposed to low dose ionizing radiation and 47 controls. The influence of genotype of DNA repair genes (XRCC1(399), XRCC3(241) and XPD(751)) on micronuclei (MN) frequency was also investigated. Centromere negative micronuclei (MNC-) frequency was significantly higher in radiographers than in controls, whereas similar centromere positive micronuclei (MNC+) frequency was observed in both groups. Poisson regression analyses revealed that the MNC- frequency was significantly associated with radiation occupational exposure and with cumulative-radiation doses in radiographers, after adjusting for confounding variables such as age, smoking, alcohol intake and genotypes. Compared to homozygous wild-type subjects, MNC- frequency in radiographers with variant XRCC3 genotype was significantly higher using univariate analysis. There were no differences in MNC- or MNC+ frequencies by genotype in controls. In conclusion, scoring of MNC- is a useful cytogenetic biomonitoring method for radiographers. Polymorphisms in XRCC3 might contribute to the increased genetic damage in individuals occupationally exposed to chronic ionizing radiation.

Titanium dioxide nanoparticles induce apoptosis through the JNK/p38-caspase-8-Bid pathway in phytohemagglutinin-stimulated human lymphocytes.

We investigated the signaling pathways underlying nano-TiO(2)-induced apoptosis in cultured human lymphocytes. Nano-TiO(2) increased the proportion of sub-G1 cells, activated caspase-9 and caspase-3, and induced caspase-3-mediated PARP cleavage. Nano-TiO(2) also induced loss of mitochondrial membrane potential, which suggests that nano-TiO(2) induces apoptosis via a mitochondrial pathway. A time-sequence analysis of the induction of apoptosis by nano-TiO(2) revealed that nano-TiO(2) triggered apoptosis through caspase-8/Bid activation. We also observed that inhibition of caspase-8 by z-IETD-fmk suppressed the caspase-8/Bid activation, caspase-3-mediated PARP cleavage, and apoptosis. Nano-TiO(2) activated two MAPKs, p38 and JNK. In addition, the selective p38 inhibitor SB203580 and selective JNK inhibitor SP600125 suppressed nano-TiO(2)-induced apoptosis and caspase-8 activation to moderate and significant extents, respectively. Knockdown of protein levels of JNK1 and p38 using an RNA interference technique also suppressed caspase-8 activation. Our results suggest that nano-TiO(2)-induced apoptosis is mediated by the p38/JNK pathway and the caspase-8-dependent Bid pathway in human lymphocytes.

Risk assessment of hydroquinone: differential responses of cell growth and lethality correlated to hydroquinone concentration.

Hydroquinone (HQ) is a major metabolite of benzene and has been used as an antioxidant, a stabilizer, a photographic reducer, and an ingredient in skin lighteners. In this study, the effects of low (5 microM) and high (50 microM) concentrations of HQ were investigated on cell growth and lethality in Jurkat cells. Intracellular reactive oxygen species (ROS) levels were increased with both HQ concentrations. Fifty micromolar HQ markedly increased phosphorylation of ERK and activation of caspase-9/-3, followed by PARP cleavage. The addition of ERK inhibitor PD98059 or N-acetylcysteine (NAC) abolished HQ-induced apoptosis. Five micromolar HQ activated ERK protein, but not JNK or p38. However, S-phase recruitment was decreased by preincubation with NAC, but not PD98059. Thus, high levels of ROS contributed to HQ-induced apoptosis via ERK signaling and the caspase pathway, whereas low quantities of ROS resulted in S-phase recruitment in the cell-cycle distribution.