Nicotine interacts with DNA lesions induced by alpha radiation which may contribute to erroneous repair in human lung epithelial cells

PURPOSE

Epidemiological studies show that radon and cigarette smoke interact in inducing lung cancer, but the contribution of nicotine in response to alpha radiation emitted by radon is not well understood.

MATERIALS AND METHODS

Bronchial epithelial BEAS-2B cells were either pre-treated with 2 µM nicotine during 16 h, exposed to radiation, or the combination. DNA damage, cellular and chromosomal alterations, oxidative stress as well as inflammatory responses were assessed to investigate the role of nicotine in modulating responses.

RESULTS

Less γH2AX foci were detected at 1 h after alpha radiation exposure (1-2 Gy) in the combination group versus alpha radiation alone, whereas nicotine alone had no effect. Comet assay showed less DNA breaks already just after combined exposure, supported by reduced p-ATM, p-DNA-PK, p-p53 and RAD51 at 1 h, compared to alpha radiation alone. Yet the frequency of translocations was higher in the combination group at 27 h after irradiation. Although nicotine did not alter G2 arrest at 24 h, it assisted in cell cycle progression at 48 h post radiation. A slightly faster recovery was indicated in the combination group based on cell viability kinetics and viable cell counts, and significantly using colony formation assay. Pan-histone acetyl transferase inhibition using PU139 blocked the reduction in p-p53 and γH2AX activation, suggesting a role for nicotine-induced histone acetylation in enabling rapid DNA repair. Nicotine had a modest effect on reactive oxygen species induction, but tended to increase alpha particle-induced pro-inflammatory IL-6 and IL-1β (4 Gy). Interestingly, nicotine did not alter gamma radiation-induced γH2AX foci.

CONCLUSIONS

This study provides evidence that nicotine modulates alpha-radiation response by causing a faster but more error-prone repair, as well as rapid recovery, which may allow expansion of cells with genomic instabilities. These results hold implications for estimating radiation risk among nicotine users.

New Insights into the Understanding of Mechanisms of Radiation-Induced Heart Disease

OPINION STATEMENT

Cancer patients who receive high-dose thoracic radiotherapy may develop radiation-induced heart disease (RIHD). The clinical presentation of RIHD comprises coronary artery atherosclerosis, valvular disease, pericarditis, cardiomyopathy, and conduction defects. These complications have significantly reduced due to the improved radiotherapy techniques. However, such methods still could not avoid heart radiation exposure. Furthermore, people who received relatively low-dose radiation exposures have exhibited significantly elevated RIHD risks in cohort studies of atomic bomb survivors and occupational exposures. The increased potential in exposure to natural and artificial ionizing radiation sources has emphasized the necessity to understand the development of RIHD. The pathological processes of RIHD include endothelial dysfunction, inflammation, fibrosis, and hypertrophy. The underlying mechanisms may involve the changes in oxidative stress, DNA damage response, telomere erosion, mitochondrial dysfunction, epigenetic regulation, circulation factors, protein post-translational modification, and metabolites. This review will discuss the recent advances in the mechanisms of RIHD at cellular and molecular levels.

Frequencies of Chromosome Aberrations are Lower in Splenic Lymphocytes from Mice Continuously Exposed to Very Low-Dose-Rate Gamma Rays Compared with Non-Irradiated Control Mice

Chromosome aberrations have been one of the most sensitive and reliable biomarkers of exposure to ionizing radiation. Using the multiplex fluorescence in situ hybridization (M-FISH) technique, we compared the changes, over time, in the frequencies of translocations and of dicentric chromosomes in the splenic lymphocytes from specific pathogen-free (SPF) C3H/HeN female mice continuously exposed to 0.05 mGy/day (18.25 mGy/year) gamma rays for 125 to 700 days (total accumulated doses: 6.25-35 mGy) with age-matched non-irradiated controls. Results show that the frequencies of translocations and of dicentric chromosomes increased significantly over time in both irradiated and non-irradiated control mice, and that the frequencies were significantly lower, not higher, in the irradiated mice, which differs from our previous reports of increased chromosome aberration frequencies at higher radiation dose rates of 1 mGy/day and 20 mGy/day. These results will be useful when considering the radiation risk at very low-dose rates comparable to regulatory dose limits.

Pattern of chromosomal aberrations persisting over 30 years in a Chernobyl Nuclear Power Plant accident survivor: study using mFISH

The long-term in vivo cytogenetic effects of high-dose radiation exposure can be traced in accidentally irradiated persons, and particularly useful for developing strategies of monitoring and therapy of such patients, as well as for elucidating the fundamental aspects of hematopoiesis and radiobiology. Using 24-color fluorescent in situ hybridization (mFISH), we analysed the frequency and the spectrum of chromosomal aberrations (CA) in peripheral blood lymphocytes of the Chernobyl Nuclear Power Plant (NPP) accident victim 30, 31, 32 and 33 years after acute accidental exposure to high-dose gamma radiation of the whole body. Totally, 993 metaphase cells were analyzed (or 219, 272, 258, 244 cells each year), of which 297 were aberrant. Our study demonstrated a constant aberrant cell frequency at 28% in 2016-2018 years, while in 2019, a significant increase up to 35% occurred due to contribution of significantly elevated frequency of simple aberrations in the absence of evident recent genotoxic factors. Four clonal aberrations were detected, three of which persisted for more than one year at a frequency up to 2.5% of analyzed cells. The distribution of 731 breakpoints per individual chromosomes was nearly proportional to their physical length, excepting Chromosomes 13 and 20, which were significantly breakpoint-deficient compared to the genome median rate. Monitoring of the long-term effects on chromosomal instability caused by radiation exposure is important for understanding and predicting the long-term effects of ionizing radiation.

Destabilizing Effects of Ionizing Radiation on Chromosomes: Sizing up the Damage

For long-term survival and evolution, all organisms have depended on a delicate balance between processes involved in maintaining stability of their genomes and opposing processes that lead toward destabilization. At the level of mammalian somatic cells in renewal tissues, events or conditions that can tip this balance toward instability have attracted special interest in connection with carcinogenesis. Mutations affecting DNA (and its subsequent repair) would, of course, be a major consideration here. These may occur spontaneously through endogenous cellular processes or as a result of exposure to mutagenic environmental agents. It is in this context that we discuss the rather unique destabilizing effects of ionizing radiation (IR) in terms of its ability to cause large-scale structural rearrangements to the genome. We present arguments supporting the conclusion that these and other important effects of IR originate largely from microscopically visible chromosome aberrations.

Occam's broom and the dirty DSB: cytogenetic perspectives on cellular response to changes in track structure and ionization density

Given equal doses, it is well-known that densely ionizing radiations are more potent in causing a number of biological effects compared to sparsely ionizing radiations, such as x- or gamma rays. According to classical models of radiation action, this results from differences in the spatial distribution of lesions along charged particle tracks. In recent years investigators have been barraged with the alternative narrative that this is instead due to 'qualitative' differences in the types of molecular lesions that each type of radiation produces. The present review discusses, mainly from a cytogenetic perspective, the merits and shortcomings of these seemingly contradictory viewpoints. There may be a kernel of truth to the idea that qualitative differences in the types of molecular lesions produced at the nanometer level affect RBE/LET relationships, but to ignore the fact that such differences result from longer-range spatial distributions of lesions produced along charged particle tracks is an unjustifiably narrow stance tantamount to employing Occam's Broom. Not only are such spatial considerations indispensable in explaining the impact of ionization density upon higher-order biological endpoints, particularly chromosome aberrations, the explanations they provide render arguments based principally on the quality of IR damage largely superfluous.

Assessment of Genomic Instability in Medical Workers Exposed to Chronic Low-Dose X-Rays in Northern China

The increasing use of ionizing radiation (IR) in medical diagnosis and treatment has caused considerable concern regarding the effects of occupational exposure on human health. Despite this concern, little information is available regarding possible effects and the mechanism behind chronic low-dose irradiation. The present study assessed potential genomic damage in workers occupationally exposed to low-dose X-rays. A variety of analyses were conducted, including assessing the level of DNA damage and chromosomal aberrations (CA) as well as cytokinesis-block micronucleus (CBMN) assay, gene expression profiling, and antioxidant level determination. Here, we report that the level of DNA damage, CA, and CBMN were all significantly increased. Moreover, the gene expression and antioxidant activities were changed in the peripheral blood of men exposed to low-dose X-rays. Collectively, our findings indicated a strong correlation between genomic instability and duration of low-dose IR exposure. Our data also revealed the DNA damage repair and antioxidative mechanisms which could result in the observed genomic instability in health-care workers exposed to chronic low-dose IR.