Induction of micronuclei in human, goat, rabbit peripheral blood lymphocytes and mouse splenic lymphocytes irradiated in vitro with gamma radiation

Genomic Instability and Cyto-Genotoxic Damage in Animal Species

Genomic instability is a condition that may be associated with carcinogenesis and/or physiological disorders when genetic lesions are not repaired. Besides, wild, captive, and domesticated vertebrates are exposed to xenobiotics, leading to health disorders due to cytogenotoxicity. This chapter provides an overview of tests to assess cytogenotoxicity based on micronuclei (MNi) formation. Bone marrow micronuclei test (BmMNt), peripheral blood erythrocyte micronuclei test (PBMNt), and lymphocyte cytokinesis blocking micronuclei assay (CBMN) are discussed. The most illustrative studies of these techniques applied in different vertebrates of veterinary interest are described. The values of spontaneous basal micronuclei in captive, experimental, and farm animals (rodents, hamsters, pigs, goats, cattle, horses, fish) are summarized. In addition, a flow cytometry technique is presented to reduce the time taken to record MNi and other cellular abnormalities. Flow cytometry is helpful to analyze some indicators of genomic instability, such as cell death processes and stages (necrosis, apoptosis) and to efficiently evaluate some biomarkers of genotoxicity like MNi in BmMNt, PBMNt, and CBMN. The intention is to provide veterinary professionals with techniques to assess and interpret cytogenotoxicity biomarkers to anticipate therapeutic management in animals at risk of carcinogenesis or other degenerative diseases.

Cytogenetic Damage of Human Lymphocytes in Humanized Mice Exposed to Neutrons and X Rays 24 h After Exposure

Detonation of an improvised nuclear device highlights the need to understand the risk of mixed radiation exposure as prompt radiation exposure could produce significant neutron and gamma exposures. Although the neutron component may be a relatively small percentage of the total absorbed dose, the large relative biological effectiveness (RBE) can induce larger biological DNA damage and cell killing. The objective of this study was to use a hematopoietically humanized mouse model to measure chromosomal DNA damage in human lymphocytes 24 h after in vivo exposure to neutrons (0.3 Gy) and X rays (1 Gy). The human dicentric and cytokinesis-block micronucleus assays were performed to measure chromosomal aberrations in human lymphocytes in vivo from the blood and spleen, respectively. The mBAND assay based on fluorescent in situ hybridization labeling was used to detect neutron-induced chromosome 1 inversions in the blood lymphocytes of the neutron-irradiated mice. Cytogenetics endpoints, dicentrics and micronuclei showed that there was no significant difference in yields between the 2 irradiation types at the doses tested, indicating that neutron-induced chromosomal DNA damage in vivo was more biologically effective (RBE ∼3.3) compared to X rays. The mBAND assay, which is considered a specific biomarker of high-LET neutron exposure, confirmed the presence of clustered DNA damage in the neutron-irradiated mice but not in the X-irradiated mice, 24 h after exposure.

Determination of cytogenetic markers for biological monitoring in coypu (Myocastor coypu)

Cytogenetic tests are used to assess the influence of physical and chemical factors with potential mutagenic and genotoxic properties on the animal organism. The test results make it possible to eliminate mutagens, as well as helping predict possible genetic consequences in animal cells and assess animal resistance. The aim of this study was to examine, using cytogenetic tests, the spontaneous chromosome and DNA damage in coypu lymphocytes. Four tests: fragile site (FS), bleomycin (BLM), micronucleus, (MN) and comet were used for the first time in coypu cells. The averages with standard deviations obtained in the research were as follows: 3.30 ± 0.80 fragile sites/cell; 0.63 ± 0.80 BLM damage/cell; 6.10 ± 0.53% binucleated cells with MN; and 3.24 ± 0.63% DNA in tail. The present analysis showed high interindividual variation in spontaneous chromosomal and DNA damage levels. In the case of micronucleus, fragile sites, and comet assays, the differences between animals were statistically significant. The data suggest that these assays are sensitive enough to detect some effects on an individual animal and can be proposed as tools for coypu biomonitoring.

The distinct microbial community in Aurelia coerulea polyps versus medusae and its dynamics after exposure to 60Co-γ radiation

Radiation (e.g., nuclear leakage) is a common harmful factor in the ocean that potentially affects the microbial community in nearby benthic hosts such as jellyfish polyps, which is essential for the maintenance of jellyfish populations and high-quality medusae. After comparison with the microbial community of medusae, the effect of ⁶⁰Co-γ on the microbial community in Aurelia coerulea polyps was dynamically tested using 16S rRNA gene sequencing. Our results suggested that Proteobacteria (76.19 ± 3.24%), Tenericutes (12.93 ± 3.20%) and Firmicutes (8.33 ± 1.06%) are most abundant in medusae, while Proteobacteria (29.49 ± 2.29%), Firmicutes (46.25 ± 5.59%), and Bacteroidetes (20.16 ± 2.65%) are the top three phyla in polyps. After ⁶⁰Co-γ radiation, the proportion of Proteobacteria increased from 29.49 ± 2.29% to 59.40 ± 3.09% over 5 days, while that of Firmicutes decreased from 46.25 ± 5.59% to 13.58 ± 3.74%. At the class level, Gammaproteobacteria continually increased during the 5 days after radiation exposure, whereas Bacilli declined, followed by partial recovery, and Alphaproteobacteria and Flavobacteriia remained almost unchanged. Intriguingly, Staphylococcus from Firmicutes and three other genera, Rhodobacter, Vibrio, and Methylophaga, from Proteobacteria greatly overlapped according to their KEGG functions. It is concluded that the microbial community in A. coerulea polyps is distinct from that in the medusae and is greatly affected by ⁶⁰Co-γ exposure, with a growth (0-3 d) period and a redistribution (3-5 d) period. The dynamic change in the microbial community is probably an important self-defense process in response to external interference that is regulated by the host's physiological characteristics and the intense interspecific competition among symbiotic microbes with similar functions and functional redundancies.

Effect of dose rate on residual γ-H2AX levels and frequency of micronuclei in X-irradiated mouse lymphocytes

The biological risks associated with low-dose-rate (LDR) radiation exposures are not yet well defined. To assess the risk related to DNA damage, we compared the yields of two established biodosimetry end points, γ-H2AX and micronuclei (MNi), in peripheral mouse blood lymphocytes after prolonged in vivo exposure to LDR X rays (0.31 cGy/min) vs. acute high-dose-rate (HDR) exposure (1.03 Gy/min). C57BL/6 mice were total-body irradiated with 320 kVP X rays with doses of 0, 1.1, 2.2 and 4.45 Gy. Residual levels of total γ-H2AX fluorescence in lymphocytes isolated 24 h after the start of irradiation were assessed using indirect immunofluorescence methods. The terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay was used to determine apoptotic cell frequency in lymphocytes sampled at 24 h. Curve fitting analysis suggested that the dose response for γ-H2AX yields after acute exposures could be described by a linear dependence. In contrast, a linear-quadratic dose-response shape was more appropriate for LDR exposure (perhaps reflecting differences in repair time after different LDR doses). Dose-rate sparing effects (P < 0.05) were observed at doses ≤2.2 Gy, such that the acute dose γ-H2AX and TUNEL-positive cell yields were significantly larger than the equivalent LDR yields. At the 4.45 Gy dose there was no difference in γ-H2AX expression between the two dose rates, whereas there was a two- to threefold increase in apoptosis in the LDR samples compared to the equivalent 4.45 Gy acute dose. Micronuclei yields were measured at 24 h and 7 days using the in vitro cytokinesis-blocked micronucleus (CBMN) assay. The results showed that MNi yields increased up to 2.2 Gy with no further increase at 4.45 Gy and with no detectable dose-rate effect across the dose range 24 h or 7 days post exposure. In conclusion, the γ-H2AX biomarker showed higher sensitivity to measure dose-rate effects after low-dose LDR X rays compared to MNi formation; however, confounding factors such as variable repair times post exposure, increased cell killing and cell cycle block likely contributed to the yields of MNi with accumulating doses of ionizing radiation.

Mouse and human cells versus oxygen

Mice and humans are at opposite ends of the mammalian spectrum of longevity. A major question in biology is whether this difference can be accounted for by differences in the properties of cells from these two species. A new publication from Judith Campisi's lab reports that human cells in culture are more resistant than mouse cells to the damaging effects of 20% oxygen. The greater burden of DNA damage sustained by mouse cells causes them to rapidly enter a phase of culture in which most cells enter permanent growth arrest (replicative senescence). However, some mouse cells usually escape from senescence and then grow into an immortal cell line. This never happens in human fibroblast cell cultures. Human cells also eventually enter replicative senescence in culture, but this phenomenon is caused by shortening of telomeres and not by DNA damage of the type responsible for mouse cell senescence. Human fibroblasts never spontaneously escape from senescence. This Perspective reviews differences between mouse and human cells that could account for these differences in behavior. Some evidence indicates that human cells are generally more resistant than mouse cells to oxidative damage to DNA, but more needs to be done to confirm this finding and to understand the underlying mechanisms. Whether or not there are differences in the amount of DNA damage caused by oxygen or in the early phase of repair, there may be important differences in the later consequences of DNA damage. Mouse cells appear to be able to continue to divide with DNA damage that has not been repaired or has been misrepaired, and becomes fixed in the form of chromosomal abnormalities. The checkpoints that cause cells to stop dividing when chromosomes develop abnormalities (aberrations or shortened telomeres) appear to operate more efficiently in human cells. Much more work is needed to understand the basis for these differences and the implications for aging and cancer.

Mutagenicity of gamma-radiation, mitomycin C, and etoposide in the Hprt and Tk genes of Tk(+/-) mice

The recently developed Tk(+/-) mouse detects in vivo somatic cell mutation in the endogenous, autosomal Tk gene. To evaluate the sensitivity of this model, we have treated Tk(+/-) mice with three agents that induce DNA damage by different mechanisms, and determined spleen lymphocyte mutant frequencies (MFs) in the autosomal Tk gene and in the X-linked Hprt gene. gamma-Radiation, which produces single- and double-strand breaks by nonspecific oxidative stress, efficiently increased Hprt MF, but not Tk MF. Mitomycin C, which produces bulky DNA monoadducts and crosslinks, was mutagenic in both the Hprt and Tk genes, but the response was greater in the Tk gene. An inhibitor of the ligase function of DNA topoisomerase II, etoposide, did not increase Hprt MF, and induced a small, but nonsignificant increase in Tk MF. Combined with previous data, the results indicate that the two genes are differentially sensitive to many agents, and that the Tk gene is more sensitive than the Hprt gene to some, but not all types of DNA damage.