Induction of micronuclei by X-radiation in human, mouse and rat peripheral blood lymphocytes

New Properties of a Well-Known Antioxidant: Pleiotropic Effects of Human Lactoferrin in Mice Exposed to Gamma Irradiation in a Sublethal Dose

We studied the effects of human lactoferrin (hLf), a multifunctional protein from the transferrin family, on integral (survival, lifespan during the experiment, body weight, behavior, subfractional compositions of blood serum) and systemic (hemoglobin level, leukocyte number, differential leukocyte count, histological structure of the liver and spleen) parameters of the body in mice after acute gamma irradiation in a sublethal dose. The experiments were performed on male C57BL/6 mice. The mice in the experimental groups were exposed to whole-body gamma radiation in a dose of 7.5 Gy from a ⁶⁰Co source. Immediately after irradiation and 24 h after it, some animals received an intraperitoneal injection of hLf (4 mg/mouse). Single or repeated administration of hLf had a positive pleiotropic effect on irradiated animals: animal survival increased from 28% to 78%, and the mean life expectancy during the experiment (30 days) increased from 16 to 26 days. A compensatory effect of hLf on radiation-induced body weight loss, changes in homeostasis parameters, and a protective effect on the structural organization of the spleen were demonstrated. These data indicate that Lf has potential as a means of early therapy after radiation exposure.

Animal Lymphocyte Metaphase Chromosome Preparation

Metaphase chromosome analysis of lymphocytes is the gold standard for biodosimetry to estimate the levels of radiation exposure in various animals as well as humans. Animals, including experimental, companion, and wild animals, are powerful and indispensable models for researching radiation injury, safety, and therapy. Moreover, biodosimetry of animal models can be used to support human biodosimetry data and may be useful for estimating environmental contamination by radioactive materials. The basic restraint procedure and venipuncture technique are different depending on each animal type. The general procedure evaluating metaphase chromosomes is similar to the human blood technique except for a minor modification in the initial culture. This chapter will introduce basic mouse, rat, rabbit, dog, cat, cow, horse, goat, pig, and wild boar venipuncture and blood sampling techniques for metaphase chromosome preparation and analysis.

Radioprotective effect of lactoferrin in mice exposed to sublethal X-ray irradiation

The radioprotective effect of lactoferrin (LF) was studied in mice subjected to sublethal X-ray irradiation. The mice were randomly divided into the Control (non-irradiated mice fed a standard diet without LF), IR (irradiated mice fed a standard diet) and IR+LF (irradiated mice fed LF) groups. The mice were fed daily for 7 days prior to irradiation and for 30 continuous days following irradiation. The survival ratio of the mice in the IR+LF group was significantly increased compared with the IR group between days 15 and 30 after irradiation. The body weight of the mice in the IR+LF group was increased compared with the IR group, and the difference was statistically significant. Blood was collected from the mice via the tail vein on days 2, 7, 14, 21 and 30 following irradiation. The laboratory indicators, including leukocyte, erythrocyte and platelet counts recovered more rapidly following irradiation in the IR+LF group compared with the IR group. Treatment of the irradiated mice with LF significantly reduced the DNA damage. In the hepatic tissue the level of superoxide dismutase in the IR+LF group was significantly increased, while malondialdehyde was significantly decreased compared with the IR group. These findings indicate that LF may prevent radiation damage and may have potential as a treatment for patients with cancer who receive radiotherapy.

Peripheral blood lymphocyte micronucleus frequencies in men from areas of Kerala, India, with high vs normal levels of natural background ionizing radiation

We have measured the frequencies of micronuclei (MN) in adult male individuals living in areas of the Kerala coast, southwest India, with either high (HLNRA, >1.5mGy/year) or normal levels of natural ionizing radiation (NLNRA, ≤1.5mGy/year). Blood samples were obtained from 141 individuals, 94 from HLNRA and 47 from NLNRA, aged 18-72, and were subjected to the cytokinesis-block micronucleus (CBMN) assay. An average of 1835 binucleated (BN) cells per individual were scored. The overall frequency of MN (mean±SD) was 11.7±6.7 per 1000 BN cells. The frequencies of MN in the HLNRA (11.7±6.6) and NLNRA (11.6±6.7) were not statistically significantly different (P=0.59). However, a statistically significant (P<0.001) age-dependent increase in MN frequency was observed among individuals from both HLNRA and NLNRA. No natural background radiation dose-dependent increase in MN frequency was seen. MN frequency was not influenced by tobacco smoking or chewing but it was increased among individuals consuming alcohol. Chronic low-dose radiation in the Kerala coast did not have a significant effect on MN frequency among adult men.

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.

SFTG international collaborative study on in vitro micronucleus test

This study on the in vitro micronucleus assay, comprising 11 laboratories using human lymphocytes, was coordinated by an organizing committee supported by the SFTG (the French branch of the European Environmental Mutagen Society). Nine coded substances were assessed for their ability to induce micronuclei in human lymphocytes in vitro, mitomycin C being used as a positive control. Cultures were exposed to the test substances for a short (early or late) time or for a long time, followed by a short or long recovery period, in the presence of cytochalasin B. Each chemical was evaluated, generally in two laboratories, using three treatment schedules at least twice. The data were assessed for acceptability, and then classified as negative, positive or equivocal. Two of seven genotoxic compounds, namely colchicine and bleomycin, clearly induced micronuclei. Reproducible results were difficult to obtain for some substances, which tended to be those acting at specific stages of the cell cycle. Cytosine arabinoside, diethylstilboestrol and 5-fluorouracil were classified as equivocal. Urethane and thiabendazole were classified as negative. The two presumed non-genotoxic compounds, mannitol and clofibrate, did not induce micronuclei. Repeat testing, exposing cells at both an early and late time after mitogenic stimulation, was needed to detect substances classified as equivocal. These results show the importance of achieving sufficient inhibition of nuclear division to avoid the possibility of missing an effect. The evaluation of micronuclei in mononucleated as well as binucleated cells was particularly useful to detect aneugens. There were no false positive results using lymphocytes, indicating a high specificity. It is concluded that the clastogenic or aneugenic potential in vitro of the substances tested was correctly identified in this study, but that refining the protocol to take into account factors such as the stages of the cell cycle exposed to the compound, or the duration of recovery would be likely to improve the sensitivity of detection using lymphocytes.

SFTG international collaborative study on in vitro micronucleus test I. General conditions and overall conclusions of the study

This study, coordinated by the SFTG (French branch of European Environmental Mutagen Society), included 38 participants from Europe, Japan and America. Clastogens (bleomycin, urethane), including base and nucleoside analogs (5-fluorouracil and cytosine arabinoside), aneugens and/or polyploidy inducers (colchicine, diethylstilboestrol, griseofulvin and thiabendazole), as well as non-genotoxic compounds (mannitol and clofibrate), were tested. Four cell types were used, i.e. human lymphocytes in the presence of cytochalasin B and CHO, CHL and L5178Y cell lines, in the presence or absence of cytochalasin B, with various treatment-recovery schedules. Mitomycin C was used as a positive control for all cell types. Mannitol and clofibrate were consistently negative in all cell types and with all treatment-recovery conditions. Urethane, known to induce questionable clastogenicity, was not found as positive. Bleomycin and mitomycin C were found positive in all treatment-recovery conditions. The base and nucleoside analogs were less easy to detect, especially 5-fluorouracil due to the interference with cytotoxicity, while cytosine arabinoside was detected in all cell types depending on the treatment-recovery schedule. Aneugens (colchicine, diethylstilboestrol and griseofulvin) were all detected in all cell types. In this study, the optimal detection was ensured when a short treatment followed by a long recovery was associated with a long continuous treatment without recovery. There was no impact of the presence or absence of cytochalasin B on the detection of micronucleated cells on cell lines. Scoring micronucleated cells in both mononucleated and binucleated cells when using cytochalasin B was confirmed to be useful for the detection and the identification of aneugens. In conclusion, these results, together with previously published validation studies, provide a useful contribution to the optimisation of a study protocol for the detection of both clastogens and aneugens in the in vitro micronucleus test.

[Absence of chromosomic and genotoxic damage from the radiation dose administered in scintigraphic examinations]

INTRODUCTION

The cytokinesis-blocked (CB) micronucleus test (MN) on irradiated human lymphocytes is normally used to evaluate chromosomal and genotoxic damage produced by various physical and chemical agents.

OBJECTIVE

Determine any possible genotoxic effect induced by the different types of ionizing radiation employed in medical diagnostic radiology and nuclear medicine.

MATERIAL AND METHODS

The frequency of the MN appearance was determined in CB lymphocyte cultures of a total of 4 different groups of patients: (1) in 35 supposedly healthy volunteers to establish the MN spontaneous frequency in the medium; (2) in 9 volunteers to measure the in vitro dose-response curves in order to calculate the MN frequency following X-ray irradiation and gamma radiation; (3) in 25 patients in whom a specific diagnostic and/or therapeutic procedure employing diagnostic radiology techniques involving X-ray exposure was applied, and (4) in 26 patients in whom the diagnostic procedure in question involved nuclear medicine techniques (scintiscan).

RESULTS

A lineal relationship was observed between the MN frequency and the dose of ionizing radiation administered in vitro, both in X-rays and gamma radiation. A significant increase in the MN is observed after radiation is given to patients during medical diagnostic radiology examinations when compared with the control values obtained from the same patients prior to being subjected to the radiological procedure (p < 0.01). No significant MN increase is observed following exposure to radiation involved in diagnostic examinations in patients studied in Nuclear Medicine.

CONCLUSION

Ionizing radiation employed in complex medical diagnostic radiology examinations produces a significant increase in the MN appearance frequency and as such indicates both radiation induced chromosomal and genotoxic damage. However, the ionizing radiation used in diagnostic nuclear medicine examinations does not induce any significant increase in MN appearance frequency.

Monitoring DNA damage following radiation exposure using cytokinesis–block micronucleus method and alkaline single-cell gel electrophoresis

The structure of DNA can be damaged as a result of exposure to ionizing radiation. Determining the frequency of chromosome aberrations is a well-known method to estimate the dose of radiation received in acute and chronic exposures. In the past few years, cytogenetic analysis has benefited from the development of new techniques, such as the micronucleus (MN) and comet assays, which provide additional information concerning repair capacity after exposure. The present article discusses the use of peripheral blood lymphocytes for the assessment of populations exposed to ionizing radiation. Also discussed are individual factors that interfere with the frequency of mutations and their impact in the selection of control individuals for the monitoring of radiation exposure and in the interpretation of results.

Low doses of gamma-radiation induce nonlinear dose responses in Mammalian and plant cells

The percentage of cells with chromosome aberrations or micronuclei induced by low doses of acute (dose rate of 47 cGy/min) or chronic (dose rate of 0.01 cGy/min) gamma-irradiation was studied in vitro in Chinese hamster fibroblasts, human lymphocytes, and Vicia faba seeds and seedlings. The sensitivity of the indicated biological entities to low doses was greater than expected based on linear extrapolation from higher doses. The dose-response curves for cytogenetic damage that were obtained were nonlinear when evaluated over the full range of the doses used. At very low doses, the dose-response curves appeared linear, followed by a plateau region at intermediate doses. At high doses the dose response curves again appeared linear with a slope different from that for the low-dose region. There was no statistically significant difference between the yields of cells with micronuclei induced by low doses of acute versus chronic irradiation. Similar data were obtained both for human lymphocyte culture and for roots and seeds of Vicia faba. Our experiments revealed that the dose range over which the plateau occurs depends on the type of cells irradiated. We have also shown that the modifying effects of the repair inhibitor caffeine and the radioprotector mercaptoethylenamine (MEA) are absent at low doses of gamma irradiation and that caffeine increased the number of cells with cytogenetic damage when evaluated over the plateau region. In the presence of MEA, the upper end of the plateau region was extended from just above 1 Gy to about 2 Gy. We therefore provide direct evidence that a plateau exists in the dose-response curve for the indicated radiation-induced stochastic effects. Furthermore, our results suggest that, for low linear energy transfer radiation, the induction of DNA repair occurs only after a threshold level of cytogenetic damage and that the higher yield of cytogenetic damage per unit dose at low radiation doses is attributable to an insignificant contribution or the absence of DNA repair processes.

Gamma ray induced bone marrow micronucleated erythrocytes in seven strains of mouse

We have investigated the effect of gamma-radiation on the frequency of bone marrow micronucleated erythrocytes in seven inbred strains of adult male mice. Twenty animals of each strain viz. Swiss, C57BL/6, C57BR/cd, C3H, CBA, DBA, and AKR were irradiated at 0.0, 0.125, 0.25, 0.50, and 1.00Gy of gamma-rays at a dose rate of 0.46Gy/min using a 60Co-teletharapy machine. Animals were sacrificed 24h post-irradiation, bone marrow smears were made and stained in May-Grunwald Giemsa for evaluating the frequency of micronucleated erythrocytes as indicators of chromosomal damage. About 2000 polychromatic erythrocytes (PCEs) and the corresponding normochromatic erythrocytes (NCEs) were scored for each mouse. Thus, at least 8000 PCEs were scored for each dose point in all the groups. The spontaneous frequency of mn-PCEs per thousand (per thousand ) cells varied considerably among the strains with C57BR/cd (3.47 per thousand ) exhibiting highest as compared to CBA (2.47 per thousand ) and DBA (2.35 per thousand). Radiation exposure, even at lowest dose of 0.125Gy, induced a significant increase in the frequency of mn-PCEs and a dose dependent response was observed among all the strains. However, the animals irradiated at lower doses (0.125-0.50Gy) showed marked differences in the extent of radiation induced chromosomal damage among the various genotypes. At highest dose of radiation (1.00Gy), genotype dependent variability in the frequency of mn-PCEs was not so marked but relatively comparable among the various strains. This study clearly shows that the magnitude of variability of radiation induced chromosomal damage among different strains of mouse can be different at different doses. Therefore, use of single dose point comparisons and/or use of only higher doses of radiation for ascertainment of genotype dependent variability in mouse may lead to erroneous conclusions.

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.

Plasma 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) levels and immune response

For determination of whether plasma 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) pesticide levels (< or =1-32 ppb) are associated with immune suppression or DNA damage in lymphocytes, 302 individuals residing in Moore County, North Carolina, in 1994-1996 provided a blood specimen, underwent a skin test, and answered a questionnaire concerning factors affecting plasma organochlorine pesticide levels and the immune system. The blood specimens were analyzed for levels of plasma DDE (a metabolite of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane), numbers and types of blood cells, immunoglobulin levels, mitogen-induced lymphoproliferative activity, and lymphocyte micronuclei. When DDE levels were categorized as 1 or less, more than 1 to 2, more than 2 to 4.3, more than 4.3 to 7.6, and more than 7.6 ppb, individuals with higher plasma DDE levels had lowered mitogen-induced lymphoproliferative activity (concanavalin A, range: 74,218 dropping to 55,880 counts per minute, p = 0.03) and modestly increased total lymphocytes (range: 2.0-2.3 x 10(3)/microl, p = 0.05) and immunoglobulin A levels (range: 210-252 mg/dl, p = 0.04). There were no consistent differences in response to the skin tests by plasma DDE levels. Plasma DDE levels were not associated with a higher frequency of micronuclei. The authors conclude that relatively low levels of plasma DDE are associated with statistically significant changes in immune markers, although the magnitude of the effects are of uncertain clinical importance.

Assessment of DNA damage in lymphocytes of workers exposed to X-radiation using the micronucleus test and the comet assay

The mutagenic and carcinogenic effects of genotoxic agents on exposed people have constituted an increasing concern. Therefore, the objective of this work was to assess DNA damage in lymphocytes of workers exposed to X-radiation using the cytokinesis-blocked micronucleus test and the comet assay (single-cell gel electrophoresis), and to compare these two techniques in the monitoring of exposed populations. The cytokinesis-blocked micronucleus test and the comet assay were employed in the monitoring of 22 workers occupationally exposed to X-radiation in a hospital in southern Brazil. The frequency of dicentric bridges was also measured. The results of both assays and the frequency of dicentric bridges revealed a significant increase in genetic effects on the cells of exposed individuals. Age was significantly correlated with micronucleus frequency and damage index in the comet assay. The concomitant analysis of dicentric bridges when determining micronucleus frequency does not require much extra work, and may serve as a reference to the type of mutagenic effect (clastogenic or aneugenic). The combination of the alkaline comet assay with the cytokinesis-blocked micronucleus test appears to be very informative for the monitoring of populations chronically exposed to genotoxic agents.

Effects on the immune system associated with living near a pesticide dump site

In this paper, we report results of the second phase of a larger study designed to evaluate the effects on the immune system of living near a Superfund site containing organochlorine pesticides, volatile organic compounds, and metals. Phase II was conducted to determine whether living near the site, consisting of six locations in Aberdeen, North Carolina, is associated with higher plasma organochlorine levels, immune suppression, or DNA damage. Each of 302 residents of Aberdeen and neighboring communities provided a blood specimen, underwent a skin test, and answered a questionnaire. Blood specimens were analyzed for organochlorine pesticides, immune markers, and micronuclei. Of 20 organochlorines tested, only DDE was detected in the blood of participants (except for one individual). Age-adjusted mean plasma DDE levels were 4.05 ppb for Aberdeen residents and 2.95 ppb (p = 0.01) for residents of neighboring communities. Residents of 40-59 years of age who lived within a mile of any site, but particularly the Farm Chemicals site, had higher plasma DDE levels than residents who lived farther away. Residents who lived near the Farm Chemicals site before versus after 1985 also had higher plasma DDE levels. Overall, there were few differences in immune markers between residents of Aberdeen and the neighboring communities. However, residents who lived closer to the dump sites had statistically significantly lower mitogen-induced lymphoproliferative activity than residents who lived farther away (p < 0.05). Residential location was not consistently associated with frequency of micronuclei or skin test responses. Although some statistically significant differences in immune markers were noted in association with residential location, the magnitude of effects are of uncertain clinical importance.

Evaluation of occupational genotoxic risk in a Brazilian hospital

Many therapeutic, diagnostic and prophylactic procedures used in hospitals are of potential genetic risk. An evaluation was made of genotoxic occupational risk in 42 workers from the Hospital de Clínicas de Porto Alegre, RS, Brazil, who had been occupationally exposed to lead (solder), ethylene oxide (sterilization area), antineoplastic drugs (nurses and pharmacists) or ionizing radiation. They were compared with 42 unexposed individuals. There was an increase in the frequency of binucleated cytochalasin-blocked lymphocytes with micronuclei, though it was not significant (P = 0.058). The groups exposed to antineoplastic drugs and radiation had a significant increase in micronuclei frequency (P = 0.038 and P = 0.022, respectively). The high frequencies of dicentric bridges suggest the action of clastogenics in these two groups. These results suggest that the safety procedures adopted were very important to protect workers from exposure to mutagenic agents and should be improved in the radiological and chemotherapeutical areas.

An evaluation of the feasibility of using cytogenetic damage as a biomarker for alachlor exposure

Alachlor is a widely used herbicide for which there is significant human exposure, principally through groundwater contamination and inhalation. Because alachlor is purported to be carcinogenic and mutagenic, we initiated studies to determine if induced cytogenetic damage could be used as a biomarker for exposure to this herbicide. Both isolated and whole blood human lymphocytes were exposed to alachlor using several protocols. The lymphocytes were cultured for analysis of sister chromatid exchange (SCE), chromosome aberrations (CAs), micronuclei (MN) in cytochalasin B-induced binucleated cells, and proliferation kinetics using the replicative index (RI). In addition, CD rats were injected with either 10 or 50 mg kg-1 of alachlor, 2-chloro-N-(2,6-diethylphenyl) acetamide (CDEPA) or 2, 6-diethylanaline (DEA). After 24 h, the peripheral blood lymphocytes were removed and cultured for SCE and RI analysis. Alachlor did induce a concentration-related increase in SCE in vitro, but neither it nor its metabolites (CDEPA or DEA) induced a significant increase in SCEs or an alteration of RI in vivo. At the highest in vitro concentration tested, alachlor induced a statistically-significant increase in MN, but no concomitant increase in CAs was seen. From analyses of our data and the literature on alachlor clastogenicity and exposure levels, we concluded that cytogenetic damage may not be an adequately sensitive marker for evaluating human exposure to alachlor.

Protective effect of vanillin on radiation-induced micronuclei and chromosomal aberrations in V79 cells

Vanillin (VA), an anticlastogen, has been demonstrated to inhibit gene mutations in both bacterial and mammalian cells. However, the data on its effect against radiation-induced cytogenetic damage are limited. The aim of this study was to investigate the protective effect of VA on radiation-induced chromosomal damage in V79 cells. Exponentially growing cells were exposed to five doses of X-rays (1-12 Gy) and UV radiation (50-800 microJ x 10(2) cm-2 and posttreated with 3 concentrations of VA (5, 50 or 100 micrograms ml-1 for 16 h for micronucleus (MN) and 18 h for structural chromosomal aberration (SCA) analyses. MN and SCA assays were performed concurrently according to standard procedures. Results indicate that there was a dose related increase in the percent of micronucleated binucleated cells (MNBN) (5.6 to 79.6) and percent of aberrant cells (Abs) (12 to 98) with X-ray treatment alone. Inhibition studies showed that the addition of VA at 100 micrograms ml-1 significantly reduced the percent of MNBN (21 to 48) induced by X-ray at 1, 2, and 4 Gy. There was a slight decrease in percent MNBN at 5 and 50 micrograms VA ml-1. All three concentrations of VA decreased percent Abs (15.7 to 57.1) induced by X-rays at all doses. UV radiation alone significantly increased percent MNBN (3.5 to 14.8) and percent Abs (17 to 29). Addition of 50 or 100 micrograms VA ml-1, significantly decreased percent MNBN (31.7 to 86.2) and percent Abs (54.5 to 90.9) at all doses of UV radiation. A decrease in percent MNBN (2.8 to 72.4) and percent Abs (34.8 to 66.7) was also noted at 5 micrograms VA ml-1. These data clearly indicate the protective effect of VA on radiation-induced chromosomal damage, suggesting that VA is an anticlastogenic agent.

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

The frequencies of gamma-ray-induced micronuclei (MN) in cytokinesis-blocked (CB) lymphocytes at several doses were measured in three donors of four species (human, goat, rabbit, mouse). Measurements performed after irradiation showed a dose-related increases in MN frequency in each of the donors studied. The relative sensitivity of mouse in spleen lymphocytes (SLs), goat in peripheral blood lymphocytes (PBLs) and rabbit PBLs compared with human PBLs was estimated by best fitting linear-quadratic model based on the radiation-induced MN data over the range from 0 to 400 cGy. In the case of MN frequency with 0.2, the relative sensitivities of mouse SLs, goat PBLs and rabbit PBLs were 1.67, 0.98 and 0.39, respectively. These data indicate that the induction of MN in CB cells following irradiation is similar in human and goat PBLs, and PBLs from rabbit were much less sensitive to the MN induction effects of gamma-radiation than those from human. Compared with the radiation-induced MN formation in the PBLs of human, the SLs of mouse were more radiosensitive.

Dose-response of X-irradiated human and equine lymphocytes

We have investigated and compared DNA damage and cell killing induced in human and equine lymphocytes after in vitro X-irradiation. Our data show that the cytogenetic and the lethality effects are both greater in equine lymphocytes, but that the difference is wider for lethality. The ratios between doses inducing the same effect are 1.3, 1.7 and 9.4 for the number of binucleated cells with micronuclei, micronucleus frequency in binucleated cells and DNA synthesis inhibition, respectively. The very different radiosensitivity observed for the two mammalian species encourages us to use their lymphocytes in cell radiobiology studies.

Analysis of mitomycin C-induced micronuclei in lymphocytes from malnourished infected children

The purpose of this study was to determine if peripheral blood lymphocytes from malnourished children with gastrointestinal or respiratory bacterial infection show increased frequencies of Mitomycin C (MMC)-induced micronuclei as compared to well-nourished, infected children. The results indicate that cells from malnourished, infected children had greater chromosome damage. This may indicate that such children would be more susceptible to environmental damage and malignant transformation. Micronucleus frequencies were analyzed in binucleate cells produced by the cytokinesis block method; the overall micronucleus frequency was significantly higher in binucleate cells from malnourished, infected children. The mean micronucleus frequency in MMC-free cultures was 4.3/1000 in malnourished infected children and 1.0/1000 in well-nourished infected children. In MMC-exposed cultures the mean induced micronucleus frequency was 32.6 +/- 6.1 vs. 12.9 +/- 2.3; 68.6 +/- 12.1 vs. 21.0 +/- 5.1, and 88.1 +/- 16.2 vs. 41.7 +/- 5.0 for malnourished and well-nourished children at 20, 40, and 60 ng/ml MMC, respectively. The number of binucleated cells with more than one micronucleus was also higher in malnourished, infected children at all doses tested, including cells with two micronuclei in MMC-free cultures from malnourished, infected children. This increase was not found in peripheral blood lymphocytes from well-nourished infected children.

Frequency of micronucleated-binucleated lymphocytes is not significantly affected by the harvest time following G0 exposure to X-radiation

Whole blood from two male individuals was X-irradiated using a linear accelerator at 200 cGy/min to give a total exposure of 300 cGy. Lymphocytes were cultured using standard techniques with the addition of 3 micrograms/ml cytochalasin B at 26 h to produce binucleation through the inhibition of cytokinesis for the scoring of micronuclei after the first nuclear division. Replicate cultures from each individual were harvested at 48, 68, 70, 72, 74, 76, 92, 94, 96, 98 and 100 h postinitiation using a cytocentrifuge. Slides were stained with acridine orange, and binucleated cells were scored for the presence of micronuclei. There were no statistically significant differences in the frequency of micronucleated binucleates between replicate cultures, between individuals, or among cultures harvested from 48 to 100 h postinitiation. This indicates that the phytohaemagglutinin-stimulated lymphocytes are a relatively homogeneous population of cells with respect to X-radiation-induced chromosome damage. In addition, these data show that for determining the frequency of micronuclei in lymphocytes irradiated in G0, the harvest time (up to at least 100 h postinitiation) is not critical as long as analysis is confined to the first mitosis after irradiation (i.e. the binucleated cells).

Induction of micronuclei in human sperm-hamster egg hybrids at the two-cell stage after in vitro gamma-irradiation of human spermatozoa

The efficiency of the micronucleus test to assess radiation-induced chromosomal damage in human spermatozoa has been investigated. Micronuclei were scored in human sperm-hamster egg hybrids at the two-cell stage, after exposure of human spermatozoa to in vitro gamma-rays at doses of 0.00, 0.10, 0.25, 0.50, 1.00, 2.00, and 4.00 Gy. The relationship between the yield of micronuclei per two-cell stage as well as the percentage of two-cell stages with micronuclei and the different doses of irradiation were fitted to linear equations. To evaluate whether scoring micronuclei is useful for the quantification of chromosomal damage occurring in human spermatozoa, induced micronuclei at the different doses of sperm irradiation were compared to the induction of breaks and fragments in sperm-derived chromosomes. After interspecific fertilization of zona-free hamster oocytes by irradiated spermatozoa, a total of 699 fertilized eggs at the two-cell stage and a total of 387 sperm-derived complements were analyzed. The incidence of fertilized eggs with micronuclei at the two-cell stage coincided well with the incidence of sperm-derived chromosome breaks and fragments (e.g., 8.9% vs. 6.7% in the 0.25 Gy group and 52.8% vs. 58.6% in the 4.00 Gy group). A similar correlation was found between the number of micronuclei per two-cell stage and the number of breaks and fragments per sperm complement (0.09 vs. 0.07 in the 0.25 Gy group and 0.71 vs. 0.81 in the 4.00 Gy group). The results show that this test system can be used for the quantification of spontaneous or induced chromosomal damage in human spermatozoa.

Bleomycin sulfate-induced micronuclei in human, rat, and mouse peripheral blood lymphocytes

The sensitivity to micronucleus (MN) induction of human, mouse, and rat peripheral blood lymphocytes (PBLs) exposed to bleomycin sulfate (BLM) in vitro was compared in cytochalasin B-induced binucleated (BN) cells. For the PBLs of each species, either 0, 5, 10, 20, 40, 60, 80, or 160 micrograms/ml BLM was added to 5 ml aliquots of whole blood for 4 hr at 37 degrees C in a 5% CO2 atmosphere. Leukocytes were isolated on a density gradient and cultured in the presence of phytohemagglutinin to stimulate blastogenesis, and cytochalasin B was added to each culture at 21 hr postinitiation to prevent cytokinesis. A total of 4,000 BNs/concentration/species was analyzed for MN in two independent experiments. In addition, multiple-MN-BNs were quantitated, and the nucleation index was determined. Significant increases both in total MN-BNs and multiple-MN-BNs were observed at all concentrations in all species. All three species' concentration-response curves gave good fits (r2 values from 0.87 to 0.95) to either a linear or a square root model (y = mx + b or y = m[x]0.5 + b, respectively; where y = the percentage of MN-BN, m is the slope, and b is the y-intercept). The MN induction in the human and rat PBLs was not statistically different, but both were significantly less sensitive than the response shown by the BLM-exposed mouse PBLs. This difference in MN susceptibility was observed only at BLM test concentrations > or = 20 micrograms/ml. The nucleation index was significantly decreased in all species at either 80 or 160 micrograms/ml.

Micronucleus frequency in spleen lymphocytes from severely malnourished rats during lactation

The purpose of this ex vivo study was to determine if severe malnutrition increases the frequency of micronuclei in spleen lymphocytes of experimentally malnourished rats during lactation. Micronucleus frequencies were analyzed in binucleate cells produced by the cytokinesis block method. The overall micronucleus frequency was significantly higher in binucleate cells from malnourished rats (21.30/1000) as compared to that observed in control rats (11.50/1000). The number of binucleate cells with more than one micronucleus was also higher in malnourished rats than in controls (3.10/1000 vs. 1.20/1000). These results indicate that severe malnutrition produces cellular damage in vivo, as was evidenced by the increased micronucleus frequency in rat spleen lymphocytes in vitro. This damage may produce negative effects for the further development of the organism, since the spleen is an important lymphopoietic organ in rodents.

Cytogenetic damage in marrow cells of mice after injections of yttrium-90-labeled monoclonal antibody

Chromosome aberrations, micronuclei and sister-chromatid exchanges were quantified in marrow cells of athymic nude and B6C3F1 mice at various times up to 14 days after injection of 90Y-labeled monoclonal antibody CO17-1A. Aberrations, predominantly of the chromatid type, were sharply elevated at 24 h post-injection then declined in a curvilinear fashion over the 14 days. Micronucleus numbers among polychromatic erythrocytes peaked 3-4 days after treatment, then declined exponentially but remained at higher than expected levels. Sister-chromatid exchanges were roughly double the control rate with no apparent relation to post-treatment time.

Micronuclei and 3AB index in human and canine lymphocytes after in vitro X-irradiation

The comparative study of different species could be of interest, both applied and pure, to the field of cytogenetic damage induced by genotoxic agents. For as accurate as possible an evaluation of the inter-species response differences to radiation, we have carried out a comparison between the behaviors of human and canine lymphocytes, using the micronucleus assay (MN test) according to the cytokinesis-block method. Up to 4 Gy doses, canine lymphocytes have been found to be about three times more radiosensitive than human lymphocytes, due to blastization inhibition (binucleation failure), and, for 1 and 2 Gy doses, about 1.3 times more radiosensitive, due to MN yields. We discuss whether the differing chromosome number (dog 78 and man 46) could have any effect on the cytogenetic response. 3-Aminobenzamide, which inhibits poly(ADP-ribose)polymerase activity, is able to increase the genotoxic effect of X-rays in human lymphocytes, with a different response at the individual level. The same phenomenon with the same characteristics is also found in canine lymphocytes at the inter-individual level. Our in vitro radiobiological study confirms that the cytogenetic response obtained in blood from selected breeds of mammalian species can be utilized for applications in environmental studies.

Micronucleus induction in cytokinesis-blocked mouse bone marrow cells in vitro following in vivo exposure to X-irradiation and cyclophosphamide

A cytokinesis-block micronucleus (MN) method for the simultaneous but separate measurement of chromosome damage in erythroid and myeloid bone marrow cells is described. MN induction in cytokinesis-blocked mouse bone marrow cells in vitro following in vivo exposure to x-ray or cyclophosphamide (CP) was investigated. Immediately after whole body irradiation with acute doses of either 0, 1, 2 or 4 Gy x-rays, or 2 hr after treatment with either 0, 12.5, 25, or 50 mg CP/kg body weight, bone marrow cells were collected and then cultured in medium supplemented with 3.0 micrograms/ml cytochalasin B for 24 hr. The binucleated cells were scored in erythroid, myeloid, lymphoid and other cells. The myeloid/erythroid (M/E) ratio was decreased by x-irradiation or CP treatment in a dose-dependent manner. The dividing index (DI; binucleated cells/binucleated + mononucleated cells; %) was decreased in both erythroid and myeloid cells in the same manner. Dose-dependent increases in MN frequency were observed following x-irradiation in both erythroid and myeloid cells. A similar dose-dependent MN induction was observed with CP. The MN frequency in myeloid cells was much greater than in erythroid cells (about 4-fold following 4 Gy exposure, and more than 10-fold after 50 mg/kg CP). Lymphoid and other cells were not suitable for scoring DI and MN frequency because of insufficient numbers of binucleated cells. These results suggest that micronuclei can be identified in both myeloid and erythroid cells and that myeloid cells are more susceptible to x-ray or CP-induced chromosomal damage than erythroid cells as expressed by MN induction.

Measurement of micronuclei by cytokinesis-block method in bovine lymphocytes

The present study was carried out in order to set up a standardized quantitative assay for spontaneous micronuclei in bovine lymphocytes. For this purpose the cytokinesis-block micronucleus (MN) method, originally proposed by Fenech and Morley (1985) for human lymphocytes, was applied to peripheral blood lymphocytes of 20 healthy cows of Italian Friesian breed. The results demonstrate that the optimal concentration of cytochalasin B to obtain the highest frequency of binucleated cells (mean = 400.26 +/- 23.76/1000 cells scored) was 6 micrograms/ml. The baseline frequency of spontaneous MN formation in 500 binucleated cells was 12.3 +/- 4.1, i.e., 3 times higher than that reported in human lymphocytes (Fenech and Morley, 1985; Scarfi et al., 1991). The possible reason(s) for this difference (sensitivity to cytochalasin B, chromosome number, environmental genotoxic pollutants) is discussed.

The cytokinesis-block micronucleus technique and its application to genotoxicity studies in human populations

The development of the cytokinesis-block (CB) technique has made the human lymphocyte micronucleus assay (MN) a reliable and precise method for assessing chromosome damage. Recent studies in our laboratory have confirmed that this method is a sensitive indicator of in vivo radiation exposure in patients undergoing fractionated partial-body radiotherapy and rodents exposed to uniform whole-body irradiation, thus supporting the application of the cytokinesis-block micronucleus (CBMN) assay for biological dosimetry. To further define the use of this assay in biomonitoring, we have also undertaken extensive studies to determine the spontaneous level of MN in normal human populations and its relationship to various lifestyle factors. During the past year, we have also developed a new variation to the CBMN assay that enables the conversion of excision-repairable lesions to MN within one cell-cycle using cytosine arabinoside. With this method the slope of the in vitro dose-response curves was increased by a factor of 1.8 for X-rays, 10.3 for ultraviolet (254 nm) radiation, and approximately 40-fold for methylnitrosourea. Consequently, the CBMN assay can now be used not only to measure whole chromosome loss or chromosome breaks but also excision repair events. The versatility and simplicity of the CBMN assay together with new developments in automation should enable its successful application in monitoring exposed populations as well as identifying mutagen-sensitive individuals within a population.

The cytokinesis-block micronucleus technique: a detailed description of the method and its application to genotoxicity studies in human populations

The development of the cytokinesis-block (CB) technique has transformed the human-lymphocyte micronucleus assay (MN) into a reliable and precise method for assessing chromosome damage. Recent studies in our laboratory have confirmed that this method is a sensitive indicator of in vivo radiation exposure in (a) patients undergoing fractionated partial-body radiotherapy and (b) rodents exposed to uniform whole-body irradiation, thus supporting the application of the cytokinesis-block micronucleus (CBMN) assay for biological dosimetry. To further define the use of this assay in biomonitoring we performed extensive studies to determine the spontaneous level of MN in normal human populations and its relationship to various life-style factors. We have also developed a new variation to the CBMN assay that permits the conversion of excision-repairable lesions to MN within one cell-cycle using cytosine arabinoside. With this method the slope of the in vitro dose-response curves was increased by a factor of 1.8 for X-rays, 10.3 for ultraviolet (UV, 254 nm) radiation and approximately 40-fold for methylnitrosourea. Consequently the CBMN assay can now be used to measure not only whole chromosome loss or chromosome breaks but also excision-repair events. The versatility and simplicity of the CBMN assay together with new developments in automation should ensure its successful application in monitoring exposed populations as well as in identifying mutagen-sensitive individuals within a population.

The mouse splenocyte assay, an in vivo/in vitro system for biological monitoring: studies with X-rays, fission neutrons and bleomycin

A modified mouse splenocyte culture system was standardized after testing different mitogens (i.e., phytohemagglutinin (PHA), concanavalin A (Con A)). The mitotic index was determined for comparison between different mitogens. Following selection of appropriate mitogen (PHA 16, Flow), a series of experiments were conducted to evaluate the application of a cytokinesis-block for scoring micronuclei and assays for chromosomal aberrations produced by treatment in G0 and G2 for the purposes of biological dosimetry following in vivo and/or in vitro exposure to X-rays, fission neutrons and bleomycin. In the X-irradiation studies, the frequencies of micronuclei and chromosomal aberrations (i.e., dicentrics and rings) increased in a dose-dependent manner. These data could be fitted to a linear-quadratic model. No difference was observed between irradiation in vivo and in vitro, suggesting that measurement of dicentrics and micronuclei in vitro after X-irradiation can be used as an in vivo dosimeter. Following in vivo irradiation with 1 MeV fission neutrons and in vitro culturing of mouse splenocytes, linear dose-response curves were obtained for induction of micronuclei and chromosomal aberrations. The lethal effects of neutrons were shown to be significantly greater than for a similar dose of X-rays. The relative biological effectiveness (RBE) was 6-8 in a dose range of 0.25-3 Gy for radiation-induced asymmetrical exchanges (dicentrics and rings), and about 8 for micronuclei in a dose range of 0.25-2 Gy. Furthermore, the induction of chromosomal aberrations by bleomycin was investigated in mouse G0 splenocytes (in vitro) and compared with X-ray data. Following bleomycin treatment (2 h) a similar pattern of dose-response curve was obtained as with X-rays. In this context a bleomycin rad equivalent of 20 micrograms/ml = 0.50 Gy was estimated.