Micronuclei and chromosome aberrations in bone marrow cells and lymphocytes of humans exposed mainly to petroleum vapors

Regulation of cGAS and STING signaling during inflammation and infection

Stimulator of interferon genes (STING) is a sensor of cyclic dinucleotides including cyclic GMP-AMP, which is produced by cyclic GMP-AMP synthase (cGAS) in response to cytosolic DNA. The cGAS-STING signaling pathway regulates both innate and adaptive immune responses, as well as fundamental cellular functions such as autophagy, senescence, and apoptosis. Mutations leading to constitutive activation of STING cause devastating human diseases. Thus, the cGAS-STING pathway is of great interest because of its role in diverse cellular processes and because of the potential therapeutic implications of targeting cGAS and STING. Here, we review molecular and cellular mechanisms of STING signaling, and we propose a framework for understanding the immunological and other cellular functions of STING in the context of disease.

Spectrum of stable and unstable rearrangements in lymphocytic chromosomes investigated in Bhopal population 30 years post MIC disaster amid co-exposure to lifestyle, living, and occupational hazards

Immediate assessment of genetic damage in methyl isocyanate (MIC) gas-exposed population in small and heterogeneous samples using diversified study designs and solid-stained metaphases could not depict the actual genetic impact of MIC on accidentally exposed individuals. The outcome of the then large multi-center genetic screening program was not available to the public and scientific community. Also, the routine and regular epidemiological health survey does not capture the genetic and long-term effect of MIC. Therefore, genetic screening was carried out 30 years post disaster during 2015-2017 with a view to screen the present status of chromosomal consequences in lymphocytic cells. Participants were recruited from moderate (34) and severely (78) exposed and unexposed (35) cohorts with their informed consent. Analysis of ~100 mitotic cells and karyotyping of at least 10-15 and all abnormal metaphases detected structural and numerical alterations, including stable and replicable ones. Clonal abnormalities were detected with monosomal and complex karyotypes, trisomy 8, del5q/20q, loss of Y, etc. Among all, X-chromosome was frequently involved in numerical alterations. Structural aberrations appeared higher in the then exposed populations, though abnormalities cannot be linked directly to MIC exposure 30 years post disaster. Collectively, all rearrangements were markedly higher in the severely exposed population. Altogether, the detected abnormalities appeared random and indicated genomic instability, suggesting follow-up at shorter intervals for the individuals detected with clonal aberrations. G-banding has facilitated recognition of chromosomal involvement and their breakpoints and classification of structural rearrangements. The present data has been derived from the 30-year post-disaster genetic screening.

Mutagenicity monitoring in humans: Global versus specific origin of mutations

An underappreciated aspect of human mutagenicity biomonitoring is tissue specificity reflected in different assays, especially those that measure events that can only occur in developing bone marrow (BM) cells. Reviewed here are 9 currently-employed human mutagenicity biomonitoring assays. Several assays measure chromosome-level events in circulating T-lymphocytes (T-cells), i.e., traditional analyses of aberrations, translocation studies involving chromosome painting and fluorescence in situ hybridization (FISH) and determinations of micronuclei (MN). Other T-cell assays measure gene mutations. i.e., hypoxanthine-guanine phosphoriboslytransferase (HPRT) and phosphoribosylinositol glycan class A (PIGA). In addition to the T-cell assays, also reviewed are those assays that measure events in peripheral blood cells that necessarily arose in BM cells, i.e., MN in reticulocytes; glycophorin A (GPA) gene mutations in red blood cells (RBCs), and PIGA gene mutations in RBC or granulocytes. This review considers only cell culture- or cytometry-based assays to describe endpoints measured, methods, optimal sampling times, and sample summaries of typical quantitative and qualitative results. However, to achieve its intended focus on the target cells where events occur, kinetics of the cells of peripheral blood that derive at some point from precursor cells are reviewed to identify body sites and tissues where the genotoxic events originate. Kinetics indicate that in normal adults, measured events in T-cells afford global assessments of in vivo mutagenicity but are not specific for BM effects. Therefore, an agent's capacity for inducing mutations in BM cells cannot be reliably inferred from T-cell assays as the magnitude of effect in BM, if any, is unknown. By contrast, chromosome or gene level mutations measured in RBCs/reticulocytes or granulocytes must originate in BM cells, i.e. in RBC or granulocyte precursors, thereby making them specific indicators for effects in BM. Assays of mutations arising directly in BM cells may quantitatively reflect the mutagenicity of potential leukemogenic agents.

Results of micronucleus assays with individuals who are occupationally and environmentally exposed to mercury, lead and cadmium

Millions of humans are exposed occupationally and environmentally to lead, mercury and cadmium compounds. Mercury compounds are less abundant but some of them belong to the most toxic chemicals which are known. We evaluated the literature to find out if these metals act in humans as genotoxic carcinogens and if their health effects can be predicted by use of micronucleus (MN) assays with lymphocytes and/or with other genotoxicity tests. Numerous studies showed that lead and mercury induce cancer in humans and also in animals, in vitro experiments with cultured cells indicate that they cause DNA damage via different molecular mechanisms including release of reactive oxygen species and interactions with DNA repair processes. Also in most human studies, positive results were obtained in MN tests with lymphocytes (all 15 occupational studies with lead yielded positive results, with mercury 6 out of 7 investigations were positive). For cadmium, there is clear evidence that it causes cancer in humans; however, induction of chromosomal damage was only seen in high dose experiments with mammalian cells while results of animal and human studies yielded conflicting results (only in 2 of 5MN trials with humans positive findings were reported). Possibly, non-genotoxic mechanisms such as inhibition of apoptosis and interaction with signaling pathways account for the carcinogenic properties of cadmium species. The findings of MN studies with lead and mercury are in excellent agreement with results which were obtained with other endpoints (e.g. chromosomal aberrations and comet formations) and it is evident that this approach can be used for occupational and environmental monitoring of exposed individuals. Important future tasks will be the realization of larger studies with a uniform standardized protocol, the additional evaluation of anomalies other than MN (nuclear buds and bridges) and the combination of such trials with investigations which allow to define the molecular mechanisms relevant for exposed humans.

Effects and mechanisms of kerosene use-related toxicity

Kerosene is a heterogeneous hydrocarbon substance that continues to find many uses worldwide due to its economic viability and ease of availability. In spite of kerosene's many uses, it is known to cause harm to various body organs and systems. Major affected body organs/systems are the pulmonary system, central nervous system, cardiovascular system, the skin, immune system and liver. This review discusses the various kerosene-mediated adverse health effects and possible mechanisms by which kerosene is likely to inflict such effects. These mechanisms are quite varied and include induction of inflammation, loss of effectiveness of pulmonary surfactants, hypoxia, production of highly reactive oxidative metabolites, extraction of endogenous epidermal and membrane lipids, necrosis, hormonal and enzymatic levels changes, and immunosuppression. Understanding of the above will allow for proper relevant policy formulation and targeted kerosene-mediated morbidity and mortality preventive and management initiatives.

Genotoxic effects of lead: an updated review

Lead is a ubiquitous toxic heavy metal with unique physical and chemical properties that make it suitable for a great variety of applications. Because of its high persistence in the environment and its use since ancient times for many industrial activities, lead is a common environmental and occupational contaminant widely distributed around the world. Even though the toxic effects of lead and its compounds have been investigated for many years in a variety of systems, the data existing with regard to its mutagenic, clastogenic and carcinogenic properties are still contradictory. The International Agency for Research on Cancer has classified lead as possible human carcinogen (group 2B) and its inorganic compounds as probable human carcinogens (group 2A). Furthermore, although the biochemical and molecular mechanisms of action of lead remain still unclear, there are some studies that point out indirect mechanisms of genotoxicity such as inhibition of DNA repair or production of free radicals. This article reviews the works listed in the literature that use different parameters to evaluate the genotoxic effects of lead in vitro, in vivo and in epidemiological studies.

Evaluation of the reticulocyte micronucleus assay in patients treated with radioiodine for thyroid cancer

In the case of accidental radiation exposure, biological dosimetry has an important role. Previous studies have indicated that the flow cytometric micronucleus (MN) assay in human transferrin receptor positive reticulocytes (Tf-Ret) in blood could be a sensitive biomarker for chromosome damage. In the present investigation, the utility and sensitivity of this method was studied in 44 young patients from Belarus, who were treated with 131I for thyroid cancer. Red marrow (RM) is the critical organ in radioiodine therapy (RIT). In our patients, it was exposed to 100-700 mSv low-dose rate irradiation within 2-4 days. About 3 days after 131I administration, the frequency of micronucleated-Tf-Ret (f(MN-Tf-Ret)) increases within 1 day to a maximum and declines in the following 2-5 days to its value before treatment. A total dose of 100 mSv was easily detectable. The sensitivity of the assay after acute irradiation may be 50 mSv. The method should be useful for monitoring individuals after a radiation accident, provided blood samples can be obtained within a few days after exposure. The time-course of f(MN-Tf-Ret) is interpreted using a model, which considers the exponential exposure of red marrow in RIT as well as the kinetics of erythroblast maturation and reticulocyte migration into the peripheral circulation. Similar modelling was done on published data of MN in immature mouse erythrocytes. Striking similarities in the kinetic and in the yield of MN-induction were found between these two species. This lends support for the use of the mouse as a model for the MN-induction in humans.

Cytogenetic monitoring of men occupationally exposed to airborne pollutants

A study of structural chromosomal aberration frequencies in peripheral blood lymphocytes was performed in a group of 20 professional drivers exposed to airborne pollutants and 20 matching controls. The subjects in the latter group were of the same sex (males) and of similar age as the exposed ones, and also had similar habits of smoking and alcohol. A statistically significant increase of chromosomal aberration was observed in the exposed subjects over the control group. An increasing trend of aberrations was observed with the duration of service (exposure) in the exposed individuals. This study clearly indicates the effect of occupational exposure to airborne pollutants.

Human cytogenetic biomonitoring using flow-cytometric analysis of micronuclei in transferrin-positive immature peripheral blood reticulocytes

We have developed a method to isolate and analyze nascent human reticulocytes in peripheral blood for the presence of micronuclei (MN). For a very short time peripheral reticulocytes show residual expression of the transferrin receptor. Using immunomagnetic separation of cells expressing the transferrin receptor, a population of immature reticulocytes (Trf-Ret) was isolated from peripheral blood. In humans, the spleen actively removes micronucleated erythrocytes but during the short lifetime of the isolated Trf-Ret only a fraction (less than about 20%) of the MN-containing reticulocytes will have been eliminated. Cells were stained with the fluorescent dyes Thiazole Orange for RNA and Hoechst 33342 for DNA and analyzed by flow cytometry and fluorescence microscopy. Baseline frequencies of MN-Trf-Ret on a group of healthy donors were found to be 1.1% for males and 1.4% for females; however, the gender difference was not significant. The frequency of MN-Trf-Ret in the studied group increased with age, and was dependent on blood group. In three donors studied over 4 months, the baseline level remained stable. In cancer patients treated with radiation or chemotherapy, the frequency of MN-Trf-Ret increased 10- to 20-fold after 1-4 days, depending on the treatment. A high correlation between flow and manual analysis of MN-Trf-Ret was seen. We believe the method has a high potential as a sensitive and rapid method for biological monitoring in presumed exposed groups and individuals.

Determination of diesel genotoxicity in firebreathers by micronuclei and nuclear abnormalities in buccal mucosa

Diesel or its derivatives could have aneuploidogenic and/or clastogenic activity. Hence, the genotoxicity of diesel gases has been studied, considering exposure to them as potentially carcinogenic. The results obtained by different authors suggest the need to know the effects of direct and chronic exposure to diesel in humans, as in the case of the street workers called 'firebreathers' who fill their buccal cavity with diesel and then spread it to a burning torch many times during the day in order to give a 'dragon show' for 5 h a day and 6 days a week. The buccal samples of eight firebreathers were collected, processed and scored according to the criterion established by Tolbert et al., 1992 and then compared with positive and negative control groups. The results revealed that diesel was not micronucleogenic although it induces some nuclear abnormalities.

No significant increase in sister-chromatid exchanges in cultured blood lymphocytes from workers in a large oil refinery

In order to assess the potential genotoxic effects of occupational exposure to petrochemicals, the incidence of sister-chromatid exchanges (SCE) in cultured lymphocytes was studied. Blood samples were taken from 233 individuals (184 exposed and 49 worksite controls) in an oil refinery and from 47 community control persons. The data showed a non-significant elevation of SCE frequency in occupationally exposed workers when compared to non-exposed individuals. The mean SCE frequency per cell ranged from 7.55 +/- 0.55 in blood of lube oil blending and canning (LOBC) workers to 9.13 +/- 0.71 in catalytic cracking and water treatment (CCWT) workers. The control values were 6.2 +/- 0.67 and 7.21 +/- 0.45 in the community and worksite individuals, respectively. Furthermore, the SCE frequencies were influenced neither by age nor by smoking.

The frequency of micronuclei in bone-marrow erythroblasts during the treatment of childhood acute lymphoblastic leukaemia

We scored the frequency of micronuclei in bone-marrow erythroblasts from 41 patients with childhood acute lymphoblastic leukaemia (childhood ALL) at diagnosis and during their 2-year treatment cycle in order to see whether there would be any variation in the cytogenetic damage induced by chemotherapy. We found that most patients showed the same trend in micronucleus frequency, with a progressive rise from the diagnostic slide through induction to pre-intensification and completion of treatment. The rise was attributed to damage to the erythroblasts occurring as a result of chemotherapy, and was judged not prognostically significant in this study.

Cell division, chromosomal damage and micronucleus formation in peripheral lymphocytes of healthy donors: related to donor's age

Spontaneous baseline frequencies of chromosome aberrations, micronucleus counts and cell division were analysed in peripheral lymphocytes of 127 normal healthy individuals in vitro. Cells were subjected to culture for 48 h in serum and PHA supplemented culture medium RPMI 1640. 100 metaphases were observed for chromosome aberrations and 1000 cells each for micronucleus counts and mitotic index. Regression analyses were carried out to see the effect of age on spontaneous abnormalities. The correlation of aberrations, micronucleus formation and mitotic index with donor's age is highly significant. The elevation of abnormalities and depression of mitotic index were linear to the increase of donor's age, with a higher frequency in males. Aged males and females from the age range of 40-70 years showed larger numbers of aberrations. Individuals with the smoking habit possessed higher frequencies of abnormalities than non-smokers.

No increase in chromosome aberrations in workers from an oil catalytic cracking plant

A study of structural chromosome aberration frequencies in blood lymphocytes was performed in a group of 20 oil catalytic cracking unit workers and in 26 subjects belonging to the office staff of an oil refining plant, as well as in 35 matched controls. Subjects in the latter group were of the same sex (males) and similar age as the exposed group, and had similar smoking habits. Benzo[a]pyrene levels in workplace air samples were also determined. The cytogenetic analysis failed to show any differences between the exposed and control groups. A slight increase in benzo[a]pyrene level above the Cuban national standard of 1 ng/m3 was found during the air sample analysis in the oil catalytic cracking unit.

Increased frequency of micronuclei in B and T8 lymphocytes from smokers

The frequency of micronuclei was measured in peripheral B lymphocytes and some T lymphocyte subpopulations from 5 medium-tar cigarette smokers, and 5 non-smokers with no regular exposure to tobacco smoke. The peripheral lymphocytes were stimulated in vitro with phytohemagglutinin and B lymphocytes and the various T lymphocyte subsets were classified by a recently developed MAC (Morphology, Antibody, Chromosomes) method which allows the immunologic identification of different cell lineages. An increased frequency of micronuclei was observed in B and especially in the suppressor/cytotoxic T8 lymphocytes from smokers, as compared with non-smoker values. In non-smoker cultures, no differences in the frequency of micronuclei were observed among the different T lymphocyte subsets. In these cultures, B cells tended to have a higher frequency of micronuclei than did T cells. The proportions of B cells and the various T subpopulations among mitotic and interphasic lymphocytes from smokers and non-smokers were also determined. The proportions of B cells and T cell subsets among all mitotic lymphocytes were similar in smokers and non-smokers. Contrarily, a significant decrease in the proportion of T8 lymphocytes among all interphasic lymphocytes was observed in cultures derived from smokers.

Micronucleated lymphocytes in people occupationally exposed to potential environmental contaminants: the age effect

This work is part of a research project on 2 groups of tannery workers (i.e., workers employed in the tanning process and those employed in the finishing department), and 2 control groups consisting of individuals paired with each exposed person according to sex, age and smoking habit. The whole study included the evaluation of micronuclei as well as of chromosomal aberrations and sister-chromatid exchanges in peripheral blood lymphocytes. Data on micronucleus analysis in both controls and exposed persons are shown in this paper. There was no statistically significant difference between MN frequencies in the 2 groups of exposed and controls, nor any positive correlation with smoking habit. The effect of age on basal frequency of micronucleated cells clearly emerges in the present study: both controls and exposed show an increase in MN frequency due to age. This could be correlated with a higher sensitivity to breaks, rearrangements or aneuploidogenic events of circulating lymphocytes in aged people.

Frequency of micronuclei induced in peripheral lymphocytes by trimethyltin chloride

The clastogenicity of trimethyltin chloride was evaluated in human peripheral blood lymphocytes with micronucleus counts (MNC) as the endpoint. Two concentrations (0.5 micrograms and 1.0 microgram) of trimethyltin chloride were added to lymphocytes of healthy male and female subjects of different age groups, in mitogen-stimulated and serum-supplemented culture medium (RPMI 1640, Gibco) for 48 h at 37 degrees C. A significant increase in micronucleus counts was observed with both doses, which was more pronounced with the lower dose. ANOVA in male and female donors revealed significant differences between age groups (P less than 0.001), chemical concentrations (P less than 0.001) and for the interaction of these 2 factors (P less than 0.05 in females only). However, no regular increase or decrease in MNC frequencies was observed with the donor's age. Higher frequencies of MNC enhancement were observed in male individuals than in females.

Relation between occupational exposure to organic solvents and chromosome aberrations in non-Hodgkin's lymphoma

Chromosome analysis of lymphoma cells was performed in 54 untreated patients with non-Hodgkin's lymphoma (NHL). 10 patients had a history of daily occupational handling of organic solvents for at least 1 year (exposed group) and 44 patients had never (or only for shorter periods) worked with solvents (unexposed group). There were no differences between exposed and unexposed patients regarding age, clinical stage or histologic malignancy grade. The patients were assigned to three categories: Patients with 0-4, 5-9, or greater than or equal to 10 cytogenetic events producing clonal aberrations of the lymphoma cells. The proportions of exposed patients in these categories were 2/26 (8%), 5/20 (25%) and 3/8 (38%); respectively, i.e. with increasing numbers of events there was an increasing probability of previous exposure to solvents (p = 0.035, trend analysis). 5 of 7 exposed patients (71%) with intermediate or high-grade lymphomas displayed translocations involving the band 14q32. Such 14q+ markers were found in only 5 out of 28 unexposed patients (18%) with lymphomas of comparable malignancy grade (p = 0.01). Among unexposed patients with intermediate or high-grade lymphoma the most common clonal aberration was 6q- which occurred in 10 out of 28 patients (36%). This abnormality was not observed in the exposed patients with lymphomas of corresponding malignancy grades (p = 0.08). It thus appears that the number of clonal chromosome aberrations is especially large in NHL patients with a history of occupational exposure to organic solvents. Moreover, such exposure may be associated with characteristic cytogenetic changes in the lymphoma cells.

Radiation induction of micronuclei in human lymphocytes

An examination of the cytokinesis-blocked micronucleus technique confirmed its potential usefulness as a method of biological dosimetry for radiation accidents. Several advantages and disadvantages of the system are discussed. It has been demonstrated that under the conditions of these experiments, the blocking agent, cytochalasin B does not induce micronuclei or unstable chromosome aberrations. The induction of sister-chromatid exchanges proved just significant. Analysis of the dose response for 250 kVp X-rays indicates that although the Y = alpha D + beta D2 model fits the data, the relationship does not correspond to that for total aberration induction as might have been expected. The background frequency of micronuclei and the value of the alpha coefficient are higher than for total aberrations and the beta term is lower. This indicates that simple incorporation of acentric chromosome fragments into micronuclei may not wholly account for the phenomenon.

Correlation between bone marrow karyotype and the occurrence of erythroblast micronuclei and nuclear budding in patients with myelodysplastic syndromes

147 patients with myelodysplastic syndromes were investigated for the presence of micronuclei and nuclear budding in bone marrow erythroblasts. The patients were divided into subgroups on the basis of bone marrow karyotype, 31 healthy bone marrow donors constituted a control group. Patients with monosomy 7 or 7q- and patients with major karyotypic abnormalities (MAKA) had significantly more erythroblasts with micronuclei and nuclear budding than the control group. Patients with a 5q- chromosome as the sole karyotypic aberration had more micronuclei than the controls. For other patients with MDS the differences were statistically nonsignificant.

The present state and perspectives of micronucleus assay in radiation protection. A review

The occurrence of micronuclei proved to be a sensitive biological indicator of clastogenic effects of many chemical and physical agents. The possibility of using the micronucleus technique in radiation protection as an alternative to the traditional chromosomal analysis has recently been followed with increasing interest. This review outlines the main biological and practical aspects of the micronucleus assay and discusses its potential to serve as a rapid and reliable measure of radiation overexposures and hypersensitivities.

Effects of metals on chromosomes of higher organisms

An analysis of the available data on the clastogenic effects of metals and their compounds on higher organisms indicates some general trends. Following chronic exposure to subtoxic doses, a decrease in mitotic frequency and an increase in the number of chromosomal abnormalities are observed. These effects are usually directly proportional to the dose applied and the duration of treatment within the threshold limits. Recovery after acute treatment is inversely related to the dosage. The ultimate expression of the effects depends on certain factors, including the mode and vehicle of administration; the form administered; the test system used; the rate of detoxification, distribution, and retention in the different tissues; and interaction with foreign and endogenous substances as well as the mode of action with the biological macromolecules. In mammals, the clastogenic activity of the metals within each vertical group of the periodic table is directly proportional to the increase in atomic weight, electropositivity, and solubility of the metallic cations in water and lipids, except for Li and Ba. This pattern of inherent cytotoxicity increases with successive periods in the horizontal level. It is enhanced by the formation of covalent and coordinate covalent complexes by heavy metals with the biological macromolecules. In plants, the solubility of the metals in water is of much greater importance. The degree of dissociation of metallic salts and the rate of absorption affect significantly the frequency of chromosomal aberrations. In assessing the effects of environmental metal pollution, the presence of other metals and toxic chemicals and the level of nutrition should be taken into account, since in nature, metals occur in combination and these factors modify the cytotoxic effects to a significant extent.

Population monitoring for genetic damage induced by environmental physical and chemical agents

The short-term tests performed in vitro on different systems, from phage to human cells, or in vivo, on laboratory animals, allow only a qualitative estimate of the action of mutagenic agents, and the extrapolation of such experimental results to man may encounter many difficulties.Direct biomonitoring of populations exposed to chemicals could represent a more realistic approach for an evaluation of the hazards to man. Certain methods are still under development. Nevertheless, other ones can already by used routinely, e.g. the cytogenetic observations on peripheral blood lymphocytes and the Ames test for mutagenic substances in urine, and can provide useful suggestions how to set threshold limits for chemical substances encountered in the working environment.

Tabulation and assessment of 113 human surveillance cytogenetic studies conducted between 1965 and 1984

There is an increasing tendency to monitor human exposure to genotoxic chemicals by the assessment of chromosomal aberrations or sister-chromatid exchanges (SCEs) in peripheral blood lymphocytes. In order to assess the sensitivity of these techniques, and to discern minimal criteria for their conduct, a survey of 113 human lymphocyte cytogenetic surveillance studies conducted between 1965 and 1984 has been undertaken. The present survey indicates the urgent need for standardization of study protocols. It is suggested that a common method of reporting chromosomal aberrations should be adopted, and that this should be based on the system described by Scott et al. It is also suggested that a minimum acceptable size of control and exposed populations should be agreed, and that potentially important factors such as the gender, the period and extent of exposure and individual smoking habits be defined in advance of the commission of future surveillance studies. As general awareness of the possible hazard presented by exposure of man to genotoxic chemicals increases, so appropriate preventative industrial hygiene measures will be instituted. This implies that future human cytogenetic surveillance studies may yield either weakly positive or negative data. This emphasizes the current need for agreement on appropriate study protocols. The formation of a central repository for control databases, and its subsequent updating and use by those involved in human cytogenetic surveillance studies, is recommended. Minimal experimental criteria for the design of future studies are also outlined.

The in vitro micronucleus assay for detection of cytogenetic effects induced by mutagen-carcinogens: comparison with the in vitro sister-chromatid exchange assay

The sensitivity of a cytogenetic assay, as expressed by the in vitro induction of micronuclei (MN), was compared to the in vitro induction of sister-chromatid exchanges (SCEs). Chinese hamster lung (V79) cells were exposed to 3 known alkylating agents: methyl methanesulphonate (MMS), ethyl methanesulphonate (EMS) and N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and to 5 newly synthesized naphthofurans: 2-nitro-7-methoxynaphtho[2,1-b]furan (A), 2-nitro-8-methoxynaphtho[2,1-b]furan (B), 2-nitronaphtho[2,1-b]furan (C), 2-nitro-7-bromonaphtho[2,1-b]furan (D) and 7-methoxynaphtho[2,1-b]furan (E). The induction of MN only was also analysed after exposure of the cells to 4 alcohols: ethanol, methanol, butanol and propanol. The lowest dose at which a significant effect could be observed was determined. In both assays, MNNG, MMS and EMS were equally active with the following order of potency: MNNG greater than MMS greater than EMS, the latter being a very weak inducer of MN and SCE. Compounds A and B were also very effective in both assays. Compound C was a more active inducer of SCE than MN. Compounds D and E were not active in either assay. None of the 4 alcohols induced MN. Our results are compared with the previously published data on in vitro and in vivo induction of SCE and MN. We conclude that the MN in vitro assay which detects clastogens as well as agents affecting the spindle apparatus, is a good indicator of genotoxicity, though slightly less sensitive than the in vitro SCE test. It could provide a rapid, simple and inexpensive complementary short-term test for the evaluation of potentially mutagenic chemicals.

Micronuclei in human bone-marrow cells: evaluation of the micronucleus test using human leukemia patients treated with antileukemic agents

The relevance of the micronucleus test to human studies was investigated by using bone marrow from leukemic patients treated with antileukemic drugs. The median incidence of micronucleated erythrocytes and erythroblasts, respectively, increased from control values of 0.04 and 0.72% to 0.29 and 25.3% in leukemic cases; and the frequency of micronucleated erythroblasts was inevitably higher than the control value in cases that showed a higher frequency of micronucleated erythrocytes, but the reverse was not true. These results indicate that almost the same changes of micronucleus formation that are observed in the mouse micronucleus test are produced in human bone marrow by antileukemic drugs--mutagenic compounds--and, if the micronuclei were scored restrictively in erythroblasts, the application of the micronucleus test to human bone marrow would be reasonable.

Biologic monitoring of exposure to chemical mutagens in the occupational environment

Occupational exposure to chemical mutagens can be monitored by measuring the chemical interaction that occurs between the exposing agent and biologic macro-molecules. Such interaction is detectable in the body fluids as adducts of, e.g., DNA or glutathione. The mutagenic compounds or their metabolites can also be measured from urine samples, by use of bacterial mutagenicity assays. Much basic research is still needed before these methodologies are applicable for routine monitoring. At present, cytogenetic approaches appear to be nearest to routine surveillance in detecting early biologic effects in exposed humans. Studies on structural chromosome aberrations or sister chromatid exchanges (SCEs) in peripheral blood lymphocytes obviously detect different molecular injuries, and the results from in vivo occupational exposures do not necessarily correlate. Somatic chromosome damage should always be considered a warning sign of potentially adverse effects, and such damage should lead to decreased exposure to the causative agent.