Azathioprine, a clastogen in human somatic cells? Analysis of chromosome damage and SCE in lymphocytes after exposure in vivo and in vitro

Structure and assembly of the mammalian mitochondrial supercomplex CIII2CIV

The enzymes of the mitochondrial electron transport chain are key players of cell metabolism. Despite being active when isolated, in vivo they associate into supercomplexes¹, whose precise role is debated. Supercomplexes CIII₂CIV_1-2 (refs. ^2,3), CICIII₂ (ref. ⁴) and CICIII₂CIV (respirasome)^5-10 exist in mammals, but in contrast to CICIII₂ and the respirasome, to date the only known eukaryotic structures of CIII₂CIV_1-2 come from Saccharomyces cerevisiae^11,12 and plants¹³, which have different organization. Here we present the first, to our knowledge, structures of mammalian (mouse and ovine) CIII₂CIV and its assembly intermediates, in different conformations. We describe the assembly of CIII₂CIV from the CIII₂ precursor to the final CIII₂CIV conformation, driven by the insertion of the N terminus of the assembly factor SCAF1 (ref. ¹⁴) deep into CIII₂, while its C terminus is integrated into CIV. Our structures (which include CICIII₂ and the respirasome) also confirm that SCAF1 is exclusively required for the assembly of CIII₂CIV and has no role in the assembly of the respirasome. We show that CIII₂ is asymmetric due to the presence of only one copy of subunit 9, which straddles both monomers and prevents the attachment of a second copy of SCAF1 to CIII₂, explaining the presence of one copy of CIV in CIII₂CIV in mammals. Finally, we show that CIII₂ and CIV gain catalytic advantage when assembled into the supercomplex and propose a role for CIII₂CIV in fine tuning the efficiency of electron transfer in the electron transport chain.

A follow-up cytogenetic study of workers highly exposed inside the Chernobyl sarcophagus

Data are presented on some of the engineers and scientists who regularly entered highly radioactive areas of the sarcophagus chamber constructed around the ruins of the Chernobyl reactor. Previous investigations on six of them by unstable chromosomal aberrations, quartz fibre electrometers and, in some cases, tooth electron spin resonance have all indicated high doses accumulated over several years of work inside the sarcophagus. Here, the authors present the data on eleven of the men who agreed to be monitored cytogenetically although two have since died aged 45 and 66 y. The present data were combined with the previous to examine the time-courses of these individuals' changes in their aberration frequencies. As expected, dicentric aberrations showed a clear drop down to 2-3 per 100 cells since the men ceased working inside the sarcophagus. In contrast, the translocation yields remained at a high level showing no tendency to decrease and so proved reliable for retrospective biodosimetry. These data are particularly useful in demonstrating the value of FISH long after high but protracted and fractionated exposure.

Technical report: automated classification of first and second cycle metaphases

Based on the technical configuration of the Metafer2 metaphase finder (Metasystems, Altlussheim, Germany), an automated system was developed that is able to discriminate first/M1 or second cycle/M2 metaphases. For an evaluation of the system in fluorescence plus Giemsa stained preparations of human lymphocytes, a learning sample and an independent test sample was used. Between 8 and 14 separated chromosomes per metaphase were sufficient to achieve correct classification rates between 95 and 100%. For practical application the system can be most efficiently used for biodosimetry of human radiation exposure which requires scoring of thousands of metaphases exclusively in M1. An application for selection of M2 for SCE scoring in mutagenicity testing was possible, but does not provide a comparable advantage.

Genotoxicity of 4-chloro-o-toluidine in Salmonella typhimurium, human lymphocytes and V79 cells

In the absence of a metabolizing system (S9 mix) 4-chloro-o-toluidine (4-COT) was found to be ineffective in a combination of assays for gene mutations in Salmonella typhimurium, for chromosome aberrations and sister chromatide exchanges in human lymphocytes, and for the induction of spindle disturbances in V79 Chinese hamster cells. In the presence of S9, 4-COT was also ineffective in producing structural or numerical changes in mammalian cells, but the yields of 4-COT induced revertants in S. typhimurium strains TA 100 and TA 98 were about 2-fold higher than those in controls.

Combined FISH painting and harlequin staining for cell cycle-controlled chromosome analysis in human lymphocytes

We present a simple method that allows scoring of FISH-painted chromosomes exclusively in the first division human lymphocytes. It consists of a combination of FISH with chromosome-specific libraries and a differential sister chromatid staining after BrdU treatment of lymphocyte cultures. The method allows a precise quantification of induced chromosome damage for human biodosimetry.

Effect of activated oxygen species in human lymphocytes

The cytogenetic effectiveness of activated oxygen species (AOS) generated by the superoxide forming xanthine-xanthine oxidase (X/XO) system was studied in human lymphocyte cultures. The observed chromosome damage was exclusively of the chromatid type. In the experiments a clear dependence of aberration induction on XO concentration and exposure time could be demonstrated. While using anti-AOS agents, the H2O2 antagonist catalase and the hydroxyl radical scavenger formate reduced X/XO induced chromosome damage whereas superoxide dismutase (SOD) did not. In the presence of SOD, aberration frequency was even enhanced. The results indicate that the chromosome damage is caused indirectly via H2O2 formation from spontaneous dismutation of superoxide, whereas H2O2 might be reduced intracellularly giving rise to the highly reactive hydroxyl radical. This effect might be enhanced by SOD, possibly by raising the intracellular amount of easily membrane passing H2O2. Thus, referring to chromosome aberrations, SOD, which is generally reported to protect from AOS, is capable of increasing oxygen mediated biological damage. This observation might be explained by the involvement of DNA associated transition metal, like iron or copper ions, in reducing H2O2. DNA bound copper ions, thought to be necessary for maintenance of DNA quaternary structure, might represent a generator complex for the hydroxyl radical by reduction of X/XO derived hydrogen peroxide. This might cause 'site specific damage' to the DNA which is subsequently converted into chromatid-type aberration by S-dependent misreplication and/or misrepair. This is different to the formation of radiation induced chromosome aberrations which arise by an S-phase independent mechanism.

Dicentric and translocation analysis for retrospective dose estimation in humans exposed to ionising radiation during the Chernobyl nuclear power plant accident

Chromosome analyses were carried out in peripheral blood lymphocytes obtained between September 1991 and March 1992 from 15 persons exposed to ionising radiation during the Chernobyl nuclear power plant accident. At present, all are being treated for symptoms of the delayed stage of the cutaneous radiation syndrome. Biological dose-equivalent estimates were determined, either by measuring the frequency of dicentric and ring chromosomes in first division unstable cells from conventional preparations (Qdr method), or by measuring the frequency of stable translocations using two-colour fluorescence in situ hybridisation (FISH) with composite whole chromosome-specific DNA libraries for human chromosomes 1, 4 and 12 (chromosome painting) and a degenerate alpha-satellite pancentromeric DNA probe. With both methods fairly comparable individual estimates between 1.1 and 5.8 Gy were obtained for 12 of 15 individuals. Three individuals exhibited no elevated aberration frequencies. Perspectives and limitations of chromosome painting for dose reconstruction of past radiation exposures are discussed.

Chromosome aberrations in nuclear power plant workers: the influence of dose accumulation and lymphocyte life-time

Chromosome analyses were performed in blood lymphocytes of 22 nuclear power plant workers with a mean accumulated radiation dose of 390 mSv (270-530 mSv). Nineteen workers had received 300 mSv 4-16 years prior to sampling. The frequency of dicentrics and ring chromosomes (1.75 x 10(-3)) was significantly elevated as compared to a control group (0.58 x 10(-3)). Based on the initial slope of an in vitro 60Co gamma-ray curve, a biological dose estimate of only 110 mSv was derived. This can be interpreted in terms of an "equivalent-acute" dose at the time of blood sampling which can be derived by weighting annual doses during working periods of 12-30 years for a mean life-time m of lymphocytes. The annual doses were additionally weighted for a uniform distribution during a whole year. Using m = 10 years, a mean "equivalent-acute" dose of 90 mSv (64-157 mSv) is obtained, which compares more closely to the biologically estimated dose than 20 mSv (7-71 mSv) based on m = 4.3 years.

Sister-chromatid exchange: second report of the Gene-Tox Program

This paper reviews the ability of a number of chemicals to induce sister-chromatid exchanges (SCEs). The SCE data for animal cells in vivo and in vitro, and human cells in vitro are presented in 6 tables according to their relative effectiveness. A seventh table summarizes what is known about the effects of specific chemicals on SCEs for humans exposed in vivo. The data support the concept that SCEs provide a useful indication of exposure, although the mechanism and biological significance of SCE formation still remain to be elucidated.

Cytogenetic effects of promutagens in genetically engineered V79 Chinese hamster cells expressing cytochromes P450

V79 Chinese hamster cell lines genetically engineered to express rat CYP2B1, CYP1A1, CYP1A2, and their parental cell lines V79-MZ, without acetyltransferase, and V79-NH, with acetyltransferase, were studied for chromosome aberrations and sister chromatid exchange induced by aflatoxin B1, cyclophosphamide, benzo[a]pyrene, 7,12-dimethylbenz[a]anthracene and dimethylnitrosamine. The parental V79 cell lines did not show clastogenic effects. Significant clastogenic effects were observed after an 18 h exposure to aflatoxin B1 and cyclophosphamide in CYP2B1 expressing cells, to benzo[a]pyrene in CYP1A1 and CYP1A2 expressing cells, to 7,12-dimethylbenz[a]anthracene and dimethylnitrosamine in cells, expressing CYP1A2 with or without acetyltransferase, and to cyclophosphamide in cells expressing both CYP1A2 and acetyltransferase. A significant sister chromatid exchange inducing effect was found after a 24 h exposure in each of the genetically engineered cell lines, except for benzo[a]pyrene and 7,12-dimethylbenz[a]anthracene in CYP2B1 expressing cells, and for benzo[a]pyrene in cells expressing both CYP1A2 and acetyltransferase. Thus, a battery of cell lines genetically engineered for metabolic competence may serve as a tool for investigating chromosomal changes induced by activated xenobiotics.

The in vitro micronucleus test on isolated human lymphocytes

The in vitro micronucleus test was performed on isolated human lymphocytes using the cytokinesis-block technique with and without a rat liver metabolizing system. Positive control substances were used to evaluate this test: a direct agent (vincristine) requiring no metabolic activation, and three promutagens (cyclophosphamide, benzo[a]pyrene and dimethylbenz[a]anthracene). All of them, when compared with controls, caused a significant increase in micronucleus frequency, with a clear dose response. Five compounds were then tested in this in vitro micronucleus test: safrole, azathioprine, procarbazine, diethylstilbestrol and o-toluidine. The chemicals were examined with and without exogenous metabolic activation. Of these five compound, o-toluidine was found to be a marked direct genotoxic agent and azathioprine gave positive results with or without metabolic activation (a better response was noted without the addition of S9 mix). Diethylstilbestrol gave conflicting results and was considered inconclusive. Two chemicals, safrole and procarbazine, were found to be non-genotoxic in this test system, whatever the protocol used.

Increased frequency of chromosome aberrations in long-term cultured cerebrospinal fluid lymphocytes of patients with multiple sclerosis

A method employing long-term lymphocyte culturing was developed to study chromosome aberrations in samples with very few cells. It was used to examine lymphocytes from the cerebrospinal fluid (CSF) and peripheral blood (PB) in 23 patients with clinically definite multiple sclerosis (MS), nine patients with other neurological diseases (OND), and eight healthy individuals. MS patients had significantly more aberrations in CSF lymphocytes than in PB lymphocytes (6.4 vs 4.1; P = 0.003). In contrast, no such difference was noted among patients with OND (3.8 vs. 3.7; P = 0.89) or healthy controls (3.6 vs 3.5; P = 0.90). CSF lymphocytes from MS patients had more aberrations than CSF lymphocytes from healthy controls (P = 0.012), but there was no difference between PB lymphocytes from MS patients and controls (P = 0.58). The patients with OND were similar to healthy controls both in CSF (3.8 vs 3.6; P = 0.91) and PB lymphocytes (3.7 vs 3.5; P = 0.90).

Sister-chromatid exchange in human B- and T-lymphocytes exposed to bleomycin, cyclophosphamide, and ethyl methanesulfonate

Sister-chromatid exchange (SCE) frequencies were investigated in mitogen-stimulated cultures of highly purified human peripheral blood B- and T-lymphocytes exposed to bleomycin (BM), cyclophosphamide (CP), or ethyl methanesulfonate (EMS). In untreated controls, T-lymphocytes showed twice as many SCEs as B-lymphocytes. CP (with metabolic activation) and EMS significantly increased the SCE frequencies. EMS induced a similar, dose-dependent SCE increase in both cell populations, whereas CP induced more SCEs in T- than in B-lymphocytes. No clear SCE increase was found in B- and T-lymphocytes treated with BM.

Chromosome aberrations induced in human lymphocytes by 16.5 MeV protons

In a track segment irradiation experiment with 16.5 MeV protons the induction of dicentrics was studied in human T-lymphocytes. The dose-response relationship was linear quadratic with estimated parameters alpha = (0.44 +/- 0.07) x 10(-1) Gy-1 and beta = (1.95 +/- 0.30) x 10(-2) Gy-2. With respect to X-rays a limiting RBE of 1.1-1.2 exists. The present findings are compared with data from other laboratories obtained with 4.9 and 8.7 MeV protons. It was found that the data do not fit theoretical predictions on a proportional relationship between alpha values and LET. Using the microdosimetric quantity yD (25 nm), the dose average of the lineal energy, for characterization of these proton radiations, at a relevant site diameter of 25 nm the ratio of yD = 1.15 is in accordance only with the observed alpha ratio of 1.0 +/- 0.23 for 8.7 and 16.5 MeV protons. In contrast to the prediction of a constant beta at low LET values, the quadratic coefficients increase with increasing LET between 3 and 8 keV/microns.

Nonrandom chromosome changes in multiple sclerosis

In order to study the role of genetic factors in multiple sclerosis, cytogenetic analysis was performed on 48 patients with the clinically defined disease. We found a high incidence of subjects (50%) with abnormal chromosomes, showing premature centromere division of the X chromosome and structural aberrations, translocations, or deletions that could suggest preferential breakpoints. Correlation between clinical and cytogenetic data showed that cytogenetic abnormalities were more common in patients with high frequency of relapse or with a progressive form of the disease.

Azathioprine, a genotoxic agent to be considered non-genotoxic in man

Azathioprine, an immunosuppressive drug, has been used for 25 years. Azathioprine is rapidly converted into a number of metabolites after absorption. Maximum blood levels in experimental animals (mice) were 11.3 micrograms/ml after a dosage of 33.3 mg/kg. Generally, levels of less than 1 microgram/ml are found. As azathioprine is ineffective in hypoxanthine guanine phosphoribosyltransferase (HPRT)-deficient patients, it will be clear that for immunosuppressive activity azathioprine must be metabolised. Regarding mutagenic activity, its mutagenicity for bacteria seems irrelevant for man because the nitroimidazole moiety can be reduced by bacteria but not or hardly at all by mammalian tissues. So 6-mercaptopurine (a metabolite of azathioprine) and its metabolites should be regarded as the active compounds. In vitro azathioprine can induce chromosome aberrations and other cytogenetic events at high, non-physiological doses. However, in view of the low blood levels it is unlikely that azathioprine can induce chromosome aberrations in kidney transplant patients. It is more probable that azathioprine inhibits the elimination of such aberrant cells through its immunosuppressive activity. It should be pointed out that in microbial mutagenicity systems also, azathioprine concentrations that are not reached in patients are needed to obtain an increased mutation rate.

Time-effect relationship of chromosome aberrations in peripheral lymphocytes after radiation therapy for seminoma

The time-effect relationship of dicentrics and cells containing unstable chromosome abnormalities (Cu cells) was studied in peripheral lymphocytes of 40 blood samples from 23 patients suffering from seminoma during a time period of 0-1720 days after radiation therapy. Nine patients were studied before treatment. Since the half-time for the disappearance of damaged cells from circulating blood is an increasing function of post-exposure time it can only be expressed as a differential value. The present model discriminates between the mean lifetime m for lymphocytes and a parameter q which is the differential half-time for the decline of damaged cells immediately after exposure (t = 0). If the time t is short compared with m the decline is asymptotically time-hyperbolic rather than exponential and can be described by q only. According to recalculations of previous data, comprising 30 years post exposure, m approximates 10 years. Differential half-times can be derived for any time post treatment within the analysed time period for the decline of the incidence of dicentrics. For example at the end of therapy (t = 0) the differential half-time was calculated to be 0.4 years and at 1720 days post exposure 3.6 years resulted. The corresponding values for the percentage of Cu cells cannot be derived for t = 0; at 1720 days 3.9 years resulted.

Spontaneous sister-chromatid exchange frequencies in human B and T lymphocytes at BrdU borderline concentrations for sister-chromatid differentiation

Human peripheral blood B and T lymphocytes, highly purified by immunologic methods, were supplemented with gamma-irradiated unseparated autologous mononuclear cells to restore helper functions and stimulated with pokeweed mitogen and phytohemagglutinin, respectively. Spontaneous sister-chromatid exchange (SCE) frequencies were investigated in proliferating B and T lymphocyte cultures labeled with the cell-type-specific borderline concentrations of 5-bromodeoxyuridine (BrdU) for sister-chromatid differentiation (SCD). B lymphocytes from 6 different donors showed mean values of 3.28-3.72 SCE events/cell. In T lymphocytes, mean values of 6.30-7.28 SCEs/cell were observed. The differences between the SCE distributions of the cell populations are highly significant. The results show that the differences in the spontaneous SCE frequencies between human B and T lymphocytes were not due to a difference in the uptake of BrdU.

Fecapentaene causes sister-chromatid exchanges in human lymphocytes

Fecapentaenes are potent mutagenic compounds found in human feces that are considered as potential colon carcinogens. It is demonstrated that a synthetic racemic all-trans fecapentaene-12 (fec-12) causes a strong dose-dependent increase in the frequency of sister-chromatid exchanges (SCE) in human lymphocytes exposed at different stages of the cell cycle. The SCE-inducing capacity is consistent with published results on the DNA-damaging activity of fec-12 such as formation of DNA single-strand breaks and interstrand cross-links.

A comparative analysis of data on the clastogenicity of 951 chemical substances tested in mammalian cell cultures

A literature review was conducted using original papers published during 1964-1985 on the in vitro clastogenicity of chemical substances. Results of tests on 951 chemical substances were abstracted from over 240 reports to form the database. The evaluation of these data relied on each author's original conclusion on a positive or negative outcome. Of these 951 substances, 447 (47%) were consistently positive either with or without activation; 417 (44%) were negative in the direct test but not tested with metabolic activation systems; 4 were negative but tested only with activation; and 30 (3%) were clearly negative both with and without activation. The remaining 53 substances gave variable results when tested under different experimental protocols or in different cell types, but were positive in at least one test. Although discrepant results were found associated with some cell types, the addition of metabolic activation systems tended to eliminate such variability. No one cell appeared to be superior in response to all clastogens. For screening purposes, the choice of cell may thus depend more on the general usefulness and reliability of a cell type than on a strong response to a particular chemical. However, the use of a suitable metabolic activation system does appear to be of critical importance. The concentration at which clastogenic effects were detected varied extensively for different test substances, ranging from a minimum of 4.3 X 10(-8) to 6.9 X 10(2) mM. Possible mechanisms of action for substances active at only high levels are discussed, but no satisfactory explanation is available at this time. The relevance of tests conducted at concentrations high enough to alter significantly the osmolarity and other culture conditions is considered, and caution urged in the interpretation of test results obtained under physiologically stressful conditions. The clastogenic potential was compared quantitatively using an index of effective concentration (D20) and one which estimates the number of cells with exchange aberrations expected per mg/ml (TR) for data obtained by using a uniform protocol and cultures of Chinese hamster lung (CHL) cells. Both values were distributed over a wide range, demonstrating the variety of genotoxic potential in chemicals. In general, a substance which was active at only high concentrations produced fewer exchange-type aberrations. In vivo activity, as measured by tumourigenic effect and formation of micronuclei in bone marrow, tended to be greater for substances with a D20 below 10(-2) mg/ml and a TR value over 10(3).(ABSTRACT TRUNCATED AT 400 WORDS)

Proliferation kinetics of human B- and T-lymphocytes

Human peripheral blood B- and T-lymphocytes, highly purified by immunological methods, were supplemented with gamma-irradiated unseparated autologous mononuclear cells to restore helper functions and stimulated with pokeweed mitogen and phytohaemagglutinin, respectively. Proliferation kinetics of the cell populations were investigated using 5-bromodeoxyuridine (BrdU) labelling of the cell cultures and chromosome preparation at different times after stimulation. The percentages of metaphase cells having replicated for one, two or three generations in the presence of BrdU were determined following sister chromatid differential staining. In all donors, the changes in these percentages were faster in B- than in T-lymphocytes, indicating a longer cell cycle time in the latter population.

Dose-response relationship for chromosome aberrations induced by fecapentaene-12 in human lymphocytes

Chromosome analyses were carried out in human lymphocytes exposed to a synthetic racemic all-trans fecapentaene-12 at 2-24 microM. A dose-dependent increase of the incidences of chromatid-type changes with distinct saturation at higher doses could be observed. The results reveal for the first time that fec-12 is a potent direct-acting mutagen in human lymphocytes.

Analysis of cytogenetic effect in human lymphocytes induced by metabolically activated 2-nitropropane

Chromosome analyses were carried out in human lymphocytes treated in vitro with 2-nitropropane (2-NP) in the presence and absence of the mammalian metabolic activation system, S9 mix. Without S9 mix, only the frequency of gaps was significantly increased at 80 mM 2-NP as compared to controls. With S9 mix, the incidences of gaps and chromatid-type aberrations were significantly increased at 60 mM and 80 mM. Sister-chromatid exchanges (SCE) have been induced at concentrations as low as 7.5 mM. The present findings demonstrate that in human lymphocytes, 2-NP requires metabolic activation to express clastogenicity and SCEs.

Storage of irradiated human blood; a source of error in quantitative chromosome analysis

Human whole blood was irradiated with 2.5 Gy of 220 k Vp X-rays and stored before culture with 9.7 microM BrdU and 19.4 or 38.7 microM BrdU for 0, 24, 48 and 72 h. The frequency of dicentrics and ring chromosomes was determined in cells staining as first division (M1) metaphases with the fluorescence plus Giemsa technique. Storage had no influence on the observed aberration yields in 44 h cultures containing 9.7 microM BrdU. In 66 h cultures at 19.4 microM BrdU the observed yields after 2 and 3 days' storage were significantly lower as compared to cultures from fresh blood. No storage effect was revealed in 66 h cultures containing 38.7 microM BrdU. In cases where cytogenetic radiation dosimetry has to be carried out using blood samples which have been in transit for 2-3 days, the findings are of relevance for a correct determination of the chromosome damage in M1 cells.

Cytogenetic effects in lymphocytes of formaldehyde workers of a paper factory

Chromosome analyses were carried out in lymphocytes from 20 male papermakers exposed to formaldehyde (FA) for 2-30 years. 20 male workers from the same factory but without FA exposure served as controls. In the exposed group a significantly increased incidence of dicentrics or dicentrics and ring chromosomes was observed for 11 workers currently employed as supervisors. In contrast to 9 operators their total mean exposure time to FA was about 2.5 times longer. No significantly higher SCE values were found for smoking or for non-smoking FA workers compared with the corresponding control subjects.

Occupational exposure to anticancer drug--potential and real hazards

Many anticancer agents have been shown to be mutagenic, teratogenic and carcinogenic in experimental systems and second malignancies are known to be associated with several specific therapeutic treatments. Anticancer agents thus represent a class of occupational carcinogens, the handling of which should involve no unnecessary exposure. The available methodologies to detect possible exposures from ambient air and from biological samples are discussed, and the published data on results are reviewed. Analytical methods are available for the detection of most frequently used anticancer drugs from all groups, i.e., alkylating agents, mitotic inhibitors, antimetabolites and antibiotics. The ambient samples taken from sites of admixture of cytostatics have often shown detectable, but low concentrations of anticancer agents. Urine samples from patients under chemotherapy as well as from personnel handling the drugs occupationally in hospitals have been analyzed both chemically and for excreted mutagenicity. Both cisplatin and cyclophosphamide have been detected in the urine of patients; furthermore, cyclophosphamide was observed in the urine of nurses who formulate and deliver this drug. Urinary mutagenicity assays have given both positive and negative results in various groups of nursing and pharmacy personnel. Cytogenetic methods have, likewise, been applied for monitoring purposes. Most of the available data concerns chromosome aberrations (CA) or sister-chromatid exchanges (SCE) induced in peripheral blood lymphocytes of patients under chemotherapy. A few studies on groups occupationally exposed to anticancer drugs have given positive results, but also negative reports have appeared for these same cytogenetic parameters. No studies are as yet available on the possible carcinogenic effects of occupational handling of anticancer drugs. Two recent case-referent studies among hospital personnel have pointed to slightly increased risks of disorders in pregnancy outcome; one of the studies has shown an excess of spontaneous abortions and other malformations in children of females with a history of work with anticancer agents.

Chromosome changes with time in lymphocytes after occupational exposure to toluene

Chromosome analyses were carried out in peripheral lymphocytes of 27 workers exposed to toluene in a rotogravure plant. At the time of blood sampling all of them had not been exposed to toluene for at least 4 months up to 5 years. Up to 2 years after cessation of exposure to toluene a higher incidence of chromatid-type aberrations could be observed than in controls. After longer post-exposure periods the aberration yields can no longer be distinguished from background level. No differences were revealed in SCE frequencies of smoking or non-smoking workers post toluene exposure compared with the corresponding controls.

Chlorambucil-induced chromosome damage to human lymphocytes is dose-dependent and cumulative

Sister chromatid exchanges (SCEs), a sensitive measure of chromosome damage, were counted in peripheral-blood lymphocytes from 10 patients with Behcet's syndrome receiving chlorambucil. All patients had abnormal counts. Damage was related to both daily dose and duration of therapy and was occurring at a greater rate than its repair. The patient who had been treated the longest and had received the highest total dose also had the highest SCE count. He died from acute leukaemia. SCE analysis may provide a method for detecting patients at risk from oncogenic effects of cytotoxic drugs.

Monitoring patients on long-term drug therapy for genotoxic effects

The problems associated with the design and conduct of experiments involving surveys of human population sister chromatid exchange (SCE) frequencies are discussed. It is suggested that the problems of variation between culture occasions may be overcome by the rigid control of experimental conditions and the inclusion of the same negative controls (herein called "base controls") on all culture occasions. In addition, all experimental subjects are cultured, as far as possible, at the same time as controls drawn from the same population and matched for age (+/- 5 yr) and sex. Many factors in such surveys remain uncontrolled but the collection of data on potential environmental mutagen exposure in all subjects is suggested as a mechanism to measure and evaluate such factors. Data are reported on SCE frequencies in lymphocytes from patients receiving 4 separate drugs for chronic conditions. Using a square root transformation of SCE frequencies and the analysis of variance, there is clear evidence for a rise in SCE frequency in patients receiving sulphasalazine (SASP) and azathioprine (Aza). On the other hand, patients receiving atenolol or chlorpropamide show no evidence of a rise in SCE frequency.

The suitability of the human lymphocyte micronucleus assay system for biological dosimetry

Human whole blood was irradiated with 220 keV X-rays at doses of 0-4.0 Gy. After incubation periods of 48, 60, 72, 84 and 96 h, lymphocytes were prepared without colcemid pretreatment according to 2 different methods, and micronuclei were scored. The crucial point of lymphocyte preparation was found to be the osmotic pressure of the hypotonic solution. Only a method that preserves the cytoplasm of lymphoblasts is suitable for a correct association of micronuclei with the main nucleus. Similar as for structural chromosome changes, now their intercellular distribution can be analysed. This is necessary for the derivation of appropriate statistical weights which have to be used for more reliable regression analyses. For 48 h, the data can be described by the linear model, for 84 and 96 h, by the linear-quadratic model. For 60 and 72 h no such definite conclusions can be drawn. For calibration purposes a standardized culture time cannot be recommended. Because the background frequency is high, the lymphocyte micronucleus assay system is not sensitive enough to detect a significant increase in the incidence of micronuclei after exposure to low doses (less than 0.3 Gy).

Cytogenetic effects of an alkyl-lysophospholipid derivative in human peripheral lymphocytes exposed in vitro and in vivo

Chromosome analyses were carried out in human lymphocytes exposed to an antitumor alkyl-lysophospholipid (ALP) in vitro and in vivo. There was no evidence for a significant clastogenic effect or incidence of an increased sister-chromatid exchange (SCE) after short-term and long-term treatment of unstimulated or stimulated lymphocytes with concentrations of 0.1-50 micrograms ALP per ml. Cell proliferation was delayed after G0 exposure to 50 micrograms/ml. Although no ALP monotherapy was present for 3 cancer patients examined before and during ALP treatment with accumulated doses of 15-516 mg/kg, the cytogenetic data were in accord with the negative experimental results.

The stimulation of human B and T lymphocytes by various lectins

The response of human peripheral blood lymphocytes to different lectins was tested in vitro by monitoring DNA synthesis, blast transformation, and mitotic activity. One group of lectins - RCA, VGA, HPA, PNA, and UEA - showed no stimulating effects at all. WGA and VVA induced DNA synthesis and blast transformation but failed in stimulating mitosis. The mitogens PHA, ConA, LCA, and PWM showed peaks of mitotic activity at 50-60 hours for PHA, 70 hours for ConA, 80 hours for LCA, and between days 4 and 5 for PWM. The stimulation of different subpopulations of lymphocytes was investigated by immunological methods for the detection of B- and T-cell-specific surface structures during the whole incubation period. PHA proved to be a predominantly T cell stimulating agent, whereas ConA seemed to activate a higher proportion of B cells than yet known. PWM and the so-called T cell mitogen LCA turned up to stimulate a large number of B cells, but lead also to a T cell activation. The analysis of SCE events in stimulation experiments with these two lectins showed the early proliferation of a cell population with low SCE frequencies and the late propagation of a cell population with higher SCE rates. It could be assumed that the first population is represented by B- and the second by T-cells.

Chromosome aberrations induced in patients treated with chemotherapeutic drugs and irradiation for acute lymphatic leukemia

Chromosome analyses were carried out in lymphocytes of ten children with ALL, prior to and during combined therapy with antineoplastic drugs and cranial irradiation. Chromosome preparations from group I (four patients) were analysed by conventional staining. For group II (six patients) the FPG technique (fluorescence plus Giemsa) was applied after BrdU treatment of cultures and cells were scored exclusively in first division. A significant clastogenic effect could not be detected in samples collected during or after chemotherapy for either group. After cranial irradiation of those patients in group II. linear dose-effect relationships for dicentric plus ring chromosomes, and for excess acentrics, could be demonstrated after correction for the relative amount of irradiated volume.

Dose-effect relationship for 14.5 MeV (d + T) neutron-induced chromosome aberrations in human lymphocytes irradiated in a man phantom

Human lymphocytes were irradiated with 14.5 MeV (d + T) neutrons at the positions sternal, retrosternal, liver and gonads of a waterfilled Plexiglas man phantom of 37 degrees C. After BUdR treatment of lymphocyte cultures and FPG-staining of metaphases, exclusively first post-irradiation divisions (M1-cells) were analysed. A regression analysis was carried out by means of a weighted least-squares method. Dose-effect relations of dicentrics and acentrics could be fitted by the linear-quadratic model. A comparison of the dose-effect curves established with either conventional or FPG-staining technique revealed statistically significant differences. The M1-evaluation yielded about 46 per cent more dicentrics and about 37 per cent more acentrics. The consequences of these results are discussed in relation to the application of chromosome analysis in 'biological dosimetry'.

Application of conventional and FPG staining for the analysis of chromosome aberrations induced by low levels of dose in human lymphocytes

Human peripheral lymphocytes were irradiated with 0.05-0.5 Gy of 220 keV X-rays. After application of either a conventional or the fluorescence plus Giemsa (FPG) staining technique, the dose response for dicentrics and acentrics was studied. The analysis of exclusively first-division cells (M1), carried out by the FPG method, revealed significantly higher aberration yields as compared with the results of the conventional method. The data from M1 cells support the assumption of a linear dose response for both dicentrics and acentrics. The results are discussed with regard to the application of chromosome analyses for a cytogenetic dosimetry after exposure to low levels of ionizing radiation.

Chromosomal aberrations and sister-chromatid exchanges (SCEs) in patients undergoing long-term Imuran therapy

13 patients treated daily for an extended time with Imuran and prednisone and 4 patients treated in the same way with Imuran only were cytogenetically analysed for the induction of structural chromosomal aberrations and SCEs. There was an increase in the number of aberrations and SCEs in nearly all patients analysed. However, we did not find any dose-dependent cumulative effect on chromosomal damage, with the exception of 1 patient tested in a small group of 4 patients involved in a prospective cytogenetic study, who showed a significant time-dependent increase in the number of aberrations.

Sister chromatid exchange (SCE) and structural chromosome aberration in mutagenicity testing

Data from previous studies published on the induction by mutagens of sister chromatid exchanges (SCEs) and structural chromosome damage were compared qualitatively and quantitatively. Although a good correlation between the incidence of both cytogenetic phenomena has been pointed out in many previous publications, about 30% of the agents for which comparable data were available yielded non-corresponding qualitative results concerning both indicator effects. However, even in groups with good qualitative agreement distinct quantitative differences indicated different molecular mechanisms of the formation of SCEs and breaks. Additional information supporting the importance of these differences for the validity of both indicator systems has been derived from the results obtained using strong clastogens exhibiting a low or no SCE-inducing activity and vice versa, from special observations on chromosomal breakage syndromes, and from studies on the action of known co- and anti-clastogens on SCE-induction by chemical mutagens. As a result, it has been suggested that the SCE-technique should be considered as a valuable additional method for cytogenetic mutagenicity testing, which, however, is not adequate to replace the classical methods of analysis of structural chromosome damage.

Cell-growth kinetics and karyotype analysis of human memory lymphocytes responding to alloantigen and mitogen

Peripheral-blood lymphocytes were primed in vitro with the mitogen phytohemagglutinin (PHA) or with allogeneic cells and their memory responses studied following sequential restimulation with either mitogen or alloantigen. Chromosome preparations were made every 24 hours following exposure to the stimulating agents. Cultures were labeled with BUdR for sister-chromatid staining of the chromosomes which provided information about the kinetics of cell growth and rates of sister chromatid exchange. Cultures containing n BUdR were used for the investigation of cell karyotypes after chromosome-banding. Following PHA as well as alloantigen restimulation, an earlier reaction of the responding cells was observed. The peak response after the first stimulation was found at 120 h with allogeneic stimulation and at 60 h with mitogen stimulation. In the second round of stimulation, the peak occurred after 48 h (allogeneic) and 36 h (PHA) and following the third stimulation after 36 h (allogeneic) and 24 h (PHA). The speed of cell growth was decreased following restimulation with either alloantigen and mitogen. In contrast to the allogeneic restimulation, the number of cells responding after PHA restimulation was decreased. No systematic numerical or structural aberration of the karyotype was detected following repeated stimulation with either alloantigen or mitogen. In this sense, the lymphocyte subpopulations selected by repeated stimulation did not differ from the starting material. On the other hand, the sister-chromatid exchange (SCE) frequency was increased following allogeneic restimulation, whereas it remained constant with PHA restimulation.

On the mutagenicity of nitroimidazoles

Regarding mutagenicity, metronidazole is one of the best-investigated compounds of the nitroimidazoles. This drug is mutagenic on bacteria, especially if base-pair tester strains are used and bacterial nitroreductases are present. The serum levels attained in man after intake of this drug are sufficient to cause mutations in bacteria. Furthermore, interaction with and binding to DNA occurs under anaerobic conditions and sometimes DNA breaks are observed. However, metronidazole does not show mutagenic activity in mammalian cells in vitro; the micronucleus test is negative and chromosome aberrations are only found under anaerobic conditions. With microbial systems the mutagenicity of 47 nitroimidazoles has been investigated. Only 4 compounds were always negative in the applied test systems. Because with base-pair tester strains mutagenicity was assessed, this class of compounds should be regarded as a base-pair mutagen. In fungi, some compounds (e.g. ZK 26173 and azathioprine) are potent mutagens, whilst with most investigated nitroimidazoles only a weak or no mutagenic activity could be detected. Somewhat similar observations have been made in tests with Drosophila melanogaster, a test for gene mutations in mammalian cells, the micronucleus test, cytogenic tests and the dominant lethal test. The reduction products of metronidazole, misonidazole and 1-methyl-2-nitro-5-vinylimidazole, cause DNA damage if the nitro group is reduced in the presence of DNA. Reduction products are formed by microbes in the gut or by mammalian cells under anaerobic conditions. No teratological effect due to metronidazole or most other nitroimidazoles has been observed. Metronidazole is carcinogenic in mice and rats, and dimetridazole in rats. Up to the present, no carcinogenic effects have been observed in man. Azathioprine is probably carcinogenic for man. It is unlikely that the therapeutic applications of the presently used nitroimidazoles, except for azathioprine, will cause an increase in the tumor incidence in man or will cause other genotoxic effects, although such effects cannot be excluded with certainty.

Analysis of structural chromosome changes and SCE after occupational long-term exposure to electric and magnetic fields from 380 kV-systems

Chromosome analyses were carried out in lymphocytes of 32 workers occupationally exposed for more than 20 years to 50 Hz alternating electric magnetic fields in 380 kV switchyards. As compared with a control group of 22 workers of similar age and occupation but without field exposure neither the yields of structural chromosome changes nor the SCE-frequencies were increased. The difference of cytogenetic data after occupational exposure to ionizing radiation is discussed.

Chromosome changes in human lymphocytes after separate and combined treatment with divalent salts of lead, cadmium, and zinc

Unstimulated human lymphocytes in whole blood were treated for three hours with lead, cadmium, and zinc acetate separately and in combinations of two or three metal salts with different concentrations of between 10(-3) and 10(-5) moles, respectively. Untreated cultures and sodium acetate-treated samples served as controls. Chromosome analysis from 48 cultures revealed higher incidences of chromatid-type aberrations and gaps only for cultures exclusively treated with cadmium. The results are discussed under the respect of heavy metal metabolism in human lymphocytes.