A comparison of chromosomal aberrations induced by in vivo radiotherapy in human sperm and lymphocytes

Aneuploidy: a common and early evidence-based biomarker for carcinogens and reproductive toxicants

Aneuploidy, defined as structural and numerical aberrations of chromosomes, continues to draw attention as an informative effect biomarker for carcinogens and male reproductive toxicants. It has been well documented that aneuploidy is a hallmark of cancer. Aneuploidies in oocytes and spermatozoa contribute to infertility, pregnancy loss and a number of congenital abnormalities, and sperm aneuploidy is associated with testicular cancer. It is striking that several carcinogens induce aneuploidy in somatic cells, and also adversely affect the chromosome compliment of germ cells. In this paper we review 1) the contributions of aneuploidy to cancer, infertility, and developmental abnormalities; 2) techniques for assessing aneuploidy in precancerous and malignant lesions and in sperm; and 3) the utility of aneuploidy as a biomarker for integrated chemical assessments of carcinogenicity, and reproductive and developmental toxicity.

Is there a relationship between sperm chromosome abnormalities and sperm morphology?

This review explores the relationship between sperm chromosomal constitution and morphology. With the advent of techniques for obtaining information on the chromosome complements of spermatozoa, this relationship has been studied in fertile men and in men with a high frequency of chromosomal abnormalities. Using human sperm karyotype analysis, no relationship between sperm chromosome abnormalities and morphology was found in fertile men, translocation carriers or post-radiotherapy cancer patients. Fluorescence in situ hybridization (FISH) analysis has not generally revealed a specific association between morphologically abnormal sperm and sperm chromosome abnormalities, but has indicated that teratozoospermia, like other forms of abnormal semen profiles (aesthenozoospermia, oligozoospermia) is associated with a modest increase in the frequency of sperm chromosome abnormalities. However, FISH studies on some infertile men and mouse strains have suggested that certain types of morphologically abnormal spermatozoa, such as macrocephalic multitailed spermatozoa, are associated with a very significantly increased frequency of aneuploidy. Thus, there may be an association between sperm morphology and aneuploidy in infertile men with specific abnormalities.

Cross-species sperm-FISH assays for chemical testing and assessing paternal risk for chromosomally abnormal pregnancies

The father, like the mother, can transmit genetic defects to his offspring that are detrimental for normal development and a healthy life. Epidemiological studies have identified associations between several paternal exposures and abnormal reproductive outcomes, but these types of studies are inherently complex and expensive, and the risk factors for the paternal contribution to abnormal reproductive outcomes remain poorly understood. Several sensitive methods have been developed for detecting mutations and chromosomal damage directly in sperm. These assays are potential bioindicators for paternal risk factors for infertility, spontaneous abortions, aneuploidy syndromes, and genetic diseases in children. Among these methods, fluorescence in situ hybridization (FISH) has been adapted for the detection of numerical and structural chromosomal abnormalities in the sperm of an expanding number of species, including humans and rodents. Sperm FISH has identified several potential paternal risk factors such as age, drugs, lifestyles, and various environmental/occupational exposures. Here, we summarize the status of the development and usage of these sperm-FISH assays and suggest strategies for prioritizing chemical agents for epidemiological investigations to assess paternal risk for abnormal reproductive outcome.

Lymph nodes in the irradiated field influence the yield of radiation-induced chromosomal aberrations in lymphocytes from breast cancer patients

PURPOSE

To measure chromosomal aberrations in blood lymphocytes from breast cancer patients treated with radiotherapy after quadrantectomy or tumorectomy.

METHODS AND MATERIALS

Twenty-two breast cancer patients treated with breast-conserving surgery and radiation were evaluated. Adjuvant chemotherapy was also given to 9 patients. Blood samples were obtained before radiotherapy, after about one-half of the fractions, and at the end of the treatment of the whole breast (50 Gy). Chromosome aberrations in peripheral blood lymphocytes were measured using chemical-induced premature chromosome condensation combined with fluorescence in situ hybridization.

RESULTS

Radiation treatment produced a significant increase in the yield of chromosomal aberrations. A large interindividual variability was observed. The variability was not related to field size, previous chemotherapy, or treatment morbidity. Chromosome aberrations in lymphocytes at the end of the treatment were significantly higher in the group of patients with no lymph nodes surgically removed before the treatment than in the group of patients with more than 10 lymph nodes removed.

CONCLUSION

The number of lymph nodes within the radiation field is an important factor affecting the yield of radiation-induced chromosomal aberrations in breast cancer patients.

Radiation- and chemical-induced structural chromosome aberrations in human spermatozoa

Previous studies on the clastogenic effects of mutagens on human sperm chromosomes were reviewed. A marked increase of structural chromosome aberrations (SCAs) has been reported in the spermatozoa irradiated in vitro with five kinds of ionizing radiation (137Cs gamma-, 60Co gamma-, X-, and 3H beta-rays and 252Cf neutrons). The micronucleus (MN) test with hybrid two-cell embryos generated from human sperm and hamster oocytes was shown to be useful as a simple and rapid method for assessing the effects of radiation. Radiosensitivity of human spermatozoa was highest, being followed by golden hamster, Chinese hamster and mouse spermatozoa. Chromosome-damaging effects were also found with some chemicals (bleomycin, daunomycin, methyl methanesulfonate, triethylenemelamine, neocarzinostatin, N-methyl-N'-nitro-N-nitorosoguanidine and mitomycin C (MMC)), but not with other chemicals (urethane, nitrobenzene, dioxin, cyclophosphamide (CP), benzo(a)pyrene (BP) and N-nitrosodimethylamine (NDMA)). The clastogenicity of chemical metabolites was confirmed for CP and BP, by using the S9-based metabolic activation system. The results of sperm chromosome analysis from cancer patients who had undergone radio- and/or chemotherapy were contradictory among investigators and further studies are necessary. The importance of mutagenicity testing with human spermatozoa is discussed.

Chromosomal aberrations induced by chemotherapy and radiotherapy in lymphocytes from patients with breast carcinoma

PURPOSE

Stable chromosomal aberrations (SCAs) have been found in circulating lymphocytes from patients treated for breast carcinoma. Therefore, we tried to define their incidence in such patients, to determine an in vitro dose-effect relationship, and to correlate these data with clinical parameters.

METHODS AND MATERIALS

This prospective study included 25 patients who, after surgery, underwent either radiotherapy (RT) alone (n = 15) or RT combined with chemotherapy (n = 10). SCAs were scored using the fluorescent in situ hybridization technique before RT and 4 and 12 months after RT. Dose-effect curves were established by in vitro irradiation of blood samples with 2 and 4 Gy, before and after treatment.

RESULTS

In all patients, the rate of SCAs increased significantly after external irradiation. No significant decrease in SCAs was observed during the first year after RT. RT and chemotherapy had no effect on the lymphocyte in vitro dose-effect relationship. No relationship was found in the distribution of patients between the yield of SCAs scored after external irradiation and after in vitro irradiation. SCAs after RT or in vitro irradiation did not correlate with family history of breast carcinoma or acute toxicity of treatment. More significantly, the yield of SCA after external irradiation was strongly related to the irradiation of the internal mammary chain and the supraclavicular lymph node area, suggesting that the volume of irradiated blood vessels was an essential parameter in determining the rate of SCAs.

CONCLUSION

A high and stable yield of SCAs persisted at least 1 year after external irradiation. The nature of the volume irradiated containing large blood vessels was the major determinant of the observed biologic dose.

Multicolor FISH analysis of chromosomal breaks, duplications, deletions, and numerical abnormalities in the sperm of healthy men

Transmitted de novo structural chromosomal abnormalities, the majority of which are paternally derived, can lead to abnormal reproductive outcomes as well as genetic diseases in offspring. We developed and validated a new multicolor FISH procedure (sperm ACM, which utilizes DNA probes specific for the alpha [1cen], classical, [1q12], and midi [1p36.3] satellites of chromosome 1) which utilizes DNA probes specific for three regions of chromosome 1 to detect human sperm that carry numerical abnormalities plus two categories of structural aberrations: (1) duplications and deletions of 1pter and 1cen, and (2) chromosomal breaks within the 1cen-1q12 region. In healthy men, the average frequencies of sperm with duplications and deletions were (a) 4.5 +/- 0.5 and 4.1 +/- 1.3 per 10(4) involving 1pter and (b) 0.9 +/- 0.4 and 0.8 +/- 0.3 per 10(4) involving 1cen, respectively. The frequency of sperm exhibiting breaks within the 1cen-1q12 region was 14.1 +/- 1.2 per 10(4). Structural aberrations accounted for 71% of the abnormalities detected by sperm ACM, which was significantly higher than numerical abnormalities (P=2x10-8). Our findings also suggest that, for healthy men, (a) sperm carrying postmeiotic chromosomal breaks appear to be more prevalent than those carrying products of premeiotic or meiotic breakage or rearrangements, (b) the high frequency of chromosome breaks measured after "fertilization" by the hamster-egg cytogenetic method already appear to be present and detectable within human sperm by FISH, and (c) there are nonrandom and donor-specific distributions of breakpoint locations within 1q12 in sperm. FISH facilitates the analysis of much larger numbers of sperm than was possible when the hamster-egg method was used. Therefore, FISH-based procedures for simultaneously detecting chromosomal breaks, rearrangements, and numerical abnormalities in sperm may have widespread applications in human genetics, genetic toxicology, and reproductive medicine.

Minisatellite mutation frequency in human sperm following radiotherapy

Screening pedigrees for inherited minisatellite length changes provides an efficient means of monitoring repeat DNA instability but has given rise to apparently contradictory results regarding the effects of radiation on the human germline. To explore this further in individuals with known radiation doses and to potentially gain information on the timing of mutation induction, we have used an extremely sensitive single molecule approach to quantify the frequencies of mutation at the hypervariable minisatellites B6.7 and CEB1 in the sperm of three seminoma patients following hemipelvic radiotherapy. Scattered radiation doses to the testicles were monitored and pre-treatment sperm DNA was compared with sperm derived from irradiated pre-meiotic, meiotic and post-meiotic cells. We show no evidence for mutation induction in any of the patients and discuss this finding in the context of previous population studies using minisatellites as reporter systems, one of which provided evidence for radiation-induced germline mutation.

Sequential chromosome aberration analysis following radiotherapy - no evidence for enhanced genomic instability

Chromosome analysis of peripheral blood lymphocytes using block staining was performed on 18 cancer patients who had received fractionated radiotherapy doses totalling 35-80 Gy. Samples were obtained from 13 individuals within 1 year of treatment and thereafter approximately annually up to a maximum of eight times (range: three to eight samples per individual). Sampling of the remaining five patients started later. Frequencies of cells with unstable chromosome aberrations showed a steady decline whereas frequencies of cells with just chromatid aberrations and gaps were initially low and remained so. There was no subsequent rise in any aberrant cell type in later years and thus no suggestion that the radiation exposure had induced a persistent or late manifesting state of genomic instability.

Measurements of the equivalent whole-body dose during radiation therapy by cytogenetic methods

Estimates of equivalent whole-body dose following partial body exposure can be performed using different biophysical models. Calculations should be compared with biodosimetry data, but measurements are complicated by mitotic selection induced in target cells after localized irradiation. In this paper we measured chromosomal aberrations in peripheral blood lymphocytes during radiotherapy, and estimated the equivalent whole-body dose absorbed, by using the novel technique of interphase chromosome painting. Premature chromosome condensation was induced in stimulated lymphocytes by incubation in calyculin A, and slides were hybridized in situ with whole-chromosome DNA probes specific for human chromosomes 2 and 4. Reciprocal exchanges were used to estimate the equivalent whole-body dose, based on individual pre-treatment in vitro calibration curves. Equivalent whole-body dose increased as a function of the number of fractions, and reached a plateau at high fraction numbers. Chromosomal aberration yields were dependent on field size, tumour position and concurrent chemotherapy. Results suggest that interphase chromosome painting is a simple technique able to give a reliable estimate of the equivalent whole-body dose absorbed during therapeutic partial-body irradiation.

DNA damage in human and mouse spermatozoa after in vitro-irradiation assessed by the comet assay

The comet assay is widely employed as a method to measure DNA damage in a wide variety of cell types following genotoxic insult. We have used this method in order to characterise DNA damage in spermatozoa following in vitro irradiation with 137Cs gamma rays. In contrast to somatic cells, the DNA of mammalian spermatozoa is bound by protamine molecules allowing a sixfold more highly compact structure and thus rendering conventional cell lysis protocols ineffective. Therefore, this new method uses an extensive lysis step to ensure effective removal of DNA-associated proteins allowing DNA damage to be scored reproducibly in both murine and human spermatozoa. Mouse spermatozoa collected from the vas deferens at post-mortem or human spermatozoa provided by donors were irradiated with doses of gamma-rays from 0-100 Gy using a 137Cs source and then processed for both alkaline and neutral comet assays. Under neutral electrophoresis conditions, which permits the measurement of double-stranded DNA breaks, a linear increase in the amount of DNA damage measured was observed with increasing radiation dose for both murine and human spermatozoa. Similarly, using alkaline electrophoresis conditions to examine DNA single-strand breaks and alkali-labile sites, a linear relationship was also observed for murine sperm but in contrast no such relationship was apparent for human spermatozoa subjected to the same radiation treatments. Interestingly, unirradiated sperm (both human and mouse) showed extensive DNA migration from the nucleus after alkaline assay. Since it is unlikely that the DNA of normal spermatozoa contains high numbers of single-strand breaks and damage was not detected for unirradiated sperm in the neutral assay, it is more likely that this DNA migration is due to the presence of high numbers of alkali labile sites within sperm DNA and that these may be related to the highly condensed structure of spermatozoal DNA. The large radiation doses used in these experiments to produce measurable amounts of DNA damage reflects the high radioresistance of spermatozoa compared to somatic cells and this may also be related to the differences in DNA packaging and conformation. In conclusion, this work shows that the comet assay represents a new method for examining DNA damage in spermatozoa and should be evaluated for use in reproductive toxicity testing.

Genetics of human sperm

PURPOSE

Chromosome abnormalities in sperm were studied by fluorescence in situ hybridization to determine the frequency and distribution of abnormalities in normal men and the effect of donor age on the frequency of abnormalities. Studies of chemotherapy and infertility patients assessed any increased risk in these populations.

METHODS

Multicolor fluorescence in situ hybridization was performed on the sperm samples to assess aneuploidy frequencies for chromosomes 1, 2, 4, 9, 12, 13, 15, 16, 18, 20, 21, X, and Y as well as "sex ratios" and frequencies of diploid sperm.

RESULTS

Most chromosomes yielded disomy estimates of approximately 0.1%, whereas the frequencies for chromosome 21 and the sex chromosomes were significantly elevated. The only chromosome to show a significant paternal age effect was YY disomy. Chemotherapy patients did not have an increased risk of aneuploid sperm 2-13 years after treatment. Infertility patients had an increased risk of disomy for chromosome 1, 13, 21, and XY.

CONCLUSIONS

Multicolor fluorescence in situ hybridization analysis allows comparison of sperm from various populations of men and has demonstrated that infertile patients have a significant increase in the frequency of aneuploid sperm.

Biodosimetry of heavy ions by interphase chromosome painting

We report measurements of chromosomal aberrations in peripheral blood lymphocytes from cancer patients undergoing radiotherapy treatment. Patients with cervix or esophageal cancer were treated with 10 MV X-rays produced at a LINAC accelerator, or high-energy carbon ions produced at the HIMAC accelerator at the National Institute for Radiological Sciences (NIRS) in Chiba. Blood samples were obtained before, during, and after the radiation treatment. Chromosomes were prematurely condensed by incubation in calyculin A. Aberrations in chromosomes 2 and 4 were scored after fluorescence in situ hybridization with whole-chromosome probes. Pre-treatment samples were exposed in vitro to X-rays, individual dose-response curves for the induction of chromosomal aberrations were determined, and used as calibration curves to calculate the effective whole-body dose absorbed during the treatment. This calculated dose, based on the calibration curve relative to the induction of reciprocal exchanges, has a sharp increase after the first few fractions of the treatment, then saturates at high doses. Although carbon ions are 2-3 times more effective than X-rays in tumor sterilization, the effective dose was similar to that of X-ray treatment. However, the frequency of complex-type chromosomal exchanges was much higher for patients treated with carbon ions than X-ray.

Chemotherapy induces transient sex chromosomal and autosomal aneuploidy in human sperm

Each year more than 20,000 children and young persons of reproductive age are exposed to known mutagens in the form of chemo- and/or radiotherapy for cancer in the States. As more of these treatments are effective there is growing concern that genetic defects are introduced in the germ cells of these young patients. It is well documented for male rodents that treatment with chemo- and radio-therapeutic agents before mating can cause genetic damage in the germ line, and the magnitude of heritable effects depends on the spermatogenic cell stage treated. Similar germinal effects are suspected to occur in humans but remain unproven. Hodgkin's disease (HD) is an example of a malignancy which is typically diagnosed during a patient's reproductive years. In our study we observed eight male HD patients who were treated with NOVP (Novanthrone, Oncovin, Vinblastine, Prednisone) chemotherapy. We evaluated sperm aneuploidy using multi-colour fluorescence in situ hybridization (FISH), and found approximately 5-fold increases in sperm with disomies, diploidies and complex genotypes involving chromosome X, Y and 8. Increases in sex chromosome aneuploidies arose from segregation errors at meiosis I as well as meiosis II. The aneuploidy effects were transient, however, declining to pretreatment levels within approximately 100 days after the end of the therapy. When compared with normal men, some HD patients showed higher proportions of certain sperm aneuploidy types even before their first therapy.

Detection of aneuploidy in human and rodent sperm using FISH and applications of sperm assays of genetic damage in heritable risk evaluation

Efficient molecular methods are being developed for detecting various types of cytogenetic genetic damage in sperm, especially numerical aneuploidy for chromosomes involved in trisomies that survive at birth. These methods provide new approaches for identifying potentially detrimental environmental exposures, genetic predisposition, chromosomal rearrangements, and physiologic factors which may increase a man's risk of fathering a genetically defective offspring. Corollary methods are also being developed for detecting sperm aneuploidy in laboratory rodents and these will be used to make inter-species comparisons of mutagen sensitivities and for investigating mechanisms of induction and persistence of aneuploidy. Validated assays for detecting genetic alterations in human and rodent sperm (of which sperm aneuploidy is a first example) permit comparisons of somatic and germinal response to mutagens within individuals, comparisons of human and rodent germinal sensitivity to mutagens, and can be applied in an extended parallelogram model to sperm for assessing heritable risk resulting from paternal mutagen exposures.

Neutrons and carcinogenesis: a cautionary tale

The best estimates for radiation induced cancer and leukemia are based on the Japanese survivors of Hiroshima and Nagasaki. With the earlier dosimetry systems of the 1960s, it was possible to drive an RBE (relative biological effectiveness) for neutrons from the Japanese data, because it was thought that there was a significant neutron dose at Hiroshima compared with Nagasaki. The estimated RBE of about 20 was consistent with laboratory estimates for oncogenic transformation in vitro and tumors in animals. The revised dosimetry of the 1980s [DS 86] essentially eliminated the neutron component at Hiroshima, and consequently removed the only neutron RBE estimate based on human data. However, recent neutron activation measurements indicate that there may indeed have been thermal neutrons at Hiroshima, and measurements of the ratio of inter- to intra-chromosomal aberrations in peripheral lymphocytes of survivors also tend to indicate that the biologically effective dose was dominated by neutrons. Another area in which the large biological effectiveness of neutrons assumes importance is the production of photoneutrons in high energy medical linear accelerators (Linacs). An increasing number of accelerators operating in the 18 to 20 MV range are coming into routine clinical use and at this energy, photoneutrons generated largely in the collimators result in a total body dose to the patient. The increased risk of second malignancies must be balanced against the slight improvement in percentage depth doses compared with more conventional machines operating at 6 to 10 MV, below the threshold for photoneutron production.

Mutagenesis and human genetic disease: an introduction

This special issue attempts to provide a fresh perspective on the importance of germ-cell mutagenesis studies and restate the questions and challenges inherent in efforts to minimize the incidence of human genetic diseases. We are working in a time when rapidly advancing molecular technologies provide the tools that permit a more detailed understanding of germ-cell mutagenesis and genetic disease. Meanwhile, discoveries of new genetic disease phenomena challenge our abilities to conceive and develop research models for their study. It is hoped that the collection of articles in this issue will serve to stimulate interest in scientists of varied disciplines and help focus those interests on the issues surrounding the relationship between environmental mutagens and human genetic disease.

Mouse dominant lethal and sperm abnormality studies with combined exposure to X-rays and mitomycin C

The induction of dominant lethal effects and sperm abnormalities in Pzh:Swiss male mice after treatments with X-rays and mitomycin C (MMC) was investigated. Combinations of high (1.00 Gy + 5.25 mg/kg bw MMC) and low (0.25 Gy + 1.75 mg/kg bw MMC) doses of both agents were used. Exposure to high doses of X-rays + MMC induced an increased rate of dominant lethal mutations in spermatogonia and late spermatocytes. Combined treatment with low doses of X-rays and MMC was not mutagenic in any stage of spermatogenesis. MMC increased the frequency of abnormal spermatozoa after exposure alone and in combination with X-rays. Treatment with two high doses (1.00 Gy + 5.25 mg/kg bw MMC) induced 58.4% abnormal spermatozoa. After combined exposure to low doses of both agents 35.7% spermatozoa with malformations were observed.

Chromosomal damage in sperm of patients surviving Hodgkin's disease following MOPP (nitrogen mustard, vincristine, procarbazine, and prednisone) therapy with and without radiotherapy

Following fusion with hamster eggs, human sperm chromosomes from six Hodgkin's disease patients were analyzed to determine the genotoxic effects of therapy. Each patient had received two to six cycles of MOPP (nitrogen mustard, vincristine, procarbazine, and prednisone), with or without radiotherapy, from 3 to 20 years before the study. A total of 571 cells from the six patients were analyzed; 9.8% of the cells had structural aberrations, and 1.6% were hyperhaploid. Analysis of 5998 metaphases from a control group of 24 male donors revealed only 6.9% of cells with structural aberrations and 0.8% aneuploidy. The increase in hyperhaploidy in the patients was statistically significant. Thus, results of this study suggest that the MOPP regimen, with or without radiotherapy, is capable of causing chromosome abnormalities in the sperm of Hodgkin's disease patients.

Human germ cell mutagens

Human genetic disorders constitute a major public health burden in this country and around the world. The possibility that exposures to mutagenic environmental agents may result in induced genetic damage in human germ cells and thereby increase the incidence of genetic disease has been investigated in research laboratories and in epidemiology studies for decades. The capacity of ionizing radiation and some chemicals to induce transmissible genetic damage in the germ cells of laboratory mammals has been clearly demonstrated and extensively investigated. To date, no clear evidence of such effects in humans has been reported although increased frequencies of chromosomal aberrations have been detected in human sperm following exposures to radiation or chemotherapeutic agents. Evolving methods to detect molecular changes in DNA offer to improve our abilities to detect induced genetic changes. The integration of these methods into mutation epidemiology studies promises to help resolve some of the questions regarding human genetic risk.

Biological and biophysical techniques to assess radiation exposure: a perspective

Biological dosimeters measure biologically relevant effects of radiation exposure that are in some sense an estimate of effective dose, whereas biophysical indicators serve as surrogates of absorbed dose in a manner analogous to conventional thermoluminescent dosimeters (TLD). The biological and biophysical dosimeters have the potential to play an important role in assessing unanticipated or occupational radiation exposures. For example, where the exposure is large and uncertain (i.e. radiation accidents), accurate dose information can help in deciding the most appropriate therapy and medical treatment. Another useful area is that of lifetime accumulated dose determination, and the ability to distinguish between and integrate the exposures from natural and anthropogenic (medical X-rays, indoor radon, natural background radiation, occupational and non-occupational exposures). Also, the possibility to monitor individual response and differences in inherent or induced radiation sensitivity may have important implications for radiation protection. More commonly, this type of dosimetry could be used for routine monitoring to detect and quantify unsuspected exposure, for regulatory purposes or for epidemiological studies of the long-term effects of radiation exposure (e.g. in Japanese A-bomb survivors or in the population surrounding Chernobyl). This review is a comparative study of the existing techniques and their future prospects. It summarizes the sensitivity, reproducibility, limiting dose, dose-rate, energy, LET response, sources of variability and uncertainty, and other practical aspects of each bio-indicator. The strengths and weaknesses of each approach are evaluated on the basis of common criteria for particular applications, and are summarized for each assay both in the text and in tabular form, for convenience. It is clear that no single indicator qualifies to reliably measure occupational exposures at the current levels of sensitivity conventional dosimetry services provide. Most of the bio-techniques are applicable to the detection of relatively high radiation exposures at relatively short times after exposure. Some of the bio-indicators have been identified that are, or offer future prospects for becoming, appropriate bio-indicators for dosimetry needs. However, all methods are subject to biological and other variables that are presently uncontrolled, and represent a major source of uncertainty. These include variations in background signals not directly associated with radiation exposure, inter- and intra-individual variability of radiation response, and genetic and environmental effects. Although these factors contribute to the lack of confidence in biological dosimetry, promising bio-indicators may be applied to large populations to establish the inherent variability and confounding factors that limit quantitative data collection and analysis, and reduce reliability and reproducibility.

Methods and concepts in detecting abnormal reproductive outcomes of paternal origin

There is conclusive evidence that exposures of human males to ionizing radiation or certain chemicals can diminish sperm production and reduce fertility. Of approximately 100 chemical agents and mixtures that have been evaluated in men by semen analysis, about half (mostly drugs and a few occupational exposures) reduced sperm quantity and quality; several of these agents also affected the fertility of exposed men. It is now well recognized that the importance of the father in reproduction goes beyond fertilization. Abnormalities in paternal chromosomes (structural and numeric) have been found in various abnormal reproductive outcomes, including chromosomal abnormality syndromes among newborns. In rodent systems, exposure of males to mutagens before mating induces transmissible cytogenetic and genetic abnormalities as well as morphologic defects and cancer among offspring. Consistent with animal findings, there is growing epidemiologic evidence of associations between male exposures to exogenous agents and abnormal reproductive outcomes (fetal loss, birth defects, childhood cancer, etc.). However, no clear links have been established between exposure, mechanism of transmission, and abnormal reproductive outcomes. It is not known to what extent male-mediated birth defects and childhood cancer are due to genetic, epigenetic, or nongenetic causes. Viewed in a multigenerational context, the role of the father in abnormal reproductive outcomes is dependent on his exposure history and susceptibilities as well as those of his mate. Relevant exposures may occur any time between conception of the parents and production of their fertilizing gametes, including their development in utero, childhood, and adolescence. Efficient measurements (including biomarkers) of relevant exposure, early biologic effects, and susceptibility in human males are under development. An integrated approach is recommended for assessing male reproductive and genetic toxicity that utilizes biomarkers in (a) epidemiologic studies of exposed human populations, (b) risk characterization in sensitive laboratory species, and (c) in vivo and in vitro studies of the molecular mechanisms of action of toxicants. A special category of "bridging" biomarkers is needed for evaluating animal data for risk assessment and for discriminating among genetic, epigenetic, and nongenetic mechanisms of abnormal reproductive outcomes of paternal origin.

Detection of genetic damage in human sperm

Assessment of genetic damage in human sperm is now possible using the hamster oocyte/human sperm fusion technique. This cross-species in vitro assay provides precise human sperm karyotypes that can be banded for identification of individual chromosomes and numeric and structural abnormalities. This technique is time-consuming and difficult but there are now 11 laboratories in 7 different countries reporting results on normal men and men at increased risk of sperm chromosomal abnormalities. Men who have been exposed to radiotherapy and chemotherapy have been shown to have an increased frequency of chromosomal abnormalities in their sperm. A few laboratories have reported results on the use of fluorescence in situ hybridization (FISH) of interphase sperm nuclei. This appears to be a promising new technique for the assessment of aneuploidy and FISH results from our laboratory correlate well with our frequency of aneuploidy determined by sperm chromosome analysis. Thus it is possible that, in the future, FISH might be used as a simple rapid screen of potentially aneugenic agents.

Influence of different occupations with possible mutagenic effects on reproduction and level of induced chromosomal aberrations in peripheral blood

In a group of 200 dysfertile couples (400 persons), the possible role of different occupations in failures of reproduction was assessed. These couples were examined from different points of view, classical genetic examination (pedigree, kayrotype, etc.) included. The suspected genotoxic effects in the personal history were checked also by testing the level of induced chromosomal aberrations. A significantly increased level of induced chromosomal aberrations was detected in 37 persons, i.e., 9.3% of the whole group under study. The average level of induced aberration in these subjects was 6.8%, as opposed to the control group (fertile and dysfertile persons without any unusual exposure to mutagens) with a mean of 1.58% aberrant cells in peripheral blood. Most of the occupations with demonstrated genotoxic effects involve daily contact with chemicals of different types. In some persons also intensive therapy in the recent past had genotoxic effects.

Significance of structural chromosome aberrations in human sperm: analysis of induced aberrations

A significant increase in the incidence of structural chromosome anomalies has been observed in the sperm of patients treated with radio and/or chemotherapy for different types of cancer when analyzed by the interspecific fertilization of hamster eggs. The analysis of these aberrations shows that while in controls only 9.4% of structural abnormalities are of the stable type, in treated patients this figure increases to 39.3%, thus indicating that the anomalies have not been produced during the fertilization of the hamster egg. However, it is possible that part, or even most, of the breaks appear as a result of a reduced repair capacity of sperm chromosomes in the cytoplasm of the hamster egg.

Genotoxic effects of radiotherapy and chemotherapy on the circulating lymphocytes of breast cancer patients. I. Chromosome aberrations induced in vivo

Unstable chromosome aberrations were scored in peripheral blood lymphocytes (PBL) serially collected from 21 breast cancer patients before and after radiotherapy (RT), chemotherapy (CT) and combined treatments. Local radiotherapy as treatment for mammary cancer induced unstable chromosome aberrations in peripheral blood lymphocytes. Only a fraction of these lymphocytes were exposed to irradiation during treatment and the chromosomal damage observed in PBL was equivalent to that induced by irradiation in vitro with 2 Gy at high dose rate, i.e., about 4% of the total dose delivered locally. Chemotherapy alone did not induce such anomalies. Apart from the observed interindividual variations in either the level or the fate of dicentrics with time, different features of chromosome damage were found when chemotherapy was given before or after local cobaltotherapy: secondary chemotherapy did not alter the frequency and the overdispersed distribution of dicentrics observed after first-line radiotherapy; in contrast, when CT was given before radiotherapy, a lower dicentric frequency was scored, the distribution of dicentrics was not always found to be overdispersed and there was a time-dependent decrease in dicentrics after in vivo exposure.