Etoposide induces chromosomal abnormalities in mouse spermatocytes and stem cell spermatogonia

Severe sperm DNA fragmentation may persist for up to 3 years after cytotoxic therapy in patients affected by Hodgkin lymphoma and non-Hodgkin lymphoma

STUDY QUESTION

Does sperm DNA recover from damage in all men after 2 years from the end of cytotoxic treatments?

SUMMARY ANSWER

The current indication of 2 years waiting time for seeking natural pregnancy after cytotoxic treatment may not be adequate for all men, since severe sperm DNA damage is present in a proportion of subjects even after this timeframe.

WHAT IS KNOWN ALREADY

Data in the literature on sperm DNA fragmentation (SDF) in lymphoma patients after cytotoxic treatments are scarce. The largest longitudinal study evaluated paired pre- and post-therapy (up to 24 months) semen samples from 34 patients while one study performed a longer follow-up (36 months) in 10 patients. The median/mean SDF values >24 months after therapy did not show significant differences but the studies did not explore the proportion of patients with severe DNA damage and the analysis was done on frozen-thawed samples.

STUDY DESIGN, SIZE, DURATION

In this study, 53 Hodgkin lymphoma (HL) and 25 non-Hodgkin lymphoma (NHL) post-pubertal patients were included over a recruitment period of 10 years (2012-2022). Among them, 18 subjects provided paired semen samples for SDF analysis at the three time points. SDF was evaluated in patients before (T0) and after 2 (T2) and 3 years (T3) from the end of, cytotoxic treatments (chemotherapy alone or in combination with radiotherapy). A cohort of 79 healthy, fertile, and normozoospermic men >18 years old served as controls (recruited between 2016 and 2019).

PARTICIPANTS/MATERIALS, SETTING, METHODS

SDF was evaluated on fresh semen samples (i.e. spermatozoa potentially involved in natural conception) from patients and controls using TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) assay coupled with flow cytometry. SDF median values were compared between groups: (i) HL and NHL patients versus controls at the three time points; (ii) HL versus NHL patients at baseline; and (iii) patients at T0 versus T2 and T3. Severe DNA damage (SDD) was defined for SDF levels above the 95th percentile of controls (50%) and the proportion of patients with SDD at all time points was established.

MAIN RESULTS AND THE ROLE OF CHANCE

At T0, patients displayed higher median SDF than controls, reaching statistical significance in the NHL group: 40.5% [IQR: 31.3-52.6%] versus 28% [IQR: 22-38%], P < 0.05. Comparing SDF pre-treatment to that post-treatment, HL patients exhibited similar median values at the three time points, whereas NHL showed significantly lower values at T3 compared to T0: 29.2% [IQR: 22-38%] versus 40.5% [IQR: 31.3-52.6%], P < 0.05. The proportion with SDD in the entire cohort at T2 was 11.6% and 13.3% among HL and NHL patients, respectively. At T3, only one in 16 NHL patients presented SDD.

LIMITATIONS, REASONS FOR CAUTION

TUNEL assay requires at least 5 million spermatozoa to be performed; hence, severe oligozoospermic men were not included in the study. Although our cohort represents the largest one in the literature, the relatively small number of patients does not allow us to establish precisely the frequency of SDD at T2 which in our study reached 11-13% of patients.

WIDER IMPLICATIONS OF THE FINDINGS

Our data provide further insights into the long-term effects of cytotoxic treatments on the sperm genome. The persistent severe DNA damage after 2 years post-treatment observed in some patients suggests that there is an interindividual variation in restoring DNA integrity. We propose the use of SDF as a biomarker to monitor the treatment-induced genotoxic effects on sperm DNA in order to better personalize pre-conceptional counseling on whether to use fresh or cryopreserved spermatozoa.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by grants from the Istituto Toscano Tumori (ITT), Fondazione Ente Cassa di Risparmio di Firenze, the European Commission-Reproductive Biology Early Research Training (REPROTRAIN). C.K., G.F., V.R., and A.R.-E. belong to COST Action CA20119 (ANDRONET) which is supported by the European Cooperation in Science and Technology (www.cost.eu). The authors declare no conflict of interest.

TRIAL REGISTRATION NUMBER

N/A.

YTHDF2 promotes DNA damage repair by positively regulating the histone methyltransferase SETDB1 in spermatogonia†

Genomic integrity is critical for sexual reproduction, ensuring correct transmission of parental genetic information to the descendant. To preserve genomic integrity, germ cells have evolved multiple DNA repair mechanisms, together termed as DNA damage response. The RNA N6-methyladenosine is the most abundant mRNA modification in eukaryotic cells, which plays important roles in DNA damage response, and YTH N6-methyladenosine RNA binding protein 2 (YTHDF2) is a well-acknowledged N6-methyladenosine reader protein regulating the mRNA decay and stress response. Despite this, the correlation between YTHDF2 and DNA damage response in germ cells, if any, remains enigmatic. Here, by employing a Ythdf2-conditional knockout mouse model as well as a Ythdf2-null GC-1 mouse spermatogonial cell line, we explored the role and the underlying mechanism for YTHDF2 in spermatogonial DNA damage response. We identified that, despite no evident testicular morphological abnormalities under the normal circumstance, conditional mutation of Ythdf2 in adult male mice sensitized germ cells, including spermatogonia, to etoposide-induced DNA damage. Consistently, Ythdf2-KO GC-1 cells displayed increased sensitivity and apoptosis in response to DNA damage, accompanied by the decreased SET domain bifurcated 1 (SETDB1, a histone methyltransferase) and H3K9me3 levels. The Setdb1 knockdown in GC-1 cells generated a similar phenotype, but its overexpression in Ythdf2-null GC-1 cells alleviated the sensitivity and apoptosis in response to DNA damage. Taken together, these results demonstrate that the N6-methyladenosine reader YTHDF2 promotes DNA damage repair by positively regulating the histone methyltransferase SETDB1 in spermatogonia, which provides novel insights into the mechanisms underlying spermatogonial genome integrity maintenance and therefore contributes to safe reproduction.

Elevated Levels of Lamin A Promote HR and NHEJ-Mediated Repair Mechanisms in High-Grade Ovarian Serous Carcinoma Cell Line

Extensive research for the last two decades has significantly contributed to understanding the roles of lamins in the maintenance of nuclear architecture and genome organization which is drastically modified in neoplasia. It must be emphasized that alteration in lamin A/C expression and distribution is a consistent event during tumorigenesis of almost all tissues of human bodies. One of the important signatures of a cancer cell is its inability to repair DNA damage which befalls several genomic events that transform the cells to be sensitive to chemotherapeutic agents. This genomic and chromosomal instability is the most common feature found in cases of high-grade ovarian serous carcinoma. Here, we report elevated levels of lamins in OVCAR3 cells (high-grade ovarian serous carcinoma cell line) in comparison to IOSE (immortalised ovarian surface epithelial cells) and, consequently, altered damage repair machinery in OVCAR3. We have analysed the changes in global gene expression as a sequel to DNA damage induced by etoposide in ovarian carcinoma where lamin A is particularly elevated in expression and reported some differentially expressed genes associated with pathways conferring cellular proliferation and chemoresistance. We hereby establish the role of elevated lamin A in neoplastic transformation in the context of high-grade ovarian serous cancer through a combination of HR and NHEJ mechanisms.

Chromosome 17 translocation affects sperm morphology: Two case studies and literature review

We present two cases of infertile males with teratozoospermia stemming from chromosome 17 translocation. The patients present karyotypes that have not been previously reported. Genes located on breakpoints (17p11.2, 9q31, and 11p15) were analysed to find the probable mechanism affecting sperm morphology. Our results suggest that ALKBH5, TOP3A, and LLGL1 interactions may be an underlying cause of abnormal sperm head morphology. Translocation of chromosome 17 occurred in conjunction with chromosome 9 and chromosome 11 translocation in the two cases, resulting in oligozoospermia and asthenozoospermia, respectively. These abnormal phenotypes may involve meiosis- and motility-related genes such as LDHC, DNHD1, UBQLN3, and NUP98. Translocation is thus a risk factor for sperm morphological abnormalities and motility deficiency. The interaction network of 22 genes on breakpoints suggests that they contribute to spermatogenesis as a group. In conclusion, this study highlighted the importance of investigating genes linked to sperm morphology, together with chromosome 17 translocation and reproductive risks. For patients interested in screening before a future pregnancy, we recommend preimplantation genetic diagnosis to reduce the risk of karyotypically unbalanced foetuses and birth defects.

Regenerative medicine for male infertility: a focus on stem cell niche injury models

Stem and progenitor cells located within stem cell niches maintain the renewal and regeneration of tissues and organs throughout the life of an adult organism. Stem cell niche component dysfunction might alter the activity of stem cells and ultimately lead to the development of difficult-to-treat chronic or acute disorders. Of note, some cases of idiopathic male infertility, a highly prevalent diagnosis with no specific treatment options, might be associated with a spermatogonial stem cell(SSC) niche disturbance. To overcome this disease entity, approaches aiming at launching the regeneration of an altered stem cell niche are worth considering. Particularly, mesenchymal stromal cells (MSCs) or their secretome might fulfill this task due to their promising contribution in recovering injured stem cell niches. However, the successful application of MSC-based treatment is limited by the uncovered mechanisms of action of MSCs and their secretome. Specific animal models should be developed or adapted to reveal the role of MSCs and their secretome in a stem cell niche recovery. In this review, in a bid to consider MSCs and their secretome as a therapeutic regenerative approach for idiopathic male infertility we focus on the rationale of SSC niche injury modeling.

Meiotic susceptibility for induction of sperm with chromosomal aberrations in patients receiving combination chemotherapy for Hodgkin lymphoma

Improvements in survival rates with gonad-sparing protocols for childhood and adolescence cancer have increased the optimism of survivors to become parents after treatment. Findings in rodents indicate that chromosomal aberrations can be induced in male germ cells by genotoxic exposures and transmitted to offspring and future generations with effects on development, fertility and health. Thus, there is a need for effective technologies to identify human sperm carrying chromosomal aberrations to assess the germ-line risks, especially for cancer survivors who have received genotoxic therapies. The time-dependent changes in the burden of sperm carrying structural chromosomal aberrations were assessed for the first time in a cancer setting, using the AM8 sperm FISH protocol which simultaneously detects abnormalities in chromosomal structure and number in sperm. Nine Hodgkin lymphoma (HL) patients provided 20 semen samples before, during, and after NOVP therapy (Novantrone, Oncovin, Velban and Prednisone) and radiation therapy that produced scattered gonadal doses from <0.05 to 0.6 Gy. Late meiosis was found to be the most sensitive to NOVP treatment for the production of sperm with chromosomal abnormalities, both in structure and number. Earlier stages of spermatogenesis were less sensitive and there was no evidence that therapy-exposed stem cells resulted in increased frequencies of sperm with abnormalities in chromosomal structure or number. This indicates that NOVP therapy may increase the risks for paternal transmission of chromosomal structural aberrations for sperm produced 32 to 45 days after a treatment with these drugs and implies that there are no excess risks for pregnancies conceived more than 6 months after this therapy. This clinical evaluation of the AM8 sperm FISH protocol indicates that it is a promising tool for assessing an individual's burden of sperm carrying chromosomal structural aberrations as well as aneuploidies after cancer therapy, with broad applications in other clinical and environmental situations that may pose aneugenic or clastogenic risks to human spermatogenesis.

Proteomic Analysis Reveals that Topoisomerase 2A is Associated with Defective Sperm Head Morphology

Male infertility is widespread and estimated to affect 1 in 20 men. Although in some cases the etiology of the condition is well understood, for at least 50% of men, the underlying cause is yet to be classified. Male infertility, or subfertility, is often diagnosed by looking at total sperm produced, motility of the cells and overall morphology. Although counting spermatozoa and their associated motility is routine, morphology assessment is highly subjective, mainly because of the procedure being based on microscopic examination. A failure to diagnose male-infertility or sub-fertility has led to a situation where assisted conception is often used unnecessarily. As such, biomarkers of male infertility are needed to help establish a more consistent diagnosis. In the present study, we compared nuclear extracts from both high- and low-quality spermatozoa by LC-MS/MS based proteomic analysis. Our data shows that nuclear retention of specific proteins is a common facet among low-quality sperm cells. We demonstrate that the presence of Topoisomerase 2A in the sperm head is highly correlated to poor head morphology. Topoisomerase 2A is therefore a potential new biomarker for confirming male infertility in clinical practice.

Risks of genetic damage in offspring conceived using spermatozoa produced during chemotherapy or radiotherapy

BACKGROUND

Men who have just started cytotoxic therapy for cancer are uncertain and concerned about whether spermatozoa collected or pregnancies occurring during therapy might be transmitting genetic damage to offspring. There are no comprehensive guidelines on the risks of different doses of the various cytotoxic, and usually genotoxic, antineoplastic agents.

OBJECTIVES

To develop a schema showing the risks of mutagenic damage when spermatozoa, exposed to various genotoxic agents during spermatogenesis, are collected or used to produce a pregnancy.

MATERIALS AND METHODS

A comprehensive literature review was performed updating the data on genetic and epigenetic effects of genotoxic agents on animal and human spermatozoa exposed during spermatogenic development.

RESULTS

Relevant data on human spermatozoa and offspring are extremely limited, but there are extensive genetic studies in experimental animals that define sensitivities for specific drugs and times. The animal data were extrapolated to humans based on the stage when the cells were exposed and the relative kinetics of spermatogenesis and were consistent with the limited human data. In humans, alkylating agents and radiation should already induce a high risk of mutations in spermatozoa produced within 1 or 2 weeks after initiation of therapy. Topoisomerase II inhibitors and possibly microtubule inhibitors produce the greatest risk at weeks 5-7 of therapy. Nucleoside analogs, antimetabolites, and bleomycin exert their mutagenic effects on spermatozoa collected at 7-10 weeks of therapy.

DISCUSSION AND CONCLUSIONS

A schema showing the time from initiation of therapy at which specific antineoplastic agents can cause significant levels of genetic damage in conceptuses and live offspring was developed. The estimates and methods for computing the level of such risk from an individual patient's treatment regimen will enable patients and counselors to make informed decisions on the use of spermatozoa or continuation of a pregnancy.

Exposure to Chemotherapy During Childhood or Adulthood and Consequences on Spermatogenesis and Male Fertility

Over the last decade, the number of cancer survivors has increased thanks to progress in diagnosis and treatment. Cancer treatments are often accompanied by adverse side effects depending on the age of the patient, the type of cancer, the treatment regimen, and the doses. The testicular tissue is very sensitive to chemotherapy and radiotherapy. This review will summarize the epidemiological and experimental data concerning the consequences of exposure to chemotherapy during the prepubertal period or adulthood on spermatogenic progression, sperm production, sperm nuclear quality, and the health of the offspring. Studies concerning the gonadotoxicity of anticancer drugs in adult survivors of childhood cancer are still limited compared with those concerning the effects of chemotherapy exposure during adulthood. In humans, it is difficult to evaluate exactly the toxicity of chemotherapeutic agents because cancer treatments often combine chemotherapy and radiotherapy. Thus, it is important to undertake experimental studies in animal models in order to define the mechanism involved in the drug gonadotoxicity and to assess the effects of their administration alone or in combination on immature and mature testis. These data will help to better inform cancer patients after recovery about the risks of chemotherapy for their future fertility and to propose fertility preservation options.

Use of antioxidant could ameliorate the negative impact of etoposide on human sperm DNA during chemotherapy

RESEARCH QUESTION

A previous study showed that N-acetylcysteine (NAC), used after in-vitro exposure to the gonadotoxic chemotherapeutic drug etoposide, has the ability to decrease DNA damage in human spermatozoa; however, it showed no benefit when used before exposure. This study aimed to evaluate the impact of the NAC on the preservation of sperm quality during in-vitro exposure to etoposide.

DESIGN

Twenty semen samples were submitted to four experimental conditions: control, NAC-only incubation, etoposide-only incubation, and concomitant etoposide and NAC incubation. After in-vitro incubation, semen parameters, sperm chromatin condensation, sperm DNA fragmentation, sperm oxidative stress and sperm metabolism were used to evaluate the role of NAC in protecting human spermatozoa from etoposide.

RESULTS

Etoposide did not affect semen parameters, nor did it cause sperm oxidative damage or alterations in glycolytic profile. However, it induced chromatin decondensation and DNA fragmentation, which were fully prevented by NAC.

CONCLUSIONS

NAC was able to protect sperm DNA integrity during etoposide treatment in vitro, suggesting that NAC may be useful as an adjuvant agent in preserving male fertility during chemotherapy treatments.

GCNA Interacts with Spartan and Topoisomerase II to Regulate Genome Stability

GCNA proteins are expressed across eukarya in pluripotent cells and have conserved functions in fertility. GCNA homologs Spartan (DVC-1) and Wss1 resolve DNA-protein crosslinks (DPCs), including Topoisomerase-DNA adducts, during DNA replication. Here, we show that GCNA mutants in mouse and C. elegans display defects in genome maintenance including DNA damage, aberrant chromosome condensation, and crossover defects in mouse spermatocytes and spontaneous genomic rearrangements in C. elegans. We show that GCNA and topoisomerase II (TOP2) physically interact in both mice and worms and colocalize on condensed chromosomes during mitosis in C. elegans embryos. Moreover, C. elegans gcna-1 mutants are hypersensitive to TOP2 poison. Together, our findings support a model in which GCNA provides genome maintenance functions in the germline and may do so, in part, by promoting the resolution of TOP2 DPCs.

Chemically induced aneuploidy in germ cells. Part II of the report of the 2017 IWGT workgroup on assessing the risk of aneugens for carcinogenesis and hereditary diseases

As part of the 7th International Workshops on Genotoxicity Testing held in Tokyo, Japan in November 2017, a workgroup of experts reviewed and assessed the risk of aneugens for human health. The present manuscript is one of three manuscripts from the workgroup and reports on the unanimous consensus reached on the evidence for aneugens affecting germ cells, their mechanisms of action and role in hereditary diseases. There are 24 chemicals with strong or sufficient evidence for germ cell aneugenicity providing robust support for the ability of chemicals to induce germ cell aneuploidy. Interference with microtubule dynamics or inhibition of topoisomerase II function are clear characteristics of germ cell aneugens. Although there are mechanisms of chromosome segregation that are unique to germ cells, there is currently no evidence for germ cell-specific aneugens. However, the available data are heavily skewed toward chemicals that are aneugenic in somatic cells. Development of high-throughput screening assays in suitable animal models for exploring additional targets for aneuploidy induction, such as meiosis-specific proteins, and to prioritize chemicals for the potential to be germ cell aneugens is encouraged. Evidence in animal models support that: oocytes are more sensitive than spermatocytes and somatic cells to aneugens; exposure to aneugens leads to aneuploid conceptuses; and, the frequencies of aneuploidy are similar in germ cells and zygotes. Although aneuploidy in germ cells is a significant cause of infertility and pregnancy loss in humans, there is currently limited evidence that aneugens induce hereditary diseases in human populations because the great majority of aneuploid conceptuses die in utero. Overall, the present work underscores the importance of protecting the human population from exposure to chemicals that can induce aneuploidy in germ cells that, in contrast to carcinogenicity, is directly linked to an adverse outcome.

Protective role of N-acetylcysteine (NAC) on human sperm exposed to etoposide

Background

Although recent progress in cancer treatment has increased patient survival and improved quality of life, reproductive side effects are still for concern. One way to decrease gonadal impairment is to use cytoprotectors. In testicular cancer, etoposide is generally used in combination with other agents, but there are no in-vitro studies of sperm exposure to etoposide and cytoprotectors, namely N-acetylcysteine (NAC).

Methods

Twenty semen samples were individually divided into five groups: control, incubation with NAC alone, incubation with etoposide alone, sequential exposure of NAC followed by etoposide (pre-treatment) and sequential exposure of etoposide followed by NAC (post-treatment). Sperm characteristics, chromatin condensation (aniline blue), DNA fragmentation (TUNEL), oxidative stress (OxyDNA labelling) and glutathione quantification were used to evaluate the capabilities of NAC as a prophylactic (pre-treatment) or ameliorator (post-treatment) agent over the effects caused in sperm during in-vitro exposure to etoposide.

Results

No deleterious effects were observed on sperm motility or sperm membrane integrity. Results revealed that prophylactic use of NAC (pre-treatment) increased rates of immature sperm chromatin as compared to ameliorator use of NAC (post-treatment), and increased rates of sperm DNA fragmentation in relation to controls. Pre and post-treatment with NAC increased oxidative levels in comparison to controls, but also increased levels of cellular antioxidant glutathione.

Conclusions

The results indicate that NAC has the ability to counteract etoposide-induced toxicity rather than preventing the etoposide cytotoxic effects over sperm DNA, suggesting that the administration of NAC to cells formerly exposed to etoposide is preferable to its prophylactic use. As the results evidenced that NAC seems to be more efficient in attenuating sperm etoposide cytotoxic effects instead of being used as a chemoprophylactic agent, this reinforces the idea that there might be a new NAC mechanism over DNA.

Depletion of SMC5/6 sensitizes male germ cells to DNA damage

The structural maintenance of chromosomes complex SMC5/6 is thought to be essential for DNA repair and chromosome segregation during mitosis and meiosis. To determine the requirements of the SMC5/6 complex during mouse spermatogenesis we combined a conditional knockout allele for Smc5, with four germ cell–specific Cre-recombinase transgenes, Ddx4-Cre, Stra8-Cre, Spo11-Cre, and Hspa2-Cre, to mutate Smc5 in spermatogonia, in spermatocytes before meiotic entry, during early meiotic stages, and during midmeiotic stages, respectively. Conditional mutation of Smc5 resulted in destabilization of the SMC5/6 complex. Despite this, we observed only mild defects in spermatogenesis. Mutation of Smc5 mediated by Ddx4-Cre and Stra8-Cre resulted in partial loss of preleptotene spermatocytes; however, spermatogenesis progresses and mice are fertile. Mutation of Smc5 via Spo11-Cre or Hspa2-Cre did not result in detectable defects of spermatogenesis. Upon exposure to gamma irradiation or etoposide treatment, each conditional Smc5 mutant demonstrated an increase in the number of enlarged round spermatids with multiple acrosomes and supernumerary chromosome content. We propose that the SMC5/6 complex is not acutely required for premeiotic DNA replication and meiotic progression during mouse spermatogenesis; however, when germ cells are challenged by exogenous DNA damage, the SMC5/6 complex ensures genome integrity, and thus, fertility.

Genotoxicity of Casiopeina III-Ea in mouse bone marrow cells

Casiopeina III-Ea® (Cas III-Ea®) is a chelated copper complex with antineoplastic activity that is capable of reducing tumor size and inducing antiproliferative and apoptotic effects. However, little is known about its in vivo genotoxic effects. Therefore, this study evaluated two cytogenetic and two proliferative parameters 24 h after the administration of Casiopeina III-Ea® to male CD-1 mice. Three doses of Cas III-Ea® were administered by intraperitoneal injections of 1.69, 3.39 and 6.76 mg/kg (corresponding to 1/8, 1/4 and 1/2 of LD₅₀, respectively). A reduction in the mitotic index (MI) and an increased numbers of cells with structural chromosomal aberrations (SCA) were detected. Additionally, a low but significant increase in the frequency of sister chromatid exchange (SCE) was observed at the highest dose. Changes in the DNA replication index (RI) were not observed. These results indicate that Casiopeina III-Ea® shows cytotoxic and clastogenic activity in bone marrow cells from treated mice.

Meiotic interstrand DNA damage escapes paternal repair and causes chromosomal aberrations in the zygote by maternal misrepair

De novo point mutations and chromosomal structural aberrations (CSA) detected in offspring of unaffected parents show a preferential paternal origin with higher risk for older fathers. Studies in rodents suggest that heritable mutations transmitted from the father can arise from either paternal or maternal misrepair of damaged paternal DNA, and that the entire spermatogenic cycle can be at risk after mutagenic exposure. Understanding the susceptibility and mechanisms of transmission of paternal mutations is important in family planning after chemotherapy and donor selection for assisted reproduction. We report that treatment of male mice with melphalan (MLP), a bifunctional alkylating agent widely used in chemotherapy, induces DNA lesions during male mouse meiosis that persist unrepaired as germ cells progress through DNA repair-competent phases of spermatogenic development. After fertilization, unrepaired sperm DNA lesions are mis-repaired into CSA by the egg's DNA repair machinery producing chromosomally abnormal offspring. These findings highlight the importance of both pre- and post-fertilization DNA repair in assuring the genomic integrity of the conceptus.

Low-dose etoposide-treatment induces endoreplication and cell death accompanied by cytoskeletal alterations in A549 cells: Does the response involve senescence? The possible role of vimentin

Background

Senescence in the population of cells is often described as a program of restricted proliferative capacity, which is manifested by broad morphological and biochemical changes including a metabolic shift towards an autophagic-like response and a genotoxic-stress related induction of polyploidy. Concomitantly, the cell cycle progression of a senescent cell is believed to be irreversibly arrested. Recent reports suggest that this phenomenon may have an influence on the therapeutic outcome of anticancer treatment. The aim of this study was to verify the possible involvement of this program in the response to the treatment of the A549 cell population with low doses of etoposide, as well as to describe accompanying cytoskeletal alterations.

Methods

After treatment with etoposide, selected biochemical and morphological parameters were examined, including: the activity of senescence-associated ß-galactosidase, SAHF formation, cell cycle progression, the induction of p21^{Cip1/Waf1/Sdi1} and cyclin D1, DNA strand breaks, the disruption of cell membrane asymmetry/integrity and ultrastructural alterations. Vimentin and G-actin cytoskeleton was evaluated both cytometrically and microscopically.

Results and conclusions

Etoposide induced a senescence-like phenotype in the population of A549 cells. Morphological alterations were nevertheless not directly coupled with other senescence markers including a stable cell cycle arrest, SAHF formation or p21^{Cip1/Waf1/Sdi1} induction. Instead, a polyploid, TUNEL-positive fraction of cells visibly grew in number. Also upregulation of cyclin D1 was observed. Here we present preliminary evidence, based on microscopic analyses, that suggest a possible role of vimentin in nuclear alterations accompanying polyploidization-depolyploidization events following genotoxic insults.

Biomarkers of occupational exposure do anticancer agents: a minireview

The majority of anticancer agents has in common DNA-damaging properties and affects not only target-cells but also non-tumour cells. Its genotoxicity has been demonstrated in experimental models and in cancer patients treated with chemotherapy. Health care personnel involved in the preparation and administration of chemotherapy is therefore at risk for adverse health effects, since most environmental sampling studies demonstrated that there is widespread contamination of work surfaces and equipments with anticancer drugs. Adherence to safety guidelines and proper use of personal protective equipment are insufficient to prevent significant absorption, as evidenced by the presence of detectable amounts of drugs in urine samples and increased frequency of genotoxicity biomarkers. In this minireview, a critical appraisal of the most important biomarkers used for the evaluation of occupational exposure to anticancer agents as well as a summary of the key findings from several studies published in this field is performed.

Laboratory methods for the detection of chromosomal structural aberrations in human and mouse sperm by fluorescence in situ hybridization

The father, like the mother, can transmit genetic defects that are detrimental for development and genetic health for his children, but the mechanisms for paternally mediated abnormal reproductive outcomes remain poorly understood. A battery of sensitive methods has been developed for detecting genetic damage associated with infertility, spontaneous abortions, as well as inherited defects in children such as aneuploidy syndromes, translocation carriers, and certain genetic diseases directly in sperm. Among these, fluorescence in situ hybridization (FISH) sperm-based assays for measuring numerical abnormalities and structural chromosomal aberrations are now available for an expanding number of species including humans, rodents, and several domesticated animals. This new generation of sperm FISH methods has identified several paternal risk factors such as age, various drugs, lifestyles, and various environmental and occupational exposures. These sperm FISH assays provide new opportunities to identify and characterize male reproductive risks associated with genetic, lifestyle, and environmental factors. This chapter outlines the laboratory methods for the detection of sperm with chromosomal structural aberrations in humans (ACM assay) and mice (CT8 assay) that have been validated for detecting environmental germ cell mutagens.

Tandem repeat mutation, global DNA methylation, and regulation of DNA methyltransferases in cultured mouse embryonic fibroblast cells chronically exposed to chemicals with different modes of action

Mutations at expanded simple tandem repeat (ESTR) DNA sequences provide a useful tool for screening germline mutation. However, the mechanisms resulting in induced mutations are unknown and provide an impediment to the utility of the method. Induced ESTR mutations arise through a nontargeted mechanism resulting in destabilization of the repeat locus. We hypothesized that alterations in DNA methylation, or in DNA methyltransferase expression, may be associated with this indirect mechanism of mutation. DNA mutation frequency was measured in C3H/10T1/2 mouse embryonic fibroblast cells following chronic exposure to six chemicals exhibiting different modes of genotoxic action: N-nitroso-N-ethylurea (ENU); benzo(a)pyrene (BaP); etoposide (ETOP); okadaic acid (OA); cisplatin (CisPt); and 5-azacytidine (5azadC). Induced mutation ranged from 2-fold (ENU, BaP, ETOP), to 1.3-1.4 fold (OA, 5azadC), to nonresponsive (CisPt). Global DNA methylation, measured using the cytosine extension assay, revealed hypomethylation following exposure to ENU and 5azadC, hypermethylation following BaP and OA exposure, and no change following treatment with ETOP or CisPt. DNA methyltransferase transcription (Dnmt1, Dnmt3a, Dnmt3b) was significantly affected by all treatments except ETOP, with the vast majority of changes being downregulation. There was no direct correlation between ESTR mutation, global methylation, or DNA methyltransferase transcription. However, 4/5 ESTR mutagens caused changes in global methylation, while the noninducer (CisPt) did not cause changes in methylation. We hypothesize that chemicals that modify chromatin conformation through changes in methylation may compromise the ability of mismatch repair enzymes (or other enzymes) to access and repair secondary structures that may form across ESTR loci resulting in mutation.

Frequency of human sperm carrying structural aberrations of chromosome 1 increases with advancing age

OBJECTIVE

To investigate the association between male age and the frequency of sperm with de novo structural chromosomal abnormalities.

DESIGN

Semen specimens collected from two groups of 10 healthy, nonsmoking men, aged 22-28 and 65-80 years, were analyzed with the use of a multicolor fluorescence in situ hybridization assay for detecting breaks, segmental duplications and deletions, and aneuploidy and diploidy involving chromosome 1.

SETTING

Healthy volunteer workers and retirees from a government research environment.

MAIN OUTCOME MEASURE

Sperm carrying numerical and structural chromosomal abnormalities.

RESULT(S)

We detected significant increases in the frequency of sperm carrying breaks and segmental duplications and deletions of chromosome 1 among older men compared with younger men. Older men carried twice the frequency of sperm with segmental duplications and deletions of chromosome 1. The frequency of sperm carrying breaks within the 1q12 fragile-site region nearly doubled in older men. In contrast to female gametes, there was no effect of age on the frequency of sperm with numerical chromosomal abnormalities.

CONCLUSION

Our findings suggest that advancing male age is associated with a gradual and significant increase in the risk of fathering children with various chromosomal defects such as segmental aneusomy syndromes.

Assessing human germ-cell mutagenesis in the Postgenome Era: a celebration of the legacy of William Lawson (Bill) Russell

Birth defects, de novo genetic diseases, and chromosomal abnormality syndromes occur in approximately 5% of all live births, and affected children suffer from a broad range of lifelong health consequences. Despite the social and medical impact of these defects, and the 8 decades of research in animal systems that have identified numerous germ-cell mutagens, no human germ-cell mutagen has been confirmed to date. There is now a growing consensus that the inability to detect human germ-cell mutagens is due to technological limitations in the detection of random mutations rather than biological differences between animal and human susceptibility. A multidisciplinary workshop responding to this challenge convened at The Jackson Laboratory in Bar Harbor, Maine. The purpose of the workshop was to assess the applicability of an emerging repertoire of genomic technologies to studies of human germ-cell mutagenesis. Workshop participants recommended large-scale human germ-cell mutation studies be conducted using samples from donors with high-dose exposures, such as cancer survivors. Within this high-risk cohort, parents and children could be evaluated for heritable changes in (a) DNA sequence and chromosomal structure, (b) repeat sequences and minisatellites, and (c) global gene expression profiles and pathways. Participants also advocated the establishment of a bio-bank of human tissue samples from donors with well-characterized exposure, including medical and reproductive histories. This mutational resource could support large-scale, multiple-endpoint studies. Additional studies could involve the examination of transgenerational effects associated with changes in imprinting and methylation patterns, nucleotide repeats, and mitochondrial DNA mutations. The further development of animal models and the integration of these with human studies are necessary to provide molecular insights into the mechanisms of germ-cell mutations and to identify prevention strategies. Furthermore, scientific specialty groups should be convened to review and prioritize the evidence for germ-cell mutagenicity from common environmental, occupational, medical, and lifestyle exposures. Workshop attendees agreed on the need for a full-scale assault to address key fundamental questions in human germ-cell environmental mutagenesis. These include, but are not limited to, the following: Do human germ-cell mutagens exist? What are the risks to future generations? Are some parents at higher risk than others for acquiring and transmitting germ-cell mutations? Obtaining answers to these, and other critical questions, will require strong support from relevant funding agencies, in addition to the engagement of scientists outside the fields of genomics and germ-cell mutagenesis.