Effects of X-irradiation on mouse testicular cells and sperm chromatin structure

Evaluation of Stallion Testicular Cell Types by Flow Cytometry

Flow cytometry procedures can be used for evaluation of both spermatogenic efficiency and diagnose disorders of stallion spermatogenesis. Aims of this study were to compare two testicular sample acquisition techniques (needle aspirate-N and tissue wedge-T) and results when using flow cytometry and histology procedures. Testicular cell types were stained with acridine orange, and nine regions (R2 to R10) were identified and enumerated following acquisition by either N or T. Testes were also grouped and analyzed by size and sexual maturity (Small [immature] compared with Large [mature]) and used to determine if flow cytometry procedures could be used to detect differences. For both N and T, percentages of 2n cell types were greater in the Small than Large testes, whereas percentages of 1n cell types in N were greater in the Large than Small testes (P < .05). Testicular cell types in N regions were correlated to similar T regions (r between 0.51 and 0.99; P < .05) in both groups. Flow cytometry and histology scores were correlated in both groups (r between -0.95 and 0.93, P < .05). There were small differences in number of testicular cell types from N and T. With both sample acquisition methods, there was discrimination between the Small and Large testes, therefore, evaluation of testicular cell types using flow cytometry procedures might have clinical applications. Results with comparison of flow cytometry to histology procedures indicate that flow cytometry can be applied clinically to identify changes in testicular cell types of stallions using a needle aspirate.

Small RNAs in Rat Sperm Are a Predictive and Sensitive Biomarker of Exposure to the Testicular Toxicant Ethylene Glycol Monomethyl Ether

Testicular histology and semen parameters are considered the gold standards when determining male reproductive toxicity. Ethylene glycol monomethyl ether (EGME) is a testicular toxicant with well-described effects on histopathology and sperm parameters. To compare the predictivity and sensitivity of molecular biomarkers of testicular toxicity to the traditional endpoints, small RNAs in the sperm were analyzed by next generation RNA-sequencing (RNA-seq). Adult rats were exposed to 0, 50, 60, or 75 mg/kg EGME by oral gavage for 5 consecutive days. Testis histology, epididymal sperm motility, and sperm small RNAs, including microRNAs (miRNAs), mRNA fragments, piwi-interacting RNAs (piRNAs), and tRNA fragments (tRFs), were analyzed 5 weeks after cessation of exposure. Testicular histology showed a significant dose-dependent increase in retained spermatid heads (RSH), while sperm motility declined with increasing dose. RNA-sequencing of sperm small RNAs was used to identify significant dose-dependent changes in percent mRNA fragments (of total reads), percent miRNAs (of total reads), average tRF length, average piRNA length, and piRNA and tRF length-distributions. Discriminant analysis showed relatively low predictivity of exposure based on RSH or motility compared to the average read length of all assigned RNAs. Benchmark dose (BMD) modeling resulted in a BMD of 62 mg/kg using RSH, whereas average read length of all assigned RNAs resulted in a BMD of 47 mg/kg. These results showed that sperm small RNAs are sensitive and predictive biomarkers of EGME-induced male reproductive toxicity.

The Sperm Chromatin Structure Assay (SCSA(®)) and other sperm DNA fragmentation tests for evaluation of sperm nuclear DNA integrity as related to fertility

Thirty-five years ago the pioneering paper in Science (240:1131) on the relationship between sperm DNA integrity and pregnancy outcome was featured as the cover issue showing a fluorescence photomicrograph of red and green stained sperm. The flow cytometry data showed a very significant difference in sperm DNA integrity between fertile and subfertile bulls and men. This study utilized heat (100°C, 5min) to denature DNA at sites of DNA strand breaks followed by staining with acridine orange (AO) and measurements of 5000 individual sperm of green double strand (ds) DNA and red single strand (ss) DNA fluorescence. Later, the heat protocol was changed to a low pH protocol to denature the DNA at sites of strand breaks; the heat and acid procedures produced the same results. SCSA data are very advantageously dual parameter with 1024 channels (degrees) of both red and green fluorescence. Hundreds of publications on the use of the SCSA test in animals and humans have validated the SCSA as a highly useful test for determining male breeding soundness. The SCSA test is a rapid, non-biased flow cytometer machine measurement providing robust statistical data with exceptional precision and repeatability. Many genotoxic experiments showed excellent dose response data with very low coefficient of variation that further validated the SCSA as being a highly powerful assay for sperm DNA integrity. Twelve years following the introduction of the SCSA test, the terminal deoxynucleotidyl transferase-mediated fluorescein-dUTP nick end labelling (TUNEL) test (1993) for sperm was introduced as the only other flow cytometric assay for sperm DNA fragmentation. However, the TUNEL test can also be done by light microscopy with much less statistical robustness. The COMET (1998) and Sperm Chromatin Dispersion (SCD; HALO) (2003) tests were introduced as light microscope tests that don't require a flow cytometer. Since these tests measure only 50-200 sperm per sample, they suffer from the lack of the statistical robustness of flow cytometric measurements. Only the SCSA test has an exact standardization of a fixed protocol. The many variations of the other tests make it very difficult to compare data and thresholds for risk of male factor infertility. Data from these four sperm DNA fragmentation tests plus the light microscope acridine orange test (AOT) are correlated to various degrees.

Absence of Peroxiredoxin 6 Amplifies the Effect of Oxidant Stress on Mobility and SCSA/CMA3 Defined Chromatin Quality and Impairs Fertilizing Ability of Mouse Spermatozoa

Oxidative stress, the imbalance between reactive oxygen species production and antioxidant defenses, is associated with male infertility. Peroxiredoxins (PRDXs) are antioxidant enzymes with a wide distribution in spermatozoa. PRDX6 is highly abundant and located in all subcellular compartments of the spermatozoon. Infertile men have lower levels of sperm PRDX6 associated with low sperm motility and high DNA damage. In order to better understand the role of PRDX6 in male reproduction, the aim of this study was to elucidate the impact of the lack of PRDX6 on male mouse fertility. Spermatozoa lacking PRDX6 showed significantly increased levels of cellular oxidative damage evidenced by high levels of lipid peroxidation, 8-hydroxy-deoxyguanosine (DNA oxidation), and protein oxidation (S-glutathionylation and carbonylation), lower sperm chromatin quality (high DNA fragmentation and low DNA compaction, due to low levels of protamination and a high percentage of free thiols), along with decreased sperm motility and impairment of capacitation as compared with wild-type (WT) spermatozoa. These manifestations of damage are exacerbated by tert-butyl hydroperoxide treatment in vivo. While WT males partially recovered the quality of their spermatozoa (in terms of motility and sperm DNA integrity), Prdx6(-/-) males showed higher levels of sperm damage (lower motility and chromatin integrity) 6 mo after the end of treatment. In conclusion, Prdx6(-/-) males are more vulnerable to oxidative stress than WT males, resulting in impairment of sperm quality and ability to fertilize the oocyte, compatible with the subfertility phenotype observed in these knockout mice.

Luminal fluid of epididymis and vas deferens contributes to sperm chromatin fragmentation

STUDY QUESTION

Do the luminal fluids of the epididymis and the vas deferens contribute to sperm chromatin fragmentation (SCF) in mice?

SUMMARY ANSWER

The luminal fluids of both organs are required for activating SCF in mice, but the vas deferens luminal fluid does this more efficiently than that of the epididymis.

WHAT IS KNOWN ALREADY

Mice sperm have the ability to degrade their DNA in an apoptotic-like fashion when treated with divalent cations in a process termed SCF. SCF has two steps: the induction of reversible double-strand DNA breaks at the nuclear matrix attachment sites, followed by the irreversible degradation of DNA by nuclease. Single stranded DNA breaks accompany SCF.

STUDY DESIGN, SIZE, DURATION

Luminal fluids from two reproductive organs of the mouse (B6D2F1 strain), the epididymis and vas deferens, were extracted and tested for SCF activation with divalent cations using four different combinations of the sperm and the surrounding luminal fluids: (i) in situ--sperm were kept in their luminal fluid and activated directly; (ii) reconstituted--sperm were centrifuged and resuspended in their luminal fluid before SCF activation; (iii) mixed--sperm were centrifuged and resuspended in the luminal fluid of the other organ; (iv) no luminal fluid--sperm were centrifuged and reconstituted in buffer. All four experiments were performed without (controls) and with divalent cations (resulting in SCF). For each experimental condition, two different mice were used and the analyses averaged.

PARTICIPANTS/MATERIALS, SETTING, METHODS

DNA damage by SCF was analyzed by three different methods, the sperm chromatin structure assay (SCSA), terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling (TUNEL) analysis and field inversion gel electrophoresis.

MAIN RESULTS AND THE ROLE OF CHANCE

In all three assays that we used, the vas deferens luminal fluid was much more efficient in stimulating SCF in the sperm from either source than that of the epididymis (P < 0.0001). Vas deferens sperm were capable of initiating lower levels of SCF in the absence of luminal fluid (P < 0.0001).

LIMITATIONS, REASONS FOR CAUTION

Analyses were performed in only one species, the mouse, but we used three separate assays in our analysis.

WIDER IMPLICATIONS OF THE FINDINGS

The data suggest that the luminal fluid of the male reproductive tract interacts with sperm during their transit providing a mechanism to degrade the DNA. We hypothesize that this is part of an apoptotic-like mechanism that allows the reproductive tract to eliminate defective sperm. The SCF model also allowed us to identify differences in the types of DNA lesions that the three tests can identify, providing important background information for the use of these tests clinically.

Cryopreservation of Ram Semen Facilitates Sperm DNA Damage: Relationship Between Sperm Andrological Parameters and the Sperm Chromatin Structure Assay

We hypothesized that cryopreservation and incubation in conditions that mimic the female genital tract following insemination increases the susceptibility of ram sperm DNA to denaturation. Ram sperm samples (n = 12) underwent the sperm chromatin structure assay (SCSA) and semen quality tests, including motility parameters, viability, and chlortetracycline fluorescence (CTC) patterns. We also assessed correlations between SCSA variables and semen quality parameters. Analyses were performed for both fresh and cryopreserved samples at 0, 3, and 20 hours of incubation in synthetic oviductal fluid (SOF; 39 degrees C, 5% CO(2)). The SCSA variables, mean alpha t (X alpha(t)) and standard deviation of alpha t (SD alpha(t)), were higher because of cryopreservation (P <.05, P <.001, respectively) after 20 hours in SOF. For both fresh and frozen spermatozoa, SCSA values (X alpha(t), SD alpha(t), and the percentage of cells outside the main population of alpha(t) [%COMP alpha(t)]) increased during incubation in SOF. Motility was negatively correlated with both SD alpha(t) and %COMP alpha(t), ranging from -0.39 (P <.01) to -0.59 (P <.001) for both fresh and cryopreserved semen; viability also was negatively correlated with X alpha(t), SD alpha(t), or %COMP alpha(t) (-0.36; P <.05, -.40 and -.46; P <.01, respectively) in fresh semen. The %COMP alpha(t) was positively correlated to the percentage of CTC pattern AR (P <.001) and negatively correlated to the percentages of patterns F and B (-0.33 to -0.60, P <.05 to P <.001). Variation among ejaculates within ram was observed (P <.01). Cryopreservation clearly facilitates DNA damage in physiological conditions. The low to moderate correlations between SCSA variables and classical semen quality parameters indicate that the SCSA provides additional information to standard tests for evaluating ram sperm quality.

Direct and delayed X-ray-induced DNA damage in male mouse germ cells

Sperm DNA integrity is essential for the accurate transmission of paternal genetic information. Various stages of spermatogenesis are characterized by large differences in radiosensitivity. Differentiating spermatogonia are susceptible to radiation-induced cell killing, but some of them can repair DNA damage and progress through differentiation. In this study, we applied the neutral comet assay, immunodetection of phosphorylated H2AX (γ-H2AX) and the Sperm Chromatin Structure Assay (SCSA) to detect DNA strand breaks in testicular cells and spermatozoa at different times following in vivo X-ray irradiation. Radiation produced DNA strand breaks in testicular cells that were repaired within the first few hours after exposure. Spermatozoa were resistant to the induction of DNA damage, but non-targeted DNA lesions were detected in spermatozoa derived from surviving irradiated spermatogonia. These lesions formed while round spermatids started to elongate within the testicular seminiferous tubules. The transcription of pro-apoptotic genes at this time was also enhanced, suggesting that an apoptotic-like process was involved in DNA break production. Our results suggest that proliferating spermatogonia retain a memory of the radiation insult that is recognized at a later developmental stage and activates a process leading to DNA fragmentation.

DNA fragmentation dynamics allows the assessment of cryptic sperm damage in human: evaluation of exposure to ionizing radiation, hyperthermia, acidic pH and nitric oxide

Sperm DNA fragmentation (SDF) is not a static seminal parameter, since the longevity of sperm DNA decreases progressively with time following ejaculation or thawing. While the dynamics of SDF is a species-specific characteristic, in the case of humans, there is still significant variation within patients. To evaluate the suitability of the dynamic SDF assay to assess the adverse effects of agents that cause genetic damage, fresh semen samples from different donors were exposed in vitro to (1) increasing acute doses of ionizing radiation, (2) elevated temperature (41 °C and 45 °C), (3) acidic pH (pH 4) and (4) the nitric oxide (NO) donor sodium nitroprusside (SNP). Sperm DNA fragmentation was analyzed after an incubation period of chronic (24h), or acute (1h) exposure to each treatment followed by incubation at 37 °C over a period of 24h. SDF was assessed using the sperm chromatin dispersion (SCD) test. Dynamic SDF for each treatment was analyzed using Kaplan-Meier survival curves. All agents, except for ionizing radiation, accelerated SDF kinetics following chronic exposure over a 24h period. Transient exposure to NO and heat but not acidic pH increased the basal (T0) level of SDF. Despite the removal of the three toxicants, the remaining sperm following acute exposure showed a decrease in their expected DNA longevity. It is concluded that the assessment of sperm DNA fragmentation dynamics is an effective methodological approach for revealing latent damage associated with toxicants that is not initially expressed following a single initial observation of SDF.

Evaluation of motility, membrane status and DNA integrity of frozen–thawed bottlenose dolphin (Tursiops truncatus) spermatozoa after sex-sorting and recryopreservation

Artificial insemination (AI) with sex-sorted frozen–thawed spermatozoa has led to enhanced management of ex situ bottlenose dolphin populations. Extended distance of animals from the sorting facility can be overcome by the use of frozen–thawed, sorted and recryopreserved spermatozoa. Although one bottlenose dolphin calf had been born using sexed frozen–thawed spermatozoa derived from frozen semen, a critical evaluation of in vitro sperm quality is needed to justify the routine use of such samples in AI programs. Sperm motility parameters and plasma membrane integrity were influenced by stage of the sex-sorting process, sperm type (non-sorted and sorted) and freezing method (straw and directional) (P<0.05). After recryopreservation, sorted spermatozoa frozen with the directional freezing method maintained higher (P<0.05) motility parameters over a 24-h incubation period compared to spermatozoa frozen using straws. Quality of sperm DNA of non-sorted spermatozoa, as assessed by the sperm chromatin structure assay (SCSA), was high and remained unchanged throughout freeze–thawing and incubation processes. Though a possible interaction between Hoechst 33342 and the SCSA-derived acridine orange was observed in stained and sorted samples, the proportion of sex-sorted, recryopreserved spermatozoa exhibiting denatured DNA was low (6.6±4.1%) at 6 h after the second thawing step and remained unchanged (P>0.05) at 24 h. The viability of sorted spermatozoa was higher (P<0.05) than that of non-sorted spermatozoa across all time points after recryopreservation. Collective results indicate that bottlenose dolphin spermatozoa undergoing cryopreservation, sorting and recryopreservation are of adequate quality for use in AI.

High levels of DNA fragmentation in spermatozoa are associated with inbreeding and poor sperm quality in endangered ungulates

Inbreeding is known to cause deleterious effects upon reproduction and survival, but its effects upon sperm DNA integrity have not been examined. In the present study, we analyzed this relationship among three endangered ungulates: Gazella cuvieri, Gazella dama mhorr, and Gazella dorcas neglecta. In addition, we examined whether levels of sperm DNA fragmentation are associated with semen quality. The magnitude of sperm DNA damage in the two species with high levels of inbreeding (G. cuvieri and G. dama mhorr) was extremely high when compared to the species with low levels of inbreeding (G. dorcas neglecta) and to values previously reported for outbred populations. Levels of sperm DNA fragmentation significantly increased with inbreeding and age. Increased DNA damage in sperm was associated with increased sperm head abnormalities, lower percentage of sperm with an intact acrosome, and poor motility. Our findings suggest that the link between inbreeding and semen quality is mediated by the effects of inbreeding upon sperm DNA damage. The deleterious effects of inbreeding upon the paternal genome likely decrease male fertility and may cause genetic damage to future generations. Because inbreeding is common among endangered species, high levels of sperm DNA damage may have considerable impact upon the viability of their populations.

Toxicants and human sperm chromatin integrity

The integrity of the paternal genome is essential as the spermatozoon can bring genetic damage into the oocyte at fertilization and contribute to the development of abnormal pregnancy outcome. During the past two decades, many assays have been developed to measure sperm DNA strand breaks, chromatin structure and compaction and assess the proteins associated with the DNA, as well as epigenetic modifications. Using these assays, it has been shown that exposure to physical agents or chemicals, including therapeutic drugs and environmental toxicants, can affect the integrity of sperm chromatin, inducing structural, genetic and/or epigenetic abnormalities. The mechanisms by which such damage is triggered are still largely unresolved and the susceptibility of each individual will depend on their genetic background, lifestyle and exposure to various insults. Depending on the nature of the chemicals, they may directly target the DNA, induce an oxidative stress, or modify the epigenetic elements. The significance of measuring the sperm chromatin integrity comes from the fact that this end-point correlates well with the low IVF and ICSI outcomes, and idiopathic infertility. Nevertheless, it is hard to establish a direct link between the paternal sperm chromatin integrity and the health of the future generations. Thus, it seems essential to undertake studies that will resolve the impact of chemical and environmental factors on chromatin structure and epigenetic components of human spermatozoa and to elucidate what sperm nuclear end-points are predictors of the quality of progeny outcome.

Cytogenetic damage in preimplantation mouse embryos generated after paternal and parental gamma-irradiation and the influence of vitamin C

Cytogenetic damage expressed as micronuclei (MN) in 4-8-cell embryos generated after irradiation of male or male and female mice in the absence and presence of vitamin C was investigated. Male NMRI mice were whole body exposed to 4 Gy gamma-rays and mated with non-irradiated superovulated female mice in 6 successive weeks after irradiation in a weekly interval. In experiments involving irradiation of both male and female mice, irradiated male mice for 6 weeks post irradiation were mated with female mice irradiated after induction of superovulation. Effect of 100 mg/kg vitamin C (ascorbic acid) on the frequency of MN was also studied. Pregnant animals were euthanized and embryos flushed from the oviducts and fixed on slides. The rate of MN observed in embryos generated from irradiated male compared with control group dramatically increased (P<0.01). Frequency of MN in this group decreased dramatically after vitamin C treatment (P<0.01). Frequency of MN in embryos generated by mating both male and female irradiated mice was higher than that observed for those embryos generated by irradiated male mice alone. However, a considerable modifying effect of vitamin C was observed for this group too (P<0.05). Results indicate that irradiation of gonads during spermatogenesis and preovulatory stage oocytes may lead to unstable chromosomal aberrations and probably stable chromosomal abnormalities affecting pairing and disjunction of chromosomes in successive preimplantation embryos expressed as MN. The way vitamin C reduces clastogenic effects of radiation on germ cells leading to reduced frequency of MN in pre-embryos might be due to its antioxidation and radical scavenging properties.

Spermatozoal sensitive biomarkers to defective protaminosis and fragmented DNA

Human sperm DNA damage may have adverse effects on reproductive outcome. Infertile men possess substantially more spermatozoa with damaged DNA compared to fertile donors. Although the extent of this abnormality is closely related to sperm function, the underlying etiology of ensuing male infertility is still largely controversial. Both intra-testicular and post-testicular events have been postulated and different mechanisms have been proposed to explain the presence of damaged DNA in human spermatozoa. Three among them, i.e. abnormal chromatin packaging, oxidative stress and apoptosis, are the most studied and discussed in the present review. Furthermore, results from numerous investigations are presented, including our own findings on these pathological conditions, as well as the techniques applied for their evaluation. The crucial points of each methodology on the successful detection of DNA damage and their validity on the appraisal of infertile patients are also discussed. Along with the conventional parameters examined in the standard semen analysis, evaluation of damaged sperm DNA seems to complement the investigation of factors affecting male fertility and may prove an efficient diagnostic tool in the prediction of pregnancy outcome.

Sperm DNA damage: clinical significance in the era of assisted reproduction

Evidence suggests that damage to human sperm DNA might adversely affect reproductive outcomes and that the spermatozoa of infertile men possess substantially more sperm DNA damage than do the spermatozoa of fertile men. This is particularly relevant in an era where advanced forms of assisted reproductive technologies are commonly used (technologies that often bypass the barriers to natural selection), because there is some uncertainty regarding the safety of using DNA-damaged spermatozoa. In this review, we outline our current understanding of how sperm DNA is organized, what causes sperm DNA damage, what impact this damage may have on reproductive capacity and whether tests of sperm DNA damage are clinically useful.

CONSERVATION SCIENCE IN A TERRORIST AGE: THE IMPACT OF AIRPORT SECURITY SCREENING ON THE VIABILITY AND DNA INTEGRITY OF FROZEN FELID SPERMATOZOA

In response to growing terrorism concerns, the Transportation Security Administration now requires that all checked baggage at U.S. airports be scanned through a cabinet x-ray system, which may increase risk of radiation damage to transported biologic samples and other sensitive genetic material. The objective of this study was to investigate the effect of these new airport security regulations on the viability and DNA integrity of frozen felid spermatozoa. Semen was collected from two domestic cats (Felis silvestris catus) and one fishing cat (Prionailurus viverrinus), cryopreserved in plastic freezing straws, and transferred into liquid nitrogen dry shippers for security screening. Treatment groups included frozen samples from each male scanned once or three times using a Transportation Security Administration-operated cabinet x-ray system, in addition to non-scanned samples (i.e., negative control) and samples previously scanned three times and exposed to five additional high-intensity x-ray bursts (i.e., positive control). Dosimeters placed in empty dry shippers were used to quantify radiation exposure. Following treatment, straws were thawed and spermatozoa analyzed for post-thaw motility (percentage motile and rate of progressive movement), acrosome status, and DNA integrity using single-cell gel electrophoresis (i.e., the comet assay). Dosimeter measurements determined that each airport screening procedure produced approximately 16 mrem of radiation exposure. Our results indicated that all levels of radiation exposure adversely affected (P < 0.05) post-thaw sperm motility, but the percentage of acrosome-intact spermatozoa did not differ (P > 0.05) among treatment groups. Results also showed that the amount of double-stranded DNA damage was greater (P < 0.05) in sperm samples from both cat species scanned three times compared to samples scanned once or negative controls. Findings suggest that new airport security measures may cause radiation-induced damage to frozen spermatozoa and other valuable biologic samples transported on passenger aircraft and that alternative modes of sample transportation should be used whenever possible.

Meta-analysis of sperm DNA fragmentation using the sperm chromatin structure assay

Meta-analyses were conducted to investigate the relationship of sperm DNA fragmentation on pregnancy outcome using in-vivo fertilization, IUI, routine IVF and ICSI. Couples with no known infertility problems were 7.0 times (CI 3.17, 17.7) more likely to achieve a pregnancy/delivery if the DNA fragmentation index (DFI) was <30% (n = 362, P = 0.0001) using in-vivo fertilization. Infertile couples using IUI were 7.3 times (CI 2.88, 18.3) more likely to achieve a pregnancy/delivery if their DFI was <30% (n = 518, P = 0.0001). With routine IVF, infertile couples were approximately 2.0 times (CI 1.02, 2.84) more likely to become pregnant if their DFI was <30% (n = 381, P = 0.03). For ICSI and/or routine IVF, the results showed a non-significant trend where infertile couples were 1.6 times (CI 0.92, 2.94) more likely to achieve a pregnancy/delivery if the DFI was <30% (n = 323,P = 0.06). The in-vivo and IUI meta-analyses were similar, indicating that IUI infertility patients with <30% DFI have as good a statistical probability of obtaining a pregnancy/delivery as in-vivo presumably fertile couples with the same DFI. These meta-analyses show that the Sperm Chromatin Structure Assay infertility test was significantly predictive for reduced pregnancy success using in-vivo, IUI and routine IVF, and to a lesser extent ICSI fertilization.

Male gonadal dose of ionizing radiation delivered during X-ray examinations and monthly probability of pregnancy: a population-based retrospective study

Background

Male gonadal exposure to ionizing radiation may disrupt spermatogenesis, but its influence on the fecundity of couples has been rarely studied. We aimed to characterize the influence of male gonadal dose of ionizing radiation delivered during radiodiagnostic on the monthly probability of pregnancy.

Methods

We recruited a random sample of women who retrospectively described 1110 periods of unprotected intercourse beginning between 1985 and 1999 and leading either to a live birth or to no pregnancy; their duration was censored after 13 months. The male partner answered a telephone questionnaire on radiodiagnostic examinations. We assigned a mean gonadal dose to each type of radiodiagnostic examination. We defined male dose for each period of unprotected intercourse as the sum of the gonadal doses of the X-ray examinations experienced between 18 years of age and the date of discontinuation of contraception. Time to pregnancy was analysed using a discrete Cox model with random effect allowing to estimate hazard ratios of pregnancy.

Results

After adjustment for female factors likely to influence fecundity, there was no evidence of an association between male dose and the probability of pregnancy (test of homogeneity, p = 0.55). When compared to couples with a male gonadal dose between 0.01 and 0.20 milligrays (n = 321 periods of unprotected intercourse), couples with a gonadal dose above 10 milligrays had a hazard ratio of pregnancy of 1.44 (95% confidence interval, 0.73–2.86, n = 31).

Conclusion

Our study provides no evidence of a long-term detrimental effect of male gonadal dose of ionizing radiation delivered during radiodiagnostic on the monthly probability of pregnancy during the year following discontinuation of contraceptive use. Classification errors due to the retrospective assessment of male gonadal exposure may have limited the statistical power of our study.

Flow cytometry applications in the evaluation of sperm quality: semen analysis, sperm function and DNA integrity

Flow cytometry (FCM) has been extensively used to study mammalian sperm in the areas of reproductive toxicology (to monitor effects from environmental, occupational and therapeutic exposures), veterinary science (to preselect the gender of offspring by sorting X- and Y-chromosome-bearing sperm) and clinical andrology (to assess individual fertility potential). Using FCM, a variety of sperm features can now be rapidly measured on a cell-by-cell basis such as sperm count, viability, acrosomal integrity, mitochondrial function and DNA integrity; the last one is involved in postfertilization failure and embryo toxicity. It is foreseen that only a multiplex approach, which includes FCM assays together with the new genomics/proteomics methods, could increase the predictive power of fertility status and help identify susceptible subpopulations of men at risk for infertility, spontaneous abortions and birth defects.

Evaluation of DNA damage in different stages of mouse spermatogenesis after testicular X irradiation

To evaluate whether DNA alterations in mature spermatozoa could stem from DNA damage induced in immature germ cells, testis cells and spermatozoa were analyzed by the comet assay and by the sperm chromatin structure assay 14, 45 and 100 days after in vivo X irradiation of the testes. These times were selected, according to the mouse seminiferous epithelium cycle, to follow the DNA damage induced in different germ cell compartments. The cytotoxic action was assessed by DNA flow cytometric analysis of testicular cells. A dose-dependent increase of DNA damage in testis cells was observed 14 days after irradiation, whereas mature sperm cells were not affected. On the other hand, an increase in DNA strand breaks was seen in spermatozoa 45 days after treatment. DNA damage returned to the control levels 100 days after irradiation. The methods used to evaluate DNA damage gave comparable results, emphasizing the correlation between DNA fragmentation and susceptibility of sperm chromatin to denaturation. Both techniques showed the high radiosensitivity of differentiating spermatogonia. The overall results showed that DNA damage induced in pre-meiotic germ cells is detectable in primary spermatocytes and is still present in mature spermatozoa.

Male genital tract antioxidant enzymes: their source, function in the female, and ability to preserve sperm DNA integrity in the golden hamster

Recently, we reported that male accessory sex gland (ASG) secretions protect sperm genomic integrity by demonstrating that DNA damage was more extensive in sperm not exposed to the secretions. The present study was conducted to find out if ASGs secrete the main antioxidant enzymes superoxide dismutase (SOD), glutathione peroxidase (GPx or GSH-Px), and catalase (CAT) and if the most abundant one, SOD, can protect those sperm that were not exposed to ASG secretions against NADPH-induced oxidative stress. Four experimental groups of male golden hamsters were used: intact animals with proven fertility, animals with all major ASGs removed (TX), animals that were bilaterally vasectomized, and sham-operated controls. SOD, CAT, and GPx activities were measured in secretions from all 5 ASGs and sperm-free uterine flushing from virgin females and those mated with the experimental males. The alkaline comet assay was used to analyze DNA integrity of the TX group sperm after incubation in a medium containing 50 U/mL of SOD along with 0 to 20 mmol/L NADPH. The main antioxidant enzyme in ASGs was SOD from coagulating glands (P <.05) and GPx together with CAT from ampullary glands (P <.05). Uterine flushing of ejaculates that contained ASG secretions had more SOD and CAT activities than those with epididymal secretions alone (P <.05 and P <.001, respectively), whereas activity of GPx was the same (P >.05). Addition of SOD in vitro dose dependently decreased the incidence of single-strand DNA damage in sperm not exposed to ASG secretions incubated in the presence of 0 to 20 mmol/L NADPH (P <.001). These results indicated that, in terms of abundance, SOD was the main antioxidant enzyme secreted by male ASGs, whereas CAT was the second one. The GPx activity came from both epididymis and ASGs. We conclude that ASG secretions play a significant role in protecting sperm against oxidative stress.

Sperm DNA damage and cancer treatment

Cancer treatments are well known to adversely affect male fertility. Reduction of sperm output arises from the cytotoxic effects of chemo- or radiotherapy upon the spermatogenic epithelium. However, if the epithelium survives there is a hazard to reproduction as the treatments are also mutagenic. The presence of DNA damage in the male genome is shown in animal experiments where there is transgenerational expression as a variety of effects ranging from miscarriage to carcinogenesis. The application of DNA damage methodology to sperm provides the opportunity for direct assessment. The Comet and Chromatin structure assays (SCSA) measure DNA damage by different principles, however, conclusions arising from the data are similar. DNA damage is present in sperm from fertile and infertile men and there is some association with infertility. Both assays detect sperm DNA damage after in vivo treatment with genotoxic agents. In a man treated with chemotherapy for cancer there was increased and persistent DNA damage in sperm. This information is consistent with the generation of human genetic diseases after conception with sperm carrying high loads of DNA damage. Whilst studies have not supported any association between paternal cytotoxic cancer therapy and genetic disease in their children, it would be unwise to discount these observations. The institution of better surveillance of genetic disease in the offspring of men surviving cytotoxic therapies may provide more robust risk assessment.

Germ cell and dose-dependent DNA damage measured by the comet assay in murine spermatozoaa after testicular X-irradiation

The single-cell gel electrophoresis (Comet) assay has been widely used to measure DNA damage in human sperm in a variety of physiological and pathological conditions. We investigated the effects of in vivo radiation, a known genotoxin, on spermatogenic cells of the mouse testis and examined sperm collected from the vas deferens using the neutral Comet assay. Irradiation of differentiating spermatogonia with 0.25-4 Gy X-rays produced a dose-related increase in DNA damage in sperm collected 45 days later. Increases were found when measuring Comet tail length and percentage of tail DNA, but the greatest changes were in tail moment (a product of tail length and tail DNA). Spermatids, spermatocytes, differentiating spermatogonia, and stem cell spermatogonia were also irradiated in vivo with 4 Gy X-rays. DNA damage was indirectly deduced to occur at all stages. The maximum increase was seen in differentiating spermatogonia. DNA damaged cells were, surprisingly, still detected 120 days after stem cell spermatogonia had been irradiated. The distribution of DNA damage among individual sperm cells after irradiation was heterogeneous. This was seen most clearly when changes in the Comet tail length were measured when there were discrete undamaged and damaged populations. After increasing doses of irradiation, an increasing proportion of cells were found in the damaged population. Because a proportion of undamaged sperm cells remains after all but the highest dose, the possibility of normal fertility remains. However, fertilization with a spermatozoa carrying high amounts of DNA damage could lead to effects as diverse as embryonic death and cancer susceptibility in the offspring.

Increased levels of comet-detected spermatozoa DNA damage following in vivo isotopic- or X-irradiation of spermatogonia

To investigate whether DNA damage arising in spermatogenic germ cells can be detected in resultant sperm, we have irradiated murine testis and collected spermatozoa from the vas deferens 45 days later. These cells were derived from spermatogonia present at the time of irradiation. Two forms of irradiation were used, external X-rays (4Gy) and internal auger electrons from contamination of the male mouse with the isotope Indium-114m (1.85MBq), which was localised in the testis. Both forms of irradiation produced a profound fall in vas deferens sperm count and testis weight, Indium-114m being more effective. Using the neutral Comet assay for double strand break detection, significant increases in sperm comet tail length and moment were observed. The levels of damage were similar for both treatments. Care had to be taken during the assay to distinguish between sperm and somatic cells as the proportion of the latter increased after irradiation. We conclude that the comet assay can detect DNA damage in spermatozoa after the in vivo exposure of male germ cells to a known testicular genotoxic agent. The assay may be useful for the assessment of sperm DNA damage (double stranded) associated with male infertility and post-fertilization developmental abnormalities in the offspring.

Effects of single and split doses of cobalt-60 gamma rays and 14 MeV neutrons on mouse stem cell spermatogonia

The long-term effects of ionizing radiation on male gonads may be the result of damage to spermatogonial stem cells. Doses of 10 cGy to 15 Gy (60)Co gamma rays or 10 cGy to 7 Gy 14 MeV neutrons were given to NMRI mice as single or split doses separated by a 24-h interval. The ratios of haploid spermatids/2c cells and the coefficients of variation of DNA histogram peaks as measures of both the cytocidal and the clastogenic actions of radiation were analyzed by DNA flow cytometry after DAPI staining. The coefficient of variation is not only a statistical examination of the data but is also used here as a measure of residual damage to DNA (i.e. a biological dosimeter). Testicular histology was examined in parallel. At 70 days after irradiation, the relative biological effectiveness for neutrons at 50% survival of spermatogonial stem cells was 3.6 for single doses and 2.8 for split doses. The average coefficient of variation of unirradiated controls of elongated spermatids was doubled when stem cells were irradiated with single doses of approximately 14 Gy (60)Co gamma rays or 3 Gy neutrons and observed 70 days later. Split doses of (60)Co gamma rays were more effective than single doses, doubling DNA dispersion at 7 Gy. No fractionation effect was found with neutrons with coefficients of variation.

DNA flow cytometry of human semen

The aim of this study was the evaluation of DNA flow cytometry for the analysis of male infertility. 171 ejaculates from 155 patients with fertility problems were analysed by flow cytometry and by conventional microscopical procedures. Using flow cytometry, it was possible to determine the relative proportions of the various cell populations: mature haploid and abnormal diploid mature spermatozoa, cellular fragments, immature germ cells (haploid round spermatids, diploid cells, S phase and 4C cells), and of leukocytes as indicators of infection. A linear association was observed between sperm concentration in semen as quantified by light microscopy and by flow cytometry, even with fewer than 20x10(6) spermatozoa/ml. Eight classes of histograms, each with differing fractions of spermatozoa and other particles, were obtained and correlated with the results of the spermiograms. During the 10 year follow-up, the two patient groups with a low sperm concentration or a high concentration of cellular debris exhibited significantly impaired fertility. The two patient groups with >/=5% diploid spermatozoa and with malcondensed sperm chromatin were also subfertile. No ovulatory disorders were revealed in the 155 female partners. DNA flow cytometry thus provides an additional dimension to semen analysis not easily gained by other methods and has the advantage of being rapidly performed and interpreted. We therefore recommend application of this technique in the diagnosis of male infertility.

Measurement of apoptosis

The cell dying by apoptosis undergoes a sequence of morphological, biochemical, and molecular changes which are characteristic, and often unique, to this mode of cell death. Specific features of apoptotic cells resulting from these changes, which serve as markers used to reveal the apoptotic mode of cell death and to quantify the extent of apoptosis in cultures or in tissue, are reviewed. Analysis of these features by flow or image cytometry is the most commonly used approach to detect, quantify, and study various aspects of apoptosis. Flow or laser scanning cytometry also offer all the advantages of rapid, accurate and multiparametric measurements to investigate the biological processes associated with cell death. Numerous methods have been developed to identify apoptotic and necrotic cells, which are widely used in various disciplines, particularly in oncology and immunology. The methods based on changes in cell morphology, plasma membrane molecular structure and transport function, function of cell organelles, DNA stability to denaturation and endonucleolytic DNA degradation are reviewed and their applicability in the research laboratory and in the clinical setting is discussed. The most common pitfalls and improper use of the methodology in analysis of cell death and in data interpretation are also discussed.

Reproductive toxicity of 1,3-butadiene in the mouse: cytogenetic analysis of chromosome aberrations in first-cleavage embryos and flow cytometric evaluation of spermatogonial cell killing

Reproductive effects of 1,3 butadiene inhalation have been evaluated in male mice by reduction of post-meiotic germ cells, alteration of sperm chromatin structure and transmission of chromosome aberrations to one-cell embryos. Animals were exposed for 5 consecutive days for 6 h per day to butadiene concentrations of 130, 500 or 1300 ppm. The testicular fraction of post-meiotic germ cells was measured by flow cytometric analysis on the basis of their DNA content. Round spermatids were discriminated from mature, elongated spermatids by their different degree of chromatin condensation. Butadiene-induced cytotoxic effects on differentiating spermatogonia were shown by a concentration-dependent decrease of round spermatids occurring 21 days after chemical exposure, confirmed by a similar decrease of elongated spermatids measured in testes sampled 7 days later. Statistically significant effects were seen already at 130 ppm. An incomplete repopulation of the elongated spermatid compartment observed 35 days after exposure to 1300 ppm suggested that, at the highest concentration tested, butadiene toxicity extended to stem cells. Alterations of sperm chromatin were revealed by its increased sensitivity to acidic denaturation in situ. The percentage of abnormal sperm was significantly increased after butadiene exposure of differentiating spermatogonia and spermatocytes. This suggested the induction of persistent effects interfering with chromatin remodelling during spermiogenesis. Chromosome-type structural aberrations were significantly elevated in first-cleavage embryos conceived by males mated during the first and second week after the end of exposure. The lowest effective tested concentration was 500 ppm, the same reported for dominant lethal induction under identical exposure conditions. As in the dominant lethal assay, the effect of this dose was confined to exposed sperm, while both sperm and late spermatids were affected by the inhalation of 1300 ppm. A quantitative comparison between the effects induced by intraperitoneal injections of diepoxybutane or butadiene inhalations suggested that other reactive intermediates, in addition to diepoxybutane, might contribute to mediate butadiene-induced reproductive toxicity.