Immunochemical detection of DNA damage induction and repair at different cellular stages of spermatogenesis of the hamster after in vitro or in vivo exposure to ionizing radiation

Bisphenol A Induces Oxidative Stress in Bone Marrow Cells, Lymphocytes, and Reproductive Organs of Holtzman Rats

Bisphenol A (BPA) is an estrogenic chemical used in the production of polycarbonate plastics and epoxy resins. Our earlier studies have demonstrated that BPA is a potent reproductive and genotoxic agent and affects the normal physiological functions. The objective of this study was to evaluate whether exposure to BPA induces oxidative stress. The male Holtzman rats were orally gavaged with BPA (0.01 mg and 5.0 mg/kg/bw) over the period of 6 days. Animals were euthanized by cervical dislocation at the end of the treatments; bone marrow cells and blood lymphocytes were aspirated; testis and epididymis were collected, immediately frozen in liquid nitrogen, and stored at −80°C. These samples were utilized for the determination of lipid peroxidation and various antioxidant enzymes such as superoxide dismutase, catalase, and nonenzymatic reduced glutathione. The results demonstrated that BPA caused an increase in lipid peroxidation and a decrease in activity of various enzymatic and nonenzymatic antioxidants in bone marrow cells, blood lymphocytes, and testicular and epididymal tissues. The findings of the current study suggest that BPA exposure induced oxidative stress, which could be one of the possible mechanisms causing reproductive and genetic toxicity.

Freezability of water buffalo bull (Bubalus bubalis) spermatozoa is improved with the addition of curcumin (diferuoyl methane) in semen extender

Effects of curcumin as antioxidant in extender were evaluated on freezability of buffalo spermatozoa. Semen from each of the five bulls (n = 3 replicates, six ejaculates/bull, a total of 30 ejaculates) was diluted in Tris-citric acid extender containing curcumin (0.5, 1.0, 1.5 or 2.0 mM) or control. At pre-freezing and post-thawing, total antioxidant contents (μM/L) and lipid peroxidation levels (μM/ml) were higher (p < .05) and lower (p < .05) respectively, with 1.5 and 2.0 mM compared to 0.5 and 1.0 mM curcumin and control. At post-thawing, progressive motility (PM, %) and rapid velocity (RV, %) were higher (p < .05) with 1.5 mM compared to other doses of curcumin and control (except in case of RV, 1.5 was similar with 1.0 mM). Kinematics (average path velocity, μm/s; straight-line velocity, μm/s; curved-line velocity, μm/s; straightness, %; linearity, %), in vitro longevity (%, PM and RV) and DNA integrity (%) at post-thawing were higher (p < .05) with 1.5 mM compared to control. At post-thawing, supravital plasma membrane integrity (%) and viable spermatozoa with intact acrosome (%) were higher with 1.5 compared to 2.0 mM curcumin and control. We concluded that freezability of water buffalo spermatozoa is improved with the addition of 1.5 mM curcumin in extender.

DNA Double Strand Break Response and Limited Repair Capacity in Mouse Elongated Spermatids

Spermatids are extremely sensitive to genotoxic exposures since during spermiogenesis only error-prone non homologous end joining (NHEJ) repair pathways are available. Hence, genomic damage may accumulate in sperm and be transmitted to the zygote. Indirect, delayed DNA fragmentation and lesions associated with apoptotic-like processes have been observed during spermatid elongation, 27 days after irradiation. The proliferating spermatogonia and early meiotic prophase cells have been suggested to retain a memory of a radiation insult leading later to this delayed fragmentation. Here, we used meiotic spread preparations to localize phosphorylate histone H2 variant (γ-H2AX) foci marking DNA double strand breaks (DSBs) in elongated spermatids. This technique enabled us to determine the background level of DSB foci in elongated spermatids of RAD54/RAD54B double knockout (dko) mice, severe combined immunodeficiency SCID mice, and poly adenosine diphosphate (ADP)-ribose polymerase 1 (PARP1) inhibitor (DPQ)-treated mice to compare them with the appropriate wild type controls. The repair kinetics data and the protein expression patterns observed indicate that the conventional NHEJ repair pathway is not available for elongated spermatids to repair the programmed and the IR-induced DSBs, reflecting the limited repair capacity of these cells. However, although elongated spermatids express the proteins of the alternative NHEJ, PARP1-inhibition had no effect on the repair kinetics after IR, suggesting that DNA damage may be passed onto sperm. Finally, our genetic mutant analysis suggests that an incomplete or defective meiotic recombinational repair of Spo11-induced DSBs may lead to a carry-over of the DSB damage or induce a delayed nuclear fragmentation during the sensitive programmed chromatin remodeling occurring in elongated spermatids.

Impact of tributyltin on antioxidant and DNA damage response in spermatozoa of freshwater prawn Macrobrachium rosenbergii

Effects of tributyltin (TBT) on antioxidant [total superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione reductase (GR)] and DNA damage levels in the spermatozoa were studied and reported here for the first time in the freshwater prawn Macrobrachium rosenbergii. Three groups of (n = 10 in each group) fishes were exposed to three different nominal concentrations of TBT viz., 1, 2, and 4 mg L(-1) along with control group for 90 days. Significant decrease of antioxidant and increased DNA damage levels were seen at higher doses of 2 and 4 mg L(-1). In prawn, the antioxidant level plays a vital role in sperm protection, activation, differential functions related to the physiology, and reproductive behavior. This study serves as a biomonitoring tool to assess the TBT effects on reproductive behavior of aquatic biota.

Localisation and quantification of alkali-labile sites in human spermatozoa by DNA breakage detection-fluorescence in situ hybridisation

The localisation and quantification of constitutive alkali-labile sites (ALSs) were investigated using a protocol of DNA breakage detection plus fluorescence in situ hybridisation (DBD-FISH) and alkaline single-cell gel electrophoresis (SCGE or comet assay), in spermatozoa of infertile and fertile men. Semen samples from 10 normozoospermic patients undergoing infertility treatment and 10 fertile men were included in this study. ALSs were localised and quantified by DBD-FISH. The region most sensitive to alkali treatment in human spermatozoa was located in the basal region of the head. ALSs were more frequent in spermatozoa of infertile men than in those of fertile men. These results were confirmed by SCGE comet assays. In conclusion, the most intense localisation of hybridisation signals in human spermatozoa, representing the highest density of constitutive ALSs, was not randomly distributed and was predominantly located in the base of the head. Moreover, infertile men presented with an increase in ALS frequency. Further studies are necessary to determine the association between ALS, sperm chromatin organisation and infertility.

Localization of alkali-labile sites in donkey (Equus asinus) and stallion (Equus caballus) spermatozoa

The presence of constitutive alkali-labile sites (ALS) has been investigated using a protocol of DNA breakage detection-fluorescence in situ hybridization and comet assay in spermatozoa of donkey (Equus asinus) and stallion (Equus caballus). These results were compared with those obtained using a similar experimental approach using somatic cells. The relative abundance of ALS was of the order of four times more in spermatozoa than in somatic cells. Alkali-labile sites showed a tendency to cluster localized at the equatorial-distal regions of the sperm. The amount of hybridized signal in the ALS in the sperm of donkey (Equus asinus) was 1.3 times greater than in stallion (Equus caballus), and the length of the comet tail obtained in donkey sperm was 1.6 times longer than that observed in stallion (P < 0.05); however, these differences were not appreciated in somatic cells. In conclusion, ALS localization in sperm is not a randomized event and a different pattern of ALS distribution occurs for each species. These results suggest that ALS represents a species-specific issue related to chromatin organization in sperm and somatic cells in mammalian species, and they might diverge even with very short phylogenetic distances.

Single-cell pulsed-field gel electrophoresis to detect the early stage of DNA fragmentation in human sperm nuclei

Single-cell pulsed-field gel electrophoresis (SCPFGE) with dual electrode pairs was developed to detect the early stage of DNA fragmentation in human sperm. The motile sperm were purified by the commonly used density-gradient centrifugation technique and subsequent swim-up. The sperm were embedded in a thin film of agarose containing bovine trypsin (20 µg/mL) and were then lysed. Prior to SCPFGE, proteolysis of DNA-binding components, such as protamine and the nuclear matrix was essential to separate the long chain fibers from the fibrous and granular fragments derived from a single nucleus. The overall electrophoretic profiles elucidated the course of DNA fragmentation. A few large fibrous fragments were observed at the beginning of the process, however, as the fragmentation advanced, the long chain fibers decreased and shortened, and, conversely, the granular fragments increased until finally almost all the DNA was shredded. Although the ejaculate contained sperm with heterogeneous stages, the purified motile sperm exhibited several dozens of uniformly elongated fibers arising from the tangled DNA at the origin, whereas a part of these fibers gave rise to fibrous fragments beyond the tip of the elongated fibers, and their numbers and sizes varied among the sperm. Conventional intra-cytoplasmic sperm injection (ICSI) usually depends on intra-operative light microscopic observation to select a sperm for injection. The present results revealed that sperm motility could not give full assurance of DNA integrity. SCPFGE is likely to serve an important role in the preoperative differential diagnosis to determine the competence of the sperm population provided for injection.

Oxidative stress in zebrafish (Danio rerio) sperm

Laboratories around the world have produced tens of thousands of mutant and transgenic zebrafish lines. As with mice, maintaining all of these valuable zebrafish genotypes is expensive, risky, and beyond the capacity of even the largest stock centers. Because reducing oxidative stress has become an important aspect of reducing the variability in mouse sperm cryopreservation, we examined whether antioxidants might improve cryopreservation of zebrafish sperm. Four experiments were conducted in this study. First, we used the xanthine-xanthine oxidase (X-XO) system to generate reactive oxygen species (ROS). The X-XO system was capable of producing a stress reaction in zebrafish sperm reducing its sperm motility in a concentration dependent manner (P<0.05). Second, we examined X-XO and the impact of antioxidants on sperm viability, ROS and motility. Catalase (CAT) mitigated stress and maintained viability and sperm motility (P>0.05), whereas superoxide dismutase (SOD) and vitamin E did not (P<0.05). Third, we evaluated ROS in zebrafish spermatozoa during cryopreservation and its effect on viability and motility. Methanol (8%) reduced viability and sperm motility (P<0.05), but the addition of CAT mitigated these effects (P>0.05), producing a mean 2.0 to 2.9-fold increase in post-thaw motility. Fourth, we examined the effect of additional cryoprotectants and CAT on fresh sperm motility. Cryoprotectants, 8% methanol and 10% dimethylacetamide (DMA), reduced the motility over the control value (P<0.5), whereas 10% dimethylformamide (DMF) with or without CAT did not (P>0.05). Zebrafish sperm protocols should be modified to improve the reliability of the cryopreservation process, perhaps using a different cryoprotectant. Regardless, the simple addition of CAT to present-day procedures will significantly improve this process, assuring increased and less variable fertilization success and allowing resource managers to dependably plan how many straws are needed to safely cryopreserve a genetic line.

Semen molecular and cellular features: these parameters can reliably predict subsequent ART outcome in a goat model

Currently, the assessment of sperm function in a raw or processed semen sample is not able to reliably predict sperm ability to withstand freezing and thawing procedures and in vivo fertility and/or assisted reproductive biotechnologies (ART) outcome. The aim of the present study was to investigate which parameters among a battery of analyses could predict subsequent spermatozoa in vitro fertilization ability and hence blastocyst output in a goat model. Ejaculates were obtained by artificial vagina from 3 adult goats (Capra hircus) aged 2 years (A, B and C). In order to assess the predictive value of viability, computer assisted sperm analyzer (CASA) motility parameters and ATP intracellular concentration before and after thawing and of DNA integrity after thawing on subsequent embryo output after an in vitro fertility test, a logistic regression analysis was used. Individual differences in semen parameters were evident for semen viability after thawing and DNA integrity. Results of IVF test showed that spermatozoa collected from A and B lead to higher cleavage rates (0 < 0.01) and blastocysts output (p < 0.05) compared with C. Logistic regression analysis model explained a deviance of 72% (p < 0.0001), directly related with the mean percentage of rapid spermatozoa in fresh semen (p < 0.01), semen viability after thawing (p < 0.01), and with two of the three comet parameters considered, i.e tail DNA percentage and comet length (p < 0.0001). DNA integrity alone had a high predictive value on IVF outcome with frozen/thawed semen (deviance explained: 57%). The model proposed here represents one of the many possible ways to explain differences found in embryo output following IVF with different semen donors and may represent a useful tool to select the most suitable donors for semen cryopreservation.

Effect of cryopreservation on sperm DNA integrity in patients with teratospermia

OBJECTIVE

To test whether sperm with abnormal head morphology are more likely to undergo DNA damage and/or chromatin modification during the process of freeze-thawing.

DESIGN

In this prospective study, the semen samples from forty-four men attending the infertility clinic were included. Samples were divided into aliquots to allow direct comparison of fresh and frozen spermatozoa from the same ejaculate. The sperm morphology and the sperm DNA damage were evaluated before and after cryopreservation. The relationship between sperm head abnormalities and freeze-thaw-induced DNA modification was assessed.

SETTING(S)

University hospital fertility center.

PATIENT(S)

Men attending infertility clinic for semen analysis.

INTERVENTION(S)

The normospermic and teratospermic semen samples were evaluated for DNA damage before and after cryopreservation by comet assay and acridine orange bindability test.

MAIN OUTCOME MEASURE(S)

Elucidation of association between sperm morphologic defect and cryodamage.

RESULT(S)

A threefold increase in the amount of DNA damage was observed in teratospermic samples compared with their normospermic counterparts, indicating a higher susceptibility of morphologically abnormal sperm to cryodamage.

CONCLUSION(S)

The susceptibility of morphologically abnormal sperm to DNA damage/chromatin modification during the freeze-thaw process is significantly higher than that of sperm with normal morphology.

Alkali-labile sites in sperm cells from Sus and Ovis species

Constitutive alkali-labile sites (ALSs) have been investigated using a protocol of DNA breakage detection-fluorescence in situ hybridization (DBD-FISH) in sperm cells from Sus domesticus (pig), Ovis gmelini musimon (mouflon) and Ovis aries (sheep). The results were compared with those obtained using leucocytes from the same species. Whole comparative genomic hybridization (W-CGH) showed that most of the constitutive ALSs in somatic and germ line cells in all species examined were constrained to particular repetitive satellite DNA sequences located in the pericentromeric constitutive heterochromatin of each chromosome. However, their relative abundance was different among cells of the same organism (leucocytes/sperm cells), and this trend was not maintained when the different species were compared. Thus, in mouflon, the density of ALSs in leucocytes when compared with that observed in sperm cells indicated abundance of the order of eight times less. In sheep, both leucocytes and sperm cells exhibited a large quantity of ALSs, being of the order of four times more abundant in sperm cells. In the pig genome, leucocytes showed a high abundance of ALSs (of the order of 12 times more that in sperm cells) but only involved the metacentric chromosomes of the karyotype. ALSs were not present in the acrocentric chromosomes. Contrary to mouflon and sheep, ALSs were relatively scarce in sperm cells from pig. These results suggest that ALSs are a transient structural feature in the cells of any organisms and point to a non-universal model of chromatin organization in sperm cells among mammals.

Effects of ageing on spermatozoal chromatin and its sensitivity to in vivo and in vitro oxidative challenge in the Brown Norway rat

BACKGROUND

The goals of our study were to examine chromatin packaging and integrity in spermatozoa taken from the caput and cauda epididymides of young (4-month-old) and old (21-month-old) Brown Norway rats and to assess whether spermatozoal sensitivity to oxidative treatments is altered with age.

METHODS

Oxidative treatments consisted of (i) in vivo oxidative challenge by systemic administration of the glutathione-depleting drug l-buthionine-[S,R]-sulphoximine (BSO) and (ii) in vitro oxidative challenge by incubating collected spermatozoa with hydrogen peroxide (H(2)O(2)). Chromatin parameters assessed included quantification of thiols, nuclear chromomycin A3 (CMA3) penetration, DNA breaks by TdT (terminal deoxynucleotidyl transferase)-mediated dUDP nick-end labelling (TUNEL) and ease of DNA dissociation by acridine orange (AO) staining.

RESULTS

In spermatozoa from older rats, we found decreases in thiols, CMA3 penetration and the percentage of cells that undergo DNA dissociation. Administration of BSO had oxidizing effects on the thiol groups. It also decreased CMA3 penetration and DNA dissociation and increased TUNEL staining. Furthermore, BSO treatment sensitized cauda epididymidis spermatozoa, from older animals, to H(2)O(2).

CONCLUSIONS

Overall, we show that spermatozoa from older rats have altered chromatin packaging and integrity and that spermatozoa from the cauda epididymidis are more responsive to combined in vivo and in vitro oxidative challenge than spermatozoa from young rats.

Assessment of the cryopreservation of equine spermatozoa in the presence of enzyme scavengers and antioxidants

OBJECTIVE

To evaluate the effect of the addition of enzyme scavengers and antioxidants to the cryopreservation extender on characteristics of equine spermatozoa after freezing and thawing.

SAMPLE POPULATION

2 ejaculates collected from each of 5 stallions.

PROCEDURE

Equine spermatozoa were cryopreserved in freezing extender alone (control samples) or with the addition of catalase (200 U/mL), superoxide dismutase (200 U/mL), reduced glutathione (10 mM), ascorbic acid (10 mM), alpha-tocopherol (25, 50, 100, or 500 microM or 1 mM), or the vehicle for alpha-tocopherol (0.5% ethanol). After thawing, spermatozoal motility was assessed via computer-assisted analysis and DNA fragmentation was assessed via the comet assay. Spermatozoal mitochondrial membrane potential, acrosomal integrity, and viability were determined by use of various specific staining techniques and flow cytometry.

RESULTS

The addition of enzyme scavengers or antioxidants to cryopreservation extender did not improve spermatozoal motility, DNA fragmentation, acrosomal integrity, viability, or mitochondrial membrane potential after thawing. Superoxide dismutase increased DNA fragmentation, likely because of the additional oxidative stress caused by the generation of hydrogen peroxide by this enzyme. Interestingly, the addition of the vehicle for alpha-tocopherol resulted in a significant decrease in live acrosome-intact spermatozoa.

CONCLUSIONS AND CLINICAL RELEVANCE

The addition of antioxidants to the cryopreservation extender did not improve the quality of equine spermatozoa after thawing, which suggests that the role of oxidative stress in cryopreservation-induced damage of equine spermatozoa requires further investigation. Our data suggest that solubilizing alpha-tocopherol in ethanol may affect spermatozoal viability; consequently, water-soluble analogues of alpha-tocopherol may be preferred for future investigations.

Innocuity of tetradecyl-dimethyl-benzyl ammonium fluoride on the DNA of human spermatozoa

Tetradecyl-dimethyl-benzyl-ammonium fluoride (TDBAF) is a powerful new spermicide. In cases of failure of local contraception, there is a theoretical risk that a spermatozoon exposed to a sublethal concentration of spermicide might suffer DNA strand breaks, with transmission of damaged DNA to the oocyte. The present study aims to ascertain the innocuity of TDBAF in this regard. Spermatozoa from 32 fertile men were exposed to a sublethal concentration of TDBAF. The degree of DNA fragmentation was measured by modified terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-biotin end labeling (TUNEL) assay, pulsed field gel electrophoresis of purified sperm DNA and radioenzymatic labeling. With the TUNEL assay, a statistically significant increase in sperm labeling was observed after TDBAF treatment compared to the controls. However, pulsed field gel electrophoresis and enzymatic labeling of purified DNA showed no evidence of augmented DNA fragmentation in TDBAF-treated sperm. Under electron microscopy, TDBAF caused sperm chromatin decondensation. In the TUNEL assay, this phenomenon would allow easier access of terminal transferase to its DNA substrate, explaining the apparent increase in DNA fragmentation in the presence of TDBAF. In conclusion, the use of TDBAF as a spermicide does not place progeny at heightened risk of abnormalities should pregnancy occur. In regard to the TUNEL assay, we suggest that pretreatment of spermatozoa with TDBAF promotes a more accurate measurement of sperm DNA fragmentation.

Reactive oxygen species and cryopreservation promote DNA fragmentation in equine spermatozoa

The objective of this study was to examine the effect of reactive oxygen species (ROS) and cryopreservation on DNA fragmentation of equine spermatozoa. In experiment 1, equine spermatozoa were incubated (1 hour, 38 degrees C) according to the following treatments: 1) sperm alone; 2) sperm + xanthine (X, 0.3 mM)-xanthine oxidase (XO, 0.025 U/mL); 3) sperm + X (0.6 mM)-XO (0.05 U/mL); and 4) sperm + X (1 mM)-XO (0.1 U/mL). In experiment 2, spermatozoa were incubated (1 hour, 38 degrees C) with X (1 mM)-XO (0.1 U/mL) and either catalase (200 U/mL), superoxide dismutase (SOD, 200 U/mL), or reduced glutathione (GSH, 10 mM). Following incubation, DNA fragmentation was determined by the single cell gel electrophoresis (comet) assay. In experiment 3, equine spermatozoa were cryopreserved, and DNA fragmentation was determined in fresh, processed, and postthaw sperm samples. In experiment 1, incubation of equine spermatozoa in the presence of ROS, generated by the X-XO system, increased DNA fragmentation (P <.005). In Experiment 2, the increase in DNA fragmentation associated with X-XO treatment was counteracted by the addition of catalase and GSH but not by SOD, suggesting that hydrogen peroxide and not superoxide appears to be the ROS responsible for such damage. In experiment 3, cryopreservation of equine spermatozoa was associated with an increase (P <.01) in DNA fragmentation when compared with fresh or processed samples. This study indicates that ROS and cryopreservation promote DNA fragmentation in equine spermatozoa; the involvement of ROS in cryopreservation-induced DNA damage remains to be determined.

Regulated transposition of a fish transposon in the mouse germ line

Tc1/mariner elements are able to transpose in species other than the host from which they were isolated. As potential vectors for insertional mutagenesis and transgenesis of the mouse, these cut-and-paste transposons were tested for their ability to transpose in the mouse germ line. First, the levels of activity of several Tc1/mariner elements in mammalian cells were compared; the reconstructed fish transposon Sleeping Beauty (SB) was found to be an order of magnitude more efficient than the other tested transposons. SB then was introduced into the mouse germ line as a two-component system: one transgene for the expression of the transposase in the male germ line and a second transgene carrying a modified transposon. In 20% of the progeny of double transgenic male mice the transposon had jumped from the original chromosomal position into another locus. Analysis of the integration sites shows that these jumps indeed occurred through the action of SB transposase, and that SB has a strong preference for intrachromosomal transposition. Analysis of the excision sites suggests that double-strand breaks in haploid spermatids are repaired via nonhomologous end joining. The SB system may be a powerful tool for transposon mutagenesis of the mouse germ line.

DNA polymerase lambda (Pol lambda), a novel eukaryotic DNA polymerase with a potential role in meiosis

A new gene (POLL) encoding a novel DNA polymerase (Pol lambda) has been identified at mouse chromosome 19. Murine Pol lambda, consisting of 573 amino acid residues, has a 32% identity to Pol beta, involved in nuclear DNA repair in eukaryotic cells. It is interesting that Pol lambda contains all the critical residues involved in DNA binding, nucleotide binding and selection, and catalysis of DNA polymerization, that are conserved in Pol beta and other DNA polymerases belonging to family X. Murine Pol lambda, overproduced in Escherichia coli, displayed intrinsic DNA polymerase activity when assessed by in situ gel analysis. Pol lambda also conserves the critical residues of Pol beta required for its intrinsic deoxyribose phosphate lyase (dRPase) activity. The first 230 amino acid residues of Pol lambda, that have no counterpart in Pol beta, contain a BRCT domain, present in a variety of cell-cycle check-point control proteins responsive to DNA damage and proteins involved in DNA repair. Northern blotting, in situ hybridization analysis and immunostaining showed high levels of Pol lambda specifically expressed in testis, being developmentally regulated and mainly associated to pachytene spermatocytes. These first evidences, although indirect, suggest a potential role of Pol lambda in DNA repair synthesis associated with meiosis.

Effect of freeze-thawing procedure on chromatin stability, morphological alteration and membrane integrity of human spermatozoa in fertile and subfertile men

Cryopreservation is known to impair sperm motility and decrease the fertilization rate by detrimental effects on acrosomal structure and acrosin activity. However, the consequences of cryopreservation on the integrity of the sperm nucleus, chromatin stability and centrosome are less clear. The present study was designed to determine the effect of the freeze-thawing procedure on chromatin condensation (aniline blue staining) and the morphology (strict criteria) and membrane integrity of human spermatozoa. The structural and functional characteristics of the sperm plasma membrane were measured by the eosin-test and hypo-osmotic swelling test which were done separately. Sperm cryopreservation was performed on semen samples from two groups of men classified as fertile (n = 20) and subfertile (n = 72), based on their reproductive history and semen analysis according to WHO guidelines. The mean percentage of condensed chromatin, morphologically normal spermatozoa and membrane integrity in all semen samples investigated (n = 92) decreased significantly (p = 0.0001) after freeze-thawing, in comparison to the value observed prior to freezing. By comparing the semen samples between fertile and subfertile patients, significantly (p = 0.0009) greater damage was demonstrated in the subfertile than in the fertile group. Furthermore, no significant difference was observed between the two groups with regard to the morphological alteration and structural as well as functional damage of the sperm membrane. In conclusion, the freeze-thawing procedure significantly affects chromatin structure and sperm morphology, especially in the head and the tail regions, and this may explain the lower fertilization rate and IVF/ICSI outcome when frozen-thawed spermatozoa are used. In addition, this study demonstrates that chromatin condensation is a sensitive parameter for the evaluation of cryodamage of semen samples from fertile and subfertile patients, though subfertile patients with very poor semen characteristics have yet to be studied. It is therefore recommended that chromatin condensation be used as an additional parameter for the assessment of sperm quality after freeze-thawing.

Influence of p53 zygosity on select sperm parameters of the mouse

The influence of p53 gene zygosity on select parameters of mouse sperm was investigated by employing knock-out animal models. The background incidence of sperm shape abnormalities, total sperm count, and DNA double strand breaks were determined in p53 nullizygous (-/-) and heterozygous (+/-) mice and these estimates were compared to the corresponding measures in p53 wild-type (+/+) and the inbred C57Bl6 mouse strains. There were no qualitative differences in the incidence of sperm shape abnormalities and sperm counts regardless of p53 zygosity. However, the number of DNA double strand breaks, as measured by the comet assay, were significantly lower in the p53 knock-out mice. This apparent decrease was interpreted to be the result of a possible change in DNA-protein and/or DNA-DNA cross-linking in the germ cells of the knock-out mice. These data show that there is no evidence of increased incidence of gross alterations in spermatogenesis (no significant loss in sperm production nor any increase in the proportion of abnormal sperm produced) in knock-out mice deficient or absent in p53 protein; however, there appear to be changes at the genomic level where the degree of cross-linking was apparently elevated in DNA from p53 nullizygous and heterozygous mice.

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.

Flavonoids modulate comet assay responses to food mutagens in human lymphocytes and sperm

The flavonoids, silymarin, myricetin, quercitin, kaempferol, rutin and kaempferol-3-rutinoside have been examined in combination with the food mutagens, 3-amino-1-methyl-5H-pyrido (4,3-b)indole (Trp-P-2) and 2-amino-3-methylimidazo-(4,5-f) quinoline (IQ), in the Comet assay in human lymphocytes from donor A and human sperm from donor B. These compounds alone have been shown to produce positive responses in the Comet assay, as have the food mutagens. However, in combination with the food mutagens, the flavonoids produced antigenotoxic effects since DNA damage was reduced in the Comet assay in lymphocytes and sperm. The assays were performed in the absence of metabolic activation, since when quercetin and kaempferol were examined in blood with metabolic activation, there was little or no difference in response to that obtained in its absence. In the blood, there was an exacerbation or synergy of response at the lowest doses of the flavonoids. In the sperm, with silymarin, myricetin and quercitin, antigenotoxic effects only were observed, but with kaempferol, in general, there were no protective effects. The food mutagen, 2-amino-1-methyl-6-phenylimadazo (4,5-b)pyridine (PhIP), was also examined in addition to Trp-P-2 and IQ in combination with silymarin and myricetin in donors A and C in human lymphocytes only. Similar exacerbation of effects were found at low doses of these flavonoids with antigenotoxic effects at high doses. This was confirmed in the Ames test. There were slightly different profiles in lymphocytes and sperm, but antigenotoxic effects were observed over a similar dose range. This would suggest that effects occur in somatic and germ cells on a one-to-one ratio. These results have implications for man in terms of risk assessment and in the modulation of isolated food constituents.

The enzymatic activity of Cu/Zn superoxide dismutase does not fluctuate in mouse spermatogenic cells despite mRNA changes

In the mammalian testis, multiple mRNAs encoding the copper zinc superoxide dismutase (SOD-1) are expressed in postmeiotic male germ cells. Here we relate SOD-1 mRNA levels to SOD-1 protein and enzyme activity levels in mouse spermatogenic cells. Although the sizes and relative amounts of the multiple SOD-1 mRNAs vary as male germ cells enter meiosis and proceed into the postmeiotic stages of spermatogenesis, the amount of SOD-1 protein and enzyme activity does not fluctuate significantly, suggesting a precise control of SOD-1 activity in male germ cells.

Two potential clinical applications of the alkaline single-cell gel electrophoresis assay: (1). Human bladder washings and transitional cell carcinoma of the bladder; and (2). Human sperm and male infertility

Part 1: The alkaline single-cell gel electrophoresis (comet) assay was used to analyse the integrity and DNA content of exfoliated cells extracted from bladder washing specimens from 9 transitional cell carcinoma patients and 15 control patients. DNA damage, as expressed by % tail DNA and tail moment values, was observed to occur in cells from both control and bladder cancer samples. The extent of the damage was, however, found to be significantly greater in the cancer group than in the control group. Comet optical density values were also recorded for each cell analysed in the comet assay and although differences observed between tumour grades were not found to be statistically significant, the mean comet optical density value was observed to be greater in the cancer group than in the control population studied. These preliminary results suggest that the comet assay may have potential as a diagnostic tool and as a prognostic indicator in transitional cell carcinoma. Part 2: Baseline DNA damage in sperm cells from 13 normozoospermic fertile males, 17 normozoospermic infertile males and 11 asthenozoospermic infertile males were compared using a modified alkaline comet assay technique. No significant difference in the level of baseline DNA damage was observed between the 3 categories of sperm studied; however the untreated sperm cells were observed to display approximately 20% tail DNA. This is notably higher than the background DNA damage observed in somatic cells where the % tail DNA is normally less than 5%. Sperm from the 3 groups of men studied were also compared for sensitivity to DNA breakage, using the modified alkaline comet assay, following X-ray irradiations (5, 10 and 30 Gy) and hydrogen peroxide treatments (40, 100 and 200 microM). Significant levels of X-ray-induced damage were found relative to untreated control sperm in the two infertile groups following 30 Gy irradiation. Significant damage in hydrogen peroxide-treated sperm was observed in sperm from fertile samples, at 200 microM and in infertile samples at 100- and 200-microM doses relative to controls. These results therefore indicate that fertile sperm samples are more resistant to X-ray- and hydrogen peroxide-induced DNA breakage than infertile samples. Further studies involving greater numbers of individuals are currently in progress to confirm these findings.

Translation of a testis-specific Cu/Zn superoxide dismutase (SOD-1) mRNA is regulated by a 65-kilodalton protein which binds to its 5' untranslated region

Mouse testes contain two distinct superoxide dismutase (SOD-1) transcripts which differ by 114 nucleotides in their 5' untranslated regions (UTRs) (W. Gu, C. Morales, and N. B. Hecht, J. Biol. Chem. 270:236-243, 1995). The shorter SOD-1 mRNA, a somatic type SOD-I mRNA (SSOD-1), is ubiquitously expressed in all somatic tissues as well as in testes. The larger SOD-1 mRNA, a testis-specific SOD-1 mRNA (TSOD-1), derived from an alternative upstream start site, is transcribed solely in postmeiotic germ cells and is translationally regulated during spermiogenesis. Since the two mRNAs have identical nucleotides except that TSOD-1 has an additional sequence at its 5' terminus, we have proposed that the extra 5' UTR sequence may be involved in the translational control of the TSOD-1 mRNA during spermiogenesis. Here we show that, when assayed in a cell-free system, TSOD-1 is translated only slightly less efficiently than SSOD-1. RNA gel retardation and UV cross-linking assays reveal that a testicular cytoplasmic protein (Cu/Zn superoxide dismutase RNA-binding protein [SOD-RBP]) of about 65 kDa specifically binds to the extended 5' UTR of TSOD-1. After purification of SOD-RBP by RNA affinity chromatography, we demonstrate that SOD-RBP can repress the in vitro translation of TSOD-1 mRNA but not SSOD-1 mRNA or cotranslated luciferase mRNA. We conclude that SOD-RBP serves as a repressor in the translation of TSOD-1 mRNA during spermiogenesis and thereby fine-tunes the level of Cu/Zn superoxide dismutase produced in maturing germ cells.

Inhibitory effects of paracetamol on DNA repair in mammalian cells

Paracetamol blocks DNA replication by inhibiting deoxyribonucleotide (dNTP) synthesis and may therefore also interfere with DNA repair. In the present work various mammalian cell types were treated with genotoxic agents and allowed to repair in the presence or absence of paracetamol. Alkaline elution was used to assay DNA single-strand breaks plus alkali-labile sites (= SSBs). Resting human mononuclear blood cells (MNC) exposed to 4-nitroquinoline N-oxide (NQO, 3 microM) plus 0.3 mM paracetamol contained twice as many DNA SSBs compared to MNC exposed to NQO alone, and the level of SSBs decreased more slowly during repair in the presence of paracetamol. Deoxyribonucleosides reversed the effects of paracetamol. SSBs induced by MMS or X-rays (2.6 Gy) were not increased by paracetamol. Resting and growth-stimulated MNC, HL-60 cells, rat hepatocytes and human fibroblasts exposed to UV-C (3-12 J/m2) showed varying levels of transient SSBs formed during repair but these were consistently higher in the presence of paracetamol (0.3-1 mM). In rat testicular cells SSBs were induced by NQO and the levels were further increased in the presence of paracetamol, whereas after UV almost no SSBs were detected during repair. The cell-type specific levels of transient SSBs after UV did not correlate with the rate of incision of DNA lesions, measured as the rate of SSB accumulation in the presence of repair inhibitors Ara C plus hydroxyurea. Transient SSBs were present in resting MNC for at least 24 h after UV and paracetamol increased these breaks 4-fold however the overall rate of removal of excisable photodamage during repair did not appear to be reduced by the presence of paracetamol. The present data indicate that paracetamol interferes with nucleotide excision repair in several mammalian cell types. This constitutes a mechanism by which paracetamol may contribute to genotoxicity in humans.

Antioxidant system in rat testicular cells

The activity of the enzymes involved in the antioxidant defence--superoxide dismutase (SOD), glutathione peroxidase (GPx), reductase (GR), S-transferase (GST)--as well as the glutathione (GSH) levels were measured in different rat testicular cell populations. A differential distribution of these components among testicular cell types was clearly observed. Sertoli and peritubular cells had elevated SOD and GSH-dependent enzyme activities associated with a high GSH content. Compared with the somatic cells, pachytene spermatocytes (PS) and round spermatids (RS) presented a different antioxidant system characterized by higher SOD activity and GSH content associated with very low GSH-dependent enzyme activity. Spermatozoa exhibited the same enzymatic system as PS and RS but were devoid of GSH. Interstitial tissue displayed high GSH content, moderate SOD and GSH-related enzyme activity except for GPx which was very elevated. It is concluded that the different categories of testicular cells probably display a highly variable susceptibility to oxidative stress.

Effect of IR laser radiation on germ cell DNA content after one cycle of the seminiferous epithelium

The effect of IR laser radiation on rat germ cells was investigated by cytophotometric quantification of the nuclear DNA content after a 15-day resting period. Two different doses of radiation energy were applied: 28.05 J/cm2 and 46.80 J/cm2. Both doses were found to increase the percentages of both spermatogonia with a 4c DNA content and primary spermatocytes with a > 4c DNA content. The elongating and elongated spermatids had a c DNA nuclear content, except for a small proportion (5%) of elongating cells that displayed a 2c DNA content at 28.05 J/cm2. Results revealed an increase in the germ cell DNA content after one cycle of the seminiferous epithelium after in vivo exposure to IR laser light. The laser sensitivity of the germ cells appeared to be related to their stage of differentiation and to the radiation energy applied, and the spermatogonia were the most sensitive. In all cases the lowest dosage induced the highest alteration.

Induction and repair of DNA single-strand breaks and DNA base damage at different cellular stages of spermatogenesis of the hamster upon in vitro exposure to ionizing radiation

Alkaline elution has been used for quantitative detection of DNA damage caused by ionizing radiation in unlabeled somatic and germ cells. Both the induction and subsequent repair have been studied for two classes of DNA damage, viz. single-strand breaks (SSB), and base damage (BD) recognized by the gamma-endonuclease activity in a cell-free extract of Micrococcus luteus bacteria. The high sensitivity of the assay permitted the measurement of induction and repair of SSB and BD after in vitro exposure of hamster germ cells in different cellular stages of spermatogenesis (spermatocytes, round and elongated spermatids), and of bone-marrow cells, to biologically relevant doses (0-8 Gy) of 60Co gamma-rays. A dose-dependent increase was observed for both types of lesions, which was similar for most cell types. The elongated spermatids, however, showed a lower induction frequency of SSB (and perhaps BD). Spermatocytes, round spermatids and bone-marrow cells had normal, fast repair of the SSB when compared with the repair reported for cultured rodent cells and human lymphocytes. In contrast, the elongated spermatids showed hardly any SSB repair. The initial rate of repair of BD in spermatocytes and bone-marrow cells was in the same range as that for SSB, but only 60-70% of the initial BD was repaired within 1 h, whereas after that period no SSB were detectable. The round spermatids hardly repaired any BD within the first hour after irradiation, but after 7 h only a few BD could be detected. In elongated spermatids repair of BD could not be measured due to a high background level of this type of damage.

Selective aflatoxin B1-induced sister chromatid exchanges and cytotoxicity in differentiating B and T lymphocytes in vivo

The purpose of this study was to assess the genotoxic and cytotoxic effects of the fungal metabolite aflatoxin B1 (AfB1) on the developing immune system of the chick embryo, a model in vivo system. Of particular interest was the assessment of AfB1-mediated selective toxicity toward developing B lymphocytes as compared to T lymphocytes. In vivo bromodeoxyuridine (BrdU) labelling of DNA was used to detect the induction of sister chromatid exchanges (SCE) in lymphocytes and to assess the progression of these cells through successive cell cycles. Cytotoxicity was also assessed by studying the entrance and maintenance of cells in mitosis (mitotic index). Graded doses of AfB1 (1.09-17.4 micrograms/g embryo) were applied to chick embryos at 18 days of incubation (DI). Embryos also received two doses of BrdU at 3 mg/200 microliters (3 hr apart) to provide continuous labelling of B and T lymphocyte replicating DNA. B and T lymphocytes were harvested 20 hr post-AfB1/BrdU exposure from the bursa and thymus, respectively, and were processed for cytogenetic analyses. AfB1 induced dose-related increases in SCE in B lymphocytes; this induction was 6- to 8-fold that of controls at the higher doses tested. AfB1-mediated induction of SCE in T cells was just 2-fold that of controls at the highest dose tested. AfB1 reduced the progression of B cells and to a lesser extent T cells through successive rounds of replication. Furthermore, AfB1 dramatically reduced the mitotic index of B cells but not of T cells. These data indicate both selective genotoxicity and cytotoxicity of AfB1 toward B cells in the late stage embryo.

Increased sensitivity of damaged DNA to digestion with nuclease S1 as assessed in single cells by flow cytometry

DNA sensitivity to digestion with nuclease S1 was investigated in cells irradiated with gamma rays, or treated with the antitumor drug adriamycin (Adr). The nuclease-resistant DNA fraction was determined by propidium iodide staining. Treated cells were found to be more sensitive to nuclease digestion than the undamaged controls. Gamma ray-induced strand breaks were detectable at doses up to 10 Gy; an increase in the reaction temperature, from 37 degrees to 63 degrees C, was necessary in order to detect higher levels of damage. Nuclease S1 sensitivity in Adr-treated cells showed a single-peak, concentration-dependent relationship, in agreement with the known self-inhibitory effect exerted by high drug doses. Determination of DNA digestion could be performed in combination with other cellular parameters (e.g., protein content). Detection of drug-resistant cells in a heterogeneous population of small-cell lung carcinoma was achieved on the basis of the different sensitivity of the cells to enzymatic digestion. These results indicate that nuclease S1 may be a useful probe for studying in single cells DNA alterations induced by drugs or radiation.

Ascorbic acid protects against endogenous oxidative DNA damage in human sperm

Damage to the DNA of germ cells can lead to mutation, which may result in birth defects, genetic diseases, and cancer. The very high endogenous rate of oxidative DNA damage and the importance of dietary ascorbic acid (AA) in preventing this damage has prompted an examination of these factors in human sperm DNA. The oxidized nucleoside 8-hydroxy-2'-deoxyguanosine (8-oxo-7,8-dihydro-2'-deoxyguanosine; oxo8dG), 1 of approximately 20 major products of oxidative damage to DNA, was measured in DNA isolated from human sperm provided by healthy subjects and compared to the seminal fluid AA levels. This relationship was studied in two groups. In a group of 24 free-living individuals 20-50 years old high levels of oxo8dG were correlated with low seminal plasma AA. The endogenous level of oxo8dG in this group was 13 fmol per microgram of DNA or approximately 25,000 adducts per sperm cell. The second group of individuals was maintained on a controlled diet that varied only in AA content. When dietary AA was decreased from 250 to 5 mg/day, the seminal fluid AA decreased by half and the level of oxo8dG in sperm DNA increased 91%. Repletion of dietary AA for 28 days (from 5 mg/day to 250 or 60 mg/day) caused a doubling in seminal fluid AA and reduced oxo8dG by 36%. These results indicate that dietary AA protects human sperm from endogenous oxidative DNA damage that could affect sperm quality and increase risk of genetic defects, particularly in populations with low AA such as smokers.