Inter- and intra-tumoral heterogeneity in DNA damage evaluated by comet assay in early breast cancer patients

There are no clinical tools to functionally assess degree of DNA damage in breast cancer. The comet assay is an accepted research tool for assessing DNA damage, however, most cancer studies have assessed lymphocytes as surrogate cells. The aim of this pilot study was to use the comet assay in early breast cancer directly in tumor tissue to compare DNA damage between and within traditionally defined subgroups, and to explore intra-tumoral heterogeneity. Scrapings of tumor and healthy breast tissue were obtained at primary surgery from 104 women. Comet assay was applied to quantitatively assess DNA damage, revealing substantial inter- and intra-subgroup variation. Marked intra-tumoral heterogeneity was evident across all subgroups. The degree of DNA damage for an individual could not be predicted by breast cancer subgroup. Comet assay warrants further study as a potential clinical tool for identification of tumoral DNA damage and ultimately, individualised use of DNA damaging therapy.     

Sperm DNA damage output parameters measured by the alkaline Comet assay and their importance

The alkaline Comet assay has shown high diagnostic value to determine male reproductive health and prognostic ability to predict ART success. Here, spermatozoon was analysed in 47 fertile donors and 238 patients, including 132 couples undergoing ART [semen was collected: Group I – within 3 months of their treatment (n = 79); and Group II – 3 months prior to their treatment (n = 53)]. We introduce four Comet distribution plots (A, B1, B2 and C) by plotting the level of DNA damage (x‐axis) and percentage of comets (y‐axis). Fertile donors had low mean DNA damage, olive tail moment and per cent of spermatozoa with damage and increased type A plots. Comet parameters were associated with clinical pregnancies in Group I. About 66% of couples with type A distribution plot were successful after ART, whereas couples with type B1, B2 and C distribution plots achieved 56%, 44% and 33% pregnancies respectively. The efficiency of the Comet assay was due to complete decondensation process, where the compact sperm nuclear DNA (28.2 ± 0.2 μm³) is decondensed to ~63 μm³ (before lysis) and ~1018 μm³ (after lysis). A combinational analysis of all the Comet output parameters may provide a comprehensive evaluation of patient's reproductive health as these parameters measure different aspects of DNA damage within the spermatozoa.     

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.     

精子DNA损伤与辅助生殖技术

精子DNA损伤与辅助生殖技术(ART)结局密切相关,精子DNA损伤影响到ART中的受精比率、胚细胞发育、妊娠率和子代的健康。同时,精子低温冷冻保存和诸多体外处理技术均能影响精子DNA的完整性。检测精子DNA断裂指标(DFI),采取适当措施获得DNA无损伤或损伤较小的精子,对改善ART结局十分必要。现就精子DNA损伤与ART相关性的研究做一综述。     

Sperm DNA damage and cytokines in varicocele: A case-control study

Varicocele is a vascular disease characterised by the abnormal enlargement of the pampiniform plexus veins and a well-known cause of male infertility. The aim of this study was to investigate the relationship between sperm DNA fragmentation (SDF) and inflammation in the pathogenesis of varicocele. We included 84 varicocele patients and 85 normozoospermic healthy controls, further analysed according to the body mass index, the smoking habit (smokers/non-smokers) and the varicocele severity (low/high grade). Semen parameters, SDF (by TUNEL) and inflammatory cytokines (by Luminex xMAP analysis) were evaluated. Varicocele patients showed significantly reduced semen parameters (volume, total sperm number, progressive motility, normal morphology) and increased SDF. Moreover, we observed a significant reduction of IFN-γ, IL-6, TNF-α and an increase of IL-10. No difference was reported according to the smoking habit, body mass index and varicocele severity. The observed cytokines pathway suggests the establishment of a chronic inflammatory condition, which may contribute to the alteration of semen quality. A thorough knowledge of the cytokine network might contribute to better understanding the link between inflammation and semen quality in varicocele and its impact on reproductive health.     

The neutral comet assay detects double strand DNA damage in selected and unselected human spermatozoa of normospermic donors

The occurrence of DNA breaks in human sperm is of concern to genetic safety in artificial reproduction techniques. Here, we have explored the neutral comet assay (NCA) for evaluating the frequency of spermatozoa with double strand (ds) DNA breaks in normospermic donors. The NCA results into DNA tail formation by fibre extension and by the separation of DNA fragments. Gamma-irradiated native, lysed and lysed plus RNA and protein degraded human sperm nuclei have been used to assess sensitivity and specificity of fragment formation as an indication for ds DNA breaks. At 5 and 10 Gy gamma irradiation, the sensitivity increases in the order: native, lysed, lysed plus RNA and protein degraded. At 10 Gy, a uniform response between donors was obtained. For technical and biological reasons, the NCA underestimates the true incidence of ds DNA breaks by an unknown factor. Semen samples of six healthy normospermic donors were differentiated by swim up and by Percoll density centrifugation, followed by the NCA. In native semen, percentages of sperm nuclei with ds DNA breaks ranged from 15 to 25%. Swim up and selection for high-density sperm nuclei (high Percoll fraction) reduced the frequency of sperm with ds DNA breaks by about one third, whereas an increased frequency was found in the low Percoll fraction. In conclusion, the response to gamma irradiation of DNA fragment formation indicates the NCA to demonstrate ds DNA breaks which is in keeping with theory and experimental results from somatic cells. Ds DNA breaks are a characteristic of the sperm population of normal donors. Current sperm selection procedures reduce the fractions of sperm with ds DNA breaks, yet are not effective in eliminating these cells.     

Sperm DNA damage in men from infertile couples

Aim： To investigate the prevalence of high levels of sperm DNA damage among men from infertile couples with both normal and abnormal standard semen parameters. Methods： A total of 350 men from infertile couples were assessed. Standard semen analysis and sperm chromatin structure assay （SCSA） were carried out. Results： Ninety-seven men （28% of the whole study group） had a DNA fragmentation index （DFI） 〉 20%, and 43 men （12%） had a DFI 〉 30%. In the group of men with abnormal semen parameters （n = 224）, 35% had a DFI 〉 20%, and 16% had a DFI 〉 30%, whereas these numbers were 15% and 5%, respectively, in the group of men with normal semen parameters （n = 126）. Men with low sperm motility and abnormal morphology had significantly higher odds ratios （ORs） for having a DFI 〉 20% （4.0 for motility and 1.9 for morphology） and DFI 〉 30% （6.2 for motility and 2.8 for morphology） compared with men with normal sperm motility and morphology. Conclusion： In almost one-third of unselected men from infertile couples, the DFI exceeded the level of 20% above which, according to previous studies, the in vivo fertility is reduced. A significant proportion of men with otherwise normal semen parameters also had high sperm DNA damage levels. Thus, the SCSA test could add to explaining causes of infertility in cases where semen analysis has not shown any deviation from the norm. We also recommend running the SCSA test to choose the appropriate assisted reproductive technique （ART）.     

精子DNA损伤与不明原因复发性流产的关系

目的:探讨不明原因复发性流产与男方精子DNA损伤的关系。方法:精子DNA断裂损伤检测采用精子染色质扩散试验(sperm chromatin dispersion,SCD),以DNA断裂指数(DNA fragmentation index,DFI)表示。分别测定不明原因复发性流产(试验组,56例)男方与无流产史(对照组,31例)男方精子的DFI。结果:试验组DFI(11.0%～56.9%)高于30%的有21例(37.5%),对照组DFI(10.0%～36.8%)高于30%的有8例(25.8%)。复发性流产组的男方精子DFI均数比对照组精子DFI高(29.4%vs 25.5%),且差异显著(P<0.05)。结论:不明原因复发性流产可能与精子DNA损伤存在一定关系。     

Shortening of alkaline DNA unwinding time does not interfere with detecting DNA damage to mouse and human spermatozoa in the comet assay

The comet assay was performed on mouse and human spermatozoa to examine the effect of alkaline DNA unwinding time. The spermatozoa were treated in vitro with the DNA-damaging agents, methyl methanesulfonate (MMS) or hydrogen peroxide (H₂O₂), and then embedded in agarose gel on glass slides. The slides were immersed in alkaline solution (>pH 13) for 1, 5, 10 and 20 min, and then subjected to the electrophoresis under neutral conditions. In mouse spermatozoa, comet tails seen in solvent controls became brighter and longer as the alkaline DNA unwinding time increased. However, in the MMS-treated mouse spermatozoa, a smaller difference in the damage from that in the solvent control was seen with time within a dose. DNA damage induced by H₂O₂ could also be detected accurately after alkali treatment for 1–20 min. In human spermatozoa, DNA damage induced by MMS and H₂O₂ could be detected in a dose-dependent manner after alkali treatment for 1 min. The ability of the comet assay to detect DNA damage was not adversely affected by the short period (1 min) of the alkaline DNA unwinding time.     

Sperm DNA damage: importance in the era of assisted reproduction

PURPOSE OF REVIEW: With the proliferation of assisted reproductive technologies, there is an increasing awareness of the importance of sperm DNA damage. With the recent advent of in-vitro fertilization/intracytoplasmic sperm injection, we are bypassing the normal natural selection barriers and potentially introducing sperm with damaged DNA. To date, these consequences are still largely unknown. RECENT FINDINGS: Infertile men possess substantially more DNA-damaged sperm than fertile men, and this DNA damage may adversely affect reproductive outcomes. There may be a threshold level of DNA damage beyond which embryo development and subsequent pregnancy are impaired. Protamine deficiency and the effect of reactive oxygen species have been implicated in the etiology of sperm DNA damage. Assays of DNA damage are being used clinically to quantify objectively the degree of DNA damage in the sperm of infertile men in the hope of identifying more accurate ways of gauging fertility potential. SUMMARY: There now exists clinical evidence to show that sperm DNA damage is detrimental to reproductive outcomes. Tests for DNA damage may provide better prognostic information and may allow for better decision-making than standard semen parameters when evaluating the infertile couple. The etiology of the DNA damage and the full extent of the damage on reproductive outcomes need further study.     

Sperm DNA damage and seminal antioxidant activity in subfertile men

Supraphysiological ROS levels can lead to apoptosis, lipid peroxidation, and DNA and protein damage. This pilot study aimed to investigate the sperm oxidative damage in subfertile men, to describe the relationship between the antioxidant system and ROS. Sixty-four semen samples were categorised according to the evaluated routine parameters (WHO, WHO laboratory manual for the examination and processing of human semen, 2010). Results were cross-referenced with the DNA damage [Comet (n = 53) and TUNEL (n = 49) assays], antioxidant enzyme activity [SOD (n = 51), CAT (n = 48) and GST (n = 48)], and content of total thiols (n = 36), lipid hydroperoxides (n = 35) and MDA (n = 31). Compared to pathospermic samples, normozoospermic presented 40%–45% fewer spermatozoa with fragmented DNA, 19% fewer hydroperoxides, and slightly higher total thiols and MDA levels. Asthenozoospermic/asthenoteratozoospermic samples had the lowest GST activity. SOD and CAT showed a similar trend. Our results evidenced significant positive correlations between DNA damage and immotile spermatozoa; SOD and CAT, GST and total thiols; CAT and GST; total thiols and sperm concentration; and MDA levels and head/midpiece abnormalities and hydroperoxides. This work contributes to the existing body of knowledge by showing that the oxidative status correlates with the classic sperm analysis parameters. Oxidative stress and DNA damage evaluation might be a valuable diagnostic and prognostic tool in cases of idiopathic male subfertility.     

Sperm DNA damage and its clinical relevance in assessing reproductive outcome

The routine examination of semen, which assesses sperm concentration, percentage motility and morphology,does not identify subtle defects in sperm chromatin architecture. The focus on the genomic integrity of the male gamete has intensified recently due to the growing concern that genetic diseases may be transmitted via assisted reproductive techniques (ART). Accordingly, the intent of this review is to describe the details of the informationpertaining to mitochondfial/nuclear sperm DNA damage with an emphasis on its clinical significance and its relationship with male infertility. Assessment of sperm DNA damage appears to be a potential tool for evaluating semen samples prior to their use in ART. Testing DNA integrity may help select spermatozoa with intact DNA or with the least amount of DNA damage for use in assisted conception. In turn, this may alleviate the financial, social and emotional problems associated with failed ART attempts.     

高原环境对青年男性精子DNA损伤的影响

目的:探讨长期高原作业是否能造成精子DNA的损伤。方法:以53例驻守低海拔地区的部队官兵为对照组,51例高海拔地区的部队官兵为观察组进行调查和对照研究,通过单细胞凝胶电泳技术和染色质扩散实验,检测精子DNA的损伤情况。结果:观察组在进入高原前的各项指标与对照组之间均无明显差异(P>0.05)。观察组的总彗星细胞发生率、各级彗星细胞发生率(G1、G2、G3)和DNA异常精子百分率在进入高原地区前分别为:(5.56±3.98)%、(3.72±1.85)%、(1.57±1.07)%、(0.27±0.34)%和(16.59±12.07)%,进入高原地区半年后均有升高,分别为:(11.15±8.59)%、(5.97±3.26)%、(3.83±2.13)%、(1.35±1.53)%和(22.03±15.33)%,与半年前相比差异显著(P<0.05);二级彗星细胞发生率(G2)和DNA异常精子百分率在1年后有所下降,分别为(3.32±1.83)%和(20.54±15.52)%,但仍比进入高原地区前有明显升高(P<0.05)。结论:长期在高原地区作业可引起精子DNA损伤,但对生育潜能的影响有待进一步研究。加强高原地区作业人员的男性生殖健康预防保健工作仍然十分重要。     

Sperm DNA damage is associated with assisted reproductive technology pregnancy

The literature suggests an association between sperm DNA damage and assisted reproductive technology (ART) outcomes. However, previous studies involved the transfer of multiple embryos, which has complicated the interpretation of the results. The aim of this study was to determine the relationship between the levels of sperm DNA damage and fertilization rate, embryo development as well as pregnancy outcome, following single embryo transfer. Patients (n = 113) undergoing in vitro fertilization (IVF) (n = 45) and intra-cytoplasmic sperm injection (ICSI) (n = 68) were assessed for their levels of sperm DNA damage in the sample used for insemination. DNA damage was determined using terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate-nick end labelling (TUNEL). The relationship between DNA damage and outcomes were assessed using regression analysis. Overall data showed no association between sperm DNA damage and fertilization rate, or embryo development in vitro. However, when IVF was the insemination method, there was a significant negative correlation between fertilization rates and sperm DNA damage (p < 0.05). When ICSI was the insemination technique, low sperm DNA damage was associated with successful pregnancy (37.8 +/- 5.7% DNA damaged sperm) compared with failed implantation (52.9 +/- 3.9% DNA damaged sperm, p < 0.05). Our results suggest that sperm DNA damage as measured by the TUNEL assay may provide an indicator for patients with poor fertilization rates and/or those unable to achieve pregnancy following ART treatment.     

精子DNA损伤、核蛋白组型转换与顶体酶活性及精液参数的相关性分析

目的:探讨精子DNA损伤、精子核蛋白组型转换与顶体酶活性及精液参数的相关性。方法:收集535例精液标本,采用精子染色质扩散(sperm chromatin dispersion,SCD)检测精子DNA损伤,并与精子核蛋白组型转换、顶体酶活性和WHO手册(第4版)精液参数进行相关性分析。结果:精子DNA损伤与精子核蛋白组型转换、顶体酶活性、精子浓度及前向运动精子这些指标之间比较均具有显著性差异(P<0.01);精子DNA损伤与年龄、核蛋白组型转换、精子浓度和D级精子比例之间呈显著正相关(P<0.01或P<0.05),而与顶体酶活性呈显著负相关(P<0.001),多元逐步回归分析显示年龄、精子浓度、D级精子比例、核蛋白组型转换及顶体酶活性是5个独立的相关变量。精子核蛋白组型转换、顶体酶活性、精子密度和前向运动精子这4个指标的异常率在精子DNA异常组(DFI≥30%)中均显著的高于正常组(DFI<30%)。结论:精子DNA损伤与精子核蛋白组型转换、顶体酶活性及WHO(第4版)精液各参数之间存在密切的联系,可能是评价精子质量的另一项重要的指标。     

Sperm preparation: state-of-the-art--physiological aspects and application of advanced sperm preparation methods

For assisted reproduction technologies (ART), numerous techniques were developed to isolate spermatozoa capable of fertilizing oocytes. While early methodologies only focused on isolating viable, motile spermatozoa, with progress of ART, particularly intracytoplasmic sperm injection (ICSI), it became clear that these parameters are insufficient for the identification of the most suitable spermatozoon for fertilization. Conventional sperm preparation techniques, namely, swim-up, density gradient centrifugation and glass wool filtration, are not efficient enough to produce sperm populations free of DNA damage, because these techniques are not physiological and not modeled on the stringent sperm selection processes taking place in the female genital tract. These processes only allow one male germ cell out of tens of millions to fuse with the oocyte. Sites of sperm selection in the female genital tract are the cervix, uterus, uterotubal junction, oviduct, cumulus oophorus and the zona pellucida. Newer strategies of sperm preparation are founded on: (i) morphological assessment by means of 'motile sperm organelle morphological examination (MSOME)'; (ii) electrical charge; and (iii) molecular binding characteristics of the sperm cell. Whereas separation methods based on electrical charge take advantage of the sperm's adherence to a test tube surface or separate in an electrophoresis, molecular binding techniques use Annexin V or hyaluronic acid (HA) as substrates. Techniques in this category are magnet-activated cell sorting, Annexin V-activated glass wool filtration, flow cytometry and picked spermatozoa for ICSI (PICSI) from HA-coated dishes and HA-containing media. Future developments may include Raman microspectrometry, confocal light absorption and scattering spectroscopic microscopy and polarization microscopy.     

An immunochemical assay to detect DNA damage in bovine sperm

An immunochemical assay has been developed to detect oxidative damage in bovine sperm DNA. Sperm DNA contains a large amount of oxidative damage as a result of exposure to exogenous agents, but damage also can caused by normal metabolic processes and the absence of DNA repair in the later stages of spermatogenesis. A freeze-thaw procedure performed on extended bovine sperm in straws did not induce additional DNA damage immediately after thawing compared with nonfrozen extended sperm. The data suggest that the amount of oxidative damage correlated to the percentage of artificially inseminated cows returning to service within 56 days postinsemination, because a number of sires with high sperm concentrations had a large variation in fertility after artificial insemination. These observations have led to the conclusion that by measuring DNA damage in thawed sperm, one might predict the fertility of bulls with high semen concentration.     

Sperm motility and DNA integrity affected by different g‐forces in the preparation of sperm in urine specimens

Retrograde ejaculation, a common type of anejaculation, is attributable to many causes, some of which can be treated with medication and some of which cannot. For infertility treatment, sperm must be collected from the urine of the patients. Our study attempts to ascertain the effects of different g‐forces on sperm motility, morphology and DNA integrity in sperm preparation by the Sil‐Select? density gradient method of isolating sperm from urine specimens. Forty‐seven semen samples with normal semen analyses according to World Health Organisation (WHO) 1999 criteria were included in this study. Semen samples of 1 ml were mixed with 20 ml alkalinised normal urine and then divided equally into tubes A and B. The two samples were prepared by the Sil‐Select? density gradient centrifugation method at 350 g (tube A) and at 700 g (tube B). Total motile sperm after centrifugation at 700 g was significantly higher than after centrifugation at 350 g [6.7 (0.4–23.0) million versus 3.1 (0.1–13.7) million] (P < 0.001). There was no significant difference between the either the percentage of sperm with normal morphology or with DNA damage between centrifugation at 350 g and 700 g (P > 0.05), although centrifugation at 700 g achieves a higher number of total motile sperm compared with Sil‐Select? sperm preparation at 350 g centrifugation.