DNA fragmentation of spermatozoa and assisted reproduction technology

Paternal effects on cell division in the preimplantation embryo

Cell divisions in the human preimplantation embryo can be compromised by deficiencies in sperm nuclear genome or sperm-derived developmentally relevant cytoplasmic factors, oocyte activating substance and centriole. Sperm nuclear deficiencies are usually not detected before the 8-cell stage of embryo development, when a major expression of sperm-derived genes has begun. Sperm cytoplasmic deficiencies can be detected as early as the 1-cell zygote and then throughout the preimplantation development. The terms 'late paternal effect' and 'early paternal effect' have been suggested to denote these two pathological conditions. The late paternal effect is associated with an increased incidence of sperm DNA fragmentation. No association with sperm DNA damage has been found for the early paternal effect. The diagnosis of the late paternal effect is thus based on the examination of sperm DNA integrity, which should be performed in cases of repeated assisted reproduction failure even if morphologically normal embryos result from fertilization with the patient's spermatozoa. The only element leading to the diagnosis of the early paternal effect is poor zygote and embryo morphology and low cleavage speed. The absence of increased sperm DNA damage does not exclude the presence of this pathology. ICSI with testicular spermatozoa has recently been shown to be an efficient treatment for the late paternal effect. The use of oral antioxidant treatment in this indication has also given promising results.

Seminal elastase-inhibitor complex, a marker of genital tract inflammation, and negative IVF outcome measures: role for a silent inflammation?

There is no consensus on whether and how male genital tract inflammation affects sperm fertilizing potential. The aims of this prospective study were to evaluate the elastase-inhibitor complex in seminal plasma (s-EI) level, a marker of male genital tract inflammation, in men undergoing in vitro fertilization (IVF) having no clinical signs of inflammation, and its association with semen characteristics, and the predictive role of s-EI for the outcome of IVF in terms of fertilization, embryo development to the blastocyst stage and pregnancy. The study involved 104 male partners of infertile couples with normal spermiogram undergoing IVF. On the day of oocyte retrieval, spermiogram and s-EI assessment using homogeneous immunoassay were performed. The outcome of IVF according to the s-EI level was assessed in 85 cycles with two or more oocytes. In 67 cycles embryos were cultured to the blastocyst stage. Spearman's and Pearson's correlation tests, chi-square test, and multiple linear and logistic regression analyses were used for statistical evaluation. Increased s-EI level (> or =250 microg/L) was detected in semen of 32% of men, and in 24% of men without leucocytospermia. We found an association between the s-EI level and semen leucocytes (r = 0.49, p = 0.004) but not with classical sperm characteristics. No correlation between the s-EI level and fertilization was observed. Increased s-EI levels were associated with a poorer blastocyst development rate (p = 0.03) and a higher number of arrested embryos (p = 0.04). Extended embryo culture to the blastocyst stage shows a negative effect of clinically silent male genital tract inflammation on embryo developmental potential.

Efficient treatment of infertility due to sperm DNA damage by ICSI with testicular spermatozoa

BACKGROUND

Sperm DNA damage (fragmentation) is a recently discovered cause of male infertility for which no efficient treatment has yet been found. Previous findings have suggested that clinically relevant sperm DNA damage may occur at the post-testicular level. This study was undertaken to assess the clinical usefulness of ICSI with testicular spermatozoa in this indication.

METHODS

The percentage of spermatozoa with fragmented DNA, assessed by terminal deoxyribonucleotidyl transferase-mediated dUTP nick-end labelling assay, and ICSI outcomes were compared in two sequential attempts performed, respectively, with ejaculated and testicular spermatozoa in 18 men with increased sperm DNA fragmentation.

RESULTS

The incidence of DNA fragmentation was markedly lower in testicular spermatozoa as compared with ejaculated spermatozoa. No differences in fertilization and cleavage rates and in embryo morphological grade were found between the ICSI attempts performed with ejaculated and with testicular spermatozoa. However, eight ongoing clinical pregnancies (four singleton and four twin) were achieved by ICSI with testicular spermatozoa (44.4% pregnancy rate; 20.7% implantation rate), whereas ICSI with ejaculated spermatozoa led to only one pregnancy which was spontaneously aborted.

CONCLUSIONS

These data show that ICSI with testicular spermatozoa provides the first efficient assisted reproduction treatment option for men with high levels of sperm DNA damage.

Nicotinic infertility: assessing DNA and plasma membrane integrity of human spermatozoa

Infertility remains a major problem in society, with recent data suggesting its presence in one of four couples. The objective of the present study was to evaluate the impact of nicotine (0.25, 0.5 and 0.75 mm), as a major component of cigarette smoke, in vitro, on sperm membrane [by spermatocrit and lipoperoxidation (LPO) tests], DNA integrity (by Comet assay), and viability of spermatozoa (by eosin staining) from normozoospermic men. Sperm samples were washed and diluted with phosphate-buffered saline. A drop in spermatocrit values and an increase in thiobarbituric acid-reactive substances/LPO rate was observed with the addition of nicotine, predominantly at a concentration of 0.75 mm, indicating a deleterious effect of nicotine on sperm membrane intactness. There was also a strong negative correlation between LPO rate and percentage viable sperm cell (r = -0.990). Data obtained from Comet assay technique revealed that nicotine could induce double-stranded DNA breaks (11% in 0.75 mm concentration) in the sperm nuclei. The value of r between LPO rate and percentage Comets was found to be +0.976. Taken together, nicotine proved to be a potential oxidant agent in the category of environmental factors to the integrity of sperm plasma membrane and DNA.

Sequence of ejaculation affects the spermatozoon as a carrier and its message

It is a widespread misunderstanding that the human ejaculation produces a homogeneous fluid with constant environment for the spermatozoa. On the contrary, spermatozoa are mainly expelled together with the zinc-rich prostatic fluid in the first ejaculation fractions. In nature, these spermatozoa most likely enter the cervical mucus before any significant contact with the later, sperm hostile fractions takes place. Spermatozoa collected in the laboratory for diagnosis, treatment or research purposes face challenges in the form of light, high oxygen concentration, low carbon dioxide concentration, increased pH, extreme variations in osmolarity, and changed bioavailability of zinc and calcium in the man-made laboratory product called seminal plasma. Possible future implications of these unphysiological conditions are discussed in relation to assisted reproduction and sperm research.

Update on the impact of Chlamydia trachomatis infection on male fertility

With approximately 90 million cases annually, infection with Chlamydia trachomatis is the most prevalent sexually transmitted bacterial disease in the world. Considering that these infections are often asymptomatic and cause major complications like acute pelvic inflammatory disease, ectopic pregnancy, infertility or infant pneumonia, the estimated costs for diagnosis and treatment in the USA amounts to 2.2 million US dollars for each 500 cases. Therefore, there is a high need for correct, quick and cost-effective diagnosis and treatment of this urogenital tract infection. New innovative therapies provide good results with regard to efficacy and patients' compliance. The success rates of treatments are at least 95%. However, the occurrence of antibiotic resistance should not be ignored and new treatment schemes must be developed. The state-of-the-art of diagnosis and treatment of chlamydial infections as well as the pathophysiology is discussed in this review. In conclusion, infections with C. trachomatis is an important public health problem, especially in third world and developing countries, and more socio-economic studies linking secondary prevention of chlamydial infections, infertility and adverse pregnancy outcome are needed to understand more of its aetiology. In addition, diagnosis and treatment should be improved. Data in men revealed that past infections but not present infections are more related to male infertility. There is still controversial results. In future studies, function of the seminal vesicles and evaluation of the antioxidant capacity should be taken into account when role of C. trachomatis infection on male fertility is assessed.

Chemiluminescence technique for measuring reactive oxygen species

Accurate assessment of reactive oxygen species (ROS) concentrations may help in the diagnosis of infertility. The chemiluminescence technique, which uses a luminometer to measure ROS, is a common method of assessment. A better understanding of the chemiluminescence technique will allow its proper application in reproductive medicine. A wide range of luminometers are available in the market, and laboratories should select the instruments that suit their individual needs.

Founders' Lecture. Human spermatozoa: fruits of creation, seeds of doubt

Deoxyribonucleic acid damage in the male germline is associated with defective fertilisation, impaired embryonic development, reduced implantation, abortion and childhood disease. Oxidative stress and the retention of excess residual cytoplasm by the spermatozoa are frequently associated with the induction of such damage. The redox cycling of xenobiotics by oxido-reductases in the germline, the patient’s age, the incidence of genital tract infections and Sertoli cell dysfunction are all possible contributors to DNA damage in germ cells. Collateral peroxidation of unsaturated fatty acids in the sperm plasma membrane generally ensures that spermatozoa experiencing severe oxidative DNA damage cannot participate in the process of fertilisation. The adaptive termination of pregnancy through the selective vulnerability of genes involved in placentation may also help prevent the vertical transmission of damaged DNA. However, the ultimate safeguard against this form of damage will be to understand the biochemical basis of oxidative stress in human spermatozoa, so that the underlying causative mechanisms can be addressed in a logical manner.

Chromatin condensation and DNA damage of human epididymal spermatozoa in obstructive azoospermia

Obstructive azoospermia (OA) includes patients with different aetiologies of obstruction such as congenital bilateral absence of vas deferens (CBAVD), post-vasectomy/failed vaso-vasostomy, or unknown (idiopathic). The frequency of DNA-damaged spermatozoa and abnormal chromatin condensation in epididymal spermatozoa of OA patients was investigated for the different aetiology subgroups. DNA damage in caput epididymis spermatozoa was assessed with the TdT-UTP nick-end labelling (TUNEL) assay and chromatin condensation status was measured with chromomycin A3 (CMA3) stain (n = 60 patients). All epididymal sperm samples showed high levels of TUNEL positivity (mean and SD, 43 +/- 17%). CMA3 rates showed large variation within the samples (mean and SD, 53 +/- 21%, range 7-97%); however, a significant difference in chromatin condensation was found between the different aetiologies of obstruction. The highest percentage of CMA3 positivity was found in the CBAVD and idiopathic groups (60 +/- 17 and 65 +/- 18% respectively) compared with the post-vasectomy samples (37 +/- 17%) or ejaculated spermatozoa from normozoospermic males (29 +/- 12%). In conclusion, despite the normal testicular histology in OA men, chromatin condensation differed between OA patients. The physiological heterogeneity found in chromatin condensation between patient subgroups is probably influenced by the aetiology of the obstruction.

Assessment of DNA fragmentation and aneuploidy on poor quality human embryos

In human assisted reproduction, low embryo quality due to retarded growth and abnormal cellular morphology results in fewer embryos suitable for transfer. This study aimed to assess the extent of DNA fragmentation and aneuploidy in spare slow growing or arrested human embryos. In 19 assisted reproduction cycles, a total of 57 embryos unsuitable for embryo transfer were used for simultaneous apoptosis and aneuploidy assessment. Among them, 31 (54.3%) showed DNA fragmentation by terminal deoxynucleotidyl transferase-mediated dUDP nick-end labelling (TUNEL) analysis. Among 26 embryos that were negative for TUNEL, interpretable fluorescence in-situ hybridization (FISH) results were obtained for 25 embryos (96.2%). Sixteen embryos were detected to be chromosomally abnormal (64.0%); three were found to be chaotic, six had complex aneuploidy, six had complete monosomy and one was polyploid. The results show that a high level of DNA fragmentation and aneuploidy are common in embryos with slow growth and/or low quality. More detailed studies are needed to assess the effect of factors such as ovarian stimulation regimens and in-vitro culture conditions. Moreover, application of simultaneous TUNEL and FISH techniques can be informative regarding DNA integrity and aneuploidy.

Sperm preparation for ART

The onset of clinical assisted reproduction, a quarter of a century ago, required the isolation of motile spermatozoa. As the indication of assisted reproduction shifted from mere gynaecological indications to andrological indications during the years, this urged andrological research to understand the physiology of male germ cell better and develop more sophisticated techniques to separate functional spermatozoa from those that are immotile, have poor morphology or are not capable to fertilize oocytes. Initially, starting from simple washing of spermatozoa, separation techniques, based on different principles like migration, filtration or density gradient centrifugation evolved. The most simple and cheapest is the conventional swim-up procedure. A more sophisticated and most gentle migration method is migration-sedimentation. However, its yield is relatively small and the technique is therefore normally only limited to ejaculates with a high number of motile spermatozoa. Recently, however, the method was also successfully used to isolate spermatozoa for intracytoplasmic sperm injection (ICSI). Sperm separation methods that yield a higher number of motile spermatozoa are glass wool filtration or density gradient centrifugation with different media. Since Percoll as a density medium was removed from the market in 1996 for clinical use in the human because of its risk of contamination with endotoxins, other media like IxaPrep, Nycodenz, SilSelect, PureSperm or Isolate were developed in order to replace Percoll. Today, an array of different methods is available and the selection depends on the quality of the ejaculates, which also includes production of reactive oxygen species (ROS) by spermatozoa and leukocytes. Ejaculates with ROS production should not be separated by means of conventional swim-up, as this can severely damage the spermatozoa. In order to protect the male germ cells from the influence of ROS and to stimulate their motility to increase the yield, a number of substances can be added to the ejaculate or the separation medium. Caffeine, pentoxifylline and 2-deoxyadenosine are substances that were used to stimulate motility. Recent approaches to stimulate spermatozoa include bicarbonate, metal chelators or platelet-activating factor (PAF). While the use of PAF already resulted in pregnancies in intrauterine insemination, the suitability of the other substances for the clinical use still needs to be tested. Finally, the isolation of functional spermatozoa from highly viscous ejaculates is a special challenge and can be performed enzymatically to liquefy the ejaculate. The older method, by which the ejaculate is forcefully aspirated through a narrow-gauge needle, should be abandoned as it can severely damage spermatozoa, thus resulting in immotile sperm.

Biochemical markers of sperm function: male fertility and sperm selection for ICSI

The expression of a 70 kDa chaperone protein, HspA2 (formerly called CK-M), has been identified in mature human spermatozoa. The central role of HspA2 has been established, as the expression level of this protein is related to sperm cellular maturity, DNA integrity, chromatin maturity, chromosomal aneuploidy frequency and sperm function, including fertilizing potential. The spermiogenetic events of cytoplasmic extrusion and remodelling of the plasma membrane, which facilitate the formation of zona pellucida binding site(s) in human spermatozoa, are related. Finally, the presence of the hyaluronic acid (HA) receptor on the plasma membrane of mature sperm coupled with the HA-coated slide sperm-binding assay, facilitates the testing of infertile men and the selection of single mature spermatozoa for ICSI. Because mature spermatozoa have no residual cytoplasm, the HA-bound sperm fraction is also enriched in spermatozoa that are normal by the Kruger strict morphology method.