DNA damage of human spermatozoa in assisted reproduction: origins, diagnosis, impacts and safety

Rapid rates of sperm DNA damage after activation in tench (Tinca tinca: Teleostei, Cyprinidae) measured using a sperm chromatin dispersion test

Spermatozoal haplotypic DNA is prone to damage, leading to male fertility problems. So far, the assessment of sperm DNA breakage has been challenging because protamines render the nuclear chromatin highly compacted. Here, we report the application of a new test to quantify DNA fragmentation in spermatozoa of an externally fertilizing teleost fish. The sperm chromatin dispersion (SCD) test uses a species-specific lysing solution to generate controlled protein depletion that, followed by DNA-specific fluorescent labelling, allows an easy morphological discrimination between nuclei affected by DNA damage. Using tench (Tinca tinca) as our model, we first trialled the test against established, but more technically demanding, assays employing in situ nick translation (ISNT) and the comet assay. The SCD test showed high concordance with ISNT, comet assay measures and a chromatin-swelling test, confirming the application of this straightforward SCD technique to various aspects of reproductive biology. Second, we examined between-male variation in DNA damage, and measured changes through time following spermatozoal activation. Between-male variation in the basal levels of average DNA damage ranged from 0 to 20% of sperm showing damage, and all showed increases in DNA fragmentation through time (0-60 min). The rates of DNA damage increase are the fastest so far recorded in sperm for a living organism, and may relate to the external fertilization mode. Our findings have relevance for broodstock selection and optimizing IVF protocols routinely used in modern aquaculture.

Physiologic and pathologic levels of reactive oxygen species in neat semen of infertile men

OBJECTIVE

To define physiologic levels of reactive oxygen species in infertile men and establish a cutoff value of reactive oxygen species level in neat semen with a high sensitivity and specificity to differentiate infertile men from fertile donors (controls).

DESIGN

Reactive oxygen species levels were measured in the neat semen samples (n = 51) from fertile donors and infertile patients (n = 54).

SETTING

Reproductive research laboratory at a tertiary care hospital.

PATIENT(S)

Infertile patients from male infertility clinic.

INTERVENTION(S)

Reactive oxygen species measurement in neat semen sample using luminol-based chemiluminescence method, receiver operating characteristic curves.

MAIN OUTCOME MEASURE(S)

Seminal reactive oxygen species levels, cutoff value, sensitivity and specificity, positive and negative predictive values.

RESULT(S)

The best cutoff value to distinguish between healthy fertile donors and infertile men was 0.0185 x 10(6) counted photons per minute/20 x 10(6) sperm. At this threshold, the specificity was 82% and the sensitivity was 78%. This value can be defined as basal reactive oxygen species level in infertile men.

CONCLUSION(S)

Reactive oxygen species levels in neat semen samples as measured by luminol-based chemiluminescence are a highly specific and sensitive test in the diagnosis of infertility. This test also may help clinicians treat patients with seminal oxidative stress.

DNA fragmentation and meiotic segregation in sperm of carriers of a chromosomal structural abnormality

OBJECTIVE

To determine the meiotic segregation and DNA fragmentation in spermatozoa of carriers of a chromosomal structural abnormality.

DESIGN

Case series.

SETTING

University hospital.

PATIENT(S)

Thirty-seven male carriers of a chromosomal structural abnormality (21 with a balanced reciprocal translocation, 7 with a robertsonian translocation, 9 with a pericentric inversion).

INTERVENTION(S)

Meiotic segregation was analyzed by the human sperm-hamster oocyte fusion technique or by fluorescent in situ hybridization, and DNA fragmentation was detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay.

MAIN OUTCOME MEASURE(S)

Relationships between abnormal sperm parameters, DNA fragmentation, and meiotic mechanisms.

RESULT(S)

The average rates of chromosomally unbalanced spermatozoa were 55.22%, 14.09%, and 18.43% for reciprocal translocation, robertsonian translocation, and pericentric inversion carriers, respectively. The rates of DNA fragmentation were significantly higher in the whole group of carriers of a chromosomal structural abnormality and in each specific group than in the control group. No correlations between sperm DNA fragmentation and parameters of spermogram, age, or percentage of unbalanced chromosomal gametes were found.

CONCLUSION(S)

The DNA fragmentation rate depends solely on the presence of a chromosomal structural abnormality, and, therefore, a chromosomal structural abnormality predicts DNA fragmentation. Both meiotic segregation and DNA fragmentation studies should be integrated in the genetic exploration of male carriers of a chromosomal structural abnormality.

Double probing of human spermatozoa for persistent histones, surplus cytoplasm, apoptosis and DNA fragmentation

Individual spermatozoa were assessed with pairs of probes for persistent histones and cytoplasmic retention, persistent histones and DNA fragmentation, and persistent histones and apoptotic markers. The individual spermatozoa were treated sequentially with combinations of probes for these cytoplasmic and nuclear biochemical markers. Sperm fields were recorded with computer-assisted imaging, and staining patterns with the two probes in the same spermatozoa were examined and scored as light, intermediate or dark (mature to arrested-maturity spermatozoa). The effects of arrested sperm maturation were similar with respect to the cytoplasmic and nuclear characteristics of spermatozoa in 84% of cells, indicating that cytoplasmic and nuclear attributes of arrested sperm maturation are related. However, there were moderate (intermediate-dark or intermediate-light patterns, 14.5% of cells) or major (light-dark patterns, 1.6% of cells) discrepancies in the intensity of the double staining patterns. Thus, testing with single maturity markers may not be fully reliable. These findings are important with respect to: (i) arrested sperm maturation; (ii) potential efficacy of antioxidant and similar therapeutic strategies in subfertile men, as spermatozoa with infrastructure defects due to mismaturation or maturation arrest are unlikely to respond to interventions; and (iii) detection of adverse male environmental exposures.

Contributions of spermatozoa to embryogenesis: assays to evaluate their genetic and epigenetic fitness

During fertilization, spermatozoa contribute genetic and epigenetic factors that affect early embryogenesis. Genetic factors include a haploid genome with intact coding regions and regulatory regions for essential genes. The DNA must contain the proper copy number of essential genes, and cannot have increased single- or double- stranded DNA breaks. Epigenetic factors include a functional centrosome, proper packaging of the chromatin with protamines, modifications of histones, and imprinting of genes. Additionally, the fertilizing spermatozoon provides mRNAs and micro RNAs, which may contribute to the embryonic transcriptome and regulate embryonic gene expression. These epigenetic factors, directly or indirectly, affect the expression of genes in the developing embryo. Each of these contributions represents areas of potential sperm dysfunction, and they are the focus of ongoing research to develop assays which will allow further analysis of their clinical significance. This review briefly describes the current status of research into the genetic and epigenetic contributions of spermatozoa to embryogenesis, and the quest for clinical screening assays. The challenges to validation and clinical application of such testing are also discussed.

Oxidative stress and male infertility--a clinical perspective

Oxidative stress occurs when the production of potentially destructive reactive oxygen species (ROS) exceeds the bodies own natural antioxidant defenses, resulting in cellular damage. Oxidative stress is a common pathology seen in approximately half of all infertile men. ROS, defined as including oxygen ions, free radicals and peroxides are generated by sperm and seminal leukocytes within semen and produce infertility by two key mechanisms. First, they damage the sperm membrane, decreasing sperm motility and its ability to fuse with the oocyte. Second, ROS can alter the sperm DNA, resulting in the passage of defective paternal DNA on to the conceptus. This review will provide an overview of oxidative biochemistry related to sperm health and will identify which men are most at risk of oxidative infertility. Finally, the review will outline methods available for diagnosing oxidative stress and the various treatments available.