Effects of seminal plasma and flash-freezing on DNA structure of stallion epididymal sperm exposed to different potentiators of DNA damage

Determination of Ram (Ovis aries) Sperm DNA Damage Due to Oxidative Stress: 8-OHdG Immunodetection Assay vs. SCSA®

Conventional DNA analysis techniques can hardly detect DNA damage in ruminant spermatozoa due to high DNA compaction in these cells. Furthermore, these techniques cannot discriminate whether the damage is due to oxidative stress. The main purpose of this study was to evaluate the efficacy of two techniques for determining DNA damage in ovine sperm when the source of that damage is oxidative stress. Semen samples from twenty Manchega rams (Ovis aries) were collected and cryopreserved. After thawing, the samples were subjected to different levels of oxidative stress, and DNA oxidation was quantified using an 8-hydroxy-2′-deoxyguanosine (8-OHdG) immunodetection assay and Sperm Chromatin Structure Assay (SCSA®). For this purpose, we evaluated five different concentrations of an oxidation solution (H2O2/FeSO4•7H2O) on ram sperm DNA. Our study with the 8-OHdG immunodetection assay shows that there are higher values for DNA oxidation in samples that were subjected to the highest oxidative stress (8 M H2O2/800 µM FeSO4•7H2O) and those that were not exposed to high oxidative stress, but these differences were not significant (p ≥ 0.05). The two SCSA® parameters considered, DNA fragmentation index (DFI %) and high DNA stainability (HDS %), showed significant differences between samples that were subjected to high concentrations of the oxidation agent and those that were not (p < 0.05). We can conclude that the 8-OHdG immunodetection assay and SCSA® detect DNA damage caused by oxidative stress in ovine sperm under high oxidative conditions; SCSA® is a more straightforward method with more accurate results. For these reasons, an oxidative-stress-specific assay such as 8-OHdG immunodetection is not needed to measure DNA damage caused by oxidative stress in ram sperm samples.

Ovine sperm DNA oxidation quantification using an 8-OHdG immunodetection assay

Our aim was to optimize 8-hydroxy-2'-deoxyguanosine (8-OHdG) immunodetection in order to detect DNA damage caused by oxidative stress that may not be detected by other DNA integrity analysis techniques, especially due to the high compaction of DNA in ruminants. Semen samples from 6 rams were cryopreserved. After thawing, samples were subjected to the DNA oxidation quantification using an 8-OHdG immunodetection assay by flow cytometry. We have evaluated two different incubation times (30 min vs. overnight) at 4°C of the primary antibody (monoclonal anti-8-OHdG antibody). We have also compared the results of this technique with the sperm chromatin structure assay (SCSA^® ). The analysis revealed that there were no significant differences (p > .05) between different incubation times. However, overnight incubation seems to cause more non-specific binding of the secondary antibody. Significant differences (p < .05) between subjects and oxidation controls (8 M H₂ O₂ /800 μM FeSO₄ •7H₂ O) were evident. We can conclude that the 8-OHdG immunodetection assay for DNA oxidation quantification of ram sperm can be performed subjecting sperm samples to a very high oxidative treatment.

Sperm DNA fragmentation: causes and identification

Sperm DNA fragmentation is referred to as one of the main causes of male infertility. Failures in the protamination process, apoptosis and action of reactive oxygen species (ROS) are considered the most important causes of DNA fragmentation. Action of ROS or changes in sperm protamination would increase the susceptibility of sperm DNA to fragmentation. Routine semen analysis is unable to estimate sperm chromatin damage. Sperm DNA integrity influences sperm functional capability, therefore tests that measure sperm DNA fragmentation are important to assess fertility disorders. Actually, there is a considerable number of methods for assessing sperm DNA fragmentation and chromatin integrity, sperm chromatin stability assay (SCSA modified), sperm chromatin dispersion (SCD), comet assay, transferase dUTP nick end labelling (TUNEL); and protamine evaluation in sperm chromatin assay, such as toluidine blue, CMA3, protamine expression and evaluation of cysteine radicals. This review aims to describe the main causes of sperm DNA fragmentation and the tests commonly used to evaluate sperm DNA fragmentation.

Effect of artificial vagina lubricants on stallion sperm quality

Commercially available vaginal lubricants, typically labeled as non-spermicidal, are used to lubricate equine artificial vaginas prior to semen collection. Improper type or amount of lubricant might affect stallion sperm quality, either after short-time exposure or following cooled storage of extended semen previously exposed to lubricant. The aim of this study was to evaluate stallion sperm quality following exposure to lubricant-containing extender for 1 h (T1h) or 24 h (T24h). Three ejaculates were collected from each of four stallions using a small volume of petrolatum to lubricate artificial vaginas, and gel-free semen was diluted to 30 × 10⁶ sperm/mL in extender containing: no lubricant (control), or 1 or 5% (v/v) HR® Lubricating Jelly (HR1 or HR5); K-Y® Jelly (KY1 or KY5); Therio-gel® (TG1 or TG5); Priority Care® Sterile Lubricating Jelly (PC1 or PC5); or Clarity® A.I. Lubricating Jelly (CL1 or CL5). Sperm were evaluated at T1h and T24h for percentages of: total and progressive sperm motility (TMOT and PMOT); curvilinear velocity (VCL; μm/s); and straightness (STR; %); viable acrosome intact sperm (VAI); sperm with abnormal DNA (COMP-α_t); viable lipid peroxidation negative sperm (VLPN); and sperm with no detectable DNA oxidative injury [8OHdG(-)]. Following short-term exposure of sperm to lubricants, KY5 reduced TMOT, PMOT, VCL, VAI, VLPN, and COMP-α_t in comparison with controls (i.e., P < 0.05). PC5 reduced TMOT, PMOT, VCL, VAI, and 8OHdG(-), and KY1 reduced TMOT, VAI, VLPN in comparison to controls (P < 0.05). Lubricant CL1, HR1 and HR5 yielded similar values to controls for all 8 endpoints, and CL5 yielded similar values to controls for all 8 endpoints (P > 0.05), except for VCL. Following long-term exposure, KY5 decreased TMOT, PMOT, VCL, VAI, VLPN, and COMP-α_t as compared to controls (i.e., P < 0.05), PC5 decreased TMOT, VCL, VAI, and 8OHdG(-)as compared to controls in PC5, and KY1 decreased TMOT, VAI, VLPN, and COMP-α_t (P < 0.05). TG5 decreased TMOT, PMOT, and VCL as compared to controls (P < 0.05). Lubricant CL5 decreased VCL (P < 0.05), and CL1, HR5, HR1, PC1, and TG1 were similar to controls for all 8 endpoints (P > 0.05). Overall, lubricant KY was the most detrimental to sperm quality, with most profound changes detected at a 5% concentration. Lubricants CL and HR were generally similar to controls and were less affected by lubricant concentration.