The source and significance of DNA damage in human spermatozoa; a commentary on diagnostic strategies and straw man fallacies

Abstract

This article considers the origins of DNA damage in human spermatozoa, the methods that are available to monitor this aspect of semen quality and the clinical significance of such measurements. DNA damage in spermatozoa appears to be largely oxidative in nature, inversely correlated with levels of nuclear protamination and frequently associated with the activation of a truncated apoptotic pathway. DNA base adducts formed as a result of oxidative attack are released from the spermatozoa into the extracellular space through the action of a glycosylase, OGG1. This creates an abasic site, which is not resolved until fertilization because spermatozoa do not possess the molecular machinery needed to continue the base excision repair pathway. The abasic sites so generated in human spermatozoa are readily detected by SCSA or the Comet assay; however, no signal is detectable with TUNEL. This is because spermatozoa lack the enzyme (APE1) needed to create the free 3' hydroxyl groups required by this detection system. Nevertheless, spermatozoa do eventually become TUNEL positive as they enter the perimortem. The American Society of Reproductive Medicine Practice Committee has suggested that DNA damage in spermatozoa should not be assessed because the correlation with pregnancy is inconsistent across independent studies. However, this is a straw man argument. The reason why such assays should be undertaken is not just that they reflect the underlying quality of spermatogenesis but, more importantly, that the DNA damage they reveal may have detrimental effects on the developmental normality of the embryo and the health of possible future children.

Mechanisms of the harmful effects of bacterial semen infection on ejaculated human spermatozoa: potential inflammatory markers in semen

“…Taking into consideration all these results, we can state that, although human sperm DNA is susceptible to damage as a result of bacterial semen infection, changes in lipid sperm membrane structures are critical for sperm fertilizing potential in this pathological condition. Moreover, this statement supports the general opinion postulated by some authors regarding the role of sperm DNA integrity as a predictor of the genetic quality of the embryo rather than of fertility [120,121]. However, further research is required in order to recommend the marker with the best prognostic power in clinical practice reflecting lipid sperm membrane damage during bacterial semen infection.…”

Analysis of the correlation between sperm DNA integrity and conventional semen parameters in infertile men

“…[33] The TUNEL assay is also im- peded by the highly compacted nature of sperm chromatin and necessitate the introduction of a chromatin decondensation step, prior to commencement of the assay in order to avoid potential artefacts. [34] On the other hand, both the TUNEL assay and the SCD test have been reported to require higher levels of DNA and chromatin damage before they can detect structural changes, indicating that they have lower sensitivity than the SCSA and the comet assay. [35] In conclusion, as far as the comet assay can detect, high degrees of sperm DNA damage are accompanied by significant impairment in all seminal parameters.…”

Effect of Seminal Transforming Growth Factorß1 (TGFß1) and Glutathione on Apoptosis in Spermatozoa from Tunisian Infertile Men

“…The principal cytotoxic reactive oxygen intermediate involved in ROS-associated damage is probably hydrogen peroxide (H2O2) generated by the intracellular dismutation of superoxide anion (O2-) under the influence of superoxide dismutase (SOD). However, Cameroun and Bernard (2007) suggested that the hydroxyl radical (HOO°), formed by the protonation of O2-, could be a potent indicator of per oxidative damaging human spermatozoa [2,52]. Though, in addition to H2O2, lipid peroxides generated as consequence of the peroxidation process also appeared to be profoundly cytotoxic, as their degradation products do.…”

“…Cell death can be developmentally controlled, with apoptosis being the most common morphologic expression of such programmed cell death [1][2][3][4]. Lethal cellular programs that lead to apoptosis may be triggered by a variety of exogenous and environmental stimuli.…”

“…Among these phenomena, it has been found that this factor induces the production of free radicals or reactive oxygen species (ROS) [2,3], which are produced by non-functional spermatozoa and leukocytes.…”