DNA Damage in Human Spermatozoa Is Highly Correlated with the Efficiency of Chromatin Remodeling and the Formation of 8-Hydroxy-2′-Deoxyguanosine, a Marker of Oxidative Stress1

Abstract

DNA damage in human spermatozoa has been associated with a range of adverse clinical outcomes, including infertility, abortion, and disease in the offspring. We have advanced a two-step hypothesis to explain this damage involving impaired chromatin remodeling during spermiogenesis followed by a free radical attack to induce DNA strand breakage. The objective of the present study was to test this hypothesis by determining whether impaired chromatin protamination is correlated with oxidative base damage and DNA fragmentation in human spermatozoa. DNA fragmentation, chromatin protamination, mitochondrial membrane potential, and formation of the oxidative base adduct, 8-hydroxy-2'-deoxyguanosine (8OHdG), were monitored by flow cytometry/fluorescence microscopy. Impairment of DNA protamination during late spermatogenesis was highly correlated (P < 0.001) with DNA damage in human spermatozoa. The disruption of chromatin remodeling also was associated with a significant elevation in the levels of 8OHdG (P < 0.001), and the latter was itself highly correlated with DNA fragmentation (P < 0.001). The significance of oxidative stress in 8OHdG formation was demonstrated experimentally using H2O2/Fe2+ and by the correlation observed between this base adduct and superoxide generation (P < 0.001). That 8OHdG formation was inversely associated with mitochondrial membrane potential (P < 0.001) suggested a possible role for these organelles in the creation of oxidative stress. These results clearly highlight the importance of oxidative stress in the induction of sperm DNA damage and carry significant implications for the clinical management of this condition.

Apoptosis and DNA damage in human spermatozoa

“…Specifically, we propose that these defective spermatozoa with their poorly compacted chromatin are particularly vulnerable to stress and respond to such adversity by defaulting to apoptosis. The latter then results in mitochondrial ROS generation that attacks the vulnerable chromatin resulting in the 8OHdG formation 55,67 and ultimately DNA fragmentation. 68 If oxidative stress is at the heart of this process, then antioxidants should surely be part of the cure.…”

“…The only element of the apoptotic cascade that can induce such damage is the ROS released from the mitochondria; it is for this reason that most of the DNA damage seen in human spermatozoa is oxidative in nature. 55 More extensive DNA fragmentation may occur post-mortem as a result of the activation of endonucleases that are integrated into the sperm chromatin, thus finalizing the destruction of the cell. 56 However, the DNA damage induced in live cells, which is the clinically relevant damage, is entirely oxidative in nature.…”

Flow cytometry for the assessment of animal sperm integrity and functionality: state of the art

“…158 Levels of 8-hydrodeoxyguanosine have in human spermatozoa been shown to be highly correlated with DNA damage. 159,160 APPLICATION OF FC FOR THE SORTING OF SPERMATOZOA BY CHROMOSOMAL SEX The practical application of sexing spermatozoa, synergistically with other reproductive techniques, could improve the efficiency of animal production both in biological and economic terms. Selection of sex has important implications for populations in which one sex has more intrinsic value (e.g., rare animal genetic resources), for instance; stud operations and female dairy replacements, or the avoidance of males for pig production, etc.…”

Which isolated sperm abnormality is most related to sperm DNA damage in men presenting for infertility evaluation

“…In their model, De Iuliis et al, propose that oxidative stress (2nd step) acts on poorly protaminated spermatids (i.e. with incomplete replacement of histones by protamines and poor chromatin compaction) that are formed as a result of defective spermiogenesis (1st step) [19].…”