Gamete-specific DNA fragmentation in unfertilized human oocytes after intracytoplasmic sperm injection

Abstract

The objective of the present study was to assess the integrity of maternal and/or paternal chromatin in injected oocytes that remained unfertilized after intracytoplasmic sperm injection (ICSI). The study was performed on 102 oocytes that failed to show pronuclear formation 18-20 h after ICSI. We used chromatin labelling with 4,6-diamidino-2-phenylindole (DAPI) to identify maternal and paternal chromatin, coupled with biotin-mediated end-labelling to assess DNA fragmentation in each gamete. It was shown that 50% of oocytes without pronuclear formation following ICSI contained chromatin with damaged DNA, and that the source of the DNA fragmentation was equally divided between the spermatozoon (25.8%) and the oocyte (24.4%). A significantly greater proportion of condensed spermatozoa in human oocytes had damaged DNA, compared to decondensed spermatozoa (24.7 compared to 5.9%, P=0.002). There was a significant increase in the incidence of DNA fragmentation in oocytes from patients older than 35 years (65+/-1.2%) compared to those from younger patients (36+/-1.0%) (P < 0.05). Further, 17% of unfertilized oocytes contained no paternal chromatin. Thus, DNA fragmentation in both spermatozoa and oocytes is associated with failure of fertilization in ICSI. In some cases of severe male factor infertility, a significant proportion of spermatozoa injected into oocytes may contain fragmented DNA. Injection of oocytes with spermatozoa containing abnormal chromatin will probably result in failure of sperm decondensation and fertilization. In older women, a significant proportion of oocytes injected may contain fragmented DNA. These observations may explain the consistent inability of most clinics to achieve fertilization rates higher than 65% with ICSI.

The correlation between male age, sperm quality and sperm DNA fragmentation in 320 men attending a fertility center

“…Probably the most important is the production of reactive oxygen species (ROS) which is excited, for example, by excessive stress, competitive sports, alcohol and drug abuse or nicotine. If produced in abundance, ROS can enter the cell nucleus, bind to the DNA and cause its fragmentation [15][16][17][18][19][20]. However, DNA fragmentation is also a feature of physiological processes like apoptosis and necrosis.…”

Intracytoplasmic Sperm Injection – Factors Affecting Fertilization

“…Many published articles indicate that DNA strand breaks are clearly detectable in ejaculated sperm and their presence is heightened in the ejaculates of men with poor semen parameters [61,62]. Nuclear DNA damage in mature sperm includes single strand nicks and double strand breaks that can arise because of errors in chromatin rearrangement during spermiogenesis, abortive apoptosis and oxidative stress [63,64]. In the same individuals, testicular samples show a significantly lower DNA damage compared to ejaculated spermatozoa (14.9%±5.0 vs. 40.6%±14.8, P<0.05), but significantly higher aneuploidy rates for the five analyzed chromosomes (12.41%±3.7 vs. 5.77%±1.2, P<0.05).…”

Case reports to suggest an algorithm for management of total fertilisation failure prior to use of donor gametes

“…Although genetic markers of sperm have not necessarily been related to TFF, both increased sperm DNA fragmentation [14] and sperm aneuploidy levels [15] have been demonstrated to impact negatively on fertilisation rates. Furthermore, a correlation between increased sperm DNA fragmentation and loss PLCζ activity has also been suggested [16]. In the presence of impaired sperm parameters, a formal urological review is recommended to exclude any reversible factors impacting on seminal quality and therefore fertilising capacity.…”