Strong correlation between double-strand DNA Breaks and total sperm DNA fragmentation in the human ejaculate

Background

Double- and single-strand DNA breaks (DSBs and SSBs, respectively) in spermatozoa, which emerge from intrinsic and extrinsic degenerative processes, are likely related to the underlying male pathology.

Aim

To determine whether the incidence of DSBs in the human ejaculate is a consistent predictor of whole sperm DNA fragmentation (W-SDF = SSBs + DSBs).

Methods

A correlation between the proportion of spermatozoa that showed whole W-SDF and those displaying only DSBs in DNA. Two patient cohorts were established: W-SDF ≤30% (low SDF; n = 153) and W-SDF ≥30% (high SDF; n = 222).

Results

An increasing level of W-SDF is associated with an increased incidence of DSBs in the ejaculate. When data from both the low and high W-SDF groups were combined, a linear relationship was observed, with DSBs increasing by 0.799 units for each unit increase in W-SDF. However, when the cohorts were analyzed separately, the relationships differed. In the low SDF group, DSBs increased linearly by 0.559 units for each unit increase in W-SDF. In the high SDF group, DSBs increased exponentially by 0.602 units per unit of W-SDF. Furthermore, the data dispersion between the two variables was significantly different between the cohorts, with the high SDF group showing 0.8 times greater variability than the low SDF group.

Conclusions

While the presence of DSBs in sperm is correlated with the W-SDF present in raw semen samples, the biological mechanisms responsible for DSBs are expressed in different proportions and/or at different levels in ejaculates with higher levels of DNA damage.