To the Editor:
Although we agree with Dr. Caroppo that the effect of DNA damage of human spermatozoa on fertilization, embryo cleavage, and implantation remains controversial, its detrimental impact on natural conception and miscarriage seems real. Advanced methods for the selection of spermatozoa with healthy DNA will become mandatory, as advocated by Dr. Caroppo (1). As we are now able to significantly reduce the number of spermatozoa with fragmented DNA (2), we will be able to compare prospectively the effect of DNA fragmentation on the outcome of assisted reproductive technology (ART).
Of course, the safety of the process is of concern. However, the safety of the Hoechst dye in combination with fluorescence activated cell sorting (FACS) has been amply documented as much mammalian offspring has been produced with sorting (3). All evidence to date indicates that this dye exerts no detrimental impact. Similarly, the UV laser was described as not having any detectable negative effect on the incidence of DNA damage or mutations in spermatozoa. Only the mechanical aspects of sorting may be detrimental, as the pressure exerted on spermatozoa during their passage through the microfluidic channels has been demonstrated to affect their viability, motility, and velocity in the presence of high pressure (50 psi), but not of lower pressure (30 psi). Here, we used milder pressure (around 20 psi), which can be decreased even further. Due to breakage of the sperm tails, motility is lost during the formation and disruption of little droplets (4). Dr. Caroppo commented that in our study the sperm motility was significantly reduced when compared with the swim-up (3). As mentioned in our report (2), this difference is considerably reduced if we limit the samples to those with lowest quality (concentration ≤10 x 106/ml). In these cases the values are 51.6% +/-14 for sorted spermatozoa and 33% +/-22 in the swim-up. Read the rest of this entry »