Magnetic cell sorting (MACS) using annexin V-conjugated microbeads eliminates 
apoptotic spermatozoa based on the externalization of phosphatidylserine 
residues. The procedure delivers two sperm fractions: annexin V-negative 
(nonapoptotic) and annexin V-positive (apoptotic). Our aim was to determine 
whether the sperm fertilizing potential can be improved by selecting a 
nonapoptotic fraction using MACS. Semen samples (n = 35) were subjected to 
separation on a density gradient followed by MACS. Extent of apoptosis was 
assessed by measuring levels of activated caspase 3 using fluorescein-labeled 
inhibitors of caspase, alterations in mitochondrial membrane potential (MMP) 
using a lipophilic cationic dye, and DNA fragmentation using terminal 
deoxynucleotidyl transferase-mediated fluorescein-dUTP nick end labeling assay. 
The sperm fertilization potential was assessed using hamster oocyte penetration 
assay and hamster oocyte-intracytoplasmic sperm injection (ICSI). Annexin 
V-negative sperm displayed superior quality in terms of high motility, low 
caspase 3 activation, MMP integrity, and small extent of DNA fragmentation. 
Annexin V-negative sperm demonstrated higher oocyte penetration capacity but 
comparable sperm chromatin decondensation (SCD) following ICSI. Conversely, the 
annexin V-positive sperm presented with poor quality and fertilization 
potential. The oocyte penetration rate was negatively correlated with apoptotic 
marker expression, whereas SCD following ICSI was only associated with apoptosis 
on sperm-damaged membranes. We conclude that apoptosis appears to impact 
sperm-oocyte penetration rate; however, it does not seem to affect early stages 
of fertilization such as SCD in spermatozoa of healthy donors. The selection of 
nonapoptotic sperm by MACS may be used to enhance results of in vitro 
fertilization by increasing sperm-oocyte penetration.