Apoptosis in human unfertilized oocytes after intracytoplasmic sperm injection

Objective: To investigate the presence of programmed cell death in unfertilized oocytes after intracytoplasmic sperm injection (ICSI), assuming that previous apoptotic events could be correlated with the fertilization failure. Design: Comparison of the rate of DNA fragmentation in human oocytes at different stages of maturation soon after pick-up (control) and in unfertilized oocytes after ICSI treatment. Setting: In vitro fertilization (IVF) laboratory with extensive ICSI experience. Patient(s): Sixty-three patients undergoing assisted fertilization by ICSI. Intervention(s): Terminal deoxynucleotidyl transferase-mediated digoxigenin-dUTP nick-end labeling (TUNEL) assay and anticaspase-3 cleaved immunoassay to detect apoptosis in control and ICSI-treated oocytes. Main Outcome Measure(s): Difference in the percentage of oocytes demonstrating DNA fragmentation between control oocytes and unfertilized ICSI treated oocytes at different stages of maturation. Result(s): The DNA fragmentation by TUNEL assay, appeared in all the immature control oocytes, but only 37% of mature oocytes showed DNA fragmentation. This DNA fragmentation was observed in 88.8% of the oocytes unfertilized after ICSI, furthermore, DNA fragmentation appeared as well in the sperm injected into the cytoplasm. Conclusion(s): The study has shown DNA fragmentation in human oocytes unfertilized after ICSI. The evidence is confirmed as well in control oocytes, free from in vitro culture or manipulation stress. Capase-3 immunoassay suggests the presence of apoptosis. The high percentage of oocytes demonstrating DNA fragmentation in the unfertilized oocytes could be correlated with fertilization failure.