Disintegration of chromosomes in dead sperm cells as revealed by injection into mouse oocytes

Intracytoplasmic sperm injection of immotile (dead) ejaculated human spermatozoa has been carried out by several centres for the treatment of infertility caused by severe asthenozoospermia (necrozoospermia). No healthy pregnancies have been reported as yet, suggesting irreversible damage to sperm DNA, centrioles and/or other important structures. We investigated this hypothesis by injection of immotile human spermatozoa obtained from several male infertility patients into mouse oocytes and analysis of the oocyte activation rate and sperm chromosome integrity. Motile spermatozoa of the same sample were used as a control. The proportion of living spermatozoa among the immotile was also assessed in each sample and was related to the results of the mouse oocyte injection test. The oocyte activation rate after injection of immotile human spermatozoa into mouse oocytes was the same or only slightly lower than after injection with initially motile spermatozoa (87-100% versus 100% respectively). The rate of normal sperm chromosome spreads correlated significantly (r = 0.90, P < 0.05) with the proportion of living immotile spermatozoa in a given sample. It varied from 4 to 48% for samples containing respectively 8 and 40% of living spermatozoa. Most of the mouse oocytes injected and activated with immotile human spermatozoa were arrested during a prolonged period of time at the interphase of the first cell cycle (from 22 to 60%). Others underwent a delayed nuclear envelope breakdown but showed signs of abnormal structure of both male and female or only the male pronuclear chromosomes. Our data demonstrate an irreversible damage of chromosomes in dead ejaculated human spermatozoa and provide an experimental basis for recommending the use of testicular or epididymal spermatozoa for treatment of male infertility due to necrozoospermia.