OXIDATIVE DAMAGE TO DNA IN HUMAN SPERMATOZOA DOES NOT PRECLUDE PRONUCLEUS FORMATION AT INTRACYTOPLASMIC SPERM INJECTION

We present the first evidence that genetically damaged human spermatoz oa are able to form normal pronuclei in oocytes after intracytoplasmic sperm injection (ICSI). The role of reactive oxygen species (ROS) as a cause of chromatin and DNA damage is well recognized. The same class of molecule can be found in the semen of males with severe infertilit y, who remained infertile until the advent of ICSI. In this study we h ave investigated the role of ROS in the induction of chromatin damage, DNA strand breakage and the subsequent ability of spermatozoa to deco ndense and form pronuclei after ICSI. Spermatozoa from normozoospermic men participating in our research programme were exposed to oxidizing environments created by coincubation with hydrogen peroxide, reduced nicotinamide adenine dinucleotide phosphate (NADPH) or activated white cells. The subsequent ability of the spermatozoa to decondense in vit ro was examined using sequential incubations in EDTA, dithiothreitol a nd sodium dodecyl sulphate, and the amounts of DNA strand breakage wer e assessed using an in-situ nick translation protocol. Finally, cells exposed to hydrogen peroxide, NADPH and activated leukocytes were micr oinjected into hamster oocytes, and their ability to decondense and fo rm normal pronuclei was determined. The results indicate that human sp erm chromatin becomes cross-linked under conditions of oxidative stres s and exhibits increased DNA strand breakage, yet the rate of pronucle us formation is no different from that of untreated control cells. The ability of genetically damaged spermatozoa to achieve normal fertiliz ation following ICSI has implications for the practice of this form of assisted conception therapy.