Doctoral Degrees (Obstetrics and Gynaecology)

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Browsing Doctoral Degrees (Obstetrics and Gynaecology) by Author "Hoogendijk, Christiaan F. (Christiaan Frederik)"

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    Sperm DNA fragmentation : implications in assisted reproductive technologies
    (Stellenbosch : Stellenbosch University, 2007-12) Hoogendijk, Christiaan F. (Christiaan Frederik); Kruger, T. F.; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Obstetrics and Gynaecology.
    ENGLISH ABSTRACT: Male fertility has for many years been defined in vitro as the ability of sperm to fertilize oocytes and to obtain early cleavage-stage embryos. Spermatozoa comprise of an extraordinary high percentage of polyunsaturated fatty acids in their plasma membrane. Due to an extremely low content of cytoplasm, sperm cells have a particularly low potential to scavenge reactive oxygen species (ROS), and are therefore highly sensitive to oxidative processes, which lead to sperm nucleus DNA damage/fragmentation. Normally, DNA fragmentation occurs in every ejaculate and can be induced by an excessive ROS production of active leukocytes or the spermatozoa themselves. Under distressed conditions, DNA fragmentation may also occur in the testis as a result of oxidative processes in the apoptotic cascade. These DNA fragmentations can be regarded as late signs of programmed cell death (apoptosis). Clinically, DNA fragmentation in spermatozoa results in significantly decreased implantation and pregnancy rates especially in patients with oligo- and/or teratozoospermia. The p-pattern normal sperm morphology has been shown to give poorer fertilization rates in vitro than the g- and n-patterns. In this study there is reported on the significant correlation found between the p-pattern normal sperm morphology and sperm DNA fragmentation as measured with the terminal deoxynucleotidyl transferase-mediated dUDP-biotin end labeling (TUNEL) assay. This finding further explains the lower fertility potential of patients presenting with p-pattern normal sperm morphology. In addition, this study explores the intricate relations between ROS in the semen, DNA fragmentation of the spermatozoa, as measured with the TUNEL assay and the sperm chromatin structure assay (SCSA ), spermatozoa apoptotic status and sperm parameters as measured with a standard semen analysis. Positive correlations were found between ROS and the apoptotic status of the sperm, as well as between sperm with non-fragmented DNA and sperm concentration and percentage motility. The results emphasize the importance of sperm selection especially when the treatment of choice is intracytoplasmic sperm injection (ICSI). An early sign of programmed cell death, also known as apoptosis, is the externalization of phosphatidylserine (PS) from the inner membrane leaflet to the outer leaflet. PS shows a high affinity to Annexin V. Apoptotic spermatozoa are able to fertilize oocytes, but embryo senescence may occur at the time when the paternal genes are activated. In this study there is reported on a novel method whereby spermatozoa can be separated on the basis of their apoptotic status through flow cytometry. Results showed that the normal sperm morphology, according to strict criteria, of the resultant nonapoptotic sperm fraction is significantly higher than that of the apoptotic counterpart. With refinement of this technique, it will be possible in future to use these separated non-apoptotic sperm cells during ICSI for fertilization. From the above it is apparent that the spermatozoon has to play a vital role in the development of the embryo from fertilization to implantation and pregnancy. It is, however, important to note that besides the gametes, there are other critical factors which contribute to a successful in vitro fertilization (IVF) cycle, among these are the in vitro culture conditions. In this regard, this study compared two sequential embryo culture systems. It was found that the more complex medium resulted in better day three embryo quality and a better blastocyst formation rate and pregnancy rate. These findings highlight the importance of a holistic perspective towards the complexity of the factors involved in affecting embryo quality and pregnancy outcome.