Male infertility may be due to oligozoospermia, asthenozoospermia and teratozoospermia. Intracytoplasmic sperm injection is used to address male infertility. However, the percentage of viable embryos obtained by this technique is very low. Pronucleus formation has been identified as one of the key events in fertilisation and gamete decondensation is vital for this process to take place. Decondensation can be initiated by chemicals such as DTT that reduce the disulphide groups between the protamine proteins that keep the DNA of the gamete condensed. An increase in decondensation should translate into a higher fertilization rate and a higher yield of embryos. The research from this thesis has compared the decondensation ability via DTT in human spermatozoa and bovine spermatozoa, to study pronucleus formation in bovine zygotes and bovine embryo formation in the presence of DTT; and lastly the cytotoxic effect of DTT using somatic cells in culture has been investigated. In this study 12 semen samples for either fertile or subfertile subjects were collected, isolated and exposed to 25 mM DTT for 0, 5, 7, and 10 minutes, washed and the morphological changes associated with decondensation was evaluated by phase contrast microscopy. After 5 and 7 minutes 11 of the 12 samples underwent decondensation while after 10 minutes several samples showed a lower rate of decondensation and this was associated with and unusual hypercondensed state, CMA3 staining revealed all spermatozoa samples evaluated were mature. However, after treatment with DTT for 5, 7 and 10 minutes an increase in fluorescence was observed indicating increased protamine thiol group reduction and subsequently increased CMA3 accessibility. For some samples reduced fluorescence was observed possible due to the supercoiling of the DNA. DTT successfully induces decondensation of human spermatozoa, however does this lead to the formation of viable embryos? Due to ethical issues associated with working with human embryos all further studies were done using bovine embryos. Spermatozoa used were derived from Friesian bulls and the samples were pooled to prevent sample bias and interindividual variation. Spermatozoa were exposed to 25 mM of DTT at 5, 7, and 10 minutes as used for human spermatozoa. No decondensation was observed using the same conditions as for human spermatozoa, therefore the ‘swim up’ medium containing heparin and regularly used in IVF procedures for bovines was used, and this resulted in successful decondensation of bovine spermatozoa after 30 minutes. The effects of DTT on pronucleus formation and embryo development were evaluated in three bovine specimens. In the first group, DTT had no significant effect on the parameters measured, namely the number of oocytes that were in metaphase II, with one pronucleus, with two pronuclei, with degeneration of the nucleus and polyspermia. In the second group the percentage cleavage and embryo formation was determined on Day 1 (group 2) and 7 (group 3) respectively and statistical differences were obtained between the control and the DTT group. DTT had no significant effect on all the early parameters measured however later in development DTT had a significant adverse effect on cleavage and eventual embryo development. <p)Cleavage and embryo formation is a process of multiple mitotic divisions resulting in an increase in the number of cells that become smaller with each cell division, while somatic cells also undergo mitotic division although the cell size remains constant. Therefore the L929 cell line, a standardized system used to test toxicity, can be used to investigate the toxic effects of DTT on a dividing cell population. In this study L929 cells were expose to 25mM DTT for 30 minutes, and lysosomal membrane integrity, cell viability and number was determined immediately following exposure and after 48 hours growth. In another experiment the L929 cell line was exposed to all concentrations used in this and other studies for 5, 10 and 20 minutes. At all concentrations and exposure times DTT was found to be cytotoxic to the L929 cell line. How exactly DTT mediates this toxic effect is unknown, however due to its high solubility DTT can cross the cell membranes. The tertiary structure of proteins, enzymes and DNA is vulnerable to the reducing effects of DTT. In conclusion, although DTT induces decondensation in human and bovine spermatozoa, in the bovine model it does not lead to viable embryo formation and this has been confirmed in cell culture where DTT at all concentrations used was found to be cytotoxic. / Dissertation (MSc (Anatomy))--University of Pretoria, 2006. / Anatomy / unrestricted

Chez l’Homme, les succès de la fécondation et d’un développement embryonnaire aboutissant à la naissance d’un enfant en bonne santé résident principalement dans la qualité des cellules reproductrices. Les dommages oxydants de l’ADN spermatique sont une cause majeure d’infertilité masculine. Afin de permettre une prise en charge thérapeutique optimale et adaptée, j’ai tout d’abord mis au point et validé un test diagnostique de l’oxydation de l’ADN spermatique par immunodétection du 8-hydroxy-2'-desoxyguanosine (8-OHdG), adduit majeur de l'oxydation nucléaire. Ce travail de thèse a déterminé, pour la première fois, un seuil d’oxydation de l’ADN spermatique en relation avec les paramètres conventionnels spermatiques. Dans un second temps, je me suis focalisée sur les atteintes de la chromatine et de l’ADN spermatique les plus fréquentes en cas d’infertilité masculine, à savoir les anomalies de condensation de la chromatine, la fragmentation et l’oxydation de l’ADN spermatique. Une corrélation entre l’oxydation de l’ADN, tout particulièrement la moyenne d’intensité de fluorescence, et le pourcentage de spermatozoïde fragmenté a été mise en évidence. Pour objectiver l’impact de ces dommages nucléaires spermatiques en pratique clinique, j’ai étudié, après cryopréservation, les effets bénéfiques d’une supplémentation en hypotaurine des milieux de sélection et de congélation/décongélation des échantillons. Une baisse de la cryocapacitation et du pourcentage de spermatozoïde fragmenté et décondensé ont été retrouvées ainsi qu’une amélioration de la vitalité et de la mobilité progressive spermatique. Enfin, comme le spermatozoïde a pour but ultime de participer à la genèse d’un nouvel individu, j’ai mis en évidence que la fragmentation et l’oxydation de l’ADN spermatique avaient un impact à des moments clés de la cinétique du développement embryonnaire précoce suite à une ICSI sans pour autant modifier l’obtention de blastocystes de bonne qualité. Ce travail de thèse a permis de mieux comprendre la physiopathologie de l’infertilité masculine et de mettre en évidence de nouveaux biomarqueurs spermatiques en lien avec un développement embryonnaire normal. / In humans, the success of fertilization and embryonic development leading to the birth of ahealthy child lies mainly in the quality of reproductive cells. Oxidative damage to sperm DNAis a major cause of male infertility. In order to provide optimal and appropriate therapeuticmanagement, I first developed and validated a diagnostic test for sperm DNA oxidation byimmunodetection of 8-hydroxy-2'-deoxyguanosine (8-OHdG), a major adduct of nuclearoxidation. This thesis work determined, for the first time, a threshold for the oxidation ofsperm DNA in relation to conventional sperm parameters. In a second step, I focused on themost common chromatin and sperm DNA disorders in male infertility, namely chromatincondensation anomalies, sperm DNA fragmentation and oxidation. A correlation betweenDNA oxidation, particularly the mean fluorescence intensity, and the percentage offragmented sperm was found. To objectify the impact of this nuclear sperm damage inclinical practice, I studied, after cryopreservation, the beneficial effects of hypotaurinesupplementation to the selection and freeze/thaw media of seed samples. A decrease incryocapacitation and the percentage of fragmented and decondensed sperm has beenfound, as well as an improvement in sperm vitality and progressive mobility. Finally, sincethe ultimate goal of the sperm cells is to participate in the genesis of a new individual, I haveshown that the fragmentation and oxidation of sperm DNA has an impact at key moments inthe kinetics of early embryonic development following ICSI without modifying the obtainingof good quality blastocysts. This thesis work has led to a better understanding of thepathophysiology of male infertility and the identification of new sperm biomarkers related tonormal embryonic development.