Male factor infertility is a contributing factor in up to 50% of infertile couples. Increasing numbers of couples undergoing assisted reproductive technology (ART) treatment and reports of a possible decline in male fertility suggest that lifestyle, occupational and environmental exposures might impair semen quality. Sperm DNA contains both DNA strand breaks and base damage that has been associated with poor semen quality but few studies have examined the role of double strand breaks (DSBs), a toxic lesion, or DNA damage such as N7-methyldeoxyguanosine (N7-MedG) arising from alkylating agents that can be toxic and mutagenic. The aim of this research was to examine the relationships between exposures, DNA damage and male fertility. Men were recruited from couples attending for ART treatment and they provided information on lifestyle, occupational and environmental exposures as well as a sperm sample. Semen concentration and motility was determined by standard techniques in the neat sample and the prepared sample that underwent density gradient centrifugation for ART treatment. DSBs were measured in individual sperm cells by the neutral Comet assay and N7-MedG levels in sperm DNA by an immunoslot blot assay. Information on ART outcomes (% fertilisation, % cleavage and clinical pregnancy) was collected and associations between DNA damage, exposures, semen quality and ART outcomes were determined. Expression of individual DNA repair proteins was also examined in individual oocytes. Men in manual work had significantly lower semen volumes and higher % immotile sperm. Exposure to dry cleaning fluids and having a fever were associated with a decrease in sperm number and while non-ionizing radiation was associated with an increase in % immotile sperm, X-ray exposure was correlated to a decrease in % progressively motile sperm. Semen parameters were significantly and negatively correlated with DSBs in neat and prepared sperm, and N7-MedG levels in neat sperm. Density gradient centrifugation improved sperm sample quality and decreased DSBs and N7-MedG levels significantly. Successful fertilization of oocytes was negatively associated with DSB levels in neat and prepared sperm and with N7-MedG levels in neat sperm. Lower DSB levels in men were associated with an increased chance of an achieving clinical pregnancy especially in ICSI couples. N7-MedG levels were significantly correlated with driving a car and exposure to detergent or printing inks and dyestuffs. DSBs were correlated negatively with exercise and positively with eating nuts and almonds or exposure to non-ionizing radiation. DNA repair gene expression in individual oocytes showed significant intra and inter-individual variability. Sperm DNA damage can reduce male fertility, but the causes of such damage remain to be identified. The variable ability of individual oocytes to repair this damage may well affect the chance for a successful pregnancy.

No / In 2013, the World Health Organization referred to tobacco smoking as an epidemic and a great threat to human health. Despite the obvious exposures from first- and secondhand smoking contributing to illnesses, an increased cancer risk, and death, there is a hidden risk to the next generation(s) from transgenerational mutations. In human populations, paternal preconceptional germ cell damage leading to genomic instability in offspring has always been difficult to evaluate as preconceptional and gestational exposures usually cannot be analyzed independently. Clear indications have been found that the effect of pre- and periconceptional paternal smoking may have been transmitted to the offspring via the spermatozoal genome and epigenome. Hence, cigarette smoke has to be considered a human germ cell mutagen due to its potential of inducing transgenerational DNA alterations in the unexposed F1 offspring of smoking-exposed fathers. For cohort studies, the practice of almost exclusively employing mother–childbirth pairs for the evaluation of lifestyle factors, such as smoking, while excluding the fathers’ contribution has to be reconsidered. Evidence now strongly points to the necessity of including the fathers in order not to miss paternal transgenerational damage in the offspring. This applies for genetic, epigenetic, and other transmissible effects.

The potential for environmental toxicants to cause genetic damage (genotoxicity) in organisms is a prominent concern because effects on DNA can compromise reproductive success and survival in organisms. Genotoxicity in male germ cells is of particular concern because damage to DNA in sperm may not be repaired and the consequences of damaged genetic material may be transgenerational (from parent to offspring). An integrated approach across multiple levels of biological organization is necessary to establish linkages between exposure to genotoxicants and subsequent effects at molecular and higher levels of biological organization. This thesis addresses the relation between toxicant-induced genotoxicity and reproductive success in zebrafish, and focuses on a model genotoxicant (hydrogen peroxide) and dissolved metals (radionuclide or non-radioactive forms) under controlled laboratory conditions. Uptake and depuration kinetics of a mixture of radionuclides (54Mn, 60Co, 65Zn, 75Se, 109Cd, 110mAg, 134Cs, and 241Am) were investigated, and radiation dose estimations were computed to link exposure and bioaccumulation with radiation dose. Cobalt (Co, non-radioactive) was selected as an environmentally relevant toxicant for investigation of genotoxicity and effects on reproductive success with a focus on male fish. Chronic exposure (12-d) to 0 – 25 mg l-1 Co resulted in reduced numbers of spawned eggs, lower fertilization success, and reduced survival of larvae to hatching. In male fish, DNA damage was detected in sperm and genes involved in DNA repair (xrcc5, xrcc6, and rad51) were induced in testes from some Co treatments, generally consistent with reduced reproductive success. No change in expression of repair genes in larvae spawned from parents exposed to Co was observed. Overall, results indicate that DNA damage and induction of DNA repair genes can occur rapidly after exposure to genotoxicants and that, if exposure levels are elevated, negative effects on reproduction can occur. Results are considered with particular focus on implications of male genotoxicity on reproductive success and the potential for transgenerational effects of toxicants.