The single-cell gel electrophoresis (Comet) assay has been widely used to measure DNA damage in human sperm in a variety of physiological and pathological conditions. We investigated the effects of in vivo radiation, a known genotoxin, on spermatogenic cells of the mouse testis and examined sperm collected from the vas deferens using the neutral Comet assay. Irradiation of differentiating spermatogonia with 0.25-4 Gy X-rays produced a dose-related increase in DNA damage in sperm collected 45 days later. Increases were found when measuring Comet tail length and percentage of tail DNA, but the greatest changes were in tail moment (a product of tail length and tail DNA). Spermatids, spermatocytes, differentiating spermatogonia, and stem cell spermatogonia were also irradiated in vivo with 4 Gy X-rays. DNA damage was indirectly deduced to occur at all stages. The maximum increase was seen in differentiating spermatogonia. DNA damaged cells were, surprisingly, still detected 120 days after stem cell spermatogonia had been irradiated. The distribution of DNA damage among individual sperm cells after irradiation was heterogeneous. This was seen most clearly when changes in the Comet tail length were measured when there were discrete undamaged and damaged populations. After increasing doses of irradiation, an increasing proportion of cells were found in the damaged population. Because a proportion of undamaged sperm cells remains after all but the highest dose, the possibility of normal fertility remains. However, fertilization with a spermatozoa carrying high amounts of DNA damage could lead to effects as diverse as embryonic death and cancer susceptibility in the offspring.
This study investigated whether chemotherapy using fludarabine (FLU) caused testicular damage and if cytotoxicity could be detected as sperm DNA damage in the single cell Comet assay. A patient with chronic lymphocytic leukaemia requesting preservation of fertility was treated with seven monthly cycles of fludarabine (45.8 mg total dose per cycle). Testicular assessments, serum follicle stimulating hormone (FSH), luteinizing hormone (LH), and testosterone measurements, semen analysis and sperm Comet assays were carried out at presentation (pre-FLU therapy), after 1 and 7 months of FLU treatment, and finally at 11 months after completion of chemotherapy. We found that testicular damage occurred within a month, as indicated by reduced testicular volume, oligozoospermia, elevated FSH and LH, and lower testosterone concentrations. Spermatozoa with a large range of DNA damage were detected in the samples from both the control and treated men. DNA damage in the spermatozoa was marked by 7 months of FLU treatment. The high levels of sperm DNA damage seen during and possibly persisting after treatment suggests that caution should be exercised if the ejaculates from these men are used for in-vitro fertility treatment. Further experiments are needed to assess the biological significance of these DNA changes; it may, however, be prudent at present to be cautious when counselling these patients.
These results suggest that impaired spermatogenesis may lead to production of aneuploid gametes. Analysis of aneuploidy in gametes from infertile men, coupled with appropriate genetic counselling, is recommended prior to ICSI.
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