215. Analysis of DNA damage induced by pro-oxidant treatment of mammalian spermatozoa in vitro

Abstract

Defects in the male genome produced as a consequence of oxidative insult have been associated with decreased fertility levels, an elevated incidence of childhood cancer and dominant genetic disease in the offspring (1). The objective of this study was to determine the relative susceptibility of sperm DNA of different mammalian species to oxidative injury. We applied a highly sensitive quantitative PCR assay (QPCR) to measure gene-specific DNA damage in nuclear and mitochondrial compartments of spermatozoa treated with H₂O₂. Human, murine and tammar wallaby (Macropus eugenii) spermatozoa were treated with H₂O₂ (0–5 mM) over a 1 h period. After DNA purification, DNA damage was assessed in a nuclear and a mitochondrial fragment of DNA by quantitative polymerase chain reaction assay (QPCR). DNA damage was detected as a decrease amplification of the target sequences. In murine and human spermatozoa, mitochondrial DNA exhibited greater sensitivity to oxidative damage than nuclear DNA. Doses ranging from 0.25–5 mM H₂O₂ induced DNA damage of up to 0.65 lesions/10 kb in the mouse, and 1.42 lesions /10 kb in the human. No significant effect on DNA damage was observed over this dose range in the nuclear DNA fragments investigated in these species. In contrast, tammar wallaby spermatozoa were susceptible to DNA damage at the 5 mM H₂O₂ dose in both nuclear (0.51 lesions/10 kb) and mitochondrial (0.55 lesions/10 kb) genomes. This study is the first to compare DNA damage in specific DNA sequences in spermatozoa of different mammalian species. Nuclear DNA of the metatherian species, the tammar wallaby, was more susceptible to oxidative damage than that of the eutherian species. A major difference between metatherian and eutherian spermatozoa is that, in general, the former possess protamines that are not stabilised by disulfide cross-linkage. These findings therefore suggest that sperm chromatin packaging affects the susceptibility of sperm DNA to oxidative damage.

(1) Sawyer and Aitken (2000) Reprod. Med. Rev. 8, 107–126.