Antioxidant defenses and sperm swimming behavior in barn swallows from Chernobyl

Background/Question/Methods  Exposure to free radicals can affect sperm morphology and behavior. As an exogenous source of free radicals, ionizing radiation can impair sperm swimming behavior, ultimately prejudicing fertilizing capacity. Studies of barn swallows (Hirundo rustica) from radioactively contaminated areas around Chernobyl have shown that sperm motility and the frequency of abnormal sperms are both related to background radiation levels. A negative relationship between the concentration of antioxidants in plasma and liver and the frequency of abnormal sperms has also been described. However, the relationship between overall oxidative status and sperm behavior has never been investigated under conditions of variable radioactive contamination. In this study of barn swallows from the Chernobyl region, we correlated sperm motility parameters to plasma antioxidant capacity and oxidative damage levels, in order to test the hypothesis that radiation exposure can impair sperm behavior in a manner that is dependent on individual oxidative status. To this end, sperm samples obtained from 93 birds were analyzed using computer-assisted sperm analysis. A blood sample was also collected from each individual male, for quantifying total antioxidant capacity (TAC) and the level of reactive oxygen metabolites (ROMs) in barn swallow plasma.

Results/Conclusions  A principal component analysis (PCA) performed on 12 sperm behavior variables revealed four significant axes that explained 87% of the variance in our data. PC2, representing sperm with low linearity, high track velocity and ample lateral head displacement, varied directly with the combined effect of radiation and ROMs level. PC2 scores increased with increasing oxidative damage particularly where radioactive contamination was relatively high. This result was confirmed if the ratio of ROMs level to TAC was used in the model as an index of the balance between antioxidant protection and oxidative damage. PC3, representing the frequency of slow sperms and of motile sperm, also depended on the interaction between radiation level and either TAC or ROMs. PC3 scores were highest at relatively low radiation levels and high TAC or ROMs levels. These results, while confirming previous findings on the effects of radiation on sperm behavior variables, are consistent with the hypothesis that the extent of radiation effects on sperm motility depends on individual oxidative status, thus suggesting a possible radioprotective role for antioxidants in free-ranging animals exposed to the fallout from Chernobyl.