Conservation Science in a Terrorist Age: The Impact of Airport Security Screening on Viability and DNA Integrity of Frozen Felid Spermatozoa
Center for Conservation and Research of Endangered Wildlife, Cincinnati Zoo and Botanical Garden, Cincinnati, OH, USA
In response to growing terrorism concerns, the Transportation Security Administration (TSA) now requires that all checked baggage at U.S. airports be scanned through a cabinet X-ray system, which may increase the risk of radiation damage to transported biologic samples. Ionizing radiation, such as X-rays, potentially may cause both double-strand (DS) and single-strand (SS) DNA breaks. Gametes are particularly susceptible to radiation-induced damage due to reduced capacity of DNA repair mechanisms.1,2 Of particular concern, DNA damage in gametes or embryos may produce inheritable defects in resulting offspring. Other aspects of gamete function, such as sperm motility, also may be directly or indirectly affected by DNA damage. The objective of this study was to investigate the effect of these new airport security regulations on the viability and DNA integrity of frozen felid spermatozoa. Semen was collected from two domestic cats (Felis silvestris catus) and one fishing cat (Prionailurus viverrinus), cryopreserved in plastic freezing straws, and transferred into liquid nitrogen dry shippers for security screening. Treatment groups included frozen sperm samples from each male scanned once or three times using a TSA-operated cabinet X-ray system, in addition to non-scanned samples (i.e., negative control) and samples, previously scanned three times, exposed to five additional high intensity X-ray bursts (i.e., positive control). Dosimeters placed in empty dry shippers were used to quantify radiation exposure. Following treatment, semen straws were thawed and spermatozoa analyzed for post-thaw motility (percent motile, rate of progressive movement), acrosome status, and DNA integrity using single-cell gel electrophoresis (i.e., the comet assay).3-5 Dosimeter measurements determined that each airport screening procedure produced ~16 mRem of radiation exposure. Our results indicated that all levels of radiation exposure adversely affected (p<0.05) post-thaw sperm motility. However, there were no differences (p>0.05) in percentage of acrosome-intact spermatozoa among treatment groups. Results also showed that the amount of double-stranded DNA damage was greater (p<0.05) in sperm samples from both cat species scanned three times compared to samples scanned once or negative controls. Our findings demonstrate that new airport security measures may cause radiation-induced damage to frozen felid spermatozoa and suggest that similar damage may occur in other valuable biologic samples when transported on passenger aircraft. We recommend that alternative modes of sample transportation should be used whenever possible.
The authors thank the University of Cincinnati’s Radiation Safety Department for provision of dosimeters and the Transportation Security Administration at the Cincinnati-Northern Kentucky International Airport for their cooperation. We also would like to thank Helen Bateman, Jennifer Bond, Jenny Kroll, Dr. Jason Herrick, Dr. Genevieve Magarey and Dr. Mark Campbell for support with laboratory and animal procedures.
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