nanoRISK Vol 5, Iss 5

With fully conclusive findings about the toxicity of carbon nanotubes (CNTs) still up in the air, research on biomedical applications of CNTs is pushing full steam ahead. Adding to the list of potential concerns, a recent nanotoxicology study by a U.S.-Chinese research team looked into the impact of carbon nanotubes on male reproductive health. The translocation and biodistribution of nanoparticles are key factors in their toxicity evaluation in vivo. Although other nanoparticles such as gold and magnetic nanoparticles have been reported to enter testes in small quantities, it had not been established whether CNTs could enter or accumulate in the testis. "Our pilot study investigated the effects of intravenous injection of single and multiple doses of water-soluble multiwalled carbon nanotubes on the reproductive systems of male mice," says Bing Yan, Director, High-Throughput Analytical Chemistry Facility at St. Jude Children's Research Hospital in Memphis, TN. "Although our study showed that carbon nanotubes have minor effects on the male reproductive system in mice, oxidative stress and the alterations in the testes raise concerns because it is possible that these materials may accumulate at higher quantities over a longer period and may have adverse effects on male fertility." Reporting their findings in Nature Nanotechnology ("Repeated administrations of carbon nanotubes in male mice cause reversible testis damage without affecting fertility"), Yan and his colleagues together with collaborators from Shadong University in Jinan, China, conclude that carbon nanotubes, when used at their doses and schedule, can cause reversible testis damage and reactive oxygen species (ROS) generation without changing the hormonal levels, sperm health, and male mice fertility. To mimic the potential biomedical applications of the carbon nanotubes in terms of administration method and dose, the team intravenously injected the nanotube suspension through the tail vein into healthy adult male mice. The nanotubes were administered either as a single dose of 5 mg per kg or in five doses over 13 days at 5 mg per kg per dose. They then conducted reproductive toxicologic assessments on days 15, 60 and 90.