Oxidatively damaged DNA in rats exposed by oral gavage to C60 fullerenes and single-walled carbon nanotubes

Abstract

Background: C60 fullerenes and single-walled carbon nanotubes (SWCNT) are projected to be used in medicine and consumer products with potential human exposure. The hazardous effects of these particles are expected to involve oxidative stress with generation of oxidatively damaged DNA that might be the initiating event in the development of cancer.

Objective: In this study we investigated the effect of a single oral administration of C60 fullerenes and SWCNT.

Methods: We measured the level of oxidative damage to DNA as the premutagenic 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in the colon mucosa, liver, and lung of rats after intragastric administration of pristine C60 fullerenes or SWCNT (0.064 or 0.64 mg/kg body weight) suspended in saline solution or corn oil. We investigated the regulation of DNA repair systems toward 8-oxodG in liver and lung tissue.

Results: Both doses of SWCNT increased the levels of 8-oxodG in liver and lung. Administration of C60 fullerenes increased the hepatic level of 8-oxodG, whereas only the high dose generated 8-oxodG in the lung. We detected no effects on 8-oxodG in colon mucosa. Suspension of particles in saline solution or corn oil yielded a similar extent of genotoxicity, whereas corn oil per se generated more genotoxicity than the particles. Although there was increased mRNA expression of 8-oxoguanine DNA glycosylase in the liver of C60 fullerene-treated rats, we found no significant increase in repair activity.

Conclusions: Oral exposure to low doses of C60 fullerenes and SWCNT is associated with elevated levels of 8-oxodG in the liver and lung, which is likely to be caused by a direct genotoxic ability rather than an inhibition of the DNA repair system.

Keywords: DNA damage; DNA repair; cancer; nanoparticle; oxidative stress.

Figure 1

ROS production [in arbitrary units (AU)] by C₆₀ fullerenes, SWCNT, Printex 90 carbon black, and SRM2975 in Hank’s balanced saline solution detected as 2′,7′-dichlorofluorescein. Each point represents the mean ROS production of duplicate replicates in two independent experiments; the dotted line represents incubations without particles (quadruplicate in two independent experiments). ^*p < 0.05 compared with incubations without particles.

Figure 2

Level of 8-oxodG in liver (A), lung (B), and colon (C) tissue 24 hr after oral exposure to a single dose of C₆₀ fullerenes or SWCNT suspended in saline or corn oil. Values shown are mean ± SE of 8 treated animals and 10 control animals. ^*p < 0.05 compared with the control group (single-factor effect of particle exposure, ANOVA).

Figure 3

OGG1 repair activity in the liver 24 hr after exposure to a single dose of C₆₀ fullerenes or SWCNT dissolved in saline or corn oil. The activity is indicated as the number of repair incisions in arbitrary units (AU) of substrate nuclei treated with Ro19-8022 and white light, which generate oxidative damage to the DNA. Values shown are mean ± SE for 8 treated animals and 10 control animals).