REVIEW ARTICLE Toxicity of pristine versus functionalized fullerenes: mechanisms of cell damage and the role of oxidative stress Andreja Trpkovic • Biljana Todorovic-Markovic • Vladimir Trajkovic Received: 27 March 2012 / Accepted: 12 April 2012 Ó Springer-Verlag 2012 Abstract The fullerene C 60 , due to the physicochemical properties of its spherical cage-like molecule build exclu- sively from carbon atoms, is able to both scavenge and generate reactive oxygen species. While this unique dual property could be exploited in biomedicine, the low water solubility of C 60 hampers the investigation of its behavior in biological systems. The C 60 can be brought into water by solvent extraction, by complexation with surfactants/ polymers, or by long-term stirring, yielding pristine (unmodified) fullerene suspensions. On the other hand, a modification of the C 60 core by the attachment of various functional groups results in the formation of water-soluble fullerene derivatives. Assessment of toxicity associated with C 60 preparations is of pivotal importance for their biomedical application as cytoprotective (antioxidant), cytotoxic (anticancer), or drug delivery agents. Moreover, the widespread industrial utilization of fullerenes may also have implications for human health. However, the altera- tions in physicochemical properties imposed by the utili- zation of different methods for C 60 solubilization profoundly influence toxicological effects of fullerene preparations, thus making the analysis of their potential therapeutic and environmental toxicity difficult. This review provides a comprehensive evaluation of the in vitro and in vivo toxicity of fullerenes, focusing on the com- parison between pristine and derivatized C 60 preparations and the mechanisms of their toxicity to mammalian cells and tissues. Keywords Fullerenes Á Cytotoxicity Á Genotoxicity Á Oxidative stress Á In vitro Á In vivo Introduction Fullerenes, the spherical carbon cage sp 2 -hybridized mol- ecules, represent a third carbon allotrope. The C 60 mole- cule, consisting of 60 carbon atoms, was the first fullerene discovered by Kroto et al. (1985) in soot derived from ablation of graphite with laser. Numerous fullerenes with other carbon numbers, for example higher fullerenes (C 70 , C 76 ,C 78 ,C 82 ) and the lower-order fullerenes (C 28 ,C 36 ), have been subsequently produced (Diederich et al. 1991; Guo et al. 1992; Piskoti et al. 1998). Fullerenes have since been found to occur naturally in materials affected by high- energy events such as lightning strikes, in meteors and geologic samples (Buseck et al. 1992; Pizzarello et al. 2001). The most common fullerene in natural occurrence is C 60 , a stable icosahedron with C 5 –C 5 single bonds forming 12 pentagons and C 5 –C 6 double bonds forming 20 hexa- gons (Kra ¨tschmer et al. 1990). Thirty carbon double bonds present in the C 60 structure readily accept free radicals, so C 60 has been designated as a ‘‘free radical sponge’’ (Krusic et al. 1991). On the other hand, C 60 is able to generate highly reactive oxygen species (ROS) after excitation by visible or UV light (Arbogast et al. 1991; Guldi and Prato 2000). Fullerenes efficiently generate singlet oxygen ( 1 O 2 ) upon irradiation via energy transfer to oxygen (type II photochemical mechanism) (Arbogast et al. 1991). The photoirradiation of fullerenes may also result in the A. Trpkovic (&) Á B. Todorovic-Markovic Vinca Institute of Nuclear Sciences, University of Belgrade, POB 522, Belgrade 11000, Serbia e-mail: trpkovic_a@vinca.rs V. Trajkovic (&) School of Medicine, Institute of Microbiology and Immunology, University of Belgrade, Dr. Subotica 1, Belgrade 11000, Serbia e-mail: vtrajkovic@med.bg.ac.rs 123 Arch Toxicol DOI 10.1007/s00204-012-0859-6