Cytoprotective Activities of Water-Soluble Fullerenes in Zebrafish Models - Zebrafish: Methods for Assessing Drug Safety and Toxicity - page 269

mentioned that even the least effective fullerenes in this group are three- to fourfold
more effective than glutathione (EC 50 ¼ M) (Garetz et al., 1994; Lautermann

et al., 1995; Pourbakht and Yamasoba, 2003; Ton and Parng, 2005), which has been
used successfully in animal models to protect against aminoglycoside-induced
hearing loss and renal injury.

438 m

19.4 DISCUSSION

Anionic water-soluble fullerenes have previously been shown to exhibit cytoprotective
and antioxidant effects in both cell culture and various animal models (Dugan
et al., 1996, 1997, 2001; Lai and Chiang, 1997; Tsai et al., 1997; Chi et al., 1998;
Huang et al., 1998, 2001a, 2001b; Lai et al., 1998, 2000; Chueh et al., 1999; Lin et al.,
1999, 2000, 2001, 2002, 2004; Puhaca, 1999; Straface et al., 1999; Bisaglia et al., 2000;
Fumelli et al., 2000; Lee et al., 2000; Monti et al., 2000; Tagmatarchis and
Shinohara, 2001; Yang et al., 2001; Foley et al., 2002; Murugan et al., 2002; Tzeng
et al., 2002; Bosi et al., 2003; Ali et al., 2004; Chen et al., 2004; Witte et al., 2007). Our
current results described above indicate that at least in a highly accessible zebrafish
embryo model system, water-soluble anionic fullerenes can block apoptosis of specific
cell types induced by chemical toxins and commonly used drugs whose toxicity is well
characterized in mammalian systems, including in some cases, humans. However, our
results also indicate that the mechanisms by which various modified fullerenes can
protect cells fromapoptosis are not monolithic and dependupon the specificmechanism
of toxicity, even in a single cell type. Clearly, cisplatinum and gentamicin have very
different binding and chemical activities, and the differential ability of fullerenes to
protect against these two toxins may reflect the intracellular localization of each
fullerene, the chemical reactivity against unknown reactive compounds or intermedi-
ates, or the ability to interact with proteins or other biological molecules involved in
apoptosis signaling and regulation. In this context, the ability of some anionic fullerenes
to bind to cytochrome c is of particular interest. Cytochrome c is located within
mitochondria and is released to the cytosol after apoptosis-inducing signals are
activated either at the cell surface or within the cell. Cytoplasmic cytochrome c
facilitates the activation of cytoplasmic caspase cascades, triggering irreversible steps
in the apoptosis pathway.
Our current results do not address whether or not fullerenes actually interact
directly or indirectly with cytochrome c or related proteins nor do they elucidate
whether this could occur in mitochondria, cytoplasm, or both. They do, however,
indicate that fullerenes are capable of interacting with cytochrome c in vitro (Witte
et al., 2007). Moreover, our results suggest that the ability of various fullerenes to
interact with cytochrome c is somehow linked to the ability to protect against
apoptosis induced by cisplatinum, but not gentamicin, in mechanoreceptor hair cells.
Some of our water-soluble fullerenes, such as 4, exhibit cytoprotective activity against
both cisplatinum- and gentamicin-induced apoptosis and may prove to be useful as
candidates for antiapoptosis drugs.
While some water-soluble fullerenes can exhibit cytoprotective activities,
others show predominantly toxic effects. For example, C3 (1) is largely protective