About this Journal Submit a Manuscript Table of Contents
BioMed Research International
Volume 2013 (2013), Article ID 751913, 9 pages
http://dx.doi.org/10.1155/2013/751913
Review Article

Fullerenols as a New Therapeutic Approach in Nanomedicine

1Department of Molecular Biophysics, Faculty of Biology and Environmental Protection, University of Lodz, ul. Pomorska 141/143, 90-236 Lodz, Poland
2Department of Neurobiology, Faculty of Biology and Environmental Protection, University of Lodz, ul. Pomorska 141/143, 90-236 Lodz, Poland

Received 27 July 2013; Accepted 18 September 2013

Academic Editor: Antoni Camins

Copyright © 2013 Jacek Grebowski et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Recently, much attention has been paid to the bioactive properties of water-soluble fullerene derivatives: fullerenols, with emphasis on their pro- and antioxidative properties. Due to their hydrophilic properties and the ability to scavenge free radicals, fullerenols may, in the future, provide a serious alternative to the currently used pharmacological methods in chemotherapy, treatment of neurodegenerative diseases, and radiobiology. Some of the most widely used drugs in chemotherapy are anthracycline antibiotics. Anthracycline therapy, in spite of its effective antitumor activity, induces systemic oxidative stress, which interferes with the effectiveness of the treatment and results in serious side effects. Fullerenols may counteract the harmful effects of anthracyclines by scavenging free radicals and thereby improve the effects of chemotherapy. Additionally, due to the hollow spherical shape, fullerenols may be used as drug carriers. Moreover, because of the existence of the currently ineffective ways for neurodegenerative diseases treatment, alternative compounds, which could prevent the negative effects of oxidative stress in the brain, are still sought. In the search of alternative methods of treatment and diagnosis, today’s science is increasingly reaching for tools in the field of nanomedicine, for example, fullerenes and their water-soluble derivatives, which is addressed in the present paper.

1. Introduction

In recent years, much attention has been paid to research on the bioactive characteristics of newly discovered water-soluble fullerene derivatives. Greater emphasis has been placed on their pro- and antioxidant properties [14] which result from the presence of delocalized double bonds in the fullerene cage. The poor solubility of fullerenes in polar liquids has been a major hindrance in terms of their potential biomedical applications. Therefore, the possibility of attaching polar functional groups to the carbon fullerene cage, in an effort to increase their solubility in polar solvents (especially in water), was explored. Fullerene derivatives with hydrophilic properties were obtained by adding hydroxyl groups to , resulting in a polyhydroxylated fullerene (fullerenol; fullerol, ) [58]. The general structure of fullerenol is shown in Figure 1. The fullerenol molecule can be excited and transformed into the triplet state with visible or ultraviolet light creating a reactive molecule that easily interacts with oxygen or biomolecules and has applications in photosensitization [2, 9].

751913.fig.001
Figure 1: The structure of fullerenol.

One of the first reports on the potential antioxidative properties of fullerenol is from the 1995 study, where Chiang et al. [10] showed that fullerenol acted as an effective scavenger of superoxide anions ( ) generated by the xanthine-xanthine oxidase system. The antioxidant properties of fullerenols have also been extensively described by Nielsen et al. [11] and Markovic and Trajkovic [1] in their comprehensive review papers. In addition to the ability for scavenging reactive oxygen species (ROS), fullerenols also inhibit the reaction of reactive nitrogen species by reacting directly with nitric oxide (NO) [12].

The dualistic nature of fullerenols may lead to the practical application of these compounds as cytotoxic agents against tumor cells or as protective agents in normal cells [1]. Additionally, due to their hollow spherical shape, fullerenols may be used as carriers of contrast agents, radiopharmaceuticals, and drugs, serving as promising tools with applications in medical diagnostics and therapy.

2. Fullerenols as Free Radical Scavengers

Fullerenes are considered to be effective scavengers of free radicals based on the large numbers of conjugated double bonds with low energy unoccupied molecular orbitals (LUMO), which can easily take up an electron, facilitating reactions with radical species [14]. Due to their ability to scavenge free radicals, fullerenes have been called “radical sponges” [15]. The most commonly used free radical scavengers are water-soluble derivatives such as PEG- , PVP- , and [16]. The antioxidant properties of fullerenol were tested by electron paramagnetic resonance (EPR) and by measuring the ability to scavenge the stable 2,2-diphenyl-1-picrylhydrazyl (DPPH) and hydroxyl radicals ( ) generated by the Fenton reaction. High concentrations of fullerenol (0.71–0.88 mmol/L) are more effective at scavenging hydroxyl radicals (50–82%) than DPPH (28–50%). Fullerenol may also function as an antioxidant by the donation of the hydrogen atom, abstracted from the hydroxyl group, to the particular radical compound (DPPH and ), which was confirmed by EPR detection of , a fullerenol radical. Interaction between a hydroxyl radical and fullerenol may also occur by the addition of radicals to the olefinic double bonds between carbon atoms constituting the fullerene core by the following reaction: ( –12). However, these two mechanisms are not mutually exclusive [17].

Chiang et al. [10] described fullerenol as an effective reactive oxygen species scavenger, which led to exploring fullerenol scavenging properties towards   in vivo. Interestingly, fullerenol reduced oxidative stress in dogs during small intestine transplantation [18]. During the transplantation procedure, oxidative stress occurs as a result of two independent processes. The first is linked to cell function as a result of ischemia, where there is a reduction in the level of oxygen delivered to the tissues (hypoxia) leading to a decrease in ATP concentration and subsequent accumulation of purine metabolites in excess (mainly hypoxanthine and xanthine). The second process leading to oxidative stress is reperfusion (or restoration of blood circulation) resulting in a “respiratory burst” of the previously ischemic cells. Administration of fullerenol reduced the high concentration of ROS caused by the ischemia-reperfusion injury, demonstrated by measuring levels of malondialdehyde (MDA) and glutathione (GSH) [19]. Fullerenol ( ,      22–24) also protected rat hepatocytes against damage induced by carbon tetrachloride ( ) by improving their antioxidant capacity. Treatment with led to normalized serum levels of liver injury (ALT, AST) and renal function markers (BUN, CREA) and exerted a beneficial effect on the level of reduced glutathione in the liver [20].

The antioxidant properties of fullerenol were compared to those of fullerene with two residues of malonic acid attached ( ) and metallofullerenol with gadolinium (Gd@ ) in their ability to protect human lung (A549) and rat brain cells (rBCEC) from oxidative damage. Spin-trapping provided direct evidence that fullerene derivatives can scavenge radicals formed under physiological conditions ( , and ), as well as the stable DPPH radical, preventing peroxidation of lipids [21]. The attachment of malonic acid residues or hydroxyl groups to the fullerene cage results in an electron-deficient area which facilitates the binding of free radicals to the fullerene molecule [21]. Gadolinium attachment (Gd@ ) results in a more potent antioxidant than and may be due to the higher electron affinity of Gd@ (3,14 eV) compared to (2,7 eV).

In recent years it has been observed that, besides scavenging ROS, fullerenol may also directly scavenge nitric oxide (NO) [12] synthesized by the family of nitric oxide synthase (NOS) enzymes. Nitric oxide is an important signaling molecule involved in many physiological processes, such as the regulation of vascular tone or neuromodulation, but at high concentrations exerts a cytotoxic effect [22]. Mirkov et al. [12] suggested that has the ability to scavenge NO in vivo, and treatment with fullerenol 30 min before the addition of sodium nitroprusside (SNP), a potent NO donor, to adult rat testicular interstitial cells prevented a reduction in antioxidant enzyme activity.

A review of the recent literature indicates a growing interest in highly hydroxylated fullerenols for their antioxidant properties. Xiao et al. [3] showed that highly hydroxylated fullerene protected cells from oxidative stress induced by H2O2. Fullerenol also showed a protective effect in the β-carotene bleaching assay [23]. The authors suggested that scavenges the radicals produced from the dehydrogenation of and simultaneously oxidizes them to a stable radical species (potentially the dehydrogenated fullerenol radical - ). The existence of such a radical has been confirmed by Djordjevic et al. [17] through the use of the EPR method.

Due to their properties, fullerenols can be used in radiobiology, chemotherapy, or in the treatment of neurodegenerative diseases. These issues and information on the toxicity of fullerenols in various biological systems are presented in the following sections of this paper.

3. Potential Application of Fullerenols in Radiobiology

When determining the extent of damage in biological systems exposed to low LET (linear energy transfer) radiation, it is believed that the radiation injuries arise due to the indirect action of radiation on the cell. The high water content of living cells (an average cell contains about 70% of ) makes the water molecules more susceptible to radiolysis than the other molecules, where the effects involve the transfer of radiation energy to water molecules, which in turn results in excitation and decay. [24, 25]. As a result of the radiolysis of water, a number of reactive species are formed, most of which are radicals capable of reacting with biological molecules and influencing their functions. The most reactive oxidant is the hydroxyl radical, having a very high redox potential which allows it to react with virtually every molecule found in the cell [26, 27].

In studies concerning the possible use of fullerenes for radioprotection, their water-soluble derivatives (fullerenols) are particularly interesting. Fullerenols meet all the conditions for a good radioprotectant: the presence of double bonds (C=C), high electron affinity, ease of radical binding, and reactivity towards nucleophilic substituents [28]. The radioprotective properties of fullerenol have been confirmed by in vitro studies conducted on the human acute myeloid leukemia cell line K562. Cells were preincubated with 10 mM and then irradiated with X-ray at 24 Gy. It was found that fullerenol exhibited a protective effect on the cells, their morphology, and their ability to form colonies [29]. Fullerenol also inhibited the radiation-induced inactivation of antioxidative enzymes such as superoxide dismutase and glutathione peroxidase [30].

The next step was to demonstrate the radioprotective properties of fullerenol in vivo. Mice were administered fullerenol at 10 mg/kg and 100 mg/kg 30 min prior to irradiation with X-ray at the dose of 6 to 8 Gy. Fullerenol at 100 mg/kg was protective against high doses of radiation in comparison to the control group, while the concentration of 10 mg/kg was not significantly protective [31]. The radioprotective effects of fullerenol were also observed in Wistar rats [32] where it was compared with amifostine, a compound protecting healthy tissue from damage induced by radio- or chemotherapy. Amifostine (WR 2721) is an inorganic thiophosphate activated by dephosphorylation, resulting in free active thiol production (WR 1065). The dephosphorylation process is catalyzed by alkaline phosphatase, whose concentration in normal tissues is significantly higher than in tumors [3336]. Both amifostine and fullerenol extended the life span of rats by at least 30 days after irradiation with a lethal dose of 8 Gy. Furthermore, at a dose of 100–300 mg/kg, fullerenol was more effective than amifostine at protecting white blood cells during the first and second week after irradiation. The radioprotective effects of both compounds were highly selective, with fullerenol effectively protecting spleen, small intestine, and lung, while amifostine was more effective in protecting heart, liver, and kidneys [32]. These data are in accordance with the results of Cai et al. [37], where mice were given 40 mg/kg fullerenol daily for two weeks and irradiated with a lethal radiation dose of 8 Gy, and the 30-day survival rate was determined. The survival rate for animals treated with fullerenol before irradiation was 73%, while in the control group (no fullerenol) survival was 0%. Mitochondrial dysfunction, oxidative damage (e.g., levels of MDA, GSH, and SOD activity), and the amount of carbonyl groups in liver cells were also analyzed. It has been shown that fullerenol protected superoxide dismutase (SOD), prevented the oxidation of glutathione (GSH), and decreased hepatic lipid peroxidation (the level of MDA), which were attributed to the ability of to scavenge lipid radicals and ROS. Moreover, fullerenol protected mitochondrial proteins against oxidation, supported the maintenance of the mitochondrial membrane potential, and inhibited apoptosis induced by ionizing radiation. These data indicate that fullerenol possesses radioprotective properties; however, it should be noted that the protective nature of fullerenol may be concentration dependent. Zhao et al. [38] observed that fullerenol ( –22) used at 0.25 mg/mL in Stylonychia mytilus bacteria induced a radiosensitizing effect manifested as a decrease in superoxide dismutase and catalase activity as well as increased levels of lipid peroxidation. Fullerenol used in concentrations below 0.06–0.1 mg/mL has been shown to act as a radioprotectant against gamma radiation from 60Co at doses up to 1500 Gy. This phenomenon illustrates the “concentration effect” and could be exploited when designing an experimental protocol, where, depending on the dose used, radioprotective or radiosensitizing effects may dominate.

Recent research, investigating the role of fullerenol in modulation of the response of K562 leukemic cells to irradiation, indicated that fullerenol improved survival of the irradiated cells and produced significant overexpression of antiapoptotic Bcl-2 and Bcl-xL proteins as well as cytoprotective GSTA4, MnSOD, NOS, CAT, and HO-1 genes [39].

4. Fullerenol and Chemotherapy

Chemotherapy (in addition to radiation therapy) is one of the most common treatments for cancer and may be used in a combination with surgery and/or radiation therapy. Some of the most widely used drugs in anticancer therapy are anthracycline antibiotics. Anthracyclines are well-known DNA intercalating agents and their primary mechanism of action is ascribed to interference with the function of DNA topoisomerase II. The effect of anthracyclines on cancer cells is also based on the modification of DNA structure by reactive oxygen species. The reactive species could induce DNA damage and lipid peroxidation with formation of malondialdehyde (MDA) which reacts at the exocyclic amino groups of deoxyguanosine, deoxyadenosine, and deoxycytidine to form alkylated products. The redox cycle of anthracyclines is seen in Figure 2 [40, 41].

751913.fig.002
Figure 2: One-electron redox cycle of anthracyclines. One-electron addition to the quinone moiety in the ring of carbon atoms of DOX and other anthracyclines result in the formation of a semiquinone that quickly regenerates its parent quinone by reducing oxygen to reactive oxygen species (ROS) like and . ROS generated in redox cycle of anthracyclines induce oxidative DNA damage.

Anthracycline therapy, in spite of its effective antitumor activity, induces systemic oxidative stress, which interferes with the effectiveness of the treatment and results in serious side effects such as cardiotoxicity. Heart muscle tissue has a low activity of antioxidant enzymes, which in turn leads to increased myocardial susceptibility to oxidative stress [42]. The cardioprotective effects of fullerenol have been shown in vivo on Wistar rats [43, 44]. The latency period for the appearance of reflex bradycardia on the ECG of the doxorubicin-treated group of animals was significantly longer than latency for the control group and groups pretreated with fullerenol at 30 mg/kg and 100 mg/kg. Significantly increased levels of LDH, ALAT, ASPAT, CK, and alfa-HBDH were detected in the animals treated only with doxorubicin (DOX), indicating acute myocardial membrane damage, while animals pretreated with 100 mg/kg of fullerenol showed physiological levels/activities of these enzymes. Fullerenol did not modulate any enzyme activity when given alone.

Histopathological examination of the heart with light microscopy showed that the extent of damage to heart tissue was significantly lower in animals pretreated with fullerenol compared to animals treated only with DOX. However, when fullerenol (100 mg/kg) was given alone, it caused mild vascular changes which, most likely, were reversible [44]. Considering that the DOX toxicity is based on free radical production, it can be concluded that the protective role of fullerenol relies on its high antioxidative potential, acting as a free radical scavenger and/or by removing free iron ions through the formation of the fullerenol-iron complex and preventing the Fenton/Haber-Weiss reaction [44]. The antioxidant properties of fullerenol preventing oxidative stress induced by doxorubicin in kidneys, testes, and lungs of rats were confirmed by Srdjenovic et al. [45]. Pretreatment of rats with fullerenol at 50 mg/kg or 100 mg/kg significantly lowered the level of lipid peroxidation induced by DOX and restored SOD, CAT, GSH-Px, GST, and GR to control levels. However, fullerenol-pretreated rats had higher values of lipid peroxidation compared to the control groups but lower than animals treated with DOX alone.

Beneficial effect of fullerenol on the activity of antioxidant enzymes was confirmed in erythrocytes after a single dose administration of doxorubicin in rats pretreated with [46] as well as in hepatocytes from rats with colorectal cancer [43] and mammary carcinomas [47].

Another example of the protection of cells by the fullerenol is seen in the action of antitumor drugs and against breast cancer cells. Human breast cancer cell lines MCF-7 and MDA-MB-231 were treated with fullerenol at concentrations from 0.9 to 3.9 mg/L, alone or simultaneously with other antitumor drugs (doxorubicin, cisplatin, taxol, and tiazofurin). The fullerenol alone mildly inhibited the growth of both cell lines, while simultaneous treatment with fullerenol and antitumor drugs suppressed antitumor drug-induced cytotoxicity. The level of cytotoxicity inhibition depended on fullerenol concentration, type of antitumor drug, and cell line. Protection against doxorubicin and cisplatin was more pronounced than that against taxol and tiazofurin. Fullerenol was not found to be genotoxic to either cell line [48].

The cancer treatment potential for fullerenol is based on its use as a carrier for the transport of anthracyclines. Chaudhuri et al. [49] conjugated fullerenol and doxorubicin (Ful-DOX) which was found to be relatively stable in phosphate buffer saline but temporally released active drug when incubated with tumor cell lysate. The fullerenol-doxorubicin conjugate suppressed the proliferation of cancer cell lines (mouse melanoma cell line (B16-F10), mouse lung carcinoma (LLC1), and metastatic human breast cancer cell line (MDA-MB-231)) in vitro by blocking G2-M progression, resulting in apoptosis. However, the conjugate was less efficacious against human MDA-MB-231 cells than against murine cell lines. This difference was connected with different susceptibility of MDA-MB-231 and the B16-F10 cells to the internalization of the drug-nanostructure conjugates into the cells and into the lysosomes. In an in vivo murine tumor model, fullerenol-doxorubicin had comparable antitumor efficacy to free doxorubicin without the systemic toxicity of free doxorubicin.

Interesting results were obtained by Yin et al. [50]. They observed that Gd@ could interact with collagen by regulating the assembly of collagen fibrils and changing the biophysical properties of this protein. The fibrous layers, built of collagen and surrounding the tumor surface, became thicker and softer after the treatment with Gd@ , and the metastasis of tumor was largely suppressed.

The many hydroxyl groups present on the surface of fullerenol enable not only attachment of various compounds (including drug molecules), but also the creation of multiple hydrogen bonds with various components of biological systems (such as protein domains of the plasma membrane or hydrophilic lipid heads) [51]. Our experiments have shown that fullerenol can be adsorbed to erythrocyte cytoskeletal proteins [13] and this interaction can be used as a drug transport mechanism (Figure 3). Prolonging the residence time of a substance (drug) in the circulation is possible by attaching it to residues in the erythrocyte membrane such as band 3 protein or glycophorin. This method has been described by Krantz [52] and is based on the use of “anchors”—molecules with functional groups with strong affinity for erythrocyte cytoskeletal proteins. As fullerenol is covered with polar OH groups, it is well suited to function as an “anchor” [13].

751913.fig.003
Figure 3: Fullerenol interactions with the band 3 protein and the location of fullerenol in the lipid bilayer. Fullerenol , by associating with band 3 protein, does not only prevent its degradation, but can also influence the binding sites of spectrin, band 4.1 and 4.2 proteins, or actin, leading to changes in the cytoskeleton affecting erythrocyte morphology (from [13] modified).

Since fullerenol could protect human cancer cells in vitro against irradiation as it was shown in the papers of Icević et al. [29] and Stankov et al. [39]; it is suggested that the stratagem for fullerenols use in cancer should be based more on their ability to produce phototoxic [53] or photothermal [54] effects and to attach various compounds, including drug molecules, to hydroxyl groups of fullerenol.

However, fullerenol exhibited antitumor and antimetastatic activities in vivo in EMT-6 breast cancer metastasis model and no direct toxic effects on the growth of MCF-7 tumor cells in vitro. Modulation of oxidative stress in tumor tissues, inhibition of the formation of angiogenesis factors, and subsequent reduction in tumor vessel density and the nutrient supply to tumor cells could be important mechanisms by which fullerenol inhibits tumor growth and suppresses carcinoma metastasis in vivo [55]. The antineoplastic efficiency of the particles in H22 hepatoma-implanted mice was even much higher than that of cyclophosphamide and cisplatin [47].

5. Neuroprotective Properties of Fullerenols

Biological oxidation is common in brain tissue and is accompanied by free radical formation and compounded by relatively low efficiency antioxidant defense mechanisms [5658]. Nerve cells are lipid rich, have predominantly aerobic metabolism (consuming 20% of the oxygen taken up by the body), and have a low activity of reactive oxygen species (ROS) eliminating enzymes, which make them a major target for free radical reactions [59]. Oxidative stress may mediate excitotoxic neuronal damage, resulting in an excessive stimulation of, for example, glutamate receptors [60] as well as the apoptotic death of neurons [61]. While apoptosis is part of the natural process of neurogenesis, it can also contribute to the loss of neurons in pathological conditions such as cerebral ischemia, Huntington’s disease (HD), or Alzheimer’s disease (AD) [62, 63]. Some nerve cells, particularly astrocytes and oligodendrocytes (in basal ganglia or the hippocampus), are susceptible to oxidative stress as they may accumulate iron ions as part of protein complexes [64]. The toxicity of iron ions is due to their ability to initiate the process of lipid peroxidation, which involves decomposition of lipid peroxides leading to the formation of free radical species [65, 66]. Increased levels of iron are observed in the substantia nigra of patients affected by Parkinson’s disease (PD) [67].

As there are no effective treatments for neurodegenerative diseases, alternative compounds which could prevent the negative effects of oxidative stress on the brain are still in demand. These compounds could include fullerenols, which are currently being evaluated as antioxidants for preventing the formation of amyloid plaques in AD [6872] and as protective compounds for other neurodegenerative diseases whose cause may be associated with an oxidative imbalance within cells.

Water-soluble derivatives of fullerenes (fullerenols and malonic acid derivatives) scavenge ROS more efficiently than conventional antioxidants [32, 7376]. Therefore, hydrophilic fullerene derivatives are promising candidates for use as neuroprotective and antioxidant agents, as confirmed in electrophysiological studies indicating that two fullerene derivatives ( and ) showed excellent antioxidant properties (confirmed by electron paramagnetic resonance). These fullerene derivatives decreased excitotoxicity-induced neuronal death of mouse neocortical neurons up to 80% and were antiapoptotic [74]. Similar results were obtained by Jin et al. [77], who demonstrated that fullerenols exerted a neuroprotective effect on neuronal cultures in vitro by blocking glutamate receptors and reducing the concentration of intracellular calcium.

It is interesting to note that the carboxyl derivative of effectively protected dopaminergic neurons against the harmful effects of oxidative stress caused by neurotoxins [75]. The impairment of dopaminergic neurotransmission is essential in the pathogenesis of Parkinson’s disease [78], as one of the causes of substantia nigra neuronal death in the course of PD may be the oxidation of dopamine. This may occur as a result of monoamine oxidase type B (MAOB) or autooxidation of dopamine, leading to the formation of hydrogen peroxide ( ) which in the presence of generates highly toxic radicals through the Fenton reaction. The loss of dopaminergic cells in PD only affects cells containing neuromelanin, which can bind iron ions [7981]. Interestingly, fullerenol turned out to be an effective neuroprotector in a cellular model of Parkinson’s disease. Cai et al. [76] induced oxidative stress in human neuroblastoma cells using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MTPT), a neurotoxin precursor to 1-methyl-4-phenylpyridinium (MPP+) which is oxidized to MPP by glial monoamine oxidase in astrocytes. Symptoms of Parkinson’s disease are caused by MPP+, which destroys dopaminergic neurons in the substantia nigra of the brain. MPP+ gets into dopaminergic neurons via specific transporters, leading to the inhibition of mitochondrial respiration and a reduction in the level of ATP which leads to the production of superoxide radicals and neuronal death. The authors reported that fullerenol effectively scavenged free radicals, suggesting that it may be a potential neuroprotective agent against mitochondrial dysfunction induced by MPP+. Other authors confirmed that fullerenes might accumulate in the mitochondria [82, 83].

Studies concerning the functions of particular structures of the brain are largely based on an analysis of their electroencephalographic (EEG) pattern. Electrophysiological studies conducted on hippocampal slices revealed that polyhydroxylated fullerene prevented the amplitude reduction of cell discharges caused by cumene peroxide and hydrogen peroxide [84].

In addition to its antioxidant properties, fullerenols were demonstrated to modulate the inhibition of acetylcholinesterase activity caused by certain toxic compounds in vitro [85] and were protective towards NMDA, AMPA, GABA, and KA receptors under conditions of increased oxidative stress [60, 74, 77]. Recent studies by Zha et al. [86] suggested that fullerenol protects hippocampal neurons from damage but may also induce cell death in certain doses, indicating a concentration-/dose-dependent effect.

Despite the convincing evidence concerning the neuroprotective properties of water-soluble fullerene derivatives, little is known about their mechanism of action and possible side effects occurring in the neural tissue. Therefore, the potential therapeutic properties of fullerenols in the treatment of neurologic diseases require further investigation.

6. Conclusion

The interest in hydroxylated fullerenes and their applications continues, as every year there are new reports on the impact of fullerenols on various systems. Despite convincing evidence of the potential applications of fullerenols in biomedicine, there is still insufficient knowledge about the mechanism of action of these molecules and their possible side effects.

Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

Acknowledgments

The project was funded by the National Science Centre, Poland. Funds were awarded on the basis of the Agreement no. 2011/03/N/ST4/01281.

References

  1. Z. Markovic and V. Trajkovic, “Biomedical potential of the reactive oxygen species generation and quenching by fullerenes (C60),” Biomaterials, vol. 29, no. 26, pp. 3561–3573, 2008. View at Publisher · View at Google Scholar · View at Scopus
  2. B. Vileno, A. Sienkiewicz, M. Lekka, A. J. Kulik, and L. Forró, “In vitro assay of singlet oxygen generation in the presence of water-soluble derivatives of C60,” Carbon, vol. 42, no. 5-6, pp. 1195–1198, 2004. View at Publisher · View at Google Scholar · View at Scopus
  3. L. Xiao, H. Aoshima, Y. Saitoh, and N. Miwa, “Highly hydroxylated fullerene localizes at the cytoskeleton and inhibits oxidative stress in adipocytes and a subcutaneous adipose-tissue equivalent,” Free Radical Biology and Medicine, vol. 51, no. 7, pp. 1376–1389, 2011. View at Publisher · View at Google Scholar · View at Scopus
  4. L. Xiao, H. Takada, K. Maeda, M. Haramoto, and N. Miwa, “Antioxidant effects of water-soluble fullerene derivatives against ultraviolet ray or peroxylipid through their action of scavenging the reactive oxygen species in human skin keratinocytes,” Biomedicine & Pharmacotherapy, vol. 59, no. 7, pp. 351–358, 2005. View at Publisher · View at Google Scholar · View at Scopus
  5. Z. Chen, K. Ma, G. Wang, X. Zhao, and A. Tang, “Structures and stabilities of C60(OH)4 and C60(OH)6 fullerenols,” Journal of Molecular Structure, vol. 498, no. 1, pp. 227–232, 2000. View at Publisher · View at Google Scholar · View at Scopus
  6. L. Y. Chiang, J. B. Bhonsle, L. Wang, S. F. Shu, T. M. Chang, and J. R. Hwu, “Efficient one-flask synthesis of water-soluble [60]fullerenols,” Tetrahedron, vol. 52, no. 14, pp. 4963–4972, 1996. View at Publisher · View at Google Scholar · View at Scopus
  7. K. Kokubo, K. Matsubayashi, H. Tategaki, H. Takada, and T. Oshima, “Facile synthesis of highly water-soluble fullerenes more than half-covered by hydroxyl groups,” ACS Nano, vol. 2, no. 2, pp. 327–333, 2008. View at Publisher · View at Google Scholar · View at Scopus
  8. G. Zhang, Y. Liu, D. Liang, L. Gan, and Y. Li, “Facile synthesis of isomerically pure fullerenols and formation of spherical aggregates from C60(OH)8,” Angewandte Chemie, vol. 49, no. 31, pp. 5293–5295, 2010. View at Publisher · View at Google Scholar · View at Scopus
  9. K. D. Pickering and M. R. Wiesner, “Fullerol-sensitized production of reactive oxygen species in aqueous solution,” Environmental Science & Technology, vol. 39, no. 5, pp. 1359–1365, 2005. View at Publisher · View at Google Scholar · View at Scopus
  10. L. Y. Chiang, F.-J. Lu, and J.-T. Lin, “Free radical scavenging activity of water-soluble fullerenols,” Journal of the Chemical Society, Chemical Communications, no. 12, pp. 1283–1284, 1995. View at Publisher · View at Google Scholar · View at Scopus
  11. G. D. Nielsen, M. Roursgaard, K. A. Jensen, S. S. Poulsen, and S. T. Larsen, “In vivo biology and toxicology of fullerenes and their derivatives,” Basic and Clinical Pharmacology & Toxicology, vol. 103, no. 3, pp. 197–208, 2008. View at Publisher · View at Google Scholar · View at Scopus
  12. S. M. Mirkov, A. N. Djordjevic, N. L. Andric et al., “Nitric oxide-scavenging activity of polyhydroxylated fullerenol, C60(OH)24,” Nitric Oxide, vol. 11, no. 2, pp. 201–207, 2004. View at Publisher · View at Google Scholar · View at Scopus
  13. J. Grebowski, A. Krokosz, and M. Puchala, “Fullerenol C60(OH)36 could associate to band 3 protein of human erythrocyte membranes,” Biochimica et Biophysica Acta, vol. 1828, no. 9, pp. 2007–2014, 2013.
  14. P. J. Krusic, E. Wasserman, P. N. Keizer, J. R. Morton, and K. F. Preston, “Radical reactions of C60,” Science, vol. 254, no. 5035, pp. 1183–1185, 1991. View at Scopus
  15. L. Xiao, H. Takada, X. H. Gan, and N. Miwa, “The water-soluble fullerene derivative “Radical Sponge” exerts cytoprotective action against UVA irradiation but not visible-light-catalyzed cytotoxicity in human skin keratinocytes,” Bioorganic & Medicinal Chemistry Letters, vol. 16, no. 6, pp. 1590–1595, 2006. View at Publisher · View at Google Scholar · View at Scopus
  16. A. Krokosz, “Fullerenes in biology,” Postepy Biochemii, vol. 53, no. 1, pp. 91–96, 2007. View at Scopus
  17. A. Djordjevic, J. M. Canadanovic-Brunet, M. Vojinovic-Miloradov, and G. Bogdanovic, “Antioxidant properties and hypothetic radical mechanism of fullerenol C60(OH)24,” Oxidation Communications, vol. 27, no. 4, pp. 806–812, 2004. View at Scopus
  18. H.-S. Lai, Y. Chen, W.-J. Chen, K.-J. Chang, and L.-Y. Chiang, “Free radical scavenging activity of fullerenol on grafts after small bowel transplantation in dogs,” Transplantation Proceedings, vol. 32, no. 6, pp. 1272–1274, 2000. View at Publisher · View at Google Scholar · View at Scopus
  19. H.-S. Lai, W.-J. Chen, and L.-Y. Chiang, “Free radical scavenging activity of fullerenol on the ischemia-reperfusion intestine in dogs,” World Journal of Surgery, vol. 24, no. 4, pp. 450–454, 2000. View at Publisher · View at Google Scholar · View at Scopus
  20. J.-Y. Xu, Y.-Y. Su, J.-S. Cheng et al., “Protective effects of fullerenol on carbon tetrachloride-induced acute hepatotoxicity and nephrotoxicity in rats,” Carbon, vol. 48, no. 5, pp. 1388–1396, 2010. View at Publisher · View at Google Scholar · View at Scopus
  21. J.-J. Yin, F. Lao, P. P. Fu et al., “The scavenging of reactive oxygen species and the potential for cell protection by functionalized fullerene materials,” Biomaterials, vol. 30, no. 4, pp. 611–621, 2009. View at Publisher · View at Google Scholar · View at Scopus
  22. P. Pacher, J. S. Beckman, and L. Liaudet, “Nitric oxide and peroxynitrite in health and disease,” Physiological Reviews, vol. 87, no. 1, pp. 315–424, 2007. View at Publisher · View at Google Scholar · View at Scopus
  23. S. Kato, H. Aoshima, Y. Saitoh, and N. Miwa, “Highly hydroxylated or γ-cyclodextrin-bicapped water-soluble derivative of fullerene: The antioxidant ability assessed by electron spin resonance method and β-carotene bleaching assay,” Bioorganic & Medicinal Chemistry Letters, vol. 19, no. 18, pp. 5293–5296, 2009. View at Publisher · View at Google Scholar · View at Scopus
  24. A. Krokosz and Z. Szweda-Lewandowska, “Changes in the activity of acetylcholinesterase and Na,K-ATPase in human erythrocytes irradiated with X-rays,” Cellular and Molecular Biology Letters, vol. 10, no. 3, pp. 471–478, 2005. View at Scopus
  25. A. Krokosz, R. Koziczak, M. Gonciarz, and Z. Szweda-Lewandowska, “Study of the effect of dose-rate on radiation-induced damage to human erythrocytes,” Radiation Physics and Chemistry, vol. 75, no. 1, pp. 98–105, 2006. View at Publisher · View at Google Scholar · View at Scopus
  26. M. Komorowska, A. Krokosz, and Z. Szweda-Lewandowska, “Radiation damage to human erythrocytes: influence of the composition of medium,” Radiation Physics and Chemistry, vol. 76, no. 10, pp. 1587–1593, 2007. View at Publisher · View at Google Scholar · View at Scopus
  27. Z. Szweda-Lewandowska, A. Krokosz, M. Gonciarz, W. Zajeczkowska, and M. Puchała, “Damage to human erythrocytes by radiation-generated HO radicals: molecular changes in erythrocyte membranes,” Free Radical Research, vol. 37, no. 10, pp. 1137–1143, 2003. View at Publisher · View at Google Scholar · View at Scopus
  28. J. Grębowski and A. Krokosz, “Fullerenes in radiobiology,” Postepy Biochemii, vol. 56, no. 4, pp. 456–462, 2010. View at Scopus
  29. I. Icević, V. Bogdanović, D. Zikić, S. Solajić, G. Bogdanović, and A. Djordjević, “The influence of fullerenol on cell number, cell area, and colony forming unit ability in irradiated human eritroleukemic cell line,” Hemijska Industrija, vol. 61, no. 3, pp. 167–169, 2007. View at Publisher · View at Google Scholar
  30. V. Bogdanović, K. Stankov, I. Icević et al., “Fullerenol C60(OH)24 effects on antioxidative enzymes activity in irradiated human erythroleukemia cell line,” Journal of Radiation Research, vol. 49, no. 3, pp. 321–327, 2008. View at Publisher · View at Google Scholar
  31. S. Trajkovic, S. Dobric, A. Djordjevic, V. Dragojevic-Simic, and Z. Milovanovic, “Radioprotective efficiency of fullerenol in irradiated mice,” Materials Science Forum, vol. 494, pp. 549–554, 2005. View at Publisher · View at Google Scholar · View at Scopus
  32. S. Trajković, S. Dobrić, V. Jaćević, V. Dragojević-Simić, Z. Milovanović, and A. Dordević, “Tissue-protective effects of fullerenol C60(OH)24 and amifostine in irradiated rats,” Colloids and Surfaces B, vol. 58, no. 1, pp. 39–43, 2007. View at Publisher · View at Google Scholar
  33. C. Bourgier, A. Levy, M. C. Vozenin, and E. Deutsch, “Pharmacological strategies to spare normal tissues from radiation damage: useless or overlooked therapeutics?” Cancer and Metastasis Reviews, no. 3-4, pp. 699–712, 2012.
  34. D. Citrin, A. P. Cotrim, F. Hyodo, B. J. Baum, M. C. Krishna, and J. B. Mitchell, “Radioprotectors and mitigators of radiation-induced normal tissue injury,” The Oncologist, vol. 15, no. 4, pp. 360–371, 2010. View at Publisher · View at Google Scholar · View at Scopus
  35. F. Marzatico, C. Porta, M. Moroni et al., “In vitro antioxidant properties of amifostine (WR-2721, ethyol),” Cancer Chemotherapy and Pharmacology, vol. 45, no. 2, pp. 172–176, 2000. View at Scopus
  36. S. Tabaczar, M. Talar, and K. Gwoździński, “Nitroxides as antioxidants: possibilities of their application in chemoprevention and radioprotection,” Postepy Higieny i Medycyny Doswiadczalnej, vol. 65, pp. 46–54, 2011. View at Scopus
  37. X. Cai, J. Hao, X. Zhang et al., “The polyhydroxylated fullerene derivative C60(OH)24 protects mice from ionizing-radiation-induced immune and mitochondrial dysfunction,” Toxicology and Applied Pharmacology, vol. 243, no. 1, pp. 27–34, 2010. View at Publisher · View at Google Scholar · View at Scopus
  38. Q. Zhao, Y. Li, J. Xu, R. Liu, and W. Li, “Radioprotection by fullerenols of Stylonychia mytilus exposed to γ-rays,” International Journal of Radiation Biology, vol. 81, no. 2, pp. 169–175, 2005. View at Publisher · View at Google Scholar · View at Scopus
  39. K. Stankov, I. Borisev, V. Kojic, L. Rutonjski, G. Bogdanovic, and A. Djordjevic, “Modification of antioxidative and antiapoptotic genes expression in irradiated K562 cells upon fullerenol C60(OH)624 nanoparticle treatment,” Journal of Nanoscience and Nanotechnology, vol. 13, no. 1, pp. 105–113, 2013. View at Publisher · View at Google Scholar
  40. G. L. Beretta and F. Zunino, “Molecular mechanisms of anthracycline activity,” Topics in Current Chemistry, vol. 283, pp. 1–19, 2008.
  41. G. Minotti, P. Menna, E. Salvatorelli, G. Cairo, and L. Gianni, “Anthracyclines: molecular advances and pharmacologie developments in antitumor activity and cardiotoxicity,” Pharmacological Reviews, vol. 56, no. 2, pp. 185–229, 2004. View at Publisher · View at Google Scholar · View at Scopus
  42. P. Menna, O. Gonzalez Paz, M. Chello, E. Covino, E. Salvatorelli, and G. Minotti, “Anthracycline cardiotoxicity,” Expert Opinion on Drug Safety, vol. 11, no. 1, pp. S21–S36, 2012. View at Publisher · View at Google Scholar · View at Scopus
  43. R. Injac, M. Perse, M. Cerne et al., “Protective effects of fullerenol C60(OH)24 against doxorubicin-induced cardiotoxicity and hepatotoxicity in rats with colorectal cancer,” Biomaterials, vol. 30, no. 6, pp. 1184–1196, 2009. View at Publisher · View at Google Scholar · View at Scopus
  44. V. M. Torres, B. Srdjenovic, V. Jacevic, V. D. Simic, A. Djordjevic, and A. L. Simplício, “Fullerenol C60(OH)24 prevents doxorubicin-induced acute cardiotoxicity in rats,” Pharmacological Reports, vol. 62, no. 4, pp. 707–718, 2010. View at Scopus
  45. B. Srdjenovic, V. Milic-Torres, N. Grujic, K. Stankov, A. Djordjevic, and V. Vasovic, “Antioxidant properties of fullerenol C60(OH)24 in rat kidneys, testes, and lungs treated with doxorubicin,” Toxicology Mechanisms and Methods, vol. 20, no. 6, pp. 298–305, 2010. View at Publisher · View at Google Scholar · View at Scopus
  46. V. D. Milic, K. Stankov, R. Injac et al., “Activity of antioxidative enzymes in erythrocytes after a single dose administration of doxorubicin in rats pretreated with fullerenol C 60(OH)24,” Toxicology Mechanisms and Methods, vol. 19, no. 1, pp. 24–28, 2009. View at Publisher · View at Google Scholar · View at Scopus
  47. C. Chen, G. Xing, J. Wang et al., “Multihydroxylated [Gd@C82(OH)22]n nanoparticles: antineoplastic activity of high efficiency and low toxicity,” Nano Letters, vol. 5, no. 10, pp. 2050–2057, 2005. View at Publisher · View at Google Scholar · View at Scopus
  48. V. Kojić, D. Jakimov, G. Bogdanović, and A. Dordević, “Effects of fullerenol C60(OH)24 on cytotoxicity induced by antitumor drugs on human breast carcinoma cell lines,” Materials Science Forum, vol. 494, pp. 543–548, 2005. View at Publisher · View at Google Scholar · View at Scopus
  49. P. Chaudhuri, A. Paraskar, S. Soni, R. A. Mashelkar, and S. Sengupta, “Fullerenol-cytotoxic conjugates for cancer chemotherapy,” ACS Nano, vol. 3, no. 9, pp. 2505–2514, 2009. View at Publisher · View at Google Scholar · View at Scopus
  50. X. Yin, L. Zhao, S. G. Kang et al., “Impacts of fullerene derivatives on regulating the structure and assembly of collagen molecules,” Nanoscale, vol. 5, no. 16, pp. 7341–7348, 2013. View at Publisher · View at Google Scholar
  51. J. Grebowski, A. Krokosz, and M. Puchala, “Membrane fluidity and activity of membrane ATPases in human erythrocytes under the influence of polyhydroxylated fullerene,” Biochimica et Biophysica Acta, vol. 1828, no. 2, pp. 241–248, 2013. View at Publisher · View at Google Scholar
  52. A. Krantz, “Red cell-mediated therapy: opportunities and challenges,” Blood Cells, Molecules and Diseases, vol. 23, no. 1, pp. 58–68, 1997. View at Publisher · View at Google Scholar · View at Scopus
  53. J. E. Roberts, A. R. Wielgus, W. K. Boyes, U. Andley, and C. F. Chignell, “Phototoxicity and cytotoxicity of fullerol in human lens epithelial cells,” Toxicology and Applied Pharmacology, vol. 228, no. 1, pp. 49–58, 2008. View at Publisher · View at Google Scholar · View at Scopus
  54. S. R. Grobmyer and V. Krishna, “Minimally invasive cancer therapy using polyhydroxy fullerenes,” European Journal of Radiology, vol. 81, supplement 1, pp. S51–S53, 2012.
  55. F. Jiao, Y. Liu, Y. Qu et al., “Studies on anti-tumor and antimetastatic activities of fullerenol in a mouse breast cancer model,” Carbon, vol. 48, no. 8, pp. 2231–2243, 2010. View at Publisher · View at Google Scholar · View at Scopus
  56. M. Balu, P. Sangeetha, D. Haripriya, and C. Panneerselvam, “Rejuvenation of antioxidant system in central nervous system of aged rats by grape seed extract,” Neuroscience Letters, vol. 383, no. 3, pp. 295–300, 2005. View at Publisher · View at Google Scholar · View at Scopus
  57. R. J. Reiter, “Oxidative processes and antioxidative defense mechanisms in the aging brain,” FASEB Journal, vol. 9, no. 7, pp. 526–533, 1995. View at Scopus
  58. A. Zajdel, A. Wilczok, J. Slowinski, J. Orchel, and U. Mazurek, “Aldehydic lipid peroxidation products in human brain astrocytomas,” Journal of Neuro-Oncology, vol. 84, no. 2, pp. 167–173, 2007. View at Publisher · View at Google Scholar · View at Scopus
  59. G. Buonocore, S. Perrone, and R. Bracci, “Free radicals and brain damage in the newborn,” Biology of the Neonate, vol. 79, no. 3-4, pp. 180–186, 2001. View at Publisher · View at Google Scholar · View at Scopus
  60. L. L. Dugan, V. M. G. Bruno, S. M. Amagasu, and R. G. Giffard, “Glia modulate the response of murine cortical neurons to excitotoxicity: glia exacerbate AMPA neurotoxicity,” Journal of Neuroscience, vol. 15, no. 6, pp. 4545–4555, 1995. View at Scopus
  61. L. J. S. Greenlund, T. L. Deckwerth, and E. M. Johnson Jr., “Superoxide dismutase delays neuronal apoptosis: a role for reactive oxygen species in programmed neuronal death,” Neuron, vol. 14, no. 2, pp. 303–315, 1995. View at Scopus
  62. M. Dragunow, R. L. M. Faull, P. Lawlor et al., “In situ evidence for DNA fragmentation in Huntington's disease striatum and Alzheimer's disease temporal lobes,” NeuroReport, vol. 6, no. 7, pp. 1053–1057, 1995. View at Scopus
  63. P. Calissano, C. Matrone, and G. Amadoro, “Apoptosis and in vitro Alzheimer disease neuronal models,” Communicative and Integrative Biology, vol. 2, no. 2, pp. 163–169, 2009. View at Scopus
  64. R. Dringen, G. M. Bishop, M. Koeppe, T. N. Dang, and S. R. Robinson, “The pivotal role of astrocytes in the metabolism of iron in the brain,” Neurochemical Research, vol. 32, no. 11, pp. 1884–1890, 2007. View at Publisher · View at Google Scholar · View at Scopus
  65. G. Bartosz, “Druga twarz tlenu,” Wydawnictwo Naukowe PWN, Warszawa, 2004.
  66. B. Halliwell and J. M. C. Gutteridge, Free Radicals in Biology and Medicine, Oxford University Press, London, UK, 3rd edition, 1999.
  67. S. Fahn and G. Cohen, “The oxidant stress hypothesis in Parkinson's disease: evidence supporting it,” Annals of Neurology, vol. 32, no. 6, pp. 804–812, 1992. View at Publisher · View at Google Scholar · View at Scopus
  68. H.-M. Huang, H.-C. Ou, S.-J. Hsieh, and L.-Y. Chiang, “Blockage of amyloid β peptide-induced cytosolic free calcium by fullerenol-1, carboxylate C60 in PC12 cells,” Life Sciences, vol. 66, no. 16, pp. 1525–1533, 2000. View at Publisher · View at Google Scholar · View at Scopus
  69. J. E. Kim and M. Lee, “Fullerene inhibits β-amyloid peptide aggregation,” Biochemical and Biophysical Research Communications, vol. 303, no. 2, pp. 576–579, 2003. View at Publisher · View at Google Scholar · View at Scopus
  70. C.-M. Lee, S.-T. Huang, S.-H. Huang et al., “C60 fullerene-pentoxifylline dyad nanoparticles enhance autophagy to avoid cytotoxic effects caused by the β-amyloid peptide,” Nanomedicine, vol. 7, no. 1, pp. 107–114, 2011. View at Publisher · View at Google Scholar · View at Scopus
  71. I. Y. Podolski, Z. A. Podlubnaya, and O. V. Godukhin, “Fullerenes C60, antiamyloid action, the brain, and cognitive processes,” Biofizika, vol. 55, no. 1, pp. 71–76, 2010. View at Publisher · View at Google Scholar · View at Scopus
  72. I. Y. Podolski, Z. A. Podlubnaya, E. A. Kosenko et al., “Effects of hydrated forms of C60 fullerene on amyloid β-peptide fibrillization in vitro andperformance of the cognitive task,” Journal of Nanoscience and Nanotechnology, vol. 7, no. 4-5, pp. 1479–1485, 2007. View at Publisher · View at Google Scholar · View at Scopus
  73. S. S. Ali, J. I. Hardt, and L. L. Dugan, “SOD Activity of carboxyfullerenes predicts their neuroprotective efficacy: a structure-activity study,” Nanomedicine, vol. 4, no. 4, pp. 283–294, 2008. View at Publisher · View at Google Scholar · View at Scopus
  74. L. L. Dugan, J. K. Gabrielsen, S. P. Yu, T.-S. Lin, and D. W. Choi, “Buckminsterfullerenol free radical scavengers reduce excitotoxic and apoptotic death of cultured cortical neurons,” Neurobiology of Disease, vol. 3, no. 2, pp. 129–135, 1996. View at Publisher · View at Google Scholar · View at Scopus
  75. J. Lotharius, L. L. Dugan, and K. L. O'Malley, “Distinct mechanisms underlie neurotoxin-mediated cell death in cultured dopaminergic neurons,” Journal of Neuroscience, vol. 19, no. 4, pp. 1284–1293, 1999. View at Scopus
  76. X. Cai, H. Jia, Z. Liu et al., “Polyhydroxylated fullerene derivative C60(OH)24 prevents mitochondrial dysfunction and oxidative damage in an MPP+-induced cellular model of Parkinson's disease,” Journal of Neuroscience Research, vol. 86, no. 16, pp. 3622–3634, 2008. View at Publisher · View at Google Scholar · View at Scopus
  77. H. Jin, W. Q. Chen, X. W. Tang et al., “Polyhydroxylated C60, fullerenols, as glutamate receptor antagonists and neuroprotective agents,” Journal of Neuroscience Research, vol. 62, pp. 600–607, 2000.
  78. C. A. Davie, “A review of Parkinson's disease,” British Medical Bulletin, vol. 86, no. 1, pp. 109–127, 2008. View at Publisher · View at Google Scholar · View at Scopus
  79. D. Ben-Shachar, P. Riederer, and M. B. H. Youdim, “Iron-melanin interaction and lipid peroxidation: implications for Parkinson's disease,” Journal of Neurochemistry, vol. 57, no. 5, pp. 1609–1614, 1991. View at Scopus
  80. S. J. Chinta and J. K. Andersen, “Redox imbalance in Parkinson's disease,” Biochimica et Biophysica Acta, vol. 1780, no. 11, pp. 1362–1367, 2008. View at Publisher · View at Google Scholar · View at Scopus
  81. W. Dauer and S. Przedborski, “Parkinson's disease: mechanisms and models,” Neuron, vol. 39, no. 6, pp. 889–909, 2003. View at Publisher · View at Google Scholar · View at Scopus
  82. F. Chirico, C. Fumelli, A. Marconi et al., “Carboxyfullerenes localize within mitochondria and prevent the UVB-induced intrinsic apoptotic pathway,” Experimental Dermatology, vol. 16, no. 5, pp. 429–436, 2007. View at Publisher · View at Google Scholar · View at Scopus
  83. S. Foley, C. Crowley, M. Smaihi et al., “Cellular localisation of a water-soluble fullerene derivative,” Biochemical and Biophysical Research Communications, vol. 294, no. 1, pp. 116–119, 2002. View at Publisher · View at Google Scholar · View at Scopus
  84. M.-C. Tsai, Y. H. Chen, and L. Y. Chiang, “Polyhydroxylated C60, fullerenol, a novel free-radical trapper, prevented hydrogen peroxide- and cumene hydroperoxide-elicited changes in rat hippocampus in-vitro,” Journal of Pharmacy and Pharmacology, vol. 49, no. 4, pp. 438–445, 1997. View at Scopus
  85. M. Ehrich, R. van Tassell, Y. Li, Z. Zhou, and C. L. Kepley, “Fullerene antioxidants decrease organophosphate-induced acetylcholinesterase inhibition in vitro,” Toxicology in Vitro, vol. 25, no. 1, pp. 301–307, 2011. View at Publisher · View at Google Scholar · View at Scopus
  86. Y. Y. Zha, B. Yang, M. L. Tang et al., “Concentration-dependent effects of fullerenol on cultured hippocampal neuron viability,” International Journal of Nanomedicine, vol. 7, pp. 3099–3109, 2012.