Protective effect of a novel cystine C60 derivative on hydrogen peroxide-induced apoptosis in rat pheochromocytoma PC12 cells

Oxidative stress has been considered as a major cause of cellular injuries in a variety of clinical abnormalities, especially neural diseases. One of the effective ways to prevent the reactive oxygen species (ROS) mediated cellular injury is dietary or pharmaceutical augmentation of free radical scavengers. In the present study, we describe the synthesis and characterization of a novel cystine C(60) derivative (CFD). The compound was analyzed by FT-IR, (1)H NMR, (13)C NMR, LC-MS and elemental analysis. It contains five cystine moieties per C(60) molecule. This water-soluble amino-fullerene derivative was able to scavenge both superoxide and hydroxyl radical with biocompatibility. We investigated its potential protective effects on hydrogen peroxide-induced oxidative stress and apoptotic death in cultured rat pheochromocytoma (PC12) cells. Cells treated with hydrogen peroxide underwent cytotoxicity and apoptotic death determined by MTT assay, flow cytometry analysis, PI/Hoechst 33342 staining and glutathione peroxidase assay. The CFD was able to reduce the accumulation of reactive oxygen species and cellular damage caused by hydrogen peroxide in PC12 cells. RF assay demonstrated that CFD could penetrate through the cell membrane and it has played its distinguished role in protecting PC12 cells against hydrogen peroxide-induced cytotoxicity. The results suggest that CFD has the potential to prevent oxidative stress-induced cell death without evident toxicity. Hence, we can hypothesize that the protective effect of CFD on hydrogen peroxide-induced apoptosis is related to its scavenger activity.

Synthesis and enhanced neuroprotective activity of C60-based ebselen derivatives

A C60-based ebselen derivative 4 was synthesized through the cycloaddition of C60 with the azide (3) containing the ebselen component. It was obtained in a four-step synthesis starting from 2-(chloroseleno)benzoyl chloride and 2-(2-aminoethoxy)ethanol in 53% yield (based on consumed C60). Its structure was characterized by 1H NMR, 13C NMR, IR, UV, and FAB-MS. To verify that the C60-based ebselen derivative 4 had enhanced antioxidative and neuroprotective activity, the C60 derivative 5 and the ebselen derivative 6 were selected to treat cortical neuronal cells using the same procedures as with the C60-based ebselen derivative 4. The cellular viability of different derivative treatment groups was estimated by LDH leakage assay and MTT assay. At the same final concentration (30 µmol/L), the results showed that the antioxidative and protective potencies of the C60-based ebselen derivative 4 (MTT (OD) 0.340 ± 0.035, LDH release (UL–1) 4.80 ± 0.16) against H2O2-mediated neuronal injury have an advantage over those of C60 derivative 5 (MTT (OD) 0.297 ± 0.036, LDH release (UL–1) 5.37 ± 0.31) and ebselen derivative 6 (MTT (OD) 0.267 ± 0.027, LDH release (UL–1) 5.85 ± 0.26). Correspondingly, the GPX activity of 4 (1.62 U/µmol) was higher than that of 5 (0.77 U/µmol) and 6 (1.24 U/µmol). These findings demonstrate that the incorporation of two components with similar biological activity (C60 component and ebselen component) may be a desirable way of obtaining a new and more biologically effective C60-based compound.Key words: fullerene, ebselen derivative, azide, neuroprotective activity, cellular viability.