Radiosensitization by fullerene-C60 dissolved in squalene on human malignant melanoma through lipid peroxidation and enhanced mitochondrial membrane potential

Abstract We examined fullerene-C 60 dissolved in squalene (C 60 /Sqe) for the ability to potentiate the radiosensitization under X-ray irradiation on human malignant melanoma HMV-II cells, which were treated with C 60 /Sqe and thereafter irradiated with X-ray. The cell proliferation for C 60 /Sqe was inhibited more markedly than for Sqe alone. Meanwhile, cell proliferation was almost unaltered for C 60 /squalane (Sqa) or Sqa, a hydrogenated form of Sqe, as compared to no-additive control. Thus radiosensitization of C 60 /Sqe is attributed to peroxidation of unsaturated bonds of squalene by X-ray-excited C 60 in contrast to squalane. The fluorescence images of HMV-II cells stained with Rhodamine123, an indicator for mitochondrial membrane potential, were monitored for 6 h after X-ray irradiation. C 60 /Sqe obviously exhibited more augmented fluorescence intensity on perinuclear region of HMV-II cells than Sqe alone. TBARS assay showed that the lipid peroxidation level as malondialdehyde-equivalent increased by combination of C 60 /Sqe and X-ray dose-dependently on X-ray doses. C 60 /Sqe exhibited lipid peroxidation more markedly by 1.2-fold than Sqe alone. Thus the level of lipid peroxidation of squalene was sufficiently higher in C 60 /Sqe than in Sqe in the absence of C 60 under X-ray irradiation, suggesting the combination of C 60 /Sqe and X-ray irradiation induced radiosensitization on HMV-II cells by peroxidation of absorbed Sqe in mitochondrial membrane via oxidative stress mediated by fullerene-C 60 .