Laser-induced singlet oxygen selectively triggers oscillatory mitochondrial permeability transition and apoptosis in melanoma cell lines

Singlet oxygen (O-1(2)) is an electronically excited state of triplet oxygen which is less stable than molecular oxygen in the electronic ground state and produced by photochemical, thermal, chemical, or enzymatic activation of O-2. Although the role of singlet oxygen in biology and medicine was intensively studied with photosensitisers, using of these compounds is limited due to toxicity and lack of selectivity. We generated singlet oxygen in the skin fibroblasts and melanoma cell lines by 1267 nm laser irradiation. It did not induce production of superoxide anion, hydrogen peroxide or activation of lipid peroxidation in these cells confirming high selectivity of 1267 nm laser to singlet oxygen. O-1(2) did not change mitochondrial membrane potential (& UDelta;psi m) in skin fibroblasts but induced fluctuation in & UDelta;psi m and complete mitochondrial depolarisation due to opening permeability transition pore in B16 melanoma cells. 1267 nm irradiation did not change the percentage of fibroblasts with necrosis but significantly increased the number of B16 melanoma cells with apoptosis. Thus, singlet oxygen can induce apoptosis in cancer B16 melanoma cells by opening of mitochondrial permeability transition pore (PTP) but not in control fibroblasts.

Automated summary

Singlet oxygen, an electronically excited state of triplet oxygen, can be generated by various means. The selectivity of 1267 nm laser in producing singlet oxygen was confirmed in this study. Singlet oxygen was found to induce apoptosis in cancer B16 melanoma cells but not in control fibroblasts by opening mitochondrial permeability transition pore.