Simultaneous Detection of Mitochondrial Hydrogen Selenide and Superoxide Anion in HepG2 Cells under Hypoxic Conditions.

Previous studies proposed that sodium selenite (Na2SeO3) was reduced to hydrogen selenide (H2Se) and that H2Se subsequently reacted with oxygen to generate superoxide anion (O2•-), resulting in tumor cell oxidative stress and apoptosis. However, under the hypoxic conditions of a solid tumor, the anticancer mechanism of sodium selenite remains unclear. To reveal the exact anticancer mechanism of selenite in the real tumor microenvironment, we developed a mitochondria-targeting fluorescent nanosensor, Mito-N-D-MSN, which was fabricated from mesoporous silica nanoparticles (MSNs) loaded with two small-molecule fluorescent probes and a triphenylphosphonium ion as a mitochondria-targeting moiety. With Mito-N-D-MSN, the fluctuations in the contents of mitochondrial hydrogen selenide (H2Se) and superoxide anion (O2•-) in HepG2 cells induced by Na2SeO3 were investigated in detail under normoxic and hypoxic conditions. The results showed that the mitochondrial H2Se content increased gradually, while the O2•- content remained unchanged in HepG2 cells under hypoxic conditions, which indicated that the anticancer mechanism of selenite involves nonoxidative stress in the real tumor microenvironment.