Elucidation of Selenium Metabolism in mammalian cells by speciation

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When human hepatoma HepG2 cells were exposed to sodium selenite, an unknown selenium metabolite was detected in the cytosolic fraction by HPLC coupled with an inductively coupled plasma mass spectrometer (ICP-MS). The unknown selenium metabolite was also detected in the mixture of HepG2 homogenate and sodium selenite in the presence of exogenous glutathione (GSH). The unknown selenium metabolite was identified as selenocyanate by electrospray ionization mass spectrometry (ESI-MS) and ESI quadrupole time-of-flight mass spectrometry (ESI-Q-TOF-MS). Selenocyanate was less toxic to HepG2 cells than selenite or cyanide, suggesting that it was formed to reduce the toxicity of selenite. On the other hand, selenocyanate could be assimilated to selenoproteins and selenometabolites in rats. Consequently, selenite was metabolized to selenocyanate to temporarily ameliorate its toxicity, and selenocyanate acted as an intrinsic selenium pool.