Protective effects of selenium against mercury toxicity in cultured Atlantic spotted dolphin (Stenella plagiodon) renal cells

Marine mammals are known for their low susceptibility to mercury toxicity, and selenium may play a role in this protection against mercury intoxication. To gain insight into mechanisms by which selenium might inhibit mercury toxicity in cetacean cells, we investigated the effects of sodium selenite on cell proliferation and cell death (including apoptosis, oncosis, and necrosis) of control and mercuric chloride-treated Atlantic spotted dolphin renal cells (Sp1K cells). Concurrent exposure to 80 muM Na2SeO3 provided full protection against the decrease in cell proliferation induced by 20 muM HgCl2. Pretreatment with Na2SeO3 increased the protective effects of selenium administered later in conjunction with mercury, but pretreatment alone did not provide protection against mercury given alone. Furthermore, Na2SeO3 administered after the exposure to HgCl2 did not protect cells. These data suggest that the coexistence of Na2SeO3 and HgCl2 was essential for the protective effects of Na2SeO3 against the toxicity of HgCl2 in Sp1K cells, and may involve selenium-mercury binding. This is supported by the results of an experiment in which earlier premixed mercury and selenium solutions were less cytotoxic than freshly mixed solutions. Furthermore, HgCl2 induced apoptosis in Sp1K cells, as revealed by nuclear specific dye (7-AAD) incorporation and cell flow cytometry, and this was prevented by the concurrent exposure to Na2SeO3. Inhibition of mercury-induced apoptosis in marine mammal cells, provided by selenium, may contribute to the in vivo protection. This study is the first report that addresses the mechanism of mercury-selenium antagonism in cultured cetacean cells at the cellular level.