Abstract
Inert metal-selenide colloids are found in animals. They are believed to afford cross-protection against the toxicities of both metals and selenocompounds. Here, the toxicities of metal salt and sodium selenide mixtures were systematically studied using the death rate of Saccharomyces cerevisiae cells as an indicator. In parallel, the abilities of these mixtures to produce colloids were assessed. Studied metal cations could be classified in three groups: (i) metal ions that protect cells against selenium toxicity and form insoluble colloids with selenide (Ag+, Cd2+, Cu2+, Hg2+, Pb2+ and Zn2+), (ii) metal ions which protect cells by producing insoluble metal-selenide complexes and by catalyzing hydrogen selenide oxidation in the presence of dioxygen (Co2+ and Ni2+) and, finally, (iii) metal ions which do not afford protection and do not interact (Ca2+, Mg2+, Mn2+) or weakly interact (Fe2+) with selenide under the assayed conditions. When occurring, the insoluble complexes formed from divalent metal ions and selenide contained equimolar amounts of metal and selenium atoms. With the monovalent silver ion, the complex contained two silver atoms per selenium atom. Next, because selenides are compounds prone to oxidation, the stabilities of the above colloids were evaluated under oxidizing conditions. 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), the reduction of which can be optically followed, was used to promote selenide oxidation. Complexes with cadmium, copper, lead, mercury or silver resisted dissolution by DTNB treatment over several hours. With nickel and cobalt, partial oxidation by DTNB occurred. On the other hand, when starting from ZnSe or FeSe complexes, full decompositions were obtained within a few tens of minutes. The above properties possibly explain why ZnSe and FeSe nanoparticles were not detected in animals exposed to selenocompounds.
Highlights
Besides its essential role in selenoenzymes, selenium, which is highly toxic itself at elevated levels, is implicated in metal detoxification
Can all metallic cations react with hydrogen selenide to form insoluble colloids? When they occur, do these colloids afford protection against selenium toxicity? how stable are the colloids in the presence of biological oxidizing agents such as dioxygen, oxidized glutathione, flavins,...? To answer these questions, we examined the ability of Ca2+, Cd2+, Co2+, Cu2+, Fe2+, Hg2+, Mg2+, Mn2+, Ni2+, Pb2+ Zn2+ or Ag+ cations to produce colloidal precipitates in the presence of sodium selenide
The ability of sodium selenide to react with metal ions to give insoluble complexes was questioned
Summary
Besides its essential role in selenoenzymes, selenium, which is highly toxic itself at elevated levels, is implicated in metal detoxification. Correlations could be made between the levels of mercury and selenium in either marine mammals [4] or man [5], highlighting that environmental or occupational exposition to mercury increased the content of this metal in various organs but at the same time that of selenium. These observations suggested that selenium and mercury engage themselves in innocuous complexes. The formed complexes contained equimolar amounts of selenium and cadmium [9] In these experiments, selenium was given under the form of sodium selenite. To obtain HMW Cd-Se complexes in rat plasma, the former conversion of selenite to selenide by erythrocytes is required [9,10,11]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
