Metabolism of selenium and its interaction with mercury: Mechanisms by a speciation study

Metabolic, nutritional and toxicological aspects of selenium (Se) were stud ied using a hyphenated technique. Se in biological samples was separated by HPLC and Se in the eluate was detected in-line by mass spectrometry with i onization by inductively coupled argon plasma (HPLC-ICP MS). The distributi ons of Se in the soluble fractions of various organs and body fluids were d etermined after ingestion or injection of naturally occurring Se or Se enri ched with a stable isotope in the form of selenite, selenate or selenomethi onine. Metabolic pathways specific to each Se species were discussed based on the results of speciation of each Se metabolite. Selenite in the bloodstream was taken up by red blood cells and reduced to selenide, and then the reduced form of Se (selenide) was transported to the plasma, where it was bound selectively to albumin and was then transported to the liver. On the other hand, intravenous selenate was taken up directl y by the liver. Excess Se derived from any nutritional Se species is mainly excreted in the urine after being methylated in the liver. The mechanisms underlying the interaction between Se and mercuric ions in t he bloodstream were explained by the formation of a ternary complex, {(HgSe )(n)}(m)-selenoprotein P (n is the number of (HgSe) complexes and in is the number of the binding sites for the (HgSe)(n) complex on selenoprotein P). The complex between Hg and Se in the bloodstream was thus explained by the interaction between their specific chemical species in each metabolic path way. The sensitivity of the HPLC-ICP MS method was enhanced with the use of enri ched stable isotopes by the simultaneous detection and speciation of both e ndogenous and exogenous Se.