Characterization, biological interactions and in-vivo detection of selenotrisulfide derivatives of glutathion, cysteine and homocysteine by HPLC-ICP-MS

Abstract

Thiol-containing compounds such as glutathione, cysteine and homocysteine react with selenite under specific conditions to form selenotrisulfides of significance in cellular systems. This study describes the synthesis and mass spectrometric characterization of selenotrisulfides of glutathione (GSH), cysteine (Cys) and homocysteine (HCys) by electrospray-MS (ESI-MS). The synthesized species are separated by reversed phase-ion pairing HPLC and detected by selective monitoring of Se (m/z 77, 78 and 80) using a collision/reaction cell-inductively coupled plasma-mass spectrometer (CRC-ICP-MS). The cell is pressurized using H 2 as reaction gas at a flow of 3.5 ml min 21 for minimizing Ar polyatomic ions affecting m/z 78 and 80. Separation of the species is performed in a C 8 column with a mobile phase containing 12% methanol and 0.05% heptafluorobutyric acid (HFBA). Using this hyphenated system (HPLC-ICP-MS) LDs below 1 ppb were attained for all the species under study. HPLC-ICP-MS was used also as a tool to study the presence of an excess of GSH and the pH influence on the stability of the Se-glutathion conjugate (GS-Se-SG) as model. Similarly, GS-Se-SG is evaluated as a possible substrate for the enzyme glutathione reductase (GR) in the presence of NADPH. The isolation and HPLC-ICP-MS detection of the synthesized selenotrisulfides in rat liver cytosols of exposed animals will be also discussed.

Production of Polyselenodipenicillamines, Unique Selenium Compounds

“…5) The formation of selenodiglutathione, selenocysteineglutathione, and selenodicysteine was demonstrated based on the models of selenium metabolism in cell-free systems and in rats by Gabel-Jensen et al 6) and by Braga et al, 7) who proposed the formation of selenide species-selenopersulfide (RSSeH), hydrogen selenide (H 2 Se), and hydrogen selenide anion (HSe Ϫ )-through the reduction of RSSeSR. Recently, selenodipenicillamine (PenSSeSPen), a chemically stable RSSeSR, was isolated and its bioavailability in mice was investigated by Nakayama et al 8,9) In our study aiming at discovering novel selenium compounds, the reaction of Dpenicillamine (PenSH) with H 2 SeO 3 was found to yield polyselenodipenicillamines (PenSSe 2-4 SPen), which had been overlooked previously (Chart 1).…”

XAS studies of Se speciation in selenite-fed rats

“…35 A selenosugar, glutathionylseleno-N-acetylgalactosamine, has been identified in rat liver, 19 but not in the kidneys. To the best of our knowledge, there are no previous reports of diselenide species found in vivo after Se supplementation, nor of selenotrisulfide species in rat kidneys.…”

Recent developments in selenium research

“…46,48 Selenomethionine is also retained to a greater extent than inorganic selenate or selenite, and this can be ascribed to the differing incorporation behaviour between SeMet and inorganic Se. 49 Although organic and inorganic Se are subject to different rates of absorption, both forms are nutritionally available to the body. 1 The utilisation of both organic and inorganic Se is via a common intermediate, hydrogen selenide (H 2 Se), which plays a central role in Se metabolism, utilisation and excretion.…”

“…1,3 Selenite (SeO 3 2-) first undergoes enzymatic reaction with GSH to form the Se-glutathione conjugate selenodiglutathione. 49 In the presence of excess GSH, selenodiglutathione is further reduced to glutathioselenol, which is then subsequently reduced to hydrogen selenide. 3,40,50 However, the reduction process for selenate (SeO 4 2-) is more complex and its assimilation follows the sulphate reduction pathway.…”

“…49 It has been suggested that Se toxicity arises as a result of interaction between selenite and GSH, which results in the formation of reactive selenotrisulphides that are capable of producing toxic superoxide (O 2 -) and hydrogen peroxide (H 2 O 2 ). 76 The recommended daily intake of Se for healthy adults is 55 µg/day, with a minimum requirement of 40 µg/day.…”