Inhibition of selenium supply function of selenoprotein p through adduct formation by sulforaphane

Selenium is a potent nucleophile essential for selenoenzymes, such as glutathione peroxidase (also known as GSH-Px; GPX; GPx) and selenoprotein P (also known as SelP; SEPP1; SELENOP; SeP). SeP is predominantly secreted from the liver and functions as a selenium carrier in plasma. We previously found that sulforaphane (SFN), an electrophilic phytochemical, reduces SeP production in cultured hepatocytes and mouse liver, however, the effect of electrophilic modification of SeP by SFN on selenium transport and metabolism remains unclear. In the present study, we demonstrate that sulforaphane covalently modifies selenocysteine/cysteine residues of SeP using an acidic biotin PAEC₅ maleimide labeling assay, which allows for focused-labeling of selenocysteine residues. Although the SFN-SeP adduct can be taken up by HepG2 cells and degraded by the lysosome, it was less effective in inducing GPx expression. Our findings indicate that SFN disrupts the selenium supply pathway through the formation of the SeP-SFN adduct.