GPX4 and ovarian cancer: Although selenoproteins are the predominant biologically functional form of Se synthesized by the Se metabolic system [31], we found that high doses of SS reduced GPx4 expression in an SS-dose-dependent manner, but did not affect the expression of other selenoproteins, such as selenoprotein P, TRXR1, and TRX1, in ovarian cancer cells in vitro and in vivo.