GPX4 and chronic kidney disease: The cystine/glutamate antiporter (system Xc-), comprising SLC7A11 and SLC3A2 subunits, requires NADPH to capture extracellular cystine (Cys) for conversion to cytoplasmic cysteine for GSH synthesis; therefore, the reduced GSH synthesis and diminished GPX4 activity in the CKD group may be attributable to NADPH and SLC7A11 deficiency.