BMDMs were incubated in phenol red free-medium. The glutamate level was measured after 3 h incubation with auranofin metabolites, using the Amplex® Red glutamate assay kit (Thermo Fisher Scientific, Waltham, MA, USA). According to the manufacturer’s instruction, the glutamate concentrations of the medium were measured by a fluorescence microplate reader (SpectraMAXi3x, Molecular Devices, Sunnyvale, CA, USA).