Roberts J R, Shaw C F
Department of Chemistry, University of Wisconsin-Milwaukee, 53201, USA.
Biochem Pharmacol. 1998 Apr 15;55(8):1291-9. doi: 10.1016/s0006-2952(97)00634-5.
The effect of gold ligation on the inhibition of bovine erythrocyte selenium-glutathione peroxidase (GSH-Px) was examined. The anti-arthritic drug auranofin [2,3,4,6-tetra-O-acetyl-1-thio-beta-D-glucopyranosato-S)(triethylp hosphine) gold(I)] (Et3PAuSATg) and its analogue, Et3PAuCl, exhibited experimentally equivalent Ki values (11.6+/-0.8 and 10.8+/-0.5 microM, respectively), despite the greatly disparate affinities of their ligands for gold(I): 2,3,4,6-tetra-O-acetyl-1-thiolato-beta-D-glucopyranose (ATgS-) >> Cl-. This similarity reflects ligand exchange reactions that generate the glutathione complex Et3PAuSG from the excess glutathione (GSH, 1 mM) used in the assay. The Ki values for bis(glutathionato)gold(l) (Au(SG)2-) and gold(I) thioglucose (AuSTg) were also found to be equal (2.8+/-0.4 and 2.4+/-0.5 microM, respectively). This confirms the previous postulate of Chaudiere and Tappel (J Inorg Biochem 20: 313-325, 1984) that Au(SG)2- is generated from AuSTg in the presence of excess glutathione. Since auranofin metabolites accumulate in red blood cells, the inhibition of intracellular GSH-Px was examined by using intact erythrocytes. There was greater inhibition of the reaction when the cells were resuspended in isotonic buffer than in whole blood, because serum albumin in the latter competes for the auranofin and decreases the uptake by erythrocytes. After correction for the extent of gold uptake, the Ki values were determined to be the same as those observed for Au(SG)2- in the extracellular assay, indicating loss of both the Et3P and ATgS- ligands from auranofin. Thus, the inhibition of GSH-Px by gold complexes is dependent on their ligation, and the ultimate gold(I) compound that interacts with erythrocyte GSH-Px in intact red cells, Au(SG)2-, is radically different from the original auranofin molecule.
