Ebselen, a glutathione peroxidase mimic capable of reducing simple as well as complex hydroperoxides, including those of phospholipids and cholesteryl esters in intact oxidized low-density lipoprotein (LDLox), requires the presence of low-molecular-mass thiols to be active. In plasma, the drug is thought to be transported as an inactive albumin complex. As formation of LDLox is likely to occur extracellularly, we tested under which conditions ebselen can support reduction of LDLox-associated cholesteryl ester hydroperoxides outside cells. We observed that addition of albumin-bound ebselen to whole blood, but not plasma, resulted in reduction of LDLox-associated cholesteryl linoleate hydroperoxides to the corresponding hydroxides. The observed reduction was rapid and its extent increased with increasing concentrations of ebselen. Physical contact of blood cells with LDLox was not required for this reducing activity. These results demonstrate that, in the presence of blood cells, extracellular ebselen is catalytically active. They suggest that ebselen may be considered as a drug for extracellular targets.

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