In order to exclude that the recycling pathway was involved in such OB-EV-induced impairment, the specific activity of glutathione reductase (GR), the most important enzyme for recycling GSSG within cells (56) was assayed, and we found evidence that the enzymatic function of GR in OB-EV-treated cells was unaltered, nor was it changed by treatment with both OB-EVs and NAC, thus pointing out to the de novo formation of GSH as the redox-active biosynthetic pathway possibly involved in the pro-oxidant effect of OB-EVs on human osteosarcoma cells. This evidence concerns the gene GSR and osteosarcoma.