Epalrestat ([PS) is the only aldose reductase inhibitor that is currently available for the treatment of diabetic neuropathy. Recently, we found that [PS at near-plasma concentration increases the intracellular levels of glutathione (GSH) in rat Schwann cells. GSH plays a crucial role in protecting endothelial cells from oxidative stress, thereby preventing vascular diseases. Here we show that [PS increases GSH levels in not only Schwann cells but also endothelial cells. Treatment of bovine aortic endothelial cells (BAECs), an in vitro model of the vascular endothelium, with EPS caused a dramatic increase in intracellular GSH levels. This was concomitant with the up-regulation of glutamate cysteine ligase, an enzyme catalyzing the first and rate-limiting step in tie novo GSH synthesis. Moreover, EPS stimulated the expression of thiorecloxin and heme oxygenase-1, which have important redox regulatory functions in endothelial cells. Nuclear factor erythroid 2-related factor 2 (Nr12) is a key transcription factor that regulates the expression of antioxidant genes. [PS increased nuclear Nr12 levels in BAECs. NrI2 knockdown by siRNA suppressed the [PS-induced glutamate cysteine ligase, thiorecloxin-1, and he me oxygenase-1 expression. Interestingly, LY294002, an inhibitor of phosphatidylinositol 3-kinase, abolished the [PS-stimulated GSH synthesis, suggesting that the kinase is associated with Nr12 activation induced by EPS. Furthermore, [PS reduced the cytotoxicity induced by H202 and tert-butylhydroperoxide, indicating that [PS plays a role in protecting cells from oxidative stress. Taken together, the results provide evidence that [PS exerts new beneficial effects on endothelial cells by increasing GSH, thioredoxin, and heme oxygenase-1 levels through the activation of Nr12. We suggest that EPS has the potential to prevent several vascular diseases caused by oxidative stress. c 2014 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (Iii p:// (TIT ativecommons.orgilicenses by-nc-nd/3.(1