The inositol-requiring enzyme 1 (IRE1α) RNAse inhibitor, 4µ8C, is also a potent cellular antioxidant.

Stanley M H Chan, Mark P Lowe, Ashton Bernard, Alyson A Miller, Terence P Herbert

Inositol Requiring Enzyme 1 alpha (IRE1α) is an ER-transmembrane endonuclease that is activated in response to ER stress as part of the unfolded protein response (UPR). Chronic activation of the UPR has been implicated in the pathogenesis of many common disease including diabetes, cancer and neurological pathologies such as Huntington's and Alzheimer's disease. 7-hydroxy-4-methyl-2-oxo-2H-chromene-8-carbaldehyde (4µ8C) is widely used as a specific inhibitor of IRE1α ribonuclease activity in mechanistic studies (IC50 of 6.89 µM in cultured cells). However, in this paper we showed that 4µ8C acts as a potent reactive oxygen species (ROS) scavenger both in a cell free assay and in cultured cells at concentrations lower than that widely used to inhibit IRE1α activity. We demonstrate that in vitro,4µ8C effectively decreases xanthine/xanthine oxidase catalysed superoxide production with an IC50 of 0.2 µM. In cultured endothelial and clonal pancreatic beta-cells, 4µ8C inhibits angiotensin II-induced ROS production with IC50s of 1.92 and 0.29 µM respectively. In light of this discovery, conclusions reached using 4µ8C as an inhibitor of IRE1α should be carefully evaluated. However, this unexpected off-target effect of 4µ8C may prove therapeutically advantageous for the treatment of pathologies that are thought to be caused by, or exacerbated by, both oxidative and ER stress such as endothelial dysfunction and/or diabetes.