Diroximel fumarate acts through Nrf2 to attenuate methylglyoxal-induced nociception in mice and decreases ISR activation in DRG neurons

Abstract

AbstractDiabetic neuropathic pain is associated with elevated plasma levels of methylglyoxal (MGO). MGO is a metabolite of glycolysis that causes mechanical hypersensitivity in mice by inducing the integrated stress response (ISR), which is characterized by phosphorylation of eukaryotic initiation factor 2α (p-eIF2α). Nuclear factor erythroid 2-related factor 2 (Nrf2) is a transcription factor that regulates the expression of antioxidant proteins that neutralize MGO. We hypothesized that activating Nrf2 using diroximel fumarate (DRF) would alleviate MGO-induced pain hypersensitivity. We pretreated male and female C57BL/6 mice daily with oral DRF prior to intraplantar injection of MGO (20 ng). DRF (100 mg/kg) treated animals were protected from developing MGO-induced mechanical and cold hypersensitivity. UsingNrf2knockout mice we demonstrate that Nrf2 is necessary for the anti-nociceptive effects of DRF. In cultured mouse and human dorsal root ganglion (DRG) sensory neurons, we found that MGO induced elevated levels of p-eIF2α. Co-treatment of MGO (1 µM) with monomethyl fumarate (MMF, 10, 20, 50 µM), the active metabolite of DRF, reduced p-eIF2α levels and prevented aberrant neurite outgrowth in human DRG neurons. Our data show that targeting the Nrf2 antioxidant system with DRF is a strategy to potentially alleviate pain associated with elevated MGO levels.PerspectiveThis study demonstrates that activating Nrf2 with DRF prevents the development of pain caused by MGO in mice and reduces ISR in mouse and human DRGin vitromodels. We propose that Nrf2 activators like DRF should be tested to alleviate diabetic neuropathic pain associated with elevated MGO in patients.Graphical AbstractArticle HighlightsMGO induces mechanical and cold hypersensitivity in mice that is prevented with pre-treatment with DRF.DRF pre-treatment does not protect Nrf2-knockout mice from developing pain hypersensitivity suggesting that Nrf2 is necessary for DRF’s antinociceptive effects.MMF, the active metabolite of DRF, prevents MGO-induced increase in p-eIF2a levels in mouse and human DRG neuronsin vitro.MMF prevents MGO-induced aberrant neurite outgrowth in human DRG neurons.Nrf2 activators, like the FDA-approved DRF, is an option to alleviate neuropathic pain in patients with diabetes.