Auranofin-Mediated Nrf2 Induction Attenuates Interleukin 1 Beta Expression In Alveolar Macrophages

Background: Alveolar macrophages (AMs) are resident inflammatory cells in the lung that serve as early sentinels of infection or injury. We have identified thioredoxin reductase 1 inhibition by gold compounds increases activation of nuclear factor erythroid 2-related factor 2 (NRF2)-dependent pathways to attenuate inflammatory responses. The present studies utilized murine alveolar macrophages (MH-S) to test the hypothesis that the gold compound, auranofin (AFN), decreases interleukin (IL)-1 beta expression through NRF2-mediated interactions with nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kappa B) pathway genes and/or increases in glutathione synthesis. Methods: MH-S cells were treated with AFN and lipopolysaccharide (LPS) and analyzed at 6 and 24 h. The Il1b promoter was analyzed by chromatin immunoprecipitation for direct interaction with NRF2. Results: Expression of IL-1 beta, p-I kappa B alpha, p-p65 NF-kB, and NOD-, LRR-, and pyrin domain-containing protein 3 were elevated by LPS exposure, but only IL-1 beta expression was suppressed by AFN treatment. Both AFN and LPS treatments increased cellular glutathione levels, but attenuation of glutathione synthesis by buthionine sulfoximine (BSO) did not alter expression of Il-1 beta. Analysis revealed direct NRF2 binding to the Il1b promoter which was enhanced by AFN and inhibited the transcriptional activity of DNA polymerase II. Conclusions: Our data demonstrate that AFN-induced NRF2 activation directly suppresses IL-1 beta synthesis independent of NF kappa B and glutathione-mediated antioxidant mechanisms. NRF2 binding to the promoter region of IL1 beta directly inhibits transcription of the IL1 beta gene. Collectively, our research suggests that gold compounds elicit NRF2-dependent pulmonary protection by suppressing macrophage-mediated inflammation.