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Methotrexate (MTX) is an immunosuppressant commonly used for the treatment of autoimmune diseases. Recent observations have shown that patients treated with MTX also exhibit a reduced risk for the development of cardiovascular disease (CVD). Although MTX reduces systemic inflammation and tissue damage, the mechanisms by which MTX exerts these beneficial effects are not entirely known. We have previously demonstrated that protein adducts formed by the interaction of malondialdehyde (MDA) and acetaldehyde (AA), known as MAA-protein adducts, are present in diseased tissues of individuals with rheumatoid arthritis (RA) or CVD. In previously reported studies, MAA-adducts were shown to be highly immunogenic, supporting the concept that MAA-adducts not only serve as markers of oxidative stress but may have a direct role in the pathogenesis of inflammatory diseases. Because MAA-adducts are commonly detected in diseased tissues and are proposed to mitigate disease progression in both RA and CVD, we tested the hypothesis that MTX inhibits the generation of MAA-protein adducts by scavenging reactive oxygen species. Using a cell free system, we found that MTX reduces MAA-adduct formation by approximately 6-fold, and scavenges free radicals produced during MAA-adduct formation. Further investigation revealed that MTX directly scavenges superoxide, but not hydrogen peroxide. Additionally, using the Nrf2/ARE luciferase reporter cell line, which responds to intracellular redox changes, we observed that MTX inhibits the activation of Nrf2 in cells treated with MDA and AA. These studies define previously unrecognized mechanisms by which MTX can reduce inflammation and subsequent tissue damage, namely, scavenging free radicals, reducing oxidative stress, and inhibiting MAA-adduct formation., Graphical abstract The production of reactive oxygen species (ROS) can result in lipid peroxidation. Lipid peroxidation can, in turn, result in the formation of malondialdehyde (MDA), which can spontaneously breakdown forming acetaldehyde (AA). Malondialdehyde and acetaldehyde can interact to form the stable hybrid malondialdehyde-acetaldehyde adduct (MAA) on proteins and other macromolecules. Binding of MAA-adducted proteins to cells can lead to expression of pro-inflammatory cytokines, resulting in inflammation. MAA-adducted proteins are also themselves immunogenic and can initiate an inflammatory response. Importantly, methotrexate can scavenge free radicals. This may ameliorate the formation of lipid peroxides and the resulting formation of MDA and AA. Additionally, methotrexate can directly inhibit the formation of MAA-protein adducts. Thus, methotrexate can scavenge free radicals and inhibit the formation of MAA-adducts. These are previously undescribed mechanisms by which methotrexate may reduce inflammation and the tissue damage associated with chronic inflammatory diseases.fx1, Highlights • MTX is commonly used to treat RA and is being tested in CVD patients. • MDA and AA are produced during lipidperoxidation and can interact to form MAA-adducts. • MAA-adducts are found in atheromas and in diseased synovial tissue of RA patients. • MTX scavenges the free radical O2− and prevents the formation of MAA-adducts. • Scavenging O2− may be a mechanism by which MTX reduces inflammation and disease.

The airway epithelium is a broad interface with the environment, mandating well-orchestrated responses to properly modulate inflammation. Classically, autophagy is a homeostatic pathway triggered in response to external cellular stresses, and is elevated in chronic airway diseases. Recent findings highlight the additional role of autophagy in vesicle trafficking and protein secretion, implicating autophagy pathways in complex cellular responses in disease. Th2 cytokines, IL-13 and IL-4, are increased in asthma and other airway diseases contributing to chronic inflammation. Previously, we observed that IL-13 increases reactive oxygen species (ROS) in airway epithelial cells in an autophagy-dependent fashion. Here, we tested our hypothesis that autophagy is required for IL-13-mediated superoxide production via the NADPH oxidase DUOX1. Using a mouse model of Th2-mediated inflammation induced by OVA-allergen, we observed elevated lung amounts of IL-13 and IL-4 accompanied by increased autophagosome levels, determined by LC3BII protein levels and immunostaining. ROS levels were elevated and DUOX1 expression was increased 70-fold in OVA-challenged lungs. To address the role of autophagy and ROS in the airway epithelium, we treated primary human tracheobronchial epithelial cells with IL-13 or IL-4. Prolonged, 7-day treatment increased autophagosome formation and degradation, while brief activation had no effect. Under parallel culture conditions, IL-13 and IL-4 increased intracellular superoxide levels as determined by electron paramagnetic resonance (EPR) spectroscopy. Prolonged IL-13 activation increased DUOX1, localized at the apical membrane. Silencing DUOX1 by siRNA attenuated IL-13-mediated increases in superoxide, but did not reduce autophagy activities. Notably, depletion of autophagy regulatory protein ATG5 significantly reduced superoxide without diminishing total DUOX1 levels. Depletion of ATG5, however, diminished DUOX1 localization at the apical membrane. The findings suggest non-canonical autophagy activity regulates DUOX1-dependent localization required for intracellular superoxide production during Th2 inflammation. Thus, in chronic Th2 inflammatory airway disease, autophagy proteins may be responsible for persistent intracellular superoxide production., SCOPUS: ar.j, info:eu-repo/semantics/published