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ObjectivePost-translational protein modifications with malondialdehyde-acetaldehyde (MAA) and citrulline (CIT) are implicated in the pathogenesis of rheumatoid arthritis (RA). Although precise mechanisms have not been elucidated, macrophage-fibroblast interactions have been proposed to play a central role in the development and progression of RA. The purpose of our study was to evaluate the downstream effects of macrophage released soluble mediators, following stimulation with fibrinogen (FIB) modified antigens, on human fibroblast-like synoviocytes (HFLS).MethodsPMA-treated U-937 monocytes (Mϕ) and macrophage-differentiated peripheral blood mononuclear cells (MP) were stimulated with FIB, FIB-MAA, FIB-CIT, or FIB-MAA-CIT. HFLS-RA cells were stimulated directly with FIB antigens or with supernatants (SN) from macrophages (Mϕ-SN or MP-SN) stimulated with FIB antigens. Genes associated with an aggressive HFLS phenotype, extracellular matrix proteins, and activated signaling pathways were evaluated.ResultsHFLS-RA cells treated with Mϕ-SNFIB-CIT and Mϕ-SNFIB-MAA-CIT demonstrated significant increases in mRNA expression of genes associated with an aggressive phenotype at 24-h as compared to direct stimulation with the same antigens. Similar results were obtained using MP-SN. Cellular morphology was altered and protein expression of vimentin (p

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.

Doxycycline (DOX), a derivative of tetracycline, is a broad-spectrum antibiotic that exhibits a number of therapeutic activities in addition to its antibacterial properties. For example, DOX has been used in the management of a number of diseases characterized by chronic inflammation. One potential mechanism by which DOX inhibits the progression of these diseases is by reducing oxidative stress, thereby inhibiting subsequent lipid peroxidation and inflammatory responses. Herein, we tested the hypothesis that DOX directly scavenges reactive oxygen species (ROS) and inhibits the formation of redox-mediated malondialdehyde-acetaldehyde (MAA) protein adducts. Using a cell-free system, we demonstrated that DOX scavenged reactive oxygen species (ROS) produced during the formation of MAA-adducts and inhibits the formation of MAA-protein adducts. To determine whether DOX scavenges specific ROS, we examined the ability of DOX to directly scavenge superoxide and hydrogen peroxide. Using electron paramagnetic resonance (EPR) spectroscopy, we found that DOX directly scavenged superoxide, but not hydrogen peroxide. Additionally, we found that DOX inhibits MAA-induced activation of Nrf2, a redox-sensitive transcription factor. Together, these findings demonstrate the under-recognized direct antioxidant property of DOX that may help to explain its therapeutic potential in the treatment of conditions characterized by chronic inflammation and increased oxidative stress.

Malondialdehyde-acetaldehyde adducts (MAA) have been implicated in atherosclerosis. The purpose of this study was to investigate the role of MAA in atherosclerotic disease. Serum samples from controls (n = 82) and patients with; non-obstructive coronary artery disease (CAD), (n = 40), acute myocardial infarction (AMI) (n = 42), or coronary artery bypass graft (CABG) surgery due to obstructive multi-vessel CAD (n = 72), were collected and tested for antibody isotypes to MAA-modifed human serum albumin (MAA-HSA). CAD patients had elevated relative levels of IgG and IgA anti-MAA, compared to control patients (p