licochalcone-a and Arthritis--Rheumatoid

Licochalcone A (LCA) is derived from glycyrrhizae radix with antimicrobial, antitumor and anti-inflammatory activities. However, the anti-arthritic function of LCA and underlying mechanism has not been yet explored. The current study investigated the anti-arthritic effect of LCA and elucidated the underlying mechanism. The results showed that LCA significantly suppressed arthritis via the activation of SQSTM1 (p62)/nuclear factor-erythroid 2-related factor 2 (Nrf2) signaling in the collagen-induced arthritis (CIA) model of DBA mice. In coincided with the results, this anti-arthritic effect of LCA was remarkably diminished in the collagen antibody-induced arthritis (CAIA) model of Nrf2-/- mice. These findings indicate that p62/Nrf2 signaling is a crucial pathway for the induction and treatment of arthritis. To further validate the effect of LCA on the arthritis, rheumatoid arthritis synovial fibroblasts (RASFs) isolated from the synovium of RA patients were employed in the study. In coincided with in vivo results, LCA inhibited the cell proliferation and arrested the cell cycle, induced apoptosis, suppressed pro-inflammatory cytokine secretion and increased expression of antioxidant enzymes via the activation of Keap1-Nrf2 signaling by enhancing p62 phosphorylation and expression, Nrf2 accumulation and Nrf2 nucleus translocation. Findings in the current study provide evidence that p62-Keap1-Nrf2 axis is a pivotal signaling pathway in development of arthritis and therapeutic efficacy of drugs, and LCA activates of Keap1-Nrf2 signaling to suppress arthritis by phosphorylation of p62 at Ser349. Collectively, LCA is valuable to be further investigated as a lead compound for application in anti-arthritis, and interference with the interaction between Nrf2 and Keap1 by phosphorylation of p62 may be a promising strategy for the discovery of anti-arthritic agents.

Topics: Animals; Antirheumatic Agents; Arthritis, Experimental; Arthritis, Rheumatoid; Cell Proliferation; Cells, Cultured; Chalcones; Disease Models, Animal; Fibroblasts; Glycyrrhiza; Kelch-Like ECH-Associated Protein 1; Male; Mice; Mice, Inbred C57BL; Mice, Inbred DBA; Mice, Knockout; NF-E2-Related Factor 2; Phosphorylation; Sequestosome-1 Protein; Signal Transduction

Atomic force microscopy (AFM) is appropriately applied to the examination of hard surfaces and soft samples with extremely high resolution and ultrasensitive force, which cannot be obtained by other imaging techniques, including optical and electron microscopy. In the current study, AFM was employed to evaluate the anti-arthritic effect of licochalcone A (LCA), a flavonoid isolated from the root of Chinese medicinal herb Glycyrrhiza inflate, on rheumatoid arthritis synovial fibroblasts (RASFs) at the nanoscale for the first time. The morphology, ultrastructure and stiffness of RASFs was modified by LCA as determined by AFM, suggesting that LCA most likely exerts an anti-arthritic effect based on the key role of RASFs in the progression of RA. Further studies showed that the inhibitory effect of LCA on IκBα phosphorylation and degradation as well as on p65 nuclear translocation and phosphorylation contributed to altering the morphology, ultrastructure and stiffness of the RASF membrane. Interestingly, IKKβ phosphorylation was not detectable in RASFs, indicating that LCA altered the morphology, ultrastructure and stiffness of the RASF membrane by inhibiting NF-κB activation independent of IKKβ phosphorylation. Antigen-induced arthritis (AIA) was established in Sprague Dawley (SD) rats to validate the anti-arthritic effect of LCA, and LCA significantly decreased both the arthritis scores and paw swelling in the AIA rats, suggesting that LCA inhibits the progression and development of arthritis in vivo. Collectively, AFM provides evidence at the nanoscale to predict the anti-arthritic effect of drugs on RASFs, and LCA should be further investigated as a candidate agent for the treatment of arthritis.

Topics: Animals; Arthritis, Experimental; Arthritis, Rheumatoid; Cell Nucleus; Chalcones; Elastic Modulus; Fibroblasts; Male; Microscopy, Atomic Force; NF-kappa B; NF-KappaB Inhibitor alpha; Phosphorylation; Protein Transport; Proteolysis; Rats, Sprague-Dawley; Signal Transduction; Synovial Membrane