In eukaryotes the ubiquitin proteasome pathway plays an important role in cellular homeostasis and also it exerts a critical role in regulating a wide variety of cellular pathways, including cell growth and proliferation, apoptosis, DNA repair, transcription and immune response. Defects in these pathways have been implicated in a number of human pathologies. Inhibition of the ubiquitin proteasome pathway by proteasome inhibitors may be a rational therapeutic approach for various diseases, such as cancer and inflammatory diseases. Many of the critical cytokine and chemokine mediators of the progression of rheumatoid arthritis are regulated by nuclear factor kappa B (NF-κB). In peptidoglycan/polysaccharide-induced polyarthritis, proteasome inhibitors limit the overall inflammation, reduce NF-κB activation, decrease cellular adhesion molecule expression, inhibit nitric oxide synthase, attenuate circulating levels of proinflammatory cytokine interleukin-6 and reduce the arthritis index and swelling in the joints of the animals. Since proteasome inhibitors exhibit anti-inflammatory and anti proliferative effects, diseases characterized by both of these processes such as rheumatoid arthritis might also represent clinical opportunities for such drugs. The regulation of the proteasomal complex by proteasome inhibitors also has implications and potential benefits for the treatment of rheumatoid arthritis. This review summarizes the ubiquitin proteasome pathway, the structure of 26S proteasomes and types of proteasome inhibitors, with their actions, and clinical applications of proteasome inhibitors in various diseases.

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Background: Chalcones and their derivatives are precursors of flavonoids and isoflavonoids abundantly present in edible plants. It displays a wide range of pharmacological activities, such as anticancer, antiinflammatory, antibacterial and antioxidant. AM-114 (3,5-Bis-[benzylidene-4-boronic acid]-1-methylpiperidin-4-one), a boronic-chalcone derivative exhibits potent anticancer activity through inhibition of the proteasome on human colon cancer cell line. However, the cytotoxic and anti-inflammatory effects of AM114 on THP-1 derived macrophages remain to be studied. Aim of the study: Inflammation is a complex reaction managed by a variety of immune cells such as monocytes and macrophages. In response to inflammatory stimuli, the macrophages secrete increased proinflammatory cytokines, chemokines such as interleukin-6 (IL-6) and interleukin-8 (IL-8). The proteasome complex is essential for several cellular processes including protein degradation, cellular differentiation and antigen presentation. In this study, human monocyte cell line THP-1 stimulated with interleukin-1-beta (IL-1-beta) was used as a model to investigate the in vitro effects of AM114, a proteasome inhibitor (PI), on apoptosis and release of proinflammatory cytokines. Materials and methods: The effect of AM114, with or without IL-1-beta stimulated THP-1derived macrophages, was assessed by comparing with aspirin. The cell viability was determined by MTT assay. The qualitative measurement of apoptosis was determined by acridine orange/ethidium bromide (AO/EtBr), Hoechst 33342 staining and rhodamine 123 assays. The quantitative measurement of apoptosis was carried out to determine the caspase-3 activity by spectrofluorimetric method and DNA fragmentation by agarose gel electrophoresis. The release of proinflammatory cytokines and chemokines such as IL-6 and IL-8 was also measured by enzyme linked immunosorbent assay (ELISA) method. The ANOVA was used to compare the different groups. Results: In the present study the IC50 concentration of AM114 and Aspirin on THP-1 cells were determined as 3.6 micromolar and 3900 micromolar respectively. The THP-1 derived macrophages treated with IL-1-beta showed insufficient apoptosis and increased release of proinflammatory cytokines. However the treatment of AM114, on stimulated THP-1 derived macrophages showed pronounced apoptotic features. The caspase-3 activity was increased 1.9 fold in AM114 with IL-1-beta treated THP-1 derived macrophages as compared to the unstimulated THP-1 derived macrophages pretreated with AM114. An increase of 3.2 fold in caspase-3 activity was observed in stimulated THP-1 derived macrophages pretreated with AM114 in comparison with stimulated THP-1 derived macrophages pretreated with aspirin. A significant increase of 5.0 and 3.0 fold DNA damage were observed in stimulated THP-1 derived macrophages treated with AM114 and aspirin as compared to unstimulated cells. Moreover AM114 treated cells showed significant decrease (p value less than 0.001) in the release of IL-6 and IL-8 on stimulated THP-1 derived macrophages. Conclusion: The results on the induction of apoptosis and suppression of proinflammatory cytokines suggest that AM114 is more effective than aspirin in stimulated THP-1 derived macrophages.