Background: Inflammation has been implicated in a variety of diseases associated with ageing, including cancer, cardiovascular, and neurologic diseases. We have recently established that the proteasome is a pivotal regulator of inflammation, which modulates the induction of inflammatory mediators such as TNF-α, IL-1, IL-6, and nitric oxide (NO) in response to a variety of stimuli. The present study was undertaken to identify non-toxic proteasome inhibitors with the expectation that these compounds could potentially suppress the production of inflammatory mediators in ageing humans, thereby decreasing the risk of developing ageing related diseases. We evaluated the capacity of various proteasome inhibitors to suppress TNF-α, NO and gene suppression of TNF-α, and iNOS mRNA, by LPS-stimulated macrophages from several sources. Further, we evaluated the mechanisms by which these agents suppress secretion of TNF-α, and NO production. Over the course of these studies, we measured the effects of various proteasome inhibitors on the RAW 264.7 cells, and peritoneal macrophages from four different strains of mice (C57BL/6, BALB/c, proteasome double subunits knockout LMP7/MECL-1-/-, and peroxisome proliferator-activated receptor-α,-/- (PPAR-α,-/-) knockout mice. We also directly measured the effect of these proteasome inhibitors on proteolytic activity of 20S rabbit muscle proteasomes.

Results: There was significant reduction of chymotrypsin-like activity of the 20S rabbit muscle proteasomes with dexamethasone (31%), mevinolin (19%), δ-tocotrienol (28%), riboflavin (34%), and quercetin (45%; P < 0.05). Moreover, quercetin, riboflavin, and δ-tocotrienol also inhibited chymotrypsin-like, trypsin-like and post-glutamase activities in RAW 264.7 whole cells. These compounds also inhibited LPS-stimulated NO production and TNF-α, secretion, blocked the degradation of P-IκB protein, and decreased activation of NF-κB, in RAW 264.7 cells. All proteasome inhibitors tested also significantly inhibited NO production (30% to 60% reduction) by LPS-induced thioglycolate-elicited peritoneal macrophages derived from all four strains of mice. All five compounds also suppressed LPS-induced TNF-α, secretion by macrophages from C57BL/6 and BALB/c mice. TNF-α, secretion, however, was not suppressed by any of the three proteasome inhibitors tested (δ-tocotrienol, riboflavin, and quercetin) with LPS-induced macrophages from LMP7/MECL-1-/- and PPAR-α,-/- knockout mice. Results of gene expression studies for TNF-α, and iNOS were generally consistent with results obtained for TNF-α, protein and NO production observed with four strains of mice.

Conclusions: Results of the current study demonstrate that δ-tocotrienol, riboflavin, and quercetin inhibit NO production by LPS-stimulated macrophages of all four strains of mice, and TNF-α, secretion only by LPS-stimulated macrophages of C57BL/6 and BALB/c mice. The mechanism for this inhibition appears to be decreased proteolytic degradation of P-IκB protein by the inhibited proteasome, resulting in decreased translocation of activated NF-κB to the nucleus, and depressed transcription of gene expression of TNF-α, and iNOS. Further, these naturally-occurring proteasome inhibitors tested appear to be relatively potent inhibitors of multiple proteasome subunits in inflammatory proteasomes. Consequently, these agents could potentially suppress the production of inflammatory mediators in ageing humans, thereby decreasing the risk of developing a variety of ageing related diseases.

Background: Tocotrienol (Tocomin) are naturally occurring analogues of vitamin E family and has been reported to possess a potent free radical scavenging activity. In the present study we have initially investigated protective role of tocotrienol against infection and inflammation induced alterations in tissues antioxidant defense system, as well as speculated, via in silico docking studies, that tocotrienol can act by directly binding to antioxidant enzymes.

Materials And Methods: Syrian hamsters were injected with bacterial lipopolysaccharide (LPS, 200 microg), zymosan (20 mg), or turpentine (0.5 ml) to mimic acute infection, acute systemic inflammation, and acute localized inflammation, respectively, which are responsible for the generation of plenty of free radicals that causes oxidative stress. Tocomin (10 mg) was administered daily for 10 days before and 12 h after lipopolysaccharides (LPS) or 24 h after turpentine or zymosan injection. Molecular docking studies were performed using Autodock 4.0.

Results: Our results show a significant decrease in the activities of antiperoxidative enzymes, glutathione reductase (GR), glutathione peroxidase (GPx), catalase (CAT), superoxide dismutase (SOD), glutathione-s-transferase (GST), as well as reduced glutathione (GSH), in liver and kidney of LPS, turpentine or zymosan stressed hamsters. Feeding of 10 mg Tocomin to stressed hamsters was quite effective in reversing/normalizing the altered levels of enzymatic and nonenzymatic antioxidants in liver and kidney. In order to explore the interaction between tocotrienol and antioxidant enzymes a molecular docking study was performed. The results showed good interaction in term of binding energy and inhibition constant in the following order GR > CAT > SOD > GST > GPx.

Conclusion: Our in vivo and in silico results for the first time indicate that tocotrienol significantly alleviate the condition of oxidative stress not only by its potent free radical scavenging properties but also may be by interacting directly and strongly with antioxidant enzymes as proved by molecular docking simulations.