Assessment of In-vitro Synergistic Anti-inflammatory Activity of Tocopherol and Lipoic acid

Inflammation is the body's response to the injurious stimuli aiming to remove or contain the stimuli. Macrophages are activated after exposure to lipopolysaccharides (LPS) or other antigens and they release tumor necrosis factor-alpha (TNF-alpha) and reactive oxygen species (ROS). Lipoic acid (LA) and alpha-tocopherol (alpha-TOC) are common antioxidant and they are reported to possess anti-inflammatory effects through the modulation of signal transduction and the suppression of ROS release. There are recent findings suggesting that combining LA and alpha-TOC produce synergistic antioxidant effects and therefore the combination of these agents could also have therapeutic potential in limiting inflammation. We hypothesize that LA and alpha-TOC, in a 1:1 molar ratio will exhibit synergistic anti-inflammatory activity. In this study we investigated the synergistic anti-inflammatory effects between LA and alpha-TOC as well as a co-drug derived from the two compounds in vitro. THP-1, a human monocytic cell line was used as a model to test the anti-inflammatory effects of the compounds. The inflammation was initiated using LPS extracted from Escherichia coli and then we measured TNF-alpha as a marker of inflammation by flow cytometry. We were able to achieve anti-inflammatory effect using LA and alpha-TOC. TNF-alpha was inhibited up to 71% using LA at a 500muM concentration. Alpha-TOC at 100muM concentration also inhibited up to 53% of TNF-alpha production. Combination of LA and alpha-TOC in a 1:1 molar ratio at concentrations of 50, 75, 100& mu;M were able to inhibit the production of TNF-alpha by 21%, 26%, and 45%, respectively. We also investigated the anti-inflammatory effect of the co-drug model of LA and alpha-TOC by measuring the level of TNF-alpha inhibition. The levels of inhibition for the co-drug were 8%, 17%, and 17% at concentrations of 50, 75, and 100muM, respectively. Conclusion: Our data support the notion that LA and alpha-TOC have anti-inflammatory properties as achieved by the inhibition of TNF-alpha production in LPS stimulated THP-1 cells. However, enhanced synergistic anti-inflammatory activity was not observed when THP-1 cells were pretreated with a combination of LA and alpha-TOC. The level of TNF-alpha inhibition in THP-1 cells treated with the co-drug was similar to the levels obtained with LA alone.