A quantitative study of NF-kappaB activation by H2O2: relevance in inflammation and synergy with TNF-alpha |
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Authors: | de Oliveira-Marques Virgínia Cyrne Luísa Marinho H Susana Antunes Fernando |
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Institution: | Grupo de Bioquímica dos Oxidantes e Antioxidantes, Centro de Química e Bioquímica, Faculty of Sciences, University of Lisbon, Lisbon, Portugal. vmmarques@fc.ul.pt |
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Abstract: | Although the germicide role of H(2)O(2) released during inflammation is well established, a hypothetical regulatory function, either promoting or inhibiting inflammation, is still controversial. In particular, after 15 years of highly contradictory results it remains uncertain whether H(2)O(2) by itself activates NF-kappaB or if it stimulates or inhibits the activation of NF-kappaB by proinflammatory mediators. We investigated the role of H(2)O(2) in NF-kappaB activation using, for the first time, a calibrated and controlled method of H(2)O(2) delivery--the steady-state titration--in which cells are exposed to constant, low, and known concentrations of H(2)O(2). This technique contrasts with previously applied techniques, which disrupt cellular redox homeostasis and/or introduce uncertainties in the actual H(2)O(2) concentration to which cells are exposed. In both MCF-7 and HeLa cells, H(2)O(2) at extracellular concentrations up to 25 microM did not induce significantly per se NF-kappaB translocation to the nucleus, but it stimulated the translocation induced by TNF-alpha. For higher H(2)O(2) doses this stimulatory role shifts to an inhibition, which may explain published contradictory results. The stimulatory role was confirmed by the observation that 12.5 microM H(2)O(2), a concentration found during inflammation, increased the expression of several proinflammatory NF-kappaB-dependent genes induced by TNF-alpha (e.g., IL-8, MCP-1, TLR2, and TNF-alpha). The same low H(2)O(2) concentration also induced the anti-inflammatory gene coding for heme oxygenase-1 (HO-1) and IL-6. We propose that H(2)O(2) has a fine-tuning regulatory role, comprising both a proinflammatory control loop that increases pathogen removal and an anti-inflammatory control loop, which avoids an exacerbated harmful inflammatory response. |
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