Pneumolysin-mediated activation of NFκB in human neutrophils is antagonized by docosahexaenoic acid

This study was designed to investigate the relationship between influx of extracellular Ca²⁺, activation of NFκB and synthesis of interleukin-8 (IL-8) following exposure of human neutrophils to subcytolytic concentrations (8.37 and 41.75 ng/ml) of the pneumococcal toxin, pneumolysin, as well as the potential of the omega-3 polyunsaturated fatty acid, docosahexaenoic acid, to antagonize these events. Activation and translocation of NFκB were measured using a radiometric electrophoretic mobility shift assay, while influx of extracellular Ca²⁺ and synthesis of IL-8 were determined using a radioassay and an ELISA procedure, respectively. Exposure of neutrophils to pneumolysin was accompanied by influx of Ca²⁺, activation of NFκB, and synthesis of IL-8, all of which were eliminated by inclusion of the Ca²⁺-chelating agent, EGTA (10 mM), in the cell-suspending medium, as well as by pretreatment of the cells with docosahexaenoic acid (5 and 10 μg/ml). The antagonistic effects of docosahexaenoic acid on these pro-inflammatory interactions of pneumolysin with neutrophils were not attributable to inactivation of the toxin, and required the continuous presence of the fatty acid. These observations demonstrate that activation of NFκB and synthesis of IL-8, following exposure of neutrophils to pneumolysin are dependent on toxin-mediated influx of Ca ²⁺ and that these potentially harmful activities of the toxin are antagonized by docosahexaenoic acid.