Blockade by Polyunsaturated n-3 Fatty Acids of Endotoxin-Induced Monocytic Tissue Factor Activation Is Mediated by the Depressed Receptor Expression in THP-1 Cells

Background.Monocytic hypercoagulation often occurs in inflammatory conditions. We have previously reported that polyunsaturated n-3 fatty acids (n-3 FA) including eicosapentaenoic acid (20:5) and docosahexaenoic acid (22:6) prevent the activation of monocytic tissue factor (TF) induced by bacterial endotoxin [lipopolysaccharide (LPS)] in cell cultures and animals. Hypothesis. We herein explore the mode of inhibitory action of n-3 FA to determine if LPS transmembrane signaling is blocked, exerting such antagonism. Results. Exposure of human leukemia monocytic THP-1 cells to bacterial endotoxin (Escherichia coli 0111:B04, 1.5 μg/ml) for 6 h significantly activated TF activity and the production of nitric oxide (NO), tumor necrosis factor α (TNF-α), and interleukin (IL)-1β in conditioned medium. Pretreatment with n-3 FA, 20:5 and 22:6 at 10 μM, resulted in time-dependent suppression of not only TF activation but also the elicitation of NO, TNF-α, and IL-1β. These LPS responses were substantially depressed by more than 50% after a 72-h pretreatment. FACScan analysis showed that n-3 FA readily prevented fluorescein isothiocyanate (FITC)-conjugated LPS from binding to THP-1 cells by approximately 70%. The observation that anti-CD14 mAb diminished FITC–LPS binding in a dose-dependent fashion has revealed CD14 dependency in LPS recognition. LPS upregulated CD14 expression, which was significantly arrested by n-3 FA. Similarly, the upregulation of the expression of CD11b, another proposed LPS receptor, was also minimally but significantly depressed by n-3 FA. Conclusion. The present study demonstrates that n-3 FA are able to block LPS transmembrane signaling via suppression of the receptor upregulation, mediating a variety of significant antagonisms against LPS action.