Nordihydroguaiaretic acid blocks secretory and endocytic pathways in human dendritic cells

Nordihydroguaiaretic acid (NDGA), an antioxidant and inhibitor of the lipoxygenase arm of the arachidonic acid metabolism, was recently demonstrated to inhibit transport of secretory proteins to the Golgi complex. We have investigated the effects of NDGA on the secretory and endocytic activity of cultured human blood dendritic cells (DC). Treatment with NDGA strongly diminished cytokine secretion by DC. Moreover, NDGA reduced in a dose- and time-dependent fashion fluid phase as well as receptor-mediated endocytosis in DC. Zileuton and MK-886, specific inhibitors of 5-lipoxygenase and 5-lipoxygenase-activating protein, respectively, had no effect. Likewise, N-acetyl-L-cysteine, a thiol antioxidant precursor of glutathione, did not affect DC function. Finally, serum remarkably protected the cells from the inhibitory effects of NDGA. Our data demonstrate that NDGA not only disrupts vesicular transport along the secretory route but is also a potent inhibitor of the endocytic pathways in human DC and that NDGA has inhibitory properties different from those described.