2-hydroxymethyl-1-naphthol diacetate (TAC) suppresses the superoxide anion generation in rat neutrophils

We have investigated the inhibitory effect of 2-hydroxymethyl-1-naphthol diacetate (TAC) on the respiratory burst of rat neutrophils and the underlying mechanism of action was also assessed in this study. TAC caused concentration-related inhibition of the formylmethionyl-leucyl-phenylalanine (fMLP) plus dihydrocytochalasin B (CB)- and phorbol 12-myristate 13-acetate (PMA)-induced superoxide anion (O-2(.-)) generation (IC50 10.2 +/- 2.3 and 14.1 +/- 2.1 mu M, respectively) and O-2 consumption (IC50 9.6 +/- 2.9 and 13.3 +/- 2.7 mu M, respectively) of neutrophils. TAC did not scavenge the generated O-2(.-) during dihydroxyfumaric acid autoxidation. TAC inhibited both the transient elevation of [Ca2+](i) in the presence or absence of [Ca2+](o) (IC50 75.9 +/- 8.9 and 84.7 +/- 7.9 mu M, respectively) and the generation of inositol trisphosphate (IP3) (IC50 72.0 +/- 9.7 mu M) in response to fMLP. Cytosolic phospholipase C (PLC) activity was also reduced by TAC at a same range of concentrations. The PMA-induced PKC-beta associated to membrane was attenuated by TAC (about 80% inhibition at 30 mu M). Upon exposure to fMLP, the cellular cyclic AMP level was decreased in neutrophils pretreated with TAC. TAC attenuated fMLP-induced phosphorylation of mitogen-activated protein kinase (MAPK) p42/44 (IC50 17.4 +/- 1.7 mu M), but not p38. The cellular formation of phosphatidic acid (PA) and, in the presence of ethanol, phosphatidylethanol (PEt) induced by fMLP was inhibited by TAC in a concentration-dependent manner (IC50 25.4 +/- 2.4 and 25.9 +/- 1.4 mu M, respectively). TAC had no effect on the O-2(.-) generation of PMA-stimulated and arachidonic acid (AA)-stimulated NADPH oxidase preparations. However, TAC caused concentration-related decrease of the membrane associated p47(phox) in PMA-stimulated neutrophils (about 80% inhibition at 30 mu M). We conclude that inhibition by TAC of the neutrophil respiratory burst is probably attributable to the blockade of the p42/44 MAPK and phospholipase D (PLD) pathways, the membrane translocation of PKC, and to the failure in assembly of a functional NADPH oxidase complex. Blockade of the PLC pathway by TAC probably plays a minor role. (C) 1999 Elsevier Science Inc.