Searching for polymorphonuclear neutrophils (PMNs) respiratory burst inhibitors is an important topic in the treatment of human diseases associated with inflammation.To investigate the inhibitory effects of phenolics isolated from Artocarpus styracifolius Pierre (Moraceae) on respiratory burst induced by phorbol myristate acetate (PMA).The anti-respiratory burst activities of eight phenolics (20 µM) were assessed by determining luminol-dependent chemiluminiscence in rat PMNs. Cytotoxicity of active compounds (1-1000 µM) was assayed by Trypan blue dye exclusion method. Cell-free models were employed to evaluate scavenging capacity of active compounds (20 µM) against reactive oxygen species.The PMA-induced respiratory burst was significantly inhibited (p < 0.05) by six isoprenylated phenolics (AS1-6) at the concentration of 20 µM (below the toxic concentration) with the inhibition rate ranging from 25.0 to 99.6%. The inhibitory potency estimated by IC50 was in the order of AS1 (3.1 µM) >AS6 (5.9 µM) >AS2 (9.1 µM) >AS3 (10.0 µM) >AS5 (29.7 µM) >AS4 (57.7 µM). AS1-4, four isoprenylated flavones, potently quenched superoxide anion, hydroxyl radical, and hydrogen peroxide at the concentration of 20 µM with their scavenging rates in the range of 30.1-78.1%, 35.4-69.7%, and 65.5-86.3%, respectively. In contrast, AS5-6, two isoprenylated 2-arylbenzofurans, showed less effect than that exhibited by AS1-4.The isoprenylated phenolics from A. styracifolius can potently inhibit PMA-induced respiratory burst in rat neutrophils without showing cytotoxicity. The inhibitory effects of these isoprenylated phenolics on the respiratory burst might depend on their different types of structure.
