Inhibitory effects of phenolic compounds from Artocarpus styracifolius on respiratory burst of rat neutrophils

Context: Searching for polymorphonuclear neutrophils (PMNs) respiratory burst inhibitors is an important topic in the treatment of human diseases associated with inflammation.

Objective: To investigate the inhibitory effects of phenolics isolated from Artocarpus styracifolius Pierre (Moraceae) on respiratory burst induced by phorbol myristate acetate (PMA).

Materials and methods: 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.

Results: The PMA-induced respiratory burst was significantly inhibited (p?1–6) 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.

Conclusion and discussion: 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.