Apocynin inhibits NADPH oxidase in phagocytes but stimulates ROS production in non-phagocytic cells

• Published in: Biochimica et biophysica acta Vol. 1722; no. 2; pp. 143 - 147
• Main Authors: VEJRAZKA, M, MICEK, R, STIPEK, S
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 11.03.2005
• Subjects: Acetophenones - pharmacology; Animals; Antioxidants - pharmacology; Aorta - drug effects; Aorta - metabolism; Apocynin; Cells, Cultured; Enzyme Inhibitors - pharmacology; Fibroblasts - drug effects; Fibroblasts - metabolism; Male; NADPH Oxidases - antagonists & inhibitors; NADPH-oxidase; Phagocytes - enzymology; Rats; Rats, Wistar; Reactive oxygen species; Reactive Oxygen Species - metabolism; PBS; Reactive oxygen species; F12K; DCF; Apocynin; HRP; CPS; SOD; DCFH-DA; MEM; NADPH-oxidase; ROS; STZ; HBSS; DPI; DCFH
• ISSN: 0304-4165; 0006-3002; 1872-8006
• DOI: 10.1016/j.bbagen.2004.12.008

Apocynin is a naturally occurring methoxy-substituted catechol, experimentally used as an inhibitor of NADPH oxidase. Since it acts as a potent inhibitor in studies with neutrophils and macrophages, no inhibitory effect can often be found in non-phagocyte cells. In our experiments, apocynin even stimulated reactive oxygen species (ROS) production by vascular fibroblasts. Even when added to macrophages, apocynin initially caused an increase in ROS production. The inhibition of ROS formation followed, suggesting that in the presence of leukocyte myeloperoxidase and hydrogen peroxide, apocynin is converted to another compound. Apocynin pre-activated with H 2O 2 and horseradish peroxidase (HRP) inhibited ROS production immediately. In non-phagocytes, apocynin stimulated ROS production and no inhibition was observed even after 60 min. Apocynin treated with H 2O 2 and HRP, however, decreased ROS production in the same manner as in macrophages. The stimulatory effect on ROS production can be abolished by tiron and superoxide dismutase (SOD), suggesting that superoxide was the produced species. The effect of apocynin was inhibited by diphenylene iodinium (DPI), a non-scavenging NADPH oxidase inhibitor. It can be summarized that apocynin stimulates cell superoxide production. In the presence of peroxidase and hydrogen peroxide, however, it is converted into another compound that acts as an inhibitor of superoxide production. It strongly suggests that under conditions in vivo, apocynin can have opposite effects on phagocytes and non-phagocyte cells. It acts as an inhibitor of phagocyte NADPH oxidase but also as a ROS production stimulator in non-phagocyte cells.