title: Inhibition of neutrophil superoxide generation by hypericin, an antiretroviral agent.
abstract: We previously reported that phorbol 12-myristate 13-acetate (PMA)-induced superoxide (O2.-) generation of neutrophils was inhibited by hypericin, a photosensitizing pigment found in St. Johnswort (herb Hypericin triquetrifolium Turra), via a mechanism involving protein kinase C (PKC). To obtain further insights into the mechanism of inhibition, the effects of hypericin on stimulation-dependent O2.- generation and related enzymes of neutrophils were investigated. Hypericin inhibited O2.- generation of neutrophils induced by PKC-dependent and -independent stimuli in a light- and concentration-dependent manner. Oxygen was required for the light-dependent inhibition by hypericin. NADPH oxidase activity in a cell-free system and TNF-alpha-induced tyrosyl phosphorylation of neutrophil proteins were also inhibited by hypericin in a concentration- and light-dependent manner. However, tyrosine kinase of p60src, an enzyme not bound to a membrane, was not inhibited either in the light or in the dark. Oxygen uptake of neutrophils by photosensitization with hypericin resulted in the formation of singlet oxygen (1O2), O2.-, and hydroxyl radical (.OH) and enhanced lipid peroxidation. The formation of 1O2 was inhibited by azide, a quencher of 1O2, but not by desferrioxamine (DSF), a ferric ion chelator. By contrast, both generation of .OH and lipid peroxidation were inhibited by DSF but not by azide. Furthermore, PMA-induced O2.- generation inhibited by hypericin partially recovered in the presence of azide but not DSF. These results suggested that the light-dependent inhibition of O2.- generation by hypericin might be due to inhibition of tyrosine kinase, PKC, and NADPH oxidase via an oxygen-dependent mechanism, possibly through both Type I and II photosensitization mechanisms.
mesh_terms: D000873:Anthracenes; D000998:Antiviral Agents / Q000494:pharmacology*; D001386:Azides / Q000494:pharmacology; D002478:Cells, Cultured; D003676:Deferoxamine / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006801:Humans; D008027:Light; D008054:Lipid Peroxides / Q000378:metabolism; D009247:NADH, NADPH Oxidoreductases / Q000037:antagonists & inhibitors; D019255:NADPH Oxidases; D009504:Neutrophils / Q000187:drug effects*; D010100:Oxygen; D010569:Perylene / Q000031:analogs & derivatives* / Q000494:pharmacology; D010750:Phosphoproteins / Q000378:metabolism; D019000:Phosphotyrosine / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D016897:Respiratory Burst / Q000187:drug effects*; D013481:Superoxides / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D000873:Anthracenes; D000998:Antiviral Agents; D001386:Azides; D004791:Enzyme Inhibitors; D008054:Lipid Peroxides; D010750:Phosphoproteins; D013481:Superoxides; D019000:Phosphotyrosine; D010569:Perylene; C004965:hypericin; D009247:NADH, NADPH Oxidoreductases; D019255:NADPH Oxidases; D011505:Protein-Tyrosine Kinases; D011493:Protein Kinase C; D003676:Deferoxamine; D013755:Tetradecanoylphorbol Acetate; D010100:Oxygen