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|(component of) Hypericum spp (st. John's wort)|
|1,3,4,6,8,13-Hexahydroxy-10,11-dimethylphenanthro [1,10,9,8-opqra]perylene-7,14-dione P-conformer|
|Hypericin & Visible light|
|Hypericin from Hypericum perforatum|
|Ki: ||Kd:||Ic 50:||Ec50/Ic50:|
Inhibition of neutrophil superoxide generation by hypericin, an antiretroviral agent.. T Nishiuchi; T Utsumi; T Kanno; Y Takehara; H Kobuchi; T Yoshioka; A A Horton; T Yasuda; K Utsumi (1995) Archives of biochemistry and biophysics display 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.