PubMed · 6411195
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R H Seville. 1983-08-13. Should general practitioners use dithranol?. https://doi.org/10.1136/bmj.287.6390.503
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Hypocrellin A displays photoinduced antiviral activity, in particular against the human immunodeficiency virus (HIV), as does its counterpart, hypericin. Although hypocrellin A, like hypericin, executes an excited-state intramolecular proton transfer, it differs from hypericin in two important ways. Unlike hypericin, hypocrellin A absolutely requires oxygen for its antiviral activity. Also, whereas we have previously demonstrated that hypericin functions as a light-induced proton source, we do not observe that hypocrellin A acidifies its surrounding medium in the presence of light. These results are discussed in the context of the ground- and excited-state photophysics of hypericin and its mechanisms of photoinduced virucidal activity.
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.
The location of anthracene-labeled molecules incorporated into model membranes was measured by fluorescence quenching. The depth of the anthracene group was calculated from the degree of quenching by lipids carrying a nitroxide at different depths, using the parallax analysis (Chattopadhyay & London (1987) Biochemistry 26, 39-45). A series of anthracene derivatives was examined in order to determine what polar functional groups would anchor at the membrane surface, and at what depth anchoring would occur. An anthracene with only a methyl group was not anchored at the membrane surface, but derivatives with polar or charged groups did anchor near the membrane surface as demonstrated by a shallower anthracene depth. Based on anthracene depths, protonated primary amine, secondary amine, and hydroxyl groups appear to be located 15-16 A from the center of the membrane. A quaternary amino locates more shallowly, at 18 A from the bilayer center. A protonated carboxyl group is slightly deeper, at 14 A from the center of the bilayer. Ester groups are found to be weakly anchoring, having a location dependent on the structure of the molecule to which they are attached. In methyl 9-anthracenepropionate, the ester group is located about 13 A from the bilayer center. Anthracene esters attached to cholesterol or cholesterol esters showed various depths. An anthracene ester attached to the tail of cholesterol was located 1-6 A from the center of the bilayer for a cholesterol derivative, but at 12 A from the bilayer center for a cholesterol oleate derivative.(ABSTRACT TRUNCATED AT 250 WORDS)