UNLABELLED:Hypericin, isolated from Hypericum perforatum, is an effective photodynamic substance as demonstrated by various studies. Practical forms of applications of hypericin solutions for systemic use and introduction into body cavities are, however, lacking. We developed an aqueous solution of hypericin non-covalently bound to polyvinylpyrrolidone (PVP). PVP is a poly-N-vinylamide of various degrees of polymerization and forms of intermolecular crosslinks suitable for diagnostic and therapeutic applications. We used PVP (molecular weights of PVP between 10 kD and 40 kD) as a complex forming agent to prepare hypericin for photodynamic therapy and diagnostics. In pure water, hypericin forms aggregates which are non-soluble and non-fluorescent. The hypericin-PVP complex binds more than 1000 mg of hypericin in presence of 100 g PVP or less and is soluble in 1 liter of pure water. Aqueous complex solutions of hypericin-PVP display a characteristic absorption spectrum and fluorescence emission band around 600 nm wavelength. Varying concentrations of hypericin do not cause a blue- or red-shift in the absorption maximum at 595 nm. Excitation at 200 nm to 500 nm leads to emission at 590 nm; a property conducive to diagnostic investigations both in vitro and in vivo. Furthermore, hypericin-PVP exhibits high photostability in the presence of oxygen and broad band light which ensures reproducible photodynamic therapy and diagnosis. CONCLUSION:Hypericin forms liquid molecular chromophore complexes in water when bound to PVP thus allowing investigations in biological media.

Photodynamic eradication of tumour cells in vivo depends on the presence of a photosensitizer, light delivery to the cells, and an oxygen supply. Hypericin, a polycyclic quinone with absorption maxima in the ultraviolet and visible ranges, was prepared for clinical use as a photosensitizer. Due to antitumoral and antineoplastic activities as well as the generation of singlet oxygen after photoexcitation, hypericin was applied in clinical oncology and photodynamic therapy. Hypericin was administered subcutaneously (20 micrograms hypericin in 200 microliters Nacl/pyridine solution) into the ante brachium (forearm) of two volunteers. After the diffusion and equilibration of 120 min phototesting was carried out using outdoor light exposure, halogen lamp, laser 514 nm (argon), laser 632 nm (argon dye) and laser 670 nm (diode laser), from 60 to 120 J cm-2. Positive phototests to outdoor light exposure, halogen lamp and laser 514 nm were characterized by rubescence, oozing, vesiculation and darting pain. Phototests with laser 632 nm and 670 nm showed no effects after irradiation. When hypericin was administered topically on skin, erythema and flaring could not be induced by any irradiation. These results suggest that hypericin is a potent photosensitizer only within the UV and green light ranges. This characteristic photoresponse could also be obtained in guinea pig papillary muscle (GPPM) bioassay, which may be established as a model for photosensitizer testing. Irradiation of hypericin-incubated GPPM with 514 nm (20 J cm-2) led to a decrease of the contractile force of about 31%. However, excitation with 632 nm and 670 nm did not cause inotropic effects on GPPM. In addition, hypericin and Photosan 3 were shown to be capable of sensitizing the photo-oxidation of sodium linoleate. This assay should be established for testing interactions between photosensitizers and light sources in vitro.

The influence of externally applied gaseous nitric oxide (NO) on spruce needles in relation to cGMP formation has been examined. Exposure of spruce needles (Picea abies) to gaseous nitric oxide leads to a strong and rapid increase of the cGMP concentration. Depending on the base level of cGMP in the untreated needles, the concentration of cGMP in the NO exposed needles increased up to four degrees of magnitude. The content of adenosine-3′,5′-cyclic monophosphate (cAMP) remained below the detection limit of the HPLC-method used (10− 7 moll− 1). Therefore, it was not subject to further investigation.

The effects of t-butyl hydroperoxide (tBOOH) on bovine liver catalase were investigated. tBOOH is accepted as a substrate of catalase and in the absence of hydrogen donors leads to a destruction of the enzyme via compound II formation. During the decomposition of this enzyme-substrate complex catalase serves as internal hydrogen donor which results in destruction of the enzyme. Evidence for this destruction is given by: a decrease of the Soret band in the uv/vis spectrum, iron release from the enzyme, decrease of the catalatic activity of the enzyme measured by oxygen release from hydrogen peroxide. Hydrogen donors like NADH and o-dianisidine have been found to protect the enzyme from destruction by tBOOH but lead to a structural alteration of the enzyme, shown by alteration of the electrophoretic mobility. In the presence of the hydrogen donor tBOOH is completely reduced to t-butanol, which is thought to proceed in a peroxidase-like reaction.

The described staining technique for catalase activity on polyacrylamide gel leads to sharp colourless bands on a uniform brown backgroud. It is based on the oxidation of a-dianisidine with hydrogen peroxide by the catalytic action of haemin. Catalase activity can be detected down to 0.25 U. The whole staining procedure needs about 30 min and parallel detection of peroxidase activity is possible.