tempo and hypericin

The photosensitizing effect of hypericin (HY), an antiretroviral agent, on the functions of isolated rat liver mitochondria has been investigated. The respiratory control ratio (RCR), ADP/O and membrane potential of mitochondria were decreased by HY in a light-dependent manner. Uncoupled respiration of mitochondria in the presence of succinate was also inhibited by HY in a light-dependent manner. The ID50 of hypericin for these inhibitions was approximately 0.5 microM. These inhibitory effects of HY were not observed when photosensitization was conducted under anaerobic conditions and were not affected by desferrioxamine (DSF) or superoxide dismutase (SOD). Upon photosensitization of HY, mitochondria consumed oxygen in the absence of respiratory substrate with concomitant formation of thiobarbituric acid reactive substance (TBARS). The amount of oxygen consumed was 100-times greater than that of TBARS formed. The oxygen uptake was partially inhibited by NaN3, and formation of TBARS was inhibited by DSF. Upon photosensitization of HY in the presence of mitochondrial membranes, the electron spin resonance (ESR) signal of 2,2-dimethyl-5-hydroxy-1-pyrrolidinyloxyl (DMPO/.OH) was increased by a mechanism which was suppressed by DSF. An ESR signal for singlet oxygen bound to 2,5-dimethylfuran, 2,2,6,6-tetramethyl-4-piperidone (TEMP) was also detected under light in the presence of mitochondria. This signal of the TEMP-N-oxyl radical (TEMPO) was decreased by azide, which physically quenches singlet oxygen, but was increased by DSF. These results indicate that HY might inhibit mitochondrial functions by a type II photodynamic mechanism but that lipid peroxidation of biological membranes through an active oxygen-mediated photodynamic mechanism is not involved.

Topics: Animals; Anthracenes; Antiviral Agents; Cyclic N-Oxides; Electron Spin Resonance Spectroscopy; HIV-1; Intracellular Membranes; Lipid Peroxidation; Mitochondria, Liver; Oxidative Phosphorylation; Oxidoreductases; Oxygen; Perylene; Rats; Spin Labels

When hypericin was illuminated with 580 nm light in aqueous solution, the semiquinone radical, singlet oxygen, and superoxide anion radical were detected. The formation of the semiquinone radical and activated oxygen species and the transformation and competition between them depend on the quinone and oxygen concentrations, irradiation time and intensity, and the nature of substrate. In anaerobic solution containing a high concentration of the quinone, the semiquinone radical was predominantly photoproduced. In contrast, in aerobic solution, singlet oxygen is the principal product in the photosensitization of hypericin. Besides singlet oxygen, superoxide anion radical is generated by the quinone on illumination in aerobic solution via the reduction of oxygen by the semiquinone radical, but to a lesser extent than singlet oxygen. The generation of superoxide anion radical is significantly enhanced by the presence of electron donors.

Topics: Anthracenes; Antineoplastic Agents; Benzoquinones; Cyclic N-Oxides; Electron Spin Resonance Spectroscopy; Free Radicals; Light; Oxygen; Perylene; Photosensitizing Agents; Piperidones; Reactive Oxygen Species; Singlet Oxygen; Spin Labels; Superoxides; Triacetoneamine-N-Oxyl