Scavenging of reactive oxygen species induced by hyperthermia in biological fluid

Reduction of molecular oxygen by redox active thiols: comparison of glutathione, N-acetylcysteine, cysteine, and homocysteine

The reaction properties of the thiol compounds, cysteine (Cys), N-acetyl-l-cysteine (NAC), the reduced form glutathione (GSH), and homocysteine (HCS) were compared. The main purpose of this study was to find a thiol-based anti-oxidant suitable for biological experiments and to provide clear reasoning for its selection. The availability of thiol compounds to generate superoxide by reducing molecular oxygen (O₂) at a hyperthermal temperature was discussed. An oxidative atmosphere, i.e., superoxide generation by the hypoxanthine-xanthine oxidase reaction, hydroxyl radical generation by X-ray irradiation, or direct one-electron oxidation by ferricyanide, was prepared in a reaction mixture containing 0.1 mM TEMPOL and 1 mM test compound, and the EPR signal decay of TEMPOL was observed. A reaction mixture containing 0.1 mM TEMPOL and 1 mM thiol compound was incubated at 44°C, and the EPR signal decay of TEMPOL was observed. Thiols could function as H-donors to the oxoammonium cation and produce the hydroxylamine form of TEMPOL in an oxidative atmosphere. Thiols could also irreversibly react with the oxoammonium cation. GSH and Cys could reduce O₂ to form superoxide/hydroperoxyl radical at hyperthermal temperatures, but HCS and NAC could not reduce O₂. GSH and Cys may cause reductive stress, whereas NAC is a simple tractable antioxidant.

Amplification of glutathione-mediated oxidative stress by catalase in an aqueous solution at hyperthermal temperatures

The glutathione (GSH)-mediated superoxide (O₂^•-) generation in an aqueous solution and relation of hydrogen peroxide (H₂O₂) and effect of catalase were investigated. GSH-induced O₂^•- generation in hyperthermal temperatures was measured by the nitroblue tetrazolium (NBT) mehod. Heating an aqueous solution containing GSH caused superoxide from dissolved O₂. H₂O₂ was generated simultaneously in this reaction mixture probably from the hydroperoxy radical (HO₂^•), which is equilibrated with O₂^•- in an aqueous condition, and then H₂O₂ consumed O₂^•-. Coexisting catalase in the reaction mixture, as a result, could increase O₂^•- generation. The catalase-exaggerated extracellular O₂^•- generation could give a harmful effect to living cells. This GSH-induced oxidative stress can be a part of mechanisms of hyperthermia therapy.

Analysis of the antioxidative function of the radioprotective Japanese traditional (Kampo) medicine, hangeshashinto, in an aqueous phase

Oral mucositis (OM) is a common and painful complication of radiotherapy for head and neck cancer. Hangeshashinto (HST), a Japanese traditional medicine, is known to alleviate radiotherapy- and/or chemotherapy-induced OM; however, the detailed mechanism has not yet been clarified. The aim of the present study was to clarify the details of the antioxidative functions of HST against reactive oxygen species (ROS) produced by radiation. The hydroxyl radical (•OH)-scavenging ability and the reduction ability was simultaneously measured using a modified electron paramagnetic resonance (EPR) spin-trapping method. The superoxide (O(2) (•-))-scavenging ability was estimated by an EPR redox probing method. Water suspensions of powdered HST and of its seven constitutive crude drugs were tested. In addition, some of the main water-soluble ingredients of the crude drugs were also tested. HST was found to scavenge both •OH and O(2) (•-). Furthermore, HST was observed to reduce relatively stable nitroxyl radicals. Glycyrrhizae Radix (kanzo), Ginseng Radix (ninjin), Zizyphi Fructus (taiso) and glycyrrhizin (an ingredient of kanzo) were all found to be relatively good •OH scavengers. Scutellariae Radix (ogon) and Coptidis Rhizoma (oren) demonstrated reducing ability. In addition, acteoside and berberine chloride, which are water-soluble ingredients of ogon and oren, respectively, also demonstrated reducing ability. Oren exhibited oxidative ability at higher concentrations, which may have a function in maintaining catalytic redox action. The antioxidative function of HST probably worked via a balance of scavenging ROS, reducing stable free radicals, and some minor oxidizing activities.