Dose-dependency of multiple free radical-scavenging activity of edaravone.

BACKGROUND: Edaravone is a powerful free radical scavenger that is in clinical use. However, data concerning its dose-response relationship against multiple free radicals remain sparse. The purpose of the present study was to demonstrate the dose-dependency of direct scavenging activity of edaravone against multiple free radical species. MATERIALS AND METHODS: Free radical-scavenging activities of edaravone against six free radical species were evaluated by electron spin resonance spectroscopy using spin-trapping method. RESULTS: Edaravone scavenged the following free radicals in dose-dependent manners with reaction rate constants (kedaravone) or 50% inhibitory concentration (IC50) as indicated: hydroxyl radical (kedaravone = 5.2 × 1010 M-1 s-1), superoxide anion (kedaravone/kG-CYPMPO = 0.63), tert-butyl peroxyl radical (kedaravone/kG-CYPMPO = 8.8), ascorbyl free radical (IC50 = 0.17 ± 0.06 mM), 2,2-diphenyl-1-picrylhydrazyl (DPPH, IC50 = 4.7 ± 0.3 µM), and nitric oxide (kedaravone = 7.0 × 103 M-1 s-1). CONCLUSIONS: The dose-dependent scavenging activities of edaravone against multiple free radical species were clearly illustrated. It is speculated that edaravone acts as antioxidant by dose-dependently scavenging multiple free radical species along the chain reactions of oxidative stress in surgery.

Analysis of redox states of protic and aprotic solutions irradiated by low linear energy transfer carbon-ion beams using a 2,2-diphenyl-1-picrylhydrazyl radical.

The quantitative evaluation of changes in the redox state induced by low linear energy transfer (LET) radiations such as the plateau region of heavy-ion beams via formation of reactive oxygen species is of considerable importance to eliminate the adverse effects of radiation therapy on normal tissues adjacent to a tumour. In this study, a 2,2-diphenyl-1-picrylhydrazyl radical (DPPH˙) was used as a redox probe to estimate the redox states of protic and aprotic solutions irradiated by low LET carbon-ion (C-ion) beams. The dose dependence of the decrease in the absorption band due to DPPH˙ (which was solubilised by ß-cyclodextrin (ß-CD) in water) after irradiation with low LET C-ion beams (13 keV µm-1) was similar to that after X-irradiation. Similar results were obtained when H2O was replaced with methanol or acetonitrile although the slope values of the plots of the absorbance changes vs. radiation doses were twice larger as compared to the case in ß-CD-containing H2O. Moreover, DPPH˙ was more susceptible to the C-ion beam than to X-rays in isopropyl myristate (IPM), which is one of the saturated fatty acid esters.

Solubilisation of a 2,2-diphenyl-1-picrylhydrazyl radical in water by ß-cyclodextrin to evaluate the radical-scavenging activity of antioxidants in aqueous media.

A 2,2-diphenyl-1-picrylhydrazyl radical (DPPH˙) was successfully solubilised in water by ß-cyclodextrin (ß-CD). DPPH˙/ß-CD thus obtained was demonstrated to be a powerful tool to evaluate the antioxidative activity of water-soluble antioxidants, such as ascorbate and Trolox, in aqueous buffer solutions.

Temperature-dependent free radical reaction in water.

Temperature-dependent free radical reactions were investigated using nitroxyl radicals as redox probes. Reactions of two types of nitroxyl radicals, TEMPOL (4-hydroxyl-2,2,6,6-tetramethylpiperidine-N-oxyl) and carbamoyl-PROXYL (3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-N-oxyl), were tested in this paper. Heating a solution containing a nitroxyl radical and a reduced form of glutathione (GSH) caused temperature-dependent decay of electron paramagnetic resonance (EPR) signal of the nitroxyl radical. Heating a solution of the corresponding hydroxylamine form of the nitroxyl radical showed EPR signal recovery. The GSH-dependent reduction of nitroxyl radicals at 70°C was suppressed by antioxidants, spin trapping agents, and/or bubbling N(2) gas, although heating carbamoyl-PROXYL with GSH showed temporarily enhanced signal decay by bubbling N(2) gas. Since SOD could restrict the GSH-dependent EPR signal decay of TEMPOL, O(2) (•-) is related with this reaction. O(2) (•-) was probably generated from dissolved oxygen in the reaction mixture. Oxidation of the hydroxylamines at 70°C was also suppressed by bubbling N(2) gas. Heating a solution of spin trapping agent, DMPO (5,5-dimethyl-1-pyrroline-N-oxide) showed a temperature-dependent increase of the EPR signal of the hydroxyl radical adduct of DMPO. Synthesis of hydroxyl radical adduct of DMPO at 70°C was suppressed by antioxidants and/or bubbling N(2) gas. The results suggested that heating an aqueous solution containing oxygen can generate O(2) (•-).

Spin-trapping reactions of a novel gauchetype radical trapper G-CYPMPO.

Chemical reactions of a novel gauchetype spin trap, G-CYPMPO (sc-5-(5,5-dimethyl-2-oxo-1,3,2-dioxaphosphinan-2-yl)-5-methy-1-pyrroline N-oxide, O1-P1-C6-N1 torsion angle = 52.8°), with reactive oxygen species were examined by pulse radiolysis technique with 35 MeV electron beam and by electron spin resonance spectroscopy after (60)Co γ-ray irradiation. The spin-trapping reaction rate constants of G-CYPMPO toward the hydroxyl radical and the hydrated electron were estimated to be (4.2 ± 0.1) × 10(9) and (11.8 ± 0.2) × 10(9) M(-1)s(-1), respectively. Half-lives of the spin adducts, hydroxyl radical, and perhydroxyl radical adducted G-CYPMPO were estimated to be ∼35 and ∼90 min, respectively. A comparison of the results with earlier reports using different radical sources suggests that the purity of the solution and/or the radical generation technique may influence the stability of the spin adducts.

Detoxification of 6-hydroxydopamine-induced Parkinsonian neurodegeneration by G-CYPMPO, a novel radical trapper.

2-(5,5-Dimethyl-2-oxo-2-λ(5)-[1,3,2]dioxaphosphinan-2-yl)-2-methyl-3,4-dihydro-2H-pyrroline N-oxide {2-(5,5-dimethyl-2-oxo-1,3,2-dioxaphosphinan-2-yl)-3,4-dihydro-2-methyl-2H-pyrrole N-oxide, G-CYPMPO} as the stable crystals having gauche conformation was successfully synthesized as a novel 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO)-type spin trap agent. However, the function of G-CYPMPO in vivo is still unclear. Thus, the purpose of this study was to evaluate the effects of G-CYPMPO in an in vivo model of Parkinson's disease (PD). Rats were microinjected with 6-hydroxydopamine (6-OHDA, 32nmol) in the presence or absence of G-CYPMPO (0.4, 1.2, 4nmol). We investigated behavioral and histochemical parameters in this rat model of PD. In addition, to examine the effects of G-CYPMPO against oxidative stress, we used electron spin resonance (ESR) spectrometry. Intranigral injection of 6-OHDA alone induced a massive loss of tyrosine hydroxylase (TH)-positive neurons in the substantia nigra pars compacta (SNpc). Co-microinjection of G-CYPMPO significantly prevented 6-OHDA-induced dopaminergic neurodegeneration and behavioral impairments. Immunoreactivities for glial markers, such as cluster of differentiation antigen-11b (CD11b) and glial fibrillary acidic protein (GFAP), were notably detected in the SNpc of rats injected with 6-OHDA alone. These immunoreactivities were markedly suppressed by the co-microinjection of G-CYPMPO, similar to the results in vehicle-treated rats. In addition, G-CYPMPO directly trapped hydroxyl radical (OH) generated from 6-OHDA and Fe(2+) in a concentration-dependent manner. These results suggest that G-CYPMPO attenuates 6-OHDA-induced dopaminergic neurodegeneration in a rat model of PD, and is a useful tool for biological research.

Influences of organic solvents on CYPMPO-electron spin resonance spectra in in vitro radical generating systems.

Estimation of radical scavenging capacity of lipophilic antioxidants by electron spin resonance (ESR) in vitro is a challenging issue due to their poor solubility in aqueous radical generating and measuring systems. Water-miscible organic solvents are used for this purpose. A novel radical trapping agent, 5-(2,2-dimethyl-1,3-propoxy cyclophosphoryl)-5-methyl-1-pyrroline N-oxide (CYPMPO), that has practical advantages over well-known trapping agents was synthesized. However, no available data for the influence of solvents in an ESR system that uses CYPMPO has been presented. The influences of six water-miscible organic solvents, acetonitrile (AcN), acetone, dimethyl sulfoxide (DMSO), ethanol, polyethylene glycol (PEG), and dimethoxyethane (DME), on ESR responses to Fenton Fe(2+)/H (2)O(2 )OH· and hypoxanthine/xanthine oxidase superoxide generation systems in vitro were studied. Reduction of the ESR signal to CYPMPO-OH· adducts by 55.86 ± 5.95 and 83.17 ± 2.50% compared with the control was observed in the presence of AcN and acetone, respectively, at a final concentration of 5% (v/v). AcN of less than 1% had minimal effects. DMSO, ethanol, PEG and DME at 5% (v/v) strongly inhibited the ESR signals and/or caused derangement in the signal patterns. The six water-miscible solvents at 5% (v/v) had no influence on the ESR spectra of CYPMPO-superoxide adducts. From these results, AcN, at less than 1% (v/v), is a useful water-miscible organic solvent for assessing radical scavenging capacities of lipophilic compounds in the CYPMPO-Fenton Fe(2+)/H(2)O(2) OH· reaction system in an ESR assay. Any of the solvents used in the present study can be used in a hypoxanthine/xanthine oxidase superoxide generation system.

Mechanisms underlying the anti-inflammatory effects of the Ca2+/calmodulin antagonist CV-159 in cultured vascular smooth muscle cells.

CV-159 is a unique dihydropyridine Ca(2+) antagonist with an anti-calmodulin (CaM) action. A pathogenic feature of atherosclerosis is vascular inflammatory change. In the present study, we examined whether CV-159 exerts protective effects on smooth muscle inflammatory responses. After pretreatment of rat mesenteric arterial smooth muscle cells (SMCs) with CV-159 (0.1 - 10 microM, 30 min), TNF-alpha (10 ng/ml) was applied for 20 min or 24 h. CV-159 inhibited TNF (24 h)-induced vascular cell adhesion molecule (VCAM)-1 as determined by Western blotting. CV-159 inhibited TNF (20 min)-induced phosphorylation of Akt (Ser473) and NF-kappaB p65 (Ser536). An Akt inhibitor, LY294002, and an NF-kappaB inhibitor, pyrrolidine dithiocarbamate, inhibited TNF-induced VCAM-1. An antioxidant drug, N-acetyl-L-cysteine (NAC) inhibited TNF-induced VCAM-1. NAC also inhibited TNF-induced phosphorylation of Akt and NF-kappaB. Furthermore, CV-159 inhibited TNF-induced reactive oxygen species (ROS) production as determined fluorometrically using dichlorodihydrofluorescein diacetate. A CaM inhibitor, W-7, and a calcium/CaM-dependent protein kinase type II inhibitor, KN93, inhibited TNF-induced VCAM-1. W-7 and KN93 inhibited TNF-induced phosphorylation of Akt but not NF-kappaB. The present results indicate that in vascular SMCs, CV-159 inhibits TNF-induced VCAM-1 through inhibition of NF-kappaB and Akt phosphorylation. CV-159 prevents NF-kappaB phosphorylation by inhibiting ROS, while it prevents Akt phosphorylation by inhibiting both ROS and CaM.

CV-159, a unique dihydropyridine derivative, prevents TNF-induced inflammatory responses in human umbilical vein endothelial cells.

CV-159, a 1,4-dihydropyridine derivative, has Ca(2+) antagonistic and anti-calmodulin actions. An early feature of atherosclerosis is vascular endothelial inflammatory change. We examined whether CV-159 has protective effects against endothelial inflammatory responses. After pretreatment of human umbilical vein endothelial cells (ECs) with CV-159 (10 microM, 30 min), TNF-alpha (10 ng/ml) was applied for 20 min or 24 h. Expressions of inflammatory markers and activation of inflammatory signal molecules were examined by Western blotting. Reactive oxygen species (ROS) generation was examined by using 2',7'-dichlorodihydrofluorescein diacetate. CV-159 inhibited TNF (24 h)-induced expression of e-selectin but not vascular cell adhesion molecule-1 and intercellular adhesion molecule-1. CV-159 inhibited TNF (20 min)-induced phosphorylation of JNK, p38, and NF-kappaB p65 (Ser536). A JNK inhibitor, SP600125, and a p38 inhibitor, SB203580, inhibited TNF-induced e-selectin expression. An antioxidant drug, N-acetyl-L-cysteine (NAC), inhibited TNF-induced e-selectin expression. NAC inhibited TNF-induced phosphorylation of JNK and p38 but not NF-kappaB. CV-159 inhibited TNF-induced ROS generation. Our results indicate that in ECs CV-159 specifically inhibits TNF-induced e-selectin expression through inhibition of JNK, p38, and NF-kappaB phosphorylation. It is suggested that CV-159 prevents activation of JNK and p38 through inhibition of ROS, while it prevents activation of NF-kappaB via a ROS-independent manner.

Effects of a calcium-channel blocker (CV159) on hepatic ischemia/reperfusion injury in rats: evaluation with selective NO/pO2 electrodes and an electron paramagnetic resonance spin-trapping method.

Nitric oxide (NO) and the partial pressure of oxygen (pO(2)) in the liver were simultaneously quantified in rats with partial hepatic ischemia/reperfusion injury (PHIRI). Real-time NO/pO(2) monitoring and immunohistochemical analysis for superoxide dismutase and inducible nitric oxide synthase (iNOS) and endothelial NOS (eNOS) were performed to evaluate the protective effects of a dihydropyridine-type calcium-channel blocker--CV159--on PHIRI. Serum high-mobility-group box-1 (HMGB-1) was measured to assess cellular necrosis. Moreover, we used in vitro/ex vivo electron paramagnetic resonance spin trapping to assess the hydroxyl radical (*OH)-scavenging activity (OHSA) of CV159 and the liver tissue. The NO levels were significantly higher in CV159-treated rats than in control rats throughout the ischemic phase. Immediately after reperfusion, the levels temporarily increased in waves and then gradually decreased in the treated rats but remained constant in the control rats. pO(2) was continually higher in the treated rats. In these rats, hepatic eNOS expression increased, whereas iNOS expression decreased. The treated rats exhibited significantly higher cytosolic and mitochondrial concentrations NOx (NO(2)+NO(3)). The serum HMGB-1 levels significantly decreased in the treated rats. Moreover, CV159 directly scavenged *OH and both mitochondrial and cytosolic OHSA were preserved in the treated rats. Thus, CV159-mediated inhibition of intracellular Ca(2+) overloading may effectively minimize organ damage and also have *OH-scavenging activity and the cytoprotective effects of eNOS-derived NO.

Comparison of superoxide detection abilities of newly developed spin traps in the living cells.

This study compared the superoxide detection abilities of four spin traps, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide (DEPMPO), 5-(diphenylphosphinoyl)-5-methyl-1pyrroline N-oxide (DPPMPO) and 5-(2,2-dimethyl-1,3-propoxy cyclophosphoryl)-5-methyl-1-pyrroline N-oxide (CYPMPO) in living cells. Electron spin resonance (ESR) signals of the superoxide adducts were observed when spin traps were added to a suspension of human oral polymorphonuclear leukocytes (OPMNs) stimulated by phorbol 12-myristate 13-acetate. The ESR signal of the CYPMPO-superoxide adduct (CYPMPO-OOH) increased for 24 min after the initiation of the reaction, whereas the signals from DMPO-OOH and DPPMPO-OOH peaked at 6 and 10 min, respectively. The maximum concentrations of DMPO-OOH, DPPMPO-OOH and CYPMPO-OOH in OPMNs were 1.9, 6.0 and 10.7 microM, respectively. Furthermore, CYPMPO could more efficiently trap superoxide in blood PMNs compared with DEPMPO. From these results, it was concluded that CYPMPO performs better than DMPO, DPPMPO and DEPMPO for superoxide measurements in living cell systems because it has lower cytotoxicity and its superoxide adduct has a longer lifetime.

Existence of a new reactive intermediate oxygen species in hypoxanthine and xanthine oxidase reaction.

We investigated a hypoxanthine (HPX) and xanthine oxidase (XOD) reaction by using a luminol analog 8-amino-5-chloro-7-phenylpyrido[3,4-d]pyridazine-1,4-(2H,3H)dione sodium salt (L-012)-mediated chemiluminescence (CL) response. Addition of a high activity of superoxide dismutase (SOD), a potent O2* scavenger, and of a high concentration of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), a potent spin trapping agent, diminished completely the CL response. Whereas a high concentration of dimethyl sulfoxide (DMSO), as a potent *OH scavenger could not attain to the complete diminishment of the CL response. It has been reported that luminol monoanion reacts with *OH to form luminol radical, and then resultant luminol radical reacts with O2* to elicit CL response. Complete scavenging for *OH is assumed to result in lack of luminol radical, which in turn induces lack of CL response. However, our results did not support the idea. Furthermore, we examined the effect of L-012 on the DMPO-OOH formation in the presence or absence of DMSO in the HPX-XOD system by applying an electron spin resonance (ESR)-spin trapping method. The DMPO-OOH formation was inhibited even in the presence of DMSO, and the rate constant (k2) between L-012 and O2* obtained in the presence of DMSO was 9.77 x 10(2) M(-1) s(-1) and the constant in the absence of DMSO was 2.97 x 10(3) M(-1) s(-1). The data suggests that L-012 is converted to a radical form that reacts with O2* even under the conditions of the absence of *OH. From these, we postulate that the existence of a reactive intermediate oxygen species in the HPX-XOD system.

The role of the new Ca2+ antagonist, CV159, in hepatic I/R injury-the evaluation of hepatic organ reducing activity using in vivo and ex vivo EPR.

We investigated the organ-reducing ability of 1,2-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridine-dicarboxylic acid methyl 6-(5-phenyl-3-pyrazolyloxy) hexyl ester (CV159) that exhibits selective blocking of Ca(2+)/calmodulin and inhibition of Ca(2+) overloading in living organisms (Sprague Dawley rats) using an in vivo and an ex vivo electron paramagnetic imaging technique. Decay rates in CV159-treated rats were significantly higher than those in untreated rats and were almost equal to those in the sham group. Both cytosol and mitochondrial superoxide scavenging activity in CV159-treated rats were significantly higher than those in untreated rats, and cytosol superoxide scavenging activity only was slightly higher than that in the sham group. Faint staining for anti-superoxide dismutase antibody was markedly observed in necrotic lesions in the liver of control group. Alanine aminotransferase level in CV-treated rats were significantly decreased as compared with the levels in untreated rats. Electron microscopy showed a decreased number of damaged mitochondria, whereas mitochondrial damage was significantly reduced in CV-treated animals. We conclude that CV159 retains the organ-reducing activity against radicals in hepatic I/R injury that is mediated by the inhibition of Ca(2+) overloading.

Effect of CV159-Ca(2+)/calmodulin blockade on redox status hepatic ischemia-reperfusion injury in mice evaluated by a newly developed in vivo EPR imaging technique.

1,4-Dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridinedicarboxylic acid methyl 6-(5-phenyl-3-pyrazolyloxy)hexyl ester (CV159) exhibits selective blocking of Ca(2+)/calmodulin and inhibits Ca(2+) overloading in living organisms. The effects of this antagonist in mice with hepatic ischemia-reperfusion injury were investigated using electron paramagnetic resonance imaging (EPRI) and ex vivo EPR (x-band EPR) techniques. The EPRI determined that the 3-carbamoyl-2,2,5,5-tetramethylpyrrolidine-1-oxyl half-life in CV159-treated mice was significantly shorter than that in untreated mice and was almost equal to that in the sham group. Both the cytosolic and the mitochondrial superoxide scavenging activities in CV-treated mice were significantly higher than that in untreated mice. Faint staining of the anti-superoxide dismutase antibody and strong staining of anti-inducible nitric oxide synthase antibody were observed in the liver of control group. In contrast to these findings, immunostaining of these antibodies in the liver of CV159-treated mice were reversed compared to control group. Western blotting showed that CV159 contributed to the high superoxide dismutase expression and low expression of inducible nitric oxide synthase. The alanine aminotransferase level in CV159-treated mice significantly decreased in comparison to that observed in the untreated mice. We conclude that CV159 retains its organ-reducing activity against radicals in hepatic reperfusion injury, which is mediated by the inhibition of Ca(2+) overloading.

Synthesis and characterization of a practically better DEPMPO-type spin trap, 5-(2,2-dimethyl-1,3-propoxy cyclophosphoryl)-5-methyl-1-pyrroline N-oxide (CYPMPO).

5-(2,2-dimethyl-1,3-propoxy cyclophosphoryl)-5-methyl-1-pyrroline N-oxide (CYPMPO), a new cyclic DEPMPO-type nitrone was evaluated for spin-trapping capabilities toward hydroxyl and superoxide radicals. CYPMPO is colorless crystalline and freely soluble in water. Both the solid and diluted aqueous solution did not develop electron spin resonance (ESR) signal for at least 1 month at ambient conditions. CYPMPO can spin-trap superoxide and hydroxyl radicals in both chemical and biological systems, and the ESR spectra are readily assignable. Half life for the superoxide adduct of CYPMPO produced in UV-illuminated hydrogen peroxide solution was approximately 15 min, and in biological systems such as hypoxanthine (HX)/xanthine oxidase (XOD) the half-life of the superoxide adduct was approximately 50 min. In UV-illuminated hydrogen peroxide solution, there was no conversion from the superoxide adduct to the hydroxyl adduct. Although overall spin-trapping capabilities of CYPMPO are similar to DEPMPO, its high melting point, low hygroscopic property, and the long shelf-life would be highly advantageous for the practical use.

Real-time monitoring of nitric oxide in ischemic myocardium using an NO-selective electrode calibrated by electron spin resonance.

Using a Langendorff-perfused rat heart preparation and selective electrodes, we determined nitric oxide (NO) and oxygen levels in cardiac tissue. An NO-selective electrode that was calibrated by electron spin resonance (ESR) spectroscopy was inserted into the middle of the myocardium in the left ventricle. Simultaneously, we used an O2-selective electrode to measure the partial pressure of oxygen (pO2) in the perfusate, Krebs-Henseleit (K-H) solution, that was ejected from the heart. After 30 min of aerobic control perfusion, hearts were subjected to 30 min of global ischemia followed by 30 min of reperfusion. Under ischemic conditions, with a gradually decreasing pO2, NO detected by an NO-sensitive electrode within the myocardium was gradually increased. The maximum concentration increases in NO and decreases in pO2 during global ischemia were +10.200 +/- 1.223 microM and -58.608 +/- 4.123 mmHg, respectively. NO and pO2 levels both recovered to pre-ischemia baseline values when perfusion was restarted after global ischemia (reperfusion). The presence of Nomega-nitro-L-arginine methyl ester (L-NAME, 10 mM), a NOS inhibitor, prevented ischemia/reperfusion-induced changes in NO. This study shows that an NO-selective electrode that is calibrated by ESR can provide accurate, real-time monitoring of cardiac NO in normal and ischemic myocardium.