Vitamin B-sensitized photo-oxidation of dopamine.

Kinetics and mechanism of the photo-oxidation of the natural catecholamine-type neurotransmitter dopamine (DA) has been studied in aqueous solution, under aerobic conditions, in the presence of riboflavin (Rf, vitamin B(2)) as a photosensitizer. Results indicate the formation of a weak dark complex Rf-DA, with a mean apparent association constant K(ass) = 30 m(-1), only detectable at DA concentrations much higher than those employed in photochemical experiments. An intricate mechanism of competitive reactions operates upon photoirradiation. DA quenches excited singlet and triplet states of Rf, with rate constants of 4.2 x 10(9) and 2.2 x 10(9) m(-1) s(-1), respectively. With the catecholamine in a concentration similar to that of dissolved molecular oxygen in air-saturated water, DA and oxygen competitively quench the triplet excited state of Rf, generating superoxide radical anion (O(2)) and singlet molecular oxygen (O(2)((1)Delta(g))) by processes initiated by electron and energy-transfer mechanisms, respectively. Rate constants values of 1.9 x 10(8) and 6.6 x 10(6) m(-1) s(-1) have been obtained for the overall and reactive (chemical) interaction of DA with O(2)((1)Delta(g)). The presence of superoxide dismutase increases both the observed rates of aerobic DA photo-oxidation and oxygen uptake, due to its known catalytic scavenging of O(2), a species that could revert the overall photo-oxidation effect, according to the proposed reaction mechanism. As in most of the catecholamine oxidative processes described in the literature, aminochrome is the DA oxidation product upon visible light irradiation in the presence of Rf. It is generated with a quantum yield of 0.05.

Oxidative and mutagenic effects of low intensity GSM 1800 MHz microwave radiation.

AIM: Despite a significant number of epidemiological studies on potential carcinogenicity of microwave radiation (MWR) from wireless devices and a bulk of experimental studies on oxidative and mutagenic effects of low intensity MWR, the discussion on potential carcinogenicity of low intensity MWR is going on. This study aims to assess oxidative and mutagenic effects of low intensity MWR from a typical commercial model of a modern smartphone. MATERIALS AND METHODS: The model of developing quail embryos has been used for the assessment of oxidative and mutagenic effects of Global System for Mobile communication (GSM) 1800 MHz MWR from a commercial model of smartphone. The embryos were exposed in ovo to 0.32 µW/cm2, discontinuously - 48 s - On, 12 s - Off, during 5 days before and 14 days through the incubation period. RESULTS: The exposure of quail embryos before and during the incubation period to low intensity GSM 1800 MHz has resulted in expressive statistically significant oxidative effects in embryonic cells, including a 2-fold increase in superoxide generation rate and 85% increase in nitrogen oxide generation rate, damages of DNA integrity and oxidative damages of DNA (up to twice increased levels of 8-oxo-dG in cells of 1-day old chicks from the exposed embryos). Finally, the exposure resulted in a significant, almost twice, increase of embryo mortality. CONCLUSION: The exposure of model biological system to low intensity GSM 1800 MHz MWR resulted in significant oxidative and mutagenic effects in exposed cells, and thus should be recognized as a significant risk factor for living cells.

Preparation of PEG-conjugated fullerene containing Gd3+ ions for photodynamic therapy.

A novel photosensitizer with magnetic resonance imaging (MRI) activity was designed from fullerene (C(60)) for efficient photodynamic therapy (PDT) of tumor. After chemical conjugation of polyethylene glycol (PEG) to C(60) (C(60)-PEG), diethylenetriaminepentaacetic acid (DTPA) was subsequently introduced to the terminal group of PEG to prepare PEG-conjugated C(60) (C(60)-PEG-DTPA). The C(60)-PEG-DTPA was mixed with gadolinium acetate solution to obtain Gd(3+)-chelated C(60)-PEG (C(60)-PEG-Gd). Following intravenous injection of C(60)-PEG-Gd into tumor-bearing mice, the PDT anti-tumor effect and the MRI tumor imaging were evaluated. The similar O(2)(*-)generation was observed with or without Gd(3+) chelation upon light irradiation. Both of the C(60)-PEG-Gd and Magnevist(R) aqueous solutions exhibited a similar MRI activity. When intravenously injected into tumor-bearing mice, the C(60)-PEG-Gd maintained an enhanced MRI signal at the tumor tissue for a longer time period than Magnevist(R). Injection of C(60)-PEG-Gd plus light irradiation showed significant tumor PDT effect although the effect depended on the timing of light irradiation. The PDT efficacy of C(60)-PEG-Gd was observed at the time when the tumor accumulation was detected by the enhanced intensity of MRI signal. This therapeutic and diagnostic hybrid system is a promising tool to enhance the PDT efficacy for tumor.

Quinones as photosensitizer for photodynamic therapy: ROS generation, mechanism and detection methods.

Photodynamic therapy (PDT) is based on the dye-sensitized photooxidation of biological matter in the target tissue, and utilizes light activated drugs for the treatment of a wide variety of malignancies. Quinones and porphyrins moiety are available naturally and involved in the biological process. Quinone metabolites perform a variety of key functions in plants which includes pathogen protection, oxidative phosphorylation, and redox signaling. Quinones and porphyrin are biologically accessible and will not create any allergic effects. In the field of photodynamic therapy, porphyrin derivatives are widely used, because it absorb in the photodynamic therapy window region (600-900 nm). Hence, researchers synthesize drugs based on porphyrin structure. Benzoquinone and its simple polycyclic derivatives such as naphthaquinone and anthraquinones absorb at lower wavelength region (300-400 nm), which is lower than porphyrin. Hence they are not involved in PDT studies. However, higher polycyclic quinones absorb in the photodynamic therapy window region (600-900 nm), because of its conjugation and can be used as PDT agents. Redox cycling has been proposed as a possible mechanism of action for many quinone species. Quinones are involved in the photodynamic as well as enzymatic generation of reactive oxygen species (ROS). Generations of ROS may be measured by optical, phosphorescence and EPR methods. The photodynamically generated ROS are also involved in many biological events. The photo-induced DNA cleavage by quinones correlates with the ROS generating efficiencies of the quinones. In this review basic reactions involving photodynamic generation of ROS by quinones and their biological applications were discussed.

Stimulation of phagocytosis and free radical production in murine macrophages by 50 Hz electromagnetic fields.

Effects of 50 Hz electromagnetic fields on phagocytosis and free radical production were examined in mouse bone marrow-derived macrophages. Macrophages were in vitro exposed to electromagnetic fields using different magnetic field densities (0.5-1.5 mT). Short-time exposure (45 min) to electromagnetic fields resulted in significantly increased phagocytic uptake (36.3% +/- 15.1%) as quantified by measuring the internalization rate of latex beads. Stimulation with 1 nM 12-0-tetradecanoylphorbol-13-acetate (TPA) showed the same increased phagocytic activity as 1 mT electromagnetic fields. However, co-exposure to electromagnetic fields and TPA showed no further increase of bead uptake, and therefore we concluded that because of the absence of additive effects, the electromagnetic fields-induced stimulation of mouse bone marrow-derived macrophages does not involve the protein kinase C signal transduction pathway. Furthermore, a significant increased superoxide production after exposure to electromagnetic fields was detected.

The reaction of superoxide radical with N-acetylcysteine.

The interaction of superoxide radicals with N-acetylcysteine (RSH) in an aqueous solution of pH 7 using the technique of steady state radiolysis has been investigated in this paper. The radiolytic yield of the products (G value) of RSH consumption and disulfide of N-acetylcysteine (RSSR) formation has been determined. The G value of the products is not dependent on the concentration of RSH (at the plateau of dilution curve) or on the inverse of the square root of the dose rate (dose rate)(-1/2), from which it is concluded that in this reaction there is no character of chain reaction. The disulfide of N-acetylcysteine is the only sulfur final product. Hydrogen peroxide is not a reaction product, and accordingly the reaction of O(2)(*-) with RSH does not proceed via hydrogen atom abstraction from RSH. A reaction mechanism is proposed, and an overall rate constant of 68 M(-1) s(-1) has been estimated.

Role of peroxide and superoxide anion during tumour cell apoptosis.

Apoptosis or programmed cell death was induced in the human promyelocytic leukemia cell line HL-60 by UV irradiation or treatment with cytotoxic drugs (etoposide, camptothecin, melphalan or chlorambucil). These treatments caused a rapid increase in intracellular peroxide levels. Preincubation of HL-60 cells with the hydrogen peroxide-scavenging enzyme catalase (500 U/ml) inhibited apoptosis due to UV irradiation or low concentrations of camptothecin, etoposide or melphalan, but did not protect against higher concentrations. In contrast, superoxide anion levels in the cells remained unchanged upon treatment with cytotoxic drugs, while UV irradiation led to a transient doubling in superoxide levels. Exogenous superoxide dismutase (400 U/ml) provided modest protection against UV irradiation and had no effect on cytotoxic drug-induced apoptosis. The results suggest that both hydrogen peroxide and superoxide anion may be involved in the induction of apoptosis by UV irradiation. On the other hand, while exposure to cytotoxic drugs induces a large increase in intracellular peroxide levels, catalase is able to protect the cells from apoptosis only when low concentrations of these compounds are used, thus indicating the involvement of other factors in this process, particularly at higher drug concentrations.

Light induces peroxidation in retina by activating prostaglandin G/H synthase.

Prostaglandin G/H synthase (PGHS) has been shown to generate peroxides to a significant extent in the retina and absorbs light at the lower end of the visible spectrum. We postulated that PGHS could be an important initial source of peroxidation in the retina exposed to light, which would in turn alter retinal function. Exposure of pig eyes (in vivo) to light (350 fc/3770 lx) caused after 3 h a 50% increase and by 5 h a 30% decrease in a- and b-wave amplitudes of the electroretinogram (ERG) which were comparable at 380-650 nm and 380-440 nm but were not observed at wavelengths > 450 nm. These effects of light were prevented by free radical scavengers (dimethylthiourea and high-dose allopurinol) and PGHS inhibitors (naproxen and diclofenac), but stable analogs of prostaglandins did not affect the ERG. Both increases and subsequent decreases in ERG wave amplitudes following light exposure in vivo were associated with increases in retinal prostaglandin and malondialdehyde (peroxidation product) levels, which were inhibited by the nonselective PGHS blockers, naproxen and diclofenac. Similar observations were made in vitro on isolated porcine eyecups as well as on retinal membranes exposed to light (250 fc/ 2700 lx) 380-650 nm and 380-440 nm but not at > 500 nm. Both PGHS-1 and PGHS-2 contributed equivalently to light-induced prostaglandin synthesis, as shown after selective PGHS-2 blockers, but mRNA expression of PGHS-1 and 2 was not affected by light. Finally, light stimulated activities of pure PGHS-1 and PGHS-2 isozymes, and these were also shown to produce superoxide radical (detected with fluorogenic spin trap, proxyl fluorescamine). Taken together, data suggest that PGHS- (1 and 2) is activated by short wavelength visible light, and in the retina is an important source of reactive oxygen species which in turn alter retinal electrophysiological function. PGHS thus seems a likely chromophore in setting forth photic-induced retinal injury. Findings provide an explanation for increased sensitivity of the retina to visible light predominantly at the far blue range of its spectrum.

Antioxidant effect of probucol on RO2*/O2(*-)-induced peroxidation of human low-density lipoproteins.

This study was designed to evaluate the antioxidant effect of probucol on peroxidation of low-density lipoproteins (LDLs) initiated by oxygenated free radicals (O2*-) and ethanol-derived peroxyl radicals (RO2*) generated by gamma radiolysis. Initial radiolytic yields related to the markers of lipid peroxidation [i.e. decrease in endogenous alpha-tocopherol, formation of thiobarbituric acid-reactive substances (TBARS) and conjugated dienes] were determined as a function of LDL concentration (1.5 and 3 g l(-1), expressed as total LDL) and in the absence or the presence of probucol at different concentrations (2.3 x 10(-6), 3.5 x 10(-6), 9 x 10(-6) and 20.5 x 10(-6) mol l(-1)). Our results showed that probucol was able to decrease not only the yields of TBARS and conjugated dienes but also the levels of these peroxidation products obtained at high doses (2500 Gy) compared to LDLs without probucol. Under our conditions, probucol displayed an optimal antioxidant effect for an initial concentration in LDLs equivalent to 15 probucol molecules per LDL particle, which corresponded to a pharmacologically relevant concentration of probucol. Moreover, our data showed that probucol was unable to react with RO2* and thus did not protect LDL vitamin E from free radical attack. In addition, the scavenging capacity of probucol on O2*- appeared to be very poor, and probucol more likely reacted with LDL intermediate radical products. Finally, a very significant steady-state level of probucol remained in LDLs at high doses (up to 2500 Gy), equivalent to at least 40% of the initial concentration of probucol. This addressed the question of a mechanism for regeneration of probucol in LDLs. Our results as a whole suggested that the antioxidant effect of probucol in vivo could not be explained by its scavenging capacity with regard to RO2*/O2*- free radicals.

Photosensitization by anticancer agents--10. ortho-semiquinone and superoxide radicals produced during anthrapyrazole-sensitized oxidation of catechols.

Photosensitized oxidation of catechol, 3,4-dihydroxybenzoic acid (DHBA), 3,4-dihydroxy-dihydrocinnamic acid (DHCA), and 3,4-dihydroxy-phenylalanine (DOPA) by novel anticancer agents, anthrapyrazoles (AP), has been studied employing EPR and the spin trapping technique. The formation of o-semiquinone radicals, the one-electron oxidation products of the catechols, stabilized in the form of zinc ion complexes, has been demonstrated. Rate constants for the disproportionation of the semiquinone radical/Zn2+ complexes in (DMSO)/acetate buffer (pH 4.5, 1:1 vol/vol; 100 mM Zn2+) mixture have been determined to be 0.35 x 10(4), 14 x 10(4), 8.8 x 10(4) and 3 x 10(4) M-1 s-1 for catechol, DHBA, DHCA and DOPA respectively. The presence of oxygen enhanced rather than inhibited the photogeneration of the o-semiquinone radicals and facilitated their EPR detection. The EPR spectrum of the superoxide radical adduct with the spin trap 5,5-dimethyl-1-pyrroline-N-oxide was observed for the first time during photosensitized oxidation of the catechols in acidic aqueous solutions and in DMSO/acetate buffer mixture.

Comparison of the effects of O2*-/HO* free radical- and copper ions-oxidized LDL or lipoprotein(a) on the endothelial cell releases of tissue plasminogen activator and plasminogen activator inhibitor-1.

We investigated the effects of low density-lipoproteins (LDL) and lipoprotein(a) [Lp(a)] oxidized by O2*-/HO* free radicals generated by gamma radiolysis of water, on the release of tissue Plasminogen Activator (tPA) and of its main inhibitor Plaminogen Activator Inhibitor-1 (PAI-1) by human umbilical vein endothelial cells (HUVEC). These effects were compared to those of lipoproteins issued from the same preparations but oxidized by the classical copper ions procedure. The results showed that O2*-/HO* free radical oxidized LDL and Lp(a) led to a dramatic decrease of PAI-1 release but did not affect tPA release, whereas copper oxidation of lipoproteins resulted in an increase in PAI-1 release and a decrease in tPA release. Chemical analysis revealed that O2*-/HO* free radical oxidized lipoproteins exhibited very much lower levels of phosphatidylcholine hydroperoxides, lysophosphatidylcholine and oxysterols (7-ketocholesterol, 7beta-hydroxycholesterol, 5,6beta-epoxycholesterol) than copper oxidized LDL. Thus, the discordant effects of O2*-/HO* oxidized and copper oxidized LDL and Lp(a) on the endothelial releases of PAI-1 and tPA appeared to be due to qualitatively and/or quantitatively different formation of oxidized components by the two oxidation processes.

Analytical studies on the prediction of photosensitive/phototoxic potential of pharmaceutical substances.

PURPOSE: Phototoxic responses after administration of photosensitive pharmaceutics have been recognized as undesirable side effects, and predicting potential hazardous side effects is gaining importance as new drugs are introduced to the market. In this work, we characterize the photochemical/photobiological properties of model compounds to develop an effective screening method for the prediction of phototoxic/photosensitive potential. METHODS: Twenty-one known photosensitive/phototoxic compounds and five weak/nonphototoxic compounds were subjected to ultraviolet (UV) spectral analyses and photochemical evaluation including the determination of produced reactive oxygen species (ROS) and photostability study. The photooxidation of linoleic acid was also monitored in the presence of tested compounds, guided on the formation of thiobarbituric acid reactive substances. RESULTS: Most photosensitive/phototoxic drugs tested, even weak UV absorbers, at a concentration of 200 microM showed significant production of ROS under 18 h light exposure (30,000 lx). On the other hand, ROS generated from weak/nonphototoxic compounds, including strong UV absorber benzocaine, were low or negligible. Although exposure of quinine to light resulted in significant degradation (half-life, t1/2=6.4 h), it was dramatically attenuated by the addition of ROS scavengers, especially sodium azide (t1/2=122.6 h). Furthermore, concomitant exposure of photosensitive/phototoxic compounds (200 microM) and linoleic acid (1 mM) for 18 h led to the marked formation of lipoperoxide. CONCLUSION: Results indicated that known photosensitive/phototoxic compounds tested have the ability to generate ROS under light exposure, and this photochemical reaction could be associated with their photoinstability and/or phototoxic responses. Based on these findings, determination of ROS, generated from photoirradiated compounds, may be an effective predictive model in recognizing their photosensitive/phototoxic potential.

Preparation and stabilization of aqueous/ethanolic superoxide solutions.

Methods for the generation and stabilization of alkaline aqueous and/or ethanolic superoxide solutions have been developed utilizing either high energy ionizing radiation or vacuum-uv photolysis. These solutions can be used for the study of the reactivity of superoxide radical (O-2) and its conjugate acid the perhydroxyl radical (HO2) with other compounds over the entire pH range. Frozen, they can be kept at -196 degrees C for prolonged time periods with little loss in superoxide radical. As these solutions can be rendered free of molecular oxygen, studies of the reactivity of HO2/O-2 with oxygen-sensitive compounds under virtually anaerobic conditions are possible.

[Detection of hydroxyl and superoxide radicals in radiolysis of water with time-resolved chemiluminescence]. / Détection des radicaux OH et O2- issus de la radiolyse de l'eau par chimiluminescence résolue en temps.

A new method for the detection of low concentrations of hydroxyl and superoxide radicals, formed by water radiolysis, is described in this article. The method used is the time resolved chemiluminescence. It has been performed with an electron beam delivered by a Febetron 707 accelerator. This method allows to measure hydroxyl and superoxide radical concentrations in a large range of concentrations, between 10(-5) and 10(-8) M.

[Production of superoxide radicals with pulse radiolysis of water with high linear energy transfer]. / Production de radicaux superoxydes par radiolyse pulsée de l'eau à transfert d'énergie linéique (TEL) élevé.

The radiolysis of water with heavy ions of high linear energy transfer (LET) (-dE/dx) is characterized, in deaerated medium, by the production of superoxide anions, the radiolytic yields of which increase with the LET. Radiobiological interest in such radical species comes from the oxidative stress which may be generated by their dismutation in O2 and H2O2 in anoxic medium (radiotherapy with heavy ions). A brief review of the measurements of superoxide free radicals in aqueous solution by indirect or direct methods is presented. Moreover, some experimental results obtained by pulse radiolysis with Ar18+ ions (TEL = 290 keV x microm(-1)), are described. The interpretation of the kinetics takes into account the superoxide absorbance and that of hydrogen peroxide, which is present at the millisecond time scale.

[Photogeneration of the superoxide anion oxygen radical and its role in the inactivation of yeast cells by long-wave UV light]. / Fotogeneratsiia superoksidnogo anion-radikala kisloroda i ego rol' v inaktivatsii kletok drozhzhei dlinnovolnovym UF-svetom.

Long-wave (320-400 nm) UV-induced oxygen superoxide anion radical (O2-) formation was found in yeast cells. This radical plays an important part in initiation of photodestruction reactions in DNA which serves as a main target of UV irradiation in yeast. The observed cell photoinactivation spectrum at the wavelengths 320-400 nm suggests that NADH can serve as an endogenous sensitizer of O2- formation.

[A photosynergistic lethal effect in the irradiation of yeasts with long-wave ultraviolet and visible light]. / Fotosinergicheskii letal'nyi éffekt pri obluchenii drozhzhei dlinnovolnovym ul'trafioletovym i vidimym svetom.

A lethal synergistic effect which is expressed as the nonadditive summing of the damaging effect of each irradiation separately has been found during the investigation of combined action of longwave ultraviolet (UV) rays (337 nm or 365 nm) and visible light (400-600 nm) on the yeast cells. Based on the data on different mechanisms of lethal effect of longwave UV and visible light, it has been suggested that the basis of the photosynergistic effect is the mutual intensification of the photo-destructive processes occurring in different intracellular structures and processes induced by different endogenous sensitizers.