Hydroxyl radical generation by a light-dependent Fenton reaction

Primary Processes of Free Radical Formation in Pharmaceutical Formulations of Therapeutic Proteins

Oxidation represents a major pathway for the chemical degradation of pharmaceutical formulations. Few specific details are available on the mechanisms that trigger oxidation reactions in these formulations, specifically with respect to the formation of free radicals. Hence, these mechanisms must be formulated based on information on impurities and stress factors resulting from manufacturing, transportation and storage. In more detail, this article focusses on autoxidation, metal-catalyzed oxidation, photo-degradation and radicals generated from cavitation as a result of mechanical stress. Emphasis is placed on probable rather than theoretically possible pathways.

Heme Oxygenase-1 Inhibition Potentiates the Effects of Nab-Paclitaxel-Gemcitabine and Modulates the Tumor Microenvironment in Pancreatic Ductal Adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is an aggressive malignancy with a poor prognosis. Tumor hypoxia plays an active role in promoting tumor progression, malignancy, and resistance to therapy in PDAC. We present evidence that nab-paclitaxel-gemcitabine (NPG) and/or a hypoxic tumor microenvironment (TME) up-regulate heme oxygenase-1 (HO-1), providing a survival advantage for tumors. Using PDAC cells in vitro and a PDAC mouse model, we found that NPG chemotherapy up-regulated expression of HO-1 in PDAC cells and increased its nuclear translocation. Inhibition of HO-1 with ZnPP and SnPP sensitized PDAC cells to NPG-induced cytotoxicity (p < 0.05) and increased apoptosis (p < 0.05). Additionally, HO-1 expression was increased in gemcitabine-resistant PDAC cells (p < 0.05), and HO-1 inhibition increased GEM-resistant PDAC sensitivity to NPG (p < 0.05). NPG combined with HO-1 inhibitor inhibited tumor size in an orthotopic model. In parallel, HO-1 inhibition abrogated the influx of macrophages and FoxP3+ cells, while increasing the proportion of CD8+ infiltration in the pancreatic tumors. These effects were mediated primarily by reducing expression of the immunosuppressive cytokine IL-10.

Near UV and Visible Light Induce Iron-Dependent Photodegradation Reactions in Pharmaceutical Buffers: Mechanistic and Product Studies

Near UV (λ = 320-400 nm) and visible light (λ = 400-800 nm) can lead to the oxidation of pharmaceutical proteins, which can affect efficiency and promote immunogenicity. However, no concise mechanism has been established for the photo-oxidation of pharmaceutical proteins under near UV and visible light. Here, we show that carboxylic acid buffer-Fe³⁺ complexes can function as photosensitizers, causing peptide degradation via the formation of various radicals and oxidants. Three pharmaceutical relevant carboxylic acid buffers (citrate, acetate, and succinate) were tested under near UV and visible light. Oxidation reactions were monitored for model peptides containing readily oxidizable amino acids, such as methionine- or leucine-enkephalin and proctolin peptide. Oxidation products were evaluated by RP-HPLC coupled to UV or fluorescent detection and RP-HPLC-MS/MS. Specifically for citrate buffer, the light-induced formation of H₂O₂, ^•OH, ^•CO₂^-, and formaldehyde was demonstrated. The peptides displayed oxidation of Met, hydroxylation of Tyr and Phe, as well as the formation of novel products from Tyr. Experiments with ¹⁸O₂ resulted in the incorporation of ¹⁸O into various reaction products, consistent with a metal-catalyzed activation of O₂ into reactive oxygen species. The addition of EDTA and DTPA did not prevent the oxidation of the peptides and, in some cases, enhanced the oxidation. Our results demonstrate that pharmaceutical buffer-Fe³⁺ complexes, exposed to UV and visible light, can promote various pathways of oxidation reactions in pharmaceutical formulations.

UVA irradiation increases ferrous iron release from human skin fibroblast and endothelial cell ferritin: Consequences for cell senescence and aging

UVA irradiation of human dermal fibroblasts and endothelial cells induces an immediate transient increase in cytosolic Fe(II), as monitored by the fluorescence Fe(II) reporters, FeRhonox1 in cytosol and MitoFerroGreen in mitochondria. Both superoxide dismutase (SOD) inhibition by tetrathiomolybdate (ATM) and catalase inhibition by 3-amino-1, 2, 4-triazole (ATZ) increase and prolong the cytosolic Fe(II) signal after UVA irradiation. SOD inhibition with ATM also increases mitochondrial Fe(II). Thus, mitochondria do not source the UV-dependent increase in cytosolic Fe(II), but instead reflect and amplify raised cytosolic labile Fe(II) concentration. Hence control of cytosolic ferritin iron release is key to preventing UVA-induced inflammation. UVA irradiation also increases dermal endothelial cell H₂O₂, as monitored by the adenovirus vector Hyper-DAAO-NES(HyPer). These UVA-dependent changes in intracellular Fe(II) and H₂O₂ are mirrored by increases in cell superoxide, monitored with the luminescence probe L-012. UV-dependent increases in cytosolic Fe(II), H₂O₂ and L-012 chemiluminescence are prevented by ZnCl₂ (10 μM), an effective inhibitor of Fe(II) transport via ferritin's 3-fold channels. Quercetin (10 μM), a potent membrane permeable Fe(II) chelator, abolishes the cytosolic UVA-dependent FeRhonox1, Fe(II) and HyPer, H₂O₂ and increase in MitoFerroGreen Fe(II) signals. The time course of the quercetin-dependent decrease in endothelial H₂O₂ correlates with the decrease in FeRhox1 signal and both signals are fully suppressed by preloading cells with ZnCl₂. These results confirm that antioxidant enzyme activity is the key factor in controlling intracellular iron levels, and hence maintenance of cell antioxidant capacity is vitally important in prevention of skin aging and inflammation initiated by labile iron and UVA.

Light-driven oxidation of polysaccharides by photosynthetic pigments and a metalloenzyme

Oxidative processes are essential for the degradation of plant biomass. A class of powerful and widely distributed oxidative enzymes, the lytic polysaccharide monooxygenases (LPMOs), oxidize the most recalcitrant polysaccharides and require extracellular electron donors. Here we investigated the effect of using excited photosynthetic pigments as electron donors. LPMOs combined with pigments and reducing agents were exposed to light, which resulted in a never before seen 100-fold increase in catalytic activity. In addition, LPMO substrate specificity was broadened to include both cellulose and hemicellulose. LPMO enzymes and pigment derivatives common in the environment of plant-degrading organisms thus form a highly reactive and stable light-driven system increasing the turnover rate and versatility of LPMOs. This light-driven system may find applications in biotechnology and chemical processing.

Lytic polysaccharide monooxygenases are proteins involved in the degradation of plant biomass and are promising biotechnological tools for biofuel production. Here, the authors show that their catalytic activity is significantly boosted when they are combined with photopigments and exposed to light.

Hydrogen peroxide contributes to the ultraviolet-B (280-315 nm) induced oxidative stress of plant leaves through multiple pathways

Solar UV-B (280-315 nm) radiation is a developmental signal in plants but may also cause oxidative stress when combined with other environmental factors. Using computer modeling and in solution experiments we show that UV-B is capable of photosensitizing hydroxyl radical production from hydrogen peroxide. We present evidence that the oxidative effect of UV-B in leaves is at least twofold: (i) it increases cellular hydrogen peroxide concentrations, to a larger extent in pyridoxine antioxidant mutant pdx1.3-1 Arabidopsis and; (ii) is capable of a partial photo-conversion of both 'natural' and 'extra' hydrogen peroxide to hydroxyl radicals. As stress conditions other than UV can increase cellular hydrogen peroxide levels, synergistic deleterious effects of various stresses may be expected already under ambient solar UV-B.

Antioxidant trace elements in serum of draft horses with acute and chronic lower airway disease

The aim of the present study was to evaluate the oxidative stress level and antioxidant trace elements status associated with lower airway disease in draft horses. For this purpose, venous blood samples were obtained from draft horses exhibiting signs of lower respiratory tract disorders (n = 83) and from control group (n = 20). Serum trace elements including selenium (Se), copper (Cu), zinc (Zn), manganese (Mn), and iron (Fe) were assayed. Serum malondialdehyde (MDA) and low-density lipoprotein (LDL) levels as well as plasma hydrogen peroxides (H₂O₂) concentration and activity of plasma glutathione reductase (GR), glutathione-S-transferase (GST) and catalase (CAT) were measured. There was a significant (p < 0.05) decrease of Se, Cu, Zn, and Fe in diseased horses compared with healthy ones, but the Cu/Zn ratio and Mn were increased (p < 0.05). Se was significantly (p < 0.05) decreased in chronically affected horses compared with acute cases, but Mn was increased (p < 0.05). There was an increase of MDA, LDL, and H₂O₂ levels and GR activity in diseased cases compared with healthy horses. However, there was a significant (p < 0.05) decrease of GST and CAT activity. MDA and LDL levels were increased (p < 0.05) in horses with chronic respiratory disease compared to acute cases, but CAT activity was decreased (p < 0.05). In horses with acute lower airway disease, there was a negative correlation between GR and H₂O₂ (r = -0.458), and LDL and CAT (r = -0.816). However, in chronic disease, a negative correlation was recorded between Se and MDA (r = -0.590). The results of the present study indicate that oxidative stress, with alteration of antioxidant trace element levels, is a feature of respiratory disease in draft horses.

The slowly aggregating salmon Calcitonin: a useful tool for the study of the amyloid oligomers structure and activity

Amyloid proteins of different aminoacidic composition share the tendency to misfold and aggregate in a similar way, following common aggregation steps. The process includes the formation of dimers, trimers, and low molecular weight prefibrillar oligomers, characterized by the typical morphology of globules less than 10 nm diameter. The globules spontaneously form linear or annular structures and, eventually, mature fibers. The rate of this process depends on characteristics intrinsic to the different proteins and to environmental conditions (i.e., pH, ionic strength, solvent composition, temperature). In the case of neurodegenerative diseases, it is now generally agreed that the pathogenic aggregates are not the mature fibrils, but the intermediate, soluble oligomers. However, the molecular mechanism by which these oligomers trigger neuronal damage is still unclear. In particular, it is not clear if there is a peculiar structure at the basis of the neurotoxic effect and how this structure interacts with neurons. This review will focus on the results we obtained using salmon Calcitonin, an amyloid protein characterized by a very slow aggregation rate, which allowed us to closely monitor the aggregation process. We used it as a tool to investigate the characteristics of amyloid oligomers formation and their interactions with neuronal cells. Our results indicate that small globules of about 6 nm could be the responsible for the neurotoxic effects. Moreover, our data suggest that the rich content in lipid rafts of neuronal cell plasma membrane may render neurons particularly vulnerable to the amyloid protein toxic effect.

Quercetin-iron chelates are transported via glucose transporters

Flavonoids are well-known antioxidants and free radical scavengers. Their metal-binding activity suggests that they could be effective protective agents in pathological conditions caused by both extracellular and intracellular oxidative stress linked to metal overload. Quercetin is both a permeant ligand via glucose transport proteins (GLUTs) and a high-affinity inhibitor of GLUT-mediated glucose transport. Chelatable "free iron" at micromolar concentrations in body fluids is a catalyst of hydroxyl radical (OH(•)) production from hydrogen peroxide. A number of flavonoids, e.g., quercetin, luteolin, chrysin, and 3,6-dihydroxyflavone, have been demonstrated to chelate intracellular iron and suppress OH(•) radical production in Madin Darby canine kidney cells. The most effective chelation comes from the flavonone B ring catechol found in both quercetin and luteolin. We show here that quercetin concentrations of <1μM can facilitate chelatable iron shuttling via GLUT1 in either direction across the cell membrane. These siderophoric effects are inhibited by raised quercetin concentrations (>1μM) or GLUT inhibitors, e.g., phloretin or cytochalasin B, and iron efflux is enhanced by impermeant extracellular iron chelators, either desferrioxamine or rutin. This iron shuttling property of quercetin might be usefully harnessed in chelotherapy of iron-overload conditions.

Iron-mediated photochemical decomposition of methylmercury in an arctic Alaskan lake

Sunlight-induced decomposition is the principal sink for methylmercury (CH(3)Hg(+)) in arctic Alaskan lakes and reduces its availability for accumulation in aquatic food webs. However, the mechanistic chemistry of this process in natural waters is unknown. We examined experimentally the mechanism of photochemical CH(3)Hg(+) decomposition in filter-sterilized epilimnetic waters of Toolik Lake in arctic Alaska (68 degrees 38'N, 149 degrees 36'W), a region illuminated by sunlight almost continuously during the summer. Results from in situ incubation tests indicate that CH(3)Hg(+) is not decomposed principally by either direct photolysis (i.e., no degradation in reagent-grade water) or primary photochemical reactions with dissolved organic material. The preeminent role of labile Fe and associated photochemically produced reactive oxygen species is implicated by tests that show 1) additions of Fe(III) to reagent-grade water enhance CH(3)Hg(+) photodecomposition, 2) strong complexation of ambient Fe(III) with desferrioxamine B inhibits the reaction in lake water, and 3) experimental additions of organic molecules that scavenge hydroxyl radicals specifically among reactive oxygen species (dimethylsulfoxide and formic acid) inhibit CH(3)Hg(+) degradation. Lake-water dilution and Fe(III) addition experiments indicate that Fe is not the limiting reactant for CH(3)Hg(+) photodecomposition in Toolik Lake, which is consistent with prior results indicating that photon flux is a major control. These results demonstrate that CH(3)Hg(+) is decomposed in natural surface water by oxidants, apparently hydroxyl radical, generated from the photo-Fenton reaction.

Cryopreservation of anoxygenic phototrophic Fe(II)-oxidizing bacteria

Preservation and storage of microbial stock cultures is desirable since the risk of contamination or loss of living cultures is immanent while over long periods mutations accumulate. Generally, it is rather difficult to preserve photosynthetic bacteria due to their sensitive photosynthetic membranes. Phototrophic Fe(II)-oxidizing bacteria face an additional challenge; since they are exposed to light and Fe(II) during growth, they have to cope with radicals from Fenton reactions of Fe(II)-species, light and water. Therefore, phototrophic Fe(II)-oxidizing strains are thought to be especially susceptible to genetic modifications. Here, we provide a simple and fast protocol using glycerol as cryo-protectant to cryopreserve three strains of anoxygenic phototrophic Fe(II)-oxidizing bacteria from different taxa: alpha-proteobacteria, gamma-proteobacteria and chloroflexi. All three strains investigated could be revived after 17 months at -72 degrees C. This suggests that a long-term storage of phototrophic Fe(II)-oxidizing strains is possible.

Algae extract-mediated stimulation and protection of proteasome activity within human keratinocytes exposed to UVA and UVB irradiation

Sun exposure is the major environmental influence for epidermal cells; the harmful effect of UV radiation on skin is related to the generation of reactive oxygen species that alter cellular components including proteins. It is now well established that the proteasome is responsible for the degradation of most of oxidized proteins and that impairment of proteasome function is a hallmark of cellular aging. In a previous study, we investigated the effects of UV irradiation on proteasomes in human keratinocyte cultures and showed that all three peptidase activities were decreased 24 h after irradiation of the cells. Increased levels of oxidatively modified proteins were observed in irradiated cells and were found to act as endogenous inhibitors of the proteasome. We report here on the stimulating and protective effects of an algae extract, prepared from Phaeodactylum tricornutum, on proteasome peptidase activities of human keratinocytes exposed to UVA and UVB irradiation. In addition, preserving proteasome function resulted in lowering the extent of the irradiation-induced protein oxidative damage, opening up new strategies for protection of epidermal cells against the detrimental effects of UV irradiation.

RP-HPLC study of the degradation of diclofenac and piroxicam in the presence of hydroxyl radicals

The effect of hydroxyl radical attack on two non-steroidal anti-inflammatory drugs (NSAIDs) was studied in vitro. Diclofenac and piroxicam were analysed by RP-HPLC after reaction with OH* free radicals to detect newly formed oxidation and/or degradation products. OH* free radicals were obtained by means of ferrous sulphate and ascorbic acid mixtures. During the reaction the mixtures were exposed to irradiation by a tungsten lamp to obtain an increased and more reproducible formation of hydroxyl radicals. The chromatographic profiles showed the formation of several new peaks for both diclofenac and piroxicam due to the presence of a number of degradation/oxidation products formed in the presence of OH* radicals.

Impairment of proteasome function upon UVA- and UVB-irradiation of human keratinocytes

The major environmental influence for epidermal cells is sun exposure and the harmful effect of UV radiation on skin is related to the generation of reactive oxygen species that are altering cellular components including proteins. It is now well established that the proteasome is responsible for the degradation of oxidized proteins. Therefore, the effects of UV-irradiation on proteasome have been investigated in human keratinocyte cultures. Human keratinocytes were irradiated with 10 J/cm(2) of UVA and 0.05 J/cm(2) of UVB and proteasome peptidase activities were measured in cell lysates using fluorogenic peptides. All three peptidase activities were decreased as early as 1 h and up to 24 h after irradiation of the cells. Increased levels of oxidized and ubiquitinated proteins as well as proteins modified by the lipid peroxidation product 4-hydroxy-2-nonenal were also observed in irradiated cells. However, immunopurified 20S proteasome exhibited no difference in both peptidase specific activities and 2D gel pattern of subunits in irradiated cells, ruling out the possibility that the 20S proteasome could be a target for the UV-induced damage. Finally, extracts from irradiated keratinocytes were able to inhibit degradation by the proteasome, demonstrating the presence of endogeneous inhibitors, including 4-hydroxy-2-nonenal modified proteins, generated upon UV-irradiation.

Possible role of hydroxyl radicals in the oxidation of dichloroacetonitrile by Fenton-like reaction

Dichloroacetonitrile (DCAN), is a member of haloacetonitrile group and detected in drinking water supplies as a by-product of chlorination process. The mechanism of DCAN-induced carcinogenesis is believed to be mediated by oxidative bioactivation of DCAN molecules. The present study was designed to investigate if reactive oxygen species (ROS), similar to that generated in biological systems, are capable of oxidative activation of DCAN. A model ROS generation system (Fenton-like reaction; Fe2+ and H2O2) that predominantly produces hydroxyl radical (OH*) was used. DCAN oxidation was monitored by the extent of cyanide (CN-) release. The results indicate that DCAN was markedly oxidized by this system, and the rate of oxidation was dependent on DCAN concentration. Four-fold increase in H2O2 concentration (50-200 mM) resulted in a 35-fold increase in CN- release. The rates of DACN oxidation in presence of various transition metals were in the following order; iron>copper>titanium. DCAN oxidation was enhanced significantly by the addition of vitamin C and sulfhydryl compounds such as glutathione, N-acetyl-L- cysteine, and dithiothreitol (10 mM) to 140, 130, 145 and 136% of control, respectively. Addition of H2O2 scavenger; catalase or iron chelator; desferrioxamine (DFO) resulted in a significant decrease in CN- release 47 and 41% of control, respectively. Addition of various concentrations of the free radical scavengers, DMSO, or mannitol, to the incubation mixtures caused a significant decrease in DCAN oxidation, 32 and 50% of control, respectively. Michaelis-Menten kinetic analysis of the rates of this reaction, with or without inhibitors, indicated that ROS mediated oxidation of DCAN was inhibited by catalase (Ki = 0.01 mM)>DFO (0.02 mM) > mannitol (0.09 mM) > DMSO (0.12 mM). In conclusion, our results indicate that DCAN is oxidized by a ROS-mediated mechanism. This mechanism may have an important role in DCAN bioactivation and DCAN-induced genotoxicity at target organs where multiple forms of ROS generating systems are abundant.

Nitric oxide protects nitric oxide synthase function from hydroxyl radical-induced inhibition

The interdependent relationships among nitric oxide synthase (NOS), its coenzyme, cofactors and nitric oxide (NO(free radical) were studied using electron paramagnetic resonance spectroscopy. It was found that superoxide-dependent hydroxyl free radical (OH(free radical), derived from NOS coenzyme and cofactors, inhibits NOS activity, and that endogenous NO(free radical) generated by NOS scavenges OH(free radical) and protects NOS function. These results reveal a new role for NO(free radical) that may be important in NOS function and cellular free radical homeostasis.

Acidic pH amplifies iron-mediated lipid peroxidation in cells

The goal of our study was to investigate the mechanism by which changes in extracellular pH influence lipid peroxidation processes. Ferrous iron can react with hydroperoxides, via a Fenton-type reaction, to initiate free radical chain processes. Iron is more soluble at lower pH values, therefore we hypothesized that decreasing the environmental pH would lead to increased iron-mediated lipid peroxidation. We used Photofrin, a photosensitizer that produces singlet oxygen, to introduce lipid hydroperoxides into leukemia cells (HL-60, K-562, and L1210). Singlet oxygen reacts with the PUFA of cells producing lipid hydroperoxides. Using EPR spin trapping with POBN, free radical formation from HL-60 cells was only detected when Photofrin, light, and ferrous iron were present. Free radical formation increased with increasing iron concentration; in the absence of extracellular iron, radical formation was below the limit of detection and lipid hydroperoxides accumulated in the membrane. In the presence of iron, lipid-derived radical formation in cells is pH dependent; the lower the extracellular pH (7.5-5.5), the higher the free radical flux; the lower the pH, the greater the membrane permeability induced in K-562 cells, as determined by trypan blue dye exclusion. These data demonstrate that lipid peroxidation processes, mediated by iron, are enhanced with decreasing extracellular pH. Thus, acidic pH not only releases iron from "safe" sites, but this iron will also be more damaging.

Iron supplementation may aggravate inflammatory status of colitis in a rat model

Iron supplementation is one of the principal therapies in inflammatory bowel disease. Iron is a major prooxidative agent; therefore therapeutic iron as well as heme iron from chronic mucosal bleeding can increase the iron-mediated oxidative stress in colitis by facilitating the Fenton reaction, namely production of hydroxyl radicals. In the present study colitis was induced in the iodoacetamide rat model. Forty male Whistar rats were divided into four groups, each group receiving a different diet regimen in parallel with colitis induction: Malondialdehyde was measured to assess the degree of tissue oxidative stress. There were microscopic changes, and significantly more severe colitis was seen in colonic biopsies when iron was supplemented. It was concluded that iron supplementation can amplify the inflammatory response and enhance the subsequent mucosal damage in a rat model of colitis. We suggest that the resultant oxidative stress generated by iron supplementation leads to the extension and propagation of crypt abscesses.

Presence and effects of melatonin in Trypanosoma cruzi

The unicellular organism Trypanosoma cruzi is an eukaryote whose cell cycle mainly occurs under darkness in the insect gut. The unique external phase corresponds to the metacyclic forms, the forms that are able to infect humans, which appear within the insect deyections. Thus, light may be a powerful stressor in this unicell. Epimastigote forms (the parasite forms that grow and transform to metacyclic forms in the insect gut) of Trypanosoma cruzi grow normally when cultured in a LD cycle of 0:24 hr, reaching exponential growth by the 7th day. A pulse of 2 hr of light (LD 2:22) was enough to block the growth of the epimastigotes, an effect that was correlated with the expression of heat-shock proteins during the first 120 min of light exposure. Thereafter, protein synthesis decreased. Light exposure of metacyclic forms also inhibits the parasitization ability. It is known that light regulates the production of melatonin in most animal species studied, including other unicells such as dinoflagellates. T. cruzi contains and synthesizes melatonin and, thus, light-mediated events on the parasite biological cycle could be mediated by light-induced changes in melatonin produced by this unicell. Epimastigotes cultured under continuous darkness produce melatonin over the 24 hr period in a biphasic manner. Coinciding with the melatonin peaks, there was high melatonin efflux from the parasite into the medium. Epimastigotes cultured for 7 days under a LD cycle of 2:22 hr showed a 55% reduction in melatonin content, although this reduction seems not to be related with the growth delay. In fact, incubation of epimastigotes with exogenous melatonin (1 pM) did not affect parasite growth, but significantly reduced their transformation into metacyclic forms by the 7-8th day of treatment. Thus, the light-dependent decrease in melatonin production by the unicell may be responsible, at least partially, for the light-induce parasitization inhibition. Moreover, melatonin production is highest in the metacyclic forms. These data support a link between light, melatonin production and parasitization ability of T. cruzi and suggest the participation of the indoleamine in its biological cycle.

UVA-induced oxidative damage to rat liver nuclei: reduction of iron ions and the relationship between lipid peroxidation and DNA damage

Lipid peroxidation and DNA damage and the relationship between the two events were studied in rat liver nuclei irradiated with low dose UVA. Lipid peroxidation was measured as thiobarbituric acid-reactive substances (TBARS) by spectrophotometric method and as malondialdehyde-TBA adduct by HPLC, and DNA damage was measured as 8-hydroxy-deoxyguanosine (8-OH-dGu) and strand breakage (or loss of double-stranded DNA) by a fluorometric analysis of alkaline DNA unwinding method. The results show that UVA irradiation by itself increased nuclear lipid peroxidation but caused little or no DNA strand breakage or 8-OH-dGu. When 0.5 mM ferric (Fe+3) or ferrous (Fe+2) ions were added to the nuclei during UVA irradiation, lipid peroxidation and DNA damage, measured both as 8-OH-dGu and loss of double-stranded DNA, were strongly enhanced. Lipid peroxidation occurred concurrently with the appearance of 8-OH-dGu. Fe3+ ions were reduced to Fe2+ in this UVA/Fe2+/nuclei system. Lipid peroxidation and DNA damage were neither inhibited by scavengers of hydroxyl radical and singlet oxygen nor inhibited by superoxide dismutase and catalase. Inclusion of EDTA or chain-breaking antioxidants, butylated hydroxytoluene (BHT) and diphenylamine (an alkoxy radical scavenger), inhibited lipid peroxidation but not the level of 8-OH-dGu. BHT also did not inhibit the loss of double-stranded DNA in this system. This study demonstrates the reduction of exogenous Fe+3 by UVA when added to rat liver nuclei, and, as a result, oxidative damage is strongly enhanced. In addition, the results show that DNA damage is not a result of lipid peroxidation in this UVA/Fe2+/nuclei system.

Neuroprotection by nitric oxide against hydroxyl radical-induced nigral neurotoxicity

We investigated the effects of nitric oxide on an in vitro and in vivo generation of hydroxyl radicals, and in vivo neurotoxicity caused by intranigral infusion of ferrous citrate in rats. The formation of hydroxyl radicals in vitro, without exogenous hydrogen peroxide, was dose-dependent. Some nitric oxide donors (e.g. sodium nitroprusside) stimulated, while others (nitroglycerin, diethylamine/nitric oxide, nitric oxide in Ringer's solution) suppressed hydroxyl radical generation in vitro. A significant increase in extra-cellular hydroxyl radicals was detected in a brain microdialysis study. Intranigral infusion of ferrous citrate caused long-lasting lipid peroxidation and dopamine depletion in the ipsilateral nigral region and striatum, respectively. Sub-acute dopamine depletion in the striatum was positively correlated with acute lipid peroxidation in substantia nigra. Intranigral administration of nitric oxide did not affect striatal dopamine. Interestingly, nitric oxide in Ringer's protected nigral neurones against the oxidative injury. The results demonstrate that a regional increase in the levels of iron can result in hydroxyl radical generation and lipid peroxidation leading to neurotoxicity. It also demonstrates that exogenous nitric oxide can act as hydroxyl radical scavenger and protect neurones from oxidative injury.

Bound iron admixture prevents the spontaneous generation of peroxides in total parenteral nutrition solutions

BACKGROUND

Parenteral administration of iron is a matter of controversy because it is feared that it could contribute to oxidative reactions. The aim of this study was to verify if irondextran participates in the redox reactions occurring in total parenteral nutrition (TPN) solutions.

METHODS

Irondextran was compared with different forms of iron in the interaction with peroxides. Hydroperoxide levels were measured by a colorimetric technique in TPN solutions, in presence of varying sources (FeCl2, FeSO4, irondextran, iron sorbitol) and concentrations (0-0.8 mM) of iron. The consumption and inhibition of peroxide generation were tested by analyzing the effect of iron on different sources of peroxides (H2O2, tert-butyl and cumen hydroperoxide). The free radicals produced under conditions of a Fenton-like reaction were measured by the oxidation of scopoletin. And the proportion of Fe3+ freed by both bound-iron sources was counted by measuring the masking effect on the thiol function of cysteine.

RESULTS

Free-iron admixture to parenteral nutrition induces the formation of free radicals, whereas sources of bound-iron inhibit the generation of peroxides in parenteral nutrition without implying a Fenton-like reaction.

CONCLUSION

For patients requiring iron supplementation, bound-iron should be added during the preparation of TPN solutions, because it protects against the spontaneous generation of peroxides.

Oxidative stress and antioxidant status in mouse liver: effects of dietary lipid, vitamin E and iron

The purpose of this study was to determine the effects of dietary fat, vitamin E and iron on oxidative damage and antioxidant status. Male Swiss-Webster mice (1 mo old) were fed a basal vitamin E-deficient diet that contained either 8% fish oil + 2% corn oil or 10% lard with or without 1 g dl-alpha-tocopheryl acetate. The diets without vitamin E contained either 0.21 or 0.95 g ferric citrate/kg. Diets were fed for 4 wk/kg diet. Compared with the vitamin E-supplemented groups, mice fed diets without vitamin E (with or without supplemental iron) had significantly (P < 0.05) higher hepatic levels of thiobarbituric acid-reactive substances (TBARS), conjugated dienes and protein carbonyls when they were fed fish oil, but not lard. The levels of TBARS were further increased by iron supplementation in the mice fed fish oil. Significantly lower concentrations of alpha-tocopherol and higher glutathione (GSH) were found in the liver of mice fed fish oil and vitamin E than in those fed lard and vitamin E (P < 0.05). The activities of superoxide dismutase and glucose-6-phosphate dehydrogenase were lower in the fish oil-fed mice than in those fed lard (P < 0.05). The activities of Se-GSH peroxidase, non-Se-GSH peroxidase, catalase, and glutathione reductase were not altered by dietary fat or vitamin E/iron. The results obtained provide experimental evidence of the prooxidative effects of high dietary fish oil and iron, and suggest that vitamin E protects not only lipid-soluble compounds, but also water-soluble constituents, against oxidative damage. Further, dietary lipid plays a key role in determining cellular susceptibility to oxidative stress.

Detection of hydroxyl and carbon-centred radicals by EPR spectroscopy after ischaemia and reperfusion of the rat kidney

Recent studies suggest that oxygen-derived free radicals are involved in mediating renal reperfusion injury. EPR spectroscopy and spin trapping with the spin traps DMPO and PBN, were used to detect and quantitate the formation of hydroxyl radicals in rat kidney after ischaemia-reperfusion in vivo and in vitro in the isolated rat kidney perfused in the absence of leucocytes. EPR analysis of homogenised kidneys and of venous samples did not detect radical adducts with either spin trap. With PBN, radical adducts were not detected in vitro. When DMPO was used as the spin trap in kidneys perfused without albumin in the perfusate, EPR signals characteristic of hydroxyl and carbon-centred radical adducts were detected during early reperfusion following ischaemia. These studies confirm the generation of hydroxyl radicals during ischaemia-reperfusion in kidney. During reperfusion the total DMPO adduct concentration reached 4.35 +/- 1.05 nmol/g kidney/3 min, p < 0.05. In control kidneys total adduct were present at lower concentration (2.55 +/- 1.1 nmol/g kidney/3 min). Addition of 15 mM dimethylthiourea abolished formation of these adducts following ischaemia-reperfusion but did not prevent a reduction in glomerular filtration rate. These results indicate that significant levels of hydroxyl and carbon-centred radicals are formed in the absence of circulating neutrophils during early renal reperfusion following ischaemia.

UVA-potentiated damage to calf thymus DNA by Fenton reaction system and protection by para-aminobenzoic acid

Calf thymus DNA was irradiated with low-intensity UVA (main output at 365 nm, 2 mW cm-2 or 36 kJ m-2 for 30 min), and the role of metal ions, hydrogen peroxide and reactive oxygen species (ROS) was examined. DNA damage was measured as thiobarbituric acid-reactive substances (possibly from degradation of deoxyribose) and as changes in ethidium bromide-DNA fluorescence due to unwinding from strand breaks. Under the present experimental conditions, UVA alone or in the presence of H2O2 had no effect on DNA but slightly enhanced the damage by iron/EDTA. Ultraviolet A strongly enhanced DNA damage (ca four- to five-fold) by the Fenton reaction system (50 microM Fe2+/100 microM EDTA + 0.5 mM H2O2). The results suggest that the Fenton reaction system was "photosensitized" to damage DNA by low-intensity UVA radiation. The enhanced damage by UVA was attributed in part to the reduction of Fe3+ to Fe2+. Ultraviolet A had no effect when iron (ferric or ferrous) ions were replaced by Cu2+, Zn2+, Mn2+ or Cd2+. The ROS involved in the UVA-enhanced damage to DNA by the Fenton reagents were OH and, to a lesser extent, superoxide anions. The UVA-potentiated DNA damage by the Fenton reaction system was then used to examine the protective effect of para-aminobenzoate (PABA), a UVB-absorbing sunscreen that protects against photocarcinogenesis in hairless mice. The results show that PABA and mannitol dose-dependently inhibited the damage with concentrations required for 50% inhibition at 0.1 mM and 3 mM, respectively. The protection by PABA was attributed to its radical-scavenging ability because PABA does not absorb light in the UVA region. These findings may be relevant to the biological damage by UVA and suggest that PABA is useful in protection against photocarcinogenesis by wide-range UV radiation.

NO synthase and xanthine oxidase activities of rabbit brain synaptosomes: peroxynitrite formation as a causative factor of neurotoxicity

In the present study we demonstrated that synaptosomes isolated from rabbit brain cortex contain NO synthase and xanthine oxidase that can be activated by ultraviolet B radiation and Ca2+ accumulation to produce nitric oxide and superoxide which react together to form peroxynitrite. Irradiation of synaptosomes with ultraviolet B (up to 100 mJ/cm2), or increase the intrasynaptosomal calcium concentration using various doses (up to 100 mu M) of the calcium ionophore A 23187, a gradual increase in both nitric oxide and peroxynitrite release that was inhibited by N-monomethyl-L-arginine (100 mu M) was observed. The rate of nitric oxide release and cyclic GMP production by NO synthase and soluble guanylate cyclase, both located in the soluble fraction of synaptosomes (synaptosol), were increased approximately eight fold after treatment of synaptosomes with Ultraviolet B radiation (100 mJ/cm2). In reconstitution experiments, when purified NO synthase isolated from synaptosol was added to xanthine oxidase, in the presence of the appropriate cofactors and substrates, a ten fold increase in peroxynitrite production at various doses (up to 20 mJ/cm2) of UVB radiation was observed. Ultraviolet B irradiated synaptosomes promptly increased malondialdehyde production with subsequent decrease of synaptosomal plasma membrane fluidity estimated by fluorescence anisotropy of 1-4-(trimethyl-amino-phenyl)-6-phenyl-hexa-1 ,3,5-triene. Desferrioxamine (100 mu M) tested in Ultraviolet B-irradiated synaptosomes showed a decrease (approximately 80%) in malondialdehyde production with subsequent restoration of the membrane fluidity to that of non-irradiated (control) synaptosomes. Ca(2+)-stimulated ATPase activity was decreased after Ultraviolet B (100 mJ/cm2) radiation of synaptosomes indicating that the subsequent increase of intrasynaptosomal calcium promoted peroxynitrite production by a calmodulin-dependent increase of NO synthase and xanthine oxidase activities. Furthermore, it was shown that UVB-irradiated synaptosomes were subjected to higher oxidative stress by exogenous peroxynitrite (100 mu M) compared to non-irradiated (control) synaptosomes. In summary, the present results indicate that activation of NO synthase and xanthine oxidase of brain cells lead to the formation of peroxynitrite providing important clues in the role of peroxynitrite as a causative factor in neurotoxicity.

The effects of hydroxyl radical attack on dopa, dopamine, 6-hydroxydopa, and 6-hydroxydopamine

High pressure liquid chromatography with electrochemical detection (HPLC-ED) was employed in conjugation with a sensitive and specific salicylate hydroxylation assay to evaluate the immediate effects of hydroxyl radical (.OH) attack on four catechol intermediates of eumelanin, dopamine (3,4-dihydroxyphenylethylamine), its precursor dopa (3,4-dihydroxyphenylalanine), and their respective neurotoxic trihydroxyphenyl derivatives, 6-hydroxydopamine (2,4,5-trihydroxyphenylethylamine,6-OHDA) and 6-hydroxydopa(2,4,5-trihydroxyphenylalanine, TOPA). Semiquinone and quinone species were identified as the initial products of the oxidation of these four catechol substrates. The enhanced oxidations of the catechols when exposed to .OH attack was accompanied by marked decreases in the level of each semiquinone species. Quinone levels were elevated in reactions involving .OH attack on dopamine and 6-OHDA, but absent in reactions involving radical attack on dopa or TOPA, suggesting that dopaquinone (DOQ) and TOPA p-quinone (TOPA p-Q) are oxidized more rapidly by .OH than are the quinones of dopamine and 6-OHDA. The formation of 6-OHDA p-quinone (6-OHDA p-Q) in incubations involving DA and .OH suggest that the .OH-mediated hydroxylation of DA may be a mechanism for generating this potentially cytotoxic trihydroxyphenyl. The results of this study demonstrate for the first time that semiquinone and quinone intermediates of eumelanin are the initial products derived from the .OH-mediated oxidations of dopa, DA, TOPA, and 6-OHDA. These observations suggest that if .OH is generated beyond the capabilities of cytoprotective mechanisms, the radical can rapidly oxidize catechol precursors, augment melanogenesis, and generate additional cytotoxic quinoid intermediates of eumelanin.

UVA radiation-induced oxidative damage to lipids and proteins in vitro and in human skin fibroblasts is dependent on iron and singlet oxygen

This study describes the damage that occurs to lipids and proteins that have been irradiated in vitro or in human skin fibroblasts with physiological doses of UVA radiation. Thiobarbituric acid-reactive species were formed from phosphatidylcholine after UVA radiation in vitro. By using iron chelators, this process was shown to involve iron. Ferric iron associated with potential physiological chelators was reduced by UVA radiation, but iron within ferritin was not. By enhancing the half life-time with deuterium oxide or by using scavengers, singlet oxygen was also shown to be involved in the UVA radiation-dependent peroxidation of phosphatidylcholine. UVA radiation-generated singlet oxygen reacted with phosphatidylcholine to form lipid hydroperoxides, and the breakdown of these hydroperoxides to thiobarbituric acid-reactive species was dependent on iron. We have shown that iron and singlet oxygen are also involved in the UVA radiation-dependent formation of thiobarbituric acid-reactive species in human skin fibroblasts, and we propose that a similar concerted effect of iron and singlet oxygen is involved in UVA radiation-dependent damage to fibroblast lipids. Sulphydryl groups of bovine serum albumin and human gamma-globulin were oxidised upon UVA irradiation in vitro. The use of scavengers and deuterium oxide showed that UVA radiation-dependent sulphydryl oxidation was dependent on singlet oxygen. By adding or chelating iron, UVA radiation-dependent oxidation of sulphydryl groups of bovine serum albumin and human gamma-globulin was shown to be iron-dependent. The use of catalase and hydroxyl radical scavengers demonstrated that hydrogen peroxide, but not the hydroxyl radical, was involved. The oxidation of sulphydryl groups of proteins in human skin fibroblasts that occurs as a result of UVA irradiation was also shown to involve iron, singlet oxygen, and hydrogen peroxide. We conclude that iron, singlet oxygen, and hydrogen peroxide are important redox active species involved in the deleterious effects of UVA radiation on lipids and proteins of human skin cells.

UV-mediated cataractogenesis: a radical perspective

A number of epidemiologic and experimental studies indirectly support the idea that solar ultraviolet radiation may be cataractogenic. However, the physical and cellular processes which might be involved in such cataractogenesis are by no means clear. Because a major consequence of the UV irradiation of oxygenated organic matter is the production of activated oxygen species, the involvement of oxidants has been suspected to be of importance. However, because the lens may normally exist in an hypoxic or even anoxic environment, the extent of availability of oxygen for such reactions is presently unknown. So also are the possible mechanism through which putative UV damage of the lens might eventuate in cataract. In addition to possible rapid and direct lethal damage to lens epithelium, possible cumulative damage to both lenticular DNA and proteins may occur. Furthermore, UV radiation has the potential to photolytically destroy light-sensitive nutrients and to generate damaging oxidants through interaction with ferruginous compounds. Given that Nature has probably provided the lens with substantial protective devices to ward off damaging effects of UV light, it is still an open question as to whether solar radiation contributes to cataract formation and, if so, by what mechanisms.

Ferrous-citrate complex and nigral degeneration: evidence for free-radical formation and lipid peroxidation

Increased nigral iron content in the parkinsonian brain is now well documented and is implicated in the pathogenesis of this movement disorder. Free iron in the pigmented DA-containing neurons catalyze DA autoxidation and Fenton reaction to produce cytotoxic .OH, initiating lipid peroxidation and consequent cell damage. The present results clearly demonstrate that a regional increase in the levels of the "labile iron pool" can result in the degeneration of dopaminergic nigral neurons as reflected by a significant inhibition in the expression of tyrosine hydroxylase mRNA and DA depletion. Iron-complex-induced damage of dopaminergic neurons in the substantia nigra, might have resulted from a sequence of cytotoxic events including the .OH generation and lipid peroxidation as demonstrated in this study. This free-radical-induced oxidative nigral injury may be a reliable free-radical model for studying parkinsonism and may be relevant to idiopathic Parkinson's disease. This apparent nigral injury stimulated by Fe(2+)-citrate is more severe than that produced by ferric iron and its citrate complex. Moreover, these data indicate that Fe(2+)-citrate is as potent as MPP+ in causing oxidative injury to the substantia nigral neurons. However, the nigral toxicity of MPTP and its congeners are not progressive, while Fe(2+)-citrate complex may produce a progressive degeneration of the nigrostriatal neurons which is similar to the progression of ideopathic Parkinson's disease. Thus, this unique Fe(2+)-citrate complex animal model could be used for studying neuroprotective treatments for retarding or halting the progressive nigrostriatal degeneration caused by free radicals in the iron-rich basal ganglia.

Detection and quantification of melatonin in a dinoflagellate, Gonyaulax polyedra: solutions to the problem of methoxyindole destruction in non-vertebrate material

Preservative procedures are described for the extraction and quantification of melatonin in cell material from the dinoflagellate Gonyaulax polyedra, an organism in which this indoleamine is rapidly degraded due to interaction with free oxygen radicals and photooxidation. Cells were shock-frozen in liquid nitrogen and pulverized. Various extraction methods were applied to the powder, and rates of recovery were compared. For the determination of melatonin by high performance liquid chromatography (HPLC), extractions with acetone or perchloric acid were more suitable than the use of other solvents. For purposes of radioimmunoassay (RIA), extraction with acetone gave the best results. Several other inorganic solvents, which are often applied in melatonin research, such as chloroform, dichloromethane, and diethyl ether, led to considerable losses of the indoleamine. The procedures developed for HPLC with either electrochemical or fluorescence detection also allow the quantification of other indolic compounds, in particular, tryptophan and 5-methoxytryptamine. The methods described may be of value in the further search for melatonin and related indoleamines in non-vertebrate material, especially, from unicells, multicellular plants, and invertebrates.

Ferrous ion formation by ferrioxamine prepared from aged desferrioxamine: a potential prooxidant property

The siderophore desferrioxamine (DEFOM) binds ferric ions in a 1:1 ratio resulting in a ferrioxamine (FOM) complex. When DEFOM is stored or heat degraded, the resulting FOMD undergoes an autoreduction with the transfer of electrons to the bound ferric ions forming ferrous ions which react with Ferrozine to yield a pink-coloured complex absorbing at 562 nm. Heat-aged DEFOM forms a FOMD complex with an absorption maxima changing from 432 nm to 441 nm. When the autoreduced FOMD complex is placed in a phosphate buffer at pH 7.4, ferrous ions autoxidise transferring electrons to molecular oxygen to form superoxide and hydrogen peroxide. Fenton chemistry leading to the formation of hydroxyl radicals can then occur. Studies with a variety of reactive oxygen scavengers support a role for the hydroxyl radical in damage to the detector molecule deoxyribose. However, when EDTA is present, damage to deoxyribose is decreased and the radicals causing deoxyribose degradation no longer appear to be characteristic of the hydroxyl radical.

Photosensitization with anticancer agents 19. EPR studies of photodynamic action of calphostin C: formation of semiquinone radical and activated oxygen on illumination with visible light

When calphostin C was illuminated with visible light, the semiquinone radical, singlet oxygen, and superoxide anion radical were detected. The formation of the semiquinone radical and activated oxygen species and the transformations and competitions between them depend upon the quinone and oxygen concentrations, time and intensity of illumination, and the nature of the substrate. In anaerobic solution, the semiquinone radical was predominantly photoproduced via the self-electron transfer between the excited and ground species. In aerobic solution, singlet oxygen is the principal product in the photosensitization of calphostin C. In addition to singlet oxygen, superoxide anion radical is also generated by the quinones upon illumination in aerobic solution, but to a lesser extent than singlet oxygen. The superoxide anion is produced via the reduction of oxygen by the semiquinone radical, and this process is significantly enhanced by the presence of electron donors.