Lycopene inhibits DNA damage and liver necrosis in rats treated with ferric nitrilotriacetate

Experimental and epidemiological evidence suggests that lycopene, a carotenoid present in tomatoes, tomato products, and several fruits and vegetables, may play a role in preventing certain cancers in humans. We have investigated the effect of lycopene pretreatment on lipid peroxidation, oxidative damage to DNA, and histopathological changes in liver of animals subjected to intraperitoneal (ip) ferric nitrilotriacetate (Fe-NTA) administration. Compared with control rats, liver of Fe-NTA-treated animals showed a significant increase in the 8-oxo-7,8-dihydro-2'-deoxyguanosine level and a 75% increase in malondialdehyde accumulation concomitant with histopathological changes. Five days of lycopene pretreatment (10 mg/kg body weight, ip) almost completely prevented liver biomolecule oxidative damage and protected the tissue against the observed histological alterations.

DNA damage by 3,6-dihydropyrazine-2,5-dipropanoic acid, the cyclic dimerization product of 5-aminolevulinic acid

5-Aminolevulinic acid (ALA) is a heme precursor that accumulates in lead poisoning and inborn porphyrias. It has been shown to produce reactive oxygen species upon metal-catalyzed aerobic oxidation and to cause oxidative damage to proteins, liposomes, DNA, and subcellular structures. Studies have also shown that ALA may condense to yield the cyclic product 3,6-dihydropyrazine-2,5-dipropanoic acid (DHPY). Here we propose that DHPY could be involved in DNA damage in the presence of high concentrations of ALA. Exposure of plasmid pUC19 DNA to low concentrations of DHPY (2-10 microM) in the presence of 0.1 mM Cu2+ ions causes DNA strand breaks, as demonstrated by agarose gel electrophoresis. It was also shown that in the presence of Cu2+ ions DHPY is able to increase the oxidation of monomeric 2'-deoxyguanosine to form 8-oxo-7,8-dihydro-2'-deoxyguanosine as inferred from high performance liquid chromatography measurements using electrochemical detection. Addition of a metal chelator (bathocuproine, 0.5 mM), the DNA compacting polyamines spermidine (1 mM) and spermine (1 mM) or antioxidant enzymes such as superoxide dismutase (10 microg/ml) and catalase (20 pg/ml) protect the DNA against these damages. The data presented here are discussed with respect to the increased frequency of liver cancer in patients with acute intermittent porphyria.

Singlet oxygen induces oxidation of cellular DNA

The aim of the present work was to evaluate the potential for (1)O(2) to induce oxidation of cellular DNA. For this purpose cells were incubated in the presence of a water-soluble endoperoxide whose thermal decomposition leads to the formation of singlet oxygen. Thereafter, DNA was extracted and the level of several modified DNA bases was determined by HPLC analysis coupled to a tandem mass spectrometric detection. A significant increase in the level of 8-oxo-7,8-dihydro-2'-deoxyguanosine was observed upon incubation of the cells with the chemical generator of (1)O(2), whereas the level of the other DNA bases measured remained unchanged. To demonstrate that singlet oxygen is directly involved in the formation of 8-oxo-7, 8-dihydro-2'-deoxyguanosine, the corresponding (18)O-labeled endoperoxide was used. Incubation of the cells with such a generator of (18)O-labeled singlet oxygen results in the formation of (18)O-labeled 8-oxo-7,8-dihydro-2'-deoxyguanosine in the nuclear DNA. This result clearly demonstrates that singlet oxygen, when released within cells, is able to directly oxidize cellular DNA.

Singlet oxygen induces oxidation of cellular DNA

The aim of the present work was to evaluate the potential for (1)O(2) to induce oxidation of cellular DNA. For this purpose cells were incubated in the presence of a water-soluble endoperoxide whose thermal decomposition leads to the formation of singlet oxygen. Thereafter, DNA was extracted and the level of several modified DNA bases was determined by HPLC analysis coupled to a tandem mass spectrometric detection. A significant increase in the level of 8-oxo-7,8-dihydro-2'-deoxyguanosine was observed upon incubation of the cells with the chemical generator of (1)O(2), whereas the level of the other DNA bases measured remained unchanged. To demonstrate that singlet oxygen is directly involved in the formation of 8-oxo-7, 8-dihydro-2'-deoxyguanosine, the corresponding (18)O-labeled endoperoxide was used. Incubation of the cells with such a generator of (18)O-labeled singlet oxygen results in the formation of (18)O-labeled 8-oxo-7,8-dihydro-2'-deoxyguanosine in the nuclear DNA. This result clearly demonstrates that singlet oxygen, when released within cells, is able to directly oxidize cellular DNA.

Protective effect of lycopene on lipid peroxidation and oxidative DNA damage in cell culture

A high incidence of cancer has been correlated with chronic iron overload, and carotenoids are of interest as possible anticarcinogens. We have investigated the effect of lycopene on lipid peroxidation and on the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) in CV1-P monkey cells exposed to ferric nitrilotriacetate (Fe-NTA) plus ascorbate. Cells supplemented with lycopene (20 pmol/10(6) cells) showed a reduction of 86% in Fe-NTA/ascorbate-induced lipid peroxidation (TBARS). Levels of 8-oxodGuo rose from 1.59+/-0.09 residues/10(6) dGuo in the control cells to 14.02+/-0.41 residues/10(6) dGuo after incubation with (1:4 mM) Fe-NTA/ascorbate (40 microM). Lycopene supplementation decreased in 77% the 8-oxodGuo levels in Fe-NTA/ascorbate-treated cells. These results indicate that lycopene can protect mammalian cells against membrane and DNA damage and possibly play a protective role against tumor promotion associated with oxidative damage.

trans,trans-2,4-decadienal-induced 1,N(2)-etheno-2'-deoxyguanosine adduct formation

A number of ring-extended DNA adducts resulting from the reaction of alpha,beta-unsaturated aldehydes, or their epoxides, with DNA bases have been characterized in recent years. These adducts may lead to miscoding during DNA replication, resulting, if not repaired, in mutations that can contribute to cancer development. trans,trans-2, 4-Decadienal (DDE) is one of the highly cytotoxic aldehydes endogenously formed from lipid peroxidation. To evaluate its DNA damaging potential, we have investigated the reaction of DDE with 2'-deoxyguanosine (dGuo) in the presence of peroxides. Three stable adducts were isolated by reverse-phase HPLC. Adduct A1, 3-(2-deoxy-beta-D-erythro-pentafuranosyl)-5,9-dihydro-9H-imidazo[2 , 1-i]purin-9-hydroxy, is a tautomer of 1, N(2)-etheno-2'-deoxyguanosine, a well-known reaction product of epoxy aldehydes with dGuo. Two new diasteroisomeric products, A2-1 and A2-2, 1-¿[3-(2'-deoxy-beta-D-erythro-pentafuranosyl)-5, 9-dihydro-9H-imidazo[2,1-i]purin-9-hydroxy]-7-yl¿-2-one-3-octanol, were isolated and characterized on the basis of their spectroscopic features as 1,N(2)-etheno adducts possessing a carbon side chain with a carbonyl and a hydroxyl group. The proposed reaction mechanism for the formation of adducts A2 involves DDE double epoxidation and hydrolysis of the C4 epoxy group prior to nucleophilic addition of the exocyclic amino group of dGuo to C1 of the aldehyde, followed by cyclization via nucleophilic attack on the C2 epoxy group by N-1 and elimination of H(2)O. After treatment of calf thymus DNA with DDE, formation of adducts A1 and A2 was detected by the LC/ESI/MS-MS technique. These results can contribute to a better understanding of the chemical structures of adducts resulting from the reaction of aldehydes with nucleic acid bases, a necessary step in assessing the genotoxic risks associated with this class of compounds.

Novel 1,N(6)-etheno-2'-deoxyadenosine adducts from lipid peroxidation products

trans,trans-2,4-Decadienal (DDE) is a widespread alpha, beta-unsaturated aldehyde found, for example, in food, water, and environmental pollutants. DDE is also endogenously generated as a breakdown product of lipid peroxidation in cell membranes. In the work presented here, the reaction of DDE with 2'-deoxyadenosine (dAdo) was investigated in an effort to assess its possible DNA damage potential. Besides 1,N(6)-etheno-2'-deoxyadenosine and two products, namely, 1-[3-(2-deoxy-beta-D-erythro-pentofuranosyl)-3H-imidazo[2, 1-i]purin-7-yl]-1,2,3-octanetriol (adduct I) and 1-[3-(2-deoxy-beta-D-erythro-pentofuranosyl)-3H-imidazo[2, 1-i]purin-7-yl]-1,2-heptanediol (adduct II), previously described by our group, two novel etheno adducts were identified. Thus, 1-[3-(2-deoxy-beta-D-erythro-pentofuranosyl)-3H-imidazo[2, 1-i]purin-7-yl]-1-hexanol (adduct III) and 1-[3-(2-deoxy-beta-D-erythro-pentofuranosyl)-3H-imidazo[2, 1-i]purin-7-yl]-2,3-epoxy-1-octanol (adduct IV) were isolated by reverse-phase high-performance liquid chromatography and characterized on the basis of extensive spectroscopic measurements. The formation of the adducts is likely to involve initial DDE oxidation followed by generation of reactive intermediates such as diepoxides, epoxides, and/or hydroperoxides. The subsequent reaction of the latter oxidation products with dAdo will give rise to the four described adducts. We also demonstrated here that upon oxidation, DDE reacts with calf thymus DNA, producing the four dAdo adducts. Interestingly, two of them are the expected products arising from the reaction of dAdo with 4-hydroxy-trans-2-nonenal (HNE) and trans-2-octenal, two other important breakdown lipid peroxidation products. The reactivity of DDE with DNA is lower than that of the latter aldehydes. However, DDE produced a wider variety of adducts. The characterization of the different DNA-etheno adducts and the determination of the mechanism of formation are of great importance for a better understanding of the deleterious biological effects associated with this class of compounds.

Zinc tetraruthenated porphyrin binding and photoinduced oxidation of calf-thymus DNA

The photooxidation of calf-thymus DNA has been investigated in the presence of a supramolecular tetraruthenated zincporphyrin (ZnTRP) sensitizer. A strong interaction of ZnTRP with DNA has been observed, exhibiting a gradual transition from a non-specific electrostatic binding mode to a more specific one at high DNA concentrations. Formation of O2(1delta(g)) has been detected from its near-infrared emission, after the excitation of ZnTRP in dioxygen-containing solutions. In the presence of DNA and dioxygen, ZnTRP promotes efficient photocatalytic oxidation of the 2'-deoxyguanosine sites, via their direct reaction with O2(1delta(g)), as in a previous work on the ZnTRP-photoinduced oxidation of the free nucleosides.

Purine DNA adducts of 4,5-dioxovaleric acid and 2,4-decadienal

The present overview describes recent findings on the formation of cyclic adducts of purine DNA bases after reaction with two aldehyde compounds, 4,5-dioxovaleric acid (DOVA) and 2,4-decadlenal (DDE), which are involved in 5-aminolaevulinic acid (ALA) accumulation and lipid peroxidation, respectively. ALA accumulates under pathological conditions and is associated with an increased incidence of liver cancer. The final oxidation product of ALA, DOVA, is an efficient alkylating agent of the guanine moieties in both nucleoside and isolated DNA. Adducts were produced through the formation of a Schiff base involving the N2-amino group of 2'-deoxyguanosine and the ketone function of DOVA, respectively. DDE is an important breakdown product of lipid peroxidation. It is cytotoxic to mammalian cells and is known to be implicated in DNA damage. It can bind to 2'-deoxyadenosine, yielding highly fluorescent products, including 1,N6-etheno-2'-deoxyadenosine and two other, related adducts. The reaction mechanism for the formation of DDE-2'-deoxyadenosine adducts involves epoxidation of DDE and subsequent addition of the resulting reactive intermediates to the N6 amino group of 2'-deoxyadenosine, followed by cyclization at the N1 site. Formation of endogenous DNA adducts may contribute to the genotoxic potential of ALA and DDE.

DNA damage by 5-aminolevulinic and 4,5-dioxovaleric acids in the presence of ferritin

Cellular accumulation of 5-aminolevulinic acid (ALA), the first specific intermediate of heme biosynthesis, is correlated in liver biopsy samples of acute intermittent porphyria affected patients with an increase in the occurrence of hepatic cancers and the formation of ferritin deposits in hepatocytes. 5-Aminolevulinic acid is able to undergo enolization and to be subsequently oxidized in a reaction catalyzed by iron complexes yielding 4,5-dioxovaleric acid (DOVA). The released superoxide radical (O(*-)(2)) is involved in the formation of reactive hydroxyl radical ((*)OH) or related species arising from a Fenton-type reaction mediated by Fe(II) and Cu(I). This leads to DNA oxidation. The metal catalyzed oxidation of ALA may be exalted by the O(*-)(2) and enoyl radical-mediated release of Fe(II) ions from ferritin. We report here the potentiating effect of ferritin on the ALA-mediated cleavage of plasmid DNA and the enhancement of the formation of 8-oxo-7, 8-dihydro-2'-deoxyguanosine (8-oxodGuo). Plasmid pBR322 was incubated with ALA and varying amounts of purified ferritin. DNA damage was assessed by gel electrophoresis analysis of the open and the linear forms of the plasmid from the native supercoiled structure. Addition of either the DNA compacting polyamine spermidine or the metal chelator ethylenediaminetetraacetic acid (EDTA) inhibited the damage. It was also shown that ALA in the presence of ferritin is able to increase the oxidation of the guanine moiety of monomeric 2'-deoxyguanosine (dGuo) and calf thymus DNA (CTDNA) to form 8-oxodGuo as inferred from high performance liquid chromatography (HPLC) measurements using electrochemical detection. The formation of the adduct dGuo-DOVA was detected in CTDNA upon incubation with ALA and ferritin. In a subsequent investigation, the aldehyde DOVA was also able to induces strand breaks in pBR322 DNA.

Lycopene entrapped in human albumin protects 2'-deoxyguanosine against singlet oxygen damage

The generation of electronically excited molecular oxygen 1O2 has been shown to occur in several biological systems, such as photooxidation of a variety of biological compounds and xenobiotics ("photodynamic action") and also enzymatic reactions. The high reactivity of 1O2 with unsaturated compounds, sulfides and amino groups arises from its electrophilicity and relatively long lifetime. Thus, biological targets for 1O2 having the above functional groups include unsaturated fatty acids, proteins, enzymes and DNA. There is interest in the role of nutrition in the prevention and pathogenesis of cancer. Epidemiological studies in humans have suggested that carotenoids aid in cancer prevention. Lycopene and oxycarotenoids are present at significant levels in cells and plasma. Extensively conjugated biomolecules such as carotenoids act largely on physical quenching of 1O2 and in much lesser extent on chemical reaction. In this study we observed the protective effect of beta-carotene and lycopene entrapped in human albumin (HSA) against the oxidative 1O2 attack of 2'-deoxyguanosine (dGuo). Photosensitization with methylene blue associated with Chelex resine or Polymer-Rose bengal (Sensitox) and thermodecomposition of water-soluble endoperoxide 3,3'-(1,4-naphthylidene)dipropionate were employed to generate 1O2. The detection of 8-oxo-7,8-dihydro-2'-deoxyguanosine(8-oxodGuo) and 4-hydroxy-8-oxo-7,8-dihydro-2'-deoxyguanosine(4-OH-8-oxodGuo) were performed using reversed phase HPLC with UV, electrochemical detection and by electrospray ionization mass spectrometry. Results showed a significant decrease in the amount of 8-oxodGuo in the presence of lycopene. The percentages of 4-OH-8-oxodGuo and 8-oxodGuo measured were 50% and 70% lower than the control, respectively. These data indicate that carotenoids entrapped in albumin can be an efficient quencher of 1O2 and may be of interest in protecting against the deleterious effect of this excited state molecule.

Measurement of 4,5-dioxovaleric acid by high-performance liquid chromatography and fluorescence detection

In this work we describe a sensitive method for the detection of 4,5-dioxovaleric acid (DOVA). 4,5-Dioxovaleric acid is derivatized with 2,3-diaminonaphthalene to form 3-(benzoquinoxalinyl-2)propionic acid (BZQ), a product with favorable UV absorbance and fluorescence properties. The high-performance liquid chromatographic method with UV absorbance and fluorescence detection is simple and its detection limit is approximately 100 fmol. This method was used to detect 4,5-dioxovaleric acid formation during metal-catalyzed 5-aminolevulinic acid (ALA) oxidation. Iron and ferritin were active in the formation of 4,5-dioxovaleric acid in the presence of 5-aminolevulinic acid. In addition, HPLC-MS-MS assay was used to characterize BZQ. The determination of 4,5-dioxovaleric acid is of great interest for the study of the mechanism of the metal-catalyzed damage of biomolecules by 5-aminolevulinic acid. This reaction may play a role in carcinogenesis after lead intoxication. The high frequency of liver cancer in acute intermittent porphyria patients may also be due to this reaction.

Supramolecular cationic tetraruthenated porphyrin and light-induced decomposition of 2'-deoxyguanosine predominantly via a singlet oxygen-mediated mechanism

The tetraruthenated porphyrin, mu-[meso-5,10,15,20-tetra(pyridyl)porphyrin]tetrakis[bis-(bipyridine) chloride ruthenium(II)] (TRP) is a supramolecular cationic species. The aim of the present investigation was to evaluate the photodynamic properties of TRP and Zn-TRP to damage DNA with emphasis on the mechanistic aspects. The ability for tetraruthenated porphyrin derivatives to induce photosensitization reactions has been determined using 2'-deoxyguanosine as a DNA model compound. The main photooxidation products of the targeted nucleoside were identified and classified according to their mechanisms of formation, involving either a radical pathway (type I) or a singlet oxygen-mediated mechanism (type II). Quantification of the different oxidation products provides a means to evaluate the relative contribution of type I and type II pathways associated with the oxidative photosensitization of 2'-deoxyguanosine by tetraruthenated porphyrin derivatives. Results indicate that 1O2 plays a major role in the mechanism of photooxidation mediated by these porphyrin derivatives. In addition an increase of the photosensitizing effect in the presence of zinc is observed. For each sensitizer, the ratio between type II and type I photoproducts has been calculated and compared to that of other known dyes such as methylene blue and riboflavin.

Formation of 1,N6-etheno-2'-deoxyadenosine adducts by trans,trans-2, 4-Decadienal

trans,trans-2,4-Decadienal (DDE) is an important breakdown product of lipid peroxidation. This aldehyde is cytotoxic to mammalian cells and is known to be implicated in DNA damage. Therefore, attempts were made in this work to assess the reactivity of DDE with 2'-deoxyadenosine (dAdo). It was shown that DDE is able to bind to 2'-deoxyadenosine, yielding highly fluorescent products. Besides 1, N6-etheno-2'-deoxyadenosine (epsilondAdo), two other related adducts, 1-[3-(2-deoxy-beta-D-erythro-pentofuranosyl)-3H-imidazo[2, 1-i]purin-7-yl]-1,2,3-octanetriol and 1-[3-(2-deoxy-beta-D-erythro-pentofuranosyl)-3H-imidazo[2, 1-i]purin-7-yl]-1,2-heptanediol, were isolated by reverse phase high-performance liquid chromatography and characterized on the basis of their UV, fluorescence, nuclear magnetic resonance, and mass spectrometry features. The reaction mechanism for the formation of the DDE-2'-deoxyadenosine adducts involves 2,4-decadienal epoxidation and subsequent addition to the N2 amino group of 2'-deoxyadenosine, followed by cyclization at the N-1 site. Adducts differ by the length of carbon side chain and the number of hydroxyl groups. The present data indicate that DDE can be epoxidized by peroxides, and the resulting products are able to form several adducts with 2'-deoxyadenosine and/or DNA. Endogenous DNA adduct formation can contribute to the already reported high cytotoxicity of DDE to mammalian cells.

Hydroxyl radicals are involved in the oxidation of isolated and cellular DNA bases by 5-aminolevulinic acid

5-Aminolevulinic acid (ALA) is a heme precursor, pathological accumulation of which is associated with liver cancer. We show that the reactive oxygen species produced upon ALA metal-catalyzed oxidation promote the formation of several radical-induced base degradation products in isolated DNA. The distribution of modified bases is similar to that obtained upon gamma irradiation. This observation strongly suggests the involvement of hydroxyl radicals in the ALA-mediated DNA damage. Increased levels of 8-oxo-7,8-dihydro-2'-deoxyguanosine and 5-hydroxy-2'-deoxycytidine in organ DNA of rats chronically treated with ALA were observed. This is strongly suggestive of the implication of hydroxyl radicals in the ALA-induced degradation of cellular DNA.

DNA alkylation by 4,5-dioxovaleric acid, the final oxidation product of 5-aminolevulinic acid

The heme precursor 5-aminolevulinic acid (ALA) accumulates under pathological conditions, namely, acute intermittent porphyria (AIP) and tyrosinosis, two diseases that are associated with increased liver cancer incidence. This has been previously linked to an enhanced production of reactive oxygen species generated by a metal-catalyzed ALA oxidation process, which was shown to cause DNA single-strand breaks and guanine oxidation within both isolated and cellular DNA. In the present work, we established that the final oxidation product of ALA, 4,5-dioxovaleric acid (DOVA), is an efficient alkylating agent of the guanine moieties within both nucleoside and isolated DNA. Adducts were produced through the formation of a Schiff base involving the N2-amino group of 2'-deoxyguanosine (dGuo) and the ketone function of DOVA, respectively. The modified dGuo nucleosides were characterized, following reduction into stable secondary amines, by extensive NMR, infrared, and mass spectrometry analyses. A method, based on the use of HPLC with electrochemical detection, was then developed for the sensitive measurement of the DOVA-dGuo adducts. Using this assay, we showed that the guanine moieties of isolated DNA can undergo the same reaction as the free nucleoside. The present data provide additional information on the genotoxic potential of ALA and reinforce the hypothesis that AIP may be involved in the induction of primary liver cell carcinoma.

The reaction of peroxynitrite with tert-butyl hydroperoxide produces singlet molecular oxygen

Peroxynitrite, a biological oxidant, can induce lipid peroxidation in biological membranes which leads to the formation of various hydroperoxides. Here, we report the formation of singlet oxygen (1O2) in the reaction of peroxynitrite with tert-butyl hydroperoxide (t-BOOH) used as a model compound for organic hydroperoxides. The formation of singlet oxygen was observed by (i) dimol emission in the red spectral region, (ii) monomol emission in the infrared region at 1270 nm and by (iii) chemical trapping of singlet oxygen with anthracene-9,10-diyldiethyl disulfate (EAS). The emission signal was increased when H2O was replaced by deuterium oxide and was quenched by sodium azide. When singlet oxygen was generated in the reaction of peroxynitrite with t-BOOH, the 1O2 quenching rate constant for sodium azide was estimated from a Stern-Volmer plot as 1.3 x 10(8) M(-1) S(-1) which is in line with known values. The 1O2 generation in the peroxynitrite/t-BOOH reaction was also detected by the formation of the endoperoxide of EAS. These data establish the generation of 1O2 in the reaction of peroxynitrite with t-BOOH and suggest a potential involvement of 1O2 in peroxynitrite-mediated reactions in biological systems.

Horseradish peroxidase-catalyzed conjugation of eugenol with basic amino acids

L-Lysine is shown to yield an adduct with the quinone methide intermediate formed during the horseradish peroxidase (HRP)-catalyzed aerobic oxidation of eugenol (4-allyl-2-methoxyphenol). Adduct formation is evidenced by (i) lysine quenching of the characteristic quinone methide absorption band measured at 350 nm; arginine and gamma-aminobutyric acid, but not alanine or propionic acid showed similar behaviour (ii) lysine-promoted a 400 mV decrease of the eugenol oxidation voltammetric wave (1.00 V), concomitantly with an increase in current intensity and (iii) reverse phase HPLC isolation of the lysine eugenol adduct, followed by GC-MS analysis. The MS spectrum is consistent with a 2:1 lysine:eugenol adduct (MW = 455). If operative in vivo, binding of lysine to eugenol might lead to protein inactivation and possibly be involved in eugenol toxicity.

Supramolecular cationic tetraruthenated porphyrin induces single-strand breaks and 8-oxo-7,8-dihydro-2'-deoxyguanosine formation in DNA in the presence of light

The aim of this investigation is the evaluation of DNA interaction of with tetraruthenated porphyrin (TRP) and of DNA damage in the presence of light. Direct-fluorescence and electronic absorption measurements after incubation of DNA with TRP indicate strong binding between pBR322 DNA or calf thymus DNA with the modified porphyrin. Exposure of pBR322 DNA to TRP (up to 3 microM) and light leads to single-strand break formation as determined by the conversion of the supercoiled form (form I) of the plasmid into the nicked circular form (form II). Oxidative DNA base damage was evaluated by the detection of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) after irradiation of calf thymus DNA in the presence of the TRP. The data demonstrated a dose and time dependence with each type of DNA damage. These data indicate (1) a specificity of the binding mode and (2) type I and II photoinduced mechanisms leading to strand scission activity and 8-oxodGuo formation. Accordingly, singlet molecular oxygen formation, after TRP excitation, was confirmed by near-infrared emission. From these investigations a potential application of TRP in photodynamic therapy is proposed.

Singlet molecular oxygen production in the reaction of peroxynitrite with hydrogen peroxide

Peroxynitrite and hydrogen peroxide are mediators of cytotoxicity. This study shows that the peroxynitrite anion reacts with hydrogen peroxide to release oxygen accompanied by emission of chemiluminescence (CL). Direct characterization of this light emission attributes it to the transition of singlet molecular oxygen to the triplet ground state. Chemiluminescence was monitored: (i) by dimol light emission in the red spectral region (> 610 nm) using a red-sensitive photomultiplier; and (ii) by monomol light emission in the infrared (1270 nm) with a liquid nitrogen-cooled germanium diode. These properties of photoemission and the enhancing effect of deuterium oxide on CL intensity as well as the quenching effect of sodium azide are diagnostic of molecular oxygen in the excited singlet state. For comparison, singlet molecular oxygen arising from the thermolysis of the water-soluble endoperoxide of 3,3'-(1,4-naphthylidene)dipropionate or from the hypochlorite/H2O2 system was also monitored. These novel observations identify a potential singlet oxygen-dependent mechanism contributing to cytotoxicity mediated by peroxynitrite and hydrogen peroxide.

Superoxide dismutase, catalase, and glutathione peroxidase activities in muscle and lymphoid organs of sedentary and exercise-trained rats

The effect of swimming-training upon the activities of the enzymes involved in the generation of reducing-equivalents (citrate synthase-mitochondria and glucose-6-phosphate dehydrogenase-cytosol) and of antioxidant enzymes (CuZn- and Mn-SOD, catalase and glutathione peroxidase) in the lymphoid organs (thymus, mesenteric lymph nodes and spleen) was examined. The skeletal muscles (soleus-red and gastrocnemius-white) were also studied. Although our data suggest an apparently random, organ-specific change in enzymatic activity, some interesting trends can be observed. Firstly, the increased citrate synthase and Mn-SOD activities observed in red, but not in white muscle, corroborate the well-known effect of endurance exercise-training on mitochondrial oxidative metabolism. Secondly, there was an inverse relationship between TBARs-monitored lipoperoxidation and glutathione peroxidase activity in all tissues studied, what is in accordance with the previous findings showing that such enzyme exerts the fine control of intracellular lipoperoxide concentration. Except in the case of the spleen, there was a trend for elevated glucose-6-phosphate dehydrogenase activity, coadjuvant of glutathione peroxidase in the antioxidant response to physical exercise in all tissues. Thirdly, Mn-SOD and catalase were conspicuously associated to oxidative stress in the thymus, while glutathione and catalase could be linked to this parameter in the spleen. Fourthly, the lymph nodes seem to be more dependent on the glucose-6-phosphate dehydrogenase/glutathione peroxidase pair for protection against damage promoted by physical exercise. Mn-SOD and catalase activities were lower in the lymph nodes after swimming training.(ABSTRACT TRUNCATED AT 250 WORDS)

Catabolism of 5-aminolevulinic acid to CO2 by rat liver mitochondria

5-Aminolevulinic acid (ALA), the heme precursor accumulated in plasma and several organs of carriers of acute intermittent porphyria, hereditary tyrosinemia, and saturnism, was previously shown to yield reactive oxygen species upon metal-catalyzed aerobic oxidation and to cause the in vivo and in vitro impairment of rat liver mitochondrial functions. We have studied the uptake and catabolism of [5-14C]ALA to CO2 by isolated rat liver mitochondria (RLM) with the aim of determining whether possible ALA-driven oxidative injury to mitochondria can also occur into the matrix. Using silicone oil centrifugation of [5-14C]ALA-treated RLM, ALA was found to partition evenly into the intra- and extramatrix space of the mitochondrial preparations. The yield of evolved 14CO2 is very low (0.2%), responds to the concentration of added ADP, and is inhibited by malonate (75% at 2 mM), iproniazid (45% at 2 mM), beta-chloroalanine (36% at 1 mM), and aminooxyacetate (55% at 0.1 mM). With both iproniazid and aminooxyacetate, the percentage of inhibition is the same as that observed with the latter inhibitor alone. These data indicate that ALA decarboxylation by the Krebs cycle is a minor process and that it is initiated enzymically (transaminase) and not by metal-catalyzed ALA autoxidation.

5-Aminolevulinic acid induces single-strand breaks in plasmid pBR322 DNA in the presence of Fe2+ ions

5-Aminolevulinic acid (ALA), a heme precursor accumulated in chemical and inborn porphyrias, has been demonstrated to produce reactive oxygen species upon metal-catalyzed aerobic oxidation and to cause oxidative damage to proteins, liposomes and subcellular structures. Exposure of plasmid pBR322 DNA to ALA (0.01-3 mM) in the presence of 10 microM Fe2+ ions causes DNA single-strand breaks (ssb), revealed by agarose gel electrophoresis as an increase in the proportion of the open circular form (75 +/- 7.5% at 3 mM ALA) at the expense of the supercoiled form. Addition of either anti-oxidant enzymes such as superoxide dismutase (10 micrograms/ml) and catalase (20 micrograms/ml), or a metal chelator (DTPA, 2.5 mM), or a HO. scavenger (mannitol, 100 mM) inhibited the damage (by 30, 45, 55, and 81%, respectively), evidencing the involvement of O2-., H2O2 and HO. (by the Haber-Weiss reaction) in this process. Hydrogen peroxide (100 microM) or Fe2+ (10 microM) alone were of little effect on the extent of DNA ssb. The present data may shed light on the correlation reported between primary liver-cell carcinoma and intermittent acute porphyria.

Spermine and spermidine protection of plasmid DNA against single-strand breaks induced by singlet oxygen

Oxidative damage to DNA induced by singlet molecular oxygen (1O2*) includes single-strand breaks, which the biologically occurring 1O2* quenchers spermine and spermidine are shown to prevent. These polyamines at a physiological concentration (10 mM) reduce the percentage of the open circular form of pBR322 plasmid DNA, which is generated at the expense of the native supercoiled form when the plasmids are incubated with a chemical source of 1O2*, the water-soluble endoperoxide of 3,3'-(1,4-naphthylidene)dipropionate. Spermine and spermidine can be expected to protect DNA against other damaging effects of 1O2*.

Chemiluminescent oxidation of ribose catalyzed by horseradish peroxidase in presence of hydrogen peroxide

The reaction of ribose with horseradish peroxidase in the presence of H2O2 is accompanied by light emission. The detection of horseradish peroxidase Compound II (FeO2+) indicates that the enzyme participates in a normal peroxidatic cycle. Hydrogen peroxide converts horseradish peroxidase into Compound 1 (FeO2+) which in turn is converted into Compound II by abstracting a hydrogen atom from ribose forming a ribosyl radical. In aerated solutions oxygen rapidly adds to the ribosyl radical. Based on the spectral characteristics and the enhancement of the chemiluminescence by chlorophyll-a, xanthene dyes, D2O and DABCO, it is suggested that the excited species, apparently triplet carbonyls and 1O2, are formed from the biomolecular decay of the peroxyl radicals via the Russell mechanism.

Generation of excited species catalyzed by horseradish peroxidase or hemin in the presence of reduced glutathione and H2O2

Horseradish peroxidase (HRP) (EC 1.11.1.7) catalyzes the oxidation of reduced glutathione. This reaction is accompanied by light emission, which is attributed to the generation of singlet oxygen. The chemiluminescence is directly related to thiyl radical formation, as deduced from the correlation between the time course of HRP-compound II formation and light emission in the presence of different amounts of H2O2. Superoxide dismutase has an inhibitory effect on the chemiluminescence without affecting the HRP-compound II formation. This indicates the direct involvement of superoxide radicals in the production of photoemissive species. Replacement of HRP by hemin is also accompanied by chemiluminescence.

Oxygen toxicity and hemoglobinemia in subjects from a highly polluted town

Red blood cell activities of superoxide dismutase and glutathione peroxidase, two key enzymes responsible for the control of the concentrations of activated oxygen species, were approximately two-fold higher in residents of Vila Parisi (Cubatão, Brazil)--a higher polluted neighborhood--than in a population sample from São Paulo City. The catalase levels were the same in both samples. A concurrent high concentration of methemoglobinemia and sulfhemoglobinemia was encountered in the blood of Vila Parisi residents. These data raise the possibility that the increased rate of oxyhemoglobin oxidation yielding O-.2 and H2O2 may be relevant to mutagenesis induced by HO. radicals.