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PubMed2006

Singlet oxygen quenching by thione analogues of canthaxanthin, echinenone and rhodoxanthin.

Thione analogues of three naturally occurring carotenones (canthaxanthin, echinenone, and rhodoxanthin) were synthesized just over ten years ago, and it was reported that substitution of the oxygen atom by sulphur brings about a large red shift and some broadening in the optical absorption spectrum of the compound. Since the three carotenothiones are scarce, determination of their molar absorption coefficients presents a challenge. A method for relating the molar absorption coefficient of a carotenothione (Car-S) to that of its ketone analogue (Car-O) has been developed, which has revealed that the peak molar absorption coefficient of a Car-S is only about 60% of the corresponding value for Car-O. Using methylene blue as the sensitizer and acetonitrile as the solvent, we have also investigated the quenching (under photostationary conditions) of the 1270nm phosphorescence emission of singlet oxygen by each of the six carotenoids. The data conform to the Stern-Volmer relation, and show that substitution of a carbonyl oxygen atom by sulphur does not lead to an appreciable change in the value of the quenching constant, which is close to 1.5 x 10(10)M(-1)s(-1) for all six quenchers.

Canthaxanthin↗
PubMed2005

The effect of porphyrin supramolecular structure on singlet oxygen photogeneration.

This work is to show that activity of porphyrins in singlet oxygen generation (SOG) is determined not only by their molecular structure but also by supramolecular structure of porphyrin containing systems. This is demonstrated by results of studies of SOG in the gas phase by vacuum deposited tetraphenylporphyrin (TPP) layers under photoexcitation conditions. The structure of the layers was studied by atomic force microscopy (AFM), TEM in diffraction regime (TED) and by the flicker-noise spectroscopy (FNS) method. It was shown that substrates affect the deposited layers structure only at earlier stages of the layer formation. AFM and TED data, together with FNS quantitative parameters of TPP layers, show directly that the chemical activity of solid-phase systems can be determined not only by their chemical nature but also by their supramolecular structure.

Microscopy, Atomic Force↗
PubMedDate not supplied

Singlet oxygen energy illumination during moderate cold ischemia prolongs the survival of concordant hamster xeno-heart transplants.

INTRODUCTION: Singlet oxygen energy (SOE) is a potent inhibitor of reactive oxygen species (ROS) in vitro and in vivo in certain dose ranges and can improve the levels of high-energy phosphates (HEP) in concordant hamster xeno-heart transplants. Some data indicate that a certain degree of cold ischemia (CI) might be beneficial to xenotransplants. We investigated if SOE illumination of hamster xeno-hearts during moderate cold ischemia (CI) improved graft survival. MATERIALS AND METHODS: Eighteen hearts from Golden Syrian hamsters (70 to 80 g) were subjected to 8 hours of CI in cold (+4 degrees C) saline solution (NaCL, 0.9%) before heterotopic cervical transplantation to Lewis rats (220 g). Among the treatment group (n = 8), SOE was produced by illuminating the hearts for 10 minutes every 30 minutes with photons at lambda 634 nm with the Oxylight equipment. Graft function was evaluated every 6 hours after transplantation with digital exam until cessation of heart beats. RESULTS: The graft survival of SOE-illuminated ischemic hamster xenografts was 2.34 +/- 0.56 versus 1.15 +/- 0.37 days in the control group (P < .05). All hearts displayed immediate graft function versus 70% in the controls (NS). CONCLUSIONS: SOE illumination at lambda 634 nm during moderate cold ischemia (+4 degrees C) can improve the survival of concordant hamster xeno-heart transplants. The exact mechanism(s) are currently unknown, but the effect might in part be exerted by a combination of reduced production of ROS and increased oxidative phosphorylation.

Animals↗
PubMed2002

Curcumin (diferuloylmethane), a singlet oxygen ((1)O(2)) quencher.

Curcumin (diferuloylmethane) is a major component of food flavoring turmeric (Curcuma longa), and has been reported to be anticarcinogenic and anti-inflammatory. Although curcumin was shown to have antioxidant properties, its exact antioxidant nature has not been fully investigated. In this report we have investigated the possible antioxidant properties of curcumin using EPR spectroscopic techniques. Curcumin was found to inhibit the (1)O(2)-dependent 2,2,6,6-tetramethylpiperidine N-oxyl (TEMPO) formation in a dose-dependent manner. (1)O(2) was produced in a photosensitizing system using rose bengal as sensitizer, and was detected as TEMP-(1)O(2) adducts by electron paramagnetic resonance (EPR) spectroscopic techniques using TEMP as a spin-trap. Curcumin at 2.75 microM caused 50% inhibition of TEMP-(1)O(2) adduct formation. However, curcumin only marginally inhibited (24% maximum at 80 microM) reduction of ferricytochrome c in a xanthine-xanthine oxidase system demonstrating that it is not an effective superoxide radical scavenger. Additionally, there was minor inhibition of DMPO-OH adduct formation by curcumin (solubilized in ethanol) when an ethanol control was included in the EPR spin-trapping study, suggesting that curcumin may not be an effective hydroxyl radical scavenger. Together these data demonstrate that curcumin is able only to effectively quench singlet oxygen at very low concentration in aqueous systems.

Antioxidants↗
PubMed1998

Inactivation of bacterial respiratory chain enzymes by singlet oxygen.

To distinguish the bactericidal action of singlet oxygen (1O2) from hypohalous acids, wild-type and lycopene transformant E. coli strains were exposed to each of the oxidants and then bacterial viability was investigated. 1O2 was generated by chemical and enzymatic systems at pH 4.5. ExpoSure of wild-type E. coli to 1O2 caused a significant loss of E. coli viability due to inactivation of membrane respiratory chain enzymes by 1O2. This action of 1O2 could be attenuated by lycopene in the bacterial cell membrane. In the lycopene transformant strain of E. coli, inactivation of NADH oxidase and succinate oxidase by hypohalous acids were significantly suppressed, but E. coli viability was unaffected. Based on these findings, we suggest that phagocytic leukocytes produce 1O2 as a major bactericidal oxidant in the phagosome.

Bromides↗
PubMed1999

Production of singlet oxygen by eosinophils activated in vitro by C5a and leukotriene B4.

Using the trans-methoxyvinylpyrene analogues of benzo[a]pyrene-7,8-dihydrodiol (MVP) as a singlet oxygen ((1)O2) chemiluminescence probe, we have demonstrated that guinea pig eosinophils release (1)O2 when activated with the physiological agonists C5a and leukotriene B4. This release, which occurs at agonist concentrations as low as 10(-7) M, occurs more rapidly than activation with phorbol ester (10(-6) M), is similar in level, but is more transitory. In addition, the release of (1)O2 occurs in the absence of added bromide ions and represents, we propose, an important feature of eosinophil-mediated inflammatory damage.

Acridines↗
PubMed2000

Singlet oxygen ((1)O2) inactivates plasmatic free and complexed alpha2-macroglobulin.

alpha2-macroglobulin (alpha2M) is a broad-spectrum proteinase inhibitor and one of the major plasma proteins in humans. Activated phagocytes (especially granulocytes) generate large amounts of oxidants of the HOCI- and chloramine-type that release the mild nonradical, excited (light-emitting) oxidant singlet oxygen ((1)O2). These oxidants have been shown to inactivate several specific serine protease inhibitors in human blood [e.g., alpha1-antitrypsin or alpha2-antiplasmin (plasmin inhibitor)]. The studies reported here demonstrate that nonradical oxidants also inactivate plasmatic alpha2M. The effective dose for 50% inactivation (ED50) of plasmatic alpha2M is similar to that for plasmatic alpha2-antiplasmin. Chloramines are about 1,000-fold more effective than hydrogen peroxide (ED50)=0.75 micromol chloramine T/50 microl plasma). Serine protease-serine protease inhibitor complexes are resistant to oxidants. In contrast, here it is shown that alpha2-macroglobulin, even after binding to serine proteases is sensitive to oxidation, the captured protease is released from the protease/alpha2M complex. This is the first time that oxidative inactivation of a complexed (i.e., bound to a target protease) human protease inhibitor has be shown. The (1)O2 inhibitors methionine, cysteine, cystine, or ascorbate-in contrast to the oxy-radical scavengers mannitol, superoxide dismutase, or catalase-antagonize the chloramine/NaOCl-mediated inactivation of both uncomplexed and complexed alpha2M. Thus, the oxidant involved here is of nonradicalic nature and has reaction characteristics of (1)O2. For the inhibitory function, critical oxidizable methionines or the internal thiol-ester might be targets for (1)O2. Consequently, alpha2M can also be considered a carrier for proteases, since the alpha2M-complexed proteases regain full activity in an oxidative environment. In local areas of inflammation or thrombolysis, activated phagocytes could create microenvironments of uncontrolled protease activity by generation of (1)O2.

Chloramines↗
PubMed2001

Singlet oxygen (1O(2)) disrupts platelet aggregates.

INTRODUCTION: Important mediators of activated polymorphonuclear leukocytes (PMN) are the oxidants HOCl and chloramine, which generate the nonradical photon-emitting oxidant singlet oxygen (1O(2)). Since 1O(2) inhibits platelet aggregation, we became interested in a possible oxidant mediated reversibility of platelet aggregation. METHODS: Chloramine T (CT) is a stable 1O(2) generator that mimics the natural chloramine N-chloro-taurine. Platelet-rich plasma (PRP) was incubated with CT 0-8 min after addition of the aggregation agonist (10 microM adenosine-5'-diphosphate, ADP, or 5 microg/ml collagen) and the aggregation was monitored. Platelet function was also analyzed by the platelet function analyzer, PFA-100. Fifty microliters of 200 micromol/l ADP was added to 400 microl PRP. After 1 min at 37 degrees C, 50 microl of 0 or 30 mmol/l CT was added, and after an incubation for 3 min at 37 degrees C, 50 microl of 25% glutaraldehyde was added. The samples were analyzed in a transmission microscope at x3000 and x7000 magnification. RESULTS: Chloramines inhibit platelet function in PRP: about 1 mM CT suppresses 50% of the aggregatory capacity of thrombocytes in normal PRP (effective dose 50%, ED(50)=1 mM chloramine), which is identical to the ED(50) for CT in whole blood. The ADP- or collagen-induced platelet aggregation can be reversed by addition of CT: up to 2 min after the addition of ADP as the aggregation inducer, the aggregation is reversible to more than 70% by addition of a 1O(2) release-inducer (3 mM CT). In contrast, addition of CT 8 min after the addition of ADP results only in about 50% reversal of platelet aggregation. The electron microscopic images of platelets before ADP, after incubation for 4 min at 20 micromol/l ADP, after incubation for 1 min at 20 micromol/l ADP, and a further incubation for 3 min at 3 mmol/l CT demonstrate an ADP-dependent formation of platelet aggregates, which are disrupted by 1O(2) into the single platelets; a phenomenon comparable to the decomposition of a puzzle or the continental drift of the major earth plates. The morphology of oxidized and unoxidized platelets is similar. CONCLUSION: This study demonstrates that 1O(2) inhibits and reverses platelet aggregation. The physiologic signal action and the direct anticoagulant action of 1O(2) might be a new principle for pharmacologic intervention in atherothrombosis.

Blood Platelets↗
PubMed2000

Singlet oxygen inactivates fibrinogen, factor V, factor VIII, factor X, and platelet aggregation of human blood.

Activated polymorphonuclear leukocytes participate in hemostasis. These phagocytes generate up to 5 mmol/l of oxidants of the HOCl- and chloramine-type. The present study shows, for the first time, that physiological concentrations of NaOCl or chloramines act as anticoagulants in human plasma. Prothrombin time, activated partial thromboplastin time, and thrombin time at chloramine concentrations greater than 1 mmol/l are prolonged proportional to the oxidant concentration. Plasmatic coagulation factors sensible to oxidation are fibrinogen, factor V, factor VIII, and factor X with a 50% effective dose of 2-3 mmol/l NaOCl or taurine-chloramine. Chloramines or chloramine-like agents (e.g., chloramine T(R) or vancomycin) also inactivate platelet aggregation (in whole blood or platelet-rich plasma) at an 50% effective dose of about 1.0 mmol. This irreversible oxidation of the hemostasis components is inhibited by addition of methionine, cysteine, ascorbic acid, or azide in 10-fold molar excess prior to oxidation. The oxy-radical inhibitors mannitol, superoxide dismutase, or catalase do not antagonize the action of NaOCl or chloramines. Therefore, the oxidant here involved has reaction characteristics of singlet oxygen (1O(2)), a nonradical, excited (i.e., light-emitting) oxidant. The hemostasis factors sensible to oxidation might dispose of oxidizable, for their function critical, methionine or cysteine residues. In conclusion, blood coagulation factors I, V, VIII, X and thrombocytes are sensible to nonradical oxidants of activated phagocytes. Via 1O(2) generation, polymorphonuclear leukocytes can generate a local pericellular zone of anticoagulation. The data suggest that the cell signal 1O(2) in physiological amounts is an antithrombotic agent.

Animals↗
PubMed2003

Photochemical characterization of water samples from Minnesota and Vermont sites with malformed frogs: potential influence of photosensitization by singlet molecular oxygen (1O(2)) and free radicals on aquatic toxicity.

Environmental pollutants activated by UV sunlight may have contributed to the recent decline in frog populations and the concomitant increase in malformations in the USA and abroad. UV radiation is able to mutate DNA and to initiate photosensitization processes that generate mutagenic and biologically disruptive oxygen transients. We have examined water from selected sites in Minnesota and Vermont using singlet molecular oxygen (1O(2)), detected by its phosphorescence and free radicals detected by spin trapping, as markers for photosensitization. Water from a pond in Minnesota with malformed frogs, which also causes malformations in the laboratory, photosensitized more 1O(2), even though it absorbed less UV light compared to water from a site that did not cause malformations. This suggested that unknown natural or pollutant agents were present, and that photosensitization may be involved. Although UV irradiation of the two Minnesota water samples in the presence of the spin trap 5,5-dimethyl-1-pyrroline N-oxide (DMPO) revealed the presence of the DMPO/*OH, DMPO/*H(e(aq)-) and DMPO/*C(unknown) adducts there were no qualitative or quantitative differences between them. We also examined water samples from several sites in Vermont, and compared them by measuring the quantum yield of 1O(2) photosensitization. While all the Vermont samples produced a small amount of 1O(2), there was no clear correlation with the incidence of frog malformations. However, the samples differed strongly in absorption spectra and the ability to quench 1O(2). These factors may determine how much UV light is absorbed and converted into chemical reactions. Our results show that photochemical characterization of 1O(2) photosensitization is possible in untreated natural water samples. Photosensitization falls into the category of global factors that may be closely associated with the effects of UV irradiation of the Earth's environments. Thus, photosensitization might be an important component in global amphibian malformation and decline. The observation of 1O(2) emission directly from natural water may also provide new opportunities to investigate the involvement of 1O(2) in other complex environmental processes.

Animals↗
PubMed1998

The antibiotic ceftazidime is a singlet oxygen quencher as demonstrated by ultra-weak chemiluminescence and by inhibition of AAP consumption.

We demonstrated that the cephalosporin antibiotic ceftazidime (CAZ) deactivated singlet oxygen (1O2). We then studied the mechanisms of the CAZ effects on the ultra weak chemiluminescence (uwCL) associated with the energy decay of 1O2 generated by the Mallet reaction (H2O2 + HOCl --> HCl + H2O + 1O2), and on the anthracene-9,10-dipropionic acid (AAP) consumption by 1O2 generated by irradiation of Rose Bengal (RB). The uwCL generated by the Mallet reaction was amplified (6.2 times) by CAZ. The use of red and blue filters, which absorb radiation below 610 nm and between 470 and 700 nm respectively, demonstrated that CAZ increased the uwCL by a radiation emission at wavelengths shorter than the 633 and 704 nm wavelength emissions of 1O2. CAZ was excited by scavenging the energy excess of 1O2, which so returned to its fundamental state, while CAZ deactivated with light emission between 430-480 nm. CAZ also inhibited in a dose-dependent manner the consumption of AAP by 1O2 generated by the irradiation of RB. The protection of AAP by 5 x 10(-3) M CAZ was equivalent to that of 10(-3) M histidine and 3 X 10(-6) M sodium azide. This process of 1O2 deactivation will be useful in diseases characterized by an excessive PMN activation with a release of activated oxygen species.

Anthracenes↗
PubMed1999

Glycoconjugated hypocrellin: synthesis of [(beta-D-glucosyl)ethylthiyl]hypocrellins and photosensitized generation of singlet oxygen.

In order to improve the water solubility and specific affinity for malignant tumors of hypocrellin, glycoconjugated hypocrellins have been synthesized using an improved Königs-Knörr reaction from mercaptoethanol substituted hypocrellin B and 2,3,4,6-tetra-O-acetyl-alpha-D-glucopyranosyl bromide precursors. Deprotection of glucose moieties allows the production of derivatives which had improved solubility in neutral aqueous solution and covered a range of amphiphilic character. The structures of these new protected and unprotected compounds were characterized by UV-Vis, IR, 1H-NMR and MS data. The present strategy should prove applicable to the synthesis of other glycoconjugated perylenequinone compounds. In addition, the quantum yield of singlet oxygen generation photosensitized by these glycoconjugated hypocrellins has been determined.

Glycoconjugates↗
PubMed2003

The physiology and pharmacology of singlet oxygen.

Reactive oxygen species (ROS) are generated by many different cells. Singlet oxygen (1O(2)) and a reaction product of it, excited carbonyls (C=O*), are important ROS. 1O(2) and C=O* are nonradicalic and emit light (one photon/molecule) when returning to ground state oxygen. Especially activated polymorphonuclear neutrophil granulocytes (PMN) produce large amounts of 1O(2). Via activation of the respiratory burst (NADPH oxidase and myeloperoxidase) they synthesize hypochlorite (NaOCl) and chloramines (in particular N-chlorotaurine). Chloramines are selective and stable chemical generators of 1O(2). In the human organism, 1O(2) is both a signal and a weapon with therapeutic potency against very different pathogens, such as microbes, virus, cancer cells and thrombi. Chloramines at blood concentrations between 1 and 2 mmol/L inactivate lipid enveloped virus and chloramines at blood concentrations below 0.5 mmol/L, i.e. at oxidant concentrations that do not affect thrombocytes or hemostasis factors, act antithrombotically by activation of the physiologic PMN mediated fibrinolysis; this thrombolysis is of selective nature, i.e. it does not impair the hemostasis system of the patient allowing the antithrombotic treatment in patients where the current risky thrombolytic treatment is contraindicated. The action of 1O(2) might be compared to the signaling and destroying gunfire of soldiers directed against bandits at night, resulting in an autorecruitment of the physiological inflammatory response. Chloramines (such as the mild and untoxic oxidant chloramine T (N-chloro-p-toluene-sulfonamide)) and their signaling and destroying reaction product 1O(2) might be promising new therapeutic agents against a multitude of up to now refractory diseases.

Chloramines↗
PubMed2003

Singlet oxygen (1O2)-oxidazable lipids in the HIV membrane, new targets for AIDS therapy?

Human immunodeficiency virus (HIV) is a lipid enveloped virus. The lipid envelope differs significantly from the lipid membrane of normal human cells: it contains high amounts of cholesterol, that is of importance for the virus-cell interaction (for entry and exit of the virus) at so-called lipid rafts. Cholesterol, as a R-C=C-R compound possesses an oxidazable carbenic bond. The present work suggests the inactivation of HIV by oxidation of viral cholesterol and/or unsaturated fatty acids. For oxidation, the relatively mild oxidant singlet oxygen (1O(2)) might be used. 1O(2) is generated by redoxcyclers (e.g., of the quinone type, such as vitamin K) or by chloramines (e.g., taurine-chloramine). At the 1O(2) concentrations necessary to inactivate lipid enveloped virus in human blood the oxidation-sensible critical hemostasis parameters such as thrombocytes and fibrinogen are only partly inactivated. Therefore, it is proposed to consider generators of 1O(2) as a new form of AIDS therapy.

Acquired Immunodeficiency Syndrome↗
PubMed2001

Quantum yield of singlet oxygen production by monomeric and aggregated forms of hematoporphyrin derivative.

Hematoporphyrin derivative (HpD) is a complex mixture of monoporphyrinic compounds, including hematoporphyrin, and oligomers containing up to eight porphyrin units. In methanol a sensitizer concentration-independent quantum yield of 0.64 is measured for the HpD-induced production of singlet molecular oxygen O2 (1Delta(g)). This finding is consistent with the dye components remaining unassociated in this solvent. In water pH 7.4 HpD consists of a complex mixture of non-aggregated and self- and cross-aggregated monoporphyrinic and oligomeric species, and the quantum yield of O2 (1Delta(g)) formation decreases significantly with increasing HpD concentration due to the lower quantum yield of aggregates. These variations can be quantitatively described in terms of a monomer-dimer equilibrium, with quantum yields of 0.64 and 0.11, respectively, for monomers and dimers. The yields of unassociated species are identical in methanol and water.

Dimerization↗
PubMed2003

Interaction of singlet molecular oxygen with double fluorescent and spin sensors.

Double fluorescent and spin sensors were recently used to detect transient oxidants via simultaneous fluorescence change and production of the nitroxide radical detected by electron paramagnetic resonance. One such oxidant, singlet molecular oxygen ((1)O(2)), was detected in thylakoid membrane using these probes. In the present study, we investigated the total (physical and chemical) quenching of (1)O(2) phosphorescence by sensors composed of the 2,5-dihydro-2,2,5,5-tetramethyl-1H-pyrrole moiety attached to xanthene or dansyl fluorophores. We found that the quenching rate constants were in the range (2-7) x 10(7) M(-1)s(-1) in acetonitrile and D(2)O. Quenching of (1)O(2) is usually an additive process in which different functional groups may contribute. We estimated that the (1)O(2) quenching by the amine fragments was ca. one to two orders of magnitude lower than that for the complete molecules. Our data suggest that the incorporation of a fluorescent chromophore results in additional strong quenching of (1)O(2), which may in turn decrease the nitroxide yield via the (1)O(2) chemical path, possibly having an effect on quantitative interpretations. We have also found that probes with the dansyl fluorophore photosensitized (1)O(2) upon UV excitation with the quantum yield of 0.087 in acetonitrile at 366 nm. This result shows that care must be taken when the dansyl-based sensors are used in experiments requiring UV irradiation. We hope that our results will contribute to a better characterization and wider use of these novel double sensors.

Acetonitriles↗
PubMed1997

Kinetics and dynamics of singlet oxygen scavenging by alpha-tocopherol in phospholipid model membranes.

Scavenging of singlet oxygen (1O2) by alpha-tocopherol (alpha-Toc) was investigated in liposomes. 1O2 was generated by photoirradiation in the presence of two photosensitizers, water-soluble methylene blue (MB) and lipid-soluble 12-(1-pyrene)dodecanoic acid (PDA). The rates of oxidation of alpha-Toc differed depending on the photosensitizing dye and the membrane charge: in the MB-system, alpha-Toc was oxidized fast in negatively charged dimyristoylphosphatidylcholine (DMPC) liposomes containing dicetylphosphate (DCP) and slowly in neutrally charged DMPC liposomes and positively charged DMPC liposomes containing stearylamine (SA), but in the PDA-system, the oxidation rate was independent of the membrane charge. The charge-dependent difference in the MB-system would be due to the site of 1O2 generation depending on the charge-dependent distribution of MB, because positively charged MB increased the zeta-potential of DCP-DMPC liposomes by its interaction with DCP at the membrane surface, but changed the zeta-potentials of DMPC and SA-DMPC liposomes less because of its location in the bulk water phase. The oxidation rate of alpha-Toc in liposomes was different from that in EtOH solution: in the MB system, the oxidation rate was faster in EtOH solution than in DMPC or SA-DMPC liposomes but the same as that in DCP-DMPC liposomes. However, in the PDA system, the oxidation rate was slower in EtOH solution than in DMPC liposomes with or without a charge. Membrane fluidity changed the rate of alpha-Toc oxidation in liposomes, the rate being higher in the liquid crystalline phase than the gel phase, as judged by the higher rate in DMPC liposomes than in dipalmitoylphosphatidylcholine (DPPC) liposomes at 30 degrees C. The rate constants of alpha-Toc for scavenging, the chemical reaction and physical quenching of 1O2 were determined in membranes using DCP-DMPC liposomes labeled with 1,3-diphenyl-isobenzofuran (DPBF), which traps 1O2. These constants differed in the two photosensitizing systems, being higher in the MB-system than in the PDA-system, and were lower than those in EtOH solution.

Electrochemistry↗
PubMed1998

Singlet molecular oxygen ((1)O2): a possible effector of eukaryotic gene expression.

Biological processes involving light may have both beneficial (photosynthesis) and destructive (photosensitization) consequences. Singlet molecular oxygen, (1)O2, and other reactive oxygen species such as hydrogen peroxide and hydroxyl radical, arise during the interaction of light with photosensitizing chemicals in the presence of molecular oxygen. (1)O2 oxidizes macromolecules such as lipids, nucleic acids, and protein, depending on its intracellular site of formation; and promotes detrimental processes such as lipid peroxidation, membrane damage, and cell death. Photochemical reactive oxygen species (ROS) generating systems induce the expression of several eukaryotic genes, which include stress proteins, early response genes, matrix metalloproteinases, immunomodulatory cytokines, and adhesion molecules. These gene expression phenomena may belong to cellular defensive mechanisms, or may promote further injury. Whereas the signal transduction pathways that link site-specific oxidative damage and gene expression are poorly understood, ROS may affect signalling components in the membrane, cytosol, or nucleus, leading to changes in phospholipase, cyclooxygenase, protein kinase, protein phosphatase, and transcription factor activities. Limited evidence for (1)O2 involvement in gene activation phenomena consists of deuterium oxide solvent effects, inhibition by (1)O2-quenchers, sensitization by porphyrins, chemical trapping methods, and comparative effects of photosensitizing dyes and thermolabile endoperoxides. The studies outlined in this review support an hypothesis that (1)O2 and other ROS generated during photochemical processes such as ultraviolet-A (320-380 nm) radiation exposure, or photosensitizer mediated oxidation may have dramatic effects on eukaryotic gene expression.

Animals↗