The photodynamic effect of rose bengal on proteins of the mitochondrial inner membrane

Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)1

In 2008, we published the first set of guidelines for standardizing research in autophagy. Since then, this topic has received increasing attention, and many scientists have entered the field. Our knowledge base and relevant new technologies have also been expanding. Thus, it is important to formulate on a regular basis updated guidelines for monitoring autophagy in different organisms. Despite numerous reviews, there continues to be confusion regarding acceptable methods to evaluate autophagy, especially in multicellular eukaryotes. Here, we present a set of guidelines for investigators to select and interpret methods to examine autophagy and related processes, and for reviewers to provide realistic and reasonable critiques of reports that are focused on these processes. These guidelines are not meant to be a dogmatic set of rules, because the appropriateness of any assay largely depends on the question being asked and the system being used. Moreover, no individual assay is perfect for every situation, calling for the use of multiple techniques to properly monitor autophagy in each experimental setting. Finally, several core components of the autophagy machinery have been implicated in distinct autophagic processes (canonical and noncanonical autophagy), implying that genetic approaches to block autophagy should rely on targeting two or more autophagy-related genes that ideally participate in distinct steps of the pathway. Along similar lines, because multiple proteins involved in autophagy also regulate other cellular pathways including apoptosis, not all of them can be used as a specific marker for bona fide autophagic responses. Here, we critically discuss current methods of assessing autophagy and the information they can, or cannot, provide. Our ultimate goal is to encourage intellectual and technical innovation in the field.

Reactivities of singlet oxygen: open-shell or closed-shell?

This work explores the reactivity of singlet oxygen with respect to two typical reactions: cycloaddition to anthracene and excitation energy transfer (EET) to a carotenoid using diabatic states with multistate density functional theory (MSDFT). Noticeably, the degenerate state 1Δg has distinct open-shell (OS) and closed-shell (CS) components, and the closed-shell component showed more reactivity than the open-shell one due to the strong diabatic couplings to the product diabatic states. The diabatic perspective presented in this work could also apply to general singlet fission processes.

Enhancement of the Efficacy of Photodynamic Inactivation of Candida albicans with the Use of Biogenic Gold Nanoparticles

This study reports on successful photodynamic inactivation of planktonic and biofilm cells of Candida albicans using Rose Bengal (RB) in combination with biogenic gold nanoparticles synthesized by the cell-free filtrate of Penicillium funiculosum BL1 strain. Monodispersed colloidal gold nanoparticles coated with proteins were characterized by a number of techniques including SEM-EDS, TEM, UV-Vis absorption and fluorescence spectroscopy, as well as Fourier transform infrared spectroscopy to be 24 ± 3 nm spheres. A Xe lamp (output power of 20mW, delivering intensity of 53 mW cm^-2 ) was used as a light source to study the effects of RB alone, the gold nanoparticles alone and the RB-gold nanoparticle mixture on the viability of C. albicans cells. The most effective reduction in the number of planktonic cells was found after 30 min of Xe lamp light irradiation (95.4 J cm^-2 ) and was 4.89 log₁₀ that is 99.99% kill for the mixture of RB with gold nanoparticles compared with 2.19 log₁₀ or 99.37% for RB alone. The biofilm cells were more resistant to photodynamic inactivation, and the highest effective reduction in the number of cells was found after 30 min of irradiation in the presence of the RB-gold nanoparticles mixture and was 1.53 log₁₀ , that is 97.04% kill compared with 0.6 log₁₀ or 74.73% for RB. The probable mechanism of enhancement of RB-mediated photodynamic fungicidal efficacy against C. albicans in the presence of biogenic gold nanoparticles is discussed leading to the conclusion that this process may have a multifaceted character.

Unsaturated lipids protect the integral membrane peptide gramicidin A from singlet oxygen

In contrast to expectations that unsaturated fatty acids contribute to oxidative stress by providing a source of lipid peroxides, we demonstrated the protective effect of double bonds in lipids on oxidative damage to membrane proteins. Photodynamic inactivation of gramicidin channels was decreased in unsaturated lipid compared to saturated lipid bilayers. By estimating photosensitizer (boronated chlorine e6 amide) binding to the membrane with the current relaxation technique, the decrease in gramicidin photoinactivation was attributed to singlet oxygen scavenging by double bonds in lipids rather than to the reduction in photosensitizer binding. Gramicidin protection by unsaturated lipids was also observed upon induction of oxidative stress with tert-butyl hydroperoxide.

Fluorone dyes have binding sites on both cytoplasmic and extracellular domains of Na,K-ATPase

Combination of fluorescence techniques and molecular docking was used to monitor interaction of Na,K-ATPase and its large cytoplasmic loop connecting fourth and fifth transmembrane helices (C45) with fluorone dyes (i.e. eosin Y, 5(6)-carboxyeosin, rose bengal, fluorescein, and erythrosine B). Our data suggested that there are at least two binding sites for all used fluorone dyes, except of 5(6)-carboxyeosin. The first binding site is located on C45 loop, and it is sensitive to the presence of nucleotide. The other site is located on the extracellular part of the enzyme, and it is sensitive to the presence of Na(+) or K(+) ions. The molecular docking revealed that in the open conformation of C45 loop (which is obtained in the presence of ATP) all used fluorone dyes occupy position directly inside the ATP-binding pocket, while in the closed conformation (i.e. in the absence of any ligand) they are located only near the ATP-binding site depending on their different sizes. On the extracellular part of the protein, the molecular docking predicts two possible binding sites with similar binding energy near Asp897(α) or Gln69(β). The former was identified as a part of interaction site between α- and β-subunits, the latter is in contact with conserved FXYD sequence of the γ-subunit. Our findings provide structural explanation for numerous older studies, which were performed with fluorone dyes before the high-resolution structures were known. Further, fluorone dyes seem to be good probes for monitoring of intersubunit interactions influenced by Na(+) and K(+) binding.

Partial colocalization of oxidized, N-formylkynurenine-containing proteins in mitochondria and Golgi of keratinocytes

Proteins are the dominant cellular target for oxidative reactions because they comprise the majority of macromolecules. Posttranslational oxidative protein modifications include fragmentation, aggregation and alteration of specific amino acid residues. The amino acids and amino acid residues most susceptible to oxidative modification are those containing sulfur and those with aromatic rings. Tryptophan reacts with radicals, ozone and singlet oxygen to form the end product N-formylkynurenine (NFK). We recently described a novel anti-NFK antiserum and validated its use in immunological assays for the specific detection of NFK in isolated proteins and protein mixtures. Here we photo-oxidize rose bengal-containing HaCaT keratinocyte cells and examine the results using fluorescent confocal microscopy and staining with anti-NFK antiserum and markers for both Golgi and mitochondria. We show that photosensitization mediates the accumulation of NFK and that NFK can be detected in photosensitized cells with only slightly decreased viability. Additionally, we detect NFK-modified proteins in both Golgi and mitochondria of photosensitized cells. These experiments demonstrate that we have developed a tool for the specific detection of oxidized tryptophan residues in cells and suggest that this tool could be useful in tracking the fate of these oxidized proteins.

Oxidative modification of cytochrome c by singlet oxygen

Singlet oxygen ((1)O(2)) is a reactive oxygen species that may be generated in biological systems. Photodynamic therapy generates (1)O(2) by photoexcitation of sensitizers resulting in intracellular oxidative stress and induction of apoptosis. (1)O(2) oxidizes amino acid side chains of proteins and inactivates enzymes when generated in vitro. Among proteogenic amino acids, His, Tyr, Met, Cys, and Trp are known to be oxidized by (1)O(2) at physiological pH. However, there is a lack of direct evidence of oxidation of proteins by (1)O(2). Because (1)O(2) is difficult to detect in cells, identifying oxidized cellular products uniquely derived from (1)O(2) could serve as a marker of its presence. In the present study, (1)O(2) reactions with model peptides analyzed by tandem mass spectrometry provide insight into the mass of prominent adducts formed with the reactive amino acids. Analysis by MALDI-TOF and tandem mass spectrometry of peptides of cytochrome c exposed to (1)O(2) generated by photoexcitation of the phthalocyanine Pc 4 showed unique oxidation products, which might be used as markers of the presence of (1)O(2) in the mitochondrial intermembrane space. Differences in the elemental composition of the oxidized amino acid residues observed with cytochrome c and the model peptides suggest that the protein environment can affect the oxidation pathway.

Electron transport chain of Saccharomyces cerevisiae mitochondria is inhibited by H2O2 at succinate-cytochrome c oxidoreductase level without lipid peroxidation involvement

The deleterious effects of H202 on the electron transport chain of yeast mitochondria and on mitochondrial lipid peroxidation were evaluated. Exposure to H2O2 resulted in inhibition of the oxygen consumption in the uncoupled and phosphorylating states to 69% and 65%, respectively. The effect of H2O2 on the respiratory rate was associated with an inhibition of succinate-ubiquinone and succinate-DCIP oxidoreductase activities. Inhibitory effect of H2O2 on respiratory complexes was almost completely recovered by beta-mercaptoethanol treatment. H2O2 treatment resulted in full resistance to Qo site inhibitor myxothiazol and thus it is suggested that the quinol oxidase site (Qo) of complex III is the target for H2O2. H2O2 did not modify basal levels of lipid peroxidation in yeast mitochondria. However, H2O2 addition to rat brain and liver mitochondria induced an increase in lipid peroxidation. These results are discussed in terms of the known physiological differences between mammalian and yeast mitochondria.

Depolarization and cardiolipin depletion in aged rat brain mitochondria: Relationship with oxidative stress and electron transport chain activity

A noticeable loss of cardiolipin, a significant accumulation of fluorescent products of lipid peroxidation and an increased ability to produce reactive oxygen species in vitro are characteristics of aged rat brain mitochondria, as has been demonstrated in this study. In contrast mitochondrial electron transport chain activity is not significantly compromised except a marginal decline in complex IV activity in aged rat brain. On the other hand, a striking loss of mitochondrial membrane potential occurs in brain mitochondria during aging, which may be attributed to peroxidative membrane damage in this condition. Such mitochondrial dysfunctions as reported here may lead to uncoupling of oxidative phosphorylation, ATP depletion and activation of apoptotic cascade in aged rat brain.

Lipid peroxidation associated cardiolipin loss and membrane depolarization in rat brain mitochondria

Oxidative stress induced by Fe2+ (50 microM) and ascorbate (2 mM) in isolated rat brain mitochondria incubated in vitro leads to an enhanced lipid peroxidation, cardiolipin loss and an increased formation of protein carbonyls. These changes are associated with a loss of mitochondrial membrane potential (depolarization) and an impaired activity of electron transport chain (ETC) as measured by MTT reduction assay. Butylated hydroxytoluene (0.2 mM), an inhibitor of lipid peroxidation, can prevent significantly the loss of cardiolipin, the increased protein carbonyl formation and the decrease in mitochondrial membrane potential induced by Fe2+ and ascorbate, implying that the changes are secondary to membrane lipid peroxidation. However, iron-ascorbate induced impairment of mitochondrial ETC activity is apparently independent of lipid peroxidation process. The structural and functional derangement of mitochondria induced by oxidative stress as reported here may have implications in neuronal damage associated with brain aging and neurodegenerative disorders.

Photodynamic inactivation of the Na,K-ATPase occurs via different pathways

The photodynamic, i.e., the light-induced, inactivation of the Na,K-ATPase in the presence of the sensitizer rose bengal was studied under different conditions. The shape of inactivation curves of the enzyme activity was analyzed as well as partial reactions of the pump cycle. Both experimental approaches showed the existence of two different time constants of inactivation of the ion pump, which reflect two pathways of a photodynamic modification. This is supported by the following observations: (1) The amplitude of the initial fast decay of enzyme activity was enhanced in the presence of D2O and reduced in the presence of the singlet oxygen scavenger imidazole. (Similar results were found for the SR Ca-ATPase.) (2) Contrary to the fast enzyme inactivation the slow process shows an inverse dose-rate behavior. (3) Inactivation of the partial reactions of Na+ -binding and of K+-binding to the membrane domain of the Na,K-ATPase showed only a single time constant, which corresponded to the slower time constant of enzyme inactivation. In the presence of high concentrations of singlet oxygen the fast time constant dominated the inactivation of the ATP-induced partial reaction for which the cytoplasmic domains of the enzyme play an important role. The data support the conclusion that fast inactivation is due to modification of the cytoplasmic domains and slow inactivation due to modifications of the membrane domain of the ion pumps.

Topical rose bengal: pre-clinical evaluation of pharmacokinetics and safety

BACKGROUND AND OBJECTIVES

Rose bengal (RB) is a potent photosensitizer that has largely been overlooked as a potential photodynamic therapy (PDT) agent. In this study, the feasibility of topical delivery of RB to the epidermis has been evaluated.

STUDY DESIGN/MATERIALS AND METHODS

Topical formulations of RB were assessed on murine and rabbit skin for pharmacokinetic properties, cutaneous toxicity, and photosensitization.

RESULTS

Hydrophilic formulations (<or=1% RB) exhibited rapid, selective, uniform delivery to the epidermis, with no significant acute cutaneous toxicity in normal skin. Illumination (532 nm) elicited no acute phototoxicity for light intensities <or=100 mW/cm(2) at a light dose of 100 J/cm(2); use of higher intensities resulted in superficial thermal damage. Repeat treatment of rabbit skin (weekly for four weeks) elicited minor phototoxicity only at the highest concentration (1% RB).

CONCLUSIONS

These results indicate that RB is safe for PDT treatment of skin disorders, exhibiting negligible effects in normal skin.

Photo-activation of hypericin with low doses of light promotes apparent photo-resistance in human histiocytic lymphoma U937 cells

We have observed that exposure of U937 cells, pre-incubated for 18 h with 0.2 microM hypericin, to 599 nm laser radiation with a fluence of 2.5 J/cm(2) renders them insensitive to higher light doses. In fact, pre-sensitized cells appear to be fully resistant to light doses that normally determine massive cellular apoptosis in experimental photo-dynamic therapy. The appearance of the photo-resistance, as measured by evaluating the changes in levels of expression of pro and anti apoptotic proteins, PARP fragmentation and cell viability is exclusively observed with exposure to light doses not exceeding 5-6 J/cm(2). Above this energy, necrosis replaces apoptosis upon photo-stimulation of U937 cells. Here, we describe the appearance of photo-resistance in hypericin-loaded U937 cells, but could not fully unravel the molecular mechanism underlying this process. However, the observed stimulation of the expression of the HSP-70 protein upon photo-induced stress may suggest its involvement in this process.

Antioxidant adaptive response of human mononuclear cells to UV-B: effect of lipoic acid

Supplementation of human mononuclear cells with 3 and 6 mM of lipoic acid produces an inhibition of the antioxidant adaptive response triggered by treatment with UV-B light (0.30 W/m2 for 15 min). Supplementation with 1.5 mM of lipoic acid gives no conclusive results. The adaptive response is characterized by an increase in the activities of superoxide dismutase, catalase, glutathione peroxidase and DT-diaphorase. Catalase (5.5 +/- 0.6 pmol/mg prot) increases its activity by up to 22 +/- 3 pmol/mg prot, after irradiation with UV-B. Supplementation with 3 and 6 mM of lipoic acid completely inhibits the adaptive response. The activities of the membrane-bound mitochondrial enzymes succinate dehydrogenase and cytochrome oxidase do not increase after UV-B exposure. Moreover, their activities are found to decrease and the addition of lipoic acid does not prevent this effect. The inhibition of the antioxidant response by lipoic acid in human cells appears as indirect evidence of the existence of oxidative stress in the development of this response. As lipoic acid behaves as an effective antioxidant, it seems that its action decreases the intracellular oxidative signals necessary to develop the adaptive response in human mononuclear cells.

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.

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.

Imaging the mitochondrial permeability transition pore in intact cells

The involvement of mitochondrial permeability transition pore (MTP) in cellular processes is generally investigated by indirect means, such as changes in mitochondrial membrane potential or pharmacological inhibition. However, such effects could not be related univocally to MTP. In addition, source of errors could be represented by the increased retention of membrane potential probes induced by cyclosporin A (CsA) and the interactions between fluorescent probes. We developed a direct technique for monitoring MTP. Cells were co-loaded with calcein-AM and CoCl2, resulting in the quenching of the cytosolic signal without affecting the mitochondrial fluorescence. MTP inducers caused a rapid decrease in mitochondrial calcein fluorescence which, however, was not completely prevented by CsA. Besides the large and rapid efflux of calcein induced by MTP agonists, we also observed a constant and spontaneous decrease of mitochondrial calcein which was completely prevented by CsA. Thus, MTP likely fluctuates between open and closed states in intact cells.

Effects of Photofrin photodynamic action on mitochondrial respiration and superoxide radical generation

Cyanide-resistant respiration increases after irradiation of isolated mitochondria in the presence of Photofrin. This suggests an enhancement of electron leakage which has been evaluated by measuring superoxide radical formation in submitochondrial particles incubated with 6 micrograms/ml Photofrin in the medium and irradiated with increasing doses of light at 365 nm. After a dose of 4.5 kJ/m2 has been delivered, superoxide generation increases by a factor of approximately 2.5 at the level of NADH dehydrogenase and by a factor approximately 1.5 in the cyt bc1 region. These effects have been compared with changes observed in NADH-, succinate- and ascorbate-driven respiration and their implications discussed.

Oxidative stress associated with exercise, psychological stress and life-style factors

Oxidative stress is a cellular or physiological condition of elevated concentrations of reactive oxygen species that cause molecular damage to vital structures and functions. Several factors influence the susceptibility to oxidative stress by affecting the antioxidant status or free oxygen radical generation. Here, we review the effect of alcohol, air pollution, cigarette smoke, diet, exercise, non-ionizing radiation (UV and microwaves) and psychological stress on the development of oxidative stress. Regular exercise and carbohydrate-rich diets seem to increase the resistance against oxidative stress. Air pollution, alcohol, cigarette smoke, non-ionizing radiation and psychological stress seem to increase oxidative stress. Alcohol in lower doses may act as an antioxidant on low density lipoproteins and thereby have an anti-atherosclerotic property.

Mitochondrial sites of hydrogen peroxide production in reperfused rat kidney cortex

Electron transport and production of O2-/H2O2 by the NADH dehydrogenase flavin-semiquinone (FMNH.) and ubisemiquinone (UQH.) were studied in a model of in vivo ischemia-reperfusion in rat kidney. H2O2 production rates were assessed in isolated mitochondria using either succinate, with and without antimycin, or malate-glutamate, with and without rotenone. Respiratory activities of isolated mitochondria and activity of NADH- and succinate-cytochrome c reductase and of NADH- and succinate-dehydrogenase in submitochondrial particles were measured to evaluate the electron flux throughout respiratory carriers. The mitochondrial H2O2 production rate was approximately 1.5- and 4-times increased in ischemic and ischemic-reperfused kidneys, respectively. Ischemia caused a marked decrease in the electron transport throughout the NADH-UQ segment with no significant changes either in the NADH dehydrogenase activity or in the electron flux trough the succinate-cytochrome oxidase segment. Reperfusion did not further affect the NADH-ubiquinone segment but markedly inhibited the succinate-supported oxygen consumption, succinate-cytochrome c reductase and succinate dehydrogenase activity. Our results show a redistribution of the electron flux with an increased rate of superoxide anion/hydrogen peroxide production at NADH dehydrogenase in mitochondria subjected to ischemia only. After 10 min reperfusion an impairment of the electron flow at succinate-cytochrome c segment is established and hydrogen peroxide production by UQH. increases up to maximal values becoming the major source of superoxide anion/hydrogen peroxide.

Photodynamic action increases leakage of the mitochondrial electron transport chain

Rat liver submitochondrial particles were treated with rose bengal or flavin mononucleotide and irradiated with visible or near UV light. In both cases, oxygen consumption is impaired after irradiation while O2-. production increases significantly. This suggests that exogenous or endogenous photosensitizers can induce more electron leakage in the mitochondrial respiratory chain. Photobiological implications in dermatology are discussed.

Laser photosensitization of cells by hypericin

Administering a light dose of 90 J/cm2 at 599 nm during incubation with hypericin to a highly differentiated normal epithelial cell line (FRTL-5), derived from Fisher rat thyroid, and to a neoplastic cell line (MPTK-6), derived from the lung metastases of a thyroid carcinoma induced in Fisher rats, produces cell kill at drug doses 1000 times lower than those necessary to cause the same mortality in the dark. The photocytocidal activity of this polycyclic quinone drug on neoplastic cells is superior to that of antitumor anthraquinone drugs, such as daunomycin and mitoxanthrone, and to the photosensitized antiviral activity previously reported for hypericin.

Effect of low-intensity argon laser irradiation on mitochondrial respiration

We studied influences of low-intensity argon laser irradiation at various wavelengths on mitochondrial respiration in vitro. Isolated guinea pig liver mitochondria were suspended in an isotonic buffer solution (pH 7.4, 37 degrees C). The mitochondrial suspension was introduced into a constant temperature reaction chamber in which an irradiation fiber, a thermocouple, an oxygen electrode, and a stirrer were installed. Under respiratory conditions of state 4, state 3, and uncoupled respiration, mitochondrial oxygen consumption was measured during low-intensity argon laser irradiations at 351nm, 458 nm, and 514.5 nm. The 351 nm and the 458 nm irradiations at 200 mW inhibited uncoupled respiration by 19% and 11%, respectively, and the irradiation at 351 nm inhibited state 3 respiration as well by 10%. In contrast, the 514.5 nm irradiation enhanced both state 3 and uncoupled respiration by 6-7%. Temperature reference experiments indicated that the thermal effect alone could not account for the effects of laser irradiation on mitochondrial oxygen consumption. These results suggest that the 351 nm and the 458 nm laser irradiation may injure the mitochondrial inner membrane, while the 514.5 nm laser irradiation may slightly promote the rate of ATP synthesis.

Photoinactivation of influenza virus fusion and infectivity by rose bengal

Rose bengal inactivated influenza virus upon exposure to light. Infectivity and fusion were inactivated with the same dose dependence, supporting the suggestion that the virucidal activity of photodynamic agents against enveloped viruses may be generally due to inactivation of their fusion protein(s). Concentrations required for inactivation were found to depend upon the ratio of rose bengal to virus, rather than on the nominal aqueous concentration. Fusion-competent virosomes were inactivated similarly to intact virus particles. The HA2 portion of the influenza fusion protein HA underwent two different, apparently mutually exclusive modifications upon illumination with rose bengal: cross-linking, and conversion to a form that moved slightly more slowly on sodium dodecyl sulfate polyacrylamide gel electrophoresis. Inactivation of viral fusion was inhibited by oxygen removal or addition of azide or beta-carotene, and was enhanced by D2O, consistent with partial involvement of singlet oxygen. The possibility of a second mechanism of viral photoinactivation, by direct interaction between the viral fusion protein and the photoactivated dye, is also discussed.

Cellular stress by light and rose bengal in human lymphocytes

Human lymphocyte cultures were supplemented with 10(-8)-10(-4) M Rose Bengal and irradiated with fluorescent light (Philips 40-W daylight-fluorescent lamp, 380-550 nm) and chromosomal aberrations and catalase and superoxide dismutase activities in the cells were determined. Chromosomal lesions and both enzymatic activities increased additively or synergistically in human lymphocytes after Rose Bengal supplementation and fluorescent light irradiation. Chromosomal lesions (expressed as chromosomal aberrations/cells) were (a) 0.12 +/- 0.03, (b) 0.18 +/- 0.12, (c) 1.58 +/- 0.11 and (d) 3.20 +/- 0.17 in the following conditions: (a) control; (b) after 3 h light irradiation, (c) supplemented with 10(-5) M Rose Bengal and (d) with dye treatment and light irradiation. Superoxide dismutase activity was: (a) 16.5 +/- 1.5; (b) 19.5 +/- 1.2; (c) 29.2 +/- 1.5 and (d) 35.4 +/- 2.1 U/mg protein and catalase activity was: (a) 10.3 +/- 0.5, (b) 12.8 +/- 0.7, (c) 22.4 +/- 0.5 and (d) 27.6 +/- 1.1 U/mg protein in the same experimental conditions. These findings suggest that Rose Bengal supplementation plus fluorescent light irradiation of human lymphocytes lead to the synthesis of superoxide dismutase and catalase in a manner similar to the heat-shock response. A threshold of chromosomal damage (about 2 chromosomal aberrations/cell) is apparently required to activate oxidative stress genes.

Antiretroviral activities of hypericin and rose bengal: photodynamic effects on Friend leukemia virus infection of mice

The ability of hypericin to protect mice from splenomegaly resulting from infection with Friend leukemia virus (FLV) was re-examined in light of recent evidence showing that light is absolutely required for this drug's antiviral activity. FLV-induced splenomegaly was not prevented or ameliorated in mice injected with 100 micrograms hypericin, either mixed with the FLV inoculum or administered 1 day p.i., either under normal laboratory light or in the dark. These results contradict previous findings. Both hypericin and rose bengal, however, inactivated the FLV inoculum at low doses (< 11 micrograms), provided that the mixture was illuminated for 1 h under a normal fluorescent desk lamp. This procedure protected mice completely from FLV-induced splenomegaly, and provided a possible explanation for the discrepancy between our results and those reported previously. We conclude that for FLV, as for other enveloped viruses studied previously, illumination of hypericin with the virus is absolutely required for hypericin's antiviral (virucidal) effects, thus limiting its potential usefulness as an antiretroviral agent.

Influence of the peptide bond on the singlet molecular oxygen-mediated (O2[1 delta g]) photooxidation of histidine and methionine dipeptides. A kinetic study

The dye-sensitized photooxidation of L-histidine (His) and L-methionine (Met) and their simplest dipeptides with glycine (Gly) (His-Gly, Gly-His Gly-Met) and Met-methyl ester (Met-ME) mediated by singlet molecular oxygen (O2[1 delta g]) was studied. The overall rate constants in acetonitrile-H2O (kt) for O2(1 delta g) quenching were measured by time-resolved phosphorescence detection. In H2O a competitive kinetic method was employed. In both solvents the reactive rate constants (kr) were determined to discriminate between the overall and physical contributions to the quenching. The kinetic and mechanistic aspects of the interaction are discussed. For His-Gly, the peptide bond has practically no effect on the kinetics of photooxidation. For Gly-His the overall rate constant is much higher than that for His and His-Gly, in both H2O and acetonitrile-H2O. The main contribution to kt (for Gly-His) is the physical quenching of O2(1 delta g). In water the kt/kr ratio for free His and His-Gly is 1.0, reaching a value of 2.0 in the organic solvent-H2O mixture. The rates of -NH2 loss upon sensitized photooxidation in all cases parallel the trend of kr values. The main results for the His series indicate that: (1) a polar environment favors autoprotection (i.e. an increase in the contribution of physical quenching) against photodynamic effects; (2) only the rate constant for reactive interaction with O2(1 delta g) does not depend on the location of the peptide bond involving His. For Met derivatives the kt values are higher in both solvents than that for free Met.(ABSTRACT TRUNCATED AT 250 WORDS)

Photodynamic inactivation of infectivity of human immunodeficiency virus and other enveloped viruses using hypericin and rose bengal: inhibition of fusion and syncytia formation

The mechanism of the antiviral activity of hypericin was characterized and compared with that of rose bengal. Both compounds inactivate enveloped (but not unenveloped) viruses upon illumination by visible light. Human immunodeficiency and vesicular stomatitis viruses were photodynamically inactivated by both dyes at nanomolar concentrations. Photodynamic inactivation of fusion (hemolysis) by vesicular stomatitis, influenza, and Sendai viruses was induced by both dyes under similar conditions (e.g., I50 = 20-50 nM for vesicular stomatitis virus), suggesting that loss of infectivity resulted from inactivation of fusion. Syncytium formation, between cells activated to express human immunodeficiency virus gp120 on their surfaces and CD4+ cells, was inhibited by illumination in the presence of 1 microM hypericin. Hypericin and rose bengal thus exert similar virucidal effects. Both presumably act by the same mechanism--namely, the inactivation of the viral fusion function by singlet oxygen produced upon illumination. The implications of this photodynamic antiviral action for the potential therapeutic usefulness of both hypericin and rose bengal are discussed.

Photoactivation of hypericin generates singlet oxygen in mitochondria and inhibits succinoxidase

Photosensitized inhibition of mitochondrial succinoxidase by hypericin was measured in vitro and found to be drug-dose, light-dose, and wavelength dependent. Singlet oxygen generation, monitored using the singlet oxygen trap tetramethylethylene, and oxygen consumption in isolated mitochondria sensitized by hypericin were also light-dose and wavelength dependent. Unequivocal evidence for the generation of singlet oxygen was obtained using kinetic isotope ratios of products from the reaction between singlet oxygen and geminally deuterated tetramethylethylene. An action spectrum for the inhibition of succinoxidase was measured at wavelengths between 400 and 700 nm and found to parallel the recorded visible absorption spectrum of hypericin in isolated mitochondria. The greatest singlet oxygen generation, oxygen consumption, and succinoxidase inhibition occurred with white light or 600 nm irradiation. These data are consistent with a type II singlet-oxygen-mediated mechanism for hypericin induced photosensitized inhibition of mitochondrial succinoxidase.