Cellular and subcellular mechanisms of photodynamic action: the 1O2 hypothesis as a driving force in recent research

Selenium-induced enhancement of hematoporphyrin derivative phototoxicity in murine bladder tumor cells

The phototoxicity of hematoporphyrin derivative (Hpd) to murine bladder tumor (MBT-2) cells was studied in vitro. It was observed that selenium in the form of sodium selenite enhanced Hpd-sensitized photodamage in MBT-2 cells under conditions where selenite alone was non-toxic. Sodium selenite enhanced the fluorescence emission of Hpd and augmented the Hpd-sensitized photooxidation of tryptophan. The data suggest that sodium selenite is able to disaggregate Hpd, thereby enhancing Hpd-sensitized phototoxicity.

Potentiation of the generation of reactive oxidants by human phagocytes during exposure to benoxaprofen and ultraviolet radiation in vitro

The effects of ultraviolet (UV) radiation on the spontaneous membrane-associated oxidative metabolism of human polymorphonuclear leukocytes (PMNL) and mononuclear leukocytes (MNL), co-incubated in the presence and absence of the non-steroidal, anti-inflammatory drug (NSAID) benoxaprofen at various concentrations, were investigated in vitro. Assays of superoxide generation and luminol-enhanced chemiluminescence (CL) were used to detect the production of reactive oxidants by PMNL and MNL. Benoxaprofen in the absence of UV radiation caused a dose-related activation of superoxide production and CL by PMNL. Exposure of PMNL to UV radiation in the absence of benoxaprofen caused a slight increase in superoxide generation and an unsustained slight increase in CL within 10 s. Exposure of both MNL and PMNL to UV radiation in the presence of benoxaprofen had a marked synergistic effect on both superoxide generation and CL. These effects were also achieved with UVA irradiation but were not detected when adherent cell depleted MNL or sodium fluoride (NaF) (10-2 M) pulsed PMNL, or PMNL from children with chronic granulomatous disease, were used. The pro-oxidative effects of benoxaprofen and UV radiation alone and in combination are dependent on intact phagocyte membrane-associated oxidative metabolism. It is postulated that the pro-oxidative interactions which occur between human phagocytes, benoxaprofen and ultraviolet radiation cause the dermatological side-effects of benoxaprofen.

Evaluation of chemically-induced phototoxicity to aquatic organism using Paramecium as a model

Phototoxicity evaluation using Paramecium aurelia as a model revealed that 4 out of 21 pesticides produced lethal toxicity to cells. Four commonly used synthetic dyes (bromophenol blue, rose bengal, benzanthrone and methylene blue) also exhibited toxicity. Well known phototoxic agents like hematoporphyrin, riboflavin, and anthracene produced positive phototoxic response. Psoralen, a DNA cross-linking agent, also produced phototoxicity to the cells. The results clearly demonstrate that the synergistic action of chemical agents and sunlight produce lethal effects to aquatic organism.

Photodynamic mutagenic action of acridine compounds on yeast Saccharomyces cerevisiae

The photodynamically produced mutagenicity and toxicity of 8 acridine compounds were compared in Saccharomyces cerevisiae under resting and growing conditions. Without irradiation none of the acridines induced respiratory-deficient ('petite') colonies, indicative of mitochondrial DNA damage, in resting cells; and only acriflavine and proflavine induced 'petites' in growing cells. Also, without irradiation none of the acridines were significantly toxic or mutagenic for nuclear DNA under resting or growing conditions. However, with irradiation, acriflavine, proflavine, acridine yellow and rivanol became effective 'petite'-inducing mutagens and highly toxic for resting cells, while acriflavine, proflavine, and acridine orange became effective nuclear mutagens for resting cells. Acridine, quinacrine and 9-aminoacridine were not at all biologically effective with irradiation for resting cells. The results presented here indicate that singlet oxygen is generated by a photodynamic mechanism when acriflavine is irradiated, and further, that acridine, quinacrine and 9-aminoacridine are ineffective photosensitizers, because they are incapable of generating singlet oxygen with irradiation.

Studies of the limited degradation of mucus glycoproteins. The mechanism of the peroxide reaction

The reaction between ovarian-cyst glycoproteins and H2O2 was investigated in the presence of a number of inhibitors and catalysts. Azide and 2H2O were separately found to have little effect, implying that singlet oxygen was not involved. Superoxide dismutase was destroyed by H2O2, but mannitol had no effect: thus generalized attack by OH., whether originating from HO2.- or more directly, is not indicated. The glycoproteins contained trace quantities of Cu and Fe, amounting to about 2 atoms of metal per glycoprotein molecule. Treatment of the glycoproteins with the strong chelator DETAPAC (diethylenetriaminepenta-acetic acid) or Chelex resin eliminated the reaction with H2O2; activity could be restored by addition of Cu2+ or Fe2+ in millimolar quantities. It was concluded that metal-ion catalysis is an essential step in the attack of H2O2 on glycoproteins. Spectroscopic and other evidence showed that Cu2+ (and probably Fe2+) complexes strongly with poly-L-histidine, and implies that the Cu2+ or Fe2+ in the glycoproteins is complexed with some of the histidine residues in the glycosylated backbone. Neither polyhistidine nor polyproline reacted with H2O2 in the absence of metal ions, but small quantities of Cu2+ or Fe3+ caused degradation. This was rapid with polyhistidine, which was converted largely into aspartic acid, but slower with polyproline, where limited conversion into glutamic acid occurs. These findings confirm the original hypothesis that peroxide attack on glycoproteins occurs largely at the histidine residues, with simultaneous peptidolysis. The mechanism most probably involves the liberation of OH. by an oxidation-reduction cycle involving, e.g. Cu+/Cu2+: specificity of attack at histidine is due to the location of the metal at these residues only.

The photodynamic action of eosin, a singlet-oxygen generator : Some effects on leaf tissue of Pisum sativum L

Eosin, a xanthene dye capable of the photodynamic generation of singlet oxygen ((1)O2), was shown to promote injury to leaf tissue of Pisum sativum L. in the presence of visible light. Chloroplasts appeared particularly sensitive to this action, displaying a rapid inactivation of photosynthesis. Investigation of chloroplast disruption involved analysis of pigment loss, ribulose 1,5-bisphosphate carboxylase (EC 4.1.1.39) activity, NADPH-glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13) activity, photosynthetic electron transport and ultrastructural examination. The initial loss of photosynthetic activity was associated with damage to the thylakoid membranes. Early stages of damage were accompanied by the production of ethane.

The cytotoxic and photodynamic inactivation of micro-organisms by Rose Bengal

Rose Bengal was cytotoxic to the following bacteria at the concentrations given in parentheses (highest concentrations of dye in mol/l at which growth occurred on nutrient medium): Brochothrix thermosphacta and Deinococcus radiodurans (1 X 10(-6) or less); Streptococcus, Micrococcus, Staphylococcus, Bacillus, Arthrobacter and Kurthia spp. (1 X 10(-5)-1 X 10(-4], and Pseudomonas spp. and Enterobacteriaceae (5 X 10(-3)-1 X 10(-2) or greater). These organisms were killed rapidly when suspended in illuminated (170 microE/m2/s) solutions of Rose Bengal (1 X 10(-4) mol/l) providing oxygen was present. Singlet oxygen was identified as the lethal agent, because the rate of killing was increased by dissolving the dye in deuterium oxide while the organism were protected against photoinactivation by L-histidine or crocetin. Yeasts from chilled foods were killed in illuminated solutions of Rose Bengal but a light intensity of 315 microE/m2/s was needed for a death rate comparable with that of bacteria. The yeasts present in a range of chilled meat and dairy products failed to form colonies on Rose Bengal (5 X 10(-5) mol/l) media exposed continuously to modest illumination (55-80 microE/m2/s).

Dye-sensitized photo-oxidation of enzymes

Heart lipoamide dehydrogenase, liver alcohol dehydrogenase and egg-white lysozyme are photo-oxidized in the presence of various dye sensitizers. The photodynamic process is preceded by the binding between the enzyme and the sensitizers. Among the commonly used dyes, halogenated xanthines and thiazine are effective sensitizers for the photo-inactivation of these three enzymes. Histidine residues are the primary target for the sensitized photo-oxidation that inactivates lipoamide dehydrogenase and alcohol dehydrogenase. However, the destruction of tryptophan residues is responsible for the photo-inactivation of lysozyme. The deuterium medium effect and the quenching effect by various scavengers of the potential photo-oxidative intermediates implicate the participation of the mixed type I-type II mechanism, with the involvement of singlet oxygen being of greater importance, in the photo-inactivation of the enzymes.

Cytofluorometric quantitation of acridine orange uptake by cultured cells

The vacuolar accumulation of the lysosomotropic weak base acridine orange (AO) within living cells in culture was studied by cytofluorometry. Mouse peritoneal macrophages, malignant human glioma cells, and normal human glial cells were utilized. Exposure to AO resulted in granular bright red fluorescence, as well as a diffuse weak green background fluorescence. To obtain reproducible "staining" conditions, the red granular fluorescence was measured as a function of dye concentration and staining time. Exposure to high concentrations of AO (greater than 10 micrograms/ml) was found to cause cell damage in combination with markedly changed fluorescence distribution for the cell population with reduced mean fluorescence and increased variability. Granular uptake of AO was pH-dependent and almost zero at pH 5.5. AO fluorescence, as measured by cytofluorometry, was found to be roughly linear to the amount of AO present in the cells, as measured by spectrofluorometry after cell solubilization, indicating negligible fluorescence quenching. AO labelling of living cells might serve as a useful indicator of the condition of the cellular vacuolar (lysosomal) apparatus.

Photodynamic activity of acridine orange: peroxide radical induction in DNA and synthetic polynucleotides

As shown by electron paramagnetic resonance, acridine orange induces the formation of peroxide radicals in DNA when dye-DNA mixtures frozen at 77 K are irradiated with visible light. The reaction is oxygen dependent and strongly reduced by the addition of an electron scavenger. Factors of the medium can modulate the reaction: an ionic strength increased up to 0.3 greatly enhances the dye efficiency whereas the presence of phosphate ions has an inhibiting influence. Acridine orange, which is slightly less efficient than proflavine on native DNA, induces an important peroxide radical formation in poly(dG).poly(dC) but has no action on the poly(dA).poly(dT)polymer.

Induction of cytoplasmically inherited respiration-deficient ('petite') mutants by photodynamic action of acridine compounds

All acridines used (acriflavine, proflavine, acridine orange and 3-azido-10-methylacridinium chloride) produced killing in yeast cells when activated with visible light. Acriflavine, proflavine and 3-azido-10-methylacridinium chloride, but not acridine orange, produced petite and sectored colonies. Both cell killing and petite induction by light activation of acriflavine resulted apparently from photodynamic action mediated by singlet oxygen (1O2) since the effect were prevented by either sodium azide or anaerobiosis. The biological effects of 3-azido-10-methylacridinium chloride, which was developed as a potential photoaffinity probe for studying the binding and biological effects of acridines, appeared to be due to a photodynamic action analogous to that of acriflavine. Sodium azide or anaerobiosis prevented the light-activated effects of 3-azido-10-methylacridinium chloride despite the fact that the initial chemical breakdown of the azido derivative induced by light was not affected. Cells suspended in D2O demonstrated an enhanced response to 3-azido-10-methylacridinium chloride with irradiation. These results indicate that singlet oxygen mediates the light-activated biological effects of both acriflavine and 3-azido-10-methylacridinium chloride.

Dimethylsulfoxide increases the survival and lysosomal stability of mouse peritoneal macrophages exposed to low-LET ionizing radiation and/or ionic iron in culture

Reactive oxygen-derived free radicals form excessively during irradiation of biological structures, but also normally in many cellular oxidative processes, albeit in small amounts. Unless scavenged by protective mechanisms, such radicals may induce peroxidation of polyunsaturated fatty acids resulting in membrane damage. The process may be catalysed to a considerable extent by transitional metals with the capacity to form redox systems, such as Fe3+ in equilibrium Fe2+. In the present study, it is shown that radiation by X-rays and/or exposure to ionic iron (Fe3+) causes decreased survival in parallel with lysosomal labilization of cultured mouse peritoneal macrophages (MPMs). The latter event was demonstrated as a reduced capacity of lysosomes in living MPMs to retain acridine orange during photo-oxidative stress caused by continuous exposure to blue light of short wavelength. The effects of X-irradiation, and/or lysosomal iron-loading, could be counteracted by the addition of the .OH-scavenging drug dimethylsulfoxide (DMSO) to the cell culture medium. The findings suggest that X-irradiation may damage certain sensitive G0 cells, such as Kupffer cells, serous cells of salivary glands and old macrophages, which normally have substantial concentrations of metals within their vacuolar apparatus, possibly by lysosomal damage involving .OH-mediated lipid peroxidation.

The role of active oxygen (1O2 and O(2)) induced by crude coal tar and its ingredients used in photochemotherapy of skin diseases

Crude coal tar (CCT) and certain photoreactive ingredients of CCT are photosensitizing agents used in the treatment of skin diseases (psoriasis, atopic eczema, etc.). Limited information is available in elucidating the mode of action of CCT in clearing psoriasis or causing skin photosensitization reactions. The production of singlet oxygen (1O2) and superoxide radicals (O(2) or HO2), the formation of interstrand cross-links (ICL) in DNA, and the skin photosensitization reaction caused by CCT or the ingredients present in tar preparations have been examined. Both type I (oxygen-independent) and type II (sensitized reactions requiring molecular oxygen) reactions are induced by CCT. Our data show that CCT and some of the photoreactive ingredients present in CCT produce 1O2, O(2), and ICL in DNA upon exposure to UVA radiation. Based on the equivalent concentration, the efficiency of various agents to produce 1O2 was of the following order: hematoporphyrin greater than phenanthridine greater than acridine greater than methylene blue greater than CCT greater than fluoranthrene greater than anthracene greater than pyrene greater than 8-methoxypsoralen greater than anthralin greater than chloroquine greater than anthralin dimer. The O(2) formation with CCT and its ingredients was also of the same order except for anthracene which was found to be a strong producer of O(2). The therapeutic effectiveness of CCT appears to be due to: (a) its cytotoxic effects, and (b) the production of 1O2, O(2), and ICL by CCT and its photoreactive ingredients. The skin photosensitizing (smarting, edema, and erythema responses) and carcinogenic properties of CCT may also be related to the production of 1O2 and O(2) and the formation of ICL which appear to be responsible for inducing the damage to the DNA and cell membrane.

Toxicity of activated oxygen: lack of dependence on membrane unsaturated fatty acid composition

Membrane unsaturated fatty acid oxidation has been suggested as a mechanism of toxicity for a variety of activated oxygen species. We have tested this hypothesis by manipulating the fatty acid composition of an Escherichia coli mutant that is unable to synthesize unsaturated fatty acids. To provide a wide range of susceptibility to membrane oxidation we have replaced the naturally occurring monoenoic acyl chains with cyclopropanes to greatly reduce the unsaturation level and with linoleate to increase the membrane unsaturation. These cultures were treated with ozone, hydrogen peroxide, singlet oxygen and paraquat. In no case was there substantial protection from toxicity afforded by cyclopropanes nor was there enhancement of toxicity to cells with the polyunsaturated membranes. We suggest, therefore, that oxidation of membrane unsaturated fatty acids is not an essential component of the toxicity to E. coli of active oxygen species.

Evidence for the involvement of activated oxygen in fungal degradation of lignocellulose

Oxygen has been shown to be necessary as a cosubstrate for the fungal degradation of lignins. In this work, the active forms of oxygen were tentatively identified in three ways: --effect of chemically generated active radicals and molecular species on lignocellulosic complexes, --use of activated oxygen scavengers in culture media of ligninolytic fungi, --characterization of active forms of oxygen by specific reactions. The data obtained strongly suggest that two main oxygen species are involved, namely OH radical and singlet oxygen (1O2). Chemical or enzymic scavengers inhibit the degradation of lignocelluloses by Phanerochaete chrysosporium. The fungus has been demonstrated to synthesize OH.

Effects of sodium azide on phototaxis of the blue-green alga Anabaena variabilis and consequences to the two-photoreceptor systems-hypothesis

Experiments with sodium azide support the earlier report that two different photoreceptor systems participate in the absorption of the phototactically active light in Anabaena variabilis. The one of them, represented by the phycobiliproteins and chlorophyll a, is responsible for positive and negative phototaxis around 440 nm and between 580 and 700 nm. This system is sensitive to sodium azide which is able to reverse the negative reaction at high fluence rates to a positive one. The second one which absorbs light between 500 and 560 nm and above 700 nm is insensitive to azide. It triggers only negative responses in absence and presence of azide as well. P750 is obviously not a photoreceptor pigment of this system, since there is no indication for its occurrence in Anabaena. Even photobleaching of the photosynthetic pigments at high fluence rates is prevented by azide. The noncyclic photosynthetic electron transport is not severely inhibited by azide because photokinesis is only in part impaired. Therefore, the hypothesis is suggested that the phototactic reaction-sign reversal generator of Anabaena is controlled by the level of an active oxygen species, probably singlet oxygen, which is quenched by azide.

Comparative mutagenicity of 4 DNA-intercalating agents in L5178Y mouse lymphoma cells

The mutagenicity of 4 known intercalating agents acridine orange (AO), quinacrine mustard (QM), proflavin (PF) and ethidium bromide (EB) has been investigated in L5178Y mouse lymphoma cells. Methyl methanesulfonate (MMS) was used as a positive control in these studies. AO, QM and PF induced mutation in the excess thymidine- and thioguanine-selective systems. These 3 compounds were negative in the ouabain- and cytosine-arabinoside-selective systems while EB was positive only in the cytosine arabinoside system. It would appear that the EB-induced mutagenesis is different from that of AO, QM and PF though all are intercalating agents. Since the molecular origin of cytosine arabinoside mutants is unknown, further interpretation of the EB results is not possible.