Showing papers in "Journal of Photochemistry and Photobiology B-biology in 2002"
TL;DR: Different strategies, including polymer-PS conjugation or encapsulation of the drug in colloidal carriers such as oil-dispersions, liposomes and polymeric particles, have been investigated to improve tumour targeting and to minimize the side effects.
Abstract: In photodynamic therapy, one of the problems limiting the use of many photosensitizers (PS) is the difficulty in preparing pharmaceutical formulations that enable their parenteral administration. Due to their low water solubility, the hydrophobic PS cannot be simply injected intravenously. Different strategies, including polymer-PS conjugation or encapsulation of the drug in colloidal carriers such as oil-dispersions, liposomes and polymeric particles, have been investigated. Although these colloidal carriers tend to accumulate selectively in tumour tissues, they are rapidly taken up by the mononuclear phagocytic system. In order to reduce this undesirable uptake by phagocytic cells, long-circulating carriers that consist of surface modified carriers have been developed. Moreover, considerable effort has been directed towards using other types of carriers to improve tumour targeting and to minimize the side effects. One of the approaches is to entrap PS into the lipophilic core of low-density lipoproteins (LDL) without altering their biological properties. The LDL receptor pathway is an important factor in the selective accumulation of PS in tumour tissue owing to the increased number of LDL receptors on the proliferating cell surface. Specific targeting can also be achieved by binding of monoclonal antibodies or specific tumour-seeking molecules to PS or by the coating of PS loaded carriers.
840 citations
TL;DR: The photodegradation of pesticides is reviewed, with particular reference to the studies that describe the mechanisms of the processes involved, the nature of reactive intermediates and final products.
Abstract: The photodegradation of pesticides is reviewed, with particular reference to the studies that describe the mechanisms of the processes involved, the nature of reactive intermediates and final products. Potential use of photochemical processes in advanced oxidation methods for water treatment is also discussed. Processes considered include direct photolysis leading to homolysis or heterolysis of the pesticide, photosensitized photodegradation by singlet oxygen and a variety of metal complexes, photolysis in heterogeneous media and degradation by reaction with intermediates generated by photolytic or radiolytic means.
563 citations
TL;DR: The central theme of the work was the investigation of the effectiveness of the various screening compounds from the different species studied in order to gain some perspective of the evolutionary adaptations from lower to higher plant forms.
Abstract: We analysed and compared the functioning of UV-B screening pigments in plants from marine, fresh water and terrestrial ecosystems, along the evolutionary line of cyanobacteria, unicellular algae, primitive multicellular algae, charophycean algae, lichens, mosses and higher plants, including amphibious macrophytes. Lichens were also included in the study. We were interested in the following key aspects: (a) does the water column function effectively as an ‘external UV-B filter’?; (b) do aquatic plants need less ‘internal UV-B screening’ than terrestrial plants?; (c) what role does UV screening play in protecting the various plant groups from UV-B damage, such as the formation of thymine dimers?; and (d) since early land ‘plants’ (such as the predecessors of present-day cyanobacteria, lichens and mosses) experienced higher UV-B fluxes than higher plants, which evolved later, are primitive aquatic and land organisms (cyanobacteria, algae, lichens, mosses) better adapted to present-day levels of UV-B than higher plants? Furthermore, polychromatic action spectra for the induction of UV screening pigments of aquatic organisms have been determined. This is relevant for translating ‘physical’ radiation measurements of solar UV-B into ‘biological’ and ‘ecological’ effects. From the action spectra, radiation amplification factors (RAFs) have been calculated. These action spectra allow us to determine any mitigating or antagonistic effects in the ecosystems and therefore qualify the damage prediction for the ecosystems under study. We summarize and discuss the main results based on three years of research of four European research groups. The central theme of the work was the investigation of the effectiveness of the various screening compounds from the different species studied in order to gain some perspective of the evolutionary adaptations from lower to higher plant forms. The induction of mycosporine-like amino acids (MAAs) was studied in the marine dinoflagellate Gyrodinium dorsum, the green algal species Prasiola stipitata and in the cyanobacterium Anabaena sp. While visible (400–700 nm) and long wavelength UV-A (315–400 nm) showed only a slight effect, MAAs were effectively induced by UV-B (280–315 nm). The growth of the lower land organisms studied, i.e. the lichens Cladina portentosa, Cladina foliacaea and Cladonia arbuscula, and the club moss Lycopodiumannotinum, was not significantly reduced when grown under elevated UV-B radiation (simulating 15% ozone depletion). The growth in length of the moss Tortula ruralis was reduced under elevated UV-B. Of the aquatic plants investigated the charophytes Chara aspera showed decreased longitudinal growth under elevated UV-B. In the ‘aquatic higher plants’ studied, Ceratophyllum demersum, Batrachium trichophyllum and Potamogeton alpinus, there was no such depressed growth with enhanced UV-B. In Chara aspera, neither MAAs nor flavonoids could be detected. Of the terrestrial higher plants studied, Fagopyrum esculentum, Deschampsia antarctica, Vicia faba, Calamagrostis epigejos and Carex arenaria, the growth of the first species was depressed with enhanced UV-B, in the second species length growth was decreased, but the shoot number was increased, and in the latter two species of a dune grassland there was no reduced growth with enhanced UV-B. In the dune grassland species studied outdoors, at least five different flavonoids appeared in shoot tissue. Some of the flavonoids in the monocot species, which were identified and quantified with HPLC, included orientin, luteolin, tricin and apigenin. A greenhouse study with Vicia faba showed that two flavonoids (aglycones) respond particularly to enhanced UV-B. Of these, quercetin is UV-B inducible and mainly located in epidermal cells, while kaempferol occurs constitutively. In addition to its UV-screening function, quercetin may also act as an antioxidant. Polychromatic action spectra were determined for induction of the UV-absorbing pigments in three photosynthetic organisms, representing very different taxonomic groups and different habitats. In ultraviolet photobiology, action spectra mainly serve two purposes: (1) identification of the molecular species involved in light absorption; and (2) calculation of radiation amplification factors for assessing the effect of ozone depletion. Radiation amplification factors (RAFs) were calculated from the action spectra. In a somewhat simplified way, RAF can be defined as the percent increase of radiation damage for a 1% depletion of the ozone layer. Central European summer conditions were used in the calculations, but it has been shown that RAF values are not critically dependent on latitude or season. If only the ultraviolet spectral region is considered, the RAF values obtained are 0.7 for the green alga Prasiola stipitata, 0.4 for the dinoflagellate Gyrodinium dorsum, and 1.0 for the cyanobacterium Anabaena sp. In the case of P. stipitata, however, the effect of visible light (PAR, photosynthetically active radiation, 400–700 nm) is sufficient to lower the RAF to about 0.4, while the PAR effect for G. dorsum is negligible. RAFs for some damage processes, such as for DNA damage (RAF=2.1 if protective effects or photorepair are not considered [1]), are higher than those above. Our interpretation of this is that if the ozone layer is depleted, increased damaging radiation could overrule increased synthesis of protective pigments. In addition to investigating the functional effectiveness of the different screening compounds, direct UV effects on a number of key processes were also studied in order to gain further insight into the ability of the organisms to withstand enhanced UV-B radiation. To this end, the temperature-dependent repair of cyclobutane dimers (CPD) and (6–4) photoproducts induced by enhanced UV-B was studied in Nicotiana tabacum, and the UV-B induction of CPD was studied in the lichen Cladonia arbuscula [2]. Also, photosynthesis and motility were monitored and the response related to the potential function of the screening compounds of the specific organism.
394 citations
TL;DR: It is suggested that ascorbic acid exhibited significantly higher protective efficiency with respect to DNA strand breaks and survival than NAC while NAC appears to be especially effective in defending the photosynthetic apparatus from oxidative damage.
Abstract: Reactive oxygen species (ROS) are involved in the oxidative damage of the cyanobacterium Anabaena sp. caused by UV-B (280-315 nm) radiation. UV-B-induced overproduction of ROS as well as the oxidative stress was detected in vivo by using the ROS-sensitive probe 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA). Thiobarbituric acid reactive substances (TBARS) and fluorometric analysis of DNA unwinding (FADU) methods were adapted to measure lipid peroxidation and DNA strand breaks in Anabaena sp. Moderate UV-B radiation causes an increase of ROS production, enhanced lipid peroxidation and DNA strand breaks, yielding a significantly decreased survival. In contrast, the supplementation of UV-A in our work only showed a significant increase in total ROS levels and DNA strand breaks while no significant effect on lipid peroxidation, chlorophyll bleaching or survival was observed. The presence of ascorbic acid and N-acetyl-L-cysteine (NAC) reversed the oxidative stress and protected the organisms from chlorophyll bleaching and the damage of photosynthetic apparatus induced by UV-B significantly, resulting in a considerably higher survival rate. Ascorbic acid also exhibited a significant protective effect on lipid peroxidation and DNA strand breaks while NAC did not show a substantial effect. These results suggest that ascorbic acid exhibited significantly higher protective efficiency with respect to DNA strand breaks and survival than NAC while NAC appears to be especially effective in defending the photosynthetic apparatus from oxidative damage.
290 citations
TL;DR: The results suggest that the more effective induction of T cell apoptosis can be responsible for the greater clinical efficacy of XeCl laser compared to NB-UVB.
Abstract: Earlier we reported that a 308-nm xenon chloride (XeCl) UVB laser is highly effective for treating psoriasis. As ultraviolet B light seems to cause T cell apoptosis, in the present study we studied the ability of the XeCl laser to induce T-cell apoptosis in vitro, and then compared the apoptosis-inducing capacities of narrow-band UVB (NB-UVB) light and the XeCl laser. The role of laser impulse frequency and intensity in the therapeutical and apoptosis-inducing efficacy of XeCl laser was also investigated. Both XeCl laser and NB-UVB induced T cell apoptosis, but quantitative induction was greater with XeCl laser. Changes in the frequency and intensity of impulses of XeCl laser did not influence its therapeutic and T cell apoptosis-inducing efficacy. These results suggest that the more effective induction of T cell apoptosis can be responsible for the greater clinical efficacy of XeCl laser compared to NB-UVB. Additionally, the optical properties of the XeCl laser (a monochromatic, coherent, pulse-mode laser; easier precise dosimetry, there are no ‘contaminating’ wavelengths) can make this laser light an ideal tool for studies of the mode of action of UVB light.
149 citations
TL;DR: It was found that only the dendritic mono-adduct inhibits cell growth, whereas the tris-malonic acid adduct has little effect and it is proposed that the two fullerene derivatives may interact with the cell membrane in different ways thus causing the observed effects.
Abstract: The cytotoxic and photocytotoxic effects of two water-soluble fullerene derivatives, a dendritic C60 mono-adduct and the malonic acid C60 tris-adduct were tested on Jurkat cells. Cell growth and vitality were determined by a cell counting and staining technique. After 2 weeks cultivation in the presence of the fullerene derivatives, it was found that only the dendritic mono-adduct inhibits cell growth (within 2 weeks the cell number decreased to 19%), whereas the tris-malonic acid adduct has little effect. The growth inhibition is reversible; cultivating the same cells further in the absence of fullerene, the cell number increased to 106.4%. Other experiments showed that these fullerene derivatives become toxic when irradiated with UVA or UVB light. The cell death is mainly caused by membrane damage and it is UV dose-dependent. Tris-malonic acid fullerene was found to be more phototoxic than the dendritic derivative. This result is in contrast to the singlet oxygen quantum yields determined for the two compounds. We propose that the two fullerene derivatives may interact with the cell membrane in different ways thus causing the observed effects. Further experiments will be done to determine the location and concentration of the two compounds in and on the cells.
134 citations
TL;DR: The increased UV-B induces the production of ROS in vivo detected by using the ROS-sensitive probe 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA), and ROS formation was greatly enhanced by the addition of methyl viologen due to the fact that this redox system diverts electrons from PSI to oxygen and thus forms ROS.
Abstract: Reactive oxygen species (ROS) are involved the damage of living organisms under environmental stress including UV radiation. Cyanobacteria, photoautotrophic prokaryotic organisms, also suffer from increasing UV-B due to the depletion of the stratospheric ozone layer. The increased UV-B induces the production of ROS in vivo detected by using the ROS-sensitive probe 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA). Ascorbic acid and N-acetyl-L-cysteine (NAC) scavenged ROS effectively, while alpha-tocopherol acetate or pyrrolidine dithiocarbamate (PDTC) did not. The presence of rose bengal and hypocrellin A increased the ROS level by photodynamic action in the visible light. The presence of the herbicide, 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU), increased ROS production slightly, and ROS formation was greatly enhanced by the addition of methyl viologen due to the fact that this redox system diverts electrons from PSI to oxygen and thus forms ROS. UV-B induces ROS generation by photodynamic action and inhibition of the electron transport by damaging the electron receptors or enzymes associated with the electron transport chain during photosynthesis.
127 citations
TL;DR: Usnic acid resulted to be the best UVB filter, with an in vivo protection factor similar to Nivea sun Spray LSF 5, and most of the single compounds studied in vitro resulted to have higher or similar filtering power than octylmethoxycinnamate.
Abstract: Natural substances extracted from lichens and boldo tree were tested in vivo and in vitro as possible UV-light filters. The protection factors were compared with that found for the references: Nivea sun Spray LSF 5, octylmethoxycinnamate (OMC) and 4-tert.-butyl-4'-methoxy dibenzoylmethane (BM-DBM). The stability of the single compounds was studied through UV-Vis spectroscopy. Usnic acid resulted to be the best UVB filter, with an in vivo protection factor similar to Nivea sun Spray LSF 5. Most of the single compounds studied in vitro resulted to have higher or similar filtering power than octylmethoxycinnamate. The protection factors as well as the good UV-light absorption of their photo-products suggest that these natural substances may be useful as new filters in sun-screen preparations.
110 citations
TL;DR: The ROS assay appears to be feasible for determining sensitizer concentration in regular grip biopsy tissue samples, and an excellent correlation was found between fluorescence measurement by OFS and ROS determination for m-THPC.
Abstract: Photodynamic therapy induces the production of reactive oxygen species (ROS) within tissues exposed to laser light after administration of a sensitizer. In the context of continuing clinical and commercial development of chemicals with sensitizing properties, a minimally invasive assay is needed to determine the tissue kinetics of fluorescent or non-fluorescent photoreactive drugs. The level of ROS was determined ex vivo from 1 mm 3 biopsy samples using 2′-7′ dichlorofluorescin diacetate (DCFH-DA), a fluorescent probe which was converted into highly fluorescent dichlorofluorescein (DCF) in the presence of ROS. This assay was tested on meta(tetrahydroxyphenyl)chlorin ( m -THPC, FOSCAN ® ), a powerful and fluorescent sensitizer, and bacteriochlorophyll derivative WST09 (TOOKAD ® ), a near-infrared absorbing sensitizer that is only slightly fluorescent. In conjunction with the ROS assay, the tissue accumulation of m -THPC was determined on biopsy samples using an optic fibre spectrofluorometer (OFS). DCF fluorescence was proportional to the level of oxidation induced by horseradish peroxidase used as a control and to the concentration (range: 0–5 μg ml −1 ) of both selected photosensitizers irradiated in a tube together with DCFH. Regardless of the organ studied, an excellent correlation was found between fluorescence measurement by OFS and ROS determination for m -THPC. m -THPC (2 mg kg −1 iv) accumulation in tumour tissues was best after 48 h, and the best signal was obtained in liver. With non-fluorescent WST09 (2 mg kg −1 ), ROS determination showed the best tumour uptake 48 h after injection, with a tumour/muscle ratio of 5.4. The ROS assay appears to be feasible for determining sensitizer concentration in regular grip biopsy tissue samples.
108 citations
TL;DR: UV-B treatment resulted in the increase in the transpiration rate and consequently the decrease in water use efficiency (WUE), which affected water relations and production of buckwheat, but not the potential of seeds for germination.
Abstract: The effect of enhanced UV-B radiation on buckwheat (Fagopyrum esculentum Moench. variety ‘Darja’), an important high elevation crop, was studied in order to estimate its vulnerability in changing UV-B environment. Plants were grown in outdoor experiments from July to October under reduced and ambient UV-B levels, and an UV-B level simulating 17% ozone depletion in Ljubljana. During the development the following parameters were monitored: light saturated photosynthetic activity, transpiration, potential and effective photochemical efficiencies of photosystem II, the contents of photosynthetic pigments and methanol soluble UV-B absorbing compounds. At the end of the experiment, growth rate and production of seeds were estimated. In the following growth season the seeds collected from plants exposed to different UV-B treatments were tested for germination capacity. Total UV-B absorbing compounds during plant development were increased by UV-B radiation, photosynthetic pigments (chlorophyll a and b and carotenoids) decreased. Photosynthetic rate was lowered in an early stage of development. UV-B treatment resulted in the increase in the transpiration rate and consequently the decrease in water use efficiency (WUE). The disturbances in water economy and in photosynthesis affected the reproduction potential negatively; the production of seeds in plants cultivated under ambient and enhanced UV-B was 57 and 39% of the production of specimens treated with reduced UV-B, respectively. The germination of seeds collected from treated plants revealed on average about 95% success, independently of the treatment, but the time needed for germination was the shortest for seeds developed under enhanced UV-B level treatment. Enhanced UV-B radiation affected water relations and production of buckwheat, but not the potential of seeds for germination. This is the final, accepted and revised manuscript of this article. Use alternative location to go to the published article. Requires subscription. (Less)
90 citations
TL;DR: The preliminary results of cell viability test indicate hypocrellins can effectively damage the Hela cells under two-photon illumination, and suggest that the hypocrellin can be potential two- photon phototherapeutic agents.
Abstract: The photophysical and photochemical properties of hypocrellins (HA and HB) are examined with two-photon excitations at 800 nm using femtosecond pulses from a Ti:sapphire laser. The two-photon excited fluorescence spectra of HA and HB are very similar to those obtained by one-photon excitation, which may indicate that the two-photon induced photodynamic processes of hypocrellins are similar to one-photon induced photodynamic processes. The two-photon excitation cross sections of HA and HB are measured at 800 nm as about 34.8×10 −50 cm 4 s/photon and 21.3×10 −50 cm 4 s/photon, respectively. The large two-photon cross sections of both HA and HB, suggest that the hypocrellins can be potential two-photon phototherapeutic agents. As an example for two-photon photodynamic therapy of hypocrellins, we also further examine the cell-damaging effects of HA upon two-photon illumination. Our preliminary results of cell viability test indicate hypocrellins can effectively damage the Hela cells under two-photon illumination.
TL;DR: Results for suspension-cultured tobacco cells indicated that formation of CPDs and 6-4PPs induced by UV-B was temperature-independent in a non-cellular system.
Abstract: Two photoproducts of DNA damage, i.e. cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts (6-4PPs), induced by UV-B radiation in suspension-cultured tobacco cells were quantified by enzyme-linked immunosorbent assay (ELISA) with monoclonal antibodies. CPDs and 6-4PPs were induced in tobacco cells by UV-B radiation. Photorepair of CPDs was faster than that of 6-4PPs. UV-B radiation induces formation of CPDs and 6-4PPs even at 0 °C, but low temperature significantly decreases the UV-B-induced (in contrast to UV-C-induced) formation of CPDs and 6-4PPs. Low temperature also retarded the removal of CPDs and 6-4PPs under white light, and almost no photorepair of CPDs and 6-4PPs was detected at 0 °C. When purified DNA from tobacco cells grown in darkness was irradiated with UV-B, formation of CPDs and 6-4PPs took place at the same speed at different temperatures. It indicated that formation of CPDs and 6-4PPs induced by UV-B was temperature-independent in a non-cellular system. Based on our results for suspension-cultured tobacco cells, not only the photorepair but also UV-B-induced formation of CPDs and 6-4PPs are temperature-dependent.
TL;DR: Results indicated that in Cladonia, UV-B radiation induces the accumulation of phenolic compounds that may have a protective role.
Abstract: The response of the lichen, Cladonia arbuscula (Wallr.) Flot. ssp. mitis (Sandst.) Ruoss to enhanced UV-B (280-315 nm) radiation was investigated with respect to: (a) changes in phenolic content; (b) differential pigment accumulation under visible and UV radiation with increasing distance from thallus apices; and (c) the internal distribution of UV-B radiation within the thallus measured with quartz optical fibres. In a short-term experiment, lichens were exposed for 7 days in a growth chamber to visible light with or without additional UV-B radiation. For a longer term experiment, lichens were grown outdoors under both natural UV radiation, and supplemental UV-A (315–400 nm)+UV-B provided by lamps. Controls were placed under filters that removed the radiation below 290 nm from the natural sunlight. The concentration of total phenolic compounds was measured spectrophotometrically at the termination of the experiments, in different parts of the lichen podetia. UV-exposed lichens showed increased accumulation of phenolics compared to those not grown under UV. At the termination of the long-term experiment, fibre optic measurements of the penetration of radiation into lichen thallus reflected the influence of growth under UV radiation, whereby UV was more strongly attenuated as compared to that in lichens not exposed to enhanced levels of UV-B radiation. Results indicated that in Cladonia, UV-B radiation induces the accumulation of phenolic compounds that may have a protective role. In addition, the morphological distribution of phenolic compounds was different under visible and supplemental UV-B radiation. Internal radiation measurements served to visualise the attenuation of radiation with thallus depth for different wavelengths in the UV-B waveband.
TL;DR: It was found that transient changes in calcium caused by light can modulate NGF release from the myotubes and also affect the nerves innervating the muscle, and the NGF is probably responsible for the beneficial effects of low-level light.
Abstract: Low energy laser irradiation therapy in medicine is widespread but the mechanisms are not fully understood. The aim of the present study was to elucidate the mechanism by which the light might induce therapeutic effects. Skeletal muscle cultures were chosen as a target for light irradiation and nerve growth factor (NGF) was the biochemical marker for analysis. It was found that there is a transient elevation of intracellular calcium in the myotubes immediately after irradiation (P<0.001). Preincubation of the myotubes with either the photosensitizers 5-amino-levulinic acid (5-ALA), or with hematoporphyrin (Hp) enhanced the elevation of cytosolic calcium (P<0.001) after helium/neon irradiation (633 nm) with an energy of 3 J/cm2. In addition, helium/neon irradiation augmented the level of NGF mRNA fivefold and increased NGF release to the medium of the myotubes. Thus, it is speculated that transient changes in calcium caused by light can modulate NGF release from the myotubes and also affect the nerves innervating the muscle. The NGF is probably responsible for the beneficial effects of low-level light.
TL;DR: Results indicate that constitutive levels of flavonoids in these grass and sedge species are adequately high to protect them against ambient and elevated levels of solar UV-B radiation.
Abstract: An investigation was carried out to find whether enhanced levels of UV-B radiation induce increased concentrations of flavonoids in the leaves of the grass species Deschampsia antarctica, Deschampsia borealis and Calamagrostis epigeios and the sedge Carex arenaria. Whether the enhanced levels of UV-B influenced the proportions of the various flavonoids in the leaves was also studied. Increased flavonoid concentrations would improve the UV-B shielding of UV-B susceptible tissues. Using HPLC analysis the flavonoids orientin and luteolin were identified in D. antarctica, orientin in D. borealis and tricin in C. arenaria. Neither flavonoid concentrations nor the proportion of the various flavonoids in climate room grown D. antarctica and D. borealis plants differed between individuals grown under 0, ambient or elevated UV-B levels. After 12 weeks of growth biomass production and shoot-to-root ratios of D. antarctica were not affected by elevated UV-B radiation. Greenhouse grown C. epigeios plants contained higher concentrations and different proportions of flavonoids grown under elevated levels of UV-B than when grown under ambient or 0 UV-B. In C. epigeios plants grown in their natural habitat in the field under ambient or elevated levels of UV-B, flavonoid concentrations and proportions were the same in plants from both treatments. In the leaves of the sedge C. arenaria grown in a greenhouse flavonoid concentrations and proportions were not affected by UV-B radiation. Leaves were harvested four times during the growing season from C. arenaria plants grown in their natural habitat in the field under ambient or elevated levels of UV-B. Leaves harvested in January contained higher concentrations of flavonoids when grown under elevated UV-B than when grown under ambient UV-B radiation. In leaves harvested in May, September and December flavonoid concentrations were the same in plants grown under ambient or elevated UV-B. The proportion of the different flavonoids was the same for both treatments in all months. These results indicate that constitutive levels of flavonoids in these grass and sedge species are adequately high to protect them against ambient and elevated levels of solar UV-B radiation.
TL;DR: The results of this study showed that Photofrin, a porphyrin derivative which is presently used as a tumor-photosensitizing agent in photodynamic therapy (PDT), can also act as an efficient tumor radiosensitizer.
Abstract: The use of ionizing radiation for tumor treatment represents a well established therapeutic modality. The efficiency and selectivity of radiotherapeutic protocols can be often enhanced by the addition of specific chemical compounds that optimise the response of the tumor to the incident radiation as compared with peritumoral tissue districts. The results of this study showed that Photofrin, a porphyrin derivative which is presently used as a tumor-photosensitizing agent in photodynamic therapy (PDT), can also act as an efficient tumor radiosensitizer. To test this possibility, we used nude mice subcutaneously implanted with human bladder cancer RT4. The mice were injected with different porphyrin-type photosensitizing agents, including Photofrin, 5-aminolevulinic acid, chlorin e(6), haematoporphyrin, protoporphyrin, Zn-tetrasulphophtalocyanine, and irradiated with 5 and 15 Gy using a Siemens X-ray device. Even though all the porphyrins accumulated in significant amounts in the neoplastic lesion, only Photofrin significantly improved the response of the tumor to irradiation by increasing the doubling time of the tumor volume from 6.2 days in the untreated control group to 10.9 days in the 5 and 15 Gy-irradiated groups. The tumor response was maximal with injected Photofrin doses of 7.5 mg/kg, and was not further enhanced by injection of higher doses. Our hypothesis is, that the radiosensitizing effect of Photofrin seems to be due to some oligomeric constituents which could specifically react with radiogenerated-radicals thereby amplifying the effect of the X-ray radiation.
TL;DR: The possible generation mechanism was explored by Electron Paramagnetic Resonance (EPR) and time-resolved transient spectra techniques, showing that singlet oxygen (1O2) and superoxide radical anion (O2*-) were produced via energy transfer and electron transfer, respectively and the application of HB-TiO2 chelate in environment protection and bacteria sterilization was implied.
Abstract: TiO2 semiconductor colloids have been successfully employed in environmental clean-up, antibacterial and bactericidal action under ultraviolet light due to its strong redox ability and high yield of active oxygen species (1O2, O2*-), *OOH) generation. Hypocrellin B, isolated from Hypocrella bambusae (B.et.Br) Sacc, a natural pigment with strong and broad absorption over the visible light region, was used in our work in an attempt to extend the photoresponse of TiO2 to visible light and maintain the high generation of active oxygen under visible light illumination. The formation of the HB-TiO2 chelate was characterized by UV-Vis and surface enhanced raman spectroscopy (SERS) and it was found that the chelate still had high efficiency of active oxygen generation. The possible generation mechanism was explored by Electron Paramagnetic Resonance (EPR) and time-resolved transient spectra techniques, showing that singlet oxygen (1O2) and superoxide radical anion (O2*-)) were produced via energy transfer and electron transfer, respectively. The application of HB-TiO2 chelate in environment protection and bacteria sterilization was implied.
TL;DR: CY-III (3,3'-diethylcarbothiocayanine iodide) and CY-II appear to be promising photosensitizers, in spite of previous reports on the inefficiency of the former cyanine, and the rapid photobleaching of the latter compound.
Abstract: The present work has been carried out to obtain detailed information about the photophysical and photobiological properties of selected cyanines, in view of their possible use as photosensitizing agents. All the cyanines studied by us except CY-IV (3,3′-diethyl-4,4′-oxacarbocyanine), expressed an accelerated photobleaching in aqueous medium, a poor generation of singlet oxygen, and a relative weak photosensitizing activity towards albumin. On the cellular level, all cyanines exhibited a significant phototoxicity towards Balb/c 3T3 cells, upon irradiation with a total fluence of 30 J/cm 2 . CY-III (3,3′-diethylcarbothiocayanine iodide) and CY-II (1,1′-diethyl-4,4′-carbocyanine iodide) appear to be promising photosensitizers, in spite of previous reports on the inefficiency of the former cyanine, and the rapid photobleaching of the latter compound.
TL;DR: To investigate the wavelength dependence of MAA synthesis in the marine dinoflagellate Gyrodinium dorsum, the organism was exposed to polychromatic radiation from a solar simulator for up to 72 h and the most effective wavelength range was around 310 nm.
Abstract: The synthesis or accumulation of mycosporine-like amino acids (MAAs) is an important UV tolerance mechanism in aquatic organisms. To investigate the wavelength dependence of MAA synthesis in the marine dinoflagellate Gyrodinium dorsum, the organism was exposed to polychromatic radiation (PAR and UV) from a solar simulator for up to 72 h. Different irradiance spectra were produced by inserting various cut-off filters between lamp and samples. A polychromatic action spectrum for the synthesis of MAA synthesis was constructed. PAR and long wavelength UV-A radiation showed almost no effect while the most effective wavelength range was around 310 nm. Shorter wavelengths where less effective in the induction of MAA synthesis. Wavelengths below 300 nm damaged the organisms severely as indicated by a decrease in chlorophyll a absorption.
TL;DR: It is concluded that this type of nido-carboranylporphyrin is a promising sensitizer for both the boron neutron capture therapy and the photodynamic therapy of tumors.
Abstract: The total synthesis of tetra(4-carboranylphenyl)porphyrins 4 and 6 and their zinc(II) complexes 5 and 7 are described. These compounds were characterized by analytical and spectroscopic methods and, in the case of 5, by X-ray crystallography. The water-soluble nido-carboranylporphyrins 6 and 7 were found to have low dark toxicity towards V79 hamster lung fibroblast cells, using a clonogenic assay (50% colony survival, CS50>300 μM). Upon light activation nido-carboranylporphyrin 6 effectively induced DNA damage in vitro. Two different methods were used to assess the extent of DNA damage: the super-coiled to nicked DNA and the alkaline Comet assay using human leukemia K562 cells. Significant PDT-induced DNA damage was observed for porphyrin 6 using both assays, compared to light-only and porphyrin-only experiments. It is concluded that this type of nido-carboranylporphyrin is a promising sensitizer for both the boron neutron capture therapy and the photodynamic therapy of tumors.
TL;DR: It is likely, therefore, that several chemical pathways contribute to the breakdown of dissolved ALA at physiological pH, and temperature studies of the formation kinetics of the UV absorbing product indicate that a complex formation process is involved.
Abstract: 5-Aminolevulinic acid (ALA) is being assessed for photodynamic therapy of cancer and other diseases worldwide. However, its stability properties in solution are not well understood yet. The breakdown of ALA in pH-buffered solutions was examined in this work. Solutions of ALA in PBS buffered to physiological pH were found to be unstable, leading to a breakdown product that absorbs photons around 278 nm. The ability of the solution to stimulate porphyrin production in cells is gradually lost upon breakdown, though the kinetics for this are different from those for formation of the UV absorbing product. It is likely, therefore, that several chemical pathways contribute to the breakdown of dissolved ALA at physiological pH. Temperature studies of the formation kinetics of the UV absorbing product also indicate that a complex formation process is involved.
TL;DR: Investigation of terrestrial microbial communities in micro-habitats covered by snow and ice in Antarctica shows that changing ice and snow covers cause relative changes in microbial UV exposure at least as great as those caused by changing ozone column abundance.
Abstract: Bacillus subtilis spore biological dosimeters and electronic dosimeters were used to investigate the exposure of terrestrial microbial communities in micro-habitats covered by snow and ice in Antarctica. The melting of snow covers of between 5- and 15-cm thickness, depending on age and heterogeneity, could increase B. subtilis spore inactivation by up to an order of magnitude, a relative increase twice that caused by a 50% ozone depletion. Within the snow-pack at depths of less than ∼3 cm snow algae could receive two to three times the DNA-weighted irradiance they would receive on bare ground. At the edge of the snow-pack, warming of low albedo soils resulted in the formation of overhangs that provided transient UV protection to thawed and growing microbial communities on the soils underneath. In shallow aquatic habitats, thin layers of heterogeneous ice of a few millimetres thickness were found to reduce DNA-weighted irradiances by up to 55% compared to full-sky values with equivalent DNA-weighted diffuse attenuation coefficients ( K DNA ) of >200 m −1 . A 2-mm snow-encrusted ice cover on a pond was equivalent to 10 cm of ice on a perennially ice covered lake. Ice covers also had the effect of stabilizing the UV exposure, which was often subject to rapid variations of up to 33% of the mean value caused by wind-rippling of the water surface. These data show that changing ice and snow covers cause relative changes in microbial UV exposure at least as great as those caused by changing ozone column abundance.
TL;DR: The wavelength-dependent induction of the synthesis of this substance was investigated using simulated solar radiation in combination with 15 cut-off and one broad-band filter, showing a clear maximum at 300 nm in the long-wavelength UV-B range, but there is still some induction caused by UV-A and PAR.
Abstract: The chlorophyte Prasiola stipitata produces a UV-absorbing substance with an absorption maximum at 324 nm. The wavelength-dependent induction of the synthesis of this substance was investigated using simulated solar radiation in combination with 15 cut-off and one broad-band filter. The algae were exposed from three different distances (89, 100 and 119 cm) to the solar simulator producing a maximum of 203.58, 1.24 and 46.86 W/m(2) and a minimum of 107.94, 0.64 and 24.44 W/m(2) irradiances for PAR, UV-B and UV-A, respectively. A polychromatic action spectrum was calculated from the pooled results showing a clear maximum at 300 nm in the long-wavelength UV-B range, but there is still some induction caused by UV-A and PAR. The ratio of the effectiveness from PAR to UV-A to UV-B amounts to 1:2:22.
TL;DR: The marine diatom Thalassiosira weissflogii was cultured under a light regime simulating the daily rise and fall of the sun, causing a daily cycle in non-photochemical quenching and chlororespiration is thought to cause the reduction of PQ and, as the PQ-pool is in equilibrium with Q(A), also a reduction ofQ(A).
Abstract: The marine diatom Thalassiosira weissflogii was cultured under a light regime simulating the daily rise and fall of the sun. The light regime caused a daily cycle in non-photochemical quenching. Remarkable were the changes in fluorescence directly after a light-to-dark transition that occurred in addition to the changes induced by non-photochemical quenching. A transient non-photochemical reduction of PQ and of QA was indicated by a transient increase in apparent Fo and by changes in the shape of the fluorescence induction curve. The observed changes developed approximately the first 100¯120 s after a light-to-dark transition and could be reversed by the application of far-red illumination. Chlororespiration is thought to cause the reduction of PQ and, as the PQ-pool is in equilibrium with QA, also a reduction of QA. The function and ecological relevance of chlororespiration are discussed. [KEYWORDS: Chlororespiration; Dynamic light; Electron transport; Fluorescence; Fluorescence induction; Thalassiosira weissflogii]
TL;DR: The results obtained can support the postulated earlier polarons and hopping model of conductivity in synthetic dopa-melanin and explain the long time-constants calculated from the photocurrent rise and decay curves.
Abstract: The photoconductivity effect in synthetic dopa-melanin polymer with relation to the charge hopping conduction has been investigated. Measurements of the rise and decay of photocurrents upon visible radiation (400-800 nm) and at temperatures of 293-326 K allowed the determination of the major trapping levels as follows: 56, 35 and 26 kJ/mol. Spectral response of the steady-state photocurrent in the range 367-1100 nm showed significant departures from the absorption spectrum of melanin. The high concentration of traps or recombination centers can explain the long time-constants calculated from the photocurrent rise and decay curves. The results obtained can support the postulated earlier polarons and hopping model of conductivity in synthetic dopa-melanin.
TL;DR: The highest tumour to normal skin PpIX ratio was observed 3 h after application of 8% ALA-Me, suggesting that light exposure should be performed at this time in order to achieve an optimal PDT effect in this tumour model.
Abstract: Accumulation of protoporphyrin IX (PpIX) was investigated in normal skin and UV-induced tumours in hairless mice after topical application of a cream containing 2, 8 or 16% of 5-aminolevulinic acid methyl ester (ALA-Me). Higher levels of PpIX were measured in tumours compared to normal skin. The maximal amount of PpIX was reached at 1.5, 3 and 4 h after 2, 8 and 16% ALA-Me application, respectively. Higher tumour to normal skin PpIX fluorescence ratios were measured after application of 8 and 16% ALA-Me than after application of 2%. After irradiation with a broad spectrum of visible light from a slide projector, more than 90% of PpIX was bleached by fluences of 36 and 48 J/cm2, at fluence rates of 10 and 40 mW/cm2 respectively. At these fluences, the PpIX photobleaching rate was significantly higher (P<0.05) in normal mouse skin than in tumours. In addition, for a given fluence, more PpIX was photobleached at the lower fluence rate (10 mW/cm2) than at the higher fluence rate (40 mW/cm2) in normal skin (P<0.001) as well as in tumours (P<0.05) after exposure to 24 J/cm2 of light. In conclusion, the highest tumour to normal skin PpIX ratio was observed 3 h after application of 8% ALA-Me, suggesting that light exposure should be performed at this time in order to achieve an optimal PDT effect in this tumour model.
TL;DR: The results indicate that the studied cyanobacterium, Anabaena sp.
Abstract: A polychromatic action spectrum for the induction of an ultraviolet-absorbing/screening mycosporine-like amino acid (MAA) has been determined in a filamentous and heterocystous nitrogen-fixing rice-field cyanobacterium, Anabaena sp. High-performance liquid chromatographic (HPLC) studies revealed the presence of only one type of MAA, which was identified as shinorine, a bisubstituted MAA containing both glycine and serine groups having a retention time at 2.8 min and an absorption maximum at 334 nm. Exposure of cultures to simulated solar radiation in combination with various cut-off filters (WG 280, 295, 305, 320, 335, 345, GG 400, 420, 455, 475, OG 515, 530, 570, RG 645, 665 and a broad-band filter, UG 11) clearly revealed that the induction of the MAA takes place only in the UV range. Photosynthetic active radiation (PAR) had no significant impact on MAA induction. The ratio of the absorption at 334 nm (shinorine) to 665 nm (chlorophyll a) and the action spectrum also showed the induction of MAA to be UV dependent peaking in the UV-B range at around 290 nm. The results indicate that the studied cyanobacterium, Anabaena sp. may protect itself from deleterious short wavelength solar radiation by its ability to synthesize a mycosporine-like amino acid in response to UV-B radiation and thereby screen the negative effects of UV-B.
TL;DR: Certain variations in the fluorescence and photochemical parameters of Cph1 with temperature of the sample and intensity of the excitation light and dependence of the emission spectra on excitation wavelength were observed and are interpreted as a manifestation of the Cph 1 heterogeneity which may be due to the existence of different conformers of the chromophore and photoproduct formation under excitationLight.
Abstract: Recombinant dimeric full-length Cph1 holophytochrome and its C-terminally-truncated monomeric species [Cph1Delta2, comprising the chromophore-bearing N-terminal sensory module (residues 1 to 514)] from the cyanobacterium Synechocystis expressed in E. coli and reconstituted in vitro with phycocyanobilin (PCB) were investigated with the use of fluorescence spectroscopy and photochemistry in the temperature range from 85 to 293 K. Holoprotein assembly in Cph1 apparently proceeds via intermediate states with the emission maximum at 680-690 nm (I685) and 700 nm (I700) and a half-life time, at room temperature, of < or =5 s. Conversion of the putative I685 into mature Cph1 involves relaxation of the chromophore into a more flexible conformation. Cph1 and Cph1Delta2 were closely similar in their spectroscopic and photochemical characteristics (position of the emission band and its width, character of the temperature dependence of the fluorescence and activation energy of the fluorescence decay, kinetics and extent of the Pr conversion at low and ambient temperatures), suggesting that there is no immediate effect of the C-terminus on the photochemical properties of the chromophore in Cph1 and that chromophore-chromophore interactions in the dimer are not significant. The latter is also supported by the lack of energy transfer from the phycoerythrobilin (PEB) to PCB in the mixed PEB/PCB adduct of Cph1. At the same time, certain variations in the fluorescence and photochemical parameters of Cph1 with temperature of the sample and intensity of the excitation light and dependence of the emission spectra on excitation wavelength were observed. These variations are interpreted as a manifestation of the Cph1 heterogeneity which may be due to the existence of different conformers of the chromophore and photoproduct formation under excitation light.
TL;DR: It is suggested that UV-A or UV-B irradiation alone or combined with MV cause considerable oxidative damage in E. gracilis cells, and rutin supplementation may suppress their adverse effects.
Abstract: The effects of ultraviolet radiation (UV-A: 320–400 nm and UV-B: 280–320 nm) and methyl viologen (MV) single or combined exposure, on the cell growth, viability and morphology of two strains of the unicellular flagellate Euglena gracilis, using the Z strain as a plant model and the achlorophyllous mutant SMZ strain as an animal model were investigated. Cell growth was not affected by MV only, whereas UV-A or UV-B single and combined exposure with MV inhibited the cell growth or decreased the viability. The SMZ strain had a higher number of abnormal cells than the Z strain after the third dose of UV-B was delivered simultaneously with MV. The abnormal cell number decreased when E. gracilis SMZ cells were preincubated with 100 μM rutin prior to the UV-B and MV exposure. There were higher abnormal cell numbers with groups exposed to UV rather than MV single exposure. Combined exposure to UV-B and 200 μM MV induced the highest levels of TBARS in both strains, and with the supplementation of rutin these high levels were suppressed. These results suggest that UV-A or UV-B irradiation alone or combined with MV cause considerable oxidative damage in E. gracilis cells, and rutin supplementation may suppress their adverse effects.
TL;DR: Results suggest that enhanced UV-B radiation will alter foliar flavonoid composition and concentrations in forest tree species, which could impact tissue protection, and ultimately, competition, herbivory or litter decomposition.
Abstract: Chromatographic analyses of foliage from several tree species illustrate the species-specific effects of UV-B radiation on both quantity and composition of foliar flavonoids. Pinus ponderosa, Quercus rubra and Pseudotsuga menziesii were field-grown under modulated ambient (1x) and enhanced (2x) biologically effective UV-B radiation. Foliage was harvested seasonally over a 3-year period, extracted, purified and the flavonoid fraction applied to a mu Bondapak/C(18) column HPLC system sampling at 254 nm. Total flavonoid concentrations in Quercus rubra foliage were more than twice (leaf area basis) that of the other species; Pseudotsuga menziesii foliage had intermediate levels and P. ponderosa had the lowest concentrations of total flavonoids. No statistically significant UV-B radiation-induced effects were found in total foliar flavonoid concentrations for any species; however, concentrations of specific compounds within each species exhibited significant treatment effects. Higher (but statistically insignificant) levels of flavonoids were induced by UV-B irradiation in 1- and 2-year-old P. ponderosa foliage. Total flavonoid concentrations in 2-year-old needles increased by 50% (1x ambient UV-B radiation) or 70% (2x ambient UV-B radiation) from that of 1-year-old tissue. Foliar flavonoids of Q. rubra under enhanced UV-B radiation tended to shift from early-eluting compounds to less polar flavonoids eluting later. There were no clear patterns of UV-B radiation effects on 1-year-old P. menziesii foliage. However, 2-year-old tissue had slightly higher foliar flavonoids under the 2x UV-B radiation treatment compared to ambient levels. Results suggest that enhanced UV-B radiation will alter foliar flavonoid composition and concentrations in forest tree species, which could impact tissue protection, and ultimately, competition, herbivory or litter decomposition.