Showing papers in "Journal of Photochemistry and Photobiology B-biology in 1999"
TL;DR: A cascade of reactions connected with alteration in cellular homeostasis parameters (pHi, [Cai], cAMP, Eh, [ATP] and some others) is considered as a photosignal transduction and amplification chain in a cell (secondary mechanisms).
Abstract: Cytochrome c oxidase is discussed as a possible photoacceptor when cells are irradiated with monochromatic red to near-IR radiation. Four primary action mechanisms are reviewed: changes in the redox properties of the respiratory chain components following photoexcitation of their electronic states, generation of singlet oxygen, localized transient heating of absorbing chromophores, and increased superoxide anion production with subsequent increase in concentration of the product of its dismutation, H2O2. A cascade of reactions connected with alteration in cellular homeostasis parameters (pHi, [Cai], cAMP, Eh, [ATP] and some others) is considered as a photosignal transduction and amplification chain in a cell (secondary mechanisms).
1,157 citations
TL;DR: It is demonstrated that CPDs are induced by UVA radiation and not by contaminating UVB wavelengths, and are likely to contribute to the mutagenic specificity of UVA.
Abstract: DNA damage profiles have been established in plasmid DNA using purified DNA repair enzymes and a plasmid relaxation assay, following exposure to UVC, UVB, UVA or simulated sunlight (SSL). Cyclobutane pyrimidine dimers (CPDs) are revealed as T4 endonuclease V-sensitive sites, oxidation products at purine and pyrimidine as Fpg- and Nth-sensitive sites, and abasic sites are detected by Nfo protein from Escherichia coli. CPDs are readily detected after UVA exposure, though produced 103 and 105 times less efficiently than by UVB or UVC, respectively. We demonstrate that CPDs are induced by UVA radiation and not by contaminating UVB wavelengths. Furthermore, they are produced at doses compatible with human exposure and are likely to contribute to the mutagenic specificity of UVA [E. Sage et al., Proc. Natl. Acad. Sci. USA 93 (1996) 176–180]. Oxidative damage is induced with a linear dose dependence, for each region of the solar spectrum, with the exception of oxidized pyrimidine and abasic sites, which are not detectable after UVB irradiation. The distribution of the different classes of photolesions varies markedly, depending on wavelengths. However, the unexpectedly high yield of oxidative lesions, as compared to CPDs, by UVA and SSL led us to investigate their production mechanism. An artificial formation of hydroxyl radicals is observed, which depends on the material of the sample holder used for UVA irradiation and is specific for long UV wavelengths. Our study sheds light on a possible artefact in the production of oxidative damage by UVA radiation. Meanwhile, after eliminating some potential sources of the artefact ratios of CPDs to oxidized purine of three and five upon irradiation with UVA and SSL, respectively, are still observed, whereas these ratios are about 140 and 200 after UVC and UVB irradiation.
227 citations
TL;DR: Transmission electron microscopy of the in vivo-formed plaque biofilms reveals considerable damage to bacteria in the biofilm, vacuolation of the cytoplasm and membrane damage being clearly visible after PDT.
Abstract: Seven-day oral plaque biofilms have been formed on natural enamel surfaces in vivo using a previously reported in situ device. The devices are then incubated with a cationic Zn(II) phthalocyanine photosensitizer and irradiated with white light. Confocal scanning laser microscopy (CSLM) of the biofilms shows that the photosensitizer is taken up into the biomass of the biofilm and that significant cell death is caused by photodynamic therapy (PDT). In addition, the treated biofilms are much thinner than the control samples and demonstrate a different structure from the control samples, with little evidence of channels and a less dense biomass. Transmission electron microscopy (TEM) of the in vivo-formed plaque biofilms reveals considerable damage to bacteria in the biofilm, vacuolation of the cytoplasm and membrane damage being clearly visible after PDT. These results clearly demonstrate the potential value of PDT in the management of oral biofilms.
152 citations
TL;DR: It is concluded that a change in the pH value of the surrounding medium leads to achange in the lipophilicity of chlorin e6, likely to influence its binding to the serum proteins as well as its interaction with the plasma membrane of cells and may also be related to the selective tumor uptake of the drug.
Abstract: Chlorins are attractive compounds for photodynamic therapy because of their high absorption in the red spectral region. In this study, the absorbance, fluorescence excitation and fluorescence emission spectra of chlorin e6 have been recorded as functions of pH in phosphate-buffered saline (PBS) solution with and without fetal calf serum (FCS). For pure PBS solutions, variation of the pH of the solution results in a shift of both the absorption and the fluorescence spectrum as well as in a decrease of the fluorescence intensity. Spectrophotometric and fluorimetric titration curves, based on observed changes, have been plotted. There is an indication of aggregate formation at low pH values (pH < 5). The presence of 5% FCS results in a shift of the titration curve, from an inflection point at about 6.5 to one at about 7.6. Pronounced spectral changes of the fluorescence emission spectra of protein-bound chlorin e6 (change of spectral shape, decrease of peak intensity) are also observed. The partition coefficients in the 1-octanol-water system increase with decreasing pH. Thus, relatively more of the drug is incorporated in the octanol phase at low pH. Cellular uptake of chlorin e6 in the presence of serum is significantly higher at pH 6.7 as compared with that at 7.3 and 7.6. We conclude that a change in the pH value of the surrounding medium leads to a change in the lipophilicity of chlorin e6. Such a change is likely to influence its binding to the serum proteins as well as its interaction with the plasma membrane of cells and may also be related to the selective tumor uptake of the drug.
129 citations
TL;DR: It is found that myxoxanthophyll, which is preferentially synthesized in high light, exhibits the strongest protection and that echinenone is the most stable carotenoid under photo-oxidative conditions.
Abstract: Light-dependent carotenoid formation has been investigated in the cyanobacterium Synechocystis PCC 6803. Upon transfer of cultures from low- (35 μmol m −2 s −1 ) to high-intensity illumination (500 μmol m −2 s −1 ), a decrease of the endogenous carotenoids to 85% of the initial value is observed. Treatment with norflurazon, an inhibitor that blocks the synthesis of coloured carotenoids, demonstrates a much stronger degradation of the existing carotenoids, which was more pronounced at high light intensities. However, the amounts of the accumulating precursor phytoene reveal that de novo biosynthesis is enhanced under high-light conditions. Nevertheless, this upregulated synthesis cannot fully compensate for carotenoid loss by photodegradation. The potential of the carotenoids from Synechocystis to protect against photosensitized and radical peroxidation reactions has been evaluated. It is found that myxoxanthophyll, which is preferentially synthesized in high light, exhibits the strongest protection and that echinenone is the most stable carotenoid under photo-oxidative conditions.
114 citations
TL;DR: A three-channel dosimeter has been developed to measure solar radiation in the UV-B (280-315 nm), UV-A (315-400 nm) and PAR (400-700 nm) wavelength bands.
Abstract: A three-channel dosimeter has been developed to measure solar radiation in the UV-B (280–315 nm), UV-A (315–400 nm) and PAR (400–700 nm) wavelength bands. A total of 31 instruments have been installed in Europe from Abisko in Northern Sweden to Gran Canaria, covering most light-climate zones. In addition, instruments are installed in India, Africa, New Zealand and South America. Seven of the instruments have been installed under water (each in conjunction with a terrestrial instrument), and two instruments are located in high mountain locations (Zugspitze, Germany and Sierra Nevada, Spain). The instruments use an integrating Ulbricht sphere and silicon photodiodes in combination with custom-made filters. All instruments are carefully calibrated to ensure a high standard of quality control and documentation. The software records all data (three light channels, external and internal temperature and depth for the underwater instruments) at 1 min intervals, displays them on a PC, stores the data on disk and transmits the data to the central server in Pisa (http://power.ib.pi.cnr.it:80/eldonet), where all available data can be seen in graphical form and downloaded as ASCII files.
98 citations
TL;DR: Laser-induced fluorescence investigations have been performed in connection with photodynamic therapy of basal cell carcinomas and adjacent normal skin following topical application of 5-aminolaevulinic acid (ALA) to study the kinetics of the protoporphyrin IX (PpIX) build-up.
Abstract: Laser-induced fluorescence (LIF) investigations have been performed in connection with photodynamic therapy (PDT) of basal cell carcinomas and adjacent normal skin following topical application of 5-aminolaevulinic acid (ALA) in order to study the kinetics of the protoporphyrin TX (PpIX) build-up. Five superficial and 10 nodular lesions in 15 patients are included in the study. Fluorescence measurements are performed prior to the application of ALA, 2, 4 and 6 h port ALA application, immediately post PDT (60 J cm(-2) at 635 nm), and 2 h after the treatment. Hence, the build-up, photobleaching and re-accumulation of PpIX can be followed. Superficial lesions show a maximum PpIX fluorescence 6 h post ALA application, whereas the intensity is already the highest 2-4 h after the application in nodular lesions. Immediately post PDT, the fluorescence contribution at 670 Mm from the photoproducts is about 2% of the pre-PDT PpIX fluorescence at 635 nm. Two hours after the treatment, a uniform distribution of PpIX is found in the lesion and surrounding normal tissue. During the whole procedure, the autofluorescence of the lesions and the normal skin does not vary significantly from the values recorded before the application of ALA. (C) 1999 Elsevier Science S.A. All rights reserved. (Less)
97 citations
TL;DR: In this paper, arrays of light-emitting diodes can be used to generate single-turnover flashes of light that saturate Q A reduction in green algae, without poisoning the organism with herbicide that blocks Q A − reoxidation.
Abstract: We demonstrate that arrays of light-emitting diodes can be used to generate single-turnover flashes of light that saturate Q A reduction in green algae. The fast version of a double-modulation fluorometer can measure induction during a single-turnover saturating flash (flash fluorescence induction). The method allows the effective antenna size, antenna heterogeneity and connectivity of Photosystem II to be measured without poisoning the organism with herbicide that blocks Q A − reoxidation. Using the same instrument, we have also measured the functional heterogeneity of Photosystem II by the fluorescence transient related to the flash-induced advancement of S-states in the oxygen-evolving complex.
94 citations
TL;DR: It is found that UV-A radiation causes massive increases in carotenoid levels without slowing the growth of D. bardawil in culture.
Abstract: The effect of supplementing visible light (i.e., wavelengths in the range 400–700 nm) with ultraviolet-A radiation (320–400 nm) during the growth of Dunaliella bardawil has been investigated. This study focuses on the accumulation of carotenoids. Previous investigations have found that large increases in carotenoids are induced by high-intensity photosynthetically active radiation (PAR) and by various environmental stresses (e.g., high salinity, nutrient deficiencies or low temperature), which significantly reduce growth rates. This study has found that UV-A radiation causes massive increases in carotenoid levels without slowing the growth of D. bardawil in culture. By supplementing various levels of PAR with UV-A radiation (38 μmol m −2 s −1 ) during growth, carotenoid:chlorophyll ratios increase by 80–310%. Per unit protein, UV-A produces a 0–35% decrease in chlorophyll coupled with a doubling of total carotenoids. These large increases in carotenoids are induced by UV-A at all salinities (0.5 to 3.0 M), and at all visible photosynthetic photon flux densities (30–1500 μmol m −2 s −1 ) tested. Induced carotenoid levels are proportional to the intensity of UV-A when growth PAR is held constant. Blue light (200 μmol m −2 s −1 ) is no more effective than white light in carotenoid induction, indicating that this is not a shared blue-light/near-UV effect. UV-B (290–320 nm) is also ineffective in inducing carotenoid increases during growth.
92 citations
TL;DR: An ultraviolet absorbing mycosporine-like amino acid (MAA) was detected in a filamentous and heterocystous cyanobacterium, Anabaena sp., isolated from a rice paddy field near Varanasi, India.
Abstract: An ultraviolet-absorbing mycosporine-like amino acid (MAA) has been detected in a filamentous and heterocystous cyanobacterium, Anabaena sp., isolated from a rice paddy field near Varanasi, India. The MAA is isolated and purified by high-performance liquid chromatography. Only one MAA is detected with a retention time of around 2.8 min and an absorption maximum at 334 nm. The MAA is identified as shinorine, a bisubstituted MAA containing both glycine and serine groups. There is an increase in the amount of MAA when the cultures are exposed to photosynthetically active radiation and ultraviolet radiation (PAR+UV) in comparison with the cultures exposed to PAR only. This shows that UV stress induces the synthesis of MAA in this cyanobacterium and thus may protect the organism against deleterious high solar radiation, particularly during summer seasons in the tropics.
88 citations
TL;DR: In this paper, the role of chilling temperatures on photoinhibition of photosystems I and II under weak light has been examined in cucumber, a chilling-sensitive plant.
Abstract: The role of chilling temperatures on photoinhibition of photosystems I and II (PSI and PSII) under weak light has been examined in cucumber, a chilling-sensitive plant. The extent of PSII photoinhibition, determined by pulse-modulated fluorescence in vivo, is closely related to the redox state of the PSII electron acceptor QA, measured as a fluorescence parameter, 1 − qp. On the other hand, the extent of PSI photoinhibition, which is only observed in chilling-sensitive plants at chilling temperatures, cannot be related to the redox state of QA, suggesting that the underlying mechanism is different from that of PSII photoinhibition. Chilling treatment at low photon flux densities is found to enhance cyclic electron flow around PSI. Both PSI photoinhibition and enhanced cyclic electron flow show similar temperature dependence, with the threshold temperature at 10°C.
TL;DR: The results indicate that UV-B signal pathway(s) involve ROS in both green and etiolated tissue, but differences do exist with respect to the relationships between antioxidant capacity, ROS levels and changes in the level of photosynthetic transcripts.
Abstract: Reactive oxygen species (ROS) have been shown to be components of the signal transduction pathway(s) leading to the down-regulation of photosynthetic genes in response to UV-B radiation in green organs. Young, etiolated tissue has been found to be more tolerant of damaging UV-B radiation. In this paper the effects of supplementary UV-B radiation on the expression of photosynthetic genes, generation of ROS and activity of antioxidant enzyme systems have been studied in etiolated pea buds and compared with previously published results from green buds. Transcripts for Lhcb, RbcS and rbcL are down-regulated in green buds but transiently up-regulated in etiolated buds. ROS levels increase in response to UV-B radiation in green buds but transiently in etiolated buds. However, ROS levels are generally higher in etiolated than green buds. After 54 h treatment, differences between the initially etiolated and green buds are no longer detectable. UV-B causes similar increases in the activities of ascorbate peroxidase, superoxide dismutase and glutathione reductase in both green and etiolated buds, without measurably affecting transcript levels. The results indicate that UV-B signal pathway(s) involve ROS in both green and etiolated tissue, but differences do exist with respect to the relationships between antioxidant capacity, ROS levels and changes in the level of photosynthetic transcripts.
TL;DR: The results suggest that the reactions of oxidized riboflavin radical might be involved in DNA photosensitization in vivo and in vitro.
Abstract: Using 248 nm laser flash photolysis, it has been demonstrated that the neutral oxidized radical of riboflavin (RF(–H) ) resulting from rapid deprotonation of the radical cation (RF + ) can be generated via monophotonic ionization when it is directly excited with a 248 nm laser and via oxidation by the SO 4 − radical in aqueous solution. The RF(–H) or RF + reacts with both purine nucleotides and pyrimidine nucleotides via electron transfer to give the radical cations of nucleotides. These results suggest that the reactions of oxidized riboflavin radical might be involved in DNA photosensitization in vivo and in vitro.
TL;DR: The data suggest that UV-B may be involved both in the impairment and the recovery of photosynthesis of D. dichotoma.
Abstract: Daily variations of photosynthetic performance of the brown alga Dictyota dichotoma (Hudson) Lamouroux (Dictyotales) (estimated by Fv/Fm ratio and net O2-based photosynthesis) have been determined under full-spectrum solar radiation (PAR+UV-A+UV-B), solar radiation depleted of ultraviolet-B (PAR+UV-A) and solar radiation depleted of total ultraviolet (photosynthetically active radiation, PAR). In the daily course, the photosynthetic response of the alga is inhibited by the three solar radiation conditions at midday, but recovers during the afternoon to those values measured in the early morning only under PAR + UV-A + UV-B, or PAR alone. Under solar radiation depleted of UV-B, the recovery of photosynthesis is significantly lower than in the other two solar radiation conditions. The relative electron transport rate (ETR) as a function of PAR is calculated for the three radiation treatments, at noon after 2 h exposure. The ETR is strongly inhibited under these conditions. In the PAR and PAR + UV-A + UV-B treatments, photosynthesis recovers after 1.5 h in low irradiance (< 10 μmol photons m−2 s−1) and attains values measured in the early morning. In the absence of UV-B, the inhibitory effect is persistent, visible as a low initial slope and lower ETR at higher levels of irradiance. These data suggest that UV-B may be involved both in the impairment and the recovery of photosynthesis of D. dichotoma.
TL;DR: Initial clinical trials show that the in vivo quantitative assessment of the spatial and temporal alterations of light-scattering properties, induced in epithelial dysplasias and malignancies of the cervix and larynx, is capable of detecting incipient lesions.
Abstract: A novel approach to the problem of non-destructive detection and staging of tissue lesions is presented. The method relies on the in vivo quantitative assessment of the spatial and temporal alterations of light-scattering properties, induced in epithelial dysplasias and malignancies of the cervix and larynx, after topical application of acetic acid solution. Initial clinical trials show that the method is capable of detecting incipient lesions and that differences in the dysplasia and malignancy grade are clearly manifested in the measured temporal characteristics of the phenomenon.
TL;DR: Original spectral analysis of the multicomponent photoisomer mixture has been specially designed to provide the most effective use of the D-dosimeter in situ, and Spectral selectivity (exceptional sensitivity of certain parameters to the spectral composition of UV radiation) extends the usefulness of the method.
Abstract: The biologically important process of endogenous synthesis of vitamin D under UV solar irradiation is widespread in the biosphere and inherent to most animals and plants. A new method of biological dosimetry of UV radiation based on an in vitro model of vitamin D synthesis ('D-dosimeter') is discussed. Unlike the vast majority of biodosimeters, the action of which depends on the UV sensitivity of DNA and thus reflects damaging effects of UV radiation, the process of vitamin D synthesis is beneficial by its nature. To date, the complex network of photo- and thermoreactions of vitamin D synthesis in vitro is well understood, and an adequate mathematical model is available, ensuring a link between biological and physical units. Original spectral analysis of the multicomponent photoisomer mixture has been specially designed to provide the most effective use of the D-dosimeter in situ. Spectral selectivity (exceptional sensitivity of certain parameters to the spectral composition of UV radiation) extends the usefulness of the method.
TL;DR: The results suggest that theUV-B effect on growth is mediated through leaf expansion, which is particularly sensitive to UV-B, and that Pinto is more tolerant than Vilmorin, and also that NADP-ME plays a key role in biosynthesis of these compounds.
Abstract: The effects of UV-B radiation on growth, photosynthesis, UV-B-absorbing compounds and NADP-malic enzyme have been examined in different cultivars of Phaseolous vulgaris L. grown under 1 and 12 mM nitrogen. Low nitrogen nutrition reduces chlorophyll and soluble protein contents in the leaves and thus the photosynthesis rate and dry-matter accumulation. Chlorophyll, soluble protein and Rubisco contents and photosynthesis rate are not significantly altered by ambient levels of UV-B radiation (17 microW m-2, 290-320 nm, 4 h/day for one week). Comparative studies show that under high nitrogen, UV-B radiation slightly enhances leaf expansion and dry-matter accumulation in cultivar Pinto, but inhibits these parameters in Vilmorin. These results suggest that the UV-B effect on growth is mediated through leaf expansion, which is particularly sensitive to UV-B, and that Pinto is more tolerant than Vilmorin. The effect of UV-B radiation on UV-B-absorbing compounds and on NADP-malic enzyme (NADP-ME) activity is also examined. Both UV-B radiation and low-nitrogen nutrition enhance the content of UV-B-absorbing compounds, and among the three cultivars used, Pinto exhibits the highest increases and Arroz the lowest. The same trend is observed for the specific activity and content of NADP-ME. On a leaf-area basis, the amount of UV-B-absorbing compounds is highly correlated with the enzyme activity (r2 = 0.83), suggesting that NADP-ME plays a key role in biosynthesis of these compounds. Furthermore, the higher sensitivity of Vilmorin than Pinto to UV-B radiation appears to be related to the activity of NADP-ME and the capacity of the plants to accumulate UV-B-absorbing compounds.
TL;DR: In this paper, the photoinduced electron-transfer reaction in a DNA helix has been studied using 9-amino-6-chloro-2methoxyacridine (ACMA) selectively intercalated at an internucleotide site of a DNA.
Abstract: The photoinduced electron-transfer reaction in a DNA helix has been studied using 9-amino-6-chloro-2-methoxyacridine (ACMA) selectively intercalated at an internucleotide site of a DNA. The photoexcited ACMA is used as an electron acceptor, and guanine in DNA as an electron donor. ACMA-DNA conjugates possessing guanine at 5′ or 3′ direction(s) with different distance(s) from the intercalated ACMA have been prepared for a systematic examination of the distance dependence of the electron-transfer reaction in a DNA helix. In DNA consisting of only the (dA-dT) base pair, the fluorescence of the singlet-excited ACMA decays in a mono-exponential manner with a longest lifetime of 22.8 ns. The fluorescence lifetime of the excited ACMA decreases with incorporation of guanosine depending on the distance between the ACMA and guanine. When an ACMA and a guanine are directly stacked, the decay lifetime markedly decreases, showing a forward electron-transfer rate, kfet, of ≈ 1010 s−1. Treating the kinetic data according to kfet = AexpβR), where R is the separation distance in A, gives a β value of 1.47 A−1. Moreover, as a model compound for ACMA, the redox potential of quinacrine dihydrate bi (tetrafluoroborate) has been measured by cyclic voltammetry in acetonitrile. Comparison of the redox potential with those of nucleobases has revealed that only guanine can quench the fluorescence of ACMA and a free-energy change ΔG ° = − 0.46 eV has been evaluated for this electron-transfer reaction.
TL;DR: CD44V6, its lectins and MHC-I are significantly decreased in PROb and REGb cells after both BPD and Photofrin PDT treatment, implying that the rate of metastatic reduction is probably not linked simply to these changes.
Abstract: Photodynamic therapy (PDT) induces among numerous cell targets membrane damage and alteration in cancer cell adhesiveness, an important parameter in cancer metastasis. We have previously shown that hematoporphyrin derivative (HPD)-PDT decreases cancer cell adhesiveness to endothelial cells in vitro and that it reduces the metastatic potential of cells injected into rats. The present study analyzes the influence of PDT in vivo on the metastatic potential of cancers cells and in vitro on the expression of molecules involved in adhesion and in the metastatic process. Photofrin and benzoporphyrin derivative monoacid ring A (BPD) have been evaluated on two colon cancer cell lines obtained from the same cancer [progressive (PROb) and regressive (REGb)] with different metastatic properties. Studies of BPD and Photofrin toxicity and phototoxicity are performed by colorimetric MTT assay on PROb and REGb cells to determine the PDT doses inducing around 25% cell death. Flow cytometry is then used to determine adhesion-molecule expression at the cell surface. ICAM-I, MHC-I, CD44V6 and its lectins (aHt1.3, PNA, SNA and UEA) are studied using cells treated either with BPD (50 ng/ml, 457 nm light, 10 J/cm2) or Photofrin (0.5 microgram/ml, 514 nm light, 25 J/cm2). Changes of metastatic patterns of PROb cells have been assessed by the subcutaneous injection of non-lethally treated BPD or Photofrin cells and counting lung metastases. First, we confirm the metastatic potential reduction induced by PDT with respectively a 71 or 96% decrease of the mean number of metastases (as compared with controls) for PROb cells treated with 50 ng/ml BPD and 10 or 20 J/cm2 irradiation. Concerning Photofrin-PDT-treated cells, we find respectively a 90 or 97% decrease (as compared with controls) of the mean number of metastases for PROb cells treated with 0.5 microgram/ml Photofrin and 25 or 50 J/cm2 irradiation. Then, we observe that CD44V6, its lectins (aHt1.3, PNA, SNA) and MHC-I are significantly decreased (compared with the other molecules tested) in PROb and REGb cells after both BPD and Photofrin PDT treatment. These modifications in adhesion-molecule expression, particularly of CD44V6, can thus account only for part of the decrease in the metastatic potential of PDT-treated cancer cells. Changes in adhesion-molecule expression induced by PDT are only transient, implying that the rate of metastatic reduction is probably not linked simply to these changes.
TL;DR: A series of neutral meso-arylglycosylporphyrins has been tested in order to evaluate their potency as antifungal agents against the yeast Saccharomyces cerevisiae and Amphiphilic porphyrin derivatives are shown to exhibit the more pronounced photoactivity.
Abstract: A series of neutral meso-arylglycosylporphyrins has been tested in order to evaluate their potency as antifungal agents against the yeast Saccharomyces cerevisiae. Photodynamic activity of these molecules results in intracellular damage as evidenced by the loss of clonogenicity and DNA fragmentation. The ability of these photosensitizers to permeate yeast cells is determined by microspectrofluorimetry and is correlated with their antifungal potency. Amphiphilic porphyrin derivatives are shown to exhibit the more pronounced photoactivity.
TL;DR: In this paper, the photomorphogenesis and essential-oil chemical composition of Mentha piperita were studied under UV-A irradiation during the night period and during the day period.
Abstract: UV-A radiation (360 nm) affects the photomorphogenesis and essential-oil chemical composition of Mentha piperita. Total phenols and chlorophyll b are also affected by UV-A. When UV-A is given during the day (UV-A+W), a significant increase is found in total leaf area, leaf-area index, chlorophyll a/b ratio, total phenols, total essential-oil content, menthofuran and menthol. UV-A irradiation during the night period induces a typical shade-avoidance syndrome, with stem elongation, decreased leaf area and leaf-area index, decreased protein and total phenol content, and decreased essential-oil and menthol content. The possible interference of UV-A with phytochrome is discussed.
TL;DR: In this article, the photobleaching of compounds of the 5,10,15,20-tetrakis(m-hydroxyphenyl)porphyrin series at different reduction levels (m-THPP 1, m-THPC 2, m -THPBC 3) has been studied using an argon laser (514 nm) by observing the diminution of absorbance of band I (for 2 and 3) and of band IV (for 1) with time.
Abstract: The photobleaching of compounds of the 5,10,15,20-tetrakis(m-hydroxyphenyl)porphyrin series at different reduction levels (m-THPP 1, m-THPC 2, m-THPBC 3) has been studied in methanol and in methanol–water (3:2, v/v) using an argon laser (514 nm) by observing the diminution of absorbance of band I (for 2 and 3) and of band IV (for 1) with time. Under the conditions studied here, true photobleaching only occurs for m-THPC (2) and m-THPBC (3), with photomodification being the major process for m-THPP (1). The rates for the photobleaching of 2 and 3 are presented in different solvents. The photobleaching rate of the bacteriochlorin 3 is found to be 90 times higher than that of the chlorin 2 in methanol–water (3:2, v/v). Singlet oxygen appears to be the reactive species responsible for the photobleaching of 2 and 3 and the photomodification of 1.
TL;DR: In this paper, the spectral effective solar UV irradiance on the orientation of the receiver with respect to the sun has been determined for relatively cloud-free days at a sub-tropical Southern Hemisphere latitude for the solar zenith angle range 35-64 degrees.
Abstract: The dependence of the spectral biologically effective solar UV irradiance on the orientation of the receiver with respect to the sun has been determined for relatively cloud-free days at a sub-tropical Southern Hemisphere latitude for the solar zenith angle range 35-64 degrees. For the UV and biologically effective irradiances, the sun-normal to horizontal ratio for the total UV ranges from 1.18 +/- 0.05 to 1.27 +/- 0.06. The sun-normal to horizontal ratio for biologically effective irradiance is dependent on the relative effectiveness of the relevant action spectrum in the UV-A waveband. In contrast to the total UV, the diffuse UV and diffuse biologically effective irradiances are reduced in a sun-normal compared with a horizontal orientation by a factor ranging from 0.70 +/- 0.05 to 0.76 +/- 0.03.
TL;DR: ALA/PDT has a potential for the eradication of small tumours but careful patient selection with endoluminal ultrasound is needed when using ALA/ PDT to treat oesophageal cancer.
Abstract: Photodynamic therapy (PDT) is a novel technique for local endoscopic treatment of gastrointestinal neoplasia. Current photosensitisers for PDT may cause prolonged skin phototoxicity. 5-Aminolaevulinic acid (ALA), a precursor of the photosensitiser protoporphyrin IX (PpIX), is more acceptable because of its short half-life and preferential accumulation in mucosa and mucosal tumour. We have treated 12 patients, median age 73 years (range 55–88) with oesophageal adenocarcinoma arising from Barrett’s metaplasia (two carcinomas-in-situ, grade 0; 10 carcinomas, grade l–llA based on endoluminal ultrasound in two and CT scanning in 10 patients). ALA (60 and 75 mg/kg body weight) was given orally in two or five equally divided doses. The PpIX distribution in stomach, normal oesophagus, Barrett’s mucosa and carcinoma was measured by quantitative fluorescence photometry. PDT was performed using laser light (630 nm) delivered via a cylindrical diffuser 4–6 h after the first dose of ALA. The patients received one to four sessions of PDT. PpIX accumulation in the mucosa was two to three times that in the lamina propria. The differential distribution between carcinomatous and normal oesophageal mucosa was less marked (carcinoma:normal mucosa ratio=1.4). Higher doses of ALA increased PpIX accumulation in all tissues but did not increase the differential PpIX distribution between tumour and normal oesophageal mucosa. After PDT using ALA (ALA/PDT), all mucosa showed superficial white necrotic changes and the histology confirmed fibrinoid necrosis. One patient with carcinoma-in-situ had the tumour eradicated after one treatment with no recurrence at 28 months. Another patient with a small T1 tumour required four ALA/PDT treatments, and died of other disease after 36 months. There was no evidence of recurrence. The tumour bulk in the other carcinomas was not significantly reduced. ALA/PDT has a potential for the eradication of small tumours but careful patient selection with endoluminal ultrasound is needed when using ALA/PDT to treat oesophageal cancer.
TL;DR: Lower cell viability is found when this photosensitizer is entrapped in egg-yolk lecithin instead of solvent-PBS or for Cremophor EL micelles with Cl2SiPc, and the photodynamic effect is connected with the type of delivery system used.
Abstract: Dichlorosilicon phthalocyanine (Cl 2 SiPc) and bis(tri- n -hexylsiloxy) silicon phthalocyanine (HexSiPc) have been evaluated in vitro as potential photosensitizers for photodynamic therapy (PDT) against the human amelanotic melanoma cell line M6. Each photosensitizer is dissolved in a solvent-PBS mixture, or entrapped in egg-yolk lecithin liposomes or in Cremophor EL micelles. The cells are incubated for l h with the sensitizer and then irradiated for 20 min, l h or 2 h (λ > 480 nm, 10 mW cm −2 ). The photocytotoxic effect is dependent on the photosensitizer concentration and the light dose. Higher phototoxicity is observed after an irradiation of 2 h: treatment with a solution of photosensitizer (210 −9 M) leads to 10% (HexSiPc in egg-yolk lecithin liposomes) or 20% (Cl 2 SiPc in DMF-PBS solution) cell viability. After 1 h incubation and 20 min of light exposure, the photodynamic effect is connected with the type of delivery system used. For HexSiPc, lower cell viability is found when this photosensitizer is entrapped in egg-yolk lecithin instead of solvent-PBS or for Cremophor EL micelles with Cl 2 SiPc. Liposome-delivered HexSiPc leads to lipid damage in M6 cells, illustrated by an increase of thiobarbituric acid-reacting substances (TBARs), but the change is not significant with Cremophor EL. The same is observed for the antioxidative defences after photodynamic stress. The cells irradiated with HexSiPc entrapped in liposomes display an increase of Superoxide dismutase (SOD) activity and a decrease of glutathione (GSH) level, glutathione peroxidase (GSHPx) and catalase (Cat) activities.
TL;DR: The photoreceptors for both the adaptation of the photosynthetic apparatus to low-light conditions and for the regulation of the spermine/putrescine ratio are, at least, very similar.
Abstract: In this contribution we describe the changes in structure and functioning of the photosynthetic apparatus of the unicellular green alga Scenedesmus obliquus induced by inhibition or induction of polyamine biosynthesis. The synthesis or inhibition is controlled by white light of low and high intensities, as well as by blue and red irradiation. We observe that a decrease of the intracellular putrescine level and, vice versa, an increase of spermine, indicated by a raised ratio of spermine to putrescine, simulate a low-light photoadapted photosynthetic apparatus. Action spectra of the spermine/putrescine ratio compared with action spectra on characteristics of photoadaptation, e.g., chlorophyll biosynthesis, or the rate of primary photochemistry and electron transport, show that the photoreceptors for both the adaptation of the photosynthetic apparatus to low-light conditions and for the regulation of the spermine/putrescine ratio are, at least, very similar. We show that the photoreceptor is primarily a blue-light receptor with a superimposed red-light receptor that absorbs around 680 nm.
TL;DR: It seems evident that Haematoporphyrin dimethyl ether (HPde) is able to act as a photosensitizer as well as a radiosensitizers for combined treatment of Ehrlich ascites carcinoma and gamma-irradiation.
Abstract: Ehrlich ascites carcinoma growth and cell damage have been examined after photodynamic therapy (PDT), radiotherapy (RT) and combined treatment. Haematoporphyrin dimethyl ether (HPde) is used as a photosensitizer for PDT and tested as a radiosensitizer for RT. For PDT a non-coherent light source (370 < lambda < 680 nm) equipped with filters is used. gamma-Irradiation consists of 60Co irradiation at a dose of 2 Gy. Both PDT and RT induce a significant delay and inhibition in tumour growth (33 and 38%, respectively). Nevertheless cell damage after these treatments is different: after PDT the cell membrane integrity is damaged and no serious chromosomal aberrations are observed; whereas after gamma-irradiation there is no cell membrane integrity damage, but more significant DNA injuries are observed. It seems evident that HPde is able to act as a photosensitizer as well as a radiosensitizer. Combining PDT and RT produces an additive effect, not dependent on the sequence in which the two treatments are given, when a 1 h time window is used.
TL;DR: It is proposed that UV-A radiation induces an enhancement of the efficiency of light capture mediated by a relaxation of pigment packing in the light-harvesting antennae of this intertidal red macroalga, while the reverse is promoted by UV-B radiation.
Abstract: The effect of ultraviolet (UV) radiation on thallus absorption, package effect, the concentration of photosynthetic pigments, photosynthetic oxygen production and effective quantum yield has been studied in the intertidal red macroalga Porphyra umbilicalis in the laboratory. High doses of UV-A and UV-B radiation result in a rapid decrease of thallus absorption and, after a 6 h exposure, total absorption is reduced to 25% of the initial value. Moreover, significant differences in the absorption peaks of the main pigments are found: while chlorophyll a (Chl a ) and phycocyanin absorption peaks decrease by 65–67%, carotenoids and phycoerythrin (PE) peaks decrease by 75–82%. Uncoupling of the transfer of energy between PE and Chl a by UV is revealed by a gradual increase of fluorescence of PE up to 11 h of exposure, followed by a subsequent decrease of fluorescence of the PE, in parallel with the photobleaching of the pigments. Thalli with higher pigment concentration present a greater sensitivity to UV radiation, as revealed by a more pronounced decrease in total thallus absorption, oxygen production and effective quantum yield, and a less effective recovery under low irradiation. Exposure of the thalli to artificial UV radiation in an experimental chamber with spectra and doses more similar to those of the natural environment reveals that PAR + UV-A radiation promotes a gradual increase of the total absorption over 24 h; in contrast, PAR + UV-A + UV-B induces a significant decrease of the thallus absorption. However, the concentration in vitro of Chl a , carotenoids and biliproteins does not change in any of these light treatments. The spectrally averaged in vivo absorption cross section normalized to Chl a ( a * ) increases after 24 h in PAR + UV-A, but it does not change in PAR and PAR + UV- A + UV-B, indicating that the degree of packing of the pigments in the membranes of the thylakoids (package effect) is decreased by PAR + UV-A, but that the reverse is induced by PAR + UV-A + UV-B. It is proposed that UV-A radiation induces an enhancement of the efficiency of light capture mediated by a relaxation of pigment packing in the light-harvesting antennae of this intertidal macroalga, while the reverse is promoted by UV-B radiation.
TL;DR: The central role of rhodopsin in the phototransduction cascade becomes evident by examining the main reports on light-activated conformational changes of r Rhodopsin and its interaction with transducin.
Abstract: Recent studies on rhodopsin structure and function are reviewed and the properties of vertebrate as well as invertebrate rhodopsin described. Open issues such as the 'red shift' of the absorbance spectra are emphasized in the light of the present model of the retinal-binding pocket. The processes that restore the rhodopsin content in photoreceptors are also presented with a comparison between vertebrate and invertebrate visual systems. The central role of rhodopsin in the phototransduction cascade becomes evident by examining the main reports on light-activated conformational changes of rhodopsin and its interaction with transducin. Shut-off mechanisms are considered by reporting the studies on the sites of rhodopsin phosphorylation and arrestin binding. Furthermore, recent findings on the energetics of phototransduction point out that the ATP needed for photoreception in vertebrates is synthesized in the outer segments where phototransduction events take place.
TL;DR: In this article, the fluorescence of anthocyanin pigments in water extracts of Brassica oleracea L (red cabbage) has been studied and three fluorescent species, ZI, ZII and ZIII, are distinguished.
Abstract: The fluorescence of anthocyanin pigments in water extracts of Brassica oleracea L (red cabbage) has been studied The fluorescence spectra and fluorescence excitation spectra of pigments in starting extracts and in chromatographic fractions have been measured It has been stated that the group of fluorescent anthocyanins (or other fluorescent species as well) exists in water extracts of red cabbage Attempts to separate the fluorescence spectra, characteristic of these compounds, have been undertaken by choosing proper parameters for measurements of fluorescence spectra and fluorescence excitation spectra and deconvolution of registered fluorescence spectra Three fluorescent species, ZI, ZII and ZIII, are distinguished Their fluorescence spectra are centred at 363, 434 and 519 nm, respectively It is suggested that fluorescence investigations, apart from the standard methods of visible absorption spectroscopy, may extend the possibilities of analysis and registration of the changes of anthocyanins in these extracts