Showing papers in "Journal of Photochemistry and Photobiology B-biology in 1990"
TL;DR: In the ongoing clinical trial of ALA-induced Pp IX photodynamic therapy, the response rate for basal cell carcinomas following a single treatment has been 90% complete response and 7.5% partial response for the first 80 lesions treated.
Abstract: 5-Aminolaevulinic acid (ALA) is a precursor of protoporphyrin IX (Pp IX) in the biosynthetic pathway for haem. Certain types of cells have a large capacity to synthesize Pp IX when exposed to an adequate concentration of exogenous ALA. Since the conversion of Pp IX into haem is relatively slow, such cells tend to accumulate photosensitizing concentrations of Pp IX. Pp IX photosensitization can be induced in cells of the epidermis and its appendages, but not in the dermis. Moreover, since ALA in aqueous solution passes readily through abnormal keratin, but not through normal keratin, the topical application of ALA in aqueous solution to actinic keratoses or superficial basal cell or squamous cell carcinomas induces Pp IX photosensitization that is restricted primarily to the abnormal epithelium. Subsequent exposure to photoactivating light selectively destroys such lesions. In our ongoing clinical trial of ALA-induced Pp IX photodynamic therapy, the response rate for basal cell carcinomas following a single treatment has been 90% complete response and 7.5% partial response for the first 80 lesions treated. The cosmetic results have been excellent, and patient acceptance has been very good.
1,546 citations
323 citations
TL;DR: Resistance of Gram negative bacteria to porphyrin photosensitization is the main impediment to its use as a broad spectrum antibacterial method.
Abstract: Photoactivated porphyrins display a potent cytotoxic activity towards a variety of Gram positive bacteria, mycoplasma and yeasts, but not Gram negative cells. The prerequisite for photosensitization of a microbial cell is the binding of porphyrin to the cytoplasmic membrane in a pH-dependent manner. On illumination, the membrane bound, and possibly, cytoplasmic porphyrin molecules generate singlet oxygen and radicals which sensitize biomolecules and lead to cell death. The immediate inhibition of cell growth on photodynamic treatment is accompanied by alterations in cell wall and membrane synthesis, leading to the formation of large mesosomes adjacent to the unaccomplished septa. Hemin bound to microbial cells exerts cytotoxic activity by peroxidative and oxidative reactions independent of light. Future research in the field may enhance the possibility of using porphyrin photosensitization for treatment of microbial infections. Such clinical use will be unrelated to the antibiotic resistance of the pathogen. Resistance of Gram negative bacteria to porphyrin photosensitization is the main impediment to its use as a broad spectrum antibacterial method.
312 citations
TL;DR: This work concerning the interaction of UVA radiation with cultured cells is reviewed with particular emphasis on the involvement of cellular oxidative stress in the biological effects of this radiation on eucaryotic cells.
Abstract: Recent work concerning the interaction of UVA radiation (320 – 380 nm) with cultured cells is reviewed with particular emphasis on the involvement of cellular oxidative stress in the biological effects of this radiation on eucaryotic cells. Possible chromophores are considered and their role in generation of various oxidant species including hydrogen peroxide, superoxide anion, singlet oxygen and hydroxyl radical. DNA and membranes are discussed as possible targets for the lethal action of long wavelength radiation. Four mechanisms of cellular defence are proposed: (1) DNA repair; (2) antioxidant enzymes; (3) endogenous free radical quenchers; (4) inducible protection.
270 citations
TL;DR: This review summarizes research that has been carried out on selected types of chlorins, some of which may have important applications as sensitizers for PDT.
Abstract: The photodynamic therapy (PDT) of tumors involves illumination of the tumorous area following the administration of a tumor-localizing photodynamic sensitizer. Hematoporphyrin derivative (HPD) and Photofrin II (a purified form of HPD), the main sensitizers used clinically for PDT to date, are complex mixtures of porphyrins; furthermore, these preparations absorb light very poorly in the red region of the spectrum (wavelengths greater than 600 nm) where light penetration into mammalian tissues is greatest. Thus there is considerable interest in identifying new sensitizers that localize more effectively in tumors, absorb more strongly at longer wavelengths and can be prepared in high purity. Much of this interest has been directed towards chlorins (reduced porphyrins), which typically absorb strongly in the red. This review summarizes research that has been carried out on selected types of chlorins, some of which may have important applications as sensitizers for PDT.
189 citations
TL;DR: The photodynamic therapy (PDT) of tumors involves illumination of the tumorous area following the administration of a tumor-localizing photodynamic sensitizer as mentioned in this paper, which typically absorbs light very poorly in the red region of the spectrum (wavelengths greater than 600 nm).
Abstract: The photodynamic therapy (PDT) of tumors involves illumination of the tumorous area following the administration of a tumor-localizing photodynamic sensitizer. Hematoporphyrin derivative (HPD) and Photofrin II (a purified form of HPD), the main sensitizers used clinically for PDT to date, are complex mixtures of porphyrins; furthermore, these preparations absorb light very poorly in the red region of the spectrum (wavelengths greater than 600 nm) where light penetration into mammalian tissues is greatest. Thus there is considerable interest in identifying new sensitizers that localize more effectively in tumors, absorb more strongly at longer wavelengths and can be prepared in high purity. Much of this interest has been directed towards chlorins (reduced porphyrins), which typically absorb strongly in the red. This review summarizes research that has been carried out on selected types of chlorins, some of which may have important applications as sensitizers for PDT.
170 citations
TL;DR: 3H-BPD-MA localized in tumors better than in other tissues except kidney, liver and spleen, and was observed in all tissues at 3 h post injection and decreased rapidly during the first 24 h, but after 24 h the clearance from tissues was rather slow.
Abstract: The biodistribution of a new and very potent photosensitizer, benzoporphyrin derivative—monoacid, ring A (BPD-MA), was determined in normal and P815 (mastocytoma) or M1 (rhabdomyosarcoma) tumor-bearing DBA/2J mice. A dose of 80 μg Of 3H-BPD-MA was determined at 3, 24, 48, 72, 96 and 168 h post injection. The following tissues were tested: blood, brain, heart, intestine, kidney, lung, liver, muscle, skin, stomach, spleen, thymus and tumor. The biodistribution of 3H-BPD-MA in normal and tumor-bearing mice was comparable overall. 3H-BPD-MA localized in tumors better than in other tissues except kidney, liver and spleen. The tumor to tissue ratios were in the range 1.5 – 3 at 24 h post injection and increased further during the next 72 h. The highest levels of 3H-BPD-MA were observed in all tissues at 3 h post injection and decreased rapidly during the first 24 h. After 24 h the clearance from tissues was rather slow. The preliminary clearance data obtained in a group of five normal mice indicated that the majority of the injected dose (60%) cleared from the body via the bile and feces, while only about 4% cleared via kidneys and urine. Studies in which 3H-BPD-MA was extracted from tumor, kidney and liver 3 and 24 h after injection showed that, at 3 h, all the photosensitizing activity in tumor was retained. At 24 h only 39% of the activity was retained and considerably less active material was present in liver and kidney.
139 citations
TL;DR: Attempts were made to measure 1O2 IR luminescence during PDT of cell suspensions and two murine tumour models using the photosensitizers Photofrin II and aluminium chlorosulphonated phthalocyanine, with a negative result.
Abstract: Singlet oxygen (1O2) is thought to be the cytotoxic agent in photodynamic therapy (PDT) with current photosensitizers. Direct monitoring of 1O2 concentration in vivo would be a valuable tool in studying biological response. Attempts were made to measure 1O2 IR luminescence during PDT of cell suspensions and two murine tumour models using the photosensitizers Photofrin II and aluminium chlorosulphonated phthalocyanine. Instrumentation was virtually identical to that devised by Parker in the one positive report of in vivo luminescence detection in the literature. Despite the fact that our treatments caused cell killing and tissue necrosis, we were unable to observe 1O2 emission under any conditions. We attribute this negative result to a reduction in 1O2 lifetime in the cellular environment. Quantitative calibration of our system allowed us to estimate that the singlet oxygen lifetime in tissue is less than 0.5 microsecond. Some technical improvements are suggested which would improve detector performance and perhaps make such measurements feasible.
118 citations
TL;DR: A two-fold mechanism of selective biodistribution is advanced, one involving normal tissue vs. tumor tissue selectivity, the other involving intracellular vs. intercellular distribution of sensitizer ionic species.
Abstract: Photochemotherapeutic agents are photosensitizers that are selectively retained by neo-plastic tissue. When tumor tissue containing these drugs is irradiated with visible electromagnetic radiation, the photosensitizing reaction may lead to tumor eradication, termed photodynamic therapy. Exogenous photosensitizers commonly used in clinical trials are mainly porphyrin derivatives. Phthalocyanines are currently being investigated as “second generation” photochemotherapeutic agents. The mechanism by which these photosensitizers are selectively retained in neoplastic tissue is unclear. This review examines the role of tissue and cellular pH as a factor in selective biodistribution. The pH values of normal and tumor tissue are summarized and the ionic species distribution diagram of porphyrins is presented. A two-fold mechanism of selective biodistribution is advanced, one involving normal tissue vs. tumor tissue selectivity, the other involving intracellular vs. intercellular distribution of sensitizer ionic species.
116 citations
113 citations
TL;DR: In this paper, the authors used pump-probe measurements using time-resolved resonance Raman spectroscopy for monitoring both the triplet state and the forbidden (1Ag−*) excited singlet state.
Abstract: Considerable interest has been shown in the carotenoids for many years due to their wide ranging roles in photochemistry, photobiology and photomedicine and their possible use as a chemopreventative treatment for cancer. Studies about 20 years ago identified the triplet—triplet absorption of β-carotene; this work was of importance in understanding the protective role of these molecules in photosynthesis and bacterial photosynthesis and in porphyric disease treatment. Recently, attention has turned to the very weak fluorescence of these systems using picosecond measurements; results are related to the antenna role of carotenoids in photosynthesis. Photoisomerization continues to be studied with many of the recent developments based on pump-probe measurements using time-resolved resonance Raman spectroscopy for monitoring both the triplet state and the forbidden (1Ag−*) excited singlet state. Interest is also currently centred on the interaction of singlet oxygen with carotenoids; these studies are of value in photophysics (e.g. determination of the carotenoid lowest triplet energy level) and in photomedicine (e.g. evaluation of the use of carotenoids as chemopreventative drugs).
TL;DR: MB-PDA is a weak mutagen and the induction of mutations by this treatment is restricted to high survival rates, however, it seems that this treatment can impair the repair systems in E. coli.
Abstract: The effects of the photodynamic action of methylene blue (MB-PDA) on strains of Escherichia coli were investigated to determine whether the dye could be used in photodynamic therapy (PDT). Using the method of alkaline sucrose gradient sedimentation, it was shown that in darkness MB induces a type of prelesion in DNA that transforms into single-strand breaks in alkaline conditions, provided that the dye is present during the processing of the gradient. This prelesion is completely reversible if the cells are washed immediately to remove the dye. However, after illumination with white light, the prelesions become "fixed" stable lesions, irreversible even after successive washings. The lethal damage induced by MB-PDA in E. coli can be repaired by the excision-repair system (about 30%) and by the recA-dependent repair system (about 70%). Polymerase I enzyme participates actively in the repair of the damage. MB-PDA is a weak mutagen and the induction of mutations by this treatment is restricted to high survival rates. Moreover, MB-PDA does not induce the SOS system (an inducible repair system dependent of the recA and loxA genes products), as measured by Weigle reactivation. However, it seems that this treatment can impair the repair systems in E. coli.
TL;DR: Present evidence indicates that the selective photothermal damage of macromolecules or subcellular organelles requires pulsed excitation at picosecond or nanosecond regimes, while microsecond or millisecond domains are effective in the case of cells or similar structures.
Abstract: Photothermal damage of tissues or endotissular compartments may be induced by pulsed irradiation of either endogenous chromophores (e.g. hemoglobin, melanin) or externally added dyes; the latter should have short triplet lifetimes and mainly decay from electronically excited states by nonradiative pathways. Potential photothermal sensitizers are some metallo derivatives of porphyrins and porphyrinoid compounds, azo dyes and triphenylmethane derivatives. These dyes have the additional property of significant absorbance at wavelengths longer than 600 nm, which can penetrate deep into biological tissues. Spatial confinement of the photothermal process depends on the absorption coefficient of the photoexcited chromophore and its thermal relaxation time. Present evidence indicates that the selective photothermal damage of macromolecules or subcellular organelles requires pulsed excitation at picosecond or nanosecond regimes, while microsecond or millisecond domains are effective in the case of cells or similar structures. The possible use of photothermal sensitization in the treatment of tumors is briefly discussed.
TL;DR: In this paper, the effect of UVB radiation on sugar beet (Beta vulgaris L.) plants was investigated under growth chamber conditions in order to investigate the importance of the background light quality for the effect on plants.
Abstract: Experiments were conducted under growth chamber conditions in order to investigate the importance of the background light quality for the effect of UVB (280–320 nm) radiation on plants. Three week-old sugar beet (Beta vulgaris L.) plants were irradiated for three weeks with enhanced levels of UVB radiation with the following background light conditions: white light (WL) (350–700 nm), WL+UVA (supplementary UVA, 320–400 nm) and "yellow" light (YL) (450–700 nm). The effects of the enhanced UVB radiation were estimated on leaf area, fresh and dry weights of storage roots, chlorophyll and carotenoids, peroxidase activity, fluorescence induction and ultraweak luminescence (UL). Plants grown under YL+UVB died after 10 days. The lowest values for leaf area and fresh and dry weights of storage roots were observed under WL+UVA+UVB conditions. Under WL+UVA and WL+UVA+UVB the decrease in total chlorophyll was mainly a result of the reduction in chlorophyll a. Photosystem II appeared to be inhibited by UVB radiation, while the addition of UVA suggested an ameliorating effect with respect to the rise time kinetics of the chlorophyll fluorescence induction curves. UL of leaves was highest in plants grown under WL+UVB conditions. It is suggested that part of the UL derives from lipid peroxidation. Protective measures may have been afforded by the increase in carotenoids under YL and WL+UVB radiation. Also the leaf peroxidase activity was highest under WL+UVB conditions. (Less)
TL;DR: The data suggest that the photodynamic activity of the pigments in living tissues is probably determined by the monomeric pigment molecules formed in hydrophobic cellular structures.
Abstract: The triplet states of pheophorbide a and pheophytin a were studied in several environments by direct measurement of the phosphorescence of the pigments and photosensitized singlet oxygen (1O2 luminescence. The spectra, lifetimes and quantum yields of phosphorescence and the quantum yields of 1O2 generation were determined. These parameters are similar for monomeric molecules of both pigments in all the environments studied. Aggregation of the pigment molecules leads to a strong decrease in the phosphorescence and 1O2 luminescence intensities, which is probably due to a large decrease in the triplet lifetime and triplet quantum yield in the aggregates. The results obtained for pheophorbide a and pheophytin a are compared with those previously, reported for chlorophyll a. The data suggest that the photodynamic activity of the pigments in living tissues is probably determined by the monomeric pigment molecules formed in hydrophobic cellular structures. Aggregated molecules seem to have a much lower activity.
TL;DR: Some aspects of anticancer porphyrin transport, cellular uptake and photosensitizing properties in cell membranes and lipoproteins are discussed.
Abstract: The mechanisms of the phototoxic effect of anticancer porphyrins used in the photodynamic therapy (PDT) of tumours are not yet completely understood. Irradiation of porphyrins gives rise to singlet oxygen which reacts with key residues of proteins, polyunsaturated fatty acids and cholesterol in membranes, leading to inactivation of various enzymes and transporters. Lipoproteins, mainly low density lipoproteins (LDL), are efficient carriers of anticancer porphyrins in blood and can deliver these photosensitizers to tissues through the apolipoprotein (apo) B/E specific LDL receptor pathway. In this review, we discuss some aspects of anticancer porphyrin transport, cellular uptake and photosensitizing properties in cell membranes and lipoproteins.
TL;DR: The compositions of Photofrin II and haematoporphyrin derivative (HPD) were examined and structures for the hydroxyl-containing precursors to the dimer and trimer, and for the acid-stable oligomeric material in Phot ofrin II, are suggested.
Abstract: The compositions of Photofrin II and haematoporphyrin derivative (HPD) were examined. Dihaematoporphyrin ester was unambiguously synthesized and shown by high performance liquid chromatography (HPLC) not to be a significant component of Photofrin II. Hydrolysis studies showed the presence of an acid-stable oligomer in Photofrin II which comprised about 40% of the total sample. A dimer derivative was isolated from this oligomeric material by fully dehydrating the methyl-esterified acidic hydrolysis product of Photofrin II. The structure of this dimer, in which two porphyrin units are linked by a three-carbon bridge containing a double bond and a methyl group, was determined by nuclear magnetic resonance (NMR) and fast atom bombardment (FAB) mass spectrometry. An analogous trimer was also isolated and identified. Structures for the hydroxyl-containing precursors to the dimer and trimer, and for the acid-stable oligomeric material in Photofrin II, are suggested. The acid-stable oligomeric material is produced in the sodium hydroxide polymerization step of the preparation of Photofrin II.
TL;DR: A pH-sensitive twofold mechanism is proposed for the selective biodistribution of porphyrin-type photochemotherapeutic agents, one involving tissue distribution and the other involving cell membrane penetration by the neutral zwitterion.
Abstract: Volumetric titration of aqueous solutions of haematoporphyrin IX (HP) yields two inflexion points, whereas four pK values can be obtained via mathematical fitting of the experimental data Assignment of all pK protonation sites is made A zwitterion is proposed as the neutral species of HP Evaluation of the pK values of HP in the presence of sodium dodecyl sulphate (SDS) leads to a drastically altered ionic species distribution On the basis of the distribution diagrams obtained, a pH-sensitive twofold mechanism is proposed for the selective biodistribution of porphyrin-type photochemotherapeutic agents, one involving tissue distribution and the other involving cell membrane penetration by the neutral zwitterion
TL;DR: PDT appears to be a promising cancer treatment for different histological tumors that penetrate the host tissue definitely less than a laser beam of 630 nm, which is the appropriate wavelength for PDT.
Abstract: The results of a clinical study of photodynamic therapy (PDT) on early stage cancer in head and neck surgery are presented in this report. 30 patients with T1 malignancies of the face and oropharynx have been treated primarily with PDT. After the longest follow up of 14 months two patients revealed recurrence of the disease or residual tumor, two patients have been retreated because of residual dysplastic cells in the control biopsy, and all other patients stay histologically proven free of disease. Hence, PDT appears to be a promising cancer treatment for different histological tumors that penetrate the host tissue definitely less than a laser beam of 630 nm, which is the appropriate wavelength for PDT. Deeper-penetrating malignomas may be accessable for PDT using insertable filters when applying interstitial laser light.
TL;DR: The physicochemical properties of dicarboxylic porphyrin interactions with membranes appear to be dominated by the charge of the propionic acid chains and the hydrophobic character of other peripheral substituents.
Abstract: The physicochemical properties of dicarboxylic porphyrins are examined with particular emphasis on acid—base equilibria. Interactions with membranes appear to be dominated by the charge of the propionic acid chains and the hydrophobic character of other peripheral substituents. A physicochemical basis for the effect of pH on the incorporation of porphyrins within membranes is given. The effect of lowered tumour pH on the incorporation of porphyrins within membranes and on porphyrin retention is discussed.
TL;DR: High performance liquid chromatography analysis of the liver and tumor extracts of [14C]Ga-PcS3-treated animals did not reveal desulfonation of the dye, however, urine analysis showed the presence of radioactive metabolites lacking the characteristic phthalocyanine absorption.
Abstract: The biodistribution and metabolism of 14C-labeled disulfonated and trisulfonated gallium phthalocyanine (Ga-PcS) was studied in radiation-induced fibrosarcoma tumor-bearing C3H mice. The [14C]Ga-PcS compounds were prepared via the condensation of [14C]phthalic acid and sulfophthalic acid in the presence of gallium chloride and characterized by their spectroscopic and chromatographic properties. The tissue concentrations of the dyes was measured by scintillation counting of the 14C and by extraction and fluorescence measurements. Elevated dye levels were found in the liver, lungs, kidneys and spleen as well as in the tumor. Lower sulfonation of Ga-PcS favored liver and spleen uptake whereas higher dye sulfonation resulted in greater kidney uptake. Both dyes showed high tumor uptake with peak concentrations exceeding those of most tissues except for the liver in the case of Ga-PcS2. The highest tumor uptake was observed with Ga-PcS3. Both dyes were slowly excreted from the body. The liver—feces pathway was favored in the case of Ga-PcS2 with high activities persisting in the liver, even after 21 days. The Ga-PcS3 was preferentially excreted via the kidney—urine pathway. High performance liquid chromatography analysis of the liver and tumor extracts of [14C]Ga-PcS3-treated animals did not reveal desulfonation of the dye.
TL;DR: Effectiveness for cancer localization was examined in 11 cases: four were early stage (three lung cancer and one vocal cord cancer), four were stage I, two were stage III and one was stage IV, all cases were squamous cell carcinoma except for one case of adenocarcinoma.
Abstract: Equipment has been developed for the early-stage diagnosis and treatment of cancer using an excimer dye laser. The excimer laser beam is obtained by exciting XeCl. A 405 nm beam tuned by DPS dye is used for tumour localization and a 630 nm beam obtained with a rhodamine B dye is used for treatment. The equipment was applied clinically on the basis of extensive experimental research. Effectiveness for cancer localization was examined in 11 cases: four were early stage (three lung cancer and one vocal cord cancer), four were stage I, two were stage III and one was stage IV. All cases were squamous cell carcinoma except for one case of adenocarcinoma. Fluorescence was recognized in all lesions and the equipment was effective for localization.
TL;DR: To eliminate the masking effect of the background luminescent of endogenic substances in biological tissues and to increase the luminescence contrast values of malignant tumours, sarcoma-implanted mice were administered with ytterbium porphyrins instead of free porphyrsin radicals.
Abstract: To eliminate the masking effect of the background luminescence of endogenic substances in biological tissues and to increase the luminescence contrast values of malignant tumours, sarcoma-implanted mice were administered with ytterbium porphyrins instead of free porphyrin radicals. This was followed by in vivo luminescence localization of tumours using fibre-laser spectrofluorometry. The luminescence contrast values obtained reached 10—45 which is evidently not a limit.
TL;DR: The photoreceptor cells of invertebrate animals differ from those of vertebrates in morphology and physiology and the present knowledge of the different structures and transduction mechanisms of the two animal groups is described.
Abstract: The photoreceptor cells of invertebrate animals differ from those of vertebrates in morphology and physiology. Our present knowledge of the different structures and transduction mechanisms of the two animal groups is described. In invertebrates, rhodopsin is converted by light into a meta-rhodopsin which is thermally stable and is usually re-isomerized by light. In contrast, photoisomerization in vertebrates leads to dissociation of the chromophore from opsin, and a metabolic process is necessary to regenerate rhodopsin. The electrical signals of visual excitation have opposite character in vertebrates and invertebrates: the vertebrate photoreceptor cell is hyperpolarized because of a decrease in conductance and invertebrate photoreceptors are depolarized owing to an increase in conductance. Single-photon-evoked excitatory events, which are believed to be a result of concerted action (the opening in invertebrates and the closing in vertebrates) of many light-modulated cation channels, are very different in terms of size and time course of photoreceptors for invertebrates and vertebrates. In invertebrates, the single-photon events (bumps) produced under identical conditions vary greatly in delay (latency), time course and size. The multiphoton response to brighter stimuli is several times as long as a response evoked by a single photon. The single-photon response of vertebrates has a standard size, a standard latency and a standard time course, all three parameters showing relatively small variations. Responses to flashes containing several photons have a shape and time scale that are similar to the single-photon-evoked events, varying only by an amplitude scaling factor, but not in latency and time course. In both vertebrate and invertebrate photoreceptors the single-photon-evoked events become smaller (in size) and faster owing to light adaptation. Calcium is mainly involved in these adaptation phenomena. All light adaptation in vertebrates is primarily, or perhaps exclusively, attributable to calcium feedback. In invertebrates, cyclic AMP (cAMP) is apparently another controller of sensitivity in dark adaptation. The interaction of photoexcited rhodopsin with a G-protein is similar in both vertebrate and invertebrate photoreceptors. However, these G-proteins activate different photoreceptor enzymes (phosphodiesterases): phospholipase C in invertebrates and cGMP phosphodiesterase in vertebrates. In the photoreceptors of vertebrates light leads to a rapid hydrolysis of cGMP which results in closing of cation channels. At present, the identity of the internal terminal messenger in invertebrate photoreceptors is still unsolved.(ABSTRACT TRUNCATED AT 400 WORDS)
TL;DR: It is proposed that the light-labile phytochrome pool regulates the synthesis of the photosynthetic apparatus in light-grown plants and that theLight-stable phy tochrome pool functions in the EOD-FR elongation response, the latter pool being present and functional in the au mutant.
Abstract: The effect of end-of-day (EOD) far-red (FR) light treatment on tomato (Lycopersicon esculentum Mill.) plants of the wild type (WT) and an aurea (au) mutant (which is deficient in the spectrophotometrically detectable light-labile phytochrome pool in etiolated seedlings) was studied. Both the WT and au mutant exhibit a quantitatively similar EOD-FR response (i.e. stimulation of elongation growth) indicating that phytochrome is functional in light-grown seedlings of the au mutant. However, no dramatic effects of EOD-FR light on leaf elongation, chlorophyll, carotenoid and soluble protein levels were observed in either the WT or au mutant. The au mutant contained less chlorophyll and more soluble protein per unit fresh weight than the WT. Although practically no anthocyanin could be detected in leaves of the au mutant, the WT showed a tenfold reduction in anthocyanin in response to EOD-FR light. The lower productivity of the au mutant compared with the WT results from its reduced leaf surface area, since its maximum rate of photosynthesis or photosynthetic efficiency appears to be slightly higher than that of the WT. Phytochrome was extracted and partially purified from light-grown plants of the WT and au mutant and was quantified by spectrophotometry. On a fresh weight basis the phytochrome content of au-mutant plants was 66% of that of WT plants. It is proposed that the light-labile phytochrome pool regulates the synthesis of the photosynthetic apparatus in light-grown plants and that the light-stable phytochrome pool functions in the EOD-FR elongation response, the latter pool being present and functional in the au mutant.
TL;DR: There is good evidence that 8-methoxypsoralen is photocarcinogenic in psoriatic patients undergoing long-term photochemotherapy (PUVA) in the U.S.A. but this conclusion has not been supported by two major European studies which have indicated that PUVA is a tumour promoter of damage initiated by other agents.
Abstract: There is good evidence that 8-methoxypsoralen is photocarcinogenic in psoriatic patients undergoing long-term photochemotherapy (PUVA) in the U.S.A. However, this conclusion has not been supported by two major European studies which have indicated that PUVA is a tumour promoter of damage initiated by other agents. Variation in PUVA treatment protocols in the U.S.A. and Europe may partly account for the different conclusions. There is much interest in the therapeutic potential of monofunctional psoralens. It is hoped that these may reduce long-term risk. Monofunctional and cross-linking psoralens have been shown to be photocarcinogenic in mouse skin. The relative risk of different compounds may be assessed in the mouse, but it is important to base comparisons on dose protocols that have been shown to be therapeutically effective.
TL;DR: In this paper, a number of indolic compounds were studied as quenchers of singlet molecular oxygen generated by photosensitization and the ratio of the chemical (reactive) and physical quenching paths was a function of the substitution pattern of the quencher.
Abstract: A number of indolic compounds were studied as quenchers of singlet molecular oxygen. O2(1Δg) generated by photosensitization. The ratio of the chemical (reactive) and physical quenching paths was a function of the substitution pattern of the quencher. Indoles substituted in position 3 gave measurable reaction rates, whereas the parent indole and those derivatives substituted in other nuclear positions predominantly gave physical interaction. The results are discussed in terms of the formation of an exciplex with partial polar character between O2(1Δg) and the indolic compound.
TL;DR: A correlation was found between the side-chain structure of the porphyrins and metalloporphyrin derivatives and their affinity for tumour tissue and that of the metallophorbines, which contained hydrophobic groups showed a high affinity.
Abstract: The tumour-localizing abilities of various kinds of porphyrin derivatives in tumour-bearing hamsters were assessed by nitrogen-pulsed laser spectrofluorometry (N2-PLS). On examination of porphine derivatives (from haemoglobin), it was found that the dimer and acetylated and amidated compounds had a high affinity for tumour tissue; the dimer and hydroxylated compound of phorbine derivatives (from chlorophyll) also showed a high affinity. Furthermore, of the metalloporphines (gallium, zinc and indium complexes), those which contained hydrophilic groups showed a high affinity for tumour tissue; of the metallophorbines (gallium, zinc and indium complexes), those which contained hydrophobic groups showed a high affinity. A correlation was found between the side-chain structure of the porphyrins and metalloporphyrins and their affinity for tumour tissue.