bluuebunny/crossref_metadata_2025_split huggingface dataset:
PHOTOCHEMISTRY and PHOTOBIOLOGY OF MELANOGENIC METABOLITES: FORMATION OF FREE RADICALS*
Authors: Koch Walter H. , Chedekel Miles R. 
Published: January 2008

AbstractNormal melanocytes produce specialized subcellular organelles called melanosomes within which the biochemical processes of melanogenesis occurs. During sunlight‐induced melanogenesis, the melanocyte‐specific enzyme tyrosinase catalyzes the oxidative polymerization of 3,4‐dihydroxyphenyl‐alanine (DOPA) to melanin. Nucleophilic addition of cysteine to tyrosinase‐generated dopaquinone leads to the formation of cysteinyldopas, precursors of pheomelanin and excreted by‐products of eumelanogenesis. Under conditions of low sulfhydryl content, dopaquinone undergoes a 1,4 intramolecular cycloaddition to yield, after further oxidation, 5,6‐dihydroxyindoles and/or 5,6‐dihydroxy‐2‐carboxyindoles. These indolic melanogenic intermediates and their O‐methylated metabolites, like cysteinyldopas, are excreted by actively pigmenting as well as dormant melanocytes. Indeed, it has been determined that in humans, the serum and urine concentrations of these melanogenic metabolites increase dramatically following exposure to sunlight, UVA (315‐400 nm), UVB (290‐315 nm) exposure, as well as during PUVA therapy and in melanoma patients, and thus have proved to be excellent biochemical markers of normal and pathological melanocyte function. While controlled light exposure or PUVA therapy generally lead to 100‐300% increases in 5‐S‐cysteinyldopa (5SCD) and 5‐methoxy‐6‐hydroxyindole‐2‐carboxylic acid (6HMICA) serum levels (normal concentration about 4–16 nmol l‐1), the local concentrations in the skin and especially in the actively pigmenting melanocyte may be as high as 200 μM.Evidence is presented to document that a number of catecholic melanin precursors, including cysteinyldopas and dihydroxyindoles, are photochemically unstable in the presence of biologically relevant ultraviolet radiation (i.e. wavelengths ± 300 nm). Initial photochemical processes involve free radical production; continued photolysis yields polymeric photoproducts. Radicals produced during melanogenic metabolite photolysis have been identified by ESR spin trapping, laser flash photolysis and pulse radiolysis techniques and include hydrated electrons (eaq), hydrogen atoms (H'), hydroxyl radicals (OH), semiquinones, aryl thiyl (ArS), and alanyl carbon‐based radicals. In vitro investigations of the potential photobiological significance of these reactions have demonstrated photolysis of cysteinyldopas may lead to photoinitiated DNA binding and single strand break induction. The above mentioned radical species may also damage proteins and initiate lipid peroxidation. Definitive evidence for the occurrence of these phototoxic reactions in vivo is currently unavailable, however our in vitro studies suggest a possible role for melanogenic metabolite photolysis in acute and chronic solar responses of human skin.
ANALYSIS OF FLASH PHOTOLYSIS DATA BY A GLOBAL FIT WITH MULTI‐EXPONENTIALS–I. DETERMINATION OF THE MINIMAL NUMBER OF INTERMEDIATES IN THE PHOTOCYCLE OF BACTERIORHODOPSIN BY THE ‘STABILITY CRITERION’
Authors: Maurer R. , Vogel J. , Schneider S. 
Published: January 2008

AbstractA major problem in establishing a kinetic scheme for photo‐induced reaction sequences is the determination of the unknown number of important intermediates. It is shown that in addition to the χ2‐value and the distribution of the residuals obtained from a least‐squares fit of the experimental curves by a sum of exponentials, the stability of the apparent rates towards an increase of the number of exponentials with arbitrary test values can be used as an additional criterion. Experimental data describing the photocycle of bacteriorhodopsin after the appearance of intermediate K (t > 1 μs) are analysed with the described algorithm. It is found that 5 exponentials are necessary and sufficient for the fit.
ISOLATION and CHARACTERIZATION OF THE PHOTOADDUCTS OF 5,7‐DIMETHOXYCOUMARIN and ADENOSINE
Authors: Cho Tae Heung , Shim Hyun Kwan , Shim Sang Chul 
Published: January 2008

AbstractThe isolation and structural characterization of the photoadducts of 5,7‐dimethoxycoumarin and adenosine are described. Two of the major photoadducts were isolated by preparative column chromatography and reverse‐phase high performance liquid chromatography. Structure of the products was determined by UV, FT‐IR, mass spectrometry, 1H NMR and 13C NMR studies, including the homonuclear decoupling, COSY method and DEPT experiments. The photoadducts were not C4‐cycloadducts but simple addition products in contrast to pyrimidine base adducts. Covalent bonds were formed between the carbon‐3 or carbon‐4 of the pyrone ring of 5,7‐dimethoxycoumarin and the carbon‐5’of ribose ring in adenosine.
PURE SINGLET OXYGEN CYTOTOXICITY FOR BACTERIA
Authors: Dahl ThomasA. , RobertMiddenand W. , Hartman PhilipE. 
Published: January 2008

AbstractWe have modified the separated‐surface‐sensitizer singlet oxygen generating system previously described (Midden and Wang, 1983) for the efficient exposure to pure singlet oxygen of bacteria collected on membrane filters. Physical separation of the photosensitizer and the bacteria eliminates the possibility of direct interaction between bacteria and photoexcited sensitizers that could lead to Type I (non‐singlet oxygen) photooxidation processes. This system was used to examine the bacterial cytotoxicity of singlet oxygen. The role of singlet oxygen was confirmed by measuring the decrease in cytotoxicity as the distance between the singlet oxygen source and the bacteria was increased. The gas phase half‐life of the intermediate responsible for cell killing, determined from this distance dependence analysis (24 ± 6 ms), is the same as that calculated from literature data for the gas phase half‐life of singlet oxygen (53 ± 37 ms). Killing of various strains of Salmonella lyphimurium and Escherichia coli was compared at the same dose of singlet oxygen. Bacteria were killed by singlet oxygen at levels several orders of magnitude lower than those effective in killing by H2O2. Altered DNA repair capacities (uvrB, recA, xth, nth, pKM101) did not affect survival. Incomplete cell wall lipopolysaccharide formation decreased survival following singlet oxygen exposure. Overproduction of the singlet oxygen quencher histidine increased survival, as did accumulation of the dipeptide carnosine (β‐alanyl‐L‐histidine). No evidence for mutagenicity of exogenous singlet oxygen exposure was obtained in a variety of S. typhimurium strains killed to 35% survival.
STUDIES ON THE in vitro O2‐DEPENDENT INACTIVATION OF NADH‐GLUTAMATE SYNTHASE FROM Chlamydomonas reinhardii STIMULATED BY FLAVINS
Authors: Gotor Cecilia , Márquez AntonioJ. , Vega JoséM. 
Published: January 2008

AbstractThe NADH‐glutamate synthase (EC 1.4.1.14) complex fromChlamydomonas reinhardiimay experiencein vitrotwo kinds of 02‐dependent inactivation stimulated by flavins.A peroxide‐mediated inactivation of enzyme, which affects the NADH‐ and MVt‐glutamate synthase activities of the complex, but not the NADH‐dehydrogenase activity, can be obtained by aerobic incubation of the enzyme with NAD(P)H plus flavin. This inactivation of enzyme seems to be due to a permanent modification of sulfhydryl groups near the active site for L‐glutamine or 2‐oxoglutarate. The addition of 10 mM dithioerythritol to inactive NADH‐glutamate synthase produces a significant, but not complete, reactivation of the enzyme.On the other hand, the NADH‐glutamate synthase is highly susceptible to a photodynamic inactivation caused by singlet02.Aerobic incubation of the active enzyme with flavin under illumination leads to the irreversible inactivation of all the activities associated with the enzymatic complex.
PHOTODYNAMIC THERAPY OF MALIGNANT BRAIN TUMORS: CLINICAL and NEUROPATHOLOGICAL RESULTS
Authors: Kostron H. , Weiser G. , Fritsch E. , Grunert V. 
Published: January 2008

Abstract Fourteen patients with malignant brain tumors were treated 17 times with photodynamic treatment following either intravenous, selective intraarterial or direct intratumoral injection of Photofrin II. In eight patients the photodynamic treatment was followed immediately by single dose radiation of 4 Gy of ionizing radiation. The three injection modalities resulted in 2.5 μ.g. 3.2 μ.g and 9.8 μ,g g−1 tumor tissue respectively after 3 days. The histological examination immediately after light irradiation after intravenous and intra‐arterial injection demonstrated a predominantly vascular and cellular effect whereas the direct injection resulted in a direct cellular effect with little effect on vascular structures.The median survival time for the three patients with multiple recurrences of the glioblastoma was 5 months, five patients with the first recurrence have a survival time of 2 to 7 months following PDT and six patients with the primary manifestation are surviving now up to 12 months. The intraarterial and direct intratumoral injection was tolerated well by the patients without increased skin phototoxicity.These results indicate that the direct intratumoral and selective intraarterial injection of HPD are a feasible route for PDT however they are too preliminary to allow a final conclusion of the value of this modified PDT in the treatment of malignant brain tumors.
PHOTOINDUCED DEGRADATION AND MODIFICATION OF PHOTOFRIN II IN CELLS in vitro
Authors: Moan Johan , Rimington Claude , Malik Zvi 
Published: January 2008

Abstract—Human cells of the line NHIK 3025 were incubated with Photofrin II (PII) and exposed to light. Fluorescence‐ and absorption spectra of PII in the cells were measured. Light exposure resulted in a degradation of PII in the cells and changes in the shape of the fluorescence spectra. These changes are probably partly due to a photochemical modification of PII and to a relocalization of PII in the cells. Notably, a destruction of binding sites for PII on or close to proteins was caused by the light exposure. The rate of the light‐induced decay of the porphyrin fluorescence intensity was only slightly increasing with the PII concentration, indicating that each porphyrin molecule is mainly degraded by photoproducts originating from itself. On the other hand, the rate of the degradation of porphyrin binding sites on the proteins increased with increasing PII concentrations.The excitation spectrum of PII in cells has a peak at285–290 nm attributed to energy transfer from proteins to porphyrins located close to the proteins. The intensity of this peak relative to the intensity of the Soret band increases with decreasing porphyrin concentrations. This might indicate that some of the binding sites close to proteins have a higher affinity for the porphyrin than binding sites at longer distances from the proteins.
ULTRAVIOLET RADIATION ‐ INDUCED MALIGNANT MELANOMA IN Monodelphis domestica
Authors: D. Ley Ronald , A. Applegate Lee , Padilla R. Steven , D. Stuart Thomas 
Published: January 2008

Abstract—Several lines of evidence support the hypothesis that ultraviolet radiation (UVR) is involved in the etiology of cutaneous melanoma in humans. However, progress in understanding the mechanisms involved in induction of melanotic tumors by UVR has been hindered by lack of a suitable animal model. During the course of multiple exposures (3 times/wk for 70 wk) of the South American opossum, Monodelphis domestica, to UVR, we first observed the appearance of areas of dermal melanocytic hyperplasia (MH) on the exposed skin. Post‐UVR exposure to photoreactivating light (320–500 nm) suppressed the occurrence of MH. We also observed at 100 weeks from first exposure that 10 of 46 surviving animals had developed melanotic tumors which arose, presumably, from areas of MH. Tumors on three of the 10 animals have been classified as malignant melanomas based on metastasis to lymph nodes. We conclude from these results that UVR can act as a complete carcinogen for melanoma induction and, based on the photoreactivation of MH induction, that DNA damage is involved in melanoma formation.
PHOTOSENSITIZED OXIDATION OF BIOMATERIALS and RELATED MODEL COMPOUNDS
Authors: Davila Jorge , Harriman Anthony 
Published: January 2008

Abstract—Aluminium trisulfonatophthalocyanine (AIPCS), a dye being widely advocated for use in photodynamic therapy, produces singlet oxygen with a quantum yield of 0.34 in oxygenated water at pH 7. Triplet A1PCS abstracts an electron from a variety of amines and phenols, the rate of electron transfer depending upon the thermodynamic driving force, forming the AIPCS radical anion. This latter species reduces molecular oxygen to superoxide ions with high efficiency. The triplet state also abstracts an electron from biological components, including NADH, vitamin C, cysteine, methionine, tyrosine, tryptophan, uracil, and guanine, but not from DNA. These results suggest that photoinduced electron abstraction from appropriate biomaterials could compete with singlet oxygen production under in vivo conditions.
TRIPLET STATE OF METALLOPORPHYCENES: ZnPCl, PdPC2, PtPC2, and NiPC2
Authors: Toporowicz Moshe , Ofir Hanna , Levanon Haim , Vogel Emanuel , Koucher Matthias , Pramod Kakumanu , Fessenden Richard W. 
Published: January 2008

Abstract—We report on a study of the photoexcited triplet state, at low temperatures in ordered liquid crystals, and at room temperatures in the liquid phase, of some new metalloporphycenes: normal zincporphycene, ZnPCl; Pd(II), and Ni(II) complexes of 2,7,12,17‐tetra‐n‐propylporphycene, PdPC2, PtPC2, and NiPC2, respectively. The triplet state at low temperature is obtained by selective laser excitation and its magnetization response is detected by EPR in the 250 ns time scale. From triplet EPR line shapes and triplet spin polarization directions it is concluded that the zinc cation lies above the molecular plane and the palladium cation fits into the porphycene's cavity. Such a proposed structure implies a strong spin‐orbit interaction in PdPC2, thus resulting in an out‐of‐plane active spin state (z‐axis), whereas that in ZnPCl, having a smaller spin‐orbit interaction, in‐plane (x,y‐axes) are the active spin states. Laser photolysis of the metalloporphycenes gives rise to detectable triplets of ZnPCl, PdPC2 and PtPC2 with triplet lifetimes of 26, 5 and 0.2 µs, respectively. The sensitization experiment, using β‐acetonaphthone as a sensitizer to produce the triplet, results in detectable transients of only ZnPCl and PdPC2 with much longer triplet lifetimes of 85 and 20 µs, respectively. The short triplet lifetime of PtPC2 (and probably that of NiPC2) do not allow for triplet detection with the present sensitizer. However, the latter two metalloporphycenes quench the triplet lifetime of β‐acetonaphthone from 29 to 10µs.
PHOTOCONTROL OF ANTHOCYANIN SYNTHESIS IN TOMATO SEEDLINGS: A GENETIC APPROACH*
Authors: Adamse Paulien , Peters Janny L. , Jaspers Patricia A. P. M. , Tuinen Ageeth VAN , Koornneef Maarten , Kendrick Richard E. 
Published: January 2008

Abstract—The photocontrol of anthocyanin synthesis in dark‐grown seedlings of tomato (Lycopersicon esculentum Mill.) has been studied in an aurea (au) mutant which is deficient in the labile type of phytochrome, a high pigment (hp) mutant which has the wild‐type level of phytochrome and the double mutant au/hp, as well as the wild type. The hp mutant demonstrates phytochrome control of anthocyanin synthesis in response to a single red light (RL) pulse, whereas there is no measurable response in the wild type and au mutant. After pretreatment with 12 h blue light (BL) the phytochrome regulation of anthocyanin synthesis is 10‐fold higher in the hp mutant than in the wild type, whilst no anthocyanin is detectable in the au mutant, thus suggesting that it is the labile pool of phytochrome which regulates anthocyanin synthesis. The au/hp double mutant exhibits a small (3% of that in the hp mutant) RL/far‐red light (FR)‐reversible regulation of anthocyanin synthesis following a BL pretreatment. It is proposed that the hp mutant is hypersensitive to the FR‐absorbing form of phytochrome (Pfr) and that this (hypersensitivity) establishes response to the low level of Pfl. (below detection limits in phytochrome assays) in the au/hp double mutant.
DETERMINANTS OF PHOTOSENSITIZATION BY PURPURINS
Authors: Kessel David 
Published: January 2008

Abstract—Studies were carried out on two purpurins, NT2 and an analog, Sn.NT2H2. Both are photosensitizers, but the latter is substantially more effective against neoplastic cells in vivo. These hydrophobic dyes can be solubilized via Cremophor EL emulsions. We found both dyes to be approximately equitoxic to murine leukemia L1210 cells in culture, in terms of intracellular concentrations. But uptake of NT2 was 10‐fold less efficient than Sn.NT2H2, i.e. a 10‐fold higher extracellular level of NT2 was needed to produce an equitoxic response. Fluorescence measurements indicate that NT2 partitions to a very hydrophobic intracellular environments; its phototoxicity was related to inhibition of biosynthesis of DNA. In contrast, SN.NT2H2 was accumulated at more hydrophilic loci (the apparent dielectric constant is consistent with a membrane interface) and mediated photodamage at sites of membrane transport.
SINGLET OXYGEN GENERATION OF PORPHYRINS, CHLORINS, AND PHTHALOCYANINES
Authors: Kimel S. , Tromberg B. J. , Roberts W. G. , Berns M. W. 
Published: January 2008

Abstract—The production of singlet oxygen was measured indirectly for three classes of photosensitizers: porphyrins (Photofrin II, TPPS4), chlorins (MACE, DACE), and a phthalocyanine (CASPc). Buffered solutions of sensitizers and singlet oxygen acceptors were irradiated with a CW dye laser and the oxygen depletion was monitored electrochemically with a Clark‐type microelectrode. A comparison of oxygen‐depletion rate constants and quantum efficiencies yields the order of efficiency of the sensitizers: TPPS4> MACE > PII > DACE > CASPc. For singlet oxygen acceptors the order was: furfuryl alcohol > imidazole > tryptophan. CHO cell suspensions were also used as acceptors. Here the order of efficiency (per absorbed photon) was PII > MACE = CASPc. Expressed in terms of oxygen depletion per cell the order was CASPc = PII > MACE. When performing cell clonogenicity studies the order of efficiencies, expressed as percentage cell kill per unit weight of sensitizer, was CASPc > PII > MACE = DACE. The discrepancy between the efficiencies of sensitizers to generate singlet oxygen and their cytotoxicity was explained in terms of photodegradation (for the chlorins), intracellular localization (for PII), and contributions from a Type I mechanism (for CASPc).
EFFECTS OF ORAL RETINOID (VITAMIN A AND ETRETINATE) THERAPY ON PHOTOCARCINOGENESIS IN HAIRLESS MICE
Authors: Kelly Graham E. , D.Meikle William , Sheil A. G. Ross 
Published: January 2008

Abstract—Oral retinoid therapy has been considered for the prevention of skin carcinogenesis in humans, although animal studies have failed to provide any evidence of a protective effect of these drugs in the one‐step photocarcinogenic system. In this study, oral therapy with vitamin A or a synthetic analogue, etretinate, was tested for ability to protect hairless mice(Skh‐hrl) from the development of skin tumours following exposure to broad‐band light(280–700 nm) for 25 weeks. Retinoids were given by gavage 3 times weekly either at low dosage(2000 IU vitamin A or 4 mg etretinate per kg body weight) or high dosage(10 000 IU vitamin A or 20 mg etretinate per kg body weight). None of the retinoid therapies compared to control mice(gavage vehicle only) modified skin tumour production in terms of time to onset of tumours, total tumour yield, or the types of tumours produced.
TWO‐DIMENSIONAL IMAGING OF ULTRA‐WEAK EMISSION FROM INTACT SOYBEAN ROOTS
Authors: Ichimura Teijiro , Hiramatsu Mitsuo , Hirai Nobuyuki , Hayakawa Tsuyoshi 
Published: January 2008

Abstract—Two‐dimensional imaging of photons emitted from soybean roots was achieved with an ultra‐high sensitivity photon‐counting image acquisition system. The detected images reveal that a soybean root itself emits very weak light and photon flux from the growing point of the root is more intense than that from other parts of the roots.
SINGLET MOLECULAR OXYGEN QUENCHING BY SATURATED AND UNSATURATED FATTY‐ACIDS AND BY CHOLESTEROL
Authors: Vever‐Bizet C. , Dellinger M. , Brault D. , Rougee M. , Bensasson R. V. 
Published: January 2008

Abstract—The rate constants of molecular singlet oxygen quenching by saturated and unsaturated fatty‐acids and by cholesterol‐membrane critical components ‐ membrane critical components ‐ have been measured by time resolved detection of the 1270 nm phosphorescence of singlet molecular oxygen [O2(1δg)]. We have determined (i) an increment of 5.7 times 102M‐1s‐1per ‐CH2‐ in C6D6and CD3OD for saturated fatty acids between C4and C20, (ii) an increment of 3 times 104M‐1s‐1per non‐conjugated cu‐double bond for C18unsaturated fatty acids, identical in C6D6and CD3OD, (iii) a lower quenching rate constant by a factor of 2.7 for thetrans‐C16andtrans‐C18as compared to the corresponding cis‐monounsaturated fatty acids, (iv) a rate constant of O2(1δg) quenching by cholesterol of 5.7 times 104M‐ls‐lin benzene. These rate constants are compared to those obtained for other membrane cellular components.
A NEW DOSIMETER FOR ULTRAVIOLET‐B RADIATION
Authors: Wong C. F. , Fleming R. , Carter S. J. 
Published: January 2008

Abstract— A type of polycarbonate plastic was found to be sensitive to ultraviolet (UV) radiation. The damage to the material due to UV exposure was revealed by etching in a strong alkaline solution. The latent effect can be retained in the material for a period of at least 30 days. The material was tested for use as a detector of ultraviolet‐B (UV‐B 280–320 nm) radiation.The response of the detector in the wavelength region between 254 and 365 nm was determined using a set of narrow‐band filters and a 200 W UV xenon‐mercury lamp. The maximum UV effect in the detector was observed at a wavelength of 290 nm. The spectral response curve was found to be similar to the human erythema action spectrum.The detector may be miniaturized for dosimetric applications. The dose response curve is linear in the region up to an erythemal dose of 300 mJcm−2. Laboratory and field tests showed that the dosimeter response to UV exposure was additive and was independent of dose rate. Further experiments suggested that the dosimeter was stable against changes in temperature and humidity.
THE BIOLOGICAL EFFECTS OF UV‐B ON THE EYE
Authors: Taylor Hugh R. 
Published: January 2008

Abstract–The adverse effects of ultraviolet‐B (UV‐B) radiation on the eye have been suspected but only recently have they been quantified by epidemiologic studies in humans. These studies became possible as methods to qualify individual ocular UV‐B exposure were developed. A consistent dose‐dependent association between ocular UV‐B exposure and two common types of cataract (cortical and posterior subcapsular) has been shown. Although suggested by experimental studies, at present, evidence does not exist to link UV‐B exposure to senile macular degeneration. Ocular exposure to UV‐B is also associated with several corneal changes, pterygium, climatic droplet keratopathy, and acute photokeratitis (snow blindness). Significant reduction in ocular UV‐B exposure results from the use of eyeglasses and hats.