bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluorescence Properties of Isolated Intact Normal Human Corneas
Authors: Uma L. , Sharma Yogendra , Balasubramanian D.
Published: January 2008

Abstract— We have examined the fluorescence properties of excised intact normal human corneas from over a hundred donors, using synchronous excitation fluorescence spectroscopy. In some of the corneas from the donors, a fluoro‐phore with an excitation band centered at 330 nm was observed. This fluorophore does not seem to correspond to the dityrosine moiety or to any photoproducts of tryptophan. Isolated corneas irradiated with light of 295 nm wavelength do not produce any fluorescent photoproducts, suggesting that the intact tissue has endogenous quenchers, radical scavengers and antioxidants that inhibit its photodamage. The non‐tryptophan fluorophores that accumulate in some corneas thus appear to arise largely from the nonenzymatic glycosylation (glycation) of the constituent proteins as similar fluorophores are detected in the corneas of rats in which diabetes is induced.
Supramolecular Cationic Tetraruthenated Porphyrin Induces Single‐Strand Breaks and 8‐Oxo‐7,8‐dihydro‐2′‐deoxyguanosine Formation in DNA in the Presence of Light
Authors: Onuki Janice , Ribas Adriana V. , Medeiros Marisa H. G. , Araki Koiti , Toma Henrique E. , Catalani Luiz H. , Di Mascio Paolo
Published: January 2008

Abstract— The aim of this investigation is the evaluation of DNA interaction of with tetraruthenated porphyrin (TRP) and of DNA damage in the presence of light. Direct‐fluorescence and electronic absorption measurements after incubation of DNA with TRP indicate strong binding between pBR322 DNA or calf thymus DNA with the modified porphyrin. Exposure of pBR322 DNA to TRP (up to 3 μM) and light leads to single‐strand break formation as determined by the conversion of the supercoiled form (form I) of the plasmid into the nicked circular form (form II). Oxidative DNA base damage was evaluated by the detection of 8‐oxo‐7,8‐dihydro‐2′‐deoxyguanosine (8‐oxodGuo) after irradiation of calf thymus DNA in the presence of the TRP. The data demonstrated a dose and time dependence with each type of DNA damage. These data indicate (1) a specificity of the binding mode and (2) type I and II photoinduced mechanisms leading to strand scission activity and 8‐oxodGuo formation. Accordingly, singlet molecular oxygen formation, after TRP excitation, was confirmed by near‐infrared emission. From these investigations a potential application of TRP in photodynamic therapy is proposed.
Rapid Initiation of Apoptosis by Photodynamic Therapy
Authors: Luo Yu , Chang C. K. , Kessel David
Published: January 2008

Abstract— Photodynamic therapy (PDT) of neoplastic cell lines is sometimes associated with the rapid initiation of apoptosis, a mode of cell death that results in a distinct pattern of cellular and DNA fragmentation. The apoptotic response appears to be a function of both the sensitizer and the cell line. In this study, we examined photodynamic effects of several photosensitizers on murine leukemia P388 cells. Two drugs, a porphycene dimer (PcD) and tin etiopurpurin (SnET2), which localized at lysosomal sites, were tested at PDT doses that resulted in 50% loss of viability (LD50), measured by the 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide (MTT) assay. An oligonucleosomal pattern of DNA degradation was observed within 1 h after irradiation. Neither sensitizer antagonized PDT‐mediated internucleosomal DNA cleavage by the other. Very high PDT doses with either agent abolished this rapid internucleosomal cleavage. Exposure of cells to high concentrations of either sensitizer in the dark also resulted in rapid DNA fragmentation to nucle‐osomes and nucleosome multimers; this effect was not altered by the antioxidant 6‐hydroxy‐2,5,7,8‐tetramethyl‐chroman‐2‐carboxylic acid (trolox), although the latter could protect cells from cytotoxicity and apoptotic effects caused by LD50 PDT doses. Photodamage from two cat‐ionic sensitizers, which localized at membrane sites, caused rapid DNA cleavage to 50 kb particles; however, no further fragmentation was detected after 1 h under LD10, LD50 or LD95 PDT conditions. Moreover, the presence of either cationic sensitizer inhibited the rapid internucleosomal cleavage induced by SnET2 or PcD photodamage. The site of photodynamic action may therefore be a major determinant of the initiation and rate of progression of apoptosis.
Protecting Fibrinogen with Rutin during UVC Irradiation for Viral Inactivation
Authors: Marx Gerard , Mou Xioude , Freed Richard , Ben‐Hur Ehud , Yang Chi , Horowitz Bernard
Published: January 2008

Abstract— Fibrinogen solutions were irradiated with UVC (254 nm) to inactivate contaminating viruses. In order to protect fibrinogen during UVC irradiation, 0.5 mM rutin was added prior to UVC exposure and subsequently removed during processing. Viral kill by 0.1 J/cm2 UVC resulted in the following inactivation values (log 10): non‐lipid‐enveloped viruses: Parvo 5.5; encephalomyocarditis virus 6.5; hepatitis A virus 6.5: lipid‐enveloped viruses: human immunodeficiency virus 5.7; vesicular stomatitis virus 5.7. Fibrinogen irradiated with 0.5 mM rutin did not significantly differ from unirradiated material in terms of clot time and breaking strength. In the absence of rutin, UVC irradiation of fibrinogen at similar fluence led to loss of solubility, increased clot time and the cleavage of fibrino‐peptides that reacted with dinitro‐phenyl hydrazine as a test for ketonic carbonyl groups. High‐performance liquid chromatography and mass spectrometry data showed that rutin exposed to UVC formed numerous breakdown, oxidation and combinational products. Experiments with 3H‐rutin showed that after UVC irradiation, subsequent processing by a C18 resin and alcohol precipitation removed >99% rutin, representing <10 ppm rutin in the final fibrinogen preparations. Residual 3H‐rutin was not covalently bonded to the fibrinogen. Immunochemical studies with rabbit antisera to UVC irradiated (with rutin) fibrinogen showed the absence of neoimmungens. By all measures, rutin prevents fibrinogen degradation during virucidal UVC irradiation.
Comparison of Green and Lowtran Radiation Schemes with a Discrete Ordinate Method UV Model
Authors: Weihs P. , Webb A. R.
Published: January 2008

Abstract— Using the same input parameters for the calculations, the Green and Lowtran codes for calculating UV irradiances were compared to the discrete ordinate method (DOM) model by Stamnes et al, which was used as a reference. The comparisons were performed at 305 and 380 nm for different ozone concentrations, aerosol optical depths and aerosol absorption characteristics. No obvious dependencies on optical depth, single scattering albedo or column ozone were found for the ratio of the Green and the Lowtran code to the DOM model. At 380 nm the Green model agrees with DOM within 10%, whereas the Lowtran code shows discrepancies of ±25%. At 305 nm the Green model shows 10% higher values than the DOM model at low zenith angles and up to 80% lower values for zenith angles between 60 and 80°. The Lowtran code shows 60% higher values than DOM at small zenith angles and 60% lower values at large zenith angles. When the spectra from each model were weighted with the erythemal action spectrum the Green model overestimated the DOM results by less than 10% for zenith angles less than 50°. Discrepancies between DOM and Lowtran models exceeded 10% except for a small range of zenith angles.
Overexpression of Medaka (Oryzias latipes) Photolyase Gene in Medaka Cultured Cells and Early Embryos
Authors: Funayama Tomoo , Mitani Hiroshi , Shima Akihiro
Published: January 2008

To study the role and the regulation of the photolyase gene in the Medaka (small teleost), we constructed a eu‐karyotic expression plasmid of the Medaka photolyase gene and introduced it into Medaka cells in vitro and in viva The expression plasmid contains a cytomegalovirus enhancer and a thymidine kinase promoter to overex‐press the photolyase gene of the Medaka. First, we trans‐fected this construct into cultured Medaka cells and established several lines of transfectant. Every transfectant showed enhanced ability of pyrimidine dimer repair in the presence of fluorescent light. In the transfectant that showed the most enhanced ability of photorepair, the augmented transcription of photolyase gene was observed compared with that of progenitor OL32 cells. In this transfectant, we also observed an enhanced rate of UV survival with 20 min of fluorescent light treatment after irradiation with a 400 J/m2 UV sunlamp. Next, the expression construct was microinjected into the embryos of the Medaka at the one cell stage. Compared with the nontreated counterparts, the overexpression of a photolyase gene was detected in the microinjected embryos, but we failed to detect a significant increase in photo‐reactivability of death at the midblastula stage.
Excited‐State Raman Spectroscopy of Inorganic Compounds
Authors: Zink Jeffrey I.
Published: January 2008

Abstract— Raman spectra of inorganic complexes in excited electronic states are discussed. A brief overview of the field of transient Raman spectroscopy and experimental considerations are presented. Two examples from the author's laboratory are used to illustrate the type of information that can be obtained. The first example, an excited‐state Raman spectroscopic study of K3[Mn(CN)5NO], is chosen because it illustrates the connections between excited‐state molecular structure and vibrational properties. The pump pulse causes a change from a linear sp‐hybridized NO containing a triple bond to a bent sp2‐hybridized NO containing a double bond. Both the NO stretch and normal modes involving other ligands are measured and interpreted. The second example is chosen to illustrate the vibrational consequences of photoinduced electron transfer. The Raman spectra of W(CO)4(diimine) complexes (diimine = 2,2'‐bipyridine, 4,4'‐dimethyl‐2,2'‐bipyridine, and isopropyl‐pyridine‐2‐carbaldehyde imine) in the lowest tungsten to diimine charge transfer excited state are discussed. The excited‐state peaks are assigned to ligand ring deformation modes and to carbonyl stretching modes. The totally symmetric cis‐carbonyl stretching mode in the charge transfer excited state is about 50 cm' higher in energy than that of the molecule in the ground electronic state. The increase is interpreted in terms of loss of metal‐car‐bonyl back‐bonding in the charge transfer excited state. Finally, a summary of the field's strengths and difficulties and a brief discussion of the future perspectives are presented.
A Novel Singlet Oxygen Reaction
Authors: Lin Yong‐Yue , Li Guo‐Bao , Zhang Yuan‐Hong , Leung Hiu‐Kwong
Published: January 2008

Abstract— 1‐Aryl‐2‐methyl‐4,5‐dihydropyrrol‐3‐carboxylic acid ethyl ester (a cyclic enamine) was observed to dehydrogenate to give 1‐aryl‐2‐methyl‐pyrrol‐3‐carboxylic acid ethyl ester upon irradiation in the presence of oxygen and in the presence or absence of meso‐tetraphenylporphine (TPP). N‐Aryl cyclic amines were shown to be singlet oxygen sensitizers.
Differential Suppression of the Human Mixed Epidermal Cell Lymphocyte Reaction (MECLR) and Mixed Lymphocyte Reaction (MLR) by Cis‐Urocanic Acid
Authors: Hurks H. M. H. , Out‐Luiting C. , Van der Molen R. G. , Vermeer B. J. , Claas F. H. J. , Mommaas A. M.
Published: January 2008

Abstract— Cis‐urocanic acid (UCA), formed in the stratum corneum by UV irradiation of trans‐UCA has been proposed as a mediator of UV‐induced immunosuppression in the skin. In this study, we examined the in vitro effect of cis‐UCA (6‐100 μg/mL) on the human mixed lymphocyte reaction (MLR) and the mixed epidermal cell lymphocyte reaction (MECLR). Addition of cis‐UCA (purified or in a mixture with trans‐UCA) did not affect the MLR but was able to induce a 20% suppression of the MECLR responses. Because this effect of cis‐UCA on the MECLR was not as strong as could be expected from previous in vivo results, we designed a set of experiments in order to enhance the in vitro immunosuppressive capacity of cis‐UCA. Firstly, we preincubated epidermal cells with UCA (50 u.g/mL) for 3 or 6 days before culture in the MECLR because in vivo repeated UV exposure can lead to a photostationary state, where cis‐UCA may be present for several weeks. This pretreatment with cis‐UCA resulted in a maximal decrease of the MECLR responses of 27%, whereas trans‐UCA had no effect. Secondly, we investigated whether UVB irradiation of epidermal cells could make cells more sensitive to cis‐UCA. However, addition of trans‐ or cis‐UCA did not potentiate the reduced alloac‐tivating capacity of UVB‐irradiated cells. Finally, we examined the possibility of a synergistic effect of cis‐UCA with histamine. Addition of histamine suppressed the MLR and MECLR responses, but neither cis‐ nor trans‐UCA were able to modulate this decrease. We conclude that cis‐UCA can partly downregulate the human MECLR but not the MLR. The mechanism involved in this differential downregulation is not known. In this respect it is striking that cis‐UCA does not potentiate the UVB‐ or histamine‐induced suppression of the MECLR.
Comparative Study of Ru(bpz)32+Ru(bipy)32+and Ru(bpz)2CI2 as Photosensitizers of DNA Cleavage and Adduct Formation
Authors: Vicendo Patricia , Mouysset Serge , Paillous Nicole
Published: January 2008

Abstract— The efficiency of ruthenium complexes for photosensitizing DNA damage depends on the oxidizing character of their ligands. Here we report on the difference in behavior of tris(2.2'‐bipyrazyl)ruthenium(II) (Ru[bpz]32+), tris(2,2′‐bipyridyl)ruthenium(II) (Ru[bipy]32+) and cis‐dichlorobis(2,2′‐bipyrazyl)ruthenium(II) (Ru[bpz]2Cl2). Upon irradiation at 436 nm, Ru(bpz)32+was far less stable than Ru(bipy)32+. Ru(bpz)32+in phosphate buffer containing NaCl undergoes a photoanation reaction leading to the formation of Ru(bpz)2Cl2, as previously reported also in organic media. In the presence of phage φX174 DNA, Ru(bpz)32+photosensitized the formation of single strand breaks with an efficiency that was, at the beginning of irradiation, similar to that of Ru(bipy)32+. After 8 min of irradiation, the cleavage efficiency of Ru(bpz)32+reached a plateau that may correspond to its photode‐composition. For the same conditions, Ru(bpz)2Cl2 did not induce DNA breakage. Scavenging experiments showed that, in the presence of oxygen, DNA cleavage induced by Ru(bpz)32+partly resulted from the formation of singlet oxygen and hydroxyl radical while in the absence of oxygen an additionnal mechanism involving electron transfer between the excited state of the ruthenium complex and DNA is proposed. The ICP measurement showed that Ru(bpz)32+and Ru(bpz)2Cl2 gave rise to covalent binding onto DNA in contrast with Ru(bipy)32+, which did not bind to DNA under the experimental conditions. The results are discussed with regard to the potential use of these photosensitizers in phototherapy.
Cell Cycle Effects and Concomitant p53 Expression in Hairless Murine Skin after Longwave UVA (365 nm) Irradiation: A Comparison with UVB Irradiation
Authors: de Laat Annemarie , Kroon Ellemiek D. , de Gruijl Frank R.
Published: January 2008

Abstract— Ultraviolet A (UVA,315–400 nm) radiation is known to be a complete carcinogen, but in contrast to UVB (280‐315 nm) radiation, much of the cell damage is oxygen dependent (mediated through reactive oxygen species), and the dominant premutational DNA lesion(s) remains to be identified. To investigate further the basic differences in UVA and UVB carcinogenesis, we compared in vivo cellular responses, viz. cell cycle progression and transient p53 expression in the epidermis, after UVA1 (340‐400 nm) exposure with those after broadband UVB exposure of hairless mice. Using flow cytometry we found a temporary suppression of bromodeoxyuridine (BrdU) uptake in S‐phase cells both after UVB and UVA1 irradiation, which only in the case of UVB is followed by an increase to well over control levels. With equally erythemogenic doses (1‐2 MED), the modulation of BrdU uptake was more profound after UVB than after UVA1 irradiation. Also, a marked transient increase in the percentage of S‐phase cells occurred both after UVB and after UVA1 irradiation, but this increase evolved more rapidly after UVA1 irradiation. Further, p53 expression increased both after UVB and UVA1 irradiations, with peak expression already occurring from 12 to 24 h after UVA1 exposure and around 24 h after UVB exposure. Overall, UVA1 radiation appears to have less of an impact on the cell cycle than UVB radiation, as measured by the magnitude and duration of changes in DNA synthesis and cells in S phase. These differences are likely to reflect basic differences between UVB and UVA1 in genotoxicity and carcinogenic action.
Evidence Regarding the Possible Role of c‐Phycoerythrin in Ultraviolet‐B Tolerance in a Thermophilic Cyanobacterium*
Authors: Wingard Christopher E. , Schiller Jonathan R. , Castenholz Richard W.
Published: January 2008

Abstract— It was recently reported that a strain of Nostoc spongiaeforme (cyanobacteria) with the photopigment c‐phycoerythrin (c‐PE) may be more tolerant of the adverse effects of UVB radiation than the same strain lacking c‐PE due to chromatic adaptation (CA) (Tyagi et al., Photochem. Photobiol. 55,401–407, 1992). It was proposed that this increased UVB tolerance may be due to the presence of c‐PE, perhaps as a function of the ability of strains with c‐PE to chromatically adapt. We tested the role of c‐PE in UVB tolerance by comparing the short‐and long‐term effects of UVB exposure on photosynthesis, pigmentation and the protein contents of four experimental cultures of the thermophilic cyanobacterium Os‐cillatoria cf. amphigranulata. These cultures consisted of a wild‐type strain that produces c‐PE, a green pigment variant (subcloned from the parent wild‐type strain) incapable of producing c‐PE and two chromatically adapted color forms of the wild‐type strain that varied with regard to their total c‐PE content. There were no significant results suggesting a role for c‐PE in UVB tolerance. It is concluded that the photopigment c‐PE does not confer enhanced resistance to the deleterious effects of UVB radiation on photosynthesis in this cyanobacterium.
Photochemical and Photobiotogical Studies with Acridine and Phenanthridine Hydroperoxides in Cell‐free DNA
Authors: Adam Waldemar , Groer Peter , Mielke Karsten , Saha‐Möller Chantu R. , Hutterer Rudolf , Kiefer Wolfgang , Nagel Volker , Schneider Friedemann W. , Ballmaier Daniel , Schleger Yvonne , Epe Bernd
Published: January 2008

Abstract— The acridine and phenanthridine hydroperoxides 3 and 7 were synthesized as photochemical hydroxyl radical sources for oxidative DNA damage studies. The generation of hydroxyl radicals upon UVA irradiation (Λ. = 350 nm) was verified by trapping experiments with 5,5‐di‐methyl‐1‐pyrroline N‐oxide and benzene. The enzymatic assays of the damage in cell‐free DNA from bacteriophage PM2 caused by the acridine and phenanthridine hydroperoxides 3 and 7 under near‐UVA irradiation revealed a wide range of DNA modifications. Particularly, extensive single‐strand break formation and DNA base modifications sensitive to formamidopyrimidine DNA glycosylase (Fpg protein) were observed. In the photooxida‐tion of calf thymus DNA, up to 0.69±0.03% 8‐oxo‐7,8‐dihydroguanine was formed by the hydroperoxides 3 and 7 on irradiation, whose yield was reduced up to 40% in the presence of the hydroxyl radical scavengers mannitol and fert‐butanol. The acridine and phenanthridine hydroperoxides 3 and 7 also induce DNA damage through the type I photooxidation process, for which photoinduced electron transfer from 2′‐deoxyguanosine to the singlet states of 3 and 7 was estimated by the Rehm‐Weller equation to possess a negative Gibb's free energy of cα ‐5 kcal/ mol. Control experiments with the sensitizers acridine 1 and the acridine alcohol 4 in calf thymus and PM2 DNA confirmed the photosensitizing propensity of the UVA‐ab‐sorbing chromophores. The present study emphasizes that for the development of selective and efficient photochemical hydroxyl radical sources, chromophores with low photosensitizing ability must be chosen to avoid type I and type II photooxidation processes.
Photochemical and Photobiological Studies of a Furonaphthopyranone as a Benzo‐spaced Psoralen Analog in Cell‐free and Cellular DNA
Authors: Adam Waldemar , Mielke Karsten , Saha‐Möller Chantu R. , Möller Marianne , Stopper Helga , Hutterer Rudolf , Schneider Friedemann W. , Ballmaier Daniel , Epe Bernd , Gasparro Francis F. , Chen Xinsheng , Kagan Jacques
Published: January 2008

Abstract— Photobiological activities of the benzo‐spaced psoralen analog furonaphthopyranone 3 have been investigated in cell‐free and cellular DNA. The molecular geometry parameters of 3 suggest that it should not form interstrand crosslinks with DNA. With cell‐free DNA no evidence for crosslinking but also not for monoadduct formation was obtained; rather, the unnatural furocoumarin 3 induces oxidative DNA modifications under near‐UVA irradiation. The enzymatic assay of the photosensitized damage in cell‐free PM2 DNA revealed the significant formation of lesions sensitive to formamidopyrimidine DNA glyco‐sylase (Fpg protein). In the photooxidation of calf thymus DNA by the furonaphthopyranone 3, 0.29±0.02% 8‐oxo‐7,8‐dihydroguanine (8‐oxoGua) was observed. With 2′‐deoxyguanosine (dGuo), the guanidine‐releasing photooxidation products oxazolone and oxoimidazolidine were formed predominately, while 8‐oxodGuo and 4‐HO‐8‐oxodGuo were obtained in minor amounts. The lack of a significant D2O effect in the photooxidation of DNA and dGuo reveals that singlet oxygen (type II process) plays a minor role; control experiments with tert‐butanol and mannitol confirm the absence of hydroxyl radicals as oxidizing species. The furonaphthopyranone 3 (Ered= ‐1.93±0.03V) should act in its singlet‐excited state as electron acceptor for the photooxidation of dGuo (δGETca– kcal/mol), which corroborates photoinduced electron transfer (type I) as a major DNA‐oxidizing mechanism. A comet assay in Chinese hamster ovary (CHO) AS52 cells demonstrated that the psoralen analog 3 damages cellular DNA upon near‐UVA irradiation; however, no photosensitized mutagenicity was observed in CHO AS52 cell cultures
Fluorescence and Absorption Contrast Mechanisms for Biomedical Optical Imaging Using Frequency‐Domain Techniques
Authors: Sevick‐Muraca E. M. , Lopez G. , Reynolds J. S. , Troy T. L. , Hutchinson C. L.
Published: January 2008

Abstract— The ability to optically image or detect diseased tissue volumes located deep within tissues depends upon the degree of contrast provided by differences in local optical properties. In this report, we show that the exogenous contrast offered by fluorescent compounds is superior to that provided by nonfluorescing, light‐absorbing compounds when time‐dependent measurements are employed. In addition, we show that the induced contrast is not only moderated by the preferential uptake of fluorescent agents into diseased tissue volumes of interest but also by the fluorescent optical properties and the fluorescence dynamics in the specific tissue volume. Using tissue phantom studies, we demonstrated experimentally that near‐infrared‐absorbing and fluorescent dyes such as in‐docyanine green can provide detection of diseased tissue volumes from fluorescence measurements made at the periphery of tissue when there is perfect, 100‐fold and 10‐fold partitioning in diseased tissues over that in surrounding normal tissues. Experimental results of common laser dyes show the contrast is also mediated by the quantum yield and lifetime parameters that may be dependent upon the local tissue environment.
Photodegradation and Photobinding of Tiaprofenic Acid: in vitro Versus in vivo
Authors: de Vries H. , Encinas S. , Miranda M. A. , Castell J. V. , van Henegouwen G. M. J. Beijersbergen
Published: January 2008

Abstract— The photoreactivity of the photosensitizing nonsteroidal anti‐inflammatory drug tiaprofenic acid (TA) and its photoproduct decarboxytiaprofenic acid (DTA) was studied both in the presence and in the absence of bovine serum albumin (BSA). The photoproduct DTA was found to be photostable in buffered aqueous solution at pH 7.4, but photodecomposed when BSA was present in the reaction medium. Both TA and DTA underwent irreversible photobinding to BSA in an almost quantitative way, as evidenced by radioactivity measurements using labeled (3H) compounds. In the case of TA, it has been proven that photobinding is mainly attributable to the phototoreactivity of in situ ‐generated DTA. The photo‐degradation and photobinding of TA were also investigated in the epidermis in vivo. Rats were exposed to UVA after application of TA to their shaven dorsal skin. During the initial periods of irradiation, the amount of TA decreased sharply, and the yield of the corresponding photoproduct (DTA) reached a maximum. Prolonged irradiation led to photodegradation of DTA. In vivo photobinding was studied using 3H‐TA. Photobinding took place slowly at the beginning, but its rate increased sharply after complete photoconversion of TA, when the photoproduct DTA reached the maximum concentration. Thereafter, the decrease of DTA was more pronounced than that of TA. This indicates thatalso in vivoDTA rather than TA is responsible for the photobinding to biomacromolecules in the viable layer of the epidermis. Overall, the above results suggest that irradiation of TA in buffered aqueous solution, in the presence of proteins, is a reasonable model system to study the photodegradation and photobinding behavior of this drug in vivo. From the qualitative point of view, the main conclusion is that DTA plays a key role both in vivo and in vitro: it is the major photoproduct, it undergoes further photodegradation upon prolonged irradiation, and it appears to be responsible for the photobinding process.
The Effects of UVA‐I (340‐400 nm), UVA‐II (320‐340 nm) and UVA‐I+II on the Photoisomerization of Urocanic Acid in vivo
Authors: Webber Lindsay J. , Whang Eugene , De Fabo Edward C.
Published: January 2008

Abstract— Ultraviolet B radiation (280‐320 nm) can systemically suppress contact hypersensitivity (CHS), delayed type hypersensitivity (DTH) and tumor rejection responses in mice. Several models have been postulated for the initiation of this UVB‐induced immune suppression and, although the complete mechanism is unclear, our early studies suggested that initiation is via the activation of a photoreceptor in the skin, identified as urocanic acid (UCA). Recent preliminary data from our laboratory and others indicated that UVA (320‐400 nm)‐emitting broadband sunlamps can also isomerize UCA but may not lead to immune suppression, in contrast to UVB‐emitting sunlamps, which cause both effects. Although the reason for this inconsistency is unknown, the emission spectra of UVA lamps contain differing amounts of UVB, UVA‐I (340‐400 nm) and UVA‐II (320‐340 nm) from those of UVB sources. In this study we determined a detailed dose‐response for the isomerization of UCA in mouse skin using the UVA‐I, UVA‐II and UVA‐I+II wavelength ranges. The dose‐response curves obtained were put on an equal energy basis by quantum correction and the possibility of wavelength interaction for this effect investigated. A simple additive wavelength interaction between UVA‐I, UVA‐II, and UVA‐I+II was observed for trans‐UCA photoisomerization. This result indicates that the failure of UVA‐I, UVA‐II or UVA‐I+II radiation to induce immune suppression of the CHS response in an animal model is not due to complex wavelength interactions and/or the presence of an in vivo endogenous photosensitizer of UCA isomerization. Other factors, such as downstream blocking by UVA of the cis‐UCA generated signal, may be involved.
Influence of Higher Excited Singlet States on Ultrafast Exciton Motion in Pigment‐Protein Complexes
Authors: Renger Thomas , May Volkhard
Published: January 2008

Abstract— Numerical simulations of the ultrafast exciton motion in photosynthetic antenna complexes are used to reproduce measured data of optical pump‐probe experiments. Emphasis is put on a chlorophyll aL/chlorophyll b dimer of the light‐harvesting complex of the photosystem II of higher plants (LHC‐II). To account for intramolecular excited‐state absorption the standard exciton theory is extended to the inclusion of a second higher excited singlet state per chlorophyll molecule. The density matrix theory is applied to describe the dissipative dynamics of excitons. Different mechanisms for energy relaxation and dephasing including pure dephasing processes are discussed. As a result, a further refinement of earlier calculations on the one‐color pump‐probe spectra at the LHC‐II can be presented. In particular, the presence of non‐Markovian effects with respect to the exciton‐vibrational interaction in the LHC‐II, discovered previously in the two‐color pump‐probe spectrum, is demonstrated here for the one‐color pump‐probe case.
UVR Modulates the Steady‐state Levels of Skin Collagen Transcripts in Hairless Mice
Authors: Neocleous Vassos , Young Antony R. , Brownson Carol
Published: January 2008

Abstract— Exposure to solar UV radiation (UVR) leads to changes in the extracellular matrix of the dermis, which is largely composed of collagen and elastin. Collagen and elastin proteins and their corresponding mRNA were assessed in dorsal skins of hairless mice exposed to 0.64 J/cm2 UVR (295‐400 nm), 5 days per week, over a 12 week period. A 48% increase in skin‐fold thickness was accompanied by increased elastic tissue deposition and more compressed collagen bundles as assessed histologically. Collagen I mRNA levels were similar to those in control skins at 1, 2, 3 and 6 weeks of UVR and less than control levels at 9 and 12 weeks. Collagen III mRNA levels were elevated after 1 week of UVR, remained elevated for a further 2 weeks and then returned to control levels at weeks 6, 9 and 12 when changes are occurring in collagen I transcripts. There was no evidence of corresponding changes in collagen I and III protein levels assessed using electrophoretic techniques. These results suggest that damage to the extracellular matrix, consequent on UVR, is associated with some pretranslational events. Elastin mRNA levels were unaffected by UVR, suggesting that elastic tissue hyperplasia is a posttranscriptional phenomenon.
Formation of Fluorescent and Nonfluorescent Difluoroboron Complexes in the Reaction of BF3Etherate with 21H,24H‐Bilin‐1,19‐dione Derivatives
Authors: Borle Francois , Fehr Felix , Nesvadba Petr , Gossauer Albert
Published: January 2008

On reaction with BF3 etherate, in the presence of base, bile pigments of the biliverdin and 2,3‐dihydrobiliverdin type form two kinds of difluoroboron chelates. In one of them, which displays intensive photoluminescence, the boron atom is complexed through the nitrogen atoms of the dipyrrin moiety of the ligand molecule. In the second type of chelates, which have been characterized in the present work for the first time, the boron atom is complexed through the nitrogen atoms of the pyrrole and one of the terminal lactam rings. These BF2 complexes are devoid of manifest fluorescence. Their 1H‐NMR spectra show clear through‐space 1H‐19T spin‐spin couplings that served for structure elucidation. Bile pigment analogs, in which the pyrrolic HN group has been replaced by N‐CH3 or by divalent heteroatoms, such as an O or S atom, form only the latter type of BF2 chelates.
Phytochrome‐mediated Phototropism in Adiantum Protonemata II. Participation of Phytochrome Dark Reversion
Authors: Iino Moritoshi , Shitanishi Kohji , Wada Masamitsu
Published: January 2008

A microbeam irradiation technique was used to analyze phytochrome‐mediated phototropism of the protonema of the fern Adiantum capillus‐veneris. One side of the sub‐apical zone of a dark‐adapted protonema was irradiated with a red‐light (R) microbeam to induce phototropic curvature toward the irradiated side. Except the cases where fluence‐response relationships were examined, the protonema was stimulated with the microbeam for about 30 s to provide a fluence (5.3–5.5 mmol m‐2) optimal for curvature. When the whole protonema was pretreated with a high fluence of R (about 9 mmol m‐2), no significant curvature could be induced by immediately subsequent one‐sided microbeam stimulation. It was found, however, that curvature became inducible progressively as the time of microbeam stimulation was delayed after the R pretreatment. The protonema gained nearly full responsiveness within 40 min after the pretreatment. Moreover, the inductive effect of microbeam R escaped rapidly from the reversing effect of far‐red light. These results indicated that most of the far‐red‐absorbing form of phytochrome (Pfr), which mediates the phototropic response, undergoes relatively fast dark reversion to the red‐absorbing form. The dark reversion kinetics was analyzed further by taking into account that the phototropic responsiveness after the R pretreatment was measured in the presence of background Pfr over the protonema. This analysis revealed a rate constant of about 0.002 s‐1 (t1/2˜ 6 min) for the dark reversion. It is considered that the Pfr dark reversion plays a role in establishing a lateral Pfr gradient in the unilaterally irradiated protonema.
Effects of Ultraviolet Radiation on Carbon Fixation in Antarctic Nanophytoflagellates
Authors: Figueroa Felix L. , Blanco Jose Maria , Jimenez‐Gomez Francisco , Rodriguez Jaime
Published: January 2008

Carbon fixation in Antarctic nanoflagellates dominated by cryptomonads collected during a summer cruise in 1995 decreased after short‐term exposition (3 h) under both UVA and UVA + UVB radiation compared to white light. The dose applied with artificial lamps was within the range of the natural UV radiation measured at the surface during the cruise. The depletion of C fixation was higher after UVA + UVB than after UVA alone. The inhibition of carbon fixation in the laboratory depended on the time of sample collection and, consequently, on the UV dose received in the natural environment before sampling. Thus, the cells collected in the morning showed 82% of inhibition by UVA + UVB but that collected at noon showed only 72%. The same effect was observed by UVA: 72% of inhibition in the morning samples and 62% at noon. Thus, photoprotection mechanisms seem to be operating during the day protecting the cells against a rise in UV radiation. Red fluorescence (attributed to chlorophyll) per cell, as determined by flow cytometry, was not affected by UV, however, orange fluorescence (attributed to phycoerythrin) increased clearly after UV radiation compared to that in white light. The increment of orange fluorescence was higher after UVA than after UVA + UVB radiation. The rapid increase in fluorescence emission could be due to an uncoupling of energy transfer and it is suggested as a protective mechanism against UV radiation by absorbing UV radiation.
The Role of Protein Kinase C Activity in the Killing of Chinese Hamster Ovary Cells by Ionizing Radiation and Photodynamic Treatment
Authors: Rasch Monique H. , Tijssen Karmi , Lagerberg Johan W. M. , Corver Wim E. , Van Steveninck John , Dubbelman Tom M. A. R.
Published: January 2008

In several recent studies it has been shown that protein kinase C (PKC) activity may either potentiate or antagonize cell killing by different cytotoxic agents. These apparently conflicting observations suggest that the effects of PKC activity on cell survival may depend on the different properties of different cell types but do not exclude the possibility that the effects may also depend on the nature of the cytotoxic agent. In this context the effects of PKC activation and PKC inhibition or down‐regulation on Chinese hamster ovary (CHO) cell survival after photodynamic treatment and ionizing radiation were studied. It appeared that PKC activation by short‐term incubation with 12‐0‐tetradecanoyl‐phorbol‐13‐acetate (TPA) protected CHO cells against ionizing radiation but, in contrast, sensitized the cells to photodynamic treatment. Conversely, inhibition of PKC by H7 and down‐regulation of PKC activity by prolonged incubation with TPA sensitized CHO cells to ionizing radiation but protected the cells against photodynamic treatment. These results demonstrate that in one particular cell type PKC activity may have opposite effects on cell survival following cellular damage, depending on the nature of the cytotoxic agent.
Excited‐State Dynamics of Fully Reduced Flavins and Flavoenzymes Studied at Subpicosecond Time Resolution
Authors: Enescu Mironel , Lindqvist Lars , Soep Benoît
Published: January 2008

The photophysics of the fully reduced states of a number of flavins (flavin mononucleotide, flavin adenine dinucleotide and 3‐N‐methyllumiflavin) and flavoenzymes (glucose oxidase from Aspergillus niger and the flavodehydrogenase component isolated from flavocytochrome b2) was studied using subpicosecond laser excitation at Λ. = 312 nm. The prompt transient absorption spectra (measured from 400 to 850 nm) were all closely similar in the case of the free flavins in aqueous solution. The decay of the transient absorbance obeyed biexponential kinetics with a fast component of lifetime ranging from 4 to 130 ps and a slower phase with a lifetime above 1 ns. The spectral structure changed appreciably during the rapid decay phase. In contrast, in the case of the enzymes only a very slight decay was apparent over the probed time interval (1 ns) and the shape of the spectrum remained unchanged. It is proposed that the two transient spectra appearing in the free flavins correspond to two conformations differing by their degree of nonplanarity, whereas in the flavoenzymes only one conformation is possible.
Photophysical Behavior of Angelicins and Thioangelicins: Semiempirical Calculations and Experimental Study
Authors: Elisei F. , Aloisi G. G. , Dall'Acqua F. , Latterini L. , Masetti F. , Rodighiero P.
Published: January 2008

The decay processes of the lowest excited singlet and triplet states of five methylated angelicins (4,6,4′‐trimethyl‐angelicin, MA, and four methylated thioangelicins, MTA; see Scheme 1) were investigated in live solvents by stationary and pulsed fluorometric and flash photolytic techniques. In particular, the solvent effects on absorption, fluorescence, quantum yields of fluorescence (φF) and triplet formation (φT), lifetimes of fluorescence (τF) and the triplet state (τT) and the quantum yields of singlet oxygen production (φΔ) were investigated. Semiempirical (ZINDO/S‐CI) calculations were carried out to obtain information (transition probabilities and nature) on the lowest excited singlet and triplet states. The quantum mechanical calculations and the solvent effect on the photophysical properties showed that the lowest excited singlet state (S1) is a partially allowed π,π* state, while the close‐lying S2state is n,π* in nature. The efficiencies of fluorescence, S1→T1intersystem crossing (ISC) and S1→ S0internal conversion (IC) strongly depend on the energy gap between S1, and S2and are explained in terms of the so‐called proximity effect. In fact, for MA in cyclohexane, only the S1→ S0internal conversion is operative, while in acetonitrile and ethanol, where the n.π* state is shifted to higher energy, the efficiencies of fluorescence and ISC increase significantly. The energy gap between S1and S2increases in MTA, where the furanic oxygen is replaced by a sulfur atom. Consequently, the solvent effect on the photophysical parameters of MTA is less marked than for MA;e.g.fluorescence and triplet‐triplet absorption are also detectable in the nonpolar cyclohexane. The lowest excited singlet state of molecular oxygen O2(1Dg) was produced efficiently in polar solvents by energy transfer from the T1state of MA and MTA.
GH3 Cells, Ionic Currents and Cell Killing: Photomodification Sensitized by Rose Bengal
Authors: Valenzeno Dennis Paul , Tarr Merrill
Published: January 2008

Photosensitization using Rose Bengal (RB) modifies membrane ionic currents and kills cultured mouse pituitary, GH3, cells. Here we investigate the dose‐response relationship for ionic current modification and for cell killing to assess a possible causal link. When exposed to 0.5 μM RB and 6.5 mW/cm2 of visible light, calcium current was blocked in 1.9 ± 0.2 min (meanSEM; 0.74 ± 0.08 J/ cm2; n = 18), a transient component of potassium current, tentatively identified as a delayed‐rectifier potassium current, disappeared in 52 ± 8 s (0.34 ± 0.05 J/cm2; n = 10) and a steady‐state component of potassium current, largely a calcium‐activated potassium current, disappeared in 3.5 ± 0.4 min (1.37 ± 0.16 J/cm2; n = 11). Conversely, the background leak current increased in magnitude. At 5 min of illumination, the longest time studied here, it continued to increase nearly linearly, making it the only current component studied that is still changing after 5 min of light. Under the conditions used, cell killing increased to 100% in the exposure range of4–10 min of illumination (1.6 J/cm2 to 3.9 J/cm2) when assessed using fluorescent markers, ethidium homodimer and calcein and required slightly longer exposure times when assessed using trypan blue. Thus, it is difficult to ascribe a causal role in cell killing by photosensitization to alterations of standard ion channels and known ionic currents. However, the increase in leak current has the correct dose‐response characteristics to be involved.
Effect of Magnetite Particles on Photoinduced and Nonphotoinduced Free Radical Processes in Human Erythrocytes
Authors: Chignell Colin F. , Sik Robert H.
Published: January 2008

Magnetite (Fe304) encapsulated in polystyrene microspheres dramatically decreased the time for 50% hemolysis (t1/2) of human erythrocytes irradiated (λ300 nm) in the presence of ketoprofen (0.1 mM). The magnetic microspheres were present at a very low concentration (0.002%) such that on average there was only one particle per four erythrocytes. No such effect was seen when nonmagnetic microspheres were employed or when the equivalent concentration of soluble iron (FeCl3) was present. A decrease in t1/2 was also observed when the magnetic microspheres were added after UVA/ketoprofen treatment or when they were present during hemolysis initiated by thermolysis of 2,2′‐azobis(2‐amidinopro‐pane). These findings may be attributed to an increase in the membrane concentration of lipid radicals as a result of a magnetic field‐induced increase in radicals escaping from triplet radical pairs.
Repair of (6‐4) Photoproducts in Cultured Goldfish Cells at Confluence or Treated with H2O2
Authors: Uchida Nobuhiro , Mitani Hiroshi , Shima Akihiro
Published: January 2008

Previously we reported that fluorescent light (FL) illumination prior to UV irradiation (FL preillumination) had multiple effects on the repair of cyclobutane pyrim‐idine dimers (CPD) and (6‐4) photoproducts ([6‐4] PD) in cultured goldfish cells (RBCF‐1) at the exponentially growing phase. In this study, it is shown that even under the confluent condition of RBCF‐1 cells, FL preillumination increased the disappearance of (6‐4) PD in the dark. In addition, both at confluence and at the exponentially growing phase, the disappearance of (6‐4) PD after PR treatment was increased by FL preillumination to RBCF‐1 cells. Moreover, it was found that H2O2 pre‐treatment, followed by UV irradiation, of the exponentially growing cells also enhanced the disappearance of (6‐4) PD in the dark and by photorepair treatment. The degree of enhancement by H2O2 pretreatment was almost the same as that by FL preillumination.
Near‐infrared Light Emission from Nanomolar‐level Singlet Molecular Oxygen Generated with an Ultra low Concentration Mixture of Hypochlorite and Hydrogen Peroxide
Authors: Shiraishi Takuo , Makiuchi Masao , Kakinuma Katsuko , Inaba Humio
Published: January 2008

Abstract— We report the detection of a weak near‐infrared light emission originating from 8 nM singlet molecular oxygen (1O2) produced in a mixture of 1 mM hypochlorite (OC1‐) and 8 nM hydrogen peroxide (H2O2). The measurements were made with a highly sensitive detection system for ultraweak light emission in the 1.0‐1.5 μm wavelength region. The emission intensity exhibited linear dependence for H2O2 concentrations in the range of 8‐670 nM. The mixture containing a lower concentration (33 μM) of OCl‐ pseudocontinuously emitted near‐infrared light for 5 s. The rate constant for 1O2 production obtained from the kinetic analysis agrees with that previously reported. Our results demonstrate the possibility of measuring very low concentrations of 1O2 in a OCi‐/H2O2 mixture as well as 1O2 production in intact living systems.
Regional Imager for Low‐Resolution Functional Imaging of the Brain with Diffusing Near‐Infrared Light
Authors: Danen R. M. , Wang Yong , Li X. D. , Thayer W. S. , Yodh A. G.
Published: January 2008

We have developed a near‐infrared spectroscopy system for low‐resolution regional imaging of the brain. Our regional imager employs two intensity‐modulated (frequency‐domain) diode lasers operating at 779 and 834 nm, respectively, in order to produce macroscopic waves of diffusing photons. The interaction of these diffusive waves with tissue depends on laser modulation frequency, laser wavelength and the optical properties of the sample tissue volume. The lasers can be modulated over a range of frequencies from 50 to 400 MHz. Light is coupled to and from the head using a pad that has 12 source and 4 detector positions within an area of approximately 40 cm2. The pad can be moved to different positions on the head. Measurements from different source‐detector combinations enable reconstruction of low‐resolution images of the tissue volume beneath the pad. For example, we have made two‐dimensional back‐projection images of model systems in order to demonstrate the capabilities of the regional imager. We also present preliminary results from initial clinical studies at the Children's Hospital of Philadelphia.
Nonexponential Fluorescence Decay of 7‐Azatryptophan Induced in a Peptide Environment
Authors: English D. S. , Rich R. L. , Petricht J. W.
Published: January 2008

7‐Azatryptophan is an alternative to tryptophan as an optical probe of protein structure and dynamics. 7‐Azatryptophan is synthetically incorporated into an octapeptide (NAc‐Lys‐Ala‐Cys‐Pro‐7‐azatryptophan‐Asn‐Cys‐Asp‐NH2) that mimics the active site of potato chymotrypsin inhibitor II, which is known to be a strong inhibitor of α‐chymotrypsin. The synthetic octapeptide retains some of this inhibitory activity. This is the first compound containing the 7‐azaindole chromophore to display a nonexponential fluorescence decay (well fit to two exponentials) in water when fluorescence is collected over the entire emission band. The effect of external quenchers on the fluorescence decay is monitored and seen to differ markedly for the two components. These results are discussed in terms of the solvation of the 7‐azaindole chromophore itself, which promotes or impedes excited‐state tautomerization. The fluorescence quenching of free indole and 7‐azaindole are compared. The fluorescence quenching of octapeptides containing both chromophores is also compared. It is the thesis of this article that the nonexponential fluorescence decay of the 7‐azatryptophan‐containing octapeptide is a consequence of excited‐state tautomerization of the 7‐azaindole chromophore. This tautomerization is suggested to be promoted by solvent reorganization induced by the peptide backbone or by direct interactions of the 7‐azaindole with neighboring amino acid side chains.