bluuebunny/crossref_metadata_2025 huggingface dataset:
ELEVATION OF GRP‐78 AND LOSS OF HSP‐70 FOLLOWING PHOTODYNAMIC TREATMENT OF V79 CELLS: SENSITIZATION BY NIGERICIN
Authors: Xue Liang‐yan , Agarwal Munna L. , Varnes Marie E.
Published: January 2008

Abstract— Chinese hamster V79 cells were treated with photodynamic therapy (PDT) sensitized by aluminum phthalocyanine (AlPc) or with the ionophore nigericin or with combinations of PDT and nigericin. We previously showed that PDT and nigericin interact synergistically in the killing of these cells; i.e. doses of PDT that kill no more than 10% of the cells in combination with nontoxic exposures to nigericin lead to a loss of clonogenicity of three to five orders of magnitude. Photodynamic therapy induces an enhanced rate of expression of the stress gene grp‐78 both at the transcriptional and trans‐lational levels and causes a decrease in the synthesis of the constitutive heat shock protein HSP‐70 as well as in expression of HSP‐70 mRNA. When the cells are exposed to PDT in the presence of nigericin, these effects are elicited at three‐ to four‐fold lower PDT doses. Thus, PDT in the presence of nigericin is much more effective in inducing the changes in gene expression than is PDT alone. In the absence of nigericin the PDT dose inducing a two‐fold increase in GRP‐78 accumulation causes little or no loss of clonogenicity. In the presence of nigericin, however, the PDT dose leading to a similar change in GRP‐78 level produces up to a 50% loss of clonogenicity. The fact that nigericin is dose‐modifying for both cell killing and stress responses suggests that nigericin either increases the yield of oxidative damage from a given dose of PDT or magnifies the cellular response to a constant level of oxidative stress.
PHOTOFRIN ACCUMULATION IN MALIGNANT AND HOST CELL POPULATIONS OF A MURINE FIBROSARCOMA
Authors: Korbelik Mladen , Krosl Gorazd
Published: January 2008

Abstract— Photofrin (25 mg/kg) was administered to the FsaR fibrosarcoma‐bearing mice (either syngeneic or severe combined immunodeficient [SOD]) and the tumors were excised 24 h later. The photosensitizer content in the cells dissociated from tumor tissue was analyzed using flow cytometry. Staining the cell suspensions with the monoclonal antibodies against specific membrane markers served to identify the malignant cells and various types of host immune cells infiltrating the tumor. Photofrin content was also examined in the cells from normal tissues of the tumor‐bearing mice (spleen, heart muscle, peritoneal macrophages). The results show a marked heterogeneity in the Photofrin cellular content of FsaR tumor, particularly within the population of tumor‐associated macrophages (TAM). The Photofrin levels in some TAM were lower or similar to those in the malignant cells. In contrast, a subpopulation of TAM accumulated very high levels of the photosensitizer, which exceeded by far the levels found in the other tumor cell populations. This TAM fraction was characterized by particularly high expression of interleukin‐2 receptors and increased cell size and granularity when compared to the other TAM, which suggests that these macrophages are in the activated state. Their average Photofrin content was almost 13 times higher than in the malignant cells. The lowest photosensitizer levels in the tumor were found in tumor‐infiltrating leukocytes other than TAM. In FsaR tumors growing in SCID mice, the pattern of Photofrin distribution in TAM and other cellular populations was similar to that found in tumors growing in syngeneic mice. Due to a presumably better perfusion, these tumors accumulated higher levels of Photofrin in all cellular populations. The findings of this study suggest that the tumor‐localizing effect of Photofrin can be attributed to the accumulation of extremely high levels of the photosensitizer in a subpopulation of TAM.
THE EFFECTS OF MULTIPLE UV EXPOSURES ON HIV‐LTR EXPRESSION
Authors: Schreck Steven , Panozzo John , Milton Jeffrey , Libertin Claudia R. , Woloschak Gayle E.
Published: January 2008

Abstract— Previous studies have shown that cellular stress agents such as UV radiation induce transcription from the long terminal repeat (LTR) of the human immunodeficiency virus (HIV). Using HeLa cells stably transfected with the HIV‐LTR sequence, which transcriptionally drives the chloramphenicol acetyl transferase (CAT) reporter gene, we examined the effects of multiple exposures to UVC (254 nm) on HIV‐LTR‐CAT expression. Low doses (± 5 J m‐2) had no effect on CAT expression, but up to 29‐fold induction was observed with 10 J m‐2 when cells were harvested 48 h after completion of the exposure. Little difference was noted in induction levels when cells were exposed to one 25 J m‐2 dose, viable cells were harvested at 24 h, 48 h or 72 h, and cell lysates were assayed for CAT expression. Two sequential 12.5 J m‐2 exposures, given 24 h apart, resulted in an additive effect on CAT expression; these two exposures produced CAT activity equivalent to that induced following a single 25 J m‐2 dose. This additive effect was not evident at the lower doses (≤5 J m‐2) or at the higher doses. Maximal induction was observed using doses from 25 to 37.5 J m‐2. Multiple exposures with either the low (≤5 J m ‐2) or high doses (>25 J m ‐2) did not result in an additive effect. Our data suggest that HIV‐LTR requires a specific threshold UV dose in order to elicit induction; a maximal induction dose is also evident; exposures higher than this maximal dose contribute no more to HIV‐LTR induction in viable cells.
INHIBITION OF THE ATPase ACTIVITY OF P‐GLYCOPROTEIN BY PORPHYRIN PHOTOSENSITIZATION OF MULTIDRUG‐RESISTANT CELLS in vitro
Authors: Gibson Scott L. , Al‐Shawi Marwan K. , Senior Alan E. , Hilf Russell
Published: January 2008

Abstract— The effectiveness of photodynamic therapy against P‐glycoprotein ATPase activity in multidrug‐resistant cells was studied. Chinese hamster ovary AUXB1 (drug‐sensitive) and CR1R12 (multidrug‐resistant) cell lines were compared with respect to uptake of 14C‐polyhematoporphyrin and porphyrin photosensitization. Phototoxicity of Photofrin® was similar in both cell lines, and no major differences in uptake or efflux of 14C‐polyhematoporphyrin were observed. Porphyrin photosensitization in vitro of CR1R12 cells or isolated plasma membranes from these cells caused inhibition of P‐glycoprotein ATPase activity. Application of porphyrin photosensitization at a sublethal level to CR1R12 cells resulted in a small but significant increase in adriamycin‐induced cytotoxicity. The hydrophobic “picket‐fence” porphyrin, meso‐tetrakis‐(o‐propionamidophenyl)porphyrin,α,α,α,β‐isomer, was more inhibitory toward P‐glycoprotein ATPase activity than the two less hydrophobic porphyrins tetraphenylporphine tetrasulfonate and Photofrin®.
THE PHOTOPHYSICS OF p‐AMINOBENZOIC ACID
Authors: Halpern Arthur M. , Ramachandran B. R.
Published: January 2008

Abstract— The lowest‐lying allowed UV transition in p‐aminobenzoic acid (PABA) is assigned Γ→1La based on quantitative absorption and fluorescence studies, as well as semiempirical PM3 multielec‐tron configuration interaction calculations. The oscillator strengths, fluorescence quantum efficiencies and lifetimes are reported for PABA in several polar, nonpolar, protic and aprotic solvents (aerated) at 296 K. Reasonable agreement is found between the observed radiative rate constant and that calculated from the absorption and fluorescence spectra. Shifts in the absorption and fluorescence spectra in aprotic solvents are analyzed in terms of the Onsager reaction field model; results are consistent with an increase in dipole moment of ca 4 D between the relaxed S0 and S1, states. No evidence is found for the emission from the amino‐twisted form of PABA in all solvents studied although calculations show that the amino‐twisted S, state is highly polar, but higher in energy by ca 35 kJ/mol (in vacuo). The fluorescence efficiency is excitation wavelength independent in both methylcyclohexane and water. The temperature dependence of the nonradiative rate constant (from S1) was studied in several solvents. Nonradiative decay may be due to intersystem crossing, which would be fast enough to compete with thermally activated intramolecular NH2 twisting. The phosphorescence spectrum and lifetime obtained in an EPA glass at 77 K are reported, and the triplet energy of PABA is estimated.
SINGLET OXYGEN GENERATION FROM LIPOSOMES: A COMPARISON OF TIME‐RESOLVED 1270 NM EMISSION WITH SINGLET‐OXYGEN KINETICS CALCULATED FROM A ONE DIMENSIONAL MODEL OF SINGLET‐OXYGEN DIFFUSION and QUENCHING
Authors: Fu Yingxian , Kanofsky Jeffrey R.
Published: January 2008

Abstract— Time‐resolved measurements of 1270 nm singlet‐oxygen emission following pulsed‐laser excitation were made from unilamellar dimyristoyl 1‐α‐phosphatidylcholine liposomes labeled with zinc phthalocyanine. The effect of the hydrophobic quenchers, β‐carotene and ethyl β‐apo‐8′trans carotenoate, and the hydrophilic quenchers, histidine and methionine, upon the kinetics of the 1270 nm singlet‐oxygen emission was studied. Hydrophobic quenchers principally lowered the intensity of the 1270 nm emission and caused only modest changes in the lifetime of the 1270 nm emission. The decrease in 1270 nm emission caused by hydrophobic quenchers was related to the size of the liposomes. The larger the radius of the liposome, the greater the decrease in 1270 nm emission caused by a given concentration of hydrophobic quencher. In contrast, hydrophilic quenchers principally decreased the lifetime of the 1270 nm emission. The effect of hydrophilic quenchers was independent of the size of the liposomes.

There was good agreement between the experimental results and the kinetics of the singlet‐oxygen emission calculated using a one dimensional model of singlet‐oxygen quenching and diffusion. The kinetics of singlet‐oxygen emission from liposomes without added hydrophobic quenchers closely approximated the theoretical kinetics of singlet oxygen in a homogeneous aqueous solution.
PHOTOSENSITIZATION OF MURINE TUMOR, VASCULATURE and SKIN BY 5‐AMINOLEVULINIC ACID‐INDUCED PORPHYRIN
Authors: Henderson Barbara W. , Vaughan Lurink , Bellnier David A. , Leengoed Henricus van , Johnson Patricia G. , Oseroff Allan R.
Published: January 2008

Abstract— The effects of topical and systemic administration of 5‐aminolevulinic acid (ALA) were examined in several murine tumor systems with regard to porphyrin accumulation kinetics in tumor, skin and blood, vascular and tumor cell photosensitization and tumor response after light exposure. Marked, transient increases in porphyrin levels were observed in tumor and skin after systemic and topical ALA. Rapid, transient, dose‐dependent porphyrin increases were also observed in blood; these were pronounced after systemic ALA injection and mild after topical application. They were highest within 1 h after ALA injection, thereafter declining rapidly. This matched the clearing kinetics of injected exogenous protoporphyrin IX (PpIX). Initially, vascular photosensitivity changed inversely to blood porphyrin levels, increasing gradually up to 5 h post‐ALA, as porphyrin was clearing from the bloodstream. This pattern was again matched by injected, exogenous PpIX. After therapeutic tumor treatment vascular disruption of the tumor bed, while observed, was incomplete, especially at the tumor base. Minimal direct tumor cell kill was found at low photodynamic therapy (PDT) doses (250 mg/kg ALA, 135 J/cm2 light). Significant, but limited (<1 log) direct photodynamic tumor cell kill was obtained when the PDT dose was raised to 500 mg/kg systemic ALA, followed 3 h later by 270 J/cm2, a dose that was however toxic to the animals. The further reduction of clonogenic tumor cells over 24 h following treatment was moderate and probably limited by the incomplete disruption of the vasculature. Tumor responses were highest when light treatment was carried out at the time of highest tumor porphyrin content rather than at the time of highest vascular photosensitivity. Tumor destruction did not reach the tumor base, regardless of treatment conditions.
BIOSYNTHESIS OF PTERIDINES IN Neurospora crassa, Phycomyces blakesleeanus AND Euglena gracilis: DETECTION AND CHARACTERIZATION OF BIOSYNTHETIC ENZYMES*,†
Authors: Maier Josef , Ninnemann Helga
Published: January 2008

Abstract— Occurrence, biosynthesis and some functions of tetrahydrobiopterin (H4biopterin) in animals are well known. The biochemistry of H4biopterin in other organisms than animals was hitherto not widely investigated. Recently H4biopterin was found in the phytoflagellate Euglena gracilis, in the zygomycete Phycomyces blakesleeanus and in the ascomycete Neurospora crassa. In Euglena, Neurospora and Phycomyces the enzymatic activities of GTP cyclohydrolase I, 6‐pyruvoyl tetrahydropterin synthase and sepiapterin reductase are detectable and the biosynthesis follows the same steps as were shown for animals. The biosynthetic enzymes, however, show a much lower sensitivity to those inhibitors that act on vertebrate enzymes. 2,4‐Diamino‐6‐hydroxypyrimidine as inhibitor of GTP cyclohydrolase I and N‐acetylserotonin or N‐methoxyacetylserotonin as inhibitors of sepiapterin reductase can decrease pteridine biosynthesis significantly, in vitro and in vivo. The apparent Kmvalues are in general higher when compared with the respective animal enzymes. In Neurospora, the conversion of GTP to dihydroneopterin triphosphate was closely associated with subsequent production of 6‐hydroxymethyl‐7, 8‐dihydropterin due to the high activity of dihydroneopterin aldolase, different from all other tested organisms. Investigations involving inhibition of pteridine synthesis might be a useful tool for evaluating the hypothesis that pteridines in fungi and plants are co‐chromophores of various blue light‐dependent, flavin‐containing phototrcptors.
EFFECT OF BLUE LIGHT AND RED LIGHT ON THE CONTROL PEA LEAVES TO INCREASED FLUENCE RATES OF CHLOROPLAST ACCLIMATION OF LIGHT‐GROWN PEA LEAVES TO INCREASED FLUENCE RATES
Authors: OPEZ‐JUEZ ENRIQUEL , HUGHES MARTINJ. G.
Published: January 2008

Abstract— We have investigated the possibility of the involvement of a blue light fluence‐rate sensing photoreceptor in the light acclimation of chloroplast components in light‐grown pea seedlings. Low lightgrown seedlings were acclimated for 2 days to either 20 or 200 μmolm‐2s‐2 of white, blue‐enriched, or broad‐band red light. An increase in blue‐enriched light fluence rate was more effective than that of red light in bringing about both inhibition of internode growth and the enhancement of the chlorophyll a/b ratio. Ribulose 1,5‐bisphosphate carboxylase/oxygenase and cytochrome f protein levels, per unit cell, also increased more markedly (around two‐fold) in response to an increase in blue light. The 23 kDa polypeptide of the oxygen‐evolving complex and the light‐harvesting chlorophyll d b protein of photosystem II apoprotein levels vaned under all wavelengths to a lesser extent, correlating with total protein levels or greening. These data are consistent with the hypothesis of a role for a blue photoreceptor in detecting low versus high fluence rate of light, and subsequently controlling the light acclimation responses. Nevertheless photosynthesis or other mechanisms of fluence‐rate photoperception must also be involved.
Local Photodynamic Therapy Reduces Tissue Hyperplasia in an Experimental Restenosis Model
Authors: Gonschior Peter , Gerheuser Florian , Fleuchaus Michael , Huehns Tanya Y. , Goetz Alwin E. , Welsch Ulrich , Sroka Ronald , Dellian Marc , Lehr Hans A. , Höfling Berthold
Published: January 2008

Abstract— Local photodynamic therapy may have potential in preventing myointimal hyperplasia after angioplasty. In this study, the effect of photodynamic therapy was evaluated in an experimental model of restenosis. Standardized unidirectional arterial injury with a directional atherectomy catheter was performed in porcine arteries. Animals were randomly allocated to four groups: group 1, unidirectional injury only; group 2, injury followed by local delivery of photosensitizer; group 3, injury followed by local exposure to monochromatic light; and group 4, where injury was followed by local drug delivery of photosensitizer and subsequent exposure to light (photodynamic therapy). Seven, 14 or 21 days after treatment, all experimental vessels were excised, fixed and processed for histology. An inflammatory and myoproliferative response was observed after injury in vessels from groups 1, 2 and 3. In group 4, after injury followed by photodynamic therapy, the myoproliferative response was significantly reduced. Thus, in this study, tissue hyperplasia after unidirectional injury was effectively suppressed by photodynamic therapy.
The Reaction of Triplet 2‐Methyl‐1,4‐Naphthoquinone (Menadione) with DNA and Polynucleotides
Authors: Melvin T. , Bothe E. , Schulte‐Frohlinde D.
Published: January 2008

Abstract— The photoreaction of 2‐methyl‐l,4‐naphthoquinone (MQ, menadione) with DNA and polynucleotides in argon‐saturated aqueous solution (pH 7) was studied. Results from laser flash photolysis experiments indicate that triplet quinone reacts with DNA and polyA but not detectably with polyU by one‐electron oxidation of the bases of the nucleic acid with formation of the radical anion of the quinone. Irradiation of argon‐saturated solutions containing MQ and DNA or polynucleotides (polyU, polyA, polyG or polyC) with 334 nm light leads to an increase in molecular weight for single‐stranded DNA, polyA and to a much less extent for polyU. This finding indicates crosslink formation with quantum yields in the range of 10−5‐10−3
All‐Weather Comparison between Spectral and Broadband (Robertson‐Berger) UV Measurements
Authors: Mayer Bernhard , Seckmeyer Gunther
Published: January 2008

Abstract— Spectral measurements of UV irradiance at the Fraunhofer Institute at Garmisch‐Partenkirchen, Germany, are intercompared with data from two different Robert‐son‐Berger‐type meters. More than 21000 spectra gathered during 20 months of continuous operation were used for this analysis, sampling a large variety of atmospheric conditions. At low solar zenith angles the agreement (± 10%) was quite satisfactory, whereas at high solar zenith angles the broadband instruments gave systematically lower readings than the erythemally weighted spectral data. The deviation of the spectral response of the broadband instruments from the Commission Internationale de 1'Eclairage (CIE) erythema function and the cosine error provide an explanation of the observed differences that are similar for both broadband meters. Model calculations agree quite well with the observations, if an accurate measurement of the broadband spectral response is available. An analytical fit curve was established for the ratio between broadband and weighted spectral data, as a function of solar zenith angle, enabling quick and easy checks of the stability of the spectrora‐diometric system. The relative standard deviation of the data from the fit function was only2–3% in the case of cloudless sky conditions and 5% for all sky conditions, including all types of systematic and instrumental errors.
The Induction of Partial Resistance to Photodynamic Therapy by the Protooncogene BCL‐2
Authors: He Jin , Agarwal Munna L. , Larkin Hedy E. , Friedman Libby R. , Xue Liang‐yan , Olelnick Nancy L.
Published: January 2008

Abstract— Photodynamic therapy (PDT) is an efficient inducer of apoptosis, an active form of cell death that can be inhibited by the BCL‐2 oncoprotein. The ability of BCL‐2 to modulate PDT‐induced apoptosis and overall cell killing has been studied in a pair of Chinese hamster ovary cell lines that differ from one another by a transfected human BCL‐2 gene in one of them (Bissonnette et al., Nature 359,552–554, 1992). Cells were exposed to the phthalo‐cyanine photosensitizer Pc 4 and various fluences of red light. Pc 4 uptake was identical in the two cell lines. The parental cells displayed a high incidence of apoptosis after PDT, whereas at each fluence there was a much lower incidence of apoptosis in the BCL‐2‐expressing cells. Apoptosis was monitored by (a) observation of 50 kbp and oligonucleosome‐size DNA fragments by gel electrophoresis, (b) flow cytometry of cells labeled with fluores‐cently tagged dUTP by terminal deoxynucleotidyl transferase and (c) fluorescence microscopy of acridine orange‐stained cells. The time course of apoptosis varied with the PDT dose, suggesting that only after moderately high doses (> 99% loss of clonogenicity) was there a relatively synchronous and rapid entry of many cells into apoptosis. At PDT doses reducing cell survival by 90 or 99%, significant increases in apoptotic cells were found in the population after6–12 h. Clonogenic assays showed that BCL‐2 protein inhibited not only apoptosis but overall cell killing as well, effecting a two‐fold resistance at the 10% survival level. Thus, BCL‐2‐expressing cells may be relatively resistant to PDT.
Effect of Magnesium and Calcium Complexation on the Photochemical Properties of Norfloxacin
Authors: Martínez Lydia , Bilski Piotr , Chignell Colin F.
Published: January 2008

Abstract— The fluoroquinolone antibiotics can induce skin photosensitivity in some patients and this has been ascribed to the generation of reactive oxygen species, such as singlet oxygen (O2[1Δg]). We have studied the photochemical properties of the different ionized forms of the fluoroquinolone norfloxacin upon complexation with Mg2+ and Ca2+ ions, as it is proposed that the antibiotic exists mainly as a complex in the blood plasma. We found that the norfloxacin cation (pH < 6) shows no photodegradation after UVA irradiation and has a low quantum yield of O2(1Δg) generation. The norfloxacin cation does not complex. Ca2+ or Mg2+ ions; when these ions are added to the solution, we observed no changes in the fluorescence quantum yields (φflu) and singlet oxygen yields (φΔ). In contrast, the neutral (6 ± pH > 8.5) and anionic (pH > 9) forms of norfloxacin are able to complex calcium and magnesium, and their generation of O2 (1Δg) is decreased by complexation. The neutral zwitterionic form and the anionic form also quench singlet oxygen by both chemical and physical pathways regardless of complex formation, while physical quenching is observed for the cation. At pH > 7.4, norfloxacin photobleaches and complexation to Ca2+ and Mg2+ increases the rate at which photobleaching occurs. Thus, both the pH of the medium and complexation with metal cations may affect the phototoxic potential of this antibiotic.
Saccharomyces cerevisiae Mutants Defective in Heme Biosynthesis as a Tool for Studying the Mechanism of Phototoxicity of Porphyrins
Authors: Otdek Teresa , Nhi Nguyen Bich , Rytka Joanna
Published: January 2008

Abstract— Mutants of Saccharomyces cerevisiae accumulating uroporphyrin (UP) or protoporphyrin (PP) were used as a model for the in vivo phototoxic effect of porphyrins observed in the human skin photosensitivity associated with porphyrias (porphyria cutanea tarda and erythropoietic protoporphyria). We have found that UP is localized in vacuoles and PP is present in all compartments except vacuoles in yeast cells. Endogenous PP is much more effective as a photosensitizer of yeast cells than UP. Protoporphyrin action is strictly dependent on the presence of oxygen. In contrast, UP displays a phototoxic effect even if oxygen is not present in the suspension, implicating a free radical mechanism that operates in anaero‐biosis upon photosensitization by UP. Catalase or superoxide dismutase deficiency affects photosensitization by UP. A possible mechanism of UP photosensitizing activity is discussed.
Function of the Reaction Center of Green Sulfur Bacteria
Authors: Sakurai Hidehiro , Kusumoto Noriaki , Inoue Kazuhito
Published: January 2008

The reaction center (RC) of green sulfur bacteria belongs to the Fe‐S type RC, as do the photosystem I of oxygenic photosynthetic organisms and the RC of heliobacteria. The core parts of the green sulfur bacterial and the heliobacterial RC are assumed to be homodimeric, in contrast to those of purple bacteria, photosystem I and photosystem II. This paper describes recent advances in the study of the function of the green sulfur bacterial RC.
Alkyl Ether Analogs of Chlorophyll‐a Derivatives: Part 1. Synthesis, Photophysical Properties and Photodynamic Efficacy
Authors: Pandey Ravindra K. , Sumlin Adam B. , Constantine Scott , Aoudia Mohamed , Potter William R. , Bellnier David A. , Henderson Barbara W. , Rodgers Michael A. , Smith Kevin M. , Dougherty Thomas J.
Published: January 2008

The synthesis, preliminary in vivo biological activity, singlet oxygen and fluorescence yields of a series of alkyl ether derivatives of chlorophyll‐a analogs are described. For short‐chain carbon ethers (1–7carbon units), it was observed that the biological activity increased by increasing the length of the carbon chain, being maximum in compounds with n‐hexyl and n‐heptyl chains. Related sensitizers prepared by reacting 2‐(1‐bromoethyl)‐2‐devinylpyropheophorbide‐a with (sec)alcohols were found to be less effective. Under similar treatment conditions, photosensitizers containing cis‐ and trans‐ 3‐hexenyl side chains were ineffective. Thus, both stereochemical and steric factors caused differences in sensitizing activity. In general, pyropheophorbide‐a analogs were found to be more active than related chlorin e6 derivatives, in which the isocyclic ring (ring “E”) was cleaved. Related photosensitizers in the 9‐deoxy‐ series were found to be as effective as the corresponding pyropheophorbide‐a analogs. The photosensitizers prepared from pyropheophorbide‐a methyl ester and chlorin e6 trimethyl ester have long wavelength absorption at 660 nm (ε 45000 to 50000). Reduction of the carbonyl group in the pyropheophorbide‐a to methylene (ring E) resulted in a blue shift to 648 nm (ε 38000).
Medical UV Exposures and HIV Activation
Authors: Zmudzka Barbara Z. , Miller Sharon A. , Jacobs Mary E. , Beer Janusz Z.
Published: January 2008

This paper presents the first attempt to evaluate the potential of clinical UV exposures to induce the human immunodeficiency (HIV) promoter and, thus, to upregulate HIV growth in those skin cells that are directly affected by the exposure. Using the data for HIV promoter activationin vitro, we computed UVB and psoralen plus UVA (PUVA) doses that produce 50% of the maximal promoter activation (AD50). Then, using (a) literature data for UV transmittance in the human skin, (b) a composite action spectrum for HIV promoter and pyrimidine dimer induction by UVB and (c) an action spectrum for DNA synthesis inhibition by PUVA, we estimated the distribution of medical UVB and PUVA doses in the skin. This allowed us to estimate how deep into the skin the HIV‐activating doses might penetrate in an initial and an advanced stage of UVB or PUVA therapy. Such analysis was done for normal type II skin and for single exposures. The results allow us to predict where in the skin the HIV promoter may be induced by selected small and large therapeutic UVB or PUVA doses. To accommodate changes in skin topography due to disease and UV therapy, our considerations would require further refinements. For UVB we found that, when the incident dose on the surface of the skin is 500 J/m2(290–320nm) (initial stage of the therapy), the dose producing 50% of the maximal HIV promoter activation (ADUVB50) is limited to the stratum corneum. However, with an incident dose of 5000 J/m2(an advanced stage of the therapy), ADUVB50may be delivered as far as the living cells of the epidermis and even to some parts of the upper dermis. For PUVA we found that, when the incident UVA doses are 25 or 100 kJ/m2(320–400nm) (an initial and an advanced stage of therapy, respectively), and the 8‐methoxypsoralen concentration in the blood is 0.1 μg/mL (the desired level), the combined doses to the mid epidermis (and some areas of the upper dermis) are well below the 50% HIV promoter‐activating PUVA dose (ADPUVA50). Only under the worst scenario conditions,i. e.an exceptionally high drug concentration in the patient's tissues and localization of HIV in the nearest proximity to the skin surface, would the combined PUVA dose expected during photochemotherapy exceed ADPUVA50. These results suggest that the probability of HIV activation in the epidermis by direct mechanisms is higher for UVB than for PUVA treatment. However, complexities of the UV‐inducible HIV activation and immunomodulatory phenomena are such that our results by themselves should not be taken as an indication that UVB therapy carries a higher risk than PUVA therapy when administered to HIV‐infected patients.
Quantitative Determination of Cyclobutane Thymine Dimers in DNA by Stable Isotope‐Dilution Mass Spectrometry
Authors: Podmore Ian D. , Cooke Marcus S. , Herbert Karl E. , Lunec Joseph
Published: January 2008

In order to understand the role of UV‐induced DNA lesions in biological processes such as mutagenesis and carcinogenesis, it is essential to detect and quantify DNA damage in cells. In this paper we present a novel and both highly selective and sensitive assay using capillary gas chromatography (GC) combined with mass spectrometry (MS) for the detection and accurate quantitation of a major product of UV‐induced DNA damage (cissyn cyclobutadithymine). Quantitation of the cyclobutane thymine dimer was achieved by the use of an internal standard in the form of a stable 2H‐labeled analogue. Both isotopically labeled and nonlabeled dimers were prepared directly from their corresponding monomers. Each was identified as their trimethylsilyl ether derivative by GC‐MS. Calibration plots were obtained for known quantities of both nonlabeled analyte and internal standard. Quantitation of cis‐syn cyclobutadithymine was demonstrated in DNA exposed to UVC radiation over a dose range of 0 to 3500 J m−2. Under the conditions used, the limit of detection was found to be 20–50 fmol on column (equivalent to 0.02–0.05 nmol dimer per mg DNA). The results of the present study indicate that capillary GC‐MS is an ideally suited technique for selective and sensitive quantification of cis‐syn cyclobutadithymine in DNA and hence UV‐induced DNA damage.
UVB Shielding Role of FeCI3 and Certain Cyanobacterial Pigments
Authors: Kumar Ashok , Tyagi Madhu B. , Srinivas Ganna , Singh Nilima , Kumar Har D. , Sinha Rajeshwar P. , Häder Donat‐P.
Published: January 2008

The shielding role of ferric iron (FeCl3) and certain cyanobacterial pigments (a brown‐colored pigment from Scytonema hofmanii culture filtrate and a pink extract from Nostoc spongiaeforme) against UVB‐induced damage in the filamentous, nitrogen‐fixing cyanobacterium Nostoc muscorum has been demonstrated. Addition of these colored compounds to agarose gels (1–3 mm thick) resulted in a considerable decrease in UVB transmittance through the gels. The lowest UVB transmittance (15%) occurred through a 3 mm gel containing 0.01% FeCl3 followed by S. hofmanii culture filtrate (40%) and N. spongiaeforme extract (50%). These substances appear to act as very efficient UVB‐absorbing screens. Percent survival and 14CO2 uptake of N. muscorum increased significantly if UVB exposure was given on gels containing FeCl3 or other UVB‐shielding substances. The highest protection of N. muscorum was recorded with FeCl3, followed by S. hofmanii culture filtrate and N. spongiaeforme extract. Such UV‐shielding substances if present in required concentration range may enhance the survival of cyanobacteria exposed to high levels of UVB.
Flow Cytometric Technique for Quantitating Cytotoxic Response to Photodynamic Therapy
Authors: Campbell D. L. , Fisher M. E. , Johnson J. G. , Rossi F. M. , Campling B. G. , Pottier R. H. , Kennedy J. C.
Published: January 2008

Abstract— A simple flow cytometric technique for rapid measurement of multilog cytotoxic responses to photosensitization of cellular systems is described. This technique is particularly useful for cell lines with a low colony‐forming efficiency, for which a nonclonogenic assay is required. The assay separates cell‐sized objects from cellular debris by gating on forward scatter versus side scatter, identifies viable cells by positive calcein AM and negative ethidium homodimer‐1 staining and measures cell concentration relative to an internal standard of polystyrene beads. Large numbers of cells can be analyzed rapidly.

Two patient‐derived small cell lung cancer cell lines, NCI‐H209 and SV‐E, were used to test the technique. Photoradiation survival curves of the response of these cell lines to 5‐aminolevulinic acid‐induced protoporphyrin IX photosensitization correlated with the extent of photosensitizer accumulation. There was good agreement between the results obtained using the tritiated thymidine incorporation assay and the flow cytometric cytotoxicity assay. The technique can be used to measure cytotoxic responses to photosensitization of cell lines regardless of their plating efficiencies.
Fluence‐Dependent Induction of Micronuclei by Aluminum Phthalocyanine Tetrasulfonate‐Mediated Photodynamic Therapy
Authors: Hahn Kevin A. , Panjehpour Masoud , Lu Xiaochen
Published: January 2008

Abstract— The purpose of the study was to determine if aluminum phthalocyanine tetrasulfonate (A1PcS4) photodynamic therapy (PDT) induced the formation of micronuclei in vitro and whether micronuclei formation was dependent on fiuence or cell type. NIH‐3T3 and EMT‐6 monolayer cultures were incubated in AlPcS4 (0 or 1 μg/mL) for 24 h, received 0.0, 0.5,1.0 or 1.5 J/cm 2 of 675 nm light, then reincubated and harvested at either 24, 48 or 72 h. The micronucleus frequency was determined in binucleated cells using the cytochalasin‐block method. Cytotoxicity was assessed by using the 3(4,5‐dimenthylthiazoyl‐2‐yl)2,5(diphenyl‐tetrazolium bromide) (MTT) method. The effect of treatment on cell cycle progression was determined by calculating a proliferative index.

Aluminum phthalocyanine tetrasulfonate PDT induced a fluence‐dependent increase in the frequency of micro‐nuclei in NIH‐3T3 and EMT‐6 cells. The maximal effect of PDT was obtained in both cell lines 24 h after treatment. NIH‐3T3 and EMT‐6 cells exposed to a low fiuence of 0.5 J/cm2 had a significantly lower number of micro‐nuclei per cell 48 h following PDT treatment compared to the number of micronuclei per cell observed 24 h following treatment; however, when cells were exposed to a fluence (1.0 or 1.5 J/cm2) the number of micronuclei per cell did not diminish until 72 h after PDT treatment. The results obtained from the micronucleus assay paralleled those results obtained from the MTT assay.
Phototoxicity of Some Bromine‐Substituted Rhodamine Dyes: Synthesis, Photophysical Properties and Application as Photosensitizers
Authors: Pal Prabir , Zeng Hualing , Durocher Gilles , Girard Denis , Li Tiechao , Gupta Ajay K. , Giasson Richard , Blanchard Louise , Gaboury Louis , Balassy Antonia , Turmel Chantal , Laperrière André , Villeneuve Luc
Published: January 2008

Abstract— The synthesis of some bromine‐substituted rhodamine derivatives viz., 4,5‐dibromorhodamine methyl ester (dye 2) and 4,5‐dibromorhodamine n ‐butyl ester (dye 3) are reported. These dyes were synthesized to promote a more efficient cancer cell photosensitizer for potential use in in vitro bone marrow purging in preparation for autologous bone marrow transplantation. Spectroscopic and photo‐physical characterization of these dyes together with rhodamine 123 (dye 1) are reported in water, methanol, eth‐anol and also in a microheterogeneous system, sodium dodecyl sulfate. The possible mechanism of photosensi‐tization is characterized in terms of singlet oxygen efficiency of these dyes. Singlet oxygen quantum yields for bromine‐substituted dyes are in the range of 0.3‐0.5 depending on the solvent. For dye 1 no singlet oxygen production is found. The photodynamic actions of these dyes in different cell lines are tested. It was found that dye 2 and dye 3 are efficient photosensitizers and mediate eradication of K562, EM2, myeloid cell lines (CML) and the SMF‐AI rhabdomyosarcoma line.
Attenuation of Erythemal Effective Irradiance by Cloudiness at Low and High Altitude in the Alpine Region
Authors: Blumthaler Mario , Ambach Walter , Cede Alexander , Staehelin Johannes
Published: January 2008

Abstract— The transmittance of cloudiness was examined for the daily totals of global erythemal effective irradiance and global total irradiance in Innsbruck (577 m above sea level [a.s.l.], Western Austria) for the periods 1981‐1988 and 1993‐1994 and at Jungfraujoch (3576 m a.s.l., Switzerland) for the period 1981‐1990. The influence of varying cloudiness on the daily totals of global erythemal effective irradiance is considerably greater than the influence of varying ozone. The lowest transmittance for daily totals of global erythemal effective irradiance is 9.4% in Innsbruck (577 m a.s.l.) and 23.5% at Jungfraujoch (3576 m a.s.l.); the median and the 25‐75 percentile range at 10/10 cloudiness are 41.8% (28.9‐56.7%) and 76.8% (63.5‐86.1%), respectively. The greater transmittance of global erythemal effective irradiance at Jungfraujoch originates from smaller thickness of the cloud layer in high mountains than in valleys. Similar transmittances were obtained for the daily totals of global total irradiance (300‐3000 nm) as a function of cloudiness.
Resonance‐Enhanced CARS Spectroscopy of Biliproteins: a Comparison Between Phycoerythrocyanin and Phycocyanin of Mastigocladus laminosus
Authors: Schneider S. , Prenzel C.‐J. , Brehm G. , Gottschalk L. , Zhao K.‐H. , Scheer H.
Published: January 2008

Abstract— Resonance‐enhanced coherent anti‐Stokes Raman (CARS) spectra are reported for trimers of phycoerthrocyanin (PEC) dissolved in H2O and D2O. The CARS spectra are significantly different when recorded with pump wavelength either at 585 nm or 630 nm. By comparison of the 630 nm spectra with those of phycocyanin one can conclude that there is a change in the relative location of the lowest excited states of the β84 and β155 chromophores. Upon additional illumination with 514.5 nm laser light, only the spectra recorded with 585 nm pump wavelength change. This is in accordance with earlier observations that the phycoviolobilin chromophore of the a‐subunit exhibits photochromic behavior. The changes in the CARS spectra provide evidence that it is the methine bridge between rings C and D that undergoes the geometrical changes. Furthermore, it is suggested that there are different types of photoinduced rearrangements operative and that the isomeric distribution is different in H2O and D2O.
Triplex‐Mediated, in vitro Targeting of Psoralen Photoadducts within the Genome of a Transgenic Mouse
Authors: Gunther Edward J. , Havre Pamela A. , Gasparro Francis P. , Glazer Peter M.
Published: January 2008

Abstract— Light‐activated psoralens can covalently modify DNA and are widely used to study nucleic acid secondary structure and mutagenesis. Sequence specificity can be added to the photoaddition reaction by attaching the psoralen to an oligonucleotide designed to recognize a double‐stranded DNA binding site through formation of a triple helix. We have previously used this strategy to study targeted psoralen modification of a triplex binding site within the bacterial supF gene carried in viral genomes. In the present work we report the targeting of psoralen photoadducts in vitro to a specific site in the genome of a transgenic mouse. Both 10 base and 16 base oligonucleotide‐psoralen conjugates were capable of sequence‐specific modification of genomic mouse DNA, while a truncated 8 base conjugate was not. Light activation was necessary, and a dose dependence was demonstrated for target site modification and mutagenesis. The 10 base conjugate rapidly found its target, with sequence‐specific binding occurring after just 10 min incubation in the presence of mouse DNA. The ability to target psoralen photoadducts within mammalian genomes may prove useful in the study of chromatin structure and DNA repair. Moreover, this work may lead to potential in vivo applications of targeted psoralen modification.
Photoinhibition in the Mediterranean Green Alga Halimeda tuna Ellis et Sol Measured in situ
Authors: Häder Donat‐P. , Porst Markus , Herrmann Heike , Schäfer Jochen , Santas Regas
Published: January 2008

Abstract— Photoinhibition of photosynthesis was investigated in the Mediterranean green alga Halimeda tuna measuring pulse amplitude modulation (PAM) chlorophyll fluorescence and oxygen evolution in situ under solar radiation. Exposure to solar radiation at the surface caused a drastic decline in the photosynthetic quantum yield accompanied by a decline in the photochemical quenching, while the nonphotochemical quenching dramatically increased. The algae recovered from these effects within a few hours indicating that these are mainly due to reversible photoinhibition and only to a smaller extent to nonreversible photodamage. Individuals harvested from deeper waters were more affected than those from shallower waters. Photoinhibition occurs in this alga even in its natural habitat when the sun is at high angles as shown by measuring the fluorescence parameters at hourly intervals during the course of the day. Photoinhibition was less pronounced when the short wavelength band was increasingly removed from solar radiation using cut‐off filters. After exposure of thalli to solar radiation at the water surface, oxygen production decreased drastically within 30 min; this inhibition was even more pronounced in algae harvested from deeper waters. Oxygen measurements at different depths showed optimal photosynthesis at a depth of 1 m. Also for photosynthetic oxygen production inhibited by high solar irradiance at least partial recovery could be observed within several hours. Despite the fact that UVB accounts for a very small fraction of solar radiation, it has a considerable effect on photosynthesis, whereas UVA seems to contribute only little to photoinhibition in H. tuna.
Structure‐Based Calculations of the Optical Spectra of the LH2 Bacteriochlorophyll‐Protein Complex from Rhodopseudomonas acidophila
Authors: Sauer Kenneth , Cogdell Richard J. , Prince Steve M. , Freer Andy , Isaacs Neil W. , Scheer Hugo
Published: January 2008

Abstract— The molecular structure of the light‐harvesting complex 2 (LH2) bacteriochlorophyll‐protein antenna complex from the purple non‐sulfur photosynthetic bacterium Rhodopseudomonas acidophila, strain 10050 provides the positions and orientations of the 27 bacteriochlorophyll (BChl) molecules in the complex. Our structure‐based model calculations of the distinctive optical properties (absorption, CD, polarization) of LH2 in the near‐infrared region use a point‐monopole approximation to represent the BChl Qy transition moment. The results of the calculations support the assignment of the ring of 18 closely coupled BChl to B850 (BChl absorbing at 850 nm) and the larger diameter, parallel ring of 9 weakly coupled BChl to B800. All of the significantly allowed transitions in the near infrared are calculated to be perpendicular to the C9 symmetry axis, in agreement with polarization studies of this membrane‐associated complex. To match the absorption maxima of the B800 and B850 components using a relative permittivity (dielectric constant) of 2.1, we assign different site energies (12 500 and 12260 cm−1, respectively) for the Qy transitions of the respective BChl in their protein binding sites. Excitonic coupling is particularly strong among the set of B850 chromophores, with pairwise interaction energies nearly 300 cm between nearest neighbors, comparable with the experimental absorption bandwidths at room temperature. These strong interactions, for the full set of 18 B850 chromophores, result in an excitonic manifold that is 1200 cm−1 wide. Some of the upper excitonic states should result in weak absorption and perhaps stronger CD features. These predictions from the calculations await experimental verification.
An Animal Model for Human Melanoma
Authors: Green Adele , Neale Rachel , Kelly Roger , Smith Ian , Ablett Effie , Meyers Barry , Parsons Peter
Published: January 2008

Abstract— Experimental animal models that are directly relevant to human melanoma are lacking. We propose the Angora goat as a potentially useful field model with experimental potential and to this end have examined the prevalence and site distribution of all skin cancers in 28 Angora goat herds in Queensland, Australia. The prevalence of benign melanocytic lesions (lentigines) and their experimental induction by sunlight were also investigated. Among 1731 goats over 2 years of age, 139 malignant skin tumors were excised from 95 affected animals. The prevalence of squamous cell carcinoma (SCC) was 3.8% and of melanoma, 2.2%. Main site of occurrence of melanoma (83%) was the dorsal surface of the ear; in contrast SCC occurred mostly (84%) on the perineum. Lentigines were darker and more prevalent on the exposed compared with the unexposed surface of the ear in Angoras, analogous to the higher prevalence of nevi on the exposed compared with the less exposed inner surface of the arm in humans. Lentigines, which were also found on the perineum though lighter in color than on the dorsal ear, were absent in young animals under 3 months but were numerous in 1–3 year olds. Furthermore in an experimental substudy eight goats, having one flank repeatedly shorn and the contralateral flank left unshorn, revealed consistently more solar lentigines on the shorn flank (P < 0.05) when both sides were examined after 9 months. Histopathological examination of paired skin biopsies from five of these goats also showed more abundant pigmentation in skin from the exposed, as compared with the unexposed flank. These findings indicate that sunlight induces tumors and lentigines in goats in a highly site‐specific manner. The Angora goat model may suggest paradigms for explaining the site differences observed for human melanoma and may also be useful in the future clarification of molecular changes following carcinogenic levels of sun exposure.
Photochemical and Photophysical Studies of 3‐Amino‐6‐lodoacridine and the Inactivation of λ Phage
Authors: Chen Tongqian , Voelk Eric , Platz Matthew S. , Goodrich Raymond P.
Published: January 2008

Abstract— The photochemistry and photophysics of 3‐amino‐6‐io‐doacridine (Acr‐I) was studied. Photolysis (350 nm) of Acr‐I (free base) generates products consistent with a free radical intermediate in methanol, benzene and carbon tetrachloride. The Acr‐I hydrochloride is shown to bind to calf thymus DNA and to the self‐complementary dinucleotide cytidylyl‐(3′‐5′)‐guanosine (CpG) minidu‐plex in a manner similar to that of proflavine (Acr‐NH2), a known DNA intercalator. The Acr‐I is shown to more efficiently nick supercoiled plasmid DNA pBR322 upon 350 nm or 420 nm photolysis than Acr‐NH2. The efficiency of Acr‐I‐sensitized DNA nicking is not oxygen dependent. Photolysis of the Acr‐I/(CpG)2 complex leads to cleavage of the dinucleotide and to cytidine base release by selective damage to a specific ribose moiety. Dinucleotide cleavage occurs equally well in the presence or absence of oxygen, thereby eliminating a singlet oxygen‐ or peroxyl radical‐mediated process. Photolysis of Acr‐I in the presence of a mononucleotide (GMP) or a non‐self‐complementary dinucleotide (uridylyl‐[3′‐5′]‐cytidine– UpC) does not lead to fragmentation and base release. Similarly, photolysis of the Acr‐NH2/(CpG)2 complex does not lead to fragmentation and base release. The data indicate that photolysis of an iodinated intercalator bound to CpG or plasmid DNA generates an intercalated aryl radical and that the reactive intermediate initiates a sequence of reactions that efficiently nick nucleic acids. The inactivation of Λ phage sensitized by Acr‐I with UV (350 nm) light is oxygen independent but with visible (420 nm) light is strongly oxygen dependent. The Acr‐I fluoresces more intensely when excited at 446 than at 376 nm. Thus, UV photolysis may lead to C‐I bond homolysis and free radical formation, a process that is not energetically feasible with visible light. The results demonstrate the difficulty of extrapolating model studies involving simple molecules and DNA to understanding the mechanism of viral inactivation with a particular sensitizer.