bluuebunny/crossref_metadata_2025 huggingface dataset:
The Skin Immune System in the Course of HIV‐1 Infection
Authors: Henry Michael , Tschachler Erwin
Published: January 2008

In human immunodeficiency virus‐1 (HIV‐1) infection, diseases of the skin and mucous membranes frequently dominate the clinical picture as a consequence of progressive immunodeficiency. Functional impairment of the skin immune system, manifesting as a loss of the skin delayed‐type hypersensitivity response is very likely due to the infection of immunocompetent cells of the skin by HIV‐1. Besides CD4+ T cells, antigen‐presenting Langerhans cells have been established as major targets of HIV‐1 infection. The close physical contact of Langerhans cells with T lymphocytes during immune activation suggests a central role of these cells in the dissemination of HIV‐1 and the subsequent breakdown of the skin immune system. In addition, there are indications that mucosal Langerhans cells may represent prefered target cells for certain HIV‐1 subtypes and thereby facilitate mucocutaneous transmission of HIV‐1.
Fluorescence Quenching of 1‐Pyrenemethanol by Methylviologen in Polystyrene Latex Dispersions
Authors: Nakashima Kenichi , Kido Naofumi
Published: January 2008

Fluorescence quenching of 1‐pyrenemethanol by methylviologen through photoinduced electron transfer is investigated in polystyrene (PS) latex dispersions as well as in aqueous homogeneous solutions. In aqueous homogeneous solutions, the Stern‐Volmer plot for the intensity is linear and close to that for the lifetime, indicating a dynamic quenching mechanism. In PS latex dispersions, however, the Stern‐Volmer plots for the intensity are downward curving and the decay curves are not so much affected by the quencher as those for aqueous solutions, implying a significant contribution of static quenching. The downward‐curving Stern‐Volmer plots are well described by a two‐site model that assumes accessible and inaccessible sites to the acceptor on latex particles. The Stern‐Volmer constants obtained indicate that in the latex dispersions the fluorescence quenching occurs several hundreds times more efficiently than that in an aqueous homogeneous solution. This drastic enhancement of the quenching in latex dispersions is attributed to the increase in the local concentrations of the reactants on the latex surface. We have demonstrated the usefulness of latex surfaces as a new type of reaction field for photoinduced electron transfer.
Glutathione Isopropyl Ester Reduces UVB‐lnduced Skin Damage in Hairless Mice
Authors: Kobayashi Shizuko , Takehana Makoto , Tohyama Chiharu
Published: January 2008

Abstract— The protective effect of administration of glutathione (GSH) isopropyl ester on photodamage, such as lipid peroxidation, inflammation and tumorigenesis induced by UV exposure (290–400 nm, max. 312 nm), was investigated using hairless mice. Pretreatment with 20 mg/kg GSH isopropyl ester prevented the increases of thiobarbituric acid‐reactive substance (TBARS) formation in skin and serum sialic acid, indices of lipid peroxidation and inflammatory reaction, respectively, which were caused by a single dose (15 kj/m2) of UV irradiation. The level of epidermal GSH in skins of the GSH ester‐treated mice was maintained within normal limits. When mice were exposed to UV at a dose of 2 kj/m2, three times weekly, skin tumors developed in all of them after 25 weeks. The formation of skin tumors was significantly inhibited by administration of 10 mg/kg GSH ester prior to each UV irradiation for 25 weeks. Moreover, the increases of cutaneous TBARS and serum sialic acid in the tumor‐bearing mice were also prevented by continuous pretreatment with GSH ester. Even after 24 weeks, the epidermal GSH content of the pretreated mice was mostly retained compared to nonirradiated mice. However, administration of GSH prior to acute or chronic UV irradiation had no effect on the UV‐induced damage. The present results suggest that the protection from photo‐damage afforded by pretreatment with GSH ester is due to maintenance of a normal GSH level.
Fast Redox Perturbation of Aqueous Solution by Photoexcitation of Pyranine
Authors: Kotlyar Alexander B. , Borovok Natalia , Raviv Shirley , Zimanyi Laszlo , Gutman Menachem
Published: January 2008

Abstract— Intense illumination (60‐120 MW/cm2) of an oxygen‐free aqueous solution of pyranine (8‐hydroxypyrene‐l,3,6‐tri‐sulfonate) by the third harmonic frequency of an Nd‐Yag laser (355 nm) drives a two successive‐photon oxidative process of the dye. The first photon excites the dye to its first electronic singlet state. The second photon interacts with the excited molecule, ejects an electron to the solution and deactivates the molecule to a ground state of the oxidized dye (φ+). The oxidized product, φ+, is an intensely colored compound (Λmax= 445 nm, ε= 43 000 ± 1000 M−1 cm−1) that reacts with a variety of electron donors like quinols, ascorbate and ferrous compounds. In the absence of added reductant, φ+ is stable, having a lifetime of ‐10 min. In acidic solutions the solvated electrons generated by the photochemical reaction react preferentially with H+. In alkaline solution the favored electron acceptor is the ground‐state pyranine anion and a radical, φ, of the reduced dye is formed. The reduced product is well distinguished from the oxidized one, having its maximal absorption at 510 nm with e = 25 000 ± 2000 M‐l cm−1. The oxidized radical can be reduced either by φ‐ or by other electron donors. The apparent second‐order rate constants of these reactions, which vary from 106 up to 109M−1 s−1, are slower than the rates of diffusion‐controlled reactions. Thus the redox reactions are limited by an energy barrier for electron transfer within the encounter complex between the reactants.
Molecular Mechanism of Drug Photosensitization. IX. Effect of Inorganic Ions on DNA Cleavage Photosensitized by Naproxen
Authors: De Guidi G. , Giuffrida S. , Condorelli G. , Costanzo L. L. , Miano P. , Sortino S.
Published: January 2008

Abstract— Photocleavage of DNA induced by naproxen and the correlated protective effect by some inorganic ions have been considered. The presence of a DNA complex is suggested and only associated naproxen seems to be responsible for the cleavage, for which the quantum yield of single strand breaks was calculated. The inorganic ions I‐, Mn2+, Co2+ and Cu2+ decrease naproxen‐photoin‐duced DNA cleavage. Iodide acts by a heavy atom mechanism, thus inhibiting naproxen photolysis and decreasing the amount of free radicals responsible for the photocleavage both in aerobic and anaerobic conditions. Metallic ions protect only within a range of concentrations, as for higher amounts damaging processes are observed. The protective efficiency of cations decreases with the increase of free drug concentration in the bulk of the solution, due to their involvement in the scavenging of naproxen radicals generated by photolysis of the free drug. In the presence of EDTA the cations show a better protective action. The most likely hypothesis is an inhibiting effect on the damaging processes via a redox cycle. The different behaviors of copper and of the two other cations can be justified by the influence of redox potentials of free and complexed metals and by the superoxide dis‐mutase‐like activity of copper.
Ambient Solar Radiation‐Induced Photodamage in Marine Bacterioplankton
Authors: Jeffrey Wade H. , Aas Peter , Lyons M. Maille , Coffin Richard B. , Pledger Ralph J. , Mitchell David L.
Published: January 2008

Abstract— There has been much recent concern about the effects of increased UV radiation at certain locations on the earth's surface. There have been extensive studies of ultraviolet radiation effects on phytoplankton and primary production, yet the effects of UVB upon bacterioplankton have been largely overlooked. Bacteria play a central role in the cycling of nutrients and energy flow to higher trophic levels, serving as both mineralizers and secondary producers that are consumed by higher organisms. We have begun to investigate the induction of DNA photodamage by UVB in marine planktonic communities using a highly specific radioimmunoassay to measure cyclobutane pyrimidine dimers in samples collected from the northern Gulf of Mexico. DNA damage in the bacterioplankton size‐fraction (< 0.8 μ.m) was greater than in the larger eukaryotic size fraction (>0.8 μm <120 μm) in 9 of 10 samples. Diel patterns of dimer accumulation and repair were observed in surface waters over a 48 h period in the bacterioplankton size fraction and in the larger eukaryotic plankton size fraction. Depth profiles of DNA damage in the bacterioplankton size fraction appear to be dependent on surface water mixing. Damage was greatest in surface waters, decreased with depth and could be detected to 10 m in calm seas. No net accumulation of damage was observed in moderate seas, even at the surface. Solar radiation was found to inhibit significantly both 3H‐thymidine and 14C‐leucine incorporation. Ultraviolet B was responsible for approximately half of the total inhibition of 3H‐thymidine incorporation, UVA contributing the other half of the inhibition. The vast majority of 14C‐leucine incorporation inhibition was due to UVB, suggesting that protein synthesis is less affected by UVA. The results demonstrate that direct measures of DNA damage can be made of indigenous planktonic communities and that bacterioplankton are highly susceptible to UVB damage and may serve as a more sensitive indicator of UVR stress than other microorganisms.
Developmental Responses of Amphibians to Solar and Artificial UVB Sources: A Comparative Study
Authors: Hays John B. , Blaustein Andrew R. , Kiesecker Joseph M. , Hoffman Peter D. , Pandelova Lovanna , Coyle Daniel , Richardson Timothy
Published: January 2008

Abstract— Many amphibian species, in widely scattered locations, currently show population declines and/or reductions in range, but other amphibian species show no such declines. There is no known single cause for these declines. Differential sensitivity to UVB radiation among species might be one contributing factor. We have focused on amphibian eggs, potentially the most UVB‐sensitive stage, and compared their resistance to UVB components of sunlight with their levels of photolyase, typically the most important enzyme for repair of the major UV photoproducts in DNA, cyclobutane pyrimidine dimers. Photolyase varied 100‐fold among eggs/oocytes of 10 species. Among three species–Hyla regilla, Rana cascadae, and Bufo boreas–for which resistance of eggs to solar UVB irradiance in their natural locations was measured, hatching success correlated strongly with photolyase. Two additional species, Rana aurora and Ambystoma gracile, now show similar correlations. Among the low‐egg‐photolyase species, R. cascadae and B. boreas are showing declines, and the status of A. gracile is not known. Of the two high‐photolyase species, populations of H. regilla remain robust, but populations of R. aurora are showing declines. To determine whether levels of photolyase or other repair activities are affected by solar exposures during amphibian development, we have initiated an extended study of H. regilla and R. cascadae, and of Xenopus laevis, laboratory‐reared specimens of which previously showed very low photolyase levels. Hyla regilla and R. cascadae tadpoles are being reared to maturity in laboratories supplemented with modest levels of UV light or light filtered to remove UVB wavelengths. Young X. laevis females are being reared indoors and outdoors. Initial observations reveal severe effects of both UVA and UVB light on H. regilla and R. cascadae tadpoles and metamorphs, including developmental abnormalities and high mortalities. Assays of photolyase levels in the skins of young animals roughly parallel previous egg/oocyte photolyase measurements for all three species.
Photosensitization by Norfloxacin is a Function of pH
Authors: Bilski P. , Martinez L. J. , Koker E. B. , Chignell C. F.
Published: January 2008

Abstract— Norfloxacin is a fluoroquinolone (FQ) antibiotic that has been reported to cause cutaneous photosensitivity in animals and occasionally in humans. We have studied the fluorescence and singlet oxygen (1O2)‐generating properties of norfloxacin. Upon UV excitation the drug fluoresces in water, and the relative intensities of two major fluorescence bands at ca 420 and 450 nm are affected by pH. The overall quantum yield of fluorescence (φF) is also strongly pH dependent: φF is low in 0.2 N HC1 solution (0.2), increasing steeply to 0.12 at pH 4, then gradually decreasing to 0.01 at pH 10. The changes in φF are accompanied by changes in fluorescence lifetime from 0.6 ns at pH 1 to 1.8 ns at pH 4. Norfloxacin exhibits phosphorescence in low temperature glasses. The formation of a triplet state at room temperature is also suggested by 1O2 phosphorescence in aerobic D2O. This phosphorescence is “self‐quenched” by norfloxacin itself with an efficiency that is pH dependent: kq is 7.9 ×106M−1s−1 at pD 4, decreases to 1.9 × 106M−1 s−1 at pD 7.5 but then increases about 20‐fold in alkaline D2O solutions. This quenching causes the observed 1O2 production by norfloxacin (0.1 mM) to show a maximum at around pH 8–9. However, after correction for self‐quenching, the quantum yield of 1O2 production (φso), measured by using perinaphthenone as a standard, yielded the following values: φso is about 0.07 in 0.2 N DCl solution, 0.08 at pH 7.5 and then increases smoothly to ∼ 0.2 in 0.1 M NaOD solution. The relatively high, unquenched 1O2 production at physiological pH 7.4 (φso∼ 0.08) suggests that 1O2 reactions may play an important role in the cutaneous phototoxicity of norfloxacin and other FQ antibiotics.
Photochemically Induced Solid‐State Degradation, Condensation, and Rearrangement Reactions in Lignin Model Compounds and Milled Wood Lignin
Authors: Argyropoulos Dimitris S. , Sun Yujun
Published: January 2008

Abstract— Milled wood lignin produced from alkaline hydrogen peroxide‐bleached softwood thermomechanical pulp (TMP) fibers was adsorbed on pure cellulose and irradiated for variable periods of time under oxygen and/or nitrogen. The absolute amounts of β‐O‐4 ethers, phenolic hydroxyl groups, carboxylic acids and various condensed phenolic units were quantified, nondestructively, using 31P NMR spectroscopy. Photoirradiation was found to severely cleave the β‐O‐4 ethers present in lignin with the concomitant formation of new phenolic units. The rate of this cleavage was found to be faster under oxygen than under nitrogen. The catalytic role of oxygen can be rationalized by invoking the formation of peroxy free radicals that may initiate new sites of radical generation (e.g. ketyl radicals) within the lignin causing the subsequent breakdown of the β‐O‐4 linkage. The photoirradiation was found to cause a net increase of the C5‐related condensed phenolic units in lignin. Among these, Cα‐C5 and/ or Cβ‐C5 phenolic moieties were found to predominate. Similar irradiation of a binary mixture of model compounds resembling structures present in softwood lignin resulted in 18 products that were identified and quantified using gas chromatography coupled to mass spectrometry. The photochemical products obtained supported the phenacyl and ketyl mechanistic pathways to pho‐toyellowing, whereas the detection of β‐5 coupling products (common in both the model compound and milled wood lignin studies) may point a new avenue toward the formation of light‐induced products that has not been previously considered in the solid state.
Effect of Supplementary UVB Radiation on Chlorophyll Synthesis and Accumulation of Photosystems during Chloroplast Development in Spirodela oligorrhiza
Authors: Marwood Christopher A. , Greenberg Bruce M.
Published: January 2008

Abstract— Although the effects of ultraviolet B (UVB, 290–320 nm) radiation have been studied in plants extensively, little is known about the potential impacts on maturation of chloroplasts. To address this problem, the effects of supplementary UVB on chloroplast development were examined in the aquatic higher plant Spirodela oligorrhiza. Dark‐grown Spirodela‐containing proplastids were exposed to photosynthetically active radiation (PAR) and ultraviolet A (UVA, 320–400 nm), plus supplementary UVB equivalent to 1% of PAR on a photon basis. The biosynthesis and assembly of chlorophyll (Chi) into reaction centers was followed for 4 days in situ by low temperature (77 K) Chi fluorescence. Impacts on chloroplast development were detected after only 1 h incubation in light with supplementary UVB. Fluorescence emission signals from Chi associated with the photosystem (PS) II antenna, PSII reaction centers and PSI reaction centers were detected at the same time with or without UVB, but the magnitude of PS fluorescence was diminished up to 60% in plants incubated in UVB. The Chi content was also lower in UVB‐treated plants, but to a lesser degree than anticipated by low temperature fluorescence, suggesting lack of organization and/or association of Chi with PS. Electron transport, measured with room temperature fluorescence induction, was not consistently different in plants exposed to UVB. These results suggest that with UVB, fewer and/or smaller PS form during chloroplast development, but there is not a large inhibition of Chi synthesis or PSII activity.
OpticalIy Pumped Chemiluminescence of Indole‐3‐Acetic Acid
Authors: Krylov Sergey N. , Krylova Svetlana M.
Published: January 2008

Optically pumped chemiluminescence of indole‐3‐acetic acid (IAA) was observed and studied. Rose Bengal (RB) was used as a photosensitizer. Long‐lived chemiluminescence (CL) appeared after irradiation of the IAA/RB reaction mixture by monochromatic light at 550 nm (the maximum of RB absorption) or by visible light. The CL spectrum had a maximum at 480 nm. The kinetics of the CL decay were single exponential. Single‐exponential kinetics were characterized by two experimentally measured values: initial CL intensity and exponential lifetime of the CL decay. We studied the influence of five parameters: (1) the rate of irradiation fluence, (2) the time of irradiation, (3) RIB concentration, (4) IAA concentration and (5) buffer pH on the initial CL intensity and the CL lifetime. Initial CL intensity was proportional to the rate of irradiation fluence and the concentration of RB. Saturation was observed in dependencies of initial CL intensity on the time of irradiation, the concentration of IAA and the buffer pH. The lifetime of the CL decay decreased with increasing pH and did not depend on the other four parameters. The mechanism explaining the experimental results was suggested and detailed kinetic analysis was performed to prove the proposed mechanism. Quantum yield of the CL and five rate constants that are involved in the mechanism were determined.
Time‐Resolved Fluorescence and Transient Spectroscopy in Determining Photochemical and Photophysical Channels in Reacting Systems in Solutions and Microheterogeneous Media
Authors: Whitten David G. , Farahat Mohammad S. , Gaillard Elizabeth R.
Published: January 2008

Abstract— Characterization of short‐lived intermediates in homogeneous and microheterogeneous systems has been carried out using time‐resolved spectroscopic techniques. The data obtained from these techniques have been analyzed in a relatively unconventional manner to elucidate complex transient behavior for two reactive systems. The highly nonexponential fluorescence decay for a series of fraws‐stilbene‐derivatized amphiphiles that readily form bilayer systems in aqueous media has been analyzed using a distribution of lifetimes analysis (DLA). The utility of DLA for quantitative studies was first determined by simulation of artificial decay data. Despite some limitations in DLA, qualitative conclusions as to the nature of the fluorescing species may be drawn when supplementary information such as steady‐state spectroscopic data are also considered. The results indicate that the observed fluorescence originates from different types of excited‐state species that consist of two or more trans‐stilbene units; one of the emissions is attributed to the excited state of a ground‐state aggregate while the other is assigned to an excimer that may arise from a 'defect'in the bilayer. The nonexponential nature of the decays is attributed to distributions of environments experienced by the fluorescing species. Electron transfer (ET) reactions between several excited pinacols and carbon tetrachloride in solution have been found to yield products with quantum yields that are higher than unity in the presence of oxygen, suggesting a chain mechanism for product formation. In these systems both the donor and the acceptor undergo bond fragmentation following the initial ET step. The individual steps involved in the proposed mechanism for these systems have been investigated in part using different steady‐state and time‐resolved laser spectroscopic techniques. However, it was also necessary to utilize pulse radiolysis in order to confirm the involvement of certain radical intermediates that were not observable by the usual flash photolysis techniques.
The Role of Time‐Dependent Measurements in Elucidating Static Versus Dynamic Quenching Processes
Authors: Webber S. E.
Published: January 2008

Abstract— Fluorescence quenching provides a unique method for assessing the ability of quenching species to approach a fluorophore. The distance scale depends on the mechanism of quenching (e.g. compare Forster energy transfer with the external heavy atom effect and/or electron transfer). If one is dealing with amphiphilic systems or hydrophobic surface/water interfaces then ionic and organic quenchers can be compared. While the general concepts of “static” and “dynamic” quenching are well known and often used to characterize the mechanism of fluorescence quenching, it is this author's experience that for many systems the quenching mechanism is “mixed.” The signature of this situation is when the quenching of the steady‐state intensity does not match the quenching of the average fluorescence lifetime. First a few of the standard quenching models are reviewed and then a simple approach to characterize the degree of static quenching is discussed. Finally, it is indicated that careful analysis of the fluorescence decay for the shortest timescale should be undertaken if one wishes to estimate accurately the rate of static quenching and that this may be expected to be particularly demanding in the case of fluorophores with longer lifetimes. Although fluorescence is stressed in the discussion that follows, the same concepts would apply to phosphorescence from triplet states, except for the generally longer timescale encountered.
Photooxidation of Tryptophan: O2(1Δg) versus Electron‐Transfer Pathway
Authors: Wessels Jurina M. , Foote Christopher S. , Ford William E. , Rodgers Michael A. J.
Published: January 2008

Abstract— Tris (2,2'‐bipyridyl)ruthenium(II)chloride hexahydrate (Ru[bpy]32+) free in solution and adsorbed onto antimony‐doped SnO2 colloidal particles was used as a photosensitizer for a comparison of the O2(1Δg) and electron‐transfer‐mediated photooxidation of tryptophan (TRP), respectively. Quenching of excited Ru(bpy)32+ by O2(3σg−) in an aerated aqueous solution leads only to the formation of O2(1Δg) (φ4= 0.18) and this compound was used as a type II photosensitizer. Excitation of Ru(bpy)32+ adsorbed onto Sb/SnO2 results in a fast injection of an electron into the conduction band of the semiconductor and accordingly to the formation of Ru(bpy)32+ and was used for the sensitization of the electron‐transfer‐mediated photooxidation. The Ru(bpy)33+ is reduced by TRP with a bimolecular rate constant kQ= 5.9 × 108M−1 s−1, while O2(1Δg) is quenched by TRP with kt= 7.1 × 107M−1 s−1 (chemical + physical quenching). Relative rate constants for the photooxidation of TRP (kc) via both pathways were determined using fluorescence emission spectroscopy. With Np, the rate of photons absorbed, being constant for both pathways we obtained kc= (372/Np) M−1 s−1 for the O2(1Δg) pathway and kc≥ (25013/Np) M−1 s−1 for the electron‐transfer pathway, respectively. Thus the photooxidation of Trp is more than two orders of magnitude more efficient when it is initiated by electron transfer than when initiated by O2(1Δg).
Natural Killer Cell Activity during UVR‐induced Skin Tumor Formation in the Skh Hairless Mouse
Authors: Steerenberg P. A. , Korenromp E. L. , van Loveren H. , Mol D. Q. , Geerse L. , de Gruijl F. R.
Published: January 2008

Abstract— We analyzed natural killer (NK) cell activity in the hairless albino Skh/HR1 mouse, to study whether the NK cell activity plays a role during UV radiation (UVR)‐induced carcinogenesis. In 4 h 5lCr‐release assays, spleen lymphocytes of specific pathogen‐free (spf) Skh/HR1 mice displayed 5–10% spontaneous NK cell activity. This was comparable to NK ceil activity in C57BI/6, C3H and athymic NMRI nu/nu mice, which were also kept under spf conditions. In all strains investigated, the low spontaneous NK cell activity could be increased up to 20–30% by intraperitoneal administration of polyinosinic: polycytidylic acid (polyI:C), a standardized in vivo NK cell induction method. The polyI:C potentiation of NK cells in Skh/HR1 mice was similar to that in C57Bl/6 and NMRI, but significantly less than in C3H mice. Chronic daily UV irradiation according to a protocol that was also used for induction of carcinogenesis (11–12 weeks, 95 mJ/cm2 of UV exposure from FS40 sunlamps) did not decrease NK cell activity on a cell for cell basis. Neither was the inducibility of NK spleen cell activity with poly I: C in Skh/HR1 mice during UV exposure reduced. Based on total organ basis, the pooled lymph node cells (axillary, mandibulary and inguinal lymph node) showed a doubling of NK cell activity (P < 0.001), mainly due to an almost 100% increase in the number of lymph node cells. In conclusion, UVR does not suppress the normal or inducible NK cell activity at the time of clinical appearance of skin tumors. This suggests that such suppression of NK cell activity is not likely to contribute to UVR‐induced carcinogenesis in the Skh/HRl strain.
Subcellular Localization of Photofrin and Aminolevulinic Acid and Photodynamic Cross‐Resistance in Vitro in Radiation‐Induced Fibrosarcoma Cells Sensitive or Resistant to Photofrin‐Mediated Photodynamic Therapy
Authors: Wilson B. C. , Olivo M. , Singh G.
Published: January 2008

Abstract— The subcellular and, specifically, mitochondrial localization of the photodynamic sensitizers Photofrin and aminolevulinic acid (ALA)‐induced protoporphyrin‐IX (PpIX) has been investigated in vitro in radiation‐induced fibrosarcoma (RIF) tumor cells. Comparisons were made of parental RIF‐1 cells and cells (RIF‐8A) in which resistance to Photofrin‐mediated photodynamic therapy (PDT) had been induced. The effect on the uptake kinetics of Photofrin of coincubation with one of the mitochondria‐specific probes 10N‐Nonyl acridine orange (NAO) or rhodamine‐123 (Rh‐123) and vice versa was examined. The subcellular colocalization of Photofrin and PpIX with Rh‐123 was determined by double‐label confocal fluorescence microscopy. Clonogenic cell survival after ALA‐mediated PDT was determined in RIF‐1 and RIF‐8A cells to investigate cross‐resistance with Photofrin‐mediated PDT. At long (18 h) Photofrin incubation times, stronger colocalization of Photofrin and Rh‐123 was seen in RIF‐1 than in RIF‐8A cells. Differences between RIF‐1 and RIF‐8A in the competitive mitochondrial binding of NAO or Rh‐123 with Photofrin suggest that the inner mitochondrial membrane is a significant Photofrin binding site. The differences in this binding may account for the PDT resistance in RIF‐8A cells. With ALA, the peak accumulations of PpIX occurred at 5 h for both cells, and followed a diffuse cytoplasmic distribution compared to mitochondrial localization at 1 h ALA incubation. There was rapid efflux of PpIX from both RIF‐1 and RIF‐8A. As with Photofrin, ALA‐induced PpIX exhibited weaker mitochondrial localization in RIF‐8A than in RIF‐1 cells. Clonogenic survival demonstrated cross‐resistance to incubation in PpIX but not to ALA‐induced PpIX, implying differences in mitochondrial localization and/or binding, depending on the source of the PpIX within the cells.
UVA II Exposure of Human Skin Results in Decreased Immunization Capacity, Increased Induction of Tolerance and a Unique Pattern of Epidermal Antigen‐Presenting Cell Alteration
Authors: LeVee Gordon J. , Oberhelman Lois , Anderson Tom , Koren Hillel , Cooper Kevin D.
Published: January 2008

Abstract— The risks incurred from increased exposure to UVA II (320‐340 nm) (i.e. during sunscreen use and extended outdoor exposure, tanning parlors) are not well understood. Therefore, we explored the effects of UVA II on skin immune responses in humans. After a single local exposure (4 minimum erythemal dose [MED]) using a xenon arc lamp filtered with a narrow bandpass filter (335 ± 5 nm full width at half maximum), individuals were contact‐sensitized with dinitrochlorobenzene (DNCB) through a UVA II exposure site or through normal skin. UVA II induced a marked decrease in the magnitude of skin immune responses (P < 0.0001). The UVA II group had only 29% successful sensitizations, as compared to 83% in the control group. The percentage of individuals who remained tolerant to DNCB after two sensitizations was 23.6% for the UVA II‐exposed group, as compared to 3.8% in the controls (P= 0.006). UVA II also uniquely altered the type of antigen‐presenting cells present in the epidermis. Human leukocyte antigen (HLA)‐DR+ cells in control epidermal cell suspensions (C‐EC) comprised a single, homogeneous population of Langerhans cells (LC) with the phenotype: CD1ahi DRmid CD11b− CD36− (1.5 ± 0.3% of EC). UVA II irradiation reduced the number of such LC to 0.6 ± 0.2% of EC. Although cells expressing the macrophage phenotype: CD1a DRhi CD11b+ CD36+ were increased in UVA II skin, relative to C‐EC, these comprised only 10.1 ± 6.1% of the DR+ cells, which is less than that after UVB exposure. Also distinct from UVB, a third population was found in UVA II‐EC, which exhibited a novel phenotype: CD1a+ DR+ CD36+ CDllb+; these comprised 11.1 ± 6.9% of the DR+ UVA II‐EC.

In conclusion, despite the above differences in infiltrating DR cells, both UVB and UVA II reduce the skin's ability to support contact sensitization, induce active suppression (tolerance) and induce a reduction in LC.
Photophysical Properties of Gilvocarcins V and M and Their Binding Constant to Calf Thymus DNA
Authors: Oyola Rolando , Arce Rafael , Alegria Antonio E. , Garcia Carmelo
Published: January 2008

Abstract—Absorption and emission techniques were used to characterize the ground (S0), singlet (S|) and triplet states (T1) of gilvocarcin V (GV) and gilvocarcin M (GM) in different solvents. Aggregation of GV with dimerization constant equal to 7800 M−1is observed in 10% dimethyl‐sulfoxide (DMSO)/water. The photophysical properties of the S, state of these molecules are more sensitive to changes in solvent characteristics than the corresponding ground states. The absorption of visible light by GV and GM results in a higher dipole moment of the excited state causing a red shift in the fluorescence spectra with increasing solvent polarity. The fluorescence quantum yield remains practically unchanged with changes in solvent properties unless water is present as a co‐solvent. Both φfand φfvalues corresponding to GV in DMSO are larger than those of GM, whereas in 10% DMSO/H2O the opposite is observed. Thus, GV is more susceptible to other deactivation pathways besides emission in the presence of water than GM. The relative phosphorescence quantum yield (φp= 0.03) and the triplet energy (ET= 52 kcal/mol) of GV and GM are similar. The S0‐S1energy difference is 63 kcal/mol for GV, whereas for GM it is 67. Thus, the singlet‐triplet energy difference is 11 and 15 kcal/mol, respectively. The PM3/CI calculated electronic structures of these compounds are consistent with the observed photophysical properties. The dark binding constants of GV to calf thymus DNA ([1.1–0.08] × 106M−1) are about an order of magnitude larger than those of GM ([0.24–0.018] × 106M−1) at different ionic strengths (0–2.00MNaCl). Also, the number of gilvocarcin molecules bound per base pair is smaller for GM than for GV. These differences in dark DNA binding parameters between GV and GM could have implications in the large photocytotoxic ability of GV as compared to GM.
Time‐Resolved Near Infrared Studies on Singlet Oxygen Production by the Photosensitizing 2‐Arylpropionic Acids*
Authors: de la Peña Daniel , Martí Cristina , Noneil Santi , Martínez Luis A. , Miranda Miguel A.
Published: January 2008

Abstract— Time‐resolved near infrared emission studies have been carried out on a series of nonsteroidal anti inflammatory 2‐arylpropionic acids, in order to assess their ability to photosensitize the production of singlet molecular oxygen O2(1Δg). Benoxaprofen, naproxen, tiaprofenic acid, suprofen, ketoprofen and carprofen showed quantum yields for this process (φΔ) in the range 0.2‐0.7 in acetonitrile. Deprotonation of the propionic acid moiety in mixtures of acetonitrile‐ethanol (4:1) basified with KOH produced a systematic decrease in φΔ for all compounds with the exception of naproxen. This effect was even more dramatic in D2O‐based phosphate buffer, where no singlet oxygen could be detected for benoxaprofen, ketoprofen or carprofen. The above results are consistent with the occurrence of competing photochemical reactions of 2‐arylpropionic acids in different media and particularly with the enhanced photodecarboxylation from the carboxylate anions.
Chloroplast Biogenesis 77: Two Novel Monovinyl and Divinyl Light‐Dark Greening Groups of Plants and Their Relationship to the Chlorophyll a Biosynthetic Heterogeneity of Green Plants
Authors: Mageed Haggag Awad Abd El , El Sahhar K. F. , Robertson Kenneth R. , Parham Ramin , Rebeiz Constantin A.
Published: January 2008

Abstract— On the basis of the steady‐state accumulation of divinyl (DV) or monovinyl (MV) protochlorophyllide (Pchlide) a in darkness (D) or in the light (L), green plants have been classified into three different greening groups namely dark divinyl‐light divinyl (DDV‐LDV), dark monovinyl‐light divinyl (DMV‐LDV) and dark monovinyl‐light monovinyl (DMV‐LMV) (Ionannides et al., Biochem. Syst. Ecol. 22, 211‐220,1994). Interruption of the L phase of the photoperiod by a brief period of darkness (LD condition) revealed a predominance of different chlorophyll (Chl) a biosynthetic routes, depending upon the greening group affiliation of the plant species. For example, in DMV‐LDV and DMV‐LMV plants, the predominant Chl a biosynthetic routes under the LD condition appear to be the MV Chi a biosynthetic route and/or a mixed DV‐MV Chi a biosynthetic route that bifurcates at the level of DV Pchlide a. On the basis of DV and MV Pchlide a accumulation rates after re‐darkening, this greening group is designated as a light‐dark MV (LDMV) subgroup. In DDV‐LDV plants, the predominant LD Chi a biosynthetic routes appear to be the DV Chi a biosynthetic route and/or a mixed DV‐MV Chi a biosynthetic route that bifurcates at the level of DV Chlide a. This greening group is designated as a light‐dark DV (LDDV) subgroup. It is proposed that upon inhibiting the conversion of Pchlide a to Chi a by interruption of the L phase of the photoperiod by a brief period of D, the rates of DV and MV Pchlide a regeneration may reflect the carryover rates of DV and MV Pchlide a biosynthesis in L instead of reflecting a differential use of DV and MV carboxylic biosynthetic rates in D. It is also shown that in LDMV plants, MV Chlide a and MV Chi a are formed without the participation of [4‐vinyl] Chlide a reductase. On the basis of recently published evidence, it is also argued that Pchlide oxidoreductase‐A (POR‐A) may be active in LDDV plants, while POR‐B may predominate in LDMV plant species. The evolutionary significance of the LDDV and LDMV greening subgroups is discussed.
Potassium Iodide as a Chemical Actinometer for 254 nm Radiation: Use of lodate as an Electron Scavenger
Authors: Rahn Ronald O.
Published: January 2008

Abstract— A solution of 0.6 M iodide and 0.1 M iodate in 0.01 M borate buffer (pH 9.25) can be used as a chemical actinometer to measure the incident fluence from a low‐pressure mercury lamp that puts out more than 85% of its energy at 254 nm. The actinometric solution is optically opaque to light below 290 nm and is optically transparent to wavelengths greater than 330 nm. Hence, the solution absorbs all of the germicidal wavelengths but little if any of the ambient light normally present in the laboratory. Iodate acts as an electron scavenger and prevents the back reaction of the free electron with the iodine atom following UV excitation of KI. Irradiation results in the linear formation of triiodide, which is quantitated by measuring its absorbance at 352 nm. The quantum yield for this system is approximately 0.75 0.03 at 20.7AoC or approximately three times greater than that obtained previously using nitrous oxide as an electron scavenger. A model is proposed to account for this difference. A precise expression to account for the concentration and temperature dependence of the quantum yield is given by pH = 0.75(1 + 0.23[C ‐ 0.577])(1 + 0.02[T ‐ 20.7]) where C is the concentration of iodide and T is the temperature. The concentration of iodide can be obtained from the absorbance at 300 nm prior to irradiation using 1.061 MJ cm−1 as the molar extinction coefficient. This actinometric system meets the quality criteria established by the International Union of Pure and Applied Chemistry with the caveat that it is designed to measure only germicidal radiation (i.e. wavelengths less than 290 nm).
Nonlinear Exciton Annihilation and Local Heating Effects in Photosynthetic Antenna Systems
Authors: Valkunas Leonas , Gulbinas Vidmantas
Published: January 2008

Abstract—Generation of the nonequilibrium distribution of excited vibrational modes stimulated by electronic energy relaxation in pigment‐protein complexes of the light‐harvesting antenna of some photosynthetic systems is discussed in this paper. It is shown that the simplest approach to this problem can be achieved by introducing a local temperature, which is a good parameter for describing the nonequilibrium distribution of the local vibrational modes of the pigment molecules and its nearest protein surroundings. Then the transient absorption kinetics is determined by the kinetics of the excitation relaxation as I well as the heating/cooling of the local vibrational modes. Experimentally, this process can be investigated in the i singlet‐singlet annihilation conditions that create the i greatest amount of local heating. The systems under in‐: vestigation are trimers of bacteriochlorophyll a contain‐ i ing pigment‐protein complexes from the green sulfur i bacterium Chlorobium tepid urn (so‐called FMO complexes) and aggregates of the light‐harvesting complexes of photosystem II (LHC2) from higher plants containing chlorophyll alb. It was shown that at 77 K the heat redistribution kinetics in LHC2 is on the order of 3040 ps and in FMO it is approximately equal to 26 ps. The local heating effect at room temperature is less pronounced; however, by using longer pulses and at higher excitation energies (on the order of a magnitude higher), an additional kinetics of hundreds of ps, also related to the heating/cooling process, was observed.
Transmembrane Signaling Mediated by Water in Bovine Rhodopsin
Authors: Nishimura Shoko , Kandori Hideki , Maeda Akio
Published: January 2008

Abstract— Unhydrated air‐dried films of rhodopsin from bovine rod outer segment membranes do not produce its active state, metarhodopsin II. In order to reveal requirements for its formation, we studied changes in H‐bonding of water, peptide carbonyl and carboxylic acid in the photochemical reactions by means of difference Fourier transform infrared spectroscopy, under both hydrated and unhydrated conditions. A water molecule near Glull3, which undergoes H‐bonding change in bathorhodopsin, remained in the unhydrated film, but with a weaker H‐bonding state than in the hydrated film. The other water molecules, which shift in lumirhodopsin and metarhodopsin I as well as in bathorhodopsin of the hydrated film, were not observed in the unhydrated film. Effects of the dehydration were detected in all the C=O stretching vibrations of the peptide backbone and of Asp83 in the formation of bathorhodopsin. The C=O stretching band of Asp83 of lumirhodopsin and metarhodopsin I is intensified in the unhydrated film. We propose that structural changes at the intradiscal site in the interaction between the Schiff base and Glull3 affect water molecules, the peptide backbone, Asp83 and Glul22 in helices B and C through consecutive photochemical processes to metarhodopsin II.
Photophysical Study of Pyridoxal 5′‐Phosphate and Its Schiff Base with n‐Hexylamine
Authors: Echevarria Gerardo R. , Catalán Javier , Bianco Francisco Garcia
Published: January 2008

Abstract— Phosphopyridoxal enzymes exhibit a wide variety of reactions. The activation mechanism proceeds with the formation of Schiff bases that undergo loss or transfer of one or more protons. Changes in the fluorescent properties of the pyridoxal 5′‐phosphate and its Schiff base may signal changes in the protonation state and/or in the microenvironment of the cofactor. In this paper the average fluorescence lifetime of pyridoxal 5′‐phosphate (PLP) as a function of pH was studied in a medium of 0.1 M ionic strength at 25°C. The ionic species of PLP with an unprotonated hydrogen atom were found to exhibit fluorescence lifetimes in the region of 100 ps on excitation at λ= 390 nm. The average fluorescence lifetimes for PLP in its Schiff bases with n‐hexylamine in media of low polarity are reported.
New Entrance Optics for Solar Spectral UV Measurements
Authors: Bernhard Germar , Seckmeyer Gunther
Published: January 2008

The investigation of the impact of solar UV radiation on the biosphere requires spectral measurements of solar UV radiation of high accuracy. However, the accuracy of current measurements is limited, and this can partly be attributed to the entrance optics of the instruments used for these examinations. The angular response of spectro‐radiometers measuring spectral global UV irradiance should be given by the cosine of the incidence angle. In‐tercomparison campaigns have shown that deviations from this ideal cosine response lead to uncertainties in solar measurements of more than 10%. Here we present recently developed entrance optics that reduce these uncertainties to ±4% in the UV. The new entrance optics have been characterized with respect to their angular response, transmission, weather durability, fluorescence and dependence of the angular response on wavelength and polarization. Solar spectroradiometric measurements carried out with the new optics were compared with simultaneously performed measurements of a second spectroradiometer that was equipped with a conventional diffuser. The deviations of up to 12% between both systems are quantitatively explained to within 3%.
Quinolone Antibiotic Photodynamic Production of 8‐Oxo‐7,8‐dihydro‐2‘‐deoxyguanosine in Cultured Liver Epithelial Cells
Authors: Rosen J. E. , Prahalad A. K. , Schluter G. , Chen D. , Williams G. M.
Published: January 2008

To study the basis for the phototoxicity of quinolones, a class of synthetic antibacterials, the photodynamic ability to mediate 8‐oxo‐7,8‐dihydro‐2′‐deoxyguanosine (8‐oxo‐dG) formation in cultured cells was measured for lome‐floxacin (LMX), which is strongly associated with clinical phototoxicity in humans, and ciprofloxacin (CFX), which has few reports of phototoxicity. Adult rat liver (ARL‐18) cells were exposed to the quinolones in the presence of UVA and DNA was extracted and analyzed by HPLC with electrochemical detection. Low levels of 8‐oxo‐dG were found in the DNA of nonirradiated ARL‐18 cells and this was increased up to 6‐fold in the presence of either LMX (50–400 uAf) or up to 3.6‐fold in the presence of CFX (50–400 µM) and UVA (20 J/cm2) when compared to the UVA control. Comparing separate experiments with LMX and CFX, LMX produced greater levels of 8‐oxo‐dG either after dark exposure or after UVA exposure at 20 J/cm2. Also, LMX and CFX were both shown to photodegrade in the presence of UVA, and it was determined that UVA photoinstability alone does not reflect phototoxic potential. These data suggest that the photodynamic potential of LMX and CFX to produce 8‐oxo‐dG may relate to their human clinical phototoxicity profile. We suggest that the observed clinical phototoxicity is mediated through a UVA photodynamic effect on the quinolone to form reactive oxygen species in the presence of molecular oxygen. The findings indicate that 8‐oxo‐dG formation can serve as a marker for the potential phototoxicity of new quinolones.
Charge Movements in the 13‐c/s Photocycles of the Bacteriorhodopsin Mutants R82K and R82Q*
Authors: Misra Saurav , Ebreyf Thomas G. , Crouch Rosalie K. , Menick Donald R.
Published: January 2008

We have examined light‐induced currents in oriented membranes of the bacteriorhodopsin mutants R82K and R82Q. Our results suggest that two photocurrent components found in R82K, with 30 and 300 us lifetimes, are due to the photocycle of the 13‐cis rather than the all‐trans form of the pigment. We investigated the pH dependence of these components and their correspondence to absorbance changes at 660 nm characteristic of pho‐tointermediates of the 13‐cis cycle. The presence of a D2O effect suggests that the charge motions producing these photocurrents are related to proton or protonated amino acid movement within the molecule. The current amplitudes depend on the protonation states of at least two residues, D85 and (probably) E204. In R82Q, a 10 pis photocurrent is observed that also depends on the protonation state of D85 and is similar to the 30 us current in R82K. We attempt to explain these currents in terms of a model for interacting residues in the extracellular half of the bacteriorhodopsin channel.
Diamino Acid Derivatives of Porphyrins Penetrate into Yeast Cells, Induce Photodamage, but Have No Mutagenic Effect
Authors: Zofadek Teresa , Nhi Nguyen Bich , Jagietto Izabella , Graczyk Alfreda , Rytka Joanna
Published: January 2008

The yeast Saccharomyces cerevisiae was used as a model eukaryotic organism to study the uptake of diamino acid derivatives of porphyrins and their phototoxicity with particular emphasis on possible mutagenic effects. The water‐soluble hematoporphyrin derivatives diarginate (HpD[Arg]2) and 1‐arginin di(N‐amino acid)‐protoporphyrinate used in this study are effective photosensitizers in tumor photodynamic therapy. Depending on the amino acid substituent, the porphyrin derivatives differ in their affinity for yeast cells. It is shown that HpD(Arg)2 and PP(Met)2 (Arg)2 penetrate into the yeast cell and are metabolized. Both compounds sensitize yeast cells to photodamage but have no mutagenic effect on nuclear or mitochondrial genomes.
Sun Exposure, Sunscreen and Their Effects on Epidermal Langerhans Cells
Authors: Neale Rachel , Russell Anne , Muller H. Konrad , Green Adele
Published: January 2008

This study examined the effects of chronic and current sun exposure on the number of Langerhans cells in epidermal sheets of UV‐exposed and unexposed skin of the arms and assessed the effect of sunscreens. Participants were enrolled in a skin cancer prevention trial and had been using sunscreen daily for the previous 3 years. There were significantly fewer Langerhans cells on the exposed (463 cells/mm2) than on the unexposed forearm (528 cells/mm2) (P = 0.0001). High sun exposure in the previous 2 weeks and a history of predominantly outdoor occupations were both associated with a reduced number of Langerhans cells, although age and other biological indicators of chronic exposure were not associated. Sunscreen use was protective against the effects of current but not chronic sun exposure, with a suggestion of a greater effect at higher levels of exposure. Unexpectedly, people with a past history of nonmelanoma skin cancer had more Langerhans cells in both the exposed and the unexposed skin. These results emphasize the need for continued public health education to protect the immune system from the damaging effects of UV radiation.