摘要:

Abstract—Porphyrins used as sensitizers for the photodynamic therapy (PDT) of tumors are progressively destroyed (photobleached) during illumination. If the porphyrin bleaches too rapidly, tumor destruction will not be complete. However, with appropriate sensitizer dosages and bleaching rates, irreversible photodynamic injury to the normal tissues surrounding the tumor, which retain less sensitizer, may be significantly decreased. This paper surveys the quantum yields and kinetics of the photobleaching of four porphyrins: hematoporphyrin (HP), Photofrin II (PF II), tetra(4‐sulfonatophenyOporphine (TSPP) and uroporphyrin I (URO). The initial quantum yields of photobleaching, as measured in pH 7.4 phosphate buffer in air, were: 4.7 × 10‐5, 5.4 × 10‐5, 9.8 × 10‐5, and 2.8 × 10‐5for HP, PF II, TSPP and URO respectively; thus, the rates of photobleaching are rather slow. Low oxygen concentration (2 μM) significantly reduced the photobleaching yields. However, D2O increased the yields only slightly, and the singlet oxygen quencher, azide, had no effect, even at 0.1M.Photosensitizing porphyrins in body fluids, cells and tissues may be closely associated with various photooxidizable molecules and electron acceptors and donors. Therefore, selected model compounds in these categories were examined for their effects on porphyrin photobleaching. A number inhibited and/or accelerated photobleaching, depending on the compound, the porphyrin and the reaction conditions. For example, 1.0 mMfurfuryl alcohol increased the photobleaching yields of HP and URO more than 5‐fold, with little effect on PF II or TSPP. In contrast, the electron acceptor, methyl viologen, increased the photobleaching yield of TSPP more than 10‐fold, with little accelerating effect on the other porphyrins. These results suggest that the mechanism(s) of the photobleaching of porphyrin photosensitizers in cells and tissues durin

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08527.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The photodynamic properties of the di‐and tetrasulfonated zinc and aluminium phthalocyanines and a tetrasulfonated aluminium napththalocyanine were studied using 2′‐deoxyguanosine as a DNA model compound. The major photooxidation products of this nucleoside were identified and classified according to their formation through a radical mechanism (type I) or a singlet oxygen mediated mechanism (type II). The major type I product was obtained and identified as 2,2‐diamino [(2‐deoxy‐β‐d‐erythropentofuranosyl)‐4‐amino]‐5(2H)‐oxazolone. Two major type II products were characterized as the 4R* and 4S* diastereomers of 9‐(2‐deoxy‐β‐d‐erythropentofuranosyl)‐7,8‐dihydro‐4‐hydroxy‐8‐oxoguanine. In addition a third product, also resulting from a type II photooxidation, was identified as 8‐oxo‐7,8‐dihydro‐2′‐deoxyguanosine. Quantification of these products provided a means to estimate the contribution of type I and type II pathways during the phthalocyanine and naphthalocyanine mediated photooxidation of 2′‐deoxyguanosin

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08528.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—We report here the resonance Raman studies of photooxidation of free base tetraphenylporphin (H2TPP) in the presence of external electron acceptors such as CCl4and chloranil under selective laser irradiation. From the dependence of photooxidation on the concentration of electron acceptors, polarity of solvents, excitation lines and temperatures, we have inferred that a weak triplet exciplex formed between the excited H2TPP and electron acceptor in non‐polar solvents serves as transient species and the light‐induced intermolecular charge transfer from H2TPP to the electron acceptor is the primary process involved in photooxidation. Observation of partial photooxidation in the rigid matrix at low temperatures has been interpreted to be due to long‐range quantum mechanical electron tunneling process. Almost complete photooxidation is observed in a soft matrix as the donor and acceptor molecules can attain favorable relative orientation and separation for electron transfer during the excited state lifetime of the e

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08529.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The nucleobase 5‐methylcytosine (I) is a minor component of eukaryotic DNA thought to be important in regulation of gene expression. The photochemical reactions of this nucleobase and its 2′‐deoxyribonucleoside, 5‐methyl‐2′‐deoxycytidine (II), in water have been studied. These reactions lead, respectively, to 3‐amino‐2‐methylacrylamidine (Ib) and 3‐(2‐erythro‐d‐pentopyranos‐1‐yl) amino‐2‐methylacrylamidine (IIb) as the main photoproducts. The structure of the photoproducts was established by spectroscopic methods (1H and13C NMR, UV spectroscopy, electron impact and liquid secondary ion mass spectrometry); in the case ofIb, confirmatory evidence was obtained by chemical methods (photolysis of 5‐methyl[2–13C]cytosine, hydrolysis ofN‐carbomethoxy‐3‐amino‐2‐methylacryl‐amidine and reaction ofIbwith 1,1′‐carbonyldiimidazole to giveI). The quantum yield for formation ofIbwas determined to be 1.8 × 10‐3at pH 7.5 while the quantum yield for formation ofIIbhas a lower value of 0.2 × 10‐3at pH 7.5. These quantum yields depend strongly on pH and reach maximum values of 2.0 × 10‐3at pH 7.0 (Ib) and 0.6 × 10‐3at pH 5.0 (IIb). The mechanism of formation ofIb(orIIb) is proposed to involve nucleophilic attack of water on the C‐2 position of photoexcitedI(orII), follow

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08530.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The photodynamic effect of hypericin on EMT6 mouse mammary carcinoma cells was investigatedin vitrounder aerobic and hypoxic conditions. Under aerobic conditions, hypericin‐induced photocytotoxicity was dose dependent within a 1–50 μMrange. Under hypoxic conditions, cells were resistant to hypericin‐induced phototoxicity. In the dark, no cytotoxicity was observed at any hypericin concentration tested either aerobically or hypoxically. Cellular accumulation of hypericin, examined by chemical extraction and spectroscopy, occurred under both hypoxic and aerobic conditions. Fluorescence photomicrographs of cells exposed to hypericin corroborate drug uptake in the plasma membrane and subcellular regions. Our results demonstrate that hypericin cytotoxicity to EMT6 mouse mammary carcinoma cellsin vitrois both light and oxygen‐dependent. These results suggest that EMT6 cell kill caused by photoactivated hypericin is mediated by an oxygen‐dependent mechanism, rather than by a type I oxygen‐indepen

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08531.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Cell membrane DNA (cmDNA) is a form of DNA located on the surface of human and murine T‐cells. It has recently been characterized as a target for photomodification by 8‐methoxypsoralen (8‐MOP) and long‐wave ultraviolet light (UV‐A). Whereas 8‐MOP itself is biologically inert, photoactivated 8‐MOP is covalently bound to pyrimidine bases in DNA. We have investigated the possible involvement of cmDN A photomodification in the induction of the suppression of skin allograft rejection in BALB/c mice preimmunized with 8‐MOP/UV‐A photodamaged alloreactive cells which mediates this allograft rejection. This suppression is demonstrated by inhibition of delayed‐type hypersensitivity (DTH) and mixed leukocyte culture (MLC) responses. Splenocytes from BALB/c mice undergoing rejection of CBA/j skin graft which contained an expanded population of the effector T lymphocytes that mediate the rejection were treated with DNAse to remove cmDNA before or after treatment with 8‐MOP and UV‐A prior to infusion into naive BALB/c recipients. Mice that received pretreated effector cells were tested for MLC responses to CBA/j or B10 alloantigens before and after the DTH response. The DTH response of all groups of pretreated BALB/c mice to the relevant alloantigen was specifically suppressed as compared with the response of control mice. However, adoptive transfer of the suppression of the DTH response was optimally demonstrable only in syngeneic recipients of cells from donor mice treated with photodamaged alloreactive cells. Also, splenocytes from BALB/c mice immunized with photodamaged alloreactive cells demonstrated highly significant hyporesponsiveness and suppression of the MLC response of naive mice to the relevant alloantigen in the case of the primary MLC response, and to both alloantigens in the secondary MLC response which was totally eliminated by prior pretreatment of these effector cells with DNAse. Therefore, it appears that the suppression of the DTH response can be induced by pretreatment of the effector cells with DNAse and/or 8‐MOP and UV‐A but is adoptively transferable optimally only from mice which are recipients of photodamaged alloreactive cells. Moreover, the effectiveness of this treatment is decreased by prior removal of cmDNA from these cells. The presence of cmDNA is necessary for induction of suppression of the primary and secondary MLC responses in mice treated with photodamaged

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08532.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Polymer films with immobilized photosensitive membrane protein, bacteriorhodopsin (BR), were prepared and investigated. A sensitive holographic interferometer with phase modulated optical beams was used for investigation of kinetics of dynamic hologram recording in BR polymer films. It was found that phase hologram formation consisted of two quasi‐exponential stages demonstrating existence of a diffusive process in obtained films. It was shown that the kinetics of a phase hologram recording by high intensity beams do not correlate with the exponential law. The applicability of BR polymer films as reversible photorefractive materials for dynamic holography and real‐time interferometry was disc

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08533.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Parameters of light propagation in plant leaves—absorption and scattering coefficients, asymmetry of scattering—have been estimated on the basis of measured transmission and remission as well as internal fluxes. This estimation has been carried through by solving the inverse problem of the 4‐flux radiative transfer—a theory considering forward and backward diffuse as well as directed components of the overall radiation in a multiply scattering sample. Using the gained parameters, light flux gradients in a two‐layered model leaf have been calculated at different wavelengths. Monte Carlo simulation of absorption spectra performed with the parameters obtained with this treatment is in a good agreement with experimental spectra, thus substantiating the theory. Parallel calculations with the two‐flux (Kubelka‐Munk) theory provide an estimation of the accuracy and applicability of this more simple treatment. Calculations have been performed for two d

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08534.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Exposure to artificial UV wavelengths and the UV component of sunlight delays positive phototaxis in the green algaVolvox aureus.Broad band wavelength filters were used to modify the output from UV‐B sources (280–320 nm) and natural sunlight. The delay in phototaxis by artificial UV is increased with exposure to shorter UV‐B wavelengths. Natural sunlight experiments were performed with exposure to full sunlight and to its UV component only. The UV component present in summer sunlight produced long periods of inhibition in phototaxis and even lethality, while exposure to the total spectrum of sunlight had no significant effects on movement or survival. The data indicate that although this species of alga is well equipped to deal with present levels of UV exposure, increases in the short UV‐B wavelengths in sunlight may force an alteration in patterns of phot

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08535.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The short‐term adaptation of intact leaves to an increase in light intensity was studied by an analysis of chlorophyll fluorescence and oxygen evolution monitored by photoacoustics. An increase in light intensity led to an oxygen “gush”. This “gush” was followed by a large (up to 120%) biphasic increase in the yield of oxygen evolution characterized by a fast phase (T = 0.5–2 min) and a slow phase (T = 4–20 min). The fast phase of the increase in oxygen yield was coupled to a decrease of fluorescence, whereas the slow phase was accompanied by a parallel fluorescence increase. A comparison of fluorescence parameters with oxygen yield indicates that the slow phase of the increase in oxygen yield was coupled to an increase in the antenna size of photosystem II. The slow phase was not inhibited by the uncoupler Nigericin but it was absent in chlorophyll‐b‐less barley mutants deñcient in the light harvesting chlorophylla/bprotein complex of photosystem II (LHC II). These experiments indicate that changes in the LHC II mediated energy distribution, which occur in the time‐range of several minutes, are involved in the adaptation to changing light intensities. Moreover, electrophoretic analysis of32P orthophosphate labeled leaf discs adapted to low and high light intensities suggests that the slow phase of the increase in oxygen evolution involves dephosphorylation of the 25 kDa polypeptide of LHC II, by a small extent of 12%. The trigger for the slow phase of the increase in oxygen yield does not involve the oxidation of the plastoquinone pool. It was found that in response to the increased light intensity, the plastoquinone pool became more reduced as judged by model calculations. Experiments with the uncoupler Nigericin suggest that the control of the slow phase of adaptation to increased light intensity was also not exerted by the pH gradient across the thylakoid membrane.The similarities between the adaptation to increased light intensity and the state II to state I transition suggest that both adaptation phenomena involve LHC II dephosphorylation possibly triggered by the

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb08536.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY