摘要:

Abstract—Singlet oxygen (1O2) can react with cholesterol (Ch) to give three possible ene‐addition hydroperoxides: 3β‐hydroxy‐5α‐cholest‐6‐ene‐5‐hydroperoxide (5α‐OOH), 3β‐hydroxycholest‐4‐ene‐6α‐hydroperoxide (6α‐OOH), and 3β‐hydroxycholest‐4‐ene‐6β‐hydroperoxide (6β‐OOH). The rates of dye‐sensitized photogeneration and also the fates of 5α‐OOH and 6β‐OOH in membrane bilayers have been studied and compared. Irradiation of unilamellar [14C]Ch/phospholipid vesicles in the presence of aluminum phthalocyanine tetrasulfonate or merocyanine 540 resulted in formation of 5α‐OOH and 6β‐OOH, as determined by high performance liquid chromatography with radiochemical or electrochemical detection. The initial rate of 6β‐OOH formation was 335% that of 5α‐OOH in a variety of liposomal systems. However, after a lag, 5α‐OOH invariably decayedviaallylic rearrangement to 7α‐OOH (also known to be a free radical product), whereas 6β‐OOH accumulated in unabated fashion until Ch depletion became limiting. Photooxidation of Ch in an isolated natural membrane (erythrocyte ghost) or in L1210 leukemia cells gave similar results. When the reaction was carried out in pyridine or methanol, the rate of 6β‐OOH formation relative to 5α‐OOH was reduced by approximately half, with essentially no isomerization of the latter to 7α‐OOH. These results suggest that (i) environmental factors in a lipid bilayer somehow make photogeneration of 6β‐OOH more favorable than in homogeneous solution; and (ii) due

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb09594.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The feasibility of using direct iodide (I‐) measurements to monitor the photochemistry of the halogenated pyrimidines 5‐iodocytosine and 5‐iodouracil and their corresponding deoxynucleosides was examined. Radiation from either a germicidal lamp (Λ=254 nm) or a sunlamp (Λ>290 nm) was employed to induce homolytic splitting of the carbon‐iodine bond and the release of iodine atoms. These atoms combine to form I2which reacts with water to ultimately form I‐and iodate (10‐3). The formation of I‐was followed using either high performance liquid chromatography with electrochemical detection or a specific ion electrode. 10‐3was assayed spectroscopically following its conversion to triiodide. The yields of I‐relative to starting material destroyed were either close to the theoretical limit of 83% or higher depending upon (a) the compound being irradiated, (b) the irradiation wavelength and (c) the extent of exposure. Yields of iodide>83% are generally accounted for by a concomitant reduction in the yield of iodate such that the sum I‐+ 10‐3is approx. 100%. Because iodate is photochemically reduced to iodide by 254 nm but not sunlamp irradiation, exhaustive irradiation at 254 nm converts all of the iodate present to iodide. These studies have application to the use of photochemical methods for quantitating the percent substitution of iodinated pyrimidines in DNA, and should be useful in following the photochemistry of IdUrd

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb09595.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The proposed photoprotective role of the UV‐A absorbing, extracellular pigment scytonemin was studied in the terrestrial cyanobacteriumChlorogloeopsissp. strain O‐89‐Cgs(1). UV‐A (315–400 nm) caused growth delay, cell growth restarting only when scytonemin had accumulated in the extracellular envelopes. Cultures with scytonemin were more resistant to photoinhibition of photosynthesis than cultures without scytonemin, the differential resistance being much greater to UV‐A‐caused photoinhibition than to photoinhibition caused by visible light. The presence of scytonemin in the extracellular envelopes was correlated with the inability of UV‐A radiation to induce strong photopigment fluorescence (685 nm emission), regardless of the specific content os photosynthetic pigments. The physical removal of the scytonemin containing extracellular envelopes brought about the loss of UV‐A resistance as measured by photobleaching rates of chlorophyllaunder conditions of physiological inactivity (desiccation). These observations provide strong evidence for the proposed protective role of scytonemin, as a passive UV‐A sunscr

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb09596.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Systemic effects of UVB irradiation (280–320 nm) have been shown to prevent subsequent chemical tumorigenesis induced by an initiation—promotion protocol. The present investigation was designed to determine whether initiation or promotion is prevented by UV irradiation. Groups of 25 B6DZF1/J mice received 12 weeks of intermittent dorsal UVB radiation treatments administered before, or 3 weeks after, initiation with a single application of 7,12‐dimethylbenz[a]anthracene on the ventral skin. All mice were promoted ventrally with 5 μg 12–0‐tetradecanoylphorbol‐13‐acetate (TPA) applied three times weekly throughout the experiment. UV irradiation consisted of five 30‐min exposures per week to a bank of 6 Westinghouse FS40 sunlamps. UV irradiation applied before or after initiation resulted in a decrease of 18—‐16 tumors per group of 25 mice, for a reduction of 61 and 50%, respectively, at 24 weeks after the first TPA treatment. Thus, prevention of tumor development was similar whether the UV influence was present or not during initiation. This finding suggests that the UV prevention of promotion could account for UV inhibition of skin tumors induced by an initiation—promotion regimen. Consistent with this concept, pretreatment of mice with dorsal UVB radiation was found to reduce DNA synthesis after exposure to TPA by 46%, although it did not decrease tritiated benzo[a]pyrene binding to DNA, in ventral epidermis. Thus, UVB irradiation systemically reduced TPA‐induced tumo

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb09597.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The effect of pretreatment with vitamin E on cytotoxicity, DNA single strand breaks, and chromosomal aberrations as well as on mutation induced by ultraviolet‐B light (UV‐B) was investigated in Chinese hamster V‐79 cells. Cellular pretreatment with non‐toxic levels of 25μMα‐tocopherol succinate (vitamin E) for 24 h prior to exposure resulted in a 10‐fold increase in cellular levels of α‐tocopherol. Using a colony‐forming assay, this pretreatment decreased the cytotoxicity of UV‐B light. However, alkaline elution assays demonstrated that pretreatment with vitamin E did not affect the number of DNA single strand breaks caused by UV‐B light. In addition, UV‐B exposure produced a dose‐dependent induction of chromosomal aberrations and mutations at the HGPRT locus, and neither of these actions of UV‐B was influenced by pretreatment with the vitamin. These results suggest that vitamin E protects cells from UV‐B‐induced cytotoxicity, possibly through its ability to scavenge free radicals. The results also suggest that the extent of genotoxicity induced by UV‐B light may not correlate directly with the cytotoxic action o

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb09598.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Stratospheric ozone depletion may result in increased solar UV‐B radiation to the ocean's upper layers and may cause deleterious effects on marine organisms. The primary UV‐B damage induced in biological systems is to DNA. While physical measurements of solar UV‐B penetration into the sea have been made, the effective depth and magnitude of actual DNA damage have not been determined. In the experiments reported here, UV‐B‐induced photoproducts (cyclobutane pyrimidine dimers) have been quantified in DNA molecules exposed to solar UV at the surface and at various depths in clear, tropical marine waters off Lee Stocking Island (23° 45‘ N, 76° 0.7’ W), Exuma Cays, Bahamas. [14C]thymidine‐labeled DNA or unlabeled bacteriophage øX174 DNA was placed in specially designed quartz tubes at various depths for up to five days. Following exposure, DNA samples were removed to the laboratory where UV‐B‐induced pyrimidine dimers were quantified using a radiochromatographic assay, and bacteriophage DNA inactivation by solar UV‐B was assayed by plaque formation in spheroplasts ofEscherichia coli. Pyrimidine dimer induction was linear with time but the accumulation of dimers in DNA with time varied greatly with depth. Attenuation of dimer formation with depth of water was exponential. DNA at 3 m depth had only 17% of the pyrimidine dimers found at the surface. Bacteriophage øX174 DNA, while reduced 96% in plaque‐forming ability by a one day exposure to solar UV at the surface of the water, showed no effect on plaque formation after a similar exposure at 3 m. The data collected at the water's surface showed a “surface‐enhanced dose” in that DNA damages at the real surface were greater than at the imaginary surface, which was obtained by extrapolating the data at depth to the surface. These results show the sensitivity of both the biochemical (dimers) and biological (phage plaques) DNA dosimeters. DNA dosimeters offer a sensitive, convenient and relatively inexpensive monitoring system, having both biochemical and biological endpoints for monitoring the biologically effective UV‐B flux in the marine environment. Unlike physical dosimeters, DNA dosimeters do not have to be adjusted for biological effectiveness since they are sensitive only to DNA‐mediated biologically effective UV‐B radiation. Results of pyrimidine dimer induction in DNA by solar UV accur

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb09599.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—Photodynamic therapy (PDT) of cancer combines irradiation of tumors with visible light following selective uptake of the photosensitizer by the tumor cells. PhotofrinR‐II (Pf‐II) is the only photosensitizer which is in clinical use in PDT, whereas chloroaluminum phthalocyanine tetrasulfonate (AIPcTS) has also shown promise in preclinical studies. In most such studies, the effectiveness of the photosensitizers has been assessed in implanted tumor model systems rather than in model systems where tumors are allowed to grow in their own connective tissue matrix. In this study the pharmacoki‐netics, tumor ablation capability and cutaneous photosensitization response of AlPcTS have been assessed in mice bearing chemically‐ and ultraviolet B radiation (UVB)‐induced benign skin papillomas. When tumor‐bearing animals were injected intraperitoneally with AlPcTS (5 mg/kg body wt), maximum tumor:normal skin ratio of 2.4 was observed at 48 h, at which time the mice were irradiated within the absorption spectrum of the photosensitizer. In tumor ablation studies with SENCAR mice bearing chemically‐induced skin tumors, AlPcTS resulted in greater than 80% ablation in tumor volume at 20 days post‐irradiation. In cutaneous photosensitization response, AlPcTS produced only transient effects (no effect after 24 h) in SENCAR mice. Pharmacokinetics data, tumor ablation effects and cutaneous photosensitization response of AlPcTS were comparable in SKH‐1 hairless mice bearing UVB‐induced skin tumors. Our data indicate that AlPcTS produces significant photodynamic effects towards the ablation of murine skin tumors, and that it does not produce prolonged cutan

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb09600.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The localization of many photosensitizing agents has been attributed to distribution of low density lipoprotein (LDL)‐bound drug as a function of the relative numbers of LDL receptors in different tissues. While the chlorin derivative NPe6 is a potent photosensitizing agent in the mouse, it binds mainly to mouse plasma high density lipoproteins (HDL) and albumin, with only 1% bound to LDL. This pattern suggests only a minor role for the LDL‐receptor pathway with regard toN‐aspartyl chlorin e6 (NPe6) biodistribution. Moreover, patterns of accumulation of radioactive NPe6, LDL and HDL in murine tissues are consistent with the suggestion that distribution of NPe6 to different tissues cannot be explained on the basis of an LDL‐mediated

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb09601.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—In order to assign the structural changes of the protein, observed in the Fourier transform infrared (IT‐IR) difference spectra of the rhodopsin‐metarhodopsin‐II transition, to specific regions of the protein, rhodopsin was treated by proteases. Nonilluminated and bleached rhodopsin was treated with protease K and papain. Rhodopsin digested in the bleached state was subsequently regenerated with 11 ‐cis‐retinal. From these modified samples the rhodopsin‐metarhodopsin‐II FT‐IR difference spectra were measured. Comparing the difference spectra with that of unmodified rhodopsin, clear deviations in the amide‐I and amide‐II spectral range are observed. This indicates that in the unmodified pigment conformational changes of those parts of the cytosolic surface take place which are susceptible to the proteases. From the larger spectral changes obtained with samples digested in the bleached state it is concluded that the extent of modification is larger. The difference spectra of rhodopsin modified with 10 mM dithiothreitol support the existence of the 4th loop which also undergoes conformational changes. The spectral changes are interpreted in terms of a transition of an ordered structure of the loops in rhodopsin to a more random structure in metarhodopsin‐II. The results demonstrate that by combining FT‐IR spectroscopy with protein modification by specific proteases, conformational changes of the protein can be loca

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb09602.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract—The possible involvement of Fe‐S clusters in photodynamic reactions as endogenous sensitizing chromophores in cells has been investigated, by using an artificial non‐heme iron protein (ANHIP) derived from bovine serum albumin and ferredoxins isolated from spinach and a red marine algae. Ferredoxins and ANHIP, when exposed to visible light, generate singlet oxygen, as measured by the imidazole plus RNO method. Irradiation with intense blue light of the ANHIP‐entrapped liposomes caused severe membrane‐damage such as liposomal lysis and lipid peroxidation. In the presence of ANHIP, isocitrate dehydrogenase and fructose‐l, 6‐diphosphatase were photoinactivated by blue light. However, all of these photosensitized reactions were significantly suppressed by a singlet oxygen (1O2) quencher, azide, but enhanced by a medium containing deuterium oxide. Further, the Fe‐S proteins with the prosthetic groups destroyed did not initiate the blue light‐induced reactions. In addition, the action spectrum for1O2generation from ANHIP was very similar to the visible absorption spectrum of Fe‐S centers. The results obtained in this investigation appear consistent with the suggestion that Fe‐S centers are involved in photosensitization in cellsviaa sin

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1992.tb09603.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY