摘要:

It has been suggested that ultraviolet light induces free radical formation in skin, leading to photoaging and cancer. We have demonstrated by electron paramagnetic resonance that the ascorbate free radical is naturally present in unexposed skin at a very low steady state level. When a section of SKH‐1 hairless mouse skin in an EPR cavity is exposed to UV light (4,500 J m−2−1, Xe lamp, 305 nm cutoff and IR filters), the ascorbate free radical signal intensity increases. These results indicate that UV light increases free radical oxidative stress, consistent with ascorbate's role as the terminal, small‐molecule antioxidant. The initial radicals produced by UV light would have very short lifetimes at room temperature; thus, we have applied EPR spin trapping techniques to detect these radicals. Using α‐[4‐pyridyl 1‐oxide]‐N‐tert‐butyl nitrone (POBN), we have for the first time spin trapped a UV light‐produced carbon‐centered free radical from intact skin. The EPR spectra exhibited hyperfine splittings that are characteristic of POBN/alkyl radicals, aN= 15.56 G and aH= 2.70 G, possibly generated from membrane lipids as a result of β‐scission of lipid alkoxyl radicals. Iron can act as a catalyst for free radical oxidative reactions; chronic exposure of skin to UV radiation causes increased iron deposition. Using our spin trapping system, we have shown that topical application of the iron‐chelator, Desferal, to a section of skin reduces the UV light‐induced POBN adduct radical signal. These results provide direct evidence for free radical generation and a role for iron in UV light‐induced dermatopathology. We suggest that iron chelators can serve as photoprotective agen

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb04993.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

The photochemistry of 5,5‐dimethyl‐l‐pyrrolineN‐oxide (DMPO) has been studied in benzene, cyclohexane and aqueous buffer solutions (pH 7.4) by means of electron paramagnetic resonance (EPR) and the spin trapping technique. Ultraviolet irradiation of DMPO in aqueous buffer with unfiltered UV radiation from a Xe arc lamp results in photoionization of the spin trap and the generation of the DMPO cation radical, DMPO+. The aqueous electron, eaq−, was trapped by DMPO and detected as the DMPO/H adduct. The DMPO+‐ reacted with the water to yield the DMPO/OH adduct. Ultraviolet irradiation of DMPO in nitrogen‐saturated benzene gave an unidentified carbon‐centered DMPO adduct that was replaced by hydroperoxyl and alkoxyl adducts of DMPO when oxygen was present. Experiments employing17O2gas indicated that the oxygen in the DMPO alkoxyl adduct was derived from molecular oxygen. However, UV irradiation of DMPO in cyclohexane yielded the cyclohexyl and cyclohexyloxyl adducts of DMPO in nitrogen‐saturated and air‐saturated solutions, respectively. These observations suggest that in aprotic solvents UV irradiation of DMPO generates a carbon‐centered radical (R−), derived from the trap itself, which in benzene reacts with oxygen to yield an alkoxyl radical (RO−), possiblyviaa peroxyl radical (ROO−) intermediate. In cyclohexane R−abstracts a hydrogen atom from the solvent to yield the cyclohexyl radical in the absence of oxygen and the cyclohexyloxyl radical in the presence of oxygen. These findings indicate that when DMPO is used as a spin trap in studies employing short‐wavelength UV radiation (λ<300 nm) the photoche

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb04994.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Using monochromatic laser excitation, narrowing of the porphyrins 0‐0 fluorescence line in rat muscle tissue to a width of 50‐70 cm−lat 4.2 K is observed. Fluorescence spectra at different excitation wavelengths and excitation spectra are measured. Fluorescence line peak follows the shift of the excitation frequency. Several of the most prominent vibrational frequencies of porphyrins in the excited electronic state are deter

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb04995.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractWe report measurements of the site‐to‐site diffusion coefficients in proteins and model compounds, which were measured using time‐dependent energy transfer and frequency‐domain fluorometry. The possibility of measuring these diffusion coefficients were shown from simulations, which demonstrate that donor (D)‐to‐acceptor (A) diffusion alters the donor frequency response, and that this effect is observable in the presence of a distribution of donor‐to‐acceptor distances. For decay times typical of tryptophan fluorescence, the simulations indicate that D‐A diffusion coefficients can be measured ranging from−7to−5cm2/s. This possibility was verified by studies of a methylenechain linked D‐A pair in solutions of varying viscosity. The D‐A diffusion was also measured for two labeled peptides and two proteins, melittin and troponin I. In most cases we used global analysis of data sets obtained with varying amounts of collisional quenchers to vary the donor decay time. Unfolding of troponin I results in more rapid D‐A diffusion, whereas for melittin more rapid diffusion was observed in the α‐helical state but ove

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb04996.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractFluorescence quenching of pyrene derivatives by 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy (TEMPO), 4‐oxo‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy and 4‐hydroxy‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy has been measured in homogeneous solvents and microheterogeneous systems: cetyltrimethylammonium chloride micelles, large unilamellar vesicles of dioctadecyldimethylammonium chloride and dipalmitoylphosphatidylcholine (DPPC) and rat liver microsomes. The extent of intraaggregate quenching is mostly determined by the quencher incorporation to the micro‐phases. In particular, it is observed that quenching by TEMPO in vesicles is considerably faster when the bilayer is in the liquid crystalline state. This significant increase in quenching rate with the melting of the bilayer is not observed for the other TEMPO derivatives, indicating that the effect of the lipid organization upon the solubility is related to the hydrophobicity of the solute. The data obtained in rat liver microsomes at 37°C show a pattern very similar to that observed in DPPC vesicles in

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb04997.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractThe photochemistry of the photosensitizing nonsteroidal antiinflammatory drugs tiaprofenic acid and suprofen involves the intermediacy of short‐lived species (i.e.radicals). The data obtained in the present work strongly suggest that such intermediates may be responsible for the phototoxicity of 2‐arylpropionic acids by inducing photodynamic lipid peroxidation at drug concentrations likely to be reached in the skin. This has been investigated using linoleic acid as a model lipid and determining the amount of hydroperoxides by measuring the spectrophotometric absorption at 233 nm, associated with the formation of dienic hydroperoxides. The major photoproducts of tiaprofenic acid and suprofen are derivatives bearing an ethyl side chain. Photoproducts of this type, due to the lack of polar moieties, are highly lipophilic and likely to accumulate in the lipid bilayer of cell membranes. Taking into account their ability to induce photodynamic lipid peroxidation and their marked photostability, it is conceivable that such photoproducts can participate in many catalytic cycles, playing a significant role in the mechanism of photosensitizatinn by tiprofenic acid and supro

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb04998.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractPhotosensitization of lysozyme, liposomes, ghosts and intact red blood cells (RBC) was investigated for aqueous hypericin. The effects of azide ion, 1,4‐diazabicyclo(2.2.2)octane, and superoxide dismutase on photosensitized inactivation of lysozyme in 0.5% Triton X‐100 indicate that singlet oxygen is the major inactivating intermediate with a contribution from superoxide. The singlet oxygen quantum yield (ΦΔ) scaled to methylene blue is 0.49 ± 0.06 at monochromatic wavelengths from 514 to 600 nm. Relative values of ΦΔbased on lysozyme inactivation for different vehicles are: 0.5% Triton X‐100 (1.13), human serum albumin (0.65), Cremophor‐EL(0.76), Cremophor‐RH40 (0.98), egg phosphatidylcholine (EPC) liposomes (0.04), hydrogenated soy phosphatidylcholine (HSPC) liposomes (<0.01). Hypericin photosensitized lipid peroxidation of EPC liposomes and RBC ghosts. Extensive cross‐linking of ghost membrane proteins occurred during the initial stages of lipid peroxidation. Prompt photohemolysis was used as the assay of RBC membrane damage. The photohemolysis curves are modeled with multihit target theory based on the “hit number” (n) and the target cross section (v). The values of v and the conventional “1/t50” parameter are equivalent determinants of the photohemolysis rate. The photohemolysis curves are in good agreement with n = 15 for incubation in phosphate‐buffered saline at different hypericin concentrations and with additives. The measurements for other vehicles led to n = 19 for Cremophor‐EL and n = 3 for EPC and HSPC liposomes, indicating that the kinetics of photohemolysis depend on

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb04999.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractExposure of cultured MRC5 human fibroblasts or NCTC 2544 human keratinocytes to mild doses of ultraviolet A (UVA: 320‐400 nm) radiations markedly decreased the actin reactivity with fluorescein‐labeled phalloidin. This indicates a change in the degree of poly merization of actin and thus in the organization of actin filaments. Such a phenomenon might be involved in the previously reported UVA‐induced inhibition of specific and nonspecific endocytotic proc

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05000.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractSkin tumor promotion by phorbol ester is believed to be mediated by the phospholipid‐dependent ser/ thr kinase, protein kinase C (PKC). Long‐wave ultraviolet radiation (320‐400 nm, UVA), which has also been shown to promote skin tumors, induces elevated levels of PKC in murine fibroblasts, suggesting that UVA may promote the development of basal and squamous cell skin cancers by a mechanism involving PKC. To examine UVA effects on PKC in a model relevant to skin, we maintained normal human epidermal keratinocytes (NHEK) in serum‐free medium and exposed the cultured cells to various doses of UVA or to the phorbol ester, 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA). Fifty minutes after exposure to UVA (5‐20 J/cm2), PKC activity was elevated up to three‐fold in NHEK cytosolic fractions, and membrane‐associated PKC activity was elevated up to two‐fold by UVA. The TPA treatment induced a 10‐fold increase in membrane‐associate PKC activity only. Immunoblot analysis suggested that a UVA‐induced increase in PKC protein occurred. Both UVA and TPA reduced the cell number by 50‐75% in the first 24‐48 h; however, irradiated cultures began to recover at 72 h post‐UVA due to an increased proliferative rate beginning after 48 h. Treatment with TPA induced a high level of differentiation as measured by cornified envelope formation. Ultraviolet A irradiation exposure was not followed by increased differentiation. These findings suggest that acute UVA exposure elevates PKC activity in human keratinocytes and may act through PKC to promote actinic skin cancer. The molecular mechanism is like to differ from

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05001.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

AbstractBis(di‐isobutyl octadecylsiloxy)silicon 2,3‐naphthalocyanine (isoBOSINC) is a representative of a group of naphthalocyanine derivatives with spectral and photophysical properties that make them attractive candidates for photodynamic therapy (PDT). Tissue distributions were studied in normal and in tumor‐bearing rats as a function of time following intravenous injection ofisoBOSINC as a suspension in 10% Tween 80 in saline. The dose studied was 0.25 mg/kg of body weight. The compoundisoBOSINC was isolated from several tissues and organs, as well as tumors and peritumoral muscles and skin, and quantitated by a high‐performance liquid chromatographic technique. The tumor model, anN‐(4‐[5‐nitro‐2‐furyl)‐2‐thiazolyl)formamide (FANFT)‐induced urothelial cell carcinoma, was transplanted into the hind legs of Fischer 344 rats. The dye was retained in tumors at higher concentrations than in all tissues and organs examined, except for spleen and liver. The highest concentration ratio of dye in tumorversusperitumoral muscle (24.5) occurred 9 h after injection. Serum clearance ofisoBOSINC showed similar kinetic behavior for both groups of rats, with a t1/2of elimination of ∼ 10 h. At 7 and 14 days postinjection, the levels of dye found in testes were generally higher than in most other tissues, except spleen and liver. Concentrations ofisoBOSINC were either very low or not detectable in rat brain. Trace amounts of the dye were excreted in the urine, and by day 14 approximately 17% of the dose was accounted for in the feces. The significant levels of the drug in tumors, as well as the excellent ratios of tumor‐to‐muscle concentration observed, have promising i

ISSN:0031-8655    

DOI:10.1111/j.1751-1097.1994.tb05002.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY