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Biomedical subjects

B Roeder

Publications and source records attributed to B Roeder.

15 recordsLinked to original sources
PubMed2006

Cyclodextrin/chlorophyll a complexes as supramolecular photosensitizers.

The interactions between chlorophyll a, and three cyclodextrins, hydroxypropyl-beta-cyclodextrin heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin and hydroxypropyl-gamma-cyclodextrin, were studied in aqueous solutions by means of absorption, emission and circular dichroism spectroscopy. Nanosecond laser flash photolysis and steady-state singlet oxygen generation experiments were performed to clarify the photoactivity of chlorophyll a in these systems. Moreover the photosensitizing activity of these complexes towards human leukemia T-lymphocytes (Jurkat cells) was tested and compared with that of the free sensitizer, chlorophyll a. The results obtained indicate that each cyclodextrin is able to carry the pigment in monomeric form inside of cells producing singlet oxygen.

Cell Survival↗
PubMed2004

Turnover of carbon isotopes in tail hair and breath CO2 of horses fed an isotopically varied diet.

Temporal stable isotope records derived from animal tissues are increasingly studied to determine dietary and climatic histories. Despite this, the turnover times governing rates of isotope equilibration in specific tissues following a dietary isotope change are poorly known. The dietary isotope changes recorded in the hair and blood bicarbonate of two adult horses in this study are found to be successfully described by a model having three exponential isotope pools. For horse tail hair, the carbon isotope response observed following a dietary change from a C3 to a C4 grass was consistent with a pool having a very fast turnover rate ( t1/2 approximately 0.5 days) that made up approximately 41% of the isotope signal, a pool with an intermediate turnover rate ( t1/2 approximately 4 days) that comprised approximately 15% of the isotope signal, and a pool with very slow turnover rate ( t1/2 approximately 140 days) that made up approximately 44% of the total isotope signal. The carbon isotope signature of horse blood bicarbonate, in contrast, had a different isotopic composition, with approximately 67% of the isotope signal coming from a fast turnover pool ( t1/2 0.2 days), approximately 17% from a pool with an intermediate turnover rate ( t1/2 approximately 3 days) and approximately 16% from a pool with a slow turnover rate ( t1/2 approximately 50 days). The constituent isotope pools probably correspond to one exogenous and two endogenous sources. The exogenous source equates to our fast turnover pool, and the pools with intermediate and slow turnover rates are thought to derive from the turnover of metabolically active tissues and relatively inactive tissues within the body, respectively. It seems that a greater proportion of the amino acids available for hair synthesis come from endogenous sources compared to the compounds undergoing cellular catabolism in the body. Consequently, the isotope composition of blood bicarbonate appears to be much more responsive to dietary isotope changes, whereas the amino acids in the blood exhibit considerable isotopic inertia.

Amino Acids↗
PubMed1998

Improved healing with a collagen-alginate dressing in the chemical matricectomy.

A prospective clinical trial was conducted to evaluate the efficacy of a collagen-alginate wound dressing in the postoperative management of chemical matricectomies. The study involved 20 patients and 23 separate procedures. The collagen-alginate-dressing treatment group had an average healing time of 24.4 days, compared with 35.8 days for the control group, which received treatment consisting of soaks and daily dressing changes (P < .05). The authors suggest that using a collagen-alginate wound dressing in the postoperative management of chemical matricectomies will shorten healing time, thus reducing infection rates and increasing patient compliance and satisfaction.

Adolescent↗
PubMed1993

Photophysical properties of the photosensitizer pheophorbide a studied at high photon flux densities.

The photophysical properties of pheophorbide a (Pheo a) under two-step laser activation were investigated. For the first time quantum yields of higher excited state formation were calculated. It was shown that the quantum yields of the formation of these states depend strongly on the pulse duration of the excitation source. The nonlinear properties of Pheo a are quite different in dependence on the excitation wavelength but the quantum yields of the higher excited state formation in both cases (lambda exc = 337 nm and lambda exc = 667 nm) rise up increasing the photon flux density of the laser light up to 10(26) phot cm-2 s-1. A further increase of the photon flux density has no effect on the quantum yields.

Chlorophyll↗
PubMed1990

Photophysical studies of pheophorbide a and pheophytin a. Phosphorescence and photosensitized singlet oxygen luminescence.

The triplet states of pheophorbide a and pheophytin a were studied in several environments by direct measurement of the phosphorescence of the pigments and photosensitized singlet oxygen (1O2) luminescence. The spectra, lifetimes and quantum yields of phosphorescence and the quantum yields of 1O2 generation were determined. These parameters are similar for monomeric molecules of both pigments in all the environments studied. Aggregation of the pigment molecules leads to a strong decrease in the phosphorescence and 1O2 luminescence intensities, which is probably due to a large decrease in the triplet lifetime and triplet quantum yield in the aggregates. The results obtained for pheophorbide a and pheophytin a are compared with those previously reported for chlorophyll alpha. The data suggest that the photodynamic activity of the pigments in living tissues is probably determined by the monomeric pigment molecules formed in hydrophobic cellular structures. Aggregated molecules seem to have a much lower activity.

Chlorophyll↗
PubMed1990

Photophysical properties and photodynamic activity in vivo of some tetrapyrroles.

Some of the photophysical properties (stationary absorbance and fluorescence, fluorescence decay times and singlet oxygen quantum yields) of pheophorbide a, metal-free, ClAl-, Cu- and Mg-t-butyl-substituted phthalocyanines, metal-free, ClAl- and Cu-t-butyl-substituted naphthalocyanines and of a number of tetraphenylporphyrins (5,10,15,20-tetraphenylporphyrin, 5,10,15,20-tetra(m-hydroxyphenyl)porphyrin, 5,10,15,20-tetra(p-hydroxyphenyl)porphyrin) have been studied in comparison with hematoporphyrin IX in order to select potent photosensitizers for the photodynamic treatment of cancer. The photodynamic activity of these compounds was investigated using Lewis lung carcinoma in mice. As a consequence of the photophysical parameters (relatively short singlet state lifetimes, and high singlet oxygen quantum yields) the photodynamic activities of pheophorbide a, t-butyl-substituted ClAl-phthalocyanine and ClAl-naphthalocyanine were selected for study in greater detail. Under the conditions employed in the present study, pheophorbide a was found to be the most effective sensitizer, as judged from its strong absorption at the excitation wavelength as compared with the hematoporphyrin derivative and greater singlet oxygen quantum yield relative to the phthalocyanines and naphthalocyanines. The photodynamic activity was observed to be strongly dependent on the photophysical parameters of the compounds. The primary mechanism underlying the photodynamic activity of these sensitizers probably consists of energy transfer from the lowest triplet state of the dyes to molecular oxygen, resulting in the formation of singlet oxygen (type II of photosensitization).

Animals↗
PubMed1989

Generation of free radicals by photoexcitation of pheophorbide alpha, haematoporphyrin and protoporphyrin.

An investigation of the production of radical species by photoexcitation pheophorbide alpha, haematoporphyrin and protoporphyrin was performed. In an aqueous solution containing different amounts of ethanol, the superoxide radical was detected by the spin trapping technique. In addition, secondary radicals were observed. The generation of oxygen radicals was found to dominate in solutions with a low ethanol content.

Chlorophyll↗
PubMed1987

Time-resolved fluorescence spectroscopy of hematoporphyrin, mesoporphyrin, pheophorbide a and chlorin e6 in ethanol and aqueous solution.

The fluorescence decay I(t) and time-resolved spectra I(lambda, t) of some porphyrins and chlorins in ethanol and phosphate-buffered aqueous solution were investigated with a time-correlated single-photon-counting apparatus with a mode-locked Ar+ laser (514.5 nm) as the excitation source. The fluorescence of hematoporphyrin, mesoporphyrin and pheophorbide aa is considerably influenced by the conditions of aggregation (these compounds undergo aggregation in phosphate-buffered solution but not in ethanolic solution). The fluorescence decay of chlorin e6 which remains monomeric in both solvents is single exponential in all cases. The fluorescence spectra of hematoporphyrin, mesoporphyrin and pheophorbide a in phosphate-buffered solution are shifted with respect to the spectra obtained in ethanol; moreover, a new emission band (X band) appears, whose intensity increases on increasing the amount of equilibrium aggregates and shows a fast fluorescence decay. For hematoporphyrin and mesoporphyrin the appearance of the X band emission appears to be correlated with irreversible photoprocesses leading to fluorescent photoproducts. Analysis of the reported fluorescence spectra of cancer cells after incubation with hematoporphyrin derivative suggests that the fluorescent photoproducts might be formed also in vivo.

Chlorophyll↗
PubMedDate not supplied

Antibiotic beads in the treatment of diabetic pedal osteomyelitis.

Antibiotic-impregnated polymethylmethacrylate (PMMA) beads have improved the outcome of osteomyelitis treatment in both experimental models and clinical trials. The primary benefit of antibiotic-impregnated PMMA beads is that they provide high local concentrations of antibiotic while systemic levels of antibiotic remain low. Little has been written about the specific use of antibiotic-impregnated PMMA beads in the treatment of diabetic pedal osteomyelitis. The authors review antibiotic-impregnated PMMA beads and provide examples of their use in the treatment of diabetic pedal osteomyelitis.

Absorbable Implants↗