Biomedical subjects

H K Seidlitz

Publications and source records attributed to H K Seidlitz.

13 recordsLinked to original sources

PubMed2005

Simulated solar irradiation with enhanced UV-B adjust plastid- and thylakoid-associated polyamine changes for UV-B protection.

Polyamines have been described to protect against numerous oxidative stresses in plants. Increasing UV-B radiation (280-315 nm) in the biosphere may also induce an increase in radical formation in tissues. This study employed the tobacco cultivars Bel B and Bel W3 to describe possible protective functions of polyamines against UV-B radiation in sun light simulators (GSF/Munich) with natural diurnal fluctuations of simulated UV-B. Polyamine measurements on a whole leaf basis in isolated chloroplasts and thylakoids were paralleled to photosynthetic and respiration rates, photosynthetic efficiency, leaf thickness and photosynthetic pigment compositions. The study revealed that an increase of polyamines, and especially of putrescine level in thylakoid membranes upon elevated UV-B exposure comprises one of the primary protective mechanisms in the photosynthetic apparatus of the tobacco variety Bel B against UV-B radiation. The tobacco cultivar Bel W3, sensitive to ozone, was also proved to be sensitive to UV-B. This sensitivity is attributed to its incapability to enhance putrescine level in thylakoid membranes. After prolongation of UV-B exposure, when endogenous plant balances are being gradually restored, due to secondary responses, (e.g., biosynthesis of carotenoids and of additional flavonoids) and the plant is adapting to the altered environmental conditions, then the polyamine level is being reduced. Thus, we can discriminate the UV-B induced stress period from a UV-B acclimation period.

Carotenoids↗

PubMed2004

The role of UV-B on the degradation of PCDD/Fs and PAHs sorbed on surfaces of spruce (Picea abies (L.) Karst.) needles.

Photodegradation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polycyclic aromatic hydrocarbons (PAHs) sorbed on surfaces of spruce (Picea abies (L.) Karst.) needles was investigated. The role of sunlight and, in particular, the role of short wavelength UV-B radiation were studied in a sun simulator under controlled environmental conditions. The photodegradation of PCDD/Fs and PAHs follows first-order kinetics. Simulated sunlight containing UV-B induced two phases of photodegradation kinetics for PCDD/Fs, whereas no distinct phases of the kinetics were observed for PAHs. UV-B radiation plays a much more important role on the photodegradation for PCDD/Fs than that for PAHs. Direct photolysis dominates the photodegradation of PCDD/Fs and PAHs.

Adsorption↗

PubMed2001

Determination of the calibration factor of polysulphone film UV dosemeters for terrestrial solar radiation.

Polysulphone film is used as a personal UV dosemeter in dermatological or epidemiological studies. The relative efficiency of this detector does not exactly match the action spectrum as proposed by the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and to which the UV dose and exposure limits refer. Therefore, the calibration of the dosemeter depends on the spetrum. In the present paper the variation of the calibration factor for terrestrial solar UV spectra is analysed on the basis of a two year observation period at a site near Munich. Germany. A detailed error estimation is included. It is shown that the variation of the calibration factor within this class of spectra is the main contribution to the total uncertainty of the dose determination, which can be up to 40%. The shape of the spectrum of terrestrial solar UV radiation is mainly determined by the total ozone column and the solar elevation angle. It is shown how the calibration depends on these two parameters and how this additional information can help to reduce the measurement error to a residual uncertainty of 17%. Exposure studies of terrestrial solar UV radiation using polysulphone film as a dosemeter would gain in accuracy if total ozone column values at the study's site could be measured or taken from satellite or weather service data. The interpretation of the magnitude of the dose uncertainty depends on the further use of these data.

Biocompatible Materials↗

PubMed2000

Elevated UV-B radiation reduces genome stability in plants.

Long-term depletion of the stratospheric ozone layer contributes to an increase in terrestrial solar ultraviolet-B radiation. This has deleterious effects on living organisms, such as DNA damage. When exposed to elevated ultraviolet-B radiation (UV-B; 280-315 nm), plants display a wide variety of physiological and morphological responses characterized as acclimation and adaptation. Here we show, using special sun simulators, that elevated solar UV-B doses increase the frequency of somatic homologous DNA rearrangements in Arabidopsis and tobacco plants. Increases in recombination are accompanied by a strong induction of photolyase and Rad51 gene expression. These genes are putatively involved in major DNA repair pathways, photoreactivation and recombination repair. In mutant Arabidopsis plants that are deficient in photoreactivating ultraviolet-induced cyclobutane pyrimidine dimers, recombination under elevated UV-B regimes greatly exceeds wild-type levels. Our results show that homologous recombination repair pathways might be involved in eliminating UV-B-induced DNA lesions in plants. Thus, increases in terrestrial solar UV-B radiation as forecasted for the early 21st century may affect genome stability in plants.

Arabidopsis↗

PubMed1997

Modification of global erythemally effective irradiance by clouds.

The role clouds play in the modification of global radiation is still a major uncertainty in the risk assessment of UV effects on ecological systems and human health. This study presents cloud transmission data obtained from measurements with Robertson-Berger meters and simultaneous cloud observations. The global transmission of erythemally weighted irradiance depends strongly on cloud amount and can be described by a cubic function. The comparison with results derived from long-term records of total global irradiance indicates no statistically significant difference between the attenuation of erythemal and total global radiation. The large variance of data results from lumping together data from different cloud types. Classification of data according to cloud forms yields a more satisfactory fit. The coefficient of the cubic term characterizes the ability of various cloud forms to attenuate UV radiation. It varies between 0.4 for high clouds and approximately 1.0 for cumulonimbus. This attenuation parameter allows a quantitative description of the cloud influence on irradiance and therefore a more accurate risk assessment.

Algorithms↗

PubMed1993

Photodegradation of protoporphyrin-dimethylester in solution and in organized environments.

The degradation of sensitizers used in photodynamic therapy (PDT) involves photooxidation either by molecular oxygen or by oxygen intermediates which leads to hydroxyaldehyde and formyl products or to ring opening. Our investigations focused on the spectroscopic changes which protoporphyrin-dimethylester (PP) exhibits upon irradiation. As the microenvironment strongly influences the effects, we used an aprotic organic solvent, L-alpha-phosphatidylcholine dioleoyl (DOPC) liposomes and isogenic fibrosarcoma cells (SSKII) as carriers for PP. Hydroxyaldehyde product isomers develop a new absorption band centred around 670 nm and a new emission band at 676 nm. These characteristics can be used to discriminate them from formyl products and intact PP. In organic solvents, the formation of the hydroxyaldehyde products dominates. In DOPC liposomes and cells, the hydroxyaldehyde yield drops and photooxidation results in attack of the macrocycle. Time-resolved fluorescence spectroscopy of monomeric PP in an organic solvent gives a monoexponential decay time tau of 10.1 +/- 1.3 ns. Upon irradiation a second component with a decay time of 4.9 +/- 0.6 ns, resulting from the hydroxyaldehyde product, was detected. In liposomes and cells the monomeric decay time was significantly longer (15 ns) due to the altered microenvironment. Additionally, we observed in liposomes and in cells a small contribution of a short component (1 ns) which is attributed to an aggregated sensitizer species. In irradiated cells the aggregated fraction doubles, indicating a change in the microenvironment caused by the photodynamic action of the sensitizer.

Fibrosarcoma↗

PubMed1992

Intracellular localization of meso-tetraphenylporphine tetrasulphonate probed by time-resolved and microscopic fluorescence spectroscopy.

The effects of solvent pH on spectral properties and fluorescence decay kinetics were investigated in order to characterize the microenvironment of meso-tetraphenylporphine tetrasulphonate (TPPS4) taken up by cells. Steady-state absorption and fluorescence spectra of TPPS4 in buffer solutions of different pH were used to identify a ring protonated species at pH less than or equal to 4. This dictation could also be distinguished from the unprotonated form by its altered fluorescence decay time (3.5 vs. 11.4 ns). In addition, time-resolved spectroscopy gave some evidence of a monocationic species existing at pH 6-9. This was concluded from the occurrence of another component with a decay time of 5 ns. Measurements of the spectral and kinetic properties of the fluorescence emission of single epithelial cells (RR1022) incubated with TPPS4 indicated that the sensitizer was mainly localized in a microenvironment with a pH of 5, a value which occurs intracellularly only within lysosomes. Cells kept in the dark exhibited the characteristic spectra of both the dication and the neutral form. The fluorescence decay showed two components with decay times of 2.6 ns and 10.6 ns. Irradiation of the cells changed the decay times to 4.6 ns and 13.4 ns and the dication fluorescence emission peak vanished, which is in accordance with the results obtained from buffer solutions at pH greater than or equal to 6. Therefore, we deduce that the photodynamic action leads to a rupture of the lysosomes and that the sensitizer is released into the surrounding cytoplasm.

Animals↗

PubMed1992

Optical resolution and color performance of electronic endoscopes.

We studied the optical and color performance of Olympus fiber- and electronic endoscopes, including the EVIS 100 and EVIS 200 series. The measurements showed that the optical resolution of new generation videoendoscopes equals or exceeds that of fiberendoscopes. The close-up focusing ability has been extended. The color performance of the new EVIS 200 gastroscope enables clear distinction of all mucosal hues.

Color↗

PubMed1990

Time-resolved polarization measurements of porphyrin fluorescence in solution and in single cells.

Porphyrin monomers, dimers and aggregates, which can be differentiated on the basis of their fluorescence lifetimes, are shown to possess different degrees of fluorescence polarization. This opens up new possibilities for microscopic imaging of these individual components in photosensitization and tumour detection. A rough estimate of the size of the porphyrin aggregates is obtained from the data of time-resolved fluorescence anisotropy.

Animals↗

PubMed1988

Time-resolved fluorescence in photobiology.

The article focuses on techniques and applications of time-resolved fluorescence spectroscopy in biology and medicine. Both novel methods and well-established ones are discussed and future trends are outlined. Applications including fluorescence detection of nucleic acids, proteins, coenzymes and plant pigments and fluorescence labelling of nuclei, membranes and antibodies are outlined. In addition the fluorescence properties of photosensitizers used in photodynamic therapy are discussed.

Biology↗

PubMed1987

Electronic endoscopy--the latest technology.

At present, video endoscopic systems (VE) are available from four companies. We have had an opportunity to test these instruments in clinical practice. In principle, all the VE's are similar in that they employ charge coupling devices (CCD-chips) as image sensors, but they differ significantly in CCD chip technology and in the color acquisition technique. The basic aspects of CCD chip and transmission technology of relevance to the endoscopist are discussed. The mechanical properties of the endoscopes are listed. Finally, we provide an outlook on the determinants of the optical performance of VE's. The optical performance of a VE can be characterized by its resolution and color performance.

Colonoscopes↗

PubMed1987

Video-endoscopes in comparison with fiberscopes: quantitative measurement of optical resolution.

The subject of this study was the optical performance of video-endoscopic systems (VE) in terms of maximal resolving power and resolvable picture elements. Olympus, Toshiba/Machida, Fujinon, and Welch Allyn video gastroscopes were tested. A GIF Q 10 fiberscope from Olympus was also included for comparison. The resolution measurements were made at various distances using two independent methods--electronic analysis of the TV signal, and visual evaluation of the resolution, of a standardized test target. The results obtained with the two methods were in perfect agreement. The resolution of fine details clearly depends on the distance between the distal end and the target because of decreasing image scale. Depending on the individual optical design, the various VE's show maxima at different distances. At shorter distances, the image is degraded by defocusing. An optimal distance which is as small as possible is desired for clinical routine. Apart from the fiberscope this requirement is best met by the Fuji system. The greatest resolution is obtained with the Toshiba system but at the cost of the viewing angle which is the smallest of all the systems. Fuji combines relatively high resolution with a large viewing angle. Because of the widely varying viewing angle a comparison based solely on resolution cannot represent the true imaging capability of the system. We therefore eliminated purely optical parameters and calculated the number of resolvable picture elements per line. We regard this number to be a fair characterization of both TV and fiber systems.

Fiber Optic Technology↗

PubMed1987

Color performance of video endoscopes: quantitative measurement of color reproduction.

We have conducted a study aimed at testing the color performance of video endoscopes in quantitative terms for the first time. The video endoscopes investigated were from Fuji, Olympus, Toshiba/Machida, and Welch-Allyn. The tests were carried out with an opto-electronic color analyser using standardized color charts and a neutral grey chart. Hue and chroma of the reproduced colors were measured. The Olympus video endoscope reproduces the hue very well, showing only slight color desaturation. The Fuji video endoscope had a yellowish tint, whereas the picture obtained with the WA video endoscope produced an inhomogeneous picture with a pronounced red/purplish cast at the top of the screen and almost neutral reproduction at the lower half. The Toshiba video endoscope was the only one with a color chip, and reproduced hue fairly well, but its colors were weakly saturated.

Color↗