Pál Gróf

Oxidation of guanine in cellular DNA by solar UV radiation: biological role.

Abstract. The formation of cyclobutane pyrimidine dimers (CPD) and 8‐oxo‐7,8‐dihydro‐2′‐deoxyguanosine (8‐oxodGuo) was investigated in Chinese hamster ovary cells upon exposure to either UVC, UVB, UVA or simulated sunlight (SSL). Two cell lines were used, namely AT3‐2 and UVL9, the latter being deficient in nucleotide excision repair and consequently UV sensitive. For all types of radiation, including UVA, CPD were found to be the predominant lesions quantitatively. At the biologically relevant doses used, UVC, UVB and SSL irradiation yielded 8‐oxodGuo at a rather low level, whereas UVA radiation produced relatively higher amounts. The formation of CPD was 102 and 102 more effective upon UVC than UVB and UVA exposure. These yields of formation followed DNA absorption, even in the UVA range. The calculated relative spectral effectiveness in the production of the two lesions showed that efficient induction of 8‐oxodGuo upon UVA irradiation was shifted toward longer wavelengths, in comparison with those for CPD formation, in agreement with a photosensitization mechanism. In addition, after exposure to SSL, about 19% and 20% of 8‐oxodGuo were produced between 290–320 nm and 320–340 nm, respectively, whereas CPD were essentially (90%) induced in the UVB region. However, the ratio of CPD to 8‐oxodGuo greatly differed from one source of light to the other: it was over 100 for UVB but only a few units for UVA source. The extent of 8‐oxodGuo and CPD was also compared to the lethality for the different types of radiation. The involvement of 8‐oxodGuo in cell killing by solar UV radiation was clearly ruled out. In addition, our previously reported mutation

Use of Uracil Thin Layer for Measuring Biologically Effective UV Dose

Abstract— Dimerization of uracil monomers in a polycrystalline state by UV radiation changes the absorption characteristics of a thin layer of the material. The change in optical density, measured by spectrophotometry in the250–400 nm range, as a function of the exposure time is evaluated in terms of the biologically effective UV dose. A statistical evaluation of a great number of uracil dosimeters irradiated with a TL01 lamp from Philips establishes the possibility of evaluating the biologically effective UV dose using a uracil dosimeter. Nonlinear regression procedures were introduced to correct the absorption spectra for contributions due to light scattering and to determine the optical density values required to calculate the UV dose expressed in HUunits. Comparison of cumulative daily doses and long‐term monitoring measured by the uracil thin‐layer dosimeter and a phage T7 dosimeter are given, which allow the determination of conversion factors between various biological dosimeters under different irradiation conditions.

Biological UV dosimetry-a comprehensive problem

Abstract The biologically effective dose from environmental radiation was measured using phage T7 and uracil thin layer sensors in a dosimeter developed previously (Gy. Ronto, S. Gaspar and A. Berces, Phages T7 in biological UV dose measurement, J. Photochem. Photobiol. B: Biol., 12 (1992) 285–294; P. Grof, S. Gaspar and A. Berces, Uracil thin layers in dosimetry of UV radiation, Proc. Int. Symp. Budapest Biomedical Optics, Europe, 1993 , to be published). Examples of measured daily and annual profiles are presented to demonstrate the possibilities and limits of biological dosimetry. In addition, phage T7, uracil sensor and Robertson-Berger meter results are compared. A comparison of model calculation data with the measured values is presented. On the basis of the results obtained, the application of biological dosimeters in both long-term field measurements and laboratory experiments is suggested.

Molecular interactions between DPPC and morphine derivatives: A DSC and EPR study

The interaction between different morphine derivatives (morphine, codeine, N-methyl-morphine, N-methyl-codeine) and alpha-L-dipalmitoyl phosphatidylcholine (DPPC) liposomes was studied with differential scanning calorimetry (DSC) and electron paramagnetic resonance (EPR) spectroscopy. Small unilamellar DPPC-liposomes with the given morphine-derivative were prepared by sonication. The size distribution of liposomes was checked by dynamic light scattering (DLS). The amount of entrapped morphine was determined spectrophotometrically. Our results indicate that the morphine and its derivatives principally interact with the lipid head groups, and this interaction leads to a decrease in the mobility of the polar head groups, especially in case of codeine and N-methyl-codeine.

The uncoupling of the effects of formins on the local and global dynamics of actin filaments

In this study, experiments were carried out in the conventional and saturation-transfer electron paramagnetic resonance (EPR) time domains to explore the effect of mDia1-FH2 formin fragments on the dynamic and conformational properties of actin filaments. Conventional EPR measurements showed that addition of formin to actin filaments produced local conformational changes in the vicinity of Cys-374 by increasing the flexibility of the protein matrix in the environment of the label. The results indicated that it was the binding of formin to the barbed end that resulted in these conformational changes. The conventional EPR results obtained with actin labeled on the Lys-61 site showed that the binding of formins could only slightly affect the structure of the subdomain 2 of actin, reflecting the heterogeneity of the formin-induced conformational changes. Saturation transfer EPR measurements revealed that the binding of formins decreased the torsional flexibility of the actin filaments in the microsecond time range. We concluded that changes in the local and the global conformational fluctuations of the actin filaments are associated with the binding of formins to actin. The results on the two EPR time domains showed that the effects of formins on the substantially different types of motions were uncoupled.

Liposomes for Topical Use: A Physico-Chemical Comparison of Vesicles Prepared from Egg or Soy Lecithin

Developments in nanotechnology and in the formulation of liposomal systems provide the opportunity for cosmetic dermatology to design novel delivery systems. Determination of their physico-chemical parameters has importance when developing a nano-delivery system. The present study highlights some technological aspects/characteristics of liposomes formulated from egg or soy lecithins for topical use. Alterations in the pH, viscosity, surface tension, and microscopic/macroscopic appearance of these vesicular systems were investigated. The chemical composition of the two types of lecithin was checked by mass spectrometry. Caffeine, as a model molecule, was encapsulated into multilamellar vesicles prepared from the two types of lecithin: then zeta potential, membrane fluidity, and encapsulation efficiency were compared. According to our observations, samples prepared from the two lecithins altered the pH in opposite directions: egg lecithin increased it while soy lecithin decreased it with increased lipid concentration. Our EPR spectroscopic results showed that the binding of caffeine did not change the membrane fluidity in the temperature range of possible topical use (measured between 2 and 50 °C). Combining our results on encapsulation efficiency for caffeine (about 30% for both lecithins) with those on membrane fluidity data, we concluded that the interaction of caffeine with the liposomal membrane does not change the rotational motion of the lipid molecules close to the head group region. In conclusion, topical use of egg lecithin for liposomal formulations can be preferred if there are no differences in the physico-chemical properties due to the encapsulated drugs, because the physiological effects of egg lecithin vesicles on skin are significantly better than that of soy lecithin liposomes.

Characterization of liposomal vesicles encapsulating rhodanese for cyanide antagonism.

The major mechanism of removing cyanide from the body is its enzymatic conversion by a sulfurtransferase, e.g. rhodanese, to the less toxic thiocyanate in the presence of a sulfur donor. Earlier results demonstrated that externally administered encapsulated rhodanese significantly enhances the in vivo efficacy of the given sulfur donor. Present studies are focused on liposomal carrier systems encapsulating rhodanese. Physicochemical properties, e.g. membrane rigidity, size distribution, surface potential, osmolarity, and viscosity, were determined for various liposomal lipid compositions and hydrating buffers to establish in vitro stability and in vivo fate. Lipid composition was also optimized to achieve maximum encapsulation efficiency.

Monitoring of environmental UV radiation by biological dosimeters

As a consequence of the stratospheric ozone layer depletion biological systems can be damaged due to increased UV-B radiation. The aim of biological dosimetry is to establish a quantitative basis for the risk assessment of the biosphere. DNA is the most important target molecule of biological systems having special sensitivity against short wavelength components of the environmental radiation. Biological dosimeters are usually simple organisms, or components of them, modeling the cellular DNA. Phage T7 and polycrystalline uracil biological dosimeters have been developed and used in our laboratory for monitoring the environmental radiation in different radiation conditions (from the polar to equatorial regions). Comparisons with Robertson-Berger (RB) meter data, as well as with model calculation data weighted by the corresponding spectral sensitivities of the dosimeters are presented. Suggestion is given how to determine the trend of the increase in the biological risk due to ozone depletion.

Physicochemical characterization of stealth liposomes encapsulating an organophosphate hydrolyzing enzyme

The present studies were focused on the preparation and characterization of stericaly stabilized liposomes (SLs) encapsulating a recombinant organophosphorus hydrolyzing phosphotriesterase (OPH) enzyme for the antagonism of organophosphorus intoxication. Earlier results indicate that the liposomal carrier system provides an enhanced protective effect against the organophosphorus molecule paraoxon, presenting a more effective therapy with less toxicity than the most commonly used antidotes. Physicochemical characterization of the liposomal OPH delivery system is essential in order to get information on its in vitro stability and in vivo fate. Osmolarity, pH, viscosity, and encapsulation efficiency of the SL preparation and the surface potential of the vesicles were determined. The membrane rigidity and the impact of OPH enzyme on it was studied by electron-paramagnetic resonance spectroscopy, using spin probes. The in vitro stability of the liposomal preparations, the vesicle size distribution, and its alteration during a 3-week storage were followed by dynamic light-scattering measurements. Further, the stability of encapsulated and nonencapsulated OPH was compared in puffer and plasma.

Syringotoxin pore formation and inactivation in human red blood cell and model bilayer lipid membranes.

The effect of syringotoxin (ST), a member of the cyclic lipodepsipeptides family (CLPs) produced by Pseudomonas syringae pv. syringae on the membrane permeability of human red blood cells (RBCs) and model bilayer lipid membranes (BLMs) was studied and compared to that of two recently investigated CLPs, syringomycin E (SRE) and syringopeptin 22A (SP22A) [Biochim. Biophys. Acta 1466 (2000) 79 and Bioelectrochemistry 52 (2000) 161]. The permeability-increasing effect of ST on RBCs was the least among the three CLPs. A time-dependent ST pore inactivation was observed on RBCs at 20 and 37 degrees C but not at 8 degrees C. From the kinetic model worked out parameters as permeability coefficient of RBC membrane for 86Rb(+) and pores mean lifetime were calculated. A shorter pores mean lifetime was calculated at 37 degrees C then at 20 degrees C, which gave us an explanation for the unusual slower rate of tracer efflux measured at 37 degrees C then that at 20 degrees C. The results obtained on BLM showed that the pore inactivation was due to a decrease in the number of pores but not to a change of their dwell time or conductance.