Magnetic resonances in biomedical research

Prikazana je primjena metoda magnetskih rezonancija - elektronske magnetske rezonancije (EPR) i nuklearne magnetske rezonancije (NMR) u biomedicinskim istraživanjima. Opisani su primjeri istraživanja u kojima se metoda EPR koristi za određivanje mikrogeografije aktivnog centra enzima acetilkolinesteraze i mjerenje konformacijskih promjena pod utjecajem kolinergičnih supstancija, za proučavanje promjena u fluidnosti staničnih membrana pod utjecajem neurotoksina, za određivanje transporta kokarcinogena, forbolestera kroz stanične membrane, te transporta molekula kroz tkiva s pomoću gradijenta magnetskog polja. Opisani primjeri istraživanja metodom NMR odnose se na njenu primjenu za proučavanje metaboličkih osobina skeletnih mišića, karakterizaciju tumora mozga in vitro i moguću dijagnozu tumora i raznih drugih patoloških stanja in vivo.Magnetic resonances are spectroscopic methods by which some structural changes and metabolic processes in biological systems can be followed on the molecular level. There are two main types of magnetic resonance methods: nuclear magnetic resonance (NMR) and electron paramagnetic (spin) resonance (EPR or ESR). By NMR are followed the atomic nuclei with the magnetic moment; in biological systems these are usually lH, 13C, 31P. By EPR are followed paramagnetic centres in biological systems; these are ions of the transition metal group (Fe3+, Cu2+, Mn2+), which appear as cofactors of the enzymes, or free radicals, which are intermediates in biochemical reactions. Instead of paramagnetic centres, which are native in biological systems, very often the molecules with a free radical are incorporated into the system - spin labels or spin probes. Centres with the magnetic moment serve as markers conveying the information about the metabolic f recesses in biological systems and about the changes in these processes in pathological conditions or under the influence of biologically active substances. In this work several typical applications of EPR and NMR in biomedical research are described showing a great variety of issues where magnetic resonances can be used. EPR experiments, Study of the microgeography of acetylcholinesterase active centre and the conformational changes of this centre under the influence of cholinergic substances. Changes in cell membrane fluidity under the influence of neurotoxins. Transport of cocarcinogens, forbolesters, through the cell membrane. Application of magnetic field gradient to the investigation of transport through the tissues. NMR experiments: Application of 1H-NMR to characterization of brain tumours in vitro and possible application of NMR tomography in vivo to diagnosis of tumours and other pathological conditions. Application of 31P-NMR for investigation of metabolic properties of skeletal muscles

EPR of the Sodium Laurate-Water Lyotropic Mesophases and Micellar Solution

The local orienta>tional order of molecules in lameilar and hexagonal mesophases as well as in micellar aggregates of the sodium laurate - water system was studied by EPR. As a paramagnetic probe a fatty acid spin label, dissolved in the hydrophobic environment was used. 1t was found that the ordering parameter decreases cont1nously over the whole concentration and temperature range of the mesophases irrespective of the phase transitions. From the local ordering parameter observed in cylindrical micelles, the variation of cylinder dimensions with tempeirature and concentration was estimated. In the micellar solution the concentration range where cylindrical micelles were the most stable was determined, and its relation to the maximal stab.ility region in the hexagonal phase was discussed. The rate of molecular tumbling around the cylindrical axes in the hexagonal phase was found faster t han 108 sec-1 at 100 °c

EPR relaxation study of a liquid crystal

Molecular dynamics in the nematic and smectic A phases of 4-n-butoxy-benzylidene-4'-n-octylaniline have been evaluated from the EPR data of the dissolved spin label probes. Calculations of the average concerning the nematic phase have been extended using McMillan's potential for the smectic A phase.La dynamique moléculaire des phases nématique et smectique A de 4-n -butoxybenzilidene-4'- n-octylaniline est évaluée à partir des spectres RPE de molécules marquées dissoutes. Les calculs de la moyenne pour la phase nématique ont été étendus à la phase smectique A en utilisant le potentiel de McMillan

Skin oxygenation after topical application of liposome-entrapped benzyl nicotinate as measured by EPR oximetry in vivo: Influence of composition and size

New and improved drug delivery systems are the important subject of much scientific research. The development of formulations that increase skin oxygenation and of methods for measuring oxygen levels in skin are important for dealing with healing processes affected by the level of oxygen. We have use EPR oximetry in vivo to compare the influence of liposomal formulations of different size and composition with that of hydrogel with respect to the action of the entrapped benzyl nicotinate (BN). Following the topical application of BN onto the skin of mice, pO2 increase was measured by low-frequency EPR as a function of time. The effect of BN was evaluated by 3 different parameters: lag-time, time needed for maximum pO2 increase, and overall effectiveness expressed by the area under the response-time curve. An increase in skin oxygenation was observed after BN application. The results show that the effect of BN incorporated in liposomes is achieved more rapidly than the effect from hydrophilic gel. The composition of the liposomes significantly affects the time at which BN starts to act and, to a lesser extent, the maximum increase of pO2 in skin and the effectiveness of BN action. However, the size of the liposomes influences both the effectiveness of BN action and the time at which BN starts to act. After repeated application of liposomes, the pO2 baseline increased and the response of the skin tissue was faster. Our results demonstrate that EPR oximetry is a useful method for evaluating oxygen changes after drug application and for following the time course of their action