EXPERIMENTAL STUDIES IN RATS WITH THROMBI DIFFERENT AGES

Deckblatt-Impressum Index verwendete Abkürzungen Einleitung Literaturübersicht eigene Untersuchungen Diskussion Zusammenfassung Summary Literaturverzeichnis Tabellarische Darstellung der Ergebnisse Danksagung Veröffentlichungen SelbständigkeitserklärungZiel dieser Arbeit war die MR-angiographische Detektion und Charakterisierung von Throm-ben in venösen Gefäßen. Estmalig wurden dazu eisenhaltige Nanopartikel (DDM 43/34) in der Dosis von 30 mol / kg eingesetzt. Sid sollten histologisch nachgewiesen werden. Dazu wurden in 6 Altersgruppen á 7 Tieren, 3 Kontrolltiere und je ein Tier zur Überprüfung der Laserinduktion bzw. elektrischen Herbeiführung eines intravalsalen Gerinnsels untersucht. Ein Thrombosemodell bei der Ratte sollte etabliert werden. Die Induktion mittels Strom und Laserstrahlen führten zu histologisch unbefriedigenden Ergebnissen. Durch die histologische und MR-tomographische Untersuchung (klinisches Gerät mit 1,5 Tesla) von unterschiedlich alten an der Vena jugularis von Wistar- Ratten mittels Thrombin chirurgisch induzieten Blutkoageln konnte in diesem Versuchsvorhaben folgendes gezeigt werden: Thromben werden in der MR- Angiographie als Signalaussparungen dargestellt. Mit der SPIO-unterstützten MRA lassen sich im Tierexperiment ein ausreichender Gefäßkontrast erzielen und Thromben sicher darstellen. Aufgrund der Größe der Veränderungen (Blutkoageln) erschweren histologisch inkomplette Darstellungen und angiographisch Partialvolumeneffekte den Vergleich von angiographischem und histologischem Ergebnis. Klinische MR-Tomographen erreichen keine lichtmikroskopische Genauigkeit und benötigen sehr lange Aufnahmezeiten. Dies führt am lebenden Subjekt zu schlechter MR-Bildqualität aufgrund von Verwacklungen. Das Kontrastmittel DDM43/34 kann für eine angiographische Wirkung extrem niedrig dosiert werden. Dies war der erste Einsatz von Nanopartikeln zur Darstellung und Charakterisierung von Thromben. Wenn die Partikel z.B. mit geeigneten Antikörpern gegen Epitope von Thromben versehen werden können, ist diese Idee (bei zunehmender Auflösungs- kraft der MR- Tomographen) weiterhin reizvoll und erfolgversprechender. Zur Zeit bietet der Einsatz von DDM 43/34 in der MR-Angiographie eine gute Aus-sagekraft über das Vorhandensein oder Fehlen, aber nur eine bedingte Aussagekraft über die Morphologie von intravasalen Blutkoageln der Ratte.A study was performed to detect and characterize thrombi in venous vessels by MR Angio-graphy. This was for the first time done using iron-based nanoparticles (DDM 43/34) at a dosage of 30 micromol/kg. For histologic demonstration of the nanoparticles, 42 rats having received DDM 43/34 (6 thrombus age groups each comprising 7 animals) and 3 controls without DDM 43/34 administration were examined. One animal each was killed to examine intravascular thrombus induction by laser and electric current. The 42 animals examined angiographically and histologically immediately after administration of DDM 43/34 all showed a thrombus about 1 cm in length which did not extend beyond the vascular diameter of 2 mm. Another aim was to establish a thrombus model in rats. Histology showed that thrombus induction by electric current and laser beams did not produce adequate results. Histology and MR angiography (1.5-Tesla clinical MR imager) of thrombi of different age induced surgically by means of thrombin in the jugular vein of Wistar rats yielded the following results: Thrombi are depicted by MR angiography as signal voids. SPIO- enhanced MR angiography achieves adequate vessel contrast and reliable thrombus detection in animal experiments. As a result of the size of the lesions (thrombi), incomplete histologic specimens and partial volume effects at MR angiography make it difficult to compare the results of angiography and histology. Clinical MR imagers have al lower resolution than light microscopy and image acquisition time is very long, resulting in poor image quality in living animals due to blurring. The contrast medium DDM 43/34 has angiographic effects at extremely low doses. This study for the first time used nannoparticles for the visualization and characterization of thrombi. Further investigations are worthwhile and more promising if, for instance, the particles can be coupled with suitable antibodies directed against epitopes of thrombi (and the resolution of MR imagers is improved further). With current technology, the use of DDM 43/34 in MR angiography provides good information on presence or absence but only moderate information on the morphology of thrombi in rats

Biogenic Volatile Organic Compound and Respiratory CO2 Emissions after 13C-Labeling: Online Tracing of C Translocation Dynamics in Poplar Plants

Globally plants are the primary sink of atmospheric CO(2), but are also the major contributor of a large spectrum of atmospheric reactive hydrocarbons such as terpenes (e.g. isoprene) and other biogenic volatile organic compounds (BVOC). The prediction of plant carbon (C) uptake and atmospheric oxidation capacity are crucial to define the trajectory and consequences of global environmental changes. To achieve this, the biosynthesis of BVOC and the dynamics of C allocation and translocation in both plants and ecosystems are important.We combined tunable diode laser absorption spectrometry (TDLAS) and proton transfer reaction mass spectrometry (PTR-MS) for studying isoprene biosynthesis and following C fluxes within grey poplar (Populus x canescens) saplings. This was achieved by feeding either (13)CO(2) to leaves or (13)C-glucose to shoots via xylem uptake. The translocation of (13)CO(2) from the source to other plant parts could be traced by (13)C-labeled isoprene and respiratory (13)CO(2) emission.In intact plants, assimilated (13)CO(2) was rapidly translocated via the phloem to the roots within 1 hour, with an average phloem transport velocity of 20.3±2.5 cm h(-1). (13)C label was stored in the roots and partially reallocated to the plants' apical part one day after labeling, particularly in the absence of photosynthesis. The daily C loss as BVOC ranged between 1.6% in mature leaves and 7.0% in young leaves. Non-isoprene BVOC accounted under light conditions for half of the BVOC C loss in young leaves and one-third in mature leaves. The C loss as isoprene originated mainly (76-78%) from recently fixed CO(2), to a minor extent from xylem-transported sugars (7-11%) and from photosynthetic intermediates with slower turnover rates (8-11%).We quantified the plants' C loss as respiratory CO(2) and BVOC emissions, allowing in tandem with metabolic analysis to deepen our understanding of ecosystem C flux

Transient Release of Oxygenated Volatile Organic Compounds during Light-Dark Transitions in Grey Poplar Leaves

In this study, we investigated the prompt release of acetaldehyde and other oxygenated volatile organic compounds (VOCs) from leaves of Grey poplar [Populus x canescens (Aiton) Smith] following light-dark transitions. Mass scans utilizing the extremely fast and sensitive proton transfer reaction-mass spectrometry technique revealed the following temporal pattern after light-dark transitions: hexenal was emitted first, followed by acetaldehyde and other C(6)-VOCs. Under anoxic conditions, acetaldehyde was the only compound released after switching off the light. This clearly indicated that hexenal and other C(6)-VOCs were released from the lipoxygenase reaction taking place during light-dark transitions under aerobic conditions. Experiments with enzyme inhibitors that artificially increased cytosolic pyruvate demonstrated that the acetaldehyde burst after light-dark transition could not be explained by the recently suggested pyruvate overflow mechanism. The simulation of light fleck situations in the canopy by exposing leaves to alternating light-dark and dark-light transitions or fast changes from high to low photosynthetic photon flux density showed that this process is of minor importance for acetaldehyde emission into the Earth's atmosphere

Contribution of Different Carbon Sources to Isoprene Biosynthesis in Poplar Leaves

This study was performed to test if alternative carbon sources besides recently photosynthetically fixed CO(2) are used for isoprene formation in the leaves of young poplar (Populus × canescens) trees. In a (13)CO(2) atmosphere under steady state conditions, only about 75% of isoprene became (13)C labeled within minutes. A considerable part of the unlabeled carbon may be derived from xylem transported carbohydrates, as may be shown by feeding leaves with [U-(13)C]Glc. As a consequence of this treatment approximately 8% to 10% of the carbon emitted as isoprene was (13)C labeled. In order to identify further carbon sources, poplar leaves were depleted of leaf internal carbon pools and the carbon pools were refilled with (13)C labeled carbon by exposure to (13)CO(2). Results from this treatment showed that about 30% of isoprene carbon became (13)C labeled, clearly suggesting that, in addition to xylem transported carbon and CO(2), leaf internal carbon pools, e.g. starch, are used for isoprene formation. This use was even increased when net assimilation was reduced, for example by abscisic acid application. The data provide clear evidence of a dynamic exchange of carbon between different cellular precursors for isoprene biosynthesis, and an increasing importance of these alternative carbon pools under conditions of limited photosynthesis. Feeding [1,2-(13)C]Glc and [3-(13)C]Glc to leaves via the xylem suggested that alternative carbon sources are probably derived from cytosolic pyruvate/phosphoenolpyruvate equivalents and incorporated into isoprene according to the predicted cleavage of the 3-C position of pyruvate during the initial step of the plastidic deoxyxylulose-5-phosphate pathway

Rapid conversion of isoprene photooxidation products in terrestrial plants

Isoprene is emitted from the biosphere into the atmosphere, and may strengthen the defense mechanisms of plants against oxidative and thermal stress. Once in the atmosphere, isoprene is rapidly oxidized, either to isoprene-hydroxy-hydroperoxides (ISOPOOH) at low levels of nitrogen oxides, or to methyl vinyl ketone (MVK) and methacrolein at high levels. Here we combine uptake rates and deposition velocities that we obtained in laboratory experiments with observations in natural forests to show that 1,2-ISOPOOH deposits rapidly into poplar leaves. There, it is converted first to cytotoxic MVK and then most probably through alkenal/one oxidoreductase (AOR) to less toxic methyl ethyl ketone (MEK). This detoxification process is potentially significant globally because AOR enzymes are ubiquitous in terrestrial plants. Our simulations with a global chemistry-transport model suggest that around 6.5Tgyr(-1) of MEK are re-emitted to the atmosphere. This is the single largest MEK source presently known, and recycles 1.5% of the original isoprene flux. Eddy covariance flux measurements of isoprene and MEK over different forest ecosystems confirm that MEK emissions can reach 1-2% those of isoprene. We suggest that detoxification processes in plants are one of the most important sources of oxidized volatile organic compounds in the atmosphere. Isoprene oxidation products are deposited rapidly into poplar leaves, where they undergo detoxification, and up to 1.5% are reemitted to the atmosphere as methyl ethyl ketone, according to laboratory and field experiments and chemistry-transport model simulations.Peer reviewe