bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymer‐Legierungen
Authors: Meyer Wolfgang H.
Published: December 2004

Werkstoffe auf der Basis von synthetischen oder natürlichen Polymeren sind in vielen Bereichen des zivilisierten Lebens selbstverständlich geworden. Das liegt unter anderem an den typischen Eigenschaften der Polymeren, z. B. leichte Formgebung, geringes spezifisches Gewicht und oft niedriger Preis, die ihnen im Vergleich zu den „klassischen”︁ Werkstoffen wie Holz, Metall und Keramik Vorteile verschaffen.

Besonders auf dem Gebiet der Konstruktionswerkstoffe verdrängen deshalb Polymere andere Werkstoffe aus immer mehr Anwendungsbereichen. So ist z. B. die Innenausstattung von Personenkraftwagen in den letzten Jahren fast ausnahmslos eine Domäne der polymeren Werkstoffe geworden. Der vorliegende Artikel über Grundlagen und Anwendungen von „Polymer‐Legierungen”︁ ist der erste einer Serie von Aufsätzen, die sich unter der gemeinsamen überschrift „Polymere Werkstoffe”︁ mit den vielseitigen Aspekten dieser Werkstoffklasse befassen werden und in zwangloser Folge erscheinen sollen.
Vertrauen in Wissenschaft?? Das Menetekel von Tschernobyl
Authors: Busse Martin
Published: December 2004

Offenbar ist selbst Vertrauen in Naturwissenschaft Vertrauenssache, wobei man sagen muß, daß die Sache mit dem Vertrauen in Wissenschaft nicht allzu gut steht. Das hat Tschernobyl überdeutlich demonstriert. Mit dem Artikel soll die Frage aufgeworfen werden, ob wir darüber schon hinreichend nachgedacht haben. Konkret wird behauptet, daß wir ‐ die Naturwissenschaftler ‐ es selbst waren, die ihren hergebrachten Vertrauensbonus leichtfertig verspielt haben. Das läßt sich zwar nicht beweisen; vielleicht sind aber einige doch hinreichend beunruhigt, um über diese Möglichkeit ernsthaft nachzudenken.
Ein neuartiges biologisches Prinzip: Konservierung von Decarboxylierungsenergie
Authors: Dimroth Peter
Published: December 2004

Ein neuer Typ biologischer Energiekonservierung besteht in der Nutzbarmachung von Decarboxylierungsenergie zum aktiven Na+‐Transport. Diese Art der Energiewandlung wurde bei Untersuchungen an der membrangebundenen Oxalacetat‐Decarboxylase aus dem Bakterium Klebsiella pneumoniae entdeckt und seither auch bei anderen Decarboxylasen aus anaeroben Bakterien gefunden. Alle diese Na+‐Transport‐Decarboxylasen besitzen einen sehr ähnlichen Aufbau aus Untereinheiten und scheinen nach dem gleichen Mechanismus zu arbeiten. Nach Inkorporation der gereinigten Enzyme in Liposomen kann der durch die Decarboxylierung bewirkte Transport von Na+‐Ionen beobachtet werden. Es entsteht ein elektrochemischer Na+‐Gradient über die Membran, der ‐ in Umkehrung der Reaktion ‐ die energieverbrauchende Carboxylierung des decarboxylierten Substrats betreiben kann. Die physiologische Bedeutung der Konservierung von Decarboxylierungsenergie zeigt sich am eindrucksvollsten bei dem succinat‐vergärenden Bakterium Propionigenium modestum. Dieser strikte Anaerobier bezieht seine gesamte Energie aus der Decarboxylierung von Methylmalonyl‐Coenzym A. An diesem Organismus ist die Synthese von ATP über einen Na+‐Cyclus mit der Decarboxylierung verbunden. Dies ist das erste Beispiel für einen ATP‐Synthese‐Mechanismus mit Na+ anstelle von H+ als Kopplungs‐Ion.
Chemie und Technologie der Silicone I
Authors: Schliebs Reinhard , Ackermann Jürgen
Published: December 2004

Silicone sind

eine Produktklasse, die in den letzten 40 Jahren eine kontinuierlich zunehmende technische Bedeutung erreicht hat,

die einzigen technisch bedeutenden Polymeren, die ein anorganisches „Rückgrat”︁ besitzen (außer den vergleichsweise unbedeutenden Polyphosphazenen), magnified image

Materialien, deren Synthese nicht direkt erdölabhängig ist,

Stoffe mit hoher physiologischer Inertheit und schwer entflammbar,

Polymere, die wie keine andere Gruppe für eine kaum zu überschauende Zahl von Anwendungen eingesetzt werden.

Diese und eine Reihe weiterer Eigenschaften machen die Silicone zu einer interessanten Polymerklasse, deren unterschiedliches Eigenschaftsbild im Vergleich zu anderen Polymeren haben auf ihrem anorganischen „Rückgrat”︁ beruht.
Zink, ein langweiliges Element?
Authors: Vahrenkamp Heinrich
Published: December 2004

Das Typische am Zink ist, daß es nichts Typisches an sich hat. Wer sich mit Chemie befaßt, sei es interessiert, sei es ablehnend, hat kaum eine Chance, auf das Zink aufmerksam zu werden; das steht in merkwürdigem Kontrast zu dessen Wert als Gebrauchsmetall, dem Nutzen seiner Verbindungen sowie seiner essentiellen Bedeutung für alle Arten von Lebensvorgängen.
Chemie und Technologie der Silicone II. Herstellung und Verwendung von Siliconpolymeren
Authors: Ackermann Jürgen , Damrath Volker
Published: December 2004

Siliconpolymere werden heute weit verbreitet dort eingesetzt, wo hohe Anforderungen an Werkstoffe gestellt werden. Ihr Eigenschaftsprofil – hohe Lebensdauer und große thermische Beständigkeit – hat eine Produktpalette entstehen lassen, die von Ölen über Elastomere bis zu Harzen reicht. Charakteristisches Merkmal der Silicone (chemische Bezeichnung: Polyorganosiloxane) ist ihr Aufbau aus alternierenden Silicium‐ und Sauerstoff‐Atomen. Die noch freien Valenzen des Siliciums sind durch organische Gruppen, überwiegend durch Methylgruppen, abgesättigt (Abbildung 1). Die große Beständigkeit der Silicone gegen hohe Temperaturen, UV‐Strahlung und Witterung beruht auf dem Zusammenwirken von anorganischem Grundgerüst und reaktionsträgen Methylgruppen. Die Abschirmung der polaren SiO‐Einheiten durch die frei drehbaren, unpolaren Methylgruppen und die schraubenförmige (helixartige) Konformation der Molekülketten haben zur Folge, daß zwischen benachbarten Ketten nur geringe intermolekulare Anziehungskräfte wirken. Das erklärt unter anderem die niedrige Glasübergangs temperatur (Tg = −120 °C)

Die Glasübergangstemperatur Tg ist diejenige Temperatur, bei der die Segment‐ und Seitengruppen‐Bewegungen aller Polymer‐ketten vollständig einfrieren.

der Poly(dimethylsiloxane) und die nur mäßige Festigkeit von vernetzten Siliconpolymeren.
Chemie und Biologie: Zwei Kulturen?
Authors: Hartmann Guido R.
Published: December 2004

Zwischen den beiden Quellen der Biochemie‐letzten Endes zwischen Biologie und Chemie‐verläuft ein Graben. In der Chemie wird nach der Struktur und Synthese eines Stoffes‐unabhängig von dem Ort seines Vorkommens und seiner Funktion‐gefragt. In der Biologie kommt es dagegen nicht auf das „Wie”︁ des Stofflichen, sondern auf das „Warum”︁ an. Mit diesem prinzipiellen Unterschied und dem Problem, warum sich die klassischen Chemiedisziplinen hierzulande mit der Öffnung zur Biochemie so schwer tun, befaßt sich der vorliegende Beitrag, dessen Autor‐von der Ausbildung her Physikochemiker‐seit langem als Biochemiker tätig ist.
Galenik oder wie aus einem Wirkstoff ein Arzneimittel wird. Teil I: Einführung und chemische sowie physikalische‐chemische Prinzipien
Authors: Zimmermann Ingfried
Published: December 2004

Ein pharmakologisch noch so potenter Wirkstoff ist noch lange kein Arzneimittel. Um therapeutisch anwendbar zu sein, muß für diesen Wirkstoff erst eine Darreichungsform entwickelt werden. Diese Entwicklung wird von der Galenik geleistet, deren Aufgabe es ist, die im Verlauf der Präparateentwicklung ermittelten Kenntnisse über die Verfügbarkeit eines Wirkstoffes im Organismus so umzusetzen, daß ein wirksames Arzneimittel mit reproduzierbarer Qualität hergestellt werden kann. Für diese interdisziplinäre Aufgabe muß der Galeniker nicht nur in der Lage sein, physikalisch‐chemische und verfahrenstechnische Problemstellungen zu analysieren und zu lösen, sondern er muß auch die pharmakologischen, die pharmakokinetischen und medizinischen Befunde so weit verstehen und interpretieren können, daß er seine „Übersetzerfunktion”︁ adäquat wahrnehmen kann.

In dem hier beginnenden zweiteiligen Beitrag sollen Aufgaben und Arbeitsweisen der Galenik dargestellt werden. Auf diesem Teilgebiet der Pharmazie hat vor wenigen Jahren eine grundlegende Veränderung der Aufgabenstellung und der Arbeitsweisen begonnen. Ein Abschluß dieses Prozesses ist noch nicht erkennbar.

Es ist unmöglich, Aufgabe und Arbeitsweise der Galenik im Sinne einer Definition zusammenzufassen. Es wird daher versucht, die je nach Arzneiform sehr spezifischen Arbeitsweisen und Methoden anhand einiger repräsentativer Beispiele darzustellen. Ferner soll ihre Einbindung in das Umfeld der pharmazeutischen Forschung und Entwicklung geschildert werden.

Im ersten Teil geht es darum, warum ein Wirkstoff noch kein Medikament ist, was sich hinter dem etwas unglücklichen Begriff Biopharmazie verbirgt und welche allgemeinen chemischen und physikalisch‐chemischen Prinzipien der Galeniker bei der Entwicklung einer geeigneten Darreichungsform beachten muß und für seine Zwecke einsetzen kann.

Im zweiten Teil, der im nächsten Heft erscheinen soll, werden dann Aspekte und Methoden der Rezepturentwicklung für ein Medikament beschrieben.
Einkristall‐Röntgenstrukturanalyse und chemische Strukturen auf Briefmarken
Authors: Preut Hans
Published: December 2004

In den Kapiteln „Kristalle”︁, „Röntgenbeugung”︁, „Mathematik”︁, „Computer”︁, „Kristall‐ und Molekülstrukturen”︁ und „Datenbanken”︁ begleiten wir den Autor auf einen unterhaltsamen und informativen Spaziergang durch das heute so wichtige Gebiet der Einkristall‐Röntgenstruktur‐analyse. Dabei erfahren wir nicht nur etwas von der historischen Entwicklung, sondern auch viele wichtige Details aus der Praxis des gewieften Röntgenstrukturanalytikers. Das Besondere dabei: Illustriert werden die Stationen dieses Streifzugs mit deutschen und internationalen Briefmarken aus den vergangenen 50 Jahren.
Die Erzeugung dünner Schichten. Das PECVD‐Verfahren: Gasphasenabscheidung in einem Plasma
Authors: Unger Eugen
Published: December 2004

Dünne Schichten für Komponenten der modernen Mikroelektronik entstehen oft nach einem Verfahren, das als „Plasma enhanced chemical vapor deposition”︁ (abgekürzt: PECVD) bezeichnet wird. Amorphe Solarzellen, Mikroprozessoren und Informationsspeicher sind ohne diese Methode, die physikalische Bearbeitungstechniken und chemische Reaktionsführung kombiniert, nicht vorstellbar.
Potential roles for BMP and Pax genes in the development of iris smooth muscle
Authors: Jensen Abbie M.
Published: December 2004

The embryonic optic cup generates four types of tissue: neural retina, pigmented epithelium, ciliary epithelium, and iris smooth muscle. Remarkably little attention has focused on the development of the iris smooth muscle since Lewis ([1903] J. Am. Anat. 2:405–416) described its origins from the anterior rim of the optic cup neuroepithelium. As an initial step toward understanding iris smooth muscle development, I first determined the spatial and temporal pattern of the development of the iris smooth muscle in the chick by using the HNK1 antibody, which labels developing iris smooth muscle. HNK1 labeling shows that iris smooth muscle development is correlated in time and space with the development of the ciliary epithelial folds. Second, because neural crest is the only other neural tissue that has been shown to generate smooth muscle (Le Lievre and Le Douarin [1975] J. Embryo. Exp. Morphol. 34:125–154), I sought to determine whether iris smooth muscle development shares similarities with neural crest development. Two members of the BMP superfamily, BMP4 and BMP7, which may regulate neural crest development, are highly expressed by cells at the site of iris smooth muscle generation. Third, because humans and mice that are heterozygous for Pax6 mutations have no irides (Hill et al. [1991] Nature 354:522–525; Hanson et al. [1994] Nat. Genet. 6:168–173), I determined the expression of Pax6. I also examined the expression of Pax3 in the developing anterior optic cup. The developing iris smooth muscle coexpresses Pax6 and Pax3. I suggest that some of the eye defects caused by mutations in Pax6, BMP4, and BMP7 may be due to abnormal iris smooth muscle. Developmental Dynamics 232:385–392, 2005. © 2004 Wiley‐Liss, Inc.
Multipoint constraint methods for moving body and non‐contiguous mesh simulations
Authors: Gartling David K.
Published: December 2004

A sliding mesh method is demonstrated for moving body simulations involving thermal and fluid problems. Static problems with non‐contiguous mesh constructions are also solved using the same methodology. The proposed algorithm employs a parallel implementation of multipoint constraints with an efficient node‐in‐mesh search procedure. A simple method for treating the problem of partially covered/exposed element surfaces is also summarized. Several examples of static and dynamic thermal conduction and viscous flow problems illustrate the algorithms. Published in 2004 by John Wiley & Sons, Ltd.
Parallel finite element simulation for orographic wind flow and rainfall using GIS data
Authors: Kashiyama Kazuo , Shimizu Takahiro , Kurahashi Tetsuhiro , Hamada Hidetaka
Published: December 2004

This paper presents a computational technique based on the finite element method for the orographic wind flow and rainfall. The governing equations are the unsteady Navier–Stokes equations based on Boussinesq approximation and the Kessler model for warm rain. The SUPG/PSPG method is employed for the stabilization method. The automatic mesh generation method using GIS data is utilized to develop an accurate geographic model. The present method is applied to the analysis of orographic wind flow and rainfall past a semicircular hill and an actual mountain area. Copyright © 2004 John Wiley & Sons, Ltd.
Thermoluminescence screening of non‐diagnostic sherds from stream sediments to obtain a preliminary alluvial chronology: An example from Cyprus
Authors: Deckers Katleen , Sanderson David C.W. , Spencer Joel Q.
Published: December 2004

In this paper, simple thermoluminescence (TL) dating procedures utilizing non‐diagnostic sherds from fluvial deposits are described. This approach may provide preliminary insights into the chronology of fluvial sequences in areas where transported ceramics are common, but alluvial chronologies are not well developed. Our method deviates from conventional TL‐ dating methods in that simple screening measurements are made from small, heavily abraded sherds, and dose rates are estimated rather than being measured from each sample. This results in rapid and inexpensive laboratory measurements, which can be used to support field surveys. The limitations in precision and accuracy relative to quantitative luminescence procedures are discussed. It is argued that the results can be used to estimate an approximate maximum age of alluvial deposition events. The approach is illustrated with results from a geoarchaeological survey in Cyprus. © 2005 Wiley Periodicals, Inc.
Cholangiocarcinoma: Molecular targeting strategies for chemoprevention and therapy
Authors: Sirica Alphonse E.
Published: December 2004

Cholangiocarcinomas are devastating cancers that are increasing in both their worldwide incidence and mortality rates. The challenges posed by these often lethal biliary tract cancers are daunting, with conventional treatment options being limited and the only hope for long-term survival being that of complete surgical resection of the tumor. Unfortunately, the vast majority of patients with cholangiocarcinoma typically seek treatment with advanced disease, and often these patients are deemed poor candidates for curative surgery. Moreover, conventional chemotherapy and radiation therapy have not been shown to be effective in prolonging long-term survival, and although photodynamic therapy combined with stenting has been reported to be effective as a palliative treatment, it is not curative. Thus, there is a real need to develop novel chemopreventive and adjuvant therapeutic strategies for cholangiocarcinoma based on exploiting select molecular targets that would impact in a significant way on clinical outcome. This review focuses on potential preventive targets in cholangiocarcinogenesis, such as inducible nitric oxide synthase, cyclooxygenase-2, and altered bile acid signaling pathways. In addition, molecular alterations related to dysregulation of cholangiocarcinoma cell growth and survival, aberrant gene expression, invasion and metastasis, and tumor microenvironment are described in the context of various clinical and pathological presentations. Moreover, an emphasis is placed on the importance of critical signaling pathways and postulated interactions, including those of ErbB-2, hepatocyte growth factor/Met, interleukin-6/glycoprotein130, cyclooxygenase-2, vascular endothelial growth factor, transforming growth factor-β, MUC1 and MUC4, β-catenin, telomerase, and Fas pathways as potential molecular therapeutic targets in cholangiocarcinoma. cholangiocarcinoma. (Hepatology 2005;41:5-15.)
Method for computing protein binding affinity
Authors: Karney Charles F. F. , Ferrara Jason E. , Brunner Stephan
Published: December 2004

A Monte Carlo method is given to compute the binding affinity of a ligand to a protein. The method involves extending configuration space by a discrete variable indicating whether the ligand is bound to the protein and a special Monte Carlo move, which allows transitions between the unbound and bound states. Provided that an accurate protein structure is given, that the protein–ligand binding site is known, and that an accurate chemical force field together with a continuum solvation model is used, this method provides a quantitative estimate of the free energy of binding. © 2004 Wiley Periodicals, Inc. J Comput Chem 26: 243–251, 2005
Hemodynamics of the posterior cerebral arteries in neonates with periventricular leukomalacia
Authors: Fukuda Sumio , Kuwabara Satomi , Yasuda Mari , Mizuno Keisuke , Kato Takenori , Sugiura Takahiro , Hussein Mohamed Hamed , Kato Ineko , Fujimoto Shinji , Sobajima Hisanori , Togari Hajime
Published: December 2004

Purpose

The purpose of this study was to evaluate the cerebral blood flow of the posterior cerebral arteries (PCAs) in neonates in relation to the onset of periventricular leukomalacia (PVL).

Methods

Among 57 low‐birth‐weight neonates studied, 7 were diagnosed with PVL with cyst formation on sonography and MRI. The mean cerebral blood flow velocity (CBFV) was measured in all the neonates by Doppler sonography through the posterior fontanel separately in the right and left PCA at days 0, 1, 2, 3, 4, 5, 7, 10, 14, 21, 28, 42, 56, and 70 following birth.

Results

In the 7 neonates with PVL the mean CBFV in the right PCA was significantly lower than that in neonates without PVL at days 10, 14, 21, 28, 42, 56, and 70; the mean CBFV in the left PCA of neonates with PVL was significantly lower than that in those without PVL at days 7, 10, 14, 21, 28, 42, 56, and 70. CBFV measured in neonates without PVL exhibited a gradual increase postnatally. In contrast, CBFV values for neonates with PVL plateaued after day 5 or 7.

Conclusions

The serial measurement of PCA CBFV postnatally may prove useful as a predictor of the development of PVL. © 2004 Wiley Periodicals, Inc. J Clin Ultrasound 33:24–28, 2005
Sonographic demonstration of the normal thoracic esophagus
Authors: Zhu Shang‐Yong , Liu Ruo‐Chuan , Chen Li‐Hong , Luo Feng , Yang Hong , Feng Xu , Liao Xin‐Hong
Published: December 2004

Purpose

Although conventional sonography has been used widely in evaluation of the abdominal and cervical esophagus, its use in the thoracic esophagus is seldom mentioned. The aim of this study was to assess whether conventional sonography could demonstrate the thoracic esophagus and to determine this structure's normal sonographic appearance and measurements.

Methods

Transthoracic sonography was performed in 253 healthy volunteers ranging in age from 12 to 72 years (mean, 41 ± 15 years). The subjects were examined while supine with their hands raised over their heads; the transducer was placed along the left side of the sternum sequentially from the first to the fifth intercostal spaces. The ultrasound beam was directed to the thoracic aorta using the heart as an acoustic window. The detectable length of the thoracic esophagus was measured in the longitudinal scan from the upper most part visualized to the point at which it penetrated the diaphragm. The esophageal thickness was measured on the anterior wall at the level of the left atrium.

Results

In 188 (74%) of the 253 subjects, the thoracic esophagus could be demonstrated by sonography, except for the portion under the first and second intercostal spaces. In 3 of these 188 subjects, the esophagus also was not visualized at the third intercostal space. In these 188 subjects, the esophageal wall was shown as 3 layers. The esophageal lumen appeared as 1 or 2 hyperechoic bands in longitudinal sonograms. In 163 subjects, gas artifact and the comet‐tail sign, with downward movement, were seen in the esophageal lumen after swallowing. The mean demonstrable length of the thoracic esophagus was 10.2 ± 1.9 cm and the mean thickness 3.2 ± 0.3 mm.

Conclusions

Most of the thoracic esophagus can be visualized by sonography, except for a short portion at the back of the left main bronchus. The heart and the thoracic aorta are 2 important landmarks in scanning. © 2004 Wiley Periodicals, Inc. J Clin Ultrasound 33:29–33, 2005
Estrogen promotes differentiation and survival of dopaminergic neurons derived from human neural stem cells
Authors: Kishi Yo , Takahashi Jun , Koyanagi Masaomi , Morizane Asuka , Okamoto Yo , Horiguchi Satoshi , Tashiro Kei , Honjo Tasuku , Fujii Shingo , Hashimoto Nobuo
Published: December 2004

To investigate the effect of estrogen on neuronal differentiation, especially on dopaminergic (DA) neurons, human neural stem cells (NSCs) were differentiated in the presence of 17β‐estradiol. NSCs gave rise to tyrosine hydroxylase (TH)‐positive neurons in vitro, the proportion of which was increased by 17β‐estradiol. Increase in TH‐positive neurons was abrogated by an estrogen receptor (ER) antagonist, ICI182780, suggesting ERs play a role in differentiation of DA neurons. The observation that ERs were expressed in both proliferating NSCs and postmitotic DA neurons suggested that increase in TH‐positive neurons was due to induction and support of DA neurons. 17β‐Estradiol also increased the number of DA neurons derived from human NSCs in vivo when the cells were grafted into mouse brains. These results support a possible role for estrogen in the transplantation of NSCs for Parkinson's disease. © 2004 Wiley‐Liss, Inc.
Modulation of hypoglycemia‐induced increases in plasma epinephrine by estrogen in the female rat
Authors: Adams Julye M. , Legan Sandra J. , Ott Cobern E. , Jackson Brian A.
Published: December 2004

Clinical studies have demonstrated that estrogen replacement therapy suppresses stress‐induced increases in plasma catecholamines. The present study determined whether normal circulating levels of estrogen can modulate hypoglycemia‐induced increases in plasma epinephrine (EPI). In anesthetized female rats, insulin‐induced hypoglycemia (0.25 U/kg) increased plasma EPI concentration to a significantly greater extent in 14‐day ovariectomized (OVEX) rats compared to that in sham‐operated controls. In 17β‐estradiol (E2)‐replaced OVEX rats, the hypoglycemia‐induced rise in plasma EPI was reduced significantly when compared to that in vehicle‐replaced OVEX rats. OVEX and E2 replacement had no effect on tyrosine hydroxylase or phenylethanolamine N‐methyltransferase mRNA levels in the adrenal medulla. In isolated adrenal medullary chromaffin cells, agonist‐induced increases in intracellular Ca2+ were unaffected by 48‐hr exposure to 10 nM E2. In contrast, acute (3‐min) exposure to micromolar concentrations of E2 dose‐dependently and reversibly inhibited agonist‐induced Ca2+ transients. In addition, in OVEX rats, a constant infusion of E2 significantly reduced the insulin‐induced increase in plasma EPI concentration compared to that in vehicle‐infused controls. These data demonstrate that physiologic levels of circulating E2 can modulate hypoglycemia‐induced increases in plasma EPI. This effect seems independent of steroid influence on adrenal medullary secretion or biosynthesis. In contrast, acute exposure to high levels of E2 can also suppress hypoglycemia‐induced increases in plasma epinephrine, due at least in part to inhibition of stimulus‐secretion coupling. © 2004 Wiley‐Liss, Inc.
Stimulation of G‐proteins in human control and Alzheimer's disease brain by FAD mutants of APP714–723: Implication of oxidative mechanisms
Authors: Karelson Ello , Fernaeus Sandra , Reis Katarina , Bogdanovic Nenad , Land Tiit
Published: December 2004

We report the effects of amyloid precursor protein (APP) fragment 714–723 (APP714–723; peptide P1) and its V717F and V717G mutants (peptides P2 and P3, respectively) on G‐protein activity ([35S]GTPγS binding) in membranes from postmortem human control and Alzheimer's disease (AD) brains. The peptides P1, P2, and P3 revealed a significant stimulatory effect on [35S]GTPγS binding in control temporal cortex. The most potent stimulator, P3, at 10 μM concentration enhanced [35S]GTPγS binding by 500%. The effect was threefold stronger than that for wild‐type P1 and twofold stronger than that for P2. In sporadic AD, the stimulatory effect of P1, P2, and P3 on G‐proteins was reduced significantly whereas in Swedish familial AD (SFAD), only P1 elicited marked stimulation (at 10 μM by 50%). In control sensory postcentral cortex, the stimulation of G‐proteins by P3 was 1.5‐fold lower than that in control temporal cortex, whereas in AD and SFAD the effect showed no remarkable regional difference. Treatment of membranes with H2O2 produced 1.5‐fold higher stimulation in [35S]GTPγS binding to temporal cortex than that in binding to sensory postcentral cortex. In AD and SFAD, the stimulation by H2O2 revealed no significant regional difference. Glutathione, desferrioxamine (DFO), and 17β‐estradiol markedly decreased the strong stimulatory effect by P3 on [35S]GTPγS binding to control temporal cortex, with the protective effect by DFO being most potent. The Gαo‐protein levels were not changed in AD or SFAD brain membranes as compared to levels in control membranes. We suggest that strong G‐protein stimulation by P3 in the human brain implies the specific (per)oxidation mechanism that might be affected by regional content of peroxidizing substrates and antioxidants. © 2004 Wiley‐Liss, Inc.
Metallothionein reduces central nervous system inflammation, neurodegeneration, and cell death following kainic acid‐induced epileptic seizures
Authors: Penkowa Milena , Florit Sergi , Giralt Mercedes , Quintana Albert , Molinero Amalia , Carrasco Javier , Hidalgo Juan
Published: December 2004

We examined metallothionein (MT)‐induced neuroprotection during kainic acid (KA)‐induced excitotoxicity by studying transgenic mice with MT‐I overexpression (TgMT mice). KA induces epileptic seizures and hippocampal excitotoxicity, followed by inflammation and delayed brain damage. We show for the first time that even though TgMT mice were more susceptible to KA, the cerebral MT‐I overexpression decreases the hippocampal inflammation and delayed neuronal degeneration and cell death as measured 3 days after KA administration. Hence, the proinflammatory responses of microglia/macrophages and lymphocytes and their expression of interleukin (IL)‐1, IL‐6, IL‐12, tumor necrosis factor‐α and matrix metalloproteinases (MMP‐3, MMP‐9) were significantly reduced in hippocampi of TgMT mice relative to wild‐type mice. Also by 3 days after KA, the TgMT mice showed significantly less delayed damage, such as oxidative stress (formation of nitrotyrosine, malondialdehyde, and 8‐oxoguanine), neurodegeneration (neuronal accumulation of abnormal proteins), and apoptotic cell death (judged by TUNEL and activated caspase‐3). This reduced bystander damage in TgMT mice could be due to antiinflammatory and antioxidant actions of MT‐I but also to direct MT‐I effects on the neurons, in that significant extracellular MT presence was detected. Furthermore, MT‐I overexpression stimulated astroglia and increased immunostaining of antiinflammatory IL‐10, growth factors, and neurotrophins (basic fibroblastic growth factor, transforming growth factor‐β, nerve growth factor, brain‐derived neurotrophic factor, glial‐derived neurotrophic factor) in hippocampus. Accordingly, MT‐I has different functions that likely contribute to the increased neuron survival and improved CNS condition of TgMT mice. The data presented here add new insight into MT‐induced neuroprotection and indicate that MT‐I therapy could be used against neurological disorders. © 2004 Wiley‐Liss, Inc.
Antifibrinolytics in Orthotopic Liver Transplantation: Current Status and Controversies
Authors: Xia Victor W. , Steadman Randolph H.
Published: December 2004

This article reviews the current status and controversies of the 3 commonly used antifibrinolytics—epsilon-aminocaproic acid, tranexamic acid and aprotinin—during liver transplantation. There is no general consensus on how, when or which antifibrinolytics should be used in liver transplantation. Although these drugs appear to reduce blood loss and decrease transfusion requirements during liver transplantation, their use is not supported uniformly in clinical trials. Aprotinin has been studied more extensively in clinical trials and appear to offer more advantages compared to two other antifibrinolytics. Because of the diverse population of liver transplant recipients and the potential adverse effects of antifibrinolytics, especially life–threatening thromboembolism, careful patient selection and close monitoring is prudent. Further studies addressing the risks and benefits of antifibrinolytics in the setting of liver transplantation are warranted.
Alternatives to the Double Vena Cava Method in Partial Liver Transplantation
Authors: Kishi Yoji , Sugawara Yasuhiko , Matsui Yuichi , Akamatsu Nobuhisa , Motomura Noboru , Takamoto Shinichi , Makuuchi Masatoshi
Published: December 2004

Minimizing graft congestion in partial liver transplantation is important, especially when the graft weight is marginal for the recipient metabolic demand. We prefer the double vena cava technique for reconstructing middle hepatic vein tributaries with thick, short hepatic veins because the technique can reduce the warm ischemic time of the graft and make a wide anastomosis. This technique requires a cryopreserved superior or inferior vena cava. We devised an alternative double vena cava method using iliac or femoral vein grafts and applied it to two right liver transplantation patients. There was no postoperative hepatic venous outflow block in either patient. In conclusion, application of this technique, even in the absence of a suitable vena cava, can help to minimize graft congestion.
Living Donor Liver Transplantation Using a Right Lobe Graft in An Adult With Situs Inversus
Authors: Heimbach Julie K. , Menon Narayanan K.V. , Ishitani Michael B. , Nyberg Scott L. , Jankowski Christopher J. , Lindor Keith D. , Rosen Charles B.
Published: December 2004

Situs inversus totalis is a rare anatomic variant in which there is a complete mirror image of the thoracic and abdominal viscera. The common association of situs inversus and biliary atresia has led to a variety of modifications of surgical techniques utilizing both living donor and deceased donor liver grafts, with mixed results in the pediatric liver transplant population. The use of a living donor liver graft in an adult with situs inversus has not yet been described. However, living donor liver transplantation (LDLT) has produced excellent results in the adult population, particularly in the cholestatic population, which may be disadvantaged by the model for end-stage liver disease system. This is the first report of a successful living donor right liver graft in an adult with end-stage liver disease secondary to primary sclerosing cholangitis and situs inversus totalis.
Impact of Portal Venous Pressure on Regeneration and Graft Damage After Living-Donor Liver Transplantation
Authors: Yagi Shintaro , Iida Taku , Taniguchi Kentaro , Hori Tomohide , Hamada Takashi , Fujii Koji , Mizuno Shugo , Uemoto Shinji
Published: December 2004

Several reports claim that portal hypertension after living-donor liver transplantation (LDLT) adversely affects graft function, but few have assessed the impact of portal venous pressure (PVP) on graft regeneration. We divided 32 adult LDLT recipients based on mean PVP during the 1st 3 days after LDLT into a group with a PVP ≥ 20 mm of Hg (H Group; n = 17), and a group with a PVP < 20 mm of Hg (L Group; n = 15). Outcome in the H Group was poorer than in the L Group (58.8 vs. 92.9% at 1 year). Peak peripheral hepatocyte growth factor (HGF) during the 1st 2 weeks was higher in the H Group (L: 1,730 pg/mL, H: 3,696 pg/mL;

P

< .01), whereas peak portal vascular endothelial growth factor (VEGF) level during the 1st week was higher in the L Group (L: 433 pg/mL, H: 92 pg/mL;

P

< .05). Graft volume (GV) / standard liver volume (SLV) was higher in the H Group (L / H, at 2, 3, and 4 weeks, and at 3 months: 1.02 / 1.24, .916 / 1.16, .98 / 1.27, and .94 / 1.29, respectively;

P

< .05). Peak serum aspartate aminotransferase, bilirubin levels, and international normalized ratio after LDLT were significantly higher in the H Group, as was mean ascitic fluid volume. In conclusion, early postoperative PVP elevation to 20 mm of Hg or more was associated with rapid graft hypertrophy, higher peripheral blood HGF levels, and lower portal VEGF levels; and with a poor outcome, graft dysfunction with hyperbilirubinemia, coagulopathy, and severe ascites. Adequate liver regeneration requires an adequate increase in portal venous pressure and flow reflected by clearance of HGF and elevated VEGF levels.
De Novo Neoplasia After Liver Transplantation: An Analysis of Risk Factors and Influence on Survival
Authors: Herrero Ignacio J. , Lorenzo María , Quiroga Jorge , Sangro Bruno , Pardo Fernando , Rotellar Fernando , Alvarez-Cienfuegos Javier , Prieto Jesús
Published: December 2004

Immunosuppression increases the risk of posttransplant malignancy and it may increase posttransplant mortality. The finding of factors related to the development of posttransplant malignancy may serve as a guide to avoid those risk factors and to develop strategies of posttransplant surveillance. The incidence and risk factors of malignancy were studied in 187 consecutive liver transplant recipients surviving more than 3 months. None of the 12 patients surviving less than 3 months had

de novo

neoplasia. The impact of malignancy on survival was studied in a case-control study. After a median follow-up of 65 months, 49 patients developed 63 malignancies: 25 patients had 35 cutaneous neoplasias and 27 patients had 28 noncutaneous malignancies. The 5- and 10-year actuarial rates of cutaneous neoplasia were 14 and 24% and the rates of noncutaneous neoplasia were 11 and 22%, respectively. Risk factors for the development of cutaneous malignancy were older age and Child-Turcotte-Pugh A status. Risk factors for the development of noncutaneous malignancy were older age, alcoholism, and smoking. Cutaneous neoplasia had no effect on survival, whereas patients with noncutaneous malignancy had a significant reduction of survival. The overall relative risk of cutaneous and noncutaneous neoplasia, as compared with the general population were 16.91 (95% confidence interval: 11.78-23.51) and 3.23 (95% confidence interval: 2.15-4.67), respectively. The relative risk of cancer-related mortality (after excluding recurrent malignancy) was 2.93 (95% confidence interval: 1.56-5.02). Multivariate analysis showed that noncutaneous malignancy was an independent risk factor for posttransplant mortality. In conclusion, liver transplant recipients have a higher risk of cancer-related mortality than the general population. This increased risk is due to the development of noncutaneous neoplasia. Older age, alcoholism, and smoking increase the risk of

de novo

noncutaneous neoplasia.
Persistence of Hepatitis C Virus After Successful Treatment of Chronic Hepatitis C: Is Hepatitis C Infection for Life?
Authors: Radkowski Marek , Laskus Tomasz
Published: December 2004

It is presumed that resolution of hepatitis C, as evidenced by normalization of liver function tests and disappearance of hepatitis C virus (HCV) RNA from serum, as determined by conventional laboratory assays, reflects virus eradication. In this study, we examined the expression of the HCV genome in the sera, peripheral blood mononuclear cells (PBMC), and, on some occasions, monocyte-derived dendritic cells (DC) long after resolution of hepatitis C by using a highly sensitive reverse transcription (RT)-polymerase chain reaction-nucleic acid hybridization (RT-PCR-NAH) assay. The samples obtained from 16 randomly selected patients (5 with spontaneous resolution and 11 with treatment-induced resolution), monitored for up to 5 years, were studied by qualitative and semiquantitative RT-PCR-NAH and by real-time RT-PCR to detect the HCV RNA positive strand. The replicative HCV RNA negative strand was examined in PBMC after culture with a T cell proliferation stimulating mitogen. The findings show that HCV RNA was carried in the convalescent-phase sera and/or PBMC in all 16 individuals investigated. Also, DC from six of seven patients were reactive for the HCV genome. Importantly, traces of the HCV RNA negative strand, suggesting progressing virus replication, were detected in the majority of mitogen-stimulated PBMC, including four samples collected 5 years after recovery. Sequencing of the HCV 5' untranslated region fragment revealed genotype 1b in four of nine individuals examined and genotypes 1a and 2a in three and two patients, respectively. In conclusion, these results imply that HCV RNA can persist at very low levels in the serum and peripheral lymphoid cells and that an intermediate replicative form of the HCV genome can persist in PBMC for many years after apparently complete spontaneous or antiviral therapy-induced resolution of chronic hepatitis C. (J Virol 2004;78:5867–5874.)
Diffusion tensor imaging of in vivo and excised rat spinal cord at 7 T with an icosahedral encoding scheme
Authors: Madi Saaussan , Hasan Khader M. , Narayana Ponnada A.
Published: December 2004

Regional values of fractional anisotropy (FA) and mean diffusivity (Dav) of in vivo and excised rat spinal cords were measured using an iscosahedral encoding scheme that is based on 21 uniformly distributed and alternating gradient directions with an echo planar imaging (EPI) readout. Based on the water phantom studies, this scheme was shown to provide unbiased estimation of FA. The stability of the scanner during the acquisition of diffusion tensor imaging (DTI) data was evaluated. Repeated measurements of the FA values demonstrated excellent reproducibility, as assessed by the Bland–Altman analysis. These studies demonstrated a reduced anisotropy in excised samples relative to in vivo cords. Diffusion in the spinal cord gray matter was shown to be anisotropic. The FA value in the dorsal white matter (WM) was found to be higher relative to the ventral WM. Results from these studies should provide the necessary baseline data for serial in vivo DTI of injured spinal cord. Magn Reson Med 53:118–125, 2005. © 2004 Wiley‐Liss, Inc.
Using the axis of rotation of polar navigator echoes to rapidly measure 3D rigid‐body motion
Authors: Costa Andreu F. , Petrie Daniel W. , Yen Yi‐Fen , Drangova Maria
Published: December 2004

An improved technique to prospectively correct three‐dimensional rigid‐body motion using polar spherical navigator (pNAV) echoes is presented. The technique is based on acquiring pNAVs of an object in a baseline and rotated position and determining the axis of rotation (AOR) between data sets, thereby reducing 3D rotations to a 2D, planar rotation. Finding the AOR is simplified by prerotating the baseline trajectory, which forces the axis to lie within a specific polar region of a spherical shell in k‐space. Orbital navigator echoes are interpolated from the pNAV data in planes orthogonal to the AOR and cross‐correlated to determine the 2D rotation. The rotation about the AOR is used in conjunction with its orientation to calculate the overall 3D rotation. The pNAV‐AOR technique was tested for its precision, accuracy, and processing speed in detecting compound rotations and translations of varying magnitude. In comparison to the spherical navigator echo technique, the pNAV‐AOR technique is noniterative, fast, and independent of rotation magnitude and direction. At low SNR, the technique can detect compound rotations to 0.5° accuracy in an estimated 100 msec, indicating that prospective 3D rigid‐body motion correction may be feasible with this technique. Magn Reson Med 53:150–158, 2005. © 2004 Wiley‐Liss, Inc.
Analytical approach to noncircular section birdcage coil design: Verification with a Cassinian oval coil
Authors: De Zanche Nicola , Yahya Atiyah , Vermeulen Fred. E. , Allen Peter S.
Published: December 2004

A general analytical framework is presented for the design of birdcage radiofrequency resonators on cylindrical formers having arbitrary cross‐sectional shape. The primary objective of such shapes would be to improve the sensitivity of the NMR experiment to noncircular regions of the human anatomy while maintaining field homogeneity and quadrature polarization comparable to those of standard circular birdcage coils. The shape of the corresponding radiofrequency screen, which is required to decouple the coil from the rest of the NMR system and which is key to the performance, is also provided by this methodology. The theory was tested by constructing a 3‐T, quadrature, proton coil on a shape conforming to the anthropomorphic mean of the human head, namely, the oval of Cassini. Both bench tests (Q) and in vivo spectral and imaging comparisons of the Cassinian coil with an equivalently dimensioned and constructed circular birdcage coil, respectively, predicted and demonstrated in vivo an improvement in SNR of ∼24% over the circular section coil. The experimental RF field homogeneity and quadrature performance were comparable for both coil geometries, with the circular coil being marginally superior. Magn Reson Med 53:201–211, 2005. © 2004 Wiley‐Liss, Inc.
Retrospective coregistration of functional magnetic resonance imaging data using external monitoring
Authors: Tremblay Marleine , Tam Fred , Graham Simon J.
Published: December 2004

Coregistration is essential for correcting head motion artifacts in functional magnetic resonance imaging (fMRI). Coregistration algorithms typically realign images through optimization of a similarity measure based on voxel signal intensities. However, coregistration can also be performed through external monitoring, whereby a tracking device measures head motion directly and independently of the imaging data. This paper describes development of external monitoring using fMRI‐compatible infrared cameras. Three subjects participated in block‐design fMRI experiments consisting of bilateral finger tapping alone and tapping combined with visuomotor tracking to produce controlled task‐correlated head motion. Functional MRI time‐series were coregistered using the external monitoring technique and a known image‐based algorithm for comparison. Over various performance characteristics, external monitoring and image‐based coregistration exhibited good agreement, in particular reducing signals correlated with millimeter task‐correlated motions by 50–100%, with a 5% difference between the two techniques. These results promise future applications and refinements of external monitoring in patient populations where head motion is especially problematic. Possibilities include 3D prospective coregistration during real‐time fMRI, coregistration of individual slices, and motion correction in anatomic MRI. Magn Reson Med 53:141–149, 2005. © 2004 Wiley‐Liss, Inc.
Sensitivity encoding as a means of enhancing the SNR efficiency in steady‐state MRI
Authors: Weiger Markus , Boesiger Peter , Hilfiker Paul R. , Weishaupt Dominik , Pruessmann Klaas P.
Published: December 2004

Sensitivity encoding (SENSE) with a receiver coil array is typically used as a means of reducing the scan time in MRI. The speed benefit usually comes at some expense in terms of the signal‐to‐noise ratio (SNR) efficiency, which has been notorious as the main downside of SENSE and parallel MRI in general. In this work it is shown that in steady‐state gradient‐echo imaging the parallel approach may as well be used to increase the SNR efficiency. The basic idea is to balance reduced phase encoding by increasing the repetition time. In this fashion both the acquisition duty cycle and the steady‐state magnetization can be enhanced, resulting in considerable net gains in SNR yield. It is argued that the reduction factor in parallel imaging is essentially an additional degree of freedom in optimizing the SNR. The optimal SENSE factor depends on scan, tissue, and hardware parameters, assuming values up to 3.0 and higher. The achievable SNR benefit also depends on the spoiling regime and is most pronounced for RF‐spoiled techniques. The proposed mechanism is demonstrated by simulations and phantom experiments, as well as by contrast‐enhanced angiography in vivo, achieving an approximate doubling of the SNR efficiency. Magn Reson Med 53:177–185, 2005. © 2004 Wiley‐Liss, Inc.
Dual‐velocity continuously moving table acquisition for contrast‐enhanced peripheral magnetic resonance angiography
Authors: Kruger David G. , Riederer Stephen J. , Polzin Jason A. , Madhuranthakam Ananth J. , Hu Houchun H. , Glockner James F.
Published: December 2004

Acquisition of MR angiographic data of the peripheral vasculature during continuous table motion offers certain advantages over fixed station approaches, such as the elimination of wasted time moving between stations and the ability to form a seamless image of the extended field of view. However, it has recently been demonstrated that there is an approximate twofold reduction in contrast bolus velocity as it moves from the thighs to the calves. This can potentially cause a mismatch of the moving table with the contrast peak, resulting in the table outpacing the contrast bolus distally. In this work we describe a modification to the continuous table motion technique allowing two table velocities: a high (ca. 3.6 cm/sec) velocity from the abdomen to the thighs and a low (ca. 1.6 cm/sec) velocity distally. Implications of the nonconstant velocity on k‐space sampling are described, and it is shown that lateral resolution is improved for the low‐velocity region. Correction for table deceleration during the transition time between high and low velocities is demonstrated. Contrast‐enhanced studies in 15 volunteers are free of table‐motion‐related artifact and suggest improved depiction of the contrast bolus distally. Magn Reson Med 53:110–117, 2005. © 2004 Wiley‐Liss, Inc.
Hyperpolarized 3He lung imaging at 0.5 and 1.5 Tesla: A study of susceptibility‐induced effects
Authors: Salerno Michael , Brookeman James R. , de Lange Eduard E. , Mugler John P.
Published: December 2004

Hyperpolarized 3He MRI of the human lung was performed at 0.54 and 1.5 T using identical software and hardware (except for RF coils) at both field strengths. The T of 3He gas in the lung was measured, and the effects of magnetic‐susceptibility‐induced field inhomogeneities on the appearance of interleaved‐spiral and interleaved‐echo‐planar lung images at 1.5 T were compared to those at 0.54 T. Mean T values for 3He gas in the healthy human lung were 26.8 ± 1.5 ms and 67.9 ± 1.3 ms at 1.5 and 0.54 T, respectively. At 0.54 T, interleaved‐spiral images showed markedly less blurring due to susceptibility effects compared to images acquired at 1.5 T. At both 0.54 and 1.5 T, interleaved‐echo‐planar images appeared essentially identical to corresponding GRE images, even though the data‐sampling period per echo and echo time were substantially longer for the interleaved‐echo‐planar images acquired at 0.54 T. Magn Reson Med 53:212–216, 2005. © 2004 Wiley‐Liss, Inc.